Wash away and get rid of unwanted dirts, blood, fat on raw hide, returned to normal gelatin stage, create good condition for following work. Soaking results in clear and obvious grain, spready area, less wrinkle, vein, average area, full touch.
* 20C to 25C water
* Antibiotic agent
* Uric auxiliary
* water softener
Releasing fibre structure, destroy some unwished protein, get rid of hair and corium, swelling
Lime, Sulfide, Detergent & Vric axuiliary
In between mechanical action as fleshing and splitting
Operation time: soaking and liming 48 hours, drum speed 4RPM
Control of soaking and liming through:
* Mechanical action
* Float proportion
Neutralized alkaline, clean away magnesium and calcium salt, desmelling and give way for further process.
*Water 36° to 38°c
* Ammonium salt
* Organic acids
Operation time: 2-3 hours with drum speed 8-10RPM
Clean grain, get rid of remaining soluble protein, soften fibre and improve surface of leather, developing leather suppleness and stretchiness.
Material used: Enzymes
* Amount of enzymes
* Mechanical action
Control the excessed amount of natural fat, prevent rugged touch and unpleasant smell of leather
Material used: Detergent or organic solvents
Make pelt acid in order to create good condition for tanning. Certain degree open fibre
* Formic acid
* Sulfuric acid
* Electrolyte stable fat-liquors
Transformation of protein to leather fibre. This is an irreversible chemical reaction.
Chemical reaction between trivalent chromium and oxyl bond of protein. Strong combination, rot-proof, good suppleness, high shrinkage, temperature( up to 100°c) provide cationic bond to allow anionic chemicals to combine to leather fibre later such as dyes, fat-liquors and retanning agent.
Advantage of chrome tanned leather:
* Easily operated
* Cheaper cost
* Higher tensile
* Higher grinding resistance
* Higher shrinkage temperature
* Not easy putrefaction
* Not hardening when wetted
* More flexibility on further manufacturing
* Easily transported and stored
Disadvantage of chrome tanned leather:
* Stronger water absorption
* Slippery after wetted
* Looser fibre
* Less yield in area
* Rough edge
* Chromium is a polluting heavy metal.
Traditional way of tanning using extract of different parts of plants like roots, bark, fruit, leaves. The tannin acid from the plant can react with protein and fill in between fibres forming stable leather
Commonly used vegetable tanning extracts:
* GambierThe natural extracts have different colours, densities, astringencies allowing production of various appearance and quality vegetable tanned leather.Operation: Use pits or drums, time can be from three / four days to half a month.
Advantage of vegetable leather:
* Strong water resistance
* Not so slippery after wetting
* Tight fibre construction
* Minor tensile, not easily transformed
* Better yield
* Smooth edge
* Better embraced property
* Area changed less after wetting
* Sweat resistance
Disadvantage of vegetable leather:
* Production cost higher
* Operation more complicated
* Less tensile
* Less grinding resistance
* Lower shrinkage temperature
In general practice, there are many combinations to use chrome, vegetable and other tanning agents together to achieve the optimum result and ideal leather.
Chrome free tanning
Pretanned the pelt with aldehyde and synthetic tanning agent to wet white. Wet white can be stored, transported and mechanical operated.
Then can proceed further to various tanning and retanning. This process created much less polluted elements and can be named as clean production.
Lubricating fibres to achieve better tensile strength, stretch, tearing and flexing properties
Introduce special effects such as washable, water resistance, heat retarding, pull-up
* Animals fats: Sperm oil, Neat foot oil, Lanolin, Phospholipids
* Vegetable oils: Soya, Colza, Palm
* Mineral oil
* Synthetic oil
* Resin softeners Operation:
* Water temperature 45°C – 55°C
* Time 60 – 120 min
To control moisture content in leather stretch leather fibre, improve fixation of retanning, dyeing and fat- liquoring. Unifying construction of fibre mess resulting at spreading and good touch leather. Effecting shrunken or mill grain. Keep area yield.
* Vacuum dry
* Hang dry
* Hot plate dry
* Toggle dry
To cosmetic leather surface, correct some of the defects. Imply shade, gloss and special effects and pattern as required. To level out-look of leather increasing cutting value. Finishing combination.
Binder: to cover the grain fix the colour protecting the surface, improve physical properties.