JP2001076961A - Biaxially orientated polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve slit property by constituting a biaxially orientated film of copolymerized polyethylene-2,6-naphthalate where spcified quantity of an isophthalic acid component is copolymerized and mixing the specified quantity of porous silica fine grains to a catalyst through the use of the specified quantity of metallic compound. SOLUTION: A biaxially orientated polyester film for capacitor contains 0.1 to 2 wt.% of porous silica fine grains whose average grain size is 0.5 to 5 μm and contains 2,6-naphthalene dicarboxylic acid, ethylene glycol and 0.5 to 8 mol% of isophthalic acid component. In the biaxially orientated film of copolymerized polyethylene 2,6-naphthalate, the content of a diethylene glycol component is not more than 3 mol%. Mn compound used as reactive catalyst, Sb compound and P component used as stabilizer are contained by quantity satisfying formulas (1), (2) and (3). Alkali metal is set to be not more than 10 ppm, a planar orientation coefficient to be 0.230 to 0.270 and density to be not less than 1.350 g/cm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biaxially oriented polyester film for a capacitor. More specifically, it is made of copolymerized polyethylene-2,6-naphthalate containing porous silica fine particles and modified with a specific amount of an isophthalic acid component, and is excellent in workability, and particularly, an ultrathin film capable of increasing the capacity. The present invention relates to a biaxially oriented polyester film for a capacitor.

[0002]

2. Description of the Related Art Biaxially oriented polyethylene-2,6-naphthalate film has attracted attention as a dielectric material for capacitors because of its excellent mechanical properties, thermal properties and heat resistance, and its use is increasing. is there.

In recent years, with the miniaturization of electric or electronic circuits, there has been a demand for small-sized and large-capacity capacitors, and thinning of a dielectric material film serving as a base has been promoted. . In film capacitors, the reason why the dielectric film is made thinner is that
The capacitance of a capacitor is proportional to the dielectric constant of a dielectric material and the electrode area, and inversely proportional to the film thickness. In other words, the capacitance per unit volume of a dielectric is inversely proportional to the square of the film thickness, and Because the ratio is proportional to the ratio, it is indispensable to reduce the thickness of the film in order to reduce the size or increase the capacity of the capacitor using dielectric materials having the same dielectric constant.

As described above, although the effect of thinning the film is obvious, simply reducing the thickness of the biaxially oriented film causes a new problem. For example, as the film becomes thinner, electrodes are deposited on the film. When doing,
There is a problem that workability in processes such as slitting and element winding is deteriorated.

[0005] This workability relates to the slipperiness of the film. As a method of improving the slipperiness, a method of imparting minute unevenness to the surface of a polyester film is known and used. As an example of this method, inert inorganic fine particles are added during or after the polymerization of polyester as a raw material of the film (external particle addition method), or a part or all of a catalyst used at the time of polymerization of the polyester is added in the reaction step. A method of precipitating in a polymer (internal particle precipitation method) is known.

However, in the production of an ultra-thin polyester film, if a polymer containing the same concentration of inert inorganic fine particles as the raw material polymer used in the production of a medium-thick film is used, the per-unit area of the ultra-thin film is reduced. The number of active inorganic fine particles is reduced, the distance between the fine particles on the film surface is widened, the film surface is flattened, and the slipperiness is reduced. Therefore, in order to compensate for the decrease in slipperiness due to thinning, it is necessary to increase the concentration of the contained inert inorganic fine particles or increase the particle size as the film thickness is reduced.

[0007] In this case, however, voids are formed at the interface, that is, at the time of melt extrusion at a high draft ratio or at the time of stretching, due to poor affinity between the inert inorganic fine particles and the thermoplastic polyester. As a result of the occurrence of voids, the mechanical properties (e.g., breaking strength and elongation at break) and the electrical properties (e.g., insulation defects) of the obtained film are reduced, and the film is produced at the time of film production. This also causes breakage, which causes problems such as a decrease in productivity and a lack of stability in the manufacturing process.

For the purpose of solving such a problem, the film contains porous inert inorganic particles and spherical silica particles,
A thin thermoplastic resin film of 4 μm or less, for example, a polyethylene-2,6-naphthalate film having excellent workability (handling property) and excellent film-forming properties has been proposed (Japanese Patent Application Laid-Open No. Hei 1-266145).

However, according to the study of the present inventor, when the thermoplastic resin film is a polyethylene-2,6-naphthalate film, there is obtained an advantage that there is no decrease in mechanical properties and workability and film forming properties are excellent. However, it became clear that the projections on the film surface formed by the particles made the air layer generated when the films were superposed thicker, and the capacitor capacity per volume decreased, so that it was insufficient as a capacitor film. . Also, when slitting the ultra-thin film for capacitor element winding,
It was also clarified that the tear resistance was insufficient and the film was easily broken.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrathin biaxially oriented polyester film for a capacitor which is excellent in workability, particularly slitting property, and which can increase the capacity of the capacitor.

[0011]

Means for Solving the Problems The present inventors impaired other properties by forming a biaxially oriented film from copolymerized polyethylene-2,6-naphthalate obtained by copolymerizing a specific amount of an isophthalic acid component. Improved slitting without
Furthermore, the present inventors have found that it is possible to increase the capacity of a capacitor while ensuring workability by using a specific amount of a metal compound as a catalyst during the production of a polymer and blending a specific amount of porous silica fine particles. did.

