Acid mordant dyes fastness

Acid—mordant dyes have characteristics similar to those of acid dyes which have a relatively low molecular weight, anionic substituents, and an affinity to polyamide fibers and mordant dyes. In general, brilliant shades caimot be obtained by acid—mordant dyes because they are used as their chromium mordant by treatment with dichromate in the course of the dyeing procedure. However, because of their excellent fastness for light and wet treatment, they are predominandy used to dye wool in heavy shades (navy blue, brown, and black). In terms of chemical constitution, most of the acid—mordant dyes are azo dyes some are triphenyhnethane dyes and very few anthraquinone dyes are used in this area. Cl Mordant Black 13 [1324-21 -6] (183) (Cl 63615) is one of the few examples of currentiy produced anthraquinone acid—mordant dyes. It is prepared by condensation of purpurin with aniline in the presence of boric acid, followed by sulfonation and finally by conversion to the sodium salt (146,147). 

The group includes many natural and synthetic dyes, the latter usually being obtained from anthracene. They have no natural affinity for textiles but are applied to cellulosic or protein fibres which have been mordanted previously with a metallic oxide. The acid mordant dyes are a special class of dyes applied to wool or polyamide fibres as if the were acid dyes, and then given very high wet-fastness by subsequent mordanting. 

A naturally-occurring mordant dye, used extensively until a few years ago, and now probably the only one still in use, is logwood. It yields a navy blue or a black, with what is called a good bloom, when dyed on chrome mordanted wool. Until the advent of acid mordant dyes, which will be described later, it was the only dyestuff with which wool could be dj ed black with any measure of fastness. 

The shades can be brightened by the addition of acid dyes at the commencement of the dyeing, but their presence will diminish the wet-fastness. The dyes must be unaffected by dichromate and such that can be dyed satisfactorily at the pH necessary to exhaust the acid mordant dye. Some recommended dyes are given below. 

If a correction to the shade is necessary and the standard of fastness is to be maintained, the most convenient procedure is to cool the liquor to 60°C (140°F) and add sufficient sodium acetate to convert any free sulphuric to acetic acid, and then correct with an acid mordant or a premetallized dye. If the amount of dye required is not great the wool will already contain sufficient Cr Os to combine with the acid mordant dye. A few dyes suitable for shading are shown below. 

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

Most mordant dyes are monoazo stmctures. The most important feature of this class of dyes is excellent fastness to light and washing. Mordant dyes are available ia aU shades of the spectmm with the exceptioa of bright violets, blues, and greens. To be useful, the metal complexes must be stable, ie, must not demetallize when subjected to dyebath conditions and aU aftertreatment processes, especially repeated washings. Chromium forms stable chelate rings with mordant dyes which are not affected by treatment with either weak acid or alkaU (see Coordination compounds). 

Only the products associated with acid and premetallised dyes are dealt with in this section. The auxiliaries used with mordant dyes are covered in section 5.8. Anionic acid dyes, applied principally to wool and nylon, vary widely in their fastness and level-dyeing properties (section 3.2.2) in general, the higher the wet fastness of a dye the more difficult it is to apply evenly. Hence it is not surprising that the use of auxiliaries with acid dyes is related mainly to level-dyeing properties. There are two basic aspects ... 

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. 

Mordant dyes are notoriously troublesome from the viewpoint of colour matching because the hue of the chromium complex usually differs greatly from that of the unmetallised parent dye (section 5.4.1). If other metal ions are present in the treatment bath or on the fibre during chroming, the colour obtained is likely to differ from that of the pure chromium complex. Certain important chrome dyes, including Cl Mordant Black 11 (3.29) and Black 17 (3.30), are particularly sensitive to traces of iron or copper. The hue of the black dyeings obtained is redder in the presence of copper and browner with iron contamination. The fastness to light and wet treatments may also prove inferior under these conditions. Even certain 1 2 metal-complex acid dyes show similar effects in the presence of these impurities,... 

