US 5,156,793 AGrant
Method for Incrementally Stretching Zero Strain Stretch Laminate Web in a Non-Uniform Manner to Impart a Varying Degree of Elasticity Thereto
Issue Date:1992-10-20
•20 Claims
•7 Drawing Sheets
Abstract
A "zero strain" stretch laminate web exhibiting a non-uniform degree of elasticity, as measured in the direction of elasticization at various points along an axis oriented substantially perpendicular to the direction of elasticization. Improved method and apparatus for non-uniformly stretching "zero strain" stretch laminate webs to impart elasticity thereto in the direction of stretching, at least up to the point of initial stretching are also disclosed. The "zero strain" stretch laminate material is formed of at least two plies of material which are either intermittently or substantially continuously secured to one another along at least a portion of their coextensive surfaces while in a substantially untensioned ("zero strain") condition. One of the plies is stretchable and elastomeric, while the second ply is elongatable, but not necessarily elastomeric. The second ply will, upon stretching of the laminate, be at least to a degree permanently elongated so that, upon release of the applied tensile forces, it will not return to its original undistorted configuration. This results in z-direction bulking of the laminate web when the applied tension is released as well as elastic extensibility in the direction of initial stretching, at least up to the point of initial stretching. In a particularly preferred embodiment of the present invention, the mechanical stretching of said laminate web is carried out by passing said laminate web between at least one pair of meshing corrugated rolls, the degree of meshing between said corrugated rolls being non-uniform about the periphery of said rolls, whereby said laminate web is subjected to non-uniform incremental stretching as it passes therebetween to produce a varying degree of elasticity in the resultant web.
Metadata
Assignee
- The Procter & Gamble Company
Inventors
- Kenneth B. Buell
- Gerald M. Weber
- James R. Mick
- James W. Richardson
Application Information
Application Number:US 6625371
Filing Date:1991-02-28
Priority Date:1991-02-28
Art Unit:137
Classifications
IPC:
B29C 5504
Field of Search:
264288.4;288.8;290.2;101
Patent Drawings (7 sheets)
Description
Technical Field
The present invention has relation to a "zero strain" stretch laminate web which is assembled in a substantially untensioned (i.e., "zero strain") condition and which is capable of being rendered elastic by mechanical stretching.
The present invention has further relation to method and apparatus for producing such a "zero strain" stretch laminate web, wherein predetermined portions of said web can be rendered elastic by mechanical stretching.
The present invention, in a particularly preferred embodiment, has further relation to method and apparatus for rendering predetermined portions of such a "zero strain" stretch laminate web elastic in one or more directions while the web is moving continuously at high speed in the machine direction.
The present invention has further relation to such a "zero strain" stretch laminate web comprising a multiplicity of absorbent articles, such as single use diapers, connected one to another along their waistband portions, each of the diapers in said web further including at least one elastomeric element secured to either the topsheet, the backsheet or both while said elastomeric element is in a substantially untensioned condition, at least a portion of the web containing said substantially untensioned elastomeric element being subjected to mechanical stretching which is sufficient to permanently elongate the web to which said elastomeric element is secured. To the extent that it is not secured to the elastomeric element, said permanently elongated web undergoes z-direction bulking between adjacent points of securement to the elastomeric element in a direction perpendicular to the plane of the elastomeric element when the tensile forces are released and said elastomeric element returns to its substantially untensioned configuration. Regardless of the degree of z-direction bulking, the "zero strain" stretch laminate portion of the web is thereafter elastically extensible in the direction of initial stretching, at least up to the point of initial stretching.
The present invention, in a particularly preferred embodiment, has further relation to such method and apparatus wherein the non-uniform mechanical stretching of said laminate web is carried out by passing said laminate web between at least one pair of meshing corrugated rolls, the degree of meshing between said corrugated rolls being non-uniform about the periphery of said rolls, whereby said laminate web is subjected to non-uniform incremental stretching as it passes therebetween to produce a varying degree of elasticity in the resultant web.
The present invention has further relation, in a particularly preferred embodiment, to a single use absorbent bandage structure, such as a diaper, having discrete portions which are elasticized to a varying degree and which are formed by the method and apparatus of the present invention.
Background Art
In simplest terms, a "zero strain" stretch laminate web, as those terms are used herein, refers to a laminate web comprised of at least two plies of material which are secured to one another, either intermittently or substantially continuously, along at least a portion of their coextensive surfaces while in a substantially untensioned ("zero strain") condition. At least one of said plies is preferably in the form of a continuous web to facilitate continuous, high speed processing. The other of said plies may comprise a continuous web or discrete elements or patches secured to the continuous web at predetermined locations.
As used in the foregoing context, an "intermittently" bonded laminate web shall mean a laminate web wherein prior to the application of tension the plies are initially bonded to one another at discrete spaced apart points or one wherein the plies are substantially unbonded to one another in discrete spaced apart areas. Intermittently bonded laminate webs of the first type can be formed by passing two heat bondable plies through a heated patterned embossing roll nip or by applying discrete spaced apart areas of adhesive to one of the plies before bringing it in contact with the other ply, while an intermittently bonded web of the second type can be formed by feeding an adhesively coated apertured ply or scrim between a pair of substantially continuous plies. Conversely, a "substantially continuously" bonded laminate web shall mean a laminate web wherein prior to the application of tension the plies are initially bonded substantially continuously to one another throughout their areas of interface. Substantially continuously bonded laminate webs can be formed by extruding a first substantially continuous, thermoplastic adhesive ply directly onto a second ply while the first ply is in a heated condition, passing two heat bondable plies between a heated smooth surfaced roll nip or by applying a substantially continuous adhesive coating, spray or densely patterned melt blown to one of the plies prior to bringing it in contact with the other ply.
One of the plies employed in a "zero strain" stretch laminate web of the present invention is comprised of a material which is stretchable and elastomeric, i.e., it will return substantially to its untensioned dimensions after an applied tensile force has been released. The second ply secured to the elastomeric ply is elongatable, most preferably drawable, but is not necessarily elastomeric. Whatever its composition, the second ply will, upon stretching, be at least to a degree permanently elongated so that upon release of the applied tensile forces, it will not fully return to its original undistorted configuration. To the extent that the permanently elongated second ply is not secured to the elastomeric web after the stretching operation, the permanently elongated second ply expands in the z-direction between its points of securement to the elastomeric web when the elastomeric web to which it is secured returns to its substantially undistorted configuration in the x-y plane. The greater the distance between the adjacent points of securement in the x-y plane after stretching, the greater will be the degree of z-direction expansion in the resultant laminate web. Regardless of the degree of z-direction expansion, the resulting "zero strain" stretch laminate web is thereafter elastically extensible in the direction of initial stretching, at least up to the point of initial stretching.
While the term "zero strain", which is used herein to describe stretch laminate webs to which the present invention pertains, has not to Applicants' knowledge been used by prior art workers to describe webs of the aforementioned type, it will for consistency be hereinafter used throughout the present specification to describe such webs.
One very early execution of an intermittently bonded "zero strain" stretch laminate web is disclosed in U.S. Pat. No. 2,075,189 issued to Galligan et al. on Mar. 30, 1937. According to the disclosure of the aforementioned Galligan et al. patent, two superposed continuous plies of rubber, one of which is under tension and longitudinally stretched, are passed between a pair of pressure rolls traveling at the same peripheral speed. One of the rolls is provided with relatively small or narrow projections in a desired pattern, which projections cooperate with the second roll to press together into adhesive contact small portions of the two plies of rubber so that relatively closely spaced small areas of the superposed plies will be united in a pattern similar to that of the projections on the pressure roll.
According to Galligan et al., the roll cooperating with the roll having projections may be smooth, or instead it may be provided with mating projections similar to those on the other roll. The rolls are spaced apart, depending upon the combined thickness of the two plies of rubber, to a degree sufficient to provide the desired uniting pressure without undesirably thinning the rubber of the joined areas.
Upon issuance of the joined plies from the rolls, the tension on the stretched ply is relaxed, and as a result this ply contracts in length and also slightly expands in width. Since the unstretched ply intermittently bonded thereto cannot thus contract, it is drawn up from a longitudinal direction in puckers or crinkles 4. In the specific embodiment shown in FIGS. 1 and 2 of Galligan et al., the top or crinkled ply is designated by the numeral 1, while the stretched or backing ply is designated by the numeral 2. At 3 there appear narrow parallel joint lines at the points where the two plies have been united by the pressure.
