Chemicals used for Retanning
Retanning agents
1. Inorrganic and mineral origin
Chrome, aluminium, zirconinum, titanium etc.
Aluminum certain specific properties, fine buffing properties for suede nap use an auxiliary retan.
2. Organic in nature
Vegetable or synthetic tannins, aldehydes, aminoaldehydes resins, acrylic polymer emulsions alone or in combination with urethane polymers.
Retanning filling types products based on polypeptides and organic sulphhonates / Sulphonates for imparting fullness or buffing properties.
Own filler like clay, bentonite, flour in combination with dispersants (polyphosphates, sulphonates)
Anionic charge dye and fatliquor.
3. Vegetable tanning agents
Quebracho, Mimosa, Chestnut, Myrobalan etc. These are used for fullness, firmness, grain tightness etc.
4. Synthetic tanning agents
Based either phenols or chemicals of phenolic nature or naphthalene or its derivatives. Syntan inability (lack of ability) to provide protection against perspiration to chrome tanned leather but vegetable or resin have the perspiration resistance capability. Naphthalene syntan used for clear, level dyeing with improved dye penetration and a neutralizing salt (pH of syntan around 7..5-8.5). Naphthalene and phenol based syntans are used for increased chrome content , improve buffing properties, elegant handle etc.
Naphthalene syntans have the ability to disperse the grease.
5. Acrylic polymer resin retans
Organic resin retans are based on acrylic acid, acrylamide, methacrylates and acrylonitries etc used for plumping, fullness, roundness of leather and have affinity to chrome. Excellent light fast and much improved grain break.
6. Aminoaldehyde resin retans (N2 Containing retanning agent)
Based on urea, melamine, dicyandiamine, isocyanates etc. Give good filling, plumping and superior firming up than phenolic syntans specially belly and flanks.
7. Aldehyde retanning
Aldehyde tanning is based on the principal valance cross-linkage which attaches itself mainly to the free amino (-NH2) groups of the collagen protein. Under alkaline conditions aldehyde polymerizes and the polymer - aggregates are firmly bound to the leather.
Gluteraldehyde is a dialdehyde and reacts in a wide range of pH (3.5-5.5) considered convenient for tanning or tanning at different stages of leather manufacture. Gluteraldehyde retannage adverse eeffect can be offset by combining with aluminum salts polyphosphates in the retannage.
8. Cationic resin retan
Cationic rresin retans which find use largely for fixing anionic products, especially dyes.
9. Amphoteric retans
These retanning agents become cationic under acid condition and find useful employment primarily for obtaining deeper shades in dyeing.
Typical retanning process for upper leather
GTW (Gluteraldehyde) - 2% - 20 minutes
RS3 (Acrylic) - 4%
Relugan D (melamine co-polymer resin) - 3%
GP-50 (Phenol condense) - 2%
Mimosa - 2%
DXL/AC - 1%
Run 30 minutes
DF-585 - 3%
GF-50 - 2%
Black quebracho - 4%
LS - 1%
Run 15 minutes
Acid dye (ST600) - 2%
Black KT - 0.5%
Run 45-60 minutes
Check penetrations
Drain some water
Add hot water
PF/Butan 1908 (filler)- 3%
Fatliquoring process for upper leather:
FL 327 - 2%
AC/DXL/547B - 2%
AK/808 - 2.5%
Run 45 minutes
Syntan TL - 2% - 30 minutes
Formic acid - 1.5% 10+30 minutes
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