US2064300A - Manufacture of artificial thread - Google Patents

Description

UNITED STATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL THREAD aware No Drawing. Application August 5, 1933, Serial No. 683,896

9 Claims.

This invention relates to the manufacture of 1% structures, such as yarns, filaments, horsehair, straw, film, sheets, caps, bands, tubefiah'd the like. More particularly, this invention relates to the process of purifying regenerated cellulose structures of the type mentioned and especially to that step in the purification procedure known as bleaching.

In the manufacture of regenerated cellulose Structures produced from viscose, a viscose solution is extruded into a coagulating and regenerating bath. Because of the chemical reactions which take place, the freshly formed regenerated structures contain large quantities of impurities and reaction products, most of which are objectionable and therefore normally removed. This is accomplished by purification treatments which contemplate desulphuring and bleaching the structures. The usual procedure is to wash the freshly produced regenerated cellulose structures to remove the adhering bath liquids and then subject the cellulose structures to a desulphuring treatment, whereby the sulphur and sulphur compounds are removed. Subsequent to the desulphuring treatment, the structures are washed, bleached and finished.

Complete and uniform removal of the impurities and reaction products require careful manipulation because the regenerated cellulose struc tures are easily degraded by too severe chemical treatments or by repeated handling or mechanical treatment, especially when an artificial thread constitutes the cellulose structure. The prior practice has been to carry out the purifying treatments of threads in the form of skeins. According to this procedure, the thread was reeled into skeins directly from the acid cake or from cakes which had been washed acid free or from cakes which had been washed acid free and dried. These skeins' were then processed through a series of baths, where they were desulphured, bleached, finished and dried.

When it was desired to produce packages, such as cones, cops, etc. skeins were inspected and backwound to spools and the spools in turn rewound.

Obviously, the production of a bleached package of artificial thread utilizing the skein process was a long, tedious operation, requiring skilled labor and furthermore it resulted in a definite degradation of the yarn both from mechanical handling and from severe chemical treatment, such as bleaching.

In copending application (Serial No. 432,263),

was,

now Patent 1,931,245, there is disclosed a package bleaching process which comprises treating cakes of regenerated cellulose threads prepared by the viscose process with a relatively strong alkaline bleach, for instance, a sodium hypochlorite solution containing 0.15% available chlorine and 0.05% sodium silicate. While this process permits the elimination of the costly skein treatment, it can be used only for a certain limited type of production which is not subject to rigid requirements in regard to uniformity. The alkaline bleach causes the thread to swell rapidly, thereby inhibiting the passage and penetration of the bleaching solution to the inner part of the package and as a result the outer layers of yarn in the package are subject to far greater bleaching action than are the inner layers.

It can be easily understood that no difiiculty is experienced in bleaching a single small denier strand of yarn even when a sodium hypochlorite bleach solution is used. The yarn swells of course, but since we are not dealing with a compact package, penetration is not a problem and the yarn is thoroughly bleached in a very short interval of time. However, when the thread is wound into a compact package which is dimcultly permeable even before the thread becomes swollen, the problem becomes very real and when the yarn packages are subject to drip treatment it becomes utterly impossible to get anything like uniform bleaching throughout various sections the cake.

Regenerated cellulose yarn which has not yet been dried to approach equilibrium is termed gel yarn. It has long been considered desirable to bleach the yarn in this condition because at this time the coloring matter is more easily discharged than when it has been fixed on the cellulose by drying. Heretofore, since gel yarn swells excessively when subjected to the commonly used sodium hypochlorite bleach, it has been impossible to obtain a uniformly bleached yarn when treated in package form, or if uniformity of color was obtained, it was only after seriously impairing the physical properties of that yarn more readily reached by the bleaching solution.

We have found that we can uniformly bleach artificial silk yarn wound as compact packages, such as centrifugaily spun cakes, hereafter referred to as cakes, by subjecting said cakes preferably after the desulfuring treatment and even 7 though in't'h g l state, to a bleach solution that will not appreciably swell the yarn and which therefore has a high degree of penetration and comprising a neutral aqueous solution to which small quantities of chlorine have been added, whereby bleached cakes are produced which may be wound directly into package form suitable for marketing, for example, a cone.

The nature and objects of the instant invention will become apparent from the following description and appended claims.

