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AboutZhongniu Group Co., Ltd. was established in May 2008 with a registered capital of 100 million RMB. Zhongniu Group is a large leather group that integrates the purchase and sale of yellow cowhide, blue wet leather, white wet leather, leather embryo, and finished leather production, processing, and sales. It has the right to self declare customs imports and exports and is one of the "Top Ten Leather Kings in China".
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Processing technology of blue wet skin
Release time:2025-04-17
This is the most common method used in production, especially for large quantities of hides
1. Salting Method
This is the most common method used in production, especially for large quantities of hides and skins slaughtered and processed in high-temperature, high-humidity seasons or regions. The mechanism is that salt creates a hypertonic environment, expelling water from the skin, inhibiting bacterial growth and reproduction, thus achieving the purpose of preservation. The specific method is to soak the fresh skin in a 40%-50% salt solution for several days, then shake off the salt, drain the brine, shape it, and place it in a cool, dry, ventilated place to dry or directly use it for processing and tanning.
The advantages of salting are that it has a strong ability to preserve the hides, the operation is simple, it can avoid the adhesion and breakage of skin fibers during the drying process, it is not easy to decay when it is damp, and the loss caused by moths is relatively small during storage. The disadvantages are that during the drying process of salted skins, the collagen fibers shrink, and salt grains remain in the skin, which has a certain impact on the natural structure of the dermis.
2. Chrome Tanning
Currently, the commonly used tanning agents in fur production are basic chromium salts, basic aluminum salts, and formaldehyde. The method and tanning agent used should depend on the type and characteristics of the raw hide. Tanning agents include two major categories: inorganic softeners and organic softeners. Inorganic tanning agents include basic salts of trivalent chromium, aluminum, and iron, and basic salts of tetravalent chromium and tin; organic tanning agents mainly include vegetable tanning agents (tannins), formaldehyde, synthetic tanning agents, fish oil, etc. The use of new synthetic tanning agents is also becoming increasingly widespread. The chromium salt with tanning properties is trivalent basic chromium salt, and the leather tanned with it is washable, durable, and has the best wet heat stability. The commonly used chrome tanning agent is commercial chrome salt essence, and the effective component is basic chromium sulfate, with a chromium content of 20%-25% as chromium trioxide (Cr2O3).
Factors Affecting Chrome Tanning
(1) Influence of pH Value In the initial stage of chrome tanning, the pH value is relatively low, generally 2.5-3.5, which is conducive to the penetration of tanning agents into the skin. At the end of tanning, the pH value of the tanning solution should be appropriately increased (around 4.0 is better), which is conducive to the combination of the tanning agent with the skin. If the pH value is too low (<2), the tanning agent will lose its tanning properties; if it is too high (>6), the tanning agent will precipitate, causing detanning.
(2) Influence of Chromium Salt Concentration Increasing the concentration of chromium salt in the tanning solution within a certain range will increase the amount of chromium bound to the fur, but when the chromium salt reaches a certain concentration, further increasing the concentration of chromium salt will not increase the amount of chromium bound to the skin.
(3) Influence of Retarding Agents Retarding agents are substances that can combine with inorganic tanning agents chromium and change their tanning properties. They are mainly organic acids and their sodium salts, such as formic acid, acetic acid, sodium benzoate, etc. Small-molecule retarding agents can improve the uniformity of chrome tanning. Macromolecular and long-chain polycarboxylic acid retarding agents can increase the amount of chromium bound. Generally, small-molecule retarding agents are added in the early stage of tanning, and macromolecular retarding agents are added in the later stage of tanning.
(4) Influence of Neutral Salts Neutral salts such as table salt or Glauber's salt are more suitable and are added to avoid acid swelling. Its function is to reduce the amount of chromium bound to the skin, and the effect of sulfate is more significant. Therefore, the amount of neutral salt must be controlled during the tanning process.
(5) Temperature Increasing the temperature of the tanning solution is conducive to the combination of chromium in the skin. In the later stage of tanning, the tanning solution is generally heated to increase the amount of chromium bound.
(6) Tanning Time This mainly depends on the type of fur. Generally, the tanning solution is basically absorbed by the skin within 2 hours. Extending the time does not help much in increasing the amount of tanning agent bound, but it is conducive to improving the uniformity and firmness of tanning.
3. Actual Operation of Chrome Tanning
Taking sheepskin tanning process as an example: Equipment: Paddle
Liquid volume: 22-25 liters/piece
Chromium salt dosage: 5 g/liter (calculated as Cr2O3), temperature: 30-35 ℃, salt: 35 g/liter, time: 44-48 hours, Glauber's salt: 50 g/liter, final pH value: 3.3-3.5
Operation: Put in the required amount of water, add salt to the paddle, adjust the water temperature to the specified requirements, add chrome liquid, stir well, put in the skin and rotate. Start adding alkali after 24 hours, add in 6 times, with an interval of half an hour, and adjust the pH value to the specified requirements.
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Zhongniu Group is a large-scale leather conglomerate integrating the purchase & sale of yellow cattle hides, as well as the production, processing, and sales of wet-blue, wet-white, crust leather, and finished leather.
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