IE44756B1 - Monofilament fibre of polymeric material, a method of making said fibre, and pile fabric made from said fibre - Google Patents

Abstract

A fiber which will perform in pile fabrics such as carpets is made from a low cost polymer, for example, copolymers of ethylene and vinyl acetate. This fiber is characterized by an elastic modulus of from 5,000 to 60,000 psi, an area moment of inertia of from 400 x 10-14 to 7,000 x 10-14 in4, and a stiffness parameter (as defined herein) of from 1 x 10-5 to 1 x 10-8 lb - in2. For good coverage, the pile fabric made from such fiber will have a minimum of 4,000 fibers per square inch of backing and a minimum pile height of 1/8 inch, The invention also provides for a method of making a fiber of the above characteristics which includes sequential steps of extruding, drawing, rapid cooling, drawing again and reheating under tension.

Description

This invention invention relates to a monofilament fiber of polymeric material; a method of making the fiber and to a pile fabric made from the fiber.

Nylon fiber is one of the most versatile and us.eful 5 man-made fibers developed to date. In its monofilament form it is bulked by crimping and twisted together with other bulked monofilaments to form a nylon yarn which is particularly suited for carpets. These nylon yarns, when tufted through a suitable backing, forma pile fabric that has excellent wearability and a good hand, i.e. it is pleasant to the touch.

Since the cost of n;Ion has increased substantially over the past few years, lower cost substitutes having physical characteristics r.imilar to those of nylon are being sought. Polypropylene yarns recently have been introduced which for some applications serve as a substitute for nylon carpet yarns. To date carpets employing polypropylene face yarns have lade modest penetration of the market, and polypropylene yarns now represent approximately percent of the face yarns used in the manufacture of carpets.

We have now devised a monofilament fibre which can be made from low cost polymeric materials and from which satisfactory pile fabrics can be made.

-The invention provides a monofilament fiber comprising a polymeric material and having an elastic modulus of from 5,000 to 60,000 psi, an area moment of -14 -144 κinertia of from 400 x 10 to 7,000 X 10 in , and a —8 2 stiffness parameter of from 1 x 10 to 1 x 10 lbs-in .

Elastic modulus is determined by measuring the initial slope of the stress-strain curv·· derived according to ASTM standard method No. D2256-69. Strain measurements are corrected for gauge length variations by the method described in an article entitled A Method for Determining Tensile Strains and Elastic Modulus of Metallic Filaments, ASM Transactions Quarterly, S Vol. 60, No. 4, December 1967, pp. 726-27.

The chief criterion for selecting a polymeric material is its elastic modulus. The best material so far uncovered is an ethylene-vinyl acetate copolymer having a vinyl acetate content ranging from 1 to 10 percent by weight and a melt index of from 0.5 to 9. This material will provide the monofilament with the desired elastic modulus and is also relatively inexpensive. The following thermoplastic materials will provide the monofilament with an elastic modulus within the range of from 5,000 to 60,000 psi: (a) plasticized polyvinyl chloride, (b) low density polyethylene, (c) thermoplastic rubber, (d) ethylene-ethyl acrylate copolymer, (e) ethylene-butylene copolymer, (f) polybutylene and copolymers thereof, (g) ethylene-propylene copolymers, (h) chlorinated polypropylene, (i) chlorinated polybutylene, or (j) mixtures of these thermoplastic materials. Although the ethylene-vinyl acetate copolymer has the desired elastic modulus, one problem v/ith this material is that it has a relatively low melting point. To obviate this problem and increase the heat resistance of the fiber, the molecules of the copolymer may be cross-linked.

Cross-linking may be achieved either during the manufacture •44756 of the fibfer or subsequently. Conventional irradiation techniques may be employed or the molecules of the polymer may include moieties which react under selected conditions with other molecules to effect cross-linking. As will be S discussed below in detail, it is desirable to use certain additives which greatly enhance cross-linking. Only partial cross-linking is desired so that the material retains the required elastic properties. Ordinarily, cross-linking increases the melting point of the material so that it is 200eF or greater.

The fiber of this invention makes an excellent carpet yarn when twisted together with other monofilament fibers of my invention and bulked. Such yarn, tufted or otherwise when formed into a pile fabric, provides a plush pile surface having a hand similar to that of pile surfaces formed from conventional nylon carpet yarns. It also has the other necessary physical properties to serve as a carpet yarn.

PHYSICAL PROPERTIES OF FIBER . The fibers of the invention have good hand,resist watting, wear well, and are tuftable or may otherwise be processed using conventional carpet making techniques. All these properties are necessary for the fiber to give satisfactory performance in carpets. Moreover, 1 hey have good anti-static properties and are easy to clean because of their relatively large diameter.

Hand Hand is simply how the fiber feels. When considering the hand of any fiber, one must take into account the specific textile construction in which the hand is being judged.

Since the fibers of the invention are intended mainly for use in carpet yarn, they have those physical properties which will impart good hand to the fiber in a pile construction. In such a construction the fiber acts under loads like an upright column. In other words, when one touches the fiber, a downward force is exerted on the upright fibers.

At a critical load the fibers will buckle or bend. The more rigid or stiff the fibers, the greater the load required to bend the fibers. Good hand is associated with fibers that are pliant.

