Fibrous polymeric material and its composites

FIELD OF THE INVENTION

[0002] The present invention relates to a porous, fibrous elastomeric polymeric material for durable end uses such as in garments, footwear, clothing accessories, other protective coverings, and the like. This polymeric material has a unique combination of durability properties such as abrasion and pilling resistance with an acceptable handle and air permeability. This invention also relates to water resistant, water-vapor permeable composites of the polymeric material.

BACKGROUND OF THE INVENTION

[0003] A large variety of durable end uses require use of flexible polymeric materials with high abrasion resistance. If porosity or air permeability is not a requirement of these flexible materials in specific end uses, non-porous polymer sheets and films are typically used as the material of choice. Typical examples of such end uses are raincoats, inflatable rafts, conveyor belt linings etc. made from wear resistant polymers such as polyethylene, nylon, polyurethane etc. If, in addition, the end use requires conformability then such non-porous sheets and films are made from wear resistant, but elastic polymers such as polyurethanes, polyetheresters and the like. Such films and sheets of these polymers are typically made by common polymer processing techniques such as cast extrusion or film blowing. As shown schematically in FIG. 1a, when viewed in cross-section, such polymeric films and sheets show the non-porous nature of such materials.

[0004] Porosity and air permeability are desired features in a flexible material for a number of durable end uses such as clothing and accessories, filtration etc. In these cases, the material should provide open passages from one side to the other to allow passage of air and vapors through it. Woven and knitted fabrics are examples of polymeric, air permeable materials with acceptable durability such as abrasion resistance as they are based on continuous lengths of highly oriented fibers that are first formed from the polymer, optionally towed into yarns and then woven or knitted together in subsequent steps. For example, in construction of re-usable garments and clothing accessories, woven and knitted fabrics are used as they maintain the aesthetic and functional properties of the article even after continued use over a prolonged time period. This is so because woven and knitted fabrics, typically obtained from inelastic polymers such as nylon, polyester, polypropylene, are acceptably resistant to effects such as abrasion, laundering, weathering etc. As shown schematically in FIG. 1b, when viewed in cross-section, such fabrics show a distinct assemblage of fibers organized in a regular weaving or knitting pattern. Expectedly, in these fabrics, no fusion of fibers take place and the fibers maintain their individual identity. Elastomeric properties can be imparted to such fabrics by incorporating some elastic fibers along with the hard or inelastic fibers. Suitable elastic fibers include polyurethane block copolymer based fibers as described in U.S. Pat. No. 2,692,873 and sold as Lycra™ or Spandex fibers.

[0005] Non-woven fabrics also are typical of flexible, porous materials exhibiting porosity and air permeability. However, these materials are used almost exclusively for non-durable end uses such as garments meant for single use or very limited re-use primarily because of their poor resistance to abrasive forces. Usually, under such forces the non-woven fabrics rapidly disintegrate, leading to loss of aesthetic and/or functional properties. Resistance to abrasion is one of the key requirements of a material to be suitable for durable end uses like garment and clothing accessories. Unlike knitted and woven fabrics, non-woven fabrics exhibit very poor abrasion resistance. Typically, when subjected to abrasive forces, a non-woven fabric will abrade rapidly resulting in defects such as pilling or roping which are aesthetically unappealing. The poor abrasion resistance of non-woven fabrics result from its structural characteristics. As shown schematically in FIG. 1c, when viewed in cross-section, non-woven fabrics show a random assemblage of natural or synthetic fibers lightly bonded together. Within this structure, abrasion resistance can be improved by increasing the degree of bond or entanglement between the fibers, but that comes at the expense of other desirable properties such as hand and air permeability. To date, at comparable basis weights, we are not aware of the availability of any non-woven fabric that is comparable to woven and knitted fabrics in terms abrasion resistance and hand. As a result, non-woven fabrics are generally not looked upon as a viable material for durable end uses that require air permeability. Non-woven fabrics also can be made to exhibit elastomeric properties by choosing appropriate polymers. For example, U.S. Pat. Nos. 3,439,085; 5,230,701; 4,660,228 describe elastomeric non-wovens made from polyurethane polymers. Similarly, U.S. Pat. Nos. 4,724,184 and 4,707,398 teach respectively how elastomeric non-wovens can be obtained from copolyetheramides and from copolyetheresters.

[0006] Many applications which require the wear durability described previously are also subjected to significant levels of UV radiation and weathering. As nonwovens are extended into these more harsh applications, resisting degradation due to UV radiation or weathering will be advantageous. A polymer chemistry will be required which resists this degradation, but does not negatively impact the processability or final properties of the fabric.

[0007] Non-woven fabrics are manufactured by two broad categories of processes. In the first category, referred to as fiber to web processes, staple or short fibers are converted into webs using processes such as air laying, carding, hydro-entangling etc. In the other category, referred to as polymer laid processes, bulk polymer is fiberized using an extrusion process and directly collected in form of a web. Melt blowing and spun bonding are typical examples of polymer laid processes. These manufacturing processes for non-woven fabrics are relatively less expensive than producing woven or knitted fabrics as the conventional steps of towing and weaving or knitting of fibers or yarns are eliminated. Consequently, there continues to be considerable incentive in developing non-woven fabric-like materials that can provide improved abrasion resistance or end-use durability without significantly affecting other fabric properties such hand, air permeability etc.

[0008] It is therefore apparent that there continues to be a need for a porous polymeric material that combines the cost advantage of the non-woven processing and the abrasion resistance of the non-porous film to match that of woven and knitted fabrics. In addition, resistance of such materials to UV radiation would provide significant benefits in harsh applications where the material is subject to UV radiation and weathering. Use of such abrasion resistant polymeric material would be widespread not only in extending the conventional use of non-wovens but also more remarkably in areas where woven and knitted fabrics are currently used including creation of water resistant, water vapor permeable composites described in U.S. Pat. Nos. 4,194,041; 5,026,591; 4,532,316 and 5,529,830 to W. L. Gore and Associates for durable end uses such as garments and clothing accessories for highly demanding outerwear applications.

