ceramic fiber manufacturing processing

7/28/2019 Ceramic Fiber Manufacturing Processing

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Ceramic fiber blanket production line


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Improved wet laid bonded fibrous web containing bicomponent fibers

including LLDPE

EP 0465203 A1

Abstract

A thermally bonded fibrous wet laid web containing a bicomponent fiber including apolyester or polyamide fiber component and a component consisting of a linear lowdensity polyethylene having a density in the range of 0.88 to 0.945 g/cc. A graftedHDPE can be added to the LLPDE to improve adhesion of the bicomponent fiber. Thebonded fibrous wet laid web may further include a matrix fiber selected from the groupconsisting of cellulose paper making fibers, cellulose acetate fibers, glass fibers,polyester fibers, ceramic fibers, mineral wool fibers, polyamide fibers, and othernaturally occurring fibers. It has been found that a thermally nonwoven fibrous webmade using the foregoing ingredients has improved and unexpected strength, lowerweb variability and is softer.


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Claims

1. A thermally bonded fibrous wet laid web consisting essentially of a bicomponentfiber comprising a component of polyester or polyamide; and a second


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component consisting essentially of a linear low density polyethylene (LLDPE)having a density in the range of 0.88 to 0.945 g/cc.

2. A thermally bonded fibrous wet laid web of claim 1 wherein the first component ispolyester.

3. A thermally bonded fibrous wet laid web of claim 1 wherein the LLDPE has a

density of 0.90 g/cc to about 0.940 g/cc and has a C - C alkene comonomercontent of about 1% to about 20% by weight of the LLDPE.4. A thermally bonded fibrous wet laid web of claim 3 wherein the alkene

comonomer comprises 1-octene.5. A thermally bonded fibrous wet laid web consisting essentially of a bicomponent

fiber comprising a first component of polyester or polyamide, and a secondcomponent consisting essentially of a linear low density polyethylene copolymerhaving a density in the range of 0.88 to 0.945 g/cc, and grafted high densitypolyethylene, HDPE, having initially a density in the range of 0.94 to 0.965 g/cc,which has been grafted with maleic acid or maleic anhydride, thereby providingsuccinic acid or succinic anhydride groups grafted along the HDPE polymer.

6. The thermally bonded fibrous wet laid web of claim 5 wherein the ungraftedLLDPE has a density in the range of about 0.90 g/cc to about 0.940 g/cc and hasa C - C alkene comonomer content of about 1% to about 20% by weight of theLLDPE.

7. The thermally bonded fibrous wet laid web of claim 6 wherein the alkenecomonomer comprises 1-octene.

8. The thermally bonded fibrous wet laid web of claim 5 wherein LLDPE copolymeris one having a density in the range of about 0.88 g/cc to about 0.945 g/cccontaining about 0.5% to about 35% by weight of a C - C alkene comonomer.

9. The thermally bonded fibrous wet laid web of claim 8 wherein the ungraftedLLDPE copolymer contains about 2% to about 15% by weight of 1-octene

comonomer.10. A thermally bonded fibrous wet laid web consisting essentially of a bicomponentfiber comprising a first component of polyester or polyamide and a secondcomponent consisting of linear low density polyethylene having a density in therange of 0.88 to 0.945 g/cc and a matrix fiber selected from the group consistingessentially of cellulose paper making fibers, cellulose acetate fiber, glass fibers,polyester fibers, metal fibers, mineral wool fibers, polyamide fibers and othernaturally occurring fibers.

11. A thermally bonded fibrous wet laid web of claim 10 wherein said first componentis polyester.

12. A thermally bonded fibrous wet laid web of claim 10 wherein the LLDPE has adensity of 0.90 g/cc to about 0.935 g/cc and has a C - C alkene comonomercontent of about 1% to about 20% by weight of LLDPE.

13. A thermally bonded fibrous wet laid web of claim 12 wherein the alkenecomonomer comprises 1-octene.

14. A thermally bonded fibrous wet laid web of claim 10 wherein the bicomponentfiber has a length to diameter ratio between about 100 and about 2000.

15. A thermally bonded fibrous wet laid web consisting essentially of a bicomponentfiber comprising a first component of polyester or polyamide; and a second


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component consisting essentially of linear low density polyethylene copolymerhaving a density in the range of 0.88 to 0.945 g/cc and grafted high densitypolyethylene, HDPE, having initially a density in the range of 0.94 to 0.965 g/cc,which has been grafted with maleic acid or maleic anhydride, thereby providingsuccinic acid or succinic anhydride groups grafted along the HDPE polymer

claim; and a matrix fiber selected from the group consisting essentially ofcellulose paper making fibers, cellulose acetate fibers, glass fibers, polyesterfibers, metal fibers, mineral wool fibers, polyamide fibers and other naturallyoccurring fibers.

16. The thermally bonded fibrous wet laid web of claim 15 wherein the LLDPE has a

density in the range of about 0.90 g/cc to about 0.940 g/cc and has a C - Calkene comonomer content of about 1% to about 20% by weight of the LLDPE.

17. The thermally bonded fibrous wet laid web of claim 16 wherein the alkenecomonomer comprises 1-octene.

18. The thermally bonded fibrous wet laid web of claim 15 wherein LLDPE copolymeris one having a density in the range of about 0.88 g/cc to about 0.945 g/cc

containing about 0.5% to about 35% by weight of a C - C alkene comonomer.19. The thermally bonded fibrous wet laid web of claim 15 wherein the LLDPEcopolymer contains abut 2% to about 15% by weight of 1-octene comonomer.

20. A thermally bonded fibrous wet laid web comprising a bicomponent fibercomprising a core of a polyester or polyamide; and a sheath consisting of linearlow density polyethylene copolymer having a density in the range of 0.88 g/cc to0.945 g/cc and grafted high density polyethylene, HDPE, having initially a densityin the range of 0.94 to 0.965 g/cc, which has been grafted with maleic acid ormaleic anhydride thereby providing succinic acid or succinic anhydride groupsgrafted along the HDPE polymer chain wherein the bicomponent fiber has alength to diameter ratio between about 100 and about 2,000; and a matrix fiber

selected from the group consisting essentially of cellulose acetate fibers, glassfibers, polyester fibers, ceramic fibers, wool fibers, polyamide fibers, and othernaturally occurring fibers.

21. A method of forming a thermally bonded fibrous wet laid web by wet laying fiberson paper making equipment or wet lay nonwoven equipment, the web comprisingbicomponent fibers comprising a first component consisting of polyester orpolyamide; and a second component consisting essentially of linear low densitypolyethylene having a density in the range of 0.88 g/cc to 0.945 g/cc; wherein thesteps of forming a fiber furnish by dispersion of said bicomponent fibers in acarrier medim consisting essentially of water, thickener and dispersant andsupplying the fiber furnish at a consistency in the range of 0.01 to 0.5 weightpercent fibers to the wire of a machine forming a fibrous web followed by heatingthe web to cause the second component of the bicomponent fiber melt to providethe thermally bonded fibrous web.

22. A method of forming a thermally bonded fibrous wet laid web by wet laying fiberson paper making equipment or wet lay nonwoven equipment, the web comprisingbicomponent fibers comprising a first component of polyester or polyamide, anda second component consisting essentially of linear low density polyethylenecopolymer having a density in the range of 0.88 to 0.945 g/cc and grafted high


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density polyethylene, HDPE, having initially a density in the range of 0.94 to0.965 g/cc, which has been grafted with maleic acid or maleic anhydride, therebyproviding succinic acid or succinic anhydride groups grafted along the HDPEpolymer; and matrix fibers wherein the steps of forming a fiber furnish bydispersion of said bicomponent fibers and matrix fibers in a carrier medium

consisting essentially of water and a dispersant and a thickener, and supplyingthe fiber furnish at a consistency in the range of 0.01 to 0.5 weight percent fibersto the wire of a machine forming a fibrous web an then heating the fibrous web tomelt the second component and thermally bond the fibrous web.

DescriptionBackground of the Invention 1. Field of the Invention

[0001]

The present invention relates to a thermally bonded fibrous wet laid web

containing a specific bicomponent fiber. This thermally bonded fibrous wet laidweb not only has increased web strength, but also is found to provide greaterweb uniformity. Furthermore, the web is found to be much softer than a regularpaper web. In particular, the bicomponent fiber consists essentially of a firstcomponent consisting of polyester or polyamide and a second componentconsisting of linear low density polyethylene. The thermally bonded fibrous wetlaid web may further include a matrix fiber selected from a group consisting ofcellulose paper making fibers, cellulose acetate fibers, glass fibers, polyesterfibers, ceramic fibers, metal fibers, mineral wool fibers, polyamide fibers, andother naturally occurring fibers.

2. Prior Art

[0002]

In the prior art processes of making wet laid webs or paper from fibers ofwhatever source, it is customary to suspend previously beaten fibers, or what isgenerally known as pulp, in an aqueous medium for delivery to a sheet-formingdevice, such as a Fourdrinier wire. This fiber containing aqueous dispersion iscommonly referred to in the art as a furnish. One troublesome problem at thisstage of making wet laid fibrous webs, is the tendency for the fibers to clump,coagulate or settle in the aqueous vehicle. This condition is generally referred to

as flocculation, and greatly impedes the attainment of uniform web formation.That is, flocculation causes a nonuniform distribution of fibers in the paperproduct produced therefrom and manifests not only a mottled, unevenappearance, but is also defective in such important physical properties as tear,burst, and tensile strength. Another problem in making wet laid fibrous webs is atendency of the fibers to float to the surface of the furnish.

