NZ333655A

NZ333655A - Microporous fibres having a denier of not more than 50, a elongation break of not less than 30% and a break strength of not less than 200 mpa

Info

Publication number: NZ333655A
Application number: NZ333655A
Authority: NZ
Inventors: Fu-Jya Tsai; Vasily Aramovich Topolkaraev
Original assignee: Kimberly Clark Co
Priority date: 1996-07-23
Filing date: 1997-06-19
Publication date: 1999-10-28
Also published as: JP2000514882A; HUP9903824A3; EP0914502A1; CO4850632A1; AU719272B2; PL331150A1; HUP9903824A2; DE69716603T2; EP0914502B1; KR20000067995A; WO1998003706A1; CN1097101C; KR100488383B1; ID19284A; EG21213A; CN1226292A; BR9710757A; PE100398A1; IL127472A0; AR008779A1

Description

<div class="application article clearfix" id="description"> New Zealand No 333655 International No. PCT/US97/10715 TO BE ENTERED AFTER ACCEPTANCE AND PUBLICATION Priority dates 23 07 1996,04 09 1996, Complete Specification Filed 19 061997 Classification (6) D01D5/247 Publication date 28 October 1999 Journal No 1445 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Title of Invention Microporous fibers Name, address and nationality of applicant(s) as in international application form KIMBERLY-CLARK WORLDWIDE, INC , a Delaware company of 401 North Lake Street, Neenah, Wisconsin 54956, United States of America WO 98/03706 PCT/US97/107I5 MICROPOROUS FIBERS 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 mechanical 5 properties Background of the Invention Porous fibers have included structures made by employing conventional phase 10 separation methods, Suchmethods 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 interconnected porous structure Other porous fibers have been produced by techniques which employ a blowing agent or a swelling agent to create a microporous structure Still other porous 15 materials have been produced by employing an environmental crazing technique Conventional porous fibers, such as those descnbed above, have not been able to provide desired combinations of mechanical properties and water accessibility In addition, the techniques have not adequately produced porous fibers having desired 20 combinations of small diameter, low denier, high wettability, high permeability to liquid, and high tensile strength As a result, there has been a continued need for fibers having improved porous structures Bnef Description of Invention 25 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 vanous aspects the porous fiber of the invention can effectively and efficiently produce fibers having desired combinations of small size, high wettability, high water-accessibility, high tensile strength and high elongation As a result, the fiber can have an 1 Printed from Mimosa WO 98/03706 PCTYUS97/10715 improved ability to be further processed to form nonwoven fabrics and other articles of manufacture Bnef Description of the Drawings 5 The present invention will be more fully understood and further advantages will become apparent when reference is made to the followed detailed descnption of the invention and the drawings, in which 10 Fig 1 is a scanning electron photomicrograph, taken at a magnification of 850X, showing a representative cross-sectional view of the porous fiber of the present invention, Fig 2 is a scanning electron photomicrograph, taken at a magnification of 1,700X showing an enlarged view of a portion of the cross-section shown in Fig 1, 15 Fig 3 is a scanning electron photomicrograph, taken at a magnification of 250X, showing a representative cross-sectional view of a pnor art fiber which includes a lumen, Fig 4 is a scanning electron photomicrograph taken at a magnification 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 scanning electron photomicrograph, 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 stretching process. Fig 6 is a scanning electron photomicrograph, taken at a magnification 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 photomicrograph, based on oil-immersion optical microscopy 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 2 Printed from Mimosa WO 98/03706 PCT/US97/1071S Fig 9 shows a representative view of the voids along the outer surface of another porous fiber of the invention, taken at a magnification 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 magnification of 15.000X, providing a representative view of the surface of the fiber shown in Fig 3 , 10 Fig 11 is a scanning electron photomicrograph, taken at a magnification of 15.000X, providing a representative view of the surface of the fiber shown in Fig 5, Fig 12 shows a backscattered electron photomicrograph, taken at a magnification of 5 000X, showing a representative cross-sectional view of a fiber of the invention, 15 Fig 13 shows a representative version of Fig 12 which has been digitized for image analysis, Fig 14 shows a representative, graphical plot of the gained weight of water versus time 20 for a porous fiber sample Detailed Descnption of the Invention With reference to Figs 1, 2, 7, 8, 9, 9A and 12, a porous fiber 20 includes a length-wise 25 dimension 44 and a generally cross-wise dimension 38 The porous fiber has a distinctive configuration of voids or pores 22 therein to achieve desired levels of wettability, liquid penetration and other liquid accessibility 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 30 200 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, distnbutions and configurations In its vanous aspects, the microporous fiber of the invention can provide for improved 35 wicking can more quickly bnng water or other liquid into the intenor of a fibrous article, and can accelerate the dissolution kinetics for fibrous articles which are intended to be 3 Printed from Mimosa WO 98/03706 PCT/US97/10715 flushable In addition, the microporous fiber can help provide for improved absorbency, improved distribution of liquid, improved the breathability in articles, such as surgical gowns and diapers, Improved tactile and aesthetic properties, and/or enhanced biodegradability The fibers can be formed directly into nonwoven webs with 5 conventional forming processes, such as the well known spunbond process Alternatively, the fiber may he cut into staple fibers, and may be blended with other fibers for subsequent formation into nonwoven, fibrous webs employing conventional air-laying techniques The nonwoven webs may be particularly useful for producing flushable personal care products, such as diapers, tampons, feminine pads, pantilmers, tampon 10 strings and the like In the vanous configurations of the present ir> mention the porous fiber 54 can be a synthetic fiber produced from a source material which includes a thermoplastic, onentable matenal, such as thermoplastic and onentable polymers, copolymers, blends, 15 mixtures, compounds and other combinations thereof Desirably, the thermoplastic matenals do not include highly reactive groups In particular arrangements of the invention, the source matenal can be a polyolefinic matenal For example, the source matenal may include homopolymers of polyethylene 20 or polypropylene, or may include