Acid dyes are often sodium nitrate salts of aromatic compounds. Since this type of dyeing needle is usually dyed in an acidic solution, it is an acid dye. Acid dyes are mainly used for dyeing wool. They can also be used for dyeing silk, polyester and leather. They can also be used in the manufacture of ink, paper, soap and as color lakes.
According to differences in chemical structure, dyeing conditions, etc., acid dyes can be divided into strong acid dyes, weak acid dyes, acid mordant dyes, and acid metal complex dyes.
1. Strong acid dye
This is the earliest developed acid dye, which can dye wool and leather in acid medium. It is also called acid level dye.
Strong acid dyes have a simple molecular structure, low molecular weight, and contain sulfonic acid or sulfonic acid groups. They have little affinity for wool and can migrate on wool, so they are Dye to a uniform color,
When dyeing with strong acidic dyes, although the color is bright and the leveling property is good, the dyeing is not deep, the fastness to moisture treatment is not good, and it is not resistant to shrinkage. When dyeing wool in medium, the strength of the wool will be damaged. The wool will feel bad after dyeing and the acid fastness will be weaker than the former. In order to overcome the adverse effects of strong acid dyes on dyed fibers, industrial improvements have been made to produce weak acid dyes, metal mordant dyes and complex dyes.
2. Weak acid dye
On the basis of strong acid dyes, the molecular weight is increased to produce weak acid dyes, also known as acid shrink-resistant dyes. The molecular structure of this type of dye is slightly complex. As the molecular weight increases, the affinity for wool is greater, so wool can be dyed in a weakly acidic medium. During dyeing, in addition to the salt bond between the dye molecules and the wool molecules, there is also non-polar van der Waals attraction between the two molecules. combined with each other. Therefore, the affinity between the dye molecules and wool molecules increases, the washing fastness of the dye is improved, and the dyeing is also darker. It has no effect on the strength of wool during dyeing, but the solubility of the dye in the dye bath is low.
3. Metallic mordant and complex dyes
Metallic mordant refers to the use of metal mordants during the dyeing process, or the introduction of metal atoms during the manufacturing process of the dye, thereby improving the performance of the dye. Any acid dye that can increase its fastness after being treated with a metallic mordant is called acid mordant dye.
Mordant is a method of adding metal salts (such as salt or copper salts) to dyes to improve the light fastness of the original acid dyes. This method can also be divided into three types: front mordant, post mordant, and co-mordant. The wool fiber is first treated with a mordant, and then treated with an acid mordant dye, which is called front mordant; after the wool is dyed with the acid dye first, then heavy dye is added. The wool dyed with acid mordant dyes and treated with acid mordant at the same time is called co-mordanting.
The advantages of acid mordant dyes are lightfastness, washability and shrinkage resistance, and high dye fastness. The disadvantage is that the color is dark and the dyed materials after mordant treatment need to be Color change occurs, so it is difficult to match colors.
Acidic metal complex dyes refer to metal atoms that have been introduced into azo dye molecules to form metal complexes during the preparation of dyes. The ratio of metal atoms to dye components in the molecules of this type of dye is 1:1. Therefore, it is also called 1:1 metal complex dye. When dyeing wool with 1:1 metal complex dyes, it still needs to be carried out in a strong acidic medium. Therefore, it still affects the strength and feel of the wool fiber. However, because the metal complex dye molecules can form complexes with wool fiber molecules, the dyeing process is The light fastness of the material is improved.
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