That is, according to the present invention, the average particle size is 0.5 to
0.1 to 2% by weight of 5 μm porous silica fine particles, 2,6-naphthalenedicarboxylic acid as a main dicarboxylic acid component, ethylene glycol as a main glycol component, and an isophthalic acid component as a copolymerization component at 0.1%.
A copolymerized polyethylene containing 5 to 8 mol% (based on the total dicarboxylic acid component) and having a diethylene glycol component content of 3 mol% or less (based on the total glycol component);
A biaxially oriented film composed of 2,6-naphthalate, wherein the copolymerized polyethylene-2,6-naphthalate is a manganese compound, an antimony compound used as a reaction catalyst, and a phosphorus compound used as a stabilizer represented by the following formula ( 1), containing (2) and (3) in an amount that satisfies an alkali metal content of 10 ppm or less, and a film orientation coefficient of 0.230 or more and 0.270 or less, and a density of 1.350 g. / Cm ³ or more.

[0013]

## EQU4 ## 30 ≦ Mn ≦ 100 (1)

[0014]

[Equation 5] 150 ≦ Sb ≦ 450 (2)

[0015]

## EQU6 ## 20 ≦ P ≦ 100 (3)

(Where Mn is the amount (ppm) of manganese in the copolymerized polyethylene-2,6-naphthalate,
b represents the amount (ppm) of the antimony element in the copolymerized polyethylene-2,6-naphthalate, and P represents the amount (ppm) of the phosphorus element in the copolymerized polyethylene-2,6-naphthalate. )

In the present invention, copolymerized polyethylene-2,
The main dicarboxylic acid component constituting 6-naphthalate is 2,6-naphthalenedicarboxylic acid, and the main glycol component is ethylene glycol. Here, the main dicarboxylic acid component is 9 to all dicarboxylic acid components.
0 mol% or more, preferably 92 mol% or more, and the main glycol component is 9 mol% to all glycol components.
0 mol% or more, preferably 95 mol% or more.

In the present invention, the copolymer polyethylene-2,
It is necessary that 6-naphthalate be copolymerized with an isophthalic acid component as a copolymerization component so as to account for 0.5 to 8 mol% of all dicarboxylic acid components. The copolymerization amount of the isophthalic acid component is preferably the highest ratio among all the copolymerization components. The copolymerization amount of this isophthalic acid component is 0.5 mol% with respect to all dicarboxylic acid components.
If less, the tear resistance of the film does not improve,
Breakage during slitting cannot be prevented. On the other hand, if it exceeds 8 mol%, the crystallinity of the polymer is impaired when the film is formed, resulting in a film having poor mechanical strength. The copolymerization amount of the isophthalic acid component is preferably 1 to 7 mol%.

The isophthalic acid component is preferably copolymerized by using a compound represented by the following general formula in the production reaction of copolymerized polyethylene-2,6-naphthalate.

[0020]

Embedded image

(In the formula, R represents hydrogen or a lower alkyl group.) In the above formula, R is hydrogen or a lower alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group and a butyl group. is there. Preferred examples of the compound represented by the above formula include isophthalic acid and dimethyl isophthalate.

In the present invention, the copolymerized polyethylene-2,
In 6-naphthalate, it is necessary that the copolymerization amount of the diethylene glycol component is 3 mol% or less (based on the total glycol component). This diethylene glycol component was not added to the reaction system in the form of diethylene glycol or its ester-forming derivative as a copolymer component during the production of the copolymerized polyethylene-2,6-naphthalate, but was produced as a by-product during the polymer production reaction. And copolymerized. The smaller the amount of the diethylene glycol component, the better.

When the copolymerization amount of the diethylene glycol component exceeds 3 mol%, the effect of improving the tear resistance of the film becomes greater, but the crystallinity of the polymer is impaired, so that the mechanical strength of the film is greatly reduced. However, it is not preferable. The copolymerization ratio of the diethylene glycol component is preferably 2.5 mol% or less, more preferably 2 mol% or less, based on all glycol components. In order to suppress the by-product of diethylene glycol in the polymer production reaction, the molar ratio of ethylene glycol, which is a reaction raw material, to the dicarboxylic acid component is not excessively large (for example, the molar ratio is 1.97 to 1.07 in the transesterification method). 2.30, and 1.2 to 1.6 in the direct esterification method). In addition, the shorter the monomer production reaction time, the better, and from such a point, it is preferable to select a reaction temperature and a catalyst. From the viewpoint of suppressing the copolymerization ratio of the diethylene glycol component, a transesterification method is preferable as the reaction system.

In the present invention, the copolymerized polyethylene-2,
6-Naphthalate may contain other copolymerization components in addition to the isophthalic acid component and the diethylene glycol component, as long as the object of the present invention is not impaired. Although other copolymer components are effective in improving tear resistance, they should be used with great care because they greatly reduce the mechanical properties of the film, for example, Young's modulus. The amount is preferably not more than 3 mol%, more preferably not more than 1 mol%, particularly preferably not more than 0.1 mol%, based on the total amount of the copolymer components other than diethylene glycol.

