Preparation of nylon for dyeing with disperse dyes

The preparation of nylon goods for dyeing usually involves scouring with a detergent and soda ash (sodium carbonate) solution at 70 °C. This removes any soluble sizing material, lubricants, and spin finishes that might hinder access of the dye solution to the fibre surface.

Heat setting of nylon fabrics has already been discussed. This process may be performed before or after dyeing, preferably the latter. It causes variations in dye substantivity and may be non-uniform, leading to unlevel dyeings. Dry heat setting in hot air decreases the rate of dyeing of nylon 6.6 and 6 with both acid and disperse dyes, but setting in steam increases their dyeing rates. Steam setting, however, decreases the wet fastness of dyeings with disperse dyes, particularly if setting is carried out after dyeing. The more open fibre structure resulting from heat setting in steam allows easier dye desorption during washing of the dyed material. If it is necessary to bleach nylon that has become yellow from over-vigorous heat setting in dry air, peracetic acid or sodium chlorite solution can be used