US3264705A - Process for improving the pill resistance of two-component acrylonitrile polymers - Google Patents

Description

Aug. 9, 1966 F. J. KO RIK fi fifi PROCESS FOR IMPROVING T PILL RESISTANCE OF TWO-COMPONENT ACRYLONITRILE POLYMERS Filed Sept. 8. 1960 2 Sheets-Sheet L F I G" 1 '2 \2 8 g X I IO M '2 T s 4 7 l4 5 3 3 INVENTOR FRANK JOSEPH KOVARIK ATTORNEY MERS 2 Sheets-Sheet 2 Aug. 9, 1966 F. J. KOVARIK PROCESS IMPROVING THE PILL RESISTANCE TWO- NT ACRYLONITRILE POLY PONE Filed Sept. 8, 1960 FIG-1A INVENTOR FRANK JOSEPH KOVARIK ATTORNEY United States Patent 3 264 705 PROCESS FOR IMPRovrN THE PILL RESISTANCE 0F TWO-CONWONENT ACRYLONITRILE PQLY- MERS FrankJoseph Kovarik, Waynesboro, Va., assignor to E. I. du Pont de Nernours and Company, Wilmington, Dei.,

a corporation of Delaware Filed Sept. 8, 1960, Ser. No. 54,697 5 Claims. (Cl. 28-76) This invent-ion relates to improved crimped composite filaments and a process of making them.

It has been proposed to produce helically crimped composite synthetic polymeric filaments having the capacity of changing the amount of crimp upon being exposed to the effect of a swelling agent and upon reverting to the original crimp upon removal of the swelling agent. This characteristic is, for convenience, referred to as reversible crimp and is observed by the squirming of the filaments upon both application and removing of the swelling agent. The value of this crimp reversibility is evidenced by the ability of the filaments in yarns, when embodied in a fabric, to squirm or twist around in the fabric under the influence of a swelling agent such as water (and also on removal of the swelling agent), but, nevertheless, to regain the original crimp in the fabric with removal of the swelling agent, as by drying. 'Fabrics containing these filaments acquire a high degree of fullness or covering power as a result of the swelling treatment and retain or even increase this fullness after being subjected to such treatments repeatedly.

It has been found that the high degree of crimp reversibility in the fibers necessary to produce yarns and fabrics with good bulk, compressional resilience, response to finishing treatments, and recovery from glazing is generally accompanied by a high level of crimp frequency. This high level of crimp frequency leads to a rough wool-like handle in knitawear and woven-wear fabrics and does not afford soft fabrics similar to those made from cashmere, for example.

For some applications, especially in fabrics from woolen-spun yarns, the use of these recent fibers is restricted by a phenomenon known as pilling.

One object of this invention is to produce a crimped composite filaments that aifords fabrics that are density stable to washing and ironing and are pill resistant.

Another object is to produce composite filaments having a reversible crimp and a low level of crimp that affords soft, cashmere-like fabrics.

These and other subjects are accomplished as described more fully below.

Filaments of the invention consist of at least two fiberforming compositions of polymers of acrylonitrile in eccentric relationship at least one of which contains 50 or more milliequivalents per kilogram of polymer of ionizable groups in excess of the ionizable groups contained in the other components. After the filaments are extruded and the fiber structure established, the solidified fibers are drawn from 1.1 to X and relaxed in the presence of a plasticizing medium such as steam under a tension of at least 0.01 gram per denier. The extent of relaxation should be at least 50% of the boil-off shrinkage of the as-drawn yarn prior to drying the filaments. After relaxation, the fibers are mechanically crimped if desired, then dried and given a hot relaxation treatment to permit the development of a helical crimp.

More specifically, the composite filament comprises at least 2 polymers of acrylonitrile eccentnically disposed toward each other and has 5 to 10 helical crimps per inch of extended length, a crimp product of less than 100, a crimp reversibility (ECR) of -50%, a tenacity of at least 2 grams per denier and is characterized by a high ice resistance to pilling when spun into yarn and knitted or woven into a fabric.

The amount of relaxation may vary from 50 to 99-]-% of the boil-oif shrinkage of the as-drawn yarn. Preferably a relaxation of at least of the boil-off shrinkage of the as-drawn yarn is used. Boil-off shrinkage is that fiber shrinkage which takes place upon exposure to boiling water for a period of at least about 5 minutes.

