Method for the non-resin fluid-assisted injection molding of a resin

摘要

A method for the non-resin fluid-assisted injection molding of a resin to produce a shaped resin article having an improved surface finish, which comprises effecting an excess filling of a mold cavity of a sealed mold with a molten resin to form a molten resin mass having opposite, first and second surfaces respectively facing opposite inner walls of the mold cavity, wherein the excess filling is performed in a specific excess filling ratio which corresponds to an excess ratio of a resin by an amount corresponding to 30 to 90% of the difference between the volume of the mold cavity and the volume exhibited by the resin in accordance with the shrinkage thereof when the molten resin filled in the mold cavity is cooled to room temperature, and subsequently introducing a pressurized non-resin fluid into the mold cavity on a side of the first surface of the molten resin mass to thereby press the second surface of the molten resin mass against the cavity inner wall remote from the side of the introduction of the non-resin fluid. By the non-resin fluid- assisted injection molding method of the present invention, the occurrence of a sink mark on a front surface of a shaped resin article can be effectively prevented without causing the problem of the occurrence of burrs (flashes) .