MXPA01002865A - Elastic nonwoven webs and films - Google Patents

Abstract

The present invention is generally directed to elastic nonwoven webs and films made from thermoplastic polymers. In particular, the present invention is directed to forming nonwoven webs and films from an elastomeric polymer and then cross-linking the polymer in order to improve the stretch characteristics of the article. Cross-linking also makes the article more temperature resistant. In one embodiment, the elastomeric polymer is a metallocene-catalyzed copolymer of polyethylene. Elastic layers made in accordance with the present invention can be combined into laminates and used in various products, such as diapers and other personal care articles.

Description

FILMS AND NON-WOVEN ELASTIC FABRICS FIELD OF THE INVENTION The present invention is generally directed to the process of crosslinking thermoplastic polymers used to make fibers and films in order to improve temperature resistance and to decrease the amount of tension-release that fibers and films may have suffered during use. . More particularly, the present invention is directed to crosslinked metallocene-crosslinked elastomeric polymers contained in fibers and films which are used in bonded-tapered and bound-stretched laminates.

BACKGROUND OF THE INVENTION Fabrics, films and laminates made from high-density elastomeric films and elastomeric fibers are used for a variety of applications where stretchability is required. For example, waistbands, leg bands, women's care products, adult care products and diapers use elastic components to provide such items with elastic properties and better fit.

Several elastic products previously described in the past have been previously produced. For example, in US Pat. No. 4,663,220 issued isneski et al., Which is hereby incorporated by reference in its entirety, the synthesis of the elastomeric products of the extrudable materials containing polyolefin is described. In this reference, the extrudable elastomeric compositions are formed by mixing block copolymer AB '(where "A" and "A" are each thermoplastic end blocks including styrene and where "B" is an elastomeric middle block) with a polyolefin. The polymer mixture mentioned above is extrudable when subjected to conditions of high pressure and temperature. block copolymer A-B-A 'imparts elastic properties to the products formed from the composition.

Such compositions are extruded by the molded s to an appropriate combination of elevated pressure and temperature. The pressure and temperature will vary depending on the polyolefin used. These extrudable compositions can be formed into a variety of products such as non-woven elastomeric ela with variable basis weights. Here, the terms "elastic" and "elastomeric" are used to refer to materials that, with the application of a force, are stretchable to a stretched length of about 125 percent of their original relaxed length.

However, when such elastomeric materials are released from a stretched position, the fibers typically return to their original relaxed length, but instead exhibit permanent elongation. For example, if the elastic laminate is stretched over a surface and left in this situation stretched or stressed for a period of time, the resistance forces exerted by the elastomeric fibers in the surface laminate decrease. Therefore, when the laminate is removed from the surface and released from its stretched position, the fibers within the laminate will become permanently elongated when they relax, reducing the stretch characteristics of the fabric. This lengthening process is known as tension relaxation.

When such tension relaxation occurs with the elastomeric fibers, the functioning of such fibers is adversely affected. Fibers that have undergone significant stress relaxation will not provide laminates that require adjustment properties and retention force.

Therefore, there is currently a need for a process to improve the performance of the elastomeric fibers so that they suffer less stress relaxation.

SYNTHESIS OF THE INVENTION The present invention recognizes and alleviates the above and other problems experienced in the prior art.

The present invention is generally directed to a process for cross-linking elastomeric polymers such as metallocene-catalyzed polymers., contained within elastic fibrous fabrics, laminates, foams and the like. For example, the metallocene-catalyzed elastic fibers and films can usually contain elastomers which are catalyzed with ethylene metallocene and a comonomer such as butene, hexene, octene and the like. The polymers are of low density due to their short chain branching (as opposed to the typical high density polymers which normally do not contain a significant amount of chain branching). The polymer chains contained within the elastomeric polymers are not normally chemically bonded together. A cross-linking process, however, creates the bond between the chains, making the fibers and films made of the polymer stronger, more resistant to temperature and less likely to undergo tension relaxation.

According to the present invention, there are several methods available in order to crosslink the elastomers contained within the fibers and the films. For example elastomers can be crosslinked by exposing the fiber or film to an electron beam irradiation.

In an alternate embodiment, a cross-linking agent can be combined with the elastomers which initiates cross-linking after the fibers and films have been formed. For example, in one embodiment, the cross-linking agent may be a peroxide which causes the elastomers to cross-link when exposed to heat.

