US3046082A - Viscose process for the manufacture of low-shrink rayon - Google Patents

Description

July 24, 1962 R. L. MITCHELL ETAL 3,045,082

VISCOSE PROCESS FOR THE MANUFACTURE OF LOW-SHRINK RAYON Filed Dec. 27, 1960 L L E wmw STIT S m fl 5 TANHKW TN mm z m Wm w 3% @mm Mt oziwmo 2 M 6255 2 m G 2 @2522; @2223 53% oh @259; wzjdza 92 Q wzfiiim -ma wziSo 295% 55x5 E355 :2; D D D @2225 1055b 00 x lj 3,04%,082 Patented July 24, 1952 3,046,032 VISCGSE PRQCESS FOR THE MANUFACTURE OF LZBW-SHRRNK RAYON Reid Logan Mitchell and Delrnont K. Smith, Morristown,

and Ralph C. Welton, Morris Plains, N.J., assignors to Rayonier Incorporated, Shelton, Wash, a corporation of Delaware Filed Dec. 27, 1960, Ser. No. 78,779 7 Claims. ((11. 18-54) This invention relates to the viscose process, and has for its object the provision of an improved regenerated filament and staple fiber from which low-shrinking fabrics can be formed, and an improved process for producing the filaments and staple fibers. The invention produces regenerated cellulose filaments (known as rayon) that shrink less than cotton which may be considered practically shrink-free only after sanforia ng. This is accomplished without sacrificing the desirable qualities of rayon, such as high strength, flex and abrasion toughness,

easy dyeability, moisture absorbency, good color, soft hand, excellent uniformity, etc.

Numerous attempts have been made previously to produce an acceptable washable rayon, but such attempts have failed, due either to the fact that freedom from progressive shrinkage was not obtained or because the shrinkresistant character was accompanied by deterioration in other properties that rendered the fiber unusable. Such low-shrink rayon as made with resin applications or other devices has been impracticable because of brittleness, poor hand, and low strength and wear resistance. The invention overcomes the difficulties which have made the production of washable rayon heretofore impracticable. The improved rayon can be subjected to repeated and severe laundering with practically no shrinkage and without sacficing the other desirable properties of rayon.

In the course of our experimental investigations we discovered a process for producing low-shrink filaments and staple fibers which can be formed into washable fabrics having amazing dimensional stability in laundering. The invention is based upon a system of regenerative-fixing subsequent to a very high amount of primary stretch followed by complete relaxation.

The invention is carried out by the spinning of viscose under conditions which result in filaments having an appreciable amount of skin, most advantageously by producing filaments which are nearly or entirely allskin, and to this end the spinning is under preferred conditions of retarded regeneration needed to produce the desired skin effect. The viscose filaments are spun into an acid regenerating bath and are subjected as soon as possible to a primary stretch of at least 90%, preferably a multistage stretch while in contact with strong acid spin bath carryover, at a preferred temperature of from to 70 C., and the filaments are then subjected to a secondary stretch of at least 20% in a dilute acid bath to complete regeneration. The completely regenerated filamenfs are subject to a relaxation treatment in a suitable liquid medium which causes the filaments to swell, such as by immersion in a hot dilute alkaline solution of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium sulfide, or potassium thiocyanate. This relaxation treatment, accompanied by the entire controlled and progressive stretching, removes any internal structural imbalances that would contribute to the capacity of the filaments to shrink in water as in laundering. When staple fibers are to be formed which is an important variation ofrthe invention, the regenerated filaments prior to Washing are cut into staple fibers and the mass of such fibers is washed and then immersed, preferably in a hot dilute solution of sodium hydroxide for a shorttime. A preferred treatment is to immerse the fibers in an aqueous solution containing about 1% sodium hydroxide at about 90 C. for a short time, say, about one to five minutes, and then wash and finish the filaments in the conventional manner. In carrying out a process of the invention, we may use any suitable viscose composition in any of the Well known procedures for forming rayon filaments having a structure that is substantially all-skin. The types of acid regenerating spin baths widely used are satisfactory such as a modified Mueller bath, preferably under conditions when either the viscose or the spin bath contains an active regeneration retardant to insure the formation of an effective high proportion of skin.

It is preferred, in forming the viscose, to use cellulose xanthate having a uniform chain length at a degree of polymerization of from 300 to 800, derived from such cellulose as, for example, Rayocord-X, Cordenier-J, Cor denier-X, of Rayonier Incorporated, or other high-alpha cellulose pulps, prehydrolyzed kraft, cotton linters, resinfree pulp, cold-caustic refined pulp, high purity pulp of a high degree of polymerization (DP) and uniform chain length, and preoxidized pulp of high purity low DP and uniform chain length.