Although other factors affect the hand of pile fabrics, the chief factor is the fiber stiffness which is a function of the material properties of the fiber, the geometry of the fiber, and the manner in which load is applied to the fiber. In general terms, one may compare the hand of different fibers by comparing the stiffness parameter (Kf) of the fibers, where each fiber has a uniform cross-section and is composed of the same material throughout. This stiffness parameter is the product of the elastic modulus (E-p) of the fiber and the area moment of inertia (If) of the fiber: Kf = E£ x If 47 5*6 Historically, man-made fibers have been engineered so that the physical properties of such fibers are about the same as textile fibers found in nature, for example, cotton or wool. Natural textile fibers are generally thin, S having a diameter less than about 2 mils, and have a high elastic modulus (E£), for example, a modulus .greater than about 200,000 psi. Thus, synthetic fibers are thin and have a high-modulus. Such thin, high modulus fibers have a stiffness parameter generally ranging between lx 10*5 and 1 x 10'® Ibs-in^. In general, any fiber having a stiffness factor (Kf) within this range will feel soft and pliant. Note, because conventional fibers have a relatively high elastic modulus, usually well above 200,000 psi, they must have a relatively low moment of IS inertia, otherwise they would feel too stiff.

Under normal loading conditions, fibers bend about a neutral axis where the moment of inertia will be a minimum value. The moment of inertia (If) about this neutral axis is calculated using the following equation: where dA is any incremental area of the fiber's crosssection and y is the distance any such incremental area is from the, neutral axis. The above equation illustrates that the moment of inertia of the fiber is a function of the fiber's cross-sectional configuration. Thus, the hand of a fiber may be altered by changing the cross-sectional configuration of the fiber. Specific examples of fibers having different cross-sectionaL configurations and the specific equations for calculating the moments of inertia for such fibers are given in a.paper presented at the 47th annual meeting of the ASTM, Vol 44, (1944).

The Cross-sectional configuration of the fibers of the 5 invention is not critical so long as the moment of inertia falls within the range of from 400 x 10 to 7,000 x 10 in*. However,the fibers preferably have a generally circular crosssection. For fibers with a uniform circular cross-sectional configuration, the moment of inertia (1^) may be calculated by the following formula: ird^ where d is the fiber diameter. Consequently, to have the required moment of inertia (If), such a fiber would have a diameter in a range of from about 3 to about 6 mils, preferably from 4 to 5 mils. in terms of d.enier, the fibersusually have a denier of from 25 to 150 for fibers made of material having a specific gravity in the range of from 0.90 to 1.4.

Table I below compares the stiffness parameter (Kf) of conventional nylon and polypropylene fibers and the fibers of the invention, all having circular cross-sections. Note the (Kf) of all the fibers are within the range of from 1 χ lo to 1 x 10“ lb-ίη , but the diameter, and consequently the 1/, for the fiber of the invention (ImLD) is significantly larger than conventional fiber and the (E^) of the fiber of the invention is.substantially lower than conventional fiber. .4 473 6 TABLE I Comparative Values of for Conventional Fibers and the Fiber of the Present Invention Fiber Type d (in) Cin4)xl014 E, - (lb/in2) ,Kf (lb-inz)xl0 ' . Nylon 0.001 4.908 250,000 1.227 0.001 4.908 500,000 2.454 0.0015 24.850 250,000 6.212 0.0015 24.850 500,000 12.425 10 Polypropylene 0.002 78.539 2-50,000 19.635 0.002 78.539 300,000 23.562 0.003 397.607 250,000 99.402 lmLD 0.003 397.607 50,000 19.880 15 0.003 397.607 25,000 9,940 0.003 397.607 5,000 1.988 0.004 1256.637 50,000 62.831 0.004 1256.637 25,000 31.416 20 . 0.004 1256.637 5,000 6.283 0.005 3067.961 50,000 153.398 0.005 3067.961 25,000 76.699 0.005 3067.961 5,000 15.339 25 0.006 6361.725 50,000 318.086 0.006 6361.725 25,000 159.043 0.006 6361.725 5,000 31.8086 *47Se MATTING RESISTANCE Resistance to matting is a complex phenomenon due to a combination of several factors, including the ability of the fibers to recover on being deformed and their ability to avoid becoming entangled with each other. When a fiber is elongated beyond its yield point it will plastically deform until it breaks. During matting the fiber is bent, elongating or straining portions of the fiber. For good matting resistance, one consideration is that the fiber should not yield substantially when bent. In other words, when the force causing the fiber to bend' is released, the fiber should spring back to its original shape or very close to it. The manner in which the bending force is applied will affect the fiber's recovery. For example, a fiber will recover differently where a load is exerted only momentarily compared to a load maintained for a long duration.

The elastic properties and the large diameter impart matting resistance to the fibers of the invention. Because the fibers have a large diameter, they will be strained much more under normal matting conditions than conventional fibers.

