The production and application of EVA foams in China started relatively late, but due to the excellent processing performance and extensive application of the products, the demand growth has been very rapid in recent years, which has attracted many manufacturers to enter the industry. Benefiting from the steady development of China's manufacturing industry, Industrial upgrading, and broader applications will be developed and other favorable factors, China's EVA foam material market will maintain rapid growth
What is EVA?
EVA is ethylene-vinyl acetate copolymer (also known as ethylene-vinyl acetate copolymer) is made by the ethylene (E) and vinyl acetate (VA) obtained by copolymerization, referred to as EVA polymerization method using high-pressure bulk polymerization, solution polymerization , Emulsion polymerization, suspension polymerization.
What is the use of EVA?
EVA particles can be produced into various types of EVA sheet, and then through the plate after processing, such as red type can be used as packaging lining, hot pressing can be made of soles. Electronics, hardware, toys, etc. can be used EVA material Wait.
EVA foam formula
EVA foam formula is generally composed of the following raw materials: Ingredients, fillers, foaming agent, bridging agent, foam promoter, lubricant.
Ingredients
Of course, in order to improve the physical properties of the product, you can also add some other appropriate materials, such as rubber, POE, but also can even add a little TPR to enhance certain physical properties. EVA main indicator is the VA Content, its level and EVA foam products have all the properties of a direct relationship.Of course, the specific ingredients or depends on the product requirements.
Filler
Filler, the current general use of calcium carbonate or talc, its use and reduce costs, increase product rigidity, etc., but also play a little role in thermal conductivity. Generally particle size as a quality indicator (of course, the water content is also a Aspects), say 120 heads, 400 heads etc. In principle, the finer the better, of course, the price will be higher.
Foaming agent
Foaming agent, are generally accustomed to high temperature foaming agent, the decomposition temperature of more than 220. There are low temperature foaming agent, the decomposition temperature at 140 degrees, as well as the temperature foaming agent, etc. Because the price difference is not large, and high temperature foaming Relatively stable agent will be some, so now do a lot of EVA are used in high temperature, but also with the use of the specific amount, according to the specific rate.
Bridging agent
Bridging agent, now the most used is DCP (phthalic acid di-sec octyl ester) .General practice when the material, the temperature is controlled as much as possible below 120 degrees.Some products require the smell, you can use another type of bridge Agent BIPB, which is generally used in conjunction with TAIC DCP dosage, in the flat foam and mold small foam, the general 0.5-0.6Phr, foam injection in the general 0.8-1.0Phr. Of course, there are also a little less There are different uses of this.
Foaming accelerator
Foam accelerator, now used more than two, zinc oxide powder, and zinc stearate powder alone can achieve the desired effect, but the stability of the product may be even better.Zinc oxide can make the decomposition of AC The temperature is reduced to about 160 degrees, easy to produce.Generally zinc oxide dosage too much product shrinkage will be relatively larger.Of course, too little foam speed is too slow, so it is best not to be less than 1.0hr /
Lubricant
Lubricants, generally with stearic acid. In fact, it does not much effect, is to let practice, 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.
Three big craft
EVA foam in general there are three kinds of technology, the traditional flat-panel large foam technology, the mold in the small foam process and injection process. The new Park below and we take a look!
1, injection process
This process will slowly become the mainstream, a process is out of the product is simple and convenient, but the mold is relatively high precision. Process principle is similar to the plastic injection molding industry, but the injection mold is immediately open, and the mold temperature is different, EVA injection is the plastic injection mold temperature and mold opening time has been adjusted.Now well-known sports shoes are used in this type of body. High efficiency!
2, the traditional large flat foam technology
Now the factory size smaller generally use this process, the cost of machinery and equipment is relatively low.This process is mainly used as a 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 CM.
3, the mold of small foam process
This process is mainly used in shoe materials, sports shoes to do the first two in the end of the foam.According to the recipe of a good material granulation, into a good mold, foam out is the general look. The difficulty is the mold And the symmetry of the formula, otherwise it is difficult to control the magnification and hardness at the same time.Often the size of the hardness is not enough, the hardness of the size of small enough.Flameting conditions more flexible, depending on the product structure, of course, mainly the impact of time.
to sum up: EVA is biodegradable; with PVC prices are similar; light weight; odorless; does not contain heavy metals; phthalate-free; high transparency, softness and toughness; super low temperature (-70C); anti Water, salt and other substances; high heat paste; low paste temperature; can be screen printing and offset printing. The prospects are bright.