Patent ID: 6866811

Claim:
A method for injection-molding a molded article having a hollow portion by means of an injection-molding apparatus, said apparatus comprising: a mold assembly having a first-molten-resin injection portion for injecting a first molten thermoplastic resin into a cavity of the mold assembly, a second-molten-resin injection portion for injecting a second molten thermoplastic resin into the cavity of the mold assembly, and a pressurized-fluid introducing portion for introducing a pressurized fluid into the second molten thermoplastic resin injected into the cavity; a first injection cylinder communicating with the first-molten-resin injection portion; and a second injection cylinder communicating with the second-molten-resin injection portion; said method comprising: injecting the first molten thermoplastic resin from the first injection cylinder into the cavity through the first-molten-resin injection portion; initiating injection of the second molten thermoplastic resin from the second injection cylinder into the cavity through the second-molten-resin injection portion, without bringing the second molten thermoplastic resin into contact with the first molten thermoplastic resin injected into the cavity, concurrently with the start of said injecting the first molten thermoplastic resin into the cavity, during said injecting the first molten thermoplastic resin into the cavity, or after completion of said injecting the first molten thermoplastic resin into the cavity; and introducing the pressurized fluid into the second molten thermoplastic resin in the cavity from the pressurized-fluid introducing portion during said injecting the second molten thermoplastic resin into the cavity or after completion of said injecting the second molten thermoplastic resin into the cavity thereby to form the hollow portion only inside the second molten thermoplastic resin, which hollow portion does not extend to the first molten thermoplastic resin, and to bring the second molten thermoplastic resin into contact with the first molten thermoplastic resin.