Experiments indicate that the fiber will be elongated or strained up to about 25% cf its original length. However, the fiber can be fabricated so that it will not in tension permanently deform more than 10 percent, preferably no more than 5 percent, at elongations up to about 25% at strain rates in the range of from about 5 to about 50 min1. Conventional fibers will be elongated or strained up to about 10 percent in normal use. For the fiber of the invention to have a .-.-44756 matting resistance equivalent to conventional fiber its permanent deformation at 25 percent strain must be about equal to conventional fiber's permanent deformation at 10 percent strain. Table II sets forth data which indicates S this to be the case. Permanent deformation was determined by ASTM test method D1774-72 on monofilament fibers.

TABLE II ξ Permanent Deformation Sample @ 25¾ strain @ 10¾ strain lmLD (0% gel) 6.55 . - ltnLD (31¾ gel) 4.40 - lmLD (36¾ gel). 3.80 - lmLD (50¾ gel) 1.50 - Polypropylene - 2.95 Nylon - 1.95 The fibers of the invention resist matting because they tend to avoid becoming entangled with each other. This is due to their large diameters. The smaller the fiber diameter and the closer the fibers are packed together, the greater the frictional forces holding the fibers together or in a matted condition {Since the carpets using the fiber of the invention will generally have a fewer number of fibers per square inch of carpet backing than conventional carpets and these are larger diameter fibers, the frictional forces are substantially lower than conventional carpets, and therefore, they tend to resist matting. 447S6 Fiber of the invention was used in pile carpet that was subjected to a tetrapod walker test and compared with nylon carpet. Table III sets forth the test results which indicate that under such dynamic matting conditions» the fiber of the invention S is equivalent to nylon.

TETRAPOD WALKER TEST RESULTS TABLE III Total Pile Height (nils) Cycles/0 6,345 20,130 85,530 164,000 444,820 687,620 SAMPLE EVA(20Mrad) 466 468 460 440 431 396 406 Nylon 450 439 441 444 447 437 404 IS Carpets of fiber of the invention and carpets of nylon fiber were also subjected to static loads. Carpet using fiber of the invention did not perform as well as nylon fiber, but it was satisfactory.

Wear Resistance To attain good wear, i.e., avoid loss of fiber from the carpet, the fiber must be able to withstand pulling and repeated rubbing. The material of the fiber of the invention is inherently,weaker than the material used in conventional fibers. Consequently, one would suspect that the fibers of tne invention would not be able to withstand wear. However, because the fiber of the invention is substantially thicker than conventional fiber, there is more material present. Because of this additional material the fiber of the invention wears as well as conventional fiber. ...4 47 86 Specifically, carpets wear out mainly when fibers are lost because they are broken by being pulled or abraded.

Many different types of forces tend to pull fibers from the backing. Thus in use the fibers are subjected to stress.

Stress (σ) is the tensile force (F) acting on the fiber divided by the cross-sectional area (A) of the fiber: .

F . σ = A Since the forces acting on conventional nylon fibers and on fibers of the invention will under most circumstances be equal, if the cross-sectional area of the fiber of the invention was equal to that of conventional fiber it would break or not wear as well as nylon fiber. However, this is not the case. Fiber of the invention, since it has a substantially larger diameter than conventional fiber, has a much larger area. Thus, although the stress (σ) that the fiber of the invention can Withstand to yield or fracture is lower than that of nylon, the larger area (A) of the fiber, when multiplied by the stress (σ), yields an equivalent θ force (F) to deform or break the fiber.

In abrasive wear, rubbing action forces tiny dirt particles to cut through fibers. Nylon, being a hard material, is not readily cut by these particles. In contrast, the material we use in the fiber of the invention is substantially softer than nylon. Thus, in abrasive wear, dirt particles will cut through fiber of the invention with less difficulty. Because more material is present, however, the fiber will wear as well as nylon fiber which is relatively thin.

Tuftability For the fiber to be tufted or otherwise be handled during processing it must have a certain inelasticity and strength. If the fiber is too elastic it will act like a rubber band. Thus, instead of a tufting needle forcing fiber through the carpet backing, it will simply stretch the fiber. On release of the needle, the fiber will spring back into its original state and a tuft will not be formed. We have found that if the elastic modulus exceeds 5,000 psi 10 the fiber will be sufficiently inelastic for tufting. The fiber also should have enough strength so that it will not break during tufting or other carpet making processes. We have found that if the fiber has an ultimate tensile strength of at least 5,000 psi it will be suitable for most carpet making processes. Moreover, lubricant can be used to reduce frictional forces leading to breakage.

PILE FABRIC In accordance with cur invention, a pile fabric is 20 made using the above described monofilament fiber. The monofilament fiber is bulked by conventional textile processes, for example, knit-deknitting or stuffer box processes. Approximately 15 to 50 such fibers are twisted together and then bulked to form a carpet yarn. Also, the fiber may be blended with conventional fibers, such as continuous nylon fiber. Preferably, there are from 0.5 to 2.0 twists per linear inch of yarn. This yarn has a denier ranging between 1,500 and 4,000.

Although the yarn of fiber t>£ the invention is substantially different .from the type of yarn normally used in carpet making processes, it can be tufted throu;h conventional carpet backings to form a pile fabric. In accordance with this in5 vention, such a pile fabric will have for comparable carpet constructions substantially fewer fibers per square inch of backing than conventional pile carpets made of nylon yarn.

