JPH0733964A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the title film of high quality which is excellent in surface smoothness, slip property, high-speed winding, and scratch resistance. CONSTITUTION:The film contains (A) synthetic calcium carbonate particles having an average particle diameter of 0.8-1.5mum, (B) calcium carbonate particles having an average particle diameter of 0.4-0.7mum, (C) kaolin particles having an average particle diameter of 0.2-0.6mum, and (D) fine particles of at least one inorganic oxide which have particle diameters of 0.03-0.1mum. The amounts of the particles (A), the sum of the particles (B) and (C), and the sum of the particles (C) and (D) are 0.004-0.1wt.%, 0.2-0.6wt.%, and more than 0.5wt.% but not more than 1.0wt.%, respectively, based on the film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, and more particularly to a polyester film for a magnetic recording medium which is excellent in flat slipperiness, scratch resistance and winding property.

[0002]

2. Description of the Related Art Generally, polyester represented by polyethylene terephthalate is widely used for magnetic recording media such as magnetic tapes, floppy disks and data cartridges because it has excellent physical and chemical characteristics.

When used as a biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors that affect the workability of the film manufacturing process and the processing process in each application, and further the quality of the product. Has become. Especially when used as a magnetic tape coated with a magnetic material on the surface of a polyester film, the friction between the coating roll and the film surface at the time of coating the magnetic material and the resulting abrasion of the film are extremely severe,
Wrinkles and scratches on the film surface are likely to occur.

In recent years, in order to reduce the cost, along with the speeding up in each manufacturing process of video tapes and soft tapes and the use of inexpensive parts, there has been a further demand for improvement in the abrasion resistance of the base film and the winding property at high speeds. It's getting stronger.

In particular, in the case of manufacturing a video tape for software, which has been in increasing demand in recent years, there is a step of dubbing a blank tape in a Baumkuchen shape from a master tape at a high speed, and then winding the dubbed tape in a Baumkuchen shape again. During this high-speed dubbing, the fixed guide roll scratches the tape and scrapes the tape, resulting in white powder. As a result, there arises a problem that dropout (loss of signal) increases. Further, after high-speed dubbing, a winding deviation may occur in the step of winding the tape in a Baumkuchen shape again, and in a severe case, the tape may pop out, making it difficult to wind.

In the step of loading the tape into the cassette, particularly when a rough guide pin having a rough surface is used for cost reduction, scratches are generated on the surface of the tape to generate white powder, resulting in an increase in dropout. There is also a problem.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide a high quality polyester film for a magnetic recording medium, which is excellent in flat slipperiness, scratch resistance and winding property. To provide.

[0008]

The polyester film for a magnetic recording medium of the present invention has an average particle size of 0.8 to 1.5 μm.
m of the synthetic calcium carbonate particles (A) and an average particle size of 0.
4-0.7 μm calcium carbonate particles (B), average particle size 0.2-0.6 μm kaolin particles (C), and particle size 0.03-0.1 μm at least one inorganic oxide A biaxially oriented polyester film for a magnetic recording medium, comprising the fine particles (D) composed of a substance, wherein the synthetic calcium carbonate particles (A) are contained in the polyester film in an amount of 0.004 to 0.1% by weight. % Of the calcium carbonate particles (B) and the kaolin particles (C),
In the polyester film, the total amount is 0.2 to
0.6% by weight, and the total amount of the kaolin particles (C) and the fine particles (D) is more than 0.5% by weight and 1.0% by weight or less in the polyester film. It is contained in a proportion, whereby the above object is achieved.

The polyester used in the present invention is a crystalline polyester whose main repeating unit is ethylene terephthalate, but is not particularly limited. However, it is preferable that 80 mol% or more of the repeating units consist of ethylene terephthalate.

Other copolymerizable components include dicarboxylic acid components such as isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-dicarboxyldiphenyl, 4,4'-. Examples include dicarboxylbenzophenone, bis (4-carboxylphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4dicarboxylic acid. Examples of the glycol component include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. An oxycarboxylic acid component such as p-oxybenzoic acid may also be included. As another copolymerization component, a small amount of a compound containing an amide bond, a urethane bond, an ether bond, a carbonate bond or the like may be contained.