Examples of other copolymerizable components include compounds having two ester-forming functional groups, for example, oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, 5-sodium sulfoisophthalic acid. Acid, terephthalic acid, 2-potassium sulfoterephthalic acid, 2,7
Oxycarboxylic acids such as naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, diphenyletherdicarboxylic acid, p-oxyethoxybenzoic acid, propylene glycol, 1,2- Propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-
Cyclohexane dimethanol, 1,4-cyclohexane dimethanol, p-xylylene glycol, ethylene oxide adduct of bisphenol A, ethylene oxide adduct of bisphenol sulfone, triethylene glycol, polyethylene oxide glycol, polytetramethylene oxide glycol, neopentyl Glycol and the like.

The copolymerized polyethylene-2,6-naphthalate is obtained by blocking a part or all of the hydroxyl group and / or the carboxyl group at the terminal of the polymer molecule with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Or a polymer whose molecular chain has been modified with a tri- or higher-functional ester-forming compound such as glycerin or pentaerythritol in a small amount so as to obtain a substantially linear polymer. There may be.

In the present invention, the copolymerized polyethylene-2,
6-Naphthalate can be produced by a conventionally known method of producing polyethylene-2,6-naphthalate except that isophthalic acid or an ester-forming derivative thereof is used as a copolymerization component. For example, an esterification reaction of 2,6-naphthalenedicarboxylic acid and isophthalic acid with ethylene glycol, or an ester-forming derivative of 2,6-naphthalenedicarboxylic acid (particularly, a lower alkyl ester) and an isophthalic ester-forming derivative (particularly, Preferably, a method of producing a monomer or oligomer by subjecting a lower alkyl ester) to a transesterification reaction with ethylene glycol and then subjecting them to a polycondensation reaction under reduced pressure to produce a polymer having a desired molecular weight.

Although a reaction catalyst and a stabilizer are used in the above reaction, a manganese compound is preferably used as a transesterification catalyst. Examples of the manganese compound include oxides, chlorides, carbonates, and carboxylate salts.
Of these, acetate is particularly preferably used. Also,
When the transesterification reaction is substantially completed, a phosphorus compound is added to deactivate the transesterification catalyst. As the phosphorus compound, trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate and orthophosphoric acid can be preferably used. Of these, trimethyl phosphate is particularly preferred. As the polycondensation catalyst, an antimony compound is used. As the antimony compound, antimony trioxide is particularly preferably used.

The copolymerized polyethylene-2,6-naphthalate is produced under the condition that the catalyst and the stabilizer are contained in the polymer in an amount satisfying the following formulas (1), (2) and (3). Is preferred.

[0030]

## EQU7 ## 30 ≦ Mn ≦ 100 (1)

[0031]

[Equation 8] 150 ≦ Sb ≦ 450 (2)

[0032]

## EQU9 ## 20 ≦ P ≦ 100 (3)

(Wherein, Mn is the amount of manganese in the copolymerized polyethylene-2,6-naphthalate (ppm);
b represents the amount (ppm) of the antimony element in the copolymerized polyethylene-2,6-naphthalate, and P represents the amount (ppm) of the phosphorus element in the copolymerized polyethylene-2,6-naphthalate. )

When the content of the manganese element is less than 30 ppm in the copolymerized polyethylene-2,6-naphthalate, the transesterification reaction is insufficient. On the other hand, when the content exceeds 100 PPm, the insulation resistance (CR value) of the film decreases, and May not be suitable as a polyester film. Further, when the content of the antimony element is less than 150 ppm, the polycondensation reactivity is reduced and the productivity is deteriorated. On the other hand, when the content is more than 450 ppm, the thermal stability of the polymer is inferior, and cutting during film formation and mechanical The strength of the target may be reduced. Further, when the amount of the phosphorus element is less than 20 ppm, the transesterification catalyst is not completely deactivated, the thermal stability of the polymer is poor, and the mechanical strength of the obtained film is unfavorably reduced. On the other hand, when the content exceeds 100 ppm, the thermal stability of the polymer is poor, which causes cutting or reduction in mechanical strength at the time of film formation, and furthermore, the CR value is lowered, which is not preferable because it is not suitable as a film for capacitors.

In the present invention, the copolymerized polyethylene-2,
6-naphthalate must further have an alkali metal content of 10 ppm or less. When the alkali metal content exceeds 10 ppm, the CR
It is not preferable because the value decreases and becomes unsuitable as a film for a capacitor. The biaxially oriented polyester film of the present invention has many fine projections on the surface of the film, and some or all of these fine projections are dispersed and contained in the copolymerized polyethylene-2,6-naphthalate. Derived from porous silica fine particles.

