JPH07225938A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high quality film excellent in flatness and lubricity having satisfactory running performance and wear resistance at the time of repetitive use and excellent also in running performance after storage at high temp. and humidity. CONSTITUTION:This polyester film contains 0.01-1.0wt.% spherical sodium calcium aluminosilicate particles having 0.6-2mum average particle diameter and 0.05-2wt.% practically amorphous fine particles of a multiple oxide having 0.01-0.2mum average particle diameter. The multiple oxide is a compd. consisting of two or more kinds of metallic elements including Al and oxygen. In the compd., the pref. molar ratio of Al to (Al+M) (M is metallic elements other than Al) is 0.3-0.9.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially oriented polyester film for magnetic recording media. More specifically, biaxial orientation for magnetic recording media that is flat and slippery, has good runnability and wear resistance during repeated use, and has excellent runnability after storage at high temperature and high humidity. Regarding polyester film.

[0002]

2. Description of the Related Art Generally, polyester is widely used for magnetic recording media such as magnetic tapes, floppy disks and data cartridges because of its excellent physical and chemical properties.

Particularly in the case of a magnetic tape having a polyester film surface coated with a magnetic material, it is generally used without a back coat layer for cost reduction except for some high grade grades. Therefore, during repeated use in a VTR or cassette tape recorder at room temperature, the base polyester film contacts and rubs against the guide pins, causing wear between them and causing problems such as poor running performance. There is. Further, when the tape is assembled in the cassette and then repeatedly run, white powder adheres to the surface of the plastic guide pin, resulting in the problem of head clogging.

Further, there are increasing opportunities to use magnetic recording media (for example, audio cassette tapes, video tapes, floppy disks, etc.) in automobiles and outdoors.
Along with the diversification of these usage environments, there is a problem that the running property becomes unstable after being stored in an environment of high temperature and high humidity (for example, 60 ° C. and 80 RH%). Further, usually, the deformation of the tape becomes remarkable at a high temperature, so that the distortion of the recording signal, that is, the so-called wow and flutter phenomenon easily occurs.

Generally, in order to improve the running property and abrasion resistance, it is sufficient to add inert fine particles to polyester to roughen the film surface. More specifically, a method for adjusting the form, particle size distribution, average particle size, and hardness of the inert fine particles is disclosed. On the other hand, in order to maintain good electromagnetic conversion characteristics, it is preferable to make the film surface as smooth as possible. Thus, it is generally difficult to satisfy both at the same time.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to solve these problems of the prior art, to be flat and slippery, to have good running property and wear resistance during repeated use, and to have high temperature and high temperature. An object of the present invention is to provide a high-quality biaxially oriented polyester film for a magnetic recording medium, which is excellent in running property after storage under high humidity.

[0007]

The present inventors have found that the present invention can achieve the above object. That is, the present invention provides 0.01 to 1.0% by weight of spherical sodium calcium aluminosilicate particles having an average particle size of 0.6 to 2 μm, and substantially amorphous particles having an average particle size of 0.01 to 0.2 μm. A biaxially oriented polyester film for a magnetic recording medium, characterized in that it contains 0.05 to 2% by weight of a conductive complex oxide fine particle. Further, in the present invention, the substantially amorphous composite oxide fine particles are composed of a compound composed of two or more different metal elements containing aluminum and an oxygen element, and the aluminum molar ratio [Al / (Al + M ) Molar ratio, M is a metal element other than Al] is 0.3 to 0.9. The biaxially oriented polyester film for magnetic recording media described above.

The polyester used in the present invention is not particularly limited as long as it is a crystalline polyester whose main repeating unit is ethylene terephthalate.
Further, it is particularly preferable that 80 mol% or more of the repeating unit consists of ethylene terephthalate.

