CA1109218A - Melt-drawing, cooling, attenuating, and heat treating under tension, of filament - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

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

M~LT-DR~ING, COOLING, ~TTE'N~i~rrIN~, AND FIEAT TREATING UN~ER TE~SIOM, OF FILAMENT

BACKGROUND

Nylon fiber is one of the most versatile and useful man-made fibers developed to date. In its monofilament form it is bulked by crimping and the crimped filament is twisted to~ether with other bul~ed monofilaments to form a nyloJl yarn which is particularly suited for carpets. These nylon yarns, when tufted through a suitable backing, form a pile fabric that has excellent wearability and a good hand, i.e., it is pleasant to the touch.
Since the cost of nylon has increased substantially over the past few years, lower cost substitutes having physical characteristics similar to that of nylon are being sought.
Polypropylene yarns recently have been introduced which for some applications serve as a substitute for nylon carpet yarns.
TG date carpets employing polypropylene face yarns have made modest penetration of the market, and polypropylene yarns now represent approximately 5 percent of the face yarns used in the manufacture of carpets.

THE INVENTION

I have invented a novel monofilament fiber made of low cost polymeric material. My fiber is characterized by having an elastic modulus of from abou~ 5,000 to about 60,000 psi, an area moment of inertia of from about 400 x 10 14 to about 7,000 x 10 1 in4, and a stiffness parameter (as d~fincd belo~) of from about 1 x 10 5 to about 1 x 10 8 lb - in . Elastic modulus is determined by measuring the initial slope of the stress-strain curve derived according to ASTM standard method 9~"
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No. D2256-69. Strain measurements are corrected for gauge length variations by the methocl described in an article en-titled "A ~lethod for Determining Tensile Strains and Elas~ic ~lodulus of ~letallic ~ilaments," AS~I Trans~ctions Quarterly, Vol. 60~ No. 4, December 1967J 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 about 1 to about 10 percent by weight and a melt index of from about 0 5 to about 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) plas~icized 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 thermoplastics.
Although the ethylene-vinyl acetate copolymer has the desired elastic modulus, one problem with this material is that it has a relatively low melting point. To ob-viate this problem and increase the heat resistance of the fiber, the molecules of the copolymer are cross-linked.
Cross-linking may be achieved either during the manufacture 3 I~ 3982-O-USA

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of the fiber or subsequently. Conventional irradiation tecl-niques 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 l~ill be discussed below in detail, it is desirable to use certain additives ~hich 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 tihe material so that it is 200F 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 other-wise formed into a pile fabric, forms 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 ~o serve as a carpet yarn.

PHYSICAI, PROPERTIES OF FIBER
My fiber has good hand, resists matting, wears well, and is tuftable or may otherwise be processed using con-ventional carpet making techniques. All these properties are necessary for the fiber to give satisfactory per-ormance in carpets. Moreover,it has good anti-static properties and is easy to clean because of its large diameter.

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Hand ~ land is simply how the fiber feels. I~hen considering the hand of any fiber, one must take into account the speciic textile construction in which the hand is being judged Since I believe my fiber will be used mainly in carpe~ yarn, I have built into it those physical properties which will impart good hand to the fiber in a pile construc-tion. 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 ~ith 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 diferent fibers by comparing the stiffness parameter (Kf) of the fibers, where each ~iber has a uniform cross-section and is composed of the same material throughout. This stiff-ness parameter is the product of the elastic modulus (Ef) of the fiber and the area moment of inertia (If) of the fiber:

Kf = Ef x If ID 39~2-O-US/\

i~ 218 Historically, man-made fibers have been engineered so that the physical properties of such fibers are about the same as textile fibers ound in nature, for example, cotton or wool. Natural textile -fibers are generally thin, having a diameter less than about 2 mils, and have a high elastic modulus (Ef), 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 (Kf) generally ranging between about 1 x 10 5 and about 1 x 10-8 lbs-in2. In general, any fiber having a stiffness factor (Kf) witllin 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 lol- moment of inertia, otherwise they would feel too stiff.
Under normal loading conditions, ibers 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:
20If = S y2dA
where dA is any incremental area of the fiber's cross-section 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 Z5 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 con~igurations and the 6 IU ~a~ A