In accordance with the principles of this invention, the preferred embodiment contemplates subjecting cakes of artificial silk to water in which chlorine has been homogeneously distributed and which, for convenience, will be referred to as chlorine water. Insofar as the instant invention is concerned, the cakes may be given a preliminary drying but can be treated directly after being Washed acid free. The treatment may also be eifected bef re orjifterlthe desulpill lfiil llfiration.

The chlorine water bleach is preferably applied to the cakes by the drip process, but it is obvious that any other applying procedure may be employed, as vacuum, pressur omentrifueal treatment. Likewise, the'chlor'in e water bleach chiming one phase of this invention is not restricted for use with cakes only. It also may be used to treat a package of yarn on a bobbin, and other cellulosic structures.

The yarn which may be treated by the instant invention may be of the bright or low luster variety.

The composition of the bleaching solution may vary within wide limits. It may comprise water to which from 3 to or even more parts of chlorine per million parts of water have been added. Excellent results are secured by employing water to which 20 to 50 parts of chlorine per million parts of water have been added. It is to be understood, however, that as the concentration of the chlorine is increased, degradation of the yarn becomes noticeable.

The chlorine water bleaching solution may be easily and simply prepared. It can be prepared by bubbling chlorine directly into water. A suitable baflle arrangement can be installed to insure thorough mixing. The chlorine water bleach is best prepared with the aid of a metering device, such as anycommercial chlorinator, and preferably an automatic chlorinator, whereby the concentration of available chlorine in the water is maintained in proportion to the flow of the water to the point of application of the chlorine water bleach. This method of preparing the bleach solution makes it possible to very accurately control the concentration thereof. For instance, the concentration of chlorine in the water may be controlled to within plus or minus one part per million even over long periods of time.

The activity of a bleach is dependent upon the pH value of the solution and is at a maximum near or at the neutral point, i. e. a pH of 7. Thus, by preparing a chlorine water bleach at or near the neutral point, it is immaterial whether the bleaching is effected on cakes having a slightly alkaline or acid reaction. The activity of the bleach comes to a maximum or that of the virgin solution as the acid or alkali is washed from the threads, that is, the bleaching activity is greater as the pH of the fresh chlorine water bleached is reached. This results in a more uniform product being prepared from day to day and offers a process having greater operating tolerances.

Because the bleaching solution is substantially neutral, i. e. has a pH of approximately 7, the yarn is little swelled and penetration of the package is easily attainable. Thus, gel yarn, although it is readily and largely swelled by the usual bleaching solutions, may be bleached satisfactorily in package form with a dilute solution of chlorinated Water.

As indicated, this invention relates to the bleaching of a package of yarn with a solution which adequately and satisfactorily bleaches it and which does not swell the yarn. Though we have indicated a preference for a neutral solution, it is to be understood as has been indicated, that yarn which has not been completely freed from acid or alkali, resulting from earlier steps in the process, may be subjected to this bleaching treatment and that some deviation from neutrality can be permitted without departing from the spirit of this invention. For the purpose of this application, by a neutral solution We mean one having a pH of 6.0-8.0, such as 6.5-7.8, and preferably 6.8-7.0.

Among other things the period of time necessary for eifecting the desired degree of bleach depends upon the concentration of the chlorine in the solution. Packages of yarn may even be treated over a. long period of time, such as 10 to 20 hours, with a chlorine water bleach containing, for example, 20 to 50 parts per million of available chlorine without appreciably degrading the yarn. The prolonged bleaching treatment results in a thoroughly and unfirmly bleached package.

The instant invention does not contemplate reusing the bleach solution. Consequently, there is no accumulation of salts in the solution, and irrespective of the type of yarn treated, the result is a good uniform white yarn which has sustained very little loss in physical properties. The bleaching of yarn with virgin solution at all times permits the bleaching phase of a purification procedure to follow closely after a desulphuring operation and before the cakes or packages of yarn have been washed alkali free. This is an advantage because in treating the yarn with virgin solution there is no building up of salts or products of bleaching in the chlorine water bleach solution which would decrease the effectiveness thereof and produce a non-uniform product.

