US3790997A

US3790997A - Process of producing random three-dimensional crimped acrylic fibers

Info

Publication number: US3790997A
Application number: US00163037A
Authority: US
Inventors: R Hagell
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1968-09-20
Filing date: 1971-07-15
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12

Abstract

Acrylic homocomponent fiber having random three-dimensional crimp is prepared by stuffer-box crimping tow under hot-wet conditions, cooling the crimped tow and then crimping the tow again under hot-wet conditions. These fibers, in staple form are especially suited for use in preparing improved sliver knit pile fabrics.

Description

'ited States Patent [191 agell 5] Feb. 12, 1974 [54] PROCESS OF PRODUCING RANDOM 2,968,857 1/1961 Swerdloff et al 28/72.l4

THREEDIMENSIONAL CRIMPED 1;; lg/lurfhie et a]. tan ey ACRYLIC FIBERS 3,174,208 3/1965 Saito et al.. 28/1.6 X [75] Inventor: Ronald A. Hagell, Lugoff, S.C. 3,259,953 7/1966 Baer 28/1.3 3,399,177 8/1968 Reader 161/173 X [731 Asslgneel and 3,447,998 6/1969 Fitzgerald 161/173 p y Wflmmgton, 1391- 3,461,521 8/1969 Eskridge 28/7211 [22] Filed: July 15, 1971 [21] Appl 1 3 037 Primary Examiner-Louis K. Rimrodt Related US. Application Data [62] Division of Ser. No. 761,160, Sept. 20, 1968, [57] ABSTRACT abandoned.

Acrylic homocomponent fiber having random three- [52] US. Cl. 28/72.11, 28/7214 dimensional crimp is prepared by stuffepbox crimping [51] lilt- C] D02g tow under hot wet condiions cooling the crimped Field of. Search 1.6, tow and then the tow g i under hot wet 161/173 conditions. These fibers, in staple form are especially [56] e ere es Cite Egress-for use in preparing improved sliver knit pile UNITED STATES PATENTS 2,865,080 12/1958 Hentschel 28/].3

3 Claims, No Drawings PROCESS OF PRODUCING RANDOM THREE-DIMENSIONAL CRIMPED ACRYLIC FIBERS CROSS REFERENCE TO RELATED APPLICATIONS This application-is a divisional of application Ser. No. 761,160, filed Sept. 20, 1968, now abandoned.

The invention relates to a novel process for producing improved acrylic fiber.

BACKGROUND OFYTHE INVENTION In recent years, pile fabrics made by the sliver knit route have become commercially important for producing simulated furs used in fur coats and other garments, for linears in jackets, raincoats, and topcoats, and for other textile articles such as throw rugs. Acrylic fibers have been used in a large part of this market because of the highly desirable bulk, cover, and softness of the finished sliver knit pile fabrics.

In the production of the sliver knit fabrics, a sliver of staple fibers is fed to a knitting machine in such a way that tufts of fiber are removed from the sliver and engaged by the thread being knitted into fabric with the free ends of the fibers in each tuft projecting from one side of the fabric. The surface of the pile fabric is then sheared to the desired pile height and subjected to fur ironing (also called electrifying) to smooth, parallelize, and polish and fibers comprising the surface of the fabric; after which the fabric may again be sheared to trim the surface 'to a uniform height. A large fraction of the weight of the staple fiber starting material is frequently converted to waste in the production of these fabrics, especially in making liner fabrics, since the desired height of the pile is frequently much less than half of the length of the staple fibers in the sliver. Although it has been considered a desirable goal to make the sliver from staple fibers short enough to provide approximately the desired pile height and minimize shearing losses, the conventional acrylic fibers available in the trade hitherto do not cohere sufficiently well in sliver form to permit the production of acceptable sliver when the staple fiber length is less than about 1% inches, leading to excessive sliver breakage and stack losses in the knitting step. The starting material sliver is accordingly formed from staple fibers long enough to provide a sliver strong enough to be readily processed.

