CA2257862A1 - Microporous fibers - Google Patents

Abstract

A porous fiber (54) includes a distinctive configuration of voids (52) therein to achieve advantageous levels of wettability, liquid penetration and mechanical properties. The fiber has a denier of not more than about 50, and a percent elongation at break of not less than about 30 %. The fiber can also have a tensile strength at break of not less than about 200 MPa.

Description

CA 022~7862 1998-12-lO
WO 98/03706 PCTrUS97/10715 MnCROPOROUS ~BERS .

Field of the Invention The present invention relates to fibers. More particularly, the invention relates to synthetic, porous fibers which are wettable and which exhibit improved me~,hanical 5 properties.

Back~round of the Invention Porous fibers have included stnuctures made by employing conventional phase 10 separation methods. Such methods generally involve mixing a polymer resin with a diluent or a plasticizer, quenching the polymer solution in a liquid medium to induce phase separation, and washing away the diluent to leave behind an interconnectedporous structure. Other porous fibers have been produced by techniques which employ a blowing agent or a swelling agent to create a ,,,;c~uporuus structure. Still other porous 15 materials have been produced by employing an environmental crazing technique.
Conventional porous fibers, such as those described above, have not been able toprovide desired cor.,bi"~Lions of mechanicai properties and water accessihi~ity. In addition, the techniques have not adequately produced porous fibers having desired 20 combinations of small diameter, low denier, high weLLdbiliLy, high permeability to liquid, and high tensile strength. As a result, there has been a continued need for fibers having improved porous structures.

Brief Desc. il.tion of the Invention Generally stated, the present invention provides a distinctive porous fiber which includes voids therein to achieve desired levels of wettability and liquid penetration while still having good mechanical properties. The fiber can have a denier of not more than about 50, and can have a percent elongation at break of not less than about 30%. The 30 fiber can also have a tensile strength at break of not less than about 200 Mpa.

In its various aspects, the porous fiber of the invention can effectively and efficiently produce fibers having desired combinations of small size, high w~LLabiiily, high water-accessihility, high tensile strength and high elongation. As a result, the fiber can have an CA 022~7862 1998-12-10 W 098/03706 PCTrUSg7/10715 improved ability to be further processed to form nonwoven fabrics and other articles of manufacture.

Brief Description of the Drawin~s The present invention will be more fully understood and further advantages will become apparent when reference is made to the followed detailed description of the invention and the drawings, in which:

10 Fig. 1 is a scanni,)g electron photo"~ic ug(aph, taken at a ",a~.,iricalion of 850X, showing a representative cross-sectional view of the porous fiber of the present invention;

Fig. 2 is a scan~l;, ,g electron phoLomi-,- ugraph, taken at a magnification of 1 ,700X, showing an enlarged view of a portion of the cross-section shown in Fig. 1;
Fig. 3 is a scanning electron photomicrograph, taken at a magnification of 250X, showing a representative cross-sectional view of a prior art fiber which includes a lumen;

Fig. 4 is a scanui"g electron photomicrograph, taken at a "-ay..iricdLion of 8,000X, 20 showing an enlarged view of the cross-section shown in Fig. 3 at a location adjacent to the outer surface of the fiber;

Fig. 5 is a scann ,g electron photo-~ic.ugraph, taken at a magnification of 250X, showing a representative cross-section view of another prior art fiber which includes a lumen, and 25 was produced by an incremental sL,~Lchi-,g process;

Fig. 6 is a scanni--g electron photomicrograph, taken at a ma~"iricaLion of 5,000X, showing an enlarged view of a portion of the cross-section shown in Fig. 5;

30 Fig. 7 is an optical photomicrograph, based on oil-immersion optical microscopy taken at a magnification of 1500X, showing a representative view of the voids on the surface and in the bulk of a porous fiber of the invention;

Fig. 8 is an optical photo"-k,,ugraph, based on oil-immersion optical ~ uscopy taken at 35 a magnification of 1,500X, showing another view of the voids along the surface and in the bulk of a porous fiber of the invention;

CA 022~7862 1998-12-10 W O 98/~3706 PCTrUS97110715 Fig. 9 shows a representative view of the voids along the outer surface of another porous fiber of the invention, taken at a mayl ,iricalion of 3,000X;

5 Fig. 9A representatively shows a schematic view of particular pores shown in Fig. 9;

Fig. 10 is a scanning electron photomicrograph, taken at a ,.,a~"iricdlion of 15,000X, providing a representative view of the surface of the fiber shown in Fig. 3;

Fig. 11 is a scannillg electron phoLc",,;~,lugraph, taken at a magnification of 15,00ûX, providing a representative view of the surface of the fiber shown in Fig. 5;

Fig. 12 shows a backscattered electron photo~ ,ugraph, taken at a ,,,ayniricalion of 5,000X, showing a representative cross-sectional view of a fiber of the invention;
Fig. 13 shows a representative version of Fig. 12 which has been riigiti,ed for image analysis;

Fig. 14 shows a representative, graphical plot of the gained weight of water versus time for a porous fiber sample.

Detailed DescriPtion of the Invention With reference to Figs. 1, 2, 7, 8, 9, 9A and 12, a porous fiber 20 includes a length-wise dimension 44 and a generally cross-wise dimension 38. The porous fiber has a di:,lin. ~ e configuration of voids or pores 22 therein to achieve desired levels of wei' '~ ' ~, Iiquid penetration and other liquid acces-cihility. The fiber can have a denier (d) per fiber of not more than about 50, and desirably has a percent elongation at break of not less than about 30%. The fiber can also have a tensile strength at break of not less than about 200 MPa. In particular aspects of the invention, the porous fiber 54 can also include other properties, and can include voids or pores having distinctive shapes, sizes, distributions and configurations.

In its various aspects, the microporous fiber of the invention can provide for improved 3~ wicking can more quickly bring water or other liquid into the interior of a fibrous article, and can accelerate the dissolution kinetics for fibrous articles which are intended to be CA 022~7862 1998-12-10 WO 98/03706 PCTrUS97/10715 flushable. In addition, the microporous fiber can help provide for improved absorbency, improved distribution of li~uid, improved the breathability in articles, such as surgical gowns and diapers, improved tactile and aesthetic properties, and/or enhanced biodegradability. The fibers can be forrrled directly into nonwoven webs with conver,lional forming prooesses, such as the well known spunbond process.
Altematively, the fiber may be cut into staple fibers, and may be blended with other fibers for sl Ihsequent formation into nonwoven, fibrous webs employing conventional air-laying te~l1r~ es. The nonwoven webs may be particularly useful for producing flushablepersonal care products, such as diapers, tampons, feminine pads, pantiliners, tampon 10 strings and the like.

In the various configurations of the present invention, the porous fiber 54 can be a synthetic fiber produced from a source material which includes a thermoplastic, orientable material, such as thermoplastic and orientable polymers, copolymers, blends, 15 mixtures, compounds and other combinations thereof. t)esirably, the thermoplastic materials do not include highly reactive groups.

In particular arrangements of the invention, the source material can be a polyolefinic n,ate,ial. For example, the source material may include homopolymers of polyethylene 20 or polypropylene, or may include copolymers of ethylene and polypropylene. In other arrangements, the source material may include another polymer l"~enal, such as apolyether, a copolyether, a polyamid, a copolyamid, a polyester or a copolyester, as well as copolymers, blends, mixtures and other combinations thereof.

25 The the~ oplasLic material is melt processible, and in particular aspects of the invention, the material can have a melt flow rate (MFR) value of not less than about 1 g/10 minutes (based on ASTM D1238-~). Alternatively, the MFR value can be not less than about1Qg/10 minutes, and optionally, can be not less than about 20 g/10 minutes. In other aspects of the invention, the MFR value can be not more than 200 9/10 minutes.
30 Alternatively, the MFR value can be not more than about 100g/10 minutes, and optionally, can be not more than about 40 g/10 minutes to provide desired levels of process~ ity.

