US2598120A - Vat dyeing of acrylonitrile polymers using potassium ions - Google Patents

Description

Patented May 27, 1952 VAT DYEING F ACRYLONITRILE POLY- MERS USING POTASSIUM IONS Esther Meryl Griflith, Bloomington, Ill., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 3, 1949, Serial No. 79,521

13 Claims. 1

This invention relates to the modification of polymers of acrylonitrile. More particularly, it relates to the dyeing of structures comprising acrylonitrile polymers.

This is a continuation in part of m Serial No. 771,704, now abandoned.

By structures is meant shaped articles, such as yarns, films, bristles, fabrics, tubings, molded articles and the like, and by acrylonitrile polymers is meant those polymers containing at least 85% by weight of acrylonitrile.

Acrylonitrile polymers containing a major portion of acrylonitrile are relatively insoluble, unreactive and hydrophobic materials. These characteristics make the dyeing of structures prepared from such polymers a diflicult problem. Indeed, standard commercial dyeing techniques cannot be used satisfactorily. For example, only light shades are obtained on dyeing structures of polyacrylonitrile with dispersed acetate, basic and certain vat colors. This is true for copolymers of acrylonitrile prepared using up to of other vinyl type monomers. These copolymers retain the desirable properties of polyacrylonitrile and show only a slightly enhanced dye receptivity. Since the physical and chemical properties of shaped articles prepared from acrylonitrile polymers make the articles of considerable commercial interest, solutions to the difiicult dyeing problems are highly desirable.

Accordingly, it is an object of this invention to provide a satisfactory process for dyeing acrylonitrile polymers. A further object is the provision of methods for uniformly dyeing structures of acrylonitrile polymers. A still further object is the provision of dyed structures of such polymers which are deeply and uniformly dyed and which are fast to light and to washing. Other objects will appear hereinafter.

The objects of this invention are accomplished by treating the structures of this invention with an aqueous dye bath containing a vat dyestufi of the indigo, thioindigo or related type, alkali, a readily ionizable potassium compound and a reducing agent and then oxidizing the leuco dyestuif on the article.

The invention will be more clearly understood by referring to the examples and discussion which follow. These examples are given for illustrative purposes and are not to be construed in any sense as limitative. Parts, proportions and percentages are by weight unless otherwise indicated.

Emample I A dye bath was prepared using 400 parts of Water, 2 parts of 6,6'-dibromo-4,4'-dimethyly application 2,2-bis-thionaphthen-indigo, 10 parts of sodium hydrosulfite, 0.8 part of sodium hydroxide, and 27.6 parts of potassium carbonate (4 equivalent weights per 100 parts of polymer). pH of this bath was 11.4. Ten parts of polyacrylonitrile yarn was kept immersed in the bath for one hour, the bath being heated to 97 to 98 C. After this time the yarn was rinsed in cold water and immersed in a bath containing 400 parts of water and four parts of nitric acid. This oxidation bath was heated to 98 C. and the treatment lasted for one hour. After scouring the sample in 0.5% soap solution at 98 C., rinsing, and drying, the yarn was found to be dyed a strong pink shade.

If, in the dye bath above, the potassium carbonate is replaced by four equivalent weights per 100 parts of polymer of sodium carbonate (21.2 parts), only a weak pink shade is obtained on the'fiber after dyeing. The weak shade is similar to that obtained using a dye bath having a pH of 11.2 and containing no salt.

Example II Ten parts of polyacrylonitrile yarn was immersed in a dye bath containing 400 parts of water, 2 parts of 5,5-dichloro-6,6'-dimethyl- 2,2'-bis hydrosulfite, 0.8 part of sodium hydroxide and 27.6 parts of potassium carbonate (4 equivalent weights per 100 parts of polymer). The pH of this bath was 11.4. The bath was heated to 98 C. for one hour. After rinsing, oxidizing and soaping, as described in the previous example, the yarn was a strong red-violet shade.

If the potassium carbonate in this bath is replaced by sodium carbonate, only a weak shade is obtained.