specific equations for calculating the moments of inertia for such fibers are ~iven in a paper presented at the 47th annual meeting of the AST~I, Vol 44, (1944).
The cross-sectional configuration of my fiber is not critical so long as the moment of inertia falls within the range of from about 400 x 10 to about 7,000 x 10-14 in4.
However, my fiber preferably has a generally circular cross-section. For fibers with a uniform circular cross-sectional configuration, the moment of inertia (If) may be calculated by the following formula:
~d4 If = . __ 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, pre-ferably from about 4 to abou~ 5 mils. In terms of denier, my iber usually has a denier of from 25 to 150 for fibers made of material having a specific gravity in the range of rom about 0.90 to about 1;4.
Table I belol~ compares the stiffness parameter (Kf) of conventional nylon and polypropylene fibers and the fibers of my invention, all having circular cross-sections. Note the (Kf) of all the fibers are within the range of from about l x 10-5 to about 1 x 10-8 lb-in2, but the diameter, ., and consequently the If, for my fiber ~lmLD) is significant-ly larger than conventional fiber and the (Ef) of my fiber is substantially lower than conventional fiber.

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T AnLE I
Comparative Values of Kf for Conventional Fibers and the Fiber o~ thc Prescnt Inv~ntion Fib r (in)(in4)~10~l4(lb/in2)(lb-in2)xlO~8 Nylon 0.0014.908 250,000 1.227 0.0014.9n8 sn() ~ nnn ~ 4 0.001524.850 250,000 6.212 0.001524.850 500,000 12.425 Polypropylene 0.002 78.539 250,000 19.635 0.00278.539 300,000 23.562 0.003397.607 250,000 99.402 lmLD 0.003397.607 5Q,000 19.SS0 0.003397.607 25,000 9,9~10 0.003397.607 5,000 1.988 0.0041256.637 50,000 62.831 0.0041256.637 25,000 31.416 0.0041256.637 5,000 6.283 0.0053067.961 50,000 153.~98 0.0053067.961 25,000 76.6~99 0.0053067.961 5,000 15.339 0.0066361.725 50,000 31~ .086 0.0066361.725 25,000 159.043 0.0066361.725 5,000 31.8086 ',,"7q,, ~

w ~ -~IATTING RESISTANCE
_ Resistance to matting is a complex phenomenon due to a combination of several factors, including the ability of tlle fibers to recover on being deformed and their ability to avoid becoming entangled with each other. I~rhen 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 tlle fiber. For good matting resistance, one consideration is tilat the fiber should not yield substantially when bent. In other words, when the force causing the fiber to bcnd is released, the fiber should spring back to its origlnal 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 exer~ed only momentarily compared to a load maintained for a long duration.
The elastic properties o my fiber and its large di-ameter impart matting resistance to my fiber. Because my fiber has a large diameter it will be strained much more under normal matting conditions than conventional fibers.
~Iy experiments indicate that my fiber will be elongated or strained up to about 25% o, its original length. ~lowever, my 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 min 1 Conventional fibers will be elongated or strained up to about 10 percent in normal use. For my fiber to have a matting resist~nce equivalent to conventional fiber its permanent deformation at 25 pe~cent strain must be about equ:ll to con~el1tional ~lber's ~-crm;ll1cl1t de'~-o~lll;ltiCIl ;It 1(1 percent strain. 1able II sets fortl1 d..ta ~ icl1 in~icates this to be t]le case. Perrnanent deformatioll was determined by AST~1 test metl1ocl Dl774-72 on monofilament fibers.

TABLE II
% Permlnent Deformation Sample @ 25~ strain @ 10% strain lmLD (0% gel) 6 . 55 .
lmLD (31~o gel) 4.40 lm~D (36% gcl) 3.80 lmLD (50% gel) l.50 Polypropylelle 2.95 Nylon l.95 ~ Iy fibers also resist matting because tl1ey tend to avoid becoming cntaTIglecl with eacl1 othcr. Ihis is due to their large cliame~ers. The smaller the fiber cliameter an~1 the closer thc fibers are packed togctllcr tl1e greater the frictional forces holcling the ~ibers together or in a matted conclition. Since the carpets using my fibcr ~ill generally have fewer fib:~rs per square inch Of carpet backing th~ll conventional carpets anc1 tliesc arc lar~er diameter filoers the frictional forces are substantially -- lower than conventional carpets, al1cl tl1ereforc they tend to resist mattillg.

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,/ .. 1 0 My fiber was used in pile carpet that was subjected to a tetrapod walker test and comparecl Witll nylon carpet.
Table III sets forth the test results whicll indicate that under such dynamic matting conditions rny fiber is equiva-lent to nylon.