Such melt p,ucessible, thel"~oplastic material can, for example, be provided by a 35 homopolymer polypropylene. Commercially available polyolefins, such as HimontPF 301, PF 304, and PF 305, Exxon PP 3445, Shell Polymer E5D47, are aiso CA 022~7862 1998-12-lO
W O 98/0370~ PCT~US97/10715 represenLaLi~te of suitable materials. Still other suitable materials can include, for example, random copolymers, such as a random copolymer conLai, .i"g propylene and ethylene (e.g. Exxon 9355 conLa;"ing 3.5 % ethylene), and homopolymers, such as homopolymer polyethylene, which have MFR values similar to those mentioned herein.
5 The polymer resins may contain small amounts (e.g. about 0.05 to 5 parts of additive to 100 parts of resin) of processing additives, such as calcium sterate or other acid scavengers. Other additives can include, for example, silicon glycol copolymers,organosilicone compounds, olefinic elastomers, and low molecular weight parafins or other lubricating additives. Various pigment additives may also be incorporated. For 10 ~Xdlll, le, pigment concentrates such as a titanium dioxide pigment concentrate with low molec~ r weight polyethylene plasticizer can be employed as a processing additive. The various additives can have a plasticizing effect, can improve the strength and softness of the fiber, and can help facilitate one or more of the extrusion, fiber spil Ini, ,9, and aLIt:L11lill9 processes.
The source material for the fiber 54 can also include a further supplemental material, and the supplemental material may include a filler material, and/or a surfactant or other surface-active ",~Lerial. The filler material can be a particulate maLelial which can help provide porosity-initiating, debonding sites to enhance the desired formation of pores 20 during the various ~ Lcl ~ ,9 operations applied to the fiber. The filler material can help provide a desired suRace-modified fiber, and can help enhance a desired "sliding effect~
generated during subsequent sLI~t-,hillg operations. In addition, the filler material help preserve the pores that are generated during the various stretching operations.

25 Where the supplemental material includes a surface-active material, such as a surfactant or other ",~Lerial having a low surface energy (e.g. silicone oil), the surface-active "~aLerial can help reduce the surface energy of the fiber as well as provide lubricdLion among the polymer segments which form the fiber. The reduced surface energy and lubrication can help create the "sliding effect" during the subsequent sl,~Lchin g 30 operations.

The supplemental filler material can be organic or inorganic, and the filler material is desirably in the form of individual, discrete particles. The fillers may be subjected to a surface treatment with various coatings and su, ~a.;L~nLs to impart an affinity to the 35 polymer resin in the source material, to reduce agglomeration, to improve filler dispersion, and to provide a conL~olled interact;on with fluids, such as body fluids, blood CA 022~7862 1998-12-lO
W O 98/03706 PCTrUS97/10715 orwater. i=xamples of an inorganic filler can include metal oxides, as well as hydroxides, carbonates and sulfates of metals. Other sui~hle inorganic filler n~dlelials can include, for e~cd,nl~le~ calcium carbonate, various kinds of clay, silica, alumina, barium sulfate, sodium cd,Londle, talc, magnesium carbonate""ay"esium sulfate, barium ca,i onale, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, titanium dioxide, powdered metals, glass ll,ic,uspheres, orvugularvoid-conld;. ,9 pariicles. Still other inorganic fillers csn include those with particles having higher aspect ratios, such as talc, mica, and wollaslv, ,ile, but such fillers may be less effective. Represel ,lali~e organic fillers can inciude, for example, pulp powders, wood powders, c~11~ ~'.,se 10 derivatives, chitin, c.l,ilosan powder, powders of highly crystalline, high melting polymers, beads of highly crosslinked polymers, powders of organo~ ' ~ 3nes, and the like; as well as con,b;.,dlions and derivatives thereof.

In particular aspects of the invention, the fillers can have an average particle size which 15 is not more than about 10 microns (~lm). Alternatively, the average particle size can be not more than about 5 ~Lm, and optionally, can be not more than about 1 ~Lm to provide improved processibility. In other aspects of the invention, the top cut particle size is not more than about 25 ,~Lm. Altematively, and the top cut particle size can be not more than about 10 ~Lm, and optionally can be not more than about 4 ~lm to provide improved 20 process~hility during the formation of fibers having the desired size and porous structure. The fillers may also be surface-modified by the incorporation of surFactants, and /or other materials, such as stearic or behenic acid, which can be employed to improve the process~ ity of the source material.

25 Examples of suitable filler materials can include one or more of the following:
(1) Dupont R-101 TiO2, which is available from E.l. DuPont de Nemours, and can be sl ~pp'.ed in a conce, ILI dle form by Standrich Color Corporation, a business having offices located in Social Circle, Georgia 30279. This material can provide good process~ y.

(2) Pigment Blue 15:1(10 % copper), which is distributed by Standridge Color Corporation. Fibers produced with this ~ eri~l may break more often.

(3) OMYACARB ~ UF CaCO3, which is available from OMYA, Inc., a business having offices located in Proctor, Vermont 05765. This ~I;alerial can have a top cut particle size of about 4 ~rn and a average particle size of about ().7~1m, and can provide 35 good processibiiity. This filler can be coated with a surfactant, such as Dow Corning 193 CA 022~7862 1998-12-lO
WO g8/03706 PCTrUS97/10715 surfactant, before the compoundin~ or other combining with the source material 56. The filler can also be coated with other appropriate surfactants, such as those mentioned elsewhere in the present description.

(4) OMYACARB ~ UFT CaCO3 coated with stearic acid, which is available from 5 OMYA, Inc. This m~lerial can have a top cut particle size of about 4 llm and a mean particle size of about 0.7,um, and can provide good proces ~ y.
(5) SUPERCOATrM CaCO3which is available from ECC International, a business having offices located in Atlanta, Geor~ia 30342, ~775 Peachtree-Dunwoody Road. This material can have a top cut particle size of about 8 ,Lm and a mean particle size of 10 about 1 ~Lm. Fibers produced with this ",dl~rial may break more often.

(6) Powdered polydimethyl silses~uioxane (#22 or #23 Dow Coming Additive), which is available from Dow Coming, a business having offices located in Midland, Michigan 48628-0997. This material can provide good procescihility, while some a~_1cn,e,dlions may be observed.
The suFplemental material can optionally include a surface-active material, such as a surfactant or other material having a low surface energy (e.g. silicone oil). In particular aspects of the invention, the surfactant, or other surface-active ",aLerial, can have a Hydrophile-Lipophile Balance (HLB) numberwhich is not more than about 18.
20 Altematively, the HLB number is not more than about 16, and optionally is not more than about 15. In other aspects of the invention, the HLB number is not less than about 6.
Alternatively, the HLB number is not less than about 7, and optionally the HLB number is not less than about 12. When the HLB number is too low, there can be insufficient w:lLdbilily. When the HLB number is too high, the su,ra~.lahl may have insufficient 25 adhesion to the polymer matrix of the source material, and may be too easily washed away during use. The HLB numbers of commercially available SUI ra~,la"l:. can, for example, be found in McCUTCHEON's Vol 2: Functional Materials, 1995.

A suitable surfactant can include silicon glycol copolymers, carboxilated alcohol 30 ethoxylates, various ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated fatty esters and the like, as well as combinations thereof. Other sl lit~hle su, raclanLs can, for example, include one or more of the following:
(1) su,ra~,Lal1ts composed of ethoxylated alkyl phenols, such as IGEPAL RC-620, RC-630, CA- 620, 630, 720, C0-530, 61Q, 630, 660, 710 and 730, which are available 35 from Rhone-Poulenc, a business having offices located in Cranbury, New Jersey.

