Alloys of immiscible polymers

Abstract

An extrudable composition is provided which is made from at least two thermoplastic polymers in a biconstituent construction. One of the thermoplastic polymers is present as a dominant continuous phase and the other one or more polymers are present as a non-continuous phase or phases in an amount of 1.5 weight percent or less. No compatibilizer is necessary. The polymer of the non-continuous phase or phases has a polymer melt temperature higher than 30° C. below the polymer melt temperature of the continuous phase. The polymer of the dominant phase may be, for example, polypropylene and the non-continuous phase may be, for example, polyamide. The extrudable composition may be used to produce fibers which are generally between about 5 and 50 microns in diameter. The fibers may be made into nonwoven fabrics.

Description

BACKGROUND OF THE INVENTION

[0002] Thermoplastic resins have been extruded to form fibers and webs for a number of years. The common thermoplastics for this application are polyolefins, particularly polypropylene, and polyesters. Each material has its characteristic advantages and disadvantages vis a vis the properties desired in the final product to be made from such fibers.

[0003] Blends and alloys of two or more polymers are areas of some interest because of a desire to combine the desirable properties of such polymers. Dr. Leszek A. Utracki, in his work “Polymer Alloys and Blends: Thermodynamics and Rheology” (ISBN 0-19-520796-3, Oxford University Press, New York, N.Y., 1989) discusses the history of development in this area at some length.

[0004] Examples of alloy or biconstituent fibers may be found in U.S. Pat. No. 5,108,827 to Gessner which teaches blends wherein the polymer of the noncontinuous phase (or phases) has a melt temperature at least 30° C. below the melt temperature of the continuous phase. Other examples may be found in U.S. Pat. No. 5,534,335 to Everhart et al., commonly assigned, which teaches the use of a compatibilizer to make polymers miscible.

[0005] There remains a need for an extrudable composition which may be used for fabric production from fibers where the composition is an alloy of polymers wherein the polymer melt temperature of the non-continuous phase is higher than 30° C. below that of the continuous phase (and may even be higher), which does not use a compatibilizer and in which desired characteristics are enhanced.

SUMMARY OF THE INVENTION

[0006] An extrudable composition is provided which is made from at least two thermoplastic polymers. A compatibilizer is not necessary. One of the thermoplastic polymers is present as a dominant continuous phase and the other one or more polymers are present as a non-continuous phase or phases. The polymer of the non-continuous phase or phases is present in an amount of 1.5 weight percent or less and has a polymer melt temperature less than 30° C. below the polymer melt temperature of the continuous phase. The polymer of the non-continuous phase or phases may even have a polymer melt temperature greater than the polymer melt temperature of the continuous phase. The extrudable composition may be extruded into biconstituent fibers which may further be processed into nonwoven fabrics.

BRIEF DESCRIPTION OF THE FIGURES

[0007] FIG. 1 is a schematic drawing of a process for extruding the composition of this invention including a main extruder, a side extruder and a mixer.

[0008] FIG. 2 is a cut-away drawing of a mixer suitable for use in mixing the extrudable composition of this invention.

[0009] FIG. 3 is a cross-sectional view of a mixer suitable for use in mixing the extrudable composition of this invention.

DEFINITIONS

[0010] As used herein, the term “nonwoven fabric or web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).

[0011] As used herein, the term “microfibers” means small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 0.5 microns to about 50 microns, or more particularly, microfibers may have an average diameter of from about 2 microns to about 40 microns. Another frequently used expression of fiber diameter is denier, which is defined as grams per 9000 meters of a fiber and may be calculated as fiber diameter in microns squared, multiplied by the density in grams/cc, multiplied by 0.00707. A lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. For example, the diameter of a polypropylene fiber given as 15 microns may be converted to denier by squaring, multiplying the result by 0.89 g/cc and multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a denier of about 1.42 (152×0.89×0.00707=1.415). Outside the United States the unit of measurement is more commonly the “tex”, which is defined as the grams per kilometer of fiber. Tex may be calculated as denier/9.

[0012] As used herein, the term “spunbonded fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and have average diameters (from a sample of at least 10) larger than 7 microns, more particularly, between about 10 and 20 microns. The fibers may also have shapes such as those described in U.S. Pat. No. 5,277,976 to Hogle et al., U.S. Pat. No. 5,466,410 to Hills and 5,069,970 and U.S. Pat. No. 5,057,368 to Largman et al., which describe fibers with unconventional shapes.