Example III Ten parts of knit tubing prepared from a copolymer containing acrylonitrile and 5% styrene was immersed in a dye bath containing 400 parts of water, 2 parts of 5,5'-dichloro-7,7'- dibromoindigo, 20 parts of sodium formaldehyde sulfoxylate, 1.5 parts sodium hydroxide and 39.2 parts of potassium acetate (4 equivalent weights per parts of polymer). The pH of thisbath was 11.2. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and sc aping, as described in Example I, the yarn was a strong blue shade. If four equivalent weights per 100-parts of .polymer of sodium acetate (32.8 parts) is used in place of the potassium acetate in this example, a weak shade results, similar to that obtained when no salt is used.

-thionaphthen-indigo, 10 parts of sodium Example IV Ten parts of a film prepared from the 90/10 copolymer of acrylonitrile/methacrylic acid was immersed in a dye bath containing 400 parts of water, 2 parts of 5,5,7,7'-tetrabromoindigo, 20 parts of sodium formaldehyde sulfoxylate, 1.5 parts of sodium hydroxide and 25.8 parts of potassium chloride (4 equivalent weights per 100 parts of polymer). The pH of thisbath was 10.9. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and soaping, as described in Example I, the yarn was a strong blue shade. If four equivalent weights per 100 parts of polymer of sodium chloride (23.4 parts) is used in place of the potassium chloride in this example, a weak shade results, similar to that obtained when no salt is used.

Example V Ten parts of knit tubing prepared from a blend of 95% polyacrylonitrile and 5% polyvinylpyridine was immersed in a dye bath containing 400 parts of water; 2 parts of 2thionaphthen2- acenaphthylene-indigo, 20 parts of sodium formaldehyde sulfoxylate and 1.5 parts of sodium hydroxide and 34.8 parts of potassium sulfate (4 equivalent weights per 100 parts of polymer). The pH of this bath was 10.8. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and soaping, as described in Example I, the yarn was a strong scarlet shade. If four equivalent weights per 100 parts of polymer of sodium sulfate (28. parts) is used in place of the potassium sulfate in this example, a weak shade results, similar to that obtained when no salt is used.

Example VI If four equivalent weights per 100 parts of polymer of sodium carbonate (21.2 parts) is used in place of the potassium carbonate in this example, a weak shade results, similar to that obtained when no salt is used.

Example VII Ten parts of polyacrylonitrile knit tubing was immersed in a dye bath containing 400 parts of water, 2 parts of 2-(5,7-dibromoindole)-5'-bromo-2'-thionaphthen-indigo, parts of sodium hydrosulfite and 2 parts of potassium hydroxide. The pH of this bath was 12.5. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and soaping,

as described previously, the yarn was dyed to an I intermediate shade of violet.

Ezvample VIII Ten parts of polyacrylonitrile knit tubing was immersed in a dye bath containing 400 parts of water, 2 parts of 6,6'-dibromo-4,4'-dimethyl- 2,2-bis-thionaphthen-indigo, 20 parts of sodium formaldehyde sulfoxylate, 0.8 part of sodium hydroxide and 157 parts of' potassium acetate (16 equivalent weights per parts of polymer). The pH of this bath was 11.2. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and soaping, as described in Example I, the yarn was a strong pink shade. If 16 equivalent weights per 100 parts of polymer of sodium acetate (131 parts) is used in place of the potassium acetate in this example, a weak shade results, similar to that obtained when no salt is used.

Example IX Ten parts of polyacrylonitrile knit tubing was immersed in a dye bath containing 400 parts of water, 2 parts of 6,6-dibromo-4,4-dimethyl- 2,2'rbis-thionaphthen-indigo, 20 parts of sodium formaldehyde sulfoxylate, 0.8 part of sodium hydroxide and 314 parts of potassium acetate (32 equivalent weights per 100 parts of polymer). The pH of this bath was 11.3. The bath was heated to 98 C. and the dyeing continued for one hour. After rinsing, oxidizing and soaping, as described in Example I, the yarn was an intermediate pink shade. If 32 equivalent weights per 100 parts of polymer of sodium acetate (262 parts) is used in place of the potassium acetate in this example, a, weak shaderesults, similar to that obtained when no salt is used.