[0003]


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For the manufacture of fibrous wet laid webs from conventionally used fiberssuch as cellulose, methods are known for attaining uniform dispersion of thefibers and reducing and even preventing the occurrence of flocculation. One ofthe more effective means has been to add a small amount of karaya gum to thefiber furnish. However, this has proved unsuccessful in various applications but

other agents such as carboxymethyl cellulose or polyacrylamide have been usedto attain the desired result of the cellulose in the furnish.

[0004]

Fibrous wet laid webs may also be made from other natural or synthetic fibers inaddition to the wood cellulose paper-making fibers. A water furnish of the fibers isgenerally made up with an associative thickener and a dispersant. The cellulosepulp is dispersed in water prior to adding the dispersant, followed by the additionof the associative thickener in an amount in the range up to 150 pounds per tonof dry fiber making up the water furnish and then the addition and dispersion of

the natural and/or synthetic fibers. Finally, the dispersion of mixed fibers in awater carrier is diluted to the desired headbox consistency and dispensed ontothe forming wire of a conventional paper-making machine. An anti-foam agentmay be added to the dispersion to prevent foaming, if necessary, and a wettingagent may be employed to assist in wetting the fibers if desired. A bonded fibrousweb may be formed from the fiber furnish on a high speed conventionalFourdrinier paper making machine to produce a strong, thermally bonded fibrouswet laid web.

[0005]

In prior art processes for wet lay wherein the textile staple fibers are polyesterfibers, water-based binders are generally added to the process to insureadhesion between the cellulose fibers and the polyester fibers. Generally, fromabout 4% to about 35% binder material is employed. One of the problemsencountered using a water based binder is the binder leaches out of the resultantweb in such applications as filters. Addition of binders increases cost and resultsin environmental problems. Furthermore, latex binders have a short shelf life andrequire special storage conditions. Also, the latex binders may be sensitive to thecondition of the diluent water employed.

[0006]

It is well known to blend bicomponent fibers with natural and synthetic fibers indry processes of making nonwoven fabrics. For example, in European Patent

Application No. 0 070 164 to Fekete et al there is disclosed a low density, highabsorbent thermobonded, nonwoven fabric comprising a staple lengthpolyester/polyethylene bicomponent fiber and short length natural cellulosefibers. The U. S. Patent No. 4,160,159 to Samejima discloses an absorbentfabric containing wood pulp combined with short-length, heat fusible fibers.


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Although these patents disclose the use of the combination of bicomponent fibersand cellulose fibers, the disclosure is not directed to a wet lay application. Manyproblems arise in attempting to incorporate a heat fusible fiber such as abicomponent fiber into a wet lay fibrous web.

[0007]

Such nonwoven textile fabrics are normally manufactured by laying down one ormore fibrous layers or webs of textile length fibers by dry textile cardingtechniques which normally align the majority of the individual fibers more or lessgenerally in the machine direction. The individual textile length fibers of thesecarded fibrous webs are then bonded by conventional bonding (heating)techniques, such as, for example by point pattern bonding, whereby a unitary,self-sustaining nonwoven textile fabric is obtained.

[0008]

Such manufacturing techniques, however, are relatively slow and it has beendesired that manufacturing processes having greater production rates bedevised. Additionally, it is to be noted that such dry textile carding and bondingtechniques are normally applicable only to fibers having a textile cardable lengthof at least about 1/2 inch and preferably longer and are not applicable to shortfibers such as wood pulp fibers which have very short lengths of from about 1/6inch down to about 1/25 inch or less.

[0009]

More recently, the manufacture of nonwoven textile fabrics has been done by wetforming technique on conventional or modified paper making or similar machines.Such manufacturing techniques advantageously have much higher productionrates and are also applicable to very short fibers such as wood pulp fiber.Unfortunately, difficulties are often encountered in the use of textile length fibersin such wet forming manufacturing techniques.

[0010]

Problems encountered in attempting to incorporate a heat fusible fiber such as abicomponent fiber into a wet lay process is attaining uniform dispersion of the

bicomponent fiber as well as attaining a thermally bonded web with sufficientstrength such that the thermally bonded web is usable. It has been found in thepast that bicomponent fibers containing a sheath of high density polyethylene(HDPE) and a core of polyester are difficult to uniformly disperse in wet laysolutions. When dispersion of fibers has been attained, fibrous webs producedtherefrom have been found to have lacked the desired strength.

[0011]


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European Patent Application 0 311 860 discloses a bicomponent fiber having apolyester or polyamide core and a sheath component consisting of a copolymerstraight-chain low density polyethylene; and the bicomponent fiber can be formedinto a web through the use of known methods of making nonwoven fabricsincluding wet laying. The copolymer polyethylene is defined as consisting of

ethylene and at least one member selected from the class consisting of anunsaturated carboxylic acid, a derivative from said carboxylic acid and acarboxylic acid and a carboxylic acid anhydride. The application fails to provideany details regarding the copolymer polyethylene into a wet lay process or theresulting properties of the web produced therefrom.

[0012]

There remains a need to develop a thermally bonded wet lay fibrous webincluding a suitable heat fusible bicomponent filament which will not onlyincrease the strength of the web, but also avoid problems associated with adding

binders.

SUMMARY OF THE INVENTION

[0013]

The present invention is directed to a thermally bonded fibrous wet laid webincluding a specific bicomponent fibers so as to yield a thermally bonded web notonly having increased strength, but also greater web uniformity and softer than aregular paper web. In particular, the thermally bonded fibrous wet laid web of thepresent invention consists essentially of a bicomponent fiber comprising a first

fiber component of polyester or polyamide, and a second component consistingessentially of a linear low density polyethylene (LLDPE) having a density in therange of 0.88 g/cc to 0.945 g/cc.

[0014]

Furthermore, the present invention includes a thermally bonded fibrous wet laidweb comprising a bicomponent fiber consisting essentially of a first component ofpolyester or polyamide, and a second component consisting essentially of alinear low density polyethylene having a density in the range of 0.88 g/cc to 0.945g/cc; and a matrix fiber selected from the group consisting essentially of cellulose

paper making fibers, cellulose acetate fibers, glass fibers, polyester fibers,ceramic fibers, mineral wool fibers, polyamide fibers and other naturally occurringfibers.

Brief Description of the Drawings

[0015]


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Figure 1 shows a graph illustrating the relationship of tensile strength to variouslevels of bicomponent fibers in a thermally bonded web as described in Example2.

[0016]

Figure 2 shows a graph illustrating the relationship of elongation to various levelsof bicomponent fibers in a thermally bonded web as described in Example 2.

[0017]

Figure 3 shows a graph illustrating the relationship of the Elmendorf tear tests tovarious levels of bicomponent fibers in a thermally bonded web as described inExample 2.

[0018]

Figure 4 shows a graph illustrating the relationship of the Mullen Burst test tovarious levels of bicomponent fibers in a thermally bonded web as described inExample 2.

Description of the Preferred Embodiments

[0019]

A thermally bonded fibrous wet laid web of the present invention is prepared froma specific bicomponent fiber and optionally a matrix fiber. Processes to make

such thermally bonded fibrous wet laid web would also use suitable dispersantand thickeners.

[0020]

Bicomponent fibers suitable for the present invention include a first component ora backbone polymer of polyester or polyamide or polypropylene. Polyester,polyamides and polypropylene are well known textile materials used in themanufacture of fabrics and other applications. Although polyester andpolyamides have been listed, any suitable backbone polymer would includepolymers having a higher melting point than the LLDPE. Generally the backbone

polymer has a melting point at least 30C higher than that of the secondcomponent.

[0021]

Also included in the bicomponent fiber is a second component consistingessentially of a linear low density polyethylene. Such polymers are termed"linear" because of the substantial absence of branched chains of polymerized


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monomer units pendant from the main polymer "backbone". It is these linearpolymers to which the present invention applies. In some, there is a "linear" typeethylene polymer wherein ethylene has been copolymerized along with minoramounts of alpha, beta-ethylenically unsaturated alkenes having from 3 to 12carbons per alkene molecule, preferably 4 to 8. The amount of the alkene

comonomer is generally sufficient to cause the density of the polymer to besubstantially in the same density range of LDPE, due to the alkyl sidechains onthe polymer molecule, yet the polymer remains in the "linear" classification; theyare conveniently referred to as "linear" low density polyethylene.

[0022]

The LLDPE polymer may have a density in the range of about 0.88 g/cc to about0.945 g/cc, preferably about 0.90 g/cc to about 0.940 g/cc. It is evident topractitioners of the relevant arts that the density will depend, in large part, on theparticular alkene(s) incorporated into the polymer. The alkenes copolymerized

with ethylene to make LLDPE comprises a minor amount of at least oneolefinically unsaturated alkene of the form C - C, most preferably from C - C;1-octene is especially preferred. The amount of said alkene may constitute about0.5% to about 35% by weight of the copolymer, preferably about 1% to about20%, most preferably about 1% to about 10%.

