SK5299A3 - 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

The invention relates to microporous fibers. In particular, the invention relates to synthetic porous fibers which are wettable and exhibit improved mechanical properties.

BACKGROUND OF THE INVENTION

The porous fibers have a structure that is formed using conventional phase separation methods. Such methods generally include mixing the polymerization resin with a diluent or plasticizer, ending the reaction of a solution of the polymer in a liquid medium to induce phase separation, and washing the diluent, leaving the porous structure interconnected. Other porous fibers were obtained by techniques that use a blowing agent or swelling agent to form a microporous structure. Still other porous materials have been produced using environmentally damaging methods.

Conventional porous fibers, such as those described above, are unable to provide the desired combinations of mechanical properties and water availability. Furthermore, these techniques do not adequately produce porous fibers having the desired combinations of small diameter, low denier, high wettability, high liquid permeability, and high tensile strength. As a result, there is a continuing need for fibers having an improved porous structure.

SUMMARY OF THE INVENTION

The present invention relates to a characteristic porous fiber which contains voids in order to achieve the desired degree of wettability and liquid permeability while still having good mechanical properties. The fiber may have a denier (weighing unit used for textile

150 (B fibers) of not more than 50 and may have a percent elongation at break of not more than about 30%. The fiber may also have a tensile strength of at least about 200 MPa.

Due to its different properties, the porous fiber of the present invention can give efficient and effective fibers having the desired combination of small dimensions, high wettability, high water availability, high tensile strength and high elongation. As a result, the fiber may have an increased ability to be further processed into nonwoven fabrics and other articles of manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood and further advantages will become apparent with reference to the following detailed description of the invention and the accompanying drawings, in which:

Fig. 1 is a photograph taken by means of a scanning electron microscope at a magnification of 850 *, which shows a representative section of a porous fiber according to the present invention.

Fig. 2 is a photograph taken with a scanning electron microscope at a magnification of 1700 *, showing an enlarged section of the section shown in FIG. First

Fig. 3 is a photograph taken using a scanning electron microscope at a magnification of 250 x, showing a representative cross-section of a prior art fiber containing a lumen (longitudinal cavity).

Fig. 4 is a photograph taken with a scanning electron microscope at a magnification of 8,000 x showing an enlarged section of the section shown in FIG. 3 at a location close to the outer surface of the fiber.

Fig. 5 is a photograph taken with a scanning electron microscope at a magnification of 250 x, showing a representative cross-section of another prior art porous fiber that includes a lumen and was formed by an incremental stretching method.

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Fig. 6 is a photograph taken with a scanning electron microscope at a magnification of 5000 x, showing an enlarged section of the section shown in FIG. 5th

Fig. 7 is an optical photomicrograph taken with optical t

an oil immersion microscope at a magnification of 1500 x, which shows a representative view of the voids on the surface and mass of the porous fiber of the present invention.

Fig. 8 is an optical photomicrograph made with an oil immersion optical microscope at a magnification of 1500 x showing a different view of the voids on the surface and in the mass of the porous fiber according to the present invention.

Fig. 9 shows a representative view of the voids along the outer surface of another porous fiber of the present invention at a magnification of 3,000x.

Fig. 9A shows a representative schematic view of the particular pores shown in FIG. 9th

Fig. 10 is a photograph taken with a scanning electron microscope at a magnification of 15,000 x, showing a representative view of the fiber surface shown in FIG. Third

Fig. 11 is a photograph taken using a scanning electron microscope at a magnification of 15,000 x, showing a representative view of the surface of the fiber shown in FIG. 5th

Fig. 12 is a photograph taken by a scanning electron microscope with detection of backscattered radiation at a magnification of 5,000x, showing a representative cross-section of a fiber according to the present invention.

Fig. 13 shows a representative version of FIG. 12, which has been digitized for image analysis.

Fig. 14 is a representative graph of water weight gain over time for a porous fiber sample.

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DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, 2, 7, 8, 9, 9A and 12, the porous fiber 20 has a longitudinal dimension 44 and a generally transverse dimension 38. The porous fiber has a characteristic void or pore configuration 22 that achieves the desired level of wettability, liquid penetration, and other types of availability for liquids. The fiber may have a denier (d) per fiber of at most about 50 and preferably has a percent elongation at break of at least about 30%. The fiber may also have a tensile strength of at least about 200 MPa. In particular embodiments of the present invention, the porous fiber 54 may also have other properties and may include voids or pores having certain shapes, sizes, layouts, and configurations.

In various embodiments, the microporous fiber of the present invention can provide improved fluid intake, can more rapidly absorb water or other liquids into the interior of the fiber product, and can accelerate the dissolution kinetics of fiber products which are thought to be disposable products. In addition, the microporous fiber may help to obtain improved absorbency, improved fluid distribution, improved breathability of articles such as surgical gowns and diapers, improved tactile and aesthetic properties, and / or increased biodegradability. The fibers can be processed directly into nonwovens by conventional molding methods. Alternatively, the fiber may be cut into staple fibers and mixed with other fibers for sake

The subsequent formation of nonwoven fibrous webs using conventional air techniques. Nonwoven fabrics may be particularly suitable for making disposable personal care products such as diapers, tampons, female pads, panties, tampon plaits and the like.

In various configurations of the present invention, the porous fiber 54 may be a synthetic fiber made of a starting material that includes a thermoplastic, orientable material, such as thermoplastic and

150 / B orientable polymers, copolymers, mixtures, compounds, and other combinations thereof. The thermoplastic materials preferably do not contain highly reactive groups.

In a particular embodiment of the present invention, the starting material may be a polyolefin material. For example, the starting material may include homopolymers of polyethylene or polypropylene, or may include copolymers of ethylene and polypropylene. In other embodiments, the starting material may also include other polymerization material, such as a polyether, copolyether, polyamide, copolyamide, polyester or copolyester, as well as copolymers, mixtures, and other combinations thereof.

The thermoplastic material is melt processable and, in particular embodiments of the present invention, the material may have a melt flow rate (MFR) of at least about 1 g / 10 minutes (measured according to ASTM D1238-L). Alternatively, the MFR may be at least about 10 g / 10 minutes and optionally may be at least 20 g / 10 minutes. In other embodiments of the present invention, the MFR may be at least 200 g / 10 minutes. Alternatively, the MFR may be at least 100 g / 10 minutes and optionally may be at least about 40 g / 10 minutes to achieve a sufficient level of processability.