Example X Example XI Woven fabric (250 parts) prepared from high- 1y drawn (9X) polyacrylonitrile yarn was dyed under pressure in an autoclave using an aqueous dyebath prepared according to the following formula:

5000 parts water 12.5 parts 6,6-dibromo-4,4-dimethy1-2,2-bisthionaphthen-indigo 25 parts caustic soda 25 parts sodium hydrosulfite 2.5 parts high molecular weight alkanol sulfate (wetting agent) 25 parts sodium formaldehyde sulfoxylate 500 parts potassium carbonate (2.9 equivalent weights per 100 parts of polymer) The dye paste was vatted at 82 C. with half the water and half the caustic soda and sodium hydrosulfite required in the above formula. The remaining components of the formula were then added.

The fabric was placed in an autoclave on a revolving reel. The dye liquor was added and the autoclave sealed. The temperature of 127 C. was maintained for 15 minutes by holding the pressure at 20 p. s. i. gauge. After cooling the autoclave, the fabric was removed, rinsed well in Water, and oxidized for 15 minutes in a boiling aqueous solution containing 5 grams/liter acetic acid and 5 grams/liter of 30% H202. fabric was then rinsed in water and secured for 15 minutes in boiling aqueous solution containing 5 grams/liter'of soap. Magnified cross-sew The dyed tion'photographs of the dyed fibers showed that penetration by the dyestuff was complete. The dyeing was level and the fabric did not crock under severe test. The physical properties of the polyacrylonitrile fibers were not impaired by this pressure dyeing technique.

The pressure pad-steam vat dyeing technique described by Scull in U. S. 2,424,857 was tried at 127 Crwith little success. Color was applied to the polyacrylonitrile fabric but the dyed piece was most unlevel, crooked slightly, and the fibers were found upon microscopic examination to be dyed merely onthe surface.

Vat dyeing must be done in alkaline media because the reduced leuco form of the dyestuff is insoluble in acid media. When acrylonitrile polymers are vat dyed in baths having a pH below but above 7, weak shades result. The addition of ionizable potassium compounds to such baths does not improve the dyeing appreciably. Accordingly, in the process of this invention enough alkali should be present in the bath to maintain a pH of 10 or more throughout the dyeing. However, when the pH exceeds 12.5, the enhanced dyeing effect afforded by the presence of potassium ion diminishes rapidly. Therefore, it is preferred to operate the dyebaths of this invention at a pH range of 10 to 12.5. These highly alkaline baths exert no adverse effect on the acrylonitrile polymers of this invention.

Any alkali capable of giving the desired pH may be used in this invention. For example, lithium, sodium, and potassium hydroxides may be used. As disclosed in Example VII, potassium hydroxide may be the sole source of potassium ions. In such instances, however. only intermediate shades are obtained since the maximum optimum pH value of 12.5 is reached before a sufficient potassium ion concentration is reached. For this reason, it is preferred to use other potassium salts along with potassium hydroxide. It is also possible, as shown in Example X, to use potassium salts of weak acids, such as potassium carbonate, as the only alkali and as the source of potassium ion.

Further, other inorganic or organic alkaline materials may be used in the dye bath. For example, as disclosed in copending application Serial Number 771,379, new U. S. Patent No. 2,543,994, aromatic amines may be used effectively as carriers in the vat dyeing of acrylonitrile polymers. The amines disclosed in that application may be added to the baths of this invention. Likewise, potassium salts of such amines as anthranilic and sulfanilic acid may be added.

In general, potassium ion from nearly any source can be used in the process of this invention. In addition to the potassium compounds disclosed above, any of the following compounds, among others, may be used, either alone or in mixtures: potassium bromide, potassium iodide, potassium fluoride, potassium arsenate or the arsenite, potassium bicarbonate, potassium cyanlde, potassium sulfide, potassium nitrite, potassium nitrate, potassium phosphate, potassium sulfite, potassium thiosulfate, potassium hydrosulfite, and potassium salts of organic acids, such as potassium succinate, oxalate, tartrate, formate, propionate or benzoate. Thus salts of inorganic and organic acids which are ionizable in the dye baths are operative in this invention. It is preferred to use potassium compounds which do not cause oxidation under the conditions of dyeing employed. In general, any hot-water soluble potassium compound may be used. It

iii

may be added to the dye bath either before or after the dyestuff is reduced to its leuco form.

