Hot Melt Adhesive Composition

1. Technical Field

This invention relates to hot melt adhesive and sealant compositions which can be used, for example, as sealants for double glazing units to be used as windows, as adhesives for automobile windows, as architectural glass sealants, as sealants in solar collectors, as load bearing sealants in automotive, appliance, or aerospace applications, or as jet apron sealants. In particular, this invention relates to such adhesive and sealant compositions which are based on alkali metal ionomers of random copolymers prepared from ethylene, methyl acrylate, and at least one carboxylated unsaturated monomer, and the improvement of viscosity stability of such compositions, particularly when such compositions are subjected to high temperature, such as just prior to and during application of the adhesive.

2. Background Art

U.S. Pat. No. 4,031,058, granted June 21, 1977 to Cella, discloses certain hot melt adhesive and sealant compositions based on sodium or potassium ionomers of random ethylene/methyl acrylate/monoethyl maleate terpolymers. The compositions of Cella are representative of compositions improved by the present invention. Similar compositions can be prepared from related terpolymers wherein the monoethyl maleate is replaced by other carboxylated monomers such as acrylic acid, methacrylic acid and maleic acid.

The present invention relates to hot melt adhesive and sealant compositions which are based on alkali metal ionomers of random copolymers of ethylene, methyl acrylate and at least one carboxylated monomer, to the improvement of the viscosity stability of such compositions, particularly at high temperature, by including in such compositions 0.05-10 (preferably 0.1-10) parts/100 parts of copolymer of ammonium polyphosphate, and to masterbatch compositions useful in the preparation of such improved adhesive and sealant compositions. In addition to the improved viscosity stability, such adhesive and sealant compositions offer the following noteworthy characteristics:

1. High mechanical strength and dead load creep resistance extending up to 100.degree. C. while still allowing pumping at 150.degree.-200.degree. C.

2. Low temperature flexibility down to -60.degree. C.

3. Outstanding oil and jet fuel resistance.

4. Excellent weathering and ultra-violet resistance.

5. Good adhesion to many substrates, including glass and metals, without priming.

As described in greater detail in U.S. Pat. No. 4,031,058, one type of random copolymer which can be improved by the present invention contains about 50 to 60 wt. % polymerized methyl acrylate units, about 3 to 5 wt. % polymerized maleic acid monoethyl ester (monoethyl maleate) units and about 35 to 47 wt. % polymerized units of ethylene. Suitable copolymers may contain other carboxylated unsaturated termonomers in place of the monoethyl maleate, and may also contain minor amounts of other polymeric units such as those listed in U.S. Pat. No. 3,264,272, granted Aug. 2, 1966 to Rees. Useful carboxylated unsaturated termonomers include those represented by the general formula ##STR1## where X is H--, --COOH or --COOR, where R is C.sub.1 to C.sub.6 alkyl

and where Y is H or CH.sub.3 --.

Preferred termonomers are monoethyl maleate, acrylic acid and maleic acid. Between about 5% and about 60% of the carboxylic acid groups in the copolymer are neutralized with an alkali metal, preferably sodium and/or potassium ions. Processes for the neutralization of acid groups in random ethylene copolymers are taught in U.S. Pat. No. 3,404,134, granted Oct. 1, 1968 to Rees. Preferably, the copolymer prior to neutralization has a molecular weight such that the melt index of the copolymer is within the range of about 1 to 30 g per 10 minutes, ASTM D 1238, 190.degree. C., 2160 g weight.

The adhesive and sealant compositions of the present invention will generally contain, in addition to the terpolymer ionomer and the ammonium polyphosphate, one or more of the following: tackifying resin, plasticizer and filler. The masterbatch compositions of the present invention will contain the terpolymer ionomer, the ammonium polyphosphate, and at least one, but generally not all, of the additives described hereinafter. Preferably, the masterbatch compositions contain only the terpolymer ionomer, the ammonium polyphosphate, and an inorganic filler, generally carbon black. The base terpolymer ionomer is difficult to isolate in the raw state, and carbon black provides an unusually strong reinforcing interaction with the ionic groupings, which greatly enhances sealant strength. In preparing the novel adhesive and sealant compositions of this invention, one can also use a conventional masterbatch free of ammonium polyphosphate and add the polyphosphate during adhesive or sealant preparation.

