Dyeing dyestuff application

The split into the various textile dyestuff application areas has, over recent years, seen a shift towards the two main outlets of disperse dyes for polyester and reactive dyes for cellulosics (mainly cotton), at the expense of directs and vat dyes for cotton, cationic dyes for acrylics and acid dyes for polyamide. The latter fibre has shown a comeback in recent years with the popularity of microfibres in sports and leisure wear. The position in 1998, with disperse dyes dominating in value terms, was as shown in Table 2.6. 

Since 1973, the U.S. International Trade Commission has reported the manufacture and sales of dyes by application class only. In 1972, the last year for which statistics are available by chemical class, 3900 metric tons of triarylmethane dyes were manufactured, which represents approximately 4% of total dyestuff production in the United States. At that time, there were 185 triarylmethane dyes Us ted in the Colour Index. From the latter half of the 1970s through the 1980s, annual dye production in the United States, including triarylmethane dyes, changed very litde. In 1981, methyl violet, with an annual production of 725 t, was the only triarylmethane dye for which production statistics were available. Some triarylmethane dyes were imported, eg, malachite green (163 t in 1981), methyl violet (40 t), new fuchsine (30 t), and other dyes totalling less than 15 t. 

Cellulose acetate yarn, when it appeared on the market in 1921, presented a new problem because it had no adequate affinity for any of the existing dyestuffs. The first satisfactory method of coloration was due to Holland Ellis who observed that many simple insoluble azo dyes would be absorbed by cellulose acetate from an aqueous dispersion, stabilized with sulphated fatty alcohols or similar surface active compounds. A large number of dyes whose application depends on this principle have now made their appearance and are known as the disperse dyes. The demand for this group has increased very significantly with the advent of the truly synthetic man-made fibres. 

Manufacturers Literature. The manuals, technical bulletins, and reports issued by the Calco Chemical Division, American Cyanamid Co. Ciba Co. Sandoz Chemical Works E. I. du Pont de Nemours Co. General Dyestuff Corp. Division of General Aniline Geigy Go. Inc. National Aniline Division, Allied Chemical and Dye Corp. and Imperial Chemical Industries are valuable sources of information on new dyes and applications. There are other companies that publish literature equally as valuable and useful. 

Standard polyester fibers contain no reactive dye sites. PET fibers are typically dyed by diffusiag dispersed dyestuffs iato the amorphous regions ia the fibers. Copolyesters from a variety of copolymeri2able glycol or diacid comonomers open the fiber stmcture to achieve deep dyeabiHty (7,28—30). This approach is useful when the attendant effects on the copolyester thermal or physical properties are not of concern (31,32). The addition of anionic sites to polyester usiag sodium dimethyl 5-sulfoisophthalate [3965-55-7] has been practiced to make fibers receptive to cationic dyes (33). Yams and fabrics made from mixtures of disperse and cationicaHy dyeable PET show a visual range from subde heather tones to striking contrasts (see Dyes, application and evaluation). 

Engel A (1994) Fluorine-Containing Dyes. B. Other fluorinated dyestuffs. In Organofluorine Chemistry Principles and Commercial Applications (Eds RE Banks, BE Smart, JC Tatlow), pp. 321-338. Plenum Press, New York. 

Fluoran compounds generally lack color stability, and therefore had lost their value as dyestuff for textile finishing. It is, however, very interesting that the old-fashioned fluoran compounds have come around as leuco dyes for use in the new applications. 

Identification of dyes on dyed textiles is traditionally carried out by destructive techniques [493], TLC is an outstanding technique for identification of extracted dyestuffs and examination of inks. Figure 4.9 shows HPTLC/SERRS analysis of acridine orange [492], Wright et al. [494] have described a simple and rapid TLC-videodensitometric method for in situ quantification of lower halogenated subsidiary colours (LHSC) in multiple dye samples. The results obtained by this method were compared with those obtained by an indirect TLC-spectrophotometric method and those from HPLC. The total time for the TLC-videodensitometric assay of five standards and four samples applied to each plate was less than 45 min. The method is applicable for use in routine batch-certification analysis. Loger et al. [495,496] have chromatographed 19 basic dyes for PAN fibres on alumina on thin-layer with ethanol-water (5 2) and another 11 dyes on silica gel G with pyridine-water... 

