JP2000173856A - Biaxially oriented polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film suitable for a capacitor dielectric body which is capable of enhancing a capacitor much in electrostatic capacity keeping high breakdown voltage characteristics. SOLUTION: A film has physical properties where film thickness (t) is 2.5 μm or below through a weight method, a deviation in thickness Δt/t in the lengthwise direction of the film is 0.15 or below, and the average grain diameter (d) 50 (μm) of particles which are the largest in average grain diameter of particles contained in the film and the thickness (t) of the film are so set as to satisfy a formula (1). 0.5t<=d50<=1.0t...(1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film for a capacitor. More specifically, the present invention relates to a biaxially oriented polyester film for a capacitor dielectric having high capacitance and high withstand voltage characteristics.

[0002]

2. Description of the Related Art Biaxially oriented polyester films have various properties such as mechanical properties, heat resistance, electrical properties, and chemical resistance in a highly balanced manner and are excellent in cost performance. Widely used as industrial materials for packaging, plate making, etc. Among these applications, for capacitors, with the miniaturization of electrical equipment,
Demand for capacitors made from miniaturized polyester films is growing rapidly.

In recent years, with the development of electronic equipment and the like, high electrical characteristics of such polyester film capacitors have been demanded, and capacitance is first mentioned as a representative of the electrical characteristics. When obtaining a high capacitance, the most required property of the base film is to reduce the film thickness.On the other hand, in order to improve the handleability when processing the film, i.e., to improve the slipperiness and abrasion resistance of the film. In order to improve the good, usually, a method of containing fine particles in the film is widely adopted, but with the thinning, during the processing step, particularly, wrinkles at the time of winding, to significantly impede the productivity, Usually, this is dealt with by increasing the content of fine particles in the film.

[0004] However, the above-mentioned prescription alone causes the following problems. In other words, an increase in the amount of contained particles increases the probability of causing dielectric breakdown due to particles, so that the withstand voltage characteristics of the capacitor are significantly reduced. In addition, of the thickness variation of the base film, a portion locally thinner than the set thickness lowers the withstand voltage characteristics, and this becomes more remarkable as the thickness is reduced.

Further, it has been proposed that the handling properties and withstand voltage characteristics of a film are satisfied by laminating a thin film layer containing particles and a layer substantially containing no particles (Japanese Patent Laid-Open No. 3-197136). However, when the total film thickness is reduced to about the size of the particles to be added, the following fatal defects occur. That is, (A) the thinning proceeds too much, and it is practically impossible to cope with the lamination. (B) Since the average particle diameter of the particles is near or larger than the thickness of the layer containing the particles, coarse protrusions on the surface become large, and the dielectric breakdown caused by the particles is not completely eliminated.

As described above, there is a trade-off between improving the capacitance of the capacitor by reducing the thickness of the base film and decreasing the withstand voltage characteristics of the capacitor, and it is extremely difficult to satisfy both of them at the same time.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a biaxially oriented polyester suitable for a capacitor dielectric which achieves high capacitance while maintaining high withstand voltage characteristics. It is an object of the present invention to provide a film.

[0008]

Means for Solving the Problems The present inventor has conducted intensive studies in view of the above-mentioned problems, and as a result, if the average particle size of the particles, the film thickness and the thickness unevenness satisfy a specific relationship, excellent characteristics are obtained. The inventors have found that the film can be used as a base film for a capacitor, and have completed the present invention. That is, the gist of the present invention is that the thickness t of the film by the gravimetric method is 2.5 μm or less, and the thickness unevenness Δ in the longitudinal direction of the film.
t / t is 0.15 or less, and the average particle diameter d50 of the particle A having the largest average particle diameter among the particles in the film.
(Μm) and the thickness t of the film satisfy the following expression.

[0009]

[Formula 2] 0.5t ≦ d50 ≦ 1.0t ......

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester constituting the film of the present invention refers to a polyester in which 80% or more of the repeating units have an ethylene terephthalate unit or an ethylene-2,6-naphthalate unit.