It should be noted that during preparation of the masterbatch, temperature control is important to provide efficient mixing while avoiding thermal degradation of the polymer. A preferred procedure comprises mixing the masterbatch, materials in an internal mixer at 70.degree.-205.degree. C., preferably 80.degree.-160.degree. C., and extruding the resulting blend at 100.degree.-205.degree. C., preferably 130.degree.-195.degree. C. If temperatures in excess of those specified are used, the resulting masterbatch will produce hot melt sealants which have a tendency to increase in viscosity, particularly in the absence of ammonium polyphosphate, or even undergo gelation. While this undesirable instability can be substantially overcome or even eliminated by the presence of ammonium polyphosphate, it is still recommended that masterbatch preparation be performed within the suggested temperature ranges. It should be further noted that during preparation of the masterbatch from the terpolymer, interaction of the terpolymer with the basic alkali metal compound to form the ionomer should be substantially completed before the ammonium polyphosphate is added. The amount of ammonium polyphosphate use is relatively small; thus it may be convenient to add it in the form of a blend with a minor portion of the carbon black and/or a minor portion of the random copolymer.

Tackifiers suitable for use in the compositions of the present invention include commercially available resins such as

(a) "Picco" 6110 resin sold by Hercules Incorporated, which is a highly aromatic hydrocarbon resin, petroleum based, with a softening point, R and B, of 108.degree.-112.degree. C. and a density at 200.degree. C. of 1060 kg/m.sup.3 ;

(b) "Picco" 6140 resin sold by Hercules Incorporated, which is a highly aromatic hydrocarbon resin, petroleum based, with a softening point, R and B, of 140.degree.-144.degree. C. and a density at 25.degree. C. of 1070 kg/m.sup.3 ;

(c) "Piccovar" AP-10 sold by Hercules Incorporated, which is an alkyl-aromatic product that is soluble in aliphatic hydrocarbons, with a color range on the coal tar scale of 4-6, a softening point of 10.degree. C., a maximum acid number of 1, a maximum saponification number of 1, a specific gravity of 0.93 and a melt viscosity of 0.1 Pa.s at 85.degree. C., 1.0 Pa.s at 63.degree. C. and 10 Pa.s at 40.degree. C.; and

(d) "Piccoumaron" 10 sold by Hercules Incorporated, which is a polyindene type polymer with a color range on the coal tar scale of 3-5, a softening point of 10.degree. C., a maximum acid number of 1, a maximum saponification number of 1, a specific gravity of 1.04, and a melt viscosity of 0.1 Pa.s at 95.degree. C., 1.0 Pa.s at 55.degree. C., and 10 Pa.s at 40.degree. C.

Other tackifying resins can also be used, see, e.g., U.S. Pat. No. 3,573,240, issued Mar. 30, 1971 to Flanagan. The amount of tackifying resin in the hot melt adhesive of the present invention is between about 0 parts by wt. to about 250 parts by wt. per 100 parts by wt. of the random copolymer of ethylene, methyl acrylate and at least one carboxylated unsaturated monomer. Mixtures of tackifiers can also be used.

Selection of tackifiers, as well as selection of the other compounding additives, is dictated by compatibility as well as by the properties desired in the sealant. Tackifying resins are considered incompatible either if they are difficult to incorporate into the rubber or if phase separation ("blooming") occurs on standing. Compatibility can be readily determined using a pressed slab of 50/50 tackifier/masterbatch composition. Most common types of tackifier are compatible, but the results summarized in Table 1 below will offer an additional guidance.