The amount of potassium ion used in the practice of this invention can be varied over wide limits. It is preferred to use between 4 and 20 equivalent weights of the potassium compound per 100 parts of polymer to get strong shades. Intermediate shades, which are satisfactory for some purposes, can be obtained with concentrations as low as two equivalent weights or as high as 32 equivalent weights per 100 parts of sample. The acrylonitrile polymers which are generally used commercially for the preparation of the shaped articles described in this invention must, of course, be of a sufficiently high molecular weight to possess fllmor filament-forming properties. The polymers employed possess an average molecular weight within the range of 25.000 to 750,000 or even higher and preferably between the range of 40 ,000 to 250,000 as calculated from viscosity measurements by the Staudinger equation:

N Molecular we1ght-- wherein:

K,,,=1.5X l0 viscosity of solution N", specific VlSGOSlty and C=concentration of the solution expressed as the number of moles of the monomer (calculated) per liter of solution.

It is to be understood, however, that acrylonitrile polymers having molecular weights below or above the range indicated may be subjected successfully to the process of this invention.

The acrylonitrile polymers of commercial interest are those containing by weight of the polymer of acrylonitrile. These polymers include polyacrylonitrile and copolymers and interpolymers of acrylonitrile with other polymerizable monomers. These monomers include, among others, vinyl acetate, vinyl chloride, acrylic and methacrylic acids and their derivatives or homologues, methyl vinyl ketone, vinyl pyridine and homologues thereof, and isobutylene or other polymerizable hydrocarbons. Polymers containing less than 85% of acrylonitrile can usually be dyed by standard processes, since inclusion of greater amounts of such ma terials as acrylic acid, methyl vinyl ketone and the like, leads to better dye receptivity. If desired, the process of this invention can be used to dye such polymers. However, since it is preferred to use polymers having at least 85% acry-' lonitrile to get the benefit of superior properties, such as toughness and chemical inertness, the process of this invention is chiefly of interest in the dyeing of structures prepared from polymers containing a major portion of acrylonitrile.

The yarns described herein are prepared by conventional wet or dry spinning techniques from solutions of polyacrylonitrile or copolymers containing 85% or more acrylonitrile in dimethyl formamide, tetramethylene sulfone or other known volatile solvents for these polymers as described in United States Patents Nos. 2,404,714 to 2,404,727, inclusive. On leaving the spinning cell, the yarn is collected in a suitable package and this yarn package may then be washed free of residual solvent. In order to obtain full bene fit of the properties of these yarns, it is desirable to draw the yarn from" 2 to 10 times its original length. Moreover, when heated under tension for extendedperiods of time,-the yarns show a remarkable retention of tenacity; while, on the other hand, if the yarns afterdrawing are heated in the-relaxed state at temperatures in the order of 130 to 200 C'., the yarns tend to shrink somewhatand such an after-treatment can be used to increase the elongationof the yarns to apoint where they are satisfactory for use in the textile art.-

The structures such as yarns, films, fabrics and the like maybe prepared bythe usual techniques, for example, yarnsor fibers may be prepared as described above by dry spinning or wet spinning according to such procedures described in ,copending applications Serial Numbers 496,376, 735,666, and 746,651, now U. S. Patents Nos.'2,426,719; 2,451,420;and 2,467,553, respectively. Films may be prepared in similar ways, or by casting techniques. Fabrics of the new compositions of matter of this invention may be prepared by any of the well-known knitting or weaving techniques.

In addition to the dyes described in the above examples, it is possible to use indigo, thioindigo, bis-2,1-naphthioindigo, and similar indigo and thioindigo vat colors. Some improvement in dyeingwith: certain anthraquinone vat colors is also obtained upon using the potassium compounds but the effect is much less marked than that obtained with the indigo and thioindigo dyes. It is preferred to use an indigo or a thioindigo dye in any desired amount. By the use of any of the above or other indigo and thioindigo vat colors, strong shades that are fast to washing and crocking are obtained.

