Reagent used in simultaneous dyeing and degumming fabrics
United States Patent 2169881

My invention relates to novel reagents intended primarily for use as color stabilizers in baths for the simultaneous degumming and dyeing of materials made of silk alone or of silk and other yarns. Silken fabrics are almost exclusively prepared from yarns which contain the sericin and other...

Harold, Mosher Hugh
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8/625, 8/628, 8/629, 8/630, 8/635, 8/917, 123/146.5R
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My invention relates to novel reagents intended primarily for use as color stabilizers in baths for the simultaneous degumming and dyeing of materials made of silk alone or of silk and other yarns.

Silken fabrics are almost exclusively prepared from yarns which contain the sericin and other natural impurities intact about the inner core of fibroin or silky matter. The horny integument is maintained intact about the fibroin as a protection for the latter because the delicate silk fiber is easily abraded by the mechanical agencies employed in throwing and weaving or knitting the yarn into finished fabrics. The fibroin re18 quires a protective size and, fortunately, nature furnishes such a lacquer in the sericin with which she encloses the fibroin. The size, however, is stiff and brittle and requires plasticization and lubrication in order to fabricate effectively. The requisite plasticization and lubricity are imparted to the sericin by soaking the raw yarn in solutions which may contain in a dispersed form, various oils of either a saponifiable or mineral nature, glycerine, alkalies and soaps or sul26 phonated oils. Sulphated fatty alcohols, fat acid condensates, pine oil, cresylic acid and other wetting agents and antiseptics are frequently employed for special purposes.

The natural impurities present on raw silk and 80 the various ingredients employed to plasticize and lubricate the sericin, mask and obscure the natural brilliance and softness of the fibroin and prevent the silk from acquiring the colors employed in dyeing. Consequently, almost all silk 38 fabrics are first submitted to an operation designed to remove all extraneous matter from the fibroin. This operation is variously known as boil-off, degumming and scouring, the three terms being synonymous and designating the same operation.

The elimination of the sericin with its attendant impurities is accomplished by the use of a fairly high degree of alkalinity, (pH values between 9.7 and 10.5), potent emulsifying agents, elevated temperatures (over 95" C.) and a prolonged exposure of the silk to the stripping solutions (from one to three hours).

The reagents most generally employed in degumming are red and olive oil soaps frequently augmented in potency by small additions of soda ash, tri-sodium phosphate and other alkaline salts and sulphonated oils, or the so-called boiloff oils which are mixtures of sulphated oils and 65 potash soaps adjusted and buffered with basic salts, penetrants and auxiliaries to a pH of about 10.2.

Subsequent to degumming the silk is generally dyed, with or without bleaching and converted into the finished articles of commerce. Most of the heavier types of broad goods survive the degumming, bleaching and dyeing operation without any perceptible fabric deterioration. However, knitted silk merchandise such as silk hosiery does not exhibit the same resistance. Such fabrics are generally of light and fragile construction and care must be exercised in preventing excessive abrasion. This is generally accomplished by dyeing the silk material in a bath containing at the start of the operation most of the sericin on the fabric. As degumming proceeds, the dyestuffs affix themselves upon the filaments and the dissolved sericin acts as a fiber protectorant.

Technically, two methods of treating light and fragile fabrics are in common commercial use, the so-called split and single bath processes.

The former accomplishes the emulsification of the natural or artificially added throwing oils and greases in a preliminary operation with a minimal loss of silk gum or sericin. The actual elimination of the sericin with a simultaneous dyeing occurs in a subsequent degumming and dyeing liquor. The single bath process aims at elimination of the oil, fats and waxes as well as the removal of sericin and the dyeing of the fabrics in a single boil-off operation.

The performanice of these operations is complicated by virtue of the fact that knit goods, particularly silk hosiery, are rarely composed solely of a single kind of textile fiber. The toes, heels and tops of hosiery are frequently of cotton or rayon and sometimes even of unions of the two, while the seam-yarns are invariably made of cotton threads. This necessitates the employment of dyes in the degumming bath which will impart the same tone and color effect to cotton or rayon as well as to silk. The selection of the colors suitable for this operation is very limited. Few dyestuffs will dye silk and cellulosic fibers the same shade in the alkaline conditions of the bath. Direct colors which simultaneously dye both cotton and silk do not operate effectively at that basicity, and the equilibrium of the dye on cotton and silk fluctuates materially with slight variations in the pH and temperature of the bath. Milling colors are even more objectionable, so the dyer is limited to the choice of some six or eight true cotton and a similar number of true .silk shades. (I. e. dyestuffs which have a tinctorial effect only toward the single kind of fiber.) Few as these colors are, yet they are sufficient to produce any hosiery shade demanded by the industry. They dye level at the pH of the dye bath, feed and shade evenly and possess the requisite light and wash fastness.