copolymers of ethylene and polypropylene In other arrangements the source matenal may include another polymer material, such as a polyether, a copolyether, a polyamid, a copolyamid, a polyester or a copolyester, as well as copolymers, blends, mixtures and other combinations thereof 25 The thermoplastic matenal is melt proressible and in particular aspects of the invention, the matenal can have a melt flow rate (MFR) value of not less than about 1 g/10 minutes (based on ASTM D1238-L) Alternatively, the MFR value can be not less than about 10g/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 g/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 processibility Such melt processible, thermoplastic matenal can, for example, be provided by a 35 homopolymer polypropylene Commercially available polyolefins, such as Himont PF 301, PF 304, and PF 305, Exxon PP 3445, Shell Polymer E5D47, are also 4 Printed from Minon WO 98/03706 PCT/US97/10715 representative of suitable materials Still other suitable materials can include, for example, random copolymers, such as a random copolymer containing propylene and ethylene (e g Exxon 9355 containing 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, olefimc elastomers, and low molecular weight parafins or other lubncating additives Various pigment additives may also be incorporated For 10 example, pigment concentrates such as a titanium dioxide pigment concentrate with low molecular weight polyethylene plastlcizer can be employed as a processing additive The vanous 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 spinning, and stretching processes 15 The source material for the fiber 54 can also include a further supplemental matena!, and the supplemental material may include a filler matenal, and/or a surfactant or other surface-active matenal The filler material can be a particulate matenal which can help provide porosity-initiating, debonding sites to enhance the desired formation of pores 20 during the vanous stretching operations applied to the fiber The filler matenal can help provide a desired surface-modified fiber, and can help enhance a desired "sliding effect" generated dunng subsequent stretching operations In addition, the filler matenal help preserve the pores that are generated dunng the vanous stretching operations 25 Where the supplemental matenal includes a surface-active matenal, such as a surfactant or other matenal having a low surface energy (e g silicone oil), the surface-active matenal can help reduce the surface energy of the fiber as well as provide lubncation among the polymer segments which form the fiber The reduced surface energy and lubncation can help create the "sliding effect" dunng the subsequent stretching 30 operations The supplemental filler matenal can be organic or inorganic, and the filler matenal is desirably in the form of individual, discrete particles The fillers may be subjected to a surface treatment with vanous coatings and surfactants to impart an affinity to the 35 polymer resin in the source matenal, to reduce agglomeration, to improve filler dispersion, and to provide a controlled interaction with fluids, such as body fluids, blood 5 Printed from Miraooi WO 98/03706 PCT/US97/10715 or water Examples of an inorganic filler can include metal oxides, as well as hydroxides, carbonates and sulfates of metals Other suitable inorganic filler matenals can include, for example, calcium carbonate, vanous kinds of clay, silica, alumina, banum sulfate, sodium carbonate, talc, magnesium carbonate, magnesium sulfate, banum carbonate, 5 kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, titanium dioxide, powdered metals, glass microspheres, or vugular void-containing particles Still other inorganic fillers can include those with particles having higher aspect ratios, such as talc, mica, and wollastonite, but such fillers may be less effective Representative organic fillers can include, for example, pulp powders, wood powders cellulose 10 denvatives, chitin, chitosan powder, powders of highly crystalline, high melting polymers, beads of highly crosslinked polymers, powders of organosilicones, and the like, as well as combinations 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 (jun) Alternatively, the average particle size can be not more than about 5 nm and optionally, can be not more than about 1 urn to provide improved processibility In other aspects of the invention, the top cut particle size is not more than about 25 ^ Alternatively, and the top cut particle size can be not more than about 10 nm, and optionally can be not more than about 4 nm to provide improved 20 processability dunng 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 matenals, such as steanc or behenic acid, which can be employed to improve the processibility of the source matenal 25 Examples of suitable filler matenals can indude one or more of the following (1) Dupont R-101 TiOj, which is available from E I DuPont de Nemours, and can be supplied in a concentrate form by Standnch Color Corporation, a business having offices located in Social Circle, Georgia 30279 This matenal can provide good processibility 30 (2) Pigment Blue 15 1(10 % copper), which is distnbuted by Standndge Color Corporation Fibers produced with this matenal may break more often (3) OMYACARB*UF CaC03, which is available from OMYA, Inc, a business having offices located in Proctor, Vermont 05765 This matenal can have a top cut particle size of about 4 ^ and a average particle size of about 0 7nm. and can provide 35 good processibility This filler can be coated with a surfactant, such as Dow Coming 193 6 Print"°d from Mimosa WO 98/03706 PCT/US97/10715 surfactant, before the compounding or other combining with the source matenal 56 The filler can also be coated with other appropriate surfactants, such as those mentioned elsewhere in the present descnption (4) OMYACAR B ® U FT CaCOj coated with steancacid, which is available from 5 OMYA, Inc This matenal can have a top cut particle size of about 4 nm and a mean particle size of about 0 7^i n, and can provide good processibility (5) SUPERCOAT™ CaC03 which Is available from ECC International, a business having offices located in Atlanta Georgia 30342, 5775 Peachtree-Dunwoody Road This matenal can have a top cut particle size of about B pm and a mean particle size of 10 about 1 pm Fibers produced with this matenal may break more often (6) Powdered polydimethyl silsesquioxane (#22 or #23 Dow Coming Additive), which is available from Dow Coming, a business having offices located in Midland, Michigan 48628-0997 This matenal can provide good processibility, while some agglomerations may be observed 15 The supplemental matenal can optionally include a surface-active matenal, such as a surfactant or other matenal having a low surface energy (e g silicone oil) In particular aspects of the invention, the surfactant, or other surface-active matenal, can have a Hydrophile-Lipophile Balance (HLB) number which is not more than about 18 20 Alternatively, 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 wettability When the