EVA foaming process

    EVA foaming formula is generally composed of the following raw materials: main material, filler, foaming agent, bridging agent, foaming accelerator, lubricant.

    The main material, clearly, is EVA and/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 even add a little TPR to enhance certain physical properties. For EVA, the main indicator is the VA content, and its level is almost directly related to all the properties of EVA foam products. of course. Some can also be foamed with only PE. The specific ingredients used depend on the product requirements.

    As a filler, calcium carbonate or talc is generally used at present. Its purpose is to reduce costs, increase product rigidity, etc., and also play a role in heat conduction. Generally, the particle size is used as the quality index (of course, the water content is also one aspect), such as 120 mesh, 400 mesh, etc. In principle, the finer the better, of course the price will be higher. The dosage in the formula I have seen is 40Phr (the dosage is the percentage of the main ingredient) L foaming agent,

    Generally, AC series foaming agents are used, such as AC-3000H. AC series foaming agents are high-temperature foaming agents with a decomposition temperature of more than 220 degrees. There are also low-temperature foaming agents, such as AD-300, which has a decomposition temperature of 140 degrees, and medium-temperature foaming agents. Because the price difference is not big, and the high temperature foaming agent will be relatively stable, so now many old EVA products are changed to high temperature, and some are used together. The dosage of AC depends on the specific magnification.

    Bridging agent,

    Now, DCP is more commonly used, and TAIC, PL400, etc. were also used in the past. The half-life of DCP is 1 minute at 180 degrees and 10 minutes at 130 degrees. Therefore, in general, the temperature should be controlled below 120 degrees as much as possible when training materials. Some products have requirements for smell, you can use another bridging agent BIPB, which is generally used in conjunction with TAIC. The dosage of DCP is generally 0.5-0.6Phr in flat foaming and small in-mold foaming, and 0.8-1.0Phr in injection foaming. Of course, there are some appropriate additions and subtractions, and there are also different usages. There are two kinds of foaming accelerators, zinc oxide powder and zinc stearate powder.

    We used these two combinations before, but now we only use zinc oxide. A single type can also achieve the effect, and the stability of the product may be better. Zinc oxide can reduce the decomposition temperature of AC to about 160 degrees, which is convenient for production. We have a consensus that the general amount of zinc oxide does not exceed 0.2Phr, and excessive product shrinkage will be relatively large. Of course, if there is too little, the foaming speed will be too slow, so it should not be less than 1.0hr/

    Lubricant,

    Stearic acid is generally used. In fact, it doesn't have much effect, it just makes the machine not stick to the machine when training materials. Too much is not good, because it can reduce the friction between the components, so that most of the physical properties are reduced. Recommend 0.5Phr

    The excipients that can be added to the EVA formulation are mixed. Just talk about the main ones

    1 Leftovers. The leftover material is the extra material tails, side strips and so on after making the product. They are all foamed. This kind of thing is a cost killer, using it can greatly reduce production costs, of course, it will also bring about physical performance impact. Almost all of these types of EVA are in use, so I won't go into details.

    2 Antistatic agent Some products require antistatic function, and EVA foam product itself is very electrostatic, so some antistatic agent needs to be added to the formula. Generally, the antistatic agents used in EVA are mixtures, and the specific components of MS are very complicated. I can't say clearly for a while, the dosage is 3%-5%.

    3 Flame retardant EVA foam products used as some packaging materials may need to be flame retardant. Flame retardants can be added to the formulation to achieve flame retardant effects. The flame retardant Mg(OH)2 and Al(OH)3 commonly used in plastics also have a certain effect on EVA foam products, but the amount is relatively large, we use 12%-20%, but for products with high flame retardant requirements , They are not very useful. There is a product in Japan that has a very good flame retardant effect, but it does not meet the ROHS directive. So in a word, I don’t know how to deal with high flame retardant requirements.

    4 Quick-curing agent The EVA foaming process takes time. If you want to increase the daily output and reduce the energy consumption of the product, you can appropriately add a quick-curing agent to shorten the time required for foaming. The common quick-curing agent on the market now is TAIC, which should be a bridging agent to be exact. Adding an appropriate amount of TAIC can indeed shorten the time, but with its addition, the size of the product will be reduced accordingly, and the time-lapse effect is not very satisfactory. I don't know in Fujian. Now there are several places in Guangdong where another kind of quick-curing agent is used. The amount of addition is small, and the time-saving effect is still considerable.

    5 Colorants Foamed products are generally colored, so you need to add colorants to the formula to color. EVA foam products can use toner, color glue, of course, color masterbatch. MS products can’t be matched with a computer. It may be because the color changes too much before and after foaming, and the computer will not match.

    Generally speaking, there are three processes for EVA foaming. Traditional flat foaming is large, small foaming and injection in the mold. (Called in Taiwan)

    The traditional flat foam is now generally used in small factories. The cost of machinery and equipment is relatively low. This process is made of plates, which are then made into products through processes such as punching and edging. The foaming conditions are relatively fixed, the temperature is between 160-170, the time is determined by the thickness of the mold, generally 90-110 seconds/MM, the pressure is 150KG/square

      In-mold small foaming This process is mainly used in shoe materials. Sports shoes do the first foaming of the second midsole. According to the formula, the material is granulated, weighed, and then placed in the opened mold, and the foaming is the general appearance of the shoe. The difficulty of this process is the symmetry of the mold and formula, otherwise it is difficult to control the magnification and hardness at the same time. Often the size is qualified and the hardness is not enough. The hardness is enough and the size is small. The foaming conditions of this process are more flexible, depending on the shape and structure of the product, of course, it is mainly the change of time. The temperature change is not large. Let alone stress conditions. Speaking of the second midsole, here is the second molding. The foamed rough embryo is ground off the skin, pressed into the finished mold, and heated and cooled in two steps to form the product. The heating temperature is 125-135, and the pressure is 50KG/square CM. After heating for a certain period of time, then water cooling. Take it out is the second midsole. The size of the compressed bottom is relatively stable, and the physical properties are relatively better.

     Injection This kind of craft should be mainstream in the future. One process is the product. It's just that the precision of the mold is higher. The principle is similar to injection molding in the plastics industry. It's just that the injection mold is opened immediately, and the mold temperature is different. That is to say, the injection of EVA is nothing more than adjusting the mold temperature and mold opening time of plastic injection molding as follows. It seemed that a friend from Shanghai called me last time, and later let his injection molding machine be used to make foamed baby wheels. Most types of well-known sports shoes are made using this method. Compared with other methods, the efficiency is really worse than that. Moyuan EVA manufacturer