Such polyesters are usually subjected to a polycondensation reaction via a transesterification reaction using (1) a lower alkyl ester of an aromatic dicarboxylic acid and glycol as main starting materials, or (2) an aromatic dicarboxylic acid. It is obtained by performing a polycondensation reaction via an esterification reaction by using glycerol and glycol as main starting materials. In order to carry out these reactions, a method of adding a metal compound as a catalyst is usually used. For example, compounds such as Ca, Mg, Mn, and Li are generally used as transesterification catalysts, and compounds such as Sb, Ti, Ge, Sn, and Co are generally used as polycondensation reaction catalysts.

However, when the content of such a metal compound is large, when the film is used as a dielectric of a capacitor, electric characteristics are deteriorated. In light of this fact,
In the present invention, it is preferable to employ the esterification reaction method of the above (2), which can reduce the content of the metal compound. In addition, the metal component present in the polyester is, in terms of metal element, excluding particles, excluding antimony in the range of 10 to 300 ppm, more preferably 10 to 200 ppm.
pm, in particular in the range from 10 to 150 ppm,
Other than that, it is preferable that the metal component is not substantially contained. Here, “substantially not contained” means that the total amount of metal components other than particles and antimony is 100 ppm or less, preferably 50 ppm or less. When the metal component content exceeds 100 ppm or the antimony content is 3
If it exceeds 00 ppm, the withstand voltage characteristics tend to be insufficient. On the other hand, when the content of antimony is less than 10 ppm, the productivity during the production of polyester is reduced. There is also a method of using a metal other than antimony as a catalyst in the production of polyester, but in such a case, the thermal stability of the polyester tends to decrease, and particularly when used as a recycled material, there is a problem that the withstand voltage characteristics deteriorate. May occur.

In the present invention, a phosphorus (P) compound may be contained in the polyester, if necessary. Phosphorus compounds generally have the effect of inactivating metal compounds, improving the thermal stability of polyesters, and improving electrical properties.
It may be advantageous to have about ppm. In addition, the polyester of the present invention may contain another third component as long as the conditions do not deviate from the above range.

As the aromatic dicarboxylic acid component, for example, besides terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxy) Benzoic acid and the like can be used. As the glycol component, other than ethylene glycol, for example, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol,
One or more of neopentyl glycol and the like can be used.

The intrinsic viscosity of the polyester is usually 0.45 or more, preferably 0.50 to 1.0, and more preferably 0.52 to 0.80. If the intrinsic viscosity is less than 0.45, there may be a problem that the productivity at the time of producing the film is reduced or the mechanical strength of the film is reduced. On the other hand, from the viewpoint of melt extrusion stability of the polymer, the intrinsic viscosity preferably does not exceed 1.0.

The polyester film of the present invention must have a thickness t measured by a gravimetric method of 2.5 μm or less, and preferably less than 2.0 μm. t is 2.5 μm
If it exceeds, the capacity of the capacitor as a final product is small and unsuitable. The polyester film of the present invention,
Prevents the occurrence of scratches during film production and capacitor production,
In order to improve the handleability by giving the film a slippery property, the polyester contains particles to form appropriate protrusions on the film surface.The biggest feature of the present invention is that the particle size of the particles to be contained is specified. In the range of

That is, the average particle diameter d50 of the particles A having the largest average particle diameter among the particles in the film of the present invention.
(Μm) needs to be in the range of 0.5 t to 1.0 t, preferably 0.5 t to 0.9 t, with respect to the gravimetric thickness t (μm) of the film. When the average particle diameter d50 of the particles A in the film exceeds 1.0 t, the particle density in a state of penetrating or near penetrating in the thickness direction increases, and electrical breakdown occurs mainly thereat. Degraded and unsuitable. Conversely, particles A in the film
If the average particle size d50 of less than 0.5t, the ability to form projections on the film surface is poor, and the winding workability is reduced,
When the film is wound into a roll during the film forming process and the capacitor manufacturing process, wrinkles occur, which is inappropriate.

