JP2002205332A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film not generating shift of a recording track when formed into a magnetic tape and excellent in running durability and storage stability. SOLUTION: The biaxially oriented polyester film is characterized by that the Young's modulus in the longitudinal direction of the film is 6-15 GPa, the coefficient of thermal expansion in the lateral direction of the film is 0-12 ppm/ deg.C, a peak temperature of tan δ is 120-180 deg.C and a peak value is 0.10-0.25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film suitable for high density magnetic recording media.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are used for various applications because of their excellent thermal properties, dimensional stability and mechanical properties, and their usefulness as base films for magnetic tapes and the like is well known. . In recent years, in order to reduce the weight, size, and long-term recording of equipment, magnetic tapes have been required to have a thinner base film and higher recording density. There is an increasing demand for improved stability. However, when the film is thinned, the mechanical strength becomes insufficient and the stiffness of the film becomes weak, or it becomes easy to expand in the longitudinal direction, and it becomes easy to shrink in the width direction.
There are problems such as the occurrence of track deviation, deterioration of head touch and deterioration of electromagnetic conversion characteristics.

[0003] As a base film that can meet the above requirements, an aramid film has been conventionally used in view of strength and dimensional stability. Aramid films are disadvantageous in terms of cost because of their high price, but are currently used because there is no substitute for performance.

[0004] On the other hand, as a conventional technique for increasing the strength of a biaxially oriented polyester film, there is known a method of stretching a film stretched in two longitudinal and transverse directions again in the longitudinal direction to increase the strength in the longitudinal direction. (For example, Japanese Patent Publication No. 42-927)
No. 0, JP-B-43-3040, JP-B-46-
1119, JP-B-46-1120, JP-A-50-133276, JP-A-55-22915, etc.) are as follows: (1) the tape is cut when used; (2) rigidity in the width direction Edge damage occurs due to shortage, (3) errors occur during recording / reproduction due to misalignment of the recording track, (4) insufficient strength and difficulty in handling thin films, and desired electromagnetic conversion characteristics cannot be obtained, etc. At present, many problems remain when applied to large-capacity, high-density magnetic recording tapes.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to provide good dimensional stability during film processing, to prevent recording track misalignment when using a magnetic tape, to improve running durability, An object of the present invention is to provide a biaxially oriented polyester film having excellent storage stability, workability, and electromagnetic characteristics.

[0006]

The object of the present invention is to provide a film having a Young's modulus in a longitudinal direction of 6 to 15 GPa, a coefficient of thermal expansion in a film width direction of 0 to 12 ppm / ° C., and a tan δ of Peak temperature 120-180
This is achieved by forming a biaxially oriented polyester film having a range of ° C and a peak value in the range of 0.10 to 0.25.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester used in the present invention is a polyester containing an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main components. As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-
Use of naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, and the like Of these, terephthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be preferably used. As the alicyclic dicarboxylic acid, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. One of these acid components may be used alone, or two or more of them may be used in combination. Further, an oxyacid such as hydroxyethoxybenzoic acid may be partially copolymerized.

The diol component includes, for example, ethylene glycol, 1,2-propanediol, 1,3-
Propanediol, neopentyl glycol, 1,3-
Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-
Cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,4-cyclohexane dimethanol,
Diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2′-bis (4′-β-hydroxyethoxyphenyl) propane and the like can be used. Among them, ethylene glycol,
Examples thereof include 1,4-butanediol, 1,4-cyclohexanedimethanol, and diethylene glycol, and particularly preferred is ethylene glycol. These diol components may be used alone or in combination of two or more.

Further, trimellitic acid,
Pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, lauryl alcohol,
A polyfunctional compound such as phenyl isocyanate may be copolymerized to the extent that the polymer is substantially linear.

The polyester of the present invention includes polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalenedicarboxylate (hereinafter referred to as PE).
N), or copolymers and modified products thereof.

Although the intrinsic viscosity of the polyester of the present invention is not particularly limited, from the viewpoint of the stability of film production,
It is preferably in the range of 0.55 to 2.0 (dl / g), more preferably 0.65 to 1.5 (dl / g).
It is.

It is preferable that the polyester used in the present invention contains 5% by weight or more of polyimide because the glass transition temperature and the tan δ peak temperature of the film are increased and the dimensional stability against the temperature is improved. Further, from the viewpoint of increasing the strength by stretching and increasing the crystallinity of the film, the content of the polyimide is preferably 30% by weight or less. More preferable content of polyimide is 7 to
25% by weight, and more preferably the content is 1%
It is in the range of 0 to 20% by weight. Since the melt viscosities of polyester and polyimide are greatly different, if the content of polyimide is less than 5% by weight, it may be difficult to obtain sufficient kneading with an extruder to be compatible with each other, The effect may not be sufficiently obtained. Also,
If the content of the polyimide exceeds 30% by weight,
Forming may be difficult. The polyimide used is not particularly limited as long as it is a polymer containing a cyclic imide group as a repeating unit and a polymer having melt moldability. For example, U.S. Pat.
No. 27, Japanese Patent No. 2622678, Japanese Patent No. 260
No. 6912, Patent No. 2606914, Patent No. 2596
No. 565, Patent No. 2596566, Patent No. 25984
Japanese Patent No. 7859836, Japanese Patent No. 2598536, Japanese Patent No. 2599171,
No. 48885, Patent No. 2565556, Patent No. 25
No. 64636, Patent No. 25664637, Patent No. 256
No. 3548, Japanese Patent No. 2563547, Japanese Patent No. 2558
No. 341, Patent No. 2558339, Patent No. 28345
There is a polymer described in the publication No. 80. As long as the effects of the present invention are not impaired, the polyimide main chain may contain structural units other than cyclic imides, for example, aromatic, aliphatic, alicyclic ester units, oxycarbonyl units, and the like. .

The polyimide of the present invention is represented by the following general formula.

[0014]

Embedded image Ar in the above formula is an aromatic group having 6 to 42 carbon atoms, R is a divalent aromatic group having 6 to 30 carbon atoms, and an aliphatic group having 2 to 30 carbon atoms. Groups, 4 ~
It is a divalent organic group selected from the group consisting of alicyclic groups having 30 carbon atoms.

