US2566455A - Process for the continuous manufacture of viscose products - Google Patents

Description

Patented Sept. 4, 1951 PROCESS FOR THE CONTINUOUS MANU- FACTURIE F 'VISCOSE' PRODUCTS Robert Levison, Ede, and Barend Jan, Blomberg, Velp, Netherlands, assignors to American Enka Corporation, Enka, N. 0., a corporation of Delaware No Drawing. Application March 16, 1949, Serial ,No. 81,844. In the Netherlands May 7, 1948 'The present invention relatesto a continuous process for manufacturing viscose products, and

more particularly to. a process in which freshly formed viscose threads are aftertreated by passing a large number of such threads through treating zones or in parallel relationship and in a sub- ,stantially linear direction through successive ,treating baths'at such high speeds that the treatment time in each individual zone or bath is only afew seconds.

When' manufacturing products from viscose,

ous aftertreatments for the purpose of obtaininggail end-product consisting of pure, cellulose hydrate, which has been completely freed of residues formed during the decomposition of the viscose and freed from spinbath constituents and from sulphur and other impurities.

In manufacturing viscose rayon according to the discontinuous process in which the threads are coagulated and partially regenerated in the spinbath, the threads containing the acids and salts from the spinbathare collected on bobbins or in pots and thereafter allowed to remain for several hours so that complete regeneration of the cellulose, or better said, the decomposition of the xanthate is effected. In certain cases, after the threads'have left the spinbath they are subjected to further regeneration in a second bath containing sulphuric acid, and, if desired, sodium sulphate, and then collected on bobbins or in pots.

However, even in this case it is necessary to store the packages for some time in order to assure complete decomposition of th xanthate.

After the packages have been stored for a sufiixcie'nt time, they are pressure and/or vacuum washed with water to remove the acid and salts and thereafter desulphurized, and if necessary,

bleached, and finally dried; In this discontinuous process since the threads have been completely "regenerated prior to washing, desulphurizing and bleaching, no problem existed with respect to the desulphurizing and bleaching operation. The

threads were properly desulphurized and bleached to a pure white product. i

In the most widely used continuous system for the manufactureand aftertreatment of viscose threads, the threads are subjected to the various aftertreatments by passing them around thread- ;storage,othread-advancing devices in a multi- 4 Claims. (Chm-54) 2 plicity of convolutions. During their passage around the ,devices they are subjected to the required treatments, such as, partia1 decomposition, final decomposition, desulphurizing, bleaching and drying. However, even in this type of continuous process the time factor is not critical because the individual treatment operations consume, for example, from 40 seconds to one minute, which, if acid and washing treatments are given, are sufficient to effect proper desulphurization and bleaching.

In all of the known discontinuous processes, and the continuous processes with thread storage, during the preparation and aftertreatment of threads spun from viscose the decomposition of the xanthate was advanced by the liquid carried along by the thread from the original spinbath'; when the decomposition seemed insuflicient, complementary acid baths wer employed; Since, in these processes, time was no factor, it was not discovered that the sodium sulphate used in the baths or formed. during the decomposition of the xanthate. had a disadvantageous efiect on the decomposition of the thread, and therefore e steps were taken to remove the salts. As a matter of fact, it is well known that freshly spun threads which are only partially decomposed require a certain amount of salt in the acid baths to prevent turgor-action, which is caused by swelling of the interior of the filaments to a greater extent than the exterior because of a skinlike formation at the exterior of the filaments. This turgescent swelling results in the threads bursting open and sticking together upon subsequent treatment with water. or dilute acid baths free of salt.

A more recently developed. continuous system for manufacturing rayon products is described and claimed in U. S. Patent No. 2,334,325, U. S. Patent No. 2,459,254, U. S. application Serial No. 18,408,,now U; S. Patent No. 2,539,980 and U. S.

application Serial No. 713,905, now U. S. Patent No. 2,513,057 (both assigned to the same assignee as the present application), French Patent No. 884,700 and Britain application Serial No. 9,912/47. This group of patents and applications relate to a high speed continuous process in which the threads are passed in parallel, linearly through successive treating baths at high rates of speed, for example, from meters per minute to meters or more per minute. This type of continuous spinning is very simple and considerably cheaper to install and maintain than the systems involving the storage devices. However, one disadvantage of this system is that due to the lack of space in a rayonmanufactur tions.

generated, i. e., the xanthate is not remains in the finished product whereby a yellow discoloration occurs. While it is necessary to have a certain amount of salt present during the decomposition, as soon as the decomposition of the xanthate has reached an advanced state, the salts should be washed out, because the presence of salt will appreciably delay further decomposition. of the last-remaining very'small amounts of xanthate residues. 7

