Disperse dyes have many varieties and wide chromatograms, and their sensitivities to pH are very different. Dyeing solutions with different pH values often lead to different dyeing results, which affect the depth of color, and even cause color change in serious cases. In weakly acidic medium (pH4.5～5.5), disperse dyes are in the most stable state.
The pH of commercial dye solutions varies, some are neutral and some are slightly alkaline. Before dyeing, adjust to the specified pH with acetic acid. During the dyeing process, sometimes the pH value of the dye solution will gradually increase. If necessary, formic acid and ammonium sulfate can be added to keep the dye solution in a weakly acidic state.