Method for injection molding thick-walled articles
AssigneeAsahi-Dow Limited
InventorsTadashi Nagumo, Akio Yasuike, Hiroshi Kataoka
Life of this patent
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Abstract
Molten synthetic resin material containing foaming agent in an amount of 0.05 to 5 percent by weight is injected into a pre-pressurized mold cavity in a mold which is closed by a relatively low clamping force having a coefficient in the range of 10 to 40, said coefficient being represented as a ratio of clamping force to maximum injection shot volume. The above injection step is carried out for at least 3 seconds. After the injection step has been initiated, the pre-pressurized mold is released to atmosphere during the injection step at the soonest. At least two molds may be used to be alternately charged with said material.
Claims3
A method for the production of foamed articles having an average wall thickness of between 3.5 mm and 100 mm by injecting a molten synthetic resin material with a foaming agent contained therein from an injection cylinder means into a cavity of a mold means, said method comprising the steps of:
- (a) clamping said mold means by a relatively low clamping force having a coefficient in the range of between 10 and 40, said coefficient being represented as a ratio of clamping force (ton) to maximum injection shot volume (liter);
- (b) pre-pressurizing the cavity of said mold means by supplying thereto a gas which has such a pressure at least above 3 kg per square centimeter so that the diffusion of the blowing gas produced from said foaming agent will be substantially prevented;
- (c) injecting an amount of molten synthetic resin material that is insufficient to fill the cavity and which contains a foaming agent in an amount about 0.05% by weight to about 5% by weight into said pre-pressurized cavity from the injection cylinder means for a predetermined time in the range of between 3 and 20 seconds;
- (d) releasing said pressurized gas from said mold cavity no earlier than immediately before completing said injection step for expanding the injected foamable resin material to fill said mold cavity;
- and
- (e) cooling said mold means at least during said injection step.
Method as claimed in claim 5, wherein said mold means is actuated to move alternately said mold cavities along a linear path to a position in which said material is injected thereinto from said injection cylinder means.
Dependencies are inferred from the claim text.