Dye affinity

Dye affinity is an important dyeing factor for all dyes and dyeing process. Most of the properties of a dye depend on the dye affinity and dye reactivity. In simple terms, dye affinity (also neutral affinity) is the dye absorbing capacity (of textile fibres, yarn, fabrics). It varies between wide limits depending on the state of dyebath equilibrium between the fibre and the dye in solution. A number of factors play an important role in this process, e.g. dyeing liquor ratio, dye physical and chemical characteristics (it could be organic or inorganic), additions to the dyebath (such as dye acid, organic or inorganic salts and dyeing auxiliaries), dyeing time (time from start to end of dyeing), dyeing temperature (temperature vary according to dyes and dyeing property), and the degree of purity (purity of all dyes, chemicals, acids, salts and auxiliaries), extent of drawing and degree of crystallinity (rate of crystalline region and amorphous region) of the fibre being dyed, as well as the number of dye bonding groups available in the fibre (it means the reactivity of dyes). For dye affinity- controlled dyeing processes, a temperature is selected at which diffusion proceeds at a relatively fast rate inside the dye bath . If it is assumed, as a model, that a dyebath exhaustion equilibrium is established momentarily at any one time, then the kinetics of exhaustion are given by the change in chemical equilibrium. For synthetic polyamide fibres and natureal wool fibre, the chemical equilibrium between the dye in the textile fibre (concentration CF) and the dye in the liquor (CL) can be approached by a superimposed Langmuir and Nernst distribution with the pH-dependent distribution coefficients kL and kN, and the saturation value SL. The pH dependencies are both dye and fibre-specific.

Dye affinity of wool, treatments to improve,

a) Pretreat for 1 h at the boil in a 5% inorganic potassium thiocyanate solution, rinse, dye in the presence of 20% sodium sulphate and 5% acetic acid 30%;

b) Bring the yarn to the boil in a solution of 2,5–4% solution of sodium thiosulphate or neutral sodium  sulphite or sodium tetraborate, boil for 1 h, hydroextract and dry;

c) Treat the natural wool fibre for 20–30 min. in a liquor containing 1–1,5% active chlorine under weakly acidic conditions, treat in a fresh bath with 1–2 g/l sodium dithionite as an antichlor and bleach.

Dye ager is a horizontal continuous-dyeing machine for all conventional textile fabrics (including difficult qualities such as cotton velvet and lining fabrics) with all classes of dye, by the pad-steam process and the wet-in-wet process of vat dyeing voluminous fabrics in which dye is applied on a preceding padder and the reducing agent padded on directly before the ager entry using a special applicator unit. A high degree of reproducibility is achieved by the ager.

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