Classification of Reactive Dyes

A valuable classification of reactive dye types has been formulated recently [1]. Three groups relating to the most important control parameter in each case may be distinguished.

Group 1: Alkali-controllable reactive dyes
These dyes have optimal temperatures of fixation between 40 and 60°C. They are characterised by relatively low exhaustion in neutral salt solution before alkali is added. They have high reactivity and care in addition of alkali is necessary to achieve level dyeing, preferably at a controlled dosage rate. Typical examples of dyes belonging to this group have dichlorotriazine, chlorodifluoropyrimidine, dichloroquinoxaline or vinylsulphone reactive systems.
Group 2: Salt-controllable reactive dyes
Dyes in this group show optimal fixation at a temperature between 80°C and the boil. Such dyes exhibit comparatively high exhaustion at neutral pH, so it is important to add salt carefully to ensure that dyeings are level. Electrolyte addition is often made portionwise or preferably at a controlled rate of dosage.

Dyes with these properties typically have low-reactivity systems such as trichloropyrimidine, aminochlorotriazine or bis(aminochlorotriazine). Aminofluorotriazine dyes in the Cibacron F (CGY) range have high substantivity and should thus be regarded as salt-controllable but they are sufficiently reactive for fixation at 60°C or even lower temperatures by batchwise application.

Group 3: Temperature-controllable reactive dyes
This group is represented by those dyes that react with cellulose at temperatures above the boil in the absence of alkali, although if desired they can be applied under the same conditions as the salt-controllable group with alkaline fixation at a temperature between 80°C and the boil. Dyes in this group have self-levelling characteristics so there is no need to use auxiliary products to facilitate level dyeing. Good results can be achieved by controlling the rate of temperature rise.

At present only the Kayacelon React (KYK) range of bis(aminonicotinotriazine) dyes belong to this group.

References:

1. T Sugimoto J.S.D.C., 108 (1992) 497.