SUMMARY OF THE INVENTION

[0009] It is a purpose of the present invention to provide a porous polymeric material that exhibit properties in between that offered by a non-porous film and that offered by fibrous non-woven fabric. For example, the material of the invention demonstrates durability properties such as abrasion resistance at a level significantly greater than conventional non-woven fabrics such that it can perform at least comparably to certain woven and knitted fabrics while maintaining comparable air permeability. In addition to the enhanced durability of the material, resistance to UV radiation is possible.

[0010] The purpose is accomplished herein by creating a three dimensional porous material comprised of polymeric fibers fused together randomly along portions of their length such that the cross-section comprises a network of irregular shapes of polymer that are interconnected so as to define void space, said material having a bulk density of at least 0.35 g/cc. The material is elastomeric and has a moisture vapor transmission rate of at least 1000 g/m2/day.

[0011] In another aspect, the material is defined as a three dimensional porous material comprised of

[0012] polymeric fibers fused together randomly along portions of their length such that the cross-section comprises a network of irregular shapes of polymer that are interconnected so as to define void space; said material

[0013] having a bulk density of at least 0.35 g/cc;

[0014] being elastomeric;

[0015] having a moisture vapor transmission rate of at least 1000 g/m2/day;

[0016] having a basis weight between 30 and 300 g/m2; and

[0017] having an abrasion resistance of at least 100 cycles.

[0018] The polymeric materials of this invention have a novel structure that imparts to it durability properties that are far superior to conventional non-woven fabrics. The structure of this invention also provides for little resistance to the through passage of air, which is important to applications requiring this combination of properties. These properties makes the polymeric material of this invention a viable alternative to conventional woven and knitted fabrics in many applications. This aspect of the invention can be defined as

[0019] a three dimensional porous material comprising polymeric fibers fused together randomly along portions of their length such that the cross-section comprises a network of irregular shapes of polymer that are interconnected so as to define void space; said material

[0020] having a bulk density of at least 0.35 g/cc;

[0021] being elastomeric;

[0022] having an air permeability of at least 10 cm3/cm2/sec;

[0023] having a basis weight between 30 and 300 g/m2; and

[0024] having an abrasion resistance of at least 100 cycles.

[0025] Many end uses which require a combination of wear durability and permeability, as described previously, are also subjected to significant levels of UV radiation and weathering. It would thus be advantageous for the material to have a polymer chemistry which resists this degradation, but does not negatively impact the processability or final properties of the material.

[0026] It is also a purpose of the present invention to use this material to create novel water resistant, water vapor permeable composites or laminates with improved durability properties such as abrasion resistance without compromising other functional attributes such as water vapor permeability, water resistance and handle that are retained over the intended life of articles such garments and clothing accessories made from these composites.

DEFINITIONS

[0027] As used in this application:

[0028] “Porous” with respect to films and membranes means full of passages or channels from one side to another.

[0029] “Non-porous” with respect to films and membranes means having no passages or channels.

[0030] “Flexible” means bendable without breaking.

[0031] “Water resistant” means the material in question passes the water resistance test described further below.

[0032] “Water vapor permeable” means that the material in question has a moisture vapor transmission rate (MVTR) of at least 1000 grams/m2/day.

[0033] “Durable” or “durability” means that the material in question is abrasion resistant.

[0034] “Garment” means any article that can be worn, and includes footwear, hats, gloves, shirts, coats, trousers, etc.

[0035] “Fibrous” means fiber-like structures.

[0036] “Elastomeric” means a material capable of stretching at least 50% of its original length when a force is applied and upon release of the stretching force will return to at least 80% of its original length.

[0037] “Air Permeable” means that the material has an air permeability, as determined by the test described herein, of at least 10 cm3/cm2/sec.

[0038] “Irregular” means not of any regular geometrical shape.

[0039] “Ribbon” means a narrow three dimensional strip.

[0040] “Microporous” means a structure not visible to the naked eye.

[0041] “Coalesced” means merged to the point that individual identity is lost.

[0042] “Fabric” means a material made from textile fibers or yarns.

[0043] “Non-woven fabric” means a porous, textile-like substance composed primarily or entirely of fibers randomly assembled in a web without use of a weaving or knitting process.

[0044] Percentage stretch and recovery are defined as

%stretch=(Ls/Lo−1)×100

%recovery=([Ls−Lf]/[Ls−Lo])×100

[0045] where Lo is the original length, Ls the length when a stretching force is applied, and Lf is the length when the stretching force is released.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]
FIG. 1A is a schematic view of the cross-section of a non-porous polymeric film of the prior art.

[0047]
FIG. 1B is a schematic view of the cross-section of a woven fabric of the prior art.

[0048]
FIG. 1C is a schematic view of the cross-section of a non-woven fabric of the prior art.

[0049]
FIG. 2A is a photomicrograph of the cross-section of a commercial elastomeric non-woven fabric of comparative example 3 at a magnification of 200×.

[0050]
FIG. 2B is a photomicrograph of the cross-section of a commercial elastomeric non-woven fabric of comparative example 7 at a magnification of 400×.

[0051]
FIG. 3A is a schematic view of the surface of the polymeric material of this invention.

[0052]
FIG. 3B is a schematic view of a cross-section of the polymeric material of this invention.

[0053]
FIG. 4A is a photomicrograph of the surface of the polymeric material of this invention as described in Example 1 at a magnification of 100×. Basis Weight: about 130 g/m2.

[0054]
FIG. 4B is a photomicrograph of the cross-section of the polymeric material of this invention as described in Example 1 at a magnification of 200×. Basis Weight: about 130 g/m2.

[0055]
FIG. 5A is a photomicrograph of the surface of the polymeric material of this invention as described in Example 2 at a magnification of 100×. Basis Weight: about 130 g/m2.

[0056]
FIG. 5B is a photomicrograph of the cross-section of the polymeric material of this invention as described in Example 2 at a magnification of 450×. Basis Weight: about 130 g/m2.

[0057]
FIG. 6 is a photomicrograph of the cross-section of the polymeric material of this invention at a magnification of 500×. Basis Weight: about 80 g/m2.

[0058]
FIG. 7 is a photomicrograph of the cross-section of the polymeric material of this invention at a magnification of 600×. Basis Weight: about 40 g/m2.