In the present invention, the polyester can be produced by any method such as direct reaction of aromatic dicarboxylic acid and glycol, direct polymerization method, transesterification reaction of dimethyl ester of aromatic carboxylic acid with glycol, and transesterification method. Can be used.

In the present invention, at least four kinds of particles having different raw materials and average particle diameters are contained in the film, and these particles have different functions to improve film characteristics.

The synthetic calcium carbonate particles (A) are contained in the film for the purpose of improving the winding property especially at high speed after forming the magnetic tape. The average particle size of the synthetic calcium carbonate particles (A) is 0.8 to 1.5 μm. Preferably 0.
9 to 1.3 μm, more preferably 1.0 to 1.2
μm. When the average particle size is less than 0.8 μm, the winding property of the film under high speed running becomes insufficient. Conversely, 1.5
If it exceeds μm, especially in the case of a video tape, the surface flatness of the obtained film deteriorates, and the electromagnetic conversion characteristics after forming a magnetic tape deteriorate. Furthermore, scratch resistance is also deteriorated.

The synthetic calcium carbonate particles (A) are contained in the polyester film in a proportion of 0.004 to 0.1% by weight. Preferably, the content ratio is 0.01 to
0.09% by weight, more preferably 0.02 to
It is 0.1% by weight. When the content is less than 0.004% by weight, the protrusion density on the film surface becomes low,
The winding property at high speed becomes insufficient. Conversely, 0.1% by weight
If it is contained in a ratio exceeding 1, the surface flatness of the obtained film is lowered, especially in the case of a video tape, and the electromagnetic conversion characteristics after forming a magnetic tape are deteriorated. Furthermore, scratch resistance is also deteriorated.

It is particularly preferable that the synthetic calcium carbonate particles (A) used in the present invention are synthetic calcium carbonate particles (A) having a calcite type or vaterite type structure.

Further, in the present invention, the particle form of the synthetic calcium carbonate particles (A) is preferably close to spherical and uniform in particle size from the viewpoint of slipperiness and winding property.
The “particles close to spherical” in the present invention means that the “area ratio of the particles to the circumscribed circle” defined by the following formula (II) is 75.
Refers to particles in the range of -100%. In the present invention, “particles having a particle size that is almost uniform” has a “particle size variation degree” of 20 defined by the following formulas (III) and (IV).
% Or less of particles. If the degree of variation in particle size exceeds 20%, the protrusion shape on the film surface becomes irregular,
It becomes difficult to precisely adjust the projection form on the film surface.

[0017]

[Equation 1]

[0018]

[Equation 2]

[0019]

[Equation 3]

In order to further increase the affinity between the polyester and the synthetic calcium carbonate particles (A), for example, Japanese Patent Application Laid-Open No. 2 (1994)
The surface of the synthetic calcium carbonate particles (A) may be treated with a compound such as a polyether-based acrylic copolymer salt disclosed in JP-A-178333.

The calcium carbonate particles (B) used as the second particles of the present invention are contained mainly for improving the slipperiness and running properties of the film. The winding property is not so high as that of the synthetic calcium carbonate particles (A), but it has an improving effect.
The average particle size of the calcium carbonate particles (B) is 0.4 to 0.
It is 7 μm. The thickness is preferably 0.43 to 0.65 μm, and more preferably 0.45 to 0.6 μm. When the average particle size is less than 0.4 μm, the slipperiness and the running property are insufficient. In addition, the winding property becomes poor. Conversely, 0.7
When the thickness exceeds μm, the surface smoothness of the obtained film is poor, especially in the case of a video tape, and the electromagnetic conversion characteristics after forming a magnetic tape are deteriorated. The calcium carbonate particles (B) may be natural products or synthetic products, but the particle structure is preferably either calcite type or vaterite type.

The kaolin particles (C) used as the third particles are contained mainly for improving the slipperiness and scratch resistance of the film. The kaolin particles also have the effect of improving the winding property, although they are not as effective as the synthetic calcium carbonate particles (A). Further, although not as good as the calcium carbonate particles (B), there is also an effect of improving the running property. The average particle diameter of the kaolin particles (C) is 0.2 to 0.6 μm. It is preferably 0.25 to 0.55 μm, more preferably 0.
It is 3 to 0.5 μm. If the average particle size is less than 0.2 μm, slipperiness and scratch resistance will be insufficient. Rollability and runnability are also reduced. On the other hand, when the thickness exceeds 0.6 μm, the surface smoothness of the obtained film is deteriorated, especially in the case of a video tape, and the electromagnetic conversion characteristics after forming a magnetic tape are deteriorated. Considering the scratch resistance, the kaolin particles (C) are not synthetic spherical particles, but natural plate-like particles.