[0023]

The LLDPE polymer may have a melt flow value (MFV) in the range of about 5gm/10 min to about 200 gm/10 min as measured in accordance with ASTM D-1238(E) at 190C. Preferably the melt flow value is in the range of about 7 gm/10

min to about 120 gm/10 min, most preferably about 10 gm/10 min to about 105gm/10 min. Practitioners of the relevant arts are aware that the melt flow value isinversely related to the molecular weight of the polymer.

[0024]

The second component of the bicomponent fiber may also include a grafted highdensity polyethylene (HDPE), in a blend with the LLDPE wherein the HDPE hasbeen grafted with maleic acid or maleic anhydride, thereby providing succinicacid of succinic anhydride groups grafted along the HDPE polymer chain. TheHDPE for use in the present invention is a normally solid, high molecular weight

polymer prepared using a coordination-type catalyst in a process whereinethylene is homopolymerized. The HDPE which is used in making the graftedHDPE in accordance with the present invention is characterized as having a meltflow value in the range of about 5 g/10 min to about 500 g/10 min according to

ASTM D-1238(E) at 190C and a density in the range of about 0.94 g/cc to about0.965 g/cc, preferably a MFV about 7 gms/10 min to about 150 gms/10 min and adensity of about 0.945 g/cc to about 0.960 g/cc. The anhydride or acid groupsgenerally comprise about 0.0001 to about 10 wt. percent, preferably about 0.01


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to about 5 wt. percent of the HDPE. The ratio of grafted-HDPE/ungrafted LLDPEof the present blend is in the range of about 2/98 to about 30/70, preferably about5/95 to about 20/80.

[0025]

The maleic acid and maleic anhydride compounds are known in these relevantarts as having their olefin unsaturation sites conjugated to the acid groups, incontradistinction to the fused ring and bicyclo structures of the non-conjugatedunsaturated acids of e.g., U. S. Pat. No. 3,873,643 and U. S. Pat. No. 3,882,194and the like. Fumaric acid, like maleic acid of which it is an isomer, is alsoconjugated. Fumaric acid, when heated rearranges and gives off water to formmaleic anhydride, thus is operable in the present invention. Other alpha, betaunsaturated acids may be used.

[0026]

The grafting of the succinic acid or succinic anhydride groups onto ethylenepolymer may be done by methods described in the art, which involve reactingmaleic acid or maleic anhydride in admixture with heated polymer, generallyusing a peroxide or other free-radical initiator to expedite the grafting.

[0027]

Grafting may be effected in the presence of oxygen, air hydroperoxides, or otherfree radical initiators, or in the essential absence of these materials when themixture of monomer and polymer is maintained under high shear in the absence

of heat. A convenient method for producing the graft copolymer is the use ofextrusion machinery, however, Banbury mixers, roll mills and the like may alsobe used for forming the graft copolymers.

[0028]

Another method is to employ a twin-screw devolatilizing extruder (such as aWerner-Pfleider twin-screw extruder) wherein maleic acid (or maleic anhydride)is mixed and reacted with the LLDPE at molten temperatures, thereby producingand extruding the grafted polymer. The so-produced grafted polymer is thenblended, as desired, with LLDPE to produce the blends of this invention.

[0029]

Manufacture of bicomponent filaments of either the sheath/core configuration orthe side-by-side configuration by the use of spinning packs and spinnerets is wellknown in the art. A conventional spinning process for manufacturing a fiber with asheath/core configuration involves feeding the sheath-forming material to thespinneret orifices in a direction perpendicular to the orifices, and injecting the


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core-forming material into the sheath-forming material as it flows into thespinneret orifices. Reference is made to U. S. Patent Nos. 4,406,850 and4,251,200 which discloses bicomponent spinning assemblies and describe theproduction of bicomponent fibers. These patents are incorporated by reference.

[0030]

Bicomponent fibers of the present invention may be either eccentric orconcentric. It is understood, however, that the bicomponent fibers having side-by-side configurations or multi-segmented bicomponent fibers are also consideredto be within the scope of the present invention.

[0031]

It has been found that such bicomponent fibers generally have a length todiameter ratio of between about 1:100 and about 1:2000. Such lengths are

generally found to be about 1 mm to about 75 mm and preferably about 10 mmto 15 mm long. Diameters of the fibers are from about 0.5 dpf to about 50 dpf.Such bicomponent fibers are generally cut on conventional process machineswall known in the art.

[0032]

The second ingredient that may be used in the present invention is the matrixfibers. Such fibers can be generally characterized by the fact that all these fibersprovide chemical bonding sites through hydroxyl or amine groups present in thefiber. Included in the class of such matrix fibers are the cellulose paper making

fibers, cellulose acetate fibers, glass fibers, polyester fibers, metal fibers, ceramicfibers, mineral wool fibers, polyamide fibers, and other naturally occurring fibers.

[0033]

In the process for dispersing the bicomponent fibers and matrix fibers in afurnish, a whitewater system of water, thickener and dispersant is employed. Thedispersant acts first to separate fibers and wet out the surface of the fibers. Thethickener acts to increase the viscosity of the water carrier medium and also actsas a lubricant for the fibers. Through these actions, the thickener acts to combatflocculation of the fibers.

[0034]

Various ingredients may be used as a thickener. One class of nonionicassociative thickeners comprise relatively low (10,000 - 200,000) molecularweight ethylene oxide based urethane block copolymers and are disclosed in U.S. Patent Nos. 4,079,028 and 4,155,892, incorporated herein by reference.These associative thickeners are particularly effective when the fiber furnish


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contains 10% or more staple length hydrophobic fibers. Commercial formulationsof these copolymers are sold by Rohm and Haas, Philadelphia, PA, under thetrade names ACRYSOL RM-825 and ACRYSOL RHEOLOGY MODIFIER QR-708, QR-735, and QR-1001 which comprise urethane block copolymers intocarrier fluids. ACRYSOL RM-825 is 25% solids grade of polymer in a mixture of

25% butyl carbitol (a diethylene glycol monobutylether) and 75% water.ACRYSOL RHEOLOGY MODIFIER QR-708, a 35% solids grade in a mixture of60% propylene glycol and 40% water can also be used.

[0035]

Similar copolymers in this class, including those marketed by Union CarbideCorporation, Danbury, Conn. under the trade names SCT-200 and SCT-275 andby Hi-Tek Polymers under the trade name SCN 11909 are useful in the processof this invention. Other thickeners include modified polyacrylamides availablefrom Nalco Chemical Company.

[0036]

Another class of associative thickeners, preferred for making up fiber furnishescontaining predominantly cellulose fibers, e.g. rayon fibers or a blend of woodfibers and synthetic cellulosic fibers such as rayon comprises modified nonioniccellulose ethers of the type disclosed in U. S. Patent No. 4,228,277 incorporatedherein by reference and sold under the trade name AQUALON by Hercules Inc.,Wilmington, Delaware. AQUALON WSP M-1017, a hydroxy ethyl cellulosemodified with a C-10 to C-24 side chain alkyl group and having a molecularweight in the range of 50,000 to 400,000 may be used in the whitewater system.

[0037]

The dispersing agents that may be used in the present invention are synthetic,long-chain, linear molecules having an extremely high molecular weight, say onthe order of at least 1 million and up to about 15 million, or 20 million, or evenhigher. Such dispersing agents are oxygen-containing and/or nitrogen-containingwith the nitrogen present, for example, as an amine. As a result of the presenceof the nitrogen, the dispersing agents have excellent hydrogen bondingproperties in water. The dispersing agents are water soluble and veryhydrophylic.

[0038]

It is also believed that these long chain, linear, high molecular weight polymericdispersing agents are deposited on and coat the fiber surface and make itslippery. This development of excellent slip characteristic also aids in deterringthe formation of clumps, tangles and bundles. Examples of such dispersantagents are polyethylene oxide which is a nonionic long chain homopolymer and


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has an average molecular weight of from about 1 million to about 7 million orhigher; polyacrylamide which is a long straight chain nonionic or slightly anionichomopolymer and has an average molecular weight of form about 1 million up toabout 15 million or higher, acrylamide-acrylic acid copolymers which are long,straight chain anionic polyelectrolytes in neutral and alkaline solutions, but

nonionic under acid conditions, and possess an average molecular weight in therange of about 2 - 3 million, or higher; polyamines which are long straight chaincationic polyelectrolytes and have a high molecular weight of from about 1 millionto about 5 million or higher; etc. A preferred dispersant is an oxyalkylated fattyamine. The concentration of the dispersing agents in the aqueous media may bevaried within relatively wide limits and may be as low as 1 ppm and up to as highas about 200 ppm. Higher concentrations up to about 600 ppm may be used buttend to become uneconomical due to the cost of the dispersing agent and maycause low wet web strength. However, if recovering means is provided wherebythe aqueous medium and the dispersing agent therein is recycled and reused,then concentrations up to 1,000 ppm or even higher can result.

[0039]

The fiber concentration in the fiber slurry may also be varied within relatively widelimits. Concentrations as low as about 0.1% to 6.0% by weight of the furnish aresuitable. Lighter or heavier ranges may be employed for special productsintended for special purposes.

