JP2000108201A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film suitable for a base film for a high density magnetic recording tape in which cutting or stress elongation deformation are scarcely generated at the time of using as the base film for the magnetic recording tape, and which has excellent running durability and preservability. SOLUTION: In the biaxially oriented polyester film having 7 GPa or more of either Young's modulus (YmMD) of a lengthwise direction or Young's modulus (YmTD) of a width direction, a half-value width of a diffraction peak of a crystal surface of a main chain direction of a polyester in a circumferential direction obtained at the time of rotating the film at its normal as an axis is in a range of 55 to 85 degrees by means of a crystal orientation analysis according to a wide angle X-ray diffractometer method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a biaxially oriented polyester film. More specifically, a base for high-density magnetic recording media that has high rigidity in all directions in the film plane and improves the running durability of the tape when used as a tape for magnetic recording and the storage stability in the environment where the tape is used. The present invention relates to a biaxially oriented polyester film suitable as a film.

[0002]

2. Description of the Related Art In recent years, magnetic recording tapes have been reduced in thickness and recording density for miniaturization and long-term recording. Requests are getting stronger. Due to these developments in the field of magnetic recording tapes, there is an increasing demand for base films to have higher strength and to improve morphology and dimensional stability in use environments.

[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. Although it is expensive and disadvantageous in terms of cost, it is currently used because there is no substitute. On the other hand, a high-strength polyester film obtained by a conventional technique (for example, Japanese Patent Publication No. 42-9270,
JP-B-43-3040, JP-B-46-1119, JP-B-46-1120, and JP-A-50-13
No. 3,276, Japanese Patent Application Laid-Open No. 55-22915), the tape is cut during use, edge damage occurs due to lack of rigidity in the width direction, dimensional change due to stress elongation deformation or environmental conditions, and recording tracks Error occurs during recording and playback,
There are problems such as insufficient strength, difficulty in handling thin films, and the inability to obtain desired electromagnetic conversion characteristics, and many problems remain when applied to large-capacity, high-density magnetic recording tapes. .

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tape which is hardly cut or stress-elongated when used as a base film for a magnetic recording tape, and has excellent running durability and storage stability. An object of the present invention is to provide a biaxially oriented polyester film suitable as a base film for a high density magnetic recording tape.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by making the structure and physical properties of the film after the biaxial stretching heat treatment specific, the polyester film The present inventors have found that edge damage of a magnetic recording tape using the same can be reduced and running durability and storage stability can be improved, and the present invention has been completed.

That is, the gist of the present invention is that the Young's modulus in the longitudinal direction (YmMD) or the Young's modulus in the width direction (YmT
D) A biaxially oriented polyester film having a Young's modulus of 7 GPa or more, which is obtained by rotating the polyester film about its normal line in a crystal orientation analysis by a wide-angle X-ray diffractometer method. Can be
A biaxially oriented polyester film, wherein a half-width in a circumferential direction of a diffraction peak of a crystal plane in a polyester main chain direction is in a range of 55 degrees or more to 85 degrees or less.

The biaxially oriented polyester film of the present invention includes the following preferred embodiments: (a) The crystal size in the polyester main chain direction is in the range of 45 ° to 90 °. (B) The sum of the Young's modulus in the longitudinal direction (YmMD) and the Young's modulus in the width direction (YmTD) is from 13 GPa or more to 25 GPa.
The Young's modulus in an oblique direction (45 ° or 135 ° when the longitudinal direction is 90 ° and the width direction is 0 °) is in the range of 6 GPa to 10 GPa. (C) Creep compliance after 30 minutes at a temperature of 50 ° C. and a load of 28 MPa is in the range of 0.11 GPa ⁻¹ or more and 0.35 GPa ⁻¹ or less. (D) The tear propagation resistance in the width direction when the film thickness is converted to 5 μm is in the range of 0.7 g or more to 1.8 g or less. (E) The polyester is polyethylene terephthalate. (F) The refractive index (n _ZD ) in the thickness direction is from 1.470 to 1.485, and the plane orientation coefficient (f _n ) is from 0.175 to 0.195. (G) The density of the film is from 1.385 or more to 1.400.
Be in the following range. (H) The temperature at which the film begins to contract heat is 70 ° C. or higher, and the temperature is
The heat shrinkage at 0 ° C. is 0.5% or less. The biaxially oriented polyester film according to the present invention as described above is particularly suitable as a base film for a high-density magnetic recording medium.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail together with preferred embodiments. The polyester referred to in the present invention is a polymer obtained by condensation polymerization of a diol and a dicarboxylic acid. Dicarboxylic acids are represented by terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like, and diols are ethylene glycol,
Trimethylene glycol, tetramethylene glycol,
It is represented by cyclohexanedimethanol and the like. Specifically, for example, polymethylene terephthalate, polyethylene terephthalate, polypropylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6 -Naphthalate or the like can be used. Of course, these polyesters may be homopolymers or copolymers. Examples of copolymerization components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, and phthalic acid. A dicarboxylic acid component such as isophthalic acid and 2,6-naphthalenedicarboxylic acid can be copolymerized in an amount of 10 mol% or less. In the case of the present invention, in particular, polyethylene terephthalate, polypropylene terephthalate,
It is preferably at least one selected from polyethylene isophthalate, polyethylene naphthalate (polyethylene-2,6-naphthalate) and a copolymer thereof from the viewpoint of mechanical strength, heat resistance, chemical resistance, durability and the like. Among them, in the present invention, polyethylene terephthalate is particularly preferred in view of film properties and cost.

The intrinsic viscosity (IV) of the polyester is 0.1.
The range from 6 dl / g to 1.0 dl / g is preferred, and the range from 0.65 dl / g to 0.80 dl / g is more preferred from the viewpoints of film forming properties, dimensional stability and tear resistance. preferable.

In the biaxially oriented polyester film of the present invention, one of the Young's modulus in the longitudinal direction (YmMD) and the Young's modulus in the width direction (YmTD) is 7G.
Pa or more, in the crystal orientation analysis by the wide-angle X-ray diffractometer method, obtained when the polyester film is rotated about its normal line, the circumferential direction of the diffraction peak of the crystal plane in the polyester main chain direction. It is necessary that the half width is in the range of 55 degrees or more and 85 degrees or less. The circumferential half width of the diffraction peak of the crystal plane in the polyester main chain direction indicates the spread of the distribution in the direction of crystal orientation of the biaxially oriented polyester film, and this half width is 55%.
If the degree is less than 80 degrees, a film having high strength in all directions in the plane of the film cannot be obtained, and if the half width exceeds 85 degrees, the tear propagation resistance of the film becomes small and the tape is easily broken. This is because the object of the present invention cannot be achieved. Here, the crystal plane in the polyester main chain direction is a crystal plane whose normal line is closest to the polyester main chain direction among the crystal planes detected as diffraction peaks by the wide-angle X-ray diffractometer method. The (-105) plane is used for terephthalate, and the (-306) plane is used for polyethylene-2,6-naphthalate. The half width is 60
The range of not less than 85 ° and not more than 85 ° is more preferable, and the range of not less than 65 ° and not more than 80 ° is most preferable for obtaining the effects of the present invention.

