CA2209785A1

CA2209785A1 - Polyolefin-polyamide conjugate fiber web

Info

Publication number: CA2209785A1
Application number: CA002209785A
Authority: CA
Inventors: Ty Jackson Stokes
Original assignee: Individual
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 1995-01-27
Filing date: 1996-01-19
Publication date: 1996-08-08
Also published as: CN1077166C; KR100384662B1; EP0805881B1; AU701435B2; MX9705613A; EP0805881A2; BR9606851A; JPH10513506A; US5534339A; WO1996023915A3; AR000814A1; AU4761596A; DE69621226D1; WO1996023915A2; KR19980701719A; DE69621226T2; ZA96620B; CN1179184A; PL321600A1; JP3872815B2

Abstract

The present invention provides a conjugate fiber containing a polyolefin and a polyamide selected from polycaprolactam, copolymers of caprolactam and hexamethylene adipamide, hydrophilic copolymers of caprolactam and ethylene oxide diamine, and blends thereof, wherein the polyamide has a number average molecular weight up to about 16,500. Further provided are a nonwoven fabric produced from the conjugate fiber and the process of producing the nonwoven fabric.

Description

CA 0220978~ 1997-07-11 W 096/23915 PCTrUS96/00767 POLYOLEFIN-POLYAMIDE CONJUGATE FIBER WEB

CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. Patent 5,424,115 granted June 13, 1995.

BACKGROUND OF THE INVENTION
The present invention is related to conjugate fibers of two different 10 thermoplastic polymers and nonwoven webs produced therefrom. More specifically, the invention is related to conjugate fibers and nonwoven webs of a polyolefin and a polyamide.
Conjugate fibers cont~ l at least two component compositions that occupy distinct cross sections along substantially the entire length of the fibers, and they are 15 produced by simultaneously and contiguously extruding a plurality of molten fiber-forming polymeric compositions to spinning orifices of a spinneret to form unitary filament strands. In general, component compositions for conjugate fibers are selected from dirrerent polymers having different shrinkage properties and/or complementarily advantageous chemical and physical properties. Component 20 polymers having dirrelent shrinkage properties are typically utilized to impart crimpability in the conjugate fibers, and component polymers having different advantageous properties are utilized to impart different functionalities in the fibers.
Since ~irrer~nt polymers have different melting and processing temperatures as well as have ~ ' 'rer~nt rhec IG~-- ' melt properties, it is usually necessary or 25 de~ lE to process and maintain component polymer compositions for conjugate fibers at different temperatures until just prior to combining the melted polymer compositions as unitary filament strands. In many cases, when different melted polymers are combined to fomm unitary strands, there emerge numerous processing difficulties such as nonuniformity of the strands, spin breaks and bending 30 phenomena of ~",scl''ied strands at the tip of the spinneret. Such processingdifficulties prevent proper formation of fibers and, thus, nonwoven fabrics. In addition, especially for fiber-spinning processes that employ pneumatic drawing steps, e.g., meltblown fibers and spunbond fibers, the filament strands exiting the spinneret tend to bundle or rope during the drawing process unless the processing 35 conditions are carefully tailored for each polymer combination. Such controlled processing conditions ensure, for example, proper quenching of the component polymers forming the filament strands and separation of the extruded strands until CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 they are deposited onto the forming surface. There have been many approaches to solve these processing difficulties in spinning conjugate fibers of different polymer compositions. For example, British Pat. No. 965,729 discloses a spinneret containing angularly placed orifices that is inclined in the opposite direction to the bending direction of the extruded conjugate fiber strands. However, the teaching of the patent may only be practical for large production runs since a specific spinneret has to be constructed for each combination of different polymers. U.S. Pat. No.
3.536 80~ to Uraya et al. ~iiccl~s~c a method of separately extruding and maintaining component polymer compositions at different temperatures until just prior to 0 co" lLi n ,9 and extruding into unitary fiber strands in order to alleviate the processing diffficulties by keeping the melt viscosities of the component polymer compositions substantially at the same level. The teaching of Uraya et al. utilizes the fact that linear thermoplastic polymers in general decrease their melt viscosity as the melt temperature increases. However, the process of ensuring the thermal profile of each component polymer melts requires a cumbersome or complex spinneret u,~er, IL,ly that contains insulation layers. In addition, the temperature dirr~ ,~,.ce of the polymer components of the unitary filament strands creates processing diffficulties in handling the extruded filaments. For e~c~, I ~r le, component polymers having dirre,~ ,~t melt temperatures tend to solidify at dirrerent rates, and insufficiently quenched polymer components of the conjugate filaments tend to cause random fusing or roping of the filament strands before the filaments can be properly deposited on a forming surface.
Of various conjugate fibers having different polymers, conjugate fibers of a polyolefin and polyamide co",~ ~.,ation are highly useful. U.S. Pat. No. 3,788,940 to Ogata et al., for example, ~ic~lQs~s conjugate fibers conl~ y a polyolefin and along-carbon chain polyamide, e.g., nylon-11, nylon-12, nylon-11/lû, nylon-11/11 or nylon-11/12. Long-carbon chain polyu", ~es have melting and processing temperatures that are lower than more commonly available and conventional nylons, i.e., nylon 6 and nylon 6/6. The melting and processing temperatures of 30 these long-carbon chain polya",i les are practically comparable to those of polyolefins such that these polyamides and polyolefins can easily be processed to form conjugate fibers. In contrast, more conventional and economical polyamides,i.e., nylon 6 and nylon 6/6, have significantly higher melting points and, thus, have to be melt-processed at a higher processing temperature range than typical 35 polyolefins. Moreover, as is known in the art, a thermoplastic polymer is typically CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 melt-processed at a temperature- significantly higher than the melting point of the polymer in order to accommodate the typical temperature fluctuation of the melt-processing equipment, e.g., an extruder, and, thus, to avoid accidental solidification or freeze up of the polymers in the melt-processing equipment and to provide a composition melt that has a properly processible melt viscosity. In general, when a composition melt is underheated, the melt has an elongational viscosity or a melt elasticity that is too high to allow proper drawing of the extruded filaments: and when a melt is overheated, the extruded filaments from the melt cannot be quenched properly and sufficiently. Consequently, overheated and underheated 0 melts do not properly form useful filaments, e.g, cause spin breaks and form fused and/or roped fibers. Accord- Igly, conventional polyamides and polyolefins have been melt-processed at dirr~:r~nt processing temperatures and, therefore, typically required specialized processing equipment to produce conjugate fibers.
There r~r, ,s a need for providing polymer compositions for 15 polyolefin/polyamide conjugate fibers that can be processed with conventionalpolyolefin processing equipment and that contc ~ polymer components which need not be processed at dirr~r~:nt processing temperatures.