In another alternate embodiment, a silane can be used as a cross-linking agent. The silane will cause the elastomers to crosslink when exposed to moisture and to a catalyst such as a tin catalyst.

In a further alternate embodiment, the crosslinking agent may be a photoinitiator which initiates and crosslinking the elastomers when subjected to electromagnetic radiation such as ultraviolet radiation.

Other objects, features and aspects of the present invention are discussed in more detail below.

DETAILED DESCRIPTION OF THE PREFERRED INCORPORATIONS It should be understood by one with an orderly skill in the art that the present discussion is a description of sol example incorporations, and that is not intended as limiting the broader aspects of the present invention, whose broader aspects are involved in the construction d example.

The present invention is generally directed to a process for cross-linking elastomeric polymers, particularly elastomers catalyzed with matalocene. Fibers, films and foams made of such an elastomer typically comprise linear low density polyethylene with high comonomer content. Due to their stretch properties, these types of items are commonly used and elastic laminates and other elastic-type products. The comonomer may be butene, hexene, octene, or the like, in a preferred embodiment of this invention the comonomer and octene.

Elastic cross-linking polymers, which are used to form fibrous fabrics, foam films according to the present invention, offer many advantages, especially in applications where the properties of stretching of the polymer are used; For example, him Cross-linking of polymers has been found to improve polymer temperature resistance, making the polymer better suited for higher temperature applications. The cross-linked elastomeric polymers according to the present invention also reduce the stress relaxation of the polymer. Accordingly, when used in elastic application, the cross-linked elastomeric polymers according to the present invention retain their elastic properties for a longer period of time and are prone to irreversible damage due to overstretching.

In the present invention, an elastic laminate is a product comprising two or more layers such as foams, films and / or non-woven fabrics, joined together to form a laminate wherein at least one of the layers has the characteristic of a laminate. an elastic polymer. Examples of elastic laminates include but are not limited to stretched-attached laminates and closely-bonded laminates.

The "stretched-attached" refers to an elastic member that is being attached to another elastic member while the elastic member is extended to at least about 2 percent of its relaxed length. "Stretched-attached laminate" refers to a composite material that has at least two layers in which one layer is a foldable layer and the other layer It is an elastic layer. The layers are joined together when the elastic cap is in an extended condition so that with the layers relaxed, the collapsible layer is collected. The elastic composite material of multiple layers can be stretched until the non-elastic layer is fully extended. A type of stretch-bonded laminate is described, for example, in the United States of America Patent Number 4,720.41 issued to Vander Wielen and others.; which is incorporated herein by reference. Other composite elastic materials are described and described in U.S. Patent Nos. 4,789,699 to Klaffer et al., 4,781,966 to Taylor, 4,657,802 to Morman, and 4,655,760 to Morman, and others. all of which are incorporated herein by reference to them.

"Narrow-bonded" refers to an elastic member which is being attached to a non-elastic member while the non-elastic member is extended or narrowed. "Narrow-bonded laminate" refers to a composite material having at least two layers in which one layer is an elastic non-constricted layer, and the other layer is an elastic layer. Examples of narrowed and bonded laminates are those such as those described in United States Patents Nos. 5,226,992, 4,981,747, 4,965,122 and 5,336.54 all assigned to Morman et al. incorporated herein by reference thereto. The member elastic used in the rolled and bonded laminates, in the bound and bonded laminates and in other similar laminates can be a film, for example, a micropore film or a fibrous web, such as a fabric made of melt blown fibers or a foam. The film can be formed by extruding a filled elastomeric polymer and subsequently stretching it to make it microporous.

Fibrous elastic fabrics can also be formed from an extruded polymer. For example, as indicated above, in an embodiment the fibrous tissue may contain blown fibers with fusion. The fibers can be continuous discontinuous. The meltblown fabrics can be conventionally made by extruding a thermoplastic polymeric material through a matrix to form fibers. Upon exiting the molten polymer fibers from the matrix, a high pressure fluid, such as heated air or steam, attenuates the filaments of molten polymer to form fine fibers. The surrounding cold air is induced inside the hot air stream to cool and solidify the fibers. The fibers are then randomly deposited on a foraminous surface to form a tissue. The fabric has integrity but can be further joined if desired.