The chlorine water bleach process for purifying yarn shows a further distinct advantage over the prior art sodium hypochlorite method of purification because it allows a uniform, thorough bleaching of packages, such as cakes, without degradation. As a consequence, the yarn may be wound directly to cones for marketing to a trade requiring a bleached yarn. This eliminates the expensive intervening steps of winding and handling skeins and also eliminates the troublesome backwinding processes involved in going from skeins to cones, both of which seriously degrade the yarn and lessen its value.

The chlorine water bleach process has additionally the distinct advantage over other processes in that it allows the treatment of the yarn which has not been previously dried and it allows the treatment of this yarn over a long period of time, such as 10 to 20 hours or more, without an objectionable loss of physical properties. This long treatment with a dilute, active bleach is conducive to a high degree of uniformity, both as to degree of bleach and resulting physical properties.

The chlorine water bleach is characterized by 8. BLEACHING & DYETNETEUTU TREATMENT & CHEMICAL MODIFL CATION F TEXTILES & FIBERS,

a rapid penetration, which, together with the long period of treatment, tends to level out the differences in degree of bleach between the outside and inside of the cakes or between the first threads exposed to the bleach and the last. As a consequence, the product is uniformly bleached and can be subsequently uniformly dyed. This is in contrast to the treatment of cakes with the usual strong sodium hypochlorite bleaches where considerable swelling of the yarn occurred and penetration was greatly retarded. In treatments with strong alkaline hypochlorite bleaches, the treatment must be short, as, for example, 3 hours. This short treatment and poor penetration resulted in a wide variation in bleach and dyeing characteristics between the first and last threads exposed to the bleach. This difference could not be leveled out without seriously degrading the threads in a long treatment when such a bleach was used with cakes. The yarn on the outside thereof was overbleached and degraded before the inner portions were fully bleached.

In order to more fully explain the nature of the invention, several illustrative examples are hereafter set forth. It is to be understood that the invention is not restricted to the precise procedure, conditions and concentration described in the examples.

Example I.A relatively large, dense package, such as a freshly spun acid bucket cake of viscose yarn, spun at about 7000 R. P. M. and containing about 0.8 pounds of 150 denier, 40 filament yarn, is subjected to a softening treatment, such as set forth in application Serial No. 524,308. This softened cake is drip washed for 8 to 10 hours with soft water at approximately 25 C. Thereafter, the cake is subjected to a desulphuring treatment, which comprises drip washing with a sodium carbonate solution at C. to C. for approximately 3 to 5 hours. The cake is then again washed by the drip method for 1 hour, after which the cake is treated or washed by the drip method for 10 to 14 hours with chlorinated water containing 20 parts per million of chlorine (0.002%) and having a pH value of 6.8-7.0. The cake is then washed with soft water, using the drip method, for 1 hour, after which it may be finished, such as with a soap-oil emulsion or any other well-known softening agent. The cake is then dried and wound directly into a bleached package.

In place of the cake above described, a cake, such as formed in accordance with the invention described in application Serial No. 628,317, may be used, in which case it is not necessary to soften it prior to processing.

The yarn is uniformly bleached and in color closely approximates yarn bleached in the form of skeins for a period of 30 minutes, using a sodium hypochlorite solution containing about 75 times the quantity of available chlorine as is present in the instant chlorine water bleach solution. The yarn is sufficiently white to form an excellent base for dyeing pastel shades.

Example II.A bobbin of vis arn which has been washed acid free, desulphurgd and dried to less thaniflkmoisture-eontentis rewound misting, as set forth in application Serial No. 570,476, upon a perforated bobbin which has been made corrosion resistant to the bleach liquor. This yarn is themsuhiected-toa-pressurewashillglLQMmentionfiizofihoum at 5 to 10 po unds pressure, depending upon the permeability of the package (the flow through the package being about 8 to 10 gallons per hour). Soft water cones to be sold as a bleached package.

containing 30 to 40 parts per million of chlorine (0.003% to 0.004% available chldririe) and having a pH value of 6.8-7.0 is used at a temperature of approximatelyBOiC. At the end of the treatment, the bobbin of yarn is separately washed in chlorine-free water for 15 minutes and then dried. Such bobbins of yarn may be wound directly into Example III .A freshly formed bucket cake of regenerated cellulose thread spun from viscose at about 7700 R. P. M. and containing about 0.8 pounds of denier, 40 filament yarn, is wrapped in cheesecloth and then placed in a perforated bucket where it is centrifugally Washed. The bucket is revolved at approximately 4000 R. P. M. and water or a purification solution is directed against the inner Wall of the cake under any suitable pressure, for example, 3 to 4 pounds, so that 15 to 25 pounds per minute will flow through the cake. Soft water is first directed against the cake for a few minutes or until substantially all the acid is removed, then a hot sodium carbonate desulphuring solution is caused to react with the cake for about a half hour.