In a succeeding step of the process disclosed in the Galligan et al. patent, the foregoing intermittently bonded composite comprising a two ply crinkled material is very highly stretched in a lateral direction (substantially parallel to the joint lines 3), the tension being sufficient to stretch the top crinkled ply 1 beyond its elastic limit. However, the applied tension remains within the elastic limit of the bottom or backing ply 2. If desired, the lateral stretching may be to a point as high as eight times the original width of the undistorted composite.
Since the top ply 1 is laterally stretched beyond its elastic limit, its crinkles 4 are necessarily permanently thinned out in a lateral direction so that when the lateral tension on the laminate sheet is released, the superficial area of the material in any crinkle, when spread flat, will be much greater than that of the corresponding portion of the backing ply 2. As a result, when the backing ply 2 laterally contracts, the crinkles 4 on the top ply 1 are drawn up from a lateral direction, and since their superficial area is much greater than before, the contracting effect of the backing ply causes the crinkles to assume a highly irregular and distorted form between the joint lines 3, i.e., it produces z-direction bulking of the composite, as generally shown in FIGS. 5, 6 and 7. Galligan et al. suggest that the resultant "zero strain" stretch laminate material is particularly suitable for use in the making of bathing suits, bathing caps, shoes, aprons and other articles.
Another early execution of an intermittently bonded "zero strain" stretch laminate web, which is specifically suggested for uses such as toweling, wiping material and expendable garment material, is disclosed in U.S. Pat. No. 3,025,199 issued to Harwood on Mar. 13, 1962. In particular, Harwood suggests the formation of a scrim comprised of intersecting sets of threads or filaments 2 and 3 which are bonded to one another at their points of intersection to form a reticulated reinforcing network 1. A pair of nonwoven layers 4 and 5 of fibers are preferably attached to the opposite sides of the reinforcing network 1 formed by the intersecting threads.
The laminate web structure disclosed by Harwood is thereafter subjected to a stretching operation in one or more directions to permanently expand the nonwoven webs 4,5 secured to the opposed surfaces of the reinforcing network 1. According to Harwood, this may be carried out by stretching the laminate web crosswise (i.e., in the cross-machine direction) via suitable roll means or by appropriately guided conveyor chains equipped with means for gripping and applying opposed tensile forces to the side margins of the web (i.e., tentering apparatus). If lengthwise stretching of the laminate web is desired, Harwood teaches that this may be effected by cooperative low and high speed roll pairs.
Since the threads 2,3 used to form the reticulated reinforcing network 1 of Harwood are, in a particularly preferred embodiment, resilient, the network 1 tends to restore itself to a predetermined substantially undistorted configuration as soon as any tensile forces which have been applied to the laminate web are removed. As a result, the permanently expanded outermost plies 4 and 5 shown in the cross-section of FIG. 4 of the Harwood patent exhibit z-direction bulking in the unbonded areas 6 which coincide with the openings in the resilient network 1.
More recent executions of both intermittently bonded and substantially continuously bonded "zero strain" stretch laminate webs comprised of synthetic polymer plies and intended for single use or disposable apparel applications are disclosed in commonly assigned U.S. Pat. No. 4,107,364 issued to Sisson on Aug. 15, 1978 and commonly assigned U.S. Pat. No. 4,209,563 issued to Sisson on Jun. 24, 1980. The commonly assigned Sisson patents, which are hereby incorporated herein by reference, teach that the "zero strain" stretch laminate webs therein disclosed are particularly well suited for single use apparel applications because of their relatively low cost compared to conventional cloth materials. The Sisson patents further teach that such "zero strain" stretch laminates may be constructed in many different forms ranging from extremely lightweight versions suitable for lingerie applications to heavier versions suitable for apparel waistband applications.
In a preferred embodiment, Sisson's "zero strain" stretch laminate comprises at least one ply comprised substantially of synthetic polymeric filaments which are relatively elastomeric and at least one ply comprised substantially of synthetic polymeric filaments which are relatively elongatable but relatively nonelastic. In a particularly preferred embodiment the plies are bonded to one another to form a coherent laminate web.
As pointed out earlier herein, Sisson discloses two types of web bonding configurations: substantially continuous bonding, as can be accomplished via a heated smooth roll nip; and substantially intermittent bonding at a plurality of spaced apart points, as can be accomplished via a heated patterned embossing roll nip.
Laminate webs employing either bonding configuration are thereafter mechanically worked as by stretching, preferably substantially uniformly, in at least one direction followed by substantially complete relaxation to develop a low modulus of elasticity in the direction of stretching. In the case of the intermittently bonded laminate webs, the elongatable but relatively nonelastic ply is permanently elongated by the stretching operation. Accordingly, it is bulked and bunched between the intermittent bonds securing it to the relatively elastomeric ply when the applied tension is released, i.e., it is bulked to a significant degree in the z-direction to produce a "zero strain" stretch laminate web which is elastically extensible in the direction of initial stretching, at least up to the point of initial stretching. In the case of the substantially continuously bonded laminate webs, the permanently elongated polymeric filaments which are relatively inelastic do not retract when tension is released on the laminate web. Consequently they are caused to undergo looping, bulking and bunching on a much finer scale, i.e., between their bond points to the relatively elastomeric polymeric filaments when tension is released on the laminate web. While the z-direction bulking is less pronounced in such continuously bonded laminate webs, "zero strain" stretch laminate webs of the latter type are also elastically extensible in the direction of stretching, at least up to the point of initial stretching.
Numerous examples of "zero strain" stretch laminate webs employing either continuous or intermittent bonding configurations and methods for producing such webs are disclosed in the aforementioned commonly assigned Sisson patents.
Sisson's suggestion to employ "zero strain" stretch laminate materials in single use or disposable items of wearing apparel has been followed by a number of subsequent workers in the art. See, for example, U.S. Pat. No. 4,525,407 issued to Ness on Jun. 5, 1985, which discloses disposable diapers and surgical gowns incorporating one or more "zero strain" stretch laminate composites comprised of an untensioned elastic member intermittently bonded to an unstretched less extensible substrate, the resulting laminate being rendered elastic by stretching.
FIGS. 1-3 of Ness disclose a simple two layer "zero strain" stretch laminate web which is intended for use as an elastic bandage or wrap. The laminate web comprises a nonapertured elastic member 10 and an unstretched, nongathered substrate 12, which before it is stretched, is less easily extensible than the elastic member and which has less elastic recovery than the elastic member. The substrate and the elastic member are intermittently bonded at spaced apart points 14 in a regular or irregular pattern. The laminate web is thereafter stretched in the directions of the arrows shown in FIG. 2. Upon release of the applied tensile forces, the elastic member 10 causes puckering, i.e., z-direction bulking, of the permanently elongated substrate 12 between bonding points 14, as generally shown in FIG. 3. Like the aforementioned "zero strain" stretch laminate webs of Galligan et al., Harwood and Sisson, the resultant laminate web disclosed by Ness is thereafter elastically extensible in the direction of initial stretching, at least up to the point of initial stretching.
Another elastic composite web embodiment 30 is illustrated in FIGS. 5-8 of Ness. The latter embodiment employs a reticulated elastic element 20 having transverse strands 22 and longitudinal strands 24. The reticulated elastic element 20 of Ness appears to be generally similar to the resilient reticulated reinforcing member 1 disclosed in FIGS. 1-4 of the aforementioned Harwood patent. Like Harwood, Ness also employs a first substrate 28 having less extensibility than the elastic member 20 and less elastic recovery than the elastic member. A second substrate 30, which has substantially the same physical properties as substrate 28, and which "sandwiches" the elastic member 10, is also employed by Ness.