HLB number is too high, the surfactant may have insufficient 25 adhesion to the polymer matnx of the source matenal, and may be too easily washed away dunng use The HLB numbers of commercially available surfactants can, for example, be found in McCUTCHEON's Vol 2 Functional Matenals, 1995 A suitable surfactant can include silicon glycol copolymers carboxilated alcohol 30 ethoxylates, vanous ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated fatty esters and the like, as well as combinations thereof Other suitable surfactants can, for example, include one or more of the following (1) surfactants composed of ethoxylated alkyl phenols, such as IGEPAL RC-620, RC-630, CA- 620, 630, 720, CO-530, 610, 630, 660, 710 and 730, which are available 35 from Rhone-Poulenc a business having offices located in Cranbury, New Jersey 7 Printed from Mimom WO 98/03706 PCT/US97/10715 (2) surfactants composed of silicone glycol copolymers, such as Dow Coming D190, D193, FF400, and D1315, which are available from Dow Coming, a business having offices located in Midland, Michigan (3) surfactants composed 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 Gurnee, IL 60031 (4) surfactants composed of ethoxylated alcohols, such as Genapol 26-L-98N, Genapol 26-L-60N, and Genapol 26-L-5, which are available from Hoechst Celanese Corp , a business having offices located in Charlotte, NC 28217 10 (5) surfactants composed of carboxilated alcohol ethoxylates, such as Matlowet 4700 and Marlowe! 4703, which are available from Huls Amenca Inc, a business having offices located in Piscataway, NJ 08854 (6) ethoxylated fatty esters, such as Pationic 138C, Pationic 122A, and Pationic SSL, which are available from RITA Corp , a business having offices located in 15 Woodstock, IL 60098 The source material for the porous fiber 54 can include not less than about 0 35 wt% of the supplemental matenal, where the weight percentage is determined witn respect to the total weight of the combined source matenal In particular aspects of the invention, the 20 amount of supplemental matenal is not less than about 0 5 wt%, and may desirably be at least about 1 wt% Alternatively, the amount of supplemental matenal ts 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 matenal 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 optionally can be not more than about 15 wt% to provide desired processibility charactenstics In particular aspects of the invention the source matenal can include not less than about 0 35 wt% of the filler matenal In particular aspects of the invention, the amount of filler 30 matenal is not less than about 0 5 wt% Alternatively, the amount of filler matenal is not less than about 1 wt%, and optionally is not less than about 5 wt% In other aspects of the invention, the amount of filler matenal can up to about 50 wt% or more The amount of filler matenal may desirably be not more than about 30 wt% Alternatively, the amount of filler matenal can be not more than about 20 wt% and optionally can be not more than 35 about 10wt% 8 Printed fron Mimos i WO 98/03706 PCT/US97/10715 In further aspects of the invention where the supplemental matenal includes a surface-active matenal, the amount of surface-active matenal, such as surfactant, may be at least about 0 1 wt% Alternatively, the amount of surface-active matenal is at least about 5 1 wt%, and optionally, is at least about 3 wt% In other aspects of the invention, the amount of surface-active matenal is not more than about 20 wt% Alternatively, the amount of surface-active matenal is not more than about 15 wt%, and optionally, is not more than about 10 wt% 10 A suitable technique for forming the porous fiber 54 is descnbed in U S Patent Application Senal No 08/697,996 entitled METHOD AND APPARATUS FOR MAKING MICROPOROUS FIBERS WITH IMPROVED PROPERTIES, filed September 4, 1996 by F J Tsaietal (attorney docket No 12,242), the entire disclosure of which is hereby incorporated by reference in a manner that is consistent (not in contradiction) herewith 15 Conventional porous fibers have often included lumens theiein The lumen is typically a bore extending through a tube of fiber matenal, 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 fabncs 25 The porous fiber 54 of the present invention, however, is substantially free of lumens As a result, the fiber can exhibit an increase in melt strength dunng the fiber formation, and the greater melt strength can improve the in-line spinnability 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 mechanical properties to facilitate the subsequent processing of the fiber For example, the improved mechanical properties can improve the ability to further process the fibers to produce nonwoven fabric webs In its vanous aspects, the porous fiber 54 can also exhibit improved combinations of small diameter, low denier, tensile strength, elongation, and toughness (where toughness 35 is the ability to absorb energy, as descnbed in the Dictionary of Fiber & Textile Technology. Hoechst Celanese, 1990) 9 Printed from Mimosa WO 98/03706 PCT/US97/10715 The vanous 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 Aitemativaly, the porous fiber denier can be not more than 5 about 20, and optionally can be not more than about 10 In other aspects, 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 performance In other aspects, the K'n^ile strength at break of the porous fiber 54 can be not less than 10 about 200 mega-Pas^l (MP-; Alternatively, the tensile strength can be not less than about 250 MPa, and optionally can be not less than about 300 MPa In other aspects, the method and apparatus of the invention can provide for a fiber tensile strength which is not more than about 10G0 mega-Pascal (MPa) Alternatively, 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 improved performance and processibility dunng subsequent manufactunng 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 Lf is the final 2C length of the fiber at break, and Li is the initial length of the fiber pnorto 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 apparatus 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 performance attnbutes and processing capabilities In still other aspects of the invention, the porous fiber 54 can have a toughness index of not less than about 0 1 gram-centimeter per denier-centimeter (g-cm/demer-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 Additional 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 Alternatively, 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 10 Printed from Mirrtor t WO 98/03706 PCT/US97/10715 elongation-at-break, and then dividing by 2 For example, a typical calculation would be (grams laad-at-break x elongation-at-break)/(denierx 2), and may have the units of (grams-cm)/(demer-cm) 5 Suitable testing techniques for obtaining the data for determining the vanous mechanical properties of the porous fiber are further descnbed in the Test Procedures section, set forth hereinbelow The porous fiber 54 can advantageously provide improved water accessibility 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 