Disperse dyeing

Disperse dyes were introduced in 1923 by British Celanese and the British Dyestuffs Corporation for acetate fibres and are today standard for polyester, polyamide and acetate. About 60 percent are monoazo dyes, about 25 percent anthraquinone derivatives with brilliant reds, blues and turquoises. The dyes are water-insoluble and milled with dispersing agents to particle sizes below 1 micrometre.

Standard dyeing takes place in the HT autoclave (high temperature) at 130 degrees Celsius under pressure. At this temperature the crystalline structure of polyester opens and the dye diffuses into the fibre as a monomolecular solution. Alternatively, thermosol dyeing runs continuously at 200-215 degrees without pressure.

Disperse-dyed polyester reaches excellent wash fastness (5) and good light fastness (6-7). Drawbacks are wet-fastness challenges on polyester-cotton blends (migration into cotton during ironing) and the energy demand of HT dyeing.