[0040]

It has been found that the bicomponent and matrix fibers may be equally

dispersed through an aqueous medium by adding a suitable dispersing agentand thickener to the resulting fiber slurry stirring and agitation of the slurry. Thedispersing agent is added to the aqueous medium first and then the bicomponentfibers followed by the thickener and the matrix fibers are subsequently addedthereto. The individual bicomponent fibers and matrix fiber are dispersed in thefurnish uniformly through stirring with a minimum amount of fiber flocculation andclumping.

[0041]

It is believed that by so doing the fibers enter a favorable aqueous environment

containing the dispersing agent which is immediately conducive to theirmaintaining their individuality with respect to each other whereby there issubstantially no tendency to flocculate or form clumps, tangles or bundles. This,of course, is to be contrasted to the prior situation wherein when bicomponentfibers are initially placed in an unfavorable aqueous environment not containingany high molecular weight, linear polymeric, water soluble, hydrophilic dispersingagent, which environment is conducive to the loss of fiber individuality whereby


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the fibers flocculate and form clumps, tangles, and bundles and tend to migrateeither to the top or the bottom of the furnish.

[0042]

It has been found that specific types of dispersing agents are required indispersing the bicomponent fibers of the present invention to arrive at theconditions of nonflocculation.

[0043]

After the wet laid web has been formed, execess water is removed from the webby passing the web over a suction slot. Then the web is dried and thermallybonded by passing the web through a drying machine raised to sufficienttemperature to melt the second component of the bicomponent fiber which thenacts as an adhesive to bond the bicomponent fiber to other bicomponent fibers

and matrix fibers upon cooling. One such machine is a Honeycomb SystemThrough-air Dryer. The heating temperature may be from 140C to 220C,preferably 145C to 200C. The thermally bonded web is then cooled with theadhesive bonds forming at below the resolidification of the second component.

[0044]

The invention will be described in greater detail in the following exampleswherein there are disclosed various embodiments of the present invention forpurposes of illustration, but not for purposes of limitation of the broader aspectsof the present inventive concept.

Experimental Procedure A. Bicomponent Fibers

[0045]

Bicomponent fibers were made having a substantially concentric sheath/coreconfiguration. The core was made from a standard 0.64 IV semi-dull polyethyleneterephthalate. The sheath was made from a polymer described for the specificbicomponent fiber.

[0046]

Bicomponent fiber A was made having a sheath of linear low densitypolyethylene containing from 1 - 7% 1-octene wherein the polymer had a densityof 0.930 g/cc, a melt flow value of 18 gm/10 min at 190C according to ASTM D-1236(E). Such a LLDPE is commercially available from Dow Chemical Companyor Aspun Resin 6813.

[0047]


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Bicomponent fiber B was made having a sheath made from a blend of LLDPEand grafted HDPE wherein the blend had a density of .932 g/cc and a melt flowvalue of 16 gm/10 min at 190C. The HDPE was grafted with maleic anhydride tocontain 1 wt.% succinic anhydride groups. This sheath material is described in U.S. Patent No. 4,684,576. The ratio of grafted HDPE/LLDPE was 10/90.

[0048]

Each type of the bicomponent fibers were made by coextruding the core andsheath polymers, and drawing the resulting filaments by processes well known tothose skilled in the art, to obtain the desired denier and sheath/core ratio. Thebicomponent fibers were cut to have a length of about 0.5 inch.

B. Wet Lay Process

[0049]

A batch fiber-water furnish was made with 500 liters of water at an ambienttemperature in a mix tank equipped with an agitator rotating at 500 rpm. To thefurnish was added in the following order:

o a) 20 ml of the dispersing agent Milese T which is commercially availablefrom ICI Americas, Wilmington, Delaware;

o b) 250 grams of the selected bicomponent fibers;o c) 1 liter of 1% solution having a solids content of 35% of the viscosity

modifier Nalco 061 commercially available from Nalco ChemicalCompany, Napierville, Illinois;

o

d) 15 ml of a dispersant for a matrix fiber such as glass fibers KatapolVP532SPB commercially available from GAF Corporation located in NewYork, New York; and

o e) 250 grams of a matrix fiber pursuant to the experiment. [0050]

Prepared in a separate tank with an agitator was a white water solutioncontaining 1100 liters of water, 40 ml of Milese T, and 2 liter of 1% solution Nalco061. The furnish and the white water solution were both pumped to the headboxof a wireformer. Pump rates were 24 l/min of the furnish and 30 l/min of the whitewater to give a .044% consistency, i.e. grams of fiber to water.

[0051]

Once the web was formed, it is then dried and thermally bonded thereafter toproduce a thermally bonded fibrous web. The bonded web was then tested forsuch properties including tensile strength, tear strength, elongation and MullenBurst and the strength tests were done in the machine direction (MD) and thecross direction (CD). The tensile strength test is used to show the strength of a


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specimen when subjected to tension wherein a 1 inch wide sample by 7 incheslong was pulled at 12 inch/min with a 5 inch jaw space. Elongation is thedeformation in the direction of the load caused by tensile force and the reading istaken at the breaking load during the tensile test. The tear tester used was anElmendorf Tear Tester which is a tester designed to determine the strength of the

thermally bonded wet laid fabric. The Mullen Burst Test is an instrumental testmethod that measure the ability of a fabric to resist rupture by pressure exertedby an inflated diaphragm.

Example 1

[0052]

Wet laid webs were made up of bicomponent fibers and glass fibers andthermally bonded at 204C into a thermally bonded web. The thermally bondedweb was tested to demonstrate the present invention and compare it to a wet laid

web made using a commercially available HDPE/PET bicomponent fiber.

[0053]

The glass fibers are made from silica base, having a thickness of 15 microns anda length of 0.5 inch. Such fibers are commercially available from Grupo Protexa,Mexico. The ratio of bicomponent fibers to glass fibers was 50/50. Thebicomponent fibers and glass fibers were added to the water furnish as describedin the wet lay process.

[0054]

In Experiment 1 (the control), a bicomponent fiber was used having a PET coreand a HDPE sheath, wherein the sheath/core ratio was 50/50 and the fiber has adenier of 2 dpf and a cut length of 3/8 inches. Such bicomponent fibers arecommercially available as K-56 fiber type from Hoechst Celanese Corporation.

[0055]

Experiment 2 was similar to Experiment 1, but the bicomponent fiber wasreplaced with bicomponent fiber A having sheath/core ratio of 50/50, a denier of2 dpf, and a cut length of 0.5 inches.

[0056]

Experiment 3 was similar to Experiment 1 and 2, but the bicomponent fiber usedwas bicomponent fiber B having a denier of 3 dpf, a cut length of 0.5 inches anda sheath core ratio of 50/50.

[0057]


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The webs were tested for the tensila strength and tear strength in both themachine direction and cross direction. Also, the webs were tested for the MullenBurst test. The results of the example are set forth in Table 1.

[0058]

Thermally bonded wet laid web produced in Experiment 1 was the control using aprior art bicomponent fiber of a HDPE sheath and PET core. It's tensile strengthwas 2.09 lbs./in. in the machine direction, 2.15 lbs./in in the cross direction; thetear strength was 217.3 grams in the machine direction and 213.3 grams in thecross direction; and the Mullen Burst test value of 7.3 PSI.

[0059]

Experiment 2 demonstrates that by replacement of the prior art HDPE/PETbicomponent fiber with bicomponent fiber A in the wet laid web of the presentinvention, the tensile strength and tear strength in both the machine and crossdirections significantly increase as does the Mullen Burst Test value whichindicates improved adhesion of the bicomponent fiber to the glass fiber in thiscase. In fact, the strength increase is about 50% over the control.

[0060]

Experiment 3 demonstrates that employing a bicomponent fiber having a PETcore and a sheath made from a blend of granted HDPE and LLDPE in the wetlaid web of the present invention again significantly increases the tensile strengthvalue 200% of the values for the control while maintaining high tear strength andMullen Burst value. The slightly lower tear strength when compared toExperiment 2 is a further indication of superior bonding between the glass fibersand this bicomponent fiber.


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Example 2

[0061]

Thermally bonded wet laid webs were made up of varying amounts of

bicomponent fibers and varying amounts of PET fibers used as matrix fibers. Thewebs were thermally bonded at 160C. The thermally bonded webs were testedfor strength, elongation and Mullen Burst. These values were compared to a wetlaid web made up with a commercially available PET/HDPE bicomponent fiber(K-56) and varying amounts of PET matrix fiber.

[0062]

In Experiments 1 A-D (the controls) a bicomponent fiber having a PET core andHDPE sheath as described in Example 1, Experiment 1, was used. The PETmatrix fibers had a denier of 1.5 dpf and a cut length of 0.5 inches.

[0063]

Experiments 2 (A-D) were similar to Experiment 1, but the bicomponent fiber wasreplaced with bicomponent fiber B having a sheath core ratio of 40:60, a denierof 3 dpf, and a cut length of 0.5 inches.

[0064]

Experiments 3 (A-C) were similar to Experiment 2 except the bicomponent fiberB had a sheath core ratio of 30:70.

[0065]

Experiments 4 A-D were similar to Experiment 2, except the bicomponent fiber Bhad a sheath core ratio of 20:80.

[0066]

The webs were tested for tensile strength, elongation Elmendorf tear strengthand Mullen Burst values. The results of the Example are set forth in Table 2.


