Strong nonwoven fabrics from engineered multiconstituent fibers

Abstract: The present invention provides a thermally-bonded nonwoven fabric that is made from a web which comprises from 100 to 5 percent by weight of multiconstituent fibers. Said multiconstituent fibers are composed of highly dispersed blends of at least two different immiscible thermoplastic polymers and have a dominant continuous polymer phase with at least one noncontinuous phase dispersed therein. The noncontinuous phase exists as an elongated fibrillar polymer domain oriented generally in the direction of the fiber axis. No single polymer domain cross-section of said noncontinuous phase or phases is larger than 0.1% of the cross-sectional area of said fiber. The polymer of the noncontinuous phase or phases has a Polymer Melt Temperature (PMT) at least 30°C below the PMT of the continuous phase. The fiber is configured such that said noncontinuous phase or phases occupy a substantial portion of the fiber surface. In addition to such fabrics, laminates --made by combining nonwoven fabrics made from the materials and processes as described herein with films, paper, tissue, woven fabrics, or nonwoven fabrics such as meltblowns-- are also contemplated. The fabric according to the invention readily bonds to other materials of the sorts mentioned, and is therefore suitable for use in filtration media, medical and clean room garments, CSR wrap, absorbent article backsheets, and other barrier structures.

Description: Background of The Invention 1. Field of the Invention This invention relates to nonwoven fabrics made by thermally bonding fibrous webs made from certain types of multiconstituent fibers, and to laminates incorporating said fabrics. Thermal bonding of the nonwoven fabrics may be accomplished by calender or "through air" techniques or ultrasonically. The multiconstituent fibrous webs may contain other fibers in addition to the thermoplastic multiconstituent fibers. The nonwoven fabrics produced according to the present invention may be optimized as to softness and strength characteristics. 2. Description of the Prior Art Structured multicomponent fibers -- made by coextrusion of different polymers in a variety of structured configurations -- have long been well-known. Some relevant references are: Davies US-A-3 595 731, Gerlach US-A-4 361 609, Kiriyama US-A-4 568 506, and Uchikawa US-A-4 770 925. A few references cite fibers and nonwoven fabrics made from polymer blends wherein the dominant continuous phase is lower melting than is the dispersed discontinuous phase; see Kubo EP-A-0 277 707, Wincklhofer US-A-3 620 892 and Vassilatos US-A-4 632 861. By definition, to thermally bond such fibers, portions of the continuous fiberphase are raised to temperatures where partial molecular relaxation of the continuous lower melting phase occurs. Relaxation occurs not only at the bond site proper but also in the fiber region surrounding the bond site which is responsible for distributing a load or strain throughout the bonded fiber network. Although thermally-bonded nonwoven fabrics can be made from these materials, strength is compromised. Some instances are also known wherein blends of different polymers are extruded from the orifices of spinnerets in order to make fibers containing "free form" microfibrils which can then be separated from the matrix polymer: Breen US-A-3 382 305, and Twilley US-A-3 369 057. Graham US-A-4 769 279 refers to meltblown fibers and fabrics made from blends of ethylene/acrylic copolymer with a second fiber-forming polymer such as a polyvinyl, a polyamide, and a polyolefin. Graham does not disclose thermally-bonded nonwoven fabrics from engineered fibers, however. Furthermore, the Graham disclosure is limited to blends based upon low viscosity ethylene/acrylic copolymers. Finally, Sugihara et al. US-A-4 477 516 discloses a nonwoven fabric containing composite fibers in which one component contains 50-100% linear low density polyethylene and 50-0% of another kind of polyethylene and the other component is a polymer having a melting point 30°C or more higher than that of the polyethylenes. The first polymer component constitutes at least part of the fiber surface and extends continuously in the longitudinal direction. The composite shape of the first component may be either a side-by-side or sheath and core type configuration. Summary of The Invention The present invention provides nonwoven fabrics made of engineered multiconstituent fibers. By "engineered" fibers, we mean oriented fibers made by melt-spinning blends of two or more immiscible polymers that are highly dispersed and that contain a dominant continuous phase which is substantially higher in melting point than the discontinuous phase or phases. One