Substrates 28 and 30 of Ness are secured at least to the opposing surfaces of the reticulated elastic member 20 while the elastic member is in a substantially untensioned condition. The substrates 28 and 30 may, if desired, also be bonded to one another through the openings in the reticulated elastic member. According to the teachings of Ness, when the laminate web is thereafter stretched in the longitudinal direction, the substrates 28,30 undergo permanent elongation and may become delaminated from one another, but remain intermittently bonded to the reticulated elastic member 20 at the intermediate sites comprising the transverse and/or longitudinal strands of the reticulated member. Once tension on the web has been released, the reticulated elastic member 20 restores the web to the substantially undistorted configuration of the reticulated elastic member 20, thereby causing z-direction bulking of the permanently elongated substrates 28,30 between their spaced apart points of securement to the longitudinal strands 22 of the elastic member in a direction substantially perpendicular to the direction of stretching. The cross-section of the resultant elastic composite web of Ness shown in FIG. 9 is generally similar to that of the "zero strain" stretch laminate web shown in FIG. 4 of the aforementioned Harwood patent.
In addition to the foregoing "zero strain" stretch laminate web embodiments, FIGS. 9-12 of the Ness patent disclose the use of the elastic composite materials to provide extensible legband portions 136,137 and extensible waistband portions 138,139 along the opposed side edges and ends, respectively, of a disposable diaper. Such elastic composite materials may be incorporated into garments or bandages during manufacture and may, if desired, be stretched to provide subsequent elastic extensibility in the direction of initial stretching. According to Ness, the latter stretching operation may either be performed by the end user or applier of the product as it is being applied or it may be stretched during the manufacturing process.
An automated method for stretching a laminate web comprising a reticulated elastic 210 heat sealed to a pair of opposing plastic film layers 214,216 is disclosed in FIG. 14 of Ness. In the disclosed embodiment, the three layers comprising the composite are fed into a nip formed between a pair of smooth, heated, counter-rotating rolls 224,226 to heat seal the reticulated elastic to the two layers of film 214,216 to form a heat sealed three-layer composite 228. The heat sealed composite 228 is then fed into the nip formed between a second pair of counter-rotating rolls 230,232 which may be cooled to ensure that the thermal bonding is "set". The composite web 234 emerging from the second pair of counter-rotating rolls 230,232 is then fed into the nip of a third pair of counter-rotating rolls 236,238 rotating at a faster peripheral speed than the second pair of counter-rotating rolls 230,232 to effect drafting of the composite web 234 between the two pairs of rolls.
According to Ness, this drafting stretches the films 214,216 and ruptures the heat seal bonds which were previously formed between the films 214,216 through the apertures in the reticulated elastic scrim. Stretching the composite with elastic in the longitudinal direction may also, according to Ness, rupture the seal between the longitudinal strands and the film(s), leaving only the transverse strands bonded to the film layers 214,216. As the stretched composite 244 emerges from the third pair of counter-rotating rolls 236,238, the longitudinal or machine direction tension is relaxed and the composite 244 is fed to a windup 246 that is rotating at a peripheral speed approximately equal to the peripheral speed of the second pair of counter-rotating rolls 230 and 232.
While stretching a laminate web by applying tension to widely separated points of support, e.g., first roll pair 230,232 and second roll pair 236,238, does serve to permanently elongate the substantially inelastic film plies 214,216, Applicants have learned that the uniformity of elongation in such a "zero strain" stretch laminate web, as measured along the unsupported portion of the composite web 234, decreases as the distance between the first roll pair 230,232 and the second roll pair 236,238 increases. For any given distance between the first and second roll pairs, this nonuniformity becomes more pronounced as the difference in peripheral speed between the second roll pair 236,238 and the first roll pair 230,232 increases, i.e., as the composite web 234 undergoes a greater degree of stretching.
Applicants have further learned that these nonuniformity problems can be avoided or at least minimized by following one of the specific suggestions set forth in the aforementioned commonly assigned Sisson patents. Namely, to incrementally stretch the "zero strain" stretch laminate material by passing it through an incremental stretching system, such as the nip formed between a pair of meshing corrugated rolls which have an axis of rotation substantially perpendicular to the direction of web travel. The meshing corrugated rolls support the laminate web at plural closely spaced apart locations corresponding to the width of the corrugations during the stretching operation. This causes substantially uniform incremental stretching of each unsupported segment of the web between adjacent support points rather than highly localized stretching as often occurs when only the outermost extremities of the web are subjected to tension.
Sisson's suggestion to incrementally stretch a "zero strain" stretch laminate material by passing it between corrugated rolls to impart elastic extensibility thereto has also been followed by at least one subsequent worker in the art. See, for example, U.S. Pat. No. 4,834,741 issued to Sabee on May 30, 1989 and hereby incorporated herein by reference.
Sabee, like Ness, discloses a single use garment, such as a disposable diaper, employing a "zero strain" stretch laminate material comprising an untensioned elastomeric element secured between a pair of drawable elements in its opposed waistband and legband portions. The elastic elements 41 shown in FIG. 1 of Sabee are affixed in the waistband portions of the diaper web while in a substantially relaxed condition to a drawable topsheet web, a drawable backsheet web or both. The bonding configuration employed by Sabee may be either intermittent, as by passing the laminate material through a pressure nip formed between two rolls, one of which is heated and contains a plurality of raised points on its surface, or continuous, as by depositing a thin band of viscoelastic hot melt pressure sensitive adhesive onto one of the webs and thereafter pressing the hot melt pressure sensitive adhesive to the other web by passing the laminate through a pressure nip formed between a pair of smooth surfaced rolls.
Regardless of which bonding configuration is employed, the portions of the diaper web containing elastic web elements 41 are thereafter laterally stretched in the cross-machine direction by the meshing corrugations on pairs of corrugated rolls 31, as generally shown in Sabee's FIGS. 5 and 6. Simultaneously the coinciding portions of the drawable topsheet and backsheet webs in the area of elastic element attachment are incrementally stretched and drawn to impart a permanent elongation and molecular orientation thereto in the cross-machine direction. Because corrugated rolls 31 have their meshing corrugations aligned substantially parallel to the machine direction, incremental stretching of the web takes place in the cross-machine direction. Accordingly, the fully processed waistband portions of Sabee's diaper web are thereafter elastically extensible in the cross-machine direction, at least up to the point of initial stretching.
A similar machine direction stretching operation is preferably carried out with respect to the opposed legbands, which include untensioned elastic elements 42, by passing the diaper web of Sabee between another pair of meshing corrugated rolls 89, as generally shown in FIGS. 12 and 13. Because corrugated rolls 89 have their meshing corrugations aligned substantially parallel to the cross-machine direction, incremental stretching of the web takes place in the machine direction. Accordingly, the legband portions of Sabee's diaper web are thereafter elastically extensible in the machine direction, at least to the point of initial stretching.
While Sisson's suggestion to use corrugated rolls to incrementally stretch a "zero strain" stretch laminate web has been used to advantage to produce single use disposable garments having substantially uniformly elasticized portions, Applicants have discovered a number of applications where a non-uniform degree of elasticity, as measured in the direction of web stretching at various points along an axis oriented substantially perpendicular to the direction of web stretching, is particularly desirable. For example, when the finished elasticized article is to be applied across a surface which undergoes differing degrees of expansion and contraction in use, such as the surface of a baby's belly or the opposed surfaces of a baby's hips. In such instances, it has been found desirable that those portions of the article to be fitted across such surfaces exhibit varying degrees of elasticity, as measured in the direction of elasticization at various points along an axis oriented substantially perpendicular to the direction of elasticization, to enhance the degree of comfort and fit when the article is applied and worn.
Objects of the Invention
Accordingly, it is an object of the present invention to provide improved method and apparatus for incrementally stretching "zero strain" stretch laminate webs in a non-uniform manner to provide a varying degree of elasticity therein.
It is a further object of the present invention to provide such method and apparatus which accomplishes the foregoing objective by incrementally stretching a "zero strain" stretch laminate web between sets of opposed meshing teeth exhibiting a differing degree of meshing along their points of contact with the web.
It is a further object of the present invention, in a particularly preferred embodiment, to accomplish the foregoing objectives by employing at least one set of meshing corrugated rolls, at least one of said corrugated rolls having corrugations of non-uniform profile along its point or points of contact with a "zero strain" stretch laminate web passing between said meshing corrugated rolls.
It is still another object of the present invention to produce articles which are elasticized to a varying degree using method and apparatus of the present invention.