[0013] As used herein, the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.

[0014] As used herein, “filament arrays” means substantially parallel rows of filaments which may be such as those disclosed in U.S. Pat. Nos. 5,385,775 and 5,366,793.

[0015] As used herein, “multilayer laminate” means a laminate wherein some of the layers are spunbond and some meltblown such as a spunbond/meltblown/spunbond (SMS) laminate and others as disclosed in U.S. Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 5,169,706 to Collier, et al, U.S. Pat. No. 5,145,727 to Potts et al., U.S. Pat. No. 5,178,931 to Perkins et al. and U.S. Pat. No. 5,188,885 to Timmons et al. Such a laminate may be made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer and then bonding the laminate in a manner described below. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step. Such fabrics usually have a basis weight of from about 0.1 to 12 osy (6 to 400 gsm), or more particularly from about 0.75 to about 3 osy. Multilayer laminates may also have various numbers of meltblown layers or multiple spunbond layers in many different configurations and may include other materials like films (F) or coform materials, e.g. SMMS, SM, SFS, etc.

[0016] By the term “similar web” what is meant is a web which uses essentially the same process conditions and polymers as the inventive web except those noted. According to Webster's New Collegiate Dictionary (1980), “similar” means 1) having characteristics in common; strictly comparable, 2) alike in substance or essentials; corresponding. Using this commonly accepted meaning of the word similar, this term means that all other conditions are essentially the same except for the conditions mentioned. It should be noted that not all conditions will be exactly identical between the different polymers since the changes in the composition itself cause process changes, in for example, the pressure drop or temperatures needed.

[0017] As used herein, the term “coform” means a process in which at least one meltblown diehead is arranged near a chute through which other materials are added to the web while it is formed. Such other materials may be pulp, superabsorbent particles, cellulose or staple fibers, for example. Coform processes are shown in commonly assigned U.S. Pat. No. 4,818,464 to Lau and U.S. Pat. No. 4,100,324 to Anderson et al. Webs produced by the coform process are generally referred to as coform materials.

[0018] As used herein, the term “polymer” generally includes but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the molecule. These configurations include, but are not limited to isotactic, syndiotactic and random symmetries.

[0019] As used herein, the term “monocomponent” fiber refers to a fiber formed from one or more extruders using only one polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc. These additives, e.g. titanium dioxide for coloration, are generally present in an amount less than 5 weight percent and more typically about 2 weight percent.

[0020] As used herein, the term “conjugate fibers” refers to fibers which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. Conjugate fibers are also sometimes referred to as multicomponent or bicomponent fibers. The polymers are usually different from each other though conjugate fibers may be monocomponent fibers. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the conjugate fibers and extend continuously along the length of the conjugate fibers. The configuration of such a conjugate fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another or may be a side by side arrangement, a pie arrangement or an “islands-in-the-sea” arrangement. Conjugate fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 4,795,668 to Krueger et al. and U.S. Pat. No. 5,336,552 to Strack et al. Conjugate fibers are also taught in U.S. Pat. No. 5,382,400 to Pike et al. and may be used to produce crimp in the fibers by using the differential rates of expansion and contraction of the two (or more) polymers. Crimped fibers may also be produced by mechanical means and by the process of German Patent DT 25 13 251 A1. For two component fibers, the polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired ratios. The fibers may also have shapes such as those described in U.S. Pat. No. 5,277,976 to Hogle et al., U.S. Pat. No. 5,466,410 to Hills and U.S. Pat. Nos. 5,069,970 and 5,057,368 to Largman et al., which describe fibers with unconventional shapes.

[0021] As used herein, the term “biconstituent fibers” refers to fibers which have been formed from at least two polymers extruded from the same extruder as a blend. The term “blend” is defined below. Biconstituent fibers do not have the various polymer components arranged in relatively constantly positioned distinct zones across the cross-sectional area of the fiber and the various polymers are usually not continuous along the entire length of the fiber, instead usually forming fibrils or protofibrils which start and end at random. Biconstituent fibers are sometimes also referred to as multiconstituent fibers. Fibers of this general type are discussed in, for example, U.S. Pat. Nos. 5,108,827 and 5,294,482 to Gessner. Bicomponent and biconstituent fibers are also discussed in the textbook Polymer Blends and Composites by John A. Manson and Leslie H. Sperling, copyright 1976 by Plenum Press, a division of Plenum Publishing Corporation of New York, IBSN 0-306-30831-2, at pages 273 through 277.

