Biaxially oriented polyester film for use in floppy disc
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United States of America Patent
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Feb 11, 1992
Grant Date -
N/A
app pub date -
Oct 18, 1990
filing date -
Oct 24, 1989
priority date (Note) -
Expired
status (Latency Note)
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Abstract
The present invention provide a biaxially oriented polyester film for use in a floppy disc, which has a coefficient of thermal expansion (.alpha..sub.T) in film plane of (1.0.+-.0.5).times.10.sup.-5 mm/mm/.degree.C. and a heat shrinkage of not higher than 0.09% after treatment the film for 72 hours under conditions of a temperature of 60.degree. C. and a humidity of 80% RH in any directions in film plane, and simultaneously satisfies the following equations (1) to (5): 1.490.ltoreq.n.sub..alpha. .ltoreq.1.500 (1) 0.155.ltoreq..DELTA.P.ltoreq.0.168 (2) 1.600.ltoreq.n.ltoreq.1.603 (3) 40.ltoreq.X.sub.100 .ltoreq.60 (4) 1.385.ltoreq..rho..ltoreq.1.400 (5) wherein n.sub..alpha. represents a refractive index in film thickness direction, .DELTA.P represents a degree of planar orientation, n represents an average refractive index, X.sub.100 represents a crystal size (.ANG.) of (110) face, and .rho. represents a density (g/cm.sup.3). The biaxially oriented polyester film of the present invention has excellent dimensional stability and flatness and is suitable for use as the base film of floppy disc.
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