Stabilized Siloxane-Containing Melt-Extrudable Thermoplastic Compositions

Surface-segregatable, melt-extrudable thermoplastic compositions which are related to the compositions of the present invention are described and claimed in copending and commonly assigned application Ser. No. 181,359, entitled SURFACE-SEGREGATABLE, MELT-EXTRUDABLE THERMOPLASTIC COMPOSITION, filed of even date in the names of Ronald S. Nohr and J. Gavin MacDonald. Novel benzotriazolyl-substituted siloxanes useful as additives in such surface-segregatable, melt-extrudable thermoplastic compositions and in the compositions of the present invention are described and claimed in copending and commonly assigned application Ser. No. 181,624, now abandoned, entitled BENZOTRIAZOLYL-SUBSTITUTED SILOXANES, filed of even date in the names of Ronald S. Nohr, J. Gavin MacDonald, and William E. Maycock. Novel 2,2,6,6-tetraalkylpiperidyl-substituted polysiloxanes also useful as additives in such surface-segregatable, melt-extrudable thermoplastic compositions and in the compositions of the present invention are described and claimed in copending and commonly assigned application Ser. No. 181,623, now abandoned, entitled TETRAALKYLPIPERIDYL-SUBSTITUTED POLYSILOXANES, filed of even date in the names of Ronald S. Nohr, J. Gavin MacDonald, and William E. Maycock. Novel siloxanes containing at least one benzotriazolyl/tetraalkylpiperidyl substituent useful as additives in such surface-segregatable, melt-extrudable thermoplastic compositions and in the compositions of the present invention are described and claimed in copending and commonly assigned application Ser. No. 181,463, entitled SILOXANE CONTAINING BENZOTRIAZOLYL/TETRAALKYLPIPERIDYL SUBSTITUENT, filed of even date in the names of William E. Maycock, Ronald S. Nohr, and J. Gavin MacDonald, now U.S. Pat. No. 4,859,759. William E. Maycock, Ronald S. Nohr, and J. Gavin MacDonald. The use of a post-formation, gentle heat treatment in the formation of nonwoven webs from such surface-segregatable, melt-extrudable thermoplastic compositions and the compositions of the present invention is described and claimed in copending and commonly assigned application Ser. No. 181,282, entitled METHOD OF FORMING A NONWOVEN WEB FROM A SURFACE-SEGREGATABLE THERMOPLASTIC COMPOSITION, filed of even date in the names of Ronald S. Nohr and J. Gavin MacDonald, now U.S. Pat. No. 4,857,251. The use of a heated compaction roll in the formation of spubonded nonwoven webs from such surface-segregatable, melt-extrudable thermoplastic compositions and the compositions of the present invention is described and claimed in copending and commonly assigned application Ser. No. 181,601, now abandoned, entitled METHOD OF FORMING A SPUNBONDED NONWOVEN WEB FROM A SURFACE-SEGREGATABLE THERMOPLASTIC COMPOSITION, filed of even date in the names of Ronald S. Nohr and J. Gavin MacDonald.

The present invention relates to a surface-segregatable, melt-extrudable thermoplastic composition. More particularly, the present invention relates to a stabilized thermoplastic composition containing a siloxane-based additive which surface segregates in a controllable manner upon melt extrusion to form fibers and films having modified surface characteristics.

Polymers are used widely throughout the world to make a variety of products which include blown and cast films, extruded sheets, injection molded articles, foams, blow molded articles, extruded pipe, monofilaments, and nonwoven webs. Some of such polymers, such as polyolefins, are naturally hydrophobic, and for many uses this property is either a positive attribute or at least not a disadvantage.

There are a number of uses for polyolefins, however, where their hydrophobic nature either limits their usefulness or requires some effort to modify the surface characteristics of the shaped articles made therefrom. By way of example, polyolefins are used to manufacture nonwoven webs which are employed in the construction of such disposable absorbent articles as diapers, feminine care products, incontinence products, and the like. Frequently, such nonwoven webs need to be wettable. Wettability can be obtained by spraying or coating the web with a surfactant solution during or after its formation. The web then must be dried, and the surfactant which remains on the web is removed upon exposure of the web to aqueous media. Alternatively, a surfactant can be included in the polymer which is to be melt-processed, as disclosed in U.S. Pat. Nos. 3,973,068 and 4,070,218 to R. E. Weber. In that case, however, the surfactant must be forced to the surface of the fibers from which the web is formed. This typically is done by heating the web on a series of steam-heated rolls or "hot cans". This process, called "blooming", is expensive and still has the disadvantage of ready removal of the surfactant by aqueous media. Moreover, the surfactant has a tendency to migrate back into the fiber which adversely affects shelf like, particularly at high storage temperatures. In addition, it is not possible to incorporate in the polymer levels of surfactant much above 1 percent by weight; surfactant levels at the surface appear to be limited to a maximum of about 0.33 percent by weight. Most importantly, the blooming process results in web shrinkage in the cross-machine direction and a significant loss in web tensile strength.

Other methods of imparting wettability to, or otherwise affecting the surface characteristics of, shaped articles made from polyolefins and other hydrophobic polymers are known. Representative examples of a number of such methods are described in the paragraphs which follow.

U.S. Pat. No. 4,578,414 to L. H. Sawyer and G. W. Knight describes wettable olefin polymer fibers. The fibers are formed from a composition comprising a polyolefin resin and one or more defined surface-active agents. Such agents may be present in an amount of from about 0.01 to about 5 percent by weight. The surface-active agents can be (1) an alkoxylated alkyl phenol in combination with a mixed mono-, di-, and/or triglyceride; (2) or a polyoxyalkylene fatty acid ester; or (3) a combination of (2) with any part of (1). The preferred polyolefin is polyethylene, and all of the examples employed an ethylene/1-octene copolymer, the latter apparently being a minor component. The surface-active agents are stated to bloom to the fabricated fiber surfaces where at least one of the surface-active agents remains partially embedded in the polymer matrix. The patent further states that the permanence of wettability can be controlled through the composition and concentration of the additive package.

Polysiloxane/polyoxazoline block copolymers are disclosed in U.S. Pat. No. 4,659,777 to J. S. Riffle and I. Yilgor. The copolymers are stated to be useful as surface-modifying additives for base polymers. Such use apparently has primary reference to personal care products where the surface properties to be imparted include glossiness, smoothness, and lubricity. However, incorporation of the copolymers into fibers is stated to impart surface stain resistance, antistatic properties, flame retardancy, and wettability by both polar and nonpolar solvents. Such incorporation preferably is in the range of from about 1 to 5 parts by weight. Suitable base polymers include some vinyl polymers, acrylate polymers, polyurethanes, cellulose derivatives, and polyethylene, polypropylene, ethylenepropylene copolymers, and copolymers of ethylene with, for example, vinyl acetate. However, the single example illustrating incorporation of the disclosed copolymers into a base polymer employed as the base polymer poly(vinyl chloride), and the resulting mixture was used to cast films from solution.

U.S. Pat. No. 4,672,005 to M. E. Dyer describes a process for improving the hygroscopic, soil release, and other surface properties of a polymer substrate. The process involves contacting the substrate with an aqueous mixture containing a water-soluble vinyl monomer and a hydrophobic vinyl monomer. Polymerization of the watersoluble vinyl monomer then is initiated by a polymerization initiator, thereby forming a vinyl polymer on the surface of the polymer substrate.

U.S. Pat. No. 4,698,388 to H. Ohmura et al. describes a method for modifying the surface of a polymer material by means of a block copolymer. The block copolymer consists of a hydrophilic polymer portion formed from a vinyl monomer and a polymer portion which is compatible with the polymer material, also formed from a vinyl monomer. The block copolymer is added to the polymer material by, for example, coating the material with a solution or suspension of the block copolymer, mixing the block copolymer with the polymer material during formation of the article, forming a film from the block copolymer which then is melt-pressed or adhered to the surface of the polymer material, and coating the surface of the polymer material with powdered block copolymer.

Polymer compositions having a low coefficient of friction are described by U.S. Pat. No. Re. 32,514 to D. J. Steklenski. The compositions comprise a blend of at least 80 percent by weight of a polymer and at least 0.35 percent by weight of a crosslinked silicone polycarbinol. The polymer preferably is a blend of cellulose nitrate and a hydrophobic acrylate polymer. The silicone polycarbinol in general is a hydroxy-terminated polysiloxane or hydroxysubstituted polysiloxane. The compositions typically are prepared by dissolving the polymer or polymer blend, silicone polycarbinol, and crosslinking agent in a suitable solvent and casting a film from which the solvent is allowed to evaporate.

Canadian Pat. No. 1,049,682 describes the inclusion in a thermoplastic polymer of from 0.1 to 10 percent by weight of a carboxy-functional polysiloxane. Suitable thermoplastic polymers include polyolefins. Such inclusion is stated to enhance the properties or characteristics of the themoplastic polymer in one or more ways. By way of illustration, products or articles made from the polymer mixture were stated to have self-lubricating properties and increased resistance to wear. For molded articles, less friction during transfer, injection or extrusion molding was observed, and better release of parts from the molds was obtained. See, also, German Published patent application (Offenlegungschrift) No. 2,506,667 [Chem. Abstr., 84:91066z (1976)].

Other, similar references which may be of interest include R. H. Somani and M. T. Shaw, Macromolecules, 14, 886 (1981), which describes the miscibility of polydimethylsiloxane in polystyrene; and S. N. Pandit et al., Polym. Compos., 2, 68 (1981), which reports the use of a vinyltriethoxysilane polymer as a coupling agent in glass fiber-reinforced polypropylene.

It also may be noted that polysiloxanes have been utilized in the production of nonwoven webs or fabrics, or products made therefrom, as illustrated by the references which follow.

U.S. Pat. No. 3,360,421 to S. Sands describes a bonded nonwoven backing material having perforate selvage which is used in the manufacture of carpet. In the production of the nonwoven backing material, a nonwoven web is produced from a polyolefin such as polyethylene or polypropylene. The resulting web then is subjected to bonding conditions, followed by applying to the web a lubricant which can be, among other things, methyl hydrogen polysiloxane and dimethyl polysiloxane.

A finish composition for application to a continuous filament polypropylene sheet is disclosed in U.S. Pat. No. 3,766,115 to S. Sands. The composition comprises a mixture of two polysiloxane components, the first of which is a dyeable component comprising a primary or secondary aminoalkyl- or aminoalkoxyalkylpolysiloxane fluid having an amine functionality in the range of 4-7 percent and being substantially free of other reactive groups. The second component is a lubricant component comprising a polydialkyl/arylsiloxane fluid having hydroxy end groups and being substantially free of other reactive groups. The polypropylene sheet typically is a spunbonded sheet made from isotactic polypropylene.

U.S. Pat. No. 3,867,188 to P. E. Campbell and J. G. Kokoszka relates to a spunbonded nonwoven fabric which is especially useful as a carpet backing. The fabric has on it a silicone-glycol copolymer having the general formula:

in which G is a radical of the structure --R(C.sub.3 H.sub.6).sub.z OH, R is an alkylene radical containing from 1 to 18 carbon atoms, x has an average value of from 40-90, y has an average value of from 1-10, and z has an average value of from 1-10. The copolymer, a modified polysiloxane, apparently is employed as a lubricant which coats a spunbonded nonwoven fabric. The fabric, in turn, is employed as a carpet backing. The addition of the modified polysiloxane to the backing is stated to reduce damage to the backing which results from the tufting process used to manufacture the carpet.

U.S. Pat. No. 3,929,509 to H. T. Taskier describes a hydrophilic microporous film which is useful as a battery separator. The film comprises a hydrophobic microporous film coated with a silicone glycol copolymer surfactant, preferably at a level of from 2 to 20 percent by weight, based on the uncoated film. In preferred embodiments, the surfactant coating comprises a mixture of a silicone glycol copolymer surfactant and a second surfactant which preferably is an imidazoline tertiary amine. The silicone glycol copolymer surfactant preferably is a polyoxyethylene polymethylsiloxane.

A yarn finish formulation is disclosed in U.S. Pat. No. 4,105,569 to R. J. Crossfield. In preferred embodiments, the formulation contains a hydrocarbon-soluble, long molecular chain polymeric viscosity improver, such as polyisobutylene, and a polysiloxane. Preferably, the polysiloxane is an alkoxylated polysiloxane, such as a dimethylpolysiloxane with substituted polyethylene glycol or polypropylene glycol side chains or mixed polyethylene/polypropylene glycol side chains.

U.S. Pat. No. 4,563,190 to R. Topfl describes a siloxane/oxyalkylene copolymer as an optional component of a dyeing assistant for dyeing or printing polyamide fiber material with anionic dyes. See also U. S. Pat. Nos. 4,444,563 to H. Abel and 4,426,203 to H. Abel and J. Oxe.

U.S. Pat. No. 4,645,691 to I. Ona and M. Ozaki describes a method for treating materials with organopolysiloxane compounds. The method involves applying to the material a composition containing a silicone compound which has one or more alkoxysilylalkyl groups and one or more polyoxyalkylene groups. The materials to be treated preferably are fibers and fiber-containing materials.

For a limited review of similar applications of silicones, see A. J. Sabia and R. B. Metzler, Nonwovens Ind., 14, 16 (1983). Also note British Pat. No. 1,273,445 [Chem. Abstr., 76: 89559z (1972)], which describes the use of a block polysiloxane, among other materials, in the preparation of a leather substitute.

It may be noted that the above review briefly discusses polysiloxanes which have been modified by inclusion of a poly(oxyalkylene) moiety; such modified polysiloxanes can be employed in the composition of the present invention as an additive.

