JPH0673205A - Biaxially oriented polyester film - Google Patents

Abstract

(57) [Summary] [Object] To provide a biaxially oriented polyester film which is excellent in abrasion resistance and therefore does not generate abrasion powder of the film in the calendaring process and is excellent in scratch resistance. [Structure] A polyester film comprising an acid component mainly containing an aromatic dicarboxylic acid and at least one glycol component. This polyester film contains 100 to 20000 of inert inorganic compound fine particles (A) having an average particle diameter of 0.01 to 1.0 μm and a Mohs hardness of 5 or more.
Inactive inorganic compound fine particles (B) having an average particle size of 0.1 to 2.0 μm and a Mohs hardness of 2.5 or more and less than 5 in the range of 100 ppm to 20000 ppm,
In addition, 10 particles of the inert inorganic compound (C) having an average particle diameter of 0.1 to 5.0 μm and a Mohs hardness of less than 2.5 are used.
It is contained in the range of 0 to 20000 ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film suitable as a base film for magnetic tape.

[0002]

2. Description of the Related Art Polyesters, particularly polyethylene terephthalate, have excellent physical and chemical properties, and biaxially oriented polyester films obtained by adding fine particles of inorganic compounds or organic compounds called lubricant particles to polyester are magnetic tapes. It is widely and commonly used as a film for use.

Recently, as the speed of the magnetic tape manufacturing process has been increased, there has been a demand for a film having more excellent abrasion resistance in the calendar processing in the magnetic tape manufacturing process. The calendering step is a step of forming a magnetic layer by coating and drying the magnetic layer composition on a polyester film, and then smoothing the surface of the magnetic layer. In this calendering process, since this film passes between the calender rolls to which extremely high pressure is applied, the projections on the film surface mainly formed by the lubricant are scraped off to generate abrasion powder. When such abrasion powder adheres to the calender roll surface, the magnetic layer surface of the film becomes rough,
As a result, the electrical characteristics of the resulting magnetic tape are degraded. Further, when a film having poor abrasion resistance is used as a magnetic tape, abrasion powder is also generated in the running system in the tape deck, resulting in deterioration of electrical characteristics of the magnetic tape and dropout.

Recently, the demand for scratch resistance in addition to abrasion resistance is increasing for magnetic tape base films. The scratches are scratches (for example, scratches of the tape with a cassette pin at the time of high-speed dubbing) that are applied to a portion in contact with the magnetic tape, and scratches that are scratched by the abrasion powder generated in the running system in the tape deck. Such a magnetic tape having poor scratch resistance causes contamination in the manufacturing process and an increase in dropout.

The above improvements in wear resistance and scratch resistance are very important because they lead to the improvement of the quality of the magnetic tape.

As a method for improving the abrasion resistance, for example, JP-A-60-195727 discloses a method of reducing the crystallinity of the base film.

However, in this method, when the film after coating the magnetic layer is slit into a predetermined width and processed into a magnetic tape,
There is a problem that so-called burr and mustache are significantly generated from the cut surface of the film and powder is generated, so that dropouts increase in the obtained magnetic tape.

As a method for improving the abrasion resistance and the scratch resistance, for example, JP-A No. 1-311131 discloses that certain fine particles as a lubricant in a polyester film, for example, an inert gas having a Mohs hardness of 6 or more. A method of adding fine particles is described.

Although this method improves the scratch resistance of the film, it does not have sufficient abrasion resistance.

[0010]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and its object is to have excellent abrasion resistance, and therefore, to prevent generation of abrasion powder of a film in the calendaring step, Another object of the present invention is to provide a biaxially oriented polyester film having excellent scratch resistance.

[0011]

The biaxially oriented polyester film of the present invention is a polyester film comprising an acid component mainly containing an aromatic dicarboxylic acid and at least one glycol component, wherein the polyester film is Inert inorganic compound fine particles (A) having an average particle size of 0.01 to 1.0 μm and a Mohs hardness of 5 or more are 100 to
The average particle size is 0.1 to 2.0 in the range of 20000 ppm.
Inactive inorganic compound fine particles (B) having a micrometer and a Mohs hardness of 2.5 or more and less than 5 are in the range of 100 to 20,000 ppm, and have an average particle size of 0.1 to 5.0 μm and a Mohs hardness of less than 2.5. The present invention is characterized by containing certain inactive inorganic compound fine particles (C) in the range of 100 to 20,000 ppm, whereby the above object can be achieved.

