Process for the manufacture of concentrated liquid dyeing prepa rations of low salt content

Abstract

Abstract 1359898 Dye solutions and dispersions; optical brighteners CIBA-GEIGY AG 1 Feb 1972 [2 Feb 1971] 4729/72 Headings D1B and D1P [Also in Division C4] Solutions and dispersions of dyes and optical brighteners e.g. anionic, cationic and disperse dyes, which contain salt are passed under pressure over a permeable membrane which allows low molecular weight salts and impurities to pass through whilst the dyes are retained in the original solution, thus concentrating the dye. The dye or optical brightener may be further evaporated to dryness, the membrane preferably is cellulose acetate and has a cut off level of MW 300 to 10,000, the preferred pressure being 3 to 100 atmospheres. Water is added to the solution or dispersion as the process proceeds, press cakes and filter cakes of dye or optical brightener being used to form the initial solution or dispersion.

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