Finishing of leather

Application of “Top Coat’’ the final coat
Top coat agents
Top coats are the final coats applied in the finishing process they serve several purposes depending on the type of leather.
1. Protection from soiling moisture, solvents and abrasives as well as damage caused by impacts and scratching furthermore they should be resistant to heat up to 100⁰ C and cold up to 30⁰ C if possible.
2. Imparting of the desired surface handle (dry, smooth, blunt, fatty, waxy or greasy).
3. Imparting of a matt or gloss effect with all possible intermediate stages.
Application of top coating agents
The products can be used alone or, if compatible, in combination according to the respective requirements as glossy, dull softness and feel. Except for patent leather the top coats should be sprayed in thin coats. However, they should not be sprayed too dry in order to ensure adequate film formation.
Casein products
The products used are non thermoplastic binders such as milk casein modified casein products and blood and egg albumen .a distancing is made between hart and soft products in general the harder products should be used for high gloss top coat thorough fixation of casein based top coats is required to achieve sufficient water resistance
In most cases products are applied in the water diluted compared to solvent diluted cellulose products they give the leather a pleasing handle. Dyed products are used for black leathers to avoid gray fog and to achieve brilliant black shade.
Nitrocellulose and CAB lacquers
Top coats on the basis of nitrocellulose lacquers are used less frequently. The cellulose aceto butyrate

Lacquers, which are more expensive but not inflammable and provide better fastness to amine and light are now increasingly employed both groups of products should never be applied as top coats on pure casein finishes because the casein films are not solubilized and adhesion is therefore not sufficient. Polyurethane products
Besides the solvent soluble polyurethane lacquers which are employed for production of mirror-bright patent leather and for easy-care finishes, the water-diluble one-component polyurethane dispersions are becoming more popular. These top coats are water-resistant fast to ageing and do not require additional fixation. Combined application is possible to improve the handle and fastness properties of the solvent-soluble or water-diluble nitrocellulose lacquers.
Polyamide lacquers
Polyamides are polymerized or polycondensed amino acids (textile raw material for nylon Perlon). Copolymers, which are soluble in mixture of alcohols and hydrocarbons, are obtained by additional condensation with dicarboxylic acids and diamines. In the leather industry they are used alone or with nitrocellulose lacquers. Such top coats increase water-resistance, improve flexing endurance and resistance; improve flexing endurance and fastness to rubbing. Furthermore they inhibit migration of brightening dyes, avoid damage to the finish during spraying of plastic soles in shoes production and improve the lightfastness of dyeing.