The process may be carried out with conventional viscose compositions comprising about 7.5% of cellulose and 6.5% of sodium hydroxide, or in any suitable proportions of cellulose to sodium hydroxide varying from 4% to 13% of cellulose and from 5% to 13% of sodium hydroxide such as the following:

5.0% cellulose and 5.0% caustic soda 6.0% cellulose and 5.0% caustic soda 6.5% cellulose and 7.5% caustic soda 7.5% cellulose and 6.5% caustic soda 8.0% cellulose and 7.0% caustic soda 9.0% cellulose and 6.0% caustic soda 9.6% cellulose and 5.0% caustic soda 10.0% cellulose and 5.0% caustic soda 10.0% cellulose and 7.0% caustic soda 13.0% cellulose and 13.0% caustic soda The viscose solution may be prepared according to the usual practice to have a salt (sodium chloride) index varying from 4 to 20, by xanthating the alkali cellulose with the desired amount of carbon bisulfide, say, about of the bisulfide. One may xanthate with the usual 34% of carbon bisulfide and then add to the mixed viscose an additional amount of carbon bisulfide to bring it to the desired sodium chloride index. It is also preferred to spin the viscose into a spin-bath containing from 7 to 10% of sulfuric acid (H 80 at a temperature of from to C., and to stretch the filaments under controlled conditions while in contact with the spin-bath or spin-bath carryover. When the usual type of acid-spin bath is used there are advantages in reducing the salt index, say from 14-20 to 10-12, the H in the spin bath from 913% to 710%, and the ZnSO from 6-12% to 1-6%.

The copending patent application of Mitchell, Berry and Wadman, Serial No. 810,991, filed May 5, 1959, and now Patent No. 2,942,931, describes the addition to viscose of physical mixtures of polyethylene glycol and dimethylamine, preferably in equal amounts of from 0.05 to 0.5% each based on the weight of the viscose to control the regeneration and produce all-skin filaments at especially attractive hi h windup speeds. We may use the process of said patent application up to and including the initial or primary stretch.

The spinning operation is carried out in the process and a suitable acid bath to stretch the filaments initially while in contact with the spin bath at least preferaby about but usually not over about Then the filaments are led into a dilute hot acid. bath containing from 1-6%, preferably about 4%, of sulfuric acid at from 80 C. to 100 0, preferably about 90 C., to stretch them an additional 5% to 50%, preferably about 30%, to fix the crystal structure and to complete regeneration. This dilute hot bath is uesd to dilute the filament salt content to permit further stretch and to decompose and remove the last traces of xanthates. It merely tolerates the adhering or residual salts from the primary spin bath as the important agent is the hot dilute sulfuric acid.

The regenerated filaments may be superficially washed with hot water and subjected to the relaxation treatment. After washing they may be cut into staple fibers, opened,

washed and contacted with the swelling agent, for example dilute caustic solution containing from 0.1% to 2%, preferably about 1%, of sodium hydroxide, at a temperature varying from 80 C. to 100 C. for a short time, say, about one to five minutes to effect complete relaxation. Solutions of other swelling agents may be used as follows: potassium hydroxide 1.4%, lithium hydroxide 0.6%, sodium carbonate sodium sulfide 3.0% and potassium thiocyanate 3.0%

The accompanying drawing is a fiow sheet illustrating a typical operation carried out for the production of staple fibers according to the invention. It is to be understood that in the production of continuous filaments the cutting operation is to be omitted.

The following examples illustrate operations carried out in accordance with the process of our invention to produce the improved washable and low-shrink regenerated filaments:

Example I A viscose of 7.5% cellulose and 6.5% sodium hydroxide content was prepared from Cordenier-J wood pulp containing 96.6 alpha cellulose, having an intrinsic viscosity of 6.0, degree of polymerization of 1140, and General Electric brightness of 89. The viscose, modified by addition at the mixing stage of 0.1% (based on the Weight of the viscose) dimethylamine and 0.1% polyethylene glycol (M.W. 1540), was extruded at 10.0 sodium chloride index through an 1100-hole spinnere'tte into a spin bath comprising 7.8% sulfuric acid, 16% sodium sulfate and 6.0% zinc sulfate. The filaments were led through a bath-fed tube for 26 inches, combined with other lIOO-filament yarn ends and with strong primary bath still clinging thereto given a 5-stage progressive primary stretch of 100% with tension build-up to about one gram/denier maximum while still in an incompletely regenerated, plastic state. The filaments were then led into a dilute, 4% sulfuric acid bath at 90 C. to impart a secondary stretch of an additional 30% at a tension of about one g./denier and to fix by completing regeneration. The regenerated filaments were led onto a thread advancing drum showered with hot water to provide a preliminary wash, and then under a low tension of about 0.1 g./ denier wound up at 90 meters/minut on a cone with zero twist.