The length of time of the relaxation treatment is not critical and may be from 0.5 second to 10 minutes. Preferably, this is from 0.5 to 2 seconds when it is used as part of a continuous process.

The relaxation can take place in any type of heating medium having a temperature of about 100 C. which has a plastioizing action on the yarn such as organic vapors, or steam. Steam at pressures of from 0 to 5 p.s.i. gage is preferably used. Temperatures as high as 120 C. may be used.

The process can be continuous or batch. Preferably the relaxation is done continuously in conjunction with a wash-drawing process as this affords lower crimp levels. The beneficial results of pill reduction of fabrics containing the fibers may also be obtained by a batch process wherein the drawn and wet filaments are lagged in some manner as in cans before the relaxation step.

The process is most advantageously used on tows of 5,000 to 450,000 denier.

By the expression polymer of acrylonitrile is meant the homopolymer of acrylonitrile or copolymers of acrylonitrile and monoethylenically unsaturated addition type monomers containing at least acrylonitrile. Suitable comonomers include the ethylenically unsaturated sulfonic acids as methallyl sulfonic acids and others as disclosed in US. Patents 2,527,300 and 2,601,256 and other monomers as disclosed in Jacobson US. 2,436,- 926 and in Arnold US. 2,456,360.

The two polymers selected as components must have the required difference in shrinkage and in swellability so that the composite filament crimps and a reversible crimp results. To develop crimp in the composite filaments, the shrinkability of one component should be at least 0.2% greater than the shrinkability of the other component, that is, said component has at least 0.2% greater loss of the original length upon shrinkage than the other component. The shrinkability of a component is determined by measuring the shrinkage, upon immersion in boiling water under no tension, of a monocomponent filament made from the component polymer (spun and otherwise processed under substantially the same conditions as the composite filament). One component of the crimped filament should have a reversible length change after shrinkage of at least 0.05% and preferably at least 0.10% more than that of the other component, that is, said component has at least 0.05 greater change in length of the original length upon swelling than the other component. The reversible length change of a component is determined by measuring the increase in length of a monocomponent filament of the component polymer (spun and subjected to after-treatments under the same conditions as the composite filament) upon being immersed in the aqueous medium used for the testing of the crimp reversibility of the composite filament. Measurements are obtained with strands of approximately denier and approximately 15 inches long as follows: The samples (previously relaxed by a boil-off) are clamped in a tensile tester with a small amount of slack and held in the proper medium (air, cold water, or hot water) for about 2 minutes. The mechanically driven clamp is then started at a low rate of elongation (0.3 inch per minute); it is stopped and reversed immediately when the stressstrain curve starts to depart from the zero line. The true length of the sample is then calculated from the clamp distance in the starting position and the chart distance be tween the start of the test and the point where the stressstrain'curve began.

After wet tests the samples are dried (while clamped) by means of a hair dryer, and the length of dry strand at room temperature determined as above. Wet to dry cycles are repeated until the length change becomes constant. As a rule some shrinkage occurs during the first cycle. For most samples, satisfactory results are obtained with three cycles.

The reversible length change is calculated in percent, based on the final dry length of the sample.

length wet-length dry 100 Reversible length change: final length y Results from at least four different strands are averaged.

to obtain a representative value. Suitable polymers, methods for selecting them, and crimping methods such as by heat, :boil-oif or steam'are described in coassignedand copending Taylor application, Serial No. 771,677, filed November- 3, 1958, now US. Patent 3,038,237.

The crimp reversibility of the composite filaments of' this invention is determined by the following test.

A single filament is separated from. the single end or tow of drawn, unrelaxed fibers. A three-inch length of the filament is attached to-opposite sides of a rectangular copper Wire frame with 30% slack. between the ends. .The

rack and filament is then boiled off for minutes to develop the crimp. The 'crimped filament is then transferred to a special viewing holderby tapingor gluingthe ends so that about 10% slack is present and the filament length between the clamped ends is approximately 2.5 inches. The filament and viewing holder are then mountedvertically in a stoppered test tube containing desiccant. The tube is stored vertically overnight: (1824 hours) at 70 C. Following this conditioning period to dry the filament the tube is then brought to room temperature (approximately 25 C.). After allowing 30 minutes for cooling, the total number of crimps in thefilament between the fixed ends is counted. In counting, any crimp reversal points present are ignored. The desiccant is then removed from the glass tube, the tube filled with water and stored vertically at 70 C. for 6 hours. The number of crimps in the. wet fiber is counted as above.