For good coverage, the minimum number of monofilament fibers will be 4,000 per square inch of backing and the minimum pile height will be one-eight of an inch. In contrast, the minimum number of monofilament fibers used in conventional nylon carpets is approximately 21,000 per square inch of backing.

Because there are a fewer number of fibers in a square inch of carpet backing for oar pi e fabric, this pile fabric 'will feel slightly cooler to the touch than nylon pile fabrics.

The reason for this is that there are less dead air spaces, and consequently, the fabric is a poorer insulator than conventional carpets. Thus, when the hand touches this carpet, more heat from the hand flows into, this carpet than conventional carpets: hence the cooler touch.

The? pile fabric of this invention also has a slightly smoother feel than conventional nylon pile fabrics. This is mainly due to the reduced number of fibers in a square inch of backing. Because fewer fibers are present, the coefficient of friction of the pile fabric of the invention is less than the coefficient of friction of conventional nylon pile fabrics.

The lower co-efficient of friction and poorer insulating properties of the fabric of the invention actually provide an advantage, namely reduction of carpet burns. Carpet burns are caused by rapidly rubbing one's skin qgainst the pile. Carpets having a high coefficient of friction and good insulating properties are mere likely to produce a carpet burn. The reason is that the higher coefficient of friction produces more heat which, due to the carpet's good insulating properties, is not conducted away from the skin.

The invention provides a method of making the fiber of the invention, which comprises the sequential steps of: (a) extruding the polymeric material through an orifice to form a molten monofilament, (b) drawing the molten monofilament while in the liquid state to reduce its diameter to the range of from 4 to 20 mils, (c) rapidly cooling the drawn, molten monofilament to form a solid monofilament, (d) drawing the solid monofilament to reduce its diameter to the range of from 3 to 5 mils, and (e) heating the drawn, solid monofilament to a temperature above 100°F but below its melting point while the monofilament is under tension to prevent the diameter of the monofilament from sinking substantially, the monofilament so produced having an elastic modulus of from 5,000 to 60,000 psi, an area moment of inerta -14 -14 4 of from 400 x 10 to 7,000 x 10 in , and a stiffness —5 —8 2 parameter of from 1 x 10 to 1 x 10 Ibs-in .

In making the fiber, the polymer material is extruded using conventional equipment such as described ift a paper presented by D. Poller and O.L. Riedy, Effect of Monofilament Die Characteristics on Processability and Extrudate Quality, 20th Annual SPE Conference, 1964, paper XXII-2. Specifically the polymeric material is drawn through an orifice preferably -5 -S having an area in the range Of from 8 x 10 to 70 x 10 2 in . Preferably the temperature of the molten polymer is below about 550°P. This extrusion step forms a molten monofilament which is drawn in the liquid state to reduce its diameter to the range of from 4 to 20 mils, preferably from 7 to 9 mils. This drawn monofilament is then rapidly cooled to form a solid monofilament. Cooling may be achieved by simply feeding the molten-monofilament into a water bath maintained at a temperature in the range of from about ambient to 150°F. The monofilament is then drawn in the solid state to reduce its diameter to the range of from 3 to 6 mils. This drawing step is conducted at a temperature below 100°F, The drawn solid monofilament is then subsequently heated to a temper5 ature above 100°F but below the melting point of the polymeric material to heat set the fiber. This heating step is conducted with the monofilament in tension to prevent the diameter of the monofilament from shrinking substantially. Heat setting is desirable in order to increase the shrink resistance of the fiber. Preferably, the fiber is twisted together prior to heat setting. Optionally, the fiber may be heat set during the bulking process. For example, in the knit-deknitting process the knitted sock would be held in tension and heated.

To improve the heat resistance of the fiber, it is preferable to partially cross-link the molecules of the polymeric material. Most preferably this is achieved by irradiating the fiber with an electron beam either as yarn or in carpet fomi, The dosage of radiation should be sufficient to cross-link to the molecules to the extent that they have a gel content greater than 30% but less than 90%. The preferred gel content is 45-55%. Gel content of the ethylenevinyl acetate fiber is determined according to the following procedure.

Fibers are wound around a metal wire screen and subjected to solvent elution in hot xylene near the boiling point for 24 hrs, Gel content is then calculated using the formula: Wf % gel = x 100 where W_ is the initial weight of the sample and Wf is tne final weight after elution.

In addition to irradiating the fiber, cross-linking may be achieved by the addition of, for example, peroxides to the polymeric material. For example, a vinyl silane grafted by a peroxide to the polyethylene chain serves as a cross-linkS ing mechanism.

In accordance with our invention, the polymeric material may be partially cross-linked prior to the drawn solid monofilament being heat set. This would permit the fiber to be heat set at higher temperatures, and therefore, increase its shrink resistance. Preferably, in the first crosslinking step the polymeric material is cross-linked to the extent that the gel content is no greater than 15¾, and in the second cross-linking step the polymeric material is partially cross-linked to the extent that the gel con15 tent is no greater than 90¾.

To enhance cross-linking there may be distributed throughout the polymeric material fine particles of silicon dioxide or titanium dioxide. The particle size of these oxides range between 100 angstroms and 1 micron and the amount used is below 1 volume percent. This small amount of oxide improves the efficiency of the irradiation step. For example, a polymeric material irradiated at a dosage of 10 megarads (MR) will have a gel content of 25-28¾. When this same polymer includes 0.2 volume £ silicon dioxide and is ir25 radiated at the same dosage, the gel content is 40-45¾.