mg/sec In other aspects, the water uptake rate can be not more than about 15 mg/sec Alternatively, the water uptake rate can be not more than about 5 mg/sec, and optionally can be not more than about 15 15 mg/sec to provide improved benefits In companson, a nonporous fiber will have a water-uptake rate of less than 0 1 mg/sec, as illustrated by Examples B, 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 companson, a 25 nonporous fiber will have a water-uptake amount of less than O 1 mg in 60 sec, as illustrated by Examples 8, 9 and 10 set forth below Suitable testing techniques for obtaining the data for determining the vanous water accessibility properties of the porous fiber are further descnbed 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 distnbuted over the outer surface of the fiber and can also be distnbuted through the interior of the fiber In particular aspects, the porous structure 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 11 Print-ed from Mimosa their long, major a\cs 48 aligned substantially along a length-wise, longitudinal dimension 44 of the fiber In particular aspects of the invention, the elongate voids can have a major axis 48 whciein the length 42 of the major axis is not less than about 0 1pm Alternatively, the major axis length is not less than about 0 2pm, and optionally is not less than about 0 25pm In other aspects, the length of the major axis is not more than about 30pm Alternatively, the major axis length 42 is not more than about 10pm, and optionally is not more than about 7pm to provide improved performance To help provide for the desired combination of mechanical strength and water accessibility, particular aspects of the invent*— have fibers in which the voids of desired pore size dimensions constitute at least about _>0% 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 or fiber cross-section In further aspects of the porous fibers of the invention, the voids having a major axis length within the range of about 0 25 - 10 pm 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 0 25 - 10 pm 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 or fiber cross-section to provide improved mechanical and water accessibility properties 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 photomicrograph or other imaging or measuring mechanism employed to determine the aspect ratio In further aspects of the invention, the aspect ratio is not less than about 1 3 Alternatively, the aspect ratio .s not less than about 1 5, and optionally 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 optionally is not more than about 15 to provide improved porosity characteristics and fiber performance The major axis of each elongate pore or void is typically an axis aligned substantially along the longitudinal dimension of the fiber, and can typically be represented by the largest length measurement of each pores 12 / / 7 **» ) As illustrated in Tigs 7, 8, 9 and 9A, the porous structure of the fiber 54 can have pores distributed along the outer surface of the fibei The suifaeo poies have a distribution with a pore number per unit of outer surlace area (average distributional density) of not less than about 0 01 5 /j.tm2 (0 01 voids per (.mi") Alternatively, the pore numbei per unit of outer suiface area is not less than about 0 015 /(.inr, and optionally is not less than about 0 05 /(.inr In furthci aspects, the pore number per unit ol outei surtace area is not more than about 10 /f.im2 Alternatively, the pore number per unit ol outer suiface aiea is not more than about 8 /pm\ and optionally is not more than about 5 /(.tirr to provide improved wettability and liquid penetration 10 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 micron1 (pm2) Alternatively, the average pore area (per pore) is not less than about 0 002 pm2, and optionally is not less than 15 about 0 03 pm2 In other aspects, the average pore area (per pore) is not more than about 20 pm2 Alternatively, the average pore area (per pore) is not more than about 10 pm2, and optionally is not more than about 3 pm2 to provide improved wettability and liquid penetration 20 The porous structure of the fiber 54 can also have pores distnbuted along its cross-sectional area to provide a pore number per unit area which is not less than about 0 01/pm2 Alternatively, the pore number per unit of area is not less than about 0 015/pm2, and optionally is not less than about 0 1/ym2 In other aspects, the pore number per unit area is not more than about 10/pm2 Alternatively, the pore number per 25 unit area is not more than about 8/prrT and optionally is not more than about 5/pm2 to provide improved wettability and liquid penetration In further aspects, the porous structure of the fiber 54 has pores distnbuted 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 less 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% Alternatively, the percent pore area is not more than about 50%, and optionally is not 35 more than about 20% to provide improved wettability and liquid penetration 13 7 1 lie fibei enn include a plurality ol voids winch are initiated tit sttucturdl discontinuities ol the Hbei matenal With reference to hgs 1, 2, 9, OA and 12, pailtcular aspccts ol the porous liber can include a plurality ol voids or pores winch are inninly initialed at sliuetural irregulnnties or other physical non-homogeneities ol the fiber material, and which are stretched and expanded 5 thcrelrom Such initiator, structural non-homogeneities can bo provided by one or moie ol the following mechanisms particulate filler/polymer resin interfaces, density aiul/oi modulus fluctuations in a fibei matenal, submicron size voids and/or air bubbles, any type of inclusions having a modulus and/oi density which vanes Irom that ot the fiber material, as well as combinations ol the mechanisms More particularly, the fiber can desirably include a plurality of 10 stretchcd or otherwise extended voids wherein each of the voids can be associated with a particulate initiator 50 provided by a material composed of a multiplicity ol individual particles, such as a paniculate tiller matenal The pores or voids can substantially surround the initiators or can be immediately 15 adjacent to the initiators The pores may also be located in the areas between individual initiators 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 substantially elongated elliptical shape, and/or may have a 20 substantially 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 sphencal shape or a slightly oval or egg shape In a particular aspect of the microporous fibers of this invention, substantially no specific pattern 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 pattern or regular arrangement of the voids is observed in a representative cross-sectional view of the fiber Accordingly, the arrangement of the voids in the fiber matenal can be irregular, and may be substantially random, with some irregular clustenng For example, there may be such clustenng in the areas of agglomeration of any incorporated filler matenal The observed structure 