[0022] As used herein, the term “blend” means a combination of two or more polymers while the term “alloy” means a sub-class of blends wherein the components are immiscible but have been compatibilized. “Miscibility” and “immiscibility” are defined as blends having negative and positive values, respectively, for the free energy of mixing. Further, “compatibilization” is defined as the process of modifying the interfacial properties of an immiscible polymer blend in order to make an alloy.

[0023] As used herein, the term “garment” means any type of non-medically oriented apparel which may be worn. This includes industrial work wear and coveralls, undergarments, pants, shirts, jackets, gloves, socks, and the like.

[0024] As used herein, the term “infection control product” means medically oriented items such as surgical gowns and drapes, face masks, head coverings like bouffant caps, surgical caps and hoods, footwear like shoe coverings, boot covers and slippers, wound dressings, bandages, sterilization wraps, wipers, garments like lab coats, coveralls, aprons and jackets, patient bedding, stretcher and bassinet sheets, and the like.

[0025] As used herein, the term “personal care product” means diapers, training pants, absorbent underpants, adult incontinence products, and feminine hygiene products.

[0026] As used herein, the term “protective cover” means a cover for vehicles such as cars, trucks, boats, airplanes, motorcycles, bicycles, golf carts, etc., covers for equipment often left outdoors like grills, yard and garden equipment (mowers, roto-tillers, etc.) and lawn furniture, as well as floor coverings, table cloths and picnic area covers.

[0027] As used herein, the term “outdoor fabric” means a fabric which is primarily, though not exclusively, used outdoors. Outdoor fabric includes fabric used in protective covers, camper/trailer fabric, tarpaulins, awnings, canopies, tents, agricultural fabrics and outdoor apparel such as head coverings, industrial work wear and coveralls, pants, shirts, jackets, gloves, socks, shoe coverings, and the like.

Test Methods

[0028] Cup Crush:

[0029] The softness of a nonwoven fabric may be measured according to the “cup crush” test. The cup crush test evaluates fabric stiffness by measuring the peak load (also called the “cup crush load” or just “cup crush”) required for a 4.5 cm diameter hemispherically shaped foot to crush a 23 cm by 23 cm piece of fabric shaped into an approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped fabric is surrounded by an approximately 6.5 cm diameter cylinder to maintain a uniform deformation of the cup shaped fabric. An average of 10 readings should be used. The foot and the cup are aligned to avoid contact between the cup walls and the foot which could affect the readings. The peak load is measured while the foot is descending at a rate of about 0.25 inches per second (380 mm per minute) and is measured in grams. The cup crush test also yields a value for the total energy required to crush a sample (the “cup crush energy”) which is the energy from the start of the test to the peak load point, i.e. the area under the curve formed by the load in grams on one axis and the distance the foot travels in millimeters on the other. Cup crush energy is therefore reported in gm-mm. Lower cup crush values indicate a softer laminate. A suitable device for measuring cup crush is a model FTD-G-500 load cell (500 gram range) available from the Schaevitz Company, Pennsauken, N.J.

[0030] Melt Flow Rate:

[0031] The melt flow rate (MFR) is a measure of the viscosity of a polymer. The MFR is expressed as the weight of material which flows from a capillary of known dimensions under a specified load or shear rate for a measured period of time and is measured in grams/10 minutes at a set temperature and load according to, for example, ASTM test 1238-90b.

[0032] Grab Tensile Test:

[0033] The grab tensile test is a measure of breaking strength and elongation or strain of a fabric when subjected to unidirectional stress. This test is known in the art and conforms to the specifications of Method 5100 of the Federal Test Methods Standard 191 A. The results are expressed in pounds to break and percent stretch before breakage. Higher numbers indicate a stronger, more stretchable fabric. The term “load” means the maximum load or force, expressed in units of weight, required to break or rupture the specimen in a tensile test. The term “strain” or “total energy” means the total energy under a load versus elongation curve as expressed in weight-length units. The term “elongation” means the increase in length of a specimen during a tensile test. Values for grab tensile strength and grab elongation are obtained using a specified width of fabric, usually 4 inches (102 mm), clamp width and a constant rate of extension. The sample is wider than the clamp to give results representative of effective strength of fibers in the clamped width combined with additional strength contributed by adjacent fibers in the fabric. The specimen is clamped in, for example, an Instron Model TM, available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154, which have 3 inch (76 mm) long parallel clamps. This closely simulates fabric stress conditions in actual use.