In the above general formula, Ar is, for example,

[0016]

Embedded image Can be mentioned. As R, for example,

[0017]

Embedded image

[0018]

Embedded image Can be mentioned.

These may be present alone or in combination of two or more in the polymer chain, as long as the effects of the present invention are not impaired.

The polyimide of the present invention is not particularly limited, but as a preferred example from the viewpoint of melt moldability with polyester and handleability, for example, as shown by the following general formula, an ether bond is contained in a polyimide constituent component. And polyetherimide, which is a polymer composed of structural units.

[0021]

Embedded image Here, in the above formula, R ₁ is a divalent organic group selected from the group consisting of a divalent aromatic or aliphatic group having 2 to 30 carbon atoms and an alicyclic group.

The above R ₁ and R ₂ are, for example, aromatic groups represented by the following formula groups:

[0023]

Embedded image Can be mentioned.

In the present invention, a polyetherimide having a glass transition temperature of 350 ° C. or lower, more preferably 250 ° C. or lower is preferable, and has a structural unit represented by the following formula.
The condensate of 2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride with m-phenylenediamine or p-phenylenediamine has properties such as compatibility with polyester, cost and melt moldability. Most preferred from a viewpoint. This polyetherimide is called "Ultem"
(Registered trademark) is a trademark of General Elect.
available from ric.

[0025]

Embedded image

The polyimide of the present invention is not particularly limited. However, from the viewpoint of melt moldability with polyester and handleability, other preferable examples of A
r is

Embedded image Wherein R in the above general formula is

[0027]

Embedded image Can be mentioned.

The above polyimide can be produced by a known method. For example, a group consisting of the above-mentioned tetracarboxylic acid and / or acid anhydride as a raw material capable of deriving Ar, and the above-mentioned aliphatic primary diamine and / or aromatic primary diamine which are raw materials capable of deriving R. And a compound obtained by dehydrating and condensing one or more compounds selected from the group consisting of a polyamic acid and a ring closure by heating. Alternatively, a method of chemically ring-closing using an acid anhydride and a chemical ring-closing agent such as pyridine and carbodiimide, heating the above-mentioned tetracarboxylic anhydride and the above-mentioned R-derived diisocyanate to carry out decarboxylation to carry out polymerization. Methods and the like can be exemplified.

Examples of the tetracarboxylic acid used in the above method include pyromellitic acid, 1,2,3,4-benzenetetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2 ', 3,3'-biphenyltetracarboxylic acid, 3,3', 4,4'-benzophenonetetracarboxylic acid, 2,2 ', 3,3'-benzophenonetetracarboxylic acid, bis (2,3-di Carboxyphenyl) methane, bis (3,4-dicarboxyphenyl) methane, 1,1′-bis (2,3-dicarboxyphenyl) ethane, 2,2′-bis (3,4-dicarboxyphenyl) propane , 2,2'-bis (2,3-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) ether, bis (2,3-dicarboxyphenyl) ether, bis (3 - dicarboxyphenyl) sulfone, bis (2,3-carboxyphenyl)
Sulfone, 2,3,6,7-naphthalenetetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid,
1,2,5,6-naphthalenetetracarboxylic acid, 2,
2′-bis [(2,3-dicarboxyphenoxy) phenyl] propane and / or its acid anhydride are used.

Examples of the diamine include benzidine, diaminodiphenylmethane, diaminodiphenylethane, diaminodiphenylpropane, diaminodiphenylbutane, diaminodiphenylether, diaminodiphenylsulfone, diaminodiphenylbenzophenone,
o, m, p-phenylenediamine, tolylenediamine,
Xylene diamines and the like and aromatic primary diamines and the like having an aromatic primary diamine hydrocarbon group as a structural unit, ethylene diamine, 1,2-propane diamine, 1,3-propane diamine, 2,2-dimethyl-
1,3-propanediamine, 1,6-hexamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,11-undecamethylenediamine, 12-
Dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 1,3-cyclohexanediamine,
1,4-cyclohexanediamine, 1,4-cyclohexanedimethylamine, 2-methyl-1,3-cyclohexanediamine, isophoronediamine and the like, and hydrocarbon groups of these exemplified aliphatic and alicyclic primary diamines as structural units And aliphatic and alicyclic primary diamines.

The polyester resin composition containing 5 to 30% by weight of polyimide used in the present invention contains the polyester and the polyimide and is compatible with each other. The term “compatible” as used herein means that the obtained chip has a single glass transition temperature (Tg). As described above, it is generally known that the Tg when both are compatible exists between the Tg of the polyester and the Tg of the pellet of the polyimide. The glass transition temperature in the present invention can be determined from the heat flux gap at the time of temperature rise in the differential scanning calorimetry according to JIS K7121. When it is difficult to make a determination only by a method using differential scanning calorimetry, a morphological method such as dynamic viscoelasticity measurement or microscopic observation may be used in combination. When determining the glass transition temperature by differential scanning calorimetry, it is also effective to use a temperature modulation method or a high sensitivity method. If the composition has two or more glass transition temperatures, the polyester and the polyimide are not compatible in the composition.

When the polyester and the polyimide are compatible with each other, the timing of adding the polyimide to the polyester is not particularly limited, and may be added before the polymerization of the polyester, for example, before the esterification reaction, or after the polymerization and the melt extrusion. It may be added before. Among them, it is preferable to pelletize polyester and polyimide before melt extrusion to obtain a master chip from the viewpoint of melt moldability. In the pelletizing, the polyester and the polyimide are supplied to the twin-screw kneading extruder and melt-extruded, in order to compatibilize the polyester and the polyimide, and to obtain the polyester composition of the present invention and the hollow molded article made of the same. preferable.

It is preferable to add a compatibilizer if necessary, since the dispersion diameter can be controlled. In this case, the type of the compatibilizer differs depending on the type of the polymer, but the amount of addition is preferably 0.01 to 10% by weight.

The biaxially oriented polyester film of the present invention preferably contains inert particles. Examples of inert particles include clay, mica, titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, aluminum silicate, alumina and zirconia, and the like, and acrylic acid. And organic particles containing styrene or the like as a constituent component, so-called internal particles precipitated by a catalyst or the like added at the time of the polyester polymerization reaction. Among them, particularly preferred are polymer crosslinked particles, alumina, spherical silica, and aluminum silicate.