Such melt-processable thermoplastic materials can be obtained, for example, as a polypropylene homopolymer. Commercially available polyolefins such as Himont PF 301, PF 304 and PF 305, Exxon PP 3445, Shell Polymer E5D47 are also representative examples of suitable materials. Still other suitable materials may 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 a polyethylene homopolymer having an MFR value similar to those disclosed herein. The polymerization resins may contain a small amount (for example, about 0.05 to 5 parts additive per 100 parts resin) of process additives such as calcium stearate or other acid scavengers. Other additives may include, for example, silicone glycol copolymers, organosilicon compounds, olefin elastomers and

150 / B low molecular weight paraffins and other lubricating additives. Various pigments may also be used. For example, pigment concentrates such as titanium dioxide pigment concentrate as well as low molecular weight polyethylene plasticizers can be used as process additives. The various additives may have a plasticizing effect and may improve the strength and softness of the fiber and may assist one or more properties such as elongation, spinning and elongation.

The starting material for the fiber 54 may also include another additional material, and the additional material may include a filler and / or a surfactant or other surfactant material. The filler material may be a particulate material that can assist in initiating porosity, disrupting site bonds to increase the desired pore formation during the various drawing operations applied to the fiber. The filler material can help to provide the desired surface-modified fiber and can help to increase the desired "slip effect" produced during ¹ 'of subsequent stretch operations. In addition, the filler material helps to retain pores that are formed during various drawing operations.

When the additional material comprises a surfactant material such as a surfactant or other material having low surface energy (e.g., silicone oil), the surfactant material can help reduce the surface energy of the fiber as well as provide lubrication between the polymerization segments that form the fiber . Reducing surface energy and lubrication can help create a "gliding effect" during subsequent. dragging operations.

The additional filler material may be organic or inorganic, and the filler material is preferably in the form of discrete particles. Pinidio can be subjected to surface treatment with various coatings and surfactants to give it affinity to the polymerization resin in the starting material, further to reduce agglomeration, improve filler dispersion and ensure controlled interaction with fluids such as body fluids, blood and Water.

150 / B

Examples of inorganic fillers may include metal oxides as well as metal hydroxides, carbonates or sulfates. Other suitable inorganic fillers may include, for example, calcium carbonate, various forms

Clay, silica, alumina, barium sulfate, sodium carbonate, talc, magnesium carbonate, magnesium sulfate, barium carbonate, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, titanium dioxide, powdered metals, glass microspheres and hollow particles. Still other inorganic fillers may include fillers whose particles have a higher ratio of dimensions in different directions, such as talc, mica and wollastonite, but such fillers may be less effective. Representative organic fillers can be, for example, cellulose powders, wood powders, cellulose derivatives, chitin, chitosan powder, high crystalline high melting point polymer powders, high crosslinked polymer beads, organosilicate powders, and the like, as well as combinations and derivatives thereof.

In particular embodiments of the present invention, the fillers may have a mean particle size not greater than about 10 microns (µπι). Alternatively, the mean particle size may be at most 5 µπι and optionally may be at most about 1 µπι to achieve improved processability. In other embodiments of the present invention, the upper particle size is not more than about 25 µπι. The alternative upper particle size is not more than about 10 µπ and optionally not more than about 4 µπ to ensure improved processability during the formation of a fiber having the desired size and porous structure. The fillers may also be surface modified using surfactants and / or other materials such as stearic or behenic acid, which may also be used to improve the processability of the starting material.

Examples of suitable filler materials may include one or more of the following:

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1. Dupont R-101 T1O2 supplied by E.l. DuPont de Nemours and can also be supplied in a concentrated form by Standrich Color Corporation, headquartered in Social Circle, Georgia 30279. This material ensures good workability.

2. Pigment Blue 15: 1 (10% copper) distributed by Standridge Color Corporation. The fibers formed with this material tear more frequently.

3. OMYACARB® UF CaCO3, supplied by OMYA, Inc., based in Proctor, Vermont 05765. This material can have an upper particle size of about 4 µm and an average particle size of about 0.7 µm and can provide good processability. The filler may be surface-treated with a surfactant such as Dow Corning 193 surfactant prior to combining or further combination with the starting material 56. The filler may also be surface treated with other suitable surfactants such as those disclosed in elsewhere in the description of the present invention.

4. OMYACARB® - UFT CaCO3 stearic acid treated, available from OMYA, Inc. This material can have an upper particle size of about 4 µm and a mean particle size of about 0.7 µm and provides good processability.

5. SUPERCOAT ™ CaCO ₃ , supplied by ECC International, Atlanta, Georgia 30342, 5775 Peachtree - Dunwoody Road. This material may have an upper particle size of about 8 µm and a mean particle size of about 1 µm. The fibers formed by this material tear more frequently.

6. Polydimethyl silsesquioxane powder (# 22 or # 23 Dow Corning Additive) supplied by Dow Corning, based in Midland, Michigan 48628-0997. This material guarantees good workability, although agglomerate formation has been observed.

150 / B

The additional material may optionally include a surfactant material, such as a surfactant or other material that has a low surface energy (e.g., silicone oil). In particular embodiments of the present invention, the surfactant or other surfactant material may have a Hydrophile-Lipophile Balance (HLB) value of at most about 18. Alternatively, the HLB value is at most about 16 and optionally at most about 15. V In other embodiments of the present invention, the HLB value is not less than about 6. Alternatively, the HLB value is not less than about 7 and optionally the HLB value is not less than 12. If the HLB value is too low, wettability will not be sufficient. If the HLB value is too high, the surfactant may have insufficient adhesion to the polymerization matrix of the starting material and may be too easily washed off during use. HLB values of commercially available surfactants can be found, for example, in McCUTCHEON's Vol. 2: Functional Materials 1995.

Suitable surfactants may include silicone-glycol copolymers, carboxylated alcohol ethoxylates, various ethoxylated alcohols, ethoxylated alkyiphenols, ethoxylated fatty esters and the like, as well as combinations thereof. For example, other suitable surfactants may include one or more of the following:

1. Surfactants composed of ethoxylated alkylphenols such as IGEPAL RC-620, RC-630, CA-620, 630, 720, CO-530, 610, 630, 660, 710 and 730, supplied by Rhone-Poulenc , which is based in Cranbury, New Jersey.

2. Surfactants consisting of silicone-glycol copolymers such as Dow Corning D190, D193, FF400 and D1315, supplied by Dow Corning, based in Midland, Michigan.

3. Surfactants composed of ethoxylated mono- and diglycerides, such as Mazel 80 MGK, Masil SF 19 and Mazel 165C, supplied by PPG Industries, headquartered in Gurnee, IL 60031.