In the polyester, copolymerization components other than the above (terephthalic acid, ethylene glycol) include isophthalic acid, p-β-oxyethoxybenzoic acid,
2,6-naphthalenedicarboxylic acid, 4,4'-dicarboxyl diphenyl, 4,4'-dicarboxyl benzophenone, bis- (4-carboxylphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, Dicarboxylic acid components such as cyclohexane-1,4-dicarboxylic acid; propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, polyethylene glycol,
A glycol component such as polypropylene glycol or polytetramethylene glycol; an oxycarboxylic acid component such as p-oxybenzoic acid can be arbitrarily selected and used.
Further, a compound containing a small amount of amide bond, urethane bond, ether bond, carbonate bond or the like may be contained as a copolymerization component.

In the present invention, as the method for producing polyester, a direct polymerization method in which a dicarboxylic acid and a glycol are directly reacted, a transesterification method in which a dimethyl ester of a dicarboxylic acid and a glycol are transesterified, etc.
Any manufacturing method can be applied.

In the present invention, 2 having different compositions and average particle sizes are used.
Specific kinds of particles (spherical sodium calcium aluminosilicate particles, complex oxide particles) are contained in the polyester film in a specific amount, and these particles serve to improve different film properties.

Spherical sodium calcium aluminosilicate particles are contained in the film for the purpose of improving the running property and abrasion resistance particularly during repeated use. The spherical sodium calcium aluminosilicate particles are composite oxide particles mainly composed of calcium (Ca), sodium (Na), aluminum (Al) and silicon (Si), and the Ca element as a constituent element. Is 3 to 10 wt% in terms of CaO, and Na element is 5 to 5 in terms of Na ₂ O.
12 wt%, Si element is 50-60 wt% in terms of SiO ₂ and Al element is 20-30 wt% in terms of Al ₂ O _3.
The particles are contained.

The average particle size of the spherical sodium calcium aluminosilicate particles is required to be 0.6 to 2 μm, preferably 0.7 to 1.6 μm, more preferably 0.8 to 1.2 μm. is there. Average particle size is 0.6 μm
When it is less than 1, the running property during repeated use is deteriorated, which is not preferable. On the other hand, when it exceeds 2 μm, the surface flatness of the obtained film is deteriorated and the electromagnetic conversion characteristics after forming a magnetic tape are deteriorated. Further, the running property and wear resistance during repeated use are also deteriorated.

The average particle diameter of the spherical sodium calcium aluminosilicate particles is improved by improving the particle dispersibility by wet crushing with a bead mill or the like and ultrasonic dispersion after mixing and stirring in a glycol component, or by centrifugal separation and filtration. By removing the agglomerated particles, the above range can be achieved.

The content of the spherical sodium calcium aluminosilicate particles is required to be 0.01 to 1.0% by weight in the polyester film, preferably 0.1 to 0.8% by weight, more preferably Is from 0.2
It is 0.6% by weight. If the content is less than 0.01% by weight, the running property during repeated use deteriorates. On the other hand, if the content exceeds 1.0% by weight, the running property after repeated use will reach a peak, which will be uneconomical in terms of cost, and the surface flatness of the resulting film will deteriorate, forming a magnetic tape. Later electromagnetic conversion characteristics are also deteriorated. Furthermore, the wear resistance during repeated use also deteriorates.

Further, the particle form of the spherical sodium calcium aluminosilicate particles is close to spherical and has a uniform particle size from the viewpoints of running property during repeated use, abrasion resistance, and fluctuation of reproduction output after magnetic tape formation. It is preferable to be close. The “particles close to a sphere” in the present invention means the following formula (I).

[0017]

[Equation 1]

The "area ratio of the particle to the circumscribing circle" defined by means a particle in the range of 90 to 100%. Further, “particles having a particle size that is almost uniform” means the following formulas (II) and (III)

[0019]

[Equation 2]

The "particle size variation degree" defined by is 20
% Or less of particles are shown.

If the degree of variation in particle size exceeds 20%, the projections on the film surface become irregular, and it tends to be difficult to precisely adjust the projections on the film surface. In addition, there is a tendency that the reproduction output fluctuation after the magnetic tape is formed becomes worse. That is, the “dispersion degree of particle diameter” is preferably 20% or less, and more preferably 10% or less. In order to reduce the "variation of particle size" to 20% or less, it is difficult to adopt the steps of crushing a natural product in ethylene glycol, centrifugation and filtration, and it is preferable to use a synthetic product. . However, it is preferable not only to use the synthetic product as it is, but also to improve particle dispersibility by wet disintegration and ultrasonic dispersion treatment in ethylene glycol, or to remove aggregated particles by centrifugation and filtration.