While it is desirable from the viewpoint of sliver cohesion to employ acrylic fibers which are well crimped and have sufficient stability to retain their crimp during sliver processing, the production of pile fabrics also requires that the'crimp be removed and the fiber pulled out to a permanently straight condition at the fabric surface in the fur ironing step. On the other hand, it is desirable to retain as much crimp in the fiber as possible at the base of the pile, so that the fabric will have a high degree of cover and will not seem thin." Unfortunately, the conventionally crimped acrylic staple fibers available in the trade have sufficient crimp stability that it is frequently necessary to fur iron sliver knit pile fabrics several times to obtain the required degree of smoothness, luster, and polish in the surface of the pile fabric. When repeated passages of the pile fabric through the fur ironer are required, the-cost of finishing is greatly increased. The extensive working of the fabtie also tends to reduce its cover to a lower level than desired.

SUMMARY OF THE INVENTION 2. cooling the crimped tow to less than about 60C.,

and 3. reheating with steam to a hot and wet condition,

, and

4. stufi'er box crimping the reheated tow while hot and wet.

The resultant crimped tow preferably is then cut into staple form and dried if necessary. The staple form is especially well suited for use in preparing sliver knit pile fabrics.

It is to be understood that the term wet is used herein to characterize the moisture content of the tow, i.e., the wet tow contains a measurable water content (e.g., greater than about 1 percent by weight) although the tow does not necessarily feel wet to the touch.

In a preferred process embodiment of the invention, (sometimes referred to herein as Process Embodiment A) drawn homocornponent acrylic tow is:

l. crimped at 60 C. while wet (preferably 60 90% water by weight) by passing the tow through a stufi'er box crimper;

2. cooled below 60C. while maintained wet (preferably 30 50 percent water by Weight) immediately following crimping; and

3. crimped at 95C. while wet (preferably 30 50 percent water by weight) by passing the tow through a stuffer box crimper.

The fibers are preferably cut into staple length fiber and then dried.

In another preferred process embodiment of the invention (sometimes referred to herein as Process Embodiment B), drawn homocornponent acrylic tow is:

l. crimped at 60 70Cqwhile wet (preferably 60 percent water by weight) by passing the tow through a stuffer box crimper;

2. cooled below 60C. immediately following crimp- 3. dried while in a' condition free to relax; and

4. crimped at 80 C. while wet (preferably about 2 percent water by weight) by passing the tow through a stuffer box crimper.

The fibers are preferably cut into staple length fibers; no drying is necessary.

The crimping temperatures are suitably maintained by conventional means. For example, the fibers are preferably heated by steam immediately prior to passing into the stuffer chamber.

The crimping moisture level in the first crimping step is preferably attained simply as a result of the water content of the tow immediately after it is washed and drawn (e.g., as in a typical continuous process for producing acrylic fiber). It is important in Process Embodiment A that the fiber be maintained wet after the first crimping, although this is not significant if the fibers are to be subsequently dried as in Process Embodiment B.

The cooling step immediately following crimping is important, otherwise the crimp may be pulled out in subsequent processing.

The crimping moisture level, in the second crimping step in Process EmbodimentA, is attained by maintaining the moisture level in the cooling step which immediately follows the first crimping step. The crimping moisture level in the second crimping step in Process Embodiment B is attained preferably by heating the tow in 100C. steam for less than about one second.

The stable fiber cut from tow produced as above has random three-dimensional crimp and forms sliver of excellent cohesion, which can be readily converted to a sliver knit pile fabric, even when the staple fiber length is below an inch (down to about k inch). This higher cohesion permits the use of staple lengths shorter than the lower limit of about 1% inches length of conventionally crimped acrylic staple which could be used without excessive sliver breakage and stack losses during knitting. Since a lower minimum staple fiber length is provided by this invention, a significant reduction in waste from shearing losses is realized; the fiber length may be short enough to more closely approximate the desired pile height. Furthermore, these three-dimensionally crimped fibers also offer significant improvement in the fur ironing particularly in cover and fabric aesthetics (e.g., smoothness, luster and polish). For example, sliver knit pile fabrics prepared according to the preferred process referred as Process Embodiment A above, can be fur ironed to a given level of smoothness, luster and polish much more readily than fabrics made from conventional acrylic fibers, only about half the number of passage through the fur ironer being required. Surprisingly, better cover is obtained while realizing reduced finishing costs. The fabrics prepared by the process referred to as Process Embodiment B above, for the same number of fur ironing passages as the conventional fabrics, have excellent smoothness, luster and polish, and strikingly enhanced cover compared thereto.