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4. Surfactants composed of ethoxylated alcohols such as Genapol 26-L-98N, Genapol 26-L-60N and Genapol 26-L-5, supplied by Hoechst Celanese Corp., located in Charlotte, NC 282 17.

5. surfactants composed of carboxylated alcohol ethoxylates such as Marlowet 4700 and Marlowet 4703, available from Huls America Inc., located in Piscataway, NJ 08854.

6. ethoxylated fatty esters such as Pationic 138C, Pationic 122A and Pationic SSL supplied by R.I.T.A. Corp., which is based in Woodstock, IL 60098.

The starting material for the porous fiber 54 may comprise no less than about 0.35% by weight. additional material, wherein the weight percentages are determined relative to the total weight of the combined starting material. In particular embodiments of the present invention, the amount of additional material is at least about 0.5% by weight and is desirably at least 1% by weight. Alternatively, the amount of additional material is at least 5 wt. and optionally at least 10 wt. In other embodiments of the present invention, the amount of additional material may be up to about 50% by weight. or more. The amount of additional material is preferably at most about 30 wt. Alternatively, the amount of additional material may be at most about 20 wt. and optionally may be at most 15 wt% to ensure good processability.

In particular embodiments of the present invention, the starting material may comprise at least 0.35 wt. fillers. In particular embodiments of the present invention, the amount of filler is at least about 0.5% by weight. Alternatively, the amount of filler is at least about 1 wt. and optionally at least 5 wt. In other embodiments of the present invention, the amount of filler may be up to about 50% by weight. or more. The amount of filler may preferably be at most 30 wt. Alternatively, the amount of filler may be at most about 20% by weight. % and optionally at most about 10 wt.

150 / B

In other embodiments of the present invention, wherein the additional material comprises a surfactant, the amount of surfactant such as a surfactant may be at least about 0.1 wt%. Alternatively, the amount of surfactant material may be at least 1 wt. and optionally may be at least about 3 wt. In other embodiments of the present invention, the amount of surfactant material may be at most 20% by weight. Alternatively, the amount of surfactant material may be at most about 15% by weight. % and optionally at most about 10 wt.

Suitable techniques for forming the porous fiber 54 are described in U.S. Patent Application Ser. No. 08 / 697,996, entitled " Method and Apparatus for Making Microporous Fibers with Improved Properties, "

On September 4, 1996, Applicants F. J. Tsai et al. (attorney docket No. 12,242), the contents of which are incorporated herein by reference in a manner that is consistent (and does not contradict) the present invention.

Conventional porous fibers often contain lumens. The lumen is typically a cavity passing through the tubular fibrous material as shown in FIG. Accordingly, the lumen typically forms a hollow fiber in which the ratio of the outer diameter of the tube to the diameter of the opening in the tube is in the range of 50: 1 to 50: 48. Lumen fibers are usually more difficult to manufacture and may be susceptible to undesirable collapse when fibers are processed at high speeds. In addition, such fibers have shown inadequate mechanical strength properties, which makes further processing of the fibers into nonwoven products problematic.

However, the porous fiber 54 of the present invention is substantially free of lumens. As a result, the fiber may exhibit an increase in melt strength during fiber formation, and greater melt strength may improve fiber spinability and extensibility. For example, a simpler die design can be used to form the formed fiber. The porous fiber may also exhibit increased mechanical strength, which provides improved shape stability, and may exhibit further improvements in mechanical properties that facilitate

150 / B post-processing of the fiber. For example, improved mechanical properties can improve the fiber processing capability to form nonwovens. In various particular embodiments, the porous fiber 54 may also exhibit improved combinations of small diameter, low denier, strength

I.

tensile, elongation, and toughness (where toughness is the ability to absorb energy as described in "Dictionary of Fiber and Textile Technology", Hoechst Celanese 1990).

Different configurations of the porous fiber 54 may have a relatively small diameter and a relatively low denier. In particular embodiments, the porous fiber may have a denier of at most about 50. Alternatively, the porous fiber denier may be at most about 20 and optionally may be at most about 10. In other embodiments, the porous fiber may have a denier of about 0.5 or less and optionally a denier of about 0. , 1 or less to ensure improved behavior.

In other embodiments, the tensile strength of the porous fiber 54 may be at least about 200 MegaPascal (MPa). Alternatively, the tensile strength of the fiber may be at least about 250 MPa and optionally may be at least about 300 MPa. In other embodiments, the method and apparatus for practicing the present invention may provide the fiber with a tensile strength of not more than about 1000 MPa. Alternatively, the tensile strength of the fiber may be at most about 750 MPa, and optionally may be at most about 450 MPa to ensure improved behavior and processability during subsequent fiber processing.

In other embodiments, the porous fiber 54 may have a percent elongation at break of not more than about 30%, wherein the elongation is determined by the following formula:

(Lf-LQ / L, where Lf is the ultimate fiber length at break and L is the initial fiber length before loading. Alternatively, the elongation at break may be at most about 50% and optionally at least about 90%. In other embodiments, the method and devices for practicing the present invention ensure that the porous fiber 54 can have a percent elongation at break of up to about 500% or more.

150 / B may be at most about 160% to ensure the desired behavior and processing capability.

In still other embodiments of the present invention, the porous fiber 54 may have a toughness of at least about 0.1 gram-centimeter per denier-centimer (gcm / denier-cm). Alternatively, the fiber may have a toughness of at least about 1.5 gcm / denier-cm and optionally may have at least about 2 g-cm / denier-cm. Other embodiments of the present invention may provide a porous fiber 54 having a toughness index of at most about 20 g-cm / denier-cm. Alternatively, the fiber toughness index may be at most about 10 g-cm / denier-cm and optionally may be at most about 5 g-cm / denier-cm to provide improved performance. The toughness index represents the fiber's ability to absorb energy and is determined by multiplying the fiber's toughness by elongating it at break and then dividing it by two.

For example, a typical calculation is:

(grams of burst load x elongation at burst) / (denier x 2), and can have as units (gram-cm) / (denier-cm).

Suitable test techniques for data acquisition to determine the various mechanical properties of the porous fiber are further described in the test procedure section below.

The porous fiber 54 may advantageously provide improved water availability. In particular embodiments of the present invention, the water uptake of the porous fiber 54 may be at least 0.1 mg / sec. Alternatively, the water uptake rate may be at least about 0.15 mg / sec. Optionally, it may be at least about 0.2 g / sec. In other embodiments, the water uptake rate may be at most about 15 mg / sec. Alternatively, the water uptake rate may be at most about 5 mg / sec. and optionally may be at most about 1.5 mg / sec to obtain an improved beneficial effect. For comparison, the porous fiber will have a water uptake rate of less than 0.1 mg / sec, as illustrated in Examples 8, 9 and 10 below.