The biaxially oriented polyester film of the present invention may have a single layer or a laminated structure of two or more layers. Although not particularly limited, a laminated structure having two or more layers is more preferable. When it is a single layer, for example, when used for a magnetic recording medium, if particles are included, the protrusions on the surface are not aligned,
Electromagnetic conversion characteristics and runnability may deteriorate. further,
In the case of three layers, the effect of the present invention is further improved, which is preferable. The thickness of the outermost layer is not particularly limited, but may be 0.1 to 10 times the average diameter of the particles contained in the outermost layer,
The effect of the present invention is further improved, which is preferable. This is because if the value is below the lower limit of this range, there is a possibility that the electromagnetic conversion characteristics will be poor. On the other hand, if the value exceeds the upper limit of this range, there is a possibility that the traveling performance will be poor.

The biaxially oriented polyester film of the present invention may contain other various additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber and the like as long as the effects of the present invention are not impaired.
Organic lubricants such as antistatic agents, flame retardants, pigments, dyes, fatty acid esters, and waxes can also be added.

The inert particles contained in the biaxially oriented polyester film of the present invention have an average particle size of 0.001 to 2 μm.
It is preferably 0.005 to 1 μm, and more preferably 0.01 to 0.5 μm. 0.001
When it is smaller than μm, it does not play a role as a film surface protrusion, and when it is larger than 2 μm, it is not preferable because it easily falls off as coarse protrusion.

The content of the inert particles contained in the biaxially oriented polyester film of the present invention is 0.01 to 3% by weight.
Is more preferable, more preferably 0.02 to 1% by weight, and still more preferably 0.05 to 0.5% by weight. 0.01
When the amount is less than 3% by weight, the effect of improving the running characteristics of the film is insufficient, and when the amount is more than 3% by weight, the film aggregates into coarse projections and easily falls off.

The biaxially oriented polyester film of the present invention may be a single layer or a laminated structure of two or more layers. In the present invention, it is particularly preferable to adopt a two-layer structure in which a film layer having a role of improving the running property and the handling property of the film is laminated on one side of the base layer portion of the film. Note that the base layer portion is a layer having the largest thickness in the layer thickness, and the other portion is a laminated portion. Physical properties such as elastic modulus and dimensional stability, which are important for magnetic material applications, are determined mainly by the physical properties of the base layer.

In the laminated portion of the film layer of the present invention, when the relationship between the average particle size d (nm) of the inert particles and the laminated thickness t (nm) satisfies 0.2d ≦ t ≦ 10d, the laminated portion is uniform. This is preferable because a projection having a height can be obtained.

The biaxially oriented polyester film of the present invention has a Young's modulus in the longitudinal direction of 6 to 15 GPa, a coefficient of thermal expansion in the width direction of 0 to 12 ppm / ° C., and a peak temperature of tan δ. Is 120-180
It is necessary that the range of ° C and the peak value be in the range of 0.10 to 0.25.

In recent magnetic recording material applications, further thinning of the base film and high-density recording for long-time recording are required. In the present invention, the most important characteristics for satisfying the requirements are a process for forming a magnetic tape and a dimensional stability in a longitudinal direction and a width direction of the tape due to temperature, humidity, tension, etc. in a drive of the magnetic tape. I paid attention. By setting the peak temperature and peak value of Young's modulus, coefficient of thermal expansion, tan δ as the index of the dimensional stability in the above range, the process in the magnetic tape and the longitudinal direction with respect to the temperature, humidity, and tension of the environment in which the magnetic tape is used. It was also found that a highly rigid biaxially oriented polyester film with little deformation in the width direction and excellent workability and track deviation when formed into a magnetic tape, running durability, storage stability and the like was obtained.

When the Young's modulus in the longitudinal direction is smaller than 6 GPa, the longitudinal tension in the tape drive causes contraction in the width direction due to elongation and deformation in the longitudinal direction, thereby causing a displacement of the recording track. Further, dropouts occur frequently, and the storage stability of data is deteriorated, and the electromagnetic conversion characteristics are deteriorated. Conversely, if it is larger than 15 GPa, the tape is likely to break or the Young's modulus in the width direction is insufficient, which causes edge damage. More preferably in the range of 6.5 to 14.5 GPa, most preferably 7-1.
The range is 4 GPa. If the coefficient of thermal expansion in the width direction is less than 0 ppm / ° C., the magnetic tape shrinks in the width direction due to a process of processing into a magnetic tape or a rise in temperature in a drive, causing a track shift or the like. Conversely 12 ppm
If it exceeds / ° C, it expands in the width direction, and the workability, storage stability, and the like deteriorate. More preferably 1-1
In the range of 1 ppm / ° C, most preferably 2-10 ppm /
It is in the range of ° C. Furthermore, the peak temperature of tan δ is 120
When the temperature is lower than ℃, the glass transition temperature also decreases, and the workability deteriorates, for example, the dimensions change due to heating in the processing step and the like. On the other hand, when the temperature is higher than 180 ° C., the film forming property deteriorates.
When the tan δ peak value is larger than 0.25,
The crystallinity of the film decreases, and the dimensional stability deteriorates.
If it is smaller than 0.10, the mobility of the molecule becomes worse,
Stretching becomes difficult. More preferably, the peak temperature is 125
To 170 ° C, the peak value is in the range of 0.12 to 0.23, more preferably the peak temperature is in the range of 130 to 165 ° C, and the peak value is in the range of 0.14 to 0.20.

The Young's modulus in the width direction of the biaxially oriented polyester film of the present invention is preferably 4.5 GPa or more from the viewpoint of suppressing edge damage and improving slitting properties, and suppresses a decrease in the Young's modulus in the longitudinal direction. From the viewpoint, it is preferably 9.0 GPa or less. More preferably, it is in the range of 5-8.5 GPa, and still more preferably 5.5.
８8 GPa.

In the biaxially oriented polyester film of the present invention, the heat shrinkage in the width direction at 100 ° C. for 30 minutes is 0 from the viewpoint of suppressing wrinkling due to heat history in the tape processing step.
% From the viewpoint of frictional heat between the magnetic tape and the magnetic recording head, suppression of shrinkage in the width direction due to heat history in the tape processing step, durability of the film surface, and data storage stability. It is preferably at most 3%. More preferably in the range of 0 to 0.25%, most preferably 0%
０．２0.2%.