The substantially amorphous complex oxide fine particles (hereinafter sometimes simply referred to as complex oxide fine particles) used as the second particles in the present invention are mainly used under high temperature and high humidity (eg, It is contained in order to improve the running property of the film after storage in an environment of 60 ° C., 80 RH%, etc. Further, although not so much as the spherical sodium calcium aluminosilicate particles, it also has the effect of improving the running property and abrasion resistance during repeated use.

In the present invention, "substantially amorphous" means, for example, that the amorphous degree calculated from the peak in intense X-ray diffraction is 90% or more.

The composite oxide fine particles are composed of a compound composed of two or more different metal elements containing aluminum (Al) and an oxygen element, and are mainly Al-OM.
(M is a metal element other than Al) is an amorphous complex oxide composed of a bond. The metal element other than Al represented by M is preferably silicon (Si) or titanium (T
i), zirconium (Zr), tungsten (W), and the like. In addition, in the present invention, Si is also included in the metal element.

Specific examples of the complex oxide fine particles include binary complex oxide fine particles such as Al / Si, Al / Ti, and Al / Zr, Al / Si / Ti, Al / Si / Zr,
Examples include ternary complex oxide particles such as Al / Ti / Zr.

Al molar ratio of the complex oxide fine particles [Al
/ (Al + M) molar ratio, M is a metal element other than Al] is preferably 0.3 or more and 0.9 or less, and more preferably 0.5 to 0.8. If the Al molar ratio is less than 0.3, the particle dispersibility in polyester tends to be insufficient. On the other hand, when the Al molar ratio exceeds 0.9, the effect of improving wear resistance during repeated use tends to be insufficient.

The composite oxide fine particles are produced by various methods, but covalent AlCl ₃ , SiCl ₄ , and Ti are used.
Starting from metal chlorides such as Cl ₄ and ZrCl ₄ ,
The method of burning in the presence of hydrogen and oxygen is preferred.

The composite oxide fine particles thus obtained have a structure which is considerably different from a mixture of individual metal oxide fine particles (aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, etc.). That is, the composite oxide fine particles have a structure (Al-
It is formed by a complex oxide having a bond represented by OM) as a main constituent component, and depends on the abundance ratio of metal elements,
Structural features of each single metal oxide (eg, crystalline form)
Most of them are amorphous metal oxides having a very small value.

The complex oxide fine particles may contain impurities such as chlorine ions derived from the manufacturing process up to a ratio of 5% by weight or less with respect to the complex oxide fine particles.
When the impurity content (chlorine ion content) exceeds 5% by weight, thermal decomposition of the polyester tends to be remarkable during polyester polymerization and during melt extrusion of the polymer to prepare an unstretched sheet.

The average particle size of the composite oxide fine particles is 0.
It is necessary to be 01 to 0.2 μm. Preferably 0.0
3 to 0.15 μm, more preferably 0.05 to
It is 0.1 μm. If the average particle size exceeds 0.2 μm,
Abrasion resistance during repeated use and high temperature and high humidity (eg 6
The effect of improving the running property of the film after storage in an environment of 0 ° C., 80 RH%, etc. becomes insufficient. On the other hand, if it is less than 0.01 μm, the aggregation of the composite oxide fine particles in the polyester becomes severe, and coarse projections that adversely affect the electromagnetic conversion characteristics occur, which is not preferable. Even if aggregation is suppressed, the effect of improving the running property of the film after storage in an environment of high temperature and high humidity becomes insufficient.