The Young's modulus (YmM) in the longitudinal direction of the film
If one of the Young's modulus D) or the Young's modulus in the width direction (YmTD) is less than 7 GPa, the rigidity of the film is insufficient, and the stress elongation deformation (especially in the longitudinal direction) and the edge damage (especially in the width direction) in the state of the thin film tape. This is not preferable because the occurrence of the susceptibility tends to occur. The Young's modulus of one of YmMD and YmTD is more preferably 8 GPa or more from the viewpoint of elongation deformation and edge damage of the tape. It is preferable that the upper limit of either the Young's modulus in the longitudinal direction (YmMD) or the Young's modulus in the width direction (YmTD) of the film does not exceed 14 GPa from the viewpoint of avoiding breakage of the magnetic tape.

The crystal size in the polyester main chain direction of the film of the present invention is preferably in the range of 45 ° to 90 °. Here, the polyester main chain direction is the normal direction of the crystal plane closest to the polyester main chain direction, and in polyethylene terephthalate, (−10)
5) In the case of polyethylene 2,6-naphthalate,
306) The normal direction of the plane. When the crystal size is less than 45 °, elongation and deformation of the tape become large, and edge damage is liable to occur, and storage stability after tape processing is deteriorated. It should be noted that when the crystal size exceeds 90 °, the frequency of tape breakage increases. The crystal size varies depending on the polyester to be used.
The range is preferably equal to or less than Å, and more preferably, equal to or more than 55 ° and equal to or less than 80 °. When the polyester used is polyethylene-2,6-naphthalate, the range is more preferably from 50 ° to 65 °.

The sum of the Young's modulus (YmMD) in the longitudinal direction and the Young's modulus (YmTD) in the width direction (YmTD) of the film of the present invention.
mMD + YmTD) is from 13 GPa or more to 25 GPa
The following range, and the Young's modulus in the oblique direction is 6G
It is preferably in the range from Pa or more to 10 GPa or less. Here, the Young's modulus in the oblique direction is the Young's modulus in the direction of 45 degrees or 135 degrees in the film plane when the longitudinal direction of the film is 90 degrees and the width direction is 0 degrees. When the sum of the Young's modulus is less than 13 GPa and the Young's modulus in the oblique direction is less than 6 GPa, elongation deformation due to stress is likely to occur. On the contrary, the sum of Young's modulus is 2
If the modulus exceeds 5 GPa and the Young's modulus in the oblique direction exceeds 10 GPa, it should be noted that the tear resistance and heat shrinkage characteristics of the film deteriorate, and the effect of the present invention is hardly obtained.
The sum of the Young's modulus (YmMD) in the longitudinal direction of the film and the Young's modulus (YmTD) in the width direction (YmMD + YmTD) is:
More preferably, the Young's modulus in the oblique direction is in the range of 7 GPa to 9 GPa.

Further, depending on the rigidity of the magnetic layer coated on the base film and the use conditions of the tape, YmMD and YmT
The ratio of D (YmMD / YmTD) is preferably in the range of 0.6 to 1.3 from the viewpoint of suppressing edge damage of the tape,
The range of 0.7 to 1.2 is more preferable. When a magnetic layer is added to the base film to increase the rigidity of the magnetic layer, the YmMD is preferably 6.0 GPa or more.
mMD / YmTD) is preferably in the range of 0.6 to 0.9.

In the present invention, the temperature is 50 ° C., the load is 28 MPa.
The creep compliance after a lapse of 30 minutes under the above condition is preferably in the range of 0.11 GPa ^-1 or more and 0.35 GPa ^-1 or less. When the creep compliance of the present invention exceeds 0.35 GPa ^-1 , the tape is easily stretched and deformed due to the tension during the running or storage of the tape, and the track is easily shifted during recording and reproduction. Conversely, when the creep compliance is less than 0.11, the tape frequently breaks. The creep compliance of the present invention is 0.15 G
The range from Pa ^-1 or more to 0.30 GPa ^-1 or less is more preferable. Here, the creep compliance of the present invention is described in “Introduction to Polymer Chemistry (Second Edition)”, page 150 (published by Kagaku Dojin).

In the biaxially oriented polyester film of the present invention, the tear propagation resistance in the width direction when the film thickness is converted to 5 μm from the viewpoint of tape cutting and running durability is as follows:
The range is preferably from 0.7 g or more to 1.8 g or less. The tear propagation resistance in the width direction of the present invention is from 0.8 g or more to 1.5 g.
g or less is more preferable.

As described above, in the present invention, the polyester used is preferably polyethylene terephthalate. In this case, the refractive index (n _ZD ) in the thickness direction of the film is from 1.470 or more to 1.485 or less. The plane orientation coefficient (f _n ) preferably ranges from 0.175 or more to 0.195 or less. When the refractive index (n _ZD ) in the thickness direction of the present invention exceeds 1.485 and the plane orientation coefficient (f _n ) is less than 0.175, elongation deformation occurs due to stress applied to the magnetic tape during running of the magnetic tape. Track misalignment. When the refractive index (n _ZD ) in the thickness direction is less than 1.470 and the plane orientation coefficient (f _n ) exceeds 0.195, the tear propagation resistance of the film decreases,
It should be noted that the tape is likely to break. The refractive index (n _ZD ) in the thickness direction of the film of the present invention is 1.47.
3 or more to 1.482 or less, and a plane orientation coefficient (f _n ) of 0.4 or more.
A range from 180 or more to 0.193 or less is more preferable.

The density of the biaxially oriented polyethylene terephthalate film of the present invention is from 1.385 or more to 1.400.
The following ranges are preferred. The density of the film of the present invention is 1.
If it is less than 385, the structure of the film is insufficiently fixed, so that the preservability of the tape tends to deteriorate. If the density of the film exceeds 1.400, the tear propagation resistance of the film decreases, and tape cutting occurs. This is because it becomes easier.

In the biaxially oriented polyethylene terephthalate film of the present invention, the heat shrinkage initiation temperature is 70 ° C. or more and the heat shrinkage rate at a temperature of 80 ° C. is 0.5% or less from the viewpoints of elongation and deformability of the tape and storage stability. preferable. More preferably, the heat shrinkage initiation temperature is 75 ° C. or more, and the heat shrinkage at a temperature of 80 ° C. is 0.3% or less. The heat shrinkage starting temperature of the present invention is 7
Less than 0 ° C or 0.5% thermal shrinkage at 80 ° C
In the case of exceeding, the dimensional stability tends to be impaired, and thermal deformation tends to occur when the temperature of the magnetic tape rises due to frictional heat between the magnetic tape and the recording head during running, and the storage stability of the tape tends to deteriorate. So be careful. The upper limit of the heat shrinkage initiation temperature is preferably higher from the viewpoint of dimensional stability, but in the case of a biaxially oriented polyethylene terephthalate film, if the temperature exceeds 105 ° C., the Young's modulus of the film falls within the range of the present invention. Is not preferable because it becomes difficult. The heat shrinkage at a temperature of 80 ° C. is -0.2%.
If it exceeds (the direction of thermal elongation), it is not preferable because it causes wrinkles in the processing step of the magnetic tape.

The biaxially oriented polyester film of the present invention is suitable for a base film of a high-density magnetic recording tape such as a magnetic tape for data storage and a magnetic tape for digital video cassette. It is suitable for base films such as Advanced Intelligent Tape (AIT), Digital Linear Tape (DLT), and Linear Tape Open (LTO). The magnetic recording density is preferably 30 GB (gigabyte) or more, more preferably 70 Gb.
B, even more preferably 100 GB or more.

The thickness of the biaxially oriented polyester film of the present invention can be appropriately determined according to the use and purpose. Usually, for use in magnetic recording media, the range is preferably from 1 μm to 20 μm. 2 μm for coated magnetic recording media for data
The range is preferably from 15 μm to 15 μm, and more preferably from 3 μm to 9 μm for data evaporation magnetic recording media.