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In addition, the amount of water taken up by the porous fiber 54 may be at least 0.1 mg in 60 seconds. Alternatively, water intake may be at least about 0.2 mg in 60 seconds, and optionally may be at least about 0.3 mg in 60 seconds. In other embodiments, the water intake may be at most about 25 mg in 60 seconds. Alternatively, the water intake may be at most about 5 mg in 60 seconds, and optionally may be at most about 2.5 mg in 60 seconds to obtain an improved beneficial effect. For comparison, the non-porous fiber will have a water uptake of less than 0.1 mg in 60 seconds, as illustrated in Examples 8, 9, and 10 below.

Suitable test techniques for obtaining data to determine various values relating to the availability of water in the porous fiber are further described in the section on test procedures to be given below.

The set of voids or pores 52 that create the desired porosity of the fiber 54 may be distributed on the outer surface of the fiber and may also be distributed in the inner portion of the fiber. In particular embodiments, the porous fiber structure 54 includes elongated voids of generally ellipsoidal and / or double conical shape, such as those represented in FIG. 7, 8, 9 and 9A. Preferably, the elongated voids 52 have a longer major axis 46 directed substantially along the longitudinal longitudinal dimension 44 of the fiber. In particular embodiments of the present invention, the elongated voids may have a major axis 46 whose length 42 in the major axis direction is not less than about 0.1 µm. Alternatively, the major axis length is at least about 0.2 µm and optionally the major axis length is at least about 0.25 µm. In other embodiments, the major axis length is at most about 30 µm. Alternatively, the length of the major axis 42 is at most about 10 µm and optionally is at most about 7 µm to achieve improved properties.

To facilitate obtaining the desired combinations of mechanical strength and water availability, in particular embodiments of the present invention, fibers are formed in which the void space with dimensions required for pore size represents at least about 30% of the total number of pores either on or in the fiber surface or both . alternately

150 / B the void space with the dimensions required for the pore size is at least about 50% and optionally represents at least about 60% of the total number of pores either on or in the fiber surface, or both.

In other embodiments of the porous fibers of the present invention, the voids having a major axis direction in the range of about 0.25 10 µm represent at least about 30% of the total number of pores either on or in the fiber surface or both. Alternatively, voids with a pore size of 0.25-10 pm represent at least about 50% and optionally represent at least about 60% of the total number of pores either on or in the fiber surface, or both, to ensure improved mechanical properties and water availability .

The elongated pores or voids may also have a predetermined ratio of their dimensions, which is defined by the ratio of the length 42 of the major axis of the pore 48 and the length 40 of the minor axis of the pore 46 that extends perpendicular to the major axis, such as. are observed in photomicrographs or determined by other imaging or measuring techniques used to determine the aspect ratio. In other embodiments of the present invention, the aspect ratio is at least about 1.3. Alternatively, the dimension ratio is at least about 1.5 and optionally at least about 2. In other embodiments, the dimension ratio is not greater than about 50. The alternative dimension ratio is not greater than about 20, and optionally not more than 15, to guarantee improved properties regarding with porosity and fiber behavior. The major axis of each elongated pore or void space is typically an axis that runs substantially parallel to the longitudinal dimension of the filament and can typically be represented by t

the largest measured dimension of each pore.

»» ‘T

As shown in FIG. 7, 8, 9 and 9A, the porous structure of the fiber 54 may have pores distributed along the outer surface of the fiber. The surface pores have a distribution in which the number of pores per unit surface area is at least about 0.01 pm ² , alternatively the number of pores per unit surface area is at least about 0.015 pm ^2, and optionally is at least about 0.05 pm ² . In other embodiments, the number of pores per unit surface area is at most about 10 µm ^-2 . alternately

150 / B the number of pores per unit surface area is at most about 8 μιτί ² and optionally is at most about 5 μηΥ ² to ensure improved wettability and liquid permeability.

As shown in FIG. 1, 2, 12 and 13, the porous structure according to the present invention may have a fiber cut surface 54

I porous voids with a mean pore area (relative to one pore) of at least about 0.001 micron ² (μιτι ² ). Alternatively, the mean pore area (relative to one pore) is at least about 0.002 μιτι ^2, and optionally is at least about 0.03 μιτι ² . In other embodiments, the mean pore area (relative to one pore) is at most about 20 µm ² . Alternatively, the mean pore area (relative to one pore) is at most about 10 μιτι ^2, and optionally is at most about 3 μηι ² to ensure improved wettability and liquid permeability.

The porous structure of the fiber 54 may also have pores distributed along its cut area such that the number of pores per unit area is at least about 0.01 μιτι- ² . Alternatively, the number of pores per unit area is at least about 0.015 µm ^2, and optionally is at least about 0.1 µm ² . In other embodiments, the number of pores per unit area is> * at most about 10 μιτι ² . Alternatively, the number of pores per unit area is at most about 8 μιτί ^2, and optionally is at most about 5 μιτί ² to ensure improved wettability and liquid permeability.

In other embodiments, the porous fiber structure 54 has pores distributed along its cut area such that the sum of the areas of the individual pores intersected by the cut gives a total pore area that is at least about 0.1% of the total fiber cut area (percent of the pore area is at least about 0.1 %). Alternatively, the percent pore area is at least about 1% and optionally is at least about 2%. In other embodiments, the percentage of pore area is at most about 70%. Alternatively, the percentage of pore area is at most about 50% and optionally at most about 20% to provide improved wettability and liquid permeability.

Referring to FIG. 1, 2, 9, 9A and 12, in particular embodiments of the porous fiber, may comprise sets of voids or pores which have arisen mainly in structural irregularities or other physical inhomogeneities of the fiber material and which are stretched therefrom, or

150 / B expanded. Such an initiator, structural inhomogeneity, may be formed by one or more of the following mechanisms: a particular transition between filler and polymerization resin, fluctuations in density and / or fiber material modulus, submicron-sized voids and / or air bubbles, any type of admixture having a dimension and / or a density different from the same fiber material parameter, as well as a combination of these mechanisms. More particularly, the fiber may preferably comprise a plurality of elongated or otherwise elongated voids, each void may be associated with a particular initiator 50 formed by a plurality of particulate material, such as particulate filler material.