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The results as shown in Table 2 are included in the graphs shown in Figures 1-4.

[0067]


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Experiments 1 A-D were the controls using a commercially availablebicomponent fiber of a HDPE sheath and PET core. When only PET fiber is usedin the wet lay, the web has no strength. At 60% bicomponent fiber, 40% PETmatrix fiber, the web has only 2.6 lbs. of strength and a Mullen Burst value of16.6.

[0068]

Experiments 2 A-D demonstrates that by replacement of the HDPE/PETbicomponent fiber with bicomponent fiber B having a 40% sheath of the presentinvention, the strength of the web increases significantly as do the values for theMullen Burst test.

[0069]

Experiments 3 A-C demonstrates that by using the bicomponent fiber B having a

30% sheath, that 100% bicomponent fiber B web has a strength of 11.2 lbs.,which is significantly higher than the Experiment 1-D.

[0070]

Experiments 4 A-D demonstrates that using the bicomponent fiber B having only20% sheath still results in a strength superior to that of the Experiment 1-C at60% bicomponent: 40% PET fiber mix.

Example 3

[0071]

Thermally bonded wet laid webs were made up of varying amounts ofbicomponent fibers and PET fibers such that the total of the two fibers is 100%.The webs were thermally bonded at 370F and were tested for tensile,elongation, Mullen Burst and tear.

[0072]

Experiments 1, 2 and 3 were similar in that each contained 100% bicomponentfiber and no matrix fiber. Experiment 1 (control) contained a bicomponent fiber as

described in Example 1, Experiment 1. Experiment 2 contained bicomponentfiber A and Experiment 3 contained bicomponent fiber B.

[0073]

Experiments 4, 5 and 7 were similar in that each contained 75% bicomponentfiber and 25% PET fiber of 1.5 dpf and cut length of 0.5 inches. Experiment 4


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(control) contained the PET/HDPE bicomponent fiber; Experiment 5 containedbicomponent fiber A and Experiment 6 contained bicomponent fiber B.

[0074]

Experiments 7, 8 and 9 each contained 50% bicomponent fiber and 50% PETfiber. Experiment 7 (control) contained the PET/HDPE bicomponent fiber;Experiment 8 contained bicomponent fiber A and Experiment 9 containedbicomponent fiber B.

[0075]

Experiments 10, 11 and 12 each contained 25% bicomponent fiber and 75% PETfiber. Experiment 10 (control) contained the PET/HDPE bicomponent fiber;Experiment 11 contained bicomponent fiber A and Experiment 12 containedbicomponent fiber B.

[0076]

The thermally bonded webs were tested for tensile strength, elongation,Elmendorf tear and Mullen Burst. The results of the test are set forth in Table 3.


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The control Experiments 1, 4, 7 and 10 each containing the PET/HDPEbicomponent fiber, have lower strengths as demonstrated by the lower tensileand Mullen Burst values when compared to similar thermally bonded webscontaining the bicomponent fibers of the present invention.

[0077]

It is apparent that there has been provided in accordance with the invention, thatthe thermally bonded fibrous wet laid web and a method of preparing such a webincorporating a specific bicomponent fiber, fully satisfies the objects, aims andadvantages as set forth above. While the invention has been described inconjunction with specific embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to those skilled in the


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art in light of the foregoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications and variations that fall within the sphere and thescope of the invention.

Elastic bicomponent and biconstituent fibers, and methods of making

cellulosic structures from the same

US 6811871 B2

Abstract

The elasticity of elastic, absorbent structures, e.g., diapers, is improved without a significant

compromise of the absorbency of the structure by the use of bicomponent and/or biconstituent

elastic fiber. The absorbent structures typically comprise a staple fiber, e.g., cellulose fibers, and

a bicomponent and/or a biconstituent elastic. The bicomponent fiber typically has a core/sheathconstruction. The core comprises an elastic thermoplastic elastomer, preferably a TPU, and the

sheath comprises a homogeneously branched polyolefin, preferably a homogeneously branchedsubstantially linear ethylene polymer. In various embodiments of the invention, the elasticity is

improved by preparation techniques that enhance the ratio of elastic fiber:cellulose fiber versuscellulose fiber:cellulose fiber bonding. These techniques include wet and dry high intensity

agitation of the elastic fibers prior to mixing with the cellulose fibers, deactivation of hydrogen

bonding between cellulose fibers, and grafting the elastic fiber with a polar group containingcompound, e.g. maleic anhydride.

DescriptionCROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No. 10/195,279, filed Jul. 15, 2002,which claims benefit of U.S. Provisional Application No. 60/306,003, filed Jul. 17, 2001.

FIELD OF THE INVENTION

This invention relates to elastic fibers. In one aspect, the invention relates to bicomponent elasticfibers while in another aspect, the invention relates to biconstituent elastic fibers. In another

aspect, the invention relates to bicomponent and biconstituent elastic fibers having a core/sheath

construction. In yet another aspect, the invention relates to such fibers in which the polymer that

forms the sheath has a lower melting point than the polymer that forms the core. In still anotherembodiment, the invention relates to methods of forming elastic cellulosic structures from a

combination of cellulosic fibers and elastic bicomponent and/or biconstituent fibers having acore/sheath construction.

BACKGROUND OF THE INVENTION

Cellulosic structures are known for their absorbency, and this property makes these structures

useful in a wide variety of applications. Typical examples of such applications are diapers,

wound dressings, feminine hygiene products, bed pads, bibs, wipes, and the like. The purpose of


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these products, of course, is to absorb and retain liquids, and the efficiency of these products in

performing these tasks is determined, in large part, by their structure. U.S. Pat. Nos. 4,816,094,

4,880,682, 5,429,856 and 5,797,895 describe various such products, their construction and thematerials from which they are made, and each is incorporated herein by reference.

Typically, absorbent cellulosic structures are made of materials that do not easily stretch. Forexample, cellulose fibers are, for all intent and purpose, inelastic and in many cellulosic

structures, e.g. a diaper, they are bonded to one another in a relatively inelastic manner, e.g.,

through the use of a latex. Unfortunately, many of these structures require some degree ofelasticity for reasons of comfort and use, e.g., a diaper conforming to the contours of the human

body or a wipe having the touch and drape of cloth, and if the structure is not sufficiently elastic,

gaps will form within it. Gaps reduce the absorbency of the structure by preventing the migration

of the liquid to all parts of the structure.

Demand exists for better form-fitting absorbent products. This usually means that not only must

the products have improved elasticity, but they must also be thin and light. Elasticity has been

chased to date by adding to or replacing some of the cellulose fibers with an elastic fiber. Forexample, U.S. Pat. No. 5,645,542 to Anjur et al., the disclosure of which is incorporated herein

by reference, describes absorbent products made from a wettable staple fiber (e.g., cellulosefiber) and a thermoplastic elastic fiber, e.g., a polyolefin rubber. However, the mere blending of

staple fibers with elastic fibers often is not enough to obtain the full benefit of the elastic fiber

without compromising the absorbency of the staple fiber. Cellulose fibers (the commonest of the

staple fibers) tend to adhere to one another as opposed to adhering with an elastic fiber. As aresult, unless a highly uniform mixture of the two fibers is formed during the construction of the

absorbent structure, the two types of fibers tend to segregate and the benefit of the elastomeric

fibers is reduced or lost.

Accordingly, the absorbent product industry has a continuing interest in the design andconstruction of absorbent products with improved elasticity without a compromise inabsorbency. This interest extends to both the nature of the fibers from which the absorbent

products are made, and the methods by which these absorbent products are constructed.

SUMMARY OF THE INVENTION

In one embodiment, the invention is a bicomponent fiber of a core/sheath construction in which

the core comprises the thermoplastic elastomer, preferably a thermoplastic polyurethane (TPU),

and the sheath comprises the homogeneously branched polyolefin. Preferably, the polymer of the

sheath has a lower melting point than the polymer of the core, and more preferably the polymerof the sheath has a gel content of less than 30 percent.

In another embodiment, the invention is a biconstituent fiber in which one constituent comprisesthe thermoplastic elastomer, preferably a TPU, and the other constituent comprises the

homogeneously branched polyolefin. Preferably, the constituent that forms the majority of the

external surface of the fiber has a lower melting point than the other constituent, and preferablyhas a gel content of less than 30 percent.


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In another embodiment, the invention is a blend of fibers (or simply a fiber blend) comprising

(i) an elastic fiber comprising an elastic core and an elastic sheath, and (ii) at least one fiber other

than the elastic fiber of (i). The core of the elastic fiber preferably comprises a thermoplasticelastomer, preferably a TPU, and the sheath of the elastic fiber preferably comprises a

homogeneously branched polyolefin, more preferably a homogenously branched, substantially

linear ethylene polymer. The polymer of the sheath has a melting point below the melting pointof the polymer of the core, and preferably the polymer of the sheath has a gel content of less than30 weight percent. The fiber of (ii) is essentially any fiber other than the fiber of (i), preferably a

fiber of cellulose, wool, silk, a thermoplastic polymer, silica or a combination of two or more of

these. In another embodiment of the invention, the fibers of (i) are melt bonded to the fibers of(ii), preferably by exposure to a temperature that is at or slightly below the melt temperature of

both the fiber of (ii) and the polymer of the core of fiber (i) but above the melt temperature of the

polymer of the sheath of fiber (i). In yet another embodiment of this invention, the melt bonded

fiber blend is substantially free of any added adhesives, e.g., glue.

