Azoic dyes application

These products, which have been copied by other manufacturers under various tradenames, are designed specifically for printing applications. Azoic dyeing applications were catered for in 1967 when Hoechst introduced the Azanil salts, a limited range of mixtures of substantive triazenes and Naphtols that can be absorbed onto the fabric and the colour developed by acidification of the dyebath. 

Azoic dyes contain the azo group (and formic acid, caustic soda, metallic compounds, and sodium nitrate) especially for application to cotton. 

Overall, the application procedures for azoic dyeing are quite complex since many factors must be taken into account, such as ... 

These are the only ranges of precursor products in the Colour Index that are still commercially significant. Azoic dyes have a close formal relationship to those monoazo pigments derived from BON acid or from acetoacetanilides (section 2.3.1) and some are chemically identical with them, although they are used in a totally different way. Azoic components are applied to produce insoluble azo dyes within the textile substrate, which is almost always cotton. Corresponding azoic components for the dyeing of cellulose acetate, triacetate and polyester fibres were once commercially important, but are now obsolete because of environmental hazards and the time-consuming application procedure. 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

Most azoic dyes belong to the carbocyclic azo class, but these dyes are formed in the fiber pores during the application process. 

Another approach for removing reactive dye hydrolysates from the fibre and from the wash water (decolourised waste water) is the use of peroxidases (oxidative active enzymes such as Baylase RP). This multipurpose enzymatic rinse process saves time, energy and water but it is restricted mainly to jet applications. The question of the potential toxicity of the resulting aromatic nitro-compounds (cleavage products of the reactive azoic dyes) has to be resolved. 

The nature of substrate selects the type of dye needed, and methods of dye application. The development of new substrates led to new dyes and dyeing methods and influenced the dyeing technology in a fundamental manner. The dyeing of any substance (e.g., textile fiber) is based on a physico-chemical equilibrium process, namely diffusion and sorption of dye molecules or ions. These processes may be followed by chemical reactions in the substrate, for example, in the application of vat, reactive, azoic, and chrome dyes [9]. 

It has been known for a long time that it is possible to dye acetate fibres with azoic dyes provided the right combinations are selected and suitable modifications in the method of application are made. Wallwork (J.S.D.C., 1935, 51,415) proposed a reversal of the norrnal procedure by impregnating with the base first, diazotizing, and then coupling with the /i-hydroxynaph-thoic acid derivative or, alternatively, impregnating with a mixture of the... 

Azoic dyes can be applied to unions but there are many complications. An alkali concentration of 4 g per litre is sufficient to keep most of the coupling components in solution, and the application should be carried out cold in as short a liquor as possible. The coupling is accomplished in a separate bath with the diazotized base and 25 g per litre of common salt to prevent the coupling component from migrating into the liquor. Development requires 20 to 30 minutes, after which the material is acidified and scoured. 

Dyes Requiring Chemical Reaction before Application Vat dyes Azoic dyes Sul fur dyes... 

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. 

Most dyes do not chemically react with the cellulose molecule to affix the color. The roles of interchain hydrogen bonding and van der Waals forces in the application of azoic, direct, sulfur, and vat dyes are the physical and chemical effects and are not classical chemical reactions. Tme chemical reaction between cellulose and the dye molecule occurs with reactive dyes, which comprise different chemical types (see Section 9.6.2.3). Such chemical reaction results in covalent bond formation between the dye molecules and the C6 hydroxyl groups of... 

Dye allergens are found in the disperse, acid, azoic, basic, direct, pigment, reactive, solvent, and vat application classes. No dye allergens belong to the mordant and sulfur application classes. Almost 50% of the 70 reported dye allergens are disperse, about 20% are reactive, and 10% are acid. 

Effect of Heat Sticks at 230C Melts at 260C Acceptance of Dye Disperse and azoic dyestuffs recommended Available in a wide variety of solution dyed colors, including black for automotive applications. 

Both vat and sulfur dyes must be chemically reduced before application to a fiber, whereas azoic or naphthol dyes are formed through reaction of two separate dye components after appl ication to the fiber. These dyes tend to penetrate the fiber less than other dyes, and care must be exercised in application to get reasonable fastness properties. 

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