Classification of dyes on the basis of applications:
(i) Direct Dyes:
The fibres are soaked in a hot solution of dye and then dries after taking out. These dyes applied directly to fibre and are more useful to the fabrics containing H-bonding like cotton, rayon, wool, silk and nylon.
Examples:
Martius yellow, Congo red etc.
(ii) Acidic Dyes:
These dyes are used in slightly acidic medium and are generally sulphonic acid and its derivatives. These are water soluble. These do not have an affinity for cotton but are used for silk, wood etc.
(iii) Basic Dyes:
These dyes contain basic group (like – NH2 group) and react with anionic sites present on the fabric. These are used to dye nylons and polyester.
Example:
Aniline yellow.
(iv) Disperse Dyes:
Disperse dyes are water-insoluble. Their dyes are finely grinding and are available as a paste or a powder that gets dispersed in water. These particles are dissolved in the fibres and impart colour to them. These dyes were originally developed for the dyeing of cellulose acetate but now they are used to dye nylon, cellulose triacetate and acrylic fibres too.
(v) Reactive Dyes:
Reactive dyes react with fibres molecules to form a chemical compound. Reactive dyes were originally used for cellulose fibres only but now their various types are used for wool, silk, nylon, acrylics and their blends as well.
Example:
Prussian red.
(vi) Ingrain Dyes:
These dyes are also known as ‘ice-colours’ because they react at low temperatures. Ingrain dyes are those which are synthesized directly on the fabric.
Example:
Azo-dye.