[0034] Trap Tear Test:

[0035] The trapezoid or “trap” tear test is a tension test applicable to both woven and nonwoven fabrics. The entire width of the specimen is gripped between clamps, thus the test primarily measures the bonding or interlocking and strength of individual fibers directly in the tensile load, rather than the strength of the composite structure of the fabric as a whole. The procedure is useful in estimating the relative ease of tearing of a fabric. It is particularly useful in the determination of any appreciable difference in strength between the machine and cross direction of the fabric. In conducting the trap tear test, an outline of a trapezoid is drawn on a 3 by 6 inch (75 by 152 mm) specimen with the longer dimension in the direction being tested, and the specimen is cut in the shape of the trapezoid. The trapezoid has a 4 inch (102 mm) side and a 1 inch (25 mm) side which are parallel and which are separated by 3 inches (76 mm). A small preliminary cut of ⅝ inches (15 mm) is made in the middle of the shorter of the parallel sides. The specimen is clamped in, for example, an Instron Model TM, available from the Instron Corporation, 2500 Washington St., Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II available from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154, which have 3 inch (76 mm) long parallel clamps. The specimen is clamped along the non-parallel sides of the trapezoid so that the fabric on the longer side is loose and the fabric along the shorter side taut, and with the cut halfway between the clamps. A continuous load is applied on the specimen such that the tear propagates across the specimen width. It should be noted that the longer direction is the direction being tested even though the tear is perpendicular to the length of the specimen. The force required to completely tear the specimen is recorded in pounds with higher numbers indicating a greater resistance to tearing. The test method used conforms to ASTM Standard test D1117-14 except that the tearing load is calculated as the average of the first and highest peaks recorded rather than the lowest and highest peaks. Five specimens for each sample should be tested.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The extrudable composition of this invention is an alloy of at least two immiscible polymers. The alloy of polymers used to make the composition of this invention is such that the polymer melt temperature of the non-continuous phase is in the range of from higher than 30° C. below to any value greater than that of the continuous phase. The extrudable composition may be extruded to form fibers which are biconstituent and the fibers may be further processed into nonwoven fabrics.

[0037] The alloy should be essentially free of any compatibilzer. Compatibilizers include compounds such as zinc ionomers of ethylene-methacrylic acid or modified polypropylene with maleic anhydride and others described in U.S. Pat. No. 5,534,335. It is believed, though applicants do not wish to be bound by any particular theory, that a compatibilizer has polar and non-polar parts and the polar part reacts with or is attracted to a polar part of one of the polymers to be alloyed. The non-polar part of the compatibilizer remains available for reaction with or attraction to the dominant phase polymer and this results in more intimate mixing. The reduction in the interfacial energy caused by the compatibilizer allows the size of the discontinuous phase to be reduced within the continuous phase.

[0038] Another class of compatibilizer is poly(olefin-methacrylic acid) where the acid groups are partially or fully neutralized by metal ions.

[0039] Commercial examples of compatibilizers which should be avoided include Exxelor® polymer modifier PO1015 or VA1803 available from Exxon Chemical Company, and the family of Surlyn® ionomers available from E.I. Dupont de Nemours Inc., particularly Surlyn® 9020 ionomer.

[0040] Exxelor® polymer modifier P01015 is a proprietary chemical which has a melt flow rate of 120 g/10 min., a density of 0.91 g/cm3 and has 0.4 weight percent of grafted maleic acid/anhydride. Exxelor® polymer modifier VA1803 has a melt flow rate of 3 g/10 min., a density of 0.86 g/cm3 and has 0.7 weight percent of maleic acid/anhydride. Surlyn® 9020 ionomer has a melt flow rate of 1.0 g/10 min. and a density of 0.96 g/cm3. The Surlyn® ionomer resins are based on ethylene and methacrylic acid di- and ter- polyers which have been partially reacted with metallic salts (generally zinc or sodium) to form ionic crosslinks between the acid groups within a chain or between neighboring chains.

