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Technical lecture on chrome-free tannage of chrome-free leather II

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Lecture by tanning expert Yan LAN on chrome-free tanning technology

After the tannin extract retanned white wet leather with liquid ratio (water volume) and internal temperature D imitation pure vegetable tanning, the finished leather with pure vegetable tanning style can be obtained by retanning operation with vegetable tanning agent as the main retanning agent.C "Reverse" metal retanning. The process by which a small amount of metal retanning agent is applied to the whole tanning and retanning sections without the use of metal tanning agents until the end of the retanning section, just before the drum is released.B synthetic retanning agent A cationic metal (non-chromium) retanning agent TWS system tanned white wet leather is very different from chrome tanned blue wet leather, chrome tanning leather is tanned by metal tanning agent, showing strong cationic property;TWS tanned leather is tanned by non-metallic tanning agent, and it is amphoteric and slightly anionic.Therefore, the key control points to pay attention to in the retanning process of white wet leather tanned by TWS are as follows: Retanning is the "golden touch" in the tanning process, and various styles of leather blanks are mainly "touched" by retanning, and retanning is also the most common use of leather chemical materials, the most prone to problems, such as:Chemical material absorption is not good, penetration is not deep, the tightness of the leather embryo is not enough, not resistant to fall, easy to "chicken feet" pattern, leather body is stiff, no foam sense and Q elastic sense and so on;Retanning workshop critical control point hotline: 13929107802 was introduced for you

< Key control point in tanning section > For finished leather requiring soft heart and Q-elasticity, the charge property of TWS white wet leather should be adjusted first with cationic or zwitterionic chemical compound, then the initial retanning of white wet leather with foam type, low convergence and tanning synthetic tanning agent is used, and finally the deep retanning of synthetic tanning agent with good tanning and filling property is used.For example, HT and TJ-R772 of Tingjiang Company belong to foam type synthetic tanning agents;TJ-R7210 is a synthetic tanning agent with good tanning properties and filling properties.For the finished leather that needs a very "solid" core, the TWS white wet leather can usually be retanned with non-chromium metal tanning agent first. In this way, the subsequent steps can be filled, dyed and fatted according to the train of thought of chrome wet blue leather.TWLZ, TWN, etc. of Tingjiang Company belong to non-chromium metal tanning agents, which can be used for retanning white wet leather tanned by TWS.In any leather after the primary tanning of the tanning agent, the amount of tanning agent binding must gradually decrease from the surface to the core. By smoothing, the core (reticulated layer) of the less tanning agent binding is exposed, so that it is tanned again with various retanning agents to ensure that the rawhide protein is fully tanned, and to determine the style of the finished leather.At this time, the choice of retanning agent is particularly key!This issue continues with the introduction of the problems and solutions in the mass production of chrome-free tanned leather. Discussion on issues of interest to professionals is very welcome

This process means that there is no metal tanning agent in the main tanning process, and there is no metal tanning agent in the early stage of the retanning process, but at the end of the retanning process, a small amount of metal tanning agent is used for retanning.This method is a crucial step in creating a light, bubbly NAPPA leather with a bouncing feel from white wet leather tanned with TWS!

However, if the reverse retanning step is not well controlled, the grain surface of the leather embryo is too tight, too hard, and the tearing strength is not good.The key to control is: the choice of non-chromium metal tanning agent (zirconium tanning agent, aluminum tanning agent, or zirconia-aluminum tanning agent can be used) and the amount of the tanning agent.

TJ-T7020 is recommended for non-chrome metal tanning agent.

Recommended dosage: 2.0%-3.0% is suitable;

The end point pH should be adjusted to 3.5-3.7.

Wash, out of the drum on the horse static;If time permits, it is better to let it stand for 48 hours before squeezing, stretching and vacuuming.No matter what kind of non-chrome tannant is tanned, its water absorption is very strong, which is not conducive to subsequent dry operation (especially finishing);By adding appropriate water repellent (e.g. TJ-A9992;GWP, etc.), can effectively reduce the absorbency of the leather embryo.The light resistance of the absorbent leather product of the leather embryo usually refers to the resistance to sunlight and ultraviolet light respectively. No matter which kind of non-chromium tanning agent tanned leather embryo, its light and heat resistance is a difficult problem to solve.

Sun resistant:

Temperature 50, natural light irradiation for 36 hours;

Ultraviolet light (UV) :

Temperature 50, 300W ultraviolet irradiation for 6 hours;

Heat resistance:

Constant temperature and humidity test chamber, temperature 70, humidity 95%, 48 hours;

The white wet leather tanned by the reverse retanning process TWS contains a small amount of free formaldehyde. In the retanning section, the dyeing and finishing materials with little or no aldehyde should be selected as far as possible. After reasonable treatment with the formaldehyde treatment agent TJ-A9800 in Tingjiang, the free formaldehyde of the leather germ can be reduced below 13ppm, and no formaldehyde will be released during the storage of the leather germ or finished leather.Free formaldehyde with light and heat resistance was found in the actual production process. In the retanning section, the phenomenon of bad absorption of leather chemical materials, insufficient penetration of chemical materials, and tight surface of dried leather blank were found. Most of the time, it was because the liquid ratio in the early retanning period was too large, or the internal temperature was too high, and sometimes both of them were caused.

After the TWS white wet leather is evenly trimmed, it must be controlled under the condition of small liquid ratio and low internal temperature at the initial retanning filling. The liquid ratio should be 30% and the maximum should not exceed 50%.The internal temperature should be controlled at about 30, and the maximum temperature should not exceed 35.



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