WO1999037839A1

WO1999037839A1 - Method for making a strong and soft nonwoven web

Info

Publication number: WO1999037839A1
Application number: PCT/US1998/001247
Authority: WO
Inventors: Douglas Herrin Benson; John Joseph Curro
Original assignee: The Procter & Gamble Company
Priority date: 1998-01-23
Filing date: 1998-01-23
Publication date: 1999-07-29
Also published as: CA2313115A1; AU6247098A; EP1047822A1; KR100361396B1; JP2002501127A; KR20010034253A

Abstract

The present invention provides a method for making a strong and soft nonwoven web. A neckable nonwoven web is fed in a first direction. A tensioning force is applied to the neckable nonwoven web to neck the nonwoven web. Optionally, the necked nonwoven web may be subjected to mechanical stabilization after necking to provide a stabilized extensible necked nonwoven web. The nonwoven web is then subjected to incremental stretching in a direction perpendicular to the first direction to provide a strong and soft nonwoven web.

Description

METHOD FOR MAKING A STRONG AND SOFT NONWOVEN WEB

FIELD OF THE INVENTION

The present invention relates to a method for making a strong and soft nonwoven web. Strong and soft materials, such as nonwoven webs are particularly well suited for use in disposable absorbent articles such as diapers, incontinence briefs, training pants, feminine hygiene garments, and the like, as they are able to be used in portions of the article where strength and softness can aid in the article's comfort and overall performance.

BACKGROUND OF THE INVENTION

Nonwoven webs may be manufactured into products and components of products so inexpensively that the product may be viewed as disposable after only one or a few uses. Representatives of such products include diapers, training pants, wipes, garments, incontinence briefs, feminine hygiene garments and the like.

Nonwoven webs may be treated to provide the nonwoven web with certain properties. For example, U.S. Patent No. 5,244,482 issued to Hassenboehler, Jr. et al. on September 14, 1993 discloses a method for treating a nonwoven web wherein the nonwoven web is heated at an elevated temperature and uniaxially drawn to consolidate and stabilize the nonwoven web. Such nonwoven webs are noted to exhibit an increased elasticity after processing. Such elasticity increase is recognized as being caused by the new "memory" instilled by the heating of the nonwoven web. Such drawing and setting of the nonwoven web by heating at an elevated temperature often causes fiber embrittlement and the nonwoven web to exhibit increased gloss. For many applications involving skin contact, e.g., such as in diaper coverstock, such attributes are contrary to the desired cloth-like properties of softness and non-plastic, (low gloss) appearance. Lastly, the requirement of heating the nonwoven web to consolidate and stabilize the web adds to the complexity and cost of the process. U.S. Patent No. 4,981,747 issued to Morman on January 1, 1991, discloses a

"reversibly necked" material. It is taught that the unstabilized necked material must be held under high tension on the re-wound roll until such time as the further heat setting step is performed to stabilize the material. Such a material will again suffer the deficits noted above with respect to preferred skin contact applications, and will enhance the elastic properties of the material rather than the strength and softness of the material.

U.S. Patent No. 5,226,992 issued to Morman on July 13, 1993, discloses a method of producing a composite elastic necked-bonded material. A tensioning force is applied to at least one neckable material, such as a neckable nonwoven web, to neck or consolidate the material. Instead of heating the consolidated nonwoven web, this patent teaches superposing the tensioned consolidated nonwoven web on an elastic material and joining the tensioned consolidated nonwoven web to the elastic material while the tensioned consolidated nonwoven web is in a tensioned condition. By joining the tensioned consolidated nonwoven web to the elastic material while still in a tensioned condition, the nonwoven web is constrained to its' necked dimension. It is an object of the present invention to provide a strong and soft nonwoven web, capable of being wound into stable rollstock or festooned form, suitable for subsequent conversion or combining operations.

It is also an object of the present invention to provide a post-processing method for producing a strong and soft nonwoven web. It is also an object of the present invention to provide a post-processing method for producing a strong and soft - nonwoven web that does not require heating of the neckable material to elevated temperatures.

As used herein, the term "elastic", refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 60 percent (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), and which, will recover at least 55 percent of its elongation upon release of the stretching, elongation force.

As used herein, the term "extensible" refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 60 percent without suffering catastrophic failure (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), but does not recover more than 55 percent of its elongation upon release of the stretching, elongation force.