Since the complex oxide fine particles are usually secondary agglomerated, a product having the above average particle size cannot be obtained by simply mixing and stirring a commercially available product as it is in the glycol component which is a raw material of polyester. Therefore, after mixing and stirring in a glycol component, the particle dispersibility is improved by wet crushing and ultrasonic dispersion using a bead mill, or by removing aggregated particles by centrifugation and filtration, the average particle size is within the above range. It needs to be adjusted. Also, at this time,
Substantially no particles of 2 μm or more, 0.5 μm
From the viewpoint of electromagnetic conversion characteristics and dropout, it is preferable that the volume content of particles of m or more is 5% or less.

The content of the composite oxide fine particles in the polyester film must be 0.05 to 2% by weight, preferably 0.1 to 1.5% by weight, more preferably 0.2. ~ 1% by weight. Content is 0.0
If it is less than 5% by weight, it may be exposed to high temperature and high humidity (eg 60 ° C, 80
The effect of improving the running property of the film after storage in an environment of (RH%, etc.) and the abrasion resistance during repeated use becomes insufficient. On the other hand, when the content exceeds 2% by weight, coarse projections are generated on the film surface due to aggregation of fine particles in the polyester, which causes deterioration of electromagnetic conversion characteristics and dropout.
Further, the wear resistance during repeated use also deteriorates.

As a method for adding the spherical sodium calcium aluminosilicate particles and the composite oxide fine particles to the polyester polymerization reaction system, the above particles are dispersed in a slurry form in terms of prevention of scattering of particles, supply accuracy and particle dispersibility. Is preferably added as a slurry of ethylene glycol. About 5 to 20% by weight is suitable as the slurry concentration.

The addition of the spherical sodium calcium aluminosilicate particles and the fine particles of the composite oxide to the polyester of the ethylene glycol slurry can be carried out at any stage in the polyester production process, but after the transesterification reaction or the esterification reaction. It is particularly preferable to add it after the end of the initial polycondensation.

In particular, when the direct polymerization method for producing polyester from dicarboxylic acid and glycol is adopted,
At any stage before the initiation of the initial polycondensation, a magnesium compound satisfying the following formula (IV) 0.04 ≦ Mg ≦ 0.12 (IV) is added, and the esterification reaction is substantially completed. At any stage from the start of the initial polycondensation, a phosphorus compound satisfying the following formula (V) 0.5 ≦ P / Mg ≦ 0.9 (V) is added, and then spherical sodium calcium aluminosilicate is added. It is preferable to complete the polycondensation after adding the particles and / or the fine particles of the composite oxide. Here, Mg and P represent mol% as a magnesium atom and a phosphorus atom with respect to 1 mol of polyester.

Furthermore, master chips containing a high concentration of each fine particle are individually prepared, and these master chips are appropriately blended, or if necessary, a polyester (bright resin) not containing the above fine particles is blended appropriately. -It may be diluted and adjusted to an appropriate concentration. Further, other inert fine particles may be contained for improving other characteristics as long as the effect of the present invention is not impaired.

The biaxially oriented polyester film of the present invention may be a single film, but if the film surface layer (A layer) is within the range regulated by the present invention, at least three layers such as A / B / A are selected. It may be a laminated film. For example, it is possible to add another functionality such as a light-shielding property to the B layer, or to use a recovered product for the B layer for cost reduction. Further, at least one surface of the film may be thinly coated with a coating agent containing an aqueous polymer as a film forming component, which is described in JP-A-4-253738, in order to improve the adhesion to the magnetic layer.

As the method for producing the biaxially oriented polyester film of the present invention, any method can be adopted and is not particularly limited.
An unstretched film melt-extruded on a chill roll is stretched in the longitudinal direction or the width direction (Tg) between rolls or a stenter.
-10) to (Tg + 70) ° C. (Tg: glass transition temperature of polyester) 2.5 to 5 times, preferably 3 to
Stretch 4.5 times. Then, at a temperature of Tg to (Tg + 70) ° C. in the direction perpendicular to the stretching direction of the first axis, 2.5 to 5
Stretching twice, preferably 3 to 4 times. Furthermore, (Tg +
70) to Tm ° C. (Tm: melting point of polyester) and heat set for 1 to 60 seconds. For example, in the case of polyethylene terephthalate, it is 2 to 7 at a temperature of 180 to 230 ° C.
Heat set for 2 seconds.