The average particle size of the porous silica fine particles is 0.5 to 5 μm, preferably 1 to 3 μm. Such porous silica fine particles are copolymerized polyethylene-2,
Shows high affinity for 6-naphthalate. here,
By "average particle size" is meant the "equivalent spherical diameter" of the particle at a point of 50% by weight of the total particles measured. "Equivalent spherical diameter" is an imaginary sphere (ideal sphere) having the same volume as a particle
Means the diameter of the particles, which can be calculated from an electron micrograph of the particles or a measurement by a usual sedimentation method. When the average particle size of the porous silica fine particles is less than 0.5 μm, the air squeezability is poor when the film is wound into a roll such as a master roll or a product roll (it is difficult for the entrained air to escape), and wrinkles are easily generated. Slip property (slip property)
Is insufficient and the workability in the processing step is reduced, which is not preferable. On the other hand, when the average particle size exceeds 5 μm, the film surface is excessively rough, which causes a decrease in dielectric breakdown voltage and an increase in insulation defects, which is not preferable. The average particle size of the porous silica fine particles may be larger than the film thickness. This is because the porous silica fine particles used in the present invention have a high affinity for copolymerized polyethylene-2,6-naphthalate. About 1 particle size distribution of porous silica fine particles
It is preferable that the particles hardly contain coarse particles of 0 μm or more and have a sharp distribution on the fine side.

As an example of the method for producing the porous silica fine particles, a method of dispersing primary silica particles in water to form colloidal particles, drying the sol, and forming a specific porous gel (particularly, JP-A-52-52876) is known. In order to obtain particles having a predetermined average particle size, a conventionally known particle preparation method can be used.For example, a particle having a predetermined average particle size and a particle size distribution are obtained by performing a pulverization process, a classification operation, and the like. Is preferred.

In the present invention, the amount of the porous silica fine particles added must be 0.1 to 2% by weight, preferably 0.1 to 1% by weight, based on the copolymerized polyethylene-2,6-naphthalate. is there. If the addition amount is less than 0.1% by weight, the air squeezing property at the time of film winding becomes poor. On the other hand, if it exceeds 2% by weight, the film surface becomes too rough, causing a decrease in dielectric breakdown voltage and the like. Not preferred.

In the present invention, especially for ultra-thin films, it is preferred that spherical silica fine particles are dispersed and contained in the copolymerized polyethylene-2,6-naphthalate together with the porous silica fine particles. The spherical silica fine particles have an average particle size that is not larger than the film thickness and is equal to 0.1.
1-1 μm, and the particle size ratio (major axis / minor axis) is 1.
Those having 0 to 1.2 are preferred. These spherical silica fine particles are spherical in which the shape of each fine particle is very close to a true sphere,
10 n of silica fine particles conventionally known as a lubricant
This is significantly different from ultra-fine aggregated particles of about m or aggregates of about 0.5 μm, which form aggregates (aggregated particles).

It is necessary that the average particle size of the spherical silica fine particles is smaller than the film thickness. If the average particle size is larger than the film thickness, the film around the projections due to the spherical silica fine particles is undesirably cracked, and the film is frequently broken in the steps of stretching and heat fixing. Therefore,
The average particle size of the spherical silica fine particles is preferably 90% or less of the film thickness, more preferably 80% or less of the film thickness.

Further, the average particle size of the spherical silica fine particles is as follows:
It is preferably 0.1 to 1 as long as it does not exceed the thickness of the film.
μm, and more preferably 0.2 to 0.8 μm. When the average particle size is less than 0.1 μm, the slipperiness of the film is insufficient, and the workability in the processing step is undesirably reduced. on the other hand,
If the average particle size exceeds 1 μm, the film surface is excessively rough, causing a decrease in dielectric breakdown voltage, an increase in insulation defects, and the like.

The particle size ratio (major axis / minor axis) of the spherical silica fine particles is preferably 1.0 to 1.2, more preferably 1.0 to 1.15, and particularly preferably 1.0 to 1. .1
It is.

The method for producing the spherical silica fine particles is not particularly limited as long as the above conditions are satisfied.
For example, spherical silica fine particles form monodisperse spheres of hydrous silica [Si (OH) ₄ ] from hydrolysis of ethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] as shown in the following reaction formula (Formula 2). Further, the hydrous silica monodisperse spheres can be produced by dehydrating the three-dimensionally grown silica bond (Chem. 3) (Journal of the Chemical Society of Japan, '81, No. 9, p. 15).
03).

[0044]

Embedded image Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) <sub>4
+ 4C 2 H 5 OH ≡Si-</sub> OH + HO-S≡ → ≡Si-O-Si≡ + H 2
O

[0045]

Embedded image {Si—O—Si}: Silica bond

In the present invention, the amount of the spherical silica fine particles is preferably 0.005 to 1% by weight, more preferably 0.01 to 0.8% by weight, based on the copolymerized polyethylene-2,6-naphthalate. %, Particularly preferably 0.02 to 0.6% by weight. This addition amount is 0.00
If it is less than 5% by weight, the effect of improving the slipperiness becomes insufficient, while if it exceeds 1% by weight, the film-forming properties, mechanical strength, insulation breakdown voltage and the like are lowered, which is not preferable. If the content of the porous silica fine particles or the spherical silica fine particles is too small, the synergistic effect of using two kinds of particles cannot be obtained, and the air squeezing property at the time of winding or the slip property at the time of processing is insufficient, which is not preferable.

The timing of adding the porous silica fine particles and the spherical silica fine particles to the copolymerized polyethylene-2,6-naphthalate is preferably an arbitrary stage until the polymerization of the copolymerized polyethylene-2,6-naphthalate is completed. Before the end of the transesterification reaction, it is preferably added to the reaction system (preferably as a slurry in glycol).