The surface roughness (Ra) (center line average roughness) of the magnetic recording surface of the biaxially oriented polyester film of the present invention is:
The range of 0.2 to 15 nm is preferable because the distance between the magnetic head and the magnetic tape is reduced and the electromagnetic conversion characteristics are improved. Further, the surface roughness (Ra) of the tape running surface opposite to the magnetic recording surface is preferably in the range of 5 to 30 nm from the viewpoints of handleability of the base film, winding of the film into a roll, and the like. It is very preferable to individually control the surface roughness of the front and back surfaces of the film in order to achieve both the tape running property and the electromagnetic conversion characteristics. As a method for achieving this, a method of coextruding two kinds of resins each having particles having different diameters added to polyester to form a laminated film of two or more layers is preferable. Lamination can also be suitably performed. In the case of a two-layer laminated film, the ratio (A / A) of the thickness (A) of the layer to be the magnetic recording surface and the thickness (B) of the layer on the tape running surface.
B) is preferably in the range of 80/1 to 3/1.

In the polyester film of the present invention, inorganic particles, organic particles and other various additives such as an antioxidant, an antistatic agent and a crystal nucleating agent may be added. Further, a small amount of another resin, for example, a copolymerized polyester resin having a mesogen group (a liquid crystalline structural unit) in the main chain may be added.

Specific examples of the inorganic particles include silicon oxide,
Oxides such as aluminum oxide, magnesium oxide, and titanium oxide; complex oxides such as kaolin, talc, and montmorillonite; carbonates such as calcium carbonate and barium carbonate; sulfates such as calcium sulfate and barium sulfate; barium titanate; Titanate such as potassium, phosphate such as tertiary calcium phosphate, dibasic calcium phosphate, and monocalcium phosphate can be used, but not limited thereto. These may be used in combination of two or more depending on the purpose.

Specific examples of the organic particles include polystyrene or crosslinked polystyrene particles, vinyl particles such as styrene / acrylic / acrylic crosslinked particles, styrene / methacrylic / methacrylic crosslinked particles, benzoguanamine / formaldehyde, silicone, and polytetrafluoroethylene. Although particles such as fluoroethylene can be used, the particles are not limited thereto, and any particles may be used as long as at least a part of the particles constituting the particles is organic polymer fine particles insoluble in polyester. The organic particles preferably have a spherical particle shape and a uniform particle size distribution from the viewpoint of smoothness and uniformity of formation of projections on the film surface.

The particle size, blending amount, shape and the like of these particles can be selected according to the application and purpose.
The average particle diameter is preferably in the range of 0.01 μm to 2 μm, and the blending amount is preferably in the range of 0.002% by weight to 2% by weight.

Specific examples of the copolyester resin having a mesogen group in the main chain include copolyesters obtained from monooxy-monocarboxylic acid compounds, aromatic dihydroxy compounds, aromatic dicarboxylic acids, and alkylene diols. Monooxy-monocarboxylic acid compounds include p-hydroxybenzoic acid, 6-hydroxy-
2-naphthoic acid is exemplified. As the aromatic dihydroxy compound, 4,4′-dihydroxybiphenyl, hydroquinone, 2,6-dihydroxynaphthalene, and as the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid,
4,4'-diphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,2-bis (phenoxy) ethane-
4,4'-dicarboxylic acid and the like. Examples of the alkylene diol include ethylene glycol and butane diol. The molar ratio (M / M) of the sum (M) of the copolymerization amounts of the monooxy-monocarboxylic acid compound and the aromatic dihydroxy compound and the copolymerization amount (N) of the alkylene diol.
N) is preferably in the range of 80/20 to 50/50. Preferred examples of the copolymerized polyester added to the polyethylene terephthalate film or the polyethylene naphthalate film include p-hydroxybenzoic acid,
4'-dihydroxybiphenyl, ethylene glycol,
Copolymerized polyesters composed of terephthalic acid or 2,6-naphthalenedicarboxylic acid are exemplified. The amount added to the polyester film is preferably in the range of 0.5 to 10.0% by weight.

As described above, the biaxially oriented polyester film having a specific structure and physical properties can reduce the breakage of the tape, improve the running durability and the storage stability, and is therefore extremely suitable as a base film for a high-density magnetic recording tape. It was shown. Next, a method for producing the biaxially oriented polyester film of the present invention will be described. However, it is a matter of course that the present invention is not limited by the following description unless the gist of the present invention is exceeded.

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 sequential biaxial stretching or / and simultaneous biaxial stretching. Axial stretching can be obtained by successively stretching the film at a multi-stage temperature and highly orienting the film.

In the following, a preferred production method will be described as a specific example of sequential biaxial stretching of a polyethylene terephthalate (hereinafter abbreviated as PET) film.

PET pellets (glass transition temperature Tg;
(75 ° C., melting temperature Tm; 255 ° C.) is sufficiently dried under vacuum, fed to an extruder heated to a temperature of 270 to 300 ° C., and extruded from a T-type die into a sheet. The melted sheet is brought into close contact with a drum cooled to a surface temperature of 10 to 40 ° C. by electrostatic force and cooled and solidified to obtain a substantially amorphous unstretched cast film. At this time, the refractive index in the longitudinal direction and the refractive index in the width direction are preferably 1.5
It is preferable to control the crystallinity to 70 to 1.575, and to maintain the crystallinity preferably at 1.5% or less, more preferably at 1.0% or less, from the viewpoint of exerting the effect of the next stretching.
Further, the ratio (A / B) of the maximum thickness (A) of the edge portion of the unstretched film to the thickness (B) of the central portion in the width direction is preferably 2 to 6, more preferably 3 to 5, and It is preferably used for stretching.

This unstretched film is led to a heated metal roll group (surface material: silicon), and (Tg + 25) ° C.
The film is stretched in the longitudinal direction 1.5 to 2.5 times in the temperature range of (Tg + 45) ° C. (MD stretching 1). In this case, the stretching in the longitudinal direction is preferably performed by dividing the magnification into two stages.
Next, the film was held at both ends by running clips and guided to a tenter, and after preheating the film, (Tg
+25) ° C to (Tg + 45) ° C in a temperature range of 1.5 to
Stretched 2.5 times in the width direction (TD stretching 1).
The film is stretched 3 to 5 times in the width direction at a temperature of (Tg-15) ° C to (Tg + 10) ° C (TD stretching 2). MD stretching 1 and TD
The refractive index in the longitudinal direction and the width direction of the film at the stage when stretching 1 is completed is preferably 1.590 or less, more preferably 1.580 or less. As birefringence at this time,
Preferably 0 to 0.02, more preferably 0 to 0.0
1, more preferably 0 to 0.005. The crystallinity by the density method is preferably 6% or less, more preferably 3% or less.
% Or less, more preferably 2% or less, is preferred for subsequent stretching. As described above, it is preferable that the film is stretched 1.5 to 2.5 times in the longitudinal direction and the width direction at a temperature at which the orientation and crystallinity are not increased by the stretching. When such stretching is performed, the entanglement of the polymer chains is released, and the benzene rings are oriented in plane with each other, so that a structure (stack structure) in which two or three benzene rings are vertically stacked can be formed. After forming, again, a method of performing stretching in multiple stages,
This is preferable for obtaining the film disclosed in the present invention.