As used herein, the term "highly extensible" refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 100 percent without suffering catastrophic failure (i.e., to a stretched, biased length which is at least about 200 percent of its relaxed unbiased length), but does not recover more than 55 percent of its elongation upon release of the stretching, elongation force.

As used herein, the term "stabilized" refers to a material of the present invention which is capable of being stored in a stable condition in any common or conventional web storage manner without the need for further heating or the addition of or joinder with other webs to stabilize the material. Such storage means would include for example, low tension rolls or festooned material in boxes.

As used herein, the term "nonwoven web", refers to a web that has a structure of individual fibers or threads which are interlaid, but not in any regular repeating manner.

Nonwoven webs have been, in the past, formed by a variety of processes such as, for example, meltblowing processes, spunbonding process, and bonded carded web processes.

As used herein, the term "necked material", refers to any material which has been constricted in at least one dimension by applying a tensioning force in a direction that is perpendicular to the desired direction of neck-down.

As used herein, the term "neckable material", refers to any material which can be necked. As used herein, the term "percent neckdown", refers to the ratio determined by measuring the difference between the un-necked dimension and the stabilized necked dimensions of the neckable material in the direction of necking, and then dividing that difference by the un-necked dimension of the neckable material, then multiplying by 100. As used herein, the term "composite elastic material", refers to a material comprising an elastic member joined to a stabilized extensible necked material. The elastic member may be joined to the stabilized extensible necked material at intermittent points or may be continuously bonded thereto. The joining is accomplished while the elastic member and the stabilized extensible necked material are in juxtaposed configuration. The composite elastic material is elastic in a direction generally parallel to the direction of neckdown of the stabilized extensible necked material and may be stretched in that direction to the breaking point of the stabilized extensible necked material. A composite elastic material may include more than two layers.

As used herein, the term "polymer", generally includes, but is not limited to, homopolymers, copolymers, such as, for example, block, graft, random, and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible molecular geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic and random symmetries. As used herein, the term "surface-pathlength" refers to a measurement along a topographic surface of the material in question in a specified direction.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a method of producing a stabilized extensible necked nonwoven web comprising the steps of: providing a neckable nonwoven web; feeding the neckable nonwoven web in a first direction; applying a tensioning force to the neckable nonwoven web in a direction parallel to the first direction to neck the nonwoven web in a direction perpendicular to the first direction; and subjecting the necked nonwoven web to incremental stretching in a direction perpendicular to the first direction to provide a strong and soft nonwoven web.

The method may comprise the additional step of subjecting the nonwoven web to mechanical stabilization after the nonwoven web has been tensioned in a direction parallel to the first direction.

The method may also comprise the additional step of winding the nonwoven web onto a take-up roll or festooning the stabilized extensible necked nonwoven web into box.

The method may also comprise the additional step of joining the nonwoven web to an elastic member to form a composite elastic material.

The neckable material may be any material that can be necked sufficiently at room temperature. Such neckable materials include knitted and loosely woven fabrics, bonded carded nonwoven webs, spunbonded nonwoven webs, or meltblown nonwoven webs. The neckable material may also have multiple layers such as, for example, multiple spunbonded layers and/or multiple meltblown layers or film layers. The neckable material may be made of polymers such as for example, polyolefins. Exemplary polyolefins include polypropylene, polyethylene, ethylene copolymers, propylene copolymers and blends thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following description which is taken in conjunction with the accompanying drawings in which like designations are used to designate substantially identical elements, and in which:

FIG. 1 is schematic illustration of an exemplary process for forming a strong and soft nonwoven web of the present invention; FIG. 2 is an enlarged perspective illustration of the stabilizing roller arrangement;

FIG. 3 is an enlarged perspective illustration of the cross-machine direction web enhancement arrangement;

FIG. 4 is a plan view of a spaced-apart pattern of embossments which is not suitable for setting the necked nonwoven web;

FIG. 5 is a plan view of an embossment pattern of the present invention which is suitable for setting the necked nonwoven web;

FIG. 6 is a plan view of another embossment pattern of the present invention which is suitable for setting the necked nonwoven web; and FIG. 7 is a schematic illustration of another exemplary process for forming a necked nonwoven web of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 there is schematically illustrated at 10 a process for forming a strong and soft nonwoven web of the present invention.

