Patent Publication Number: US-2020283933-A1

Title: High load bearing capacity nylon staple fibers with additive, and blended yarns and fabrics thereof

Description:
This patent application claims the benefit of priority from U.S. Provisional Application Ser. No. 62/575,091 filed Oct. 20, 2017, teachings of which are herein incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to high load bearing nylon staple fibers which contain an additive and methods for their production and their use in blended yams, fabrics and other articles of manufacture. 
     BACKGROUND OF THE INVENTION 
     Nylon has been manufactured and used commercially for a number of years. The first nylon fibers were of nylon 6,6, poly(hexamethylene adipamide). Nylon 6,6 fiber is still made and used commercially as the main nylon fiber. Large quantities of other nylon fibers, especially nylon 6 fiber prepared from caprolactam, are also made and used commercially. Nylon fiber is used in yarns for textile fabrics, and for other purposes. For textile fabrics, there are essentially two main yarn categories, namely continuous filament yarns and yarns made from staple fiber, i.e. cut fiber. 
     Nylon staple fiber has conventionally been made by melt-spinning nylon polymer into filaments, collecting very large numbers of these filaments into a tow, subjecting the tow to a drawing operation and then converting the tow to staple fiber, e.g., in a staple cutter. The tow usually contains many thousands of filaments and is generally of the order of several hundred thousand (or more) in total denier. The drawing operation involves conveying the tow between a set of feed rolls and a set of draw rolls (operating at a higher speed than the feed rolls) to increase the orientation of nylon polymer in the filaments. Drawing is often combined with an annealing operation to increase nylon crystallinity in the tow filaments before the tow is converted into staple fiber. 
     One of the advantages of nylon staple fibers is that they are readily blended, particularly with natural fibers, such as cotton (often referred to as short staple) and/or with other synthetic fibers, to achieve the advantages derivable from such blending. A particularly desirable form of nylon staple fiber has been used for many years for blending with cotton, particularly to improve the durability and economics of the fabrics made from yarns comprising blends of cotton with nylon. This is because such nylon staple fiber has a relatively high load-bearing tenacity, as disclosed in Hebeler, U.S. Pat. Nos. 3,044,250; 3,188,790; 3,321,448; and 3,459,845, the disclosures of which are hereby incorporated by reference in their entirety. As explained by Hebeler, the load-bearing capacity of nylon staple fiber is conveniently measured as the tenacity at 7% elongation (T 7 ), and the T 7  parameter has long been accepted as a standard measurement and is easily read on an Instron machine. 
     The Hebeler process for preparing nylon staple fiber involves the nylon spinning, tow forming, drawing and converting operations hereinbefore described. Improvements in the Hebeler process for preparing nylon staple fiber have subsequently been made by modifying the nature of the tow drawing operation and by adding specific types of annealing (or high temperature treatment) and subsequent cooling steps to the overall process. For example, Thompson in U.S. Pat. Nos. 5,093,195 and 5,011,645 discloses nylon staple fiber preparation wherein nylon 6,6 polymer, having for example a formic acid relative viscosity (RV) of 55, is spun into filaments which are then drawn, annealed, cooled and cut into staple fiber having a tenacity, T, at break of about 6.8-6.9, a denier per filament of about 2.44, and a load-bearing capacity, T7, of from about 2.4 to 3.2. Such nylon staple fibers are further disclosed in the Thompson patents as being blended with cotton and formed into yarns of improved yarn strength. (Both of these Thompson patents are incorporated herein by reference in their entirety.) 
     Nylon staple fibers prepared in accordance with the Thompson technology have been blended into NYCO yarns (generally at a 50:50 nylon/cotton ratio) with these yarns being used to prepare NYCO fabrics. Such NYCO fabrics, e.g., woven fabrics, find application in military combat uniforms and apparel. While such fabrics have generally proven satisfactory for military or other rugged apparel use, military authorities, for example, are continually looking for improved fabrics which may be lighter in weight, lower in cost and/or more comfortable but still highly durable or even of improved durability. 
     PCT/US2015/055333 discloses high strength or load bearing nylon yarn with break tenacity greater than 7.5 g/den and or a tenacity at 10% elongation of greater than 4.0 g/den as well as yarns, fabrics and articles of manufacture and methods for their production. 
     There is desire and benefits have been shown for adding pigments such as carbon black to a fiber particularly in military apparel. See, for example, U.S. Pat. Nos. 5,830,572, 7,008,694 and 7,320,766. 
     In addition, denim and canvas fabrics, in particular dark denim, and especially black denim, have become popular in the marketplace but are known in the industry to have fading or colorfastness issues. For example, in the case of black denim, the coloration quickly fades after repeated launderings/wear. It is also known that the addition of nylon as a blend with cotton or cellulosic fibers significantly improves the yarn and resulting fabric&#39;s durability by improving abrasion resistance. The black dyes used to dye the black denim fabric only stain the nylon and are not as dark or permanent on the nylon fiber as they are on the cotton fiber. 
     However, any blending of nylon staple with a cotton or cellulosic fiber requires high strength/high modulus. 
     Addition of additives such as pigments into a polymer prior to melt spinning of fibers has historically reduced fiber physical properties. For example, organic pigments tend to cross-link nylon, change its viscosity, form spherulites which weaken fibers, and cause increased draw tension and filament breaks. The more pigment that is added, the larger the strength loss. These reduced fiber properties have prevented or limited blending of pigmented nylon staple with cellulosic fibers due to resulting low yarn and low fabric strength issues. 
