1. What is pH sensitivity?
There are many varieties of disperse dyes, a wide range of chromatography, and very different sensitivity to pH. Dyeing solutions of different pH values often lead to different dyeing results, affecting the color depth, serious or even discoloration. In the weakly acidic medium (pH4.5～5.5), the disperse dye is in the most stable state.
The pH values of commercial dye solutions vary, some are neutral and some are slightly alkaline. Before dyeing, it must be adjusted to the specified pH value with acetic acid. During the dyeing process, sometimes the pH of the dyeing solution will gradually increase, and formic acid and ammonium sulfate may be added if necessary to keep the dyeing solution always in a weakly acidic state.
2. The effect of dye structure on pH sensitivity:
Some disperse dyes with azo structure are very sensitive to alkalis and are not resistant to reduction. Most disperse dyes with ester groups, cyano groups or amide groups will be affected by alkali hydrolysis and affect the normal color. There are also some varieties that are dyed at high temperatures under neutral or weakly alkaline conditions without color change. They can be dyed in the same bath as direct dyes or pad dyed in the same bath with reactive dyes.
When printing with disperse dyes and reactive dyes in the same paste, the printing color paste can only use dyes that are stable to alkali, so as not to be affected by the effect of baking soda or soda ash. Especially pay attention to the color matching. Before changing the dye species, you must pass the test and find out the range of the dye to pH stability.