Biaxially oriented polyester film, process for producing the same, and magnetic recording medium
AssigneeToray Industries, Inc.
InventorsHikaru Yamagata, Masaaki Kotoura, Hirofumi Hosokawa, Tetsuya Tsunekawa
Life of this patent
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Abstract
The object of this invention is to provide a biaxially oriented polyester film suitable as a base film for high density magnetic recording media, small in track deviation and excellent in traveling durability and preservability, and to provide a production method thereof. The object of this invention can be achieved by a biaxially oriented polyester film, characterized in that the dimensional change rate (A) in the transverse direction of the film is in a range of −0.3 to 0% when the film is allowed to stand at 49° C. and 90% RH for 72 hours, while being loaded with 32 MPa in the machine direction.
Claims15
A biaxially oriented polyester film, characterized in that the dimensional change rate (A) in the transverse direction of the film is in a range of −0.3 to 0% when the film is allowed to stand at 49° C. and 90% RH for 72 hours, while being loaded with 32 MPa in the machine direction.
A method for producing a biaxially oriented polyester film characterized in that the dimensional change rate (A) in the transverse direction of the film is in a range of −0.3 to 0% when the film is allowed to stand at 49° C. and 90% RH for 72 hours, while being loaded with 32 MPa in the machine direction, wherein the method comprises stretching a cast film in the machine direction and in the transverse direction, stretching the film again in the machine direction and/or in the transverse direction, heat-set treating the film and relaxation-treating the film, characterized by executing the relaxation treatment in two or more stages at a total relaxation rate of 5 to 10%.
A method for producing a biaxially oriented polyester film characterized in that the dimensional change rate (A) in the transverse direction of the film is in a range of −0.3 to 0% when the film is allowed to stand at 49° C. and 90% RH for 72 hours, while being loaded with 32 MPa in the machine direction, comprising the steps of stretching a cast film in the machine direction and in the transverse direction, stretching at a small ratio of 1.01 to 1.3 times in the transverse direction at a temperature in a range of glass transition temperature (Tg) to Tg+50° C., and stretching again in the machine direction and/or in the transverse direction.
A method for producing a biaxially oriented polyester film characterized in that the dimensional change rate (A) in the transverse direction of the film is in a range of −0.3 to 0% when the film is allowed to stand at 49° C. and 90% RH for 72 hours, while being loaded with 32 MPa in the machine direction, wherein the method comprises stretching a cast film in the machine direction and in the transverse direction, stretching the film at a small ratio of 1.01 to 1.3 times in the transverse direction at a temperature in a range of glass transition temperature (Tg) to Tg+50° C., stretching the film again in the machine direction and/or in the transverse direction, heat-set treating the film, and relaxation-treating the cast film, characterized by executing the relaxation treatment in two or more stages at a total relaxation rate of 5 to 10%.
Dependencies are inferred from the claim text.