     For example, DuPont produced pigmented nylon staple in the mid to late 1990&#39;s for use in automotive upholstery. The resulting nylon staple product had break tenacity under 5.5 grams/denier. The only end use identified at that time was for the yams to be spun in 100% form for auto/home upholstery. 
     U.S. Pat. No. 5,290,850 discloses an improved process for melt spinning a pigmented hexamethylene adipamide fiber from a melt blend of a polymer and a colored pigment wherein the polymer is a random interpolyamide or block polymer having two different difunctional recurring amide-forming moieties other than those which form hexamethylene which exhibit tenacities greater than 7.5 grams per denier. 
     There is need for additional high load bearing nylon staple fibers with additives for use in fabrics and other articles of manufacture. 
     SUMMARY OF THE INVENTION 
     Usually, adding any inorganic or organic pigment or additive to the polymer during the melt spinning process reduces the resulting fiber strength. The fiber strength loss translates into lower yarn and resulting fabric strength. The inventors herein have unexpectedly found that adding an additive into nylon polymer prior to fiber formation and drawing the fibers under a steam assist/annealing process results in the production of high strength/high modulus fibers that contain the additive. 
     Accordingly, an aspect of the present invention relates to nylon staple fiber comprising nylon polymer and an additive. The nylon staple fiber with additive of the present invention exhibits a break tenacity greater than 6.5 g/den. In one nonlimiting embodiment, the nylon staple fiber exhibits a tenacity at 10% elongation of greater than 3.0 g/den. Nonlimiting examples of additives which can be included in these fibers are pigments as well as additives included for fire or flame (FR) resistance and/or ultraviolet (UV) protection. 
     Another aspect of the present invention relates to yarn spun from the nylon staple fiber. In one nonlimiting, the yarn further comprises at least one companion staple fiber. In one nonlimiting embodiment, the nylon content of the yarn is greater than 5%. In one nonlimiting embodiment, the nylon content of the yarn is greater than 30%. In one nonlimiting embodiment, the nylon content of the yarn is greater than 50%. Such yarns can be made into fabrics and other articles of manufacture which are advantageously lightweight, comfortable, lower cost, and durable and hence especially suitable for use in or as, for example, military apparel such as combat uniforms or other rugged use apparel. 
     Another aspect of the present invention relates to articles of manufacture, at least a portion of which comprises nylon staple fiber or yarn of the present invention. 
     In one nonlimiting embodiment, the article of manufacture is fabric. 
     In one nonlimiting embodiment, the fabric is dyed a solid color and/or exhibits a uniform dark shade. 
     In one nonlimiting embodiment, the fabric exhibits improved UV light fastness over the closest comparison fabrics lacking such pigment-containing or additive-containing components. 
     In one nonlimiting embodiment, the fabric exhibits improved dye wash fastness over the closest comparison fabrics lacking such pigment-containing or additive-containing components. 
     In one nonlimiting embodiment, the fabric, is a camouflage print. This fabric is typically constructed by use of pigmented synthetic fiber such as polyamide 6,6 or nylon 6,6, though the fabric can also be greige, or non-pigmented fabric. Where the fiber is pigmented, however, printing can still occur over top of the pigmented fabric. 
     In one nonlimiting embodiment, the fabric exhibits a NIR (Near Infrared) reflectance in the range of 600-900 nm and/or a lower and flattened SWIR (Short Wave Infrared) reflectance in the range of 900-2500 nm Further, the fabric increases infrared (IR) reflectance curve separation between individual colors used in printed fabrics in the SWIR spectrum, and provides further disruption and improved camouflage effectiveness against night vision goggle surveillance. 
     In one nonlimiting embodiment, the fabric has improved flame resistant characteristics. 
     In one nonlimiting embodiment, the fabric exhibits an improved electric arc rating over the closest comparison fabrics lacking such pigment-containing or additive-containing components 
     In one nonlimiting embodiment, the article of manufacture is denim fabric. In one nonlimiting embodiment, the denim fabric is overdyed in a color similar to the pigment contained in the nylon staple fiber. Further, when the fiber is black, and the fabric is printed to a dark color, a more uniformly dyed product is obtained, because the black fiber will act to minimize or eliminate the appearance of white fiber showing through the fabric. 
     In another nonlimiting embodiment, the article of manufacture is a non-woven fabric composite. End uses for such composites include, but are not limited to, industrial (felts/backings/filtration/insulation), apparel (inclusive of liner fabrics), footwear, bag/pack hard gear, durable and semi-durable (disposable or semi disposable) clothing or PPE, including FR (chemically treated or in combination with inherent FR fiber technologies), bio chemical, or other specialty protective wear. 
     Yet another aspect of the present invention relates to a method for producing high strength or load bearing pigmented nylon staple fiber. The method of the present invention comprises melt-spinning nylon polymer with pigment into filaments, then uniformly quenching the filaments and forming a tow from a multiplicity of these quenched filaments. The tow is then subjected to drawing in the presence of steam. The drawn tow is then annealed and the resulting drawn and annealed tow is converted into staple fibers. In one nonlimiting embodiment, the annealing is performed under tension. Nylon staple fiber produced in accordance with this method has a break tenacity greater than 6.5 g/den. In one nonlimiting embodiment, nylon staple fiber prepared in accordance with this method has a tenacity at 10% elongation of greater than 3.0 g/den. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Provided by this disclosure are high strength or load bearing nylon staple fiber with additive exhibiting a break tenacity greater than 6.5 g/den and/or a tenacity at 10% elongation of greater than 3.0 g/den, yarns, fabrics and other articles of manufacture, at least a portion of which are prepared from these fibers, and methods for their production. 