In a preferred embodiment, the inert inorganic compound fine particles (A) are at least one inorganic compound selected from the group consisting of alumina and silica,
The inactive inorganic compound fine particles (B) are calcium carbonate, and the inactive inorganic compound fine particles (C) are kaolin.

Next, the present invention will be described in detail.

The biaxially oriented polyester film of the present invention contains polyester as a main component. This polyester is composed of an acid component mainly containing an aromatic dicarboxylic acid and at least one glycol component, and it is preferable that 95 mol% or more of its constitutional unit is ethylene terephthalate.

Acid components other than terephthalic acid include:
Isophthalic acid, p-β-oxyethoxybenzoic acid, 2,
6-naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, 4,4'-dicarboxybenzophenone,
Bis (4-carboxyphenyl) ethane, adipic acid,
Dicarboxylic acids such as sebacic acid, 5-sodium sulfoisophthalic acid and cyclohexane-1,4-dicarboxylic acid can be mentioned. Further, glycol components other than ethylene glycol include propylene glycol, butanediol, neopentyl glycol, diethylene glycol,
Examples thereof include cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. An oxycarboxylic acid component such as p-oxybenzoic acid can also be used. In addition, 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 as a copolymerization component.

The biaxially oriented polyester film of the present invention has an inert inorganic compound fine particle (A) having a Mohs hardness of 5 or more, an inert inorganic compound fine particle (B) having a Mohs hardness of 2.5 or more and less than 5 and a Mohs hardness. Inert inorganic compound fine particles (C) of less than 2.5 are contained.

Examples of the inert inorganic compound fine particles (A) include titanium dioxide (TiO ₂ ), iron trioxide (Fe ₃ O ₄ ), silica (SiO ₂ ), silicon carbide (Si).
C) and alumina (Al ₂ O ₃ ), of which alumina and / or silica having a high affinity for polyester are most preferable from the viewpoint of abrasion resistance and scratch resistance of the obtained polyester film.

The above-mentioned alumina is crystalline alumina hydrate such as dibsite, bayerite, northlandite, boehmite, diaspore, todite; amorphous alumina hydrate such as amorphous gel, boehmite gel and bayerite gel. Ρ, η, γ, χ, κ, δ, θ type intermediate activated alumina; or α type alumina, of which δ type or γ type intermediate activated alumina is preferable.

The above-mentioned silica can be used in any form, but spherical silica is preferable from the viewpoint of scratch resistance of the polyester film obtained.

The average particle size of the above-mentioned inert inorganic compound fine particles (A) is 0.01 to 1.0 μm, preferably 0.1.
01 to 0.5 μm, particularly preferably 0.01 to 0.1 μm
m. When the average particle diameter of the above-mentioned inactive inorganic compound fine particles (A) exceeds 1.0 μm, coarse projections occur in the obtained polyester film, and the abrasion resistance of the film deteriorates. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used as a magnetic tape, it causes dropout. On the contrary, when the average particle size of the above-mentioned inactive inorganic compound fine particles (A) is less than 0.01 μm, a part of the inactive inorganic compound fine particles (A) is condensed in the polyester to form coarse particles, and thus the film is formed. Wear resistance deteriorates. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used as a magnetic tape, it causes dropout.

The particle size distribution of the above-mentioned fine particles of inert inorganic compound (A) is sharp and 1 in order to prevent film breakage and dropout when used in a magnetic tape.
It is preferable not to contain particles of 0 μm or more, 2 μm
The volume content of the above particles is particularly preferably 5% or less.

The content of the above-mentioned inert inorganic compound fine particles (A) in the biaxially oriented polyester film of the present invention is 10
0 to 10000 ppm, preferably 1500 to 7
000 ppm, particularly preferably 2000 to 500
It is 0 ppm. When the content of the above-mentioned inert inorganic compound fine particles (A) exceeds 10,000 ppm, the scratch resistance of the film obtained on the contrary is deteriorated because the above-mentioned inert inorganic compound fine particles (A) have high hardness. Furthermore, the heat resistance of the obtained film also decreases. On the contrary, when the content of the above-mentioned inactive inorganic compound fine particles (A) is less than 100 ppm, the obtained film does not have sufficient scratch resistance.