Inorganic fillers suitable for use in the adhesive and sealant compositions of the present invention should be present in the adhesive in the amount of about 5 parts by wt. to about 200 parts by wt. per 100 parts by wt. of the copolymer of ethylene, methyl acrylate, and at least one carboxylated unsaturated monomer. Suitable inorganic fillers include carbon black, calcium carbonate, titanium dioxide, talcs, clays, mica, alumina and silica. Mixtures of fillers can also be used.

Carbon black can be used as a filler in the compositions of the present invention to increase mechanical strength and hardness and to decrease the raw materials cost, but it can also reduce adhesion. Mineral fillers such as calcium carbonate or talcs can also be added, but because the terpolymer is only partially neutralized, caution must be exercised when incorporating such materials containing metal ions to prevent an excess of ionomeric crosslinking. Thus, certain types of whiting (e.g., Super Multifex) will cause the polymer to become nervy, while others (e.g., Atomite) act as inert fillers. This reactivity can be taken advantage of to increase the degree of ionic crosslinking in a controlled manner if desired by adding up to about 2 parts by weight per 100 parts by weight of the copolymer of ethylene, methyl acrylate, and at least one carboxylated unsaturated monomer of a reactive base or salt such as potassium hydroxide, sodium acetate or sodium carbonate decahydrate. Additives containing monovalent cations are preferred. Addition of white fillers may also induce blowing at 180.degree. C. or above.

Plasticizers suitable for use in the adhesive and sealant compositions of the present invention should be present in the adhesive in an amount of about 10 parts by weight to about 150 parts by weight per 100 parts by weight of the copolymer of ethylene, methyl acrylate, and at least one carboxylated unsaturated monomer. Suitable plasticizers include the chlorinated paraffins, such as "Chlorowax" 40, sold by Diamond Shamrock Corporation, which is a 40% chlorinated paraffin and has a Brookfield viscosity of 32 poises. Polyester plasticizers such as "Harflex" 330, sold by Wallace and Tiernan Inc., a polymeric plasticizer of 1,3-butylene glycol and adipic acid, having a viscosity of 2340 centipoises at 100.degree. F. are also suitable. Preferred plasticizers include tri(2-ethylhexyl) trimellitate; di(2-ethylhexyl) sebacate; "Plastolein" 9772, sold by Emery Industries, which is a polymeric polyester plasticizer with a solidification point of -9.degree. C., a specific gravity 25.degree./25.degree. C. of 1.04, an acid number of less than 3.0 and a hydroxyl number of about 15; and "Plastolein" 9734, sold by Emery Industries, which is a polymeric polyester plasticizer with a solidification point of 13.degree. C., a specific gravity 25.degree./25.degree. C. of 1.04, an acid number greater than 3.0 and a hydroxyl number of about 17. The terpolymer used in the compositions of the present invention possesses high oil resistance and is not generally compatible with hydrocarbon oils. However, it is compatible with most other common types of plasticizers, including esters and chlorinated compounds. In general, care should be exercised in using phosphate ester plasticizers because variable results have been obtained when they are used in the compositions of this invention.

Adhesive and sealant compositions intended for certain uses must not contain components which will slowly bleed out and deposit on the substrate surfaces (fogging). The fog resistance of various tackifiers and plasticizers can be readily evaluated by heating them with a sunlamp to 70.degree. C. in a container covered with a refrigerated plate at 15.degree. C. and examining the plate for residues after periods up to one week. Data for fog resistance of common plasticizers and tackifiers are given in Tables 2 and 3 below:

The adhesive and sealant compositions of the present invention may also include various other additives generally used in hot melt adhesive and sealant compositions, such as reinforcing resins and adhesion promoters.