     Nonlimiting examples of additives included in the nylon staple fiber are pigments, additives which provide UV protection, and additives for FR resistance. 
     In one nonlimiting embodiment, the additive is a pigment present in an amount from about 10 parts per million to about 50,000 parts per million. In one nonlimiting embodiment, the pigment is carbon black. Further examples of suitable pigments are: ultramarine violet, a silicate of sodium and aluminum containing sulfur; han purple, BaCuSi 2 O 6 ; cobalt violet, cobaltous orthophosphate; manganese violet, NH 4 MnP 2 O 7 ; ultramarine, Na 8-10 Al 6 Si 6 O 24 S 2-4 ; Persian blue, (Na, Ca) 8 (AlSiO 4 ) 6 (S,SO 4 ,Cl) 1-2 ; cobalt blue, cobalt(II) stannate; Egyptian blue, (CaCuSi 4 O 10 ); han blue, BaCuSi 4 O 10 ; azurite, (Cu 3 (CO 3 ) 2 (OH 2 )); Prussian blue, ferric hexacyanoferrate; YInMn blue, (YIn 1-x Mn x O 3 ); cadmium green, a mixture of CdS and Cr 2 O 3 ; chrome green, chromic oxide; Viridian, hydrated chromic oxide; Rimnan&#39;s green, CoZnO 2 ; malachite, (Cu 2 CO 3 (OH) 2 ); Paris green, Cu(C 2 H 2 O 2 ) 2.3 Cu(AsO 2 ) 2 ); Scheele&#39;s green, CuHAsO 3 ; Verdigris, which is typically cupric acetate and/or malachite; Verona green, (K[Al,Fe III ),(Fe II ,Mg](AlSi 3 ,Si 4 )O 10 (OH) 2 ); orpiment, (As 2 S 3 ); primrose yellow, (BiVO 4 ); cadmium yellow, CdS; chrome yellow, PbCrO 4 ; cobalt yellow, (K 3 Co(NO 2 ) 6 ); yellow ochre, (Fe 2 O 3 .H 2 O); titanium yellow; mosaic gold, SnS 2 ; cadmium orange, cadmium sulfoselenide; chrome orange, (PbCrO 4 +PbO); realgar, As 4 S 4 ; cadmium red, CdSe; Indian Red; red ochre, Fe 2 O 3 ; burnt sienna; vermillion, HgS; raw umber, Fe 2 O 3 +MnO 2 +nH 2 O+Si+AlO 3 ; raw sienna; ivory black; vine black; lamp black; mars black, Fe 3 O 4 ; manganese dioxide; titanium black, Ti 2 O 3 ; antimony white, Sb 2 O 3 ; barium sulfate; lithopone, BaSO 4 .ZnS; Cremnitz white, ((PbCO 3 ) 2 ·Pb(OH) 2 ); titanium dioxide, TiO 2 ; and zinc oxide, ZnO. 
     Also provided by this disclosure are non-woven fabric composites comprising high tenacity fiber and cellulosic or recycled synthetic or natural fiber. 
     As used herein, the terms “durable” and “durability” refer to the propensity of a fabric so characterized to have suitably high grab and tear strength as well as resistance to abrasion for the intended end use of such fabric, and to retain such desirable properties for an appropriate length of time after fabric use has begun. 
     As used herein, the term “blend” or “blended”, in referring to a spun yarn, means a mixture of fibers of at least two types, wherein the mixture is formed in such a way that the individual fibers of each type of fiber are substantially completely intermixed with individual fibers of the other types to provide a substantially homogeneous mixture of fibers, having sufficient entanglement to maintain its integrity in further processing and use. 
     As used herein, cotton count refers to the yarn numbering system based on a length of 840 yards, and wherein the count of the yarn is equal to the number of 840-yard skeins required to weigh 1 pound. 
     All numerical values recited herein are understood to be modified by the term “about”. 
     Some embodiments are based on the preparation of improved nylon staple fibers with additive having certain specified characteristics and on the subsequent preparation of yarns, and fabrics woven from such yarns, wherein these improved nylon staple fibers with additive are blended with at least one other fiber. The other fibers may include cellulosics such as cotton, modified cellulosics such as fire-resistant (FR) treated cellulose, polyester, rayon, animal fibers such as wool, FR polyester, FR nylon, FR rayon, m-aramid, p-aramid, modacrylic, novoloid, melamine, polyvinyl chloride, antistatic fiber, PBO (1,4-benzenedicarboxylic acid, polymer with 4,6-diamino-1,3-benzenediol dihydrochloride), PBI (polybenzimidazole), and combinations thereof. The nylon staple fibers of some embodiments can provide an increase in strength and/or abrasion resistance to yarns and fabrics. This is especially true for combination with relatively weaker fibers such as cotton and wool. 
     The specific characteristics of the nylon staple fibers with additive prepared and used herein include fiber denier, fiber tenacity and fiber load-bearing capacity defined in terms of fiber tenacity at 7% and 10% elongation. 