embodiment of the present invention provides a thermally-bonded nonwoven fabric having a basis weight in the range of 5 through 100 g/m² that is made from a web which comprises from 100 to 5 percent by weight of a multiconstituent fiber having a fineness of 5 to 50 µm and up to 95 percent by weight of other fibers. Said multiconstituent fiber is composed of a highly dispersed blend of at least two different immiscible thermoplastic polymers and has a dominant continuous polymer phase and at least one discontinuous phase dispersed therein. The discontinuous phase exists as an elongated fibrillar polymer domain oriented generally in the direction of the fiber axis. The mean of the polymer domain cross-sections of said discontinuous phase or phases is less than 0.1% of the cross-sectional area of said fiber. The polymer of the discontinuous phase or phases has a Polymer Melt Temperature (PMT) at least 30°C below the PMT of said continuous phase. The fiber is configured such that said discontinuous phase or phases occupy a substantial portion of the fiber surface. In addition to the fabrics described above laminates --made by combining nonwoven fabrics made from the materials and processes as described herein with films, paper, tissue, woven fabrics, or nonwoven fabrics such as meltblowns -- are also contemplated. The fabric according to the invention readily bonds to other materials of the sorts mentioned, and is therefore suitable for use in filtration media, medical and clean room garments, CSR wrap, absorbent article backsheets, and other barrier structures. Brief Description of The Drawings Figure 1 is a photomicrograph of a cross-section of a 20-micron-diameter fiber enlarged 25,000 times. Figure 2 is a graphic comparison of tensile strenghts versus temperature for various fibers. Description of The Preferred Embodiments Biconstituent or multiconstituent fibers that may be used to make fabrics according to the present invention are those which are spun from an intimately-mixed blend of different polymers in which at least two of the polymers in the blend are immiscible. The choice of polymers is limited to those that are thermoplastic (including many elastomers) and that have a melt temperature below 350°C, preferably below 275°C. Examples of polymers that can be used are: Polyethenes: Low density PE (.90 - .940 g/cc) Long-chain branched PE LLDPE (made with C₃-C₁₀ alpha-1-olefin copolymers or 4-methyl-1-pentene) Medium and high density PE (.940 - .960 g/cc) Homopolymer or with copolymers described above Atactic polypropylene Polypropylene (at least 90% isotactic) Block copolymers of ethylene and propylene Random copolymers of ethylene and propylene Polybutylene Poly(4-methyl-1-pentene) [TPX] Polycarbonate Polyesters, e.g. poly(oxyethyleneoxyterephthaloy) Polyamides, e.g. poly(imino-1-oxohexamethylene) [Nylon 6] and poly(iminohexamethyleneiminoadipoyl) [Nylon 66] Poly(oxymethylene) Polystyrene Styrene copolymers, e.g. styrene acrylonitrile [SAN] Polyphenylene ether Polyphenylene Oxide [PPO] Polyetheretherketone [PEEK] Polyetherimide Polyphenylene Sulfide [PPS] Poly(vinyl acetate) [PVA] Poly(methyl methacrylate) [PMMA] Poly(methacrylate [PMA] Ethylene acrylic acid copolymer Polysulfone The biconstituent or multiconstituent fibers that make up a significant portion of the webs to be thermally bonded according to the present invention must exhibit a high degree of dispersion. In principle, the mean of the cross-sectional areas of the noncontinuous phase or phases is less than 1/1000th of the cross-sectional area of the fiber. Factors which determine the level of dispersion and phase morphology of the dispersed phase or phases in blend fibers are discussed in detail by D.R. Paul in "Polymer Blends", volume 2, chapter 16. Briefly, the dispersed-phase morphology of the blend fiber is dependent upon the relative rheologies of the blend components, the interfacial tension between the two or more phases, the polymer volume ratio, and the three stages of the blend melt preparation and processing: melt dispersion, extrusion, and extrudate draw-down prior to solidification. In general, the largest domains in the blend will exist when the polymer ratio is near 1.0; at this point the polymers are nearly cocontinuous. The domain size of the discontinuous phase will decrease as the ratio deviates from 1.0, given that the quantity of work "mixered" into the blend and the melt spinning conditions remain constant. Thermal bonding work on fabrics made from biconstituent polyethylene/polypropylene staple fibers has demonstrated weak bonding at calender temperatures at and just above the melting point of the lower melting polyethylene constituent. One of the problems with biconstituents in general in thermal bonding