According to the present invention, a neckable nonwoven web 12 is unwound from a supply roll 13 and travels in the direction indicated by the arrows associated therewith, i.e., in the machine direction or MD or first direction, as the supply roll 13 rotates in the direction indicated by the arrows associated therewith. From the supply roll 13 the neckable nonwoven web 12 passes through a nip 25 of the S-roll arrangement 26 formed by the stack rollers 28 and 30. The neckable nonwoven web 12 passes through the nip 25 of the S-roll arrangement 26 in a reverse-S path as indicated by the rotation direction arrows associated with the stack rollers 28 and 30.

The neckable nonwoven web 12 may be formed by known nonwoven extrusion processes, such as, for example, known meltblowing processes or known spunbonding processes, and passed directly through the nip 25 without first being stored on a supply roll.

From the S-roll arrangement 26 the neckable nonwoven web 12 may optionally pass through the nip 32 formed by the incremental stretching rollers 34 and 36 of the mechanical stabilization arrangement 38. Preferably, the neckable nonwoven web 12 passes directly to the cross-machine direction web enhancement arrangement 54 from the S-roll arrangement 26. The optional step of passing through the mechanical stabilization arrangement 38 will now be discussed. Because the peripheral linear speed of the rollers of the S-roll arrangement 26 is controlled to be less than the peripheral linear speed of the rollers of the mechanical stabilization arrangement 38, the neckable nonwoven web 12 is tensioned between the S- roll arrangement 26 and the nip 32 of the incremental stretching rollers 34 and 36 of the mechanical stabilization arrangement 38. By adjusting the difference in the speeds of the rollers, the neckable nonwoven web 12 is tensioned so that it necks a desired amount and is maintained in such a tensioned, necked condition. The mechanical stabilization arrangement 38 provides a stabilized necked nonwoven web.

As the nonwoven web 12 is tensioned between the S-roll arrangement 26 and the nip 32 of the incremental stretching rollers 34 and 36 tension is applied to the neckable nonwoven web in a direction parallel to the first direction or parallel to the machine or MD direction. The tensioning of the nonwoven web 12 in a direction parallel to the first direction causes the nonwoven web to neck in a direction perpendicular to the first direction or in a direction parallel to the CD or cross«-machine direction.

Entering the S-roll arrangement 26, the nonwoven web 12 has a CD surface-pathlength dimension Z. When tensioned between the S-roll arrangement 26 and the nip 32 of the incremental stretching rollers 34 and 36 of the mechanical stabilization arrangement 38 the nonwoven web 12 is necked such that its new CD surface-pathlength dimension Z' is less than the CD surface-pathlength dimension Z. CD surface-pathlength dimension Z' is preferably less than about 75% of CD surface-pathlength dimension Z, more preferably less than about 50% of CD surface-pathlength dimension Z, and most preferably less than about 30% of CD surface-pathlength dimension Z. For example, the nonwoven web 12 having a CD surface-pathlength dimension Z of 10 inches may be necked to have a CD surface-pathlength dimension Z' of 5 inches which is 50% of the CD surface-pathlength dimension Z of 10 inches. Other methods of tensioning the neckable nonwoven web 12 may be used such as, for example, tenter frames.

The neckable nonwoven web 12 may be extensible, elastic, or nonelastic nonwoven material. The neckable nonwoven web 12 may be a spunbonded web, a meltblown web, or a bonded carded web. If the neckable nonwoven web is a web of meltblown fibers, it may include meltblown microfibers. The neckable nonwoven web 12 may be made of fiber forming polymers such as, for example, polyolefins. Exemplary polyolefins include one or more of polypropylene, polyethylene, ethylene copolymers, propylene copolymers, and butene copolymers. In one embodiment of the present invention, the neckable nonwoven web 12 may be a multilayer material having, for example, at least one layer of a spunbonded web joined to at least one layer of a meltblown web, a bonded carded web or other suitable material. Alternatively, the neckable nonwoven web 12 may be a single layer of material such as, for example, a spunbonded web, a meltblown web, or a bonded carded web. The neckable nonwoven web 12 may also be a composite material made of a mixture of two or more different fibers or a mixture of fibers and particles. Such mixtures may be formed by adding fibers and/or particulates to the gas stream in which the meltblown fibers are carried so that an intimate entangled commingling of meltblown fibers and other materials, e.g., wood pulp, staple fibers and particulates such as, for example, hydrocoUoidal (hydrogel) particles commonly referred to as superabsorbent materials, occurs prior to collection of the meltblown fibers upon a collecting device to form a coherent web of randomly dispersed meltblown fibers and other materials.