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 distnbutions 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 distnbution patterns can clearly differentiate microporous fiber structure of this invention 35 from the porous fibers obtained by a phase separation method or by other stretching 14 methods, such as the incremental stretching method employed for producing CELGARD microporous fibers In a surface view of a CELGARD fiber at a magnification of 15.000X, as representatively 5 shown in Fig 11, numerous micropores of generally oval or rectangular-like shape are arranged into stnps of generally planar microporous zones aligned approximately along the direction perpendicular to the fiber length These stnps of microporous zones are further arranged into arrays in which the stnps occur in a nearly penodtc, regular fashion 10 With reference to Figs 3, 4 and 10, a porous fiber obtained by a conventional phase separation 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-hke macrovoids located adjacent to the hollow fiber lumen The 15 arrangement of the voids, particularly along the fiber cross-section, provides for a substantially regular array With reference to Fig 10, the surface of the fiber appears substantially nonporous under a magnification of 15.000X In contrast, 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 deformation in the fiber matenal The stressed regions can be observed at least along boundary edges of the extended, surface voids present on the exposed, outermost surface of the fiber In the porous fiber of the invention, the edge boundanes and edge penmeters of the fiber matenal are angular sharply defined, substantially nonfilamented 25 and substantially non-spongitorm in the .ireas surrounding the extended, elongated voids Accordingly, the voids are effectively bounded by fiber matenal 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 matenal in the regions observed between the voids generally has the form of a plateau interrupted by the voids 30 Suitable techniques for obtaining the data for determining the vanous pore size properties and pore distributions of the porous fiber are further descnbed in the Test Procedures section, set forth below 15 WO 98/03706 FCT/US97/10715 Testing Procedures Mechanical properties 5 A suitable technique for determining the mechanical properties of the porous fiber 54 can employ a Srntech tensile tester (SINTECH 1/D) 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 substantially equivalent capabilities may also be employed Mechanical properties can be evaluated with the tensile taster 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 15 (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 gnps, and is held in place when air pressure closes the gnps together The diameter of the fiber is inputted by the user before beginning the tensile testing For the hollow fiber samples, such as those shown in Examples 11 and 12, the annular cross-sectional area, n ((outer radius)2 - (inner 20 radius)2), was used for the calculation of the tensile strength In each expenment, the fiber is stretched until breakage occurs, and the equipment software or other equipment programming creates a stress-versus-strain plot and calculates 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 25 Water accessibility A suitable technique for determining the comparative water accessibility 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 little 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 sensitrvity 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 capable of measunng the maximum load 16 Printed from Mimosa WO 98/03706 PCT/US97/10715 expected dunng the testing The fiber testing for the examples 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 operably taped or otherwise secured along and against a hanging wire or similar support to provide a test sample In the test 5 sample, a 5 mm length of the support wire and its adjacently held fiber sample extends below the tape and remains exposed and available for contact with the water dunng testing The CAHN system includes a movable stage which can be translated at a steady rate up 10 and down The test samplB is hung from or otherwise mounted omo the selected loop of the balance, and a beaker of water is placed on the moveable stage The stage is brought 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, controls 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 'he one second intervals The test sample is then pulled back out of the water The data collected from an expenment is then evaluated In particular, the data can be exported into suitable spreadsheet software, such as Microsoft Excel version 5 0, and processed to generate a plot of weight versus time for the 1 minute soak in the water 25 The plot shows the trend of water uptake for the lest sample, and provides a convenient basis for companng the relative water uptake performance and the relative levels of water accessibility of different fiber samples To allow a better companson between samples 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 normalization 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 normalized weight increase versus the amount of elapsed time dunng the one minute soaking penod The water uptake rate shown in the examples was determined by calculating the slope of the plotted curve at the data point recorded in the 35 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 17 Printed Ctom Hinios i WO 98/03706 PCT/US97/10715 (60 sec) time of measurement in the data plot It should be noted that the measured and recorded weight gain may include a weight gam due to the water absorbed into the initial porous structure, as well as weight gains due to other interactions between the fiber and water For example, a coating layer of water can form on the Tiber In addition, the fiber 5 structure can swell to provide pores with increased void volume, or the fiber can otherwise change in configuration to provide an increased capacity for acqumng and holding absorbed water Scannino Electron Microscopy and Image Analysis 10 Electron photomicrographs can be generated by conventional techniques which are well known in the imaging art In addition, the samples can be prepared for the desired imaging 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 smeanng of the fiber matenal when the fiber sample is being cut and prepared for an imaging of the fiber cross-section In a suitable preparation 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 cryomicrotomy, such as by using a Relchert 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 appropnate stub and coated with gold or Au/Pd (goldypalladium) The fiber microstaicture 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 backscatter electron detectors Automated image analyses of voids and fiber pores can be conducted by well known, conventional techniques Examples of such techniques are descnbed in "APPLICATION 30 OF AUTOMATED ELECRON MICROSCOPY TO INDIVIDUAL PARTICLE ANALYSIS" by Mark S Germani, AMERICAN LABORATORY, published by International