Cones of this yarn were pulled as a tow into a staple cutter to convert the tow into 1 /2 inch length staple, flowed down a stepwise chute with water to open, collected on a screen for washing and finishing.

The out staple of 1 /2 inch length and 1 /2 denier per filament was placed in a wire basket, washed by displacement through the mat to remove acid. The mat of staple was then given a complete relaxation by displacement flow-through of 1% sodium hydroxide solution at 90 C. for one minute, then rewashed. A. finishing wash was then given in water containing 0.1% S0 then centrifuged from an oil/water emulsion to leave 0.2% of a controlled friction finish in the staple (Nopco RSF #18). The staple was then dried in a hot air steam.

Single filaments of this staple tested 4.0 grams per denier conditioned at 60% RH. and 75 F, 3.0 grams per denier wet and had an elongation of 22.0% when conditioned by subjecting them to 60% relative humidity at for a sufiicient time to bring the filaments to equilibrium. It was carded and spun into 30s and 40s count yarn, then woven into a fabric with ends/inch, and 80 picks/inch. The fabric was singed, desized, scoured and mildly bleached in conventional operations.

This fabric was subjected to a 50-cycle laundering evaluation alongside controls of similar construction fabric made from cotton, regular rayon, commercial high strength tire yarn-type rayon, high wet-modulus rayon, etc.

Dimensional stability of the fibers of the invention were remarkably better than any of the other fibers tested as illustrated by values found for fabric shrinkage. Whereas normal rayon showed a cumulative shrinkage of 7%, commercial high tenacity tire cord type rayon 7l1%, high wet-modulus rayon 3-4%, cotton 2%, the fabric made from the multi-stage-stretch-and-relaxed fibers did not shrink, but showed a net positive dimension change of +02%. Strength of fabric, toughness and abrasion resistance were higher for the rayon of this invention than for any of the other rayons tested both before and after laundering. Wet strength was roughly equivalent to that for cotton even after the severe laundering, whereas hand was much superior.

Example I! An economical viscose composition containing 9.6% cellulose and 5.0% sodium hydroxide was prepared from Rayofiber-G wood pulp cellulose containing 96% alpha cellulose, having a cuene intrinsic viscosity 3.8, degree of polymerization of 750 and General Electric instrument brightness of 93. The viscose was modified by addition of the regeneration retardants, spun under staple conditions, given multi-stage primary stretch prior to regenerative fixing, converted into staple, and given relaxation in the manner outlined in Example I.

The finished single filament strengths were 3.8 grams per denier conditioned as in Example I, and 2.8 grams per denier wet with 21.0% elongation. The color of the filaments was somewhat whiter than the filaments made in Example l, due to the pulp properties, and had enhanced dyeing characteristics of faster exhaustion and deep shade development.

Fabric made therefrom with 45s count yarn in 136 x 64 construction laundered in a 50-cycle sequence alongside controls in identical fabric construction from fibers of cotton, regular rayon, etc., showed remarkably superior dimensional stability in the same order as fabrics of more open construction described in Example 1. Whereas no shrinkage occurred in the fabric of the invention, other Example III Staple fiber produced as described in Example I was spun into a 16s count yarn and Woven into a linen-type fabric at 50 ends/inch and 40 picks/inch. Following singeing, desizing, scouring and bleaching, this fabric was subjected to a SO-cycle laundering sequence in comparison with several similar fabrics made from cotton, normal rayon staple and high wet-modulus rayon. The launderability of the fabric of this invention was outstanding, with shrinkage of less than 1% compared with 2% for cotton, 8% for regular rayon and 4% for the high wet-modulus rayon. Wear characteristics, as shown by accelerated laboratory tests and actual extended use were very good for this rayon, much superior to either the regular or high wet-modulus rayons.

Example IV The 80 x 80 fabric of Example I was singed, desized and dried. This fabric was then padded with a solution containing 4% of methylated melamine resin with 15% MgCl .6H O catalyst (based on resin Weight) and 0.2%

v ly embrittled and unusable.

Example V Staple fiber of Example I was converted into 20s twoply yarn and knitted in mens socks using a 160-needle set-up. Following scouring and dyeing the socks were looped and boarded. These socks along with comparable socks made from cotton, regular rayon, several commercial improved rayons and high wet-modulus rayon were subjected to laundering and actual wear tests over a period of several weeks. The socks from staple fiber of this invention invariably performed in a very superior manner compared with any of the other rayons, and were more or less equivalent to the cotton socks in all regards including both size stability and wear.