     Realization of the desired nylon staple fiber with additive material herein is based on the use in staple fiber manufacture of nylon polymeric filaments and tows having certain selected properties and processed using certain selected processing operations and conditions. Specifically, the inventors herein have found that introduction of steam between the feed and draw module and/or tension during annealing during production of the nylon staple fiber with additive significantly inhibits or prevents reduction in strength associated with addition of such fiber additives. In one nonlimiting embodiment of the present invention, steam is introduced into the process by addition of a steam chamber between the feed and draw modules as this allows the excess water to be removed prior to annealing. Without being limited to any particular theory, it is believed that the steam chamber adds enough heat/steam to reduce the draw force of the nylon and help localize the draw to the steam chamber and not over or at the feed roll exit. Steam can be controlled by pressure. 
     The nylon polymer itself which is used for the spinning of nylon filaments of the present invention can be produced in conventional manner. Nylon polymer suitable for use in the process and filaments of some embodiments comprises synthetic melt spinnable or melt spun polymer. Such nylon polymers can include polyamide homopolymers, copolymers, and mixtures thereof which are predominantly aliphatic, i.e., less than 85% of the amide-linkages of the polymer are attached to two aromatic rings. Widely-used polyamide polymers such as poly(hexamethylene adipamide) which is nylon 6,6 and poly(ε-caproamide) which is nylon 6 and their copolymers and mixtures thereof can be used in accordance with some embodiments. Other polyamide polymers which may be advantageously used are nylon 12, nylon 4,6, nylon 6,10, nylon 6,12, nylon 12,12, and their copolymers and mixtures thereof. Illustrative of polyamides and copolyamides which can be employed in the process, fibers, yarns and fabrics of some embodiments are those described in U.S. Pat. Nos. 5,077,124, 5,106,946, and 5,139,729 (each to Cofer et al.) and the polyamide polymer mixtures disclosed by Gutmann in Chemical Fibers International, pages 418-420, Volume 46, December 1996. These publications are all incorporated herein by reference. 
     In one nonlimiting embodiment, the polymer may further comprise a monomeric salt of sulfonated isopthalate (SIPA) or a monomeric methylpentamethyldiamine (MPMD). In one nonlimiting embodiment, the monomer is added at an amount of about 0.04 to about 4 wt. % of the nylon polymer. 
     Nylon polymer used in the preparation of nylon staple fibers has conventionally been prepared by reacting appropriate monomers, catalysts, antioxidants and other additives, including, but not limited to, plasticizers, delustrants, pigments, dyes, light stabilizers, heat stabilizers, antistatic agents for reducing static, additives for modifying dye ability, agents for modifying surface tension, etc. Polymerization has typically been carried out in a continuous polymerizer or batch autoclave. The molten polymer produced thereby has then typically been introduced to a spin pack wherein it is forced through a suitable spinneret and formed into filaments which are quenched and then formed into tows for ultimate processing into nylon staple fiber. As used herein, spin pack is comprised of a pack lid at the top of the pack, a spinneret plate at the bottom of the pack and a polymer filter holder sandwiched between the former two components. The filter holder has a central recess therein. The lid and the recess in the filter holder cooperate to define an enclosed pocket in which a polymer filter medium, such as sand, is received. There are provided channels interior to the pack to allow the flow of molten polymer, supplied by a pump or extruder to travel through the pack and ultimately through the spinneret plate. The spinneret plate has an array of small, precision bores extending therethrough which convey, the polymer to the lower surface of the pack. The mouths of the bores form an array of orifices on the lower surface of the spinneret plate, which surface defines the top of the quench zone. The polymer exiting these orifices is in the form of filaments which are then directed downwards through the quench zone. 
     The extent of polymerization carried out in the continuous polymerizer or batch autoclave can generally be quantified by means of a parameter known as relative viscosity or RV. RV is the ratio of the viscosity of a solution of nylon polymer in a formic acid solvent to the viscosity of the formic acid solvent itself. RV is taken as an indirect indication of nylon polymer molecular weight. For purposes herein, increasing nylon polymer RV is considered synonymous with increasing nylon polymer molecular weight. 
     As nylon molecular weight increases, its processing becomes more difficult due to the increasing viscosity of the nylon polymer. Accordingly, continuous polymerizers or batch autoclaves are typically operated to provide nylon polymer for eventual processing into staple fiber wherein the nylon polymer has an RV value of about 60 or less. 
     It is known that for some purposes, provision of nylon polymer of greater molecular weight, i.e., nylon polymer having RV values of greater than 70-75 and up to 140 or even 190 and higher can be advantageous. It is known, for example, that high RV nylon polymer of this type has improved resistance to flex abrasion and chemical degradation. Accordingly, such high RV nylon polymer is especially suitable for spinning into nylon staple fiber which can advantageously be used for the preparation of papermaking felts. Procedures and apparatus for making high RV nylon polymer and staple fiber therefrom are disclosed in U.S. Pat. No. 5,236,652 to Kidder and in U.S. Pat. Nos. 6,235,390; 6,605,694; 6,627,129 and 6,814,939 to Schwinn and West. All of these patents are incorporated herein by reference in their entirety. 
     In accordance with some embodiments, it has been discovered that staple fibers prepared from nylon polymer having an RV value which is generally consistent with, or in some cases higher than, that generally obtained via polymerization in a continuous polymerizer or batch autoclave, when processed with an additive and in accordance with the spinning, quenching, feeding and drawing in the presence of steam and annealing procedures described herein, unexpectedly exhibit increased fiber break tenacity and increased tenacity and 10% elongation as compared to standard product or previously described improvements. When such nylon staple fibers with additive of improved tenacity are blended with one or more other fibers such as cotton staple fibers, textile yarns of improved strength as well as lower weight can be realized. Fabrics such as NYCO fabrics woven from such yarns exhibit the advantages hereinbefore described with respect to durability, optional lighter weight, improved comfort and/or potential lower cost as well as the benefit of the selected additive color, UV protection or FR resistance. 