The stretching temperature of the TD stretching 2 is (Tg-1
5) It is preferable to carry out in a temperature range of from 0 ° C. to (Tg + 10) ° C. When the stretching is performed at a temperature of (Tg + 10) ° C. or less as described above, stretching with some necking (pseudo necking stretching) is performed. Therefore, the stretching ratio is preferably set to 3 times or more. It should be noted that if the stretching ratio of TD stretching 2 is less than 3 times, the film tends to have uneven thickness. As described above, in order to enable stretching at a high temperature at a temperature near Tg, the stretching of the MD stretching 1 and the TD stretching 1 is performed by combining the above-mentioned preferable temperature and the stretching ratio, and the characteristics of the obtained film are adjusted as described above. It is important to have a preferred range.

Next, this film is guided to a heated metal roll group (surface material = hard chrome plating mirror-finished), and a temperature of (Tg−15) ° C. to (Tg + 10) ° C. and a temperature exceeding (Tg + 10) ° C.} ~ (Tm-45) ℃
Between the metal rolls heated to a temperature range of
The film is stretched again at a temperature of two or more stages up to 8 times (MD stretching 2). The first-stage longitudinal redrawing ratio at a temperature of (Tg-15) ° C to (Tg + 10) ° C is preferably approximately 70 to 95% of the total ratio in the MD stretching step. Also, the stretching ratio of the first stage of the re-stretching in the longitudinal direction {stretching at a temperature of (Tg-15) ° C to (Tg + 10) ° C}
Is preferably divided into two or more stages and stretched.

Next, the film is gripped by clips running on both ends and guided to a tenter, and after preheating the film, {temperature exceeding (Tg + 10) ° C.} to (Tm−4)
5) While gradually increasing the temperature in the temperature range of
The film is stretched at a magnification of 2.5 times in one or two or more stages in the width direction (TD stretching 3). The stretching temperature of TD stretching 3 is a temperature at which crystallization of the film starts to rise (Tm-1).
20) to (Tm-45) ° C. This film is subsequently heat-set in a temperature range of (Tm-75) ° C. to (Tm-35) ° C., and is subjected to relaxation treatment in the width direction and / or the longitudinal direction in a cooling process from the heat setting temperature. In this case 2
At a temperature higher than the stage (for example, 180-130 ° C and 130-
(90 ° C.). In the widthwise relaxation process, a method of sequentially reducing the rail in which the clip travels in the widthwise direction, and in the longitudinal relaxation process, a method of sequentially reducing the interval between the clips gripping the film end portion is preferably used as appropriate. It can be carried out.

Further, the film was heated at (Tg-30) ° C.
The heat treatment may be performed again in the temperature range of (Tg + 110) ° C. As a method of the reheat treatment, a method of performing a heat treatment again with a heating oven or a method of performing a heat treatment again with a group of heating rolls can be suitably used as appropriate. As a method of performing re-heat treatment by a heating oven, for example, a film having an edge (a portion having a large thickness at both ends of a film formed at the time of film formation) is applied with a tension of 2 MPa or more to apply a stress in a longitudinal direction, and further, a heating oven device is used. It is preferable to stretch the film slack in the width direction by a width-developing device (for example, an expander roll or the like) at the entrance, and then heat-treat the film through nip rolls provided before and after a heating oven. At this time, the relaxation process in the longitudinal direction may be performed by reducing the traveling speed of the nip roll after the traveling speed of the preceding nip roll. As a method of performing the heat treatment again by the heating roll group, for example, a method of performing the heat treatment via nip rolls provided before and after the heating roll group is preferable. At this time, the relaxation process in the longitudinal direction may be performed by reducing the traveling speed of the nip roll after the traveling speed of the preceding nip roll.

Further, the edge of the formed film was cut off, the roll film was slit into a small width and rolled up in a roll shape, and subjected to an aging treatment at a temperature of (Tg−30) ° C. to (Tg + 30) ° C. for 1 to 10 days. Is also good.

Next, a production example to which the simultaneous biaxial stretching method is applied will be described. The basic manufacturing concept and stretching conditions of the film are the same as those in the above-described sequential biaxial stretching, and a method in which a part or all of the sequential biaxial stretching steps are simultaneously biaxially stretched can be applied. For example, a method in which MD stretching 1 and TD stretching 1 are simultaneously biaxially stretched and subsequently stretched sequentially, MD stretching 1 and TD stretching 1, TD stretching 2 and MD stretching 2
Is a method in which the first-stage stretching is simultaneously biaxially stretched, and then the subsequent stretching is sequentially performed. MD stretching 1 and TD stretching 1 are sequentially biaxially stretched, and thereafter TD stretching 2 and MD stretching 2 are performed. Stretching at the second stage, and stretching at the second stage of MD stretching 2 and TD
A method of simultaneously stretching 3, MD stretching 1, TD stretching 1,
After each of the first-stage stretching of TD stretching 2 and MD stretching 2 is sequentially stretched, the subsequent stretching of the second stage of MD stretching 2 and T
A method of simultaneously biaxially stretching D stretch 3, MD stretch 1 and TD stretch 1, first stretch of TD stretch 2 and MD stretch 2, first stretch of MD stretch 2 and each process of TD stretch 3 Are simultaneously biaxially stretched.

In the following, MD stretching 1 and TD stretching 1, TD
The following describes, as an example, a method in which each of the first-stage stretching of the stretching 2 and the MD stretching 2, the second-stage stretching of the MD stretching 2 and the TD stretching 3, that is, the simultaneous biaxial stretching of all the processes.

A substantially amorphous unstretched cast film is obtained in the same manner as described in the production example of the sequential biaxial stretching method. At this time, the refractive index in the longitudinal direction and the refractive index in the width direction are preferably controlled to 1.570 to 1.575, and the crystallinity is preferably 1.5% or less, more preferably 1.0% or less. It is preferable to keep it from the viewpoint of exerting the effect of the next stretching. Further, the ratio (A / B) of the maximum thickness (A) of the edge portion of the unstretched cast film to the thickness (B) of the center portion in the width direction is preferably 2.0 to 6.
A range of 0, more preferably 3 to 5, and even more preferably 3 to 4 is preferably used for subsequent stretching.

Both ends of the cast film are gripped with clips (gripping tools) and guided to a simultaneous biaxial stretching device, where (Tg
+25) ° C. to (Tg + 45) ° C. The film is simultaneously biaxially stretched 1.5 to 2.5 times in the longitudinal and width directions. The refractive index of the simultaneous biaxially stretched film in the longitudinal direction and the width direction is preferably 1.590 or less, more preferably 1.5
80 or less. The birefringence at this time is preferably 0 to 0.02, more preferably 0 to 0.01, and still more preferably 0 to 0.005. The degree of crystallinity according to the density method is preferably 6% or less, more preferably 3% or less, and further preferably 2% or less. Subsequently, this biaxially stretched film was subjected to (Tg-1
5) Simultaneous biaxial stretching is performed 3 to 5 times in the longitudinal direction and the width direction at a temperature of from 0 ° C. to (Tg + 10) ° C. Subsequently, the film was heated at a temperature of {(Tg + 10) ° C.}｝ (Melting point of polyester Tm−45) ° C. in the longitudinal and width directions 1.2 to 2.5 times in one or more stages. Simultaneous biaxial stretching is performed at the stage. The simultaneous biaxial stretching temperature in this step is a temperature (Tm-12) at which crystallization of the film starts to rise.
0) to (Tm-45) ° C is more preferable. This film is subsequently heat-set in a temperature range of (Tm-75) ° C. to (Tm-35) ° C., and relaxed in a width direction and a longitudinal direction in a cooling process from the heat setting temperature. In this case, at two or more stages of temperature (for example, 180-130 ° C. and 130-90 ° C.)
C.). The relaxation process in the width direction is performed by sequentially reducing the rail on which the clip travels in the width direction, and the relaxation process in the longitudinal direction is performed by a method of sequentially reducing the interval between the clips gripping the film edge.