The inert inorganic compound fine particles (B) having a Mohs hardness of 2.5 or more and less than 5 are, for example, calcium carbonate (CaCO ₃ ), barium sulfate (BaS).
O ₄ ), calcium fluoride (CaF ₂ ), and the like. Among them, calcium carbonate (CaCO ₃ ) is most preferable from the viewpoint of the running property of the obtained polyester film.

The calcium carbonate particles are classified into trigonal or hexagonal calcite, orthorhombic aragonite, and hexagonal or pseudo-hexagonal vaterite according to their crystal structure. However, any crystal form may be used, and the shape thereof may be arbitrarily selected such as chain-like spherical particles, cubic, spindle-like, columnar or needle-like, spherical and oval.

The average particle diameter of the above-mentioned inert inorganic compound fine particles (B) is 0.1 to 5.0 μm, and preferably 0.1.
2 to 2.0 μm, particularly preferably 0.25 to 1.
It is 0 μm. When the average particle diameter of the inert inorganic compound fine particles (B) exceeds 5.0 μm, coarse projections are generated on the surface of the obtained film, and the abrasion resistance of the film deteriorates. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used for a magnetic tape, it causes dropout. On the contrary, the average particle size of the inert inorganic compound fine particles (B) is 0.
When it is less than 1 μm, a part of the inert inorganic compound fine particles (B) is condensed in the polyester to form coarse particles, so that the abrasion resistance of the film is deteriorated. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used for a magnetic tape, it causes dropout.

The particle size distribution of the above-mentioned fine particles (B) of inert inorganic compound is sharp and 1 in order to prevent film breakage and dropout when used for magnetic tape.
It is preferable not to contain particles of 0 μm or more, 5 μm
The volume content of the above particles is particularly preferably 5% or less.

The content of the above-mentioned inert inorganic compound fine particles (B) in the biaxially oriented polyester film of the present invention is 10
0 to 20000 ppm, preferably 500 to 70
It is 00 ppm. Particularly preferably 1000 to 6000
It is ppm. When the content of the above-mentioned inert inorganic compound fine particles (B) exceeds 20,000 ppm, coarse projections are generated on the surface of the film, so that the abrasion resistance of the film decreases. On the contrary, when the content of the above-mentioned inactive inorganic compound fine particles (B) is less than 100 ppm, the obtained polyester film does not have sufficient slipperiness.

The inert inorganic compound fine particles (C) having a Mohs hardness of less than 2.5 include, for example, talc, carion and the like. Among them, carion is particularly preferable from the viewpoint of scratch resistance of the obtained polyester film. The above-mentioned kaolin particles may be of any type regardless of natural kaolin, synthetic kaolin, calcinability, and non-sinterability, and the shape thereof may be arbitrarily selected such as plate-like, columnar, spherical, spindle-like, and egg-like.

The average particle size of the inert inorganic compound fine particles (C) is 0.1 to 5.0 μm, preferably 0.2.
To 2.0 μm, more preferably 0.25 to 1.0 μm
m. When the average particle diameter of the above-mentioned inactive inorganic compound fine particles (C) exceeds 5.0 μm, coarse protrusions are generated on the surface of the obtained film, so that the abrasion resistance of the film deteriorates. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used for a magnetic tape, it causes dropout. On the contrary, when the average particle size of the above-mentioned inactive inorganic compound fine particles (C) is less than 0.1 μm, a part of the inactive inorganic compound fine particles (C) is condensed in the polyester to form coarse particles, so that the film is formed. Wear resistance deteriorates. Further, the abrasion powder generated deteriorates the scratch resistance of the film. Therefore, when such a film is used for a magnetic tape, it causes dropout.

The particle size distribution of the above-mentioned inert inorganic compound fine particles (C) is sharp and 1 in order to prevent film breakage and dropout when used in a magnetic tape.
It is preferable not to contain particles of 0 μm or more, 5 μm
The volume content of the above particles is particularly preferably 5% or less.

The content of the above-mentioned inert inorganic compound fine particles (C) in the biaxially oriented polyester film of the present invention is 10
0 to 20000 ppm, preferably 1500 to 7
000 ppm, particularly preferably 2500-500
It is 0 ppm. When the content of the above-mentioned inactive inorganic compound fine particles (C) exceeds 20000 ppm, coarse projections occur on the surface of the film, so that the abrasion resistance of the film decreases. On the contrary, the content of the inert inorganic compound particles (C) is 1
When it is less than 00 ppm, the obtained polyester film does not have sufficient slipperiness.