TET~APOD WALKER TEST RESULTS
TABLE_III
Total Pile l-leight (mils) Cycles/0 6,345 20,130 85/530 164,000 444,820 687,620 SAMPLE
EVA(20~1rad) 466 468 460 440 431 396 406 Nylon 450 439 441 444 447 437 404 , 1-5 Carpets of my fiber and nylon fiber ~ere also sub-jected to static loads. Carpet using my fiber did not perform as well as nylon fiber, but it was satisfactory.

l~lear 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 my fiber is in-herently weaker than the material used in conventional fibers. Consequently, one would susl)ect that my fiber would not be able to withstand wear. However, because my fiber is substantially ~hicker than conventional fiber, there is more material present. Because of this additional material my -fiber wears as well as conventional fiber.

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Specifically, carpets wear out mainly w]len fibers are lost because they are broken by l)eillg pullecl or abraded.
~lally cliffelellt types of fotccs tcll(l to ~ 11 Lil~els Llolll the backing. Thus in use the fibers are subjectecl to stress.
Stress (a) is the tensile force (F) acting on the fiber divided by the cross-sectional area (~) of the fi~er:

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a Since the forces actin~ on conve~tiolull nyloll Libels and my fibers will under most circumstances be equal, if the cross-sectional area of my fiber were equal to that of conventional fiber my fiber would break or not wear as well as nylon fiber. ~owever, this is not the case. ~Iy fiber, since it has a substantially larger diameter tllan conven-tional fiber, has a much larger area. Tllus, altl~ougll the stress (a) that my fiber can witlls~clllcl to yiel~ or fracture is lower than that of nylon, tlle larger area (A) of my fiber, when multiplied by the stress (a), yields an equivalent force (F) to deform or break the fiber.
In abrasive wear, rubbing action forces tiny clirt particles to cut through fibers. Nylon, being a harcl material, is not reaclily cut by tllese particles. In con-trast, the material I use in my fiber is substantially softer than nyloll. lhus, in abrasive wear, clirt particles will cut througll my fiber ~ith less clifficulty. Because more material is present, my fiber, however, will wear as well as nylon fiber which is relatively thin.

Tuftability For ~he fiber to be tufted or otherwise be llandled durin~ processill~ it m~lst ha~re a certaill inel~sticit~ and strength. If the fiber is too elastic it ~ill act li~e a rubber bancl. Thus, instead of a tufting needle forcing the fiber through the carpet backing~ the needle will simply stretch the fiber. ~n release of the needle, the fiber ~ill spring back into its original state and a tuft will not be formed.
I have found th~t if the elastic modulus exceeds 5,000 psi my fiber ~ill be sufficiently inelastic ror tuftin~. rl~e fiber also should have enough strength so that it .on't break during tufting or ot]ler carpet making processes. I
llave found that if my fiber has an ultimate tensile strength of at least 5,000 psi it will be suitable for most carpet making processes. ~loreover, lubricant can be use~ to re- -duce frictional forces leacling to bre.l~.lge.

PILE FABRIC
In accordance Wit]l my invention, a pile fabric is made using the above described monofilament fiber. The monofilament fiber is bulked by conventional textile pro-cesses, for example, knit-deknitting or stuffer box llro-cesses Approximately 15 to 50 such fibe-rs are t-isted together an~l thell ~ul~ed to form a carpet yarn. ~lso, my ~25 fiber may be blended with conventional flbers, such as con-tinuous nylon fiber. Preferably, there are from 0.5 to 2.0 t~ists per linear inch of yarn. Tl~is yarn has a cl~nier ranging bet-~een 1,500 an~ ~,000.

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Althou~ll tlle yarll of my fiber is sul~stallti.~
ferent from -thc type of yarn normally used in carpet maXing processes, it can be tufted througll conventional carpet backings to form a pile fabric. In accordance l~ith this in-S vention, such a pile fabric ~ill have for comparablc carpetconstructions substantially fe~er fibers per square inch of bacXing thall conventional pile carpets made of nylon yarn.
lor ~ood cove-ra~e, the milli~UIII numbel of mollo:ril;llllcllt fibcrs - l~ill be 4,000 per square inch of backing and the minimum pile height l~ill be one-eight of an inch~ In contrast, the min-irnu~n number of monofilament fibers used in con~elltional nylon carpets is api~ro~imately 20,000 per sqllare i.llCh of backlng.
Because there are fewer fibers in a square inch of carpet backing for my yi:le fabric, tllis pile fabric will feel sli~htly cooler to the touch than nylon pile fabrics.
The reasoll for tllis is that thcre are less dead air spaces, and consequelltly, the fabric is a poorer insulator than con-ventional carpets. Thus, wllen the hand touclles this carpet, more heat from t]le han~ flo~s into this carpet than conven-tional carpcts. Ilence thc cooler tOUC]I.
The pile fabric of my invention also has a slightly smoother feel than conventional nylon pile fabrics. This is maillly due to the reduced number of fibers in a square - - 25 ~--~inch of bac~ing. Because fewcr fibers arc present, tlle co-eficient of friction of the pi]e fabric of my inventioll is less than the coefficient o friction of convcntional nylon pilc fabrics.

