Various classes of colorants and its classification

1. COLOURANTS
BY
B. Venkatesh
Asst. Professor,
Dept. of Textile Technology
VFSTR University

2. INTRODUCTION
Colouring materials are mainly of three types, viz.
dyes,
pigments and
lakes (ingrain dyes).
A dye has three parts in its structure – chromophore, chromogen and
auxochrome – and is soluble in a specific medium under certain
conditions.
Chromophore is an unsaturated group that absorbs light and
reflects it at specific angle to give the hue,
e.g. azo, keto, nitro, nitroso, thio, ethylene, etc.;

3. Chromogen retains chromophore and plays a crucial role to
determine the final hue and its affinity for fibre, fastness, stability,
etc.
While auxochrome is a substituted acidic or basic group in dye
structure to intensify depth of shade,
e.g. –OH, –COOH, SO3H, –NH,etc.

4. Classification
Colouring materials are also classified in several other ways based
on their
source or origin,
chemical structure,
field of application,
ionic nature and
solubility in water, etc.

5. SOURCE OF ORIGIN
Natural colours
Synthetic colours

6. CHEMICAL STRUCTURE
Colouring materials are also classified based on their chemical
structure.
e.g., azo, nitro, nitroso, stilbene, di- and tri-phenylmethane,
xanthene, acridine, quinoline, methane, thiazole, azine, oxazine,
thiazine, anthraquinone, indigoid and phthalocyanine, etc

7. FIELD OF APPLICATION

8. IONIC NATURE
Dyes can also be classified according to electrical charge that
exists in its ionized coloured part before or during dyeing.
Based on this, direct, acid, reactive, sulphur, metal-complex,
vat and soluble vat dyes are anionic;
Basic dye is cationic
Disperse dye is non-ionic in nature

9. SOLUBILITY IN WATER
Water is the universal medium of dyeing.
It is cheaper, non toxic, easily available and can be recovered and
reused.
That is why solubility of dye in water is an important factor in dyeing.
 Direct, reactive, solubilised vat and acid dyes are water-soluble
dyes.
 Vat and sulphur dyes are water insoluble but can be taken into
solution by reduction and solubilisation.
Basic dye is soluble in acidic warm bath
while other dyes are insoluble in water under normal conditions.

10. THANK YOU