US3343241A

US3343241A - Crimping process

Info

Publication number: US3343241A
Application number: US451713A
Authority: US
Inventors: Gajjar Bharat Jaybhadra
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1965-04-29
Filing date: 1965-04-29
Publication date: 1967-09-26
Anticipated expiration: 1984-09-26
Also published as: GB1090218A

Description

p 26, 6 B. J. GAJJAR 3,343,241 I CCCCCCCCCCCCC SS INVENTOR I BHARAT JAYBHADRA GAJJAR BY WM 4% United States Patent ()fiice 3,343,241 Patented Sept. 26, 1967 3,343,241 CRIMPING PROCESS Bharat Jaybhadra Gajjar, Wilmington, Del., assignor to E. I. du Pout de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Apr. 29, 1965, Ser. No. 451,713 6 Claims. (Cl. 28-72) ABSTRACT OF THE DISCLOSURE A process for developing crimp of yarns that have a latent capacity to crimp when exposed to hot wet processing conditions. The improvement involves cooling the yarn immediately prior to the hot wet processing step.

This invention relates to warp-knitted fabrics having spun-like or textured properties. It also relates to an improved yarn finishing method that can be used for producing such fabrics.

Conventional knitted tricot fabrics, frequently made from rayon or cellulose acetate yarns, have heretofore tended to lack texture, good hand, and covering power. It has been recognized that pre-texturing of the yarns would improve these properties but the filaments employed for this purpose are of such fine denier that the mechanical quality of the pre-textured yarns is quite poor. As a consequence the use of such pre-textured yarns would cause excessive breaks in the knitting operation and would result in fabrics of poor quality. The texturing of such yarns raises still another problem; namely, a problem of economics owing to the fact that very precise control is required in the texturing of extremely fine denier yarns. This is essential to obtain the good denier uniformity needed to make an acceptable product.

One solution for improving the properties of knitted tricot fabrics is that described in Kasey US Patent 3,041,861 wherein two yarns of differing retractability, i.e., residual shrinkage, are used to form the knitted fabric. However, such fabrics, although considerably improved with respect to certain properties, still have no appreciable texture or bulk and hence typically exhibit a rather flat appearance. Then, too, such fabrics also generally lack any appreciable two-directional stretch, this being a property that would be highly advantageous for many warp-knitted fabrics.

In accordance with the invention there is provided a two-bar, warp-knitted fabric wherein the stitches are formed of first and second synthetic filamentary yarns, the ratio of the loop length of said first yarn to the loop length of the second yarns being 1.1-1.5:1, said first yarn comprising latently crimpable two-component filaments providing an average of 3 to 12 crimps per stitch length when the fabric is finished by scouring at the boil. Upon treating such a fabric to develop the latent crimpability of the two-component filamentary yarn, the fabric takes on a spun-like or textured character somewhat resembling cotton fabrics. Moreover, owing to the high degree of crimp in the treated fabric, improved covering power and an appreciable degree of two-way stretchability are provided. It is to be understood that either one or both of the two yarns comprising the warp-knitted fabric, above described, may be formed of latently crimpable two-component filaments and that it is only essential that the stated ratio of the loop length of one yarn to that of the second yarn is fulfilled.

The novel warp-knitted fabrics of the invention are conveniently knitted on an ordinary knitting machine by feeding one of the two yarns at the top front bar of the machine and by feeding the second of the yarns at the bottom back bar of the machine. The yarn composed of latently crimpable two-component filaments may be fed to either the top front bar or to the bottom back bar or to both bars of the machine. The relative tensions upon the yarns fed to the machine are adjusted so that one of the yarns, specifically a yarn composed of latently crimpable two-component filaments, forms loops which are larger than those of the other yarn. The larger loops of the stitches are formed so as to have a loop length which is 1.1 to 1.5 times the loop length of the second yarn. Ordinarily this can be achieved in a Jersey fabric if the fabric is knitted in such a manner that the bicomponent front bar to regular back bar actual knitting ratio is at least 1.38, preferably 1.45.

The novel fabrics of the invention will be further understood by reference to the drawings wherein:

FIGURE 1 is a loop diagram of a conventional prior art greige or finished tricot fabric in which the yarns of the top bar and yarns of the bottom bar have the same loop length. The yarns lay on top of one another, thus giving a fabric which was poor transmitted light cover because of the relatively large holes through which light can pass.

FIGURE 2 is a loop diagram of the front of a greige tricot fabric (Jersey stitch) of this invention prior to crimp development.

FIGURE 3 illustrates the appearance of the fabric of FIGURE 2 following development of crimp.