The fibers of this invention which are more easily fur ironed (e.g., those prepared by Process Embodiment A above) have unique crimp properties. In addition to a random three-dimensional crimp which results in greater fiber cohesion (as is characteristic of all of the fibers of this invention), the crimp is more readily removed during fur ironing, i.e., the crimp is not pulled out during knitting, but is easily ironed out during fur ironing. Due to the ease in fur ironing, the portion of the fiber nearest to the fabric surface is pulled permanently straight in fewer fur ironing passages and therefore additional passages which remove the fiber crimp at the base of the pile are not necessary. Many of the fibers possessing this crimp property are characterized by the unique temperature-tension spectra stated above, i.e., when the fiber is placed under a tension of 2 milligrams per denier at room temperature, it exhibits substantially no increase in tension, when heated to a temperature of 135C., compared to significant increases in tension in conventionally crimped acrylic fibers. Although the invention is not to be limited by the underlying theoretical considerations, it is believed that this unique temperature-tension spectra explains that the ease of crimp removal in that the repeated fur ironing passages are generally performed at approximately 135C. (e.g., 121C. (250F.) being quite common) and the crimp is removed with less force being necessary to straighten the fiber.

DEFINITIONS The term acrylic fiber," as used herein, refers to a fiber of any long chain synthetic polymer composed of at least percent by weight of acrylonitrile units of the formula,

in the polymer chain.

As is well understood, acrylic fibers may be formed from the homopolymer of acrylonitrile or from copolymers of acrylonitrile and monoethylenically unsaturated monomers polymerizable with acrylonitrile. Nonlimitative examples of preferred comonomers include methyl acrylate, methyl methacrylate, vinyl acetate, styrene, methacrylonitrile, vinyl chloride, vinylidene chloride, methyl vinyl ketone, 2-vinylpyridine, 4- vinylpyridine, 2-methyl-5-vinyl-pyridine, and sodium styrene sulfonate. Preparation of these polymers is well known, such processes being disclosed in US. Pat. Nos. 2,486,241; 2,456,238; 2,837,500; and 2,837,501 as well as many other patents.

The term homocomponent fiber refers to a fiber spun from a single source of polymer feed, so that the cross section of the fiber has substantially the same polymer composition at any point excluding particulate matter which may be present in small quantities as a delusterant dye, etc. or other auxiliary purpose.

The term random three-dimensional crimp" refers to crimps which lie in a plurality of planes randomly along the fiber, as distinct from a two-dimensional saw-tooth crimp characteristic of conventional single stuffer box crimping. Such three-dimensional crimp, as shown in FIG. 1, lies randomly in the plane of the photograph as well as in planes transverse thereto.

Measurements and Tests Temperature-Tension Spectra The tension exerted by fibers upon heating is determined by running a tension-temperature spectrum of a sample of the fibers. The values reported in the example below are determined in accordance with the following procedure. Sufficient filaments, from a sample of a tow from which the staple fibers are cut, are aligned to make a sample of about -200 denier. The filaments are cut to a length of 36 cm., handling the filaments carefully so that they do not become stretched. The filaments are gathered together into a strand and the strand is tied in a loop and weighed. The loop of fiber sample to be tested is placed in an oven consisting of the vertical leg of an inductively heated D-shaped aluminum tube having an inside diameter of 0.25 inch and having openings at the top and bottom of the vertical leg. The top of the loop is fastened in a clamp attached to a transducer (commercially available as a Stratham transducer, operating on the Wheatstone Bridge principle). The bottom of the loop is fastened to another clamp which elongates the fiber strand by means of an adjusting screw to a calibrated tension of 2 milligrams per denier, based on the loop denier (twice the denier of the straight sample from which the loop is formed). The temperature of the oven and the tension measured by the transducer are continuously and automatically recorded on a chart using conven-. tional, commercially available instrumentation. The

oven is heated at the rate of 20C. per minute and a curve showing the tension of the fiber with respect to temperature as it is heated is continuously recorded. Crimps Per Inch The number of crimps perv inch in a fiber multiply crimped according to this invention, is determined by (l) measuring the length of a single fiber, at least 1% inch long, under a tensioning weight of 150 mg.; and after relaxationof the tension, (2) counting the number of crimps (each crimp defining a complete sine wave) in the fiber when under a lower tension provided by a 5 mg. weight. The crimps per inch is calculated by dividing the number of crimps by the measured fiber length in inches. Crimp Index The crimp index refers to the change in length of the crimped fiber, at least 1%. inch long, (1) under a tensioning weight of 150 mg.; and (2) after relaxation of the tension, under a weight of 5 mg. The change in length is expressed as a percentage of the uncrimped length.