In 1871 Graebe and Liebermann discovered that alizarin (6.2) could be applied to wool by mordant dyeing after sulphonation to produce the 3-sulphonic acid (6.28). This dye is still listed in the latest revision of the Colour Index as a commercial product [11]. Although many sulphonated polyhydroxyanthraquinones have been examined, few remain in current use. Another, and more important, classic dye that continues in commercial use as an acid dye is Cl Acid Blue 45 (6.29). This dye was discovered in 1897 by Schmidt and can be made from anthrarufin (6.13) by disulphonation, subsequent dinitration and reduction. The dye gives an attractive blue on wool with good all-round fastness properties. 

Leather can be dyed with acid, direct and mordant dyes. Many of the direct dyes were based on benzidine and its congeners but the German Ordinance, covered under the toxicity of certain azo dyes in section 2.3.1.1, has meant that this is no longer an option. To improve the light fastness of the dyed leathers, 1 2 premetallised azo dyes have also been used, but once again the use of metal complex dyes is becoming less favoured. ... 

Pink Dyestuff. The superior fastness of the pink dye to all of the testing conditions indicates that it is probably a mordanted dye type. It does not demonstrate the same characteristics that are associated with either acid dyes or basic dyestuffs. Pink color intensity seems to be... 

One of the oldest known methods of producing wash-fast colors involves the use of metallic hydroxides, which form a link, or mordant (L. mordere, to bite), between the fabric and the dye. Other substances, such as tannic acid, also function as mordants. The color of the final product depends on both the dye used and the mordant. For instance, the dye Turkey Red (alizarin) is red with an aluminum mordant, violet with an iron mordant, and brownish-red with a chromium mordant. Some important mordant dyes possess a structure based on triphenylmethane, as do Crystal Violet and Malachite Green. 

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. 

Acid mordant and premetallized dyes can be applied to polyamides. They build up well into dark shades and the light- and wet-fastnesses are good. It must, however, be borne in mind that they are worse than other classes for emphasizing yarn variations. These dyes have no migrating properties once they have been taken up by the fibre and it is therefore most important to control conditions during dyeing in such a manner that the initial adsorption is uniform. 

The acid mordant and premetallized dyes are fast but lack brightness of shade. There are a number of fast acid colours which will dye wool and leave eellulose unstained when applied with ammonium sulphate or acetate. 

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. 

Chrome-tanned leather has chromium bonded to the leather fibers. This chromium can act as a mordant for acid dyes resulting in fast colors and intense shading at the surface of the leather. 

Salicylic acid is manufactured on a large scale. In the dye industry it serves for the production of valuable azo-dyes which exhibit great fastness. To some extent these dyes are applied to mordanted fibres. In addition, the acid and its derivatives are widely used in pharmacy. Being a phenolcarboxylic acid it has a powerful disinfecting action (preservative). It has further proved itself an important antirheumatic and an analgetic. The derivative in which the phenolic hydroxyl group is acetylated (aspirin) has become especially popular. The first medicament of the series was the phenyl ester of salicylic acid, salol, which is produced as a by-product in the technical process. The preparation of salicylaldehyde has been described above (p. 235). 

The members of this class dye wool and silk directly, but cotton only when the latter is mordanted by tannin. They are fast neither to acids nor to alkalis for reasons which depend on important alterations in the compounds. If a little dilute hydrochloric acid is added to an aqueous solution of crystal violet the colour changes to green. One N(CH3)2-group takes part in the change and there is formed the salt with two equivalents of acid ... 

Other Dyes. Other dye classes listed in the Colour Index include dyes lor leather, solvents, paper, and food. Leather dyes arc those acid, direct, mordant, and basic dyes that show substamivily for leather, good diffusion into it. and acceptable fastness. They are essentially applied in an analogous... 

Diamine, benzo. dianil Chicago, chlorazol, naphthamine, etc., blues and Sky flues, sulphon acid blue, sulphoncyanine, sulphonazurine, erio fast bine S W R, tolyl blue G R extra and 5 R extra, etc. a ur is not V a r or tc dant. Mordant absent t Salt Dye stuff. Confirm by boil ing with 5 per cent, sodium acetate and a piece of white cotton. CbttOn stained. ><... 

---