As the simultaneous biaxial stretching apparatus preferably used in the present invention, a simultaneous biaxial stretching tenter in which the driving system of the running tool in the longitudinal direction of the gripper (clip) is a linear motor system is preferable. The shape of the surface and the end and the gripper contacts the film, the longitudinal length (L _MD) and the width direction length ratio _{(L TD) (L MD /} L TD) is from 3 to 15 It is preferable from the viewpoint of uniform stretchability in the longitudinal direction of the end of the film. The temperature of the gripper at the film end provided for stretching is (Tg
+15) to (Tg + 50) ° C is preferred from the viewpoint of uniform stretchability in the longitudinal direction at the end of the film.

In the present invention, in order to impart surface characteristics of the film, for example, to impart easy adhesion, easy slipping, releasing property, and antistatic property, the film is formed before or after the stretching of the film. A coating material can be coated on the surface of the polyester film.

The biaxially oriented polyester film of the present invention is suitably used for a magnetic recording medium, but can also be used as an electric capacitor or a thermal transfer ribbon.

[Evaluation Method of Physical Properties] (1) Half width at circumferential direction of crystal plane diffraction peak of film by wide angle X-ray diffraction method X-ray diffractometer (Model 4036A2 manufactured by Rigaku Corporation) ) Was measured by the diffractometer method under the following conditions. X-ray diffractometer: 4036A2 type (tube type) manufactured by Rigaku Corporation X-ray source: CuKα ray (using Ni filter) Output: 40 kV 20 mA Goniometer: Slit manufactured by Rigaku Corporation: 2 mmφ-1 ゜- 1 ゜ Detector: Scintillation counter Counting and recording device: RAD-C type manufactured by Rigaku Denki Co., Ltd. 2cm × 2cm is cut out at the diffraction peak position of the crystal plane obtained by 2θ / θ scan, and aligned in the same direction. The combined sample and counter are fixed, and a circumferential profile is obtained by rotating the sample in-plane (β scan). Of the peak profiles obtained in the β scan, the valleys at both ends of the peak are used as background,
The half width (deg) of the peak was calculated.

(2) Crystal size obtained by wide-angle X-ray diffraction method X-ray diffractometer (Model 4036A2 manufactured by Rigaku Corporation)
Was measured by the transmission method under the following conditions. X-ray diffractometer: 4036A2 type manufactured by Rigaku Denki Co., Ltd. X-ray source: CuKα ray (using Ni filter) Output: 40 kV 20 mA Goniometer: Slit made by Rigaku Denki Co., Ltd. Detector: 2 mmφ-1 ゜ -1 ゜Scintillation counter Count recording device: RAD-C type manufactured by Rigaku Denki Co., Ltd. Cut out into 2 cm x 2 cm, superimposed in the same direction, set a sample fixed with a collodion-ethanol solution, and set it by wide-angle X-ray diffraction measurement. From the obtained 2θ / θ intensity data, the following Scherr is calculated from the half width of the surface in each direction.
It was calculated using the equation of er. Here, the crystal size was measured in the direction of the principal axis of orientation. Crystal size L (Å) = Kλ / β ₀ cos θ _B K: constant (= 1.0) λ: wavelength of X-ray (= 1.5418 °) θ _B : Bragg angle β ₀ = (β _E ² −β _I ² ) ^1/2 β _E : Apparent half width (actual value) β _I : Instrument constant (= 1.046 × 10 ^-2 )

(3) Young's modulus Measured using an Instron type tensile tester according to the method specified in ASTM-D882. The measurement was performed under the following conditions. Measuring device: Automatic film strength and elongation measuring device "Tensilon AMF / RTA-100" manufactured by Orientec Co., Ltd. Sample size: width 10 mm x test length 100 mm, pulling speed: 200 mm / min Measurement environment: temperature 23 ° C, humidity 65 % RH

(4) Creep Compliance The film was sampled to a width of 4 mm, and TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. was set to a sample length of 15 mm.
And the heating controller TA-1500. 50
A load of 28 MPa was applied to the film under the conditions of a temperature of 65 ° C. and 65% RH for 30 minutes, and the film elongation at that time was measured. The amount of expansion and contraction (% display, ΔL) of the film can be measured by a personal computer PC-manufactured by NEC Corporation through an AD converter ADX-98E manufactured by Canopus Electronics Co., Ltd.
9801, and the creep compliance was calculated from the following equation. Creep compliance (GPa ^-1 ) = (ΔL / 10
0) /0.028

(5) Tear Propagation Resistance AST was measured using a light load tear tester (manufactured by Toyo Seiki Seisakusho).
Measured according to MD1922. Sample size is
It was 64 x 51 mm, a 13 mm cut was made, and the indicated value when the remaining 51 mm was torn was read.

(6) Refractive Index and Plane Orientation Coefficient (f _n ) The refractive index was measured using an Appe refractometer type 4 manufactured by Atago Co., Ltd. using sodium D line as a light source according to the method specified in JIS-K7105. It measured using. The mounting liquid was measured using methylene iodide at 23 ° C. and 65% RH. The plane orientation coefficient (f _n ) was determined from each of the measured refractive indices according to the following equation. Plane orientation coefficient (f _n ) = (n _MD + n _TD ) / 2−n _ZD n _MD : refractive index in the longitudinal direction n _TD : refractive index in the width direction n _ZD : refractive index in the thickness direction

(7) Birefringence The retardation (R) of the film was measured using a Berek compensator with a NIKON polarizing microscope.
The birefringence (Δn) was determined by the following equation. Δn = R / d R: retardation (μm) d: film thickness (μm)

(8) Density and Crystallinity The density of the film was measured using a sodium bromide aqueous solution by a density gradient tube method according to JIS-K7112. Also,
Using this density, the crystallinity (%) was determined from the crystal density and the amorphous density of the polyester by the following formula. Crystallinity (%) = [(film density−amorphous density) / (crystal density−amorphous density)] × 100

(9) Thermal Shrinkage Onset Temperature A film sampled to a width of 4 mm was set to a test length of 15 mm in the TMA apparatus of the item (4), and a load of 1 g was applied thereto.
The temperature was raised to 120 ° C. at a rate of 2 ° C./min, and the amount of shrinkage (% display) at that time was measured. From the graph in which the data was output and the temperature and the amount of shrinkage were recorded, the temperature at which the shrinkage deviated from the 0% baseline was read, and that temperature was defined as the heat shrink start temperature.

(10) Heat Shrinkage Measured according to JIS-C2318. Sample size: width 10 mm, mark line interval 200 mm Measurement conditions: temperature 80 ° C., processing time 30 minutes, no load state 80 ° C. The heat shrinkage was determined by the following formula. Heat shrinkage (%) = [(L ₀ −L) / L ₀ ] × 100 L ₀ : Marking line interval before heat treatment L: Marking line interval after heat treatment

(11) Glass transition temperature Tg, melting temperature T
m, using a “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. as a differential scanning calorimeter, and “Disk Session” SSC / 520 manufactured by the company as a data analyzer.
Using 0, 5 mg of a sample was collected, heated from room temperature to 280 ° C. at a temperature rising rate of 20 ° C./min, held for 5 minutes, quenched with liquid nitrogen, and cooled again from room temperature to 28 ° C. at a rate of 20 ° C./min.
From the heat curve obtained when the temperature was raised to 0 ° C., Tg, T
m was determined.