The pores or voids may in principle surround the initiators or may be immediately adjacent to the initiators. The pores may also be located in the regions between the initiators. In addition, each of the elongated voids may have a length that is greater than the length of its ¹ ' ¹ associated initiator as it observes when looking at the voids

I *, in a longitudinal section, which is made along the length of the fiber. Due to the direction parallel to the length of the fiber, the voids may be substantially elongated in elliptical shape and / or may in principle have a double cone configuration in which the conical shapes contact with their bases. Due to the cut perpendicular to the length of the fiber, the voids may have a generally circular shape and / or a slightly oval or ovoid shape. In particular embodiments of the microporous fibers of the present invention, in principle, no pattern or regular arrangement of voids in the surface view or other longitudinal view of the fiber was observed. In another embodiment, in principle, no pattern or regular arrangement of voids was observed in a representative cross-section of the fiber. Accordingly, the arrangement of voids in the fiber material may be irregular and may in principle be random, with some irregular clumps. For example, such agglomeration may occur in the agglomeration regions of any filler material inserted. The observed porous fiber structure of the present invention may have a wide distribution

150 / B pore sizes in a particular cross-section of the fiber due to the dispersed pore distribution and the nature of the varying, tip-extending pore section along the fiber. The elongated shapes (e.g., elliptical or double conical shapes) of voids and the absence of specific void pattern patterns can clearly distinguish the microporous fiber structure of the present invention from porous fibers obtained by the phase separation method or other elongation method such as incremental elongation method used to produce microporous fiber CELGARD.

A view of the surface of the CELGARD fiber at a magnification of 15,000 x, as represented in FIG. 11, a plurality of micropores of generally oval or rectangular shape are arranged in bands of generally planar microporous regions arranged approximately in a direction perpendicular to the length of the fiber. These strips of microporous regions are further arranged in the fields in which the strips are located in an almost periodic and regular manner.

Referring to FIG. 3, 4 and 10, the porous fiber obtained by a conventional phase separation method comprises, similar to a fungus, a system of pores or voids separated by relatively thin walls. The system is assembled into lace, interconnected structures that define pores with membrane walls. In the configuration shown, the system forms layers of finger macroscopic voids disposed adjacent the hollow fiber lumen. The arrangement of the voids, in particular along the fiber cut, essentially creates a regular pattern. Referring to FIG. 10, the fiber surface appears substantially non-porous at a magnification of 15,000 x. .

In contrast to this particular embodiment, the porous fiber of the present invention may comprise pores limited by elongated areas subjected to tensile stress, which may, for example, be formed by plastic deformation of the fiber material. The stressed areas may be observed at least along the edges of the elongated surface voids located on the exposed fiber surface. In the porous fiber of the present invention there are edges and circumferential edges

150 / B of the fiber material sharp and sharply defined and essentially not fiberised and substantially dissimilar to the sponge in the areas surrounding the elongated void. Accordingly, the voids are effectively bounded by the fiber material having such edges, and these edges can be viewed along any surface, cross-sectional, or interior view of the fiber. The fiber material in the areas observed between voids is generally in the form of a plateau interrupted by voids.

Suitable techniques for obtaining data to determine the different size properties and porosity distribution of the porous fiber are further described in the test procedure section that follows.

Testing procedures

Mechanical properties:

A suitable method for determining the mechanical properties of the porous fiber 54 may use a Sintech tensile strength tester (SINTECH 1 / D) and Software Testworks 3.03. The tensile strength measuring device is

I ' _t , a device supplied by MTS System Co. The software and the software are supplied by MTS System Co., Sintech Division, which is based in Cary, NC 27513. Equipment and Software having essentially the same capabilities may also be used.

The mechanical properties can be evaluated by the tensile strength determination apparatus used in the fiber testing configuration. Testing is performed using a 10 pound (44.5 N) load cell and pneumatically driven, rubber-coated 3 inch (7.6 cm) jaws. Fiber testing is performed with a 2 inch (5.08 cm) gauge length and a clamping speed of 500.00 mm / min. A simple fiber sample is inserted perpendicular to the jaws and at their centers and maintained in position while the air pressure brings the jaws together. The fiber diameter is entered by the operator before the tensile strength measurement starts. For hollow fiber samples such as those in Examples 11 and 12, an annular fiber cross-section was used to calculate the tensile strength.

150 / B π ((outer radius) ² - (inner radius) ² ).

In each experiment, the fiber was loaded up to the point of rupture, and the software provided with the device and other programs plot the stress-strain relationship and calculate the desired mechanical properties of the sample.

T

Mechanical properties may include, for example, the Young's modulus, the tensile stress and the percentage of deformation or elongation at break.

Water availability:

A suitable method for determining the comparative water availability of a fiber may use the CAHN DCA 322 microbalance, a device supplied by ATI (Analytical Technology, Inc.), located in Madison, WI. The balance is sensitive to changes in force as small as 0.1 microgram and is equipped with two weighing positions ("A loop" and "B loop") and a tare position ("C loop"). , A loop "has a maximum load of 1.5 grams and" B loop "has a maximum load of 3.5 grams. Thus, the A loop "has better sensitivity, while the" B loop "is designed for greater load. Obviously, the operator will select a position that provides greater measurement sensitivity while being able to measure the greatest load expected to be tested.

Fiber testing for the examples described herein was performed at position A of the balance. Each fiber sample was of sufficient length (e.g., about 15 mm) to allow the fiber to be adhered with a strip or otherwise attached along or against a hanging wire or other test sample carrier. In the test sample, the 5 mm length of the carrier wire and the associated fibers are extended under the strip and remain exposed and accessible to contact with water during testing.

The CAHN system includes a movable pedestal that can be moved at a constant speed up or down. The test sample hangs from the selected balance loop or is otherwise attached to it and a beaker of water is placed on the movable base. The pedestal is raised so that the lower edge of the sample is just above the surface of the water to start the test.

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The software supplied with the CAHN system controls the experiment in accordance with the parameters specified by the operator. For fiber testing, this is placed on the balance and the balance is balanced to detect the amount of water received by the fiber when the sample is brought into contact with water. The software is set to count the force values at one-second intervals. The 2 mm length of the protruding fiber end is immersed in water and the water container stand is stopped. The test sample is left in water for 1 minute while the device collects the measured force values at one second intervals. Then the test sample is withdrawn from the water.

