Dyeing characteristics

Affinity values aie obtained by substituting concentiation foi activity in equation 4 foi the dye and, wheie appropriate, other ions in the system. A number of equations are used depending on the dye—fiber combination (6). An alternative term used is the substantivity ratio which is simply the partition between the concentration of dye in the fiber and dyebath phases. The values obtained are specific to a particular dye—fiber combination, are insensitive to hquor ratios, but sensitive to all other dyebath variables. If these limitations are understood, substantivity ratios are a useful measure of dyeing characteristics under specific appHcation conditions. 

Difficulties of incompatibility can arise with mixtures of basic dyes on acrylic fibres because of competition for the limited number of dyeing sites available and the differences between dyes in terms of affinity and rate of diffusion. The rate of uptake of each dye when applied in admixture with another is invariably slower than when the dye is applied alone at the same concentration. Competition effects of this kind can lead to serious practical problems unless the dyes are carefully designed and selected to have similar dyeing characteristics [97,98,104,105]. Dyes with exceptionally low affinity and rapid rates of diffusion have been developed, offering improved migration on acrylic fibres [106]. These dyes have migration properties not unlike those of monosulphonated acid dyes on nylon. 

Oxadithiolane 2,2,5,5-tetroxide and the corresponding benzoxadithiole tetroxide may be used to improve the dyeing characteristics of polyesters with basic dyes <7lJAP714263l). 

Dyeing Characteristics. Disperse dyes, high melting crystalline compounds w ith low solubility in the dye hath, are most frequently used for cellulose acelate and triacetate fibers. 

High dyeing rates bear the danger of unlevel dyeings. Therefore, dyes have to be carefully selected when used together in one recipe. The dye producers readily communicate their knowledge on dyeing characteristics of their dyes and on the particular requirements for all textile fibers. 

Skinkly, J. H., Practical Tests for Quantitatively Evaluating Dye Characteristics and Dye-... 

Fig. 4. Dyeing characteristics as affected by various blocking groups. Water solubility decreases washfastness and affinity increase.

---