In the biaxially oriented polyester film of the present invention, the surface roughness Ra _A of one film surface (side A) is:
The thickness is preferably 3 nm or more from the viewpoint of reducing friction with the magnetic head, and is preferably 10 nm or less from the viewpoint of electromagnetic conversion characteristics. Further, the surface roughness Ra _B of the film surface (Side B) opposite to the A side is preferably 5 nm or more from the viewpoint of handling properties in the processing step, and the transfer by pressing force when wound as a tape. It is preferably 17 nm or less from the viewpoint of reduction. More preferably Ra _A is 3～9Nm, a range Ra _B of 6～12Nm, more preferably from Ra _A is 4 to 8 nm, the Ra _B of 7～10Nm.

The biaxially oriented polyester film of the present invention has a thermal expansion coefficient (α) in the longitudinal direction from the viewpoint of dimensional stability under a high temperature condition during recording and reproduction of a magnetic tape and recording and reproduction of the magnetic tape. , -10 × 10 ^{-6 to} 5 × 10
^-6 (/ ° C.). Where-
(Minus) indicates contraction. More preferably, it is in the range of −8 × 10 ⁻⁶ to 4 × 10 ⁻⁶ (/ ° C.), and most preferably in the range of −6 × 10 ^{−6 to} 3 × 10 ⁻⁶ (/ ° C.).

The biaxially oriented polyester film of the present invention has a humidity expansion coefficient (β) of 1 from the viewpoint of the processing step for magnetic tape and the dimensional stability under the high humidity condition during recording and reproduction of the magnetic tape. It is preferably in the range of × 10 ^{-6 to} 12 × 10 ^-6 (/% RH). More preferably, 2 × 1
0 ^{-6 to} 11 × 10 ^-6 (/% RH), most preferably 3
The range is from × 10 ⁻⁶ to 10 × 10 ⁻⁶ (/% RH).

The biaxially oriented polyester film of the present invention is preferably used for magnetic recording tapes, capacitors, heat-sensitive transfer ribbons, heat-sensitive stencil sheets, and the like.
A particularly preferred application is a high-density magnetic recording medium such as for data storage that requires a uniform and fine surface morphology. The data recording capacity is preferably 30 GB
(Gigabytes) or more, more preferably 70 GB or more, and still more preferably 100 GB or more. The thickness of the base film for a high-density magnetic recording medium is preferably 3 to 7 μm. More preferably, it is 3.5 to 6.5 μm, further preferably 4 to 6 μm.

When used as a high-density magnetic recording medium, the magnetic layer is preferably a ferromagnetic metal thin film, a magnetic layer obtained by dispersing a ferromagnetic metal fine powder in a binder, or a magnetic layer formed by applying a metal oxide. An example is given. As the ferromagnetic metal thin film, iron, cobalt, nickel and other alloys are preferable. Further, as the ferromagnetic metal fine powder, ferromagnetic hexagonal ferrite fine powder, iron, cobalt, nickel and other alloys are preferable. As the binder, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof, or the like is preferable.

The magnetic layer is formed by kneading the magnetic powder with a binder such as thermoplastic, thermosetting or radiation curable,
Any of a dry method in which a magnetic metal thin film layer is directly formed on a base film by a coating method of coating and drying, a metal or alloy vapor deposition method, a sputtering method, an ion pre-coating method, or the like can be employed.

In the magnetic recording medium of the present invention, a protective film may be provided on the ferromagnetic metal thin film. With this protective film, running durability and corrosion resistance can be further improved. Examples of the protective film include oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitride protective films such as titanium nitride, silicon nitride, and boron nitride; silicon carbide, chromium carbide, and boron carbide. A carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon may be used.

The carbon protective film is a carbon film having an amorphous structure, a graphite structure, a diamond structure, or a mixture thereof formed by a plasma CVD method, a sputtering method or the like, and particularly preferably a hard carbon film generally called diamond-like carbon. It is a membrane.

For the purpose of further improving the adhesion with the lubricant applied on the hard carbon protective film, the surface of the hard carbon protective film may be subjected to a surface treatment with an oxidizing or inert gas plasma.

In the present invention, in order to improve the running durability and corrosion resistance of the magnetic recording medium, it is preferable to add a lubricant or a rust inhibitor to the magnetic film or the protective film.

Next, a method for producing the biaxially oriented polyester film of the present invention will be described. However, the present invention is not limited to the following method.

The biaxially oriented polyester film of the present invention is a film in which a sheet obtained by melt-molding a polyester resin is stretched in the longitudinal direction and the width direction by successive biaxial stretching or / and simultaneous biaxial stretching. After performing one-stage biaxial stretching in the width direction, fine stretching is performed in multiple stages in the width direction, and further stretching in the longitudinal and width directions is performed to obtain a high degree of orientation.

Hereinafter, a specific production method will be described by taking a case of sequential biaxial stretching of a polyethylene terephthalate (PET) film as an example.

First, PET pellets obtained by a conventional method were vacuum-dried at 180 ° C. for 3 hours or more,
After being melt-extruded at 0 ° C. and passed through a fiber sintered stainless steel metal filter, it is discharged in a sheet form from a T-shaped die.
The melted sheet is brought into close contact with a drum cooled to a surface temperature of 25 to 30 ° C. by electrostatic force to be cooled and solidified to obtain a substantially non-oriented unstretched polyester film.

Next, this unstretched film is biaxially stretched,
Biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. here,
Using a longitudinal stretching machine in which several rolls are arranged, stretch in the longitudinal direction using the peripheral speed difference of the rolls, then perform transverse stretching with a stenter, and further longitudinally stretch with a roll longitudinal stretching machine Next, a sequential biaxial stretching method in which lateral stretching is performed again by a stenter will be described.