In the fabric stitch shown in FIGURE 2, yarn 3 forms the larger loop and is therefore comprised of the latently crimpable two-component filaments. The loop length of yarn 4 is considerably smaller and this may or may not be formed of latently crimpable two-component filaments. The loop length of yarn 3 is the distance from point a, around the loop, and back to that point. Similarly the loop length of yarn 4 is the distance from point 12, around the loop, and back to that point. The loop length of the yarns may be determined using a microscope and measuring the indicated distances.

In FIGURE 3, the crimped configuration of yarn 3 in the stitches can be observed. It will be apparent that such stitches will provide considerably improved covering power as compared to the prior art fabric of FIG- URE 1. If yarn 3 had not initially been formed into larger loops, the tendency thereof to fully crimp would have been prevented by the other loops which it engages. As illustrated in FIGURE 3, yarn 3 has an average of 7 even crimps per stitch length.

A fabric of the invention, as illustrated in FIGURE 3, has superior bulk, thickness and cover at a given weight as compared to non-textured warp-knitted fabrics of the prior art. In addition to also exhibiting a textured quality similar to cotton fabrics, this fabric after bleaching and drying further shows a two-way elongation-potential (stretch) which is at least 50% greater (both in the wale direction and in the course direction) than a prior art fabric.

By the term latently crimpable as used herein to describe the filaments comprising the bicomponent yarns used in this invention, it is meant that although the filaments to be knitted are in a generally straight condition they nevertheless possess an inherent tendency to take on or otherwise assume an irregular contorted configuration by scouring at the boil, e.g., by exposure thereof to water at 100 C. The fibers should be capable of not merely assuming a generally curved or flexed shape but, rather, of affording a crimp frequency sufliciently high to give 3 to 12 crimps per stitch length. This is important if the fabric is to exhibit good bulk and aesthetics. It will be understood that in the final fabric the crimped fibers will be seen to possess a curved or curled configuration. In other words such fibers will trace a bend or gradual change in direction as opposed to many types of mechanically crimped fibers which exhibit an abrupt change in direction, e.g. the well known stuffer-box or saw-tooth crimped configuration.

The latently crimpable synthetic filaments of the yarns employed in the practice of the invention will be composed of either linear condensation polymers or linear addition polymers, for example, acrylonitrile polymers and copolymers; polyamides, such as polyhexamethylene adipamide, polycaproamide, poly(meta-phenylene isophthalamide), and copolyamides; polyesters such as polypivalolactone, polyethylene tere hthalate and copolyesters prepared from glycols and terephthalic and isophthalic acids; polyethylene and ethylene copolymers; polypropylene and propylene copolymers; polybenzimidazole; copolymers of acrylonitrile with small amounts of copolymerizable monomers (e.g. with 12% by weight methyl methacrylate or with 10% by weight vinyl acetate); and the like. In any case the latent capacity to crimp is built into the fiber by suitable selection of the individual components. Suitable techniques for preparing two-component fibers with latent crimp are described in US. patent to Taylor 3,038,237 and in British Patent 950,429. In one embodiment the two-component filaments may comprise two continuous components adhered to one another in side-to-side relationship along their length. Alternatively they may comprise a sheath component and a core component. A preferred class of filaments is that described in the aforementioned British patent wherein one component is a homopolyamide and the other is a copolyamide. Preferably the bicomponent fibers will retract, i.e. shrink, less than 5% in length upon scouring at the boil.

One of the yarns of the novel fabric of the invention will be composed of latently crimpable two-component filaments of the class described above. The other yarn may be identical, of the same class or of ordinary monocomponent synthetic filaments.

A corollary finding of this invention pertains to an improved method for developing the crimp of yarns comprising two-component filament that have a latent capacity to crimp when exposed to hot wet processing conditions. The improvement involves cooling the yarn in the presence of water to below C. immediately prior to crimping under essentially no tension by exposure to a heated aqueous fluid at a temperature of at least about 100 C. Although the reasons for this unexpected im- 'provement are not fully understood, it appears that the drastic change in the fiber temperature upon going from a very cold to a very hot condition causes a pronounced shock effect which in turn markedly increases the degree of crimp and bulk beyond that would otherwise The cooling of the fibers prior to crimp development according to this improved process should be sufficient to lower the fiber temperature to below 10 C. and preferably to 0 C. or below. The fibers should be exposed to water, either as a liquid or ice, at the low temperature. Cooling in an ice-water bath is especially desirable. There should be no appreciable time delay between the cooling and heating steps for full realization of this improved crimping procedure.

The development of crimp is effected by exposing the yarn comprising two-component filaments to a heated aqueous fluid at a temperature of at least about C. The heated aqueous fluid may be in the form of hot water or steam, either saturated or not but preferably the temperature of the filaments is raised essentially instantaneously, e.g. by plunging into a bath of boiling water. Textile lubricants or other additives may advantageously be included in the fluid. It will be understood that crimp development must occur while the fibers are under essentially no tension, otherwise maximum bulkiness will not be realized.