Flow properties, dead load creep resistance and high temperature strength can often be improved by adding small quantities, up to 30 phr and preferably 2 to 25, phr of reinforcing resins. Preferred reinforcing resins include

(a) "Emery" 1540 polyamide resin, sold by Emery Industries, which is a dimer acid-based polyamide resin, with a softening point of 105.degree.-115.degree. C., an amine number of 4, an acid number of 4, and a specific gravity 25.degree./25.degree. C. of 0.98;

(b) "Versamid" 900, sold by General Mills Chemicals, which is a polyamide resin, fatty acid-based, with a softening point of 170.degree.-190.degree. C., and an amine value of 40-50;

(c) "Vitel" 4709A, sold by Goodyear, which is a polyester resin, with a melting point of 130.degree. C., an inherent viscosity of 0.65, a density of 1295 kg/m.sup.3, and a carboxyl content eq/10.sup.6 g of less than 45;

(d) Styron 666U, sold by Dow Chemical, which is a polystyrene resin of s.g. 1.04, melt flow rate (ASTM D1278) 7.5 g/10 minutes and Vicat softening point 100.degree. C.; and

(e) Kraton G 1652, styrene/ethylene block copolymer sold as crumb by Shell Chemical Company; density 910 kg/m.sup.3 ; hardness Shore A 75.

Up to about 2 parts by weight of silane or polymethyl hydrogen siloxane per 100 parts of the terpolymer can be added to impart high resistance to loss of adhesion to glass in hot water soak or highly humid environments without adverse effect on other properties. Involatile silanes such as vinyl tris(2-methoxyethoxy) silane and .alpha.-methacryloxypropyl-trimethoxy silane, or polymethyl hydrogen siloxanes such as Dow Corning 1107 Fluid, are suitable. Silanes containing amino- or epoxy- groups should be avoided since they may induce crosslinking.

As mentioned above, the viscosity stability, particularly at high temperatures, of hot melt adhesive and sealant compositions which are based on alkali metal ionomers of random copolymers of ethylene, methyl acrylate and at least one carboxylated unsaturated monomer is significantly improved by including in such compositions 0.05-10 (preferably 0.1-10) phr of ammonium polyphosphate. The amount of ammonium polyphosphate required to significantly improve sealant stability is generally smaller when the polyphosphate is added to the masterbatch, rather than to the sealant composition. As little as 0.05 phr of ammonium polyphosphate will effect a significant stability increase when added to the masterbatch. When added to the sealant composition, a minimum of 0.5 phr of ammonium polyphosphate is suggested

A particularly suitable ammonium polyphosphate is "Phos-Chek" P/30 fire retardant, sold by Monsanto Company, which is an ammonium polyphosphate with a phosphorus weight percent of 32, an insolubility in water at 25.degree. C. of 92% (based upon 10 grams slurried in 100 grams of water for one hour), and has a particle size distribution such that 90 weight % will pass through a 325 mesh screen. In addition, suitable ammonium polyphosphates are those described in U.S. Pat. No. 3,562,197, granted Feb. 9, 1971 to Sears and Vandersall. In particular, suitable ammonium polyphosphates include those water-insoluble compounds having a P--O--P linkage and having the general formula

wherein n is an integer having an average value greater than 10, m/n has an average value between about 0.7 and about 1.1 and m has a maximum value equal to n+2.

These polymeric polyphosphates can be either straight chain structures or branched chain structures. It should be noted that substantially all of the nitrogen in these polyphosphates is present as the ammoniacal nitrogen and there is substantially no nuclear nitrogen present in the polyphosphates. In addition, when these polyphosphates are characterized as being substantially water-insoluble it is intended to mean that the solubility of a slurry of 10 grams of solids/100 cc. of water at 25.degree. C. for 60 minutes is about 5 grams/100 cc. of water or less.