can be that the lower melting component is distributed throughout the fiber matrix rather than being concentrated at the surface where it can be active in bonding. Therefore fibers according to the present invention are often preferably fibers with increased surface-to-volume ratios, with the ultimate being a ribbon-shaped fiber. High surface/volume fibers make more of the lower melting component available for bonding, which ultimately results in higher tensile strength fabrics and laminates. Figure 1, is a TEM photomicrograph of a RuO₄-stained polyethylene/polypropylene fiber cross-section, enlarged 25,000 times. The dark domains are polyethylene (PE); the lighter domains are the continuous polypropylene (PP) phase. The photograph demonstrates how well the PE phase is dispersed in the PP phase. It is interesting to note how the PE phases become circumferentially elongated at the fiber surface. Fibers used to make fabric in accordance with the present invention may be processed as follows: two or more polymers, selected to meet the melting point differential that characterizes the present invention, are combined and blended to form a dispersion. The dispersion is then either melt-spun into fibers, which may be formed into webs for instance by carding, airlaying, or wetlaying, or melt-spun directly into fibrous webs by a spunbonding process. The webs are then thermally-bonded to transform them into strong soft biconstituent-fiber nonwoven fabrics. The specific fabric characteristics will be dependent on the choice of precursor fiber and processing conditions. Said nonwoven fabrics may then be laminated into structures having a variety of desirable end-use characteristics. Appropriate combinations of polymers combined to make the fibers used in accordance with the present invention are intimately blended before being melt-spun into fibers or fibrous webs. A high degree of mixing is necessary in order to prepare blends that will satisfy the degree of dispersion criteria that characterizes the fibers used according to the present invention. Among the commercially available mixers that can be used are the Barmag 3DD three-dimensional dynamic mixer supplied by Barmag AG of West Germany and the RAPRA CTM cavity-transfer mixer supplied by the Rubber and Plastics Research Association of Great Britain. An example of an immiscible blend according to the present invention is a supermixed blend of linear low density polyethylene with polypropylene. Thermally-bonded nonwoven fabrics according to the present invention exhibit advantages over similar homofilament-based nonwovens. A few of those advantages are higher tensile strength/basis weight ratio, and higher tear resistance/basis weight ratio. Many of these advantages are made possible by the fact that the lower melting component of the fibers used according to the present invention effects bonding at conditions that do not cause "relaxation" or loss of molecular orientation of the higher melting component. Typically, fiber used for thermally-bonded coverstock is not highly oriented. Highly oriented polypropylene, for example, is difficult to bond thermally without loss of molecular orientation in the individual filament. In addition, fabrics made from highly drawn polypropylene are harsh and possess poor "hand". The filaments described by the present invention can be highly drawn to impart high tenacities and then thermally bonded into a nonwoven fabric with essentially no loss of individual filament tenacity. The retention of individual filament tenacity improves the strength properties of the fabric. Selection of the appropriate polymer (polyethylene for example) as the bonding constituent yields a fabric with greater softness than its homofilament counterpart. The process for manufacturing the webs to be thermally or sonically bonded according to the present invention can be any of the known commercial processes for making nonwoven fabrics, including processes that use mechanical, electrical, pneumatic, or hydrodynamic means for assembling fibers into a web, for example carding, wetlaying, carding/hydroentangling, wetlaying/hydroentangling, and spunbonding. Example 1 Biconstituent staple fiber was prepared by dry blending 40% by weight of an ethylene/1-octene linear low density polyethylene [LLDPE] having a melt index of 26.5 and a density of 0.940 grams/cc with 60% by weight of controlled rheology polypropylene [PP] having a melt flow rate of 26. The dry blend [PP/LLDPE] was fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final dTex (denier) per filament of approximately 2.2 (2.0). Line speeds and cold draw ratios were adjusted to produce two filament samples, one having 2X cold draw and another having 3.5X draw. Refer to Table I, samples 8319-2 