Additionally, polysiloxanes have been used in the manufacture of films. For example, U.S. Pat. No. 4,652,489 describes a sealable, opaque polyolefinic multilayer film. The film is composed of a polypropylene base layer, a nonsealable surface layer, and a sealable surface layer. The nonsealable layer is a combination of a propylene homopolymer and a slip agent which preferably is a polydiorganosiloxane. The polydiorganosiloxane is used in an amount of from about 0.3 to about 2.5 percent by weight and preferably comprises a polymethylphenylsiloxane or a polydimethylsiloxane.

Finally, several references are known which are or may be of interest in relation to the additive when it contains a disubstituted siloxane. Such references are described below.

Siloxane-oxyalkylene block copolymers are disclosed in U.S. Pat. No. 3,629,308 to D. L. Bailey and A. S. Pater. The copolymers are stated to be particularly useful as a foam stabilizer in the production of polyurethane resin foams. The copolymers are represented by the formula: ##STR1## in which R is a monovalent hydrocarbon group, R.sup.0 is hydrogen or a monovalent hydrocarbon group, R' is hydrogen or a monovalent hydrocarbon group, R" is a divalent hydrocarbon group, r has a value of at least 0, m is an integer that has a value of at least 2, n is a number that has a value of at least 1 (preferably at least 4), p is a number that has a value of at least 1, there are not more than three hydrogen atoms represented by R.sup.0 in the copolymer (preferably less than one or none), and at least 25 weight-percent of the groups represented by (OC.sub.m H.sub.2m) are oxyethylene groups.

U.S. Pat. No. 4,150,013 to J. O. Punderson describes melt-processible tetrafluoroethylene copolymers containing organopolysiloxanes which are useful as wire insulation coatings. The organopolysiloxane is present in an amount of between about 0.2 and 5 percent by weight, based on the weight of the resulting copolymer composition,. Representative organopolysiloxanes include polyphenylmethylsiloxane, polydimethylsiloxane, polymethylsiloxane, a copolymer of phenylmethylsiloxane and dimethylsiloxane, and the like.

A high viscosity silicone blending process is disclosed in U.S. Pat. No. 4,446,090 to E. M. Lovgren et al. The blends produced by the process are stated to have engineering properties and flame retardance superior to known blends. The process involves (a) melting a solid thermoplastic composition comprising one or more thermoplastic polymers within an extruder, (b) injecting a high viscosity silicone fluid into the molten thermoplastic composition within the extruder, and (c) blending said molten thermoplastic composition with said high viscosity silicone fluid within the extruder. The thermoplastic compositions include polyethylene and polypropylene. The silicone fluid typically is a polydimethylsiloxane. The blend can contain such additives as reinforcing fillers, antioxidants, lubricants, flame retardants, and the like. The additives can be introduced by means of the thermoplastic polymers, the silicone fluid, or both. Typical flame retardants include magnesium stearate, calcium stearate, barium stearate, antimony oxide, and decabromodiphenyloxide.

Siloxane-containing polymers are described in U.S. Pat. Nos. 4,480,009 and 4,499,149 to A. Berger. The properties of polymeric compositions are stated to be improved by the presence of a polysiloxane unit having a defined formula. The listing of polymers, however, does not include polyolefins. The disclosed compositions apparently are useful as protective coatings and as molding, extruding, laminating, and calendaring compositions. Solutions of the compositions can be used to prepare films and fibers.

U.S. Pat. No. 4,500,659 to L. A. Kroupa and E. H. Relyea relates to extrudable, curable polyorganosiloxane compositions. The compositions are similar to those of U.S. Pat. No. 4,585,830, described below. In the present case, the compositions comprise (A) a liquid triorganosiloxy end-blocked polydimethylsiloxane wherein the triorganosiloxy units are dimethylvinylsiloxy or methylphenylvinylsiloxy; (B) a reinforcing silica filler which has been reacted with a liquid or solubilized treating agent, at least one component of which is a liquid hydroxy end-blocked polyorganosiloxane wherein at least 50 percent of the silicon atoms are bonded to a fluorine-substituted hydrocarbon radical; (C) a liquid methylhydrogensiloxane having an average of at least three silicon-bonded hydrogen atoms per molecule; and (D) a platinum-containing catalyst. The bonded treating agent for the silica filler would be incompatible, i.e., insoluble, with the polydimethylsiloxane component if it were not bonded to the silica.

Olefin polymer compositions containing silicone additives are described in U.S. Pat. No. 4,535,113 to G. N. Foster and R. B. Metzler. The compositions apparently can be extruded through relatively narrow die gaps at commercial extrusion rates to provide films having improved optical and mechanical properties. The silicon additives have the formula, ##STR2## in which each R, which can be the same or different, is an alkyl radical preferably having from one to six carbon atoms, R.sup.1 is a monovalent organic radical containing at least one ethyleneoxide group, vicinal epoxy group, or amino group, and a and b, which can be the same or different, each have a value of at least 1 and generally have a value of from about 4 to about 5,000. The silicone additives typically are present in the compositions in an amount of from about 0.01 to about 5 percent by weight.

U.S. Pat. No. 4,585,830 to R. P. Sweet describes polyorganosiloxane compositions useful for preparing unsupported extruded profiles. Such compositions are stated to include a triorganosiloxy end-blocked polydiorganosiloxane containing at least two vinyl radicals per molecule, in which at least 50 percent of the silicon-bonded organic radicals are methyl; and an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule, in which said hydrogen atoms are bonded to different silicon atoms. Examples of such two types of compounds are dimethylvinylsiloxy end-blocked polydimethylsiloxanes and trimethylsiloxy end-blocked dimethylsiloxane/methylhydrogensiloxane copolymers, respectively.

From the foregoing, it is evident that surfactants have been added to polymers to impart a hydrophilic character to the surface of the shaped article made from the polymer. These efforts appear to fall into either of two categories. In the first category, the surfactant is compatible with the polymer at ambient conditions, in which case the shaped article must be bloomed or heated after formation thereof to bring the surfactant to the surface. However, the surfactant is incompatible at melt-extrusion temperatures. In the second, the surfactant diffuses spontaneously to the surface of the shaped article because it is incompatible with the polymer at any temperature. Such incompatibility at melt-extrusion temperatures prevents the use of such surfactants in the formation of melt-extruded fibers because the surfactant prevents the continuous formation of fibers. Thus, in spite of the effort carried out to date, there is a pronounced need for a means of modifying the surface characteristics of fibers and films prepared from a thermoplastic polymer which avoids the disadvantages of known methods.

This need has been met by cross-referenced application Ser. No. 181,359. Upon melt-extruding the compositions disclosed therein, however, decomposition of additive and/or polymer occasionally is observed with siloxane-containing additives having poly(oxyalkylene) moieties, particularly with extrusion equipment having residence times greater than about 10-15 minutes. Such decomposition is evidenced as a smoke which exudes from the screw pumps and other parts of the extrusion equipment. Consequently, there is a need for a method of reducing or eliminating such decomposition.

It therefore is an object of the present invention to provide a stabilized surface-segregatable, melt-extrudable thermoplastic composition.

It further is an object of the present invention to provide a stabilized surface-segregatable, melt-extrudable thermoplastic composition which comprises at least one thermoplastic polymer, at least one siloxane-containing primary additive, and at least one siloxane-containing stabilizing additive.

It also is an object of the present invention to provide a stabilized surface-segregatable, melt-extrudable thermoplastic composition comprising at least one thermoplastic polymer, at least one siloxane-containing primary additive, and at least one siloxane-containing stabilizing additive, which additives rapidly surface segregate in a controllable manner upon melt processing the composition to form a fiber or film with a well-defined interfacial surface, effective surface, subsurface, and core concentration gradient of additives which imparts hydrophilicity to the fiber or film surface.

A further object of the present invention is to provide a stabilized surface-segregatable, melt-extrudable thermoplastic composition which comprises at least one polymer, at least one primary additive, and at least one stabilizing additive, which additives contain at least one tetrasubstituted disiloxanylene group.

Yet another object of the present invention is to provide a fiber or film made from a stabilized surface-segregatable, melt-extrudable thermoplastic composition comprising at least one polymer, at least one siloxane-containing primary additive, and at least one siloxane-containing stabilizing additive, which fiber or film is hydrophilic.

These and other objects will be apparent to those having ordinary skill in the art from a consideration of the specification and claims which follow.

Accordingly, the present invention provides a stabilized surface-segregatable, melt-extrudable thermoplastic composition which comprises:

(A) at least one thermoplastic polymer;

(B) at least one siloxane-containing primary additive having at least two moieties, A and B, in which:

(1) moiety A and moiety B act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A and moiety B, taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(2) moiety B has at least one functional group which is a poly(oxyalkylene) moiety; and

(3) the molecular weight of said primary additive is in the range of from about 400 to about 15,000;

with the proviso that said primary additive cannot be a compound having the general formula, ##STR3## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one ethyleneoxy group, vicinal epoxy group, or amino group; and a and b, which can be the same or different, each have a value of at least 1; and

(C) at least one siloxane-containing stabilizing additive having at least two moieties, A' and B', in which:

(1) moiety A' and moiety B' act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A' and moiety B', taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(2) moiety B' has at least one functional group which is an aliphatic or cycloaliphatic amino group; and

(3) the molecular weight of said stabilizing additive is in the range of from about 400 to about 15,000;

with the proviso that said stabilizing additive cannot be a compound having the general formula, ##STR4## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one amino group; and a and b, which can be the same or different, each have a value of at least 1;

in which thermoplastic composition:

(a) said primary additive is present at a level in the range of from about 0.1 to about 50 percent by weight, based on the weight of said polymer; and

(b) said stabilizing additive is present at a level in the range of from about 0.1 to about 5 percent by weight, based on the weight of said primary additive.

In preferred embodiments, moiety A comprises at least one tetrasubstituted disiloxanylene group, optionally associated with one or more groups selected from the group consisting of trisubstituted silyl and trisubstituted siloxy groups, the substituents of all such groups being independently selected from the group consisting of monovalent alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted, and moiety B.

In other preferred embodiments, the additive contains a plurality of groups selected from the group represented by the following general formulae:

in which each of R.sub.1 and R.sub.2 independently is a monovalent group selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which, except for hydrogen, may be substituted or unsubstituted; each of R.sub.3 -R.sub.5, inclusive, independently is a monovalent group selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted, and B.sub.4 ; each of R.sub.6 -R.sub.11, inclusive, independently is a monovalent group selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted; each of c and d independently represents an integer from 0 to about 100 which indicates only the quantity of the respective group present in the additive without indicating or requiring, in instances when an integer is greater than 1, that such plurality of the respective group are connected to one another to form an oligomer or polymer or that all of such groups have identical substituents; and each of B.sub.1 -B.sub.4, inclusive, independently is a moiety which imparts to the additive at least one desired characteristic; with the proviso that such plurality of groups results in at least one tetrasubstituted disiloxanylene group.

In still other preferred embodiments, the additive is a compound having the general formula, ##STR5## in which each of R.sub.12 and R.sub.13 independently is a monovalent group selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which, except for hydrogen, may be substituted or unsubstituted; each of B.sub.5 and B.sub.6 independently is a monovalent group having a desired characteristic; and e represents an integer from 2 to about 100.

In yet other preferred embodiments, the additive is a compound having the general formula, ##STR6## in which each of R.sub.14 -R.sub.20, inclusive, independently is a monovalent group selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which, except for hydrogen, may be substituted or unsubstituted; B.sub.7 is a monovalent group having a desired characteristic; and f represents an integer from 1 to about 100.

In yet other preferred embodiments, the additive is a compound having the general formula, ##STR7## in which each of R.sub.21 -R.sub.23, inclusive, independently is a monovalent group selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which, except for hydrogen, may be substituted or unsubstituted; B.sub.8 is a monovalent group having a desired characteristic; and g represents an integer from 1 to about 100.

The stabilized, surface-segregatable, melt-extrudable composition of the present invention is adapted to processing by melt extrusion to form a fiber or film having a differential, increasing concentration of each additive from the center to the surface thereof, such that the concentration of additive in at least one of the interfacial surface, effective surface, and subsurface of the fiber or film is greater than the average concentration of additive in the core of the fiber or film and imparts hydrophilicity to the surface of the fiber or film. Each additive is miscible with said polymer at melt extrusion temperatures, under which conditions the additive and the polymer form a metastable solution. As the temperature of the newly formed fiber or film drops below melt extrusion temperatures, each additive becomes significantly less compatible with said polymer. Concurrent with this marked change in compatibility, the polymer begins to solidify Both factors contribute to the rapid migration or segregation of the additives which takes place in a controllable manner.

The present invention also provides a method of stabilizing a thermoplastic composition which is to be melt-extruded to form a fiber or film having a differential, increasing concentration of an additive from the center to the surface thereof, such that the concentration of additive in at least one of the interfacial surface, effective surface, and subsurface of the fiber or film is greater than the average concentration of additive in the core of the fiber or film, thereby imparting hydrophilicity to the surface of the fiber or film, which method comprises:

(A) melting a thermoplastic composition which comprises:

(1) at least one thermoplastic polymer;

(2) at least one siloxane-containing primary additive having at least two moieties, A and B, in which:

(a) moiety A and moiety B act as a single molecular unit which is compatible with said polymer at melt extrusion temperature but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A and moiety B, taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(b) moiety B has at least one functional group which is a poly(oxyalkylene moiety); and

(c) the molecular weight of said primary additive is in the range of from about 400 to about 15,000;

with the proviso that said primary additive cannot be a compound having the general formula, ##STR8## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one ethyleneoxy group, vicinal epoxy group, or amino group; and a and b, which can be the same or different, each have a value of at least 1; and

(3) at least one siloxane-containing stabilizing additive having at least two moieties, A' and B', in which:

(a) moiety A' and moiety B' act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A' and moiety B', taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(b) moiety B' has at least one functional group which is an aliphatic or cycloaliphatic amino group; and

(c) the molecular weight of said stabilizing additive is in the range of from about 400 to about 15,000;

with the proviso that said stabilizing additive cannot be a compound having the general formula, ##STR9## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one amino group, and a and b, which can be the same or different, each have a value of at least 1; in which thermoplastic composition:

(a) said primary additive is present at a level in the range of from about 0.3 to about 17 percent by weight, based on the weight of said polymer; and

(b) said stabilizing additive is present at a level in the range of from about 0.1 to about 5 percent by weight, based on the weight of said additional additive; and

(B) extruding the resulting melt through a die at a shear rate of from about 50 to about 30,000 sec.sup.-1 and a throughput of from about 0.01 to about 5.4 kg/cm/hour.

