Application of Finish:
The final look & qualities of finished leather largely depend upon how the finish was applied on the leather surfaces. Finishes are applied on leather by three methods-
1. Pad coating
2. Roller coating
3. Spray coating
Here,
- Bottom coat is generally applied by "Pad coating".
- Intermediate coat is applied on both "Pad & Spray coating".
- Top coat is always applied by "Spray coating ".
1. Pad coating:
Plush pad, with or without the plastic foam padding underneath the soft velvet like cloth, soft hair brush & sponge are generally used.
Advantages:
- Low labour cost & economical.
- Low or no maintenance cost.
- Uneven substance hide/skins receive even coats.
- Copes well with light-weight skins.
Disadvantages:
- Labour should be skilled.
- Uneven coating & streaking is possible if labour is unskilled.
- flesh side is dirty.
2. Roller coating:
The roller coating machine consists of an application roller which is grooved or has cavities which hold the liquid materials, excess liquid being wiped off by a doctor blade. The leather is introduced to the machine on a rubber conveyor.
Advantages:
- Even coating of higher density material
- Clean flesh
- Continuous production
- Suitable for long runs of single colors
- Production rate high i.e 2000 sq ft of leather coated once take 15-20 mins only
Disadvantages:
- Will only cope with small variation in substance (0.3-0.4mm)
- Good maintenance is necessary for consistent results.
- Adhesion may be poor due to less mechanical action.
3. Spray coating:
It is the most common method and is applied by means of compressed air. It is suitable
for aqueous and solvent containing finishing float. Normally compressed air is forced
through a small nozzle and to this air finish is fed in the form of fine stream. When the
finish, mixed with air, is forced out through the nozzle, atomization of finish takes place
and the mixture moves towards the leather surface.
Advantages:
- Uniformity is easily achieved
- Spray season or coat dries up on leather very quickly
Disadvantages:
- Less adhesion, less rub fastness
- Materials loss is high
★ Different types of spraying:
- Hand spray gun
- Rotary spray gun
- Reciprocating spray gun
- Airless spray