(12) Center Line Average Surface Roughness (Ra) The center line average surface roughness (Ra) was measured according to JIS-B-0601 using a high-precision thin film step meter ET-10 manufactured by Kosaka Laboratory Co., Ltd. Ra) was determined. Stylus tip radius 0.5 μm, stylus pressure 5
mg, measurement length 1 mm, cutoff 0.08 mm.

(13) Running Durability and Preservability of the Magnetic Tape A magnetic paint having the following composition is applied to the surface of the film of the present invention to a coating thickness of 2.0 μm, magnetically oriented, and dried. Next, after forming a back coat layer having the following composition on the opposite surface, performing a calendering treatment, and curing at 60 ° C. for 48 hours. 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. (Magnetic paint composition)-Ferromagnetic metal powder: 100 parts by weight-Modified vinyl chloride copolymer: 10 parts by weight-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-Cyclohexanone: 75 parts by weight-Toluene: 75 parts by weight (composition of the 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 part by weight Modified polyurethane: 20 parts by weight Modified vinyl chloride copolymer: 30 parts by weight Cyclohexanone: 200 Parts by weight ・ Methyl ethyl ketone: 300 parts by weight ・ Toluene: 100 The amount part

The cassette tape thus prepared was transferred to an IBM Ma
gstar3590 MODELB1A Tape D
The tape was run for 100 hours, and the running durability of the tape was evaluated according to the following criteria. ：: No tape end surface elongation or bending, no scraping marks Δ: There is no elongation or bending of the tape end face, but a trace of scraping is observed. ×: A part of the tape end face is elongated, wakame-like deformation is observed, and scraping marks are observed.

Further, the cassette tape created above is inserted into the IB
M Magstar 3590 Model B1A T
After the data was read into the ape drive, the cassette tape was stored in an atmosphere of 40 ° C. and 80% RH for 100 hours, and then the data was reproduced to evaluate the preservability of the tape according to the following criteria. ：: Normal reproduction without track deviation. Δ: There is no abnormality in the tape width, but reading is impossible in some parts. X: There is a change in the tape width, and reading is impossible.

[0060]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, more specific embodiments of the present invention will be described. Examples 1 to 3 and Comparative Examples 1 to 4 Using two extruders A and B, PET-I (intrinsic viscosity 0.65, glass transition temperature 75 ° C., melting temperature) was used for extruder A heated to 280 ° C. A pellet of 255 ° C., containing 0.16% by weight of spherical silica particles having an average diameter of 0.07 μm)
The extruder B, which was supplied after being vacuum-dried for 3 hours at a temperature of 280 ° C. and also heated to 280 ° C., was supplied with PET-II (having an intrinsic viscosity of 0.
65, glass transition temperature 75 ° C., melting temperature 255 ° C., 0.2% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm.
And spherical crosslinked polystyrene particles having an average diameter of 0.8 μm 0.0
(1% by weight) were supplied after vacuum drying at 180 ° C. for 3 hours, and were combined in a T-die (lamination ratio I / II =
10/1), it was brought into close contact with a cast drum having a surface temperature of 25 ° C. by static electricity and cooled and solidified to obtain a laminated unstretched film. The refractive index in the longitudinal direction of this laminated unstretched film was 1.
571, the refractive index in the width direction is 1,570, and the crystallinity is 0.5.
8%. Ratio (A / B) between the maximum thickness (A) of the edge portion of the unstretched film and the thickness (B) of the central portion in the width direction.
Is 3.8. This unstretched film was heated by a group of heating rolls (surface material: silicone rubber), stretched in the longitudinal direction at the temperature and magnification shown in Table 1, and cooled (MD stretching 1). Both ends of the film were gripped by clips and guided to a tenter, and stretched in the width direction in two stages at the temperature and magnification shown in Table 1 (TD stretching 1, 2). This film was heated by a heating metal roll and stretched in the longitudinal direction at the temperature and magnification shown in Table 2 (MD stretching 2). Next, both ends of the film were gripped with clips and guided to a tenter.
After stretching in the width direction in two stages at the temperature and magnification shown in (TD stretching 3), and subsequently heat-setting at a temperature of 200 ° C.,
In the cooling zone at 150 ° C., a relaxation treatment is performed at a relaxation rate of 3% in the width direction, and further in the zone at 100 ° C., 1.0% in the width direction
The film was relaxed at a relaxation rate, and the film was gradually cooled to room temperature and wound up. The film thickness was adjusted to 6.7 μm by adjusting the extrusion amount.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) at the edge portion of the unstretched film to the thickness (B) at the center in the width direction, and the refractive index and crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3 shows the Young's modulus, the half-width of the diffraction peak, the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness of the film obtained in Table 3. Table 4 shows the creep compliance, the heat shrinkage initiation temperature, the heat shrinkage at 80 ° C., the running durability of the magnetic tape, and the storage stability.

In Example 2, the stretching ratio in one step of MD stretching was divided into two stages, and the stretching ratio in the first stage of MD stretching 2 was divided into two stages. In Comparative Example 1, the release of the molecular chains of PET in the longitudinal direction was insufficient, and a film within the scope of the present invention could not be obtained. Comparative Example 2 shows that MD stretching 1 and T
The orientation and crystallinity of the film after the D stretching 1 became inappropriate, the film was broken in the MD stretching 2 or the TD stretching 3, and the stretching ratio was reduced. In Comparative Example 3, the release of the PET molecular chains was performed only in one direction in the longitudinal direction, and a film within the scope of the present invention could not be obtained. In Comparative Example 4, the PET was not unraveled in the longitudinal and width directions, and a film within the scope of the present invention could not be obtained.

COMPARATIVE EXAMPLE 5 When using the PET raw material of Example 1 to obtain a laminated unstretched film in the same manner as in Example 1, a molded sheet was formed under the conditions where the extrusion amount of the extruder was increased, and a cast drum was formed. A laminated unstretched film was obtained in the same manner as in Example 1 except that the surface temperature of was increased to 60 ° C., and the rotation speed of the drum was increased to increase the sheet take-up speed. The refractive index in the longitudinal direction of this laminated unstretched film was 1.574, and the refractive index in the width direction was 1,57.
2. The crystallinity was 1.8%. This unstretched film was stretched under the sequential biaxial stretching conditions of Example 1 shown in Table 1, but the film was frequently broken in the two MD stretching steps, and was stretched under the sequential biaxial stretching conditions shown in Table 1. 6.7μm thickness
Was obtained.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) at the edge of the unstretched film to the thickness (B) at the center in the width direction, and the refractive index and crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3 shows the Young's modulus, the half-width of the diffraction peak, the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness of the film obtained in Table 3. Table 4 shows the creep compliance, the heat shrinkage initiation temperature, the heat shrinkage at 80 ° C., the running durability of the magnetic tape, and the storage stability.

