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EVA foam process
EVA foam formula is generally composed of the following raw materials: Ingredients, fillers, foaming agent, bridging agent, foam promoter, lubricant.
Ingredients, it is clear that EVA and / or PE. Of course, in order to improve the physical properties of the product, some other materials, such as rubber, POE, etc., may be appropriately added, and even some TPR may be added to enhance certain physical properties. EVA, the main indicator is the VA content, the level of its decision almost all the properties of EVA foam products have a direct relationship. of course. Some can only foam with PE. What specific ingredients or products depends on the requirements.
Fillers, the current general use of calcium carbonate or talcum powder. Its purpose is to reduce costs, increase product rigidity, etc., but also play a role in thermal conductivity. Generally the particle size as a quality indicator (of course, the water content is also on the one hand), such as 120 mesh, 400 mesh and so on. In principle, the finer the better, of course, the price will be higher. The maximum amount of 40Phr I have seen in the formula (the amount of the main material as a percentage) L blowing agent,
Generally used to use AC series of foaming agent, such as AC-3000H, AC series foaming agent is a high temperature foaming agent, the decomposition temperature of 220 degrees. There are also low-temperature foaming agent, such as AD-300, the decomposition temperature at 140 degrees, as well as in the temperature foaming agent. Because the price difference is not large, while the high temperature foaming agent will be relatively stable, so a lot of old EVA are now switched to high temperature, but also with the use of. The amount of AC, according to the specific rate.
DCP is the most used now, also useful before TAIC, PL400 and so on. The half-life of DCP is 1 minute at 180 degrees and 10 minutes at 130 degrees, so when it is generally practiced, the temperature should be controlled below 120 degrees. Some products have odor requirements, you can use another bridging agent BIPB, it is generally used in conjunction with TAIC. The amount of DCP, in the flat foam and mold small foam, the general 0.5-0.6Phr, foam injection generally 0.8-1.0Phr. Of course, there are some additions and subtractions, but also different from this usage. Foam accelerator, now used more than two, zinc oxide powder, and zinc stearate powder.
In the past, we also use these two kinds of collocation, now only use zinc oxide. A single kind can achieve the result, and the stability of the product may be better. Zinc oxide can make the decomposition temperature of AC reduced to about 160 degrees, easy to produce. We have a consensus, the general amount of zinc oxide does not exceed 0.2Phr, too much product shrinkage will be relatively larger. Of course, if too little, foaming speed is too slow, so it is best not to be less than 1.0hr /
Generally with stearic acid. In fact, it does not much effect, that is, to practice material, non-stick machine. Use more but not good, because it can reduce the friction between points, so that most of the physical properties are reduced. Recommended 0.5Phr
Excipients that can be added to EVA formulations are mixed. Just talk about several types of main bar
1 scrap. Scrap is made after the product some of the extra material tail, the edge of what. They are all foamed. This kind of thing is a cost killer, using it can significantly reduce production costs, of course, will also bring the physical performance impact. Almost all of these EVA are in use, I will not go into details.
2 Antistatic Agent Some products require antistatic function, while the EVA foam product itself is very strong with static electricity, so you need to add some antistatic agent in the formula. General EVA antistatic agents are mixtures, the specific composition of MS is very complicated, sometimes I say not clear, the amount of 3% -5%.
3 Flame retardants EVA foamed products used as some packaging materials may require flame retardancy. Flame retardant can be added in the formula to achieve the effect of flame retardant. Plastic commonly used flame retardant Mg (OH) 2, Al (OH) 3, EVA foam products also have some effect, but the amount of relatively large, we use 12% -20%, but for the flame retardant products , They are not very good use. Japan has a product flame retardant ideal, but does not comply with the ROHS directive. So a word off total, high demand for flame retardant, I am not a very good idea.
4 fast-foaming agent EVA foam process takes time, if you want to increase daily output, reduce product energy consumption, you can add a proper amount of quick-start to shorten the foaming time. TAIC is the most common starter currently available on the market, which should be a bridging aid. Adding the right amount of TAIC can really shorten the time, but with it, the size of the product will be reduced accordingly, and the downscaling is not very satisfactory. Fujian I do not know, and now there are several places in Guangdong here with another kind of quick-start agent, adding a small amount of time reduction effect is still considerable.
5 Colorants Foam products are generally colored, so colorants need to be added to the formula for toning. EVA foam products can be used toner color, color plastic, of course, best to use masterbatch. MS products can not use computer color, it may be because this thing before and after the foam color change is too large, the computer is also equipped with immortality.
EVA foam in general there are three processes. Traditional large foam board, the mold of small foam and injection. (Taiwan called France)
The traditional large-scale flat-panel foam are now generally used in this small factory. The cost of machinery and equipment is relatively low. This process is made out of the plate, and then through the blanking, edging and other processes made products. Foaming conditions are relatively fixed, the temperature at 160-170, the time determined by the thickness of the mold, the general 90-110 seconds / MM, pressure 150KG / square
Small foam mold This process is mainly used in shoe materials. Sneakers do the first two in the end of the foam. According to recipe good material granulation, weighing into a good mold, foam out is the general look of shoes. The difficulty of this process is the symmetry of the mold and formula, otherwise it is difficult to control the magnification and hardness. Often qualified size, hardness is not enough. Hard enough size smaller. Foaming conditions of this process is more flexible, depending on the shape of the product structure, of course, mainly the time is the change. Changes in temperature is not large. Stress conditions do not say. Speaking of the second in front, here to introduce the second molding it. Foam in front of a good foam worn off the epidermis, pressed into the finished mold, by heating and cooling the two steps is the product molding. Heating temperature is more appropriate in the 125-135, pressure 50KG / square CM, heated for a certain time before water cooling. Come out is the second in the end. This compression into a more stable base size, the physical properties are relatively better.
Injection of this process should be the mainstream in the future. A process to make it is the product. Only mold precision higher. The principle is similar to plastic injection molding industry. But the injection mold is opened immediately, and the mold temperature is different. That is, the injection of EVA, however, is just the plastic injection mold temperature and mold opening time adjusted below. Last time it seemed that a Shanghai friend had called me and later let his injection molding machine be used to make foaming stroller wheels. Do now most well-known sports shoes are used to do this type of body. Compared with other methods, the efficiency is really worse than thousands of miles.