There are many types of foaming materials, and most thermosetting plastics and thermoplastics can be processed into foaming materials. Foaming material refers to the microporous plate raw material that is based on polymer material (plastic, vulcanized rubber, polyurethane elastomer) and has thousands of bubbles inside. It can also be regarded as a polymer filled with gas material. The four major forming processes of plastic foam materials are introduced in detail below.
Compression molding belongs to the earlier type of foaming process, so there is no standard abbreviation for compression molding foaming. Until recent years, polypropylene compression molded foaming materials have been emerging, which are crowned with "M" and defined as "MPP".
In recent years, MPP has emerged continuously, which is basically a kind of foaming PP original in China. Its manufacturing process uses a press as the main equipment for foaming. In principle, it is not substantially different from traditional foaming by molding. The main difference is that the foaming agent is not a traditional AC organic chemical foaming agent. The foaming agent only uses supercritical extraction of CO2, so the foaming ratio can reach more than 20 times, and it is in line with the principle of environmental protection.
The actual manufacturing method is to make PP into metal sheets of different thicknesses by using various production processes such as rubber compounding, injection molding, and extrusion. These metal sheets are then cut and placed in a mold in a large press, and the mold is closed.
Add the left and right templates of the jigsaw machine to increase the temperature of the PP sheet to around the melting point of PP. In addition, introduce supercritical extracted CO2 into the mold from different directions. After the PP sheet is fully pre-impregnated, the temperature of the PP sheet is reduced The temperature suitable for foaming can quickly release the working pressure of the press, so that the PP sheet can be fully foamed and cooled, and the MPP foamed sheet can be obtained.
The forming process of expandable bead rubber and plastic products, that is, in a high-pressure reactor, within a certain period of time, according to high pressure, the physical foaming agent is pre-impregnated into the fine powder of the base epoxy resin at a predetermined temperature, and then cool the temperature of the management system to room temperature to obtain expandable beads.
When in use, at a certain foaming temperature, steam or warm air is used to pre-foam the expandable beads to obtain pre-expanded expandable beads of the size of black beans.
When making the product, put the pre-expanded expandable beads into the mold to heat and relieve the pressure, so that the pre-expanded expandable plastic beads can be further expanded and combined to produce a predetermined foam material, that is, it is called the forming of expandable bead rubber and plastic products. Because all of them use physical foaming agents, the foaming ratio is very large.
Add the plastic and foaming agent to different parts of the extruder, put them under high pressure to melt in the extruder to produce a uniform aqueous solution, and then release the pressure at the die, foam, and cool to make sheets, plastic sheets and even pipes wait. In the process of extrusion and foaming, the foaming agent must form a uniform aqueous solution with the plastic under high pressure, and instantly release the pressure at the die, foam, cool, and form foaming material, and it is impossible to rely on the solid phase or the constraints of crystals, so the melt strength requirements of plastics are very high, especially the melt has strong strain hardening properties during the stretching process, so it is very difficult to foam.
Injection molding foaming is a relatively late development of foaming materials, mainly due to the discrepancy between traditional injection molding and foaming conditions.
Today's injection molding foaming materials are limited to products with a very low foaming ratio, and even foaming is not the key purpose, but just to better reduce the shrinkage and deformation of injection molded products, especially in trays, support frames, etc. Injection molding of large and medium-sized products.