Disclosure of the Invention
The present invention comprises, in a preferred embodiment, a "zero strain" stretch laminate web exhibiting a non-uniform degree of elasticity, as measured in the direction of web stretching at various points along an axis oriented substantially perpendicular to the direction of web stretching. Such non-uniformly elasticized webs may be applied across a surface which undergoes differing degrees of expansion and contraction in use, such as the surface of a baby's belly and/or the opposed surfaces of a baby's hips. In such instances, the varying degree of elasticity enhances the degree of comfort and fit when the article is applied and worn.
In yet another embodiment, the present invention comprises improved method and apparatus for non-uniformly stretching a "zero strain" stretch laminate web to impart a varying degree of elasticity thereto in the direction of initial stretching, at least up to the point of initial stretching.
In a particularly preferred embodiment, the present invention comprises method and apparatus for producing such non-uniformly stretched "zero strain" stretch laminate webs by employing one or more sets of meshing corrugated rolls, at least one of said corrugated rolls having corrugations of non-uniform profile along its point or points of contact with the "zero strain" stretch laminate web as the web passes between said meshing corrugated rolls. As a result, the portions of the laminate web passing between said rolls are non-uniformly stretched along the point or points of contact with said non-uniformly profiled corrugated roll. This, in turn, produces a "zero strain" stretch laminate web which is non-uniformly elasticized in a direction substantially perpendicular to the non-uniformly profiled corrugations.
Brief Description of the Drawings
While the specification concludes with claims that particularly point out and distinctly claim the subject matter regarded as forming the present invention, it is believed that the invention will be better understood from the following detailed description with reference to the drawings in which:
FIG. 1 is a simplified perspective view showing the assembly of a web of single use diapers, each having elastomeric patches secured thereto at regularly spaced locations along its length, said web being subjected to a non-uniform incremental stretching process using meshing corrugated rolls having corrugations which are non-uniformly profiled in the machine direction in the areas coinciding with the elastomeric patches, said web also being cut at predetermined points along its length to form a multiplicity of single use diapers, each having at least one pair of laterally stretchable side panels which exhibit a varying degree of elasticity in the direction of incremental stretching;
FIG. 2 is a simplified perspective view of a non-uniform incremental stretching assembly showing a particularly preferred embodiment of the present invention, said assembly employing a vacuum web restraint system;
FIG. 2A is a simplified view taken along view line 2A--2A in FIG. 2 and showing the manner in which idler rolls are used to cause the diaper web to wrap the lowermost corrugated rolls;
FIG. 3 is an enlarged simplified side elevation view of the corrugated rolls of FIG. 2, said view depicting how the corrugated rolls mesh with one another to a varying degree during the non-uniform incremental web stretching process of the present invention;
FIG. 4A is a simplified cross-sectional view taken at a point corresponding to section line 4A--4A in FIG. 3, which coincides with the centerline connecting the corrugated rolls, and showing the degree of meshing of the corrugations on the opposed surfaces of the corrugated rolls when the rolls are in the position shown in FIG. 3;
FIG. 4B is a simplified cross-sectional view generally similar to that of FIG. 4A, but showing the degree of meshing of the corrugations on the opposed surfaces of the corrugated rolls whenever the portion of the uppermost corrugated roll segment coinciding with section line 4B--4B coincides with section line 4A--4A;
FIG. 4C is a highly enlarged simplified cross-sectional view of an intermittently bonded "zero strain" stretch laminate web of the present invention after the web has passed through a corrugated roll nip of the type shown in FIG. 4A;
FIG. 4D is a highly enlarged simplified cross-sectional view of a substantially continuously bonded "zero strain" stretch laminate web of the present invention after the web has passed through a corrugated roll nip of the type shown in FIG. 4A;
FIG. 5 is a simplified schematic illustration of an alternative incremental web stretching system of the present invention;
FIG. 5A is a simplified cross-sectional view taken along section line 5A--5A in FIG. 5; and
FIG. 5B is a simplified cross-sectional view taken along section line 5B--5B in FIG. 5.
Detailed Description of the Present Invention
It will be readily apparent to those skilled in the art that although the following description of the present invention is in connection with a single use diaper structure having preselected non-uniformly elasticized areas, the present invention may be practiced with equal facility on nearly any web either comprised entirely of or containing discrete, isolated "zero strain" stretch laminate portions.
The diaper manufacturing process and the diapers, which are only schematically illustrated in Drawing FIGS. 1-4B, may, if desired, be generally similar to those disclosed in commonly assigned U.S. Pat. No. 4,081,301 issued to Buell on Mar. 28, 1978 and hereby incorporated herein by reference. However, the elasticized legbands of the Buell diaper are an option, and for clarity are not shown herein. The diaper web and the hourglass-shaped diapers schematically shown in FIGS. 1-4B employ elasticized side panels in one or both sets of the ear portions of the hourglass. Positioning of such discrete elastomeric elements which can be used to produce such elasticized side panels in at least one pair of ears is generally disclosed in U.S. Pat. No. 4,857,067 issued to Wood et al. on Aug. 15, 1989, which patent is also hereby incorporated herein by reference.
Referring to FIG. 1, there is shown a continuous web 1 comprised of a plurality of interconnected single use diapers 2. Each diaper is comprised of an absorbent pad element 3, a pair of elastomeric elements or patches 4a, which may be comprised of "live" synthetic or natural rubber, synthetic or natural rubber foam, elastomeric film, elastomeric nonwoven laminate, elastomeric scrim or the like, secured to the webs at predetermined spaced locations, said absorbent pad and said elastomeric patches being located intermediate a moisture-impervious backsheet 5, which is typically comprised of an elongatable polymeric material such as one mil thick polyethylene film, and a moisture-pervious topsheet 6, which is typically comprised of either an elongatable non-woven fibrous material or an elongatable apertured polymeric film.
Particularly preferred materials which can be used for elastomeric elements or patches 4a include foams having an elongation to break of at least about 400% and an extension force of about 200 grams per inch of sample width at 50% extension of its unstrained length. Exemplary foams which have been found usable are: General Foam polyurethane foam No. 40310 having a no-load caliper or thickness of approximately 80 mils and a density of approximately 2.06 pounds per cubic foot (approximately 0.033 grams per cubic centimeter), as available from General Foam of Paramus, N.J.; Bridgestone SG polyurethane foam having a no-load caliper or thickness of approximately 80 mils and a density of about 2.06 pounds per cubic foot (0.033 grams per cubic centimeter), as available from Bridgestone of Yokohama, Japan; cross-linked natural rubber foam having a no-load caliper or thickness of approximately 50 mils and a density of about 13.3 pounds per cubic foot (0.214 grams per cubic centimeter), as available from Fulflex Inc. of Middleton, R.I.; and cross-linked natural rubber foam having a no-load caliper or thickness of approximately 50 mils and a density of about 13.3 pounds per cubic foot (0.214 grams per cubic centimeter), as available from Ludlow Composites Corporation of Fremont, Ohio.
Particularly preferred materials for backsheet 5 include blends comprised of about 45-90% linear low density polyethylene and about 10-55% polypropylene. If used in unembossed form, the backsheet 5 typically exhibits a no-load caliper or thickness of approximately 1 mil. If desired, the backsheet may be embossed to a caliper of approximately 5.5 mils to enhance the web's handling and appearance characteristics. Exemplary backsheet materials which have been found to work are: RR8220 blend REDEM, as available from Tredegar Industries, Inc. of Terre Haute, Ind.; and RR5475 blend ULAB, as available from Tredegar Industries, Inc. of Terre Haute, Ind.
One particularly preferred material for moisture pervious topsheet 6 comprises a hydrophobic, nonwoven carded web having a basis weight in the range of about 18-20 grams per square yard and comprised of approximately 2.2 denier polypropylene fibers, as available from Veratec, Inc., a Division of International Paper Company, of Walpole, Mass. under the designation P8.
A particularly desirable aesthetic appearance results in the "zero strain" stretch laminate portions of the diaper web when the backsheet 5, the topsheet 6 or both are comprised of resilient three-dimensional polymeric webs of the type generally disclosed in commonly assigned U.S. Pat. No. 4,342,314 issued to Radel and Thompson on Aug. 3, 1982 and hereby incorporated herein by reference.
The continuous webs of backsheet material 5 and topsheet material 6 are preferably maintained under very slight (essentially "zero strain") tension in the machine direction to prevent wrinkling and to facilitate registration with the diaper assembly and converting operations until the completed diaper web is severed into discrete diapers 2 at knife 22.