Primarilyit was determined that the principal .aftertreatments, viz., complete decomposition of the xanthate and desulphurization are dependent on each other, in that, the desulphurizing proceeds more completely in direct relation to the degree of decomposition of the xanthate remaining in the threads. If the decomposition of the xanthate is not substantially complete or below a definite predetermined limit then the desulphurizing operation cannot be performed properly, i. e., all of the sulphur cannot be removed in the time allotted and this residual sulphur will show up in the final product which will lower thequality thereof. Onv the other hand, as soon as the decomposition of the xanthate has reached a very advanced stage, e. g., the xanthate ratio. falls-below .003 or preferably below .002, the desulphurization can be carried out in a reliable manner that is completely satisfactory for all practical purposes. Prior to the present invention when using one of the normal desulphurizing agents such as sodium sulphide, it has notbeen possible to remove all of the sulphur in a continuous process involving high speed treating. operations. Because of this, continuous spinning of this type has not been practical, and has therefore been slow in its commercial development.

v It is therefore-the object of the present invention. to provide a particular type of aftertreatment or series of aftertreatments that can be utilized effectively in this more recently developed continuousspinning system.

Another object, of the invention is to decompose the residual xanthate in. the freshly spun threads-in several seconds but so completely that the threads can be immediately desulphurized so thoroughly within; a very few seconds that nosulphurdeposits can be detected in the final product. V u

A still-further object of the invention is to employ certain materials in: the: aftertreatment baths that will accelerate the decomposition of the last remaining xanthate in the threads to quickly lower the xanthateratio below a critical point, i. e., below .003 or .002. (The'xanthate ratio, i. e., the ratio of the number of residual xanthate groups to the total number of cellulose groups (CsHmOsJ' is'determined by any of the well known chemical methods. One suit able determinative method is described in Leroy H; Smith, Synthetic Fiber Developments in Germany 1946, pages 201-204.)

Other objects and advantages of the invention will become apparent from the following detailed description.

In practicing according to the present invention and utilizing high. spinning speedsin which individual treatments are effected in less than 10 seconds, it was first determined that after the thread has been coagulated and partially regenerated in a normal sulphuric acid, salt-containing spinbath, the further decomposition of the xanthate "can be effectively accomplished by meansof a ,hot dilute acid bath containing sulphuric acid in a range of 0.5%6.0% and correspondingly 1.0% to 10% sodium sulphate, said bath being vmaintained at a temperature in the range of 60 to 95 C.

Bypassing the thread through such a hot dilute acid bath, it can be substantially completely regenerated in three or four seconds, although a small amount of residual undecomposed xanthate (X. R. about 0.02) does remain in. the

thread which must be removed prior. to desulphurization. It has been determined that the remaining amount of undecomposed xanthate can be removed or the xanthate ratio can be reduced below .003 in 3 or 4 seconds, after a thorough washing to remove the salts from the thread, by immediately passing the thread through a pure dilute sulphuric acid bath (not diluted spinbath) containing sodium. sulphate substantially below the bisulphate raltio,.i. e., for every mol of. sulphuric acid, less than 1 mol of sodium sulphate is used. This means thatthe molecular ratio of sodium sulphate to sulphuric acid is substantially less than 1:1. Therefore, it is necessary, for example, when using 3% sulphuric acid to take precautions thatthe salt content can never be as much as'4.3% sodium sulphate. Particularly good results have been achieved when using 4% sulphuric acid and 2% or less sodium sulphate, which corresponds to a molecularratio of 2.8:1. In this way thesalt content can always be maintained at a predetermined value below the bisulphate ratio because the threads being first washed and then treated with a'pure sulphuric acid bath as distinguished from a dilute spinba-th, the salt content can never increase asin the casewhere thethread containing salts is allowed to pass through the treatment bath wherein the salt content continually builds up.