In addition, the film of the present invention must have a thickness unevenness Δt / t in the longitudinal direction of 0.15 or less, preferably 0.10 or less, more preferably 0.08 or less. The term “thickness unevenness in the longitudinal direction” used herein means the maximum value tma of the thickness in the longitudinal direction of 3 m measured by a non-contact type film thickness measuring device, which will be described later in detail in the Examples section.
A value obtained by subtracting the minimum value tmin from x (Δt) by the average thickness t by the weight method. If the thickness unevenness in the longitudinal direction exceeds 0.15, there will be portions extremely thinner than the set thickness, and electrical breakdown will occur around these portions, so that the withstand voltage characteristics of the capacitor will decrease, Appropriate.

In order to realize the above-mentioned thickness unevenness in the longitudinal direction, for example, it is possible to take the following prescription, but it is not limited to this. First, a polyester raw material is supplied to an extruder, melt-extruded at a temperature equal to or higher than the melting point of polyester, and extruded as a molten sheet from a slit die. Next, the molten sheet is quenched and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

When the molten sheet comes into close contact with the drum, the sheet is covered with a plate or a cover so that the sheet does not pulsate due to the flow of gas such as ambient air. It is useful to stabilize the sheet thickness, and the effect is extremely remarkable when the film thickness is particularly small as in the present invention. In the present invention, the sheet thus obtained is biaxially stretched to form a film. To describe the biaxial stretching conditions specifically, the unstretched sheet is first stretched in the first axial direction. The stretching temperature range is usually from 70 to 150 ° C., the stretching ratio is usually from 2.5 to 6 times, and the stretching can be performed in one stage or two or more stages. Next, the uniaxially oriented film is once cooled below the glass transition point in the second axis direction, that is, in a direction orthogonal to the first axis direction, or without cooling,
For example, it is preheated to a temperature range of 80 to 150 ° C., and is further usually 2.5 to 5 times, preferably 3.0 to 3.0 at almost the same temperature.
The film is stretched 4.5 times to obtain a biaxially oriented film.

It is preferable that the stretching in the first axial direction is performed in two or more steps because good thickness uniformity can be achieved. In addition, a method of further stretching in the longitudinal direction after the transverse stretching is possible, but in any case, it is preferable to set the total stretching ratio in the longitudinal direction to 3.5 times or more. The film thus obtained is heat-treated under elongation, limited shrinkage, or constant length, usually within 30%, usually for 1 second to 5 minutes. At this time, re-stretching may be performed in the longitudinal direction, the lateral direction, or both directions during or after the heat treatment step.

In order to further exert the effects of the present invention,
It is preferable that the average particle size, the particle size distribution, and the content in the film of the particles A are in specific ranges. That is, the average particle size (d50) is 0.5 t or more and 0.50 to 2.00 μm
And the particle size distribution (d25 / d75) is preferably 0.05 to 0.40% by weight. The average particle diameter of the particles A is preferably about 0.1.
5t or more and in the range of 0.80 to 1.50 μm, the particle size distribution is preferably 2.0 or less, and the content is preferably 0.10 to 0.30% by weight.

In the case of particles having an average particle diameter of less than 0.50 μm, this alone may result in insufficient slipperiness of the film, and in the case of particles having an average particle diameter of more than 2.00 μm, the withstand voltage characteristics as a capacitor may be insufficient. Tends to decrease. If the particle size distribution of the particles A exceeds 2.5, the number of protrusions on the coarse side tends to increase, and as a result, the withstand voltage characteristics may decrease.

If the content of the particles A is less than 0.05% by weight, the film may not have slipperiness,
If it exceeds 0% by weight, the withstand voltage characteristics tend to decrease. Further, in order to further improve the slipperiness and winding workability of the film surface, in addition to the particles A, small particles B having an average particle diameter (d50) of less than 0.5 t as long as the gist of the present invention is not impaired. From 0.05 to 1.00% by weight, more preferably from 0.
It is preferable to contain 10 to 0.70% by weight.

These small particles B do not become coarse projections on the film surface, but form appropriate small projections and contribute to the winding workability. Therefore, it is preferable to further improve the effects of the present invention. When the content is less than 0.05% by weight, the improvement in winding workability tends to be small, and when the content exceeds 1.00% by weight, aggregation of particles may be caused. Small particle B
Has a particle size distribution (d25 / d75) of preferably 2.0 or less.