In addition to meltblown fabrics, however, it should be understood that other fibrous tissues can be made according to the present invention. For example, in an alternate embodiment, it is believed that fabrics bonded to elastic yarns can also be formed. Yarn-bonded fabrics are typically produced by heating a thermoplastic polymer resin to at least its softening temperature, and then extruding it through a spinning organ to form continuous fibers which can then be fed through a pulling unit. d fiber. From the fiber pulling unit the fibers are spread to a perforated surface where they are formed into a fabric and then bonded such as through chemical, thermal or ultrasonic means.

As described above, the present invention is particularly directed to cross-linked elastomeric polymers in order to improve their stretch properties. In general, preferably the elastomeric polymer is crosslinked after the fibrous tissue or the elastic film is formed. In some applications, when the elastic layer is combined into a laminated product, the elastomeric polymer can be cross-linked after the laminate has been formed.

The manner in which the crosslinked elastomeric polymer according to the present invention may vary depending on the circumstances and the desired results. For example, in a preferred embodiment of the present invention, elastic fibrous fabrics or films can be exposed to electron beam radiation which causes the elastomeric polymer contained within the fibers and the films to cross-link. Electron beam irradiation bombards the polymer chains, such as polyethylene chains, with an irradiation of energy which can break the hydrogen atoms of the chains creating reactive radical sites which cause the polymer to cross-link.

Using the electron beam irradiation to cross-link the elastomeric polymer offers several advantages over the present invention. In particular, electronic rays are able to penetrate through the full thickness of many films and fibrous tissues. It is further believed that the electronic beam can still be used to cross-link an elastomeric polymer contained within a laminated product. Therefore, according to the present invention, the elastic laminates can be formed and then subsequently subjected to an electronic beam in order to cross-link the elastomeric polymer contained within the laminate. In addition, the electronic ray irradiation causes a very fast crosslinking and can be used in a continuous process according to the present invention.

In an alternate embodiment, however, the crosslinking agent may be added to the elastomeric polymer prior to the formation of a fibrous film or tissue. For example in an embodiment, a peroxide is added to the elastomeric polymer, such as polyethylene. The addition of peroxy can cause cross-linking of polyethylene during melting, extrusion and spinning processes. For example, heat and the extruder can be used to create sources of free radical through the peroxide. The free radicals are transferred to the polyethylene, initiating the cross-linking reaction. The degree of cross linking controlled by the amount of peroxide that is added polymer.

In an alternate embodiment, the silane can be added to the polyethylene in combination with a peroxide in order to cause cross-linking. The addition of silane creates a grafting process wherein the free radicals form certain reactants on the polymer chain, such as a polyethylene chain. The silane molecules, however, cool the radical sites and therefore do not cause cross-linking to occur immediately. In order for cross-linking to occur, the polymer can be contacted with water and a catalyst, such as a tin catalyst which in an embodiment can be dibutyl tin dilaurate. Water and catalyst are necessary to create a grafted structure. Of particular advantage cross-linking using a silane can be delayed controlled until the addition of water.

In an alternate embodiment of the present invention cross-linking in the polymer, particularly polyethylene, is achieved by adding a polymeric photoinitiator. Once a photoinitiator is added to the polymer, the crosslinking of the polymer occurs when the polymer is exposed to electromagnetic radiation, and in particular, to ultraviolet radiation. The ultraviolet light breaks the bonds the additive creating free radicals which then propagate through a cross-linking reaction. In a manner similar to the reaction involving silane, in this embodiment, cross-linking can occur at any point in the fiber-forming process, in the formation of a non-woven fabric incorporating the fiber or in the formation of a film.

Various photoinitiators can be used according to the process of the present invention. Preferably, the photoinitiator is chosen so that it can withstand the extrusion temperatures without degrading or reacting. Examples of photoinitiators that can be used in the process include IRGACURE 369 or IRGACURE 907 which is available from Ciba Specialty Chemicals Corporation Terrytown, New York.

Elastomeric polymers that can be cross-linked and that can be used in elastic applications according to the present invention can vary. In general, elastomeric polymer is preferably a polyol-olefin copolymer, such as a polyethylene copolymer or possibly polypropylene. The polyolefin can be copolymerized with various monomers including, for example, ne, bute hexene and mixtures thereof.In a preferred embodiment the present invention is used an elastomeric copolymer catalyzed by metallocene As used herein, a metallocene catalyst refers to a cyclopentadiene metal derivative and can be described as a single or homogeneous site or a constricted geometry catalyst. A metallocene is a stabilized transition metal complex of ancillary ligand and may have the following general formula.