First, the unstretched polyester film is heated by a group of heating rolls, and 1.1 to 2.0 times, preferably 1.2 to 1.9 times, more preferably 1.3 to 2.0 times in the longitudinal direction.
Pre-stretch 1.8 times (MD pre-stretch). The stretching temperature is (Tg (glass transition temperature of polyester) +20) to
A range of (Tg + 100) ° C is preferable, a range of (Tg + 30) to (Tg + 90) ° C is more preferable, and a range of (Tg + 40) to (Tg + 80) ° C is more preferable. Thereafter, it is further extended in the longitudinal direction by a factor of 2 to 5, preferably 2.
The film is stretched 5 to 4.5 times, more preferably 3 to 4 times (MD stretching 1). The stretching temperature is from Tg to (Tg + 60) ° C.
It is preferably in the range of (Tg + 5) to (Tg + 55) ° C, and more preferably in the range of (Tg + 10) to (Tg + 50) ° C. Thereafter, the film is cooled by a group of cooling rolls at 20 to 50 ° C., and both ends of the film are gripped with clips, guided to a tenter, and stretched in the width direction (TD stretching 1). The stretching temperature is T
g to (Tg + 80) ° C., more preferably (Tg + 80) ° C.
g + 10) to (Tg + 70) ° C., and more preferably (Tg + 70) ° C.
(g + 20) to (Tg + 60) ° C. The stretching ratio is preferably 2.0 to 6.0 times, more preferably 3.
The range is from 0 to 5.0 times, and more preferably from 3.5 to 4.5 times.

Further, the film is heated by a group of heating rolls,
1.1 to 2.5 times, preferably 1.2 to 2.times.
It is stretched again four times, more preferably 1.3 to 2.3 times (MD stretching 2), and cooled by a group of cooling rolls at 20 to 50 ° C. The stretching temperature is preferably in the range of Tg to (Tg + 100) ° C., and more preferably (Tg + 20) to (Tg + 80).
° C, more preferably (Tg + 40) to (Tg +
60) in the range of ° C. Next, stretching in the width direction is performed again using a stenter (TD stretching 2). Stretching temperature is Tg ~
The temperature is preferably in the range of 250 ° C., more preferably (Tg + 2
0) to 240 ° C, more preferably (Tg + 4
0) to 220 ° C. The stretching ratio is 1.1 to 2.
A range of 5 times is preferred, and more preferably 1.15 to 2.2.
It is twice, more preferably 1.2 to 2.0 times. The stretched film is heat-set under tension or while relaxing in the width direction. A preferred heat setting temperature is 150 to 250 ° C, more preferably 170 to 240 ° C, and further preferably 16 to 250 ° C.
The range is from 0 to 220 ° C. In addition, this film
It is preferable to cool while relaxing in the width direction in a temperature zone of ~ 180 ° C. The relaxation rate is preferably 7% or more from the viewpoint of reducing the thermal shrinkage in the width direction, and is preferably 13% or less from the viewpoint of suppressing the occurrence of uneven thickness and wrinkles. It is more preferably in the range of 7.5 to 12.5%, and still more preferably 8 to 12%. At this time,
It is preferable to perform slow cooling in two or more stages in a range of 180 ° C and a range of 40 to 120 ° C. Thereafter, fine stretching (TD fine stretching) is performed in the width direction. The stretching temperature is preferably in the range of 40 to 75 ° C, and the stretching ratio is preferably in the range of 1.01 to 1.05. By performing this fine stretching, the degree of orientation in the width direction is improved, the structure is fixed, and the biaxially oriented polyester film of the present invention is easily obtained, which is preferable.

Thereafter, the film edge is removed, and the film is wound up on a roll. If necessary, the film may be heated in a hot-air oven in a state where the film is wound around a core (roll-shaped film). The preferred processing temperature is (Tg-1
0) to (Tg-60) C, more preferably (Tg-60).
-15) to (Tg-55) C, more preferably (Tg-20) to (Tg-50) C. The preferred treatment time is in the range of 10 to 360 hours, more preferably in the range of 24 to 240 hours, even more preferably 72 to 240 hours.
168 hours. Further, the heat treatment with the roll-shaped film can be performed in two or more stages by changing the temperature and the time within the above-mentioned temperature and time ranges. Performing the roll-shaped heat treatment is preferable because dimensional stability such as creep characteristics is improved.

[Method for Measuring Physical Properties and Method for Evaluating Effect] The method for measuring characteristic values and the method for evaluating effect are as follows.

(1) Young's modulus According to the method specified in ASTM-D882, a film having a width of 10 mm and a tensile strength and elongation automatic measuring device “Tensilon AMF / RTA-100” manufactured by Orientec Co., Ltd. was used.
A sample with a test length of 100 mm was subjected to a temperature of 23 ° C and a humidity of 65%.
The measurement was performed five times under the conditions of RH and a tensile speed of 200 mm / min, and the average value was taken.

(2) Coefficient of thermal expansion (/ ° C.) A film was sampled to a width of 4 mm, and TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. was set so as to have a test length of 15 mm.
And the heating controller TA-1500. 0.5
After a load of g was applied to the film to raise the temperature from room temperature (23 ° C.) to 50 ° C., the temperature was once returned to room temperature. Thereafter, the temperature was increased again from room temperature to 50 ° C. At this time, the displacement (ΔL μm) of the film from 30 ° C. to 40 ° C. was measured, and the thermal expansion coefficient was calculated from the following equation. Thermal expansion coefficient (/ ° C) = {ΔL / (15 × 1000)}
/ (40-30)

(3) tan δ Non-resonant forced extension vibration type device “R” manufactured by Orientec Co., Ltd.
Using HEOVIBRON "DDV-II-EA, the measurement was performed at a driving frequency of 3.5 Hz, a measurement range of -120 to 200 ° C., and a heating rate of 2 ° C./min.

Sample length: 40 mm Sample width: 4 mm Vibration displacement (strain): 16 μm (single amplitude) Initial load: about 6 g Measurement temperature interval: 2 ° C. Measurement atmosphere: nitrogen gas Test chamber atmosphere: 23 ± 2 ° C., 60 ± 5 % RH Based on the data measured under the above conditions, a graph was created with tan δ as the vertical axis (0 to 0.30) and temperature (−120 to 200 ° C.) as the horizontal axis. The temperature at that time was read, and the peak value and the peak temperature were used.

(4) Heat shrinkage rate According to the method specified in JIS-C2318, a width of 10
mm, a sample with a mark interval of about 100 mm
Heat treatment was performed at a load of 0.5 g for 30 minutes. The distance between the marked lines before and after the heat treatment was measured using a thermal shrinkage rate measuring device manufactured by Techno-Nise Corporation, and the following equation: Heat shrinkage rate (%) = [(L0−L) / L0] × 100 L0: Heat treatment Previous mark line interval L: Heat shrinkage was calculated from mark line interval after heat treatment.

