What is the reaction mechanism of reactive dyes?

Reactive dyes are used for cellulose fiber dyes, generally through three stages of adsorption, diffusion and fixation:

There is no covalent bond reaction between the dye and the fiber during the adsorption and diffusion process. When the alkali agent is added to make the pH of the dye bath alkaline, the reactive group in the reactive dye will react with the cellulose fiber.

Therefore, it is necessary for the pH value to reach the basic condition for the fixation of the reactive dyes, regardless of the influence of the alkali agent. Taking the general medium temperature (60℃) reactive dyes as an example, the fixation PH value required is 11-11.5 about.

Generally, the dyeing temperature of double-reactive reactive dyes is 60°C (the most suitable temperature for turquoise and light yellow is 80°C), then the question is, why do some factories set the dyeing temperature to 65°C?

Many years ago, dyeing equipment was not as advanced as it is now. One is the lack of automatic temperature control. The temperature control requires workers to switch the steam valve to control;

The second is that many of them are directly heated by steam, which will cause the steam condensed water to enter the dyeing bath and increase the liquor ratio during the heating process.

In order to ensure the stability of the bath ratio, dyeing engineers generally do not recommend direct heating with steam. They will set the initial dyeing temperature to 65°C, so that during the dyeing process, the temperature will gradually drop to 60°C. 65°C is an experience based on the current equipment conditions. temperature.