This increase in gel content represents a substantial increase in the melting point of the polymeric material. Also the addition of poly-functional monomers improves cross- 18 linking. For example, triallyl cyanurate or allyl acylate, alone or in combination with the oxides, are additives which enhance the cross-linking yield for a given radiation dosage.

In general, due to the large fiber diameter, the fiber of the 5 invention can be l.oaded with fillers to higher levels than conventional carpet fibers. Specifically, pigments may be used to color the fiber. Such pigments may be dispersed throughout the molten polymeric material prior to extrusion. These pigments will normally have a particle size in the range of from 1 to 25 microns. The amount of pigment normally ranges between 1/2 and 20% of the total weight of the blend. According to the invention, initially pellets of color concentrate are preferably prepared. These color concentrate pellets are blended in the extruder with non-colored pellets. The colored and non-colored pellets are then melted and mixed together thoroughly. It is also possible to color the fiber with a dispersed dye, but under some conditions this type of dye tends to bleed out of the fiber. Cross-linking subsequent to dyeing tends to fix this dye.

In addition to coloring agents, it is possible to include in the fiber flame retardants, antistatic agents, or antisoiling agents. One flame retardant of particular interest is hydrated magnesia. Hydrated magnesia will re25 lease its water rapidly at a temperature above about SOO°F.

This permits the hydrated magnesia to be blended with the molten ethylene-vinyl acetate copolymer without release of its water, since this copolymer may be extruded at temper- 19 atures below 500°F. Generally, because we use lower melting point polymeric material in the fiber manufacture, additives which are sensitive to high temperatures, and therefore, cannot be used in conventional nylon fiber, might be used in our .5 fiber, which comprises a lower melting point polymer.

Because of the large diameter of the fiber, the extrusion and cooling equipment used in the manufacture of the fiber are inexpensive. This saving in equipment cost1 plus the use of low cost polymer result in a fiber which is inexpensive relative to nylon. This is a principal advantage of the fiber. Typical equipment for making the fiber is shown in the accompanying drawings, in which: DESCRIPTION OF THE DRAWINGS IS Figure 1 is a side elevational view of an extruder and draw-line used in spinning the fiber of the invention.

Figure la is a front elevational view of the spinneret plate.

Fibure lb is an enlarged fragmentary view of the orifices in the spinneret plate.

Figure 2 is a conventional draw-winding apparatus for drawing or stretching the fiber at temperatures below 100°F.

Figure' 3 is a side elevational view of the apparatus used to Keat the fiber under tension.

Figure, 4 is a graph showing the stress-strain curves for various conventional fibers as well as the fiber of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The fiber of the invention is made using a conventional extruder 10 which includes a hopper 12 into which pellets of polymeric material are deposited, an extruder barS rel 14 where the pellets are melted, a static mixer 15, and a spinneret plate 16 through which the molten polymeric material is forced.

In accordance with the invention, the molten polymer is drawn through orifices or holes having an area in range of from 8 x 10‘s to 70 x 10^ in2. Figure la shows the spinneret plate 16 which includes three rows 17a, 17b, and 17c of aligned holes. As shown in Figure lb, the holes making up the central row 17b are offset at an angle of about 60° with respect to the holes in top and bottom rows 17a and 17c. The spacings between the top row 17a and the center row 17b and the bottom row 17c and the center row 17b are each approximately 0.065 inch. The spacing .between adjacent holes in any one row is approximately 0.075 inch. The holes may be straight or tapered at an angle of approxi· mately 15 to 30°. Each hole has a diameter of 0.016 inch.

The melted polymeric material leaves the spinneret plate 16 as a plurality of molten streams 18 of polymer which continuously flows downwardly into a water bath 20. When the molten polymer strikes the water in the bath 20, it is chilled rapidly and becomes a continuous solid monofilament fiber 21. This fiber passes around a pair of guides 22 and 24 and through a guide plate 26 into the nip of a pair of rollers 28 and 30. These rollers 28 and 30 - 21 4 4756 pull on the fiber to draw the molten polymer streams 18 so that each stream lias a diameter of 6 to 15 mils. On leaving the rollers 28 and 30 the solid monofilaments pass through a fiber guide/breaking system 32 and are wrapped about spools 34 mounted on a winder 36.

When a spool 34a is loaded, it is removed from the winder 36 and placed on the draw winding apparatus 38 shown in Figure 2. The lead ends of the fibers 21 on the spool 34a are unwound, guided about two drawing godets 40 and 42, and wrapped around a second spool 44. These godets 40 and 42 turn at different angular velocities so the fiber 21 coming off the spool 34a is stretched. This drawing or stretching operation is conducted at temperatures below 100°F. The fiber 21 is drawn so that it has a diameter in the range of from 3 to 6 mils.

As shown in Figure 3, the fiber 21 from the second spool 44 is then pulled through a heater 46 and heated to a temperature above 100°F but below the melting point of the fiber 21. When copolymers of ethylene and vinyl acetate are employed to make the fiber 21, the preferred temperature Of the heater is in the range from 150 to 200°F.