abd 8319-3, respectively. One gram samples of each fiber type were formed into a web using a lab-scale carding device. The carded webs were then bonded on a Beloit-Wheeler lab top calender using a 16%-diamond-bonded pattern and a nip pressure of approximately 71.4 kg/cm (400 PLI). Strip tensile strengths were determined for samples bonded over a range of temperatures. Carded webs made from Hercules T-185 polypropylene fiber served as a control. The biconstituent-based fabrics demonstrate superior tensile properties over the polypropylene homofilament-based fabric (see Tables II, III, and IV, and Figure 2). Example 2 Both polypropylene and PP/LLDPE dry blend samples were (seperately) fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final dTex (denier) per filament of approximately 2.2 (2.0). Line speeds and cold draw ratios were adjusted to produce filament samples having 2X draw. Refer to Table I, samples 8319-1A and 8319-2, respectively. Each fiber sample was separately carded and thermally bonded on a 36-inch-wide semicommercial line. Physical properties were then determined for the fabric samples. Data in Table V. The biconstituent fiber-based fabrics exhibited superior strip and grab tensiles, energies at yield (TEA), and tear values. Example 3 Staple biconstituent fiber containing 1% by weight of a substituted-sorbitol nucleating agent was prepared from dry blends of PP/LLDPE that was fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final dTex (denier) per filament of approximately 2.2 (2.0). Line speeds and cold draw ratios were adjusted to produce filament samples having 3.5X draw. Refer to Table I, sample 8319-7. The fiber was carded and thermally bonded on a 91.4-cm - (36-inch-) wide semicommercial line. Data in Table VI. The strip and grab tensiles, energies at yeild, and tear values were superior to a similar fiber sample without nucleating agent. Example 4 Biconstituent fiber 8342 was prepared from a dry blend of 40% by weight of an ethylene/1-octene copolymer [LLDPE] having a melt index of 50 and a density of 0.925 g/cc with 60% by weight of controlled rheology polypropylene [PP] having a melt flow of 35. Multiconstituent fiber 8343 was prepared from a dry blend of 40% by weight LLDPE having a melt index of 50 and a density of 0.925 g/cc with 55% by weight of controlled rheology PP having a melt flow of 35 and with 5% by weight of ethylene/acrylic acid copolymer [EAA] composed of low density polyethylene having a melt index of 300 and an acrylic acid content of 20%. Melt blends were then separately prepared and extruded and pelletized using a single screw extruder equipped with a 6 row Rapra cavity-transfer mixer (CTM) and a strand die cutter. The polymer-blend pellets were then separately re-extruded into filaments and melt-drawn to a final dTex (denier) per filament of 2.1 (1.9) and 3.0 (2.7), respectively. One gram samples of each fiber type were formed into webs, bonded, and tested as described in Example 1. Filament and fabric tensile properties are indicated in Table VII. END-USE EXAMPLES Example 5 8350-1A: PE film to PE/PP bicon fabric 8326-03 33.9 g/m² ((1 osy)) 8350-1B: PE film to PP fabric 8326-02 33.9 g/m² ((1 osy)) To demonstrate the ability of multiconstituent fabric to form a fabric/film laminate, five-inch-wide fabric samples of a thermally bonded multiconstituent fiber-based nonwoven fabrics were "heat sealed" to polyethylene film. Laminate samples were prepared by heat-sealing a sandwich structure composed of carded fabric (8326-02 and 8326-03) (bottom)/polyethylene film (middle)/cover fabric (8326-02) (top). The cover fabric was used to insulate the low melting film from the sealing die. Fabric and film dimensions were 12.7 cm (5") X 30.5 cm (12"). Time, pressure, and die-temperature conditions were chosen that insured optimum adhesion of the fabric to the film while maintaining the film integrity. The heat sealer used was a Hut-Theller Precision Instruments West, Model EB (Petaluma, California). Multiple heat-sealed samples were prepared by sealing across the width of the laminate sample. The die dimensions were flat, 0.95 cm (3/8") X 12.7 cm (5"), or 12.1 cm² (1.875 square inches.) Peel strengths were determined relative to a homofil fabric laminate control. Peel strengths are indicative of the level of adhesion between the fabric and film layers of the laminate. Peel strengths were determined using an Instron Model 4201 tensile tester. Strips 1-inch wide were cut from each sealed sample. The fabric was placed in the upper grip of the tensile tester and the film in the lower grip. A gauge length of 7.6 cm (3-inches) and a cross-head speed of 12.7 cm (5-inches)/minute were used. Peel strenth properties are indicated in Table VIII. The level of adhesion