It is the customary procedure in the textile industry to conduct the degumming and dyeing operation with the use of soap, sulfonated oil buffered to a pH of 10.2 and alkaline salts as the stripping agents. Such reagents are not entirely satisfactory but find use by virtue of the fact that no betrter materials have thus far been developed.

Many of the true silk and cotton colors are easily destroyed by the combined action of the high alkalinity of the bath, the elevated temperature of degumming and the reducing action of the silk sericin and the preparations employed in silk soaking.

Commercial attempts to prevent this color reduction have been only partially successful. Most attempts aim at this accomplishment by lowering the pH of the dye bath or by churning air into the dye liquor. Whatever benefits have accrued through these practices are ascribable to a lowering of the temperature or alkalinity of the dye bath and have resulted in a greatly extended time of degumming and dyeing.

With the foregoing in mind the principal object of my invention is to provide chemical reagents for the degumming and dyeing operation which effect complete color stabilization, facilitate and shorten the degumming and dyeing procedure and decrease the cost thereof.

I have found that the cause of the color change is the sericin content of the bath and that by insolubilizing the sericin which enters solution or by absorbing it by certain other colloids the color reduction can be entirely prevented. I have also found that the protectorant or color stabilizer must possess both protein coagulation and oxidizing properties. As the color stabilizer is to be employed with a degumming solution, its protein coagulation properties should be sufficiently potent to convert solubilized sericin into an insoluble colloidal form but not yet to perceptibly arrest or prevent the elimination of the sericin from the material being degummed. The stabilizer should preferably be devoid of reducing properties though this characteristic can in part be neutralized by a suitable oxidizing agent.

In stabilizing the dye employed with the degumming agent in coloring silk fabrics the liquor should have a mild oxidizing action, preferably no greater than that of hydrogen peroxide.

Among the stabilizers or protectorants usable for the purposes of my invention are:-sodium phosplhotungstate, sodium phosphomolybdate, mixtures of sodium' perborate and aluminum salts, cadmium sulfate, potassium permanganate, potassium dichromate and certain peroxides such . as magnesium peroxide.

The following examples will serve to illustrate, without limiting, my invention: Zxample 1 A degumming preparation was prepared as follows: Per cent Olive oil oap.------------------------ 75 Sodium tetrapyrophosphate ------------- 5 Cadmium sulphate----- -------------- 20 A degumming solution of 1% strength of the above was prepared and /4% Silk Brown G N (Color Index-Special) was added. The solution was heated to boiling and ten pounds of silk hosiery in the griege was added and the operation continued until the desired color shade was secured. No destruction of dye resulted. A sample degummed and dyed with comparable amounts of soap and tetrapyrophosphate was of much lighter color and showed a loss of dye in the solution of 25%.

JExample & A degumming oil of the following composition was prepared: Per cent Potassium hydroxide---------------- 6/2 Sulfonated castor oil----------------- 25 25 Cresylic acid----------------------- 10 Sodium phosphotungstate----------- 21/2 Sodium perborate------- --------- 2 A 1% solution of the above was prepared and one 30 ounce per 1000 pounds of Durol Black B (Color Index 307) was added to the solution. Ten pounds of silk sweaters were added to the solution and degumming and dyeing continued until a color match was secured.

Example 3 A degumming powder was prepared as follows: Per cent Olive oil soap---------- -------------- 25 Soda ash_------------.... --------------. Sodium tetrapyrophosphate ------------ 30 Borax ----------------- ---- 10 Sodium perborate-- -------------------- 10 Aluminum sulphate ------------------- 5 A 1% solution of the above was prepared and per 1000 pounds of the solution five ounces each of Silk Brown G N (Color Index--Special) and Silk Brown R (Color Index 234) and seven ounces of Silk Brown L (Color Index-Special) were 50 added. When the solution had reached boiling twenty pounds of raw silk skeins were entered and were simultaneously degummed and dyed.

No loss of color resulted.

I claim: 55 A silk degumming and dyeing bath, comprising soap, a boil off oil, a degumming alkaline salt, a direct dye and an oxidizing color stabilizer having protein coagulation properties sufficiently potent to convert solubilized sericin into insol- 60 uble colloidal form but not substantially to prevent elimination of sericin from the material being treated, said color stabilizer being a compound selected from the class consisting of sodium or potassium dichromate, phosphotungstate, a5 phosphomolybdate and cadmium sulfate.