(5) Surface Roughness Ra Using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory, a stylus tip radius of 0.5 m, a stylus load of 5 mg, and a measuring length of 1
mm, center line average roughness R at a cutoff value of 0.08 mm
a is scanned in the width direction of the film, and the measurement is performed 20 times.
The average was taken.

(6) Humidity expansion coefficient (/% RH) A film was sampled to a width of 10 mm, and the sample length was 200 m.
m, set to a tape elongation tester manufactured by Okura Industry, held at a temperature of 30 ° C. and a humidity of 40% RH for 30 minutes, then changed to 80% RH under a load of 10 g, held for 30 minutes, and then displaced. The amount (ΔL mm) was measured, and the following equation was used. Humidity expansion coefficient (/% RH) = (ΔL / 200) / (80
−40) to calculate the humidity expansion coefficient.

(7) Glass transition temperature (Tg) The specific heat was measured by the pseudo-isothermal method using the following apparatus and conditions.
The glass transition temperature (Tg) was determined according to JIS K7121.

Apparatus: Temperature modulation DSC manufactured by TA Instrument Measurement conditions: Heating temperature: 270 to 570K (RCS cooling method) Temperature calibration: Melting point of high-purity indium and tin Temperature modulation amplitude: ± 1K Temperature modulation cycle: 60 seconds Temperature rise Step: 5K Sample weight: 5 mg Sample container: aluminum open container (22 mg) Reference container: aluminum open container (18 mg) The glass transition temperature (Tg) is expressed by the following equation: glass transition temperature = (extrapolated glass transition start) Temperature + extrapolated glass transition end temperature) / 2.

(8) Intrinsic Viscosity The value calculated by the following equation from the solution viscosity measured in orthochlorophenol at 25 ° C. is used. ηsp / C = [η] + K [η] ² · C, where ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 m
1, usually 1.2), and K is a Haggins constant (assumed to be 0.343). The solution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

(9) Running Durability and Storage Stability of Magnetic Tape On the surface of the biaxially oriented polyester film, a magnetic paint having the following composition and a non-magnetic lower layer paint are applied in multiple layers by an extrusion coater (the upper layer is a magnetic paint. Coating thickness 0.2μ
m and the thickness of the nonmagnetic lower layer were appropriately changed. ), Magnetically align and dry. Next, after forming a back coat layer having the following composition on the opposite surface, a small test calender (steel / nylon roll, 5 steps) was used at a temperature of 85 ° C.
After calendering at a linear pressure of 200 kg / cm, 70 ° C
After curing for 48 hours, an original tape was obtained. The raw tape was slit into a 1/2 inch width, and a 670 m long magnetic tape was assembled into a cassette to form a cassette tape.

(Composition of magnetic coating material) Ferromagnetic metal powder: 100 parts by weight Na sulfonate-modified vinyl chloride copolymer: 10 parts by weight Na sulfonate-modified polyurethane: 10 parts by weight Polyisocyanate: 5 parts by weight Stearic acid: 1.5 parts by weight-Oleic acid: 1 part by weight-Carbon black: 1 part by weight-Alumina: 10 parts by weight-Methyl ethyl ketone: 75 parts by weight-Cyclohexane: 75 parts by weight-Toluene: 75 parts by weight (nonmagnetic lower layer) Composition of paint) ・ Titanium oxide: 100 parts by weight ・ Carbon black: 10 parts by weight ・ Na sulfonate-modified vinyl chloride copolymer: 10 parts by weight ・ Na sulfonate-modified polyurethane: 10 parts by weight ・ Methyl ethyl ketone: 30 parts by weight ・ Methyl Isobutyl ketone: 30 parts by weight ・ Toluene: 30 parts by weight Composition of back coat) ・ Carbon black (average particle size 20 nm): 95 parts by weight ・ Carbon black (average particle size 280 nm): 10 parts by weight ・ α-alumina: 0.1 parts by weight ・ Zinc oxide: 0.3 parts by weight ・Na sulfonic acid-modified vinyl chloride copolymer: 30 parts by weight-Na sulfonic acid-modified polyurethane: 20 parts by weight-Cyclohexanone: 200 parts by weight-Methyl ethyl ketone: 300 parts by weight-Toluene: 100 parts by weight

The cassette tape thus prepared was transferred to IBM-made Ma
gstar3590 MODELB1A Tape D
Live was run for 100 hours, and the following criteria were used: ○: No elongation of tape end face, no bend, no scraping marks observed Δ: No elongation of tape end face, no bent marks, but some scraping marks observed ×: A part of the tape end face was elongated, wakame-like deformation was observed, and scraping marks were observed. The running durability of the tape was evaluated. In addition, the cassette tape created above was copied from IBM Mags
tar3590 Model B1A Tape Dr
After reading the data using ive, the cassette tape was stored in an atmosphere of 60 ° C. and 80% RH for 100 hours, and then the data was reproduced to meet the following criteria: ：: No abnormality in tape width and no track shift再生: Normal reproduction Δ: No abnormality in tape width, but unreadable in some parts ×: Change in tape width, impossibility of reading was observed, and the storage stability of the tape was evaluated.

(10) Change in Tape Width The cassette tape prepared in the above (9) is heated at 25 ° C and 65 ° C.
After storing in an atmosphere of% RH for 24 hours, the tape was tested for running in the order of 1 to 5 in the following conditions using a tape running tester. As described above, the change in tape width before and after running was determined.
Assuming that the initial value of the tape width before traveling under the temperature, humidity, and tension of the condition 1 is L0 (μm) and the tape width after traveling under the following condition 5 is L1 (μm), the tape width change is calculated by the following equation. Calculated. Condition 1: 20 ° C., 50% RH, 85 g tension, 3 times running times Condition 2: 20 ° C., 50% RH, 140 g tension, 3 running times Condition 3: 40 ° C., 60% RH, 140 g tension, 100 running times Condition 4 : 20 ° C., 50% RH, tension 140 g, 3 times of running conditions 5: 20 ° C., 50% RH, tension 85 g, 3 times of running Tape width change (μm) = | L0−L1 |

(11) Suitability of film processing The film wound up to a width of 500 mm was supplied from an unwinder to an oven processing apparatus manufactured by Inoue Metal Industry Co., Ltd. at a conveying speed of 20 m / min.
, And wound up in a length of 100 m. At this time, the end of the wound film is 1
“×” indicates that the projections were more than 0 mm and became irregular.
Those whose end protrusion is 5 mm or more and 10 mm or less,
A mark of less than 5 mm but wrinkles observed during processing was marked as “△”, and a mark with a protrusion at the end of less than 5 mm and no wrinkles observed during processing was marked as “○”.

