How is leather dyed?

- Dec 06, 2018-

Leather dyeing is a complex physical and chemical process, which is the process of penetration and bonding of dye molecules to leather fibers, and is the total effect of physical and chemical effects. During the entire dyeing process, adsorption, diffusion, infiltration and fixation interact and alternate with each other. The leather dyeing process involves a wide range of factors, and there are many influencing factors. In addition to the interaction of various components constituting the dye liquor, the condition of the leather before dyeing, the control of the pH value, temperature and concentration during the dyeing process, and the additives added. Factors such as the cooperation of the front and the back are important.
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Then the specific process is as follows:


In order to dye the leather, the dye must be sufficiently penetrated into the deep layer of the leather to color the deep fibers. This requires that the dyeing conditions should be favorable for the penetration of the dye, and the state of the leather before dyeing is a major factor. And the degree of control is the main factor determining the state of the crust. "Neutralization" can reduce the positive charge on the surface of chrome tanned leather, which is beneficial to the penetration of anionic dyes. Neutralization and deep penetration make the deep pH value of the leather consistent with the surface, which can make the dye fully penetrate and slowly combine to meet the requirements of translucent. Therefore, we have strengthened the neutralization, so that the leather incision is neutralized and fully permeable, and the control neutralization pH does not exceed 5.5.


The uniform dispersion of the suede fibers has a greater influence on the dyeing uniformity. The fibrils at the back of the gluteal are relatively tight, and the fibers at the rim are relatively loose. Usually, the fibers are tightly bonded to the surface of the dye, and the color is deep; the dyeing of the loose parts is more permeable and the color is lighter. Filling with a simple filler such as SCC acrylic resin can not eliminate the difference in the position, but the leather buttocks will produce "pitting" when grinding, which affects the product quality. We have used the assisted acrylic resin retanning agent ART-I to solve this problem well, because ART-I acrylic resin retanning agent has obvious selective filling ability, which can greatly reduce the difference of leather parts. The fiber of the edge of the leather is tight, the fibers of the whole leather are uniformly dispersed, and the dyeing is uniform. Moreover, ART-I is an anionic material, which can slow the combination of dyes and facilitate the penetration of dyes.


Some of the raw materials for leather dyeing are: a solution of urethane resin dyed synthetic leather with a dye. Synthetic leather is focused on high-grade fabrics and is growing at a rate of 20%. Previously, urethane resins (ie, polyurethane resins) used as dyeing substrates could only be colored with pigments and could not be dyed with brightly colored synthetic leather. The dyeing solution developed this time was a solvent using dimethylformamide (DMF) to make a polyurethane. There are also public resins and the like.