     In accordance with the staple fiber preparation process herein, nylon polymer with additive, which is melt spun into tow-forming filaments through one or more spin pack spinnerets and quenched, will have an RV value ranging from 45 to 100, including from 55 to 100, from 46 to 65, from 50 to 60, and from 65 to 100. Nylon polymer of such RV characteristics can be prepared, for example, using a melt blending of polyamide concentrate procedure such as the process disclosed in the aforementioned Kidder &#39;652 patent. Kidder discloses certain embodiments in which a catalyst is added for the purpose of increasing the formic acid relative viscosity (RV). Higher RV nylon polymer available for melting and spinning, such as nylon having an RV of from 65 to 100, can also be provided by means of a solid phase polymerization (SPP) step wherein nylon polymer flakes or granules are conditioned to increase RV to the desired extent. Such solid phase polymerization (SPP) procedures are well-known and disclosed in greater detail in the aforementioned Schwinn/West &#39;390, &#39;694, &#39;129 and &#39;939 patents. 
     The nylon polymer material with additive having the requisite RV characteristics as specified herein is fed to a spin pack, for example via a twin screw melter device. In one nonlimiting embodiment, a volumetric or gravimetric feeder is used for addition of the additive. In the spin pack the nylon polymer with additive is spun by extrusion through one or more spinnerets into a multiplicity of filaments. For purposes herein, the term “filament” is defined as a relatively flexible, macroscopically homogeneous body having a high ratio of length to width across its cross-sectional area perpendicular to its length. The filament cross section can be any shape, but is typically circular. Herein, the term “fiber” can also be used interchangeably with the term “filament”. 
     Each individual spinneret position may contain from 100 to 1950 filaments in an area as small as 9 inches by 7 inches (22.9 cm×17.8 cm). Spin pack machines may contain from one to 96 positions, each of which provides bundles of filaments which eventually get combined into a single tow band for drawing/downstream processing with other tow bands. 
     After exiting the spinnerets, the molten filaments which have been extruded through each spinneret are typically passed through a quench zone wherein a variety of quenching conditions and configurations can be used to solidify the molten polymer filaments with additive and render them suitable for collection together into tows. Quenching is most commonly carried out by passing a cooling gas, e.g., air, toward, onto, with, around and through the bundles of filaments being extruded into the quenching zone from each spinneret position within the spin pack. 
     One suitable quenching configuration is cross-flow quenching wherein a cooling gas such as air is forced into the quenching zone in a direction which is substantially perpendicular to the direction that the extruded filaments are travelling through the quench zone. Cross-flow quenching arrangements are described, among other quenching configurations, in U.S. Pat. Nos. 3,022,539; 3,070,839; 3,336,634; 5,824,248; 6,090,485, 6,881,047 and 6,926,854, teachings of which are incorporated herein by reference in their entirety. 
     In one nonlimiting embodiment of the staple fiber preparation process herein, the extruded nylon filaments with additive used to eventually form the desired nylon staple fibers with additive are spun, quenched and formed into tows with both positional uniformity and uniformity of quenching conditions such as described in published U.S. Patent Application Nos. 2011/0177737 and 2011/0177738, teachings of which are herein incorporated by reference in their entirety. 
     Quenched spun filaments can then be combined into one or more tows. Such tows formed from filaments from one or more spinnerets are then subjected to a two stage continuous operation wherein the tows are drawn and annealed in the presence of steam. 
     Drawing of the tows is generally carried out primarily in an initial or first drawing stage or zone wherein bands of tows are passed between a set of feed rolls and a set of draw rolls (operating at a higher speed) to increase the crystalline orientation of the filaments in the tow. The extent to which tows are drawn can be quantified by specifying a draw ratio which is the ratio of the higher peripheral speed of the draw rolls to the lower peripheral speed of the feed rolls. The effective draw ratio is calculated by multiplying the 1 st  draw ratio and the 2 nd  draw ratio. 
     The first drawing stage or zone may include several sets of feed and draw rolls as well as other tow guiding and tensioning rolls such as snubbing pins. Draw roll surfaces may be made of metal, e.g., chrome, or ceramic. Ceramic draw roll surfaces have been found to be particularly advantageous in permitting use of the relatively higher draw ratios specified for use in connection with the staple fiber preparation process herein. Ceramic rolls improve roll life as well as provide a surface that is less prone to wrap. An article appearing the International Fiber Journal (International Fiber Journal, 17, 1, February 2002: “Textile and Bearing Technology for Separator Rolls”, Zeitz and el.) as well as U.S. Pat. No. 4,794,680, incorporated herein by reference, also disclose the use of ceramic rolls in to improve roll life and reduce fiber adherence to roll surface. 
     While the greatest extent of drawing of the tows of filaments herein takes place in the initial or first drawing stage or zone, some additional drawing of the tows will generally also take place in a second or annealing and drawing stage or zone hereinafter described. The total amount of draw to which the filament tows herein are subjected can be quantified by specifying a total effective draw ratio which takes into account drawing that occurs in both a first initial drawing stage or zone and in a second zone or stage where annealing and some additional drawing are conducted simultaneously. 
