Disperse Dyes

Disperse Dyes

Disperse dyes are often substituted azo, anthraquinone or diphenylamine compounds which are non-ionic and contain no water solubilizing groups. The dye particles are thus held in dispersion by the surface-active agent& possess inherent substantivity for hydrophobic fibre. They are marketed in the form of either an easily dispersible powder or a concentrated
aqueous dispersion. According to sublimation fastness and dyeing properties, disperse dye fall into four category where

Class A dyes had low relative molecular masses and hence poor sublimation fastness, but desirable dyeing properties, whereas Class D dyes had high relative molecular masses and therefore good sublimation fastness, but somewhat poorer dyeing properties. Classes B and C were between these two extremes.Small dye molecules with low polarity are levelling, rapid dyeing dyes with poor heat resistance. These are called low energy disperse dyes. More polar,higher molecular weight dyes have low dyeing rates, poor migration during dyeing but good heat and sublimation fastness. These constitute the high energy disperse dyes. One of important property of disperse dye is heat fastness.

The heat fastness of dyeing is dependent on the size and polarity of the molecules of the dye which in turn determine the rate of diffusion. Increases in size and/or polarity will tend to reduce the rate of diffusion which means slower fibre penetration, reduced leveling power and lower color yields. Increase in size will increase hydrophobicity (affinity towards fibre) & increase in polarity will increase hydrogen bonding potentiality which reduce sublime.