The other ingredients of the dye bath and the conditions of dyeing may be varied widely. Any of the commercial techniques in respect to these factors may be employed herein. Standard commercial dyeing processes employ 30:1 to 50:1 ratios of bath to structure. These ratiosmay be'used in this invention. In general, any-of the commercial dyeing apparatus and procedures, such as-purlfication and oxidation and the like, may be used herein. v The oxidation of the vat dyestuff on the structure may be carried out in other ways. Instead of using nitric acid, other agents for oxidation may be employed, such as aqueous solutions of sodium dichromate, hydrogen peroxide, sodium perborate and the like.

.While the temperature of the dye bath may be varied widely, it is preferred to use temperatures above 85 C. Below these temperatures the rate of dyeing is tooslow to be commerciallypractical. This rate increases rapidly with higher temperatures and in the interest of economy it is preferred to carry out thedyeing at a bath temperature between 95 and 100 C. Temperatures above 100 C. may be employed. Particularly good, results are obtained with highly drawn acrylonitrile polymer yarns when the process is carried out under pressure at temperatures exceeding 100 C., as shown in Example XI.

The vat dyeing of polyacrylonitrile articles in highly alkaline vat baths should not be conducted at temperatures of greater-than 130 C. for periods of time greatly exceeding minutes. Higher temperatures and longer periods oftime generally lead to loss in physical properties. At the lower temperatures there is no adverse effect; at the higher temperatures attack by the alkali is avoided by using very short time periods. The dyeing oihighly drawn yarns and .fabrics 8 to'strong shades can be accomplished satisfactorily at temperatures ranging'from about 100- l30 C. and periods ranging from l5-30 minutes.

This invention is of particular value in the dyeing of yarns, filaments, and fabrics and simi-' lar articles of polymers containing at least acrylonitrile. Polyesters, nylon and cotton articles do not respond appreciably tothe process of this invention. This invention afiords the only process known hitherto for dyeing acrylonitrile polymers containing at least 85% acrylonitrile to strong shades with vat colors Without the use of an organic carrier or assistant. Since potassium compounds are cheap and since relatively expensive assistants, such as amines, are not needed, the process of this invention is more economical than processes which involve the use of carriers.

The eifect of obtaining the strong shades in the dyeing of acrylonitrile polymers described in this invention appears specific to the potassium ion. For example, lithium and sodium ions do not act in a similar manner and are ineffective.

The vat dyestuffs are characterized by their fastness to light and washing. Consequently, vat dyeing is an important and popular method for the coloring of textile articles. The sale of textile materials prepared from new synthetic polymers is limited unless these materialscan be readily colored and made more appealing to the public. An important step in the development of a new synthetic fiber, therefore, is the provision of a satisfactory method for dyeing the fiber to strong shades using available commercial equipment. This is a difiicult problem when the new synthetic fiber is hydrophobic by nature; that is. it has little or no tendency to swell in the presence of water. Yarns and fibers prepared from synthetic acrylonitrile polymers, which are hydrophobic by nature, are not penetrated and colored readily in commercial dyeing procedures. Dyestuffs which are substantive on other types of polymers are not necessarily so on acrylonitrile polymers. 'In fact, it cannot be predicted which class of dyestuifs will most effectively color a new synthetic yarn. Normally, structures prepared from acrylonitrile polymers cannot be dyed satisfactorily with any dyes, such as acid, direct, sulfur, dispersed acetate, basic or vat colors. At best only light shades are obtained.

This invention provides a convenient and valuable method for dyeing structures prepared from acrylonitrile polymers. By the novel process of this invention difiicultly dyed structures of acrylonitrile polymers can be dyed eifectively at a rapid rate using standard commercial equipment. By the use of the process of this invention, vat dyeing procedures, which when normally applied to acrylonitrile polymer structures give no coloring or at most only light shades, are capable of rapidly dyeing the structures to'level shades of satisfactory strengths. The dye bath exhaust is greatly increased and the colored products produced have excessively good resistance to washing and cracking and have good light fastness.