[0041] Suitable polymer mixtures which may be used in the practice of this invention include, for example, polyolefins and polyamides, and polyolefins and polyesters.

[0042] The polyolefin which may be used in the practice of this invention may be amorphous or crystalline, atactic, isotactic or sydiotactic. Suitable polyolefins include polyethylene, polypropylene, polybutylenes and copolymers, blends and mixtures thereof and are available commercially from a number of suppliers. The particular properties of polyolefins used in fiber extrusion and nonwoven fabric production processes such as the spunbonding and meltblowing processes are known to those skilled in the art.

[0043] A polyamide which may be used in the practice of this invention may be any polyamide known to those skilled in the art including copolymers and mixtures thereof. Examples of polyamides and their methods of synthesis may be found in “Polymer Resins” by Don E. Floyd (Library of Congress Catalog number 66-20811, Reinhold Publishing, NY, 1966). Particularly commercially useful polyamides are nylon-6, nylon 6,6, nylon-11 and nylon-12. These polyamides are available from a number of sources such as Emser Industries of Sumter, S.C. (Grilon® & Grilamide nylons), Atochem Inc., Polymers Division, of Glen Rock, N.J. (Rilsan® nylons), Nyltech Industries of Manchester, N.H., among others.

[0044] Modifying the interfacial properties of the immiscible polymer blend to make an alloy is accomplished through the use of high shear mixing through the use of for example, a single screw extruder. Single screw extruders are known in the art as useful in mixing and have been developed for a number of purposes in polymer processing such as improvement in physical properties, appearance, processibility and cost reduction. A detailed description of mixing and single screw extruders is given in Mixing and Compounding of Polymers: Theory and Practice, ISBN 1569901562, edited by 1. Manas-Zloczower and Z. Tadmor, Hanser Publishers, 1994, in chapter 19 (Single Screw Extruders), by Hensen, Imping and Spanknebel.

[0045] Another method of mixing is by using a commercially available Barmag three dimensional dynamic mixer (3DD). This mixer is available from Barmag Aktiengelsellschaft, Leverkuser Strase 65, 42897 Remscheid, Germany, or in the U.S. from American Barmag Corporation, 1101 Westinghouse Boulevard, Charlotte, N.C. 28241.

[0046] FIG. 1 shows a system suitable for use in the practice of this invention. A mixture of polymers in, for example, pellet form, is introduced to the feed hopper 1. The mixture proceeds into the main extruder 2 where it is forced through the extruder 2, passing through five equally sized heating zones. The melted mixture from the extruder 2 then passes into the 3DD mixer 3 and is ultimately extruded at the exit 11. Auxiliary mixing can be provided by a side extruder 9 which receives feed from hopper 8. After exiting the side extruder 9, the melted mixture is pumped by gear pump 10 into the main extruder 2 discharge for mixing in the 3DD mixer 3. Polymers may also be mixed by placing them in separate feed tanks 4, 5, pumping them together through metering pumps 6, 7 and then into main extruder 2 discharge for mixing in the 3DD mixer 3.

[0047] Yet another method of mixing is by using a cavity transfer mixer (CTM) by Rapra Corp. which makes available its mixers in the United States through Davis-Standard of #1 Extrusion Drive, Pawcatuck, Conn. 06379 which may be used in place of a 3DD mixer. A CTM mixer is shown in FIG. 2 which shows a central shaft 12 which is surrounded by a housing 13, 14 divided in two parts for ease of illustration. The housing 13, 14 is stationary and the shaft 12 rotates in actual use. The rotation of the shaft 12 causes polymer to be forced into and out of the multitude of depressions 15 on the shaft 12 and housing 13, 14, causing good mixing. While the depressions 15 shown in FIG. 2 are circular, many other shapes are possible. The 3DD mixer uses rectangular, slot-like depressions. Rhomboid, triangular and any other shape which may be envisioned may be used. It is also possible to use pins instead of depressions and to place the pins or depressions at various angles.

[0048] FIG. 3 shows a cross-sectional view of a mixer. The shaft 16 and housing 17 have depressions 18. Polymer may enter at the inlets 19, 20 and move to the discharge 21.

