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Analyze EVA foaming formula and 3 major processes

Analyze EVA foaming formula and 3 major processesAnalyze EVA foaming formula and 3 major processesAnalyze EVA foaming formula and 3 major processesAnalyze EVA foaming formula and 3 major processes

The production and application of EVA foam materials in China started late, but due to the excellent processing performance of the products and the wide application, the demand growth has been very rapid in recent years, attracting many manufacturers to enter the industry. Benefit from the steady development of China's manufacturing industry, downstream industry upgrades, and wider application areas will be developed and other favorable factors, China's EVA foam material market will maintain rapid growth


    What is EVA?


    EVA is produced by the copolymerization of ethylene-vinyl acetate copolymer (also known as ethylene-vinyl acetate copolymer) from ethylene (E) and vinyl acetate (VA), abbreviated as EVA. The polymerization method uses high pressure bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization.


    What does EVA do?


    EVA pellets can be produced into various types of EVA sheet, and then the sheet is processed through various channels, such as punching type can be used as packaging lining, hot pressing can be made into soles. Electronic, hardware and toy industries can use EVA materials and so on.


    EVA foam formula


    EVA foaming formulas are generally composed of the following raw materials: Ingredients, fillers, foaming agents, bridging agents, foaming accelerators, and lubricants.


    Ingredients


    The main ingredient is EVA or PE. Of course, in order to improve the physical properties of the product, you can also add some other materials, such as rubber, POE, etc., and you can even add a little TPR to enhance certain physical properties. The main indicator of EVA is the VA content. Its level is directly related to all the properties of EVA foam products. of course. The specific material used depends on the requirements of the product.


    Filler


    Fillers, currently used generally calcium carbonate or talc. Its use in reducing costs, increasing product rigidity, etc., can also play a role in heat conduction. The particle size is generally used as a quality indicator (of course, the moisture 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.


    Foaming agent


    Foaming agents are generally accustomed to high-temperature foaming agents and have a decomposition temperature of over 220 degrees. There is also a low-temperature foaming agent, a decomposition temperature of 140 degrees, and medium-temperature foaming agents. Because the price difference is not large, and the high-temperature foaming agent is relatively stable, so many of the EVA's are now used in high temperature, but also with the use of. The specific amount is based on the specific magnification.


    Bridging agent


    The bridging agent, now most used is DCP (Di-Octyl Phthalate). In general practice, the temperature should be controlled below 120 degrees. Some products have odor requirements, you can use another bridging agent BIPB, which is generally used in conjunction with TAIC. The amount of DCP used is generally 0.5-0.6 Phr in slab foaming and in-mold foaming, and 0.8-1.0 Phr in injection foaming. Of course, there are also appropriate additions and deletions, and there are also differences in this usage.


    Foaming accelerator


    There are two types of foaming accelerators, zinc oxide powder and zinc stearate powder. A single one can also achieve results, and the stability of the product may be better. Zinc oxide can reduce the decomposition temperature of AC to about 160 degrees for ease of production. In general, excess zinc oxide product shrinkage will be relatively large. Of course, too little foaming speed is too slow, so it's better not less than 1.0 hr/


    Lubricant


    Lubricant, stearic acid is generally used. In fact, it does not have much effect, that is, when the material is used, it does not stick to the machine. It is not good to use more, because it can reduce the friction between points, so that most of the physical properties are reduced.


    


    Three major processes


    EVA foam generally has three processes, a conventional flat large foaming process, an in-mold small foaming process, and an injection process. The following new moorings and everyone to see!


    1, injection process


    This process will gradually become the mainstream, a process to make is the product, convenient and concise, but the precision of the mold is relatively high. The process principle is similar to the injection molding in the plastic industry, except that the injection molding is to open the mold immediately and the mold temperature is different. The injection of the EVA is to adjust the molding temperature and opening time of the plastic injection mold. Most of the well-known sports shoes now use this method. high efficiency!


    2, the traditional flat large foaming process


    Nowadays, the smaller scale of the factory generally adopts this kind of technology, and the cost of machinery and equipment is relatively low. This process is mainly used as a plate, and then made into products through blanking, edging and other processes. Foaming conditions are relatively fixed, the temperature is 160-170, the time is determined by the thickness of the mold, generally 90-110 seconds / MM, pressure 150KG / square CM.


    3、In-mold small foaming process


    This process is mainly used in shoe materials, sports shoes to do the first time the second foam in the bottom. Pellet the material according to the recipe and put it into a well-opened mold. Foaming out is the general appearance. The difficulty is the symmetry of the mold and formula, otherwise it is difficult to control the rate and hardness at the same time. Qualified hardness is often not enough, hardness is small enough. The foaming conditions are relatively flexible, depending on the product structure, and of course mainly the effect of time.


    Summary: EVA is biodegradable; similar in price to PVC; lighter weight; non-odor; no heavy metal; no phthalates; high transparency, softness and toughness; super low temperature resistance (-70C) Resistance to water, salt and other substances; high heat paste; low bonding temperature; screen printing and offset printing. The prospects are bright.


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