The diaper web forming operation is illustrated only schematically in FIG. 1. The absorbent pad segments 3 are fed into the nip between a pair of combining or laminating rolls 15 at regularly spaced, predetermined intervals. In a particularly preferred embodiment, the absorbent pad segments 3 are preferably comprised of airfelt confined within a cellulosic tissue envelope to provide pad integrity in use.
As has been pointed out earlier herein, "zero strain" stretch laminate webs of the present invention may be produced utilizing either an intermittent bonding configuration or a substantially continuous bonding configuration. The intermittent bonding configuration is normally desirable in those situations where the substantially inelastic webs in the laminate are relatively elongatable or drawable without rupture and where a high degree of z-direction bulking is desired in the finished laminate.
Conversely, a continuous bonding configuration has generally been found desirable where the degree of z-direction bulking is not of prime importance and one or more of the relatively inelastic webs in the laminate is difficult to elongate or draw without causing rupture. In the latter situation, a substantially continuous bonding configuration maintains all of the layers of the laminate in relatively close adherence to one another after the incremental stretching operation. Accordingly, even if one or more of the relatively inelastic webs is damaged to the point of rupture during the incremental stretching operation, the relatively close adherence of the damaged portions of the relatively inelastic web or webs to the elastomeric ply makes it difficult for the end user to perceive that any damage has occurred. Provided rupture of the relatively inelastic web or webs does not defeat the web's intended functionality, e.g., fluid-imperviousness, the damage which does occur to the relatively inelastic web or webs during the incremental stretching operation is not perceived as a negative in the end product. Thus, an unexpected benefit which results from the use of a continuous bonding configuration in particularly preferred "zero strain" stretch laminate webs of the present invention is that it permits the manufacturer of the elasticized article to select from a much wider range of relatively inelastic webs which may be successfully employed in laminates of the present invention. In essence, it permits the use of relatively inelastic webs which would not normally be considered drawable to any appreciable extent in "zero strain" stretch laminate webs of the present invention. Accordingly, unless expressly stated otherwise, the term "drawable" as used in the present specification and claims, is not intended to exclude relatively inelastic webs which undergo a degree of thinning or damage during the incremental stretching operation.
As can be seen in the embodiment of FIG. 1, the continuous web of moisture-impervious elongatable backsheet material is directed in close proximity to a glue applicator 10. If an intermittently bonded laminate web is desired in order to maximize the degree of z-direction bulking in the finished product, the glue applicator 10 may be used to apply discrete, spaced apart spots of adhesive in these predetermined areas of backsheet 5 where the substantially untensioned elastomeric patches 4a will be placed.
Alternatively, if a substantially continuously bonded laminate web is desired, the glue applicator 10 may be used to apply a substantially uniform and continuous application of adhesive 10a to the backsheet 5 in those predetermined areas where the substantially untensioned elastomeric patches 4a will be placed. In a particularly preferred embodiment of the latter type, the adhesive selected is stretchable and the glue applicator 10 comprises a melt blown applicating system.
One such melt blown adhesive applicating system which Applicants have found particularly well suited for producing a substantially continuously bonded "zero strain" stretch laminate web of the present invention is a melt blown spray applicator Model No. GM-50-2-1-GH, as available from J&M Laboratories of Gainesville, Ga. The latter system employs a nozzle having 20 orifices per lineal inch, as measured in the cross-machine direction, each orifice measuring approximately 0.020 inches in diameter. A Findley H-2176 Hot Melt Adhesive, as available from Findley Adhesives of Findley, Ohio is preferably heated to a temperature of approximately 340.degree. F. and applied to the backsheet 5 at a rate of approximately 7.5-10 milligrams per square inch. Heated compressed air at a temperature of approximately 425.degree. F. and a pressure of approximately 50 psig is issued through the secondary orifices in the adhesive nozzle to assist in uniformly distributing the adhesive fibrils during the laydown operation.
The intimate contact of the hot glue substantially shown as 1Oa in FIG. 1 with the backsheet web 5 for the time which passes prior to incremental stretching of the resultant "zero strain" stretch laminate portion of the diaper web provides softening of the backsheet. For some webs, such as conventional polyethylene backsheet material, this softening has been found beneficial in minimizing damage to the backsheet during the incremental web stretching process. This may be particularly important in situations where the web in question imparts some function, e.g., fluid-imperviousness, to the finished article being produced.
Alternatively, the components comprising the "zero strain" portions of the diaper web may be intermittently or continuously bonded to one another using unheated adhesive, heat bonding, pressure bonding, ultrasonic bonding, etc. In such instances, thermal energy may, if desired, be applied to the backsheet web 5 by other means well known to those skilled in the art, e.g., radiant heaters (not shown), hot air blasts (not shown), etc., to achieve a similar result.
Two rolls of elastomeric material 4 are fed under very slight (essentially "zero strain") tension at a speed which provides the desired length of elastomeric patch 4a per diaper onto an anvil roll 11 equipped with vacuum hold down ports (not shown) at its periphery. Knife 12 makes one cut per diaper and the substantially untensioned elastomeric patches 4a travel with anvil roll 11 secured to its periphery by vacuum until they reach transfer point 13. At point 13 the elastomeric patches 4a are transferred to predetermined portions of the backsheet web 5 coinciding with adhesive 1Oa, preferably by high pressure air blasts. The transfer is sequential and the surface speed of the vacuum equipped anvil roll 11 and backsheet web 5 are essentially equal.
The backsheet web 5 with elastomeric patches 4a attached thereto at predetermined points along its length is then directed to the pair of laminating or combining rolls 15.
A continuous web of a moisture-pervious topsheet material 6, such as an elongatable fibrous nonwoven web, is directed in close proximity to a second glue applicator 14 where a pattern of adhesive 14a sized to substantially match the dimensions and locations of the elastomeric patches 4a on backsheet web 5 is preferably applied. As with the backsheet material 5, the pattern of adhesive applied to the topsheet material 6 may be either intermittent or substantially continuous, depending upon the properties of the topsheet material 6 and the characteristics desired in the resultant "zero strain" stretch laminate web. If desired, adhesive applicator 14 may be identical to adhesive applicator 10.
The backsheet web 5 and topsheet web 6 and the absorbent pads 3 are brought into contact with one another at combining rolls 15. Just prior to the webs and pads coming into contact with one another, additional adhesive is preferably applied to one or both webs by means which are, for clarity, not shown in FIG. 1. The latter adhesive secures predetermined portions of the backsheet, the topsheet and the absorbent pad to one another to form the diaper web 1.
The fully assembled diaper web 1 thereafter preferably proceeds through a pair of bond setting rolls 16, which may require chilling to minimize glue bleed through.
The fully assembled diaper web 1 is then directed through a non-uniform incremental web stretching system employing opposed pressure applicators having three dimensional surfaces which are complementary to a varying degree with one another of the present invention, which is shown only schematically as 20 in FIG. 1. Details of a particularly preferred non-uniform incremental web stretching system of the present invention which can be employed as system 20 are set forth in FIG. 2.
Referring to FIG. 2, timing of the diaper web 1 containing substantially untensioned elastomeric patches 4a is such that the substantially untensioned elastomeric patches 4a contained within the diaper web substantially coincide with the corrugated or grooved segments 24 contained on uppermost corrugated rolls 25 as the diaper web 1 passes between the segments 24 of uppermost corrugated rolls 25 and the continuously corrugated or grooved lowermost corrugated rolls 21. If desired, the grooved segments 24 may be of greater overall length than the elastomeric patches 4a, as measured in the machine direction, as to impart a degree of extensibility to those portions of the topsheet and backsheet which are adjacent the elastomeric patches 4a in the finished diaper.
