Leather improves its appearance by dyeing auxiliaries, adapts it to the current fashion style, and maximizes its added value. The color fastness of leather is as important as the sensibility and granularity of leather. Therefore, modern leather dyeing is particularly important. In the production of garment leather, the quality of dyeing is the key to obtain a light coating; for suede leather, the dyed color is the final tone of leather products, so the dyeing of suede leather puts forward higher requirements to ensure the uniformity, fastness, wear resistance of suede leather, etc. On the cross section, the dye penetration is required to be uniform.
The types and functions of dyeing auxiliaries are helpful to improve the dyeing effect. It is also possible to reduce the production process of leather, save the amount of dyes and reduce the chroma of dyeing waste liquor. According to its function, leather dyeing auxiliaries can be divided into leveling agent, deepening agent and fixing agent.
Fixing agent can increase dyeing uptake and colour fastness of dyes, so it has become an indispensable auxiliary in modern dyeing. Fixing agents are mostly cationized polymer compounds. Their function is to increase the binding force between dyes and leather by changing the surface charge of leather. The reaction mechanism between fixing agent and dye is as follows:
There are many materials that can be used as fixing materials. For dyes with anion, both acid and anion can fix, but the fixing effect varies with fixing agent and dye varieties.