CA 022~7862 1998-12-10 W O 98/03706 PCTrUS971~0715 (2)su,rd-,lan~scomposed of silicone glycol copolymérs, such as Dow Corning D190, D193, FF400, and D1315, which are available from Dow Coming, a business having omces located in Midland, ~ higan.
(3) surfactants co,nposed of ethoxylated mono- and diglycerides, such as Mazel 80 5 MGK, Masil SF 19, and Mazel 165C, which are available from PPG Industries, a business having offices located in Gumee, lL 60031.
(4) sulrd1l;3nis cG",posed of ethoxylated alcohols, such as Genapol 26-L-98N, Genapol 26-L-6aN~ and Genapol 26-L-5, which are available from Hoechst Celanese Corp., a business having offices located in Charlotte, NC 28217.
(5) su.racl~nls co.l"oosed of carboxilated alcohol ethoxylates, such as Marlowet4700 and Marlowet 4703, which are available from Huls America Inc., a business having offices located in riscaLd~vay, NJ 08854.
(6) ethoxylated fatty esters, such as Pationic 138C, Pationic 122A, and PationicSS~, which are avaiiable from R.l.T.A. Corp., a business having offices located in Woodstock, lL60098.

The source material for the porous fiber 54 can include not less than about 0.35 wt% of the supplemental material, where the weight percentage is determined with respect to the total weight of the combined source material. In particular aspects of the invention, the 20 amount of supplemental l,lal~rial is not less than about 0.~ wt%, and may desirably be at least about 1 wt%. Alternatively, the amount of supplemental material is not less than about 5 wt%, and optionally is not less than about 10 wt%. In other aspects of the invention, the amount of supplemental material can be up to about 50 wt% or more. The amount of supplemental material is desirably not more than about 30 wt%. Alternatively, 25 the amount of supplemental material can be not more than about 20 wt% and oplionally can be not more than about 15 wt% to provide desired p,~,cessiL,il;ly chc,rdcLe~ ics.

In particular aspects of the invention, the source material can include not less than about 0.35 wt% of the filler material. In particular aspects of the invention, the amount of filler 30 material is not less than about 0.5 wt%. Alternatively, the amount of filler material is not less than about 1 wt%, and optionally is not less than about 5 wt%. In other ~spectc of the invention, the amount of filler material can up to about 50 wt% or more. The amount of flller material may desirably be not more than about 30 wt%. Alternatively, the amount of filler material can be not more than about 20 wt% and optionally can be not more than 35 about 10 wt%.

CA 022~7862 1998-12-10 W 098/03706 PCT~US97/10715 In further aspects of the invention where the supplemental ~I,aLe,ial includes a surface-active material, the amount of surface-active male~ ial, such as s~" r~-,lant, may be at least about 0.1 wt%. Alternatively, the amount of surface-active ",dLe,ial is at least about 5 1 wt%, and oplionalJ~, is at least about 3 wt%. In other aspects of the invention, the amount of surface-active material is not more than about 20 wt%. Alternatively, the amount of surface-active material is not more than about 15 wt%, and optionally, is not more than about 10 wt%.

10 A s~ lit~hle technique for forming the porous fiber 54 is described in U.S. Patent Appl ~ ~"on Serial No. 08/697,996 entitled METHOD AND APPARATUS FOR MAKING
MICROPOROUS FIBERS WITH IMPROVED PROPERTIES, filed September 4, 1996 by F. J. Tsai et al. (attorney docket No. 12,242), the entire disclosure of which is hereby incorporated by reference in a manner that is consi~l~nt (not in contradiction) herewith.
Conventional porous fibers have often included lumens therein. The lumen is typically a bore extending through a tube of fiber material, as representatively shown in Figs. 3 and 5. Accordingly, the lumen typically provides a hollow fiber in which the ratio of the outer diameter of the tube to the diameter of the bore can be within the range of 50:1 to 50:48.
20 Fibers with lumens usually are more tedious to manufacture, and can be susceptible to undesired collapse when the fibers are processed at high speeds. In addition, such fibers have exhibited inadequate mechanical strength properties, which have made it difficult to further process the fibers to form nonwoven fabrics.

25 The porous fiber 54 of the present invention, however, is subslanlially free of lumens. As a result, the fiber can exhibit an increase in melt strength during the fiber formation, and the greater melt strength can improve the in-line ~.. "~ability and stretchability of the fiber.
For example, simpler die designs can be employed to form the nascent fiber. The porous fiber can also exhibit increased mechanical strength to provide improved dimensional 30 stability, and can exhibit other improved me~.hanical properties to f~ t~ thesl Ihsequent processing of the fiber. For example, the improved me~i ,anical properties can improve the ability to further process the fibers to produce nonwoven fabric webs.
In its various aspects, the porous fiber 54 can also exhibit improved con,bi"dlions of small diameter, low denier, tensile strength, elongation, and toughness (where toughness 35 is the ability to absorb energy, as described in the Dictionarv of Fiber & Textile Technoloqv, HoechstCelanese, 1990).

CA 022~7862 1998-12-10 The various configurations of the porous fiber 54 can have relatively low diameter and relatively low denier. In particular aspects, the porous fiber can have a fiber denier of not more than about 50 . Alternatively, the porous fiber denier can be not more thanabout 20, and oplionall~/ can be not more than about 10. In other ~cr~ectC, the porous fiber can have a denier of about 0.5, or less, and optionally can have a denier of about 0.1, or less to provide improved perfommance.

In other aspects, the tensile sLr~nglh at break of the porous fiber 54 can be not less than 10 about 200 mega-Pascal (MPa). Alternatively, the tensile strength can be not less than about 250 MPa, and optionally can be not less than about 300 MPa. In other aspectc, the method and apparatus of the invention can provide for a fiber tensile strength which is not more than about 1000 mega-Pascal (MPa). Altemativeiy, the fiber tensile strength can be not more than about 750 MPa, and optionally can be not more than about 15 450 MPa to provide improYed performance and processibility during sl~hseqLIent manufaGturing operations.

In further aspects, the porous fiber 54 can exhibit a percent elongation to break of not less than about 30%, as determined by the formula: (LF- Li)/ L~; where L, is the final 20 length of the fiber at break, and Lj is the initial length of the fiber prior to elongation.
Alternatively, the elongation to break can be not less than about 50%, and optionally can be not less than about 90%. In further aspects, the method and appardLus of the invention provides for a porous fiber 54 which can exhibit a percent elongation to break of up to about 500%, or more. Alternatively, the elongation to break can be not more 25 than about 200%, and optionally can be not more than about 160% to provide desired pe,rulmance attributes and processing capabilities.

In still other aspects of the invention, the porous fiber 54 can have a toughness index of not less than about Q. 1 gram-ce- ,Li, ~ ,t:ler per denier-centimeter (g-cm/denier-cm).
30 Alternatively, the fiber toughness can be not less than about 1.5 g-cm/denier-cm, and optionally can be not less than about 2 g-cm/denier-cm. AddiLional aspects of the invention can provide for a porous fiber 54 which has a toughness index of not more than about 20 g-cm/denier-cm. Altematively, the fiber toughness index can be not more than about 10 g-cm/denier-cm, and optionally can be not more than about 5 g-cm/denier-cm to 35 provide improved performance. The toughness index represents the ability of the fiber to absorb energy, and is determined by multiplying the fiber tenacity times the fiber CA 022~7862 1998-12-lO
W O 98/03706 PCT~US97/10715 elong~Lion-at-break, and then dividing by 2. For example, a typical c~ tion would be (grams load-at-break x elongation-at-break)/(denier x 2), and may have the units of (grams-cm)/(denier-cm) 5 ~Su ' ' le testing techniques for obtaining the data for delelllli, l;~ lg the various mechanical properties of the porous fiber are further described in the Test Procedures section, set forth hereinbelow.

The porous fiber 54 can advantageously provide improved water accessi~ ty. In 10 particular aspects of the invention, the water uptake rate of the porous fiber 54 can be not less than 0.1 mg/sec. Alternatively, the water uptake rate can be not less than about 0.15 mg/sec, and optionally can be not less than about 0.2 mglsec. In other as~e.;L:" the water uptake rate can be not more than about 15 mg/sec. Altematively, the water uptake rate can be not more than about ~ mg/sec, and optionally can be not more than about 15 1.5 mg/sec to provide improved benefits. In comparison, a norlporuus fiberwill have a water-uptake rate of less than 0.1 mg/sec, as illustrated by Examples 8, 9 and 10 set forth hereinbelow.

