US2237844A - Method of washing threadlike structures - Google Patents

Description

patented Apr. 8, 1941 METHOD OF WASHING THREADLIKE STRUCTURES Frank B. Ridgway, Newark, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, D'eL, a corporation of Delaware No Drawing.

Application September 25, 1937,

Serial No. 165,779

2 Claims.

This invention relates to a process of washing thread-like structures. More particularly, the invention relates to the washing of packages of artificial threads, yarns, filaments, straw, horsehair or the like.

According to one method of producing regenerated cellulose threads by the viscose process, the freshly coagulated, partially regenerated threads are wound on perforated bobbins rotating at a substantially constant peripheral speed. The rayon package so produced is Washed with soft water to free it from acids, salts and other impurities, usually by the pressure method, for instance by mounting the perforated bobbin containing the cake on a suitable holding device and forcing the washing liquor outwardly through the cake.

Increasing the size of the yarn packages and increasing the tension under which the yarn is wound on the perforated bobbins has made it extremely difficult to wash economically and without deleteriously affecting the yarn. For example, when rayon is wound under a tension of 0.6, 0.1 0.8 or even 1 gram per denier on to perforated bobbins in the form of cross wound packages containing 1, 2, 3, or even more pounds of yarn, the problem becomes acute.

The desirability of producing large cakes is readily apparent since there are fewer units to handle in the production of a given amount of yarn. This economy, however, is at once lost because of the prohibitive amount of water needed to free the package from acid, salts and the like and up to the present time no adequate solution of this problem has been realized.

It is therefore an object of this invention to provide an improved process for economically washing packages of regenerated cellulose threads and especially thick, dense packages of yarn wound on perforated bobbins. Other objects will be apparent from the description that follows.

These objects are accomplished in general by reusing the water which has been forced through the bobbin cake after the water coining through the cake has become substantially neutral. More specifically, the invention comprises reusing at least 50% and even as much as 80% of the water which is forced through the package since it has been found that after washing for less than 50% and even only 10% to 20% of the total washing time, the water coming from; the cake is substantially neutral or even slightly alkaline, although the yarn comprising the cake is at this period still decidedly acid.

Since certain portions of the cake are much tighter than other portions, especially in the case of bobbins of acid yarn wound up under high tension, the washing time must be sufficiently long to remove the last trace of acid from these tight portions and it requires a long time for the water to penetrate these portions and completely remove the acid. During that part of the cycle which is necessary for removing traces of acid from these very tight portions of the package, the amount of acid removed, compared to the water flow, is so slight that the water does not become appreciably acid.

The water used may be neutral or slightly alkaline. If alkaline, the alkalinity may be due to the fact that the water used is slightly alkaline in its natural state, or alkalinity may be induced by adding an alkaline material such as NaI-ICO: or NHiOH, or both causes may contribute to alkalinity.

The water issuing from the cake when it is first put on the wash rack is very high in acid and salt concentrations, but these concentrations drop very rapidly as the washing progresses. It has now been found, for instance, that if it requires 12 hours to wash a bobbin cake of yarn acid free with a water flow through the cake of about 2 gallons per hour, the wash water coming through the cake is substantially acid free at the end of the first hour of washing and that by the end of the second hour the water issuing from the cake is neutral or even slightly alkaline (due to the natural and/or induced alkalinity of the water used). Not only is the acid substantially all removed during the first hour of washing, but salts and especially iron salts are also largely eliminated during this period.

The following specific example will serve to more clearly illustrate this invention although it is to be understood that this example is given for illustrative purposes only and is not intended to be limitative in any way.

Example A regenerated cellulose thread of 275 denier- 120 filaments is spun under a total tension of 190 grams, and collected on a perforated spinning bobbin 6 inches in diameter and 10 /2 inches long for such time as to form a cake of 1.3 pounds. The yarn is laid down to form a cake of substantially uniform thickness except for the beveled ends of the cake, which are of uniform slope and cover the end rows of perforations of the bobbin only sufficiently to prevent excessive flow of water under the ends of the yarn package. The cake of yarn so produced is mounted on a suitable wash spindle and water admitted to the interior of the perforated bobbin under a pressure of about 45 pounds or so that about 1 gallons of water pass through the cake in an hours time. During the first 2 hours of washing, the water passing through the cake is Wasted to the sewer or if desired, the first washings ma be conducted to a recovery system wherein the acid, salts and any other coagulating bath ingredients contained in the wash water may be recovered. Thereafter the washings are returned to the supply tank and used again. The cake was found to be acid free by the end of the ninth hour, but the washing was continued 2 hours longer as a safety precaution. The amount of water actually consumed in washing this yarn package containing 1.3 pounds was only 3-gallons, or 2.3 gallons per pound of yarn. The total amount of water put through the cake, however, was 16.5 or nearly 13 gallons per pound of yarn. A similar test using fresh water throughout the washing cycle also consumed a total of 16.5 gallons or 13 gallons per pound since the yarn package was freed from acid no sooner, as was determined by pouring niethylorange on the cake from time to time during the washing process.

By this process of recirculating and reusing the wash water, only about to the water consumed by the best of the prior art methods is needed to wash rayon bobbin cakes free from acid and a still greater improvement is effected when compared with prior art methods using a large flow of water through the cakes. Rayon packages containing 1, 2 or even 3 pounds of yarn can be washed in accordance with this invention with very low water consumption, being no more than 7 or 8 gallons per pound of yarn and generally no more than 5 gallons per pound of yarn. As is apparent, this is a very decided saving in the cost of producing regenerated cellulose thread.

While this invention is especially useful in connection with the washing of very large bobbins of regenerated cellulose yarn which have been wound under relatively high tension, the invention is not so limited and may be used with good results in the washing of smaller yarn packages, whether the yarn is wound on bobbins or other similar supports, or wound by the centrifugal bucket spinning process. Furthermore, the invention need not be confined to the pressure washing of yarn packages, for it is applicable to other methods of washing, such as for instance centrifugal washing or vacuum washing. In fact, quite probably as great savings can be effected through the use of this process in connection with other methods of washing as by pressure washing.

This invention has been described with reference to the washing of regenerated cellulose thread produced by the viscose process although it is equally applicable to the washing of other threadlike structures collected in package form, for instance regenerated cellulose threads or the like produced by the cuprammonium cellulose process.

The water which is reused can, of course, pass through the same bobbin or other package as it initially passed through or through another package.

It is to be understood that all other variations or modifications which conform to the spirit of the invention are intended to be included within the scope of the claims.

I claim:

1. The process comprising forcing acid-free water through acid cakes of regenerated cellulose thread, discarding the water issuing from said acid cakes until said water issuing from said acid cakes is substantially neutral at which point said cakes are still substantially acid, and thereafter reusing the water issuing from said acid cakes for further removal of acid from said acid cakes.

2. The process comprising forcing acid-free water through acid cakes of regenerated cellulose thread, discarding the water issuing from said acid cakes until said water issuing from said acid cakes is substantially neutral at which point said cakes are still substantially acid, and thereafter recirculating the water issuing from said acid cakes through said acid cakes until substantially complete removal of acid from said acid cakes is effected.

FRANK B. RIDGWAY.