The formation of a uniform mixture of polymer and foaming agent into a supercritical melt for EPP products is a very important first step. In order to obtain a supercritical melt, the first step is to obtain a suitable foaming agent, such as CO2, N2, or water, and make it a supercritical fluid. The principle of batch preparation of supercritical melt using this supercritical fluid technology. After control, it is input into the chamber 3 for soaking PVC material 4, which is controlled by an external temperature controller 5 to generate supercritical fluid of CO2 under the action of pressure and temperature.
　　In addition, the density of internal pores in ultra microporous foam materials is not only related to the content of supercritical fluid in the raw material, but also closely related to the type, properties, and processing technology of the polymer raw material. Therefore, the following points must be paid attention to during the molding of ultra microcellular foams:
　　1) Plastic must be saturated with sufficient gas and form a large number of ultrafine micropores at the same time, as the solubility of gas increases with pressure, requiring higher pressure.
　　2) During the development stage of micropores, temperature must be controlled to control the stability of the plastic matrix.
　　3) It is necessary to choose a gas that has suitable solubility and diffusion properties for the selected plastic.
　　4) In order to form a large number of super micropores, uniform nucleation must dominate the nucleation process, even if there are uneven crystal nuclei.
　　In summary, in order to apply ultrafine foam technology to industrial production, it is necessary to address the key technical issues mentioned above. We believe that with the joint efforts of researchers from various countries, ultrafine porous technology will be widely applied in the near future.
　　The rear part is connected to the extrusion molding die, and the temperature of the die is controlled. The EPP product causes the supercritical melt to expand uniformly with temperature changes while forming through the die. A cooling and coiling device is connected at the outlet of the die to ensure the continuity of material shaping and production.