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The lower coef~icient of friction and poorer insulating properties of my fabric actually provide an advantage, namely, reduction of carpet burns. Carpet burns are caused by rapidly rubbing one's skin against the pile. Carpets having a high coefficient of friction and good insulating properties are more likely to produce a carpet burn. The reason is that the higher coefficient of friction ~roduces more heat which, due to the carpet's good insulating pro-perties, is no-t conducted away from the skin.
METHOD OF MAKIN~ THE FIBER
In accordance with my meth.od of making the fiber, the polymer material is extruded using conventional e~uipment such as described in 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. Thus, this invention contemplates a method of making a fiber of polymeric material having an elastic modulus of from 5,000 to fi0,000 psi, an area moment of inertia of from 400 x 10 14 to 7,000 x 10 14 in4, and a stiffness parameter of from 1 x 10 5 to 1 x 10 8 lbs-in . The method comprises the sequential steps of extruding the polymeric material through an orifice to form a molten monofilament, drawing the molten monofilament while in the li~uid state to reduce its diameter to the range of fron~ ~ to 2U mils, rapidly cooling the drawn, molten monofilament to form a solid monofilament, and drawing the solid monofilament to reduce its diameter to the range of from 3 to 6 mils. Then, the drawn, solid monofilament is heated to a temperature above 100F but below its melting point while the monofilament is under tension to prevent the diameter of the monofilament from shrinking substantially.
The raE)id cooling can be achieved by feedincl the molten .

monofilament into a water bath maintained at a temperature in the range of from ambient to 150F.
Specifically, the polymeric material is drawn -through an orifice having an area in the range of from about 8 x 10 5 to 70 x 10 5 in2. Preferably the temperature of the molten polymer is below about 550F. This extrusion step forms a molten monofilament which is drawn in the liquid state to reduce its diameter to the range of from about 4 to about 20 mils, preferably from about 7 to about 9 mils. This drawn monofilament is than rapidly coolea 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 about 150~F., as set out above. The monofilament is - 15a -then drawn in the solid state to reduce its diameter to the range of from about 3 to about 6 mils. This drawing stcp is conducted at a temperature belbw about 100F, The drawn solid monofilament is then subsequently heated to a temper-ature above about 100F but below the melting point of thepolymeric 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-denitting process the knitted sock would be held in tension and heated.
To improve the heat resistance of the fiber, it is pre-ferable to partially cross-link the molecules of the poly-meric material. Most preferably this is achieved by irradi-ating the fiber with an electron beam either as yarn or in carpet form. 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 pre-ferred gel content is 45-55%. Gel content of the ethylene-vinyl 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 lYo is the initial weight of the sample and ~Yf is the final weight after elution.

16 ID 3~2-O-USA

, . , In addition to irradiating the fi~er, cross-linking may be achieved by t]ie a(ldition of peroxides to the poly-meric material. For e~ample, a vinyl silane graftcd by a pero~ide to the polyethylelle chain ser~es as a cross-link-ing mech.lllisnl.
In accordance ~it]l my invention, the polyllleric materialmay be partially cross-linked prior to the dra~n solid mono-filament being heat set. This ~ould permit the fiber to be heat set at higher temperatures, and therefore, increase its shrink resistance. Preferably, in the first cross-linking step the polymeric material is cross-link~cl to thc extent that the gel content is no greater than about 15%, and in the second cross-lin~ing step the polymeric material is partially cross-linked to the e~tent that the ~el con-tent is no greatcr tllan 90%.
To en}lance cross-linking there are distributed through-out the polymeric material fine particles of silicon dioxide or titanium ciioxi~le. The particle si~c of t]lcsc o~i~les ranges between lOO angstroms and 1 micron and tne amount used ZO IS belo1~ 1 volume percent. lhis small amount of o~ide im-proves the efficiency of the irradiation step. For e~ample, a polymeric material irradiated at a dosage of 10 megarads (MR) w~ill have a gel content of 25-2&%. lVhell tllis same pol~ner includes 0.2 volume % silicon dio~ide and is ir-- radiated at the sallie dosa~et the ~el contellt i.s 4~-45g.
This increase in gel content represents a substantial in-crease in the melting point of thc polylneric material. Also th~ a~ldition of poly-fllnctional monomels improves cross-~ 2~L~ ~ ~