The nonwoven web of fibers should be joined by bonding to form a coherent web structure which is able to withstand necking. Suitable bonding techniques include, but are not limited to, chemical bonding, thermobonding, such as point calendering, hydroentangling, and needling.

FIG. 2 is an enlarged perspective illustration of a preferred embodiment of the mechanical stabilization arrangement 38 employing opposed pressure applicators having three-dimensional surfaces which at least to a degree are complimentary to one another. The mechanical stabilization arrangement 38 shown in FIG. 2 comprises incremental stretching rollers 34 and 36. The neckable nonwoven web 12 passes through the nip 32 formed by incremental stretching rollers 34 and 36 as the incremental stretching rollers rotate in the direction indicated by the arrows associated therewith. Uppermost incremental stretching roller 34 comprises a plurality of teeth 40 and corresponding grooves 41 which extend about the entire circumference of roller 34. Lowermost incremental stretching roller 36 comprises a plurality of teeth 42 and corresponding grooves 43 which extend about the entire circumference of roller 36. The teeth 40 on roller 34 intermesh with or engage the grooves 43 on roller 36, while the teeth 42 on roller 36 intermesh with or engage the grooves 41 on roller 34.

The teeth 40 and 42 on rollers 34 and 36, respectively, extend in a direction substantially perpendicular to the first direction of the neckable nonwoven web 12 or in a direction substantially parallel to the width of the neckable nonwoven web 12. That is, teeth 40 and 42 extend in a direction parallel to the cross-machine or CD direction. The incremental stretching rollers 34 and 36 incrementally stretch the necked web in a direction generally perpendicular to the necked direction, i.e., in a direction parallel to the first direction, thereby stabilizing the necked nonwoven web 12 such that it remains in its necked condition after passing through the incremental stretching rollers 34 and 36 and the tension on the necked nonwoven web is released. By stabilizing the necked nonwoven web, the necked nonwoven web substantially maintains its necked dimension without returning to its precursor dimension.

After being stabilized by passing through the incremental stretching rollers 34 and 36, the stabilized necked nonwoven web 12 includes a plurality of stabilizing embossments 44. Stabilizing embossments 44 extend in a substantially linear direction parallel to one another across the entire width of the stabilized necked nonwoven web 12. The stabilizing embossments 44 are shown to be extending in a direction substantially parallel to the CD or cross-machine direction. As seen in FIG. 2, each stabilizing embossment extends across the stabilized necked nonwoven web 12 from one edge to the other edge. This is important as this sets the fibers across the entire width of the web 10

thereby stabilizing the web. If the stabilizing embossments 44 did not extend entirely across the neckable nonwoven web 12, the portion of the neckable nonwoven web that is not embossed would return to its precursor width. For example, a spaced apart pattern of embossments such as shown in Figure 4, would not effectively set the nonwoven web. The portions of the nonwoven web between the individual embossments would not be set, and therefore, would allow the nonwoven web to return to its precursor dimension.

The incremental stretching rollers 34 and 36 may include any number of teeth and grooves to provide the desired stabilization in the nonwoven web. In addition, the teeth and grooves may be nonlinear, such as for example, curved, sinusoidal, zig-zag, etc. The size and amount of engagement of the teeth and grooves on the incremental stretching rollers 34 and 36 may be of any desired dimension. In addition, the teeth and grooves may extend in a direction other than perpendicular to the travel direction of the neckable web. For example, the teeth and grooves may extend at an angle to the CD direction, but preferably not parallel to the MD or machine direction, as this type of incremental stretching would tend to expand the width of the web, thus defeating the purpose of the necking operation.

