Casting is a method of plastic processing. In the early casting, liquid monomers or prepolymers (see polymers) were injected into a mold under normal pressure, and then solidified by polymerization to form a product with the same shape as the cavity of the mold. At the beginning of the 20th century, phenolic resin was first molded by casting.
In the mid-1930s, plexiglass was cast with methyl methacrylate prepolymer (see polymethyl methacrylate). During the Second World War, unsaturated polyester casting products were developed, followed by epoxy resin casting products, and nylon monomer casting (see polyamide) in the 1960s.
With the development of molding technology, the traditional casting concept has changed. Polymer solutions, dispersions (referring to polyvinyl chloride paste) and melts can also be used for casting. The melted flat film is extruded with an extruder, and cast on a cooling drum to form a polypropylene film, which is called the extrusion-casting method.