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, my fiber can be loaded Wit}l fillers to higher levels than conventional carpet fibers. Specifically, pigments may be used to color my fiber. Such pigments may be dispersed throughout the molten polymeric material prior to e~trusion. These pigments will normally have a particle size in the range of from about 1 to about 25 microns. The amoun~ of pigment normally ranges between about 1/2 and about 20% of the tbtal weight of the blend.
According to my invention~ initially pellets of color concentrate are 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 my 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 in-clude in the fiber flame retardants, antistatic agents, or antisoiling agents. One flame retardant of particular interest is hydrated magnesia. Hydrated magnesia will re-lease its water rapidly at a temperature above about 500~.This permits the hydrated magnesia to be blended with the molten ethylene-vinyl acetate copolymer ~ithout release of its water, since this copolymer may be extruded at temper-atures below 500F. Generally, because I use lower melting point polymeric material in the fiber manufacture, additives W]liC]I are sensitive to high temperaturcs, and therefore, can-not be used in conventional nylon fiber, migllt be used in my fiber, which comprises a lo~er melting point polymer.
Because of the large diameter of the fiber, the ex-trusion and cooling equipment used in the manufacture of the fiber are inexpensive. This savings in equipment cost plus the use of low cost polymer result in a fiber which is inexpensive relative to nylon. Tllis is the principal ad-vantage of my fiber. Typical equipment for making my fiber is shown in the drawings and described in the accompanying description.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevational view of an extruder and draw-line used in spinning the fiber of my invention.
Figure la is a front elevational vlew of the spinneret plate.
Fibure lb is an enlarged fragmentary view of the ori-fice$ in the spinneret plate.
Figure 2 is a conventional draw-winding apparatus for drawing or stretching the fiber at temperatures below 100F.
Figure 3 is a side elevational vie~ of the apparatus used to heat the fiber under tension.
Figure 4 is a graph showing the stress-strain curves for various conventional fibers as well as the fiber of my nvent lon .

~ 2 DETAILED DESCRIPTION OF THE DRA~INGS
The fiber of my invention is made using a convention-al extruder 10 which includes a hopper 12 into which pel-lets of polymeric material are deposited, an extruder bar-rel 14 where the pellets are melted, a static mixer 15, and a spinneret pla~e 16 through which the molten polymeric material is forced.
In accordance with my invention, the molten polymer is drawn through orifices or holes having an area in range of from 8 x 10-5 to 70 x 10-5 in2. Figure la shows the spinneret plate 16 w]lich 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 lS 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 ma~erial 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 mono-~ilament fiber ~1. This fiber passes around a pair of guides 22 and 2~ and through a guide plate 26 into the nip oE a pair of rollers 28 and 30. These rollers 28 and 30 ID 3982-O-US~

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pull on the fiber to draw the molten polymer streams 18 so that each stream has a diameter of about 6 to about 15 mils. On leaving the rollers 28 and 30 the solid monofila-ments pass through a fiber guide/breaking system 32 and are ~rapped about spools 34 mounted on a winder 36.
When a spool 34a is loaded, lt 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 ~rapped 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 100F. 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 100F 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 about 150 to about 200F.
The fiber 21 from the spool 44 first passes through a pair of draw rolls 48 and 50 ~hich pull the fiber over a pre-- heater 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 suf-ficient to prevent the fiber from shrinking. The fiber 21,

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ho~ever, is not stretched so its diameter rcmains in the range of from 3 to 6 mils.

STRESS-STRAIN CURVES
Figure 4 contrasts the stress-strain curves of the fiber of my invention with that of conventional carpet fibers. Stress and strain or elongation were measured ac-cording to ASTM standard method ~lo. D2256-69. The Curve A
represents my fiber. In contrast to my fiber J the conven-tional fibers have higher ultimate tensile strengths ~nd 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 stress-strain curves of the conventional fibers. I`he fiber of the stress-strain Curve A was made according to Example 1.
Examples of alternate fibers are also provided.

EXA~IPLES 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. T}le polymer pellets were commercially ob-tained from U.S. Industries, Inc., under the designation NA294, a 5% vinyl acetate, ethylene-vinyl acetate copolymer, having a melt index of 2Ø The copolymer was extruded on a 3/4 inch single screw extruder through a 40 hole spinneret.