[0059]
FIG. 8 illustrates the abrasion resistance of the polymeric material of this invention and of commercial elastomeric non-woven fabrics as a function of bulk density. Solid Line shows the trend for materials of this invention. Broken Line shows the trend for commercially available elastomeric non-woven fabrics.

[0060]
FIG. 9 is a schematic representation of the preferred method of obtaining the polymeric material of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0061] As stated earlier, non-porous films made of abrasion resistant elastomeric polymeric materials are known to be flexible as well as abrasion resistant which makes them suitable for durable end uses. They, however, are not suitable for durable end uses that require air permeability, since such films, as shown schematically in FIG. 1a, are not porous in nature and are void free, shown as 10, and thus prohibit the passage of air. In such cases, synthetic woven or knitted fabrics are used as they provide the needed flexibility, porosity and abrasion resistance required. The resulting structure, as shown schematically in FIG. 1b for woven fabric, therefore is made up of individual fibers 20, grouped in yarns 21, and assembled in a regular arrangement. The porosity is derived from the spacing between the fibers and the abrasion resistance is provided by the highly oriented strong fibers itself. Woven and knitted fabrics, both elastomeric as well as non-elastomeric, are rather expensive due to a large number of processing steps involved in converting a polymer into the fabric. Considering the widespread use of these fabrics in durable end uses, it is desirable to have a material that can perform like woven and knitted fabrics but is structurally different to permit lower cost processing.

[0062] Non-woven fabrics that are made by polymer laid processes offer such processing advantages as the capability of a synthetic polymer to be directly fiberized and converted into a fabric without any need for weaving or knitting. Structurally, as shown schematically in FIG. 1c, such non-woven fabrics are made of randomly arranged fibers 22 where the fibers are thermally, chemically or mechanically lightly bonded to one another at 23. FIGS. 2a and 2b show the cross-sectional photo/micrograph of two different commercially available elastomeric non-woven fabrics made from polyurethane polymers. The structure consists essentially of randomly arranged individual polyurethane fibers that are lightly bonded to other fibers in some cases. This non-woven structure offers porosity between the fibers, but the abrasion resistance is usually very poor. As a result, these elastomeric non-woven fabrics are not suitable for durable end uses. When subjected to abrasion, the lightly bonded fibers are easily debonded and rapidly results in breakage, pilling or roping upon further abrasion. Considering its processing advantages, it would be desirable if non-woven fabrics could be made as abrasion resistant as woven and knitted fabrics without compromising other functional characteristics such as porosity and handle. To achieve that, a different fibrous structure is required to provide such improved resistance. The present invention accomplishes that.

[0063] The present invention describes a three-dimensional, porous elastomeric polymeric material, usually in the form of a sheet or film, that possess a structure which combines the structural features of a non-porous film and a non-woven fabric. Typically the material of this invention ranges in thickness from 3 to 50 mils, preferably 5 to 25 mils. The basis weight of the material can also vary from 30 to 300 grams/m2, preferably 40-200 and most preferably 80 to 150 grams/m2.

[0064]

FIGS. 3

a
and 3b schematically illustrate the structure of the material of this invention, and FIGS. 4 to 7 are photomicrographs of the same. The surface of the material invented is fibrous in nature as shown schematically in FIG. 3a and through photomicrographs in FIGS. 4a and 5a. In FIG. 3a, the surface 1 consists predominantly of randomly arranged polymeric strands 2 formed by individual fibers randomly fused to one another at least along part of its length such as to lose their individual identity. In addition, the strands 2 are also coalesced at junctions 3 where the strands have contacted each other. The strands vary in size from 10 to 100 microns. Few individual fibers 4 are also seen to be present. A different perspective of the structural features of the material of this invention can be observed from its cross-sectional view as shown schematically in FIG. 3b. In terms of definition, a cross-section represents a section of the material taken along a plane which is perpendicular to the material's surface. The cross-section of this material (see FIGS. 3b, 4b & 5b), consists primarily of irregularly shaped non-porous polymeric areas 6 along with that of few fibers 4, still existing in their individual form. The polymeric areas 6 represent the cross-section of the polymeric strands 2. The diameter of the individual fibers vary from 5 to 30 microns and the cross-sectional area occupied by the irregularly shaped areas are greater than 50% of the total cross-sectional area occupied by the polymer structure. This ratio of area to the total polymer area depends on the basis weight of the material. As seen in FIGS. 5, 6 and 7, higher basis weight material show more coalescence, thereby resulting in the ratio of strand area to polymer area to be higher. The porosity of the structure arises from the network of interconnected voids 7 that provide passages for air permeability.

[0065] Thus, in terms of photomicrographs, the polymeric material appears to have a structure that is comprised of a surface primarily containing polymeric strands fused at least at crossover points, and an inner cross section of predominantly polymeric strands fused partially at least along abutting areas, and forming a non-porous network of irregularly shaped areas of polymer that are interconnected so as to define interconnected voids.

[0066] The polymeric material of this invention, due to the novel structure described above, exhibits properties that lie between that of a non-porous film and that of a non-woven fabric. For example, the bulk density of the material of this invention is higher than that of common elastomeric non-wovens but less than that of a non-porous film. For example, as listed in Table 2, the bulk density of commonly available elastomeric non-wovens varies from 0.20 to 0.36 grams/cm3, whereas the density of the elastomeric polymers used to make these ranges from 0.9 to 1.25 grams/cm3. In comparison, the bulk density of the material of this invention is at least 0.35 grams/cm3 and most commonly in the range of 0.40 to 0.55 grams/cm3. The increased density is a natural consequence of the novel structure with reduced porosity caused by the presence of the coalesced, dense polymeric areas that are non-porous in nature. The density can be higher so long as the MVTR is above the preferred 1000 g/m2/day value. In another aspect of the invention the density can be higher so long as the air permeability is greater than the preferred 10 cm3/cm2/sec value.