The data obtained in the experiment is then evaluated. In particular, the data can be transferred to a suitable spreadsheet program, such as Microsoft Excel version 5.0, and is plotted into a graph that depicts the weight gain versus time for one minute of water infiltration. The graph shows the trend of water uptake by the test sample and provides a convenient basis for comparing relative water uptake and relative water availability levels for different fiber samples. To allow for better comparison of fiber samples of different sizes, graphically depicted water uptake data as a function of time for different samples are normalized to refer to fiber weighing 0.0416 mg. The normalization factor is the ratio of the dry test fiber weight to the reference weight of 0.0416 mg. Water uptake is determined by using a two-second curve designation graphically showing normalized weight as a function of elapsed time over a one minute period of water suction. The water uptake rate given in the examples was determined by calculating the steepness of the data curve at the point that was recorded in the first second of the measurement of the data, as representative of FIG. 14. The amount of water received in the examples is the total weight gain recorded over one minute (60 seconds) of the measurement time in a graphical representation of the data. It should be noted that the measured and recorded weight gain may include weight gain derived from water absorbed into the initial porous structure as well as weight gain due to further fiber-water interaction. For example, a thin layer may be formed on the fiber surface

150 / B water. In addition, the fiber structure can swell to form pores with increased void volume and / or the fiber can change its configuration in another way, thereby creating greater capacity to recover and retain absorbed water.

Scanning electron microscopy and image analysis

Electron micrographs can be produced by conventional methods well known in imaging techniques. In addition, samples can be prepared for the desired image formation by well known and conventional preparation methods.

Since the porous fiber of the present invention can be very compliant even at low temperatures, it is important to avoid excessive damage to the fiber material when the fiber sample is cut and prepared to display the fiber cut. Using suitable preparation methods, for example, the fiber sample may be immersed in ethanol for one hour and then immersed in Liquid Nitrogen. For fiber cross-section imaging, a 1.1 surface can be prepared by cryomicrometry, such as using a Reichert Ultracut Microtom with FCS cryosection system (Leica, Deeflield, IL) using a fresh 6 mm glass knife at -180 ° C. The resulting fiber may then be attached to a suitable support and coated with gold or an Au / Pd (gold / palladium) mixture. The fiber microstructure can be sensed by scanning electron microscopy, such as using the JSM 6400 Scanning Electron Microscope (JEOL, Peabody, MA, which is equipped with electron detectors to capture both secondary and backscattered radiation.

Automated image analysis of void spaces and fiber pores can be performed in a well known and conventional manner. Examples of such methods are described, for example, in "Application of Automated Electron 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

150 / B (Copyright 1994 by MVA, Inc., 550 Oakbrook Parkway # 200, Norcross, GA 30093), Proc. 52 ^nd Annual Meeting of the Microscopy Society of America, ed. GW Bailey and AJ Garratt - Reed, published by San Francisco Press.

Image analysis to obtain pore distribution data in Example 1 was performed at Materials Analytical Services, a laboratory based in Norcross, GA. Image analysis to obtain pore distribution data in Example 4 was performed by MVA, Inc., a laboratory based in Norcross, GA.

For example, different types of image analysis can be performed with a Noran Voyager image analysis system that uses a 5,000x magnification. Data is generated by making an average of a total of twelve fields. The system is supplied by NORAN Instrument, Inc., which is headquartered in Middleton, Wl. A system that has approximately the same performance can also be used. During image analysis, the image of the porous structure may be digitized using conventional methods. An example of a digitized image is shown representative of FIG. 13th

Optical microscopy

Optical microscopy is a suitable technique to examine the microstructure along the outer surface of the porous fiber. In particular, a conventional oil immersion optical microscopy method may be used. Using this technique, samples are prepared by placing in an immersion oil having a refractive index (Nd) of 1.516 at 23 ° C per slide and covered. The immersion oil may be oil supplied by OLYMPUS OPTICAL CO, Ltd., which is headquartered in Lake Success, NY. Samples are photographed using a 100x oil immersion lens on a high-sensitivity film such as Kodak Gold 400 ASA 35mm film using daylight illumination. A suitable microscope is the OLYMPUS BH-2 optical microscope, which is supplied by OLYMPUS OPTICAL CO, Ltd., which is headquartered in Lake Success, NY. Other optical microscopes and equipment having substantially the same capabilities may also be used.

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DETAILED DESCRIPTION OF THE INVENTION

The following examples are intended to give a more detailed description of the subject matter of the present invention. The examples are given for the purpose of representation and are not intended to limit the scope of the present invention.

Example 1

A resin consisting of polypropylene (Himont PF301) (90 wt%) and T1O2 particles as a filler (SCC 4837, supplied by Standridge Color Corporation) (10 wt%) was mixed with Dow Corning D193 surfactant (6 wt%). , where the percentages are based on the total weight of the filler and resin), by double extrusion using a Haake laboratory twin screw extruder. The TiO ₂ particle size was in the range of about 0.1 to 0.5 µιτι as determined by scanning electron microscopy (SEM). The filler concentration was measured by elemental analysis. The Dow Corning D193 surfactant had an ALB value. equal to 12.2. The fiber spinning method involved feeding the bonded materials to the inlet opening and extruding them through an extruder with one screw having a length to diameter ratio of 24 (L / D = 24/1). The extruder had three heated areas, a metering pump, an on-line static mixer and an extruder die with 4 holes, each hole having a diameter of 0.3 mm. During extrusion of the fiber, the ratio of extrusion die width to fiber diameter was 40. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid was a solution consisting of isopropanol and water, mixed in a ratio of 9 parts of isopropanol to one part of water, measured by volume. The fiber was then pulled in air 2 x (elongation ratio 2), followed by pulling 1.7x (elongation ratio 1.7) in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The thread was then

150 / B cured by heating to 80 ° C before being wound using a winder. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile tester and are shown in Tables 1 and 2. The number of pores per µm ² of the fiber cut was approximately 0.74 and the number of pores per µm ^{2 of the} outer surface was approximately 0.08.

Example 2

Resin, consisting of polypropylene 95.3% (Himont PF301), 1.4% T1O2 concentrated inorganic filler (SCC 4837, supplied by Standridge Color Corporation), and 3.3% wt. % polydimethyl silsesquioxane powder, an organic filler (Dow Corning Additive # 23) was mixed with 6 wt. (based on total resin and filler weight) silicone-glycol surfactant (Dow Corning D193) by double extrusion using a Haake twin-screw extruder. The particle size of the organic filler was in the range of 1 to 5 µm as determined by scanning electron microscopy. The pooled materials were then extruded with a single screw extruder (L / D = 24/1) containing three heated regions, an on-line static mixer, a metering pump, and a 4-hole extrusion die, each having a diameter of 0.3 mm. . The fiber spinning method involved feeding the bonded materials to the inlet and extruding them with a single screw extruder having a length to diameter ratio of 24 (L / D = 24/1). The extruder had three heated zones, a metering pump, an on-line static mixer and extruder ^{'1 1} I die with 4 holes, each hole having a diameter of 0.3 mm. During extrusion of the fiber, the ratio of extrusion die width to fiber diameter was 33. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid was a solution consisting of 2 wt. surfactant (IGEPAL RC-630) in isopropanol / water solvent. The solvent consisted of isopropanol and water, mixed in a ratio of 9 parts of isopropanol to one part of water, measured