The cake is then subjected to another washing operation for 5 to 10 minutes, and thereafter a chlorinated water solution at room temperature containing 25 parts per million of chlorine (0.0025% available chlorine) and having a pH value of 6.8-7.0 is directed against the cake for 20 to 30 minutes, and then the cake is washed for a minute or two and centrifuged.

The total time of this purification treatment is slightly over an hour, although obviously this time may vary considerably, depending upon such factors as the rate of flow and concentration of solution, the rotational speed of the bucket, the size and type of the thread comprising the cake, et cetera.

A whiter bleach may be secured by using a longer cycle or a higher concentration of chlorine in the water. However, the cake treated, according to the procedure of this example, is satisfactory for most purposes to which it may be put and can be dyed in uniform pastel shades.

Although we have described this invention as applied to the bleaching of artificial silk threads subsequent to the desulphuring treatment, it is to be understood that the bleaching treatment may precede the desulphuring treatment when it is desired.

Though the invention in its preferred embodiment contemplates treating yarn produced from viscose, it is obvious that the invention is applicable to other regenerated cellulose structures prepared from viscose, such as film, caps, bands, tubes, etc.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

We claim:

1. A method which comprises treating a compact package of yarn produced from viscose with chlorine water containing 0.0003% to 0.01% chlorine and having a pH of approximately 6.0 to 8.0 without appreciably swelling the yarn, whereby the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

2. A method which comprises treating a compact package of yarn produced from viscose with chlorine water containing 0.002% to 0.005% chlorine and having a pH of approximately 6.8 to 7.0

without appreciably swelling the yarn, whereby the chlorine water penetrates through the package and a subsantially uniform bleaching of the yarn is secured.

3. A method which comprises dripping chlorine water containing 0.0003% to 0.01% chlorine and having a pH of approximately 6.0 to 8.0 on to a compact package of yarn produced from viscose for approximately 10 to 20 hours without appreciably swelling the yarn, whereby the chlorine Water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

4. A method which comprises dripping chlorine Water containing 0.002% to 0.005% chlorine and having a pH of approximately 6.8 to 7.0 on to a compact package of yarn produced from viscose for approximately 10 to 20 hours without appreciably swelling the yarn, whereby the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

5. A method which comprises treating a compact package of yarn produced from viscose and in the gel state with chlorine water containing 0.0003% to 0.01% of chlorine and having a pH value of 6.0 to 8.0 without appreciably swelling the yarn, whereby the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

6. A method which comprises dripping chlorine water containing 0.0003% to 0.01% of chlorine and having a pH value of 6.0 to 8.0 on to a compact package of yarn produced from viscose and in the gel state for approximately 10 to 20 hours Without appreciably swelling the yarn,

whereby the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured 7. A method which comprises treating a compact package of yarn produced from viscose and in the gel state with chlorine water containing 0.002% to 0.005% of chlorine and having a pH value of approximately 6.8 to 7.0 without appreciably swelling the yarn, whereby the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

8. A method which comprises dripping chlorine water containing 0.002% to 0.005% of chlorine and having a pH value of approximately 6.8 to 7.0 on to a compact package of yarn produced from viscose and in the gel state for approximately 10 to '20 hours without appreciably swelling the yarn, whereby-the chlorine water penetrates through the package and a substantially uniform bleaching of the yarn is secured.

9. A method of bleaching a compact cake produced by spinning a viscose solution to produce an artificial thread and collecting the freshly spun thread in a bucket rotating at a speed of at least 7000 R. P. M. which comprises purifying the spun cake of yarn, and treating the said cake while still in the gel state, with chlorine water containing 0.0003% to 0.01% chlorine and having a pH value of approximately 6.0 to 8.0, without appreciably swelling the yarn whereby the chlorine water penetrates through the cake and a substantially uniform bleaching of the yarn is produced.

JOHN S. FONDA. GEORGE W. FILSON.