[0067] The porous polymeric material of this invention is elastomeric in nature. These properties are controlled by the amount of coalesced ribbons within the structure as well as the overall basis weight. Generally speaking, higher coalescence and higher basis weights produce stronger material with increased force required to stretch the material. Typically, irrespective of its orientation, the material can be stretched at least 50%, preferably at least 100% and most preferably at least 300% upon application of a tensile load. Upon removal of the load, the material recovers at least 80% of its original dimension, preferably recovers at least 90% in both the machine and the transverse directions.

[0068] The unique structure of the porous polymeric material of this invention has a remarkable effect on durability properties such as abrasion resistance. When the surface of the invented material is abraded, the polymeric strand structure being one-step closer to that of a non-porous film impart added resistance to abrasion forces. FIG. 8 compares the abrasion resistance of the invented material and commercially available elastomeric non-woven fabrics at different basis weights. Clearly, the abrasion resistance of the material of this invention is at least 2 times, more commonly 4 times higher than that offered by elastomeric non-woven fabrics of comparable basis weight but of much lower bulk densities. For a given polymer, abrasion resistance increases with basis weight particularly at higher basis weights. In general the abrasion resistance will be greater than 50 cycles. For basis weights greater than 70 gram/cm2, the abrasion resistance is preferably at least 150 cycles and most commonly at least 300 cycles. At the minimum, the high abrasion resistance of the invented material makes it comparable in performance to certain woven and knitted fabrics. Typically, the abrasion resistance of the invented material is significantly greater than that for woven, knitted or non-woven fabrics of comparable basis weights. For example, a 136 gram/m2 woven Nylon Cordura® fabric has an abrasion resistance of 430-650 cycles as compared to a 130 gram/m2 of this invention commonly having an abrasion resistance that is three-fold higher.

[0069] In general, when the basis weight is between 30 and 80 g/m2, the abrasion resistance should be at least 100 cycles. When basis weight is between 80 and 100 g/m2, the abrasion resistance should be at least 150 cycles. When it is between 100 and 150 g/m2, the abrasion resistance should be at least 300 cycles. When basis weight is between 80 and 120 g/m2, the abrasion resistance is preferably at least 750 cycles. When basis weight is between 150 and 300 g/m2, the abrasion resistance should be at least 1000 cycles.

[0070] The material of this invention can be formed using conventional polymer laid processes such as meltblowing and spunbonding with some process adjustments or subsequent operations such as densification by calendering, if necessary. The invented material, however, is preferably formed by a melt blowing process such as that described in Wente, Van A., “Superfine Thermoplastic Fibers”, in Industrial Engineering Chemistry, vol.48, pages 1342 (1965) except that a drilled die is preferably used. Referring to FIG. 9, the thermoplastic polymer is fed into an extruder 8 which feeds a melt blowing die 9. As the polymer is extruded, a high velocity stream of heated air draws and attenuates the extrudate into a stream of fine fibers 10 which is then collected on a carrier substrate 11 moving over a perforated cylindrical collector 12 to create the layered composite 14 with the invented material 13 on top of the carrier substrate 11. The collector can alternatively be a perforated belt. Usually vacuum is applied at the collector to aid in formation of a fibrous web. Alternatively, the use of the carrier substrate can be eliminated if the collector surface has the correct release properties to prevent sticking of the fibers and also provides the appropriate level of air permeability.

[0071] In the above method, the melt blown fibers are collected in a random fashion on the substrate prior to complete solidification so that the fibers are able to coalesce to one another and form the material of this invention. The carrier substrate is preferably air-permeable such as woven, knitted or non-woven fabrics or metal or plastic screen and meshes to aid and regulate the air flow through the collector which can significantly affect the coalescence within the structure formed. Preferably, the carrier fabric is a woven fabric with an air permeability of less than 100 cm3/cm2/sec. At higher substrate permeability, under identical process conditions, the material formed will typically have lower bulk density and lower abrasion resistance. However, the effect of increased air permeability of the carrier substrate or the collector can be somewhat compensated by adjusting the process conditions such as higher melt temperature, higher throughput, and shorter distance of the collector from the die to name a few.

[0072] The surfaces of the material of the invention can be patterned or embossed. If the carrier substrate or the collector possesses a pattern, such as the weave pattern in case of a woven fabric or metal screen, a mirror image of the pattern can be transferred onto one surface of the material of this invention. The clarity of the pattern will be dependent on the specific details of the melt blowing conditions employed. Alternatively, such a pattern can be created on one or both the surfaces of the invented material by using conventional secondary operations such as embossing.

[0073] Elastomeric synthetic polymers are used to create the porous polymeric material of this invention. Typically, such polymers need to be thermoplastic in nature with low modulus of elasticity, low hardness, high degree of elongation and high resistance to abrasion and wear. Commonly, such elastomeric polymers are block copolymers, preferably belonging to polyurethanes, polyetherester or polyetheramide family. Such thermoplastic elastomeric copolymers are available commercially from a number of sources such as Morthane® and Estane® brand of polyurethanes from Morton Polyurethanes (Chicago, Ill.) and B. F. Goodrich (Brecksville, Ohio), respectively. Similarly, polyetheresters are available as Hytrel® from Dupont (Wilmington, Del.); as Arnitel® from DSM (Evansville, Ind.); as Riteflex® from Ticona, (Summit, N.J.) and polyetheramides as Pebax® from Elf Atochem America, Pa.

[0074] The choice of the specific family of elastomeric polymer is dictated by the intended end use as well as the processability considerations. Hardness of the polymer dictates the stiffness, drape and the hand of the material. Typically, the hardness of the polymer should be as low as possible without compromising its abrasion resistance. The hardness can range from 60 Shore A to 60 Shore D, preferably from 60A to 40D. In addition to being soft, high elongation to break is also a characteristic of these elastomeric polymers. Typically, the elongation to break should be at least 300%, preferably at least 400%, most preferably greater than 500%. In addition to mechanical properties, other requirements such as temperature resistance, UV stability, solvent resistance etc. will also dictate the specific polymer or additive(s) to be used. In cases where a minimal amount of challenge from UV radiation or weathering will be encountered, stabilizer packages can be utilized. These stabilizer packages act by a variety of methods to control the degradation and the effects of degradation. These packages can include energy absorbing elements to protect the polymer or oxidation scavengers to minimize the effect of degradation. Instances may arise where protection from severe or long term environmental exposure is needed. In these instances, the polymer backbone should be chosen from an inherently stable chemistry. Typically, in urethane chemistry, aromatic hard segments should be replaced with aliphatic hard segments or similarly stable chemistries. These polymers can be further protected with the addition of stabilizers. These changes in chemistry must still allow for the production of the invention to be viable candidates.