In certain preferred embodiments, the polymer component of the thermoplastic composition of the present invention is a polyolefin, such as polyethylene and polypropylene. In other preferred embodiments, the polymer is a polyester, such as poly(ethylene terephthalate).

The stabilized surface-segregatable, melt-extrudable thermoplastic composition of the present invention is useful in the preparation of fibers and films which have hydrophilic surfaces. Such thermoplastic composition is particularly useful in the formation of nonwoven webs which are employed in the construction of such disposable absorbent products as diapers, feminine care products, incontinence products, and the like.

FIG. 1 is a diagrammatic representation of a wedge of fiber to illustrate certain definitions used throughout the specification and claims.

FIG. 2 consists of two hand-drawn representations of photomicrographs of a composition of the present invention, i.e., the fibers of Example 328, taken through a hot-stage microscope at two different temperatures and a magnification of 350.times..

FIG. 3 consists of two hand-drawn representations of photomicrographs of the polymer component only of the fibers of Example 328, taken through a hot-stage microscope at two different temperatures and a magnification of 350.times..

FIG. 4 consists of two hand-drawn representations of photomicrographs of the composition of Example 40 consisting of the polymer component of the fibers of Example 328 and an incompatible silicon-containing compound, taken through a hot-stage microscope at two different temperatures and a magnification of 350.times..

FIG. 5 consists of two hand-drawn representations of photomicrographs of the composition of Example 45, taken through a hot-stage microscope at two different temperatures and a magnification of 350.times..

FIG. 6 is a diagrammatic representation of a section of melt-pressed film prepared from a composition of the present invention, as described in Examples 131-176, inclusive.

FIG. 7 is a diagrammatic representation of a scanning electron micrograph, using a silicon x-ray probe, of a sample of the film of Example 172, superimposed on the diagrammatic representation of FIG. 6, which film was prepared from a composition of the present invention in which the additive was a silicon-containing compound.

FIG. 8 is a plot of silicon concentration in atom percent versus depth in .ANG. below the interfacial surface for a sample of the film of Example 172, the data for the plot having been obtained by Rutherford back scattering spectrometry.

FIG. 9 is a diagrammatic representation of a scanning electron micrograph, using a silicon x-ray probe, of a section of the spunbonded nonwoven web of Example 364 prepared from a composition of the present invention, in which the additive was a silicon-containing compound.

FIGS. 10 and 11 are plots of silicon concentrations in atom percent versus depth in .ANG. below the interfacial surface for the fibers of two spunbonded nonwoven webs made in accordance with the present invention, i.e., Examples 328 and 363, in which the additive was a silicon-containing compound, the data for the plots having been obtained by Rutherford back scattering spectrometry.

FIG. 12 consists of two hand-drawn representations of photomicrographs of a composition consisting of the polymer component of the fibers of Example 328 and a surfactant commonly used in a blooming process to render polypropylene fibers wettable, taken through a hot-stage microscope at two different temperatures and a magnification of 350.times..

A full appreciation of the uniqueness of the segregation phenomenon described herein requires an understanding of the definitions of various terms used throughout the specification and claims. The definitions, in turn, will be more fully understood by reference to FIG. 1.

FIG. 1 is a diagrammatic representation of a wedge of a fiber prepared from a surface-segregatable, melt-extrudable thermoplastic composition. Fiber 10 can be considered to consist of two major portions, surface 11 and core 15. The latter includes all of the fiber which is not included in surface 11. Surface 11 has three components: interfacial surface 12, effective surface 13, and subsurface 14. The interfacial surface in essence is the monomolecular layer of the fiber which is at the air/polymer (or nonfiber/fiber) interface. The effective surface begins at the interfacial surface and extends into the fiber a distance of about 15 .ANG.. The subsurface lies below the effective surface and extends into the fiber to a depth of about 1,000 .ANG.; thus, the subsurface has a thickness of about 985 .ANG.. Although not illustrated by a drawing, these definitions also apply to films prepared from a composition of the present invention.

In order for the surface of a fiber or film to exhibit hydrophilicity, it is not necessary for the primary additive, and moiety B in particular, to be present at the interfacial surface. Rather, such desired characteristic will be observed if the primary additive, and moiety B in particular, is within about 15 .ANG. of the interfacial surface because of the conformational changes in the primary additive which occur spontaneously at ambient conditions. Below about 15 .ANG., however, these conformational changes usually are not sufficient to make the primary additive effectively available at the interfacial surface.

Nevertheless, the presence of primary additive in the subsurface region is important because primary additive in that region often can be "coaxed" to move into the effective surface region by the application of gentle heat.

In this regard, the term "gentle heat" generally means temperatures in the range of from about 45 to about 110.degree. Celsius for periods of only a few seconds up to about a minute or so. Usually, primary additive present in the core region can be moved to the effective surface only under conditions which are closer to the prior art blooming procedure discussed earlier.

It should be noted that the term "bulk" is used herein differently from the term "core". As already pointed out, the latter term refers to that portion or region of the fiber or film which is below the subsurface layer or region. The term "bulk", on the other hand, has reference to the entire fiber or film and usually is employed in reference to elemental analyses of fiber or film samples.

As already stated, the stabilized surface-segregatable, melt-extrudable thermoplastic composition of the present invention comprises at least one thermoplastic polymer, at least one primary additive, and at least one stabilizing additive, all of which additives are siloxane-containing compounds.

The term "melt-extrudable" is equivalent to "melt-processible" and is not intended to be limited in any way. That is, the term is intended to encompass the use of the composition in any melt-extrusion process which is or may be employed to prepare fibers or films, provided the process meets the limitations imposed by the claims. Thus, the term includes the use of the composition in melt-spinning of continuous filaments; meltblowing, spunbonding, and coforming of nonwoven webs; the casting and blowing of films; and the like.

As a matter of convenience, the present invention is described in detail primarily as applied to the formation of fibers and nonwoven webs. Such description, however, is by way of illustration only and is not intended to in any way limit either the spirit or scope of the present invention.

In general, the term "thermoplastic polymer" is used herein to mean any thermoplastic polymer which can be used for the preparation of fibers or films. Examples of thermoplastic polymers include, by way of illustration only, end-capped polyacetals, such as poly(oxymethylene) or polyformaldehyde, poly(trichloroacetaldehyde), poly(n-valeraldehyde), poly(acetaldehyde), poly(propionaldehyde), and the like; acrylic polymers, such as polyacrylamide, poly(acrylic acid), poly(methacrylic acid), poly(ethyl acrylate), poly(methyl methacrylate), and the like; fluorocarbon polymers, such as poly(tetrafluoroethylene), perfluorinated ethylene-propylene copolymers, ethylene-tetrafluoroethylene copolymers, poly(chlorotrifluoroethylene), ethylene-chlorotrifluoroethylene copolymers, poly(vinylidine fluoride), poly(vinyl fluoride), and the like; polyamides, such as poly(6-aminocaproic acid) or poly(.epsilon.-caprolactam), poly(hexamethylene adipamide), poly(hexamethylene sebacamide), poly(11-aminoundecanoic acid), and the like; polyaramides, such as poly(imino-1,3-phenyleneiminoisophthaloyl) or poly(m-phenylene isophthalamide), and the like; parylenes, such as poly-p-xylylene, poly(chloro-p-xylylene), and the like; polyaryl ethers, such as poly(oxy-2,6-dimethyl-1,4-phenylene) or poly(p-phenylene oxide), and the like; polyaryl sulfones, such as poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenylene-isopropylide ne-1,4-phenylene), poly(sulfonyl-1,4-phenyleneoxy-1,4-phenylenesulfonyl-4,4'-biphenylene), and the like; polycarbonates, such as poly(bisphenol A) or poly(carbonyldioxy-1,4-phenyleneisopropylidene-1,4-phenylene), and the like; polyesters, such as poly(ethylene terephthalate), poly(tetramethylene terephthalate), poly(cyclohexylene-1,4-dimethylene terephthalate) or poly(oxymethylene-1,4-cyclohexylenemethyleneoxyterephthalogyl), and the like; polyaryl sulfides, such as poly(p-phenylene sulfide) or poly(thio-1,4-phenylene), and the like; polyimides, such as poly(pyromellitimido-1,4-phenylene), and the like; polyolefins, such as polyethylene, polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene), poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene), 1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, polychloroprene, polyacrylonitrile, poly(vinyl acetate), poly(vinylidene chloride), polystyrene, and the like; copolymers of the foregoing, such as acrylonitrile-butadiene-styrene (ABS) copolymers, and the like; and the like.

The preferred polymers are polyolefins and polyesters, with polyolefins being more preferred. Even more preferred are those polyolefins which contain only hydrogen and carbon atoms and which are prepared by the addition polymerization of one or more unsaturated monomers. Examples of such polyolefins include, among others, polyethylene, polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene), poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene), 1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, polystyrene, and the like. In addition, such term is meant to include blends of two or more polyolefins and random and block copolymers prepared from two or more different unsaturated monomers. Because of their commercial importance, the most preferred polyolefins are polyethylene and polypropylene.

Broadly stated, the primary additive must have at least two moieties, A and B, in which:

(A) moiety A and moiety B act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A and moiety B, taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures; and

(B) moiety B has at least one functional group which is a poly(oxyalkylene) moiety.

Because the primary additive is compatible with the polymer at melt extrusion temperatures, the additive is miscible with the polymer and the polymer and the additive form a metastable solution. The solution formed by the primary additive and the polymer at temperatures above melt extrusion temperatures is referred to herein as a metastable solution since the solution is not stable at temperatures below melt extrusion temperatures. As the temperature of the newly formed fiber or film drops below melt extrusion temperatures, the polymer begins to solidify which contributes to additive separating from the polymer phase. At the same time, the primary additive is becoming less compatible with the polmer. Both factors contribute to the rapid migration or segregation of the primary additive which occurs in a controllable manner.

This preferential migration or segregation is controllable because the extent or degree of migration is, at least in part, a function of the molecular weight of the primary additive, the shear rate, and the throughput. While the mechanism of additive migration or segregation is not fully understood, it appears that the rate of migration or segregation is:

(1) indirectly proportional to the additive molecular weight--the higher the additive molecular weight, the slower the rate of segregation;

(2) directly proportional to the shear rate--the higher the shear rate, the faster the rate of segregation; and

(3) indirectly proportional to throughput--the higher the throughput, the slower the rate of segregation.

There are at least three very surprising and unexpected aspects to the present invention. The first is that the primary additive as defined herein is compatible with the polymer at melt extrusion temperatures, given the fact that moieties A and B, when taken as separate molecular units, are incompatible with the polymer at any temperature. The second is that lower molecular weight primary additives perform better than higher molecular weight additives; this is contrary to the conventional wisdom of polymer additives which favors higher molecular weights. The third and perhaps most startling aspect is the rapidity with which the segregation of the primary additive takes place.

As just noted, the effect of additive molecular weight on the rate of segregation was surprising, especially in view of past experiences with polydimethylsiloxane. Upon reflection, it now appears that the movement of lower molecular weight additives through the gradually solidifying polymer is roughly analogous to the movement of small particles through a viscous fluid--the larger the particles, the greater the resistance to movement through the fluid. This analogy seem appropriate since it now is known that the additive exists as small globules in the polymer, which globules become smaller as the temperature of the molten composition increases. By imposing shear forces on the molten composition, it is believed that the globules are broken down into small globules far more quickly than would have occurred in the absence of shear. Thus, shear is a contributing factor which enhances the segregation of the primary additive to the surface of the newly formed fiber or film.

The general, the shear rate will be in the range of from about 50 to about 30,000 sec.sup.-1. Preferably, the shear rate will be in the range of from about 150 to about 5,000 sec.sup.-1, and most preferably from about 300 to about 2,000 sec.sup.-1.

It perhaps should be mentioned at this point that the compatibility requirement is critical. That is, if the primary additive is not compatible with the polymer at melt-extrusion temperatures, the composition cannot be melt processed to give satisfactory fibers or films.

By way of clarification, it already has been noted that compounds such as polydimethylsiloxane have been incorporated in polymers which were extruded, but not melt processed to give fibers or films. Such compounds migrated to the surface of the extruded article to provide a lubricated surface to aid further processing or removal from a mold. Because extrusion times were very slow compared to the melt processing times typically experienced in fiber and film formation, migration or segregation rates were not an issue. However, the incompatibility of the added compounds prevents acceptable melt-processing because of discontinuities in fiber formation and holes and other related defects in films. In addition, such compounds often reduce friction within the extruder to the point that the molten mixture rotates essentially as a plug with no downstream movement taking place.

Finally, throughput is of importance because it affects the time the newly formed fiber or film is in a sufficiently molten or fluid state to allow migration or segregation of the additive to the newly formed surfaces, even though throughput also affects the shear rate. Stated differently, it is possible to control the rate of migration or segregation by controlling the rate of cooling of the newly formed fiber or film. Thus, for any given molecular weight additive, the extent of migration can be reduced by rapidly cooling the fiber or film. Alternatively, migration can be enhanced by reducing the rate of cooling.