In addition, the water-uptake amount of the porous fiber 54 can be not less than 0.1 mg 20 in 60 sec. Alternatively, the water uptake amount can be not less than about 0.2 mg in 60 sec, and optionally can be not less than about 0.3 mg in 60 sec. In other aspects, the water uptake amount may be not more than about 25 mg in 60 sec. Alternatively, the water uptake amount can be not more than about 5 mg in 60 sec, and optionally can be not more than about 2.5 mg in 60 sec to provide improved benefits. In CG~ arisOn, a 25 nonporous fiberwill have a water-uptake amount of less than 0.1 mg in 60 sec, as illustrated by Examples 8, 9 and 10 set forth below.

Suitable testing techniques for obld;";ng the data for determining the various water accessiLllity properties of the porous fiber are further described in the Test Procedures 30 section, set forth below.

A plurality of the voids or pores 52 which impart the desired porosity to the fiber 54 can be distributed over the outer surface of the fiber and can also be distributed through the interior of the fiber. In particular aspects, the porous stnucture of the fiber 54 includes 35 elongate voids of generally ellipsoidal and/or double-conical shape, such as those representatively shown in Figs. 7, 8, 9 and 9A. Desirably, the elongate voids 52 have CA 022~7862 1998-12-10 W098/03706 PCTrUS97/107~5 their long, major axes 46 aligned substantially along a length-wise, iongitudinal dimension 44 of the fiber. In particular aspects of the invention, the elongate voids can have a major axis 46 wherein the length 42 of the major axis is not less than about 0.1,um. Alternatively, the major axis length is not less than about 0.2~m, and optionally is not less than about 0.25,um. In other aspects, the length of the major axis is not more than about 30,um. Alternatively, the major axis length 42 is not more than about 1 O~um, and optionally is not more than about 7,um to provide improved pe~ ru~ ance~

To help provide for the desired combination of mechanical strength and water 10 ~Ccescihility~ particular aspects of the invention have fibers in which the voids of desired pore size dimensions constitute at least about 30% of the total number of pores on either or both of the fiber outer surface or fiber cross-section. Alternatively, the voids of the desired pore size dimensions constitute at least about 50%, and optionally constitute at least about 60% of the total number of pores on either or both of the fiber outer surface 15 or fiber cross-section.

In further aspects of the porous fibers of the invention, the voids having a maior axis length within the range of about 0.25 - 10 um constitute at least about 30% of the total number of pores on either or both of the fiber outer surface or fiber cross-section.
20 Alternatively, the voids of the 0.25 - 10 ,um pore size dimensions constitute at least about 50%, and opLionally constitute at least about 60% of the total number of pores on either or both of the fiber outer surface or fiber cross-section to provide improved mechanical and water accessibility properties.

25 The elongate pores or voids can also have an aspect ratio value which is determined by the ratio of the length 42 of the pore major axis 48 to the length 40 of a pore minor axis 46 which is aligned perpendicular to the major axis, as observed in the phoLc"": Uyl dph or other imaging or measuring mecha,1is", employed to determine the aspect ratio. In further aspects of the invention, the aspect ratio is not less than 30 about 1.3. Alternatively, the aspect ratio is not less than about 1.5, and oplionally is not less than about 2. In other aspects, the aspect ratio is not more than about 50.Alternatively, the aspect ratio is not more than about 20, and optiol-ally is not more than about 15 to provide improved porosity .:hdldcLeristics and fiber pe, rùl ",ance. The major axis of each elongate pore or void is typically an axis aligned sul,sLantially along the 35 longitudinal dimension of the fiber, and can typically be represented by the largest length measurement of each pores.

CA 022~7862 1998-12-10 WO ~8~3,~C PCTrUS97/1071S

As illustrated in Figs. 7, 8, 9 and 9A, the porous structure of the fiber 54 can have pores distributed along the outer surface of the fiber. The surface pores have a distribution with a pore number per unit of outer surface area of not less than about 0.01 /,um2.
5 Altematively, the pore number per unit of outer surface area is not less than about Q.015 /I~mZ, and optionally is not less than about 0.05 /,um2. In further aspects, the pore number per unit of outer surface area is not more than about 10 /,um2. Altematively, the pore number per unit of outer surface area is not more than about 8 /,um2, and opLionF'~y is not more than about 5 /,um2 to provide improved wt:lLdbiliLy and liquid penel~dlion.
As illustrated in Figs. 1, 2, 12 and 13, the porous structure of the invention, with respect to the cross-sectional area of the fiber 54, can exhibit pore voids with an average pore area (per pore) of not less than about 0.001 micron2 (,um2). Altematively, the average pore area (per pore) is not less than about 0.002 ,um2, and optionally is not less than 15 about 0.03 ,um2 . In other aspects, the average pore area (per pore) is not more than about 20 ,um2. Alternatively, the average pore area (per pore) is not more than about 10 l~m2, and optionally is not more than about 3 ,um2 to provide improved ~Llat "Ly and liquid penetration.

20 The porous stnucture of the fiber 54 can also have pores distributed along its cross-sectional area to provide a pore number per unit area which is not less than about 0.01/um2. Altematively, the pore number per unit of area is not less than about 0.015/,um2, and optionally is not less than about 0.1/,um2. In other aspects, the pore number per unit area is not more than about 1 0/~um2. Alternatively, the pore number per 25 unit area is not more than about 8/um2, and optionally is not more than about 5/,um2 to provide improved welldbiliL~I and liquid penetration.

In further aspects, the porous structure of the fiber 54 has pores distributed along the fiber cross-section wherein a sum of the areas of the individual, cross-sectioned pores 30 provides a total pore area which not less than about 0.1% of the total area encompassed by the cross-sectioned fiber (a percent pore area of not ~ess than about 0.1%).
Alternatively, the percent pore area is not less than about 1%, and optionally is not less than about 2%. In other aspects, the percent pore area is not more than about 70%.
Altematively, the percent pore area is not more than about 50~/0, and optionally is not 35 more than about 20% to provide improved wettability and liquid penetration.

CA 022~7862 1998-12-lO
W O 98/03706 PCTrUS97/10715 With reference to Figs. 1, 2, 9, 9A and 12, particular aspects of the porous fiber can include a plurality of voids or pores which are mainly initiated at structural irregularities or other physical non-homogenities of the fiber material, and which are stretched and 5 expanded therefrom. Such initiator, structural non-homogenities can be provided by one or more of the following meci-anis"~s: particulate filler/polymer resin interfaces, density and/or modulus fluctuations in a fiber materiai, submicron size voids and/or air bubbles, any type of inclusions having a modulus and /or density which varies from that of the fibem.,~L~rial, as well as corlJh..,aLions of the mechanisms. More particularly, the fiber 10 can desirably include a plurality of stretched or otherwise extended voids wherein each of the voids can be assouidl~d with a particulate initiator 50 provided by a rllal~lial composed of a multiplicity of individual particles, such as a particulate filler material.