While the exact configuration, spacing and depth of the complementary grooves on the uppermost and lowermost corrugated rolls will vary, depending upon such factors as the amount of elasticity desired in the "zero strain" stretch laminate portion of the fully processed web, a peak-to-peak groove pitch of approximately 0.150 inches, an included angle of approximately 12.degree. as measured at the peak, and a peak-to-valley groove depth of approximately 0.300 inches have been employed in a particularly preferred embodiment of the present invention. The exterior peak of each corrugation on the aforementioned corrugated rolls typically exhibits a radius of approximately 0.010 inches, while the internal groove formed between adjacent corrugations typically exhibits a radius of approximately 0.040 inches. When the corrugated rolls are adjusted so that the opposing peaks on the corrugated rolls overlap one another to a varying depth ranging from about 0.125 inches to about 0.175 inches along the non-uniform radius of the uppermost corrugated roll segments, noticeably non-uniform elastic characteristics have been produced in a laminate web of the present invention comprised of 80 mil thick elastomeric polyurethane foam patches 4a substantially continuously bonded on their opposed surfaces to a one mil thick moisture impervious polymeric backsheet 5 and a nonwoven hydrophobic topsheet 6 having a basis weight in the range of about 18 to 20 grams per square yard and comprised of approximately 2.2 denier polypropylene fibers.
The degree of overlap of the opposing peaks on the aforementioned corrugated rolls may of course be adjusted, as desired, to produce more or less extensibility in the resultant "zero strain" stretch laminate portion of the web. For the aforementioned roll geometry and laminate web construction, peak-to-peak overlap depths ranging as little as about 0.050 inches to as much as about 0.225 inches are feasible.
As can be seen from FIG. 2A, the diaper web 1 is caused by idler rolls 72,74 to wrap the lowermost corrugated rolls 21 sufficiently to cover the active vacuum ports 22 located immediately adjacent each continuous set of grooves 23 on lowermost rolls 21. The vacuum ports 22, which are positioned so as to substantially coincide with the grooved segments 24 on uppermost corrugated rolls 25, are internally connected through rolls 21 to a pair of vacuum manifolds 26 which exert suction against the diaper web 1 as the diaper web is acted upon by the grooved segments 24 of uppermost corrugated rolls 25.
To minimize build up of either the adhesive used to secure the untensioned elastomeric patches 4a to the fluid-pervious topsheet web 6 and the fluid-impervious backsheet web 5 or the adhesive used to secure the coinciding portions of the topsheet web and the backsheet web to one another, the grooved segments 24 on uppermost rolls 25 and the continuous grooves 23 on lowermost rolls 21 are preferably either comprised of a low friction material, such as TEFLON.RTM. (polytetrafluoroethylene), or coated with a self-lubricating low friction material such as an aqueous dispersion of a fortified fluoropolymer, for example PERMALON.RTM. No. 503 spray coating, as available from Micro Surface Corporation of Morris, Ill.
The vacuum ports 22 on lowermost rolls 21 are preferably covered by a porous material, such as 0.090" mesh honeycomb 44, to provide support to the portions of the diaper web 1 acted upon by the vacuum and to provide a good gripping surface against the web so as to substantially prevent lateral slippage or movement of the web across the honeycomb surface whenever the web is acted upon by vacuum.
Under optimum circumstances, the maximum degree of incremental stretching which can be imparted to the "zero strain" portions of the diaper web 1 containing elastomeric patches 4a is determined by the depth of engagement between the grooves on segments 24 of uppermost corrugated rolls 25 and the continuous grooves 23 on lowermost corrugated rolls 21. However, unless the "zero strain" stretch laminate portions of the diaper web are substantially prevented from slipping or contracting in a direction substantially parallel to the direction of web stretching as it passes between the meshing corrugated rolls, the optimum degree of incremental stretching is not realized. Therefore, in its most preferred form, the non-uniform web stretching operation of the present invention is carried out while the outermost portions of all three layers comprising the "zero strain" stretch laminate composite are subjected to restraint, as generally shown in the cross-sections of FIGS. 4A and 4B, to substantially prevent the "zero strain" stretch laminate portions of the diaper web from slipping or contracting in a direction parallel to the desired direction of stretching as it passes between the meshing corrugated rolls.
However, the present invention may also, if desired, be practiced to advantage by restraining only the elongatable or drawable layer or layers of the composite, i.e., it is not an absolute requirement that the outermost portions of the elastomeric elements 4a also be restrained during the incremental stretching operation. In the latter instance, the elongatable or drawable layer or layers are still permanently elongated during the incremental stretching process, but the z-direction bulking in the resultant "zero strain" stretch laminate web may be somewhat less pronounced when the stretching tension is removed. This is due to the fact that the elastomeric layer undergoes a lesser degree of initial stretching during such a process. Accordingly, it can only undergo this same amount of retraction when it returns to its undistorted configuration.
A "zero strain" stretch laminate embodiment of the aforementioned type may also exhibit some degree of disproportionate straining in the elongatable web or webs in the areas immediately adjacent the opposed edges of the elastomeric elements 4a. In the case of an opaque polymeric backsheet web which is normally employed as a fluid-impervious barrier on a diaper, these disproportionately strained portions can become sufficiently thinned that they may even appear transparent despite the fact no rupture has taken place. In such instances the functionality, e.g., the fluid-imperviousness, of the "zero strain" stretch laminate portions of the diaper web is not impaired. Embodiments of the latter type are normally employed in situations where the aesthetic appearance of the "zero strain" stretch laminate portion of the resultant article is either hidden from view by the design or configuration of the article or, if visible, is of no concern to the user of the article.
In still another embodiment of the present invention even rupture of one or more of the elongatable nonelastic webs may not render the resultant "zero strain" stretch laminate web unacceptable for its intended purpose, e.g., rupture of the backsheet web 5 does not necessarily destroy the laminate web's functionality for its intended purpose as long as one of the other plies in the laminate web provides the desired function in the finished article. For example, some degree of rupturing in the elongatable backsheet web 5 will not destroy the fluid-imperviousness of the resultant disposable diaper web if the elastomeric patches 4a are comprised of a fluid-impervious material. This is particularly true with respect to those "zero strain" stretch laminate web embodiments employing substantially continuous bonding between the plies in question, since relatively close adherence of the plies to one another after incremental stretching renders such ply damage difficult to detect by the end user of the article.
Because the diaper web 1 shown in FIGS. 1-4B is substantially impervious to the passage of air by virtue of the presence of the uppermost moisture-impervious backsheet web 5, vacuum ports 22 covered by porous honeycomb material 44 can, if desired, be employed immediately adjacent each set of machine direction oriented grooves 23 in lowermost corrugated rolls 21. If the elastomeric patches 4a are sufficiently pervious to the passage of air, the suction forces generated by the vacuum will pass through the fluid-pervious topsheet web 6 and the elastomeric patches so as to tightly grip the overlying portions of the backsheet 5. In this instance, all three layers comprising the "zero strain" stretch laminate portions of the diaper web will be restrained during the incremental stretching operation.
If the elastomeric patches 4a were not substantially pervious to the passage of air, it would be necessary to either (a) position the vacuum ports 22 and the overlying honeycomb material 44 just outside the opposed edges of the elastomeric patches 4a so that suction forces could be exerted on the fluid-impervious elongatable or drawable backsheet web 5 through the fluid-pervious elongatable or drawable topsheet web 6; or (b) restrain all three layers comprising the "zero strain" stretch laminate portions of the diaper web by means of suitable clamping apparatus capable of acting upon the opposed surfaces of the diaper web 1. Such apparatus are disclosed in the aforementioned concurrently filed, commonly assigned U.S. patent application of Gerald M. Weber, William R. Vinnage, Jr., Douglas H. Benson and David A. Sabatelli entitled IMPROVED METHOD AND APPARATUS FOR INCREMENTALLY STRETCHING ZERO STRAIN STRETCH LAMINATE WEB TO IMPART ELASTICITY THERETO, Ser. No. 662,536 filed on Feb. 28, 1991, the disclosure of which is hereby incorporated herein by reference.
The suction forces applied to the diaper web 1 shown in Drawing FIGS. 1-4B by vacuum ports 22 acting through porous honeycomb material 44 substantially prevent those portions of the diaper web containing substantially untensioned elastomeric patches 4a from slipping or contracting in a laterally inward direction as they pass between the meshing portions of the continuous grooves 23 on lowermost corrugated rolls 21 and the grooved segments 24 on uppermost corrugated rolls 25.