In another embodiment of this invention, the blends described in the preceding paragraph are

used to build elastic, absorbent structures. Such structures include paper with elasticity, e.g.,form-fitting labels, and the absorbent padding of a disposable diaper.

In another embodiment, the invention is a fabricated article comprising elastic fiber and a

nonwoven substrate, the fiber comprising at least two elastic polymers, one polymer preferably a

thermoplastic elastomer, more preferably a TPU, and the other polymer a homogeneously

branched polyolefin, preferably a homogeneously branched, substantially linear ethylenepolymer, in which the fiber is melt bonded to the nonwoven substrate in the absence of an

adhesive. Exemplary fabricated structures of this embodiment include the leg cuffs, leg

gatherers, waistbands and side panels of a disposable diaper.

In another embodiment of the invention, the ratio of nonelastic staple fibers, e.g., cellulose fibers,bonded to elastic fibers versus nonelastic staple fibers bonded to other nonelastic staple fibers, isincreased by a method in which the elastic fiber is a hydrophobic fiber grafted with a hydrophilic

agent, e.g., a polyethylene fiber grafted with maleic anhydride. In an extension of this

embodiment, and in which the hydrophilic agent is an acid or an anhydride, e.g., maleicanhydride, once the agent is grafted to the fiber it is then reacted with an amine.

In another embodiment of the invention, for those nonelastic staple fibers that bind to oneanother due to hydrogen bonding, e.g., cellulose fibers, the ratio of nonelastic staple fibers

bonded to elastic fibers versus nonelastic staple fibers bonded to other nonelastic staple fibers is

increased by treating the nonelastic staple fibers, prior to or simultaneously with blending these

fibers with the elastic fibers, with a debonding agent, e.g., a quaternary ammonium compoundcontaining one or more acid groups. The debonding agent deactivates at least a part of the

hydrogen bonding between the nonelastic staple fibers.

In another embodiment of the invention, blending of nonelastic staple fibers with elastic fibers is

enhanced by blending the fibers in an aqueous media, preferably in the presence of a surfactant

and with intense agitation. This procedure enhances the separation of the elastic fibers from oneanother, and thus makes each fiber more accessible for bonding with a nonelastic staple fiber.


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This method can be used alone or in combination with one or more other fiber separation

embodiments of this invention.

In another embodiment of the invention, high intensity air mixing is used to separate elastic

fibers from one another prior to blending with staple fibers. This technique also promotes

separation of the elastic fibers from one another, and this, in turn, improves their accessibility forbonding with the staple fibers. This embodiment of the invention can also be used alone or in

combination with one or more other embodiments of the invention.

The three fiber separation and the grafting embodiments described above are particularly useful

in the construction of elastic absorbent structures such as diapers, wound dressings and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Elastic Bicomponent and Biconstituent Fibers

As here used, fiber or fibrous means a particulate material in which the length to diameterratio of such material is greater than about 10. Conversely, nonfiber or nonfibrous means aparticulate material in which the length to diameter ratio is about 10 or less.

As here used, elastic or elastomeric describes a fiber or other structure, e.g., a film, that will

recover at least about 50 percent of its stretched length after both the first pull and after the

fourth pull to 100 percent strain (doubled the length). Elasticity can also be described by thepermanent set of the fiber. Permanent set is measured by stretching a fiber to a certain point

and subsequently releasing it to its original position, and then stretching it again. The point at

which the fiber begins to pull a load is designated as the percent permanent set.

As here used, bicomponent fiber means a fiber comprising at least two components, i.e., ofhaving at least two distinct polymeric regimes. The first component, i.e., component A, serves

the purpose of generally retaining the fiber form during the thermal bonding temperatures. Thesecond component, i.e., component B, serves the function of an adhesive. Typically,

component A has a higher melting point than component B, preferably component A will melt at

a temperature at least about 20 C, preferably at least 40 C, higher than at the temperature atwhich component B will melt.

For simplicity, the structure of the bicomponent fibers is typically referred to as a core/sheathstructure. However, the structure of the fiber can have any one of a number of multi-component

configurations, e.g., symmetrical core-sheath, asymmetrical core-sheath, side-by-side, pie

sections, crescent moon and the like for bicomponent fibers. The essential feature on each ofthese configurations is that at least part, preferably at least a major part, of the external surface ofthe fiber comprises the sheath portion of the fiber, i.e., the adhesive, or lower melting point, or

less than 30 wt % gel, or component B, of the fiber. FIGS. 1A-1F of U.S. Pat. No. 6,225,243, the

disclosure of which is incorporated herein by reference, illustrate various core/sheathconstructions.


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As here used, biconstituent fiber means a fiber comprising an intimate blend of at least two

polymer constituents. The structure of the biconstituent fiber is an islands-in-the-sea

construction.

The bicomponent fibers used in the practice of this invention are elastic and, each component of

the bicomponent fiber is elastic. Elastic bicomponent and biconstituent fibers are known, e.g.,U.S. Pat. No. 6,140,442 the disclosure of which is incorporated herein by reference.

In this invention, the core (component A) is a thermoplastic elastomeric polymer illustrative ofwhich are diblock, triblock or multiblock elastomeric copolymers such as olefinic copolymers

such as styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene/butylene-styrene or

styrene-ethylene/propylene-styrene, such as those available from the Shell Chemical Companyunder the trade designation Kraton elastomeric resin; polyurethanes, such as those available from

The Dow Chemical Company under the trade designation PELLATHANE polyurethanes or

spandex available from E.I. Du Pont de Nemours Co. under the trade designation Lycra;

polyamides, such as polyether block amides available from Elf AtoChem Company under the

trade designation Pebax polyether block amide; and polyesters, such as those available from E.I.Du Pont de Nemours Co. under the trade designation Hytrel polyester. Thermoplastic urethanes

(i.e., polyurethanes) are a preferred core polymer, particularly Pellethane polyurethanes.

The sheath (the adhesive or component B) is also elastomeric, and it is a homogeneously

branched polyolefin, preferably a homogeneously branched ethylene polymer and morepreferably a homogeneously branched, substantially linear ethylene polymer. These materials are

well known. For example, U.S. Pat. No. 6,140,442 provides an excellent description of the

preferred homogeneously branched, substantially linear ethylene polymers, and it includes many

references to other patents and nonpatent literature that describe other homogeneously branchedpolyolefins.

The homogenously branched polyolefin has a density (as measured by ASTM/D792) of about0.91 g/cm

3or less with a melting point at or below 110 C (as measured by DSC). More

preferably, the density of the polyolefin is between about 0.85 and about 0.89 g/cm3

with a

melting point between about 50 and about 70 C. Preferably, the polyolefin has a viscosity at themelt point that permits easy flow for bonding to the staple fibers or a nonwoven fabric structure.

The melt index (MI as measured by ASTM DI238 at 190 C) for the polyolefin is at least about

30, and preferably at least about 100. Additives such as antioxidants (e.g., hindered phenolics(e.g., Irganox.RTM. 1010 made by Ciba-Geigy Corp.), and phosphites (e.g., Irgafos.RTM. 169

made by Ciba-Geigy Corp.)), cling additives (e.g., polyisobutylene (PIB)), antiblock additives,

pigments and the like can also be included in the homogeneously branched ethylene polymers

used to make the elastic fibers to the extent that they do not interfere with the enhanced fiber andfabric properties characteristic of this invention.

The gel content of the polyolefin is less than 30, preferably less than 20 and more preferably lessthan 10, weight percent. The gel content is a measure of the degree of cross-linking of the

polyolefin and because a principal function of the polyolefin is to provide a meltable exterior

component to the fiber for easy thermal bonding to staple fibers and/or nonwoven structures,


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little, if any, cross-linking of the polyolefin is preferred. In addition, usually the less cross-linked

a polyolefin, the lower its melting point.

Nonwoven structure means a group of fibers connected together in such a fashion such that the

group forms a cohesive, integrated structure. Such structures can be formed by techniques known

in the art, such as air-laid, spun bonding, staple fiber carding, thermal bonding, and melt blownand spun lacing. Polymers useful for making such fibers include PET, PBT, nylon, polyolefins,

silicas, polyurethanes, poly(p-phenylene terephthalamide), Lycra (a polyurethane made from

the reaction of polyethylene glycol and toluene-2,4-diisocyanate by E.I. Du Pont de Nemours &Co.), carbon fibers and natural polymers such as cellulose and polyamide.

As here used, staple fiber means a natural fiber or a length cut from, for example, amanufactured filament. These fibers act in the absorbent structure of this invention as a

temporary reservoir for liquid and also as a conduit for liquid distribution. Staple fibers include

natural and synthetic materials. Natural materials include cellulosic fibers and textile fibers such

as cotton and rayon. Synthetic materials include nonabsorbent synthetic polymeric fibers, e.g.

polyolefins, polyesters, polyacrylics, polyamides and polystyrenes. Nonabsorbent syntheticstaple fibers are preferably crimped, i.e., fibers having a continuous wavy, curvy or jagged

character along their length. Cellulosic fibers are the preferred staple fibers for reasons ofavailability, cost and absorbency.