For staple fibers cut shorter than 1% inch, the crimps per inch and crimp index are determined on separate samples of longer fiber cut from the same supply and processed in the same manner subsequent to cutting.

The invention will be further illustrated by the following example.

EXAMPLE This example illustrates (A) the preparation of crimped fibers according to this invention and (B) the use of such fibers in preparing sliver knit pile fabric. The improvement provided by this invention is readily seen from the comparison of fabrics of fibers of this invention with fabrics of the control fibers.

Part A: Crimped Fiber Preparation A multifilamentary tow comprised essentially of 93.6 percentacrylonitrile, 6 percent methyl acrylate, and 0.4 percent sodium styrenesulfonate is simultaneously drawn 4.5X and extracted in a water bath maintained near its boiling point. After drawing, the tow has a tow denier of approximately 320,000 and a denier per filament of about 2.1. The wet tow, containing about 60 90 percent water by weight is steam heated to a temperature of 68C., is passed at a rate of 425 yards per minute between driven feed rolls 2.5 inches wide into a stuffer box crimper into which steam at a pressure of 20 pounds per square inch is injected. A clapper pressure of 18 pounds per square inch is applied at the exit of the stuffer box crimper. The wet tow from the crimper contains 34 percent water by weight and has a shrinkage of 20 percent, when boiled off and dried at a temperature of 110C. for 30 minutes. The wet tow is cut to staple fibers having a cut length of 1% inches on a Beria cutter (rotary cutter), dried on a continuous flat-bed dryer at 127C. for minutes, and baled. The resulting staple fibers have a regular, two-dimensional, herringbone crimp; this product is designated as the Control Sample. The properties of these fibers are given in Table I below.

The following preparation illustrates the preferred process of this invention previously referred to as Process Embodiment A. Two ends of the wet tow, crimped by passing it through the stuffer box .crimper once in accordance with the above procedure, are combined and passed between perforated plates wherein the product is subjected to treatment with steam at 100C. for contact time of 0.75 seconds. The wet, steamtreated tow is then passed directly at a rate of yards per minute between driven feed rolls 6 inches wide into a stuffer box crimper. A clapper pressure of 15 to 20 pounds per square inch is applied at the exit of the stufferbox crimper. The wet tow from the crimper contains 20 percent water by weight and has a shrinkage substantially no increase in tension when heated to a temperature of 135C; these characteristics are distinct from those exhibited by the Control Sample Fibers. This (Sample A) Process Embodiment A fiber exhibits a minimum tension transition temperature which is 10C. higher and a reduced rate of tension rise with increasing temperature beyond this minimum tension transition temperature, when compared to the Control Sample Fiber.

The following preparation illustrates the second preferred process of this invention previously referred to as Process Embodiment B. A portion of the wet, oncecrimped tow which is prepared according to the procedure given at the beginning of this example is dried by passing it on a continuous flat-bed dryer at 135C. for 10 minutes. Two ends of the dried tow are combined and the product is passed between perforated plates wherein it is subjected to treatment with steam at C. for a contact time of 0.75 second. The steamtreated, once-crimped tow, slightly damp from the steam pre-treatment, is then passed directly at a rate of 70 yards per minute between driven feed rolls 6 inches wide into a stuffer box crimper. A clapper pressure of 20 pounds per square inch is applied at the exit of the stuffer box crimper. The tow from the crimper contains 2.5 percent water by weight and has a shrinkage of 1.5 percent when boiled off and dried at C. The substantially dry tow is cut to staple fibers having a cut length of 1 inch on a Beria cutter and baled. The resulting staple fibers have a random, three-dimensional crimp; this product is designated as Sample B. The properties of these fibers are also given in the Table I below.

