US 5,415,817 A · Process for molding plastic lenses

Abstract

An improved injection/compression molding process for the manufacturing of high quality concave optical lenses of thin thickness. A thermoplastic material is injected into a mold cavity of an injection/compression molding machine, the mold cavity is designed to have adjustable thickness and is initially set at a thickness greater than the lens to be produced. After the amount of the plastic injected fills the enlarged cavity, the thickness of the cavity is gradually reduced by exerting a compressional force on the thermoplastic material inside the mold cavity. During the compression stage, the injection continues and the excess thermoplastic material is squeezed into an overflow pocket inside the injection/compression mold. The injection apparatus can be switched into a pressure holding mode during and after the compression stage to prevent any backflow and post-injection shrinkage. The process disclosed in the present invention offers many significant advantages over prior art processes, including avoidance of the commonly encountered weld line and birefrigence problem, substantially improved quality control, elimination of external heating or cooling needs, increased production rate, and reduced production cost.

Claims18

Dependent claims

A process for making plastic lens using an injection/compression molding machine, said injection/compression molding machine having a mold capable of forming a mold cavity with adjustable thickness, and said process comprising the following steps:

(a) forming a mold cavity in said mold with enlarged thickness, said mold cavity has a shape similar to but greater in thickness than said plastic lens to be made, and said mold cavity is adapted to be in communication with both an injection channel and an overflow pocket both are formed in said injection/compression machine;
(b) injecting a molten plastic material into said mold cavity through said injection channel while allowing a portion of said molten plastic material to flow into said overflow pocket after said plastic material fills said mold cavity;
(c) without stopping injection of said molten plastic material, applying a compression means on said molten plastic material in said mold cavity to reduce thickness of said mold cavity, said compression means continues until a predetermined thickness is reached;
(d) cooling said plastic material to cause solidification thereof and form said plastic lens;
and
(e) removing said plastic lens from said injection/compression machine.

3 more elements

A process for molding plastic lens comprising the following steps:

(a) obtaining an injection/compression molding machine, said injection/compression molding machine having a mold comprising two opposing mold dies, said mold dies having compensating surfaces relative to two major surfaces respectively of said plastic lens to be produced, at least one of said mold dies being movable toward the other, a cavity forming means associated with said two opposing mold dies for forming a mold cavity of variable thickness, an injection means for injecting a thermoplastic material into said mold cavity via an injection channel, a compression means associated with movement of said at least one movable mold die for exerting a compressional force on said thermoplastic material and reducing thickness of said mold cavity, and at least one overflow pocket each in communication with said mold cavity via an overflow channel;
(b) forming an enlarged mold cavity having a thickness greater than said lens to be produced;
(c) injecting said thermoplastic material into said enlarged mold cavity via said injection channel and further into said overflow pocket after said thermoplastic material fills said enlarged mold cavity;
(d) before end of injecting step (c), compressing said thermoplastic material in said mold cavity by moving said movable mold die toward the other to reduce thickness of said mold cavity and urge excess part of said thermoplastic material into said overflow pockets until a predetermined thickness of said mold cavity is reached;
(e) maintaining a compressional force on said mold dies until said lens cools to below its glass transition temperature.

2 more elements

Dependencies are inferred from the claim text.

Process for molding plastic lenses

Life of this patent

Process for molding plastic lenses

Life of this patent

Abstract

Claims18