[0075] To be processable, the polymer should be thermally stable and it should also possess specific melt viscosity characteristics under the desired processing conditions. Generally, a melt viscosity less than 1000 poise is required to obtain acceptable melt blowing properties and the processing temperatures should be adjusted accordingly for the specific elastomeric polymer being used. In terms of melt flow index (MFI) measured at 195° C., 5 kg. load according to ASTM D1238-89, the polymer should exhibit an MFI greater than 10 g/10 minutes, preferably greater than 25 g./10 minutes and most preferably greater than 50 g./10 minutes.

[0076] The polymers used may be mixed with other appropriate additives such as, for example, pigments, colorants, antioxidants, stabilizers, flow promoters, slip agents, fillers, solid solvents, cross-linking agents, particulates and other processing additives. In addition, the polymers may also contain additives to impart water repellency, oil repellency, hydrophilicity, soil removal and other such characteristics. One example of such additives is the use of fluorinated compounds to impart water and oil repellency to melt blown fibers as described in U.S. Pat. No. 5,025,052. Another example is the use of cross-linking agents, like multi-functional isocyanates to improve the heat and chemical resistance of thermoplastic polyurethane polymers.

[0077] Thermoplastic polyurethanes, due to their high abrasion resistance, low hardness and excellent elastomeric properties, are the most preferred polymer to create the material of this invention. Provided they have the desired melt rheological properties for processing, such polyurethanes can be based on either polyester or polyether soft segments and can have aromatic or aliphatic isocyanate moieties forming the hard segment. Typical properties of such thermoplastic polyurethanes range from 70A to 60D for hardness, 400 to 1000% break elongation and 1.05 to 1.20 for specific gravity. In terms of processability, such polyurethanes should be processable (melt viscosity less than 1000 poise) at temperatures without significant thermal degradation.

[0078] Water resistant, water vapor permeable substrates with acceptable softness and flexibility are generally manufactured through direct coating or adhesive lamination with durable fabric layers to create durable composites that are water resistant, but water vapor permeable. As described in U.S. Pat. Nos. 4,194,041; 5,036,551 and 5,529,830, such composites are used commonly for garment applications, as they provide improved comfort by allowing the passage of moisture from perspiration while offering protection from rain and wind. The durable polymeric materials of this invention are combined with a such water resistant, water vapor permeable substrate to create durable composites of this invention.

[0079] A large variety of water resistant, water vapor permeable substrates can be used to create such durable composites. Non-porous films of hydrophilic copolymers, such as polyetherurethanes, polyetheresters and polyetheramides are typical examples of such substrates and have been described respectively in U.S. Pat. Nos. 4,194,041; 4,725,481; 4,230,838 for example. In practice, these polymers are converted into thin films by extrusion, film blowing or solvent casting. The films are then subsequently adhered to the invented material at least on one side to create the water resistant, water vapor permeable composites. Alternatively, such hydrophilic polymers can be extruded or solvent coated directly onto the invented material to create the composites of this invention. In such instances, the hydrophilic polymer can exist as a layer on the surface with minimal penetration of the porous material or it can be fully penetrated where it occupies the entire porous structure. Typically, however, the hydrophilic polymer will only be partially penetrated into the porous structure of the invented material to create enough pore occlusion to impart acceptable water resistant properties without compromising the water vapor permeability.

[0080] Microporous polymer membranes are also used as water resistant, water vapor permeable substrates. The preferred microporous polymer membrane is expanded polytetrafluoroethylene (ePTFE) which is characterized by a multiplicity of open, interconnecting microscopic voids, high void volume, high strength, softness, flexibility, and stable chemical properties. U.S. Pat. Nos. 3,953,566 and 4,187,390 describe the preparation of such microporous ePTFE membranes and are incorporated herein by reference. While retaining permeability, ePTFE membranes can be further treated to impart improved resistance to contamination by low surface tension liquids such as solvents and oils. Typically, such oleophobic ePTFE is obtained by treating it with fluoropolymers as described in U.S. Pat. No. 5,375,441.

[0081] For improved protection from wind and from contamination, composites of microporous membranes with hydrophilic polymers are also used as substrates. The continuous hydrophilic polymer layer selectively transports water vapor by diffusion, but does not support pressure driven liquid or air flow. Therefore, moisture, i.e., water vapor, is transported but the continuous layer precludes the passage of such things as air-borne particles, micro-organisms, oils or other contaminants. The continuous layer also makes the composite to be air impermeable. A preferred composite substrate is ePTFE with a coating of a continuous layer of a hydrophilic polymer such as polyurethane as described in U.S. Pat. No. 4,194,041. If needed, oleophobic ePTFE can also be used to create a composite substrate as described above.

[0082] Novel water resistant, water vapor permeable composites can be further created by combining the water resistant, water vapor permeable composites with the porous elastomeric material of this invention at least on one side of the substrate. If desired, another layer of the invented material or a layer of conventional woven, knitted or non-woven fabric can be bonded to the other side of the substrate. The preferred method of combination is through adhesive lamination. For example, as described in U.S. Pat. No. 4,532,316, a polyurethane adhesive can be used in a discontinuous pattern to create the desired composites. Alternatively, as described in U.S. Pat. No. 5,036,551, a continuous layer of hydrophilic polyurethane can be used as the adhesive to create the desired composites. Care must be taken to ensure that the temperatures encountered during the lamination step are not high enough to distort the surface of the polymeric material invented here.

[0083] The composite made using the porous elastomeric polymeric material of this invention is novel as it affords the durability properties at least comparable to composites made from conventional woven or knitted fabrics. Additionally, because of the elastomeric nature of the material, the resulting composite is soft and of acceptable hand. If the substrates used are also elastomeric in nature, the composites formed can exhibit elastic properties such as high stretch and recovery that are desirable for garments and accessories requiring form fitting characteristics. These novel composites are water vapor permeable to the level of at least 1000 g/m2/day.