(12) Electromagnetic conversion characteristics (C / N) The raw tape prepared in the above (9) was slit into a width of 8 mm to prepare a pancake. Next, a 200 m length of this pancake was incorporated into a cassette to form a cassette tape.

About this tape, a commercially available VT for Hi8
R (EV-BS3000 manufactured by Sony Corporation)
The C / N at MHz ± 1 MHz was measured. This C / N
Was compared with a commercially available MP video tape for Hi8 as follows.

+3 dB or more: ◎ + 1 dB or more and less than +3 dB: ○ less than +1 dB: ×

[0083]

EXAMPLES Examples and comparative examples for clarifying the present invention will be described below.

Example 1 Using two extruders A and B, extruder A heated to 280 ° C. was provided with polyethylene terephthalate (PET) -I
The pellets (comprising 0.4% by weight of spherical silica particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm) were vacuum-dried at 180 ° C. for 3 hours and then supplied to the extruder B, which was also heated to 280 ° C. Pellets of PET-II (comprising 1.0% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm) at 180 ° C. Supplied after vacuum drying for 3 hours. The melted PET-I and PET-II are merged in a T-die, adhered to a cast drum having a surface temperature of 25 ° C. by an electrostatic application method, and cooled and solidified, and the ratio of the laminated thickness is PET-I / PET-II. = 13/1 was obtained. This unstretched film was stretched under the conditions shown in Table 1. First, using a longitudinal stretching machine in which several rolls are arranged, the difference in the peripheral speed of the rolls is used to make one in the longitudinal direction.
The film was pre-stretched 1.7 times at 20 ° C., stretched 3.2 times at 105 ° C., and cooled. Both ends of the film are gripped by clips, guided to a tenter, stretched in the width direction, further stretched again by a roll lengthwise stretching machine, stretched again by a stenter, and heat-set at a temperature of 209 ° C.
After a relaxation treatment of 6.0% in the width direction in the cooling zone at ℃ and 1.8% in the width direction in the zone at 103 ° C.,
Fine stretching was performed 1.02 times at 60 ° C. The film was gradually cooled to room temperature and wound up to obtain a biaxially oriented polyester film. The thickness of the film was adjusted by adjusting the extrusion amount.
The thickness was 5 μm.

Table 1 shows the film forming conditions of the obtained biaxially oriented polyester film, and Tables 2 and 3 show the physical properties. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

Comparative Example 1 Except that the fine stretching in the width direction after the relaxation treatment was not performed,
A polyester film having a thickness of 4.8 μm was obtained in the same manner as in Example 1. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Comparative Example 2 A laminated unstretched film was obtained in the same manner as in Example 1. The unstretched film was stretched and heat-set in the same manner as in Example 1 except that the preliminary stretching, re-longitudinal stretching, and re-lateral stretching in the longitudinal direction were not performed, and the stretching ratio and temperature were changed to the conditions shown in Table 1. After that, relaxation treatment and fine stretching in the width direction were performed, and the film was gradually cooled and wound up to obtain a polyester film having a thickness of 5.0 μm. Table 2 shows each physical property of the obtained biaxially oriented polyester film.
It is shown in Table 3.

Example 2 A laminated unstretched film was obtained in the same manner as in Example 1. The unstretched film was stretched and heat-set in the same manner as in Example 1 except that the conditions shown in Table 1 were changed. Thereafter, a 7.5% relaxation treatment is performed in the width direction in a cooling zone at 148 ° C., fine stretching is performed 1.04 times at 65 ° C. in the width direction, and the film is gradually cooled and wound up to obtain a polyester having a thickness of 5.0 μm. A film was obtained. The obtained film was subjected to a heat treatment for 72 hours in a hot-air oven adjusted to 60 ° C. in a roll form.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

Comparative Example 3 A pellet of PET (containing 1.0% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm) was prepared. After vacuum drying at 180 ° C. for 3 hours, the mixture was supplied to an extruder, melt-extruded at 280 ° C., and discharged from a T-die into a sheet. Further, this sheet was brought into close contact with a cast drum having a surface temperature of 25 ° C. by an electrostatic application method and solidified by cooling to obtain an unstretched film. This unstretched film was treated in the same manner as in Example 1 except that the stretching conditions were changed as shown in Table 1 without performing the transverse stretching and the fine stretching in the width direction after the relaxation treatment and the roll-shaped heat treatment. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 3 PET (intrinsic viscosity 0.85) pellets (50% by weight) and polyetherimide (PEI) pellets ("Ultem" 1010 (General)
Electric (registered trademark)) (50% by weight)
The mixture is fed to a vented twin-screw kneading extruder heated to 80 ° C., melt-extruded with a residence time of 1 minute, and PEI is added at 50% by weight.
The resulting pellet (I) was obtained. Using the two extruders A and B, the obtained PE was added to the extruder A heated to 280 ° C.
I-containing pellets (I) and pellets (II) of PET (containing 0.4% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm) dry-blended at a weight ratio of 20:80 ( PET / PEI-III) to 180
Extruder B, which was supplied after vacuum drying at 280 ° C. for 3 hours and was also heated to 280 ° C., was subjected to PET (intrinsic viscosity 0.62,
A pellet (IV) of 0.7% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm and 0.1% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm was vacuum-dried at 180 ° C. for 3 hours and supplied. . These are merged in a T-die, adhered tightly on a cast drum having a surface temperature of 25 ° C. by an electrostatic application method, and cooled and solidified.
A laminated unstretched film containing PEI (T / PEI-III) / PET-IV = 18/1 was obtained. Under the conditions shown in Table 1, the obtained film was stretched, heat-set, relaxed, and finely stretched in the same manner as in Example 1, and was gradually cooled to room temperature and wound up. The film thickness was adjusted to 5.1 μm by adjusting the extrusion amount.