Asan alternative procedure for treating'the thread in a dilute sulphuric acid bath containing sodium sulphate below the bisulphate ratio for the purpose of removing the remaining amount of undecomposed xanthate, the thread can be treated in a bath containing certain oxidizing decomposing agents, such as H202, KzSzOa, H0103, HC1O4, NaOCl, NaClO2, NaNOz. Dilute solutions .of-sodium hypochlorite or sodium chlorite were found to beparticularly ellective. When using solutions of sodium hypochlorite, the best concentration range is between 0.5% and 2%, and the solution ismaintained at room temperature. When using sodium chlorite, preferably in acid solutions, the best results are attained at a higher temperature, for example 70 0. although the bath having an acid concentration of from 0.5% to 6% and sodium sulphate in a concentration of 1.0% to 10%, said bath being maintained at a temperature of from 60 to 95 C., or the threads are subjected to further regeneration by the spin bath liquid retained in the threads, but in either case the xanthate ratio can only be lowered to about 0.02 which is insufficient to effect complete desulphurization in the time available. The threads are then washed with water or other suitable treating liquid to remove the salts therefrom. Next the threads are passed through a dilute pure sulphuric acid bath containing sodium sulphate below the bisulphate ratio or through a bath containing an oxidizing agent. This treatment lowers the xanthate ratio below the critical point, namely, below .002 or at least below .003. The thus treated threads are again washed by passing them through a water bath, and are then immediately desul'phurized and bleached in suc cessive baths, and finally dried. This process is a continuous one from the beginning to the end, and each of the treatment operations are effected in 3 or 4 seconds, or less, but in any case, never more than 10 seconds.

The invention is not limited to normal rayon such as 2.5 and 5 filament denier, but is also applicable to the preparation of thicker products made from viscose such as horsehair, ribbons, and films, and when the expression threads is used in the claims it is intended to cover these other said products.

Obviously, various modifications may be made without departing from the spirit and scope of the invention, e. g., it may not be necessary to utilize the washing step between the last decornposing bath and the desulphurizing bath, pro= vided some equivalent means is used to remove the acid such as by an expressing operation.

What is claimed is:

1. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lowering the xanthate ratio to about 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 C.-95 C. and containing a lower concentration of acid and salt thanthat of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing sulphuric acid and sodium sulphate below the bisulphate ratio, and again washing the threads and effecting substantially complete desulphurization, each of said treatments being effected in less than ten seconds.

2. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lower ing the xanthate ratio to about 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 6-95" C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remain ing xanthate in the threads to a Xanthate ratio below 0.003 by treating them in a solution con taining sulphuric acid in a concentration of 0.5%- 6.0% and sodium sulphate below the bisulphate ratio, and again washing the threads and eflecting substantially complete desulphurization, each of said treatments being effected in less than ten seconds.

3. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lowering the xanthate ratio to about 0.02, which insuiiicient to permit subsequent complete desulphunization, said second bath being maintained at a temperature in the range of 60 0-95" C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing about 4.0% sulphuric acid and less than 2.0% sodium sulphate, and again washing the threads effecting substantially complete desulphurization, each of said treatments being affected in less than ten seconds.

4. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is about three or four seconds thereby lowering the xanthate ratio to about 9.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 C.- C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing sulphuric acid and sodium sulphate below the bisulphate ratio, and again washing the threads and effecting substantially complete desulphurization, each of said treatments being effected in about three or four seconds.

ROBERT LEVISON. BARE-ND JAN BLONIBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,915,952 Richter et al June 27, 1933 2,309,072 Burkholder Jan. 19, 1943 2,427,993 McLellan Sept. 23, 1947

Claims (1)

1. A PROCESS FOR THE CONTINUOUS MANUFACTURE OF VISCOSE THREADS WHICH COMPRISES EXTRUDING A MULTIPLICITY OF THREADS THROUGH SPINNERETS INTO A COAGULATING BATH CONTAINING SULPHURIC ACID AND SALTS THEREOF, PASSING THE THREADS IN PARALLEL RELATIONSHIP LINEARLY THROUGH A SECOND BATH AT SUCH A HIGH SPEED THAT THE TIME OF PASSAGE THROUGH THE BATH IS LESS THAN TEN SECONDS THEREBY LOWERING THE XANTHATE RATIO TO ABOUT 0.02, WHICH IS INSUFFICIENT TO PERMIT SUBSEQUENT COMPLETE DESULPHURIZATION, SAID SECOND BATH BEING MAINTAINED AT A TEMPERATURE IN THE RANGE OF 60* C.-95* C. AND CONTAINING A LOWER CONCENTRATION OF ACID AND SALTS THAN THAT OF THE FIRST BATH, WASHING THE THREADS FREE OF SALTS, DECOMPOSING THE REMAINING XANTHATE IN THE THREADS TO A XANTHATE RATIO BELOW 0.003 BY TREATING THEM IN A SOLUTION CONTAINING SULPHURIC ACID AND SODIUM SULPHATE BELOW THE BISULPHATE RATIO, AND AGAIN WASHING THE THREADS AND EFFECTING SUBSTANTIALLY COMPLETE DESULPHURIZATION, EACH OF SAID TREATMENTS BEING EFFECTED IN LESS THAN TEN SECONDS.