Starting with the ionomer masterbatch described hereinbefore, the adhesive and sealant compositions of the present invention can be prepared in a Sigma mixer, kneader extruder, or similar equipment. The mixing time is 45-90 minutes at 120.degree.-160.degree. C. depending on the compounding ingredients employed. The most preferred procedure is to melt the tackifying resins in the mixer and add part of the filler, if used. The masterbatch and remaining filler is then gradually added while keeping the viscosity as high as possible to maximize shear by adding only enough plasticizer to allow the mixer to operate. The remaining plasticizer is added towards the end of the mix followed by any other resins used. Silane is preferably added only a few minutes before the mixing is stopped.

If ammonium polyphosphate has not been added in the preparation of the masterbatch, it may be added during preparation of the adhesive or sealant composition. If no additional reactive base is to be added to adjust the degree of ionic crosslinking of the terpolymer, it should be added as early in the mixing process as possible and preferably added to the tackifying resin first placed in the mixer before the addition of the masterbatch. If a reactive base is to be added to adjust the level of crosslinking, the ammonium polyphosphate should be added only after this base has interacted with the terpolymer, but in any case before the addition of a reinforcing resin such as a polyamide.

The following examples identify various specific adhesive and sealant compositions of the present invention and demonstrate the superior viscosity stability of such compositions as compared with compositions without ammonium polyphosphate but which are otherwise equivalent.

A mixture of 100 parts of a random copolymer containing 42 wt. % ethylene, 54 wt. % methyl acrylate and 4 wt. % ethyl hydrogen maleate (melt index, ca. 10 g per 10 min, ASTM D1238, 190.degree. C., 2160 g weight), 43 parts of FEF carbon black and 1.2 parts of sodium carbonate decahydrate was prepared in a Banbury mixer at a temperature of 150.degree. C. The resulting mixture, Mixture A, was used to prepare two hot-melt adhesive formulations from the following ingredients:

The formulations were prepared by mixing the ingredients in a sigma blade mixer at 150.degree. C. Thermal stabilities of formulations 1-A and 1-B were determined by measuring the increase in viscosity with time at 205.degree. C. in a Brookfield HAT viscometer with a Thermosel attachment. The results are tabulated below:

The results clearly illustrate the excellent melt stability of the formulation of this invention (1-A) as compared with the control (1-B) which does not contain ammonium polyphosphate.

A mixture of 100 parts of the random copolymer of Example 1, 75 parts of FEF carbon black and 1.4 parts of sodium carbonate decahydrate was prepared in a Banbury mixer at a temperature of 150.degree. C. The resulting mixture, Mixture B, was used to prepare two hot-melt sealant formulations from the following ingredients:

Melt stabilities of formulations 2-A and 2-B were determined at 205.degree. C. using the procedures of Example 1.

The results clearly show the improved melt stability of Formulation 2-A versus the control 2-B.

Three hot-melt sealant formulations were prepared by mixing the following ingredients in a sigma-blade mixer at 150.degree. C.

Melt stabilities at 205.degree. C. of formulations 3-A, 3-B, and 3-C were determined by viscosity measurements made by the procedure of Example 1.

The improvement in melt stability of the formulations of this invention (3-A and 3-B) is again clearly evident in comparison with the control, 3-C.

Two hot-melt sealant formulations were prepared by mixing the following ingredients in a sigma-blade mixer at 150.degree. C.

Melt stability of the formulations was determined by viscosity measurements at 205.degree. C. using the procedure of Example 1. The results are tabulated below.

The superior stability of the formulation of this invention, 4-A, is evident.

A series of hot-melt sealants was prepared in which the only variable is the concentration of ammonium polyphosphate. The basic formulation for these sealants was as follows.

Melt stability of the formulations was determined by viscosity measurements at 205.degree. C. using the procedure of Example 1. The results are tabulated below:

The results demonstrate significant improvements in melt stability in the presence of ammonium polyphosphate, particularly at levels of about 1 to 5 parts/100 parts of random copolymer.