Scientific Communications, Inc , and in "INTRODUCTION TO AUTOMATED PARTICLE ANALYSIS" by T B Vander Wood (copynght 1994, MVA, Inc , 550 Oakbrook Parkway #200, Norcross, GA 30093), Proc 52nd Annual Meeting of the Microscopy Society of 35 Amenca. G W Bailey and A J Garratt Reed, Eds , published by San Francisco Press 18 Printed trom Mimosa WO 98/03706 PCT/US97/10715 The Image analyses to provide pore distribution data for Example 1 was conducted by Matenals 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, 5 Inc , a laboratory having offices located at Norcross, GA The vanous image analyses can, for example, be done with a Noran Voyager image analysis system employing a magnification of 5.000X The data are generated by taking average of a total of twelve fields The system is available from NORAN Instrument, Inc , 10 a business having offices in Middleton, Wl, and systems capable of providing substantially equivalent performance may also be employed Dunng the course of the image analyses, the image of the porous structure can be digitized employing conventional techniques An example of a digitized image is representatively shown in Fig 13 15 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-immersion optical microscopy can be employed With this technique, the samples are prepared 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 OPTICAL CO 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 suitable 25 microscope is a OLYMPUS BH-2 optical microscope, which is available from OLYMPUS OPTICAL CO LTD , , a business having offices in Lake Success, NY Other optical microscopes and equipment having substantially equivalent capabilities 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 35 19 Printed from Mimosa WO 98/03706 PCT/US97/10715 Example 1 A resin composed of polypropylene (Himont PF301) ( 90 wt%) and TiC>2 filler particles (SCC 4837 by Standndge Color Corporation) (10 wt%) was intermixed with Dow Coming 5 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 TiC>2 particle size was in the range of about 0 1 to 0 5 microns (pm), as measured by a scanning electron microscopy (SEM) The concentrations of the fillers were measured by ashes analysis The surfactant Dow Coming D193 had a HLB number of 12 2 The fiber spinning process 10 included feeding the combined matenals into a hopper and extruding the matenals through a single-screw extruder having a length-to-diameter ratio of 24 (L/D = 24/1) The extruder had three heating zones, a metenng pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 40 Dunng the 15 quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metenng 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 stretched in air by 2X (a draw ratio of 2), followed by stretching by 1 7X (a draw ratio of 1 7) in a bath provided by a second surface-active 20 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 onto a winder The mechanical properties of the resultant porous fiberwere then measured by a Sintech tensile tester, and are summanzed in the following TABLES 1 and 2 Tho number of pores per pm2 of cross-25 section of the fiber was about 0 74 and the number of pores per pm1 of external surface was about 0 08 Example 2 30 A resin composed of polypropylene 95 3 % (Himont PF301), 1 4 % Ti02 concentrate, inorganic filler (SCC 4837 by Standndge Color Corporation) 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 35 extruder The particle size of the organic filler ranged from 1 to 5 microns as measured by SEM The combined matenal was then extruded through a single-screw extruder 20 Printed from Minosi WO 98/03706 PCT/US97/10715 (L/D = 24/1), which included three heating zones, an on-line static mixer, a metenng pump, and a spinpack with 4 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 33 Dunng the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-5 active liquid delivered through a metenng coating die The first surface-active liquid was a solution composed of 2 wL% of a surfactant (IGEPAL RC-630) in a isopropanol/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 17X, and subsequently stretched by 2X In bath provided by a second surface-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 85 °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 summanzed in the following TABLE 1 15 Example 3 A resin composed of 93 2 wt % polypropylene (Himont PF301), 1 4 wt % Ti02 concentrate (SCC 4837 by Standndge Color Corporation) and 5 4 wt % CaC03 20 (Omyacarb UF from Omya Inc), which was surface-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 matenal was then extruded through a single-screw extruder (L/D = 24/1), which include an on-line 25 static mixer, a metenng pump, and a spinpack with 8 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion, the fiber was subjected to a draw-down ratio of 33 Dunng the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metenng 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 liquid was a solution composed of 1 wt% IGEPAL RC-630 in a isopropanol/water solvent The solvent was composed of isopropanol 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 21 Printed from Mimosa WO 98/03706 PCT/US97/10715 mechanical properties of the porous fiber were then measured by a Slntech tensile tester, and are summarized in the following TABLE 1 Example 4. 5 A resin composed of 8B 8 wt% polypropylene (Himont PF301), 1 3 wt% TiOz concentrate (SCC 4837 by Standndge 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 10 Haake twin-screw extruder The particle sizes of the CaC03 were within the range of 1 to 3 microns as measured by SEM The combined matenal was then extruded through a single-screw extruder (L/D = 24/1), which included three heating zones, an on-line static mixer, a metenng pump, and a spinpack with 15 holes, each hole having a diameter of 0 5 mm Dunng the extrusion-spinning operation, the fiber was subjected to a draw-down 15 ratio of 40 Dunng quenching, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metenng 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 fiber was then stretched in air by 1 5X, and subsequently stretched by 1 4X in a bath provided by a second quantity of surface-active 20 liquid The second surface-active liquid was composed Df isopropanol 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 mechanical properties of the porous fiber were then measured by a Sintech tensile tester, and are summanzed in the following TABLES 1 and 2 The number of pores per 25 pm2 of cross-section of the fiber was about 0 19 Example 5 A resin composed of polypropylene (Himont PF301) ( 90 wt%) and Ti02 filler particles 30 (SCC 4837 by Standndge Color Corporation) (10 wt%) was intermixed with Dow Coming 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 Ti02 particle size was in the range of 0 1 to 0 5 microns, as measured by a scanning electron microscopy (SEM) The concentrations of the fillers were measured by ashes analysis The surfactant Dow 35 Coming D193 had a HLB number of 12 2 The fiber spinning process included feeding the combined matenals Into a hopper and extruding the matenals through a single-screw 