Throughput typically will be in the range of from about 0.01 to about 5.4 kg/cm/hour. Preferably, throughput will be in the range from about 0.1 to about 4.0 kg/cm.hour. The throughput most preferably will be in the range of from about 0.5 to about 2.5 kg/cm/hour.

As used herein, the phrase "molten state" does not necessarily mean "flowable". Rather, the term is used to denote a condition of the thermoplastic composition in which the additive molecules still are capable of migrating or segregating to the surface of the newly formed fiber or film. Thus, the term is somewhat imprecise and not readily subject to accurate measurement. Consequently, this composition fluidity factor preferentially is described or accounted for by the term "throughput".

The controlled migration or segregation of primary additive toward the surface of the fiber or film results in a controllable differential concentration of additive in the fiber or film. If measurable migration is allowed to occur, the concentration of the primary additive in the fiber or film will increase with increasing distance from the center thereof. By the proper selection of additive, additive molecular weight, shear rate, and throughput (or rate of cooling), a substantial amount, or perhaps even all, of the primary additive can be found in the surface. Because the concentration of primary additive in the core of the fiber or film typically will vary nonlinearly from the concentration of the additive in the surface, this concentration difference is referred to herein as a differential concentration.

While the primary additive can be either a liquid or a solid, a liquid is preferred. It also is preferred that a liquid primary additive have a surface tension which is less than that of virgin polymer; the lower surface tension assures that the primary additive will be more likely to completely "wet" or cover the surface of the fiber or film as the segregation process proceeds to completion, especially under conditions favoring a large concentration differential.

As already noted, additive surface segregation is influenced by the molecular weight of the primary additive. More specifically, the lower the molecular weight of the additive, the more rapid is the rate of segregation of the additive to the surface of the fiber or film at any given temperature at which the fiber or film still is in a sufficiently molten state.

It should be apparent that the primary additive can be monomeric, oligomeric, or polymeric. Indeed, polymeric additives are required in order to achieve the higher additive molecular weights permitted by the present invention. Because lower additive molecular weights are preferred, the preferred primary additives perhaps are properly referred to as oligomers. However, such nomenclature can be misleading and reliance instead should be placed on the molecular weight of the primary additive and the other parameters already described. It is for this reason that the primary additive is not referred to as a polymeric additive, even though in many instances the additive will be oligomeric or polymeric in nature.

As already stated, the primary additive molecular weight will be in the range of from about 400 to about 15,000. This range encompasses suitable primary additive molecular weights, regardless of whether the thermoplastic composition is to be used to prepare a fiber or a film. As a practical matter, however, the suitable primary additive molecular weight range for fibers is not as broad as that for films because fiber formation generally takes place much more quickly than does film formation. Moreover, the additive molecular weight range also depends in part on whether or not an additive will be used by itself or in a mixture of additives.

Accordingly, the molecular weight range for primary additives which are to be used individually in compositions for fiber formation and not as part of a mixture of additives typically is from about 400 to about 3,000. Preferably, this range is from about 500 to about 2,000, and more preferably from about 500 to about 1,500. The most preferred range is from about 500 to about 1,000.

When primary additives are intended to be used in a mixture intended for incorporation in fiber-forming compositions, however, higher molecular weights can be employed. Although the reasons for this are not clearly understood, mixtures of additives frequently are more compatible with the polymer at melt-extrusion temperatures than are the individual additives. Although the selection of additive mixtures is somewhat empirical, in general such mixtures can utilize additives having molecular weights in the range of from about 400 to about 10,000 and preferably from about 400 to about 8,000. Fortunately, the hot stage microscope studies described in the Examples can be used as a simple screening method to estimate whether or not a given mixture can be used successfully.

In this regard, some clarification of the term "used successfully" is necessary. The successful use of an additive or a mixture of additives has reference to two factors. First, the additive or additive mixture must segregate to the target zone in order to achieve the intended properties. That is, the primary additive or additive mixture must segregate to either or both of the interfacial surface and the effective surface of the fibers, unless a mild post-formation heat treatment is going to be included in the process. Second, the composition containing the additives must process well enough in commercial-scale equipment to give a web or fabric, or a film, having the required aesthetic and physical properties.

When a primary additive is to be used for the preparation of a film, the additive molecular weight typically will be in the range of from about 400 to about 15,000. This range preferably will be from about 500 to about 8,000, and most preferably from about 500 to about 4,000. As with additives intended for fiber formation, film-formation compositions also may use additive mixtures, in which case the upper limit of the specified molecular weight ranges can be somewhat higher.

It should be noted that the foregoing molecular weight ranges are based on the assumption that oligomeric or polymeric additives will have relatively broad polydispersities, e.g., of the order of about 1.2. While narrow polydispersities certainly are achievable, usually at a higher cost, they are not necessary in the practice of the present invention, even if relatively low molecular weight additives are to be employed. As a guideline, it may be noted that for a given additive, the average molecular weight of an additive having a narrower polydispersity usually should be slightly lower than the average molecular weight of an additive having a broad polydispersity. While this guideline is not precise and is somewhat empirical in nature, one skilled in the art will be able to properly select an additive of any polydispersity without undue experimentation.

The term "additive" is used broadly herein to encompass the use of two or more primary additives in a given composition. Such two or more additives may have the same or similar moieties B, or different moieties B having the same characteristic, i.e., hydrophilicity or water wettability. On the other hand, two or more primary additives may be used which have different characteristics, which characteristics may be related or unrelated. Such two or more additives may be present in similar or significantly different amounts. Moreover, the primary additives may have the same or similar molecular weights in order to segregate in the fiber or film to approximately the same region. Alternatively, different molecular weight primary additives may be employed in order to effectively layer the additives in the surface.

The primary additive is a material which will be referred to herein loosely as a siloxane. In general, moiety A will comprise at least one tetrasubstituted disiloxanylene group, optionally associated with one or more groups selected from the group consisting of trisubstituted silyl and trisubstituted siloxy groups, the substituents of all such groups being independently selected from the group consisting of monovalent alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted. As a practical matter, moiety A often will consist of all three groups. Moreover, more than one tetrasubstituted disilixanylene group often will be present, particularly when the additive has an appreciable molecular weight.

As used herein, the term "tetrasubstituted disiloxanylene group" means a group having the following general formula: ##STR10## in which each of R.sub.33 -R.sub.36, inclusive, is a monovalent group independently selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups.

As noted, the substituents of the groups comprising moiety A can be alkyl, cycloalkyl, aryl, or heterocyclic groups which may be the same or different and which in turn may be substituted or unsubstituted. Other than the obvious requirement that such substituents not adversely affect additive stability or other properties, there are no known limitations to such substituents. However, for reasons relating primarily to commercial availability and ease of synthesis, such substituents preferably are alkyl groups and more preferably are unsubstituted alkyl groups having from 1 to 3 carbon atoms. Most preferably, such substituents are methyl groups.

More specifically, the additive preferably contains a plurality of groups selected from the group represented by the following general formulae, it being understood that not all groups need to be present and that the presence of some groups precludes the presence of others:

in which each of R.sub.1 and R.sub.2 independently is a monovalent group selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which, except for hydrogen, may be substituted or unsubstituted; each of R.sub.3 -R.sub.5, inclusive, independently is a monovalent group selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted, and B.sub.4 ; each of R.sub.6 -R.sub.11, inclusive, independently is a monovalent group selected from the group consisting of alkyl, cycloalkyl, aryl, and heterocyclic groups, each of which may be substituted or unsubstituted; each of c and d independently represents an integer from 0 to about 100 which indicates only the quantity of the respective group present in the additive without indicating or requiring, in instances when an integer is greater than 1, that such plurality of the respective group are connected to one another to form an oligomer or polymer or that all of such groups have identical substituents; and each of B.sub.1 -B.sub.4, inclusive, independently is a moiety which imparts to the additive at least one desired characteristic; with the proviso that such plurality of groups results in at least one tetrasubstituted disiloxanylene group.

Molecular weight limitations, if desired, are readily achieved by limiting the sum of c and d to the extent required to achieve the desired molecular weight.

In general, the preparation of the siloxane moiety is well known to those having ordinary skill in the art. Siloxanes that have reactive groups, such as H--Si.tbd., RO--Si.tbd., and Cl--Si.tbd., are used as starting products. Such materials are prepared either by hydrolysis of, e.g., methylchlorosilanes or by copolymerization of cyclic or linear polymethylsiloxanes with functional siloxanes. See, for example, W. Noll, "Chemistry and Technology of Silicones," Academic Press, New York, 1968; and R. Meals, "Encyclopedia of Chemical Technology," Vol. 18, 2nd Edition, 1969, p.221.

Turning now to moiety B, it is this moiety which must have at least one functional group which imparts hydrophilicity to the primary additive. Because the additive migrates or segregates toward the surface of the fiber or film upon its formation, it is the presence of moiety B in the surface of the fiber or film which results in such surface acquiring the hydrophilic characteristic or moiety B. Such characteristic clearly would not be found in the surface of the fiber or film in the absence of the primary additive.

It perhaps should be noted at this pint that the term "functional group" refers to that portion of moiety B which imparts hydrophilicity; the term is not to be equated to "reactive", although a group which also is reactive is not precluded by the term "functional group".

Moiety B need not be limited to a single desired characteristic. That is, the primary additive can contain two or more moieties B which have different characteristics. For example, a moiety B may have both a hydrophilic group and a group which is stable to actinic radiation. Alternatively, one moiety B may have a hydrophilic group while a second moiety B is stable to actinic radiation.

The point of attachment of moiety B to moiety A is not known to be critical. For example, moiety B can be a substituent of any one or more of the tetrasubstituted disiloxanylene, trisubstituted silyl, and trisubstituted siloxy groups which may be present.

As already stated, moiety B is a poly(oxyalkylene) moiety. More preferably, the alkylene portion of such moiety will contain from 2 to about 6 carbon atoms. Most preferably, moiety B is a poly(oxyalkylene) moiety in which the oxyalkylene repeating units are oxyethylene or oxypropylene or a mixture thereof.

References which disclose polysiloxanes containing one or more poly(oxyalkylene) moieties suitable for use as the additive include, among others, U.S. Pat. Nos. 2,836,748, 2,917,480, 2,991,300, 2,991,301, 3,168,543, 3,172,899, 3,236,252, 3,278,485, 3,280,160, 3,299,113, 3,356,758, 3,402,192, 3,480,583, 3,505,377, 3,509,192, 3,530,159, 3,600,418, and Re. 27,541; Belgian Pat. No. 627,281; British Pat. Nos. 892,819, 954,041, 963,437, 981,811, 981,812, 1,073,368, and 1,098,646; French Pat. Nos. 1,259,241, 1,356,962, 1,411,757, 1,413,125, 1,482,133, 1,511,661, 1,520,444, and 1,179,743; German Published Specification (Offenlegungschrift) Nos. 1,495,927, 1,570,656, 1,595,730, 2,045,360, and 2,555,053; German Pat. Nos. 1,235,594, 1,257,433, 1,301,576, 1,570,647, and 1,195,953

By way of illustration only, three types of primary additives for imparting water wettability to the surfaces of filaments, referred to hereinafter as types A, B, and C, respectively, are described below with reference to the plurality of preferred groups described earlier. In each case, moiety B is an oxyalkylene-containing moiety which is represented by the following general formula:

in which R.sub.24 is a monovalent group selected from the group consisting of hydrogen and lower alkyl; x represents an integer from 0 to about 3; and each of y and z independently represents an integer from 0 to about 100 which indicates only the quantity of the respective group present in the additive without indicating or requiring, in instances when an integer is greater than 1, that such plurality of the respective group are connected to one another to form an oligomer or polymer.

The first type, which is most preferred, consists of groups of formulae 1, 2, and 7, in which each of R.sub.9 and R.sub.10 independently is an alkyl group containing from 1 to 3 carbon atoms; R.sub.24 is an alkyl group containing from 1 to 4 carbon atoms; a is in the range of from 3 to about 60; x is 0; y is in the range of from about 5 to about 25; and z is in the range of from about 0 to about 25.

Specific examples of type A primary additives, by way of illustration only, include materials having the following general formula: ##STR11## in which B.sub.9 is --(C.sub.2 H.sub.4 O).sub.y (C.sub.3 H.sub.6 O).sub.z --R.sub.24, where e, y, z, and R.sub.24 are as already defined.

Commercially available additives of this type include TEGOPREN BC-1781, in which e has an average value of 5.5, R.sub.24 is n-butyl, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.9 is 40/60; TEGOPREN D-985, in which e has an average value of 4.3, R.sub.24 is methyl, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.9 is 70/30; and TEGOPREN V-337, in which e has an average value of 4, R.sub.24 is methyl, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.9 is 100/0.

Type A primary additives in general are prepared by heating silicon with, e.g., chloromethane in the presence of a copper catalyst at about 300.degree. C. to give dichlorodimethyl silane (see, e.g., U.S. Pat. No. 2,380,995 to E. G. Rochow) which, when reacted with water, gives a polymer having the following general formula: ##STR12## where h is an integer representing the number of repeating units in the molecule. See, for example, B. B. Hardman and A. Torkelson, "Encyclopedia of Chemical Technology," 3rd Edition, John Wiley & Sons, Inc., New York, 1982, pp. 922-962. The polymer then is reacted in the presence of trifluoroacetic acid with an oxyalkylene-containing compound having the general formula,

in which R.sub.24, y, and z are as already defined, to give the additive. See U.S. Pat. No. 2,836,748 to D. L. Bailey and F. M. O'Connor. See also U.S. Pat. No. 2,917,480, U.S. Pat. No. 3,505,377 to E. L. Morehouse, and German Pat. No. 1,259,241.

The second type of primary additives consists of groups of formulae 5-8, inclusive, in which each of R.sub.3 -R.sub.11, inclusive, independently is an alkyl group containing from 1 to 3 carbon atoms; R.sub.24 is an alkyl group containing from 1 to 4 carbon atoms; c is in the range of from about 3 to about 30; d is in the range of from about 1 to about 10; x is 3; y is in the range of from about 5 to about 25; and z is in the range of from about 0 to about 25.