150 / B by volume. The fiber was then drawn in air 1.7 times followed by 2 times in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The fiber was then cured by heating to 85 ° C in a continuous furnace before being wound by a winder. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

Example 3

Resin composed of 93.2 wt. % polypropylene (Himont PF301), 1.4% T1O2 concentrate (SCC 4837, supplied by Standridge Color Corporation) and 5.4% wt. CaCO 3 (Omyacarb UF supplied by Omya Inc.), which was coated with 6 wt. (based on the weight of the filler (a) of the silica-glycol surfactant D193) was mixed by double extrusion with a Haake laboratory twin screw extruder. The CaCO ₃ filler particle size was in the range of 1 to 3 µm as measured by scanning electron microscopy. were then extruded with a single screw extruder (L / D = 24/1), which included an on-line static mixer, a metering pump, and an extrusion die with eight orifices each 0.3 mm in diameter. a ratio of extrusion die width to fiber diameter equal to 33. During the final phase of fiber production, the fiber formed was prewetted by the first surfactant liquid that was fed through the metering nozzle. per part of water, measured by volume but it was then pulled out in air 1.7x and then pulled out twice in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The thread was then

150 / B cured by heating to 80 ° C in a continuous furnace before being wound by a coiler. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

Example 4

Resin composed of 88.8 wt. % polypropylene (Himont PF301), 1.3 wt. % Of T1O2 concentrate (SCC 4837, supplied by Standridge Color Corporation) and 9.9 wt. CaCO ₃ (Omyacarb UF supplied by Omya Inc.) which has been surface treated with 6 wt. (based on filler weight) D193 silicone-glycol surfactant was mixed by double extrusion with a Haake laboratory twin-screw extruder. The particle size of the CaCO ₃ filler ranged from 1 to 3 µm as measured by scanning electron microscopy. The pooled materials were then extruded with a single screw extruder (L / D = 24/1) that included three heated regions, an on-line static mixer, a metering pump, and a 15-hole extruder die each 0.5 mm in diameter. . During extrusion of the fiber, the ratio of extrusion die width to fiber diameter was 40. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid consisted of isopropanol and water, mixed in a ratio of 9.8 parts of isopropanol to 0.2 parts of water, measured by volume. The fiber was then drawn in air 1.5 times followed by 1.4 times in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The fiber was then cured by heating to 90 ° C in a continuous furnace before being deposited in the nonwoven fabricator. The mechanical properties of the resulting porous fiber were then measured on a strength determination device

150 / B tensile Sintech and are shown in Tables 1 and 2 below. The number of pores per µm ² of the fiber cut was approximately 0.19.

Example 5

Resin composed of polypropylene (Himont PF301, 90% by weight) and T1O2 filler particles (SCC 4837, supplied by Standridge Color Corporation, 10% by weight) was mixed with Dow Corning D193 surfactant (6% based on total weight) resins and fillers) was extruded twice with a Haake laboratory twin screw extruder. The T 10 O 2 particle size was in the range of 0.1 to 0.5 microns as measured by scanning electron microscopy. The filler concentrations were measured by elemental analysis. The Dow Corning D193 surfactant had an HLB of 12.2. The fiber extrusion method included inserting the materials into the inlet opening and extruding with a single screw extruder having a length / diameter ratio of 24 (L / D = 24/1). The extruder comprised three heated areas, a metering pump, an on-line static mixer and an extruder die with 4 orifices each 0.3 mm in diameter. During extrusion, the ratio of extrusion die width to fiber diameter was 11. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid consisted of isopropanol and water, mixed in a ratio of 9 parts isopropanol to one part water, measured by volume. The fiber was then drawn in air 1.58 times followed by 2.2 times in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The fiber was then cured by heating to 80 ° C before being wound using a winder. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

150 / B

Example 6

Resin composed of polypropylene (Himont PF301, 90% by weight) and T1O2 filler particles (SCC 4837, supplied by Standridge Coor Corporation, 10% by weight) was mixed with Dow Corning D193 surfactant (6% based on total weight) resins and fillers) was extruded twice with a Haake laboratory twin screw extruder. The TiO ₂ particle size was in the range of 0.1 to 0.5 microns as measured by scanning electron microscopy. The filler concentrations were measured by elemental analysis. The Dow Corning D193 surfactant had an HLB of 12.2. The fiber extrusion method included inserting the materials into the inlet opening and extruding with a single screw extruder having a length / diameter ratio of 24 (L / D = 24/1). The extruder comprised three heated areas, a metering pump, an on-line static mixer and an extruder die with 4 holes, each having a diameter of 0.3 mm. During extrusion, the ratio of extrusion die width to fiber diameter was 11. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid consisted of isopropanol and water, mixed in a ratio of 9 parts isopropanol to one part water, measured by volume. The fiber was then drawn in air

1.7 times followed by 1.5 times in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The fiber was then cured by heating to 80 ° C before being wound using a winder. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

150 / B

Example 7

Resin composed of polypropylene (Himont PF301, 90% by weight) and TiO ₂ filler particles (SCC 4837, supplied by Standridge Color Corporation, 10% by weight) was mixed with Dow Corning D193 surfactant (6% based on total) weight of resin and filler) of silicone glycol surfactant D193, was extruded twice by a Haake laboratory twin screw extruder. The particle size of the TiO ₂ filler was in the range of 0.1 to 0.5 microns as measured by scanning electron microscopy. The filler concentrations were measured by elemental analysis. The Dow Corning D193 surfactant had an HLB of 12.2. The fiber extrusion method included inserting the material into the inlet opening and extruding with a single screw extruder having a length / diameter ratio of 24 (L / D = 24/1). The extruder comprised three heated areas, a metering pump, an on-line static mixer and an extruder die with 4 orifices each 0.3 mm in diameter. During extrusion of the fiber, the ratio of extrusion die width to fiber diameter was 33. During the final phase of fiber production, the formed fiber was prewetted with the first surfactant liquid that was fed through the metering die. The first surfactant liquid consisted of isopropanol and water, mixed in a ratio of 9 parts isopropanol to one part water, measured by volume. The fiber was then drawn in air 1.17 times followed by 1.5 times in a bath consisting of a second surfactant liquid. The second surfactant liquid was a solution consisting of isopropanol and water, mixed in a volume ratio of 9 parts isopropanol to one part water. The fiber was then cured by heating to 80 ° C before being wound using a winder. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