The total content of calcium carbonate particles (B) and kaolin particles (C) must be 0.2 to 0.6% by weight. Preferably 0.25 to 0.55% by weight
And more preferably 0.3 to 0.5% by weight.
When the total content of the calcium carbonate particles (B) and the kaolin particles (C) is less than 0.2% by weight, slipperiness, winding property,
And the running performance becomes insufficient. The degree of the effect of improving scratch resistance is also reduced. On the contrary, if it exceeds 0.6% by weight,
Particularly in the case of a video tape, the surface smoothness of the obtained film is deteriorated and the electromagnetic conversion characteristics after forming a magnetic tape are deteriorated.

Further, the fine particles (D) composed of at least one inorganic oxide used as the fourth particles are contained for improving scratch resistance, and particularly scratch resistance with a guide pin having a rough surface. Included for improvement. As the fine particles (D) used in the present invention, single-component inorganic oxide particles such as titanium oxide, silica and alumina, or inorganic composite oxide particles thereof (for example,
Silica-titanium oxide, silica-alumina, titanium oxide-
Alumina particles) are exemplified. These fine particles are synthesized by, for example, a sol-gel method or a high temperature hydrolysis method (gas phase method).

The average particle size of the fine particles (D) used in the present invention must be 0.03 to 0.1 μm. The thickness is preferably 0.04 to 0.09 μm, and more preferably 0.05 to 0.08 μm. Average particle size is 0.03μ
With m, the effect of improving scratch resistance becomes insufficient. 0.
If it exceeds 1 μm, the effect of improving scratch resistance decreases. In particular, when it is 0.3 μm or more, the fine particles that have fallen off give a scratch to the film surface, and the effect of improving scratch resistance becomes insufficient. The total content of the kaolin particles (C) and the fine particles (D) must be more than 0.5% by weight and 1.0% by weight or less. If it is 0.5% by weight or less, the effect of improving scratch resistance cannot be sufficiently exhibited. The total content of the kaolin particles (C) and the fine particles (D) is 0.55 in terms of the scratch resistance improving effect and the economical efficiency.
It is desirable to set it to 0.8% by weight.

In the present invention, the winding index (f) of the film defined by the following formula (I) is set to less than 20 from the viewpoint of improving the winding property of the tape in the high speed dubbing process and the high speed loading process after forming the magnetic tape. It is preferable.

F = 249 (μs ^0.5 · μd ³ · AL ^0.1 ) / t ^0.06 (I) where μs is a coefficient of static friction, μd is a coefficient of dynamic friction, AL is an air leakage index (sec), and t is a film thickness (μm ).

In order to make the winding index (f) less than 20, it is preferable to coat the surface of the film with a known lubricant in addition to containing the above particles in the film in the present invention.
Alternatively, a known antistatic agent is applied to the film surface, and the film surface specific resistance value is 23 ° C and 65% RH (relative humidity).
It is also preferable to adjust to 1 × 10 ⁹ Ω / □ or less, particularly to 1 × 10 ¹² Ω / □ or less at 23 ° C. and 40% RH.

The polyester and each particle can be mixed by any method. These particles may be mixed with the molten polyester, but it is preferable to add each particle to the polyester polymerization reaction system. Considering the prevention of scattering of particles, the supply accuracy, and the dispersibility of particles, it is preferable to disperse these particles in the form of a slurry, and it is particularly preferable to add them as a slurry of ethylene glycol which is a component of polyester. As the slurry concentration,
5-20% by weight is suitable.

In the case of dispersing in a slurry form, in order to reduce coarse projections on the film surface, known dispersing methods (high pressure type homogeneous dispersing method, media dispersing method, ultrasonic dispersing method, etc.), centrifugation, filtration are carried out. Is preferably adopted.