Specific examples of type B primary additives, also by way of illustration only, include materials having the following general formula: ##STR13## in which B.sub.10 is (CH.sub.2).sub.3 --O--(C.sub.2 H.sub.4 O).sub.y (C.sub.3 H.sub.6 O).sub.z R.sub.24 where R.sub.24, y, and z are as already defined, i represents an integer from 0 to about 100, and j represents an integer from 1 to about 100.

Commercially available examples of this type include SILWET L-77, SILWET L-7500, and SILWET L-7602 (Union Carbide Corporation, Danbury, Connecticut). Other commercially available examples include TEGOPREN 5843, in which the i/j value is 13/5, R.sub.24 is hydrogen, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 100/0; TEGOPRENr 5847, in which the i/j value is 0/1, R.sub.24 is hydrogen, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 80/20; TEGOPREN 5852, in which the i/j value is 20/5, R.sub.24 is hydrogen, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 20/80; TEGOPREN 5873, in which R.sub.24 is hydrogen and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 40/60; the i/j value is 20/5, R.sub.24 is hydrogen, and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 35/65; and TEGOPREN 5878, in which R.sub.24 is hydrogen and the ethylene oxide/propylene oxide weight percent ratio in B.sub.10 is 100/0 (Th. Goldschmidt AG, Essen, Federal Republic of Germany).

The synthesis of the type B primary additives begins with a reactive silicon fluid, prepared by known methods, such as that represented by the following formula: ##STR14## in which i and j are as already defined. The fluid is reacted with a compound having the general formula,

in which R.sub.24, y, and z are as already defined, to give the additive. The reaction is carried out in the presence of a platinum/.tau.-aluminum oxide catalyst at a temperature of the order of 150.degree. C. See, e.g., U.S. Pat. No. 3,280,160 to D. L. Bailey, U.S. Pat. No. 3,172,899, also to D. L. Bailey, and U.S. Pat. No. 3,505,377 to E. L. Morehouse. The compound which is reacted with the silicone fluid is obtained by the condensation of ethylene oxide and propylene oxide with allyl alcohol in the presence of a catalytic amount of potassium hydroxide, a well-known reaction.

The third type of primary additives consists of groups of formulae 2, 4, and 7, in which each of R.sub.2, R.sub.9, and R.sub.10 independently is an alkyl group containing from 1 to 3 carbon atoms; R.sub.24 is an alkyl group containing from 1 to 4 carbon atoms; c is in the range of from 0 to about 50; x is 0; y is in the range of from about 5 to about 25; and z is in the range of from about 0 to about 25.

Specific examples of type C primary additives, again by way of illustration only, include materials having the following general formula: ##STR15## in which R.sub.21 and R.sub.24 are lower alkyl groups, g is as already defined, and each of y and z represents an integer from 0 to about 70.

A specific commercially available example is SILWET L-720 (Union Carbide Corporation, Danbury, Conn.).

Type C primary additives are prepared by the method described in U.S. Pat. No. 2,836,748 to D. L. Bailey and F. M O'Connor. Briefly, methyltriethoxysilane and mixed cyclic polydimethylsiloxanes are heated at about 150.degree. C. in the presence of potassium hydroxide as catalyst to give a material having the following general formula: ##STR16## in which g is as already defined. This material then is reacted in the presence of trifluoroacetic acid with an oxyalkylene-containing compound having the general formula,

where y, z, and R.sub.24 are as already defined, to give the additive.

In general, the weight ratio of polymer to primary additive can vary from about 1 to about 1,000. That is, the amount of primary additive in the surface-segregatable, melt-extrudable thermoplastic composition of the present invention can range from about 50 percent by weight to about 0.1 percent by weight. Because the primary additive has a significant influence on the rheology of the melt, compositions containing greater amounts of polymeric material tend to be too fluid for melt-extrusion processes. On the other hand, lower amounts typically do not result in significant surface modification of the fiber or film. As a point of interest, it was observed that although melt viscosities are reduced by inclusion of the additive in the polymer, friction within the extruder does not appear to be significantly affected if the extruder screw design is compatible with the compositions. This result is consistent with the formation of a metastable solution. But, such result is contrary to experience with other silicon-containing compounds known to have been incorporated in polymers and, thus, unexpected.

In melt-extrusion processes such as those used to prepare fibers and nonwoven webs, the weight ratio of polymer to additive preferably will be in the range of from about 6 to about 350. More preferably, such ratio will vary from about 9 to about 200, and most preferably from about 20 to about 200.

The foregoing description with respect to the primary additive applies also to the stabilizing additive, with two exceptions. First, moiety B' differs from moiety B of the primary additive, and second, the level of stabilizing additive is different from the level of primary additive.

As already stated, moiety B' of the stabilizing additive has at least one functional group which is an aliphatic or cycloaliphatic amine. Other functional groups, such as hydroxy groups and derivatives thereof, and the like, can be present, provided they do not adversely affect the ability of the amine groups to stabilize the thermoplastic composition.

Moiety B' of the stabilizing additive can be represented by the following general formula:

in which R.sub.25 represents a divalent connecting group which is attached to a silicon atom and each of R2.sub.6 and R.sub.27 is a monovalent group independently selected from the group consisting of C.sub.1 --C.sub.18 alkyl and C.sub.3 --C.sub.8 cycloalkyl, or the two groups, together with the nitrogen atom to which they are bonded, form a 5- to 7-membered saturated ring. The alky groups optionally are substituted with one or more groups consisting of hydroxy and derivatives thereof. The 5- to 7-membered ring and the cycloalkyl groups optionally are substituted with 1-3 monovalent groups independently selected from the group consisting of hydroxy and derivatives thereof and C.sub.1 -C.sub.6 alkyl. R.sub.26 and R.sub.27 preferably are C.sub.1 -C.sub.10 alkyl and most preferably are C.sub.1 -C.sub.3 alkyl.

As used herein, the term "divalent connecting group" is employed broadly to mean, without limitation, any divalent group known to those having ordinary skill in the art for covalently coupling an organic moiety to silicon, provided that such divalent group is sufficiently thermally stable at melt-extrusion temperatures.

As a practical matter, the divalent connecting group will involve alkylene, ether, or amine linkages, or combinations thereof, examples of which are listed below:

--(CH.sub.2).sub.n --, where n is an integer representing the number of repeating methylene groups and has a value of at least 3;

--O--R.sub.28 --, in which R.sub.28 represents a divalent organic group, e.g., C.sub.1 -C.sub.14 alkylene, cycloalkylen, or arylene;

--(CH.sub.2).sub.n --O--, where n is as already defined; and

--(CH.sub.2).sub.n --O--R.sub.28 --, where n and R.sub.28 are as already defined.

--NH--R.sub.29 --, in which R.sub.29 represents a divalent organic group, e.g., C.sub.1 -C.sub.14 alkylene, cycloalkylene, and arylene; and

--N(R.sub.30)--R.sub.31 --, in which R.sub.30 represents a monovalent organic group, e.g., C.sub.1 -C.sub.14 alkyl, and R.sub.31 represents a divalent organic group, e.g., C.sub.1 -C.sub.14 alkylene, cycloalkylene, and arylene.

Of the above, methylene and ether linkages, or combinations thereof, are preferred. In addition, a nitrogen atom normally will not be directly coupled to a silicon atom. However, the above listing is representative only, and the selection of these and other coupling groups is well known to those having ordinary skill in the field of synthetic organic chemistry.

The stabilizing additives useful in the present invention also are readily prepared by known methods. For example, a siloxane having one or more --Si(R.sub.32)H--groups, in which R.sub.32 is a monovalent group which can be alkyl, cycloalkyl, aryl, or heterocyclic, is reacted with allyl glycidyl ether, 4,5-epoxy-1-pentene, or another suitable epoxide to give siloxane groups having pendent epoxide groups. The epoxide groups then can be reacted with either a secondary amine or an amine having other groups which will react with the epoxide groups.

The stabilizing additive will be present in the thermoplastic composition at a level of from about 0.1 to about 5 percent by weight, based on the amount of primary additive present in the composition. The preferred level of stabilizing additive is from about 0.25 to about 2 percent by weight, based on the level of primary additive present in the composition. The stabilizing additive most preferably will be present at a level of from about 0.5 to about 1 percent by weight, based on the amount of primary additive.

The stabilized thermoplastic composition of the present invention can be prepared by any number of methods known to those having ordinary skill in the art. For example, the polymer in chip or pellet form and the additives can be mixed mechanically to coat the polymer particles with additive. If desired, the additives can be dissolved in a suitable solvent to aid the coating process, although the use of a solvent is not preferred. The coated polymer then can be added to the feed hopper of the extruder from which the fibers or film will emerge. Alternatively, the coated polymer can be charged to a heated compounder, such as a heated twin-screw compounder, in order to disperse the additives throughout the bulk of the polymer. The resulting thermoplastic composition typically is extruded as rods which are fed a chipper. The resulting chips then serve as the feed stock for a melt-processing extruder. In another method, the additives can be metered into the throat of the hopper which contains the polymer in particulate form and which feeds the extruder. In yet another method, the additives can be metered directly into the barrel of the extruder where they are blended with the molten polymer as the resulting mixture moves toward the die.

In many cases, the stabilizing additive is soluble in the primary additive. In such instances, the stabilizing additive preferably is dissolved in the primary additive. The resulting solution then is used to prepare the composition as described above.

The method provided by the present invention is a method of stabilizing a thermoplastic composition which is to be melt-extruded to form a fiber or film having a differential, increasing concentration of an additive from the center to the surface thereof, such that the concentration of additive in at least one of the interfacial surface, effective surface, and subsurface of the fiber or film is greater than the average concentration of additive in the core of the fiber or, thereby imparting hydrophilicity to the surface of the fiber or film. The method comprises:

(A) melting a thermoplastic composition which comprises:

(1) at least one thermoplastic polymer;

(2) at least one siloxane-containing primary additive having at least two moieties, A and B, in which:

(a) moiety A and moiety B act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A and moiety B, taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(b) moiety B has at least one functional group which is a poly(oxyalkylene moiety); and

(c) the molecular weight of said primary additive is in the range of from about 400 to about 15,000;

with the proviso that said primary additive cannot be a compound having the general formula, ##STR17## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one ethyleneoxy group, vicinal epoxy group, or amino group; and a and b, which can be the same or different, each have a value of at least 1; and

(3) at least one siloxane-containing stabilizing additive having at least two moieties, A' and B', in which:

(a) moiety A' and moiety B' act as a single molecular unit which is compatible with said polymer at melt extrusion temperatures but is incompatible at temperatures below melt extrusion temperatures, but each of moiety A' and moiety B', taken as separate molecular units, is incompatible with said polymer at melt extrusion temperatures and at temperatures below melt extrusion temperatures;

(b) moiety B' has at least one functional group which is an aliphatic or cycloaliphatic amino group; and

(c) the molecular weight of said stabilizing additive is in the range of from about 400 to about 15,000;

with the proviso that said stabilizing additive cannot be a compound having the general formula, ##STR18## in which each R independently is a monovalent organic group selected from the group consisting of alkyl groups; R.sup.1 is a monovalent organic group containing at least one amino group; and a and b, which can be the same or different, each have a value of at least 1; in which thermoplastic composition:

(a) said primary additive is present at a level in the range of from about 0.3 to about 17 percent by weight, based on the weight of said polymer; and

(b) said stabilizing additive is present at a level in the range of from about 0.1 to about 5 percent by weight, based on the weight of said additional additive; and

(B) extruding the resulting melt through a die at a shear rate of from about 50 to about 30,000 sec.sup.-1 and a throughput of from about 0.01 to about 5.4 kg/cm/hour.

The key to the method, of course, is the use of the stabilized surface-segregatable, melt-extrudable thermoplastic composition of the present invention which has been discussed in detail already. Otherwise, anyone having ordinary skill in the art and having familiarity with various melt-extrusion processes will be able to produce fibers and films without undue experimentation, based on the teaching provided herein. For example, nonwoven webs may be formed by meltblowing in accordance with U.S. Pat. Nos. 3,016,599, 3,704,198, and 3,849,241; or by spunbonding in accordance with U.S. Pat. Nos. 3,361,394, 3,655,862, 3,705,068, 3,802,817, 3,853,651, 4,064,605, 4,405,297, and 4,434,204; or by conforming in accordance with U.S. Pat. No. 4,100,324.

The present invention is further described by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or scope of the present invention. In the examples, all temperatures are in degrees Celcius and all parts are by weight unless stated otherwise.

For convenience, the examples are divided into seven sections describing (1) the additives and polymers employed; (2) the preparation of surface-segregatable, melt-extrudable thermoplastic compositions; (3) the preparation of melt-pressed films from the thermoplastic compositions; (4) the preparation of fibers from the thermoplastic compositions; (5) the preparation of cast films from the thermoplastic compositions; (6) the stabilization study; and (7) evaluation of a known material as an additive by way of comparison.

A. Additives

Each of the primary additives employed in the examples was a type A, B, or C additive. The structures are identified in Tables 1, 3, and 5 ("MW" represents molecular weight); if an additive were commercially available, the material designation or catalog number is given in the column labled "I.D." and a manufacturer code is given in the column labeled "Source". The properties of the additives identified in Tables 1, 3, and 5 are summarized in Tables 2, 4, and 6, respectively.

The structure of the stabilizing additive is given in Table 7 and its properties are summarized in Table 8. Finally, the structure of a control additive which lacks a moiety B is given in Table 9 and its properties are summarized in Table 10.