Either directly from the S-roll arrangement 26 or from the optional mechanical stabilization arrangement 38, the nonwoven web 12 passes to the cross-machine direction web enhancement arrangement 54. FIG. 3 is an enlarged perspective illustration of a preferred embodiment of the cross-machine direction web enhancement arrangement 54 employing opposed pressure applicators having three-dimensional surfaces which at least to a degree are complimentary to one another. The cross-machine direction web enhancement arrangement 54 shown in FIG. 3 comprises incremental stretching rollers 51 and 52. The nonwoven web 12 passes through the nip 50 formed by incremental stretching rollers 51 and 52 as the incremental stretching rollers rotate in the direction indicated by the arrows associated therewith. Uppermost incremental stretching roller 51 comprises a plurality of teeth 58 and corresponding grooves 59 which extend about the entire circumference of roller 51. Lowermost incremental stretching roller 52 comprises a plurality of teeth 60 1 1

and corresponding grooves 61 which extend about the entire circumference of roller 52. The teeth 58 on roller 51 intermesh with or engage the grooves 61 on roller 52, while the teeth 60 on roller 52 intermesh with or engage the grooves 59 on roller 51.

The teeth 58 and 60 on rollers 51 and 52, respectively, extend in a direction substantially parallel to the travel direction of the nonwoven web 12 or in a direction substantially perpendicular to the width of the nonwoven web 12. That is, teeth 58 and 60 extend in a direction parallel to the machine, MD or first direction. The incremental stretching rollers 51 and 52 incrementally stretch the nonwoven web in a direction generally perpendicular to the first or machine direction thereby causing the fibers of the nonwoven web to be oriented, at least to a degree, in the cross-machine or CD direction or perpendicular to the first direction. In addition to orienting the individual fibers of the nonwoven web in CD direction the surface-pathlength of the nonwoven web as measured in the CD direction or perpendicular to the first direction increases. As the nonwoven web 12 exits the cross-machine direction web enhancement arrangement 54 the nonwoven web 12 includes a plurality of rugosities 62. The rugosities 62 provide the nonwoven web 12 with its increased surface-pathlength as compared to the surface- pathlength of the nonwoven web 12 prior to entering the cross-machine direction web enhancement arrangement 54.

As can be seen in FIG. 3, prior to entering the nip 50 of the cross-machine direction web enhancement arrangement 54, the nonwoven web 12 has a CD surface-pathlength dimension Z'. After being subjected to the incremental stretching rollers 51 and 52 the nonwoven web has a plurality of rugosities 62 which provide the nonwoven web 12 with a new CD surface-pathlength dimension Z" which is greater than CD surface-pathlength dimension Z'. CD surface-pathlength dimension Z" is preferably at least about 10% greater than CD surface-pathlength dimension Z', more preferably at least about 20% greater than CD surface-pathlength dimension Z', and most preferably at least about 30% greater than CD surface-pathlength dimension Z\ CD surface- pathlength dimension Z" may be as much as about 200% greater than dimension Z' or more without subjecting the nonwoven web to catastrophic failure. 12

The method for determining the surface-pathlength of the nonwoven web can be found in the Test Methods section set forth in subsequent portions of the present specification.

The incremental stretching rollers 51 and 52 may include any number of teeth and grooves as desired. In addition, the teeth and grooves may be nonlinear, such as for example, curved, sinusoidal, zig-zag, etc. The size and amount of engagement of teeth and grooves on incremental stretching rollers 51 and 52 may be of any desired dimension.

The nonwoven web is both strong and soft after having passed through the cross- machine direction web enhancement arrangement. Because the nonwoven web is both strong and soft it is particularly well suited for use in disposable absorbent articles such as diapers, incontinent briefs, training pants, feminine hygiene garments, and the like, as it is able to be used in portions of the article where high strength and softness can add to the articles overall performance.

Referring now to FIG. 1, after the neckable nonwoven web 12 passes through the cross-machine direction web enhancement arrangement 54 it is wound up on take-up roll 50. Alternatively, the neckable nonwoven web 12 may be festooned into a box using conventional festooning equipment.

Conventional drive means and other conventional devices which may be utilized in conjunction with the apparatus of FIG. 1 are well known and, for purposes of clarity. have not been illustrated in the schematic view of FIG. 1.

In addition to incremental stretching, there are other suitable methods for mechanically stabilizing the necked nonwoven web. These methods include crimping, and/or creping rollers. Another suitable method includes passing the necked nonwoven web through the nip of a pair of smooth rollers. The nip pressure and/or roller engagements of such stabilizing rollers are set to provide the desired degree of stabilization to the necked web.

