Process for producing concentrated aqueous solutions of anionic azo dyes

A process for preparing a concentrated aqueous dye solution of an anionic azo dye, said solution having a dye content of from 15 to 40% by weight, by diazotization of an aromatic amine, or coupling of a diazonium salt with a coupling component, or both, in an aqueous medium, which comprises the steps of:

• carrying out the diazotization of the aromatic amine, or the coupling reaction between the diazonium salt with the coupling component, or both, at a total concentration of diazonium and coupling compound of at least 15% by weight based on the aqueous medium, and
• conducting the reaction in the presence of an auxiliary having a viscosity reducing effect on pasty phases and which is a condensation product of a phenolic compound with formaldehyde and an alkali sulfite.

A process for preparing a concentrated aqueous dye solution of an anionic azo dye, said solution having a dye content of from 15 to 40% by weight, by diazotization of an aromatic amine, coupling of a diazonium salt and a coupling component, or both, in an aqueous medium, which comprises the steps of:

• carrying out the diazotization of the aromatic amine, the coupling reaction between the diazonium salt and the coupling component, or both, at a total concentration of diazonium and coupling compound of at least 15% by weight based on the aqueous medium, and
• conducting the reaction in the presence of an auxiliary having a viscosity reducing effect on pasty phases and which is a sulfosuccinic semi-ester of ethoxylated nonylphenol-formaldehyde condensation products.

A method of reducing the viscosity of a diazotization reaction, or a coupling reaction between an aromatic amine diazo component with a coupling component, or both, during the production of a concentrated aqueous solution of an anionic azo dye, which comprises the step of:

• carrying out the diazotization of the aromatic amine diazo component, the coupling reaction between the diazonium salt and the coupling component, or both in the presence of an auxiliary which exerts a viscosity-reducing effect on pasty phases, wherein the auxiliary is a lignosulfonate, polycarboxylate, copolymer derived from unsaturated sulfonic acids with acrylic acid, condensation product of a phenol with formaldehyde and alkali sulfite, condensation product derived from naphthalene sulfonic acids or monoalkyl and dialkyl naphthalene sulfonic acids with formaldehyde having a degree of sulfonation of 80 to 200% and a mean molecular weight of 350 to 35,000, co-condensation product derived from one of the above aromatic sulfonic acid with formaldehyde, sulfosuccinic acid derivatives of ethoxylated nonyl phenol formaldehyde condensation products.