SUMMARY OF THE INVENTION
There is provided in accordance with the ,u,~se,-t invention a conjugate fiber containing a polyolefin and a polyamide selected from polycaprolactam, copolymers of c~,r~ I ~,tum and hexamethylene adipamide, hyd. ~h " -copolymers of caprolactam and ethylene oxide diamine, and blends thereof, wherein the polyamide has a number average molecular weight up to about 25 1 6,5ûû. Further provided is a nonwoven fabric produced from the conjugate fiber.
The ~.~sent invention further provides a desired method of producing conjugate flbers and nonwoven fabrics that contain a fiber-forming polyolefin and a polyamide selected from polyc~,~- ~ I clu~ ~ " copolymers of caprolactam and hexamethylene adipamide, hydrophilic copolymers of caprcl _tu.,. and ethylene 30 oxide diamine, and blends thereof, wherein the polyamide has a number averagemolecular weight up to about 16,500. The method contains the steps of melt-extruding the polyolefin, melt-extruding the polyamide, feeding the extruded polyolefin and polyamide to an orifice of a spinneret to form a unitary filament, wherein the melted polyolefin and polyamide entering the orifice are melt-CA 0220978~ l997-07-ll W O96/23915 PCTrUS96/00767 processed to have melt temperatures between the melting point of the polyamide and about 24û~C.

8RIEF DESCRiPTlON OF THE DRAWINGS
Figures 1-6 illustrate exemplary conjugate fiber cross-sectional configurations.Figure 7 shows a conjugate fiber nonwoven fabric that was produced in accordance with the present invention.
Figure 8 shows a nonwoven fabric that was produced with a conventional polycaprolactam.
Figure 9 shows another conjugate fiber nonwoven fabric that was produced in accordance with the present invention.
Figure 10 shows another nonwoven fabric that was produced with a conventional polycaprolactam.

