Leather Dyes

Leather dyeing usually involves the use of spirit or alcohol based dyes where alcohol quickly gets absorbed into moistened leather. Leather dyeing formulations are similar to lacquers. They consist of a dye or pigment, a casein or nitrocellulose resin, and a solvent.

The types of dyestuff that are used by tanneries generally varies depending on the product range needed along with the dictates of the fashion world. It is a fact that each tannery uses between 50-100 or more different types of dyestuffs.

The leather industry primarily uses anionic dyestuffs, that can be divided in the following families:

• Acid dyes
• Mordant dyes
• Direct dyes
• Basic Dyes, its use is also limited.
• Pre-metalled dyes
• Solubilised sulphur dyes
• Reactive dyes although a part of the anionic group of dyes but use limited to a certain extent.

If we see from the chemical point of view the dyes used are mostly Azo dyes, Anthraquinone dyes and Triphenylmethane dyes. Commercially speaking, popular Black dyes account for nearly 60-70% of all leather dyeing. Also, out of this a dye variety called Acid Black 210 dominates with 80-90% usage of all of the black dyes used.

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Applying high temperatures releases the fat-soluble components of conventional leather dyes out of their chemical bonds. Now these components has a tendency to migrate upwards into the layers whose task is to give the smooth finish to leather surface. This causes a visible change of color and intensity. What happens is that with the rising of humidity, it is quite likely that non-permanent dyes that are water-soluble, and low in molecular weight, will be washed out. Along with the problems like spotting and discoloration. Also there is the risk that migrating dye components can rub off on other materials such as plastics or textiles.

With latest technology of dyeing leather, the development and production of high-fastness dyes reached on top level. Now, the manufacturers get high quality leathers for making leather products.

Here is a flow chart that describes the process criteria of selection of leather dyes :

Few tests that are undertaken for testing the color fastness of dyed leather are as follows

• Color Fastness with regard to migration into plasticized Poly Vinyl Chloride
• Fastness to light the standard Xenon lamp test
• Fastness towards mild washing
• Fastness towards washing by machine
• Fastness towards perspiration
• Fastness to test of rubbing
• Fastness in water
• Fastness with respect to water spotting
• Grey scale test to ascertain the change of color and staining
• Solubility capacity of powder dyes
• Stability of dyes with regard to
  • Acid
  • Alkali
  • Hard water