As can be seen from FIG. 3, the continuous corrugations or grooves 23 on lowermost corrugated rolls 21 exhibit a substantially uniform radius R.sub.4 about the entire periphery of lowermost corrugated rolls 21. However, the corrugations or grooves on segments 24 on uppermost corrugated rolls 25 are of non-uniform radius along their points of meshing with continuous grooves 23 on lowermost corrugated rolls 21. In particular, the grooves on the lead-in portion of segments 24 exhibit an initial radius R.sub.1 which is smaller than the radius R.sub.2 of the grooves near the central portion of segments 24. In addition, radius R.sub.1 originates from a point closer to the periphery of grooved segment 24 than radius R.sub.2. Similarly, the grooves on the trailing portions of segments 24 exhibit a radius R.sub.3 which is smaller than the radius R.sub.2 of the grooves in the central portion of the grooved segments. Radius R.sub.3 also originates from a point closer to the periphery of grooved segment 24 than radius R.sub.2. Although not a requirement of the present invention, in the embodiment illustrated in FIG. 3, radius R.sub.1 is equal to radius R.sub.3.
The non-uniformity of the groove radii on segments 24, as measured parallel to the machine direction, results in a non-uniform degree of meshing between grooved segments 24 and continuous grooves 23 on lowermost corrugated rolls 21 as the "zero strain" stretch laminate portions of the diaper web 1 pass therebetween. Maximum meshing of the corrugated rolls 21,25 occurs when those portions of grooved segments 24 exhibiting a maximum radius R.sub.2 align with the centerline connecting corrugated rolls 21,25. This maximum degree of meshing is shown in the cross-section of FIG. 4A, which is a view taken along section line 4A--4A in FIG. 3.
FIG. 4B, on the other hand, is a cross-sectional view showing the lesser degree of meshing which takes place between the corrugated rolls 21 and 25 when that portion of grooved segments 24 coinciding with section line 4B--4B in FIG. 3 aligns with the centerline connecting corrugated rolls 21,25. Minimum meshing will, of course, occur at the leading and trailing edges of grooved segments 24 due to the differing origins for radii R.sub.1 and R.sub.3 relative to radius R.sub.2.
As a result of the non-uniform machine direction profile of grooved segments 24, the portions of the "zero strain" stretch laminate web which are acted upon by the meshing corrugated rolls 21,25 are incrementally stretched to a differing extent along the length of the web. Because the central portion of the "zero strain" stretch laminate comprising elastomeric patches 4a and the topsheet 6 and backsheet 5 secured thereto are subjected to the greatest degree of incremental stretching, they exhibit the greatest degree of elasticity in the direction of stretching, i.e., in the cross-machine direction. Conversely, because the leading and trailing portions of the "zero strain" stretch laminate portions of the web containing elastomeric elements 4a are incrementally stretched to a much lesser extent, these areas will exhibit a much lesser degree of elasticity in the cross-machine direction.
The cross-section of FIG. 4C reveals the condition of an untensioned intermittently bonded "zero strain" stretch laminate web of the present invention, as viewed at a point corresponding to its greatest degree of incremental stretching, while the cross-section of FIG. 4D reveals the condition of an otherwise identical untensioned substantially continuously bonded "zero strain" stretch laminate web of the present invention, as viewed at a point corresponding to its greatest degree of incremental stretching. Although both webs are elastically extensible in the direction of initial stretching, at least up to the point of initial stretching, the intermittently bonded "zero strain" stretch laminate web shown in FIG. 4C exhibits a much greater degree of z-direction bulking.
As pointed out earlier herein, non-uniformly elasticized "zero strain" stretch laminate webs of the present invention are particularly well suited for use in articles of apparel, such as disposable diapers, to improve fit and comfort when the articles are applied across portions of the wearer's body which undergo varying degrees of movement in use, in this case the opposed surfaces of the wearer's hips.
Following the non-uniform incremental stretching operation shown schematically as 20 in FIG. 1, the fully assembled diaper web 1 is preferably passed through a side notching apparatus shown schematically as 60, wherein notches intended to coincide with the wearer's legs are cut from the lateral edge portions of the fully assembled diaper web.
Finally, the diaper web 1 is cut at predetermined locations along its length by means of knife 22 to produce hourglass-shaped single use diapers having at least one pair of side panels which are elastically extensible to a varying degree, as measured in a direction parallel to the diaper waistband at various points along an axis oriented substantially perpendicular to the diaper waistband.
From the description contained herein, it is clear that the improved method and apparatus of the present invention may be employed to advantage to produce a wide range of elasticized articles either comprised entirely of or including one or more discrete, isolated "zero strain" stretch laminate web portions.
It is recognized that while non-uniformly profiled meshing corrugated rolls having their corrugations aligned substantially parallel to one another are disclosed in the accompanying Drawing Figures, the present invention may be practiced with equal facility employing non-uniformly profiled corrugated rolls wherein the corrugations are not all oriented parallel to one another. Furthermore, the corrugations on such non-uniformly profiled corrugated rolls need not necessarily be aligned parallel to either the machine or the cross-machine direction. For example, if a curvilinear waistband or legband portion which is non-uniformly elastic along its length is desired in a single use diaper, the meshing non-uniformly profiled teeth on the corrugated rolls employed to incrementally stretch the "zero strain" portions of the diaper web may be arrayed in the desired curvilinear configuration to produce a varying degree of elasticity along the desired contour rather than in a straight line.
It is also recognized that "zero strain" stretch laminate webs may be non-uniformly stretched to produce a varying degree of elasticization using pairs of meshing corrugated rolls exhibiting grooves or corrugations having a substantially uniform profile about their periphery. In such instance, means are provided to vary the center-to-center distance between the corrugated rolls as the "zero strain" stretch laminate portions of the web pass therebetween. As a result, the "zero strain" stretch laminate portions of the web are non-uniformly stretched in direct proportion to the varying degree of meshing which takes place throughout the incremental web stretching process. In a particularly preferred embodiment (not shown), the means for varying the center-to-center distance between the corrugated rolls can comprise a set of hydraulic or pneumatic cylinders operated by a predetermined pressure control logic to move one of the corrugated rolls relative to the other and thereby vary the degree of meshing as the "zero strain" stretch laminate portions of the web pass therebetween. A similar result could also be achieved using more conventional mechanical devices such as a cam and follower or an eccentrically driven linkage system.
It is further recognized that while the preferred processes herein disclosed employ meshing cylindrical corrugated rolls, the non-uniform incremental stretching operation of the present invention may also be carried out utilizing an intermittent stamping operation employing meshing platens exhibiting varying degrees of meshing to non-uniformly incrementally stretch the "zero strain" stretch laminate portions of a web or an article placed between the platens.
Such a stamping operation is illustrated schematically in FIG. 5. The diaper web 101 therein disclosed comprises a fluid-pervious topsheet 6, a fluid-impervious backsheet 5, absorbent pads 3 and substantially untensioned elastomeric patches 110 and 120 which form "zero strain" stretch laminate waistband portions 210 and curvilinear "zero strain" stretch laminate legband portions 220, respectively, in the diaper web.
The diaper web 101 is passed between at least one pair of meshing platens. The bottom platen 440, which includes uniformly profiled curvilinear teeth 520 for incrementally stretching the legband portions of the diaper web and straight teeth 510 for incrementally stretching the waistband portions of the diaper web is engaged, with diaper web 101 supported thereon, by an uppermost meshing platen 400 having toothed sections which are complementary to those on bottom platen 440, but which are non-uniformly profiled. In this regard, it should be noted that not only may the individual teeth on uppermost platen 400 be non-uniformly profiled along their length, as shown in the cross-section of FIG. 5A, but the amplitude of one tooth may vary from that of the adjacent teeth, as generally shown in the cross-section of FIG. 5B. As a result, the "zero strain" stretch laminate portions 210,220 of the diaper web 101 are non-uniformly stretched in multiple directions in accordance with the present invention.
To ensure that the maximum degree of incremental web stretching is achieved in all directions, the toothed segments 510,520 on lowermost platen 440 are preferably surrounded by resiliently deformable windows 610,620 which contact and clamp the "zero strain" stretch laminate portions 210,220 of the diaper web 101 about their periphery against a corresponding set of non-deformable windows 710,720 surrounding the complementary teeth on uppermost platen 400. This clamping action substantially prevents slipping or contraction of the "zero strain" stretch laminate portions of the web in a direction substantially parallel to any of the directions of stretching during the non-uniform stretching operation performed on the meshing platens. The resiliently deformable windows 610,620 must, of course, deform sufficiently to permit the desired degree of meshing between the opposing teeth on platens 400 and 440 during the incremental stretching operation.