22 Printed from Mirnom WO 98/03706 PCT/US97/I0715 extruder having a length-to-diameter ratio of 24 (L/D = 24/1) The extruder had three heating 2onas, a metenng pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 11 Dunng the quenching of the fiber, the 5 nascent fiber was pre-wetted with a first surface-active liquid delivered through a metenng 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 stretched in air by 1 5BX 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-parts isopropanol 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 then measured by a Sintech tensile tester, and are summanzed in the following TABLE 1 15 Example 6 A resin composed of polypropylene (Himont PF301) (90wt%) and Ti02 filler particles (SCC 4837 by Standndge Color Corporation) (10 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 extruder The TIO2 particle size was in the range of 0 1 to 0 5 microns, as measured by a scanning electron microscopy (SEM) The concentrations 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 matenals into a hopper and extruding the matenals through a single-screw 25 extruder having a length to-diameter ratio of 24 (L/D = 24/1) The extruder had three heating zones, a metenng pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 11 Dunng the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a 30 metenng 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 stretched in air by 1 17X followed by stretching 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 35 isopropanol to 1-part water The fiber was then heat-set at 80 °C before accumulation 23 Print-ed from Mimosa WO 98/03706 PCT/US97/10715 onto a winder The mechanical properties of the resultant porous fiber were then measured by a Sintech tensile tester, and are summanzed in the following TABLE 1 Example 7 5 A resin composed of polypropylene (Himont PF301) (90 wt%) and TiO* filler particles (SCC 4837 by Standndge 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 Ti02 particle size was in the 10 range of 0 1 to 0 5 microns, as measured by a scanning electron microscopy (SEM) The concentrations 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 matenals into a hopper and extruding the matenals through a single-screw extruder having a length-to-diameter ratio of 24 (L/D = 24/1) The extruder had three 15 heating zones, a metenng pump, an on-line static mixer, and a spinpack with 4 holes, each hole having a diameter of 0 3 mm Dunng the spinning extrusion of the fiber, the fiber was subjected to a draw-down ratio of 33 Dunng the quenching of the fiber, the nascent fiber was pre-wetted with a first surface-active liquid delivered through a metenng coating die The first surface-active liquid was a solution composed of 20 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 1 17X followed by stretching 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 summanzed in the following TABLE 1 Example 8 30 A resin composed of polypropylene (Himont PF301) (90 wt%) and Ti02 filler particles (SCC 4837 by Standndge 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 TiOz particle size was in the range of 0 1 to 0 5 microns, as measured by a scanning electron microscopy (SEM) The 35 concentrations 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 24 Printed from Mimosa WO 98/03706 PCT/US97/10715 the combined matenals Into a hopper and extruding the matenals through a single-screw extruder having a length-to-diameter 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 5 fiber was allowed to free-fall Dunng the quenching of the fiber, the nascent fiber was pre-wetted with a surface-active liquid delivered through a metenng coating die The 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 mpchanical properties of the resultant porous fiber were then measured by a Sintech tensile tester, and are 10 summanzed in the following TABLE 1 Example 9 This sample was composed of a commercially available polypropylene staple fiber which 15 was obtained from Amencan Barmag, a business having offices located in Charlotte, North Carolina The staple fiber had a fiber length of 38 mm, and was surfactant-modified by immersing in a solution of 10 wt% hydrophilic silicon glycol (Dow Coming 193) surfactant in acetone for 1 hour and drying at 50 °C for 6 hours before testing The properties of the fiber were measured and are summanzed in the following TABLE 1 20 Example 10 This sample was composed of a commercially available polypropylene staple fiber having a fiber length of 38 mm, and was obtained from Amencan Barmag, a business 25 having offices located in Charlotte, North Carolina The properties of the fiber were measured and are summanzed 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, Japan 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 allowed an 35 introduction of the coagulation liquid to contact the nascent fiber along both an inside and outside surface of the fiber matenal The structure has large finger-like pores within 25 Printed from Mimosa WO 98/03706 PCT/US97/10715 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 thB fiber The properties of the fiber were measured and are summanzed in the following TABLE 1 5 Example 12 This sample Is another conventional porous fiber distributed under the tradename CELGARD by Hoechst Celanese, a business having offices in Charlotte, North Carolina 10 As representatively shown in Figs 5 ,6, and 11, the fiber had a longitudinal lumen, and it is believed that the porous structure of the fiber was created by a process which employed a plurality of incremental stretching steps The structure, as shown in tha cross-sectional view includes a lamellar-like structure produced by creating inter-lamellar volume in a pre-crystalline structure In this structure, the pore contains microfibrils that 15 onented In the length-wise direction of the fibers and Joint portions which are composed of stacked lamella The properties of the fiber were measured and are summanzed in the following TABLE 1 Example 13 20 This sample is a microporous polypropylene fiber which is shown in example 1 of U S P 4,550,123 owned by Albany International, a business having offices located In Mansfield, MA According to the description 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 26 Punted from Mi-nosa WO 98/03706 PCT/US97/10715 TABLE 1 Example No Water-uptake rate (mg/scc) Water-uptake (nig per 1 rrun 1 Break stress (MPa) Elongation at break (%) Fiber size Toughness index (g-cm per dcnicr-cm) 1 0 79 1 2 427 157 4 7 d 42 2 0 58 1 1 391 111 5 7 d 27 3 084 1 5 310 95 5 8d 1 8 4 0 89 1 3 358 150 1 8d 33 5 101 1 8 295 119 16 d 22 6 0 67 1 4 231 168 18d 24 7 021 03 251 183 5 fid 2 9 8 0014 0015 47 966 68 d 28 9 0 02 0 25 220 55 2 8 d 0 75 10 0 002 0 005 362 60 2 8d 1 30 11 — 84 10 1 300 microns 0 003 12 — 51 207 300 microns 0 65 13 — 217 23 8 8d 0 30 Having thus described the invention in rather full detail, it will be readily apparent that vanous changes and modifications can be made without departing from the spint 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 27 Printed from Mimosa </div>

