Polyethylene naphthalate film

Claim 2

A biaxially oriented polyethylene naphthalate film having a center line average roughness Ra μm and a film thickness T μm defined by the following relationship: ##EQU12## prepared by electrostatically cooling a polyethylene naphthalate sheet prepared from a polyethylene naphthalate melt having a resistivity of 1×10 7 to 5×10 8 Ω.cm as measured in the molten state.

Claim 3

The biaxially oriented polyethylene naphthalate film of claim 1, which forms the base material for a magnetic recording medium.

Claim 4

The biaxially oriented polyethylene naphthalate film of claim 1, wherein the thickness of the film ranges from 4-40 μm.

Claim 5

The biaxially oriented polyethylene naphthalate film of claim 3, wherein said film thickness ranges from 4-20 μm.

Claim 6

The biaxially oriented polyethylene naphthalate film of claim 4, wherein said film thickness ranges from 4-12 μm.

Claim 7

The biaxially oriented polyethylene naphthalate film of claim 1, wherein said polyethylene naphthalate melt has an intrinsic viscosity of not less than 0.40.

Claim 8

The biaxially oriented polyethylene naphthalate film of claim 6, wherein said intrinsic viscosity ranges from 0.45-0.9.

Claim 9

The biaxially oriented polyethylene naphthalate film of claim 7, wherein said intrinsic viscosity ranges from 0.55-0.85.

Claim 10

The biaxially oriented polyethylene naphthalate film of claim 1, wherein said film has a degree of crystallinity ranging from 28-50%.

Claim 11

The biaxially oriented polyethylene naphthalate film of claim 1, wherein said film is electrostatically cooled to a temperature below 80° C. so that said film becomes substantially amorphous in structure.

Claim 12

The biaxially oriented polyethylene naphthalate film of claim 1, wherein said polyethylene naphthalate melt has a resistivity ranging from 1×10 7 to 1×10 8 Ω.cm.

Claim 13

The biaxially oriented polyethylene naphthalate film of claim 1, wherein said polyethylene naphthalate is prepared by polycondensing naphthalene-2,6-dicarboxylic acid or derivative thereof with ethylene glycol with less than 10 mol % of a third component selected from the group consisting of adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthylene-2,7-dicarboxylic acid, lower alkyl esters thereof, p-hydroxybenzoic acid, lower alkyl esters thereof, propylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol and hexamethylene glycol.

Claim 14

A biaxially oriented polyethylene naphthalate film having a center line average roughness Ra μm and a film thickness T μm defined by the relationship: ##EQU13## prepared by: extruding polyethylene naphthalate containing a phosphorus compound which controls the resistivity of the molten polyethylene naphthalate to within the range of 1×10 7 to 5×10 8 Ω.cm, as measured in the molten state, and which contains from 0.01-1 wt. % of inert fine particles, at a temperature ranging from 280° C.-320° C. into a film; electrostatically cooling said polyethylene naphthalate film such that the degree of crystallinity of the film ranges from 28-50%; stretching the film obtained in two directions; and heat-treating the biaxially oriented film obtained at 120° C.-250° C.

Claim 15

A biaxially oriented polyethylene naphthalate film having a center line average roughness Ra μm and a film thickness T μm defined by the relationship: ##EQU13## prepared by: extruding polyethylene naphthalate containing a phosphorus compound which controls the resistivity of the molten polyethylene naphthalate to within the range of 1×10 7 to 5×10 8 Ω.cm, as measured in the molten state, and which contains from 0.01-1 wt. % of inert fine particles, at a temperature ranging from 280° C.-320° C. into a film; electrostatically cooling said polyethylene naphthalate film such that the degree of crystallinity of the film ranges from 28-50%; stretching the film obtained in two directions; and heat-treating the biaxially oriented film obtained at 120° C.-250° C.

Claim 16

A magnetic tape, comprising: a biaxially oriented polyethylene naphthalate film having a center line average roughness [Ra(μm)] and a film thickness [T(μm)] defined by the following relationship: ##EQU14## which is prepared by electrostatically cooling a polyethylene naphthalate sheet prepared from a polyethylene naphthalate melt having a resistivity of 1×10 7 to 5×10 8 Ω.cm, as measured in the molten state, and a magnetic layer coated on said film.

Claim 17

A magnetic tape, comprising: a biaxially oriented polyethylene naphthalate film having a center line average roughness [Ra(μm)] and a film thickness [T(μm)] defined by the following relationship: ##EQU14## which is prepared by electrostatically cooling a polyethylene naphthalate sheet prepared from a polyethylene naphthalate melt having a resistivity of 1×10 7 to 5×10 8 Ω.cm, as measured in the molten state, and a magnetic layer coated on said film.