Foaming plastics are based on thermoplastic or thermosetting resins, which have many fine pore inside. Foaming is one of the important methods of plastic processing. The foamed plastic produced by plastic moulding machine contains gas and solid. Gas exists in foam in the form of bubbles, and the barrier between bubbles and pores is called closed pores. The connected pores are called openings, and then there are two parts: closed cell foam plastics and open cell foam plastics. The opening or obturator of foam structure is selected by the original data function and its processing technology.

Plastic foaming skills have a long history. Earlier, it was made from foam rubber in the early 20s. It was made of foam rubber. In 30s, it showed rigid polyurethane foam and polystyrene foam. In 40s, polyethylene, polyvinyl chloride, epoxy resin and phenolic foam were used. In 50s, there were expandable polystyrene foam and soft polyurethane foam.

Now, basically plastics, including thermoplasticity and thermosetting, can be foamed into foams. Industrial preparation methods include extrusion foam, injection foam, molding foam, calendering foam, powder foam and spray foam, etc. In the meantime, injection molding foaming is one of the more important methods of forming, here the key description of injection molding foaming.

Foaming Principle

The foaming methods of plastics can be divided into physical foaming method and chemical foaming method according to the different foaming agents used. Here is the first brief introduction of foaming agent.

foaming agent

Foaming agents can be roughly divided into physical and chemical foaming agents. The requirements for physical foaming agents are: non-combustion, good thermal stability, no chemical reaction in the gaseous state, and the relaxation rate in the plastic melt in the gaseous state is lower than that in the air. The commonly used physical foaming agents are air, nitrogen, carbon dioxide, hydrocarbons, freon and so on.

Chemical foaming agent is a kind of substance which can release gas such as nitrogen and carbon dioxide by heat. The requirement of chemical foaming agent is that the gas released by decomposition should be non-combustion, which has no effect on the forming and physical and chemical functions of products. The speed of releasing gas should be controlled. The foaming agent should have excellent slackness in plastic guessing. Inorganic foaming agents such as sodium bicarbonate and ammonium carbonate, organic foaming agents such as azo formamide and azodiisobutyronitrile are widely used.