DETAILED DESCRIPTION OF THE INVENTION
The present invention ~ close~ conjugate fibe,-s having a polyolefin and a polyamide, and nonwoven webs produced from the conjugate fibers. The conjugate fibers and the nonwoven webs exhibit improved strength properties, e.g., tensile strength and tear strength: abrasion resistance; bonding chu,ucteli~lics, e.g., 2 o broader bonding temperature range; and functionalities, e.g., dyeability and hydtu~h ' ~ , over polyolefin fibers and nonwoven webs ther~r,vm. In addition, the nonwoven web contains functional chemical groups, i.e., amide groups, that can be chemically modified to introduce various surface functionalities on the nonwoven web. The component polymer compositions of the present conjugate fibers, unlike conventional short~arbon chain polyamide compositions of prior art conjugate fibers, can be processed at a temperature that is typically used to melt-process polyolefins and can be processed with a conventional non-insulated conjugate fiber spinning apparatus.
Polyu".'~es, otherwise known as "nylons," suitable for the present invention include polycaprolactam (nylon 6), copolymers of caprolactam and hexamethylene adipamide ~nylon 6,6/6), and hydrophilic copolymers of c~,ur~ I ctam and ethylene oxide diamine, as well as blends thereof. Of these, the most de~i,ul_le polyamide for the present invention is polycaprolactam. In ~COId~ ce with the present invention, suitable polyu" ,i ics are low molecular weight polyu",i i~s that have a number average molecular weight equal to or less ~ =
CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 than about 16,500; desirably between about 10,000 and about 16,200: more desirably between about 11,000 and about 16,000; most desirably between about 11,500 and about 15,000. It is believed that suitable polyamides having a low number average molecular weight of 5,000 or even less can be melt-extruded into the conjugate fibers of the present invention. Particularly suitable polyamides for the present invention have a formic acid relative viscosity between about 1.8 and about 2.15, more particularly between about 1.85 and about 2, as measured in accoldu"ce with ASTM D789-66, and have a melt flow rate between about 48 9/10 min and about 100 9/10 min, more particularly between about 65 9/10 min and 95 0 9/10 min, as measured in accordance with ASTM D1238-90b, Condition 230/2.16.Optionally, the polyamide composition for the conjugate fibers may contain a small amount of a processing lubricant to improve the processibility of the polyamides.
For example, a small amount of a metal or mineral stearate, e.g., calcium, sodium, lead, barium, cadmium, zinc or magnesium stearate, can be blended into the polyamide composition to increase its melt flow rate and reduce its melt viscosity.
Desirably, up to about 5 YO, more de,i,uL,ly between about û.û1 % and about 4 %,based on the weight of the polymer, of a stearate compound is blended into the polymer composition.
It has been found that the polyamides suitable for the present invention can 2 o be melt processed at the conventional processing temperature range for polyolefins without experiencing processing difficulties, such as bending and roping of extruded conjugate filament strands. Desirably, the polyamide is melt-processed to have a melt temperature between the melting point of the polyamide and about 240~C, more desirably between about 215~C and about 238~C, most desirably between 225~C and about 235~C, especially when spunbond conjugate fibers are produced. The term "melt temperature" as used herein indicates the temperature of polymer composition melt that enters the spinning pack. It is to be noted that the processing temperature suitable for the present invention is significantly lower than the conventional processing temperature range for polycaprolactam and is not siy,,iricu,,ll~ higher than the melting point of the polyamide. Although it is not wished to be bound by any theory, it is believed that the unique low molecular weight of the suitable pol~u",- Ics for the present invention provides the required melt viscosity even at the present low melt-processing temperature range. In contrast, commercially available fiber grade polycaproluctu"~s have to be melt-- 35 processed at a higher temperature range than the processing temperature range of CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 typical polyolefins in order to obtain proper melt flow chu,~cteri,lics that arecompatible with melt-processed polyolefins. Consequently, the conjugate fiber component compositions containing the pr~sent polyamide can be processed with a conventional spinneret assembly that is maintained at the conventional operating 5 temperature range typically utilized for polyolefins.
Polyolefins suitable for the present inventions include polyethylene, e.g., highdensity polyethylene, medium density polyethylene, low density polyethylene and linear low density polyethylene; polypropylene, e.g., isotactic polypropylene and atactic polypropylene: polybutylene, e.g., poly( 1 -butene) and poly(2-butene):
10 polypentene, e.g., poly(2-pentene), and poly(4-methyl-1-pentene): polyvinyl acetate: polyvinyl chloride: polystyrene: and copolymers thereof, e.g., ethylene-propylene copolymer as well as blends thereof. Of these, more desirable polyolefins are polypropylene, polyethylene, polybutylene, polypentene, polyvinyl acetate, and copolymers and blends thereof. Most desirable polyolefins for the 15 ~ ent invention are polyolefins conventionally used in the production of nonwoven fabrics, including polypropylene, polyethylene, copolymers of polypropylene and polyethylene, and blends thereof: more particularly, isotacticpolypropylene, blends of isotacffc polypropylene and atactic polypropylene, syndiotactic polypropylene, high density polyethylene, linear low density polyethylene and blends thereof. In addition, the polyolefin component may further contain minor amounts of comp~li' .' .9 agents, ~Lr~,,ion resistance enhancing agents, crimp inducing agents and the like. Illustrative ex~, ~ S of such agents include acrylic polymer, e.g., ethylene alkyl acrylate copolymers: polyvinyl acetate: ethylene vinyl acetate: polyvinyl alcohol: ethylenevinyl alcohol and the like.
The component polymer compositions of the present invention may additionally conl~ ~ ~ other additives and processing aids. For example, nucleating agents, cGlor~..l,, pigments, wetting agents, surfactants, ~,.ti,lc~l,, odor absorbents, gellll- l~s,lubric~ and the like. These additives can be, for example, dry or 30 tumble blended with the polymeric pellets of the component polymers before the pellets are melt-processed.
Processes suitable for producing conjugate fibers are known in the art. In general, at least two flowably ,~rcces,ed component polymer compositions are fedthrough spinning orifices of a spinneret to form unitary filaments having distinct cross 35 sections along substantially the entire length of the filaments that are occupied by CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 the polymer compositions. Conjugate fibers can be prepared to have crimps or latent crimpability. Whiie it is not wished to be bound by any theory, it is believed that conjugate fibers containing component polymers of different shrinkage - properties possess subsequently activatable "latent crimpability". When such conjugate fibers are exposed to a heat treatment or mechanical drawing process, the shrinkage disparity among the component polymers of the conjugate fibers causes the fibers to crimp. An exem, ' ~ process for producing highly suitable conjugate fibers for the ~resent invention is ~icclosed in commonly assigned U.S.
Patent 5,382,4û0 to Pike et al., which in its entirety is herein incorporated byreference. Briefly, the process for making a crimped conjugate fiber web, more specifically a spunbond fiber web, ~ losed in the patent includes the steps of meltspinning continuous multicomponent polymeric filaments, at least partially quenching the multicomponent filaments so that the filaments have latent ~,i,.,iJaLI'it~, activating the latent crimpability and drawing the filaments byapplying heated drawing air, and then depositing the crimped, drawn filaments onto a forming suRace to form a nonwoven web. In general, a higher drawing air temperature results in a higher number of crimps. Optionally, unheated ambient air can be used during the drawing step to suppress activation of the latent crimpability and to produce uncrimped conjugate fibers. Multicomponent conjugate meltblown fiber and methods of making the same are di,closed in, for example, U.S. Pat. Nos. 5,238,733: 5,232,77û: 4,547,42û: 4,729,371 and 4,795,668.
The conjugate fibers of the present invention may have a wide variety of conjugate fiber configurations. Figures 1-6 illustrate exu"":los of suitable conjugate fiber configurations. Suitable conjugate fiber configurations include a side-by-side configuration (Figure 1), an eccentric sheath-core configuration (Figure 2), a concentric sheath-core configuration (Figure 3), a wedge-core configuration (Figure 4), a wedge conflguration (Figure 5) and a islands-in-sea configuration (Figure 6J.
The conjugate fibers may also be hollow fibers. The unique molecular weight polyc~ ,r~ I ~ t~,- "s of the F~r~sent invention can be melt-extruded at polyolefin 3 o processing temperatures and, thus, have a quenching profile similar to thepolyolefin component of the conjugate fibers. In addition, melted compositions of the low molecular weight poly~", Ics exhibit a reduced melt elasticity or elongational viscosity, improving the compatibility of the polyamide and polyolefin con"~onents of the conjugate fibers and drawability of the extruded filaments. It is - 35 also believed that the melt of the unique molecular weight polycaprolactams CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 exhibits improved and reduced visco-elastic properties even when the melt is cooled to a temperature near or below the melting point, i.e., even after the melt starts to solidify, further facilitating drawability of the extruded con~ugate filaments.
The present polyamide component can be conveniently processed under the s processing settings adapted for polyolefins, thereby eliminating processing difficulties and ~robl~nl5 associated with producing conjugate fibers from component polymers of different processing temperatures and melt viscosities.
Nonwoven webs or fabrics are produced from the conjugate fibers by depositing the fibers onto a forming surface. Typically, the fibers are randomly and 10 isotropically deposited to form a nonwoven web having uniform fiber coverage. If the conjugate fibers are not self-adhering at the time of nonwoven web formation, the nonwoven web has to be bonded to impart physical integrity and strength. Forexample, typical meltblown fibers are not completely quenched or solidified whenthey are deposited onto a forming surface, and therefore, the fibers form 15 autogenous interfiber bonds as they are deposited to form a meltblown fiber web.
In contrast, spunbond fibers and staple fibers are fully or substantially fully quenched when deposited to form a nonwoven web. Consequently, the resulting nonwoven web needs to be bonded in a separate bonding step. Suitable bonding processes include compr~ssion bonding processes, e.g, calender bonding, point bonding and 2 o pattem bonding processes; and noncol ",ur~"ion bonding processes, e.g., oven bonding, ;nfrared bonding and through-air bonding processes. Typically, cor ,~ression bonding processes apply a co, n~ . Iation of heat and pressure to effect interfiber bonds, e.g., by passing a nonwoven web through the nip formed by a heated smooth or pattemed roll and a smooth anvil roll. Noncompression bonding 2 5 processes elevate the temperature of the nonwoven web until at least one component of the conjugate fibers forming the nonwoven web is melted and rendered adhesive, forming autogenous interFiber bonds at crossover contact points of the fibers.
According to another embodiment of the ,~leseni invention, the nonwoven 30 webs of the ,c~-eaent invention may be laminated to form a composite material. For example, a spunbond conjugate fiber web and a meltblown fiber web of the present invention can be overlaid or sequentially formed and then thermally or adhesively bonded to form a co""~,osile fabric that has the strength properties of the spunbond web and the barrier properties of the meltblown web. An exemplary CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 process for producing such composite materials is disclosed in U.S. Pat. No. 4,û41,2û3 to Brock et al., which is herein incorporated by reference.
According to yet another embodiment of the present invention, the nonwoven webs of the present invention may be laminated to a conventional 5 monocomponent fiber nonwoven web or a film. For example, a conjugate fiber web of the present invention may be laminated to a polymeric film and then thermally point bonded to form a high strength, cloth-like liquid barrier laminate.
Such barrier laminate is highly useful as, e.g., a fabric for protective garments and a outer cover materials for diapers and other personal care articles.
As stated above, the polyamide/polyolefin conjugate fiber nonwoven web of the present invention exhibits advantageous properties including improved tensile strength, dyeability, chemical functionalities and wettability. The nonwoven web is highly suitable for producing protective garments, e.g., medical examination gowns and surgical gowns: protective covers, e.g., car covers and boat covers; disposable 15 articles, e.g, liners for diapers: and the like.
The pr~:sent invention is further illustrated with reference to the following ex~r.,~.,lcs. However, the examples are not to be construed as limiting the invention thereto.