The cycles are repeated as required to obtain reproducible results. The equilibrium crimp reversibility (ECR) or relative change in crimps/inch of extended length from 25 C. dry to 70 C. wet is obtained by the following yarn as measured under suflicient tension topull out the crimp and give an essentially straight filament or yarn. All crimp counts are stated in terms of extended length.

The crimpindex of a fiber is determined on a sample that has been boiled in water and then dried in room temperature air. 150 milligrams is determined (L This force is suificient to straighten the fiber from crimps. The load on the fiber. is then reduced to 5 milligrams and the crimped length (L determined. Crimp Index (C.I.) is calculated as follows:

Crimplndex X 100 The length of the fiber under a load of The crimp frequency is similarly determined on fibers that have been boiledin water and dried in room temperature air. The product of crimpindex andcrimp frequency is known as crimp product.

The necessary differential reversible length change. be-.

tween the components is readily obtainedby altering the content of ionizable groups in the two polymers.

Such ionizable. groups are readily obtained by-co polymerizing acrylonitrile, for! example, 'With monomers containing acid .groupssuch'as carboxylic, sulfonic or phosphonic in either the salt crime-acid form.

The following sulfonated polymerizable monomers and 1 their salts are eminently suited for use in thisinvention: p-styrenesulfonic acid, methallylsulfonic acid, allylsulfonic acid and ethylenesulfonic acid.

It will be obvious to those skilled in theart that the re,- quired ionizable groupscanbeincorporated into a polymeric component :by the blending of 2 or more poly-.

mers. The polymers should preferably be compatible.

The inclusion of from /2-15.% of certain non-ionic modifiers in copolymers of acrylonitrile'; enhancesthe ef-' fect of any ionizable groups present in the final polymer.

In general, it has been found that'the monomers that are effective in :this connection are also the sameamonomers which, when incorporated intoan acrylonitrile polymer increases the ;dyeability of'fibersmade'the'refrorn with a disperse dye, such as the blue-disperse dye'Prototype 62.]

Among the more desirable-monomers from the point ofview of enhancing the effect of ionizable group content are methyl jacryla'te,-methyl methacrylate, .methyl vinyl ketone,.- acrylarnide, N-tertiarybutylacrylamide, vi-

nyl methoxyethylether, methoxyethylacrylate' and vinyl 1 acetate;

Pilling is a well-known:phenomenon of :fabrics madel 7 from staple fiber yarns, and can be described as the tendency to form smallfclusters, clumps, .or balls or inter-.

entangled fiber endson the surface of a fabric; Pilling propensity can be measuredby actualwear tests or by laboratory tests. The test described inthe article, Random Tumble Filling Tester, by M. Baird et al. in Textile Research Journa1'26, 731-735 (1956) isused herein.-

The pilling ratings are expressed as numbers from,3

(verysevere pilling'), to +5 .(110 pilling All times, are

for 20 minutes, exposure unless otherwise stated. 7

Loop work-to-break. This is the areaunder the stressstrain curve of a loop of filament as-determined on an 1 The units are in gram-cm./denier-cm. This property and theelongation of a loop at break (loop Instron tester.

elongation) are considered to be indicative of the toughness of the fiber.