Comparative Example 6 A laminated unstretched film was obtained in the same manner as in Example 1 except that the PET raw material of Example 1 was used. The unstretched film is guided to a group of heated metal rolls, heated to a temperature of 95 ° C., stretched in the longitudinal direction at a magnification of 3.0 times, guided to a tenter, and a film end is gripped with a clip. Then 100
The film was heated to a temperature of ° C and stretched in the transverse direction at a magnification of 3.61 times. Guide this biaxially stretched film to a group of heated metal rolls,
At two-stage temperatures of 105 and 140 ° C., the film was stretched in the longitudinal direction at a magnification of 1.3 and 1.1 times. This stretched film is guided to a tenter, and the end of the film is gripped with a clip.
After heating to a temperature of 0 ° C. and stretching in a transverse direction at a magnification of 1.4 times, and subsequently performing heat setting at a temperature of 200 ° C.,
The film was subjected to a relaxation treatment in a cooling zone at a temperature of 3 ° C. at a relaxation rate of 3% in the width direction, and further subjected to a relaxation treatment at a relaxation rate of 1.0% in the width direction in a zone at 100 ° C., and was gradually cooled to room temperature and wound up. . The film thickness was adjusted to 6.7 μm by adjusting the extrusion amount.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) at the edge of the unstretched film to the thickness (B) at the center in the width direction, and the refractive index and crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3 shows the Young's modulus of the film obtained, the half width of the diffraction peak, the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness. Table 4 shows the creep compliance, the heat shrinkage initiation temperature, the heat shrinkage at 80 ° C., the running durability of the magnetic tape, and the storage stability.

Example 4 Using two extruders A and B, PET-III (intrinsic viscosity 0.75, glass transition temperature 76 ° C., melting temperature 256 ° C., average diameter 0) was heated to 280 ° C. Of 0.16% by weight of 0.07 μm spherical silica particles).
Supplied after vacuum drying at 0 ° C for 3 hours.
The extruder B heated to a temperature of PET-IV (intrinsic viscosity 0.75, glass transition temperature 76 ° C, melting temperature 256 ° C,
A pellet of 0.2% by weight of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm and 0.01% by weight of spherical cross-linked polystyrene particles having an average diameter of 0.8 μm) was vacuum-dried at 180 ° C. for 3 hours, and supplied. In the stack (stacking ratio II
(I / IV = 10/1), adhered by static electricity on a cast drum having a surface temperature of 25 ° C., cooled and solidified, and laminated unstretched film (longitudinal refractive index: 1.572, width direction refractive index: 1, 1) 570, crystallinity; 0.6%). This unstretched film was heated by a group of heating rolls (surface material: silicone rubber), stretched in the longitudinal direction to the temperature and magnification shown in Table 1, and cooled (MD stretching 1). Both ends of the film were gripped with clips and guided to a tenter, stretched in the width direction at the temperature and magnification shown in Table 1, and subsequently stretched in the width direction at the temperature and magnification shown in Table 1 (TD stretching). 1, 2).
This film was heated by a heating metal roll and stretched in the longitudinal direction at the two-stage temperature shown in Table 1 at the magnification shown in Table 1 (MD stretching 2). Except that both ends of this film were gripped with clips and guided to a tenter, and stretched in the width direction at the two-stage temperature shown in Table 1 at the magnification shown in Table 1 (TD stretching 3), the same as in Example 1 was carried out. Thus, a biaxially stretched film having a film thickness of 6.7 μm was obtained.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) at the edge of the unstretched film to the thickness (B) at the center in the width direction, and the refractive index and crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3 shows the Young's modulus, the half-width of the diffraction peak, the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness of the film obtained in Table 3. Table 4 shows the creep compliance, the heat shrinkage initiation temperature, the heat shrinkage at 80 ° C., the running durability of the magnetic tape, and the storage stability.

Example 5 Using two extruders A and B, extruder A heated to 290 ° C. was provided with polyethylene naphthalate (hereinafter abbreviated as PEN) -I (intrinsic viscosity 0.65, glass transition temperature 124).
C., a melting temperature of 265.degree. C., and a spherical silica particle having an average diameter of 0.07 .mu.m (containing 0.16% by weight).
The extruder B, which was supplied after being vacuum-dried for hours and was also heated to 290 ° C., had PEN-II (having an intrinsic viscosity of 0.65,
Glass transition temperature 124 ° C., melting temperature 265 ° C., 0.2% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm and 0.01 of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm
(% By weight) after being vacuum-dried at 180 ° C. for 3 hours, supplied and merged in a T-die (stacking ratio I / II = 1).
0/1), it was brought into close contact with a cast drum having a surface temperature of 25 ° C. by static electricity and cooled and solidified to obtain a laminated unstretched film. The refractive index in the longitudinal direction of this laminated unstretched film was 1.
649, the refractive index in the width direction is 1,648, and the crystallinity is 0.5.
7%. The unstretched film was heated by a group of heating rolls (surface material: silicone rubber), stretched in the longitudinal direction at the temperature and magnification shown in Table 1, and cooled (MD stretching 1). Both ends of the film were gripped with clips and guided to a tenter, and stretched in the width direction in two stages at the temperature and magnification shown in Table 1 (TD stretching 1, 2). This film was heated by a heating metal roll and stretched in the longitudinal direction at the temperature and magnification shown in Table 1 (MD stretching 2). Next, both ends of the film were gripped with clips and guided to a tenter, and stretched in the width direction in two stages at the temperature and magnification shown in Table 1 (TD
Stretching 3) Then, after heat-setting at a temperature of 210 ° C., a relaxation treatment is carried out at a cooling zone of 170 ° C. at a relaxation rate of 1% in the width direction, and 0.1 mm in a width of 130 ° C. zone.
The film was relaxed at a relaxation rate of 5%, and the film was gradually cooled to room temperature and wound up. The film thickness is adjusted to 6.7 μm by controlling the extrusion amount.
I adjusted to.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) at the edge portion of the unstretched film to the thickness (B) at the center in the width direction, and the refractive index and crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3 shows the Young's modulus, the half-width of the diffraction peak, the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness of the film obtained in Table 3. Table 4 shows the creep compliance, the heat shrinkage initiation temperature, the heat shrinkage at 80 ° C., the running durability of the magnetic tape, and the storage stability.

Comparative Example 7 A laminated unstretched film was obtained in the same manner as in Example 5. This unstretched film is guided to a group of heated metal rolls, heated to a temperature of 140 ° C., stretched in the longitudinal direction at a magnification of 4 times, guided to a tenter, and a film end is gripped with a clip. Heat to a temperature of 135 ° C. and 3.8
The film was stretched at twice the magnification. The biaxially stretched film was guided to a group of heated metal rolls and stretched again at a temperature of 160 ° C. in the longitudinal direction at a magnification of 1.2 times. The stretched film was guided to a tenter, and the end of the film was gripped with a clip, heated to a temperature of 190 ° C., stretched in a transverse direction at a magnification of 1.3 times, and subsequently heat-set at a temperature of 210 ° C. Thereafter, the film is subjected to a relaxation treatment in the cooling zone at 170 ° C. at a relaxation rate of 1% in the width direction, and further subjected to a relaxation treatment in the zone at 130 ° C. at a relaxation rate of 0.5% in the width direction, and the film is gradually cooled to room temperature. Wound up. The film thickness was adjusted to 6.7 μm by adjusting the extrusion amount.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) of the edge portion of the unstretched film to the thickness (B) of the central portion in the width direction, the refractive index, and the crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3
Young's modulus of the obtained film, half width of the diffraction peak,
Table 4 shows the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness. Table 4 shows the creep compliance, heat shrink initiation temperature, and heat shrinkage at 80 ° C. And the running durability and storability of the magnetic tape.

