Patent ID: 7847073

Claim:
A process for producing a liquid formulation of salts of sulfonated azo dyes, which process comprises: (a) forming an azo dye by coupling at least an equimolar amount of diazotized aminoarylsulfonic acids of the formula I H 2 N—Ar—SO 3 H (I), wherein Ar is phenylene, which may be monosubstituted by sulfo, or naphthylene, which may be mono- or disubstituted by sulfo and/or monosubstituted by hydroxyl, onto the coupling product of an unsubstituted or methyl-substituted phenylenediamine coupled with itself; (b) dissolving the azo dye in a basic medium; and then (c) subjecting the solution to a nanofiltration; wherein the process for producing the liquid formulation avoids isolation of the dye as a solid and the liquid formulation produced has an inorganic salt content of less than 2% by weight based on 100% pure dye.