The expression intrinsic viscosity With',the symbol i (n) as used herein signifies the value of ln(n) at the ordinate axis intercept (i.e., when 0 equals 0) in agraph of' as ordinate with 0 values (grams per ml. of solution) asabscissas. (n) is a symbol for relative viscosity, which is the ratio of the flow times in a viscosimeter of a poly-.

ln is the logarithm to the mer solution andthe solvent.

base. 2. All:measurements onpolymers containing acrylonitrile combined in the, polymer .moleculef. were made with DMF solutions at 25 5 Ca Referring to the. drawings:

FIGURE 1 is a central cross-sectional elevation of a spinneret assembly. which can. be, used to make .the composite filamentspof this invention;

FIGURE 1A is an enlarged portion taken from FIG URE. l to show details ofthe spinneret. at the spinning orifice;

FIGURE 2 is a transverse. crossesectional plan view of the apparatus of FIGURE '1 taken at 2+2 thereof and showingdetails of the top ofthe back plate;

FIGURE 3 is a transverse cross-sectional plan view" taken at 3-3 of FIGURE 1 showing details of the bottom of the back plate;

FIGURES 4, 5, and 6 show greatly magnified cross sections, i.e., sections perpendicular to the filament axis, of typical filaments of this invention produced by dry spinning. In these drawings one component is shaded to show the separation between components; and

FIGURE 7 is a schematic representation of apparatus that can be used in practicing the present process.

With reference to FIGURE 1, the bottom spinneret plate 2 which contains a circle of orifices 3 is held in place against back plate 1 by retaining rings 12 and 14 and by bolt 13. A fine-mesh screen 4 e.g., 200 mesh per inch, is pressed into position between, and serves as a spacer between, spinneret plate 2 and back plate 1. Back plate 1 contains two annular chambers 8 and 9 which are connected to suitable piping and filtration apparatus (not shown) to receive different spinning compositions. Lead holes 11 go from annular chamber 9 to annular space '7. Lead holes lead from annular chamber 8 to annular space 6. Annular spaces 6 and 7 are separated by wall 5 which is disposed above orifices 3 and spaced from spinneret plate 2 by screen 4 to permit free and contiguous passage of the spinning fluids from annular spaces 6 and 7 through orifices 3, the mesh of screen 4 being fine enough to permit spinning fluid passage through orifices 3, as shown in detail in FIGURE 1A.

In FIGURE 2 are shown four lead holes 10 and four lead holes 11 equally spaced within the concentric chambers 8 and 9, respectively.

In FIGURE 3 are shown the concentric inner and outer annular spaces 6 and 7, sections of bottom spinneret plate 2 and the fine-mesh screen 4 partially in section.

Operation of the described apparatus in the practice of this invention is readily understood. Separate spinning materials are supplied to the inner annular chamber 9 and outer annular chamber 8, respectively, of the back plate; the former flows from chamber 9 through the lead holes 11 into the inner annular space 7 and thence through screen 4 and orifice 3 to form a part of a composite filament, while the latter passes through the lead holes 10 to the outer annular space 6 and thence through screen 4 and the outer side of the orifice 3 to form the other part of the composite filament.

FIGURE 7 is a schematic view of a wash-draw machine followed by a diagrammatic representation of a fluid relaxation chamber and a crimper. Tow is drawn over rollers 25, 26 and through a series of water baths, 21, 22, 23, 24 while maintained under tension. This wash-draw treatment serves to extract solvent while the yarn is being drawn. The drawn yarn is then forwarded to a steam chest 28 for controlled relaxation and may then be passed directly to a crimper 30.

Example 1 A 20% solution in dimethylformamide (DMF) of polyacrylonitrile of (n) 2.0 and containing 27 milliequivalents of acid groups per kilogram of polymer (as determined by titration in a DMF solution) is extruded into a spinning cell as one component (which faces the center of the spinning cell) of a composite filament using a spinneret as shown in FIGURE 1. Simultaneously, a 27% solution in DMF of a copolymer of acrylonitrile/ styrenesulfonic acid, 96/4% by weight composition, of (n) 1.5 and analyzing 240 milliequiva-lents of acid per kilogram of polymer is extruded as the other component (which faces the Wall of the cell) of composite filaments. The spinneret contains 140 orifices 0.007 inch in diameter located on a 5.27 inch diameter circle. A mixture of carbon dioxide and nitrogen gases at 320 C. is circulated through the spinning cell, the wall of which is maintained at 180 C. The solutions are extruded at 105 C. The threadline (1090 total denier) consisting of 140 composite filaments is Wound up at 200 yards per minute (y.p.m.).