was greater for the laminate which contained the multiconstituent fiber. Examples 6 and 7 relate to breathable liquid barrier laminates with textile-like hand. Such laminates are suitable for use but not limited to use as medical and industrial garments, CSR wrap, surgical drape, and housewrap. The laminates are prepared from a layer or layers of microfibrous (for example meltblown) polymer, such as polypropylene, sandwiched between two layers of nonwoven fabric containing multiconstituent fiber according to the present invention. The discontinuous polymer phase of the multiconstituent fiber occupies a portion of the surface of the fiber such that both polymers of the blend are available for thermal or sonic bonding and/or lamination. The fabric can be bonded prior to lamination or can be directly deposited on either side of the microfibrous layer just prior to lamination. The microfibrous layer can be composed of meltblown fibers, wet laid pulps, or webs prepared by other known means. The microfibrous layer can be formed prior to the lamination or extruded or formed directly onto the multiconstituent nonwoven fabric prior to lamination. The microfibrous layer must be composed of a polymer which adheres to either the continuous or discontinuous polymer component of the multiconstituent fiber upon thermal or sonic lamination. Thus for instance, high melt flow isotactic polyproplene could be meltblown into a microfibrous web and then laminated to a fabric made from a polymer-blend fiber having a polypropylene as one of the polymer constituents. Lamination can be with known calendering or sonic bonding technology. Bond pattern and processing conditions can be tailored to impart the desired combination of strength, barrier, drape, and textile aesthetics. Example 6 Samples of flat-calendered "sandwich-type" laminates were prepared from a polypropylene meltblown web weighing 20 grams per square meter and having a nominal filament diameter of 5 microns and two outer nonwoven layers composed of a multiconstituent fiber-based nonwoven fabric like that described in Example 1 and identified as Sample No. 8326-03 in Table V. The three webs were simultaneously unwound from a backstand and fed continuously into a heated calender nip. The lamination was effected using a 55.9 cm (22") lab calender equipped with a heated smooth rubber roll and a heated smooth steel roll. The samples were prepared at varied calender roll surface temperatures, ranging from 159°C (318°F) to 152°C (306°F) for the steel roll and from 149°C (300°F) to 140°C (284°F), for the rubber roll. Nip pressure was held constant at 26.8 kg/cm (150 pounds per linear inch (pli)), and line speed was held constant at 6.71 m/min (22 feet per minute). Physical properties were determined for the resulting laminate samples and are identified as sample numbers 8331-1A through 8331-1F in Table IX. It is apparent from these data (8331-1A through 8331-1F) that a breathable liquid-barrier laminate can be obtained with excellent fabric tenacity. Example 7 A helically-bonded "sandwich-type" laminate was prepared by a procedure similar to that described in Example 6, but wherein the smooth rolls were replaced with steel rolls engraved with a diagonal line pattern such that the angle between the crisscross bond lines of the diagonal bonds opening in the machine direction (MD) measures 120 degrees, each line measuring 60 degrees off the MD axis and such that the raised bonding surfaces of each roll are flat and approximately 1 mm wide, separated by a recessed area measuring approximately 1.5 mm wide. A laminate fabric was produced at 6.7 m/min (22 fpm), 26.8 kg/cm (150 pli), at a calender roll surface temperature of 143°C (290°F) to 146°C (294°F). Physical properties were determined for the fabric which is identified as sample number 8331-04 in Table IX. It is apparent from a comparison of the thickness, tensile, and barrier properties of this fabric with those in the same Table which have been flat-calendered that significantly different properties can be obtained for laminates composed of identical starting materials. Thickness is greatly increased over the flat-calendered samples. The loft of a fibrous web contributes to its ability to filter airborne or liquidborne particles efficiently. Air permeability is equivalent to breathability, a property associated with comfort in disposable garments. Air permeability combined with liquid barrier properties defines a fabric which can be used as a protective garment in a medical or industrial end use. In addition, the range of properties exhibited by these laminates demonstrate the flexibitlity of multiconstituent fabrics in laminate applications. Example 8 By use of the isotactic polypropylene/linear low density polyethylene