Production of highly birefringent film
AssigneeHoechst Celanese Corporation
InventorsStephen J. Gust, Gregory W. Farell, Marshall D. Ledbetter
Life of this patent
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Abstract
A thin, biaxially oriented polyester film which is asymetrically oriented by stretching 1-2 times in the machine direction and about 3-5 times in the transverse direction in the plane of the film is disclosed. The film has a birefringence of at least 0.085, an optical retardation of at least 9000 nanometers and a shrinkage of less than 2% in any direction at 150.degree. C. The film produced is substantially free of color fringes when viewed in partially polarized light. There are also disclosed two processes for the production of said film.
Claims24
A process for preparing a biaxially oriented polyester film having a machine direction stretch of 1.0 to 2.0 times its length and a transverse direction stretch of 3.0 to 5.0 times its width, which comprises melt extruding a substantially amorphous polyester film and thereafter orienting the film by stretching it at a draw ratio in the range 1.0 to 2.0 in the machine direction in the plane of the film and then at a draw ratio in the range 3.0 to 5.0 in the transverse direction in the plane of the film and thereafter heat setting the film at a temperature between 180.degree. C. and 240.degree. C.
A process for preparing biaxially oriented polymeric film which comprises melt extruding a substantially amorphous polymer film and thereafter orienting the film by stretching it sequentially in two directions, trimming said film along the edges where held for stretching in the transverse direction and subsequently heat setting the film.
A thin, biaxially oriented film which comprises a transparent film structure of a polymeric film which is asymmetrically oriented by stretching 1.0-2.0 times in the machine direction in the plane of the film and 3.0 to 5.0 times in the transverse direction in the plane of the film and which is heat set at a temperature between 180.degree. and 240.degree. C.;
- said film having a birefringence of at least 0.085, an optical retardation of at least 9000 nanometers, a shrinkage of less than 2% in any direction at 150.degree. C., wherein said film structure is substantially free of color fringes upon viewing in partially polarized light.
Dependencies are inferred from the claim text.