Three-hundred-thirty ends of yarn produced as above with a combined denier of 360,000 are combined into a tow and drawn to 4 times its original length (i.e., 4 X draw ratio) through a series of water baths at 98 C. which extract the residual DMF. Th'e drawn and extracted tow is led directly from the wash-draw process to a stufier box crimper similar to that shown in Hitt U.S. 2,747,233 where it is crimped to an extent of 67 herring bone crimps per extended inch using a stuifer box temperature of 50 C. The crimped tow is then cut into 3% length staple. The cut staple, loosely arranged in a tray, is dried for 15 minutes in a circulating air oven at 270275 F. The dried staple (designated as Item A) has a weak mechanical crimp of 6-7 crimps per inch plus 68 helical crimps per inch of extended length.

The above process is repeated'using the same components, spinning conditions and wash-draw conditions but with the significant change of placing an 8 foot long steam cell between the end of the wash-draw apparatus and the stulfer box crimper. The drawn and washed tow is passed into the steam cell containing steam at atmospheric pressure at a speed of y.p.m. and is forwarded from the other end of the steam cell at 128 y.p.m. where it is fed continuously to the stuffer box crimper. Th'e tow is relaxed to an extent of 20% in the steam cell during the 1.0 second time of exposure to the steam. The crimped tow is then cut and dried as above, to yield a product of this invention designated as Item B. The as-drawn yarn has a boil-off shringage of 21%.

Both Items A and B are fibers of good quality and have the following common properties after boiling in water: a density (as determined in a heptane-carbon tetrachloride gradient tube) of 1.189, an ECR value of about 40%, a tenacity of 2.2 grams per denier, a straight elongation at the break of 30%, and an initial modulus of 50 grams per denier. Other properties in which the two items vary significantly are shown in Table I.

Knitted fabrics are made from various spunyarns of the two items and the pilling resistance tested. The superior pilling properties of fabrics made from yarns of this invention (Item B) are surprising.

A third staple fiber is made as Item B using the steam cell but omitting the stuffer box crimper. Samples taken from the tow before the cutter are straight and uncrimped. These fibers that have not been mechanically crimped have essentially the same properties as Item B above.

Sweaters and woven fabrics made from the yarns of this invention (Item B) have a soft cashmere-like handle particularly when treated with a fiber lubricant. Fabrics of similar construction made from Item A have harsh handles similar to that of number 70s wool.

TABLE I Item A Item B Steam relaxed No Yes Helical crimps/inc 13 Crimp index 10 5 Residual shrinkage, percent 3 1 Loop elongation, percent 10 17 Loop, Work to break 0. 14 0 21 Filling ratings on knitted fabrics from:

Worsted ply yarn (20/2 cotton count 14 Z/7 S tw1st) --2. 2 +3. 5 Cotton singles (10 cotton count 8.5 Z) 3. 0 +2. 5 Woolen singles (5.1 wool run, 14 Z) -2. 5 +0. 5

The rating of -3.0 indicates very severe pilling as compared with +5 for no pilling.

Results similar to those of Item B are obtained when the wet drawn tow is fed into cans and lagged for 24 hours before passing through the steam cell. When using this batch method it is important that the stored tow be fed to the steam cell in an open form equivalent to that obtained from the draw machine.

A portion of the crimped tow of Item B is cut to 3-inch lengths and another portion is cut with lengths.

continuously varying from A to 3 /2 inch on a modified Beria staple cutter and dried. Worsted ply yarns (2/30 worsted count with an .8 Z/3.5 S turns perin'ch yarn twist) are spun from both lots of cut staple and knit tubing of similar construction prepared on a 12 cut I acquard knitting machine. The fabric from 3-inch (square cut) staple has a pilling rating of 2.3 as contrastedvwith 4.5

for the fabric from theyariable length staple. The ad: vantages .of using the variable length staple are'even more striking with full fashion knit fabrics.

by continuouslydrawing, passing through. an 8 footcell .ccxnt-ainingatmospheric steam, cutting to. staple length and drying at- 130 C. The speedof the output rolls is varied to control the amount of relaxation :in the steam cell..

Similar cotton singles type yarns are spun from all items, fabrics of similar construction knitted and: submitted to the pilling test for. 20.minutes.= The pilling ratings are given in Table 'II.I The crimpyper inch. and density of the dry samples after boiling in water are given ,1

in TableII.