The shock cooling-heating procedure, above described, is particularly desirable for developing crimp in the novel warp-knitted fabrics of this invention. However, it will be apparent that it can also be used to advantage for development of crimp in any product comprising latently crimpable two-component filaments. Woven, nonwoven, and other forms of knit fabrics comprising such yarns of such filaments will also derive an enhanced bulk by the use thereof. It will be understood that any fabric to be so treated should be of a generally loose or open construction so that crimp development can freely occur.

In lieu of cooling the two-component filaments prior to crimp development, they may be treated with certain organic solvents such as benzyl alcohol, to also realize improved bulk. For most purposes this is disadvantageous, however, because of the problems associated with handling such materials.

The following examples are given to illustrate the invention, and are not intended to limit the scope thereof in any manner.

Example I A 30 denier, 14 bicomponent (trilobal cross section) heat crimpable filament yarn is used in conjunction with a 30 denier, 10 monocomponent (trilobal cross section) filament non-heat crimpable yarn to knit a tricot fabric (Fabric No. 1 on Tables I and II below) on a 28 gauge, 84 inch wide machine using a Jersey pattern (2-3, 1-0 front bar and l-0, 1-2 back bar stitch), 5" Quality, and front runner 54" back runner 38.5" for a 1.4 knitting ratio. Each filament of the 14 filament yarn consists of two continuous, adherent, eccentric components, one component (50% of the filament weight) being a sheath of poly(hexamethylene adipamide) and the second component (the other 50% of the filament weight) being a core of a copolyamide of hexamethylene adipamide and hexamethylene isophthalamide (70:30 weight ratio of the respective repeating units). Each filament of the 10 filament yarn consists of poly(hexamethylene adipamide). The greige fabric so knitted is 15.0 mils thick, has a density of 2.50 ounces per square yarn, and has a bulk of 4.49 cubic centimeters per gram. One piece of the knit fabric is kept in an ice-water bath at 33 F. for 10 minutes. Then this cold piece and a second (identical, but untreated with ice-water) piece are immediately dropped in boiling water and kept there for /2 hour. The two pieces are then removed and tumble dried. Tumble drying in laboratory is usually accomplished in a conventional domestic clothes dryer for 30 minutes at about F. As shown in Table I, similar fabrics are prepared and then processed in the same Way. Properties of the various fabrics so obtained are shown on Table II.

TABLE I.FABRIC CONSTRUCTION Fabric Filament Stitch Quality in Length of No. Fabric Layout Composition 1 Design inches 1 yfilfil in inc es 3 J Front bar: 30 denier, 14 bicomponent trilobal filament yarn 66/]66/61 2-3, 1-0 5 54 \Back bar: 30 denier, 10 monocomponent trilobal filament yarn 66 38. 5 Front bar-same as fabric 5 55. 5 Back bar-same as fabric #1"... 39. 25 {Front barsame as fabric #1 7 57. 5 Back bar-same as fabric #1.- 41.0

1 66//66/6I= Poly(hexamethylene adipamide) in the sheath (50% of filament weight) and a copolyamide of hexamethylene adipamide with hexamethylene isophthalamide (70:30 weight ratio of the respective units) in the core (50% of the filament weight); 66=

Poly(hexamethylene adipamide); 66//66/6=Poly(hexamethylene adipamide) in the sheath (50% amide of hexamethylene adipamide with caproamide (7 :30 weight ratio of the respective units) 2 Quality is the distance occupied by a 480 course rack. 3 Length 0' yarn required to form a 480 course rack.

of filament weight) and a copolyin the core (50% of filament weight NOTE: It should be noted that for eac 1 fabric, the yarn comprising bicomponent filaments forms a knit loop larger than the knit loop of monocomponent filaments, since the length of bicomponent filament yarn required to form a 480 course rack is greater than the length of monoeomponent yarn required to form a 480 course rack.

TABLE II.-F.ABRIC PROPERTIES Greige Fabric After Finishing Process A. After Finishing Process B Fiagoric Thickness, Weight, Bulk, Thickness, Weight, Bulk, Thickness, Weight, Bulk,

Mils Oz./sq. yd. cc./gm. MllS Oz./sq. yd. ccJgm. Mils 0z./sq. yd. cc./gm.

Similar results are achieved with a fabric comprising front bar yarn of filaments consisting essentially of poly (hexamethylene adipamide) in the sheath (50% of filament weight) and a core (50% of filament weight) of a copolymer of hexamethylene adipaimide with hexamethylene sebacamide (70:30 weight ratio of the respective units).