The above-mentioned inert inorganic compound fine particles (A),
The average particle diameters of (B) and (C) refer to the diameter at a point at the integrated 50% point of the equivalent spherical particle size distribution calculated based on the Stokes equation.

The above-mentioned inert inorganic compound fine particles (A),
The surface of (B) or (C) may be modified with various surface treatment agents. For example, typical surface treatment agents used for the purpose of improving the affinity with ethylene glycol or polyester include ammonium salts and alkali metal salts of polyacrylic acid, polymethacrylic acid, etc .; silane coupling agents, titanium. There are coupling agents and the like. The surface treatment agent is generally used in an amount of 5% by weight or less based on the inert inorganic compound particles.

The method of introducing the above-mentioned inert inorganic compound particles into the polyester includes a method of adding the inert inorganic compound particles into the polyester polycondensation reaction system to complete polycondensation, and a method of introducing the inert inorganic compound particles into the molten polyester. There is a method of adding and kneading, and either method can be adopted, but the former method is usually preferable from the viewpoint of dispersibility of the inert inorganic compound particles in the polyester.

In this case, the inert inorganic compound particles are usually added to the reaction system as an ethylene glycol slurry. The timing of addition depends on the inert inorganic compound particles used, but before the start of the polycondensation reaction. preferable.

As a method of incorporating the above-mentioned inactive inorganic compound fine particles into a polyester, the above-mentioned inactive inorganic compound fine particle (A), (B) and (C) -containing polyesters are independently produced and each polyester is added in a predetermined amount. A method of mixing, a method of producing a polyester containing two kinds of inert inorganic compound particles (A), (B) and (C), and mixing them in a predetermined amount (for example, A polyester containing active inorganic compound fine particles (A) and (B), or inert inorganic compound fine particles (B) and (C), or inert inorganic compound fine particles (C) and (A) is produced and mixed in a predetermined amount. Method), and a method for producing a polyester containing the above-mentioned inert inorganic compound fine particles (A), (B) and (C).

In particular, when a polyester containing ultrafine alumina particles, calcium carbonate and the like is produced, an alkali metal salt or an alkali metal salt is used for the purpose of improving the dispersibility of the fine particles of the inert inorganic compound and the electrostatic adhesion of the resulting film. An alkaline earth metal salt and phosphoric acid, a phosphoric acid alkyl ester, or their derivatives are added. In this case, the alkali metal salt or alkaline earth metal salt and the added molar ratio of phosphoric acid, phosphoric acid alkyl ester, or their derivatives (phosphoric acid or its derivative / ((alkali metal) / 2 +
(Alkaline earth metal)) is preferably 0.5 to 0.9. When the above molar ratio is less than 0.5 or more than 0.9, the added alumina ultrafine particles and calcium carbonate are likely to aggregate, so that coarse particles are generated in the polyester and the abrasion resistance of the film is reduced. May get worse. Further, the abrasion powder generated may deteriorate the scratch resistance of the film. Therefore, when such a film is used for a magnetic tape, it may cause dropout.

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. First, a polyester film to which the above-mentioned inert inorganic compound particles for forming projections on the film surface are added is biaxially stretched in the machine and transverse directions by a conventional method. The stretching order may be any of vertical and horizontal, horizontal and vertical, and simultaneous biaxial methods. In addition, three or more stages of stretching may be performed by appropriately combining transverse stretching, longitudinal stretching and simultaneous biaxial stretching.

After biaxially stretching the polyester film,
Heat treatment is performed in a tenter. Heat treatment is 190 ~ 230 ℃
It is preferable to carry out for 2 to 10 seconds because the density of the obtained polyester film is in a suitable range. further,
It is preferable to perform re-stretching of 2 to 30% in the transverse direction or both the longitudinal and transverse directions at the same time as the heat treatment, because the heat shrinkage rate of the obtained polyester film is in a suitable range.

After the heat treatment, relaxation treatment may be carried out in the horizontal and vertical directions. The relaxation in the lateral direction is preferably performed in a tenter. The relaxation temperature is preferably in the range of 130 to 170 ° C. because the heat shrinkage rate of the film is in a suitable range. Further, the relaxation rate may be appropriately adjusted in the range of 0.2 to 10% in order to obtain a desired heat shrinkage rate. On the other hand, the relaxation in the longitudinal direction may be carried out simultaneously with the relaxation in the lateral direction in the tenter, but relaxation on the heating roll is preferable. The relaxation in the machine direction is preferably performed at a temperature of 80 to 150 ° C. in order to keep the heat shrinkage rate of the film in a suitable range, and the relaxation rate is appropriately adjusted by controlling the tension between the heating roll and the front and rear rolls. do it.