W O96/23915 PCT/U~5G~0~767 Ex~
Example 1 A 1 ounce per square yard (osy), 34 g/m2, spunbond nonwoven web was prepared from side-by-side 50 wt~o polypropylene/50 wt~o polyc~pr~ ctam 5 conjugate fibers. The polypropylene used was Exxon's PD3445, which had a melt flow rate of 35 g/1û min, and the polyc~,~,rol ~;lu,-, (nylon 6) used was a wire jacket grade, 401-D, which had a formic acid relative viscosity of 1.97, a number average molecular weight of about 13,800 and a melt flow rate of 85 g/1û min. The formicacid relative viscosity was tested in accordance with ASTM D789-66, and the melt10 flow rate was tested in accordance with ASTM D1238-90b, Condition 230/2.16. The nylon 6 resins were obtained from Custom Resins, Henderson, Ky, a division of Bemis Company, Inc. The polypropylene was blended with 2 wt~o of a TiO2 concentrate contl , 19 5û wt~o of TiO2 and 5û wt~o of a polypropylene, and the mixture was fed into a first single screw extruder that had three zones. The nylon 6 was blended with 15 2 Wt7O of a TiO2 concentrate cont~ I ~g 25 wt~o of TiO2 and 75 wt7'o of nylon 6, and the mixture was fed into a second single screw extruder that had four zones. Theextruded polymers were fed to a ~ - _" ",onent spinning die through heated l~u~l~rellillg tubes and spun into round bicomponent fibers. The bicomponent spinning die had a 0.6 mm spinhole diameter and a 4:1 L/D ratio. The spinhole 20 throughput rate was 0.7 gram/hole/minute. The spinning die was maintained at one constant temperature and, thus, both of the melted component compositions were exposed to the temperature. The p, ~,ce~i,19 temperature setting profile of the extruders, transferring tubes and spinneret is shown in Table 1. The bicomponentfibers exiting the spinning die were quenched by a flow of air having a flow rate of 25 45 SCFM/inch spinneret width and a temperature of 65~F. The quenching air was"p~ l about 5 inches below the spinneret, and the quenched fibers were drawn in an c,~,~i. uli~ lg unit of the type which is described in U.S. Patent 3,802,817 to Matsuki et al. The quenched fibers were drawn with ambient air in the ~ g unit to attain 2.5 denier fibers. Then, the drawn fibers were deposited onto a fo,~,lli.-ous 30 forming surface with the assist of a vacuum flow to form a nonwoven fiber web.
The nonwoven web was point bonded by feeding the web into the nip of a steel calender roll and a steel anvil roll. The calender roll had about 310 raised square bonding points per square inch (48 points/cm2). The bonding rolls were heated to about 143~C and ~,~j~ l'e~ a nip pressure of about 15.5 kg/lineal cm.

CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 Table 1 Temoerature Settinq (~C~
5Position ' Nylon 6 Polvoroovlene Extruder Zone 1 216 166 Zone 2 241 199 oZone 3 224 221 Zone 4 229 Zone 5 23û
Trc~ r~ g Tube 229 221 Spinneret 232 2 0 Example 2 (Ex2J
E-xample 1 was repeated, except a dirrer~:nt ,~r~ce"i,lg temperature profile was used, as indicated in Table 2.

Table 2 Tem~erature Setting (~C) Position Nvlon 6 PolvDroovlene Extruder 30Zone 1 216 171 Zone 2 241 222 Zone 3 224 229 Zone 4 229 Zone S 23û
Tr~"~re" i, ,9 Tube ' 229 229 Spinneret 234 The point bonded nonwoven webs of Examples 1 and 2 that contain the low molecular weight polyamide, which was melt-processed at a unconventionally low temperature and had a melt temperature that is near or at the melt temperature of the polyolefin component, had uniform fiber coverage and caliper that are similar to conventional monocomponent fiber nonwoven fiber webs.

CA 0220978~ 1997-07-ll W O96/23915 PCTrUS96/00767 Comparative i_xample 1 IC 1) A 1 ounce polypropylene monocomponent spunbond web was prepared using PD3445 polypropylene in accordance with the procedure outlined in E-xample- 5 ~, except polypropyiene was melt-processed in both of the extruders and aconcentric sheath-core spinning pack was used. The processing temperature profile was as indicated in Table 3.
The resulting nonwoven web was tested for its grab tensile strength and tear strength. The grab tensile strength was tested in accordance with Federal Standard 0 Methods 191 A, Method 5100 (1978), and the tear strength was tested in accordance with the Trapezoidal Tear Test as described in ASTM D 1117-80, Method 14. The results are shown in Table 12.

Table 3 Temperature Settinq (~Cl Position E-xtruder 1 E-xtruder 2 E-xtruder 20Zone 1 171 171 Zone 2 199 198 Zone 3 22û 221 Zone 4 222 Zone 5 222 Tr~, l~re" i"g Tube 230 230 Spinneret 229 Comparative i-xample 2 (C2) A nylon 6/polypropylene bicomponent conjugate fiber web was produced from a fiber grade polyamide, Nylon 6 Spinning Chips, available from DSM, and 35 Exxon PD3445 polypropylene in accordance with the procedure outlined in E-xample 1 and the processing temperature profile shown in Table 4. The nylon 6 had a fommic acid relative viscosity of 2.45 and a number average molecular weight of about 19,700. The elevated processing temperature profile of the polyamide was selected in accordance with the processing recommendation and guideline of the 40 polyamide manufacturer.

CA 0220978~ 1997-07-11 Table 4 Temperature Settina ~~C) 5Position Nvlon 6 PolYcroovlene Extruder Zone 1 219 171 Zone 2 266 199 10Zone 3 263 221 Zone 4 263 Zone 5 263 Tr~ rer,i,,9 Tube 263 221 Spinneret 262 The fiber grade nylon 6 couid not properly be spun into conjugate fibers. The 2 0 polymer strands exiting the spinneret were significantly bent, and the strands randomly fused and roped during the drawing process. A nonwoven fabric was not prepared since the roped fibers would not make a useful nonwoven fabric.