FIG. 5 is a plan view of another suitable embossment pattern for stabilizing the neckable nonwoven web. The pattern includes a plurality of linear embossments 210 extending continuously across the entire width of the web 205 in a direction generally 13

parallel to the cross-machine direction. The pattern also includes a plurality of linear embossments 212 extending continuously across the entire width of the web 205 at an angle to the cross-machine direction and at an angle to the embossments 210. The web 205 also includes a plurality of linear embossments 214 extending continuously across the entire width of the web 205 at an angle to the cross-machine direction and at an angle to the embossments 210 and 212. The embossments 212 and 214 may extend at any angle to one another and to the embossments 210.

FIG. 6 is a plan view of another embossment pattern for stabilizing the neckable nonwoven web. The pattern includes a plurality of linear embossments 222 extending continuously across the entire width of the web 220 at an angle to the cross-machine direction. The web 220 also includes a plurality of linear embossments 224 extending continuously across the entire width of the web 220 at an angle to the cross-machine direction and at an angle to the embossments 222. The embossments 222 and 224 are preferably aligned perpendicular to one another. However, other angles between the linear embossments 222 and 224 may also be employed.

The embossment pattern of FIGS. 5 and 6, is provided by feeding the necked nonwoven web through a nip formed by a pair of patterned compression rollers. Each roller comprises a series of raised surfaces, similar to the teeth 40 and 42 on rollers 34 and 36, respectively. The raised surfaces on each of the rollers are complimentary and engage one another and compress the necked nonwoven web providing the embossment pattern shown in FIGS. 5 and 6. The compression provided by the patterned compression rollers sets the individual fibers to stabilize the web in its necked condition.

Alternatively, the patterned compression rollers may comprise a pattern roller having a pattern of raised surfaces and an anvil roller having a smooth surface. The raised surfaces on the pattern roller compress the necked nonwoven web against the anvil roller to provide the embossment pattern shown in FIGS. 5 and 6.

The nonwoven web may later be joined to an elastic member to form a composite elastic material. The nonwoven web and the elastic member may be joined to one another either intermittently or substantially continuously along at least a portion of their 14

coextensive surfaces while the elastic member is in either a tensioned or an untensioned condition. The nonwoven web may be joined to an elastic member after having been removed from a roll, such as take-up roll 50, or may be joined to an elastic member after having been immediately subjected to mechanical stabilization. The elastic member may be made from any suitable elastic material. Generally, any suitable elastomeric fiber forming resins or blends containing the same may be utilized for the nonwoven webs of elastomeric fibers and any suitable elastomeric film forming resins or blends containing the same may be utilized for the elastomeric films of the invention. For example, the elastic member may be an elastomeric film made from block copolymers having the general formula A-B-A' where A and A' are each a thermoplastic polymer endblock which contains a styrenic moiety such as a poly(vinyl arene) and where B is an elastomeric polymer midblock such as a conjugated diene or a lower alkene polymer. Other exemplary elastomeric films which may be used to form the elastic sheet include polyurethane elastomeric materials such as, for example, those available under the trademark ESTANE from B.F. Goodrich & Company, polyamide elastomeric materials such as, for example, those available under the trademark PEBAX from the Rilsan Company, and polyester elastomeric materials such as, for example, those available under the trade designation Hytrel from E. I. DuPont De Nemours & Company.

A polyolefin may also be blended with the elastomeric polymer to improve the processability of the composition. The polyolefin must be one which, when blended and subjected to an appropriate combination of elevated pressure and elevated temperature conditions, is extrudable, in blended form, with the elastomeric polymer. Useful blending polyolefin materials include, for example, polyethylene, polypropylene and polybutene, including ethylene copolymers, polypropylene copolymers, and butene copolymers. The elastic member may also be a pressure sensitive elastomeric adhesive sheet.

For example, the elastic material itself may be tacky or, alternatively, a compatible tackifying resin may be added to the extrudable elastomeric compositions described above to provide an elastomeric sheet that can act as a pressure sensitive adhesive, e.g., to bond the elastomeric sheet to a tensioned, necked nonelastic web. The elastic sheet may 15

also be a multilayer material that may include two or more individual coherent webs or films. Additionally, the elastomeric sheet may be a multilayer material in which one or more of the layers contain a mixture of elastic and nonelastic fibers or particles.

Other suitable elastomeric materials for use as the elastic member include "live" synthetic or natural rubber including heat shrinkable elastomeric films, formed elastomeric scrim, elastomeric foams, or the like. In an especially preferred embodiment, the elastic member comprises an elastomeric scrim available from Conwed Plastics.