TABLE II Steaming Residual Item Steaming Conditions Relaxation, Shrinkage Density Filling Crimps/inch percent After Steaming On piddled tow 0-1 1.160 +1 14 On wet staple 20 0-1 1. 159 +1 14 On dry staple 3 0-1 1. 185 2. 0 On Wet tow-tensi0ned 0 21 1. 189 -3. 0 12 do 18 13 1.189 +3.5 7 do 20 13 1. 190 +3. 5 7

Example 11 Composite filaments having as onecomponent. an

88/ 12%.mixture (analyzing SSmi-lliequivalents of acid per kilogram of polymer) of polyacrylonitrile-of. (n)

2.0 and the copolymer acrylonitrile/sodium styrene sulfilaments as in Example I. The 4 x drawn, cut and dried (3009.1 staple is'designated as Item C.. Therasedrawn yarn has a boil-off shrinkage of 21%.

Item D is made as above except for the inclusion of the steam, cell of Example I to provide 19% relaxation of the 40,000 denier tow between the wash-drawmachine and thestufler box crimper.

Both items of this example have high crimp reversibility (ECR of 40%) and a density of 1.185 after boiling in water. I

The .staple of Item C develops over 18 helical crimp per inch of extended length when boiled free of restraint in Water. It has a crimp index of 18. Item:D develops only-6 helical crimps per inch after boiling in water.. It has a crimp index of 7.

Worsted ply yarns (20/2 cotton count, 11 'Z/'5.5 twist) are spun from both items and knit fabrics of similar construction made. The fabric from Item C has a harsh raspy handle as contrasted with the soft andcashmere-like handle of the fabric from Item D. The latter fabric has an improved pilling rating over the fabric of Item C of 2 rating units.

Example III piddled from side to side onto a continuous belt and then submitted to steam at atmospheric pressure for 2 minutes,-

which causes the tensionless tow to shrink about 20% Those fibers having densities less than about =1.170are They have a tendency to absorb ian very undesirable. unusual amountof finish whichmay lead to odor diflicultiesin afinal yarn. Theytake up ;a great deal ofdye from a dye bathlbut yet'yielda relatively low color in the yarn. Furthermore, in fabrics they display an instability in density which causes the appearance of dyer streaks and lusterstreaks depending uponthe pressure placed on the fabric in ironing procedures. To the contrary the fibers. having a density of 1.180 to 1.200 are density stableand are not affected by these deficiencies:

Itiis surprising that the steaming process of this inven-' tion :per sedoes not completelyfredu ce the yarn shrinkage inthis process. As the figures; indicate, there iszappreciable residual shrinkage before drying in such filaments and it:is the high temperature drying step :that sets the yarn and reduces shrinkage.

Example IV The spinning conditions of Example I are repeated to produce composite. filaments having cross sections similar,

to those shown in FIGURE6. 20 ends of the as-spun yarn are pliedto give an .8000 denier: tow which is then drawn a total.of 2 using theapparatus of. Example I. The as-drawn yarn has a boil-01f shrinkage of about 45%.

The tow is then .cut and dried on trays in an oven at 130 C. to form Item M. L

Item N is formed using the same conditions as for M but with the inclusion of the steam cell of Example I and with the adjustment of the output rolls so that the toW has=0% relaxationd-uring the steamtreatment.

Item 0: is made in thesame way as N with the exception that the tow is'allowed to relax a total of 37% during the steaming operation; e

The abovethree processes are repeated with the substitution of a 20% solution-of polyacrylonitrilewof (n) 2.0

and spontaneously crimp. The crimped tow is out to a staple length and dried with 130 C. air for 10 minutes to provide Item E. 7

Item F is prepared by passing the above drawn bust uncrimped tow to a staple cutter and then depositing the wet and a 21% solution of, thecopolymer of Example I of (n) 2.0 to yield composite filaments: having a cross sec-' tion similar: to FIGURE 5.

tained with no steam cell, 0% relaxation in the steam cell.

Items 1 Q, and R are oband137% relaxation in the steam cefll respectively.