When the slurry is dispersed, phosphoric acid, sodium hexametaphosphate, sodium polyphosphate, sodium tripolyphosphate, phosphorus element-containing compounds such as ammonium phosphate, tetraethylammonium hydroxide, hydroxylamine, and ammonium salts of acrylic copolymers. When a cationic, anionic, amphoteric or nonionic surfactant such as a nitrogen atom-containing compound such as a sodium ion or potassium ion, or a dispersant such as a water-soluble polymer is used. Further, the dispersibility of the particles in the slurry and the polymer is further improved. By adding these dispersants, electric charges are generated on the surface of the fine particles, the dispersibility of the fine particles in the slurry and the polymer is further improved, and the formation of coarse particles causing dropout and the like is suppressed.

The addition of each particle in the present invention to the polyester of the ethylene glycol slurry can be carried out at any stage of the polyester production process, but the initial polycondensation is completed after the transesterification reaction or the esterification reaction. It is particularly preferable to add the above. Particularly when the fine particles (D) are silica fine particles, it is preferable to add them at a stage where the temperature inside the reaction vessel before the start of transesterification reaction or before the start of esterification reaction is 100 ° C. or less from the viewpoint of particle dispersibility. Furthermore, a master chip containing at least one to three kinds of fine particles in high concentration is prepared,
These master chips may be appropriately blended, or if necessary, blended and diluted with a polyester (bright resin) containing no particles to adjust the concentration appropriately.

The film of the present invention may be a monolayer film, but if the surface layer (A) of the film is within the range of the kind, particle size and blending amount of the particles specified in the present invention, it may be A / B / A or the like. It may be a laminated film composed of at least three layers. For example, it is possible to add another function such as a light shielding property to the B layer, or to use a recovered product for the B layer for cost reduction. Furthermore, in order to improve the easy adhesion to the magnetic layer on one side of the film of the present invention, JP-A-4-253738.
The coating agent containing a water-based polymer as a film-forming component described in Japanese Patent Publication No. JP-A-2003-12088 may be thinly coated.

The method for producing the biaxially oriented polyester film of the present invention may be any method and is not particularly limited. For example, there are the following production methods.

The unstretched film melt-extruded on a chill roll is stretched at a temperature of (Tg-10) ° C. to (Tg + 70) ° C. (where Tg is the glass transition temperature of polyester) between rolls or a stenter in the longitudinal direction or the width direction. .5-
It is stretched 5.0 times, preferably 3.0 to 4.5 times. Then, in the direction perpendicular to the stretching direction of the first axis (Tg) ° C.
Stretching is carried out at a temperature of (Tg + 70) ° C. to 2.5 to 5.0 times, preferably 3 to 4 times. Furthermore, (Tg + 70) ° C ~
Heat fixing at (Tm) ° C. (Tm: melting point of polyester) for 1 to 60 seconds. For example, in the case of polyethylene terephthalate, it is heat set at a temperature of 180 to 230 ° C. for 2 to 7 seconds.

Magnetic powder is applied to the surface of the biaxially oriented polyester film obtained above by a conventional method to obtain a magnetic recording medium such as a magnetic recording tape or disk.

[0037]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. Unless otherwise specified, all parts in the examples and comparative examples mean parts by weight.

The measuring methods of the particles and films obtained in Examples and Comparative Examples are shown below.

(1) Average Particle Size The particle size distribution of fine particles obtained by sufficiently dispersing in ethylene glycol slurry was measured by using a light transmission type centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type: manufactured by Shimadzu Corporation). Was measured, and the value at which the integrated value was 50% was taken as the average particle size.

(2) Average Thickness (t) Ten films were stacked and ten points of film thickness (μ were measured using an electronic thickness meter Milltron manufactured by Feinpruf.
m) was measured, and the average value was defined as the average film thickness (μm).

(3) 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.

(4) Coefficient of Friction (μs, μd) According to ASTM D-1894-63, a static friction coefficient (μs) between films under the environmental conditions of 23 ° C. and 65% RH using a thread type slip tester. ) And the dynamic friction coefficient (μd) were measured.