Comparative Example 3 (C3) 2 5 Comparative Example 2 was repeated except the melt processing temperature of nylon 6 was raised in order to decrease the melt viscosity of thepolymer composition. The processing temperature profile was as indicated in Table 5.
Table 5 Tem~erature Settina (~C) Position Nylon 6 Poly~rooYlene 35Extruder Zone 1 221 171 Zone 2 268 199 Zone 3 291 221 Zone 4 288 40Zone 5 288 T~ el l il lg Tube 287 221 Spinneret 265 CA 0220978~ 1997-07-11 W O96/23915 PCTnUS96/00767 Raising the melt temperature of the nylon composition, in order to affect the melt viscosity of the polymer, did not alleviate the fusing and roping problem. The filaments were fused and roped.

5 Com,~ live Example 4 (C4) Comparative Example 3 was repeated except the processing temperature of the nylon composition was further raised in order to further reduce the melt viscosity of the composition. The resulting fibers were formed into a nonwoven fabric in accordance with Example 1. The processing temperature profile was as indicated 10 in Table 6.
Table 6 Temoerature Settina (~Cl 5Position NYlon 6 PolyDroDvlene Extruder Zone 1 221 171 Zone 2 291 199 20Zone 3 3û3 215 Zone 4 299 Zone 5 299 Transferring Tube 299 215 Spinneret 264 Again, raising the processing temperature did not cure the fusing and roping phenomena, and in fact the roping problem was more severe. It is believed that not only the melt viscosity difference between the component compositions but also the melt temperqture disparity and thus insufficient quenching of the nyloncon,po~ilion further contributed to the roping problem. As expected, the produced 35 nonwoven fabric had a highly nonuniform fiber coverage due to the roped fibers.

Example 3 ~Ex3) Example 1 was repeated except sheath-core conjugate fibers were produced using a concentric sheath-core spinning pack. The processing temperature profile40 was as shown in Table 7.

CA 0220978~ 1997-07-11 W O 96/23915 PCT~US96/00767 Table 7 TemPerature Settina (~C~
5Position Nylon 6 Polypro~ylene Extruder Zone 1 219 171 Zone 2 239 199 10Zone 3 242 221 Zone 4 229 Zone 5 230 T.c~r,~re"i"9 Tube 230 221 Spinneret 229 Figure 7 is a photograph of the point bonded nonwoven fabric produced from this example. As can be seen from Figure 7, the nonwoven fabric had a highly uniform fiber coverage.

Comparative C~ ""~ l~ 5 (C5) 2s Comparative Example 2 was repeated except sheath-core conjugate fibers were produced using a concentric sheath-core spinning pack. The processing temperature profile was as shown in Table 8.
Table 8 Temr~erature Settina ~~C) Position NYlon 6 Polvl~ror~Ylene Extruder 35Zone 1 218 171 Zone 2 291 199 Zone 3 298 221 Zone 4 299 Zone 5 298 Tlc~ rel, i, ,9 Tube 299 221 Spinneret 238 The resulting conjugate fibers fused and roped during the drawing process.
The high molecular weight of the polyamide caused the spinning problem even CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 though the processing temperature of the polyamide component was significantly raised to influence the melt flow properties of the component. Figure 8 is a photograph of the nonwoven fabric. The photograph clear shows the fused and roped fibers and uneven coverage of the fibers forming the nonwoven fabric.

E-xample 4 (Ex4) E-xample 3 was repeated and the processing temperature profile was as shown in Table 9. Three nonwoven fabrics having conjugate fibers of dirrer~nt polymer component proportions were produced. The polymer component proportions were 50:50, 40:6û and 60:4û by weight of nylon 6 and polypropylene.
Tabie 9 Temperature Settina (~C) 15Position Nylon 6 Polvr~roPvlene E-xtruder Zone 1 171 171 Zone 2 214 198 20Zone 3 239 221 Zone 4 229 Zone 5 230 Trc~ re"i"g Tube 229 229 Spinneret 229 All of the three component polymer proportions resulted in ~ "irc,~mly extruded 30 and drawn conjugate fibers and, correspondingly, nonwoven fabrics having a uniform fiber coverage and even caliper. Figure 9 is a photograph of the nonwoven fabric which was produced from conjugate fibers having 50:5û nylon 6 and polypropylene components. The photograph shows isotropically and uniformly laid fibers of the nonwoven fabric.
The fabric shown in Figure 9 was also tested for its grab and tear strength properties in accordance with the procedures outlined in Comparative E-xample 1.The results are shown in Table 12.

