Polyethylene-2,6-naphthalate film for magnetic recording tapes

Claim 2

A polyethylene-2,6-naphthalate film for high-density magnetic tapes which is excellent in heat resistance and which has a Young's modulus of not less than 800 kg/mm2 in the machine direction and a Young's modulus of not less than 600 kg/mm 2 in the transverse direction.

Claim 3

A polyethylene-2,6-naphthalate film according to claim 1, wherein the surface roughness is not more than 0.008 µm.

Claim 4

A polyethylene-2,6-naphthalate film according to claim 1, wherein the thickness of said film is 2 to 7 um.

Claim 5

A polyethylene-2,6-naphthalate film according to claim 1, wherein said film is produced by a process comprising the steps of: melt-extruding polyethylene-2,6-naphthalate of an intrinsic viscosity of not less than 0.40 which contains 0.01 to 1 wt% of inactive fine particles having a primary particle diameter of 0.001 to 10 µm into a film, stretching the film by 1.1 to 5.0 times in the machine direction at a temperature of 120 to 170°C, stretching the film by 2.5 to 5.0 times in the transverse direction at a temperature of 120 to 180°C, heatsetting the film at a temperature of 130 to 240°C while subjecting the film to relaxation in the transverse direction by 1 to 30%, re-stretching the film in the machine direction at a temperature of 140 to 200°C by 1.5 to 2.8 times if the film has been stretched in the machine direction by 1.1 to 3.5 times in the previous stage or by 1.05 to 1.35 times if the film has been stretched in the machine direction by 3.5 to 5.0 times in the previous stage, heatsetting the film at a temperature of 180 to 260°C, and winding the film while subjecting the film to relaxation by 1 to 10% in the machine direction and in the transverse direction.

Claim 6

A process for producing a polyethylene-2,6-naphthalate film for high-density magnetic tapes being excellent in heat resistance and having a Young's modulus of not less than 800 kg/mm2 in the machine direction and a Young's modulus of not less than 600 kg/mm 2 in the transverse direction, which comprises the steps of: melt-extruding polyethylene-2,6-naphthalate of an intrinsic viscosity of not less than 0.40 which contains 0.01 to 1 wt% of inactive fine particles having a primary particle diameter of 0.001 to 10 µm into a film, stretching the film by 1.1 to 5.0 times in the machine direction at a temperature of 120 to 170°C, stretching the film by 2.5 to 5.0 times in the transverse direction at a temperature of 120 to 180°C, heatsetting the film at a temperature of 130 to 240°C while subjecting the film to relaxation in the transverse direction by 1 to 30%, re-stretching the film in the machine direction at a temperature of 140 to 200°C by 1.5 to 2.8 times if the film has been stretched in the machine direction by 1.1 to 3.5 times in the previous stage or by 1.05 to 1.35 times if the film has been stretched in the machine direction by 3.5 to 5.0 times in the previous stage, heatsetting the film at a temperature of 180 to 260°C,and winding the film while loosening the film by 1 to 10 % in the machine direction and in the transverse direction.

Claim 7

A process for producing a polyethylene-2,6-naphthalate film for high-density magnetic tapes being excellent in heat resistance and having a Young's modulus of not less than 800 kg/mm2 in the machine direction and a Young's modulus of not less than 600 kg/mm 2 in the transverse direction, which comprises the steps of: melt-extruding polyethylene-2,6-naphthalate of an intrinsic viscosity of not less than 0.40 which contains 0.01 to 1 wt% of inactive fine particles having a primary particle diameter of 0.001 to 10 µm into a film, stretching the film by 1.1 to 5.0 times in the machine direction at a temperature of 120 to 170°C, stretching the film by 2.5 to 5.0 times in the transverse direction at a temperature of 120 to 180°C, heatsetting the film at a temperature of 130 to 240°C while subjecting the film to relaxation in the transverse direction by 1 to 30%, re-stretching the film in the machine direction at a temperature of 140 to 200°C by 1.5 to 2.8 times if the film has been stretched in the machine direction by 1.1 to 3.5 times in the previous stage or by 1.05 to 1.35 times if the film has been stretched in the machine direction by 3.5 to 5.0 times in the previous stage, heatsetting the film at a temperature of 180 to 260°C,and winding the film while loosening the film by 1 to 10 % in the machine direction and in the transverse direction.

Claim 8

A process according to claim 5, wherein said inactive fine particles are at least one member of fine particles selected from the group consisting of kaolin, talc, silica, magnesium carbonate, calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, lithium fluoride, Ca, Ba, Zn and Mn salts of terephthalic acid and carbon blacks.