Alternatively, those "zero strain" stretch laminate portions 210,220 of the diaper web 101 to be incrementally stretched may be restrained by suitable vacuum means (not shown) surrounding the toothed segments 510,520 on lowermost platen 440 before the uppermost meshing platen 400 is able to exert enough force on the "zero strain" stretch laminate portions of the diaper web to cause contraction thereof in a direction substantially parallel to any of the directions of stretching.
While the present invention has been described primarily in the context of providing a single use diaper having elasticized ears or elasticized waistbands and/or legbands exhibiting a varying degree of elasticity in the direction or directions of initial stretching, it is recognized that the present invention may also be practiced to advantage in many other applications and environments. It will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and it is intended to cover in the appended claims all such modifications that are within the scope of this invention.
Claims
What is claimed is:
1. An improved method for non-uniformly stretching a predetermined portion of a zero strain stretch laminate web to impart a varying degree of elasticity thereto in the direction of stretching, at least up to the point of initial stretching, said method comprising the steps of: (a) feeding said predetermined portion of said zero strain stretch laminate web comprising a substantially untensioned first elastomeric ply intermittently secured to a substantially untensioned second poly comprising a continuous web which is elongatable, but which exhibits less elastic recovery than said first ply, between a pair of opposed pressure applicators having three-dimensional surfaces which are complementary and which can be caused to mesh to a varying degree with one another along their points of contact with said predetermined portion of said web; and (b) subjecting said predetermined portion of said zero strain stretch laminate web located between said opposed three-dimensional surfaces of said pressure applicators to non-uniform incremental stretching by causing said three-dimensional surfaces of said pressure applicators to mesh with one another to a varying degree along their points of contact with said predetermined portion of said laminate web, whereby said second elongatable ply in said predetermined portion of said zero strain stretch laminate web is permanently elongated to a varying degree by said non-uniform incremental stretching so that said predetermined portion of said laminate web is non-uniformly elastically estensible in the direction of initial stretching, at least up to the point of initial stretching, once the initial incremental stretching forces are removed from said predetermined portion of said zero strain stretch laminate web.
2. An improved method for non-uniformly stretching a predetermined portion of a zero strain stretch laminate web to impart a varying degree of elasticity thereto in the direction of stretching, at least up to the point of initial stretching, said method comprising the steps of: (a) feeding said predetermined portion of said zero strain stretch laminate web comprising a substantially untensioned first elastomeric ply substantially continuously secured to a substantially untensioned second ply comprising a continuous web which is elongatable, but which exhibits less elastic recovery than said first ply, between a pair of opposed pressure applicators having three-dimensional surfaces which are complementary to a varying degree with one another along their points of contact with said predetermined portion of said web; and (b) subjecting said predetermined portion of said zero strain stretch laminate web located between said opposed three-dimensional surfaces of said pressure applicators to non-uniform incremental stretching by causing said three-dimensional surfaces of said pressure applicators to mesh with one another to a varying degree along their points of contact with said predetermined portion of said laminate web, whereby said second elongatable ply in said predetermined portion of said zero strain stretch laminate web is permanently elongated to a varying degree by said non-uniform incremental stretching so that said predetermined portion of said laminate web is non-uniformly elastically extensible in the direction of initial stretching, at least up to the point of initial stretching, once the initial incremental stretching forces are removed from said predetermined portion of said zero strain stretch laminate web.
3. The method of claim 1 or claim 2, wherein said opposed peripheral edge portions of said zero strain stretch laminate web are restrained to prevent contraction thereof in a direction substantially parallel to the direction of non-uniform incremental stretching throughout said incremental web stretching process.
4. The method of claim 1 or claim 2, wherein said opposed pressure applicators comprise corrugated rolls having an axis of rotation substantially perpendicular to the direction of web travel and wherein said three-dimensional surfaces on said applicators comprise corrugations which mesh with one another to a varying degree as said zero strain stretch laminate web passes therebetween.
5. The method of claim 4, wherein restraint of said web is carried out by applying suction to said zero strain stretch laminate web immediately adjacent the corrugations on at least one of said meshing corrugated rolls.
9. The method of claim 8, wherein said non-uniform incremental stretching of said zero strain stretch laminate web is carried out in a curvilinear configuration.
11. The method of claim 1 or claim 2, wherein said zero strain stretch laminate web further comprises a third substantially untensioned ply which is elongatable, but which exhibits less elastic recovery than said first elastomeric ply, secured to the surface of said first substantially untensioned elastomeric ply which is opposite said second substantially untensioned ply.
12. The method of claim 11 wherein said second substantially untensioned ply is moisture-impervious.
13. The method of claim 12, wherein said second substantially untensioned ply is comprised of polymeric film.
14. The method of claim 13, wherein said second substantially untensioned ply is comprised of a resilient three-dimensional polymeric film.
15. The method of claim 11, wherein said third substantially untensioned ply is moisture-pervious.
16. The method of claim 15, wherein said third substantially untensioned, moisture-pervious ply is comprised of a non-woven fibrous material.
17. The method of claim 15, wherein said third substantially untensioned, moisture-pervious ply is comprised of a resilient apertured three-dimensional polymeric film.
18. An improved method for non-uniformly stretching a predetermined portion of a continuously moving zero strain stretch laminate web to impart a varying degree of elasticity thereto in the direction of stretching, at least up to the point of initial stretching, said method comprising the steps of: (a) continuously feeding said predetermined portion of said zero strain stretch laminate web comprising a substantially untensioned first elastomeric ply intermittently secured to a substantially untensioned second ply comprising a continuous web which is elongatable, but which exhibits less elastic recovery than said first ply, between a pair of opposed pressure applicators comprising corrugated rolls having an axis of rotation perpendicular to the direction of web travel, said corrugated rolls having three-dimensional surfaces comprising corrugations which are complementary and which can be caused to mesh to a varying degree with one another along their points of contact with said predetermined portion of said web; and (b) subjecting said predetermined portion of said continuously moving zero strain stretch laminate web located between said opposed three-dimensional surfaces of said pressure applicators to non-uniform incremental stretching by causing said three-dimensional corrugations on said corrugated rolls to mesh with one another to a varying degree along their points of contact with said predetermined portion of said laminate web, whereby said second elongatable ply in said predetermined portion of said zero strain stretch laminate web is permanently elongated to a varying degree by said non-uniform incremental stretching so that said predetermined portion of said laminate web is non-uniformly elastically extensible in the direction of initial stretching, at least up to the point of initial stretching, once the initial incremental stretching forces are removed from said predetermined portion of said zero strain stretch laminate web.
19. An improved method for non-uniformly stretching a predetermined portion of a continuously moving zero strain stretch laminate web to impart a varying degree of elasticity thereto in the direction of stretching, at least up to the point of initial stretching, said method comprising the steps of: (a) continuously feeding said predetermined portion of said zero strain stretch laminate web comprising a substantially untensioned first elastomeric ply substantially continuously secured to a substantially untensioned second ply comprising a continuous web which is elongatable, but which exhibits less elastic recovery than said first ply, between a pair of opposed pressure applicators comprising corrugated rolls having an axis of rotation perpendicular to the direction of web travel, said corrugated rolls having three-dimensional surfaces comprising corrugations which are complementary and which can be caused to mesh to a varying degree with one another along their points of contact with said predetermined portion of said web; and (b) subjecting said predetermined portion of said continuously moving zero strain stretch laminate web located between said opposed three-dimensional surfaces of said pressure applicators to non-uniform incremental stretching by causing said three-dimensional corrugations on said corrugated rolls to mesh with one another to a varying degree along their points of contact with said predetermined portion of said laminate web, whereby said second elongatable ply in said predetermined portion of said zero strain stretch laminate web is permanently elongated to a varying degree by said non-uniform incremental stretching so that said predetermined portion of said laminate web is non-uniformly elastically extensible in the direction of initial stretching, at least up to the point of initial stretching, once the initial incremental stretching forces are removed from said predetermined portion of said zero strain stretch laminate web.
20. The method of claim 18 or claim 19, wherein said opposed peripheral edge portions of said continuously moving zero strain stretch laminate web are restrained to prevent contraction thereof in a direction substantially parallel to the direction of non-uniform incremental stretching throughout said incremental web stretching process.
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