• "Li / \ .. ^ B M Y Where: L is a cyclopentadienyl or a substituted cyclopentadienyl moiety attached to the metal through the uni? -5.

L2 is an organic half which may or may not be cyclopentidienyl half, strongly bound to the metal q remains attached during the polymerization.

B is an optional font group that restricts movement of L, and of Lj and that modifies the angle between L, and L2.

M is a metal such as, for example, titanium or sirconi X and Y are halides or other organic halides such as the methyl groups.

For example, in an embodiment, the matalocene can be as follows: The elastomeric polymer catalyzed with mataloce can be a copolymer of ethylene and another monomer, such coctene, butene, hexene or mixtures thereof. The monome may be present in the copolymer in an amount of about 30 percent by weight, particularly about 7 percent about 25 percent by weight, preferably from about 14 percent about 25 percent by weight. Preferably, the other monomer copolymerized with ethylene is octene. The elastomeric polymer can have a low density ranging from about 0.8 g / cc to about 0.92 grams per cubic centimeter particularly from about 0.86 grams per cubic centimeter to about 0.90 grams per cubic centimeter.

The elastomeric catalysts catalyzed by matalocen that can be used in the present invention include the Dow Plastics AFFINITY polymers having product numbers EG 8100, EG 8200, or EG8150, all of which contain from about 23 percent to about 25 percent. Of octene In an alternate incorporation, the polymer PT 1450 AFFINITY of Do Plastics is used, which contains approximately 13. percent by weight of octene and has a density of around 0.902 grams per cubic centimeter. It has been found that these polymers not only have good elastic properties but that they are also capable of being crosslinked according to the present invention.

Specifically, it is believed that cross-linking the elastomers described above provides elastomers with a seated molecular structure. The seated molecular structure causes the non-woven fabrics and films made of the polymers to have increased temperature resistance and improved stress relieving properties.

Films and elastic fibrous webs made according to the present invention can be incorporated into a diverse variety of products where stretch properties are desired. Films and elastic woven fabrics for example, may be used alone or may be incorporated into a laminate such as a stretched-rolled laminate or a tapered-bonded laminate as described above. When incorporated into a laminate, the elastic layer made in accordance with the present invention is typically held at least one elastic layer, such as a fabric bonded with non-woven yarn. In one embodiment, an elastic layer made with the present invention can be placed between a first layer joined with outer spinning and a second layer joined with outer spinning. The elastic layer can be thermally bonded to the layers linked with spinning or fastened according to any other method. suitable.

The non-elastic layers are generally combined with the elastic layer in a way that allows the elastic layer to stretching and non-elastic layers are generally combined with the elastic layer in a manner that allows the elastic layer to stretch and contract.

Once produced the laminates of the present invention can be used in many different assorted products. For example, laminates can be used for liquid absorbent products, for personal care items, in garments, and in various other products. For example in an embodiment, an elastic laminate made in accordance with the present invention can be used as an elastic member incorporated in a diaper or other similar product. The elastic laminate can be used to comfortably secure the diaper to another garment similar to the wearer.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit of the present invention which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the incorporations can be exchanged both in whole and in part. In addition those with ordinary skill in the art will appreciate that the foregoing description is by way of example only and that no attempt is being made to limit the invention thus described in such appended claims.

Claims (30)

1. A process for producing elastic layers comprising the steps of: Extrude an elastomeric polymer in an elastic layer crosslinking said elastomeric polymer by an amount sufficient to improve the stress relieving properties of said elastic layer.

2. A process as claimed in clause 1 characterized in that said elastomeric polymer comprises a copolymer of a polyolefin.

3. A process as claimed in clause 1 characterized in that said copolymer comprises a metallocene-catalyzed copolymer of ethylene and a comonomer selected from the group consisting of butene, octene, hexene and mixtures thereof, said comonomer being present within said group. copolymer in the amount of up to about 30 percent by weight.

4. A process as claimed in clause 1 characterized in that said comonomer comprises octene, dich octene being present within said copolymer in an amount of from about 25 percent by weight.

5. A process as claimed in clause 1 characterized in that said elastic layer comprises a fibrous fabric.

6. A process as claimed in clause 5 characterized in that said fibrous tissue comprises a meltblown tea.

7. A process as claimed in clause 1 characterized in that said elastic layer comprises film.

8. A process as claimed in clause 1 characterized in that said elastomeric polymer is cross-linked by exposing said elastic layer to the irradiation of electronic beam.