B. Polymers

The polymers employed are summarized in Table 11 which is based on data supplied by the manufacturers. In the table, the melt flow rate is given in the column labeled "MFR" and was determined in accordance with ASTM Test Method D1238-82, "Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer." The polydispersity, PD, is the ratio of the weight-average molecular weight, M.sub.w, to the number-average molecular weight, M.sub.n.

Surface-segregatable thermoplastic, melt-extrudable compositions were prepared by several methods. However, only those methods are described below which permitted isolation of the composition prior to a melt-processing step; i.e., a bench-scale method and a pilot-scale method. The preparations of compositions simultaneously with melt-processing are described in conjuntion with such melt-processing.

A. Bench-Scale Method

Approximately 10 g of a polymer in pellet form was mixed in a beaker with the desired amount of primary additive. The resulting mixture was poured into the hopper of a small compounding unit (Max Mixing Extruder, No. CS-194-FA-093, Custom Scientific Instruments, Inc., New York, N.Y.). The mixture was heated in the extruder of the compounder to a temperature of 180.degree. and extruded through a die having a single, approximately 4-mm diameter, orifice. The extruded composition was collected either on aluminum foil or in a glass evaporating dish. The cooled material was cut manually into approximately 6-mm long pieces. The compositions prepared are summarized in Table 12.

B. Pilot-Scale Method

To a weighed amount of polymer, typically from about 13 to about 45 kg, in a plastic-lines fiber drum was added the desired amount of additive. The components then were mixed mechanically in a paddler mixer (Banbury, Ann Arbor, Mich.). The hopper of a twin-screw compounding unit (Egan Machinery Company, Sommerville, N.J.) was charged with the resulting mixture. The mixture was gravity-fed to the compounding screws. Compounding was accomplished at a temperature of from about 180 to about 250.degree., depending on the polymer employed. The resulting composition was extruded though a die having six orifices with diameters of about 3 mm. The extruded filaments were passed through a ten-foot water bath and then a forced-air blower. The dried filaments were pelletized in a rotary pelletizer Cumberland Company, New York, N.Y. and stored in 23-kg lots in plastic-lined boxes. The resulting compositions are summarized in Table 13. In some cases, an elemental analysis was carried out on the composition by Galbraith Laboratories, Inc., Knoxville, Tennessee. The results of the elemental analyses are summarized in Table 14.

It is evident from the data in Table 14 that each composition analyzed contained additive. However, the effectiveness of the additive remained to be demonstrated.

C. Hot-Stage Microscope Study

A hot-stage microscope study was conducted on several polymer-additive combinations in an effort to gain an insight into the compatibility aspect of the additive with the polymer. Although the study actually was done later in the program, it is reported here for convenience, except for one part which will be described in Section VI.

Briefly, polymer, either in the form of small granules or fibers, both with and without additives, was observed under a hot-stage microscope at two temperatures, 160.degree. and 220.degree., at a magnification of 350.times.. The equipment consisted of a Mettler hot-stage and a Zeiss Universal optical microscope equipped with transmitted light optics. The presence of additive globules at either temperature was an indication of the incompatibility of the additive with the polymer at the temperature of observation. The study was conducted by Ricerca, Inc., Painesville, Ohio.

The first material studied was the web of Example 327 which was prepared from a composition of the present invention consisting of polymer PPA and 3 percent by weight of additive A11. FIG. 2A is a representation of the photomicrograph at 160.degree. and FIG. 2B is a representation of the photomicrograph at 220.degree.. In FIG. 2A, additive globules 21 clearly are present. Also present are what appear to be a few particles 22 of debris or foreign matter. At 220.degree., as seen in FIG. 2B, a few additive globules 21 seem to be present, but they appear to be slightly smaller in size. Again, some debris particles 22 are present.

The existence of a large number of additive globules at 160.degree. demonstrates that the additive is incompatible with the polymer at that temperature. Moreover, the fact that the number of globules decreases significantly at 220.degree. indicates that additive compatibility with the polymer has increased substantially. Since melt-extrusion temperatures for polymer PPA typically are in the range of from about 250.degree. to about 300.degree., the additive clearly will be compatible with the polymer at melt extrusion temperatures.

The second material consisted of polymer PPA alone as a negative control. FIGS. 3A and 3B are representations of the hot-stage photomicrographs at 160.degree. and 220.degree., respectively. In FIG. 3A, crystallites 31 are seen. While not apparent from the FIGURES, such crystallites 31 differ in appearance and are distinguishable from additive globules, such as additive globules 21 in FIG. 2A. Upon heating to 220.degree., as shown by FIG. 3B, most of the crystallites 31 have disappeared; some debris 32 is present.

As a positive control, composition PP20-1 from Example 33 was studied under the same conditions. Representations of the photomicrographs are shown as FIGS. 4A and 4B. In both FIGURES, numerous globules 41 of additive D02 are apparent. Some of such globules apparently have coalesced at the higher temperature to form droplets 43 (FIG. 4B). At least one debris particle 42 is seen in FIG. 4A.

The incompatibility of additive D02 in polymer PPA at both 160.degree. and 220.degree. is striking, especially when FIG. 4B is compared with FIG. 2B. Moreover, it is clear that the additive becomes less compatible with the polymer as the temperature of the polymer increases.

This discussion of the hot-stage microscope study concludes with the results obtained with composition PP25-3 from Example 38. That composition, it will be recalled, consists of polymer PPA and a mixture of additives having molecular weights of 3,000, 3,000, and 8,000, respectively. The presence of additive globules 51 is seen in FIG. 5A which represents the hot-stage photomicrograph at 160.degree.. Such globules appear to be nearly gone at 220.degree. (FIG. 5B).

Thus, FIGS. 5A and 5B are similar to FIGS. 2A and 2B, respectively, and demonstrate that the additive mixture changes from incompatible to compatible as the temperature of the polymer is raised from 160.degree. to 220.degree..

Several other compositions of the present invention were included in the hot-stage microscope study with results similar to those shown in FIGS. 2A, 2B, 5A, and 5B.

From the foregoing, it is apparent that the use of the hot-stage microscope as just described can be used as a simple method for determining whether or not any given additive or additive mixture is likely to segregate in a controlled manner to the surface of a fiber or film as described herein. If the additive or additive mixture forms globules which remain at both 160.degree. to 220.degree., the probability is that such additive or additive mixture will not segregate to one or more of the interfacial surface, effective surface, and subsurface. In addition, the melt-processing of a composition incorporating therein such additive or additive mixture probably will not be successful. On the other hand, if the additive or additive mixture does not form globules at 160.degree., the additive or additive mixture is compatible with the polymer at temperatures below melt-extrusion temperatures and probably will remain distributed throughout the bulk of the resulting fiber or film without any controlled segregation toward the surface.

As an initial screening method, films were pressed from various of the compositions prepared and described in Section II, above. The apparatus employed was a Carver Laboratory Press, Model 2518 (Fred S. Carver, Inc., Menomonee Falls, Wis.) having heated plates. From about 1 to about 10 g of a composition was placed between two sheets of aluminum foil and the resulting assembly was placed on the bottom plate of the press, the plates having been preheated to about 180.degree.. Pressure up to about 10,000 psig was applied and maintained for no more than about 5 seconds. The pressure was released and the foil sandwich was removed from the press. The foil was removed and the film thus obtained was stored in a plastic bag. Film thicknesses of from about 1 to about 5 microns typically were obtained. The wettability of each film made with a types A, B, or C additive was qualitatively estimated by simply placing a drop of water on the surface and observing whether or not the drop wet the surface of the film. The films obtained and the results of wettability screen are summarized in Table 15.

In an effort to obtain some indication of the preferential segregation of additive(s) to the surface of the melt-pressed films, a sample of the film of Example 159 was subjected to scanning electron microscopy in conjunction with a silicon x-ray probe (Si-SEM) in accordance with standard procedures. The scanning electron microscope was manufactured by Cambridge Instruments, Cambridge, England, and the x-ray probe was manufactured by Princeton Gamma Tech, Princeton, Calif.

The sample of the film of Example 159 is represented diagrammatically by FIG. 6, in which film sample 60 has top surface 61 and front end surface 62. FIG. 7 is the diagrammatic representation of FIG. 6 on which has been superimposed the results of the Si-SEM. In FIG. 7, film sample 70 has top surface 71 and front end surface 72. Each of dots 73 represents the presence of silicon atoms.

It is clear that the additives included in the composition from which the film of Example 159 was prepared have segregated preferentially to the surface region of the film. The absence of silicon in the core region of the film is striking. The irregular distribution of silicon along top surface 71 is believed to have resulted from the irregularities present in the surface of the top plate of the press. Such irregularities include the generally streaked orientation of silicon atoms along surface 71.

Water contact angles were measured for several of the melt-pressed films. The apparatus employed was an NRL Goniometer, Model No. 100-00-115 (Rame-Hart, Inc., Mountain Lakes, New Jersey). The water used was HPLC Grade water (Fisher Scientific, Pittsburgh, Pennsylvania). The results of the measurements are summarized in Table 16.

The presence of a primary additive intended to impart water wettability clearly decreased the contact angle measurement of the film relative to the control film which did not contain additive, as expected.

Two film samples were submitted for analysis by Rutherford back scattering (RBS) spectrometry. The analyses were carried out by Charles Evans & Associates, Redwood City, California. The apparatus employed was a General Ionics Model 4110 Tandem Accelerator (General Ionics Corporation, Newburyport, Mass.) using an Evans End Station (Charles Evans & Associates). A 2.275 MeV He.sup.++ ion probe was used, with a detection angle of 160 degrees. Typical beam currents were 1-20 nanoamps. Ions were detected by surface barrier detectors. Data analysis involved the TOS source code written by Charles Evans & Associates and owned by General Ionics Corporation. The energy losses of the scattered helium nuclei give information on the nature and depth of the target atoms in the polymer matrix. The results are summarized in Table 17.

The RBS data from Table 17 for the film of Example 159 were plotted as the atomic concentration of silicon in atom percent (y-axis) versus depth in .ANG. (x-axis); the plot is shown as FIG. 8. In this and all subsequent plots of RBS data, the silicon concentrations were drawn parallel to the x-axis as lines which correspond to the depth field and the midpoints of such lines then were connected to obtain the curve shown in the plot. It is evident from FIG. 8 that most of the additives have segregated to the interfacial surface, effective surface, and subsurface of the film. Below a depth of around 1000-1250 .ANG., the concentration of silicon is very low, i.e., no more than about 0.4 atom percent.

The films from Examples 135 and 159 were subjected to electron spectroscopy for chemical analysis (ESCA). The ESCA data were collected by Surface Science Laboratories, Inc., Mountain View, Calif., using a Hewlett-Packard 5950 B spectrometer with a monochromatic aluminum K-alpha x-ray source. The scans were done with the open aperature setting for high sensitivity (low resolution). The x-ray power setting was 600-800 watts and charge neutralization was accomplished with a flood gun setting of 13 electron volts. The vacuum utilized was 10.sup.-8 Torr. The area analyzed was about 1.times.4 mm and the sampling depth was about 100 .ANG..

In addition, each film was subjected to bulk elemental analysis. The ESCA data and the results of the elemental analyses are summarized in Table 18.

It is apparent that the ESCA data and the RBS data cannot be correlated, partly because of the differences in the depths of measurements and partly because of the nonlinear concentration gradient which exists from the interfacial surface to the core of the film. Taken together, however, the data clearly establish the controlled segregation of additive toward the surface of the film.

While the primary additives clearly segregated to the surfaces of the melt-pressed films and in general were effective in imparting to the film surfaces the desired characteristics, the critical test remained to be conducted; namely, the preparation of melt-processed fibers or continuous films to determine whether or not additive segregation will occur under the conditions encountered during fiber and film formation. Thus, the preparation of fibers is the subject of the next section.

A. Meltblown Fibers from Bench-Scale Apparatus

As a simple screening method, fibers were formed by means of a bench-scale apparatus having a single orifice in the die tip. The apparatus consisted of a cylindrical steel reservoir having a capacity of about 15 g. The reservoir was enclosed by an electrically heated steel jacket. The temperature of the reservoir was thermostatically controlled by means of a feedback thermocouple mounted in the body of the reservoir. The extrusion orifice had a diameter of 0.16 inch (0.41 mm) and a length of 0.060 inch (1.5 mm). A second thermocouple was mounted near the die tip. The exterior surface of the die tip was flush with the reservoir body. Composition extrusion was accomplished by means of a compressed air piston in the reservoir. The extruded filament was surrounded and attenuated by a cylindrical air stream exiting a circular 0.075-inch (1.9-mm) gap. Attenuating air pressures typically were of the order of 5-90 psig. The forming distance was approximately 10 inches (25 cm). The attenuated extruded filament was collected on the clear plastic film of an 8.5.times.11 inch (21.6.times.27.9 cm) loose leaf protector having a black paper insert.

In each case, the material extruded consisted of a simple mixture of a polymer and the desired additive(s) in the desired amount(s). The mixtures extruded (meltblown) are summarized in Table 19.

Meltblowing conditions for any given composition depended primarily on the polymer component. Consequently, standardized conditions were utilized for each of the three polymers as summarized in Table 20.

The wettability of each web was estimated by placing a drop of water on a sample of the nonwoven material and measuring the time required for complete penetration of the water drop into the fabric (referred to hereinafter as "wetting time"). Each sample was tested with a minimum of five drops of water placed in five different locations. If all of the drops wet the web within three seconds, the web was considered to be immediately wettable (i.e., wettable). If the wetting times of the drops were greater than three seconds and equal to or less than 30 seconds, the web was considered to be slowly wettable. If wetting times were greater than 30 seconds, the web was considered to be nonwettable.