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Example 8

Resin composed of polypropylene (Himont PF301, 90% by weight) and particles. ·

TiO ₂ fillers (SCC 4837, supplied by Standridge Color Corporation, 10 wt.%) Were mixed with Dow Corning D193 surfactant (6% based on total resin and filler weight) of D193 glycol surfactant silicone was extruded twice by laboratory. Haake extruder with two screws. The particle size of the TiO2 filler ranged from 0.1 to 0.5 microns as measured by scanning electron microscopy. The filler concentrations were measured by elemental analysis. The Dow Corning D193 surfactant had an HLB of 12.2. The fiber extrusion method involved inserting the materials into the inlet opening and extruding with a single screw extruder having a length / diameter ratio of 24 (L / D = 24/1). The extruder comprised three heated areas, a metering pump, an on-line static mixer, and an extruder die with 4 orifices each 0.3 mm in diameter. The fiber was left loose during the extrusion of the fiber. During the final phase of fiber production, the formed fiber was prewetted with a surfactant liquid, which was fed through the metering spout. The surfactant liquid consisted of isopropanol and water, mixed in a ratio of 9 parts isopropanol to one part water, measured by volume. The mechanical properties of the resulting porous fiber were then measured on a Sintech tensile strength tester and are shown in Table 1 below.

Example 9

This sample consisted of a commercially available polypropylene staple fiber obtained from American Barmag, located in Charlotte, North Carolina. The staple fiber had a fiber length of 38 mm and was surface treated with a surfactant by immersion in a 10 wt% solution. of hydrophilic silicone-glycol (Dow Corning 193)

150 / B in acetone for 1 hour and dried at 50 ° C for 6 hours before testing. The fiber properties were measured and are listed in Table 1.

'

Example 10

This sample consisted of a commercially available 38 mm polypropylene staple fiber obtained from American Barmag, headquartered in Charlotte, North Carolina. The fiber properties were measured and are listed in Table 1.

Example 11

This sample is a conventional porous fiber obtained from Asahi Medical Co. Ltd., which is headquartered in Tokyo, Japan. As shown in FIG. 3, 4 and 10, the fiber has a lumen that extends longitudinally in the direction of the fiber length within it. It is believed that the porous structure in the illustrated fiber has been formed by a solution-extrusion process wherein the lumen configuration allows the coagulation liquid to enter into contact with the formed fiber both along the inner and outer surfaces of the fiber material. The structure has large finger-like pores within the inner wall of the fiber and has a sponge-like configuration of the lace pores adjacent the outer wall. In addition, the fiber typically has a thin layer on its outer surface that is skin-like and can prevent water from entering the fiber. The fiber properties were measured and are listed in Table 1.

Example 12

This sample is another conventional porous fiber sold under the trade mark CELGARD by Hoechst Celanese, located in Charlotte, North Carolina. As shown in FIG. 5,6 and 11, the fiber has a longitudinal lumen and is believed to have a porous fiber structure

150 / B was created in a manner that utilizes a number of incremental stretching steps. The structure, which is shown in section, comprises a lamella structure produced by the formation of interlamellar spaces in the recrystalline structure. In this structure, the pore comprises microfibrils which are oriented in the fiber in the longitudinal direction and the connecting parts are composed of laminated lamellae. The fiber properties were measured and are listed in Table 1.

Example 13

This sample is a microporous polypropylene fiber as shown in Example 1 of U.S. Pat. No. 4,550,123 to Albany International, which is headquartered in Mansfield, MA. As described in Example 1 of the patent, the denier fiber has 8.8 d. Other fiber properties are listed in Table 1.

150 / B

Table 1

Example no. speed reception (Mg / sec.) reception waters (mg per 1 min.) strength in turn (MPa) stretching , at break (%) size fibers index toughness (g-cm per denier-cm) 1 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 5 1.01 1.8 295 119 16d 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 1. 2,8 d 0.75 10 0,002 ' 0,005 362 60 2,8d. 1,30, 11 - - 8.4 10.1 300 μιτι 0,003 12 - - 51 207 300 μιτι 0.65 13 - - 217 23 8,8 d 0.30

Once the invention has been described in great detail, it will be readily apparent that various changes and modifications can be made without departing from the spirit of the present invention. All such modifications and changes are included within the scope of the present invention as defined in the appended claims.

Claims (20)

PATENT CLAIMS 1. A microporous fiber, characterized in that it comprises voids therein, said fiber having: a denier of at most 50; a percent elongation at break of at least about 30%; and a tensile strength of at least about 200 MPa. The fiber of claim 1, wherein said fiber has a denier of at most 20. The fiber of claim 1, wherein said fiber has a denier of at least about 10. The fiber of claim 1, wherein said fiber has a percent elongation at break of at least about 50%. The fiber of claim 1, wherein said fiber has a percent elongation at break of at least about 90%. The fiber of claim 1, wherein said voids comprise surface voids that are irregularly distributed over an outer surface of said fiber. 7.. The fiber of claim 1, wherein said voids comprise voids that are irregularly distributed in a section of said fiber. The fiber of claim 1, wherein said fiber comprises voids having an elongated shape. 31,150 / B The fiber of claim 8, wherein said fiber comprises voids having a generally ellipsoidal shape. The fiber of claim 8, wherein said elongated i the voids have their main axis substantially parallel to the longitudinal dimension of said fiber. The fiber of claim 8, wherein said elongated voids have a major axis of at least about 0.1 µπι. The fiber of claim 8, wherein said elongated voids have a major axis of at most about 30 µπι. 13. The fiber of claim 6, wherein said voids have a mean distribution density of at least about 0.01 voids. Ί. per μπι ² of the outside surface. The fiber of claim 6, wherein said voids have a mean distribution density of at most about 10 voids per µπ ^{2 of} said outer surface. The fiber of claim 7, wherein said voids have a mean distribution density of at least about 0.01 voids per µπ ^{2 of} said section. 'I. ¹ The fiber of claim 7, wherein said voids have a mean distribution density of at most about 10 voids per m ^{2 of} said section. 17. The fiber of claim 1, wherein said porous fiber is substantially free of lumens. 31,150 / B The fiber of claim 1, wherein said fiber is a fiber material and said fiber comprises a plurality of voids that have been initiated at the structural discontinuities of said fiber material. I The fiber of claim 1, wherein said fiber comprises a plurality of elongated voids each associated with a particle initiator, each of said void spaces having a length greater than the length of its associated particulate initiator. 20. The fiber of claim 1, wherein said fiber is comprised of a fiber material, and wherein said voids are bounded by a fiber material having sharp edges.