Examples of the particles used in the present invention include inorganic particles such as calcium carbonate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite and molybdenum sulfide, and crosslinked polymer particles. , Organic particles such as calcium oxalate, and precipitated particles formed during the polymerization of polyester. Examples of such particles include affinity of the particles with polyester, followability during biaxial stretching (flexibility), and hardness. Comprehensively judge such points that voids, so-called voids, are unlikely to be generated near the particles and do not deteriorate the electrical characteristics, and that when they become projections on the film surface, the shape can effectively exhibit slipperiness. At least one selected from calcium carbonate, silica, calcium phosphate, hydroxyapatite and crosslinked polymer particles It is preferable that.

In producing the polyester containing particles,
The particles may be added during the polyester synthesis reaction or may be added directly to the polyester. When it is added during the synthesis reaction, a method in which the particles are added as a slurry in which the particles are dispersed in ethylene glycol or the like at an arbitrary stage of polyester synthesis is preferable. On the other hand, when it is directly added to the polyester, it is used as dried particles or water or a compound having a boiling point of 2%.
As a slurry dispersed in an organic solvent at a temperature of
A method of adding and mixing with polyester using a shaft kneading extruder is preferred. In addition, the particles to be added may be subjected to processing such as crushing, dispersion, classification, and filtration as needed.

As a method of adjusting the content of particles, a master material containing particles at a high concentration is prepared in the above-described manner, and is diluted with a material substantially containing no particles at the time of film formation. A method of adjusting the particle content is effective. In addition, as additives other than the above-mentioned projection-forming agent, if necessary, an antistatic agent, a stabilizer, a lubricant, a cross-linking agent, an anti-blocking agent, an antioxidant, a coloring agent, a light-blocking agent, an ultraviolet absorber, etc. May be contained in a range that does not deteriorate the capacitor characteristics.

The polyester film of the present invention preferably has a specific resistance of 2 × 10 ⁸ Ωcm or more, more preferably 5 × 10 ⁸ Ωcm or more, when the film is melted. When the specific resistance is less than 2 × 10 ⁸ Ωcm, there is a tendency that withstand voltage characteristics, electric loss required for capacitors, such as dielectric loss and insulation resistance, are inferior. To make the specific resistance at the time of melting of the polyester into the above range, contained in the polyester,
A method of reducing the amount of metal added as a catalyst or a metal mixed in for other reasons, or a method of adding a phosphorus compound in a molar ratio of 0.5 or more to such a metal can be adopted. The upper limit of the specific resistance at the time of melting is about 1 × 10 ¹⁰ Ωcm due to the necessity of adding a catalyst in the production of polyester. Even if the specific resistance is higher than this, the effect of improving the electrical characteristics can no longer be expected, and the difficulty in manufacturing to achieve such specific resistance increases.

The film of the present invention can enhance the adhesiveness to the metal deposited by the coating layer. Examples of the resin constituting the coating layer include resins such as polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, and polyurethane, and copolymers of these resins. Coalescence or mixtures can be mentioned. Among these, when a coating layer containing polyester or polyurethane is used, a high degree of adhesiveness can be provided, and heat resistance and heat and humidity resistance for capacitors can be satisfied.

The coating solution used for forming the coating layer may contain methylol or a cross-linking agent as a crosslinking agent in order to improve the adhesion (blocking property), water resistance, solvent resistance and mechanical strength of the coating layer. Rolled urea-based, melamine-based, guanamine-based, acrylamide-based, polyamide-based compounds, epoxy compounds, aziridine compounds, block polyisocyanates, silane coupling agents, titanium coupling agents, zircoaluminate coupling agents , Peroxides, heat and photoreactive vinyl compounds and photosensitive resins.

Further, in order to improve the sticking property and the sliding property, silica, silica sol, alumina, alumina sol, zirconium sol, kaolin, talc, calcium carbonate, calcium phosphate, titanium oxide, and the like are contained in the coating layer as inorganic fine particles.
Barium sulfate, carbon black, molybdenum sulfide, antimony oxide sol, etc., as organic fine particles, polystyrene, polyethylene, polyamide, polyester, polyacrylate, epoxy resin, silicone resin,
It may contain a fluorine resin or the like.