(5) Air leak index (AL) The air leak index on the film surface was measured using the apparatus shown in FIG. This apparatus has a base 1, a film retainer 2 for fixing the film 4 on the base 1, and a film retainer 8 for fixing the film 5 on the film retainer 2. It has a vacuum pump 6 for eliminating the air in the gap between 5. First, the base 1
The film 4 is placed on top of the above with the B side (the side opposite to the side in contact with the chill roll) facing up. Next, the film retainer 2
Is placed on the base 1 so as to sandwich the film 4 and fixed, whereby the film 4 is fixed while applying tension. Then, the film 5 is placed on the film retainer 2 with the A surface (contact surface with the chill roll) facing down. Next, the film retainer 8 is placed on the film 5, and the film retainers 8 and 2 are fixed on the base 1 by using the screw 3. Next, the cavity 2 a and the pores 2 c provided in the film retainer 2 are connected to the vacuum pump 6 via the pipe 7. Then, when the vacuum pump 6 is driven, a tension is applied to the film 5 because the cavity 2a becomes a vacuum.

At the same time, the space between the film 4 and the film 5 is also decompressed by the vacuum pump through the pores 2d provided in the film holder 2 in a circumferential shape, and the surfaces of the film 4 and the film 5 in contact with each other are Start to adhere from the outer periphery. The state of close contact can be easily known by observing interference fringes from the upper part of the overlapping surfaces. Then, the time (seconds) from the occurrence of interference fringes on the outer peripheral portions of the overlapping surfaces of the film 4 and the film 5 to the spreading of the interference fringes on the entire surface of the overlapping surfaces until the movement stopped was measured. The measurement was performed 5 times, and the average value (second) was taken as the air leakage index.

(6) Winding index (f) Since the winding index defined by the following formula (I) has a strong correlation with the winding shape at the time of high speed dubbing after magnetic tape formation or high speed loading, the winding index (f) ) Was used to evaluate the appearance of the wound magnetic tape. The winding index (f) was ranked as follows from the winding shape of the tape in the high-speed dubbing process or the high-speed loading process after forming the magnetic tape.

F = 249 (μs ^0.5 · μd ³ · AL ^0.1 ) / t ^0.06 (I) where μs is the static friction coefficient, μd is the dynamic friction coefficient, AL is the air leakage index (sec), and t is the film thickness (μm). ).

[0047] (7) Scratch resistance The scratch resistance was measured using the apparatus shown in FIG. In this apparatus, the film 10 is unwound from a roll 14, passed through a plurality of rolls, a capstin 11, and a hard chrome-plated fixed metal pin (surface roughness: 3S) 13, and wound up by a roll 15. The tension of the film 10 is detected by the tension detecting device 12. The measurement conditions are as follows.

Width 1/2 in an atmosphere of 23 ° C. and 65% RH
The film 10 slit into inches is brought into contact with a hard chrome-plated fixed metal pin 13 at an angle of 90 °, and tension 1
Run 90 m at 127 cm / sec while giving 00 g. After running, a sample of the film was vapor-deposited with aluminum, and then the entire width of the film was observed with a microscope, and the number of scratches was visually determined and ranked as follows.

Number of scratches ◎: None ○: Small △: Intermediate between ○ and × ×: Large XX: Extremely large (Example 1) When the temperature of the esterification reaction vessel was raised to 200 ° C, terephthalate was reached. 86.4 parts of acid and 64.6 parts of ethylene glycol were charged, and while stirring, 0.03 parts of antimony trioxide, 0.088 parts of magnesium acetate tetrahydrate and 0.18 parts of triethylamine were used as a catalyst.
I prepared 6 copies. Next, the temperature is increased by pressurization and the gauge pressure is 3.
After performing the pressure esterification reaction under the conditions of 5 kg / cm ² and 240 ° C., the pressure inside the esterification reaction vessel was returned to normal pressure, and 0.040 parts of trimethyl phosphate was added. After further heating to 260 ° C. and adding trimethyl phosphate for 30 minutes, 2.0 parts as a particle content of an ethylene glycol slurry of calcite type synthetic calcium carbonate particles (A) having an average particle size of 0.88 μm was added. did. After 30 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction vessel and subjected to a polycondensation reaction under reduced pressure at 280 ° C. to obtain a polyester having an intrinsic viscosity of 0.62 [this is referred to as polyester (A)] Do].

