Leather dyes offered involve use of spirit/alcohol based dyes. This is done as alcohol quickly gets absorbed into moistened leather. As leather dyeing formulation is similar to lacquer, it consist of :
Dye or pigment
Casein/ nitrocellulose resin
Solvent
The dyestuffs used in tanneries vary depending on product range required along with dictates of the emerging market. With each tannery using between 50-100/more different types of dyestuffs, the leather industry primarily makes use of anionic dyestuffs which are divided under following families:
Acid dyes
Mordant dyes
Direct dyes
Basic Dyes, its use is also limited.
Pre-metallic dyes
Solubilised sulphur dyes
Reactive dyes although a part of the anionic group of dyes but use limited to a certain extent.
From chemical point of view, the dyes that are used are mostly :
Azo Dyes
Anthraquinone Dyes
Triphenylmethane Dyes
Technology Changes in Leather Dye : The use of high temperatures helps in releasing fat-soluble components of conventional leather dyes from their chemical bonds. These released components have tendency to migrate upwards into layers where task is to provide a smooth finish to leather surface. This causes visible change of:
Color
Intensity
With rising humidity, it is likely that water soluble non-permanent dyes and those having low molecular weight would be washed out. But with latest technology of dyeing leather, development as well as production of fastness in dyes has reached top level.
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