Referring now to FIG. 7, there is schematically illustrated another process 100 for forming a strong and soft nonwoven web of the present invention. A neckable nonwoven web 102 is unwound from a supply roll 103 and travels in the direction indicated by the arrows associated therewith, i.e., in the machine or first direction, as the supply roll 103 rotates in the direction indicated by the arrows associated therewith. From the supply roll 103 the neckable nonwoven web 102 passes through the nip 125 of the S-roll arrangement 126 formed by the stack rollers 128 and 130. The neckable nonwoven web 102 may be formed by known nonwoven extrusion processes, such as, for example, known meltblowing processes or known spunbonding processes, and passed directly through the nip 104 without first being stored on a supply roll.

The neckable nonwoven web 102 passes through the nip 125 of the S-roll arrangement 126 in a reverse-S path as indicated by the rotation direction arrows associated with the stack rollers 128 and 130. From the S-roll arrangement 126, the neckable nonwoven web 102 passes through the pressure nip 145 formed by pressure roller arrangement 140 comprised of pressure rollers 142 and 144. Because the peripheral linear speed of the rollers of the S-roll arrangement 126 is controlled to be less than the peripheral linear speed of the rollers of the pressure roll arrangement 140, the neckable nonwoven web 102 is tensioned between the S-roll arrangement 126 and the pressure nip of the pressure roll arrangement 140. By adjusting the difference in the speeds of the rollers, the neckable nonwoven web 102 is tensioned so that it necks a desired amount and is maintained in such a tensioned, necked condition. From the pressure roller 16

arrangement 140 the necked nonwoven web 102 may optionally pass through the nip 151 formed by the mechanical stabilization arrangement 152 comprised of incremental stretching rollers 153 and 154 or may pass directly to the nip 164 of the cross-machine direction web enhancement arrangement 167. A more detailed description of a suitable mechanical stabilization arrangement is provided above and is shown in FIG. 2. The cross-machine direction web enhancement arrangement 167 employs opposed pressure applicators having three-dimensional surfaces which at least to a degree are complimentary to one another. The cross-machine direction web enhancement arrangement 167 comprises incremental stretching rollers 165 and 166. A more detailed description of the cross-machine direction web enhancement arrangement comprising incremental stretching rollers is provided above and is shown in FIG. 3. After leaving the cross-machine direction web enhancement arrangement 167 the nonwoven web 102 is wound up on take-up roll 170. Alternatively, the nonwoven web 102 may be festooned into a box using conventional equipment. Conventional drive means and other conventional devices which may be utilized in conjunction with the apparatus of FIG. 7 are well known and, for purposes of clarity, have not been illustrated in the schematic view of FIG. 7.

Test Methods

Surface-pathlength measurements of nonwoven webs are to be determined by analyzing the nonwoven webs by means of microscopic image analysis methods.

The sample to be measured is cut and separated from nonwoven web. An unstrained sample length of one-half inch is to be "gauge marked" perpendicular to the "measured edge" while attached to the web, and then accurately cut and removed from the web.

Measurement samples are then mounted onto the long-edge of a microscopic glass slide. The "measured edge" is to extend slightly (approximately 1mm) outward from the slide edge. A thin layer of pressure-sensitive adhesive is applied to the glass face-edge to 17

provide a suitable sample support means. For a sample having deep rugosities it may be necessary to gently extend the sample (without imposing significant force) to facilitate contact and attachment of the sample to the slide edge. This allows improved edge identification during image analysis and avoids possible "crumpled" edge portions that require additional interpretation analysis.

Images of each sample are to be obtained as "measured edge" views taken with the support slide "edge on" using suitable microscopic measuring means of sufficient quality and magnification. Data is obtained using the following equipment; Keyence VH- 6100 (20x Lens) video unit, with video-image prints made with a Sony Video printer Mavigraph unit. Video prints are image-scanned with a Hewlett Packard ScanJet IIP scanner. Image analysis is on a Macintosh IlCi computer utilizing the software NIH MAC Image version 1.45.