In order to promote good mixing of the staple and elastic fibers, the bicomponent fibers arepreferably wetted. As here used, wetted or wettable means a fiber which exhibits a liquid

in air contact angle of less than 90 degrees. These terms and the measurement of this property are

more fully described in U.S. Pat. No. 5,645,542.

The wettable staple and elastic fibers are present in the elastomeric absorbent structure of this

invention in an amount sufficient to impart the desired absorbent and elastic properties.Typically, the staple fiber is present in an amount from about 20 to about 80 percent by weight,preferably from about 25 to about 75 and more preferably from about 30 to about 70 percent, by

weight based on the total weight of the staple fiber and elastic fiber.

Although the bicomponent and/or biconstituent fibers are used in the same manner as other

elastomeric fibers for the construction of elastic, absorbent structures, preferably these fibers areused in combination with one or more of the embodiments of this invention as described below.

In any instance, however, the use of a bicomponent or biconstituent fiber as the elastic fiber

component of elastic, absorbent structures provides an elastic, absorbent structure with improved

elasticity without compromising the absorbency of the structure. This results in lighter, thinnerand/or better form-fitting structures.

Graft-modified Elastic Fibers

In this embodiment of the invention, adhesion of the elastomeric fibers to the staple fibers is

enhanced by grafting to the elastomeric fiber a compound containing a polar group, such as acarbonyl, hydroxyl or acid group. This embodiment of the invention is applicable to both

homofil and bicomponent or biconstituent elastomeric fibers. Homofil fibers are fibers


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comprising a single component or, in other words, are essentially homogeneous throughout their

length. With respect to bicomponent and biconstituent fibers, the polar group containing

compound is grafted to the sheath component (i.e., the component that forms at least a part of theexterior surface) of the fiber.

The organic compound containing the polar group can be grafted to the elastomeric fiber by anyknown technique, e.g., those taught in U.S. Pat. Nos. 3,236,917 and 5,194,509 of which the

disclosures of both are incorporated herein by reference. For example, in the '917 patent the

polymer (i.e., the elastomeric fiber polymer) is introduced into a two-roll mixer and mixed at atemperature of 60 C. An unsaturated, carbonyl-containing organic compound is then added along

with a free radical initiator, such as, for example, benzoyl peroxide, and the components are

mixed at 30 C until the grafting is completed. In the '509 patent, the procedure is similar except

that the reaction temperature is higher, e.g. 210-300 C, and a free radical initiator is not used.

An alternative and preferred method of grafting is taught in U.S. Pat. No. 4,950,541 the

disclosure of which is also incorporated herein by reference. This procedure uses a twin-screw

devolatilizing extruder as the mixing apparatus. The elastomeric fiber, e.g., a polyolefin, and anunsaturated carbonyl-containing compound are mixed and reacted within the extruder at

temperatures at which the reactants are molten and in the presence of a free radical initiator. Inthis procedure, preferably the unsaturated carbonyl-containing organic compound is injected into

a zone maintained under pressure within the extruder.

The polymer from which the fiber is made is usually grafted with the polar group containing

compound prior to the formation of the fiber (by whatever method is used to construct the fiber).

The polar group containing organic compounds which are grafted to the elastomeric fiber are

unsaturated, i.e., they contain at least one double bond. Representative and preferred unsaturated

organic compounds that contain at least one polar group are the ethylenically unsaturatedcarboxylic acids, anhydrides, esters and their salts, both metallic and non-metallic. Preferably,the organic compound contains ethylenic unsaturation conjugated with a carbonyl group.

Representative compounds include maleic, fumaric, acrylic, methacrylic, itaconic, crotonic,

alpha-methylcrotonic, cinnamic and the like, acids and their anhydride, ester and salt derivatives,if any. Maleic anhydride is the preferred unsaturated organic compound containing at least one

ethylenic unsaturation and at least one carbonyl group.

The unsaturated organic compound component of the grafted elastomeric fiber is present in an

amount of at least about 0.01 percent, preferably at least about 0.1 and more preferably at least

about 0.5 percent, by weight based on the combined weight of the elastomeric fiber and theorganic compound. The maximum amount of unsaturated organic compound can vary to

convenience, but typically it does not exceed about 10, preferably it does not exceed about 5, and

more preferably it does not exceed about 2, weight percent.

With respect to bicomponent and biconstituent fibers, the graft can be produced by either graft-

reacting the polar group containing compound with all of the sheath component (component B1),or by using a graft concentrate or master batch (B2), i.e., the polar group containing compound

mixed with the sheath component. If such a blend of components is used, then preferably


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component B2 is between about 5 and 50, and more preferably between about 5 and 15, weight

percent of the combination of B1 and B2. The preferred concentration of the polar group

containing compound in the blend is such that after blending with the sheath component, thefinal mixture has a final polar group containing concentration of at least 0.01 percent by weight,

and preferably at least about 0.1 percent by weight.

In those situations in which a graft concentrate is used with respect to a bicomponent fiber,

preferably the graft concentrate (B2), is of a lower viscosity than the matrix adhesive material

(B1). This will enhance migration of the graft component to the surface of the fiber duringpassage of the material through a fiber-forming die. The object, of course, is to enhance the

adhesion of the bond fiber to the staple fiber by enhancing the concentration of the graft

compound to the fiber surface. Preferably, the melt index of component B2 is between 2 and 10

times the melt index of component B1.

Deactivation of Cellulose Hydrogen Bonds

In another embodiment of the invention (an embodiment in which the staple fibers are cellulosefibers), the elastic performance of the absorbent elastic structure is enhanced through the

promotion of more cellulosic-elastic fiber bonds at the expense of cellulosic-cellulosic fiberbonds. In this embodiment, the cellulosic staple fibers are treated either prior to or

simultaneously with their mixing with the elstomeric fibers with a debonding agent. These bonds

and their disruption were described in a presentation givenby Craig Poffenberger entitled Bulkand Performance, But Soft and Safe at the Insight 2000 Non-wovens/Absorbents Conference

held in Toronto from Oct. 30 through Nov. 2, 2000. With the decoupling of these hydrogen

bonds, more cellulose fiber is available to bond with the elastic fiber and the more cellulose-

elastic fiber bonds that are formed, the more elastic is the resulting absorbent structure.

Compounds that are useful in decoupling inter-fiber hydrogen bonds of cellulose fibers includequaternary ammonium compounds containing one or more acid or anhydride groups. Typical ofthese compounds are difattydimethyl, imidazolinum, N-alkyldimethylbenzyl and dialkoxylated

alkyldimethyl. The debonding agent is used in an amount of about 0.01 to about 10 percent by

weight based on the weight of cellulose fiber to be treated. Another compound that is useful indecoupling cellulose-cellulose hydrogen bonding is AROSURF PA-777, a surfactant

manufactured by Goldschmidt Corp.

This embodiment of the invention can be used alone or in combination with one or more of the

other embodiments of the invention.

Agitation in a Water Media to Separate Elastic Fibers

In this embodiment of the invention, the elastic fibers are separated from one another byagitation in a water media. Elastic fibers, typically fine denier elastic fibers, are difficult to

separate from one another and as such, are difficult to blend uniformly with staple fibers during

the construction of an elastic absorbent structure. As here used, fine denier elastic fiber meansan elastic fiber having a diameter of less than about 15 denier per filament. Fibers are typically

classified according to their diameter, and monofilament fiber is generally defined as having an


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individual fiber diameter greater than about 15 denier, usually greater than about 30 denier.

Microdenier fibers are generally defined as fiber having a diameter of less than about 100

microns.

In this embodiment, the elastic fibers are placed in an aqueous media, and then are subjected to

vigorous agitation by any conventional means, e.g. mechanical stirrer, jet pump, etc. Surfactantsand/or wetting agents can be employed and after the elastic fibers have sufficiently separated

from one another, the staple fibers can be added. In a preferred embodiment of this invention, the

staple fibers are added in combination with a debonding agent. After a homogeneous blend of theelastic and staple fibers has been formed, the water is removed, typically by filtering followed by

exposure to heat, e.g. time in an oven. Once sufficiently dry, the resulting fluff pulp is ready for

processing into an elastic absorbent structure. At this point, various additives, e.g. super

absorbent powder, can be added to the pulp. During the drawing step, care is required to avoidwarming the fibers to a temperature that would prematurely activate/melt the bond fibers.

This particular embodiment is also useful with any elastomeric fiber of any composition and

structure (including homofil fibers), and it is also useful with any staple fiber.

High Intensity Air Mixing

In this embodiment of the invention, the elastomeric fibers are separated from one another usinga high intensity air mixing technique. This technique is similar to the agitation in a water mediatechnique described above, except it does not employ an aqueous media (or for that matter, any

liquid media). The elastomeric fiber, either homofil or bicomponent, is subjected to intense

agitation, either mechanically or through pneumatic means, and once sufficiently separated, andin a further embodiment of this invention, blended with the staple fibers. While this technique

avoids the need for drying the resulting blend of fibers, it does not lend itself well to use in

combination with a debonding agent for the cellulosic fibers, or surfactants and/or wetting agentsfor use with the elastomeric fibers. Here too, however, this embodiment can be combined withone or more other embodiments of the invention, e.g., use of bicomponent or biconstituent

elastomeric fibers, graft-modified elastomeric fibers, and cellulosic fibers of which the hydrogen

bonding between fibers has previously been deactivated.