9. A process as claimed in clause 1 characterized in that said elastomeric polymer contains a photoinitiator, and wherein said elastomeric polymer is crosslinked by exposing said elastic layer to ultraviolet radiation, said active ultraviolet radiation and photoinitiator to cause said polymer to cross-link.

10. A process as claimed in clause 1 characterized in that said elastomeric polymer contains a cross-linking agent to initiate and cross-link said polymer.

11. A process as claimed in clause 10 characterized in that said cross-linking agent comprises a peroxide.

12. A process as claimed in clause 10 characterized in that said cross-linking agent comprises a silane.

13 A liquid-absorbent protective garment comprising: a liquid absorbing member; Y an elastic laminate connected to said liquid absorbent member, said elastic laminate comprises an elastic cap made of an elastomeric polymer extruded and bonded in a cross-shaped manner and an extendable non-elastic layer bonded to the elastic layer in a manner that allows the elastic layer HE stretched and contracted to provide the garment with shape notch properties.

14. A protective garment as claimed in clause 13 characterized in that said cross-linked elastomeric polymer comprises a polyethylene copolymer.

15. A protective garment as claimed in clause 14 characterized in that said copolymer comprises ethylene copolymer and a comonomer selected from the group consisting of butene, octene, hexene, and mixtures thereof, said comonomer being present within said copolymer an amount of up to about 30 percent by weight.

16. A protective garment as claimed in clause 13 characterized in that said elastic layer comprises a fibrous fabric.

17. A protective garment as claimed in clause 13 characterized in that said elastic layer comprises a film.

18. A protective garment as claimed in clause 13 characterized in that said elastomeric polymer It has been cross-linked by exposing it to electron beam irradiation.

19. A protective garment as claimed in clause 13 characterized in that said garment comprises a diaper.

20. A protective garment as claimed in clause 13 characterized in that said elastomeric polymer contains a cross-linking agent to initiate cross-linking of said polymer.

21. A protective garment as claimed in clause 13 characterized in that said cross-linking agent comprises a peroxide.

22. A protective garment as claimed in clause 13 characterized in that said cross-linking agent comprises a silane.

23 An elastic laminate comprising: an elastic layer made of an extruded elastomeric polymer, said elastomeric polymer comprises a copolymer of ethylene and a comonomer, said comonomer being selected from the group consisting of octene, butene, hexene and mixtures thereof. said comonomer is present in said copolymer in an amount of up to about 30 percent by weight, said elastomeric polymer being crosslinked in a quantity sufficient to improve the tension relieving properties of the elastic layer; Y an elastic non-stretchable layer fastened to said elastic cap in a manner that allows said elastic layer to be stretched and contracted.

24. An elastic laminate as claimed in clause 23 characterized in that said elastomeric polymer comprises a polymer catalyzed with a matalocene.

25. An elastic laminate as claimed in clause 23 characterized in that said comonomer comprises octene, said octene being present in said copolymer in an amount of from about 7 percent about 1 percent by weight.

26. An elastic laminate as claimed in clause 23 characterized in that said elastomeric polymer is cross-linked by exposing said polymer to electron beam irradiation.

27. An elastic laminate as claimed in clause 23 characterized in that said elastomeric polymer contains a photoinitiator, said elastomeric polymer being crosslinked by exposing said polymer to ultraviolet radiation.

28. An elastic laminate as claimed in clause 23 characterized in that said elastic layer comprises a fibrous tissue.

29. An elastic laminate as claimed in clause 23 characterized in that said elastic layer comprises a film.

30. An elastic laminate as claimed in clause 23 characterized in that it comprises a second extendable cap, said elastic layer being placed between said first extendable layer and said second extendable layer. SUMMARY The present invention is generally directed to woven fabrics and elastic films made of thermoplastic polymers. In particular, the present invention is directed to forming non-woven fabrics and films of an elastomeric polymer and then to crosslinking the polymer in order to improve the stretching characteristics of the article. Cross-linking also makes the article more resistant to temperature. In one embodiment, the elastomeric polymer is a copolymer catalyzed with methylene metallocene. The elastic layers made in accordance with the present invention can be combined into laminates and used in various products such as diapers and other personal care articles.