The above processes yielding Items P, Q, and R are repeatedwith the reversal of the two spinning solutions in the spinning head so that the outer portion'of the composite filament containing thehom-opolymer faces thewall of the spinning celli This produces filaments of cross section similar to FIGURE 4.; Items*S, T,' and U are obtained with no steam -cel1, 0% relaxation in the steam cell and 37% relaxation in the steam cell'respectively Pilling. ratings are determined from knit fabricsv of woolen single type yarns (5.1 run/ 8.52 twist) spun from the samples.

All items have ran ECR of about 2530% and other filament properties as shown in Table III after boiling in water.

TABLE III Residual Loop Elon- Pilling Rating Item Cross Section Steaming Conditions Crnnps/meh Shrinkage, Density gation, Work to percent percent Break MP, and S Fig. 4, 5, or 6 None 12 l. 5 1.189 9-13 0.06 3 3 3 N, Q, and T. Fig. 4, 5, or 6 Tent relax 20 3 1.189 21 .36 3 3 -3 R Fig. -dogbone.- Tensioned 37% relax 0 1.189 64 .82 -1 +3 +5 Fig. 4-dogbone. d 0 1. 187 48 -1 0 +3 Fig. 6 ac0rn. 0 1. 190 +3 +5 +5 Example V This example shows the advantages of the process of this invention with 1.35 X drawn fibers.

Fibers of the same composition as those in Example I are spun in the same manner except for spinning speeds of 400 y.p.m. and for the solution, head and cell temperatures of 60, 270 and 160 C. respectively. Four hundred fifty ends of the as-spun yarn (280 denier) are plied to give a 126,000 denier tow which is then drawn a total of 1.35 using the apparatus of Example 1. The tow is then cut and dried on trays in an oven at 130 C. to form Item V.

Item W is formed using the same conditions as for V but with the inclusion of the steam cell of Example I and allowing the tow to relax a total of 20% during the steaming operation. The as-drawn fiber has a shrinkage of about 22%.

Both fibers developed a helical crimp of about 9 crimps per inch when boiled free from restraint in water and have a negative crimp reversibility of ECR. Properties of the boiled-oil fibers and knit fabrics prepared from them are given in Table IV.

TABLE IV Item V Item W Density 1. 184 l. 189 Loop Elongation, percent. 6. 2 9. 8 Loop, Work to Break 0. 06 0.09 Filling Ratings on Fabrics fro 5.1 run, 8.5 Z twist, 20 minutes 1 +5 Yarns made from Item W are significantly tougher than V as indicated by the loop properties. This results in improved knittability of these low tenacity fibers compared to Item V.

Example VI A 21% solution in dimethylformamide (DMF) of a mixture of 86% of polyacrylonitrile of intrinsic viscosity 2.0, and containing 22 milliequivalents of acid groups per kilogram of polymer (as determined by titration in a DMF solution) and 14% of a copolymer of acrylonitrile/styrene sulfonic acid, 96/ 4% by weight composition, of intrinsic. viscosity 1.5, and analyzing 240 milliequivalents of acid per kilogram of polymer, said mixture of polymers containing 53 milliequivalents of acid groups per kilogram of polymer used, is extruded as one component (which faces the center of the spinning cell) of a composite filament using a spinneret having three concentric rings of orifices, totaling 252' in number. This solution also contains 0.04% TiO based on total polymer content. Simultaneously, a 27% solution in DMF of a copolymer of acrylonitrile/styrene sulfonic acid, 96/4% by weight composition, of intrinsic viscosity 1.5, and analyzing 240 milliequivalents of polymer and also containing 0.4% TiO polymer content used, is extruded as the other component (which faces the wall of the cell) of composite filaments.

acid per kilogram of based on total 2,050 total denier, Item B) consisting of 252 composite filaments is wound up at 350 yards per minute.

Five-hundred seventy-six ends (Item A) or 635 ends (Item B) of yarn produced as above with a combined denier of 1,300,000 are combined into a tow and drawn to four times its original length (i.e., 4 X draw ratio) through a series of water baths at 98 C. which extract the residual DMF, said water baths containing mixtures of DMF and water with not over 30% DMF.