Further, a copolymerized polyethylene-2,6-naphthalate containing individually porous silica fine particles and spherical silica fine particles is produced, and these are blended. , 6-naphthalate to form a predetermined composition. Further, it may be added at the time of film formation.

In the formation of the above-mentioned copolymerized polyethylene-2,6-naphthalate, usually, a film-like melt extruded from a die is brought into close contact with a rotary cooling drum to suppress crystallization of the polymer and to obtain an unstretched film having high flatness. A film is prepared. At this time, in order to enhance the adhesion, an electrostatic adhesion method for imparting an electrostatic charge to the film-like melt is often used. Since the copolymer polyethylene-2,6-naphthalate has a high electric resistance of the melt, the electrostatic adhesion may be insufficient. As a countermeasure, copolymerized polyethylene-2,6-naphthalate is added in an amount of 0.1 to 40 with respect to all dicarboxylic acid components.
It is preferable to contain quaternary phosphonium sulfonate having an ester-forming functional group in an amount of 0.2% by mole, more preferably 0.2% to 10% by mole. Examples of the quaternary phosphonium sulfonic acid salt having an ester-forming functional group include 3,5.
Preferred examples include tetrabutylphosphonium dicarboxybenzenesulfonate and tetraphenylphosphonium 3,5-dicarboxybenzenesulfonate. Such a compound is superior to an alkali metal element in improving electrostatic adhesion without lowering the volume resistivity of the film.

In the biaxially oriented polyester film of the present invention, the intrinsic viscosity of the polymer is preferably 0.40 or more, more preferably 0.40 to 0.80. If the intrinsic viscosity is less than 0.40, process cutting may occur frequently. The upper limit is not particularly defined, but if it is higher than 0.8, the melt viscosity is high and melt extrusion becomes difficult, which is not preferable.

The biaxially oriented polyester film in the present invention needs to have a plane orientation coefficient of 0.230 to 0.270. If the plane orientation coefficient is less than 0.230, the workability in the film forming step or the element forming step is poor due to insufficient strength, while if it exceeds 0.270, cutting during film formation frequently occurs. Preferred plane orientation coefficient is 0.230 to 0.26
5, furthermore 0.230 to 0.260. The plane orientation coefficient is preferably adjusted by adjusting the stretching ratio and temperature in the biaxial direction, and further by performing toe-in, toe-out and relaxation treatment.

The biaxially oriented polyester film needs to have a density of 1.350 g / cm ³ or more. When the density is less than 1.350 g / cm ³ , the heat deterioration resistance of the film decreases, which is not preferable. The preferred film density is 1.356 g / cm ³ or more.

The biaxially oriented polyester film preferably has a heat shrinkage (150 ° C., 30 minutes) of 3% or less. If this heat shrinkage exceeds 3%, the film shrinks in the vapor deposition step during the production of the capacitor,
There may be wrinkles. Further, from the viewpoint that the application of the film is an electrical insulating material, the film preferably has a breakdown voltage (BDV) of 260 V / μm or more, more preferably 280 V / μm or more. Surprisingly, the biaxially oriented polyester film of the present invention exhibits a slightly higher breakdown voltage (BVD) than a film consisting of unmodified polyethylene-2,6-naphthalate. This is a specific effect of the isophthalic acid component,
For example, this phenomenon cannot be seen when terephthalic acid is copolymerized.

The biaxially oriented polyester film of the present invention has a CR value (product of the capacitance C and the insulation resistance value R) of the insulation resistance characteristic of 10,000ΩF or more, and more preferably 15ΩΩF or more.
It is preferably at least 000ΩF. This CR value is 1
If it is less than 0000ΩF, the insulation resistance of the film becomes insufficient,
It may not be suitable as an electrical insulating material.

The biaxially oriented polyester film of the present invention has a pinhole frequency of 0.01 / cm ^2.
The following is preferred. This pinhole frequency is 0.
If the number is larger than 01 / cm ² , the insulating property is inferior.

The thickness of the biaxially oriented polyester film in the present invention is preferably 0.2 to 5 μm, more preferably 0.2 to 5 μm.
３3 μm is preferred. If the film thickness is less than 0.2 μm, it is difficult to form a film, while if it exceeds 5 μm, it may be difficult to reduce the size of the capacitor.

The intrinsic viscosity of the polymer, the thickness of the film, the plane orientation coefficient, the heat shrinkage, the dielectric breakdown voltage (BDV),
The pinhole, CR value, and density are each measured by the methods described below.

The biaxially oriented polyester film in the present invention is a biaxially oriented copolymerized polyethylene-2,6-naphthalate film having the above-mentioned properties. The film is preferably stretched in a biaxial direction (for example, in a longitudinal direction and a transverse direction) at a stretching ratio of 2.5 times or more. The stretching ratio in the biaxial direction may or may not be equal. Also,
The film may be a single-layer film or a laminated film.