The fiber 21 from the spool 44 first passes through a pair · of draw rolls 48 and 50 which pull the fiber over a preheater 52 and feed the fiber into the nip of an input feed roll assembly 54. The fiber passes through the heater 46 and over a feed roll 56 to the takeup spool 58. The tension on the fiber 21 as it passes through the heater 46 is sufficient to prevent the fiber from, shrinking. The fiber 21, however, is not stretched so its diameter remains in the range of from 3 to 6 mils.

STRESS-STRAIN CURVES Figure 4 contrasts the stress-strain curves of the fiber ofthe invention with that of conventional carpet fibers. Stress and strain or elongation were measured according to ASTM standard method No. D2256-69. The Curve A represents fiber of the invention. In contrast to this fiber, the conven10 tional fibers have higher ultimate tensile strengths and will elongate substantially less at higher stress levels.

The toughness or wearability of the fibers correlates to the area under the stress-strain curves. Note the area under Curve A is about the same as the area under the stress1S strain curves of the conventional fibers. The fiber of the stress-strain Curve A was made according to Example 1.

Examples of alternate fibers are also provided.

EXAMPLES OF FIBERS Example 1 Some ethylene-vinyl acetate fibers were produced in the form of bulked continuous filament yarn which contained 40 filaments. No coloring agent or additives were added during extrusion. The polymer pellets were commercially ob25 tained from U.S. Industries, Inc., under the designation NA294, a 5¾ vinyl acetate, ethylene-vinyl acetate copolymer, having a melt index of 2,0. The copolymer was extruded on a 3/4 inch single screw extruder through a 40 hole spinneret. 447 5 6 The spinneret had 0.013” diameter holes having a 30° taper.

The extruded fibers were drawn in the liquid phase to a diameter of 0.0073 inch and solidified in a parallel row on a chill roll. The temperature profile in the extruder increased from 340°F at the hopper zone to 48G°F at the exit zone. The extruder screw speed was 15 rpm and the screw was driven at 6.0'amps. The line speed on the take up was 28 feet per minute. The yarn was then draw''textured on a Pinion machine. (Pinion is a trade mark.) In jrder to do this, the yarn was treated, with a silicone finish and then drawn and textured.

The draw ratio was 3:1, with the final filament diameter being 0.0041 - 0.0043 inch (69-^6 denier). The yarn was then cross-linked, on a 3 MeV electron beam machine at a dosage of 10 Mrad.- (Gel content by elution in xylene ·> 28¾).

The mechanical properties of this fiber were as follows: diameter of 0.0041 in. (69 denier), 10¾ offset yield stress of 8780 psi (0.74 gpd), ultimate tensile strength of 13,200 psi (1.13 gpd), elastic modulus of 35,700 psi, and elongation to fracture of 85%.

‘ - Example 2 The ethylene vinyl acetate copolymer (5¾ vinyl acetate) described in Example 1 was spun into yarn composed of 20 continuous filaments. Twelve yarn ends were spun from a single spinneret. This trial was conducted on a commercial monofilament production line in which extrusion and drawing were done in-line. The yarn was spun on a 1.5 inch, single screw extruder. The hopper of the extruder was filled with NA294 ethylene vinyl acetate pellets (U.S.I. Chemicals) and . - 24 «α a prepared color concentrate. The pellet to concentrate weight ratio was 10:1. The color concentrate pellets contained 5 weight percent o£ light green pigment (Harwick). Fibers were spun through a commercial monofilament die at a throughput of 31 lb/hr and. quenched in a water bath which contained some surface finish agent in emulsion form. The extruder screw was operating at 100 rpm, and the.gear pump was operating at 30 rpm. A Fluid Dynamics filter (X13) was installed between the gear pump and the spinneret. A pressure transducer, mounted before the filter, recorded a pressure of 1600-1800 psi throughout the run. The temperature profile in the extruder was as follows: Zone 1 = 380°F, Zone 2 = 440°F, Exit = 440eF, Spinneret = 440°F. The yarns weredrawn in a parallel array in a single stage between IS godet rolls to a 3.3:1 ratio. The feed rolls rotated at 23.7 m/min, and the take up rolls rotated at 78.3 m/min.

The final yarn denier was 2650 (approximately 132 den/fil). The yarn (not individual fibers) was tested for mechanical properties. The yarn had a tensile strength of 0.87 g/den (10,200 psi), an elastic modulus of 3.4 g/den (27,200 psi), and an elongation to fracture of 113%. This yarn was bulked differently than that of Example 1. The yarn was twisted 0.75 turns per inch, then knit on a commercial machine into a long tube. This tube was subjected to electron beam ir25 radiation to a dosage of 10 Mrad and deknit. The deknit yarn had a substantial crimp and was subsequently tufted into carpet. The gel content measured on tlie yarn was 28%. 4 4?b 6 Example 5 Fiber was made from ethylene-vinyl acetate copolymer (USI designation NA294 - .5% vinyl acetate and 95% .low density polyethylene, MI=2) in identical fashion to that made in Example 1, except the additives listed in Table 4 were added during extrusion. This fiber was then exposed to electron beam irradiation. The following gel yields were obtained on drawn fiber (3:1 draw ratio) after 48 hours extraction in hot xylene: TABLE IV » Additive (wt. %) Electron Beam Dosage (Mr ad) Gel Content % . None 10 28 Si02(0.48) 10 44.1 Ti02(1.8) 10 48.7 TAC (1.0) 10 45.5 The higher gel levels improve certain carpet properties such as resilience and shrinkage resistance. At these gel concentrations, the mechanical properties are not substantially different than those presented in Example 1.

