Injection molding of plastic onto the rear side of a decorative material involves injection into a partly open tool, reduction of pressure then final tool closure to compress the plastic over the entire material

摘要

The multi-stage process involves: (a) placing a material(1) or object in an open tool(2,3); (b) partially closing the tool to a specific gap dimension(5); (c) injecting a predetermined amount of plastic(6); (d) retracting a tool slide(10) to reduce pressure applied by injected plastic on the object or material; and (e) closing the tool down to a prescribed gap(9) to compress the plastic and completely fill the cavity. The injection stage (c) and retraction of the tool slide may be repeated before the final tool closure stage. In an additional step following complete filling of the tool cavity fluid is injected either into the space between the injected melt(6) and the cavity wall or directly into the melt. Tool closure is controlled according to the injection speed and/or cavity pressure measured close to the injection point. Melt injection is controlled according to tool internal pressure melt pressure or hydraulic pressure. At least one cavity wall, preferably on the tool face contacting the plastic, is heat insulated. The insulation is a layer whose temperature can be varied which is integrated in the tool halves. An Independent claim is also made for the tool which has two parts(2,3) forming a cavity(4) and a feed channel whose cross-section is related to the gap(5) dimension so that during injection 300 bar pressure is produced in the cavity.