Further, if necessary, an antifoaming agent, a coating improver, a thickener, an antistatic agent, an organic lubricant, an antioxidant,
It may contain an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like. As a method of applying the above-mentioned coating solution to a polyester film, Yuji Harazaki, Maki Shoten, published in 1979,
A reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating device other than those described in the “coating method” can be used. The coating layer may be provided in the film manufacturing process, or may be applied after the film is manufactured. In particular, from the viewpoint of uniformity of the coating thickness and production efficiency, a coating method in the film manufacturing process is preferable.

As a method of applying in the film production process, a method of applying a coating solution to a polyester unstretched film and successively or simultaneously biaxially stretching the same, applying a uniaxially stretched polyester film, and further uniaxially stretching the film. There is a method of stretching in a direction perpendicular to the direction, or a method of applying to a biaxially stretched polyester film and further stretching in the transverse and / or longitudinal directions.

The thickness of the coating layer is usually from 0.005 to 1.0
μm, and preferably 0.01 to 0.5 μm. If the thickness of the coating layer exceeds 1.0 μm, the electrical characteristics may be deteriorated. On the other hand, when the thickness of the coating layer is less than 0.005 μm, there is a tendency that coating unevenness and coating slippage tend to occur.

[0036]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “parts” means “parts by weight”, and “pp”
"m" indicates "weight ppm". (1) Intrinsic viscosity of polymer [η] (dl / g) 1 g of polymer is phenol / tetrachloroethane = 50
/ 50 (weight ratio) in 100 ml of a mixed solvent.
Measured in ° C. (2) Average particle size (d50) (μm) and particle size distribution value (d25 / d75) of particles Particle size distribution analyzer (SA-CP) manufactured by Shimadzu Corporation
The average particle diameter (d50) was the particle diameter at 50% of the integrated volume fraction integrated from the large particle side in the equivalent spherical distribution measured by type 3). The values of the integrated volume fractions of 25% and 75% were d25 and d75, respectively, and the ratio value (d25 / d75) was taken as the particle size distribution value. The smaller the particle size distribution value, the sharper the particle size distribution of the particles. (3) Thickness t (μm) by gravimetric method First, the density (ρ; (g / cm ³ )) of the film test piece was measured by the D method (density gradient tube method) specified in JIS K7112, and then 100 ± A test piece cut to a size of 0.5 cm ² was placed on a balance, and the film mass (m;
After correctly measuring (g)) to 0.0001 g, it was calculated by the following equation. This measurement was repeated 10 times, and the median of the obtained values of t was defined as the gravimetric thickness (μm).

[0037]

## EQU3 ## t = 100 m / ρ (4) Thickness unevenness in the longitudinal direction Δt / t Thirty points in a 3 m long section in the longitudinal direction of the film were randomly extracted. Non-contact type film thickness measuring device based on the principle of optical interference (MCPD
−1000 ”), the maximum thickness (μm) and the minimum thickness (μm) are measured for each sample, and the deflection Δt
(Maximum thickness−minimum thickness) was calculated. 30 such measurements
This was repeated twice, and the average value was divided by the gravimetric thickness t obtained above to obtain the thickness unevenness Δt / t in the longitudinal direction. (Manufacture of capacitors) Using a resistance heating type metal deposition device,
With the pressure in the vacuum chamber set to 10 ^-4 Torr or less, a roll-shaped film was unwound, aluminum was vapor-deposited on the film surface to a thickness of 450 °, and the film was rolled up again. At this time, vapor deposition was performed in a stripe shape having a margin portion in the longitudinal direction of the polyester film (the width of the vapor deposition portion was 8 m).
m, width of the margin part 1 mm).