Example 4 An EVA copolymer, containing 9% vinyl acetate and having a'melt index of 3.0, was made into the new type of yarn. The fibers were colored by incorporating pigment at a level of 0.5% in the melt. Extrusion was done on a oneinch, single screw extruder, using a screen pack (mesh sizes of 40-60-60-40) and a 40 hole spinneret with a hole diameter of 0.015 inch. The temperature profile in the extruder inS creased from the hopper zone to the exit zone from 340° to 500°F at the die. The screw speed on the extruder was 20 rpm and the screw was driven at 7.0 amps. The line speed on the . take up was 38 fpm. Under these conditions, the fiber diameter was 0.009 inch. The yarn was then draw/textured on a Pinion machine. To do this the yarn was treated with a silicone finish and then drawn and textured. The draw ratio was set at 4:1, with the final filament diameter being 0.005 inch (100 denier). The yarn was cross-linked on a 3 MeV electron beam machine at a dosage of 10 Mrad. The mechanical properties of the new fibers are as follows: Diameter = 0.005 in. (100 denier), 10% offset yield stress = 7710 psi, ultimate tensile strength = 10,300 psi, elastic modulus = 39,300 psi, elongation to fracture = 79.4%.

Claims (52)

1. CLAIMS:

   A monofilament fiber comprising a polymeric material and having an elastic modulus of from 5,000 to 60,000 psi, —14 an area moment of inertia of from 400 x 10 to 7,000 x 10

   4 -5-8 in , and a stiffness parameter of from 1 x 10 to lx 10 lbs-m .
2. 2. A fiber according to claim 1, wherein the polymeric material is a thermoplastic material.
3. 3. A fiber according to claim 2, wherein the molecules

   10 of the thermoplastic material are partially cross-linked.
4. 4. A fiber according to claim 3, wherein the molecules are cross-linked to the extent that the gel content is greater than 30% but less than 90%.
5. 5. A fiber according to claim 4, wherein the thermoplastic

   15 material, after cross-linking, has a melting point of 200°F or greater.
6. 6. A fiber according to claim 2,3,4 Or 5, wherein the thermoplastic material is (a) plasticized polyvinyl chloride, (b) low density polyethylene, (c) thermoplastic rubber,

   20 (d) ethylene-ethyl acrylaie copolymer, (e) ethylene-butylene copolymer, (f) polybutyler-e and copolymers thereof, (g) ethylene-propylene copolymers, (h) chlorinated polypropylene, (i) chlorinated polybutylnne, or (j) a mixture of two or more of these thermoplast i c materials.

   25
7. 7. A fiber according t>. any preceding claim, wherein from 1/2 to 20 weight percent of additives are dispersed throughout the polymeric material.
8. 8. A fiber according to claim 7, wherein the additives have a particle size of from 100& to 25 microns.

   30
9. 9. A fiber according to any preceding claim, wherein

   - said fiber in the unbulked state has a generally circular cross-section.
10. 10. A fiber according to claim 9, having a diameter from

    3 to 6 mils.
11. 11. A fiber according to claim 9 or,10, which is in the bulked state.
12. 12. A fiber according to any preceding claim, which has a denier of from 25 to 150 and the material of which has a specific gravity in the range of from 0.90 to 1.4.
13. 13. A fiber according to claim 1, wherein the polymeric material is an ethylene-vinyl acetate copolymer having a vinyl acetate content of from 1 to 10 percent by weight and a melt index of from 0.5 to 9.
14. 14. A fiber according to claim 1, which includes hydrated magnesia.
15. 15. A fiber according to claim 1, which includes triallyl cyahurate or allyl acylate.
16. 16. A fiber according to claim 1, which includes oxides of silicon or titanium. ;
17. 17. A monofilament fiber of polymeric material having j the following physical properties: (a) an elastic modulus of from 5,000 to 60,000 psi. ' (b) an area moment of inertia of from 400 x 10 to 7,000 χ 10 -14 in 4 , —5 -,'8 (c) a stiffness parameter of from 1 x 10 to 1 x 10 · 2 lbs-ιη .

    (d) a diameter of from 3 to 6 mils, (e) does not in tension permanently deform more than 10 percent at elongations up to 25% at strain rates in the range of from 5 to 50 min and (f) has an ultimate tensile strength of at least 5,000 psi.
18. 18. A fiber according to claim 17, wherein the polymeric material is an ethylene-vinyl acetate copolymer having a vinyl acetate content of from 1 to 10 percent by weight and a melt index of from .05 to 9.