[0084] The novel materials of the invention can be converted into garments or other protective coverings by a variety of means. One of the ways these constructions can be assembled is to create seams by joining the fibrous material surface to itself or to another fabric surface.

[0085] The novel composites can be converted into water resistant, water vapor permeable garments and clothing accessories by a variety of means. One of the ways these composites can be assembled into such articles is to create water resistant seams by joining the fibrous material surface of the composite to itself or to another fabric surface of a composite. Other uses of the composites include bivy bags, tenting and other protective coverings.

TEST PROCEDURES

[0086] A variety of different tests have been used in the following examples to demonstrate the various properties of the porous polymeric materials of this invention and of the composites made from it.

[0087] In view of the difficulty in separating composites into their individual components, it is understood that when one component is said to have a certain property, such as a certain moisture vapor transmission rate, that property can be measured by testing the entire composite; for if the composite meets the test, the individual components inherently must meet the test.

[0088] Basis Weight

[0089] Basis weight was measured by cutting a 4.25 inch diameter (0.009 m2) specimen. Average weight of 3 specimens is recorded and reported in grams/m2. In cases where the sample on a substrate, the weight of both was recorded and the weight of the substrate is subtracted off later.

[0090] Thickness

[0091] Thickness was measured according to ASTM-D-1977-64 using a C & R Thickness Tester, model no. CS55 with a 2 oz. weight and a 1.1 inch presser foot. Average of at least 2 readings was recorded as the thickness in mils.

[0092] Bulk Density

[0093] Bulk density is calculated as ρW=W/25.4 T where ρW is the bulk density in grams/cm3, W is the basis weight in grams/m2 and T is the thickness in mils.

[0094] Abrasion Resistance

[0095] Samples were evaluated for abrasion resistance, as determined by visual inspection, using a modified universal wear test method. The method is based on ASTM standard D3886-92 and consists essentially of abrading a sample with a selected abradent and determining the number of cycles until a hole visually appears through the test sample.

[0096] The sample is abraded using a Commercial Inflated Diaphragm Abrasion Tester available through Custom Scientific Instruments in Cedar Knolls, N.J. (model no. CS59-391). A one pound weight is used along with a 4 psig inflation pressure to accelerate the wear. 600 grit sandpaper is used as the abradent. The abradent is replaced every 150 cycles and at the start of a new sample.

[0097] Circular samples, 4.25 inches in diameter, of products of this invention are placed on the tester with the side to be abraded, i.e., the three dimensional material, facing up and a contrasting color substrate below. The sandpaper is moved horizontally across the surface of the sample in a back and forth motion while the sample itself is being rotated 360 degrees to ensure uniform wear in all directions. A single back and forth motion is denoted as a “cycle”.

[0098] The sample is evaluated for visual wear every 150 cycles until a hole through the sample to the substrate is observed. The point of the first sign of a hole is recorded as failure.

[0099] In case of non-woven samples, pilling and roping was detected at an earlier stages. In case of composites, the surface of the polymeric material was abraded until the underlying water resistant portion of the composite became visible.

[0100] At least two specimens were tested and the abrasion resistance is reported as the average number of abrasion cycles required for the specimens to fail.

[0101] Air Permeability

[0102] Carrier substrates were evaluated for air permeability using a test method based on ISO 9237-1995E on a TexTest FX330 air permeability tester. The test method was to cut a sample which covered the 60 mm diameter test aperture. After clamping the sample in the machine, an air pressure of 100 Pa is applied to the bottom side of the sample and the volume of air passing through the sample in a given time is measured. This flow rate is recorded and reported in cm3/cm2/sec.

[0103] At least two specimens were tested and the air permeability is reported as the average value.

[0104] Stretch and Recovery

[0105] The stretch and recovery properties was measured using an Instron Model 5500R tensile testing machine. 1 inch wide and 6 inches long specimens were cut from the sample in the machine and in the transverse directions. Two marks were placed 2 inches apart in the long direction of the specimen. All the specimens were simultaneously mounted on the testing machine with the test grips spaced 3 inches apart. The crosshead is then extended by 1.5 inches at a rate of 10 inches/min to stretch the specimen by 50%. If the any of the specimens did not break, the sample was deemed to be capable of stretching at least 50% of its length. The specimens were held in the stretched state for 5 minutes and the cross head was then returned to the position at the start of the test. The relaxed specimens were then removed from the grips and after waiting for at least 1 minute, the distance (D) between the marks was measured. Per cent recovery was calculated as % recovery=100 (2−D/2), where D is in inches.

[0106] If small pieces are tested, appropriate equipment can be used.

[0107] At least 3 specimens were tested for each sample and the average percent recovery is reported along with the sample orientation.

[0108] Water Vapor Transmission Test

[0109] Water vapour transmission rate (MVTR), i.e. water-vapour-permeability, was measured by placing approximately 70 ml of a solution consisting of 35 parts by weight of potassium acetate and 15 parts by weight of distilled water into a 133 ml. polypropylene cup, having an inside diameter of 6.5 cm at its mouth. An expanded polytetrafluoroethylene (PTFE) membrane having a minimum MVTR of approximately 85,000 g/m2/24 hrs. as tested by the method described in U.S. Pat. No. 4,862,730 to Crosby and available from W. L. Gore & Associates, Inc. of Newark, Del., was heat sealed to the lip of the cup to create a taut, leakproof, microporous barrier containing the solution.

[0110] A similar expanded PTFE membrane was mounted to the surface of a water bath. The water bath assembly was controlled at 23° C. plus or minus 0.2° C., utilising a temperature controlled room and a water circulating bath. The sample to be tested was allowed to condition at a temperature of 23° C. and a relative humidity of 50% prior to performing the test procedure. Three samples were placed so that each sample to be tested was in contact with the expanded PTFE membrane mounted over the surface of the water bath, and was allowed to equilibrate for at least 15 minutes prior to the introduction of the cup assembly.