In the production of the above polyester (A),
Polymerization was carried out in the same manner except that calcite-type synthetic calcium carbonate particles (A) having an average particle size of 0.47 μm were used in place of the synthetic calcium carbonate particles (A) to obtain a polyester having an intrinsic viscosity of 0.62. [This is referred to as polyester (B)].

Further, in the production of the above polyester (A), polymerization was carried out in the same manner except that kaolin particles (C) having an average particle size of 0.37 μm were used in place of the synthetic calcium carbonate particles (A). A polyester having a viscosity of 0.62 was obtained [this is referred to as polyester (C)].

Further, instead of adding the synthetic calcium carbonate particles (A), Al / S having an average particle diameter of 0.07 μm.
i-type complex oxide fine particles (D) (where Al is Al + Si
Of ethylene glycol slurry having a molar ratio of 0.67) is added as a particle content of 2.0 parts, and the amount of trimethyl phosphate added is 0.045 parts. Polymerization was performed in the same manner as in the production method of the polyester (A) except that the time until the addition of D) was 15 minutes, and the intrinsic viscosity was 0.
58 polyesters were obtained [this is polyester (D)
]].

Further, in the production of the above polyester (A), the synthetic calcium carbonate particles (A) were not added, and a polyester having an intrinsic viscosity of 0.620 containing no fine particles was obtained [this is a polyester (E) ]].

Then, polyesters (A), (B),
2.5: 1 for (C), (D), and (E) respectively
After mixing in a weight ratio of 0: 7.5: 20: 60 and drying 29
Melt extrusion at 0 ° C to form a film, which is
Was stretched 3.6 times in the machine direction and 3.7 times in the transverse direction at 110 ° C. 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) Without using the polyester (A) containing the synthetic calcium carbonate particles (A), only the polyesters (B), (C), (D) and (E) were mixed at 9: 7. A film was obtained in the same manner as in Example 1 except that the mixture was carried out at a weight ratio of 5: 20: 63.5. In Comparative Example 1, the content of the synthetic calcium carbonate particles (A) is outside the range of the present invention.

Comparative Example 2 Without using the polyester (B) containing the calcium carbonate particles (B), only the polyesters (A), (C), (D) and (E) were 2.5:
A film was obtained in the same manner as in Example 1, except that the weight ratio was 7.5: 20: 70. In this comparative example 2,
The content of calcium carbonate particles (B) and kaolin particles (C) is outside the range of the present invention.

Comparative Example 3 Polyester (D) containing fine particles (D) composed of at least one inorganic oxide was not used, but polyesters (A), (B),
2.5: 9: 7.5: 81 only for (C) and (E)
A film was obtained in the same manner as in Example 1 except that the film was mixed in the weight ratio of. In Comparative Example 4, kaolin particles (C)
The content of the fine particles (D) is out of the range of the present invention.

Example 2 Instead of the calcite type synthetic calcium carbonate particles having an average particle size of 0.88 μm contained in the polyester (A) prepared in Example 1, a vaterite type synthesis having an average particle size of 0.75 μm was used. Polyester (A ') having an intrinsic viscosity of 0.62 was obtained by using calcium carbonate particles. A film was obtained in the same manner as in Example 1 except that the polyester (A ′) was used instead of the polyester (A).

Comparative Example 5 Polyesters (A '), (B), (C), (D), so that the content of the synthetic calcium carbonate particles (A) in the film would be 1800 ppm.
A film was obtained in the same manner as in Example 2, except that (E) and (E) were mixed in a weight ratio of 10: 9: 7.5: 20: 53.5. In Comparative Example 5, the content of the synthetic calcium carbonate particles (A) is outside the range of the present invention.

Comparative Example 6 Polyesters (A), (B), (C), so that the contents of calcium carbonate particles (B) and kaolin particles (C) in the film were 500 ppm and 1200 ppm, respectively. A film was obtained in the same manner as in Example 2 except that (D) and (E) were mixed in a weight ratio of 10: 2.5: 6: 20: 61.5. In Comparative Example 6, the contents of the calcium carbonate particles (B) and the kaolin particles (C) are outside the range of the present invention.

