Disperse Special Dyeing Processes

An important assumption, however, is assumption 6, since it separates convection and dispersion. Assumptions 7 and 8 aim to further incorporate the adsorption factor into the model. According to the theory and practice, these assrrmptions are reasonable. These basic assiunptions, and special definitions for some individttal cases, provide a basis for mathematical modelling of the dyeing process. 

Azo dyes represent the largest group of disperse dyes for two reasons (1) the ease with which an extraordinary number of molecular combinations can be generated by varying the diazo and coupling components and (2) the relatively simple process by which the dyes can be produced. With this class of dyes, manufacturers can respond much more easily to customers and end users requests for special shades and fastness characteristics. 

The use of vat dyes in pigment form for cheeses and rayon cakes suggested improved techniques for various continuous and semi-continuous padding methods for the application of vat dyes to piece goods. Most vat dyes are now marketed in forms specially prepared to yield relatively stable dispersions of extremely finely-divided particles required for pigmentation. Fhe earliest and simplest procedure was the so-called pigment-pad process illustrated diagrammatically in Fig. 20.3 Ciba review. No. 120). In this case... 

DuPont [63] claimed a process for stabilisation of dyed poly(trimethylene terephthalate) fibres by adding a speciality benzotriazole in the dye bath (Cibafast USM Ciba). The structure of this additive was not revealed, but it most probably features extra substituents in the form of sulfonic acid(s) or derivatives thereof, which would allow the additive to be dispersed or dissolved in the aqueous dye bath. 

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