Patent ID: 6730248
Filing Date: 2004-05-04
Classification: B29C,Y10T

Abstract:
A process for producing a foamed article of a thermoplastic resin composition by causing the resin composition to foam up in a cavity of a mold, comprisinga primary injection step in which a part amount of the thermoplastic resin composition is injected into the mold cavity defined by a stationary mold element and a movable mold element settled at a position confining the mold cavity to a smaller volume than the total volume of the thermoplastic resin composition necessary for making up the complete foamed article, while imposing a clamping pressure on the movable mold element so as to settle it at the position, a secondary injection step, subsequent to the primary injection step, in which the residual amount of the thermoplastic resin composition is further injected into the mold cavity, while drawing the movable mold element back from the position settled for the primary injection step so as to increase the cavity volume, and a foaming step subsequent to the secondary injection step, in which injection of the thermoplastic resin composition is stopped and the movable mold element is further drawn back so as to permit the thermoplastic resin composition to foam up, wherein the thickness L0 of the mold cavity at the start of the primary injection step is in the range from 1.0 to 1.5 mm, the injection time of the primary injection step is 1.5 seconds or less and the pressure imposed on the movable mold element in the primary injection step is in the range from 5 to 20 MPa with respect to the sectional area of the mold cavity in the projection onto the mold base plane and wherein the ratio of the thickness L0 of the mold cavity at the start of the primary injection step relative to the thickness L1 at the end of the secondary injection step, namely, L0/L1, is in the range from 0.3 to 1.0.