Injection compression molding method for compact discs or the like
AssigneeSumitomo Heavy Industries, Ltd.
InventorTakehiko Kitamura
Life of this patent
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Abstract
An injection compression molding method for compact discs or the like, includes the step of changing the clamping pressure or compression pressure, after the internal cavity pressure in the mold after injection has reached its peak, stepwise or continuously as the cooling proceeds, thereby making the applied pressure per unit area with respect to the effective pressure range constant. In a compact disc formed by this method, the residual stress after cooling is uniform, so that its optical properties are improved substantially.
Claims7
An injection compression molding method for producing optical compact discs using an injection molding apparatus which has a mold having a mold cavity and which can exert a controllably variable compression pressure on said mold to vary internal cavity pressure in said mold cavity, comprising the steps of:
- injecting a moldable liquid material into said mold cavity while applying a first predetermined compression pressure on said mold;
- applying a dwell pressure to said moldable liquid material in said mold cavity after said mold cavity is fully filled with said moldable liquid material;
- controlling the compression pressure on said mold while cooling said moldable liquid material, after the internal cavity pressure in the mold after injection has reached its peak at a time approximately when said injection stage is terminated and said dwell stage is initiated, such that the pressure per unit area applied to the moldable material is substantially constant with respect to the effective pressure applied to an unhardened portion of said moldable material to produce an optical compact disc having generally uniform residual stress.
An injection compression molding method for producing optical compact discs using an injection molding apparatus which has a mold having a mold cavity and which can exert a controllably variable compression pressure on said mold to vary internal cavity pressure in said mold cavity, comprising the steps of:
- injecting a moldable liquid material into said mold cavity while applying a first predetermined compression pressure on said mold;
- applying a dwell pressure to said moldable liquid material in said mold cavity after said mold cavity is fully filled with said moldable liquid material;
- controlling the compression pressure on said mold while cooling said moldable liquid material, after the internal cavity pressure in the mold after injection has reached its peak at a time approximately when said injection stage is terminated and said dwell stage is initiated, such that the pressure per unit area applied to the moldable material is substantially constant with respect to the effective pressure applied to an unhardened portion of said moldable material to produce an optical compact disc having generally uniform residual stress and having a substantially uniform birefringence profile.
Dependencies are inferred from the claim text.