    4475
19. 19.· A fiber according to claim 17 to 18, wherein where the polymeric material is partially cross-linked to the extent that the gel content is greater than 30% but less than 90%
20. 20. A fiber according to claim 17, 18 or 19, wherein in the unbulked state, said fiber has a generally circular cross-section.
21. 21. A fiber according to claim 17, 18, 19 or 20, wherein said fiber has a denier of from 25 to 150.
22. 22. A method of making a monofilament as claimed in claim 1, comprising the sequential steps of:

    (a) extruding the polymeric material through an orifice to form a molten monofilament, (b) . drawing the molten monofilament while in the liquid state to reduce its diameter to the range of from 4 to 20 mils,

    I (c) rapidly cooling the drawn, molten monofilament to form a solid monofilament, (d) drawing the solid monofilament to reduce its diameter ‘ to the range of from 3 to 6 mils, and (e) heating the drawn, solid monofilament to a temperature above 1OO°F but below its melting point while the monofilament is under tension to prevent the diameter of the monofilament from shrinking substantially, the monofilament so produced being as defined in claim 1.
23. 23. A method according to claim 22, whrein the molten polymeric material includes oxides of silicon or titanium.
24. 24. A method according to claim 22 or 23, wherein the polymeric material is an ethylene-vinyl acetate copolymer

    - 30 having a vinyl acetate content of from 1 to 10 percent by weight and a melt index of from 0.5 to 9.
25. 25. A method according to claim 22, 23, or 24, xdierein the extruding step is conducted at a temperature below 55O°F.
26. 26. A method according to claim 22,23,24 or 25, wherein prior to extrusion the melted polymeric material is filtered.
27. 27. A method according to any of claims 22 to 26, wherein cooling is achieved by feeding the molten monofilament into a water bath maintained at a temperature in the range of from ambient to 150°F.
28. 28. A method according to claim 22, wherein subsequent to step (e) the molecules of the polymeric material are partially cross-linked.
29. 29. A method according to claim 28, wherein the molecules are cross-linked to the extent that the gel content is greater than 30% but less than 90%.
30. 30. A method according to claim 22, wherein between steps (d) and (e), the molecules of the polymeric material are partially cross-linked to the extent that the gel content is no greater than 15%, and subsequent to step (e) the molecules are additionally cross-linked to the extent that the gel content is no greater than 90%.
31. 31. A method according to claim 22, wherein pigments are dispersed throughout the molten polymeric material.
32. 32. A method according to claim 22, wherein subsequent to step (e) the monofilament is bulked.
33. 33. A method according to claim 32, wherein during bulking, the monofilament is heated to a temperature below its melting point.

    - 31 4 47 5 6
34. 34.' A method according to claim 32, wherein during bulking the molecules of the polymeric material are partially cross-linked.
35. 35. A method according tt claim 32, wherein during bulking the monofilament i;. heated to a temperature below its melting point, and the molecules of the polymeric material are partially cross-linked.
36. 36. A pile fabric comprising a backing and yarns secured to the backing and extending outwardly therefrom,

    10 said yarns including a plurality of bulked, continuous monofilaments, said monofilaments comprising a polymeric

    .. material and having an elastic modulus of from 5,000 to

    60,000 psi, an area moment of inertia of from 400 x 10 _14 4 ?

    to 7,000 x 10 .'in ., and a stiffness parameter of from

    15 1 x 10 -5 to 1 x 10 -8 lbs-in 2 .
37. 37. A fabric according to claim 36, wherein said yarn forms a pile which has a minumum height of 1/8 inch and a . minimum density of 4,000. monofilaments per square inch of backing.

    20
38. 38. A fabric according to claim 36, wherein the · monofilaments have an'ultimate tensile strength of 5,000 psi or greater.
39. 39. A fabric according to claim 36, wherein the .:

    . molecules of the polymeric material are partially cross- i

    25 linked. J '
40. 40. A fabric according to claim 36, wherein,the polymeric: material includes additives which enhance cross-linking.·/,
41. 41. A fabric according to claim 36, wherein the polymeric: material is an ethylene-vinyl acetate copolymer having a ·

    30 vinyl acetate content of from 1 to 10·percent by weight and a melt index of from 0.5 to 9.
42. 42. A fabric according to claim 36, wherein the polymeric material includes pigment dispersed throughout.
43. 43. A fabric according to claim 42, wherein the weight percentage of pigments or additives in the yarn, based on total yarn weight, ranges from 0.5 to 20 percent.
44. 44. A fabric according to claim 36, wherein the polymeric material includes hydrated magnesia.
45. 45. A fabric according to claim 36, wherein the fibers have a generally circular cross-section prior to bulking and a diameter of from 3 to 6 mils.
46. 46. A fabric according to claim 36, wherein the monofilaments are as defined in claim 17.
47. 47. A fabric according to claim 36, wherein the monofilaments are bulked by knitting the monofilaments, irradiating the monofilament in knitted form, and then de-knitting.
48. 48. A method of making polymeric monofilament according to claim 22, substantially as herein described.
49. 49. A method of making polymeric fiber, substantially as herein described with reference to the accompanying drawings.
50. 50. Polymeric monofilament or fiber, when made by the method of any of claims 22 to 35, 48 and 49.
51. 51. Fibers of polymeric material, substantially as herein described'with reference to the Examples.
52. 52. A pile fabric according to claim 36, substantially as herein described.