Vat dyestuff redn. to leuco form - involves using slow then fast reducing agent to prevent local high concn. of leuco form and give more level dyeing

摘要

Controlled prodn. of the leuco form (IA) of vat dyestuffs (I) by redn involves treating (I) first with a slow-acting reducing agent (II) and then with a fast-reacting reducing agent (III) in the presence of the substrate to be dyed. (II) has a potential of max. -800+/- 50 mV at pH 12-14 and pref. is (IIA). (III) has a potential of max. -950 +/- 50 mV at pH 12-14 and pref. is alkali dithionite. Vatting with (II) is carried out at 50-90 deg.C (II) being added gradually over a 15-30 min. period. (III) is added gradually at 50-90 deg.C until the potential is constant at max. 950 +/- 50 mV. USE/ADVANTAGE - Use of the (II)/(III) combination prevents local high concns. of (IA), making dyeing more level than usual. Pollution is reduced since much of the dithionite can be replaced by hydroxyacetone (IIA), which is more environmentally safe. In an example, 700g bleached cotton were heated from 40-60 deg.C in 10 min. at a goods/liquor ratio of 1:12 with 0.8% of the dyestuff C.I. 69525 in the presence of 2g dispersant (Na polyacrylate) and a chelating agent (0.5g EDTA).