Page 436 - Basic Principles of Textile Coloration

DYEING NYLON AND POLYESTER VARIANTS 425

penetrate adequately into the nylon at relatively low temperatures around 120–
125 °C, under conditions that avoid total drying, a conventional Thermosol unit
can be used in place of a steamer. Some leuco vat and sulphur dyes have sufficient
substantivity for nylon that a solid shade is obtained with a combination of vat or
sulphur dyes alone. The dyes may not give exactly the same colour on the cotton
and the nylon fibres but they may be close enough to be acceptable.

20.6 DYEING NYLON AND POLYESTER VARIANTS

20.6.1 Dyeing mixtures of polyamide variants
Nylons are available with a range of amino group contents varying from ultra deep
to ultra light dyeing with acid dyes. Disperse dyes cover all these types of nylon to
about the same extent but the amount of acid dye absorbed is usually dependent
on the number of available amino groups in the nylon. The sole object of dyeing
blends of the different types of nylon with acid dyes is to achieve contrasting tone-
in-tone colour effects. The objective is purely aesthetic. Generally, the colour
contrast between two nylon variants is greater the higher the dyeing pH, the
greater the number of sulphonate groups per dye molecule and the lower the
amount of anionic levelling agent added to the dyebath. In some cases, the
reproducibility of the colour contrast effect is poor, since it is very sensitive to the
dyeing conditions. In addition, the pale dyeing nylon may give a dyeing of lower
light fastness and the deep dyeing nylon lower washing fastness.

20.6.2 Dyeing nylon/urethane mixtures
Polyurethane elastomeric fibres (spandex) are not major fibres in terms of
consumption but their use in clothing is growing. They may often consist of a
polyurethane filament core wrapped with other fibres. Their dyeability with acid
and disperse dyes is similar to that of nylon. Disperse dyes cover polyurethane
more evenly than nylon but again the wet fastness of the dyeings is only poor to
moderate. Dark shades cannot be recommended. With acid dyes, polyurethanes
dye more rapidly than nylon at lower temperatures even though the nylon will
contain more acid dye if dyed to equilibrium. In dyeing nylon/urethane blends,
cationic and amphoteric levelling agents are useful for dyes that do not level well,
such as disulphonated acid dyes. More cationic auxiliary is need for higher dye
concentrations. Anionic retarders are useful for dyeing with monosulphonated and