Oxidised sulfur dye dispersions purified by membrane separation

摘要

An aqueous sulfur dye dispersion, which has been oxidised (aerated) to remove inorganic sulfides, is subjected to separation by a semipermeable membrane in order to remove inorganic salts.
The dispersion may also be pre-treated with -

  (i) sodium sulfite or sodium nitrite, to reduce the polysulfur content;
  (ii) a surfactant, to prevent agglomeration of the dye particles.

The resultant odourless suspensions preferably have a dye particle size of