     In the process of some embodiments, the tows of nylon filaments with additive are subjected to a total effective draw ratio of from 2.3 to 5.0, including from 3.0 to 4.0. In one embodiment wherein the denier per filament of the tows is generally smaller, a total effective draw ratio can range from 3.12 to 3.40. In another embodiment, wherein the denier per filament of the tows is generally larger, the total effective draw ratio can range from 3.5 to 4.0. 
     In the process herein, most of the drawing of the tows, as noted hereinbefore, occurs in the first or initial drawing stage or zone. In particular, from 85% to 97.5%, including from 92% to 97%, of the total amount of draw imparted to the tows will take place in the first or initial drawing stage or zone. The drawing operation in the first or initial stage will generally be carried out at whatever temperature the filaments have when passed from the quench zone of the melt spinning operation. Frequently, this first stage drawing temperature will range from 80° C. to 125° C. 
     In the present invention, steam is introduced between feeding and drawing. In one embodiment, a steam chamber located between the feed and draw modules is used. 
     From the first or initial drawing stage or zone, the partially drawn tows are passed to a second annealing and drawing stage or zone wherein the tows are simultaneously heated and further drawn. Heating of the tows to effect annealing serves to increase crystallinity of the nylon polymer of the filaments. In this second annealing and drawing stage or zone, the filaments of the tows are subjected to an annealing temperature of from 145° C. to 205° C., such as from 165° C. to 205° C. In one embodiment, the temperature of the tow in this annealing and drawing stage may be achieved by contacting the tow with a steam-heated metal plate that is positioned between the first stage draw and the second stage drawing and annealing operation. In the present invention, annealing/oven drying under tension helps remove excess moisture gained during steam draw. 
     After the annealing and drawing stage of the process herein, the drawn and annealed tows are cooled to a temperature of less than 80° C., such as less than 75° C. Throughout the drawing, annealing and cooling operations described herein, the tows are maintained under controlled tension and accordingly are not permitted to relax. 
     After drawing in the presence of steam and annealing/oven drying under tension, the multifilament tows are converted into staple fiber with additive by any conventional manner, for example, using a staple cutter. Staple fiber with additive formed from the tows will frequently range in length from 2 to 13 cm (0.79 to 5.12 inches). For example, staple fibers with additive may range from 2 to 12 cm (0.79 to 4.72 inches), from 2 to 12.7 cm (0.79 to 5.0 inches), or from 5 to 10 cm. The staple fiber with additive herein can optionally be crimped. 
     The high tenacity nylon staple fiber with additive formed in accordance with the process herein will generally be provided as a collection of fibers, e.g., as bales of fibers, having a denier per fiber of from 1.0 to 3.0. When staple fibers having a denier per fiber of from 1.6 to 1.8, are to be prepared, a total effective draw ratio of from 3.12 to 3.40, such as from 3.15 to 3.30, can be used in the process herein to provide staple fibers of the requisite load-bearing capacity. When staple fibers having a denier per fiber of from 2.5 to 3.0 or 2.3 to 2.7 are to be prepared, a total effective draw ratio of from 3.5 to 4.0, or from 3.74 to 3.90, should be used in the process herein to provide staple fibers of the requisite load-bearing capacity. 
     Using this process and then annealing the fiber with additive at 180° C. using standard annealing rolls produced a significantly higher tenacity fiber with additive with a tenacity greater than 6.5 g/den. 
     In one nonlimiting embodiment of the current invention, a nylon staple fiber with additive is disclosed having a tenacity at 10% elongation of at least 3.0 g/den. 
     Fiber with properties above and with the added advantage of the present invention of additives in the fiber such as pigments, UV protectors and FR resistors can be used at lower blend ratios or spun into yarns using alternative spinning systems that significantly reduce fabric manufacturing costs and still meet existing fabrics specifications. This fiber can be used to significantly reduce yarn spinning and finished fabric costs by allowing the use of lower nylon blend levels and/or alternative spinning system while maintaining fabric properties. 
     The nylon staple fibers with additive provided herein are especially useful for blending with other fibers for various types of textile applications. Blends can be made, for example, with the nylon staple fibers of some embodiments in combination with other synthetic fibers such as rayon or polyester. Examples of blends of the nylon staple fibers herein include those made with natural cellulosic fibers such as cotton, flax, hemp, jute and/or ramie. Suitable methods for intimately blending these fibers may include: bulk, mechanical blending of the staple fibers prior to carding; bulk mechanical blending of the staple fibers prior to and during carding; or at least two passes of draw frame blending of the staple fibers subsequent to carding and prior to yarn spinning. 
     In accordance with one nonlimiting embodiment, the high load-bearing capacity nylon staple fibers with additive herein may be blended with cotton staple fibers and spun into textile yarn. Such yarns may be spun in conventional manner using commonly known short and long staple spinning methods including ring spinning, air jet or vortex spinning, open end spinning, or friction spinning. When the yarn blend includes cotton, the resulting textile yarn will generally have a cotton fiber to nylon fiber weight ratio of from 10:90 to 90:10, including from 30:70 to 70:30, and frequently a cotton:nylon weight ratio of 50:50. It is well-known in the art that nominal variation of the fiber content, e.g., 52:48 is also considered to be a 50:50 blend. 
     The nylon/cotton (NYCO) yarns of some embodiments can be used in conventional manner to prepare NYCO woven fabrics of especially desirable properties for use in military or other rugged use apparel. Thus, such yarns may be woven into 2×1 or 3×1 twill NYCO fabrics. Spun NYCO yarns and 3×1 twill woven fabrics comprising such yarns are in general described and exemplified in U.S. Pat. No. 4,920,000 to Green, incorporated herein by reference. 
