Process for the application of dye fixing agents to polyamide fiber utilizing controlled fixing agent addition

A process for increasing the washfastness of a fibrous article containing polyamide fibers dyed with anionic dye by treatment with an anionic dye fixing agent, said process comprising:

• immersing said article in a liquid bath of a solvent for said fixing agent, said solvent being selected from the group consisting of aqueous solvents and substantially non-aqueous solvents, said substantially non-aqueous solvents comprising at least about 10% by volume of a water-miscible alcohol;
• heating said bath and said article in said bath to a temperature at least equal to the dyeing transition temperature of said fiber of polyamide polymer;
• adding said fixing agent to said bath as a liquid concentrate, at least about 33% of the total fixing agent to be applied during said process being added while said bath and said article are at a temperature at least equal to said dyeing transition temperature;
• and
• stirring said bath as the fixing agent is added to said bath to mix said concentrate into said bath to form a dilute solution of said fixing agent and to provide a flow of said dilute fixing agent solution relative to said article to cause said fixing agent to be transported to said article, said stirring further providing, on the average, essentially uniform transport of said fixing agent to said article;
• said process being performed in a dyeing machine in which said stirring provides repetitive machine cycles;
• said fixing agent is being added to the bath at a fixing agent addition rate such that between about 0.04% and about 7% of the total fixing agent to be applied during said process is added to said bath during a machine cycle.