As early as August 13, 2010, Germany began to implement the hexavalent chromium ban. Before the revision of the REACH regulation, the requirements for the control of hexavalent chromium in the European Union are not the same. Some countries, including Germany, require no detection, while others require less than 1,000 ppm. The standard was only revised this year, but the European Rapex system has already seen a recall of leather products due to hexavalent chromium exceeding the standard in 2010, with only a limited number of recalls. In the second half of 2013 and 2014, the number of recalls increased significantly. For this reason, Xicco Test analyzed the recall situation in the first quarter of 2014.
I. Main types of recalled products
In the first quarter of 2014, the Rapex system recalled a total of 13 Chinese-made leather products. On average, an average of 1 leather product was recalled every week due to the detection of hexavalent chromium.
The recalled products mainly include: leather gloves, ladies' shoes, baby shoes and safety shoes. See Figure 1 for recall.
Looking at product recalls in the first quarter of 2014, women's shoes are the products with higher recall frequency, but it is unscientific to draw conclusions based on the data in the first quarter alone. In retrospect, Xicco detected 2013 Rapide statistics. Last year, high-frequency products with hexavalent chromium exceeding the standard were women's shoes. In addition, recalled products included bracelets, leather bikinis, children's shoes, and safety shoes.
Second, the problem of product treatment analysis
Product handling measures recalled in the first quarter:
Women's shoes: 6 products, 5 models recalled by Germany are all voluntarily withdrawn, and 1 other women's shoes recalled by Spain are for forced withdrawal.
Leather gloves: All 3 leather gloves were recalled by Germany and they were dealt with voluntarily;
Safety shoes: 1 safety shoes recalled by France, whose treatment is refused import (the recall is based on safety shoes standard: EN ISO 20345:2011);
Baby Shoes: All 3 baby shoes were recalled by France and the measures taken were stricter than the above products, forced withdrawal and destruction.
According to the hexavalent chromium concentration data in the recalled products, the treatment measures are not related to the detected hexavalent chromium concentration, but they are related to the product type and the recalled state.
According to the above data, Xicco's test suggests that leather products for children's products need more attention, and their law enforcement efforts are obviously greater than other products. In addition, countries that have recalled relevant products in particular need to arouse the attention of exporters, while other countries cannot ignore it.
Third, the harm and cause of hexavalent chromium
Hexavalent chromium is an invasive poison that has a stimulatory effect on the mucous membranes of the skin. It can cause dermatitis, eczema, bronchitis and rhinitis, and invades the human body through the digestive tract, respiratory tract, skin and mucous membranes, and has a carcinogenic effect.
The detection of hexavalent chromium in finished leather is a puzzling and objective problem. Because the chrome tanning agent used in tanned leather is trivalent instead of hexavalent, even if hexavalent chromium cannot be detected in the chromium powder used, hexavalent chromium can still be detected in the produced leather.
At present, it is generally believed that the production of hexavalent chromium in leather may be the use of chromium powder, which contains hexavalent chromium or hexavalent chromium, chromium-containing tanning agents, and chromium-containing salt additives, such as chromium-containing salt dyes. , pigment paste, fixative, medium water, etc.
In addition, the impact of the production process on the formation of hexavalent chromium is also more complex and is roughly summarized as follows:
1. High pH value of the bath in the wet dyeing process: During the neutralization, retanning and dyeing of the chrome tanning leather, if the pH of the process is greater than 5, trivalent chromium is easily oxidized into hexavalent. chromium.
2. Fatliquoring agent: The fatliquor itself does not contain chromium, but the fatliquoring agent usually contains unsaturated bonds. After peroxide is formed in an aerobic environment, trivalent chromium can be oxidized. The higher the iodine value is, the higher the fatliquoring agent is. Easy to promote the formation of hexavalent chromium.
3. Heating and light: This is basically the root cause of hexavalent chromium formation. The higher the temperature, the stronger the light, and the longer the action time, the higher the content of hexavalent chromium in the leather.
4. Relative Humidity in the Air: Humidity during the storage of finished leather is one of the main influencing factors. Experiments have shown that the high humidity of the air is conducive to the inhibition of hexavalent chromium in leather.
In short, the reasons that lead to the formation of hexavalent chromium in leather are very complicated. So far, the business community has not yet reached a conclusion. Different measures can only be taken to deal with this problem in light of actual production conditions.
Leather manufacturers in some European countries have done a better job in chromium treatment. That is, the use of chromium tanning agent can also be controlled in the process to almost no detectable hexavalent chromium. However, this technical problem is common in China, the Chinese tradition. During the process control of leather tannins, the details of the implementation of the process parameters are ignored, such as excessive liquid volume, low alkalinity pH at the end of the alkalinity, insufficient production time, non-washing of the blue skin, no static aging, and dechromization during subsequent processing. The use of agents and the high thermal energy generated by mechanical action are the causes of the differences.
Fourth, the leather hexavalent chromium solution
There are many reasons for the production of hexavalent chromium in leather. A single method cannot completely prevent the formation of hexavalent chromium. To meet the stringent requirements of EU standards, it is necessary to control the entire tanning process and the transportation process. For these reasons, the response plan can be roughly summarized as follows:
1. First of all, we should do a good job of hexavalent chromium screening for raw materials, especially dyes, chrome tanning agents, and chromium salts additives.
2. During the tanning process, it is necessary to ensure that the entire process parameters can be under a hexavalent chromium suppression condition, for example, to ensure the pH value is about 5 and to avoid drastic changes in the pH value, to avoid high temperature or direct ultraviolet rays in the dry finishing stage, and to wash To be full.
3. Select better processing aids: Use reductive retanning agents, usually plant retanning agents have good reducibility; avoid the use of fatliquors with higher values ​​of unsaturation.
4. Use of effective reducing agents: In the study of Duanlimin et al., it was shown that sodium bisulfite and THPS (tetramethylphosphine phosphine) have a good effect on the elimination of hexavalent chromium, and the color of the leather after THPS treatment is more Bright.
5. Leather storage conditions: Under the premise of ensuring the leather moisture content does not exceed the standard or affect its quality, the humidity in the environment is controlled at a higher level; and try to avoid prolonged exposure to high light and high temperature conditions Store.
Xicco test indicated that due to the revision of the REACH regulation, it means that full-scale upgrading of hexavalent chromium control in leather, especially after the end of the transition period, will increase its law enforcement efforts. The relevant European tanning enterprises should pay close attention to Good corporate internal product line reorganization and personnel training in laws and regulations.
In addition, the comprehensive upgrade of hexavalent chromium control is an opportunity for already established and well-established leather companies. They are able to take the lead in seizing the EU market more forcefully. The leathermaking process is backward, and companies that are unstable to hexavalent chromium control are not allowed to Not rectifying its backward production line will also cause some tanning enterprises to face severe problems of survival.
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