[0041]

The biaxially oriented polyester film of the present invention is excellent in abrasion resistance and scratch resistance because it contains a predetermined amount of three or more kinds of inert inorganic compound fine particles having different Mohs' hardness as a lubricant. In particular, it contains alumina and / or silica as the inactive inorganic compound fine particles (A), calcium carbonate as the inactive inorganic compound fine particles (B), and kaolin as the inactive inorganic compound fine particles (C). 2
The axially oriented polyester film has excellent abrasion resistance and scratch resistance. It is considered that this is because the protrusions in the film obtained by the combination of the fine particles of the inert inorganic compound having different Mohs hardnesses have flexibility in a suitable range.

[0042]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the invention is not limited to the following Examples.

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

(1) Average particle size of fine particles of inert inorganic compound Shimadzu Corporation's stretch-sedimentation particle size distribution analyzer (SA-
The value at the point of cumulative 50% in the equivalent spherical distribution obtained by CP-2 or CP-3) was taken as the average particle size.

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

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

(4) Abrasion resistance in film calendering process A polyester film having a width of 30 cm was supercalendered in four stages (linear pressure 300 kg / cm, running speed 300 m).
/ Minute) for 40000 m, and visually observing the amount of resin powder adhering to the elastic roll, and the following ranking was performed.

1 ... No resin powder powder is observed at all 2 ... Very small amount of resin powder powder is observed, but extremely small amount 3 ... A small amount of resin powder powder is observed 4 ... Large amount Resin powder powder is recognized If the obtained polyester film is rank 1 or 2, there is no problem in practical use.

(5) Scratch resistance of film A polyester film cut into a width of 10 mm is run on a plastic pin at a tension of 100 g, a wrap angle of 90 degrees, and a running speed of 150 m / min while rubbing once. Next, aluminum was vapor-deposited on the rubbing surface, and the amount of scratches was visually determined by a micrograph of the actual condition, and ranked as follows.

1 ... No scratches are recognized 2 ... Slight scratches are recognized but extremely small amount 3 ... Small amount of scratches is recognized 4 ... Large amount of scratches are recognized If the obtained polyester films are ranks 1 and 2, there is no problem in practical use. Example 1 <Preparation of Polyester a> γ-type aluminum oxide having an average particle diameter of 0.08 μm (Mohs hardness 8 to 9) and ethylene glycol were mixed and stirred with a homogenizer to obtain γ.
A slurry of 20% by weight type aluminum oxide was obtained.

On the other hand, 100 parts by weight of terephthalic acid, 70.7 parts by weight of ethylene glycol, 0.0 parts of antimony trioxide.
697 parts by weight, triethyleneamine 0.271 parts by weight and magnesium acetate 0.0931 parts by weight are mixed,
Esterification was performed at 250 ° C. and a pressure of 2.5 kg / cm ² .

After completion of the esterification, 0.0327 parts by weight of trimethyl phosphate was added to this solution, and the solution was added to the solution under atmospheric pressure to obtain 26.
Stirring was carried out at 0 ° C. After 30 minutes, the slurry was added in a predetermined amount so that the concentration of γ-type aluminum oxide was 2% by weight with respect to the produced polyester, and the mixture was further stirred for 30 minutes. After that, polycondensation reaction is performed under vacuum, and the intrinsic viscosity η
A polyethylene terephthalate composition of 0.58 was obtained (polyester a).

<Preparation of Polyester b> The same as the production of Polyester a except that calcium carbonate having an average particle size of 0.45 μm (Mohs hardness of 3) was added in place of γ-type aluminum oxide in the production of Polyester a. And the intrinsic viscosity of calcium carbonate concentration 2% by weight η =
A polyethylene terephthalate composition of 0.62 was obtained (polyester b).

<Preparation of Polyester c> In the same manner as in the production of polyester a, except that kaolin (Mohs hardness 1) having an average particle size of 0.4 μm was added in place of γ-type aluminum oxide in the production of polyester a. hand,
A polyethylene terephthalate composition having a kaolin concentration of 2% by weight and an intrinsic viscosity η = 0.62 was obtained (polyester c).