In the production of the biaxially oriented copolymerized polyethylene-2,6-naphthalate film, for example, it is melt-extruded at a normal extrusion temperature, that is, at a temperature not lower than the melting point of the polymer (hereinafter referred to as Tm) and not higher than (Tm + 70 ° C.). The film-like melt is quenched on the surface of the rotary cooling drum to obtain an unstretched film having an intrinsic viscosity of 0.40 to 0.80. In this step, it is preferable to use an electrostatic adhesion method for imparting an electrostatic charge to the film-like melt in order to increase the adhesion between the film-like melt and the rotary cooling drum. This unstretched film is stretched in the longitudinal or transverse direction at a temperature not lower than the secondary transition point (hereinafter referred to as Tg) of copolymerized polyethylene-2,6-naphthalate and not higher than (Tg + 70 ° C.) by 2.5 to 5.0 times. And then in a direction perpendicular to the stretching direction (horizontal direction if the stretching direction is a longitudinal direction) at least Tg, (Tg + 70
(C) at a temperature of not more than 2.5 to 5.0 times the stretching ratio (stretching may be such sequential biaxial stretching or simultaneous biaxial stretching; Is not particularly limited). It is preferable that the biaxially oriented film thus obtained is further heat-set at a temperature of (Tg + 70 ° C.) or more and Tm or less for 1 to 100 seconds.

[0060]

The present invention will be described in more detail with reference to the following examples. In the examples, "parts" means parts by weight, and various characteristic values were measured and evaluated by the following methods.

1. Particle Size of Particles (1-1) Particle Size of Powder Shimadzu CP50 Centrifugal Particle Size Analyzer (Centrifugal)
The particle size corresponding to 50 mass percent was read from the cumulative curve of the particles of each particle size and its abundance, which was measured using a Particle Size Analyzer and calculated based on the obtained centrifugal sedimentation curve. This value is defined as the average particle size. ("Granularity measurement technology", published by Nikkan Kogyo Shimbun, 1975, p.
247)

(1-2) Particle Size of Particles in Film A small piece of the sample film was fixed on a sample table for a scanning electron microscope, and a sputter device (JIS-JIS) manufactured by JEOL Ltd. was used.
0.25 k on the film surface under a vacuum of 1 × 10 ⁻³ torr using a 1100 type ion sputtering apparatus.
V, ion etching at 10 1.25 mA
Min., Further subjected to gold sputtering with the same apparatus, observed at 10,000 to 30,000 times using a scanning electron microscope, and at least 100 particles long diameter (Dli) using Luzex 500 manufactured by Nippon Regulator Co., Ltd. , Minor axis (Dsi) and area equivalent particle size (Di). The number average value of the area equivalent particle diameter (Di) represented by the following equation is defined as the average particle diameter (D).

[0063]

(Equation 10)

(1-3) Particle Size Ratio of Particles The major axis (Dli) and minor axis (Ds) of the particles obtained in the preceding section were obtained.
From i), the major axis (Dl) and the minor axis (Ds) represented by the following formulas
Are calculated, and calculated from these ratios (major axis / minor axis).

[0065]

[Equation 11]

[0066]

(Equation 12)

2. Intrinsic viscosity (IV) Measured at 25 ° C. using o-chlorophenol as a solvent. The unit is 100 cc / g.

3. Diethylene glycol (DEG) content The polymer is decomposed using hydrazine hydrate and quantified by gas chromatography.

4. Film forming property The film forming property is evaluated by the number of times the film breaks when a biaxially stretched film is continuously operated for 24 hours. The unit is times / 2
4 hours. Although the ultra-thin film is liable to break the film, it is usually preferable that this value be 2 times / 24 hours or less from the viewpoint of practical use. （(Good film-forming property): 2 times or less at break △ (yield dissatisfied): 3-5 times at break × (poor film-forming property): 6 times or more at break

5. Slit properties A film roll having a length of 20,000 m and a width of 500 mm was slit, and 50 slit products having a length of 10,000 m and a width of 20 mm were prepared. The slit property is evaluated based on the number of slit products including the cut portion. ◎ (excellent slitting property): Number of slit products including cut section: 0 ○ (usable): Number of slit products including cut section: within 2 × (unusable): Number of slit products including cut section: 3 that's all

6. Winding shape The winding shape when the sample film is wound up to a width of 500 mm and a length of 5000 m is observed and evaluated according to the following criteria. ：: The wound shape is beautiful, and wrinkles on the surface, winding deviation, and the like cannot be visually confirmed. ×: The winding shape is poor, and wrinkles and winding deviations on the surface can be visually confirmed.

7. Plane orientation coefficient (NS) Using an Abbe refractometer, the refractive index is measured using a sodium D line (589 nm) as a light source, and the refractive index is determined by the following equation.

[0073]

## EQU13 ## NS = (nMD + nTD) / 2-nZ

Here, nMD represents the refractive index in the machine axis direction of the biaxially oriented film, nTD represents the refractive index in the direction (width direction) orthogonal to the machine axis direction, and nZ represents the refractive index in the thickness direction of the film. Represent.

8. Dielectric breakdown voltage (BDV) Measured according to the method shown in JISC2318, n = 10
The average value of 0 is defined as a breakdown voltage (BDV).

9. CR value The CR value is a product of the capacitance C and the insulation resistance value R, and indicates insulation resistance characteristics. The sample film was heated at 23 ° C., 50% RH, 16
After adjusting the condition under the condition of time, the measurement is performed in an atmosphere of 23 ° C. and 50% RH according to the method shown in JISC2319.

10. Use Pinhole Magic Ink (registered trademark) with reagent grade ethanol 1
The solution was diluted to 0 times dropped onto the sample film was adhered to the heat-sensitive paper, spread over with an airbrush, counted the number of pinholes portion has been transferred to the thermal paper side, 3000 cm ²
Calculate the number per hit.