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The spinneret had 0.013" diameter holes having a 30 taper.
- The extruded fibers were drawn in the liquid phase to a diameter o 0.0073 inch and solidified in a parallel row on a chill roll. The temperature profile in the extrudeT
increased from 340F at the hopper zone to 480F 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 Pinlon machine. In order 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 ~69-76 denier). Tlie yarn was then cross-linked on a 3 MeV electron beam machine at a dosage of 10 Mrad. (Gel content by elution in xylene = 28%). -~15 The mechanical properties of this fiber were as follows:
diameter of 0.0041 in. ~69 denier), 10% offset yield stress of 8780 psi (0.74 gpd), ultimate tensile strength of 13,200 psi (1.13 gpd), elastic modulus of 35,70Q psi, and elongation to fracture of 85%.
20 ~ Example 2 The ethylene vinyl acetate copolymer (5% 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 ~rial was conducted on a commercial ~mono~ilament 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 _ _ , , . , _ . _ _ _ . _ . _ _ . ~ .. . . . . . .... . . . . . .

!~ ' ~, a prepared color concentrate. The pellet to concentrate weight ratio was lO:l. The color concentrate pellets con-tained 5 ~eight percent o~ light green pigment (Harwick).
Fibers were spun through a commercial monofilament die at 5 a ~hroughput of 31 lb/hr and guenched in a water bath which contained some surface finish agent in emulsion form. The extruder screw was operating at lO0 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
; 10 pressure transducer, mounted before the filter, recorded a pressure of 1600-1800 psi throughout the run. The tempera- -~
ture profile in the extruder was as follows: Zone 1 = 380F, Zone 2 = 440F, Exit = 440F, Spinneret = 440F. The yarns were drawn in a par~llel array in a single stage between 15 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 Z0 ~10,200 psi), an elastic modulus of 3.4 g/den ~27,200 psi), and an elongation to fracture of I13%-. 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 ir-25 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 the yarn was 28%.

r Example 3 Fiber was made from ethylene-vinyl acetate copolymer (USI designation NA294 - 5% vinyl acetate and 95% low density polyethylene, ~I=2) in identical fasllion to that made in Example 1, except the additives listed in Table 4 ~ere 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:
~ 10 -, TABLE IV

, ., , ,_ _ , Electron Additive Beam DosageGel Content (wt. %) (Mrad) %
,___ _ .. ,.~ . .,,., ,,,,.. ,_ None 10 28 SiO2(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 substan-- tially different than those presented in Example 1.
Example 4 An EVA copolymer, containing 9% vinyl acetate and having a melt index of 3.0, l~as made into the new type of yarn. The fibers were colored by incorporating pigment at ID 3~82-O-USA

a level of 0.5% in the melt. Extrusion ~as done on a one-inch, single screw e~trucler, 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 in-creased from the hopper zone to the exit zone from 340 to500F at the die. The screw speèd 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 dia-meter was 0.009 inch. Tlle yarn was then draw/textured on a Pinlon 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 machlne at a dosage of 10 Mrad. The mechanical properties of the ne~ fibers are as follows: Diameter = 0.005 in.
~100 denier), 10% offset yield stress = 7710 psi, ultimate ten-sile strength = 10,300 psi, elastic modulus = 39,300 psi, elon-gation to fracture = 79.4%.

.

.

Claims (79)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A monofilament fiber of polymeric material char-acterized by:
(a) an elastic modulus of from 5,000 to 60,000 psi, (b) an area moment of inertia of from 400 x 10-14 to 7,000 x 10-14in4, and (c) a stiffness parameter of from 1 x 10-5 to 1 x 10-8 lb-in2.

2. The fiber of Claim 1 where the polymeric material is a thermoplastic.

3. The fiber of Claim 2 where the thermoplastic is (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 thermoplastics.

4. The fiber of Claim 3 having dispersed therein one or more additives of the group consisting of colorants, fillers, flame retardants, antistatic agents and antisoiling agents.

5. The fiber of Claim 4 wherein said thermoplastic is partially cross-linked.

6. The fiber of Claim 5 wherein said fibers are partially cross-linked by irradiation and wherein at least one of said additives acts to enhance the radiation cross-linking thereof.

7. The fiber of Claim 6 wherein said cross-linking enhancing additive is selected from the group consisting of silicon oxide, titanium dioxide and triallyl cyanurate.

8. The fiber of Claim 4 wherein the weight percentage of additives in the fiber ranges from 0.5 to 20 percent.

9. The fiber of Claim 8 wherein said colorant additive is a pigment having a particle size ranging from about 1 to about 25 microns.

