| 摘要 |
PROBLEM TO BE SOLVED: To provide a polyester film which is made productively, possesses only a small amount of foreign materials mainly consisting of oligomers extracted on the surface after the film in made, excels in an electromagnetic conversion property and creates only a limited amount of dropout especially when it is converted to a magnetic recording medium coated with a thin metal by vacuum metallizing. SOLUTION: This polyester film is composed of a polyester layer A coated with a continuous membrane C made of an aqueous polyester resin on one of its surfaces. (1) The membrane C contains inactive particles of 0.5-30 wt.% of which an average diameter is 10-50 nm and a volumetric shape coefficient is 0.1-π/6, (2) the thickness of the membrane C is 3-50 nm, (3) a numerical average molecular weight of the aqueous polyester resin constituting the membrane C is equal to or lager than 10,000 and equal to or smaller than 1,000,000, (4) a surface roughness Wra of the surface of the membrane C side of the film is 0.1-4 nm, and (5) a number of foreign materials extracted on the surface of the membrane C side of the film is equal to or smaller than 1,000 pieces/mm2 after the film is treated at 120 deg.C for 30 minutes.
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