[0111] The cup assembly was weighed to the nearest 1/1000 g and was inverted onto the centre of the text sample.

[0112] Water transport was provided by the driving force between the water in the water bath and the saturated salt solution providing water flux by diffusion in that direction. The sample was tested for 15 minutes and the cup assembly was then removed, and weighed again to within 0.001 g.

[0113] The MVTR of the sample was calculated from the weight gain of the cup assembly and was expressed in grams of water per square meter of sample surface area per 24 hours.

[0114] At least two specimens were tested and the water vapor transmission rate is reported as the average value.

[0115] Water Resistance Test

[0116] Samples of the materials were tested for water-proofness by using a modified Suter test method, which is a low water entry pressure challenge. The test consists essentially of forcing water against one side of a test piece, and observing the other side of the test piece for indications of water penetration through it.

[0117] The sample to be tested is clamped and sealed between rubber gaskets in a fixture that holds the test piece inclined from the horizontal. The outer surface of the test piece faces upward and is open to the atmosphere and to close observation. Air is removed from inside the fixture and pressure is applied to the inside surface of the test piece, over an area of 7.62 cm (3.0 inches) diameter, as water is forced against it. The water pressure on the test piece was increased to 1 psi by a pump connected to a water reservoir, as indicated by an appropriate gauge and regulated by an in-line air valve.

[0118] The outer surface of the test piece is watched closely for the appearance of any water forced through the material. Water seen on the surface is interpreted as a leak. A sample achieves a passing grade when, after 3 minutes, no water is visible on the surface.

[0119] Force to Flex (Hand)

[0120] The peak force required to flex a sample through a defined geometric bend was measured. The device used was a Thwing-Albert Handle-O-Meter, model 211-5-10. The Handle-O-Meter has a 1000 g blade which forces a sample through a 0.25 inch wide slot having parallel sides. The peak force required to achieve this deflection is report in grams. This force is influenced by the friction between the sample and the polished face of the machine.

[0121] Samples were die cut into ten 4 inch square specimens, five of which were cut in the fill direction and five of which were cut from the warp direction. Each sample was tested in each of its four orientations: machine or cross-machine direction corresponding with sample cut direction, and inner side up, in contact with the blade or inner side down in contact with the slot. The peak load for each orientation is recorded and the sum of all four is noted as the ‘hand’. The average of 5 readings are reported.

[0122] Some of the above measurements, such as basis weight, thickness, bulk density, stretch/recovery, ideally are independent of sample size. Therefore, when adequate samples as per the described test procedures are not available, these measurements may be obtained from similar tests using smaller sample/specimen size.

[0123] Accelerated UV-Weathering Exposure (QUV Exposure)

[0124] Samples are cut and placed into a QUV Weatherometer made by Q-Panel Lab Products using UVA 340 bulbs at an intensity of 1.2 W/m2/nm (at the calibration wavelength of 340 nm). One QUV cycle lasts 24 hrs and consists of 8 hrs of UV exposure at 60° C., 4 hrs of condensation at 50° C., 8 hrs of UV exposure at 60° C. and 4 hrs of condensation at 50° C. Cycles were repeated per protocol.

[0125] UV Color Shift

[0126] UV Color Shift is the measure of color change after QUV exposure cycles. Samples (unexposed) are placed into the SPECTRALTEST TM spectrophotometer made by Datacolor International and their spectrum are read. This procedure is then repeated for samples (after exposure) and a color shift representing the difference from the unexposed to exposed is calculated. (+) Delta B* is the shift specifically in the yellow direction and is the value reported.

[0127] UV Tensile Break Retention

[0128] UV Tensile Break Retention is the measure of the loss of elasticity due to UV exposure/degradation. It was measured using a Instron Model 5500R tensile testing machine. 1 inch wide and 6 inches long specimens were cut from the sample in the machine and in the transverse directions. All the specimens were mounted on the testing machine with the test grips spaced 3 inches apart. The crosshead is then extended at a rate of 20 inches/min to stretch the specimen until break. [L(final)/L(initial)−1]*100 is noted as the % tensile break elongation (unexposed). An average of a minimum of 3 specimens is recorded. Samples from the same web undergo the pre determined number of QUV exposure cycles and are then tested again for % tensile break elongation (after exposure) using the fore mentioned procedure. UV Tensile Break Retention is then calculated as follows and reported as such.

UV Tensile Break Retention=break elongation
(after Exposure)/break elongation (unexposed)*100.

EXAMPLES

[0129] The following examples illustrate embodiments of the invention, but are not intended to limit the scope of the present invention.

Example 1

[0130] A thermoplastic polyurethane, TPU1, was synthesized from 4,4′-diphenylmethane diisocyanate (MDI)/1000 molecular weight polycaprolactone diol (PCL1000)/1,4-butane diol in the molar equivalents of 2:1:1.12 respectively using conventional polyurethane prepolymer-type synthesis technique and then converted into pellets. The resulting TPU1 has a hardness of 85 Shore A hardness, a break elongation in excess of 400% and a melt flow index of about 140 grams/10 minute (at 195° C., 5 kg.). TPU1 was used to create the fibrous polymeric material of the invention through a melt blowing technique.

[0131] A 20 inches wide horizontal melt blowing die with 0.0145 inches diameter orifices arranged in a single row with a spacing of 25 holes per inch was used. TPU1, in pellet form, was fed into a single screw extruder. The extruder temperature profile was maintained at a steady ramp profile, from the feed zone at 350° F. up to the end zone at 460° F. The melt was fed into the die, maintained at 415° F., at a throughput of 0.92 g/min/hole. The die nose piece was setback by 0.060 inches and the air gap was set at 0.060 inches. The air temperature was maintained at 440° F. at an air volume of 590 cfm.

[0132] Above conditions were used to melt blow TPU1 on to a 3.4 oz./yd2 woven fabric with an air permeability of 9.75 cm3/cm2/sec moving over a collector at 26 feet/min. A vacuum was applied at the collector which was located 10 inches from the die.

[0133] Unless otherwise specified, the resulting fibrous polymeric material was peeled from the woven fabric and tested for various properties. The results, summarized in Table 1, indicate the high bulk density and the high abrasion resistance of the invented material of this example.