For Item A, the drawn and extracted tow is led directly from the wash-draw process to a stuifer box crimper similar to that shown in Hitt, US. 2,747,233, where it is crimped to an extent of six to seven herringbone crimps per extended inch using a stuffer box heated by steam at a pressure of 3 p.s.i.g. The crimped tow is then cut into staple of lengths continuously varying from 1 to 5 inches on a modified Beria staple cutter. The cut staple is dried on a moving belt dryer at C. for twenty-five minutes. The dried staple (designated as Item A) has a weak mechanical crimp of 5 to 6 crimps per inch plus 5 to 6 helix crimps per inch of extended length.

For Item B, the above process is repeated using the same components, spinning conditions, and Wash-draw conditions, but with the significant change of placing an eight-foot long steam cell between the end of the washdraw apparatus and the stuffer box crimper. The drawn and washed tow is passed into the steam cell, containing steam at atmospheric pressure, at a speed of 200 yards per minute where it is fed continuously to the unheated stuifer box crimper. The tow is relaxed to an extent of 15% in the steam cell during the 0.94 second time of exposure to the steam. The crimped tow is then cut and dried as above, to yield a product of this invention designated as Item B.

Items A and B have the following common properties after boiling in water: a density (as determined in heptanecarbon tetra-chloride gradient tube) of 1.189, an ECR value of 30%, a tenacity of 2.5 g.p.d., and a straight elongation at break of 32%. Properties in which the two items vary significantly are shown in Table V.

What is claimed is:

1. In a process for preparing staple fiber from composite filaments, the resulting staple fiber having improved resistance to pilling which comprises simultaneously washing and drawing a tow of continuous filaments wherein said filaments have two eccentri-cally positioned sections of different acrylonitrilepolymers extending along their lengths, the improvement which comprises a controlled relaxation step provided by continuously passing said filaments under a slight tension through a heated pliasticizing medium, the tension on said filaments land the tem-perm ture of said'medium being controlled to uniformly shrink said filaments an amount equal to at least 50% of the.

3. The process of claim 1 wherein said filaments are.

drawn from about 1.1 to 10 times their original length and after shrinking are crimped.

4. The process of claim 1 wherein said medium issteam.

5. The process-of claim 1 wherein the relaxation treatment under tension is carried out in the presence of steam at about 0to 5 psi. gage.

References Cited bythe Examiner UNITED STATES PATENTS Sisson etal 28 -82 Sisson; -28-82 Appleton et al 28-72 X Rokosz 28-72 Spence et a1. 28-72 Pit'zl 28-7 2 Breen et al ,l61-'177 X Taylor 161-172 Wu 161-175 FOREIGN PATENTS Great Britain.

ROBERT'R. MAC-KEY, Primary Examiner. 2 RUSSELL C. MADER, DONALD W. PARKER, 0 2

LB. MAIER, A. J. FSMEDEROVAC,

Examiners. 1

Assistant Examiners.

Claims (1)

1. IN A PROCESS FOR PREPARING STAPLE FIBER FROM COMPOSITE FILAMENTS, THE RESULTING STAPLE FIBER HAVING IMPROVED RESISTANCE TO PILLING WHICH COMPRISES SIMULTANEOUSLY WASHING AND DRAWING A TOW OF CONTINUOUS FILAMENTS WHEREIN SAID FILAMENTS HAVE TWO ECCENTRICALLY POSITIONED SECTIONS OF DIFFERENT ACRYLONITRILE POLYMERS EXTENDING ALONG THEIR LENGTHS, THE IMPROVEMENT WHICH COMPRISES A CONTROLLED RELAXATION STEP PROVIDED BY CONTINUOUSLY PASSING SAID FILAMENTS UNDER A SLIGHT TENSION THROUGH A HEATED PLASTICIZING MEDIUM, THE TENSION ON SAID FILAMENTS AND THE TEMPERATURE OF SAID MEDIUM BEING CONTROLLED TO UNIFORMLY SHRINK SAID FILAMENTS AN AMOUNT EQUAL TO AT LEAST 50% OF THE BOIL-OFF SHRINKAGE OF SAID DRAWN FILAMENTS, AND CONVERTING THE RESULTING TOW OF RELAXED CONTINUOUS FILAMENTS TO STAPLE FIBER AND DRYING THE STAPLE FIBER AT HIGH TEMPERATURE.

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