11. Film thickness When the width of the sample film is W (cm), the length is 1 (cm), the weight is G (g), and the density is d (g / cm ³ ), the film thickness t (μm) is expressed by the following formula. calculate.

[0079]

T = G / (W × 1 × d) × 10000

12. Heat shrinkage Mark lines were placed on the sample film at intervals of 30 cm, and heat treatment was performed for a certain period of time (150 ° C,
From the change in the sample length after 30 minutes), the following formula is used.

[0081]

## EQU15 ## Thermal shrinkage (%) = (length before heat treatment−length after heat treatment) / length before heat treatment × 100

13. Amount of catalyst and amount of alkali metal in film A sample film is washed and dried twice or more with distilled acetone, and then 0.200 g is collected. Next, it is wet-decomposed with reagent grade sulfuric acid, nitric acid, etc., and 20 ml of ion exchange distilled water is added.
Use as a sample solution. This sample solution was applied to a high-frequency plasma emission spectrometer (manufactured by Jarrell Ash, Atomu Comp).
Metals qualitative and quantitative analysis is performed by Siries 800).

Examples 1-4 A mixture of dimethyl isophthalate and dimethyl 2,6-naphthalenedicarboxylate in an amount corresponding to 100 parts of dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol 60 To this mixture was added 0.03 part of manganese acetate tetrahydrate, and a transesterification reaction was carried out while gradually raising the temperature from 150 ° C to 240 ° C. On the way, when the reaction temperature reached 170 ° C., 0.024 part of antimony trioxide was added, and further, porous silica fine particles having an average particle size shown in Table 1 and spherical silica fine particles were added in the amounts shown in Table 1, and then added. 220 ° C
0.042 parts (2 mmol) of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt
1%). Subsequently, a transesterification reaction is performed, and after the transesterification reaction is completed, trimethyl phosphate 0.03
23 parts were added. Thereafter, the reaction product was transferred to a polymerization reactor, heated to 290 ° C., subjected to a polycondensation reaction under a high vacuum of 0.2 mmHg or less, and had an intrinsic viscosity of 0.2 as measured with an o-chlorophenol solution at 25 ° C. 61 dl / g, DEG
Copolymerized polyethylene-2,6-copolymer having a copolymerization amount of 1.1 mol%
Naphthalate was obtained.

After drying the polymer at 170 ° C. for 6 hours, it was fed to an extruder, melted at a melting temperature of 310 ° C., and passed through a slit die having an opening of 1 mm to have a surface finish of 0.3 S and a surface temperature of 50 ° C. It was extruded on a rotating drum to obtain an unstretched film. Then, the unstretched film is
Stretched 3.6 times in the machine direction at ℃, then stretched 3.9 times in the transverse direction at 140 ° C., and heat-set at 220 ° C. for 5 seconds to obtain a biaxially oriented copolymer polyethylene having a thickness of 1.2 μm.
A 2,6-naphthalate film was obtained.

Table 1 shows the properties of these films. Note that Mn in the film was 50 ppm and Sb was 300 pp.
m and P were 50 ppm, and the amount of alkali metal was 0 ppm. The density of the film was 1.355 g / cm ³ , and the heat shrinkage was 2.2% in the vertical direction and 1.3% in the horizontal direction.

Example 5 A biaxially oriented copolymer polyethylene was prepared in the same manner as in Example 1 except that spherical silica was not added and the film thickness was 4.5 μm.
A 2,6-naphthalate film was obtained. Table 1 shows the properties of these films.

Comparative Example 1 A film having a thickness of 1 was prepared in the same manner as in Example 1 except that dimethyl isophthalate was not used as the acid component and only dimethyl 2,6-naphthalenedicarboxylate was used (the same molar amount as dimethyl isophthalate was used). .2 μm
Of a biaxially oriented polyethylene-2,6-naphthalate film of Table 1 shows the properties of this film. The slit property was unsatisfactory.

Comparative Example 2 Biaxially oriented copolymerized polyethylene-2,6 having a thickness of 1.2 μm was prepared in the same manner as in Example 1 except that the amount of antimony trioxide was increased so that the amount of Sb in the polymer became 500 ppm. -A naphthalate film was obtained. Table 1 shows the properties of this film. The CR value is small and insufficient for capacitors.

Comparative Example 3 In Example 1, 3,5-
Example 1 except that 3,5-dicarboxybenzenesulfonic acid sodium salt was used in the amount shown in Table 1 instead of tetrabutylphosphonium dicarboxybenzenesulfonic acid salt.
In the same manner as in Example 1, a biaxially oriented copolymerized polyethylene-2,6-naphthalate film having a thickness of 1.2 μm was obtained. Table 1 shows the properties of this film. The CR value is small and insufficient for capacitors.

Comparative Example 4 The procedure of Example 1 was repeated, except that the spherical silica shown in Table 1 was added instead of the porous silica, and that the amount of manganese acetate was adjusted so that the Mn content in the polymer was 200 ppm. Thus, a biaxially oriented copolymerized polyethylene-2,6-naphthalate film having a thickness of 1.2 μm was obtained. Table 1 shows the properties of this film. Poor film-forming properties,
CR value and BDV are small and insufficient for capacitors.