While not wishing to predicate the invention on any special theory, it is our belief that the production of fibers which can be converted into fabrics which are dimensionally stable during repeated severe laundering and exhibit no progressive shrinkage is based on the sequence of processing embodying at least three essential steps: (1) high multistage primary stretch while the fiber is in a semi-plastic and pliable state prior to fixing-regeneration, (2) a hot acid regeneration step designed to completely fix the established oriented structure prior to any relaxation, and (3) complete relaxation through use of a swelling treatment.

This application is a continuation-in-part of our application Serial No. 848,512, filed October 26, 1959, and now abandoned.

We claim:

1. The improvement in the viscose process which comprises spinning viscose in an acid regenerating spin bath and stretching the filaments at least 90% in a primary stage while in contact with spin bath, then contacting the filaments which were not completely regenerated in the primary stage with a hot acid bath containing from 1% to 6% of sulfuric acid while stretching the filaments an additional 5% to 50% to completely fix and regenerate the filaments. prior to any relaxation and then subsequently immersing the filaments in an aqueous solution containing a swelling agent at an elevated temperature while the filaments are free to shrink to effect complete relaxation of the filaments producing washable filaments having practically no shrinkage and which can be converted into yarns and woven fabrics which exhibit dimensional stability during repeated severe laundering.

2. The improvement in the viscose process defined in claim 1, which comprises incorporating a regeneration retardant in the viscose to produce all-skin filaments, spinning the filaments in the primary stage at a temperature of from 40 to C. and fixing the filaments in the secondary stage in acid bath at a temperature in the range of from to 100 C.

3. The improvement in the viscose process defined in claim 2 in which the regeneration retardant is a physical mixture of about 0.2% each of polyethylene glycol and dirnethylamine.

4. The improvement in the viscose process defined in claim 1 in which the completely regenerated filaments are cut into staple fibers and said staple fibers are immersed into a solution containing from 0.1 to 2% of sodium hydroxide for about one minute at a temperature of about C.

5. The improvement in the viscose process defined in claim 1 in which the swelling agent is a compound of the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium sulfide and potassium thiocyanate in aqueous solution in amounts of about 1%, 1.4%, 0.6%, 10%, 3% and 3% respectively.

6. The improvement in the viscose process which comprises spinning the viscose in a hot acid spin bath and stretching the filaments at least 90% while in contact with the spin bath or spin bath carryover to produce filaments containing an appreciable portion of skin, then contacting the filaments with a solution containing about 4% of sulfuric acid while stretching the filaments an additional 20% to eliminate the residual xan'thate and effect complete regeneration, washing the filaments, and then contacting the filaments at zero tension while free to shrink with an aqueous swelling solution containing an alkali metal hydroxide at about 90 C. to eflect complete relaxation.

7. The improvement in the viscose process defined in claim 6 which comprises cutting the completely regenerated and washed filaments into staple fibers and then immersing the staple fibers into a dilute sodium hydroxide solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,491,938 Schlosser Dec. 20, 1949 2,611,928 Merion Sept. 30, 1952 2,952,508 Mitchell Sept. 13, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,046,082 July 24, 1962 Reid Logan Mitchell et al It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columnd, line 58, for "subject" read subjected column 3, llne 5, for "uesd" read used line 70, for

"steam" re ad stream column 4, line 1, for "75" read 75 F. column 5, line 7, for "useing" read using Signed and sealed this 6th day of November 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

Claims (1)

1. THE IMPROVEMENT IN THE VISCOSE PROCESS WHICH COMPRISES SPINNING VISCOSE IN AN ACID REGENERATING SPIN BATH AND STRETCHING THE FILAMENTS AT LEAST 90% IN A PRIMARY STAGE WHILE IN CONTACT WITH SPIN BATH, THEN CONTACTING THE FILAMENTS WHICH WERE NOT COMPLETELY REGENERATED IN THE PRIMARY STAGE WITH A HOT ACID BATH CONTAINING FROM 1% TO 6% OF SULFURIC ACID WHILE STRETCHING THE FILAMENTS AN ADDITIONAL 5% TO 50% TO COMPLETELY FIX AND REGENERATE THE FILAMENTS PRIOR TO ANY RELAXATION AND THEN SUBSEQUENTLY IMMERSING THE FILAMENTS IN AN AQUEOUS SOLUTION CONTAINING A SWELLING AGENT AT AN ELEVATED TEMPERATURE WHILE THE FILAMENTS ARE FREE TO SHRINK TO EFFECT COMPLETE RELAXATION OF THE FILAMENTS PRODUCING WASHABLE FILAMENTS HAVING PRACTICALLY NO SHRINKAGE AND WHICH CAN BE CONVERTED INTO YARNS AND WOVEN FABRICS WHICH EXHIBIT DIMENSIONAL STABILITY DURING REPEATED SEVERE LAUNDERING.

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