Shortly after Perkin had produced the first commercially successful dyestuff, a discovery was made which led to what is now the dominant chemical class of dyestuffs, the azo dyes. This development stemmed from the work of Peter Griess, who in 1858 passed nitrous fumes (which correspond to the formula N203) into a cold alcoholic solution of 2-aminO 4,6 dinitrophenol (picramic acid) and isolated a cationic product, the properties of which showed it to be a member of a new class of compounds [1]. Griess extended his investigations to other primary aromatic amines and showed his reaction to be generally applicable. He named the products diazo compounds and the reaction came to be known as the diazotisation reaction. This reaction can be represented most simply by Scheme 4.1, in which HX stands for a strong monobasic acid and Ar is any aromatic or heteroaromatic nucleus. 

As shown in Table 1 the wastewater limit for chromium is 0.5-1 mg/L and Cr is 0.1 mg/L. While conventional 1 2 and 1 1 dyes permit chromium concentrations in the dyebath at the end of the dyeing process of 3.0-13.0 mg/L Cr, the application of modem dyestuffs and optimized processes permits final concentrations to approximately 1 ppm. By general optimization of the process (e.g., dosage of acid), use of dyes with a high degree of exhaustion, and minimal concentration of free chromium [15], final bath concentrations below 4 ppm can be reached, even for black shades. By application of such procedures the exhaustion of the chromium should reach values of better than 95% of the initial value. 

The nomenclature given for these componnds is a nniversally recognised system for the naming of dyestuffs devised by the Society of Dyers and Colourists as part of their Colour Index (Cl). The Cl Generic Name is made up of the application class, the hne and a nnmber. Acid dyes are nsed on wool and polyamide, direct dyes on cel-lulosic fibres, paper and leather, disperse dyes on polyester fibres, reactive dyes on cellnlosic fibres and basic dyes on polyacrylonitrile and paper. 

An alternative way of classifying dyestuffs is by their application areas, but as there is large overlap between product structural classes and their uses, it is less satisfactory. However, from a commercial standpoint it is the application method that determines the potential of a dyestuff and the reason for its industrial manufacture and sales. In this section the different application methods will be described mainly in relation to the end use, e.g. the dyeing or printing of cotton and other fibres, the coloration of paper or leather, the use in food and cosmetics etc. 

Library of Congress Cataloging in Publication Data. Main entry under title Physical and chemical applications of dyestuffs. (Topics in current chemistry 61). Bibliography p. Includes index. 1. Dyes and dyeing—Chemistry.I. Series. QD1.F58 vol. 61 [QD441] 540 8s [547486] 75-40486 ISBN 0-387-07559-3... 

Chromium and cobalt are the metals most commonly used in dyestuffs for polyamide fibres and leather because of their kinetic inertness and the stability of their complexes towards acid. Since the advent of fibre-reactive dyestuffs, chromium and cobalt complexes have also found application as dyestuffs for cellulosic fibres, particularly as black shades of high light-fastness. Copper complexes are of more importance as dyes for cellulosic fibres and are unsuitable for polyamide fibres because of their rather low stability towards acid treatments. 

The most important azo compounds employed in the manufacture of dyes of this type are those containing the < ,o -dihydroxyazo-, the o-hydroxy-o -carboxyazo- and the o-hydroxy-o -amino-diarylazo systems. It is well established3 33-0 that these form four-coordinate copper and nickel complexes (35) in which the coordination sphere of the metal can be completed by a variety of neutral ligands. In both cases the light-fastness of the parent azo compound is improved as a result of complex formation but the nickel complexes are insufficiently stable towards acid to be of commercial interest as dyestuffs. The history of copper complexes has already been discussed (Section 58.1) and will not be considered further here, although it is worthy of mention that currently the most important copper complex dyestuffs are those containing fibre-reactive systems, e.g. (36), for application on cellulosic fibres. 

Much more important commercially are the 2 1 chromium(III) and 2 1 cobalt(III) complexes of tridentate azo compounds, which find a wider application, particularly as dyestuffs for wool, polyamide fibres and leather. These have been the subject of reviews23 24 which discuss their dyeing properties in detail. The patent literature on metal complex dyes of these types is vast but since this relates principally to the achievement of specific, desirable technical effects by appropriate substitution of the azo compounds it will not be considered in detail here. Rather will the emphasis be placed upon those aspects of dyestuffs of this type which are of general interest in the context of their coordination chemistry and, more particularly, on those areas where uncertainties exist or conflicting results have been reported. 

Metal complexes of tetradentate azomethines, e.g. (199), are reported136 to have very high light-fastness but to be tinctorially weak and dull in hue. Despite this they are of technical interest as very fast yellow to brown pigments. They find no application as dyestuffs, however, because of these deficiencies for example, the chromium complex of (200) gives dull, tinctorially weak dyeings on wool possessing poor wet-fastness properties. 

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