polymer blend fiber-based fabric described in Table V (Sample No. 8326-04C), laminates were prepared that demonstrate the flexible bonding character of these novel substrates. Film and meltblown fabric were acquired whose polymer compositions matched either that of the continuous phase or that of the noncontinuous phase of the polymer-blend fiber. The grades of each polymer were selected that suited the respective substrate manufacturing processes, and are therefore not the identical polymers used in the manufacture of the multiconstituent fiber. "Sandwich-type" laminates were prepared using the procedure described in Example 7. Physical property data appears in Table X. it is apparent from examination of this data that laminates exhibiting excellent tensile and barrier properties can be prepared by bonding the multiconstituent fiber-based fabric to substrates composed of a polymer selected from the same polymer groups represented in the multiconstituent fiber. From the above-description and specific Examples of the invention, many variation in the webs, composites, useful products, and processes of this invention will be apparent to those skilled in the relevant arts. The fabric of this invention comprises (a) from 100 to 5 percent by weight of one or more multiconstituent fibers having preferably a fineness of 0.9 (1) to 9 (10) dTex (denier) and a surface to volume ratio greater than 0.6, and (b) from 0 to 95 percent by weight of other fibers having preferably a fineness of 9 dTex (10 denier) or lower. According to a preferred embodiment of the invention the fabric consists essentially of from 50 to 5% by weight of said multiconstituent fibers and from 50 to 95% by weight of other textile fibers. The fabric may have a basis weight in the range of from about 15 grams per square meter through about 55 grams per square meter. Said multiconstituent fibers may have fineness of 1.0 to 30 microns and a round or flattened cross-sectional profile. The fabric of this invention may be formed by a procedure selected from the group consisting of carding/thermal bonding, spunbonding, wetlaying/thermal bonding, centrifugal spinning/spunbonding, wetlaying/hydroentangling/thermal bonding, and carding/hydroentangling/thermal bonding. The multiconstituent fiber may contain a nucleating or clarifying agent selected from the group consisting of substituted sorbitols, acrylic acid modified polypropylenes, organic acids, sodium benzoate, and stearates. It may further contain an additive or additives selective from the group consisting of antioxidants, thermal stabilizers, gamma ray or ultraviolet stabilizers, flame retardants, antistatic agents, TiO₂, talc, pigments or dyes, hydrophilic surfactants, hydrophobic agents, antiblocking agents, and electrically-conductive fillers. The continuous thermoplastic constituent may be selected from a group consisting of polyolefins, polyamides, and polyesters and wherein the noncontinuous phase or phases have Polymer Melting Temperatures in the range of 30°C through 50°C below the PMTs of said continuous phase, wherein said polyolefin may be isotactic polypropylene, propylene-ethylene random copolymer, propylene-ethylene block copolymer, poly (4-methyl-1-pentene), polystyrene, or linear low density polyethylene, wherein said polyamide is nylon-6, nylon-66, nylon-11, or nylon-12, and wherein said polyester is polyethyleneterephtalate, polybutyleneterephthalate, or polytetramethyleneterephthalate. The fabric may essentially consist of fibers composed of a continuous polypropylene phase in which is dispersed two discontinuous phases, one composed of linear low density polyethylene and the other of ethylene/acrylic acid copolymer. Said continuous thermoplastic constituent preferably is an isotactic polypropylene having melt flow rate of 4 to 100g/min. The other fibers may be selected from the group of consisting of cotton fibers, viscose rayon fibers, acrylic fibers, wool fibers, polypropylene fibers, polyethylene fibers, polyester fibers, polyamide fibers, polyaramid fibers, carbon fibers, chitin fibers, sheath-core bicomponent fibers, side-by-side bicomponent fibers, other bi- and multicomponent fibers, and the mixture thereof. The invention is further concerned with the use of said fabrics, particularly those laminated to a polyolefin film or a linear low density polyethylene film, to form a structure suitable as a liquid-impermeable protective barrier, which structure is particularly suitable for use as a diaper backsheet, and with the use of said fabric laminated to a microfibrous layer to form a structure suitable for use as a breathable liquid-impermeable protective barrier, wherein said microfibrous layer is a polyolefin meltblown or a wetlaid polyolefin synthetic pulp.