Elastic Absorbent Structure Construction

The elastic absorbent structure of this invention can be constructed from a blend of staple fibers

and bicomponent and/or biconstituent elastic fibers of a core/sheath construction in which the

core is a thermoplastic urethane and the sheath is a homogeneously branched polyolefin.According to this embodiment, the blend of staple and elastic fibers is prepared in any

conventional manner and/or using any one of the inventive techniques described above and,

optionally, is subsequently admixed with one or more super-absorbent polymers. This admixtureis also performed using conventional technology but due to the presence of the low melt

temperature adhesive component in the bicomponent or biconstituent fiber (i.e., the

homogeneously branched polyolefin), the fluff pulp can be bonded together with heat as low asabout 70 C to form an elastic absorbent structure, e.g. a diaper. The lower melt point of the

adhesive component of the elastic bond fibers allows the use of currently-in-use commercial


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equipment but at a lower temperature which, in turn, means the faster production rates are

achieved over both monofil elastomeric fibers and bicomponent elastomeric fibers in which the

adhesive component has a higher melt temperature. However, the lower melt temperature and/orfaster bond rate reduces or alleviates the problems of bond fiber activation in, or in-line with, the

structure making machines, e.g., a diaper-making machine.

In conventional absorbent cores or structures, the cellulosic fibers are typically bonded to one

another using latex. The latex often collects at the cellulosic fiber interfaces and, upon curing,

holds the cellulosic fibers together. The use of a bicomponent or biconstituent bond fiber withtwo distinct regimes, e.g., a core and sheath, make for a better bond system. The core has a

melting point above the oven temperature, and the sheath has melt point below the oven

temperature. The bicomponent and biconstituent fibers efficiently fuse to the cellulosic fibers

wherever they touch. The connections between the cellulosic fibers are thus longer than just thesize of the fusion joints. This, in turn, produces a more flexible structure.

Homogeneously branched ethylene polymers, particularly homogeneously branched,

substantially linear ethylene polymers, make excellent sheath materials because their meltingpoint is lower than many other elastic polymeric materials. Preferably, the sheath material will

melt at least about 20 C, more preferably at least about 40 C, below the melt point of the corematerial.

Elastic Paper Construction

Bicomponent and biconstituent elastic bond fibers are useful in the production of elastic paper,

i.e., paper with some degree of elasticity. As described above, these elastic bond fibers for elasticpaper comprise an elastic polyurethane core with an elastic homogeneously branched polyofelin,

more preferably a homogeneously branched polyolefin grafted with maleic anhydride or similar

compound. If these bicomponent elastic fibers are mixed with cellulose fibers withoutinterrupting the cellulose-cellulose hydrogen bonds, then the addition of these bicomponent orbiconstituent elastic fibers will reduce tensil and provide some measure of elasticity, but the

paper will tear at five percent strain. In other words, the benefit of the addition of bicomponent

and/or biconstituent elastic fiber is minimized if the cellulose-cellulose hydrogen bonds are notinterrupted.

If, however, the cellulose-cellulose hydrogen bonds are interrupted with bicomponent or

biconstituent elastic fiber, then the resulting paper exhibits a marked drop in tensil, significant

elastic recovery, and resists tear at five percent strain. The cellulose-cellulose hydrogen bonds

can be interrupted as taught above.

To maximize the benefit of the disrupted cellulose-cellulose hydrogen bonds, good dispersion of

the bicomponent elastic fiber with the cellulosic fiber is desired. Dispersion of the bicomponentelastic fiber within the cellulose fiber matrix is enhanced by separating the elastic fiber bundles

prior to mixing with the cellulose fibers. Here too, the separation of fiber bundles is facilitated by

either the dry (i.e., high intensity air agitation) or wet separation methods taught above, with thedry separation method preferred over the wet separation method.


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The elasticity of the paper is also influenced by the structure of the fibers. Low modulus elastic

fibers provide good fabric performance, but are awkward to process. Long bond fibers (i.e.,

bicomponent and biconstituent elastic fibers) mixed with short matrix fibers (i.e., cellulosefibers) produce a paper with better elasticity (i.e., less intersectional bonding) but the complete

dispersion is more difficult because the long flexible elastic fibers twist easily which make them

difficult to unbundle. However, if the elastic bond fibers are thick, they make for a betterdispersion although they have an adverse impact on the economics. In sum, a preferred balanceof elasticity and dispersion results from the use of a mix of low modulus fibers, the bond fibers

of which are long and thick and the matrix fibers are short.

In addition, the amount of elastic fibers in the paper also has an impact on the paper strength and

elasticity. Too few bicomponent or biconstituent elastic bond fibers results in poor bonding of

the other fibers into the fabric which results in a paper with poor strength and elasticity. Toomany such elastic bond fibers results in too many intersectional bonds and while the paper

strength is good, its elasticity is poor. The negative effect of too many bicomponent elastic bond

fibers can be reduced, however, by using a higher loft in the paper construction.

The following examples are illustrative of certain of the embodiments of this invention described

above. All parts and percentages are by weight unless otherwise noted.

SPECIFIC EMBODIMENTS EXAMPLE 1

Graft Modification of Polyethylene

A substantially linear ethylene/1-octene polymer (MI-73, density-0.87 g/cm3) is grafted with

maleic anhydride to produce a material with a MI of 34.6 and a 0.35 weight percent content of

units derived from maleic anhydride. The grafting procedure taught in U.S. Pat. No. 4,950,541 is

followed. The grafted polyethylene is used as a graft concentrate, and is let down 2:1 with anethylene/1-octene polyolefin with an MI of 30 and a density of 0.87 g/cm3. The resulting let-

down material is used to form the sheath (adhesive component) of the bicomponent elastic fiber

used in the following examples.

EXAMPLE 2A

Fiber Separation Using Intensive Mixing in an Aqueous Medium

Bicomponent, 11.2 denier elastic fiber comprising 50 percent Pellathane 2103-80PF (an

elastomeric thermoplastic polyurethane manufactured by The Dow Chemical Company) and 50

percent homogeneously branched, substantially linear ethyline/1-octene polyolefin is prepared asdescribed in Example 1 above. The thermoplastic polyurethane forms the core and the MAH-grafted ethylene polymer forms the sheath of the bicomponent fiber. A mixture of 30 percent of

this elastomeric bond fiber and 70 percent Hi Bright cellulose fibers (unbeaten, bleached kraft

softwood, macerated and soaked overnight at 1.1 percent in water) in 5 liters of water with 5grams surfactant (Rhodameer, Katapol VP-532) and 110 grams of 0.5 percent solid Magnafloc

1885 anionic polyacrylamide viscosity modifier is added to a Waring blender. The mixture is


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stirred to produce a substantially uniform mixture of elastic and cellulose fibers which are

subsequently formed into an elastic, absorbent paper.

EXAMPLE 2B

Fiber Separation Using Intensive Mixing in an Aqueous Medium and Hydrogen BondingDeactivation

Sample Designation Core/Sheath Composition* Denier

1.2 TPU/Engage (30 MI) 6.78

1.3 TPU/MAH-g-Engage (30 MI) 11.32

2.2 TPU/Engage (30 MI)



Initially, all of the five fiber systems (tows) listed above are cut to length using a scissors. A

100 g/m2

air laid pad with 12% binder fiber loading needs to incorporate 0.43 g of binder fiber byweight. Sufficient amount of fiber is cut in all cases to produce 3 pads.

Following the cutting of the fiber tows (each tow has 72 individual fiber filaments) to length, the

next step is to separate individual fibers from the tows so that these can be incorporated into

cellulose pulp and air laid into a pad. The sheath polymer(s) in all the cases are quite tacky

even at room temperature (0.870 g/cc density) and the individual fibers are completely fusedtogether in all cases over time.

To separate the fiber tows into individual filaments, 0.43 g of binder fiber is weighed and addedto a Waring blender. To this is added 2.00 g of cellulose pulp (a total of 3.195 g of cellulose

pulp is used in a 100 gsm pad). Next, a 25:1 solution of water with AROSURF PA-777

surfactant blend from Goldschmidt Corp. is added to the binder fiber plus cellulose pulp mix.The blender is activated for 2-3 seconds and during this time the binder fiber tows

instantaneously open up into individual fiber filaments. The cellulose pulp is added to the

above mix to ensure that the binder fiber filaments stay separated during the subsequent drying

process. The above procedure not only enables the separation of binder fiber into individualfilaments, but it also results in deactivating the hydrogen bonding in pulp.

The next step entails drying the binder fiber and pulp mixture. The fibers are first separated from

the water/surfactant solution using a sieve. This fiber mixture is then dried overnight in a vacuumoven at 50 C. to ensure that any residual moisture is also removed. The dried fiber mixture is

then incorporated into the air-laid chamber (an additional 1.195 gms of deactivated and driedcellulose pulp is also added at this time) and an absorbent pad structure is made using a vacuum

assist process.

EXAMPLE 3


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Elastic Paper Comparison

Eight inch by eight inch (88) elastic paper samples are prepared by using the

ceramic fiber manufacturing processing

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