Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Changing mold size or shape during molding or with shrinkage...
Patent
1993-10-22
1995-05-16
Vargot, Mathieu D.
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Changing mold size or shape during molding or with shrinkage...
2643287, 2643289, 26432812, 425555, 425808, B29D 1100
Patent
active
054158176
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.
REFERENCES:
patent: 4184835 (1980-01-01), Talbot
patent: 4284591 (1981-08-01), Neefe
patent: 4540534 (1985-09-01), Grendol
patent: 4664854 (1987-05-01), Bakalar
Shiao Po-Ling
Tuan Chi-Shen
Wu Chien-Tsung
Yeh Tzong-Ming
Industrial Technology Research Institute
Liauh W. Wayne
Vargot Mathieu D.
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