Process for producing an optical film
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United States of America Patent
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Oct 8, 2013
Grant Date -
Sep 23, 2010
app pub date -
Sep 26, 2008
filing date -
Oct 5, 2007
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Abstract
This invention provides a process for producing an optical film, which, even when a film is produced by casting using a melt casting film forming method so that the central part in the widthwise direction is thick, can finally realize a flat film having an even thickness and good flatness and possessing excellent optical properties. The production process of an optical film can meet recent demands for reduced film thickness, increased film width, and improved film quality in protective films for liquid crystal polarizing plates. The production process of an optical film by a melt casting film forming method is characterized in that, in an MD stretching step, an unstretched film after nipping is stretched in a transfer direction (MD direction) of the same film by a factor of not less than 1.1 and not more than 3.0, and, in an extruding step, the following relationship is satisfied: 10 μm≦T1−T2≦200 μm wherein T1 represents the film thickness at the central part in the widthwise direction of an extruded web, μm; and T2 represents the film thickness at both ends in the widthwise direction of the extruded web, μm.
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