[0039]

EXAMPLES Next, examples and comparative examples of the present invention will be shown. The present invention is not limited to the examples below. All parts in the examples and comparative examples mean parts by weight unless otherwise specified.

The measuring method used in the experiment will be described below. (1) Average particle size The particle size distribution of fine particles obtained by sufficiently dispersing in ethylene glycol slurry was measured using a light transmission type centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type: manufactured by Shimadzu Corporation). The value at which the integrated value was 50% was used.

(2) Average surface roughness Using a Surfcom 300A type surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.), needle diameter 1 μm, load 0.07 g, measurement reference length 0.8 m.
The average roughness (Ra: μm) of the center line when measured under the conditions of m and cutoff of 0.08 mm.

(3) Sliding property (dynamic friction coefficient) In accordance with ASTM D-1894-63, a dynamic friction coefficient (μd) between films under the environmental conditions of 23 ° C. and 65 RH% using a thread type slip tester. ) Was measured.

(4) Runnability during repeated use The runnability during repeated use was measured using the apparatus shown in FIG. In FIG. 1, 1 is a film, 11 is a crank, 12 is a free roller, 13 is a tension detecting device, 14
Indicates a polyoxymethylene (POM) guide pin, and 15 indicates a weight.

Under an atmosphere of 23 ° C. and a relative humidity of 65%, a polyester film slit to a width of 1/2 inch was
1 for fixed guide pin made of polyoxymethylene (POM)
The contacts were made at an angle of 35 °. A weight was attached to one end of the film and a constant load of 50 g was applied. Then, a crank was attached to one end on the opposite side and rotated at 10 rpm / min. The coefficient of friction after reciprocating the film 150 times was measured, and the increase (Δμk) from the initial coefficient of friction was 5
It was evaluated in stages and represented by the following rankings.

⊚: less than 0.02 ◯: 0.02 to less than 0.05 Δ: 0.05 to less than 0.10 ×: 0.10 to less than 0.15 xx: 0.15 or more The running process When the minimum value appears in the friction coefficient,
It is represented by the increment from the minimum value.

(5) Abrasion resistance after repeated use After using the apparatus shown in FIG. 1 and reciprocating the film 150 times under the same conditions as in the evaluation of running property during repeated use,
After observing the amount of white powder adhering to the fixed guide pin made of polyoxymethylene (POM) with a stereomicroscope and taking a photograph, 5
Visual evaluation was performed at each stage and the following ranking was used.

◎: Almost no white powder adheres ○: Very small amount of white powder partially adheres to the contact surface △: Intermediate between ○ and × ×: Large amount of white powder partially adheres × ×: Large amount of white powder contacts Adheres to the entire surface

(6) Running property after storage under high temperature and high humidity After the film was stored for 1 week in an environment of 60 ° C. and 80 RH%, the running property of the film was measured using the apparatus shown in FIG. . In FIG. 2, 1 is a film, 21 is a capstan, 22 is a tension detecting device (inlet), 23 is a fixed guide pin made of polyoxymethylene (POM), and 24 is a tension detecting device (outlet).

Under an atmosphere of 23 ° C. and 65 RH%, the width is 3 /
A polyester film slit into 20 inches is attached to a fixed guide pin made of polyoxymethylene (POM) with θ =
The pieces were brought into contact with each other at an angle of (152/180) π radians (152 °) and allowed to run at a speed of 4.75 cm / sec. Adjust the inlet tension T1 to be 15g, and set the film to 9
The exit tension T2 (g) after traveling 0 m is detected by the tension detection device (exit) 24, and the following formula μk '= (2.303 / θ) log (T2 / T1) = 0.868 ・ log (T2 / 15) The running friction coefficient μk ′ was calculated, and the increase (Δμk ′) from the initial friction coefficient was evaluated on a scale of 5 and expressed in the following ranking.

⊚: less than 0.02 ◯: 0.02 to less than 0.05 Δ: 0.05 to less than 0.10 ×: 0.10 to less than 0.15 xx: 0.15 or more The running process When the minimum value appears in the friction coefficient,
It is represented by the increment from the minimum value.

