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AssigneeToray Industries, Inc.
InventorsHideto Mitsuoka, Takuji Higashioji, Masato Horie, Yukari Nakamori
Estimating the term…
[Problem to be solved] To provide a biaxially oriented polyester film, which suffers only small dimensional changes due to changes in environmental temperature and humidity and due to storage, ensures low error rates, and can little abrade the magnetic head and the magnetic tape, when used as a base film of a magnetic recording medium, and which can be used to provide a high density magnetic recording medium excellent in running durability. [Solution] A biaxially oriented polyester film having an islands-in-sea structure, an average island domain size of 30 to 200 nm, and a coefficient of hygroscopic expansion of 0 to 6.0 ppm/% RH at least either in the machine direction or in the transverse direction of the film.
A biaxially oriented polyester film comprising at least two polyetherimides and an islands-in-sea structure with an average island domain size of 30 to 200 nm, and a coefficient of hygroscopic expansion of 0 to 6 ppm/% RH at least either in a machine direction or in a transverse direction or' the film, wherein an amorphous resin forming the island domains with a diameter of 30 to 200 nm contains at least one resin selected from the group consisting of polyetherimides, polyimides and polyamideimides, glass transition temperature of the amorphous resin forming the island domains with a diameter of 30 to 200 nm is 220 to 245 degrees centigrade, and total mass of the island domains with a diameter of 30 to 200 nm is 0.5 to 15 mass %.
The biaxially oriented polyester film according to claim wherein roughness Ra of surface of the film at least on one side is 0.5 to 2.0 nm.
A magnetic recording medium comprising a biaxially oriented polyester film comprising at least two polyetherimides and an islands-in-sea structure with an average island domain size of 30 to 200 nm, and a coefficient of hygroscopic expansion of 0 to 6 ppm/% RH at least either in a machine direction or in a transverse direction of the film, wherein an amorphous resin forming the island domains with a diameter of 30 to 200 nm contains at least one resin selected from the group consisting of polyetherimides, polyimides and polyamideimides, glass transition temperature of the amorphous resin forming the island domains with a diameter of 30 to 200 nm is 220 to 245 degrees centigrade, and total mass of the island domains with a diameter of 30 to 200 nm is 0.5 to 15 mass %.
Dependencies are inferred from the claim text.