Comparative Exampie 6 (C6) Comparative E-xample 5 was repeated except a different fiber grade nylon 6 - was used. Nylon 6 used was a low molecular weight fiber grade polycaprolactam, CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/OQ767 DSM 1130, which had a formic acid relative viscosity of 2.22, a number average molecuiar weight of about 16,700 and a melt flow rate of 42 9/10 min. The processing temperature profile was as shown in Table 10. The resulting fabric was tested for its grab and tear strength properties in accordance with the procedures 5 outlined in Comparative Example 1. The results are shown in Table 12.
Table 10 TemPerature Settina ~~C~
10Position NYlon 6 PolvDroPYIene Extruder Zone 1 171 171 Zone 2 214 198 15Zone 3 241 221 Zone 4 229 Zone 5 23û
T~u,lsre,,ing Tube 229 229 Spinneret 229 During the filament spinning process, spin breaks were observed, and the extruded fibers of Comparative Example 6 fused and roped during the drawing process. Although the conjugate fibers of Example 4 and Comparative Example 6 were prepared under virtually the same processing condition, only the polyamide having the low molecular weight (of Example 4J was properly spun into conjugate fibers. The comparison of the results of Example 4 and Comparative Example 6 clearly demon,l,~les that the low molecular weight polycaprolactam is uniquely suited for forming conjugate fibers in conjunction with polyolefins that are typically used to produced nonwoven fabrics.
Figure 10 show the nonwoven fabric produced in this comparative example.
Fused and roped fibers are clearly visible, and as expected, the fiber coverage is highly inadequate, forming many sections of no fiber coverage.

Example 5 (Ex5) Example 3 was repeated except linear low density polyethylene (LLDPE) was 4 o used in place of polypropylene. The linear low density polyethylene, 6811 A grade, is - commercially available from Dow Chemical. The LLDPE had a melt flow rate of ' CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 about 43 9/ 10 min, as measured in accordance with ASTM D1238-90b, Condition 230/2.16. In addition, the nonwoven fabric was bonded with a bonding roll havinga different bond pattem. The bonding roll had bond points that covered about 25~o of the total surface area and had a bond point density of about 200 regularly 5 spaced points per square inch (31 points/cm2). The processing temperature profile was as shown in Table 11, and the resulting fabric was tested for its grab and tear strength properties in accord~J"ce with the procedures outlined in Comparative Example 1. The results are shown in Table 12.
Table 11 Temperature Settinq ~~Cl Position Nvlon 6 LLDPE
15Extruder Zone 1 172 166 Zone 2 216 194 Zone 3 238 221 Zone 4 231 20Zone 5 230 T-u, l,re"i"g Tube 229 229 Spinneret 229 Table 12 Tensile Strenath IKa) Tear Strenath (Kal Examole MD CD MD CD
Ex4 15.1 11.5 3.5 3.2 35 r-x5 14.2 7.2 5.7 2.6 C1 2.5 2.4 1.9 1.5 C6 5.4 2.5 1.8 1.5 40 MD = machine direction CD = cross-machine direction The above strength data clearly demonstrate that the conjugate fiber webs 45 of the present invention have superior strength properties, such as tensile and tear CA 0220978~ 1997-07-11 W O96/23915 PCT~US96/00767 strength properties, over monocomponent nonwoven fiber webs and conjugate fiber webs produced from a conventional fiber-grade polycaprolactam.

Example 6 (Ex6) Example 3 was repeated except that the nylon 6 used was Capron~) 1767.
Cu~run6) 1767 was obtained from AlliedSignal Inc., and it had a formic acid relative viscosity of 2.1, a number average molecular weight of about 16,100 and a melt flow rate of 49 9/10 min. The processing temperature profile was as shown in Table 13.

Table 13 Temperature Settin~ (~C) Position Nylon 6 Polypropvlene Extruder Zone 1 171 171 Zone 2 218 199 Zone 3 241 229 20Zone 4 229 Zone 5 229 Transferring Tube 229 229 25 Spinneret 231 Conjugate fibers were produced and a point bonded nonwoven was prepared, although there was a minor amount of roping observed.
Example 7 (Ex7) Example 6 was repeated, except the polyamide was modified to contain sodium stearate and 681 lA LLDPE was used in place of polypropylene. The stearate was topically dusted on the polyamide pellets, and it is believed that the amount of 35 sodium stearate applied was iess than 1 wt % of ihe pellets. In addition, a wedge spinning pack was used, and the bond pattern of Example 5 was utilized. The wedge spinning pack contu:. ,ed 16 identically shaped wedges, similar to Figure 5, and the two polymer components were arranged to alternatingly occupy the wedges. The processing temperature profile was as shown in Table 14.

CA 0220978~ 1997-07-11 W O96123915 PCT~US96100767 Table 14 Temoerature Settina (~Cl 5Position Nvlon 6 LLDPE
Extruder Zone 1 240 205 Zone 2 239 210 10Zone 3 238 229 Zone 4 237 Zone 5 237 Transferring Tube 238 229 Spinneret 239 A point bonded nonwoven fabric was produced, and it was observed that zo the addition of the lubricant, sodium stearate, improved the processibility of the polyamide.

Exampie 8 (Ex8) A through-air bonded nonwoven fabric of nylon 6/LLDPE wedge conjugate 25 fibers, which had the conjugate fiber configuration described in Example 7, was produced. The nylon 6 used was custom polymerized polycaprolactam, which was produced by Nyltech, NH, and had a formic acid relative viscosity of 1.85, a number average molecular weight of about 12,500 and a melt flow rate of 94 9/lO min. The LLDPE used was 681 lA LLDPE. Conjugate fibers were produced and deposited to 30 form an unbonded nonwoven web in accordance with Example 7. The processing temperature profile was as shown in Table 15.
The unbonded nonwoven web was bonded by passing the web through a through-air bonder which was equipped with a heated air source. The through-air bonder is described in further detail in the above-mentioned U.S. Pat. No. 5,382,400.
35 The heated air velocity and the temperature of the heated air were 2ûO feet/minute (61 m/min) and 133~C, respectively. The residence time of the web in the hood was about 1 second. The resulting bonded web had a thickness of about û.9 mm and a basis weight of about 85 g/m2.