Comparative Example 5 The same procedure as in Example 1 was carried out except that spherical silica shown in Table 1 was added instead of porous silica, and that the amount of trimethyl phosphate was adjusted so that the amount of phosphorus in the polymer became 150 ppm. Thus, a biaxially oriented copolymerized polyethylene-2,6-naphthalate film having a thickness of 1.2 μm was obtained. Table 1 shows the properties of this film. Poor slipperiness,
The winding was poor.

Comparative Example 6 The procedure of Example 1 was repeated except that the copolymerization amount of the isophthalic acid component was 12 mol%, and that tetrabutylphosphonium 3,5-dicarboxybenzenesulfonate was added. An attempt was made to obtain a 2 μm biaxially oriented copolymerized polyethylene-2,6-naphthalate film. However, the sheet melt extruded from the die did not adhere well to the cooling drum, and a good product could not be obtained due to poor thickness unevenness.

Comparative Example 7 A biaxially oriented copolymerized polyethylene having a thickness of 1.2 μm was obtained in the same manner as in Example 1 except that the stretching ratio was changed to 4.8 times in the longitudinal direction and 5.5 times in the horizontal direction. A -2,6-naphthalate film was obtained. Table 1 shows the properties of this film. Many cuts were made during film formation, and long products could not be obtained.

Comparative Example 8 Biaxially oriented copolymerized polyethylene-2,6-na having a thickness of 1.2 μm was prepared in the same manner as in Example 1 except that 5 mol% of a terephthalic acid component was copolymerized instead of the isophthalic acid component. A phthalate film was obtained. Table 1 shows the properties of this film. The film-forming properties are poor, and the CR value and BVD are small, which is insufficient for capacitors.

[0095]

[Table 1]

[0096]

The present invention has the following excellent effects and is suitably used as a biaxially oriented copolymerized polyester film for a capacitor requiring an extremely thin film. (1) There is little breakage at the time of film formation and at the time of slitting, and it is useful for film formation of an ultra-thin film, and the capacity of a capacitor can be increased. (2) The film surface is appropriately roughened, the film has good slipperiness, and is excellent in workability during film formation and processing. (3) A suitable amount of catalyst and metal, high insulation resistance, and excellent CR characteristics.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) // C08J 5/18 CFD C08J 5/18 CFD F term (reference) 4F071 AA45 AA82 AB26 AD03 AD06 AE12 AF35Y AF39Y AF61Y AH12 BB08 BC11 BC13 4J002 CF081 DJ016 FA096 GQ00 4J029 AA03 AB01 AB04 AC01 AD01 AE03 BA03 CB05A CC06A JC583 JF471 JF541 KB04 KB05 5E082 AB04 BC38 BC39 FG06 FG36 PP01 PP03 PP09 PP10

Claims (5)

[Claims] 1. A composition comprising 0.1 to 2% by weight of porous silica fine particles having an average particle size of 0.5 to 5 μm, 2,6-naphthalenedicarboxylic acid as a main dicarboxylic acid component, and ethylene glycol as a main glycol. A copolymer having an isophthalic acid component of 0.5 to 8 mol% (based on the total dicarboxylic acid component) and a diethylene glycol component content of 3 mol% (based on the total glycol component) or less. A biaxially oriented film comprising a polymerized polyethylene-2,6-naphthalate, wherein the copolymerized polyethylene-2,6-naphthalate comprises a manganese compound and an antimony compound used as a reaction catalyst, and a phosphorus compound used as a stabilizer. Contains an amount satisfying the following formulas (1), (2) and (3), and has an alkali metal content of 10 ppm or less. Furthermore plane orientation coefficient of the film is 0.230 or more 0.270 or less, and the density is 1.350
g / cm ³ or more. (1) 30 ≦ Mn ≦ 100 (1) (2) 150 ≦ Sb ≦ 450 (2) (20) P ≦ 100 (3) Is a manganese copolymerized polyethylene
Amount (ppm) in 2,6-naphthalate, Sb is an amount of antimony element in copolymerized polyethylene-2,6-naphthalate (ppm), P is an amount of phosphorus element in copolymerized polyethylene-2,6-naphthalate. (Ppm). ) 2. The average particle size is smaller than the thickness of the film and 0.1 to 1 μm, and the particle size ratio (major axis / minor axis) is 1.
2. The biaxially oriented polyester film for a capacitor according to claim 1, which contains 0.005 to 1% by weight of spherical silica fine particles of 0 to 1.2. 3. The biaxially oriented polyester film for a capacitor according to claim 1, wherein the film has a thickness of 0.2 to 5 μm and a heat shrinkage (150 ° C., 30 minutes) of 3% or less. 4. A film having a dielectric breakdown voltage of 260 V / μ.
The biaxially oriented polyester film for a capacitor according to claim 1, 2 or 3, wherein the insulation resistance characteristic (CR value) is 10000ΩF or more, and the frequency of pinholes is 0.01 pieces / cm ² or less. 5. The copolymer of claim 2, wherein the intrinsic viscosity of the polyethylene-2,6-naphthalate is 0.40 or more.
Or the biaxially oriented polyester film for a capacitor according to 4.