The pores or voids can subslal llially surround the initiators or can be immediately 15 adjacent to the il lilidlor~. The pores may also be located in the areas bet\,veen individual in;tialur:,. Additionally, each of the extended voids can have a length which is larger than a length of its associated initiator, as observed when viewing the voids in a length-wise section taken along the fiber length. With respect to a direction along the fiber length, the voids can have a sub~l~"Lially elongated elliptical shape, andlor may have a20 sub5Ldl ,lially double-cone configuration with the two cones arranged base-to-base. With respect to a cross-section taken perpendicular to the fiber length, the voids can have a generally spherical shape or a slightly oval or egg shape. In a particular aspect of the microporous fibers of this invention, substantially no specific pattem or regular arrangement of the voids is observed in a surface view or other lengthwise view of the 25 fiber. In another aspect, substantially no specific pattem or regular arrangement of the voids is observed in a representative cross-sectional view of the fiber. Accordingly, the a,l~ngement of the voids in the fiber material can be irregular, and may be suL,~ ,';-'ly random, with some irregular clustering. For example, there may be such clustering in the areas of agglomeration of any incorporated filler material. The observed stnucture of the 30 porous fiber of the invention can have a broad pore size distribution in a particular cross-section of the fiber due to scattered pore distributions and the nature of the changing, tapering cross-sections of the pores along the length of the fiber. The elongated shapes (e.g. elliptical or double-conical shapes) of the voids and the lack of specific void distribution patterns can clearly differentiate microporous fiber structure of this invention 35 from the porous fibers obtained by a phase separation method or by other sL, ~Luhil lg CA 022~7862 1998-12-lO

methods such as the incremental sL~ t:tchi, l9 method employed for producing CELGARD
microporous fibers.

In a surface view of a CELGARD fiber at a "~ay,lifiGalion of 15 000X as ,c:p,~se,lLdLi~ely 5 shown in Fig. 11 numerous Ill;.,lupOl~S of generally oval or rectangular-like shape are arranged into strips of generally planar microporous zones aligned app,uxi,,,~Lely along the direction perpendicular to the fiber length. These strips of microporous zones are further arranged into arrays in which the strips occur in a nearly periodic regular fashion.

10 With ~efer~nce to Figs. 3 4 and 10 a porous fiber obtained by a conver,lional phase sepa,~Lion method includes a sponge-like system of pores or voids separated by relatively thin walls The system is assembled into a lacy interconnected structure which defines the pores with membrane-like walls. In the shown configuration the system forms layers of finger-like macrovoids located adjacent to the hollow fiber lumen. The 15 arrangement of the voids particularly along the fiber cross-section provides for a s~b:,L~nLially regular array. With reference to Fig. 10 the surface of the fiber appears subsLarlLially nonporous undera ,lla~niricaLion of 15 000X.

In conLIasL particular aspects of the porous fiber of the invention can include pores 20 bounded by tensile-stressed elongated regions which can for example be provided by a plastic defol",aLion in the fiber material. The stressed regions can be observed at least along boundary edges of the extended surface voids present on the exposed oute""osL
surface of the fiber. In the porous fiber of the invention the edge boundaries and edge perimeters of the fiber material are angular sharply defined subsLd"Lially nonfilamented 25 and substantially non-spongiform in the areas surrounding the extended elongated void.
Accordingly, the voids are effectively bounded by fiber material having such boundary edges and these boundary edges may be observed along any or all of the surface view cross-sectional view or bulk view of the fiber. The fiber material in the regions observed between the voids generally has the form of a plateau interrupted by the voids.
Suitable techniques for obtaining the data for determining the various pore sizeproperties and pore distributions of the porous fiber are further described in the Test Procedures section set forth below.

, CA 022~7862 1998-12-10 W O ~J'~S,~ PCT~US97/1071 Testinq Procedures Mec,l,anicai Properties:

5 A suitable technique for determining the mechanical properties of the porous fiber 54 can employ a Sintech tensiie tester (SINTFCH 1tD) and Testworks 3.03 software. The tensile tester is a device available from MTS System Co., a business having offices located in Cary, NC 27513. The software is available from MTS System Co., Sintech Division, a business having offices located in Cary, NC 27513. Equipment and software 10 having su~ala~.lially equivalent cal~kililies may also be employed.

Mecha,~i_al properties can be evaluated with the tensile tester using its fiber-testing configuration. The testing is conducted with a 10 pound (44.5 N) load cell, and air actuated, rubber coated 3 inch (7.6 cm) grips. The fiber testing is conducted with a 2 inch (5.08 cm) gauge length and a 500.00 mm/min crosshead speed. A single sample fiber is loaded perpendicular to and in the center of the grips, and is held in place when air pressure closes the grips together. The diameter of the fiber is inputted by the user before beginning the tensile testing. For the hollow fiber s~""~l~s, such as those shown in Examples 11 and 12, the annular cross-sectional area,7~ ((outer radius)2 - (inner 20 radius)2), was used for the calculation of the tensile strength. In each experiment, the fiber is stretched until breakage occurs, and the equipment software or other equipment proy~d~ lg creates a stress-versus-strain plot and c~culat~s the desired mechanical properties for the sample. The mechanical properties can include, for example, Young's modulus, stress at break, and % strain or elongation at break.
Water accese ' l~

A suitable technique for determining the comparative water accessil-ility properties of the fiber can employ a CAHN DCA 322 microbalance, a device which is available from ATI
30 (Analytical Technology, Inc.), a business having office located in Madison, Wl. The balance is sensitive to force changes as liKle as 0.1 micrograms and is equipped with two weighing positions (the "A" loop and the "B" loop), and a tare position (the "C" loop). The "A" loop can support a maximum load of 1.5 grams and the "B" loop can support a load of 3.5 grams. Thus, the A loop has better sensitivity while the B loop can support a heavier 35 load. It is understood that the operator will select the loop which provides the greater measurement sensitivity while also remaining c~r~le of measuring the maximum load CA 022~7862 1998-12-lO
WO 98/03706 PCT~US97/10715 expected during the testing. The fiber testing for the ex~,o?ios set forth herein was conducted on the "A" loop of the balance. Each fiber sample has a sufficient length (e.g about 15 mm) which allows the fiber to be operabiy taped or otherwise secured along and against a hanging wire or similar support to provide a test sample. In the test sample, a 5 mm length of the support wire and its adjacenLly held fiber sampie extends below the tape and remains exposed and available for contact with the water during testing.

The CAHN system includes a movable stage which can be l~anslaLed at a steady rate up 10 and down. The test sample is hung from or otherwise mounted onto the selected loop of the balance, and a beaker of water is placed on the moveable stage. The stage isbrought up so that the lower edge of the sample is just above the water surface, and the test is begun. Software, which is provided with the CAHN system, conL,ols the experiment in accordance with parameters which are input by the user. For the fiber 15 testing, the test sample is installed on the balance, and the balance is tared to provide a measure of water uptake as the sample is in contact with the water. The software is instructed to collect force readings at one second intervals. A 2 mm length of the exposed portion of the test sample is immersed into the water, and the stage is stopped.
The test sample is left in the water for 1 minute as the software collects force readings at 20 the one second intervals. The test sample is then pulled back out of the water.

The data collected from an experiment is then evaluated. In particular, the data can be exported into suitable spreadsheet software, such as ~l~i.,,usc,~( Exce/ ver~Jon 5.0, and processed to generate a plot of wei~ht versus time for the 1 minute soak in the water.
25 The plot shows the trend of water uptake for the test sample, and provides a convenient basis for co, npa, i"g the relative water uptake pe, ru" "ance and the relative levels of water a-~e s ~ ' ."ly of different fiber samples. To allow a better co" ,parison between sd"~Fles of different size fiber, the plotted data of the weight gain as function of time for the different samples were normalized based on a fiber having a weight of 0.0416 mg.
30 The norm~'i~tion factor was the ratio of the dry weight of the tested fiber to 0.0416 mg.
The water uptake rate is determined at the two-second time mark of the curve generated by plotting the no""ali~ed weight increase versus the amount of elapsed time during the one minute soaking period. The water uptake rate shown in the examples was determined by c~lculating the slope of the plotted curve at the data point recorded in the 3~ first second of the data measurement, as representatively shown in Fig. 14. The water uptake amount listed in the examples was the total weight gain recorded at the 1 minute CA 022~7862 1998-12-10 W 098/03706 PCTrUS97/10715 (60 sec) time of measurement in the data plot. It should be noted that the measured and recorded weight gain may include a weight gain due to the water absorbed into the initial porous stnJcture, as well as weight gains due to other i"Lera.,Lions between the fiber and water. For example, a coating layer of water can form on the fiber. In addition, the fiber 5 structure can swell to provide pores with increased void volume, or the fiber can othe~wise change in configuration to provide an increased capacity for acquiring and holding absorbed water.