Finishing Process A is as described above comprising a freeze treatment directly followed by a hot treatment and then tumble drying. Fnishing Process B is the same as Finishing Process A except that no freeze treatment is effected.

Both fabrics are highly satisfactory but that processed according to Process A not only has superior bulk, thickness, and cover at a given weight, but also unexpectedly has a most attractive cotton-like appearance and texture. Furthermore, when each of the fabrics has subsequently been heat set, bleached and finally dried, they show a two-way elongation-potential (stretch) that is more than 50% greater (both in the wale direction and in the course direction) than the two-way elongation-potential of a conventional tricot fabric. The fabrics processed according to process A, however, exhibit better two-way elongation-potential than do the fabrics processed according to Process B.

Example II Seven skeins are provided of 15 denier, one (round cross section) bicomponent filament =yarn, each filament being of sheath-core construction with a sheath of essentially poly-(hexamethylene adipamide) (50% of filament weight) and a core (50% of filament weight) of essentially a copolyamide of hexamethylene adipamide with hexamethylene sebacarnide (70:30 weight ratio of respective units). The length of each skein is measured under zero tension.

Five of these skeins are added to a hot-water bath at 140 F. and 'kept at 140 F. for /2 hour. Then one skein is taken out, and the water-bath is raised to 160 F. and kept at 160 F. for /2 hour. Next, a second skein is taken out, and the water bath is raised to 180 F. and kept at 180 F. for /2 hour. Then a third skein is taken out, and the water bath is raised to 200 F. and kept at 200 F. for /2 hour. A sixth skein is kept in ice for /2 hour. Finally, a fourth skein is removed from the water bath, and the water bath is raised to the boil.

Then a seventh skein along with the sixth skein is placed in the boiling water bath which contains three skeins: Nos. 5, 6 and 7. The three skeins are taken out of the water bath at the end of a /2 hour. The length of each of the seven skeins are measured after each is removed from the hot-water bath. The amount the skeins are reduced in length, i.e., from one end to the other, indicates the degree of crimping which has occurred. Table III shows the results of all measurements.

1 Added at room temp. I Added aiter freeze treatment.

It is significant that skein 5, which has been gradually brought up to the boil, undergoes a reduction in length of only 19.6% whereas skein 6, which has been rapidly plunged into boiling water, undergoes a reduction in length of 27.0%. Even more significantly, skein 7 which has first been thoroughly chilled and then plunged into boiling water undergoes a reduction in length of 35.8%.

The warp-knitted fabrics of the invention are useful for undergarments, sleepwear, gloves, sport shirts, and other types of apparel, as well as for knit hosiery.

Many other equivalent modifications will be apparent to those skilled in the art and, therefore, this invention is not intended to be limited except as indicated in the appended claims.

What is claimed is:

1. In a process for crimping a synthetic yarn composed of two-component filaments, said filaments having a latent capacity to crimp when treated by hot wet processing conditions, by the step of exposing said filaments while under essentially no tension to a heated aqueous fluid at a temperature of at least about C.; the improvement, for increasing the bulk of the crimped yarn, comprising cooling the yarn in the presence of water to below about 10 C. immediately prior to said exposure to the heated aqueous fluid.

2. Process according to claim 1 wherein the yarn is in the form of a knit fabric.

3. Process according to claim 1 wherein the cooling of the yarn is conducted in an ice-water bath at about 0 C. or below.

4. Process according to claim 1 wherein the yarn is completely immersed in said aqueous fluid immediately after cooling, thereby raising the temperature of the filaments to at least about 100 C. essentially simultaneously.

5. Process according to claim 1 wherein the twocomponent filaments are sheath-core filaments, the sheath comprising polyhexamethylene adiparnide and the core comprising a copolymer of hexamethylene adipamide and .hexamethylene isophthalamide.

References Cited UNITED STATES PATENTS 2,289,377 7/1942 Miles 8130.1 2,880,056 3/1959 Carr et a1. 264168 2,931,091 4/1960 Breen 28-72 3,017,686 1/1962 Breen et a1. 161-180 3,041,861 7/1962 Kasey 66195 MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Assistant Examiner.

Claims

1. IN A PROCESS FOR CRIMPING A SYNTHETIC YARN COMPOSED OF TWO-COMPONENT FILAMENTS, SAID FILAMENTS HAVING A LATENT CAPACITY TO CRIMP WHEN TREATED BY HOT WET PROCESSING CONDITIONS, BY THE STEP OF EXPOSING SAID FILAMENTS WHILE UNDER ESSENTIALLY NO TENSION TO A HEATED AQUEOUS FLUID AT A TEMPERATURE OF AT LEAST ABOUT 100*C.; THE IMPROVEMENT, FOR INCREASING THE BULK OF THE CRIMPED YARN,