Table I Fiber Properties Control Sample Sample A Sample B Tenacity (gpd) 2.3/2.8 2.9/2.2 2.6/ Elongation 26.5/30.5 293/212 20.0] Initial Modulus (gpd) 50.71519 48.2/43.9 46.0/ Crimps Per Inch l0.0/10.9 12.1/12.5 12.3]! 1.0 Crimp Index 12.2/16 6.0/8.7

Part B: Sliver Knit Pile Fabric 19 courses per inch and 12.5 wales per square inch. Three control sample fibers at 1% inches staple length are about the shortest conventionally crimped staple length that is suitable; shorter lengths are not sufficiently cohesive which results in sliver breakage during knitting. Significantly, the fibers of this invention, at this one inch staple length (and even at shorter lengths) are sufficiently cohesive during knitting.

Each of the sliver knit fabrics are sheared (on a pile shear machine made by the Parks and Woolson Co.) to a pile height of three-eights inch.

The sheared fabrics are then subjected to fur ironing to smooth, parallelize and polish the fibers (on a fur ironing machine made by Frank Egan and Co.). The fabrics are each ironed at a rate of 6 yds./min. in each of 4 passages through the fur ironer. The temperature for the first passage in 400F. (232C.) and 250F. (121C.) for each of the next 3 passages. Portions of each of the three fabric samples are removed after each passage through the fur ironer. The final (i.e., after the fourth passages) fabrics are again sheared to a pile height of three-eights inch as above.

The portions of the three fabrics after each fur ironing stage are examined for cover, smoothness, luster and polish. Quite surprisingly, the Process Embodiment A fabric has better cover, smoothness, luster and polish after two fur ironing passages, than the control fabric has after four such passages. The process Embodiment B fabric, after the same number of fur ironing passages as the control fabric, has excellent smoothness, luster and polish, and strikingly enhanced cover compared to the control fabric. Thus, using either of these two process embodiments of this invention, an improvement over conventionally crimped acrylic fibers is realized.

What is claimed is: 1. Process for producing fibers of random threedimensional crimp comprising:

1. stuffer box crimping homocomponent acrylic tow while hot and wet;

2. immediately cooling the crimped tow to less than about 60C.;

3. reheating the cooled crimped tow with steam to a hot and wet condition, and

4. stuffer box crimping the reheated tow while hot and wet.

2. Process of claim 1 wherein:

said tow in said crimping step (1) is maintained at a temperature between about 60 to C.;

said cooling step (2) immediately follows said crimping step (1) and maintains the said crimped tow in a wet condition; and

said crimped tow in said steps (3) and (4) is maintained at a temperature of between about to C. by contacting it with steam prior to entering the stuffer box.

3. Process of claim 1 wherein:

said tow in said crimping step (I) is maintained at a temperature between about 60 to 70C.;

said cooling step (2) immediately follows said crimping step (I); and

said crimped tow in said steps (3) and (4) is maintained at a temperature between about 80 to 95C. by contacting it with steam prior to entering the stuffer box;

said process further comprising the step of drying the crimped tow, in a condition free to relax, after cooling step (2), but prior to step (3).

Claims

2. immediately cooling the crimped tow to less than about 60*C.;
2. Process of claim 1 wherein: said tow in said crimping step (1) is maintained at a temperature between about 60* to 70*C.; said cooling step (2) immediately follows said crimping step (1) and maintains the said crimped tow in a wet condition; and said crimped tow in said steps (3) and (4) is maintained at a temperature of between about 80* to 95*C. by contacting it with steam prior to entering the stuffer box.
3. Process of claim 1 wherein: said tow in said crimping step (1) is maintained at a temperature between about 60* to 70*C.; said cooling step (2) immediately follows said crimping step (1); and said crimped tow in said steps (3) and (4) is maintained at a temperature between about 80* to 95*C. by contacting it with steam prior to entering the stuffer box; said process further comprising the step of drying the crimped tow, in a condition free to relax, after cooling step (2), but prior to step (3).
3. reheating the cooled crimped tow with steam to a hot and wet condition, and
4. stuffer box crimping the reheated tow while hot and wet.