Of the webs obtained in Examples 164-225, inclusive, those from Examples 164-213, 218-220, and 223-225, inclusive, were immediately wettable, although in some cases wettability was dependent upon fiber diameter. Those from Examples 214-217, inclusive, 221 and 222 were nonwettable. It is seen from Table 19 that Examples 214-217 employed additive A24, Example 221 employed additive B04, and Example 222 employed additive B11. According to Table 1, additive A24 has a molecular weight of about 7,900. From Table 3, it is seen that additive B04 has a molecular weight of about 3,000 and additive B11 has a molecular weight of about 15,000. All three molecular weights are high enough to prevent the rapid segregation of the additive to the effective and/or interfacial surface region of the fibers. Consequently, the fibers were not wettable.

It should be noted, however, that webs made from a composition containing a mixture of additives having molecular weights equal to or greater than about 3,000, i.e., the webs of Examples 223-225, inclusive, were wettable, while webs made from a composition containing any one of the additives used in the mixture were not wettable (i.e., the web of Example 221). This illustrates the apparent synergistic effect which can result from combining additives, even though such additives individually do not segregate under similar melt-processing conditions above the subsurface of the fibers or films.

Some qualitative observations on web quality and wettability as a function of fiber diameter are appropriate at this point, at least for webs made with polymer PPA.

Web quality was based on visual inspection or inspection under a low-power optical microscope and was rated on a scale of from 1 to 4 as follows:

4--fibers having uniform diameters with no shot present;

3--fibers having a small amount of fiber diameter nonuniformity, with small amounts of shot present (fiber diameter nonuniformity refers to variations of fiber diameter, i.e., the presence of varying large and small fiber diameters);

2--moderate fiber nonuniformity and a moderate amount of shot present; and

1--substantial fiber nonuniformity and a large amount of shot present.

Fiber diameters also were estimated visually or under the microscope and were simply classed as small, medium, or large. As will be described in greater detail later, fiber diameter is a function of attenuating air pressure--the higher the pressure, the smaller the fiber diameters.

A number of the webs obtained in Examples 164-225, inclusive, were evaluated for web quality and fiber diameter. The results of this evaluation and the wettabilities of the webs evaluated are summarized in Table 21.

The data in Table 21 substantiate the already-observed decrease in wettability associated with increasing primary additive molecular weight. In addition, however, the data suggest that there is a correlation between web quality and primary additive cloud point. That is, when the cloud point of the primary additive is above about 20.degree. C., web quality declines significantly. Thus, the cloud point of primary additives employed to impart water wettability to the surface of fibers or films preferably will be no more than about 20.degree. C. and most preferably no more than about 10.degree. C.

In order to more fully understand the segregation phenomenon, three series of the bench-scale meltblowing experiments were repeated under somewhat more carefully controlled conditions. The first series employed either polymer PPA or PPB and additive levels of two percent by weight; the process and product details are summarized in Table 22. Fiber diameters were estimated from scanning electron photomicrographs taken by Surface Science Laboratories, Inc., Mountain View, Calif. The instrument employed was a Camscan Series 4 Scanning Electron Microscope. The accelerating voltage was 24 keV, the working distance was 20 mm, and the spot size was 5. The instrument was calibrated with 0.76-micron diameter National Bureau of Standards latex spheres. Each sample was gold coated (1--.ANG. thickness) to increase conductivity under the electron beam.

In each case, a coherent web was obtained. Each web was subjected to ESCA analysis. Additionally, each web was subjected to bulk elemental analysis and the water drop test. The ESCA data and the results of the elemental analyses and water drop tests are summarized in Table 23.

From Table 23, it is seen that only two webs were not wettable; both webs were made with additive B04 which has a molecular weight of about 3,000. Interestingly, the fibers of both webs had higher bulk silicon concentrations and higher surface silicon concentrations than any of the webs which were wettable. Indeed, the fibers of the web from Example 234 had from three to nine times as much silicon in the top 100-.ANG. layer of the surface as the fibers of webs which were wettable. Notwithstanding such high concentrations, it is evident that there was insufficient additive in the effective surface to render the webs wettable. Thus, while the higher molecular weight additives will segregate to some extent, additive molecular weights of less than about 3,000 are required in order for additive to migrate to the interfacial surface or effective surface in concentrations sufficient to impart wettability to the fibers, at least for fibers having diameters in the 3-15 micrometer range.

In order to demonstrate the effect of fiber diameter on surface silicon concentration, a second series of bench-scale meltblowing experiments was carried out. In this series, the polymer was PPB and the additive was A10 at a level of two percent by weight (the additive molecular weight is 794--see Table 1). ESCA analyses were carried out on the webs, all of which were wettable. The results are summarized in Table 24.

From the discussion earlier regarding the factors influencing the segregation of the additive, it apparent that there are two competing factors in the segregation of additive during fiber formation. First, as the diameter of the fiber is diminished, the distance to the surface also is diminished, thereby contributing to higher additive concentrations in the surface region. Second, as the diameter of the fiber is diminished, the time the fiber remains in a molten state also is diminished, thereby shortening the time during which the additive can migrate toward the surface. From the data in Table 24, it is evident that the second factor was controlling since the additive concentration was reduced as the fiber diameter decreased.

As already pointed out, the higher molecular weight additives segregate toward the surface of the fiber or film, but typically do not reach either the interfacial surface or the effective surface. In cases where the additive was segregated to the subsurface and is sufficiently close to the effective surface, the additive can be "coaxed" to the effective surface by the application of relatively mild heating conditions. This phenomenon is illustrated by a third series of bench-scale meltblowing experiments.

The third series of experiments involved the incorporation of two weight percent of an additive in PPA polymer essentially as described in Examples 164-225, inclusive. An ESCA and elemental analysis was obtained for each web. The wettability of each web also was estimated by the water drop test. A sample of each web then was heated in an oven at 120.degree. degrees for 20 seconds. An ESCA analysis was obtained on the heated web and its wettability estimated as before. The results are summarized in Tables 25 and 26.

While the heat treatment did not convert every nonwettable web into a wettable one, the procedure was successful for the two lowest molecular weight additives. Whether or not such treatment can be used depends, at least in part, on whether or not the additive has segregated to the subsurface sufficiently close to the effective surface to permit a gentle heat treatment to move the material into the effective surface region. Such segregation in turn is in part dependent upon the diameter of the fibers, i.e., the time the fibers remain in a molten state. Thus, the choice of additive and heat treatment conditions is, of necessity, somewhat empirical.

The ability of primary additive to be moved from the subsurface to either the effective surface or the interfacial surface, or both, expands the types of products based on nonwoven webs prepared in accordance with the present invention. A few examples in the area of household and industrial wipes will serve by way of illustration:

(1) a wipe consisting of a single polyolefin nonwoven web prepared in accordance with the present invention, in which additive is present in either of both of the effective surfaces and the interfacial surfaces of the fibers--the wipe is hydrophilic or water wettable and is suited for washing or cleaning tasks using aqueous cleaning solutions;

(2) a wipe consisting of a single polyolefin nonwoven web prepared in accordance with the present invention, in which additive is present in the subsurface of the fibers--the web is hydrophobic or oleophilic and is suited for cleaning oily surfaces, but on washing the wipe is converted to a hydrophilic wipe because the heat of the washing or drying environment causes additive to migrate from the fiber subsurface to either or both of the fiber effective surface and interfacial surface, which conversion aids in the removal of oily residues from the wipe; and

(3) a wipe consisting of two polyolefin nonwoven layers, one prepared from virgin polymer and the other consisting of a web as described in either (1) or (2) above--in the first instance, the wipe will be effective for both water-soluble or water dispersible substances and oily substances, depending on which layer is used as the wiping layer, and in the second instance, the wipe can be converted to a wipe of the first instance by laundering.

B. Meltblown Fibers from Pilot-Scale Apparatus

Since the above bench-scale meltblowing experiments in general were successful, meltblowing trials were conducted on a pilot-scale meltblowing apparatus essentially as described in U.S. Pat. No. 4,663,220, which is incorporated herein by reference. Briefly, such meltblowing was accomplished by extruding a composition (or a simple mixture) through a 0.75-inch (19-mm) diameter Brabender extruder and then through a meltblowing die having nine extrusion capillaries per linear inch (approximately 3.5 capillaries per linear cm) of die tip. Each capillary had a diameter of about 0.0145 inch (about 0.37 mm) and a length of about 0.113 inch (about 2.9 mm). The process variables in general were as follows:

polymer extrusion rate, 2.5-3.5 g per capillary per minute;

polymer extrusion temperature, 250.degree.-300.degree., depending upon the polymer employed;

extrusion pressure, 490-510 psig;

die tip temperature, 270.degree.-275.degree.;

attenuating air temperature, 304.degree.-310.degree.;

attenuating air pressure, 8-11 psig; and

forming distance, 20-40 cm.

The collecting arrangement consisted of a rotating 15.2-cm wide drum having a diameter of 76.2 cm. The surface of the drum was a screen.

The polymer and primary additive typically were mixed by one of several methods before introducing the mixture to the feed hopper of the extruder. In the first (method A), a standard portable cement mixer was charged with 50 pounds of the polymer in pellet form. The mixer then was started and charged with the desired amount of primary additive. Mixing was allowed to continue for 20 minutes, after which time the mixture was removed from the mixer and stored in plastic-lined boxes. In a variation of that method, the primary additive was used in an amount higher than that intended for melt-processing to give a stock mixture. The stock mixture then was mixed in a similar fashion with additional polymer in a ratio calculated to give the desired final primary additive concentration (method B). In the third (method C), a metered stream of primary additive was pumped into the feed hopper about 15 cm above the feed screws as polymer pellets flowed downward by gravity into the screws. All three methods worked equally well, although method C was used with only one additive.

In each case, a coherent web was obtained which had a basis weight in the range of from about 20 to about 50 g/m.sup.2. Wettability was estimated by means of the water drop test. The trials are summarized in Table 27, along with the results of the water drop test.

The results obtained are consistent with the bench-scale meltblowing experiments. Single additives having molecular weights of the order of 3,000 or higher do not segregate to the interfacial surface or effective surface when fiber diameters are relatively small, as they are in typical meltblowing processes.

C. Spunbonded Fibers from Pilot-Scale Apparatus

Spunbonded trials were conducted on a pilot-scale apparatus essentially as described in U.S. Pat. No. 4,360,563, which is incorporated herein by reference.

The polymer and additive typically were mixed by one of the methods described above with respect to Examples 248-283, inclusive.

In each case, a web was obtained which had a basis weight in the range of from about 14 to about 60 g/m.sup.2. In some cases, webs of different basis weights were made during a trial by changing the velocity of the forming wire. Typical basis weights thus prepared were 14, 19, 36, 47, and 59 g/m.sup.2. Wettability was estimated by means of the water drop test.

Unlike the meltblown trials, however, it was discovered that when the additive level was greater than 1 percent by weight, there was no web integrity; that is, the web simply fell apart upon attempting to remove it from the forming wire, even when excellent fiber formation was obtained. The problem was overcome by running the web under a heated compaction roll before removing it from the forming wire. Thus, all of the spunbonded examples in which additive levels were greater than 1 percent by weight utilized a heated compaction roll. While a compaction roll temperature of about 66.degree. was employed, lower or higher temperatures can be used.

The trials are summarized in Table 28, along with the results of the water drop test; because wettability was independent of web basis weight, the latter is not included in the table.

Because spunbonded fibers typically have larger diameters on the average than meltblown fibers, the spunbonded webs were wettable or slowly wettable with additives having molecular weights up to about 3,000. However, the use of an additive having a molecular weight of about 8,000 did not produce a wettable web.

In order to further investigate the ability of a gentle post-formation heat treatment to bring additive to the effective surface and/or interfacial surface, ESCA analyses were carried out on three of the spunbonded webs. The webs then were heated to 110.degree. for 1 minute in a laboratory oven and the heated webs were subjected to ESCA analyses. The results of the ESCA analyses before and after heating are summarized in Table 29.

The data in Table 32 clearly show the remarkable increase in silicon concentration within the first 100 .ANG. of the surface upon exposing a web to a mild heat treatment, especially at an additive level of 1 percent by weight.

Because spunbonded webs commonly are employed as liners in disposable diapers, the mild heat treatment phenomenon was investigated by two different methods in conjunction with a simple diaper run-off test. The diaper run-off test involved removing the liner from a standard KIMBEE diaper. The linerless diaper was mounted on a plate which was inclined at a 45.degree. angle, the back edge of the diaper being at the top of the plate. The test fabric was layed over the diaper. A reservoir containing 100 ml of 0.85 percent (weight per volume) saline (cat. no. SS-442-10, Fisher Scientific, Pittsburgh, Penn.) at 37.degree. was located at the top of the plane 2 inches (5.1 cm) above the uppermost edge of the diaper's absorbent pad. The saline then was allowed to run out of the reservoir in a steady stream. Fluid which was not retained by the diaper was collected and measured, the volume of which being the run-off value.

In the first method, samples of a spunbonded nonwoven web made from a composition of the present invention and having a basis weight of 27 g/m.sup.2 were heated in an oven at two different temperatures. Run-off measurements were made on samples which had not been heat treated and those which had. In every case, the additive was A11 and the polymer was PPE. The results are summarized in Table 30.

The efficacy of the heat treatment in each case is readily apparent. It appears that 80.degree. for 3 minutes is more effective than 110.degree. for 30 seconds, at least for the webs having the two lowest concentrations of additive. Either temperature treatment, however, converts the web containing 1 percent by weight of additive into a highly wettable, highly efficient transfer layer.

In the second method, samples in continuous roll form of the same webs used in the first method were passed over two stream cans in series which were heated by steam at a pressure of 5 psig. The surfaces of the cans were at about 85.degree.. Each sample was passed over the cans at two different line speeds, after which the run-off test was performed. The results are summarized in Table 31.

The results from the second method were similar to those of the first method in that the concentration of additive leading to the most efficient transfer layer was 1 percent by weight; the slower line speed gave slightly better results at that concentration.

