Lecture on chrome-free tanning technology ①

This was a simple dredging and summary of the problems and solutions raised in the production, we are very welcome to discuss the issues by telephone no. (13929107802) :In the domestic leather industry, the TWS system of Tingjiang has been mass produced in some large and medium-sized leather enterprises. In the process of mass production, many new problems have been encountered, which are different from chrome tanning. The following is the mass production of chrome tanned leather

Tanning critical control point

A well-known saying in the industry: Tanning is key!!

Chrome free tanning is no exception, the quality of tanning control is the key to determine the skin!The penetration: liquid ratio: enhancement step is also a part of chrome-free tanning, which can further improve the tanning degree of wet white leather, make it further dehydrated, and improve the storability and machinability of wet white leather.Improper selection and operation of reinforcing agents can easily lead to over-tightening and even over-tanning of wet white leather.For the non-chrome tanning of cowhide, it is recommended to use the aid tanning agent HT for enhancement. The amount of HT is 2.5-3.0%, and the acid should be added in stages and slowly, and the pH value at the end of enhancement should be 4.5-4.8.After alkali extraction reached the requirement (pH value: 7.1-7.3) and rotated for 90-120 minutes to balance the pH value inside and outside the skin, the white wet leather inside the drum was heated with hot water to promote the combination of TWS tanning agent and skin protein more fully.It has been proved that the temperature rise in the later tanning period of the leather is controlled at 35℃(internal temperature) and the liquid ratio is 2.5-3.0.Temperature rise: After penetration of tanning agent, the pH value is increased to promote the full combination of tanning agent and collagen to complete tanning.Alkali extraction should be based on baking soda (NaHCO3) (preferably all use baking soda), soda ash (Na2CO3) as a supplement;The extraction process must be slow (within 6-7 hours), and the pH value at the end point should be 7.1-7.3.Otherwise easy to cause uneven tanning, or surface overtanning situation;Alkali extraction: High internal temperature is conducive to the combination of TWS tanning agent and skin collagen, but not conducive to penetration, so the initial internal temperature of tanning should be controlled at about 25℃, not more than 28℃;The amount of water has great influence on the penetration degree of tanning agent. The amount of water should be controlled at 50%-70%, and should not exceed 100%.Internal temperature: The penetration rate of multi-functional tanning agent TWS is slower than that of chrome tanning agent, so the penetration time of TWS should be sufficient. The rotation time will vary with the thickness of alkali skin section, such as:The thickness of alkali skin section layer is 2.5-2.8mm (single layer), and the TWS should be rotated for more than 4 hours at least (if the drum can be stopped overnight at this time, it is better) to carry out the subsequent steps;Because there is no indicator to check the penetration of TWS at present, the penetration degree of tanning agent can only be controlled by experience and rotation time.Due to its special structure, the main problems in tanning of chrome-free TWS are as follows: insufficient tanning and overtanned;The following are the main causes of these problems and to grasp the critical control points;TWS tanning system of Tingjiang, the pH value control range of leaching is relatively loose, control in 2.5-4.0 is no problem, but it is better to pass through!Especially for the high compactness requirements of shoe leather and other varieties, it is necessary to pay attention to control the degree of acid immersion.Enhanced control tanning control requirements bare skin requirements for acid leaching