Classification of Dyes

Before understanding classification of dyes, we must know the difference in between dyestuff and pigment. Beside this why we do dyeing and characteristic of dyes should also be understood well. Let us discuss these points first.

Dyestuff is organic or inorganic substances which can absorb light and reflect some lights to show color.  Actually, the dyestuff is water soluble substances. In textiles, it is used to dye textile materials. They absorbed or adsorbed into the fibre

Pigment is a substance that can absorb light and reflect some lights to show color. Not water soluble and possess no specific attraction for any particular fibre type. They usually adhere to the surface of the fibre Normally it is used for printing (with the presence of binder) or mass-coloration of the synthetic fibers. They do not belong to dyes.

Why we do dyeing/printing?

•         Because Colored products are attractive and gives pleasure/ comfort

•         In textile dyeing terms: The main objectives of dyeing are:

•         Colour the fibre uniformly

•          Achieve acceptable durability of the     colour to further treatments in production and normal use    ( colour fastness properties)

Characteristics of dyes: Following are the important poits related to characteristics of dyes:

•         Intense colour

•         Solubility in water

•         Substantivity to the fibre in question

•         Durability to wet treatment

•         Durability to further treatments in  production and normal use

•         Safe, easy to handle, and reasonably priced

Intense colour

•         The dyes have intense colours.

•         Due to intense colour small amount of dyes are sufficient to obtain desired shades.

•         In practice, the increase in weight of fibrs by dyeing is between 0.1% to 5%

Solubility in water

•         Dyes are soluble or dispersible in water

•         Water is the vehicle of exhaust dyeing; it carries the dyes to the fibres.

•         Disperse dyes are sparingly soluble in water, the require dispersing agent.

Substantivity to the fibre

•         Dyes have to be substantive to the fibre in question.

•         The affinity that a dye has particular fibre is referred to by the dyers as ‘Substantivity’

•         The substantivity of a dye to a fibre must be much stronger than affinity to water

Durability to wet treatment

•         Dye must possess the ability to become durable to wet treatment

•         A high substantivity dyes some time provide sufficient durability of the colour to a limited number of mild washing

•         So after treatment step may be taken to improve upon durability

Durability to further treatment in production and normal use

•         Dyes should have fastness to further treatment in production and normal use.

•         Example: To apply durable press finish, the dyes should withstand the low pH and high temperature

•         In addition dyes should have good fastness properties

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Safe, easy to handle, and reasonably priced

•         The dyes should be safe, easy to handle and reasonably priced