Scannin~ Electron Microscopy and Imaqe Analysis:
Electron photon.:~,ùgraphs can be generated by conventional techniques which are well known in the imaging art. In addition, the samples can be prepared for the desired i",ay;.lg by employing well known, conventional preparation techniques.

15 Since the porous fiber of the invention can be very ductile even at low temperatures, it is important to avoid an excessive smearing of the fiber ~aLerial wllen the fiber sample is being cut and prepared for an imaging of the fiber cross-section. In a suitable p,~:pa,dLion technique, the samples can, for example, be submerged in ethanol for 1 hour and then plunged into liquid nitrogen. For the fiber cross-sections, the surfaces can be 20 prepared by cryorl~ ulo~y, such as by using a Reichert Ultracut S microtome with FCS
cryo-sectioning system (Leica, Deerfield, IL), in which a fresh 6 mm glass knife at temperatures of -180 ~C is used. The resulting fiber can then be mounted on an app,upriate stub and coated with gold orAu/Pd (gold/palladium). The fiber Il u:,L,ucture can be imaged by scanning electron microscopy, such as by using a JSM
25 6400 (JEOL, Peabody, MA) scanning electron microscope with both secondary and bac.kscdLler electron detectors.

Automated image analyses of voids and fiber pores can be conducted by well known, conventional techniques. Ex&lllples of such techni~ues are described in "APPLICATION
30 OF AUTOMATED ELECRON MICROSCOPY TO INDIVIDUAL PARTICLE ANALYSISU by Mark S. Germani, AMERICAN LABORATORY, published by Inter"aLional Sci 3r)liliC
Communications, Inc.; and in "INTRODUCTION TO AUTOMATED PARTICLE
ANALYSIS" by T. B. Vander Wood (copyright 19g4, MVA, Inc., 550 Oakbrook Parkway #200, Norcross, GA 30093), Proc. 52nd Annual Meetinq of the Mk,luscopv Society of 35 America. G. W. Bailey and A. J. Garratt-Reed, Eds., published by San Francisco Press.

CA 022~7862 1998-12-10 W 098/03706 PCTrUS97/10715 The image analyses to provide pore distribution data for Example 1 was conducted by Materials Analytical Services, a laboratory having offices located at Norcross, GA. The image analyses to provide pore distribution data for Example 4 was conducted by MVA, Inc., a laboratory having offices located at Norcross, GA.

The various image analyses can, for ekd"~ le, be done with a Noran Voyager imageanalysis system employing a may"iriuc,lion of 5,000X. The data are gener~led by taking average of a total of twelve fields. The system is avaiiable from NORAN Instnument, Inc., 10 a business having offices in Middleton, Wl, and systems c~r~ of providing substantially equivalent pe,~o,i"ance may also be er", '~yed. During the course of the image analyses, the image of the porous stnucture can be digltized employing conventional techniques. An example of a digitized image is representatively shown in Fig. 13.
Optical Microscopy To examine the microstructure along the outside surface of the porous fiber, optical microscopy can be a suitable technique. In particular, conventional oil-i,l".,er:,;on optical microscopy can be employed . With this technique, the sa""~lEs are pr~pal~d by placing 20 in an immersion oil having a refractive index (Nd) of 1.516 at 23 ~C on a glass slide, and are coverslipped. The immersion oil can be an oil available from OLYMPUS OPTICALCO. LTD., a business having offices in Lake Success, NY. The samples are photographed using an oil immersion 100X objective, a high-speed film, such as Kodak Gold 400 ASA, 35 mm film, and using daylight temperature illumination. A sl l L I 'e 25 ,,,;c,uscope is a OLYMPUS BH-2 optical mic,uscope, which is available from OLYMPUS
OPTICAL CO. LTD.,, a business having offices in Lake .Success, NY. Other opticalmicroscopes and equipment having substantially equivalent c~p~hi"lies may also be employed.

30 The following Examples are to provide a more detailed understanding of the invention.
The examples are representative and are not intended to specifically limit the scope of the invention.

CA 022~7862 1998-12-10 ExamPle 1:

A resin composed of polypropylene (Himont PF301) ( 90 wt%3 and TiO2 filler particles (SCC 4837 by Standridge Color Corporation) (10 wt%) was i"te"-,;xed with Dow Coming 5 D193 su, rdcldl ,l (6 wt%, based on the total weight of the filler and the resin) by extruding twice through laboratory Haake twin screw extruder. The TiO2 particie size was in the r~nge of about 0.1 to 0.5 microns (~m), as measured by a scanning electron ~ r~copy (SEM). The concentrations of the fillers were measured by ashes analysis. The SIJI racLa~ ,t Dow Coming D193 had a HLB number of 12.2. The fiber spinning process 10 included feeding the COIll~ ed materials into a hopper and extruding the materials through a single-screw extruder having a length-to-cJid",eler ratio of 24 (L/D = 24/1). The extruder had three heating zones, a metering pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0.3 mm. During the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 40. During the 15 quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metering coating die. The first surface-active liquid was a solution cor"posed of isopropanol and water mixed in a ratio of 9-parts isopropanol to 1-part water, by volume. The fiber was then stretched in air by 2X (a draw ratio of 2), followed by sL,~tcl,ing by 1.7X (a draw ratio of 1.7) in a bath provided by a second surface-active 2Q liquid. The second surface-active liquid was a solution composed of isop~upanol and water mixed in a volume ratio of 9-parts isopropanol to 1-part water. The fiber was then heat-set at 80 ~C before accumulation onto a winder. The mechanical prupei lies of the resultant porous fiber were then measured by a Sintech tensile tester, and are su."illdli~ed in the following TABLES 1 and 2. The number of pores per l-m2 of cross-25 section of the fiber was about 0.74 and the number of pores per IJm2 of extemal surfacewas about 0.08.

ExamPle 2:

A resin composed of polypropylene 95.3 % (Himont PF301); 1.4 % TiO2concentrate, i"o,gar,ic filler (SCC 4837 by Standridge Color Cor~ordiion) and 3.3 wt.% of powdered polydimethyl silsesquioxane, organic filler (Dow Coming #23 Additive); was intermixed with 6 wt.% (based on the total weight of the resin and the filler) of a silicone glycol surfactant ~Dow Corning D193) by extruding twice through laboratory Haake twin-screw extruder. The particle size of the organic filler ranged from 1 to 5 ",i~,,c"~s as measured by SEM. The combined material was then extruded through a single-screw extruder CA 022~7862 1998-12-lO
W O 98103706 PCT~US97/10715 (UD = 24/1), which included three heating zones, an on-line static mixer, a metering pump, and a spi"pack with 4 holes, each hole having a dialneLer of 0.3 mm. During the spi. .ni. ,g extrusion of the fiber, the fiber was subjected to a draw-down ratio of 33.
During the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-5 active liquid delivered through a metering coating die. The first surface-active liquid was a solution composed of 2 wt.% of a s~" racLdnl (IGEPAL RC-630) in a isoprupanol/water solvent. The solvent was composed of isopropanol and water mixed in a volume ratio of 9-parts isopropanol to 1 -part water. The fiber was then stretched in air by 1.1 7X, and subsequently stretched by 2X in bath provided by a second suRace-active liquid. The 10 second surface-active liquid was a solution composed of isopropanol and water mixed in a ratio of 9-parts isopropanol to 1-part water, by volume. The fiber was then heat-set at 8~; ~C in an on-line oven before accumulation onto a winder. The mechanical properties of the porous fiber were then measured by a Sintech tensile tester, and are summarized in the following TABLE 1.
ExamPle 3:

A resin composed of 93.2 wt.% polypropylene (Himont PF301); 1.4 wt.% TiO2 concenl,dLe (SCC 4837 by Standridge Color Corporation) and 5.4 wt.% CaC03 20 ~Omyacarb UF from Omya Inc.), which was suriace-modified with 6 wt% (based on the weight of the filler) of silicone glycol D193 surfactant, was intermixed by extruding twice through a laboratory Haake twin-screw extruder. The particle sizes of the CaC03 filler were within the range of 1 to 3 microns, as measured by SEM. The combined material was then extruded through a single-screw extruder (i~D = 24/1), which include an on-line 25 static mixer, a metering pump, and a spinpack with 8 holes, each hole having a clia"leter of 0.3 mm. During the spinning extrusion, the fiber was subjected to a draw-down ratio of 33. During the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metering coating die. The first surface-active liquid was a solution composed of isopropanol and water mixed in a volume ratio of 9-30 parts isopropanol to 1-part water. The fiber was then stretched in air by 1 .17X, and subsequently stretched 2X stretching in a bath provided by a second quantity of surface-active liquid. The second surface-active iiquid was a solution composed of 1 wt%IGEPAL RC-630 in a isopropanol/water solvent. The solvent was composed of isop.opanol and water mixed in a volume ratio of 9-parts isopropanol to 1-part water.
35 The fiber was then heat-set at 80 ~C before accumulation onto a winder. The CA 022~7862 1998-12-10 W 098~,.C PCTrUS97/10715 mechanical properties of the porous fiber were then measured by a Sintech tensile tester, and are su, l " "a, i~ed in the following TABLE 1 ExamPie 4:

A resin composed of 88.8 wt% polypropylene (Himont PF301), 1.3 wt% TiO2 concentrate (SCC 4837 by Standridge Color Corporation), and 9.9 wt% CaC03 (Omyacarb UF from Omya, Inc.) which was surface-modified by 6 wt% (based on the weight of the filler) of silicone glycol D193 surfactant, was intermixed by extruding twice through a laboratory Haake twin-screw extruder. The particle sizes of the CaC03 were within the range of 1 to 3 ~ uns as measured by SEM. The combined ~"alerial was then extruded through a single-screw extruder (L /D = 24/1), which included three heating zones, an on-line static mixer, a metering pump, and a spinpack with 15 holes, each hole having a diameter of 0.5 mm. During the extrusion-spinning operation, the fiber was suhjer-t~d to a draw-down ratio of 4û. During quenching, the nascent fiberwas pre-wetted with a first surfacs-active liquid delivered through a metering coating die. The first surface-active liquid was composed of a mixture of isopropanol and water provided at a volume ratio of 9.8-parts of isopropanol to 0.2-parts water. The fiberwas then stretched in air by 1.5X, and sl Ihsec~Llently stretched by 1 .4X in a bath provided by a second quantity of surface-active liquid. The second surface-active liquid was composed of isop, c,panol and water mixed in a volume ratio of 9-parts isopropanol to 1-part water. The fiber was then heat-set at 90 ~C with an on-line oven, followed by collecting through a web forming box. The me~;hanical properties of the porous fiber were then measured by a Sintech tensile tester, and are summarized in the following TABLES 1 and 2. The number of pores per ,um2 of cross-section of the fiber was about 0.19.

ExamPle 5:

A resin composed of polypropylene (Himont PF301) ( 90 wt%) and TiO2 filler particles (SCC 4837 by Standridge Color Corporation) (10 wt%) was intermixed with Dow Corning D193 surfactant (6 wt%, based on the total weight of the filler and the resin) by extnuding twice through laboratory Haake twin screw extruder. The TiO2 particle size was in the range of 0.1 to 0.5 ",;~,,uns, as measured by a scanning electron microscopy (S~M). The concenl, dliol Is of the fillers were measured by ashes analysis. The s-, r~cldnl Dow Coming D193 had a HLB number of 12.2. The fiber spi,)ni. ,g process included feeding the combined materials into a hopper and extruding the materials through a single-screw CA 022~7862 1998-12-10 W 098/03706 PCT~US97/10715 extruder having a length-to-diameter ratio of 24 (UD = 24/1). The extruder had three heating zones, a metering pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0.3 mm. During the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 11. During the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metering coating die. The first surFace-active liquid was a solution composed ofisop,upallol and water mixed in a ratio of 9-parts isopropanol to 1-part water, by volume.
The fiber was then stretched in air by 1 .58X followed by stretching by 2.2X in a bath provided by a second surface-active liquid. The second surface-active liquid was a 10 solution composed of isopropanol and water mixed in a volume ratio of 9-partsisoprupanol to 1-part water. The fiber was then heat-set at 80 ~C before accumulation onto a winder. The mechanical properties of the resultant porous fiber were thenmeasured by a Sintech tensile tester, and are su~lmdli~ed in the following TABLE 1.

15 Example 6:

A resin composed of polypropylene (Itimont PF301) ( 90 wt%) and TiO2 filler particles (SCC 4837 by Standridge Color Corporation) (~0 wt%) was intermixed with Dow Coming D193 surFactant (6 wt%, based on the total weight of the filler and the resin) by extruding 20 twice through laboratory Haake twin screw extnuder. The TiO2 particle size was in the range of 0.1 to 0.5 ~ uns, as measured by a scanr,;ng electron Illi~.~Uscopy (SEM). The concenL,~Iions of the fillers were measured by ashes analysis. The surfactant Dow Corning D193 had a HLB number of 12.2. The fiber spinning process included feeding the combined materials into a hopper and extruding the materials through a single-screw 25 extruder having a length-to-dian~eler ratio of 24 (UD = 24/1). The extruder had three heating zones, a metering pump, an on-line static mixer, and a sp;npac,lc with 4 holes, each hole having a dia~eLer of 0.3 mm. During the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 11. During the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a 30 metering coating die. The first surface-active liquid was a solution composed of isopropanol and water mixed in a ratio of 9-parts isopropanol to 1-part water, by volume.
The fiber was then sLI~t~;hed in air by 1 .17X followed by ~LIeIUI ,i"g by 1 .5X in a bath provided by a second surface-active liquid. The second surface-active liquid was a solution cor,.posed of isopropanol and water mixed in a volume ratio of 9-parts 35 isoprupanol to 1-part water. The fiber was then heat-set at 80 ~C before accumulation CA 022~7862 1998-12-lO
W 098/03706 PCT~US97/10715 onto a winder. The mechanical properties of the resultant porous fiber were thenmeasured by a Sintech tensile tester, and are summarized in the foilowing TABLE 1.

E-xamPle 7:
A resin composed of polypropylene (Himont PF301) ( 90 wt%) and TiO2 filler pdl'- '-S
(SCC 4837 by Standridge Color Corporation) (10 wt%) was intermixed with Dow Corning D193 surfactant (6 wt%, based on the total weight of the filler and the resin) by extruding twice through laboratory Haake twin screw extruder. The TiO2 particle size was in the 10 range of 0.1 to 0.5 m;_~unS, as measured by a scanr,;.,g electron ",;c,uscopy (SEM). The conce~,L(dlions of the fillers were measured by ashes analysis. The surfactant Dow Coming D193 had a HLB number of 12.2. The fiber spinning process included feeding the combined ,I,aLerials into a hopper and extruding the ll,~lerials through a single-screw extruder having a length-to-diameter ratio of 24 (UD = 24t1). The extruder had three 15 heating zones, a metering pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0.3 mm. During the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 33. During the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a ",ete,i"g coating die. The first surface-active liquid was a solution composed of 20 isopru~ar,ol and water mixed in a ratio of 9-parts isop, upanol to 1 -part water, by volume.
The fiberwas then stretched in air by 1.17X followed by ~llelCh;~l9 by 1.5X in a bath provided by a second surface-active liquid. The second surface-active liquid was a solution composed of isopropanol and water mixed in a volume ratio of 9-parts isopropanol to 1-part water. The fiber was then heat-set at 80 ~C before accumulation 25 onto a winder. The mechanical properties of the resultant porous fiber were then measured by a Sintech tensile tester, and are sun""d,i~ed in the following TABLE 1.