Example 6 A laminated unstretched film was obtained in the same manner as in Example 1. This unstretched film was heated by a group of heating rolls (surface material: silicone rubber), stretched in a longitudinal direction at a temperature of 110 ° C. at a magnification of 1.5 × 1.5 in two stages, and cooled (MD Stretching 1). Hold both ends of this film with clips,
It was led to a tenter and stretched 2.0 times in the width direction at a temperature of 115 ° C., and then continuously stretched in the width direction at a temperature of 75 ° C.
Stretching was performed at a magnification of 6 times (TD stretching 1, 2). This film was heated with a heating metal roll, stretched at a temperature of 80 ° C. in the longitudinal direction at a magnification of 3.4 times, and cooled (MD stretching 2).
In the first step). Further, both ends of the film are gripped with clips and guided to a simultaneous biaxial stretching tenter, and simultaneously biaxially stretched 1.2 times in the longitudinal direction and 1.3 times in the width direction at a temperature of 160 ° C. 1.1 in the longitudinal direction at temperature
, And simultaneously biaxially stretched 1.1 times in the width direction.
After heat setting at a temperature of 0 ° C., a relaxation treatment of 2% in the longitudinal direction and a relaxation rate of 3% in the width direction in a cooling zone of 150 ° C., and further 1% in a longitudinal direction in a zone of 100 ° C. The film was relaxed in the width direction at a 1.0% relaxation rate, and the film was gradually cooled to room temperature and wound up. At this time, the temperature at the tenter entrance of the film gripper (clip) of the simultaneous biaxial stretching tenter is:
105 ° C. The film thickness was adjusted to 6.7 μm by adjusting the extrusion amount.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) of the edge portion of the unstretched film to the thickness (B) of the central portion in the width direction, the refractive index, and the crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3
Young's modulus of the obtained film, half width of the diffraction peak,
Table 4 shows the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness. Table 4 shows the creep compliance, heat shrink initiation temperature, and heat shrinkage at 80 ° C. And the running durability and storability of the magnetic tape.

Example 7 A laminated unstretched film was obtained in the same manner as in Example 1. However, the gap (A / B) between the maximum thickness (A) of the edge portion of the laminated unstretched film and the thickness (B) of the central portion in the width direction is adjusted by adjusting the gap of the lip of the die (die) in the width direction. 0 was set. Both ends of the unstretched film are gripped by clips and guided to a simultaneous biaxial stretching tenter, and simultaneously biaxially stretched at a temperature of 110 ° C. to a magnification of 2.0 times in the longitudinal direction and the width direction. Simultaneous biaxial stretching was performed at a temperature of ° C in the longitudinal and width directions at a magnification of 3.3 times. At this time, the temperature at the entrance of the tenter of the gripper of the simultaneous biaxial stretching tenter was 100 ° C. This film is heated with a heating metal roll to form a film 12
The film was stretched at a temperature of two stages of 0 ° C. and 160 at a magnification of 1.4 times and 1.1 times in the longitudinal direction and cooled. Further, both ends of the film are gripped with clips and guided to a width stretching tenter, stretched 1.3 times in the width direction at a temperature of 160 ° C., and then stretched 1.1 times in the width direction at a temperature of 190 ° C. Then, after heat-setting at a temperature of 200 ° C., a relaxation treatment is performed at a relaxation rate of 3% in the width direction in a cooling zone of 150 ° C.,
Further, the film was subjected to a relaxation treatment at a relaxation rate of 1.0% in the width direction in a zone at 100 ° C., and the film was gradually cooled to room temperature and wound up. The film thickness was adjusted to 6.7 μm by adjusting the extrusion amount.

Table 1 shows the film production conditions, and Table 2 shows the ratio (A / B) of the maximum thickness (A) of the edge portion of the unstretched film to the thickness (B) of the central portion in the width direction, the refractive index, and the crystallinity. And the refractive index, birefringence and crystallinity in the film forming process. Table 3
Young's modulus of the obtained film, half width of the diffraction peak,
Table 4 shows the crystal size, the Young's modulus in the oblique direction, the tear propagation resistance in the width direction, the refractive index in the thickness direction, the plane orientation coefficient, the density, and the surface roughness. Table 4 shows the creep compliance, heat shrink initiation temperature, and heat shrinkage at 80 ° C. And the running durability and storability of the magnetic tape.

[0077]

[Table 1]

[0078]

[Table 2]

[0079]

[Table 3]

[0080]

[Table 4]

[0081]

The Young's modulus (YmMD) in the longitudinal direction or the Young's modulus (Y in the width direction) of the film disclosed in the present invention.
mTD) has a Young's modulus of 7 GPa or more, and is obtained by rotating the polyester film around its normal line in a crystal orientation analysis by a wide-angle X-ray diffractometer method. A biaxially oriented polyester film having a half-width in the circumferential direction of the diffraction peak of the crystal plane in the range of 55 degrees or more and 85 degrees or less greatly improves the running durability and storage stability of a high-density magnetic recording tape. It is a film and its industrial value is extremely high.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI theme coat ゛ (Reference) B29L 9:00

Claims (10)

[Claims] 1. A biaxially oriented polyester film having one of a Young's modulus in a longitudinal direction (YmMD) or a Young's modulus in a width direction (YmTD) of 7 GPa or more, and a wide-angle X-ray diffractometer method. In the crystal orientation analysis by, the obtained half-width in the circumferential direction of the diffraction peak of the crystal plane in the main chain direction of the polyester film obtained when the polyester film is rotated around its normal line is from 55 degrees to 85 degrees. A biaxially oriented polyester film characterized by being within the range. 2. The crystal size in the polyester main chain direction is as follows:
The biaxially oriented polyester film according to claim 1, which is in a range from 45 ° to 90 °. 3. The sum of the Young's modulus in the longitudinal direction (YmMD) and the Young's modulus in the width direction (YmTD) is from 13 GPa or more to 2
3. The method according to claim 1, wherein the Young's modulus in a direction of 5 GPa or less and a diagonal direction (a direction of 45 degrees or 135 degrees when the longitudinal direction is 90 degrees and the width direction is 0 degrees) is in a range of 6 GPa or more to 10 GPa or less. 4. Biaxially oriented polyester film. 4. A creep compliance of 0.11 G after a lapse of 30 minutes at a temperature of 50 ° C. and a load of 28 MPa.
The biaxially oriented polyester film according to any one of claims 1 to 3, which is in a range from Pa ^-1 or more to 0.35 GPa ^-1 or less. 5. The biaxially oriented polyester film according to claim 1, wherein the tear propagation resistance in the width direction when the film thickness is converted to 5 μm is in the range of 0.7 g or more and 1.8 g or less. 6. The biaxially oriented polyester film according to claim 1, wherein the polyester is polyethylene terephthalate. 7. The refractive index (n _ZD ) in the thickness direction is 1.470.
From the above, 1.485 or less, the plane orientation coefficient (f _n ) is 0.1
The biaxially oriented polyester film according to claim 6, which is in a range of 75 or more to 0.195 or less. 8. The biaxially oriented polyester film according to claim 6, wherein the density of the film is in the range of 1.385 or more to 1.400 or less. 9. The biaxially oriented polyester film according to claim 6, wherein a heat shrinkage initiation temperature of the film is 70 ° C. or more and a heat shrinkage at a temperature of 80 ° C. is 0.5% or less. 10. A high-density magnetic recording medium using the biaxially oriented polyester film according to claim 1 as a base film.