     NYCO woven fabrics, of course, comprise both warp and weft (fill) yarns. The woven fabrics of some embodiments are those which have the NYCO textile yarns herein woven in an least one, and optionally both, of these directions. In one embodiment, fabrics herein of especially desirable durability and comfort will have yarns woven in the weft (fill) direction comprising nylon staple fibers with additive herein and will have yarns woven in the warp direction comprising nylon staple fibers with additive herein. 
     The woven fabrics of some embodiments made using yarns which comprise the high load bearing nylon staple fibers with additive herein can use less of the nylon staple fibers than conventional NYCO fabrics while retaining many of the desirable properties of such conventional NYCO fabrics. Thus, such fabrics can be made to be relatively lightweight and low cost while still desirably durable. Alternatively, such fabrics can be made using equal or even greater amounts of the nylon staple fibers with additive herein in comparison with nylon fiber content of conventional NYCO fabrics with such fabrics herein providing superior durability properties. 
     In one nonlimiting embodiment, nylon staple fiber of the present invention with pigment additive is used to produce an article of manufacture such as a denim fabric. Currently, black dyed 100% cotton denim fabric has fade and wear issues after repeated launderings. While non-pigmented, high strength nylon staple can be added to improve fabric durability and strength, fading issues remain. Adding a pigmented, high strength nylon staple of the present invention comprising an additive such as carbon black reduces the black color appearance loss and improves wear life. As will be understood by the skilled artisan upon reading this disclosure, alternative pigments for colors such as blue, green and tan can also be used. In this nonlimiting embodiment, pigmented fibers with 1-5% by weight of, for example, carbon black or denim blue coloration can be used in denim to reduce fabric fading issues and improve durability. Incorporation of these fibers into fabrics is particularly useful in articles of manufacture which are dyed a solid color and/or wherein improved uniformity in dyeing such as in dark shades is desired. 
     In some embodiments, the denim fabric may be overdyed in a color similar to the pigment contained in the nylon staple fiber. Camouflage printed fabrics may also be produced from the nylon staple fiber with additive of the present invention. 
     Such fabrics are expected to exhibit improved dye wash fastness. 
     Further, the addition of carbon black into the fiber or on the fabric as a topical treatment is known to improve concealment of the uniform/wearer when viewed through night vision goggles using Near Infrared (NIR) and Short Wave Infrared (SWIR) technology. 
     Accordingly, in another nonlimiting embodiment, nylon staple pigmented fibers of the present invention with carbon black in the range of 10 to 1000 ppm can be used to improve concealment of articles of manufacture such as uniforms containing the fiber when viewed under SWIR/NIR night vision goggles. In one nonlimiting embodiment, incorporation of a pigmented nylon staple fiber of the present invention comprising a conventional dyestuff can lower the NIR reflectance in the range of 600-900 nm without requiring any pre- or post-treatments or use of a metalized or special pigment formulations and without significantly changing the shade in the visible spectrum, thus enhancing the camouflage disruption and effectiveness against night vision goggle surveillance. 
     In another nonlimiting embodiment, incorporation of a pigmented nylon staple fiber of the present invention comprising a conventional dyestuff can lower and flatten the Short Wave Infrared reflectance (SWIR) in the range of 900-2500 nm without requiring pre- or post-treatments or use of metalized or special pigment formulations required for solid color and printed camouflage NYCO fabrics, and without significantly changing the shade in the visible spectrum thus enhancing the camouflage disruption and effectiveness against night vision goggle surveillance. In yet another nonlimiting embodiment, incorporation of a pigmented nylon staple fiber of the present invention comprising a conventional dyestuff can increase the level of separation between print colors in the SWIR in the range of 900-2500 nm without requiring pre- or post-treatments or use of metalized or special pigment formulations, thus enhancing the camouflage disruption and effectiveness against night vision goggle surveillance. Such-fabrics of the present invention are also expected to exhibit an improved electric arc rating. 
     In another nonlimiting embodiment, incorporation of nylon staple fiber with an additive providing UV protection or an additive providing FR resistance into an article of manufacture such as a fabric results in improved UV light fastness and/or flame retardance. 
     The present invention also relates to non-woven fabric composites comprising high tenacity fiber of the present invention. The high tenacity fiber can be combined with various cellulosic or recycled synthetic or natural fiber technologies. In one embodiment, the high tenacity fiber is combined with recycled denim. End uses for the non-woven fabric composites include, but are not limited to, industrial (felts/backings/filtration/insulation), apparel (inclusive of liner fabrics), footwear, bag/pack hard gear, durable and semi-durable (disposable or semi disposable) clothing or PPE, including FR (chemically treated or in combination with inherent FR fiber technologies), bio chemical, or other specialty protective wear. 
     As will be understood by the skilled artisan upon reading this disclosure, alternative methods and apparatus to those exemplified herein which result in at least a portion of the yarn on the top surface or at least a portion of the yarn on the bottom surface having fibers with a permanently modified cross-section and that are melt fused together are available and use thereof is encompassed by the present invention. 
     All patents, patent applications, test procedures, priority documents, articles, publications, manuals, and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted. 
     Test Methods and Examples 
     The following Test Methods and Examples demonstrate the present invention and its capability for use. The invention is capable of other and different embodiments, and its several details are capable of modifications in various apparent respects, without departing from the scope and spirit of the present invention. Accordingly, the Test Methods and Examples are to be regarded as illustrative in nature and non-limiting. 