10. The fiber of Claim 8 wherein said flame retardant additive is hydrated magnesia.

11. The fiber of Claim 3 having a generally circular cross-section with a diameter ranging from 3 to 6 mils.

12. The fiber of Claim 3 further characterized in not permanently deforming in tension more than 10 percent at elon-gations up to 25 percent at strain rates in the range of 5 to 50 min-1, said fiber also having an ultimate tensile strength of greater than 5,000 psi.

13. The fiber of Claim 1 wherein said polymeric material comprises an ethylene-vinyl acetate copolymer having a vinyl acetate content of 1 to 10 percent and a melt index in the range of 0.5 to 9.

14. The fiber of Claim 13 wherein said ethylene-vinyl acetate copolymer is partially cross-linked.

15. The fiber of Claim 14 wherein cross-linking is accomplished by incorporating into the polymer a peroxy activator and a cross-linking agent.

16. The fiber of Claim 14 wherein cross-linking is accomplished by irradiation.

17. The fiber of Claim 16 wherein an additive selected from the group consisting of silicon dioxide, titanium dioxide, triallyl cyanurate and mixtures thereof is dispersed therein, said additive acting to enhance the radiation cross-linking of said copolymer.

18. The fiber of Claim 17 cross-linked to the extent of having a gel content greater than 30% but less than 90%.

19. The fiber of Claim 14 having dispersed therein one or more additives of the group consisting of colorants, fillers, flame retardants, antistatic agents and antisoiling agents.

20. The fiber of Claim 19 wherein the weight percentage of additives in the fiber ranges from 0.5 to 20 percent.

21. The fiber of Claim 20 including a flame retardant additive comprising hydrated magnesia.

22. The fiber of Claim 20 including a colorant additive comprising a pigment having a particle size ranging from about 1 to about 25 microns.

23. The fiber of Claim 20 having a generally circular cross-section with a diameter ranging from 3 to 6 mils.

24. The fiber of Claim 20 further characterized in not permanently deforming in tension more than 10 percent at eon-gallons up to 25 percent at strain rates in the range of 5 to 50 min-1, said fiber also having an ultimate tensile strength in excess of 5,000 psi.

25. A method of making a monofilament of polymeric material having 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 of from 1 x 10-5 to 1 x 10-8 lbs-in2 which comprises the sequential steps of:
(a) extruding the polymeric material through an orifice of a diameter greater than about 20 mils 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 6 mils, (e) heating the drawn, solid monofilament to a temper-ature above 100°F but below its melting point while the monofilament is under tension to prevent the diameter of the monofilament from shrinking sub-stantially.

26. The method of Claim 25 wherein the rapid 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.

27. The method of Claim 25 or Claim 26 where the molten polymeric material includes oxides of silicon or titanium.

28. The method of Claim 25 or Claim 26 where 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.

29. The method of Claim 25 or Claim 26 where the extruding step is conducted at a temperature below 550°F.

30. The method of Claim 25 or Claim 26 where prior to extrusion the melted polymeric material is filtered.

31. The method of Claim 25 where subsequent to step (e) the molecules of the polymeric material are partially cross-linked.

32. The method of Claim 26 where subsequent to step (e) the molecules of the polymeric material are partially cross-linked.

33. The method of Claim 31 or Claim 32 where the molecules are cross-linked to the extent that the gel content is greater than 30% but less than 90%.

34. The method of Claim 25 or Claim 26 where 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%.

35. The method of Claim 25 or Claim 26 where pigments are dispersed throughout the molten polymeric material.

36. The method of Claim 25 where subsequent to step (e) the monofilament is bulked.

37. The method of Claim 26 where subsequent to step (e) the monofilament is bulked.

38. The method of Claim 36 or Claim 37 where during bulking the monofilament is heated to a temperature below its melting point.

39. The method of Claim 36 or Claim 37 where during bulking the molecules of the polymeric material are partially cross-linked.

40. The method of Claim 36 or Claim 37 when during bulking the monofilament is heated to a temperature below its melting point and the molecules of the polymeric material are partially cross-linked.

41. A pile fabric comprising a backing and yarns secured to the backing and extending outwardly therefrom, said yarns comprising 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 to 7,000 x 10-14in4, and a stiffness parameter of from 1 x 10-5 to 1 x 10-8lbs-in2.

42. The fabric of Claim 41 when said yarns forms a pile which has a minimum height of 1/8 inch and a minimum density of 4,000 monofilaments per square inch of backing.