The vapor-deposited film obtained as described above was slit into a tape having a width of 4.5 mm and a left or right margin having a width of 0.5 mm. The obtained left-margin and right-margin vapor-deposited polyester films, one each, were wound together to obtain a roll. At this time, the two films were wound while being shifted so that the vapor deposition portion protruded by 0.5 mm in the width direction. This wound body was pressed at a temperature of 140 ° C. and a pressure of 50 kg / cm ² for 5 minutes. Metallicon is sprayed on both sides of the roll after pressing, leads are attached, and an impregnated layer of liquid bisphenol A type epoxy resin, and a minimum thickness of 0.5 mm by heating and melting the powdery epoxy resin Was formed into a film capacitor. (5) Withstand Voltage Characteristics of Capacitor Under an environment of 23 ° C. and 50% RH, a DC voltage was applied between the electrodes of the capacitor obtained by the above method, and a voltage (V) at which dielectric breakdown occurred was measured. In the measurement, 30 points were randomly extracted, the average thereof was determined, and a value (V / μm) obtained by dividing the average by the above gravimetric method thickness was calculated to obtain a withstand voltage characteristic, which was classified as follows.

◎: Excellent: 270 V / μm or more ：: Good, no practical problem: 240 V / μm or more 270
Less than V / μm ×: Poor: less than 240 V / μm Example 1 86 parts of terephthalic acid and 70 parts of ethylene glycol were placed in a reactor, and under a pressure of 0.5 kg / mm ² at about 250 ° C.
The esterification reaction was performed for 4 hours.

Then, 0.015 parts of antimony trioxide,
Calcium carbonate particles having an average particle size of 1.10 μm and a particle size distribution value of 1.65, an average particle size of 0.35 μm, and a particle size distribution value of 1.8
0 of crosslinked polymer particles and 0.01 part of phosphoric acid. The temperature was gradually raised from 250 ° C. to 285 ° C., and the pressure was gradually reduced from normal pressure to 0.5 mmHg. After 4 hours, the polycondensation reaction was stopped to obtain a polyester (a) having an intrinsic viscosity of 0.65. This polyester (a) contained 0.15% by weight of calcium carbonate and 0.20% by weight of crosslinked polymer particles.

The polyester (a) is dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, quenched on a cooling roll using an electrostatic contact method, and formed into an amorphous sheet. did. In addition, a plate was installed in the vicinity of the point where the molten sheet was in close contact with the cooling roll, and the flow of air was shut off. The obtained sheet was stretched 2.9 times in the longitudinal direction at 84 ° C. using a roll stretching method, and then further stretched by 70%.
The film was stretched 1.3 times at ° C. The obtained uniaxially stretched film was guided to a tenter and stretched 4.0 times at 110 ° C. in the transverse direction.
Heat treatment at 230 ° C.
A 0 μm biaxially stretched polyester film was obtained. While trimming from this master roll to 500mm width,
A roll having a total length of 35000 m and a roll shape was wound on a roll core having an inner diameter of 6 inches to form a roll film.

Example 2 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of calcium acetate monohydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out a transesterification reaction. 4 hours, 2
The temperature was raised to 30 ° C. to substantially complete the transesterification reaction.

Then, 1.5 parts of hydroxyapatite particles having an average particle size of 0.90 μm and a particle size distribution value of 1.55 and crosslinked polymer particles 1.0 having an average particle size of 0.35 μm and a particle size distribution value of 1.80 were obtained. Parts were added as an ethylene glycol slurry. After the addition of the slurry, 0.06 parts of phosphoric acid and 0.04 parts of antimony trioxide were further added, and the reaction system was gradually reduced in pressure, the temperature was increased, and the polycondensation reaction was performed for 4 hours. b) was obtained. Except that no particles were added, a dilution polyester (c) having an intrinsic viscosity of 0.67 was obtained in the same manner as in (b).

Polyester (b) and polyester (c)
And a film-forming condition of 0.30% by weight of hydroxyapatite particles and 0.20% by weight of cross-linked polymer particles having a thickness of 1.50 μm by a weight method. An axially oriented polyester film was obtained, and a width of 500 mm and a total length of 3500 were obtained in the same manner as in Example 1.
A roll film of 0 m was obtained.

