Process for preparing stable, aqueous dye solutions of anionic dyes

摘要

Storage-stable, concentrated, aqueous dye solutions of water-soluble dyes are obtained when an aqueous solution or suspension of at least one anionic non-reactive crude dye is passed over a semipermeable membrane that contains ionic groups and has a pore diameter from 1 to 500 @ in order that salts and synthesis by-products having molecular weights below 500 and some of the water be separated off. The new liquid formulations are concentrated, genuine solutions which are storage-stable for several months at temperatures between about -10 DEG C and +60 DEG C and are miscible in any proportion with cold and hot water. They are suitable in particular for dyeing and printing paper, including paperboard and cardboard, which materials can be dyed for example in the pulp, by brushing or by dipping.