43. The pile fabric of Claim 41 where the monofilaments have an ultimate tensile strength of 5,000 psi or greater.

44. The pile fabric of Claim 41 where the molecules of the polymeric material are partially cross-linked.

45. The fabric of Claim 41 where the polymeric material includes additives which enhance cross-linked.

46. The fabric of Claim 41 where the polymeric material has dispersed therein one or more additives of the group con-sisting of colorants, fillers, flame retardants, antistatic agents and antisoiling agents.

47. The fabric of Claim 46 where the weight percentage of additives in the yarn based on total yarn weight ranges from 0.5 to 20 percent.

48. The fabric of Claim 46 where the polymeric material contains hydrated magnesia therein.

49. The fabric of Claim 41 where each filament has a generally circular cross-section whose diameter is from 3 to 6 mils and does not permanently deform in tension more than 10 percent at elongations up to 25 percent at strain rates in the range of from 5 to 50 min-1, and has an ultimate tensile strength of from about 5,000 to about 50,000 psi.

50. The fabric of Claim 41 where the monofilaments are irradiated.

51. The fabric of Claim 41 where said polymeric material comprises 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.

52. The fabric of Claim 51 where the monofilaments have an ultimate tensile strength of from about 5,000 to about 50,000 psi.

53. The fabric of Claim 51 where the copolymer has dispersed therein one or more additives of the group consisting of colorants, fillers, flame retardants, antistatic agents and antisoiling agents.

54. The fabric of Claim 51 where the molecules of the ethylene-vinyl acetate polymer are partially cross-linked.

55. The fabric of Claim 51 where said ethylene-vinyl acetate copolymer contains an additive which enhances radiation cross-linking.

56. The fabric of Claim 55 wherein the additive con-sists of less than 1% by volume of fine particles of silicon dioxide ranging in size from about 100 angstroms to about 1 micron.

57. The fabric of Claim 55 wherein the additive con-sists of fine particles of titanium dioxide ranging in size from about 100 angstroms to about 1 micron.

58. The fabric of Claim 51 where the monofilaments are colored by pigments having a particle size of from about 1 to about 26 microns dispersed throughout the copolymer material.

59. The fabric of Claim 58 where the weight percentage of pigments based on total yarn weight ranges from about 0.5 to about 20 percent.

60. The fabric of Claim 51 where the copolymer material contains hydrated magnesia.

61. The fabric of Claim 51 where each filament has a generally circular cross-section whose diameter is from 3 to 6 mils.

62. The fabric of Claim 61 where each filament does not permanently deform in tension more than 10 percent at elongations up to 25 percent at strain rates in the range of from 5 to 50 min-1 and has an ultimate tensile strength of from about 5,000 to about 50,000 psi.

63. The pile fabric of Claim 41 wherein said backing comprises a scrim having needled thereto a web of staple fibers.

64. The fabric of Claim 63 wherein said staple fibers comprise the fiber of Claim 1.

65. The fabric of Claim 41 wherein said pile is formed by yarn tufts extending at least 1/8 inch from the backing and forming a fabric face.

66. The fabric of Claim 65 wherein said tufts are yarn loops.

67. The fabric of Claim 66 wherein the spacing of the yarn loops on the backing is uniform.

68. The fabric of Claim 41 including a secondary backing layer secured to said fabric.

69. The fabric of Claim 65 including a backsizing coating, said coating serving to lock each yarn tuft into the fabric backing.

70. The fabric of Claim 69 wherein said backsizing coating comprises a latex adhesive.

71. Yarn comprising a continuous strand of multiple monofilament fibers of polymeric material, said polymeric mater-ial characterized by:
(a) an elastic modulus of from 5,000 to 60,000 psi, (b) an area moment of inertia of from 400 x 10-14 to 7,000 x 10-14in4, and (c) a stiffness parameter of from 1 x 10-5 to 1 x 10-8 lb-in2.

72. The yarn of Claim 71 containing 15 to 50 fibers, said fibers twisted together and bulked to form a carpet yarn.

73. The yarn of Claim 72 having from 0.5 to 2.0 twists per linear inch.

74. The yarn of Claim 72 having a denier ranging from 1,500 to 4,000.

75. The yarn of Claim 72 wherein each fiber has a generally circular cross-section with a diameter ranging from 3 to 6 mils.

76. The yarn of Claim 72 wherein said fibers are pig-mented.

77. The yarn of Claim 72 wherein said fibers have a melting point above 200° F.

78. The yarn of Claim 72 wherein said fibers comprise a partially cross-linked, ethylene-vinyl acetate copolymer having a vinyl acetate content of 1 to 10 percent and a melt index in the range of 0.5 to 9Ø

79. The yarn of Claim 72 wherein said yarn is bulked by knitting and thereafter deknitting.