| 摘要 |
Thermoplastic resins having a foamed structure only on a surface thereof are produced by treating one surface of a themoplastic resin article with a medium which is absorbable by the resin and which on heating to a temperature below the melting point of the thermoplastic resin is converted to, or generates a gas, and applying heat to the surface of the thermoplastic resin opposite to that treated with the said medium, thereby causing the treated surface to foam. Suitable foaming agents are low-boiling liquids, e.g. trichlorofluoromethane, methylene chloride, acetone, xylene, carbon tetrachloride, methyl ethyl ketone, benzene, toluene or chloroform. Suitable thermoplastic resins are polymers based on styrene, vinyl and vinylidene halides, vinyl acetate, cellulose acetate or butyrate, ethyl cellulose, acrylic and methacrylic esters, acrylonitrile, ethylene and propylene, and particularly a high-impact polystyrene which has a rubber compound grafted on to the molecule. The heating is preferably carried out by circulating a hot gas around the surface not treated with a foaming agent. |