The physical properties of the obtained biaxially oriented polyester film are shown in Tables 2 and 3. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

Comparative Example 4 Except that the fine stretching in the width direction after the relaxation treatment was not performed,
A 4.8 μm-thick polyester film was obtained in the same manner as in Example 3. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Example 4 A laminated unstretched film was obtained in the same manner as in Example 3. The unstretched film was stretched, heat-set, and relaxed in the same manner as in Example 3 except that the conditions shown in Table 1 were changed, and then slightly stretched in the width direction to obtain a 4.2 μm-thick film. A polyester film was obtained. The obtained film was rolled in a hot air oven controlled at 70 ° C. for 9 hours.
Heat treatment was performed for 0 hours.

The physical properties of the obtained biaxially oriented polyester film are shown in Tables 2 and 3. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

Example 5 Polyethylene terephthalate was converted to polyethylene-2,6-
A laminated unstretched film was obtained in the same manner as in Example 1 except that naphthalenedicarboxylate (PEN) was changed. The unstretched film was stretched, heat-set, relaxed, widthwise finely stretched, and roll-shaped heat-treated in the same manner as in Example 4 except that the conditions shown in Table 1 were changed to a thickness of 4.5.
A μm polyester film was obtained.

Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

Comparative Example 5 The stretching conditions were changed as shown in Table 1 and
The same operation as in Example 5 was performed except that the roll-shaped heat treatment was not performed. Tables 2 and 3 show the physical properties of the obtained biaxially oriented polyester film.

Examples 6 and 7 In this example, the following polyimide A,
2 shows an example of a biaxially oriented polyester film prepared using B. (1) Polyimide A 200 g of isophorone diisocyanate is added and stirred in 3000 ml of N-methyl-2-pyrrolidone (NMP) under a nitrogen atmosphere. Next, after adding 196 g of pyromellitic anhydride to this solution at room temperature, the temperature is gradually raised. Thereafter, when heating was performed at 180 ° C. for 6 hours, the generation of carbon dioxide was terminated, so the heating was stopped. The polymer solution was developed in water and washed, and then the obtained polymer was dried to obtain a polyimide A having a structural unit represented by the following formula.
I got

Embedded image

(2) Polyimide B In a nitrogen stream, 147 g (0.5 mol) of biphenyltetracarboxylic dianhydride was charged into 3000 ml of N-methyl-2-pyrrolidone (NMP). 57 g of trans-1,4-diaminocyclohexane (0.
5 mol) dissolved in 17.6 g of NMP was added dropwise, and the mixture was stirred at room temperature for 2 hours and further at 50 ° C. for 4 hours.
A polyamic acid solution was obtained. After cooling this solution, water 500
Then, the polymer was precipitated. The precipitated polymer was collected by filtration and heat-treated at 250 ° C. for 2 hours in nitrogen to obtain a polyimide B having a structural unit represented by the following formula.

Embedded image

A laminated unstretched film was obtained in the same manner as in Example 3, except that each of the obtained polyimides A and B was used in place of the polyetherimide "Ultem". The obtained film was obtained under the conditions shown in Table 1.
The film was stretched, heat-set, relaxed, and finely stretched, gradually cooled to room temperature, and wound. The film thickness was adjusted to 5.0 by adjusting the extrusion rate.
It was adjusted to μm. In the biaxially oriented polyester film obtained in Example 6, the content of polyimide A in the layer containing polyimide A was 10% by weight.
In the biaxially oriented polyester film obtained in the above, the content of polyimide B in the layer containing polyimide B is 10% by weight.

The physical properties of the obtained biaxially oriented polyester film are shown in Tables 2 and 3. As shown in Table 3, this film had a small change in tape width, and was excellent in running durability, storage stability, workability, and electromagnetic conversion characteristics.

[0103]

[Table 1]

[0104]

[Table 2]

[0105]

[Table 3]

[0106]

The biaxially oriented polyester film has a Young's modulus in the longitudinal direction, a coefficient of thermal expansion in the width direction, and ta.
By setting the peak temperature and peak value of nδ within the range of the present invention, it is possible to have characteristics suitable for a base film of a high-density magnetic recording medium in particular, to have good dimensional stability during film processing, and to improve magnetic properties. It is difficult for recording track deviation when tape is used, running durability, storage stability,
It is excellent in processability and electromagnetic conversion characteristics, and its industrial value is extremely high.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Tsunekawa 1-1-1, Sonoyama, Otsu-shi, Shiga F-term in Shiga Plant of Toray Industries Co., Ltd. (Reference) 4F210 AA24 AA26 AF16 AG01 AH38 QC05 QC06 QC13 QC14 QD04 QD16 QG01 QG15 QG18 QW12 5D006 CB01 CB02 CB07

Claims (7)

[Claims] 1. A film having a Young's modulus in the longitudinal direction of 6 to 15
GPa, the coefficient of thermal expansion in the film width direction is in the range of 0 to 12 ppm / ° C., the peak temperature of tan δ is in the range of 120 to 180 ° C., and the peak value is 0.1.
A biaxially oriented polyester film having a range of 0 to 0.25. 2. A film having a Young's modulus in a film width direction of 4.5 to 4.5.
The biaxially oriented polyester film according to claim 1, which has a strength of 9.0 GPa. 3. The heat shrinkage at 100 ° C. in the film width direction is 0.
The biaxially oriented polyester film according to claim 1 or 2, wherein the content is in the range of 0.3% to 0.3%. Ranges surface roughness Ra _A of 3~10nm according to claim 4 wherein one of the film surface (A surface), the surface roughness Ra _B of the opposite side of the film surface of the A-side (B surface) 5~17nm The biaxially oriented polyester film according to any one of claims 1 to 3. 5. The biaxially oriented polyester film according to claim 1, wherein the polyester is polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, or a copolymer or modified product thereof. 6. The biaxially oriented polyester film according to claim 5, comprising a polyester resin composition containing 5 to 30% by weight of a polyimide. 7. A magnetic recording medium for a data tape using the biaxially oriented polyester film according to claim 1 as a base film.