Using this equipment, a calibration image initially taken of a grid scale length of .500" with .005" increment-marks to be used for calibration setting of the computer image analysis program. All samples to be measured are then video-imaged and video-image printed. Next, all video-prints are image-scanned at 100 dpi (256-level gray scale) into a suitable Mac image-file format. Finally, each image-file (including calibration file) is analyzed utilizing Mac Image 1.45 computer program. All samples are measured with freehand line-measurement tool selected. Samples are measured on both side-edges and the lengths are recorded. Thin samples require only one side-edge to be measured. Thick samples are measured on both side-edges. Length measurement tracings are to be made along the full gauge length of a cut sample. In some cases multiple (partially overlapping) images may be required to cover the entire cut sample. In these cases, select characteristic features common to both overlapping-images and utilize as "markers" to permit image length readings to adjoin but not overlap.

The final determination of surface-pathlength is obtained by averaging the lengths of five (5) separate 1/2" gauge-samples of each region. Each gauge-sample "surface- pathlength" is to be the average of both side-edge surface-pathlengths. 18

While the test method described above is useful for many of the webs of the present invention it is recognized that the test method may have to be modified to accommodate some webs.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

19What is claimed is:

1. A method of producing a strong and soft nonwoven web comprising the steps of: a) providing a neckable nonwoven web; b) feeding the neckable nonwoven web in a first direction; c) applying a tensioning force to the neckable nonwoven web to neck the nonwoven web; and d) subjecting the necked nonwoven web to incremental stretching in a direction perpendicular to said first direction to provide a strong and soft nonwoven web.

2. The method of Claim 1 after step c) further comprising the additional step of: subjecting the necked nonwoven web to mechanical stabilization.

3. The method of Claim 2 wherein the step of mechanical stabilization comprises subjecting the necked nonwoven web to incremental stretching in a direction parallel to said first direction.

4. The method of Claim 3 wherein said incremental stretching comprises feeding the necked nonwoven web through a nip formed by a pair of incremental stretching rollers.

5. The method of Claim 4 wherein each said incremental stretching roller comprises a plurality of teeth and a plurality of grooves.

6. The method of Claim 2 wherein said mechanical stabilization comprises feeding the necked nonwoven web through a nip formed by a pair of patterned compression rollers. 20

7. The method of Claim 6 wherein said patterned compression rollers provide a continuous compression stabilizing embossment across the entire width of the nonwoven web.

8. The method of Claim 1 wherein said nonwoven web is a web selected from the group consisting of a bonded carded web of fibers, a web of spunbonded fibers, a web of meltblown fibers, and a multilayer material including at least one of said webs.

9. The method of Claim 8 wherein said fibers comprise a polymer selected from the group consisting of polyolefins, polyesters, and polyamides.

10. The method of Claim 9 wherein said polyolefin is selected from the group consisting of one or more of polyethylene, polypropylene, polybutene, ethylene copolymers, propylene copolymers, and butene copolymers.

1 1. The method of Claim 10 wherein said nonwoven web is a composite material comprising a mixture of fibers and one or more other materials selected from the group consisting of wood pulp, staple fibers, particulates, and super-absorbent materials.

12. The method of Claim 1 further comprising the additional step of: e) winding the nonwoven web onto a take-up roll.

13. The method of Claim 1 further comprising the additional step of: e) festooning the nonwoven web into a box.

14. The method of Claim 1 further comprising the additional step of: e) joining the nonwoven web to an elastic member. 21

15. The method of Claim 14 wherein the elastic member comprises an elastomeric polymer selected from the group consisting of elastic polyesters, elastic polyurethanes, elastic polyamides, and elastic A-B-A' block copolymers wherein A and A' are the same or different thermoplastic polymer, and wherein B is an elastomeric polymer block.

16. The method of Claim 14 wherein said elastic member comprises an elastomeric film.

17. The method of Claim 14 wherein said elastic member comprises an elastomeric scrim.

18. A method of producing a strong and soft nonwoven web comprising the steps of: a) providing a neckable nonwoven web; b) feeding the neckable nonwoven web in a first direction; c) applying a tensioning force to the neckable nonwoven web in a direction parallel to said first direction to neck the nonwoven web in a direction perpendicular to said first direction; and d) subjecting the necked nonwoven web to incremental stretching in a direction perpendicular to said first direction to provide a strong and soft nonwoven web.

19. The method of Claim 18 after step c) further comprising the additional step of: subjecting the necked nonwoven web to mechanical stabilization.

20. The method of Claim 19 wherein the step of mechanical stabilization comprises subjecting the necked nonwoven web to incremental stretching in a direction parallel to said first direction.