Лако-красочные материалы — производство

The classification of dyes according to their usage is summarised in Table 1.1, which is arranged according to the C. I. application classification. It shows the principal substrates, the methods of application, and the representative chemical types for each application class.

Although not shown in Table 1.1, dyes are also used in high-tech applications, such as in the medical, electronics, and especially the nonimpact printing indus­tries. For example, they are used in electrophotography (photocopying and laser printing) in both the toner and the organic photoconductor, in ink-jet printing, and in direct and thermal transfer printing [6] (see Chapter 6). As in traditional applications, azo dyes predominate; phthalocyanine, anthraquinone, xanthene and triphenylmethane dyes are also used. These applications are currently low volume (tens of kilograms up to several hundred tonnes per annum) but high added value (hundreds of dollars to many thousand dollars per kilogram), with high growth rates (up to 60 %).

Reactive Dyes. These dyes form a covalent bond with the fiber, usually cotton, although they are used to a small extent on wool and nylon. This class of dyes, first introduced commercially in 1956 by ICI, made it possible to achieve ex­tremely high washfastness properties by relatively simple dyeing methods. A marked advantage of reactive dyes over direct dyes is that their chemical struc­tures are much simpler, their absorption spectra show narrower absorption bands, and the dyeings are brighter. The principal chemical classes of reactive dyes are azo (including metallized azo), triphendioxazine, phthalocyanine, formazan, and anthraquinone (see Section 3.1).

High-purity reactive dyes are used in the ink-jet printing of textiles, especially cotton.

Disperse Dyes. These are substantially water-insoluble nonionic dyes for applica­tion to hydrophobic fibers from aqueous dispersion. They are used predominant­ly on polyester and to a lesser extent on nylon, cellulose, cellulose acetate, and acrylic fibers. Thermal transfer printing and dye diffusion thermal transfer (D2T2) processes for electronic photography represent niche markets for select­ed members of this class (see Chapter 6).

Direct Dyes. These water-soluble anionic dyes, when dyed from aqueous solution in the presence of electrolytes, are substantive to, i. e., have high affinity for, cellu — losic fibers. Their principal use is the dyeing of cotton and regenerated cellulose, paper, leather, and, to a lesser extent, nylon. Most of the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines, and oxazines. Aftertreatments, frequently applied to the dyed material to improve washfastness properties, include chelation with salts of metals (usually copper or chromium), and treatment with formaldehyde or a cationic dye-complexing resin.

Vat Dyes. These water-insoluble dyes are applied mainly to cellulosic fibers as soluble leuco salts after reduction in an alkaline bath, usually with sodium hydro — gensulfite. Following exhaustion onto the fiber, the leuco forms are reoxidized to the insoluble keto forms and aftertreated, usually by soaping, to redevelop the crystal structure. The principal chemical classes of vat dyes are anthraquinone and indigoid.

Sulfur Dyes. These dyes are applied to cotton from an alkaline reducing bath with sodium sulfide as the reducing agent. Numerically this is a relatively small group of dyes. The low cost and good washfastness properties of the dyeings make this class important from an economic standpoint (see Section 3.6). How­ever, they are under pressure from an environmental viewpoint.

Cationic (Basic) Dyes. These water-soluble cationic dyes are applied to paper, polyacrylonitrile (e. g. Dralon), modified nylons, and modified polyesters. Their original use was for silk, wool, and tannin-mordanted cotton when brightness of shade was more important than fastness to light and washing. Basic dyes are water-soluble and yield colored cations in solution. For this reason they are fre­quently referred to as cationic dyes. The principal chemical classes are diazahemi — cyanine, triarylmethane, cyanine, hemicyanine, thiazine, oxazine, and acridine. Some basic dyes show biological activity and are used in medicine as antiseptics.

Acid Dyes. These water-soluble anionic dyes are applied to nylon, wool, silk, and modified acrylics. They are also used to some extent for paper, leather, ink-jet printing, food, and cosmetics.

Solvent Dyes. These water-insoluble but solvent-soluble dyes are devoid of polar solubilizing groups such as sulfonic acid, carboxylic acid, or quaternary ammo­nium. They are used for coloring plastics, gasoline, oils, and waxes. The dyes are predominantly azo and anthraquinone, but phthalocyanine and triarylmethane dyes are also used.