CA 0220978~ 1997-07-11 W O96/23915 PCTrUS96/00767 Table 1 5 Temperature Settina (~C) 5Position NYion 6 PolYoropylene Extruder Zone 1 221 166 Zone 2 241 203 0Zone 3 230 230 Zone 4 228 Zone 5 230 Transferring Tube 229 230 Spinneret 234 The through-air bonded nonwoven fabric had an excellent uniform fiber 20 coverage and exhibited good flexibility and resiliency.
As can be seen from the examples, the low molecular weight polyamide of the present invention can be melt-processed with polyolefins under melt-processing conditions that are typically utilized to process polyolefins, especially to produce polyolefin nonwoven fabrics. This is highly unexpected since the melting points and 25 melt-processing temperature of conventional polyu. "i Ics are significantly higher than those of polyolefins.
The polyolefin/polycu, - ~ I ctam conjugate fibers and nonwoven webs produced therer.vr.. exhibit a co,..' i.,ation of highly desirable properties, including tensile strength, tear strength, abrasion resistance, broader bonding temperature 3 o range, dyeability and hydrophilicity over polyolefin fibers and nonwoven webs.

Claims

What is claimed is:

1. A conjugate fiber comprising a polyolefin and a polyamide selected from polycaprolactam, copolymers of caprolactam and hexamethylene adipamide, hydrophilic copolymers of caprolactam and ethylene oxide diamine, and blends thereof, wherein said polyamide has a number average molecular weight up to about 16,500.

2. The conjugate fiber of claim 1 wherein said polyamide is a polycaprolactam.

3. The conjugate fiber of claim 1 having a configuration selected from side-by-side, concentric sheath-core, eccentric sheath-core, wedge, wedge-core and islands-in-sea configurations.

4. The conjugate fiber of claim 3 having a hollow configuration.

5. The conjugate fiber of claim 1 wherein said polyamide has a number average molecular weight between about 10,000 and about 16,200.

6. The conjugate fiber of claim 1 is a spunbond fiber.

7. The conjugate fiber of claim 1 is a meltblown fiber.

8. The conjugate fiber of claim 1 wherein said polyolefin is selected from polyethylene, polypropylene, polybutylene, polypentene, polyvinyl acetate, polyvinyl chloride, polystyrene, and copolymers and blends thereof.

9. The conjugate fiber of claim 8 wherein said polyolefin is selected from high density polyethylene, linear low density polyethylene, isotactic polypropylene, blends of isotactic polypropylene and atactic polypropylene, syndiotactic polypropylene, and blends thereof.

10. A nonwoven fabric comprising conjugate fibers, said conjugate fibers comprising a polyolefin and a polyamide selected from polycaprolactam, copolymers of caprolactam and hexamethylene adipamide, hydrophilic copolymers of caprolactam and ethylene oxide diamine, and blends thereof, wherein said polyamide has a number average molecular weight up to about 16,500.

11. The nonwoven fabric of claim 10 wherein said polyamide is a polycaprolactam.

12. The nonwoven fabric of claim 10 wherein said polyolefin is selected from polyethylene, polypropylene, polybutylene, polypentene, polyvinyl acetate, polyvinyl chloride, polystyrene, and copolymers and blends thereof.

13. The nonwoven fabric of claim 10 wherein said conjugate fibers have a configuration selected from side-by-side, concentric sheath-core, eccentric sheath-core, wedge, wedge-core and islands-in-sea configurations.

14. The nonwoven fabric of claim 10 wherein said polyamide has a number average molecular weight between about 10,000 and about 16,200.

15. The nonwoven fabric of claim 10 wherein said conjugate fibers are spunbond fibers.

16. The nonwoven fabric of claim 10 wherein said conjugate fibers are meltblown fibers.

17. A laminate comprising the nonwoven fabric of claim 10 and a film.

18. A laminate comprising the nonwoven fabric of claim 10 and an additional nonwoven fabric.

19. A process of producing a conjugate fiber comprising a polyolefin and a polyamide, which comprising the steps of:
(a) melt-extruding a fiber-forming polyolefin:
(b) melt-extruding a polyamide selected from polycaprolactam, copolymers of caprolactam and hexamethylene adipamide, hydrophilic copolymers of caprolactam and ethylene oxide diamine, and blends thereof, said polyamide having a number average molecular weight up to about 16,500;

(c) feeding the extruded polyolefin and polyamide to a orifice of a spinneret to form a unitary filament, wherein the melted polyolefin and polyamide entering said orifice are melt-processed to have melt temperatures between the melting point of said polyamide and about 240°C.

20. The process of claim 19 wherein said polyamide is a polycaprolactam.

21. The process of claim 19 wherein said polyolefin is selected from polyethylene, polypropylene, polybutylene, polypentene, polyvinyl acetate, polyvinyl chloride,polystyrene, and copolymers and blends thereof.