Claims: A thermally-bonded nonwoven fabric having a basis weight in the range of 5 g/m² through 100 g/m² made from a web that comprises from 100 to 5 percent by weight of one or more multiconstituent fibers having a fineness of 5 to 50 µm (microns) and from 0 to 95 percent by weight of other fibers characterized in that , said multiconstituent fibers are composed of highly dispersed blends of at least two different immiscible thermoplastic polymers which are present as a dominant continuous polymer phase and at least one discontinuous phase dispersed therein, wherein the polymer of said discontinuous phase or phases has a Polymer Melting Temperature (PMT) at least 30°C below the PMT of said continuous phase, wherein the mean of the cross-sectional areas of said discontinuous phase or phases is less than 0.1% of the cross-sectional area of said multiconstituent fibers, and wherein said multiconstituent fibers are configured such that said noncontinuous phase or phases occupy a substantial portion of the fiber surfaces. A fabric according to claim 1 that consists essentially of from 50 to 5% by weight of said multiconstituent fibers and from 50 to 95% by weight of other textile fibers. A fabric according to claim 1 that consists essentially of 100% of said multiconstituent fibers. A fabric according to claim 1 in which said multiconstituent fibers have a fineness of 1-10 g/9000 m (1-10 denier) and a surface to volume ratio greater than 0.6. A fabric according to any of the preceding claims wherein the continuous thermoplastic constituent is selected from a group consisting of polyolefins, polyamides, and polyesters and wherein the discontinuous phase or phases have Polymer Melting Temperatures in the range of 30°C through 50°C below the PMTs of said continuous phase. A fabric according to claim 5, wherein said polyolefin is isotactic polypropylene, propylene-ethylene random copolymer, propylene-ethylene block copolymer, poly (4-methyl-1-pentene), polystyrene, or linear low density polyethylene, wherein said polyamide is nylon-6, nylon-66, nylon-11, or nylon-12, and wherein said polyester is polyethyleneterephthalate, polybutyleneterephthalate, or polytetramethyleneterephthalate. A fabric according to any of the preceding claims wherein the continuous thermoplastic constituent is an isotactic polypropylene having a melt flow rate of 4 to 100 g/min. A fabric according to claim 5 that essentially consists of fibers composed of a continuous polypropylene phase in which is dispersed two discontinuous phases, one composed of linear low density polyethylene and the other of ethylene/acrylic acid copolymer. A fabric according to claim 5, wherein the continuous polymer phase consists essentially of a polypropylene phase in which is dispersed a discontinuous phase composed of polyethylene. A fabric according to any of the preceding claims wherein said other fibers are selected from the group consisting of cotton fibers, viscose rayon fibers, acrylic fibers, wool fibers, polypropylene fibers, polyethylene fibers, polyesterfibers, polyamide fibers, polyaramid fibers, carbon fibers, chitin fibers, sheath-core bicomponent fibers, side-by-side biocomponent fibers, other bi- and multicomponent fibers, and the mixtures thereof. A laminate made by combining nonwoven fabric according to any of claims 1 to 10 with films , paper, tissue, woven or nonwoven fabrics. A laminate according to claim 11 of sandwich structure comprising in sequence a first layer of nonwoven fabric, a second layer of a polyolefin film,and a third layer of nonwoven fabric , wherein the layers are bonded to each other and wherein each of the first and third layers comprises nonwoven fabric of any one of claims 1 to 10. A laminate according to claim 12 comprising a microfibrous inner layer formed of polyethylene, particularly of linear low density polyethylene, sandwiched between outer layers formed of said nonwoven fabric. A laminate according to claim 12 comprising a microfibrous inner layer formed of polypropylene, particularly of meltblown polypropylene, sandwiched between outer layers formed of said nonwoven fabric. A laminate according to any of the claims 11 to 14, in that said outer layers are of nonwoven fabric made of spunbonded fibrous webs. Use of a laminate according to any of the claims 11 to 15 as a structure suitable as a liquid-impermeable protective barrier. Use according to claim 16 as a structure that is suitable as a diaper backsheet. Use of a laminate according to any of claims 11 to 15 laminated to a microfibrous layer as a structure suitable for use as a breathable liquid-impermeable protective barrier. Use according to claim 18 wherein said microfibrous layer is a polyolefin meltblown or a wetlaid polyolefin synthetic pulp.

Inventors: GESSNER SCOTT L, GESSNER, SCOTT L.
Applicants: FIBERWEB NORTH AMERICA INC, FIBERWEB NORTH AMERICA, INC.
Application year: 1990
Main classification: D04H1
IPC codes: B01D39, D04H1, A61F13