I. Acid dyes
Acid dyes are the biggest component of leather dyeing. Compared with direct dyes or indirect dyes, acid dyes can produce more turbulent and transparent tones. Therefore, this dye is suitable for all kinds of leather, including vegetable cake leather.
Acid dyes are often used in leather dyeing because of their bright color, complete chromatography, good permeability, convenient use and certain fastness. However, due to its small molecule, many hydrophilic groups, low affinity for fibers, poor water resistance and poor washing resistance, especially poor fastness to alkaline washing. Acid dyes commonly used in leather dyeing are Acid Orange Ⅱ and Acid Black ATT.
Second, direct dyes
The molecules of direct dyes are larger than those of acid dyes, so their properties for metal ions and neutral salts are different from those of acid dyes, and their molecular structural characteristics also determine their color characteristics. It has poor permeability, good hiding power and strong dyeing color. Compared with acid dyes, the color is not bright, but it has good wet friction resistance.
Direct dyes are used to dye N-inch leather, mainly on the surface, so they are often used in combination with acid dyes. One bath dyeing chrome tanned leather has both advantages. Acid dyes have good permeability, which makes the coloring have a certain depth, while direct dyes make the surface color thicker and the coloring more stereoscopic. Direct dye molecules are easy to aggregate, not easy to penetrate, and are more likely to deposit on the damaged parts of leather particles, resulting in dark and turbid colors. In the scars of leather, the surface of leather is uneven because of its compact and light color. When acidic or neutral salts exist or the hardness of water is high, the defects of dyeing are more obvious. Increasing bath temperature can reduce the aggregation of dye molecules and is beneficial to the dispersion and dissolution of dyes. Therefore, the dyeing effect of direct dyes is better at higher bath temperature.
Direct dyes and acid dyes are anionic dyes, so for leather dyeing, their binding properties with leather are the same, and the conditions of dyeing process are basically the same. They can be used in the same bath with anionic dyes such as diffusing agents, anionic retanning agents and fatliquoring agents, but not with cationic dyes such as cationic surfactants and basic dyes.
There are many direct dyes used in leather dyeing, and the chromatography of direct dyes is relatively complete. It is mainly used for dyeing mineral leather such as chrome tanned leather, and can also be used for dyeing vegetable tanned leather under special circumstances. Grass is negatively charged and can be infiltrated with direct dyes.
The main disadvantages of direct dyes are poor washing fastness and light fastness. Direct dyes with light fastness above grade 5 are called direct light-fast dyes. The second chapter is the wet processing technology of cowhide tanning.
Third, metal composite fuel.
Metal Complex Dyes Metal complex dyes are developed to strengthen the bonding degree and light fastness. Generally, chromium (Cr), copper (Cu) and dyes are combined, so the combination is firm and has high perspiration resistance, water resistance, washing resistance and light resistance.
Four, basic dyes
Basic dyes, also known as basic dyes, are cationic dyes because they are composed of colored parts with positive ions and colorless negative ions. Alkaline dyes are positively charged in solution, not alkaline, and do not need to be dissolved or dyed in alkaline medium.
Alkaline dyes are suitable for low-affinity leather (such as vegetable tanned leather) or register dyeing after acid dyes penetrate, and are suitable for adjusting the charge of substrates during dyeing. Traditional basic dyes are inconvenient to use and have poor fastness. After dyeing, the color is bright but the light resistance is poor, and it is easy to form insoluble metallic luster products with dissolved anionic tanning agents and hard water and precipitate on the skin surface. The improved method is to dissolve it with acetic acid (1: 10) in advance and then dilute it.