Injection molding method for producing shaped, hollow resin articles, and mold for use therein

A method for injection molding a resin while forming a hollow to produce a shaped, hollow resin article having a thickness of at least 1.0 mm, comprising:

• (1) providing a mold comprising a fixed mold half and a movable mold half mating with said fixed mold half to thereby provide a cavity defined by an inner wall surface of the fixed mold half and an inner wall surface of the movable mold half, said cavity having opposite, first and second inner wall surfaces, which respectively correspond to a front surface and a back surface of a shaped, hollow resin article to be molded by said mold;
• (2) injecting a resin in a molten form into said cavity through a gate for the cavity in an amount of at least 60% of a predetermined amount sufficient to fill the entire volume of the cavity, thereby forming a molten resin mass having opposite, front and back surfaces respectively facing the opposite, first and second inner wall surfaces of said cavity;
• (3) introducing a pressurized fluid into the molten resin mass through said gate or through an inlet for said fluid which inlet is provided independently from said gate, thereby forming a hollow in said molten resin mass, wherein the introduction of said fluid is conducted without injecting a molten resin into the cavity or while injecting a molten resin into the cavity;
• and
• (4) allowing the molten resin mass having the hollow formed therein to cool, thereby producing a shaped, hollow resin article;
• wherein at least one preselected discrete portion of said second inner wall surface of the cavity has a heat insulating member embedded therein, said heat insulating member having a heat conductivity which is 1/10.sup.4 to 1/30 of the heat conductivity of the material constituting the remainder of said inner wall surfaces of the cavity, thereby causing said fluid to flow into said molten resin mass along a line substantially corresponding to a line along which said preselected portion of said second inner wall surface of the cavity extends, so that the shaped, hollow resin article produced has a hollow in a position corresponding to said preselected portion of said second inner wall surface of the cavity.