(Example 3) Al having an average particle size of 0.07 μm contained in the polyester (D) prepared in Example 1
/ Si based complex oxide fine particles, spherical silica having an average particle diameter of 0.045 μm is used as fine particles (D) composed of at least one inorganic oxide, and polyester (D Got '). A film was obtained in the same manner as in Example 1 except that polyester (D ') was used instead of polyester (D).

(Comparative Example 7) In Example 3, polyesters (A), (B), (C), and (C) were prepared so that the content of spherical silica (D) in the film was 1000 ppm.
2.5: 9: 7.5: 5: 76 for (D) and (E)
A film was obtained in the same manner as in Example 3 except that the film was mixed in the weight ratio of. In Comparative Example 7, kaolin particles (C)
The content of the fine particles (D) is out of the range of the present invention.

Example 4 A film was obtained in the same manner as in Example 3 except that the surface of the film was antistatic coated.
Specifically, the following operation was performed. First, polyesters (A), (B), (C), (D '), and (E) were mixed in a weight ratio of 2.5: 9: 7.5: 20: 61, respectively, and dried at 290 ° C. Was melt-extruded to prepare an unstretched film. The unstretched film was stretched at 90 ° C. in the machine direction 3.
After stretching 6 times, a coating solution consisting of sodium alkylbenzene sulfonate / water / isophthalic acid (= 2/63/35) was applied on the surface, and at 110 ° C. in the lateral direction.
It was stretched 7 times. Then heat-treat at 220 ℃, thickness 15
A biaxially oriented polyester film of μm was obtained. The surface resistivity of the film at 23 ° C. and 65% RH is 8.8 ×
It was 10 ⁸ Ω / □.

[0064]

[Table 1]

As is clear from Table 1, all of the biaxially oriented polyester films for magnetic recording media obtained in Examples 1 to 4 were excellent in flatness and slipperiness, and had good winding property under high speed running and resistance to abrasion. It can be seen that the scratchability is good and the quality is high. In particular, by further coating the surface of the film with an antistatic agent, the winding property under high speed running was further improved.

[0066]

INDUSTRIAL APPLICABILITY As described above, the biaxially oriented polyester film for magnetic recording medium obtained by the method of the present invention has different synthetic calcium carbonate particles (A ), Calcium carbonate particles (B) having a specific particle size, kaolin particles (C) having a specific particle size, and fine particles (D) composed of at least one inorganic oxide having a specific particle size in a specific ratio. There is. Therefore, it is possible to obtain a high-quality biaxially oriented polyester film for a magnetic recording medium, which is excellent in flat slipperiness, extremely excellent in winding property at high speed and scratch resistance.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring the air leak index of a film.

FIG. 2 is a schematic view of an apparatus for measuring scratch resistance of a film.

[Explanation of symbols]

 1 base 2 film retainer 3 screw 4,5 film 6 vacuum pump 7 pipe 8 film retainer 10 film 11 capstan 12 tension detector 13 hard chrome plating fixed metal pin 14 feeding roll 15 winding roll

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G11B 5/704 7215-5D // B29K 67:00

Claims (2)

[Claims] 1. A synthetic calcium carbonate particle (A) having an average particle size of 0.8 to 1.5 μm and an average particle size of 0.4 to 0.7 μm.
m calcium carbonate particles (B) and an average particle size of 0.2 to
Kaolin particles (C) of 0.6 μm and a particle size of 0.03 to
A biaxially oriented polyester film for a magnetic recording medium, which comprises fine particles (D) composed of at least one inorganic oxide having a particle size of 0.1 μm, wherein the synthetic calcium carbonate particles (A) are the polyester film. In the polyester film, the calcium carbonate particles (B) and the kaolin particles (C) are contained in a proportion of 0.004 to 0.1% by weight in a total amount of 0.2 to 0.6. %, And the kaolin particles (C) and the fine particles (D) are contained in the polyester film in a total amount of more than 0.5% by weight and 1.0% by weight or less. A biaxially oriented polyester film. 2. The winding index (f) defined by the following formula is 2
The biaxially oriented polyester film for a magnetic recording medium according to claim 1, which is less than 0: f = 249 (μs ^0.5 · μd ³ · AL ^0.1 ) / t ^0.06 (I) where μs is a coefficient of static friction and μd is Dynamic friction coefficient, AL is air leakage index (sec), and t is film thickness (μm).