[0049] Distributive and dispersive mixing are essential in any good mixing or blending. Distributive mixing involves the homogenization of the dispersed particles in the matrix material. Dispersive mixing is a mechanism whereby large particles (dispersed phase) are broken up into finer particles and are evenly distributed throughout the matrix material. Important parameters for mixing are constancy of temperature, pressure and above all viscosity. The viscosity homogeneity gives information about distributive and dispersive mixing.

[0050] The fibers which may be made from the extrudable composition of this invention may be produced by the meltblowing or spunbonding processes which are well known in the art. These processes generally use an extruder to supply melted polymer to a spinneret where the polymer is fiberized. The fibers are then drawn, usually pneumatically, and deposited on a foraminous mat or belt to form the nonwoven fabric. The fibers produced in the spunbond and meltblown processes are generally in the range of from about 1 to about 50 microns in diameter, depending on process conditions and the desired end use for the fabrics to be produced from such fibers.

[0051] The fibers may also have other polymers present in a conjugate structure wherein the biconstituent blend of this invention makes up one portion of the conjugate fiber, e.g. the sheath or core, and another polymer or blend makes up the other portion.

[0052] Fabric made from fibers of the extrudable composition of this invention may be used in a single layer embodiment or as a component of a multilayer laminate which may be formed by a number of different laminating techniques including but not limited to using adhesive, needle punching, thermal calendering and any other method known in the art.

[0053] The following examples illustrate particular embodiments of the invention.

EXAMPLE 1

[0054] The polymer alloys were generally produced by compounding the ingredients in a cement mixer which should have given a relatively poorly homogenized mixture. The polyolefin used was Union Carbide's E5D47 polypropylene, a 38 g/10 min melt flow rate polymer. The polyamide used was a polyamide 6 sold as Nyltech 2169 by Nyltech Industries.

[0055] The amounts in the initial blends were 2.2 weight percent polyamide, 2.0 weight percent titanium dioxide pigment and the balance polypropylene.

[0056] The alloy was melt spun through a standard 600 hole round pack with a pin density of about 125 holes per inch (hpi), a length to exit diameter (L/D) of 6 and a 0.6 mm exit diameter. The extruder and spinpack temperatures were at about 440° F. (227° C.) and 450° F. (232° C.) respectively and throughput was typically 0.7 grams/hole/min (ghm). No mixer was attached to the extruder discharge so the extruded polymer went directly to the spinpack. The extruded fibers were thermally point bonded by calendering using an Expanded Hansen Penning bond roll with a 15% bond area to create a fabric with integrity at a calender temperature of 283° F. (139° C.) as indicated in Table 1.

[0057] Mechanical data for 2 ounce per square yard (osy) (68 gsm) spunbond fabrics made from these alloy fibers is shown in the Table in relation to a control fabric made from fibers of Union Carbide's E5D47 polypropylene alone, and shows an improvement in properties of interest.

TABLE 1
		Value	Std.
		of	Dev.,	Value of	Std. Dev.,
Test	Units	Control	Control	Example	Example	Ratio
Basis Wt.	Osy	2.05	0.03	2.09	0.07	0.98
Strip
Tensile
Peak load	pounds	11.36	0.29	24.49	0.98	116
Strain	percent	27.51	2.99	116.79	16.78	324
Energy	in-lb.	8.08	1.66	80.86	14.77	901
Grab
Tensile
Peak load	pounds	12.56	0.97	27.19	2.86	116
Strain	percent	68.17	11.01	108.64	13.75	59
Energy	in-lb.	16.91	4.42	53.30	12.48	215
Trap Tear
1st peak	pounds	6.21	0.54	14.46	1.71	133
Cup crush	Grams	285.02	13.17	262.21	36.28	8
load

[0058] The two fabrics were tested for dyeability by dipping each for one minute in boiling water containing 1 weight percent of Dupont Fiber Identification Stain #4. After the minute of boiling, the fabrics were rinsed in clean water until no dye was visible in the rinse water, and then dried on blotting paper. The stain is available from Pylan Products Co. Inc., 1001 Stewart Ave., Garden City, N.Y. 11530. It was found that the polypropylene fabric did not accept any stain while the biconstituent fiber accepted the stain, indicating that polyamide was available at the fiber surface and not entirely embedded in the polypropylene matrix.