Example 2

[0134] Using a 47″ wide vertical meltblowing die, TPU1 was converted into the polymeric material of this invention under conditions similar to that described in example 1. The melt blown TPU1 material was collected on a 4.4 oz/yd2 woven fabric with an air permeability of 47 cm3/cm2/sec. The material was then peeled off from the woven fabric and tested for various properties. The results are summarized in Table 1. The results indicate the high bulk density and the high abrasion resistance of the invented material of this example.

Examples 3-7

[0135] TPU1 was melt blown on to various woven fabrics to create the polymeric material of the invention of different basis weights. The procedure used was similar to that described in example 2. The resulting materials were peeled off from the woven fabric carriers and tested for various properties. The results are listed in Table 1. It is seen that, though structurally similar, the bulk density and the abrasion resistance of the invented material depend on the basis weight.

Comparative Examples 1-9

[0136] Various commercially available elastomeric non-woven fabrics were obtained, tested for properties and compared with the properties of the polymeric material of this invention. The results of these commercial non-woven fabrics are summarized in Table 2. It is seen that, in comparison to the invented material, these comparative samples are low in both bulk density and abrasion resistance.

Example 8

[0137] A water resistant, air impermeable and water vapor permeable substrate was made by coating ePTFE film of 18 g/m2 weight with a 12 gm/m2 layer of a hydrophilic polyurethane as described in U.S. Pat. No. 4,194,041. The substrate was then adhered to the polymeric material of example 3 on the ePTFE side using a dot pattern of polyurethane adhesive as described in U.S. Pat. No. 4,532,316 to create a water vapor permeable, water resistant composite. The composite was tested for various properties and the results are listed in Table 3.

Comparative Example 10

[0138] A composite similar to that described in Example 8 was made except that a 4 oz/yd2 woven Cordura fabric was used in place of the polymeric material of this invention. The properties of the resulting composite are provided in Table 3. The results of Example 8 & Comparative Example 10 indicate the improved hand and abrasion resistance offered to the composite by the material of this invention as compared to a woven fabric of similar weight.

Example 9

[0139] To the available hydrophilic coating side of the composite of Example 8, a 1.3 oz/yd2 knitted fabric was adhered using a dot pattern of polyurethane adhesive. The composite was tested for various properties and the results are listed in Table 3.

Comparative Example 11

[0140] A composite similar to that described in Example 9 was made except that a 4 oz/yd2 woven Cordura fabric was used in place of the polymeric material of this invention. The properties of the resulting composite are provided in Table 3. The results of Example 9 & Comparative Example 11 indicate the improved hand and abrasion resistance offered to the composite by the material of this invention as compared to a woven fabric of similar weight.

Example 10

[0141] A thermoplastic polyurethane, TPU2, was synthesized from dicyclohexylmethane-4,4′-diisocyanate/2000 molecular weight polycaprolactone diol (PCL2000)/1,4-butane diol in the molar equivalents of 2:0.44:1.65 respectively using conventional polyurethane prepolymer-type synthesis technique and then converted into pellets. The resulting TPU2 has a hardness of 88 Shore A hardness, a break elongation in excess of 2000% and a melt flow index of about 188 grams/10 minute (at 195° C., 5 kg.). TPU2 was used to create the fibrous polymeric material of the invention through a melt blowing technique similar to Example #1.

[0142] The web of this example shows the versatility of the invention so long as the polymer has appropriate characteristics. In this instance, a web with a higher degree of resistance to UV degradation was sought while maintaining the other aspects of the invention such as abrasion resistance, softness, density and air permeability. Table 1 shows properties of Example #10 to be similar to webs of the invention with comparable basis weights (Examples #1-5). However, Table 4 shows this web to have a much higher resistance to degradation due to UV exposure. This is demonstrated by the measured resistance to yellowing and by “the retention of break elongation, both of which are superior to a web of TPU1.

1TABLE 1AbrasionRecovery fromWeightThicknessBulk DensityResistance,50% StretchAir Permeabilitygm/m2milsgm/cm3Cycles% MD% TDcm3/cm2/secExample 112810.50.482333969618Example 213210.30.502037——17.3Example 3133100.521715——13.3Example 412511.80.421295969527.1Example 51188.250.563808——13.8Example 67380.36375——32.7Example 7797.250.43275——21.2Example 10111100.411200——23.3

[0143]

2

TABLE 2

Properties of Commercially Available Elastomeric Non-woven Fabrics

Abrasion

Weight
Thickness
Bulk Density
Resistance,

Sample
gm/m2
mils
gm/cm3
Cycles

Comparative Example 1
UHO1801
181
24.8
0.287
680

Comparative Example 2
UHO1501
149
23.8
0.246
180

Comparative Example 3
UHO1251
125
20.0
0.246
120

Comparative Example 4
UHO851
85
15.0
0.223
60

Comparative Example 5
UHO501
50
10.0
0.197
25

Comparative Example 6
FHO851
85
14.0
0.239
58

Comparative Example 7
TPU2
114
12.5
0.359
33

Comparative Example 8
Septon2
108
16.3
0.261
10

Comparative Example 9
2 oz./yd2
67
12.5
0.211
9

Demique ® 3

1
from Kanebo Corporation, Japan.

2
from Kurary Corporation, Japan.

3
from Kimberly-Clark Corporation, Neenah, WI.

[0144]

3

TABLE 3

Abrasion

WVTR
resistance,
Hand

gm/day/m2
cycles
grams

Example 8
10,974
3933
266

Example 9
5,284
4150
598

Comparative Example 10
13,253
693*
703

Comparative Example 11
6,194
430*
1485

woven fabric side abraded

[0145]

4

TABLE 4

Color Shift
Tensile Break Elongation

(+) delta B*
Retention %

(1 cycle)
(1 cycle
5 cycle
10 cycle
25 cycle)

Example 1
66.5
29
10
6
5

Example 10
2.11
86
33
13
0

	Number	Date	Country
Parent	09374387	Aug 1999	US
Child	09780626	Feb 2001	US

Fibrous polymeric material and its composites

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Continuation in Parts (1)