Example 3 A silica particle having an average particle size of 1.10 μm and a particle size distribution value of 1.50 was prepared in the same manner as in Example 2 except that a plate near the point where the molten sheet was in close contact with the cooling roll was not installed. 0.
20% by weight, average particle size 0.20 μm, particle size distribution value 1.6
Thus, a roll-shaped film having a weight-method thickness of 1.50 μm containing 0.50% by weight of silica particles of No. 0 was obtained.

Example 4 In the same manner as in Example 3, a roll-shaped film having a weight-average thickness of 1.50 μm and containing 0.20% by weight of calcium phosphate particles having an average particle size of 1.40 μm and a particle size distribution value of 1.90. I got Comparative Example 1 Calcium carbonate particles of 0.40 were prepared in the same manner as in Example 1 except that the particles were calcium carbonate particles having an average particle size of 0.60 μm and a particle size distribution value of 1.50.
A roll-form film having a thickness of 1.50 μm by weight method containing 1% by weight was obtained.

However, when manufacturing the capacitor, when the film after the vapor deposition is wound up again in a roll shape, the handleability is poor, the roll is wrinkled, and the roll is not proceeded to the next step, and the final capacitor is processed. I couldn't do that. Comparative Example 2 In Example 3, the particles were calcium carbonate particles having an average particle size of 1.60 μm and a particle size distribution value of 3.50, and the longitudinal stretching from the amorphous sheet was 3.4 times at 84 ° C. (one step). Stretching), except that calcium carbonate particles were contained in an amount of 0.20% by weight and the thickness by weight method was 1.66 μm.
m was obtained.

Comparative Example 3 In Example 3, the particles were silica particles having an average particle size of 2.50 μm and a particle size distribution of 3.80, and the longitudinal stretching from the amorphous sheet was 3.77 times at 84 ° C. ( In the same manner as in Example 3 except that the silica particles were 0.70
A roll-form film having a thickness of 1.50 μm by weight method containing 1% by weight was obtained.

The results obtained for Examples 1 to 4 and Comparative Examples 1 to 3 are summarized in Table 1 below.

[0050]

[Table 1]

[0051]

The film of the present invention is excellent in processability because it has a good thickness unevenness and a good particle composition with a high withstand voltage characteristic in spite of its extremely thin thickness. Electrical characteristics can be obtained, and the industrial value of the present invention is high.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) B29L 7:00 C08L 67:00 F term (reference) 4F071 AA43 AA44 AA45 AA46 AA80 AB15 AB17 AB21 AB23 AB24 AB25 AB26 AC09 AD02 AE11 AH12 BB08 BC01 4F210 AA24 AB16 AB17 AC04 AE01 AG01 AH33 QA02 QA03 QC06 QG01 QG18 5E082 AB05 BC35 EE07 EE24 EE37 FF14 FG06 FG36 GG04 HH25 HH48 JJ04 JJ22 PP03 PP09

Claims (4)

[Claims] 1. A film thickness t by a gravimetric method is 2.5 μm.
m or less, the thickness unevenness Δt / t in the longitudinal direction of the film is 0.15 or less, and the average particle diameter d50 (μm) of the particle A having the largest average particle diameter among the particles in the film and the film thickness t A biaxially oriented polyester film for a capacitor, characterized by satisfying the following formula: [Expression 1] 0.5t ≦ d50 ≦ 1.0t ... 2. The particle A has an average particle diameter (d50) of 0.5 t or more and a range of 0.50 to 2.00 μm, and a particle diameter distribution value (d25 / d75) of 2.5 or less; The biaxially oriented polyester film for a capacitor according to claim 1, wherein the content of the particles A in the film is 0.05 to 0.40% by weight. 3. A biaxially oriented polyester for a capacitor according to claim 1, wherein the polyester contains 0.05 to 1.00% by weight of particles B having an average particle diameter (d50) of less than 0.5 t. the film. 4. The method according to claim 1, wherein the particles in the film are calcium carbonate,
The biaxially oriented polyester film for a capacitor according to any one of claims 1 to 3, wherein the biaxially oriented polyester film is at least one selected from silica, calcium phosphate, hydroxyapatite, and crosslinked and crosslinked polymer particles.