Standardization of Textile Dyes

Dyers task is to give a visual impression to the human eye. The eye is a very positive organ that can detect very slight color differences. Since dyes are industrial products, they may contain impurities and colored or colorless by products, depending on their production process. Dyes are standardized not to a certain chemical composition but to a defined coloristic value. Consequently they may be composed of mixture of dyes and may contain shading components. For example all disperse and cationic blacks are mixtures of dyes.

Principles of standardization setup by special of dye producer as testing procedure for textile dyes.

a. Relative color strength in solution.

b. Relative color strength and residual color difference by reflectance measurements.

c. Solubility and solution stability.

d. Electrolyte stability of reactive dyes.

e. Viscosity of liquid dyes.

f. Dispersion behavior and dispersion properties.

The coloring properties of a dye assessed by preparing a dyed test sample whose color is evaluated. This must a principle always be done by the human eye because color perception being a objective sense impression, is not accessible to direct measurement. However, the aid of colorimetry this visual perception can be represented more or less cloyety by measurable quantities.

To test a dye dyed test a dye dyed test specimen from bath the sample dye and the standard are compared under conditions that are as identical as possible and assessed visually or colorimetrically and then calculated in relative terms to the standard. A widely used method to calculate color strength is a determination based on the weighted sum of k/s values (k is the coefficient of absorption, s is the coefficient of scatter which is used in standard specifications.

For the dyeing process in aqueous liquor the dye must have adequate solubility or dispersibility. In general good solubility is necessary for good application properties. If the solubility is poor, local coloration (specks) spots uneven effects and poor fastness can be produced.