A mixture of 100 parts by weight of a random copolymer containing 45% by weight ethylene, 52% methyl acrylate and about 3% methacrylic acid having a melt index of about 7 (ASTM D1238, 190.degree. C., 2160 g weight) was mixed on a rubber mill with 43 parts by weight FEF carbon black and 1.2 parts sodium carbonate decahydrate at 90.degree.-100.degree. C. for 5 minutes. The resulting mixture, Mixture C, was used to prepare two hot-melt sealant formulations from the following ingredients:

The melt stabilities of the formulations were determined by viscosity measurements at 205.degree. C. using the procedure of Example 1. The results are tabulated below:

The improvement in melt stability of the formulation 6B of this present invention is clearly evident in comparison with the control 6A.

Mixture A of Example 1 was employed to prepare hot-melt sealant formulations from the following ingredients:

Mixing was carried out by heating the Sigma blade mixer to 150.degree.-180.degree. C. and adding the Picco 6140 and Blackhawk 500 resins to it with the blades stopped. The ammonium polyphosphate, if used, and about a tenth of the total amount of plasticizer was next added and the mixer turned on to partially soften the resins. The Mixture A was then added and mixed for about 15 minutes until the entire mass was uniform. The Suzorite mica and Styron 666 U or Kraton G 1652 were then added and mixed for about 10 minutes, after which the remainder of the plasticizer was added. Mixing was then continued to give a total mixing time of 45-60 minutes to produce a smooth, uniform mass of the sealant. The vinyl tris(2-methoxyethoxy) silane was added about 5-10 minutes before mixing was completed.

The thermal stabilities of these formulations were determined by viscosity measurements at 205.degree. C. using the procedure of Example 1. The results are tabulated below.

The data clearly demonstrate the improved melt stabilities of the formulations of this present invention (7-B and 7-D) compared with the controls (7-A and 7-C).

Mixtures 8-A, 8-B and 8-C were prepared in an internal mixer by the procedure used for Mixture A in Example 1. The random copolymer contained 40.6 wt % ethylene, 55.2 wt % methyl acrylate and 4.2 wt % ethyl hydrogen maleate (melt index, 9.1 g per 10 min, ASTM D1238, 190.degree. C., 2160 g weight). The copolymer, carbon black and sodium carbonate were mixed for about 3 minutes and then ammonium polyphosphate was added to Mixtures 8-B and 8-C in the amounts shown below and mixing was continued for an additional 1-2 minutes.

Hot-melt sealant formulations were then prepared from the above masterbatches (Mixtures 8-A, B, C) by the mixing procedure of Example 7. The formulations employed were as follows, based on 100 parts of the above masterbatches.

The thermal stabilities of these formulations were determined by viscosity measurements at 205.degree. C. using the procedure of Example 1. The results are tabulated below.

These data clearly illustrate the improved melt stabilities of the formulations of this present invention 8E, 8F and 8G compared to the control 8D. They also demonstrate that the addition of 0.5 phr of ammonium polyphosphate to the masterbatch in 8F is at least as effective in preventing increase in melt viscosity as the addition of 2.0 phr of ammonium polyphosphate to the sealant in 8G.

The adhesive and sealant compositions of the present invention are particularly well suited for use as hot melt compositions. In addition, these compositions can be extruded into tapes suitable for cold manual application. These compositions can be used, for example, as sealants for double glazing units to be used as windows, as adhesives for automobile windows, as architectural glass sealants, as sealants in solar collectors, as load bearing sealants for automotive, appliance and aerospace applications, or as jet apron sealants. These compositions can be used as adhesives for a variety of substrates including glass, aluminum, steel, copper, zinc, brass, polycarbonate, polyvinyl chloride, and fiber reinforced plastics.

Although the best mode of the present invention, i.e., the single most preferred adhesive and sealant composition of the present invention, will depend on the particular desired end use and the specific requisite combination of properties for that use, the single most preferred composition for the widest variety of possible end uses will generally conform to the composition described in Example 7B.