EXAMPLE 2

[0059] A single screw extruder was used having a CTM mixer attached to its discharge. The screw had a length of 13.5 feet (411.5 cm) and a diameter of 4.5 inches (11.4 cm) and was charged at a rate of about 180 pounds/hour with a mixture of Exxon Chemical's Escorene® 3445 polypropylene and Nyltech 2169 nylon 6. The extruder discharge was fed into the CTM which operated at a temperature of about 460° F. (238° C.). The mixture was processed into fibers at a rate of 0.70 grams/holelminute (ghm) with 0.6 mm holes and bonded using an expanded Hansen-Pennings pattern (EHP). Up to 3 weight percent polyamide was processed using this configuration.

EXAMPLE 3

[0060] A low shear co-rotation twin screw extruder was used. The screw was charged with a mixture of Escorene® 3445 polypropylene and Nyltech 2169 nylon 6. The amounts in the initial blend were 2 weight percent titanium dioxide pigment and the balance polypropylene. Trials were conducted at 0 and 1% weight percent nylon in the polypropylene fibers. The mixture was processed into fibers through a spinplate having 400 holes and a length to exit diameter (L/D) of 4 and bonded using an expanded Hansen-Pennings pattern (EHP). The extruder and spinpack temperatures were at about 450° F. (232° C.) and throughput was typically 0.8 grams/hole/min (ghm). No mixer was attached to the extruder discharge so the extruded polymer went directly to the spinpack. The extruded fibers were thermally point bonded by calendering using an Expanded Hansen Penning bond roll with a 15% bond area to create a fabric with integrity at a calender temperature of 290° F. (143° C.). Data was collected for 5 repetitions conducted at each weight percent nylon used. The results of the trials are summarized in Table 2 below.

TABLE 2
Grab Tensile Results CD and MD
Sample			PEAKLOAD	PERCENT
ID	AVERAGE	STD DEV	lbs	IMPROVEMENT
GRAB TENSILE PEAK LOAD CD
100% PP	2137.61	488.02	4.71	—
1% Nylon	3657.60	1300.30	8.06	71
GRAB TENSILE PEAK LOAD MD
100% PP	4840.70	657.41	10.67	—
1% Nylon	8724.89	2536.50	19.23	80

[0061] Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means plus function claims are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.

[0062] It should further be noted that any patents, applications or publications referred to herein are incorporated by reference in their entirety.

Claims

1. A nonwoven fabric which is made from fibers extruded from a composition free of a compatibilizer and comprising at least two thermoplastic polymers, wherein one of said thermoplastic polymers is a polyolefin as a dominant continuous phase present in an amount between 98.5 to 99.9 weight percent, and the other one or more polymers are polyamides as a non-continuous phase or phases present in an amount between 0.1 to 1.5 weight percent, and wherein the polymer of said non-continuous phase or phases has a polymer melt temperature higher than 30° C. below the polymer melt temperature of said continuous phase.

2. The fabric of claim 1 which is dyed.

3. The nonwoven fabric of claim 1 which is made from fibers wherein said continuous phase is at least one polyolefin.

4. The nonwoven fabric of claim 1 which is made from fibers wherein the non-continuous phase or phases are substantially evenly distributed throughout said fiber.

5. The nonwoven fabric of claim 1 which is made from fibers wherein the fibers have diameters of approximately 1 to 50 microns.

6. The nonwoven fabric of claim 1 which is made from fibers which have been thermally bonded at a temperature between about 93 and about 163° C.

7. The nonwoven fabric of claim 1 which has a percent elongation of at least 50% greater than that of nonwoven fabric made from polypropylene fibers which have been bonded at a similar temperature.

8. The nonwoven fabric of claim 1 which is made by the process selected from the group consisting of spunbonding and meltblowing.

9. The nonwoven fabric of claim 3 which is made from fibers wherein the polyamides are selected from the group consisting of polyamide 6, polyamide 11, polyamide 12, and copolymers, and blends thereof.

10. The nonwoven fabric of claim 3 which is made from fibers wherein said polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylenes and copolymers, and blends thereof, and is present in an amount between 98.5 to 99.9 weight percent, said polyamide is present in an amount between 0.1 to 1.5 weight percent.

11. A personal care product comprising the fabric of claim 1.

12. An infection control product comprising the fabric of claim 1.

13. A protective cover comprising the fabric of claim 1.