Example 1 (Production of Polyester Containing Spherical Sodium Calcium Aluminosilicate Particles) The esterification reaction vessel was heated to 20
When the temperature reached 0 ° C., 86.4 parts of terephthalic acid and 64.6 parts of ethylene glycol were charged, and while stirring, 0.03 part of antimony trioxide and 0.088 part of magnesium acetate tetrahydrate were used as a catalyst. And 0.16 parts of triethylamine were charged. Next, the pressure and temperature are raised to carry out the pressure esterification reaction under the conditions of a gauge pressure of 3.5 kg / cm ² and 240 ° C., and then the inside of the esterification reaction vessel is returned to normal pressure, and 0.036 parts of trimethyl phosphate is Was added. 260 ° C
15 minutes after the temperature was raised to trimethyl phosphate, the coarse particles were cut by 30% by centrifugation, and the particles were filtered with a metal filter having an opening of 5 μm to give an average particle diameter of 0.80 μm.
The spherical sodium sodium aluminosilicate particles of ethylene glycol slurry having a particle content of 2.0
Parts were added. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction vessel and subjected to a polycondensation reaction at 280 ° C. under reduced pressure to obtain a polyester having an intrinsic viscosity of 0.62 [this is referred to as polyester (A)] Do].

(Production of Polyester Containing Fine Particles of Complex Oxide) In the above production method of polyester (A),
Instead of spherical sodium calcium aluminosilicate particles having an average particle diameter of 0.80 μm, the average particle diameter is 0.07 μ.
Polyester (A) except that substantially amorphous Al / Si-based composite oxide fine particles of m (Al molar ratio: 0.65) are used and the addition amount of trimethyl phosphate is 0.044 parts. Polymerization was performed in the same manner as in 1. to obtain a polyester having an intrinsic viscosity of 0.60 containing 2 parts by weight of the composite oxide fine particles [this is referred to as polyester (B)].

Furthermore, in the production of the above polyester (A), spherical sodium calcium aluminosilicate particles were not added, and a polyester having an intrinsic viscosity of 0.62 containing no spherical sodium calcium aluminosilicate particles was obtained. Polyester (C)].

Next, the polyesters (A), (B) and (C) were mixed in a weight ratio of 15:20:65, respectively,
After drying, it was melt-extruded at 290 ° C. and discharged in a sheet form from a T-shaped die. This molten sheet was wound around a cooling drum having a surface temperature of 30 ° C., and cooled and solidified to prepare an unstretched film. The unstretched film was stretched in the longitudinal direction at 90 ° C. by 3.6 times and then in the width direction at 110 ° C. in 3.7 times. Then, it heat-processed at 220 degreeC and obtained the biaxially oriented polyester film of 15 micrometers. The characteristics of this film are shown in Table 1.

Comparative Example 1 Example 1 was repeated except that the polyester (B) containing fine particles of composite oxide was not used, and only the polyester (A) and the polyester (C) were mixed at a weight ratio of 15:85.
A film was obtained in the same manner as in. In Comparative Example 1, the content of the composite oxide fine particles is outside the range of the present invention.

Comparative Example 2 The procedure was carried out except that the polyester (A) containing spherical sodium calcium aluminosilicate particles was not used and only the polyester (B) and the polyester (C) were mixed in a weight ratio of 20:80. A film was obtained in the same manner as in Example 1. In Comparative Example 2, the content of spherical sodium calcium aluminosilicate particles is outside the range of the present invention.

Comparative Example 3 Polyesters (A), (B) and (C) were each made to 75: 2 such that the content of spherical sodium calcium aluminosilicate particles in the film was 1.5% by weight.
A film was obtained in the same manner as in Example 1 except that the mixing ratio was 0: 5. In Comparative Example 3, the content of spherical sodium calcium aluminosilicate particles is outside the range of the present invention.