Furthermore, the physical and chemical properties of the dyed structures are comparable to the desirable properties of the undyed structures.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

I claim:

1. Aprocess of dyeing an acrylonitrilepolymer containlngat least 85% acrylonitrilewhichcomprises treating said polymer with an aqueous dye bath having a pH of from about to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potassium compound per 100 parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

2. A process for dyeing an acrylonitrile polymer containing at least 85% acrylonitrile which comprises treating said polymer at a temperature above 85 C. with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potassium compound per 100 parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

3. A process for dyeing polyacrylonitrile which comprises treating said polyacrylonitrile with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potassium compound per 100 parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

4. A process for dyeing an acrylonitrile/methacrylic acid polymer containing at least 85% of acrylonitrile which comprises treating said polymer with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potasslum compound per 100 part of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

5. A process for dyeing an acrylonitrile/styrene polymer containing at least 85% of acrylonitrile which comprises treating said polymer with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights or an ionizable potassium compound per 100 parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

6. A process for dyeing a structure prepared from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises treating said structure with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potassium compound per 100 parts of said structure, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes.

7. A process in accordance with claim 2 wherein the bath is maintained under pressure and at a temperature of about 100 C. to about 130 C.

8. A process in accordance with claim 3 wherein glge bath is heated to a temperature of at least 9. A process for dyeing a structure prepared from polyacrylonitrile which comprises treating said polyacrylonitrile with an aqueous dye bath containing about 2.9 equivalent weights of potassium carbonate per 100 parts of said polyacrylonitrile, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes, the said bath having a pH of between 10 to 12.5 and being heated under pressure at a temperature of about 130 C.

10. A process in accordance with claim 1 wherein the said bath is heated to a temperature of from about C. to about 130 C. and the treating of said polymer in said bath is carried out for from about 15 to about 30 minutes.

11. A process for dyeing an acrylonitrile polymer containing at least 85% acrylonitrile which comprises treating said polymer with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing from 2 to 32 equivalent weights of an ionizable potassium compound per parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution in said bath a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes and thereafter removing the said polymer from the said bath and oxidizing the said dye.

12. A process for dyeing an acrylonitrile polymer containing at least 85% acrylonitrile which comprises treating said polymer with an aqueous dye bath having a pH of from about 10 to about 12.5 and containing sodium hydroxide and 2 to 32 equivalent weights of an ionizable potassium compound per 100 parts of said polymer, said equivalent weights being expressed in the same units as said parts and in solution a reduced vat dye selected from the group consisting of indigo and thioindigo vat dyes and thereafter removing the said polymer from said bath and oxidizing the said dye.

13. A process in accordance with claim 12 wherein the temperature is from about 85 C. to about C.

ESTHER MERYL GRIFFITH.

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

UNITED STATES PATENTS Number Name Date 1,868,300 Wylam July 19, 1932 1,868,987 I Moorhouse July 26, 1932 1,959,980 Henderson May 22, 1934 2,067,930 Kern Jan. 19, 1937 2,086,831 Tolman July 13, 1937 2,318,133 Wentz May 4, 1943 2,371,145 Brubaker Mar. 13, 1945

Claims (1)

1. A PROCESS OF DYEING AN ACRYLONITRILE POLYMER CONTAINING AT LEAST 85% ACRYLONITRILE WHICH COMPRISES TREATING SAID POLYMER WITH AN AQUEOUS DYE BATH HAVING A PH OF FROM ABOUT 10 TO ABOUT 12.5 AND CONTAINING FROM 2 TO 32 EQUIVALENT WEIGHTS OF AN IONIZABLE POTASSIUM COMPOUND PER 100 PARTS OF SAID POLYMER, SAID EQUIVALENT WEIGHTS BEING EXPRESSED IN THE SAME UNITS, AS SAID PARTS AND IN SOLUTION A REDUCED VAT DYE SELECTED FROM THE GROUP CONSISTING OF INDIGO AND THIOINDIGO VAT DYES.