<Preparation of Polyester d> In the above-mentioned production of polyester a, the procedure of production of polyester a was repeated except that the inert inorganic compound particles were not added.
A polyethylene terephthalate composition having an intrinsic viscosity η = 0.62 was obtained (polyester d).

The polyester a, the polyester b, the polyester c, and the polyester d thus obtained were mixed and dried at a predetermined weight ratio so that the above-mentioned inert inorganic compound particles had the concentrations shown in Table 1, and then 280 Melt at ℃,
Then, it was cast on a cooling drum at 30 ° C. to obtain an unstretched film having a thickness of 220 μm. Then, this film was heated with a roll heated to 75 ° C. and an infrared heater having a surface temperature of 600 ° C. (installed at a position 20 mm away from the film), and then, in the longitudinal direction between the low speed roll and the high speed roll. It was stretched 3 times. Further, this film was stretched 4.4 times in the transverse direction at 100 ° C. in a tenter. In the tenter, after transverse stretching, heat treatment at 220 ° C. for about 1 hour, 5% re-stretching in the transverse direction simultaneously with heat treatment,
After the heat treatment, relaxation was performed in the lateral direction at 150 ° C. Then, the film is brought into contact with a roll heated to 120 ° C., and the tension between the heating roll and the rolls before and after the film is controlled to relax the film in the longitudinal direction to obtain a thickness of 15 μm.
A biaxially oriented polyester film of m was obtained.

Examples 2 to 6 and Comparative Examples 1 to 2 Polyesters a to c were prepared in the same manner as in Example 1, and then the obtained polyesters were adjusted so that the fine particles of the inert inorganic compound had the concentrations shown in Table 1. A biaxially oriented polyester film was obtained in the same manner as in Example 1 using a to d.

Examples 7 to 8 and Comparative Examples 3 to 4 Polyesters a to c were prepared in the same manner as in Example 1, and then the obtained polyesters were adjusted so that the fine particles of the inert inorganic compound had the concentrations shown in Table 1. A biaxially oriented polyester film was obtained in the same manner as in Example 1 using a to d. However,
As the polyester a, a polyester produced by the same method as in Example 1 using γ-type aluminum oxide and a polyester produced by the same method as in Example 1 using spherical silica were used.

The characteristics of the biaxially oriented polyester films obtained in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated. The results are shown in Table 1.

[0060]

[Table 1]

As is clear from Table 1, the biaxially oriented polyester films obtained in Examples 1 to 8 are excellent in wear resistance and scratch resistance in the calendering process.

[0062]

As is apparent from the above description, the present invention is excellent in abrasion resistance, and therefore does not generate abrasion powder of the film in the calendar processing step and is excellent in scratch resistance. A polyester film can be provided.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B29K 105: 16 B29L 7:00 4F (72) Inventor Hideto Ohashi 10 Toyo-cho, Tsuruga City, Fukui Prefecture No. 24 Toyobo Co., Ltd. Film Research Laboratory Tsuruga Branch (72) Inventor Yasuhiro Nishino 10-24 Toyocho, Tsuruga City, Fukui Prefecture Toyobo Co. Ltd. Film Research Laboratory Tsuruga Branch

Claims (2)

[Claims] 1. An acid component mainly comprising an aromatic dicarboxylic acid,
A polyester film comprising at least one glycol component, wherein the polyester film has an average particle size of 0.01 to 1.
Inert inorganic fine particles (A) having a particle size of 0 μm and a Mohs hardness of 5 or more in the range of 100 to 20000 ppm, an average particle size of 0.1 to 2.0 μm, and a Mohs hardness of 2.5 or more and less than 5 Inorganic compound fine particles (B) 100
In the range of up to 20000 ppm and with an average particle size of 0.1
A biaxially oriented polyester film containing inactive inorganic compound fine particles (C) having a thickness of 5.0 μm and a Mohs hardness of less than 2.5 in the range of 100 to 20,000 ppm. 2. The inactive inorganic compound fine particles (A) are at least one inorganic compound selected from the group consisting of alumina and silica, and the inert inorganic compound fine particles (B) are calcium carbonate, The biaxially oriented polyester film according to claim 1, wherein the inactive inorganic compound fine particles (C) are kaolin.