Comparative Example 4 Instead of the spherical sodium calcium aluminosilicate particles having an average particle size of 0.80 μm contained in the polyester (A) produced in Example 1, the average particle size was 3.0 μm.
Polyester having an intrinsic viscosity of 0.62 was obtained by using the spherical sodium calcium aluminosilicate particles of the above [this is referred to as polyester (D)]. Polyester (A)
A film was obtained in the same manner as in Example 1 except that polyester (D) was used instead of. In Comparative Example 4, the average particle size of the spherical sodium calcium aluminosilicate particles is outside the range of the present invention.

Example 2 Instead of the spherical sodium calcium aluminosilicate particles having an average particle size of 0.80 μm contained in the polyester (A) produced in Example 1, the average particle size was 1.12 μm.
A polyester having an intrinsic viscosity of 0.62 was obtained in the same manner as in Example 1 except that spherical sodium calcium aluminosilicate particles of m were used [this is referred to as polyester (E)]. Polyester (E) is used instead of polyester (A), and polyesters (E), (B) and (C) are mixed in a weight ratio of 20:20:60, and after drying 2
It was melt-extruded at 90 ° C. and discharged in a sheet form from a T-shaped die. This molten sheet was wound around a cooling drum having a surface temperature of 30 ° C., and cooled and solidified to prepare an unstretched film. This unstretched film was stretched 3.2 times at 110 ° C. in the width direction and then stretched 4.5 times at 80 ° C. in the longitudinal direction.
Then, it heat-processed at 220 degreeC and obtained the biaxially oriented polyester film of 7 micrometers.

Comparative Example 5 Instead of the substantially amorphous composite oxide fine particles (Al molar ratio: 0.65) contained in the polyester (B) prepared in Example 1 and having an average particle size of 0.07 μm. In addition, substantially amorphous composite oxide fine particles (A having an average particle diameter of 0.35 μm) (A
A polyester having an intrinsic viscosity of 0.62 was obtained in the same manner as in Example 1 except that 1 mol ratio: 0.65) was used [this is referred to as polyester (F)]. A film was obtained in the same manner as in Example 2 except that the polyester (F) was used instead of the polyester (B). In Comparative Example 5, the average particle size of the composite oxide fine particles is outside the range of the present invention.

[0061]

[Table 1]

As is clear from Table 1, Examples 1 and 2
The biaxially oriented polyester film for magnetic recording media of the present invention obtained in any of the above is excellent in flat slipperiness, good running property and abrasion resistance during repeated use, and further at high temperature.
It can be seen that the product has high running quality even after storage under high humidity and is of high quality.

[0063]

INDUSTRIAL APPLICABILITY The biaxially oriented polyester film for magnetic recording media of the present invention is excellent in flat slipperiness, good in running property during repeated use and good in abrasion resistance, and after storage at high temperature and high humidity. It is of high quality with excellent running performance.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for evaluating the running property and abrasion resistance of a film when repeatedly used.

FIG. 2 is a schematic view of an apparatus for evaluating the running property of a film after storage under high temperature and high humidity.

[Explanation of symbols]

 1 Film 11 Crank 12 Free Roller 13 Tension Detecting Device 14 Polyoxymethylene (POM) Fixed Guide Pin 15 Weight 21 Capstan 22 Tension Detecting Device (Inlet) 23 Polyoxymethylene (POM) Fixed Guide Pin 24 Tension Detecting Device ( exit)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area // B29K 67:00 105: 16 B29L 7:00

Claims (2)

[Claims] 1. Spherical sodium calcium aluminosilicate particles having an average particle size of 0.6 to 2 μm are added in an amount of 0.01 to 1.
Biaxially oriented polyester for magnetic recording medium, containing 0% by weight and 0.05 to 2% by weight of substantially amorphous composite oxide fine particles having an average particle diameter of 0.01 to 0.2 μm. the film. 2. The substantially amorphous composite oxide fine particles,
It is composed of a compound composed of two or more different metal elements containing aluminum and an oxygen element, and the compound has an aluminum molar ratio [Al / (Al + M) molar ratio, where M is a metal element other than Al] of 0.3 to 0. 9. The biaxially oriented polyester film for a magnetic recording medium according to claim 1, which is 9.