Acid mordant dyes application

The application range designated by this generic name in the Colour Index incorporates those acid, direct and mordant dyes with substantivity for leather and satisfactory fastness on that substrate [55]. It is a commercially important sector, the number of products listed being exceeded only by the complete acid or direct dye ranges. As expected from the sources of this selection, about 85% of leather dyes are azo compounds (35% disazo, 30% monoazo, 20% metal-complex monoazo) and the remainder are mainly yellow to orange stilbene dyes and anthraquinone or triarylmethane types in the violet to green sectors. 

Anthraquinone dyes are characterized by the presence of one or more carbonyl groups in association with a conjugated system. These dyes also may contain hydroxy, amino, or sulfonic acid groups as well as complex heterocyclic systems. Anthraquinones uses include disperse, vat, acid, mordant, and fiber reactive applications. 

Triarylmethane dyes are derivatives of triphenylmethane and diphenylnaphthylmethane. The presence of one or more primary, secondary, or tertiary amino or -OH groups in the para position to the methane carbon determines the dye color. Halogen, carboxyl, or sulfonic acid substituents also may be present on the aromatic rings. Triarylmethane colorant applications include basic, acid, solvent, and mordant dyes. Major uses are in printing inks. 

Acid dyes include metal-complexed azo structures, where the metals used are cobalt, chromium, and iron.10 Examples are 1 1 and 2 3 chromium complexes and 1 2 cobalt complexes, where the numbers employed represent the ratio of metal atoms to dye molecules. Metal-complexed dyes can be formed inside textile fibers by treating suitably dyed fibers with a solution containing metal ions.11 In this case, the metal-free forms of these azo dyes are known as mordant dyes and contain mainly ortho, ortho -bis-hydroxy or ortho-carboxy, ortho -hydroxy groups (e.g., C.I. Mordant Black 11, Mordant Yellow 8, and Mordant Orange 6). When the metal complexes are formed prior to the dye application process, the resultant dyes are known as... 

Dyes are also classified on the basis of their application. The water-soluble dyes which are the salts of sulfonic acid or phenolic compounds are named acid dyes] those which are the salts of amino compounds are called basic. If the dyeing is accomplished without use of mordants the dyes are called direct. Dyes which require the use of metallic oxides, tannin, and other substances to give fast shades are called mordant dyes. The water-insoluble dyes are known as vat dyes. The insoluble colored substance is reduced in a fermentation vat or by hydrosulfite to a soluble form which is applied to the fiber then oxidized by air to the insoluble color. Finally ingrain dyes are produced by performing one or more of the chemical reactions used for the preparation of the dye directly on the fiber. 

Chryso idine, which was discovered by Witt, is one of the few basic azo-dyestuffs, and like all basic colouring-matters dyes cotton mordanted with tannic acid. Its principal application is in cottondyeing, especially for shading purposes. It gives a yellowish-orange colour. 

There are three general classifications of acid dyes depending on their method of application acid dyes that dye directly from the dyebath, mordant dyes that are capable of forming metallic lakes on the fiber when aftertreated with metallic salts, and premetallized dyes. 

For other major apparel fibers such as wool, silk, and nylon a dye class referred to as acid dyes is routinely used for coloration. Reactive dyes have also been developed for wool and are widely used for fashion apparel items because of their bright, broad color range. A range of mordant dyes is also available for wool and other animal fibers. The mordant dyes provide very high levels of fastness, but the shade range is limited, the shades are typically dull, and the application process is complicated. For acrylic fibers the dominant dye class is the basic dye. For polyester apparel, the insoluble disperse dye range is almost exclusively used. 

Reactive Dyes Reactive dyes are dyes which usually have the basic structure of acid, direct, or mordant dyes but which in addition have a reactive group capable of covalent bond formation with the fiber. Since the fiber must have reasonable reactivity toward the dye reactive group, application of these dyes has been limited to cellulosic, protein, and nylon fibers for the most part. 

There are, of course, many varieties in each of these chemical classifications, so that the result is hundreds of individual dyes each with its own specific characteristics for hue and use on substrates. Dyers have arranged this very complex and large group of chemical products into ten categories arranged by the method of application to the fiber or substrate acid dyes, azoic dyes, basic dyes, direct dyes, disperse dyes, reactive dyes, solvent dyes, sulfur dyes, vat dyes, and mordant dyes. It is in these categories that dyestuffs are discussed in the trade. 

In some processes, there is a need to immobilize dyes, either temporarily as in the case of filter and antihalation devices or permanently as for the images in colour image transfer processes. Because the dyes normally used in these applications contain acid functional groups, the corresponding mordants are basic in nature and are usually polymeric. Polyvinyl-pyridines have utility as mordants. Other useful compounds are illustrated by the pyridinium salt (95) (49USP2484430), the morpholinium salt (96) (72BRP1245952) and the imidazole (97) (72GEP2150136). 

Azo dyes, characterized by the presence of one or more azo groups (-N=N-), are the most commercially important class of dyes. These compounds are synthesized using a diazoti-zation reaction in which a primary aromatic amine reacts with nitrous acid to form a diaz-onium salt. The diazonium compound then typically is coupled with phenols, napthols, aromatic amines, heterocycles, or a variety of other compounds containing active methylene groups. Azo dyes are used in acid, direct, disperse, fiber reactive, and mordant applications. 

Statistics for the production of basic dyes include those products listed as cationic dyes, eg, cyanines, for dyeing polyacrylonitrile fibers and the classical triarylmethane dyes, eg, malachite green, for coloring paper and other office applications (2,53). Moreover, statistics for triarylmethane dyes are also hidden in the production figures for acid, solvent, mordant, and food dyes, and also organic pigments. Between 1975 and 1984, the annual production of basic dyes in the United States varied from 5000—7700 t. However, from 1985—1990, annual production of basic dyes varied from 5000—5700 t, and the annual sales value increased from 56 to 73 million per year. 

On alumina mordants it gives a red, which is still yellower than that with isopurpurin. Its principal application is in printing, while that of isopurpurin is in dyeing. Anthraflavic acid and isoanthraflavic acid sometimes occur in the commercial products. They are entirely valueless in dyeing, and are produced in badly conducted operations. 

Morin is used largely in wool and cotton dyeing as decoction or extract of fustic. Its principal application is in shading blacks, browns, c. Wool is generally mordanted with potassium bichromate and sulphuric acid. The morin is fixed as a very stable chromium lake, which has a dull yellow colour. 

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