Insulated metal mold

An insulated metal mold comprising a molding surface defining the cavity of a mold for high pressure injection molding thermoplastic resin and having a metal layer providing the molding surface, a metal backing member, and a layer of heat-insulating means sandwiched between the metal layer and the backing member, wherein:

• (a) said metal layer has a thickness of approximately 0.001 mm to 3 mm so that the injected molten thermoplastic resin rapidly heats the metal layer to a temperature sufficient to prevent a solid layer from being formed by the injected molten thermoplastic resin on the cavity surface,
• (b) said heat-insulating means comprises a thermosetting resin composition and controls heat transmission from the metal layer to the backing member so that when the metal layer is heated to a selected temperature, the selected temperature is first maintained for a sufficient period of time to prevent a solid layer from being formed on the cavity surface by the injected molten resin during injection of the molten thermoplastic resin into the cavity, after which the metal layer cools to a temperature sufficiently to solidify the molten thermoplastic resin within a predetermined time after filling the mold cavity therewith, and
• (c) said heat-insulating means comprises at least one member selected from the group consisting of inorganic filler, metal powder filler, and fibrous filler;
• the inorganic filler consisting of a powder of at least one material selected from the group consisting of glass, silica, calcium carbonate, talc, clay and alumina, the metal powder filler consisting of a powder of at least one metal selected from the group consisting of aluminum, aluminum alloy, copper and copper alloy;
• and the fibrous filler consisting of at least one material selected from the group consisting of glass fiber, carbon fiber, asbestos fiber and whisker.