Because of the success with the Si-SEM procedure with a melt-pressed film, a similar effort was carried out with spunbonded fibers prepared from a composition containing a mixture of additives in polymer PPA, i.e., Example 351. In this case, a bundle of fibers was collected before they reached the forming wire. The bundle was cut and inserted into a small plastic tube about 19 mm long and having an inside diameter of about 3 mm, thereby packing the tube with fibers. The packed tubing was placed in liquid nitrogen, removed, and cut with a razor blade. The sample was placed on the SEM mount and sputtered with carbon before carrying out the analysis. A diagrammatic representation of the results of the analysis is shown by FIG. 9. In FIG. 9, the fibers 50 are bilobal in cross-section. As with the film analysis, each of dots 51 represents the presence of silicon atoms.

It is clear that the additives included in the composition from which the fibers of Example 351 were prepared have segregated preferentially to the surface region of the film. While the core region is not as devoid of silicon as was the core region of the film, there clearly is a lower concentration of the additives in the core region than in the area at or near the surfaces of the fibers. This result was expected, however, because of the relatively rapid formation of the fibers as compared to the film formation time. That is, the fibers remained in a molten state for a time which was much shorter than the time the film remained in a molten state. The fact that the additives segregated to the surfaces of the fibers in such a short time is, as already pointed out, a result of the influence of shear during the extrusion process.

Two samples of fibers from the spunbonded trials were submitted for analysis by RBS. The results are summarized in Table 32.

From the data for the two analyses of the same sample, it appears that the RBS procedure causes some loss of additives as evidenced by the decreased silicon concentration values. Thus, it is probable that the concentration values are lower than the actual concentrations. Nevertheless, the procedure is helpful because it gives at least a qualitative view of the segregation of the additives in the surface region and the core region adjacent thereto.

The RBS data from Table 32 for the webs of Examples 315 and 350 were plotted as already described. The plots for the two analyses of the web of Example 315 are shown as FIGS. 10A and 10B. The plot for the analysis of the web of Example 350 is shown as FIG. 11.

The plots are similar to that for the RBS analysis of the film of Example 159. FIGS. 8 and 10A are especially similar, although in the latter the concentration of silicon diminishes to the minimum concentration at around 2,000 .ANG. rather than at around 1,000 .ANG.. In FIG. 11, it is seen that the silicon concentration diminishes more slowly with depth, although all of the plots resulted in curves having similar shapes.

The webs from Examples 315 and 350 also were submitted for ESCA and bulk elemental analyses. The results of these analysis are shown in Table 33.

D. Meltblown Fibers from Pilot-Scale Coforming Apparatus

A number of larger-scale meltblowing runs were carried out on a coforming apparatus of the type described in U.S. Pat. Nos. 4,100,432 and 4,663,220, the latter patent having been identified and incorporated herein by reference in regard to Examples 248-283, inclusive; the former patent also is incorporated herein by reference.

Meltblowing was accomplished by extruding the composition from a 1.5-inch (3.75-cm) Johnson extruder and through a meltblowing die having 15 extrusion capillaries per linear inch (about 5.9 extrusion capillaries per linear cm) of die tip. Each capillary had a diameter of about 0.018 inch (about 0.46 cm) and a length of about 0.14 inch (about 3.6 mm). The composition was extruded through the capillaries at a rate of about 0.5 g per capillary per minute at a temperature of about 184.degree.. The extrusion pressure exerted on the composition in the die tip was in the range of from about 180 to about 200 psig. The composition viscosity in the die tip under these conditions was about 500 poise. The die tip configuration was adjusted to have a positive perpendicular die tip distance of about 0.01 inch (about 0.25 mm). The air gaps of the two attenuating air passageways were adjusted to be about 0.067 inch (about 1.7 mm). Forming air for meltblowing the composition was supplied to the air passageways at a temperature of about 209.degree. and a pressure of about 2 psig. The fibers thus formed were deposited on a forming screen drum which was approximately 18 inches (46 cm) below and 20 inches (51 cm) back from the die tip.

The more significant process variables generally were as follows:

barrel temperature, 280.degree.-300.degree.;

die temperature, 285-316.degree.;

melt temperature in die, 275.degree.-316.degree.;

barrel pressure, 220-570 psig;

die pressure, 55-130 psig;

primary air temperature, 235.degree.-349.degree.;

primary air pressure, 3-4.5 psig;

throughput, 7-360 g per cm of die width per hour;

forming distance, 36 cm; and

basis weight, 27-85 g/m.sup.2, with the more typical basis weights being 27, 51, and/or 85 g/m.sup.2.

The compositions which were meltblown were prepared by melt-blending polymer and additive(s) as described in Examples 43-121, inclusive. Coherent webs were formed in each case. As with previous trials, wettability of the formed webs were estimated by the water drop test as appropriate. The compositions meltblown and the results of the water drop test are summarized in Table 34.

The results of the meltblowing trials on the conforming apparatus with additives which impart water wettability to the surfaces of the fibers were consistent with those of the previous meltblowing trials.

As already pointed out, however, additive D05 moved to the surface of the fibers because it is incompatible with the polymer. Such incompatibility resulted in poor web formation; that is, the web was characterized by nonuniform fiber diameters, an unusually high proportion of discontinuous fibers, and a substantial amount of shot. The process was characterized by a frequent, almost explosive, expulsion of polymer from the die orifices which is potentially hazardous to the operators.

E. Coformed Webs from Pilot-Scale Coforming Apparatus

Two fibrous coformed nonwoven webs were formed by meltblowing a composition containing primary additive and incorporated polyester staple fibers therein.

Meltblowing was accomplished as described for Examples 352-423, inclusive. In each case, the polymer was PPA and the additive was B01 at a level of 3 percent by weight.

The more significant meltblowing process conditions were approximately as follows:

die tip temperature, 296.degree.;

primary air temperature, 284.degree.;

primary air pressure, 3.5 psig;

throughput, 179 g per cm of die width per hour;

horizontal forming distance, 51 cm; and

vertical forming distance, 43 cm.

Following the procedure illustrated by FIG. 5 of said U.S. Pat. No. 4,663,220 and described therein, 3-inch (7.6-cm) long, 40 denier per filament polyester staple (type 125, E. I. Du Pont de Nemours & Co., Inc., Wilmington, Del.) was incorporated into the stream of meltblown fibers prior to deposition upon the forming drum. The polyester fibers were first formed by a Rando Webber mat-forming apparatus into a mat having a basis weight of about 100 g/m.sup.2. The mat was fed to the picker roll by a feed roll which was positioned about 0.13 mm from the picker roll surface. The picker roll was rotating at a rate of about 3,000 revolutions per minute and fiber transporting air was supplied to the picker roll at a pressure of about 2.5 psig. While actual measurement of the position of the nozzle of the coform apparatus with respect to the stream of meltblown fiber was not made, it was estimated to be about 5.1 cm below and about 5.1 cm away from the die tip of the meltblowing die.

Two coformed webs were prepared, both of which had a width (cross-machine direction) of about 51 cm. The first web was composed of about 70 percent by weight of the polyester staple fibers and about 30 percent by weight of the meltblown fibers and the second web was composed of about 50 percent by weight of each of the two types of fibers. Each web had a basis weight of about 100 g/m.sup.2 and wet immediately when subjected to the water drop test.

Although not described in detail here, other coformed webs were similarly prepared with staple fiber:meltblown fiber ratios of 85:15, 75:25, 65:35, and 15:85. In addition, webs utilizing other sources of polyester staple fibers were prepared at each of the foregoing ratios. Such other polyester staple fibers were as follows:

3.25-inch (8.3-cm).times.25 denier (Eastman Chemical Products, Inc., Kingsport, Tenn.);

type ES 1.5-inch (3.8-cm).times.1.5 denier (Chisso Corporation, Tokyo, Japan); and

type 41-D 1.5-inch (3.8-cm).times.1.5 denier (Eastman Chemical Products, Inc.).

The procedure of Examples 424 and 425 were repeated, except that the composition was 3 percent by weight of additive B01 in polymer PEA, the secondary fibers were wood pulp fibers, and a dual meltblowing die/center secondary fiber duct arrangement was employed. The composition was meltblown through one die at a throughout of either 179 or 894 g per cm per hour. In either case, the melt temperature was about 288.degree.. The die tip pressure was either 90 or 220 psig, depending upon the throughput.

Polymer PPC was meltblown through the other die at a throughput of from about 179 to about 716 g per cm per hour. The melt temperature was in the range of from about 246.degree. to about 274.degree. and the primary air temperature was in the range of from about 280.degree. to about 302.degree.. The primary air pressure was in the 2-5 psig range.

Coformed webs containing pulp:polymer ratios of 70:30 and 90:10 were prepared. The webs wet immediately and the composition did not impede the absorbancy of the web.

V. Preparation of Cast Films

Cast films were prepared on a cast film pilot line consisting essentially of a Hexco extruder having an 8.9-cm diameter barrel, an all-purpose mixing screw, and a length-to-diameter ratio of 24 (Hexco, Inc., Addison, Ill.). The die was a 91-cm wide coathanger manifold, standard sheet die (EDI Ultraflex H-40, Extrusion Dies, Inc., Chippewa Falls, Wisc.). The chill roll and take-away system consisted of two 50.8-cm outer diameter, 91-cm wide rolls with matte finishes, water cooled or heated. The winder was a Model 191-W winder and take-away system manufactured by Gloucester Engineering Co., Gloucester, Mass. The resin feeder were Conair automatic pneumatic-type resin loaders.

Three films were prepared as summarized in Table 35. In each case, the melt temperature was about 216.degree. and the die temperature was 216.degree.-219.degree.. The chill rolls were maintained at temperatures of 16.degree. and 21.degree., respectively.

Film preparation in general was routine, although barrel pressure decreased upon switching to the higher level of additive. Attempts to cast a film with polymer PPF and 5 percent by weight additive A11 and films from polymer PEB with higher levels of additive PEGB were unsuccessful because of a loss of extruder pressure resulting from an inappropriate extruder screw design for the polymers and additive levels employed (no difficulties were encountered in compounding compositions in the pilot-scale apparatus, regardless of the polymer or additive level). All of the films prepared were wettable.

The films were subjected to both ESCA and bulk elemental analyses. The results are summarized in Table 36.

The analytical data summarized in Table 36 demonstrate that the additive in each case segregated to the film surface. Thus, the behavior of the additives is the same for both films and fibers.

When fibers were formed from compositions containing lower molecular weight primary additives, such as additives A01-A14, inclusive, and B01-B03, inclusive, smoke occasionally was observed emanating from the screw pumps. This was particularly true with equipment having longer residence times in the extruder, such as the equipment used to produce fibers as described in Part B of Section IV.

The effectiveness of stabilizing additive was demonstrated by coating particles of polymer PPE with a solution of additive D01 in additive A11. The amount of additive A11 was equal to 3 percent by weight of the amount of polymer, and the amount of additive D01 was equal to 1 percent by weight of the amount of additive A11. The coated polymer was meltblown as described in Section IV, Part B for Examples 248-283, inclusive. As a control, polymer coated with 3 percent by weight of additive A11 only also was meltblown under equivalent conditions. While smoke was observed during the meltblowing of the control, no smoke was observed upon meltblowing the polymer coated with additive A11 which contained additive D01 as a stabilizer.

In conclusion, an additive of the type described in U.S. Pat. No. 4,659,777 was evaluated both in melt-pressed films and fibers from the bench-scale meltblowing apparatus. The additive was a poly(2-ethyloxazoline)polydimethylsiloxane-(2-ethyloxazoline) block copolymer, each of the blocks having a molecular weight of about 3,000.

A melt-pressed film was prepared successfully as described for Examples 122-163, inclusive. The material contained 10 percent by weight of the additive in polymer PPA.

The surface energy of the film was estimated by means of Pillar wetting agents (Pillar Corporation, West Allis, Wisc.) to be 34-35 dynes per cm. The value for virgin polymer is about 30. The film then was subjected to ESCA analysis. None of the additive was found to be in the first 100 .ANG. below the interfacial surface.

Meltblown fibers were prepared with a bench-scale apparatus as described for Examples 164-225, inclusive. The composition consisted of 3 percent by weight of the additive in polymer PPA. Meltblowing was conducted at an air pressure of 35 psig and melt temperatures of 264.degree., 285.degree., and 308.degree.. Although webs were obtained in each case, web quality was poor and decomposition of the additive occurred at each melt temperature. Decomposition was especially severe at the highest temperature. No analyses of the webs were attempted since the additive obviously is unsuited for melt-processing procedures and does not segregate to the surface.

One last hot-stage microscope analysis is conveniently described here. The composition consisted of polymer PPA with 3 percent by weight of TRITON X-102 (Rohm and Haas Co.), a surfactant which is commonly used to make polypropylene wettable by means of the blooming technique already described; see U.S. Pat. No. 4,070,218. The representation of the photomicrographs are shown in FIGS. 12A and 12B. Globules 121 of the surfactant are seen in both FIGURES; some debris 122 in FIG. 12A also is apparent. The most noteworthy fact about the two FIGURES is that the surfactant not only is incompatible with the polymer at 160.degree., but is even less compatible at about 220.degree.. In view of FIGS. 12A and 12B, it is easy to understand why a blooming process is required to bring the surfactant to the surface of the fiber or film and why the material migrates back into the polymer.

It now should be evident that the additives described herein and the compositions of the present invention function in a manner which is different from the materials previously added to thermoplastic polymers to alter the surface characteristics of shaped articles, such as fibers and films, made therefrom. Moreover, the compositions of the present invention permit the control of the segregation phenomenon, which control was not possible with prior art procedures.

Having thus described the invention, numerous changes and modifications thereof will be readily apparent to those having ordinary skill in the art without departing from the spirit or scope of the invention. For example, the compositions of the present invention also can contain fillers, delustrants, colorizers, stabilizers, and the like.