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