Mainly to protect the pH value of the solution. Acid ATT dye is composed of acid blue black 10B and acid orange II with different dispersion functions. The precise control of the pH value of the die-cast aluminum oxide black liquid is very important.
1. When the pH value of the dyeing solution is at the scale of 5 to 6 or 3 to 3.5, the absorption effect of Acid Orange II and Acid Blue Black 10B is better, and the amount absorbed by the oxide film is also larger. The amount of these dyes meets the requirements of the ratio, and the obtained color is normal black.
2. When the pH value is around 4, the oxidation film layer has an increased effect of absorbing acid orange II, and the absorption amount is naturally added. The acid orange II in the film layer is greater than the normal ratio, so the color flashes red.
3. When the pH value returns to the scale of 3~3.5 or 5~5.5, the absorption of acid orange II by the oxide film layer will fall again, and the dyed workpiece will appear normal black again.