Example 8:

A resin composed of polypropylene (Himont PF301 ) ( 90 wt%) and TiO2 flller pa, Licl&s (SCC 4837 by Standridge Color Corporation) (10 wt%) was intermixed with Dow Coming D193 su, faulanl (6 wt%, based on the total weight of the filler and the resin) by extruding twice through laboratory Haake twin screw extruder. The TiO2 particle size was in the range of 0.1 to 0.5 ~ U1~5, as measured by a s~ann;.,g electron microscopy (SEM). The cûl)cenlralions of the fillers were measured by ashes analysis. The surraclant Dow Corning ~193 had a HLB number of 12.2. The fiber spinning process included feeding CA 022~7862 1998-12-lO
W O 98/03706 PCTrUS97/10715 the combined materials into a hopper and extruding the rnaleriais through a single-screw extruder having a length-to-diameter ratio of 24 (UD = 24/1). The extruder had three heating zones a metering pump an on-line static mixer and a spinpack with 4 holes each hole having a diameter of 0.3 mm. During the spinning extrusion of the fiber the 5 fiber was allowed to free-fall. During the quenching of the fiber the nascent fiber was pre-wetted with a surface-active liquid delivered through a metering coating die. The surface-active liquid was a solution composed of isop,upa"ol and water mixed in a ratio of 9-parts isopropanol to 1-part water by volume. The mecha~ properties of the resultant porous fiber were then measured by a Sintech tensile tester and are 10 su",n~a,i ed in thefollowing TABLE 1.

ExamPle 9:

This sample was composed of a commercially available polypropylene staple fiber which 15 was obtained from American E~armag a business having offices located in Chariotte North Carolina. The staple fiber had a fiber length of 38 mm and was SUI taclanl-modified by in""e,~i"g in a solution of 10 wt% hyd,uphilic silicon glycol (Dow Coming 193) su, r~la"l in acetone for 1 hour and drying at ~0 ~C for 6 hours before testing. The properties of the fiberwere measured and are su,.""a,i,ed in the following TABLE 1.
Example 10:

This sample was composed of a commercially available polypropylene staple fiber having a fiber length of 38 mm and was obtained from American Barrnag a business25 having oflices located in Charlotte North Carolina. The properties of the fiber were measured and are summarized in the following TABLE 1.

ExamPle 11:

30 This sample is a conventional porous fiber obtained from Asahi Medical Co. Ltd. a business having offices located in Tokyo .lapan. As representatively shown in Figs. 3 4 and 10 the fiber had a lumen which extended longitudinally along the fiber length through the fiber interior. It is believed that the porous structure in the illustrated fiber was created by a solution spinning technique where the lumen configuration aliowed an 35 introduction of the coagulation liquid to contact the nascent fiber along both an inside and outside surface of the fiber material. The structure has large finger-like pores within CA 022~7862 l998-l2-lO

the inner wall of the fiber and has a sponge-like configuration of lacy pores in the vicinity of the outer wall. In addition, the fiber typically has a thin, skin layer at its outer surface, which may prevent the penetration water into the fiber. The properties of the flber were measured and are su~""ldli~ed in the following TABLE 1.

ExamPle 12:

This sample is another conventional porous fiber distributed under the tradenameCELGARD by Hoechst Celanese, a business having offices in Cha~lolle, North Carolina.
10 As representatively shown in Figs. 5 ,6, and 11, the fiber had a longit~c'i ,al lumen, and it is believed that the porous stnucture of the fiberwas created by a prucess whichemployed a piurality of incremental sll~t~hillg steps. The structure, as shown in the cross-sectional view, includes a lamellar-like structure produced by creating inter-lamellar volume in a pre-crystalline structure. In this structure, the pore conldil Is rr,:. uriL,rils that 15 orienL~d in the length-wise direction of the fibers and joint portions which are con,~osed of stacked lamella. The properties of the fiberwere measured and are su..,l..a~i~ed in the following TABLE 1 Example 13:
This sample is a microporous polypropylene fiber which is shown in example 1 of U.S.P. 4,550,123 owned by Albany Intemational, a business having offices located in Mansfield, MA. According to the descl i~lion of example 1 in the patent, the fiber had a denier of 8.8 d. Other properties of the fiber are listed in the following TABLE 1.

WO 98/03706 PCTrUS97/1071S

Example Water- Water- Break F.long~tion Fiber Tvu~lu~
No. uptake rateuptakestressat break size index (mg/sec) (mg per(MPa)(~/O) ~g-cm per 1 min.) denier-cm) 0.79 1.2 427 157 4.7 d 4.2 2 0.58 1.1 391 111 5.7 d 2.7 3 0.84 1.5 310 95 5.8 d 1.8 4 0.89 1.3 358 150 1.8 d 3.3 1.01 1.8 295 119 16 d 2.2 6 0.67 1.4 231 168 18 d 2.4 7 0.21 0.3 251 183 5.6 d 2.9 8 0.014 0.015 47 966 68 d 2.8 9 0.02 0.25 220 55 2.8 d 0.75 0.002 0.005 362 60 2.8 d 1.30 11 --- --- 8.4 10.1 300 0.003 microns 12 --- -- -- 51 207 300 0.65 microns 13 -- --~ 217 23 8.8 d 0.30 5 Having thus described the invention in rather full detail, it will be readily apparent that various changes and modifications can be made without departing from the spirit of the invention. All of such changes and modifications are contemplated as being within the scope of the invention, as defined by the subjoined claims.

Claims (20)

We claim:

1. A porous fiber which includes voids therein, said fiber having:
a denier of not more than about 50;
a percent elongation at break of not less than about 30%; and a tensile strength at break of not less than about 200 MPa.

2. A fiber as recited in claim 1, wherein said fiber has a denier of not more than about 20.

3. A fiber as recited in claim 1, wherein said fiber has a denier of not less than about 10.

4. A fiber as recited in claim 1, wherein said fiber has a percent elongation at break of not less than about 50%.

5. A fiber as recited in claim 1, wherein said fiber has a percent elongation at break of not less than about 90%.

6. A fiber as recited in claim 1, wherein said voids include surface voids which are irregularly distributed over an outer surface of said fiber.

7. A fiber as recited in claim 1, wherein said voids include voids which are irregularly distributed through a cross-section of said fiber.

8. A fiber as recited in claim 1, wherein said fiber includes voids having an elongate shape.

9. A fiber as recited in claim 8, wherein said fiber includes voids having generally ellipsoid shape.

10. A fiber as recited in claim 8, wherein said elongate voids have major axes thereof aligned substantially along a longitudinal dimension of said fiber.

11. A fiber as recited in claim 8, wherein said elongate voids have major axes thereof which measure not less than about 0.1 µm in length.

12. A fiber as recited in claim 8, wherein said elongate voids have major axes thereof which measure not more than about 30 µm in length.

13. A fiber as recited in claim 6, wherein said voids have an average distributional density of not less than about 0.01 voids per µm2 of said outer surface.

14. A fiber as recited in claim 6, wherein said voids have an average distributional density of not more than about 10 voids per µm2 of said outer surface.

15. A fiber as recited in claim 7, wherein said voids have an average distributional density of not less than about 0.01 voids per µm2 of said cross-section.

16. A fiber as recited in claim 7, wherein said voids have an average distributional density of not more than about 10 voids per µm2 of said cross-section.

17. A fiber as recited in claim 1, wherein said porous fiber is substantially free of lumens.

18. A fiber as recited in claim 1, wherein said fiber is composed of a fiber material, and said fiber includes a plurality of voids which are initiated at structural discontinuities of said fiber material.

19. A fiber as recited in claim 1, wherein said fiber includes a plurality of extended voids, each of which has an associated particulate initiator, and wherein each said extended void has a length which is larger than a length of its associated particulate initiator.

20. A fiber as recited in claim 1, wherein said fiber is composed of a fiber material and wherein said voids are bounded by fiber material having angular boundary edges.