     Nylon Polymer Relative Viscosity 
     The formic acid RV of nylon materials used herein refers to the ratio of solution and solvent viscosities measured in a capillary viscometer at 25° C. The solvent is formic acid containing 10% by weight of water. The solution is 8.4% by weight nylon polymer dissolved in the solvent. This test is based on ASTM Standard Test Method D 789. The formic acid RVs are determined on spun filaments, prior to or after drawing, and can be referred to as spun fiber formic acid RVs. 
     Instron Measurements on Staple Fibers 
     All Instron measurements of staple fibers herein are made on single staple fibers, taking appropriate care with the clamping of the short fiber, and making an average of measurements on at least 10 fibers. Generally, at least 3 sets of measurements (each for 10 fibers) are averaged together to provide values for the parameters determined. 
     Filament Denier 
     Denier is the linear density of a filament expressed as weight in grams of 9000 meters of filament. Denier can be measured on a Vibroscope from Textechno of Munich, Germany. Denier times (10/9) is equal to decitex (dtex). Denier per filament can be determined gravimetrically in accordance with ASTM Standard Test Method D 1577. A Favimat machine having a vibration based linear density measurement such as used in a Vibroscope can also be used to determine DPF or denier per filament of the individual fiber and is comparable to ASTM D1577. 
     Tenacity at Break 
     Tenacity at break (T) is the maximum or breaking force of a filament expressed as force per unit cross-sectional area. The tenacity can be measured on an Instron model 1130 available from Instron of Canton, Mass, and is reported as grams per denier (grams per dtex). Filament tenacity at break (and elongation at break) can be measured according to ASTM D 885. 
     Filament Tenacity at 7% and 10% Elongation 
     Filament tenacity at 7% elongation (T7) is the force applied to a filament to achieve 7% elongation divided by filament denier. T7 can be determined according to ASTM D 3822. Tenacity at 10% elongation can be run on a Favimat, which is comparable to ASTM D3822. 
     Yarn Strength 
     Strength of the spun nylon/cotton yarns herein can be quantified via a Lea Product value or yarn breaking tenacity. Lea Product and skein breaking tenacity are conventional measures of the average strength of a textile yarn and can be determined in accordance with ASTM D 1578. Lea Product values are reported in units of pounds force. Breaking tenacity is reported in units of cN/tex. 
     Fabric Weight 
     Fabric weight or basis weight of the woven fabrics herein can be determined by weighing fabric samples of known area and calculating weight or basis weight in terms of grams/m 2  or oz/yd 2  in accordance with the procedures of the standard test method of ASTM D 3776. 
     Fabric Grab Strength 
     Fabric grab strength can be measured in accordance with ASTM D 5034. Grab strength measurements are reported in pounds-force in both warp and fill directions. 
     Fabric Tear Strength—Elmendorf 
     Fabric tear strength can be measured in accordance with ASTM D 1424 titled Standard Test Method for Tearing Strength of Fabrics by Falling-Pendulum Type (Elmendorf) Apparatus. Grab strength measurements are reported in pounds-force in both warp and fill directions. 
     Colorfastness to Laundering—AATCC Test Method 61 
     AATCC 61 is used to evaluate the colorfastness to laundering of textiles expected to withstand frequent launderings. Test specimens are attached to multi-fiber swatches and stainless steel balls are loaded into stainless steel canisters to replicate abrasion. The canisters are then loaded into the machine and the 45 minute test begins. After laundering, specimens are dried, conditioned, and evaluated with both the Gray Scale for Color Change and the Gray Scale for Staining. Dimensional changes of fabrics after laundering are also tested and applied to evaluations, according to AATCC Test Method 135. 
     Colorfastness to Light—AATCC Test Method 16 
     This test method provides the general principles and procedures which are currently in use for determining the colorfastness to light of textile materials. The test options described are applicable to textile materials of all kinds and for colorants, finishes and treatments applied to textile materials. 
     Test options included are: 
     1—Enclosed Carbon-Arc Lamp, Continuous Light 
     2—Enclosed Carbon-Arc Lamp, Alternate Light and Dark 
     3—Xenon-Arc Lamp, Continuous Light, Black Panel Option 
     4—Xenon-Arc Lamp, Alternate Light and Dark 
     5—Xenon-Arc Lamp, Continuous Light, Black Standard Option 
     6—Daylight Behind Glass 
     Colorimetric Analysis 
     NIR and SWIR analyses are performed using any of commercially available color spectrophotometric instruments such as an UltraScan Pro spectrophotometer, available from HunterLab. 
     Example 1: 
     Various fibers of the present invention were tested as described herein. Results are depicts in the following Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Pigment Addition T420BK Fiber Properties 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Tenacity at 
                 Tenacity at 
               
               
                   
                   
                   
                   
                 7% 
                 10% 
               
               
                 Fiber 
                   
                 Tenacity 
                 Elongation 
                 Elongation 
                 Elongation 
               
               
                 Property 
                 DPF 
                 (g/den) 
                 (%) 
                 (g/den) 
                 (g/den) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1000 ppm 
                 1.60 
                 7.29 
                 53.44 
                 1.98 
                 3.33 
               
               
                 carbon black 
               
               
                 average 
               
               
                 1.25% 
                 1.59 
                 7.04 
                 45.33 
                 1.88 
                 3.28 
               
               
                 Carbon 
               
               
                 Black 
               
               
                 Average