Claims

<div class="application article clearfix printTableText" id="claims">



The claims defining the invention ai c as follows* 

1 A porous fiber which includes a fibei material having a plurality of elongate pores therein, and wherein said pores are formed in the ilbei matenal which has been expanded and stietched away from filler matenal which is included in saul fiber matenal, said fiber having a denier ol about 50 or less, 

a percent elongation at break of about 30% or more, 

a tensile strength at bieak of about 200 MPa or more, and having said pores distributed over an outei suifaee of said fiber with an average distributional density of about 0 01 pores, oi moie per (.tin" ol said outer surface
2 A fibei as rccitcd in claim 1, wheiein said fibei has a denier of about 20 

or less
3 A fiber as iecitcd in claim 1, wherein said fiber has a denier of about 10 

oi more
4 A fibei as iecitcd in claim 1, wherein said fibei has a peicent elongation at break of about 50% or more
5 A fibei as recited in claim 1, wherein said fiber has a peicent elongation at break of about 90% oi more
6 A fibei as iecitcd in claim 1, wherein said pores include suiface pores which arc irregularly distributed over said outer surface of said fiber
7 A fibei as recited in claim 1, wherein said poies include pores which aie irregularly distributed through a cioss-section of said fiber
8 A fiber as recited in claim 1, wherein said fiber includes pores having generally ellipsoid shape
9 A fiber as recited in claim 1, wherein said elongate pores have majoi axes thereof aligned substantially along a longitudinal dimension of said fiber
10 A fiber as recited in claim 1, wherein said elongate pores have major axes thereof which measure about 0 1 (.im or more in length
11 A fiber as recited in claim 1, wherein said elongate pores have major axes thereof which measure about 30 (.im or less in length
12 A fibei as recited in claim 6, wherein said pores have an average distribution of about 10 poies, oi less, per |.im2 of said outer surface
13 A fibei as iecitcd in claim 7, wherein said pores have an average distribution of about 0 0] pores, or more per (am of said cross-section 

[R \LIDLLJ08I46 doc Kill I
14 A liber as lccitcd in claim 7, wherein said pores have an average distubution of about 10 pores, oi less, pei (.mr of said cioss-section
15 A liber as iecitcd in claim 1, wherein said poious llbei is substantially free of lumens
16 A fiber as iecitcd in claim 1, wherein said llbei includes a plurality oi pores which are initiated at said particulate filler material
17 A llbei as iecitcd in claim 1, wherein said fiber includes a plurality of extended poics, each ol which has an associated particulate initiator provided by said particulate fillet matenal, and wherein each said extended poies has a length which is larger than a length of its associated particulate filler matenal 

Dated 29 July, 1999 Kimberly-Clark Worldwide, Inc. 

Patent Attorneys for the Applicant/Nominated Pcison 

SPRUSON & FERGUSON 

-MD OF CLAIMS 

[R \L!BLL]0HI4fi doc KFM 



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