Dye:
Chemical substance/colorants that can be fixed with material, when fixed isn't fugitive.
Properties of Dye:
- Fast to light.
- Intense in color
- Solubility in water.
- Not washable with water, dil acid and alkali.
Classification of Dye:
1. Based on Chemical constitution.
2. Based on application.
1. Based on chemical constitution:
- Azo dye.
- Anthraqunoid dye.
- Di-phenyl-amine dye.
- Di-phenyl-methane dye.
- Tri-phenyl-methane dye.
- Nitro dye.
- Nitroso dye.
- Heterocyclic dye.
- Xanthen dye.
- Phthalocyanin dye.
2. Based on application:
- Acid dye
- Basic dye
- Direct dye
- Vat dye
- Sulphur dye.
- Natural dye.
★ Acid-dye:
These dyes are generally sodium or potassium salts of organic coloured acid & ionise as follows:
NaA (dye) —> Na+ + A- (coloured acid)
It is negatively charged acid protein A- which imparts colour to the fabric. For full & uniform shades the dyes are completely ionised in the solution by addition of acids.
★ Basic dye:
These dyes are generally chlorides or hydro-chlorides of coloured bases & ionise in the solution as follows:
BCl (dye) —> B+ (coloured base) + Cl-
The positively charged coloured bases actually react & imparts colour to the substances.
★ Direct dye:
Like acid dye this dye are also Na/K salts of coloured acid & behave in the same way as acid dye. This dyes can be directly used (without any pretreatment) to impart color to the fabric.
★ Vat-dye:
This group of dyes are suitable for cotton dyeing. They are insoluble in water but when reduced in an alkaline medium become soluble but practically colourless.
★ Sulphur dye:
The dye-stuff of this group contain sulphur & their chemical nature is more or less undetermined.
★ Natural dye:
Before the discovery of coal-tar dye the leather colourist had to rely upon the coloring materials derived from the vegetable substance & some of them are used even today by some tanners.