Foaming method of foamed plastics

DATE：2022/6/16 8:46:09 / READ： / SOURCE：This station

Foaming method of foamed plastics

Foamed plastics have a wide variety and wide range of uses. Their forming methods are similar to ordinary plastic forming methods. However, in the forming and finalization of foamed plastics, a large number of fine bubbles in the plastic melt or solution have to undergo the expansion and solidification finalization process. Any gas-liquid coexistence system is extremely unstable. Bubbles may expand or collapse, so there are many processes that affect their changes, Some influencing factors influence each other. Therefore, the shaping process of foamed plastics is much more complicated than that of ordinary plastics. Foamed plastics can be divided into two types: air foamed plastics and composite foamed plastics. This chapter mainly introduces the foaming method and forming principle of air foaming plastics. EVA film production line www.handern com
There are many kinds of foamed plastics with different foaming methods. The commonly used foaming methods include physical foaming, chemical foaming and mechanical foaming. EVA film production line www.handern com
1、 Physical foaming method
Physical foaming method is to use physical principles to implement foaming, including the following two methods.
1. inert gas foaming method
This foaming method is to press the inert gas into the molten polymer or paste material under pressure, and then reduce the pressure and raise the temperature, so that the dissolved gas expands and foams. The utility model is characterized in that no residue is left after gas foaming, which does not affect the performance and use of foamed plastics. But the disadvantage is that it needs high pressure and complex high-pressure equipment. Usually used in PVC, polyethylene and other foamed plastics.
2. low boiling point liquid foaming EVA film production line www.handern com
This foaming method is to use the evaporation and vaporization of low boiling point liquid for foaming. The low boiling point liquid is pressed into the polymer or dissolved in the polymer particles under a certain pressure and temperature, and then the polymer is heated and softened, and the liquid is also evaporated and vaporized for foaming. The latter method is also called the expandable bead method. Usually used in polystyrene, cross-linked polyethylene and other foamed plastics
2、 Chemical foaming EVA film production line www.handern com
The chemical foaming method is used to generate gas during the foaming process, including the following two types.
1. thermal decomposition foaming agent foaming method
The foaming method is to add a thermal decomposition foaming agent to generate gas by thermal decomposition. The utility model is characterized in that it can be foamed only by adding foaming agent into the formula without special equipment. However, the disadvantage is that sometimes the molding temperature and the decomposition temperature of foaming agent are not easy to match, which will make the foaming process difficult to control. It is often used in PVC, polyethylene and other foamed plastics.
2. foaming method of gas generated by interaction between polymer components
This foaming method uses the chemical reaction between two or more components in the foaming foam system to generate inert gas (such as carbon dioxide or nitrogen) to cause the polymer to expand and foam. In order to control the balance of polymerization reaction and foaming reaction during the foaming process, a small amount of catalyst and foam stabilizer (or surfactant) are generally added to ensure good product quality. Its characteristic is that it does not need special foaming agent, but its disadvantage is that the reaction process is complex. It is usually used in polyurethane and other foamed plastics.
3、 Mechanical foaming method
This foaming method is to use strong mechanical agitation to make the air involved in the resin lotion, suspension or solution to form a uniform foam, and then make it gel through physical or chemical changes to solidify into foamed plastics. In order to shorten the forming cycle, air can be introduced and emulsifier or surfactant can be added. It is characterized by no need to add special foaming agent, but the disadvantage is that the equipment required is high. It is usually used in urea formaldehyde, polyvinyl formal, polyvinyl acetate, polyvinyl chloride sol and other foam plastics.
The common feature of the above three foaming methods is that during the foaming process, the resin is in a plastic state of liquid or low viscosity. Only when adding foaming agent or adding solid or liquid that can generate bubbles can gas be generated to form a bubble structure. EVA film production line www.handern com

Author：admin

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