JP2001052953A - Polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the insulation resistance and voltage resistance of a capacitor by, related to a biaxial orientation film whose main component is a polyethylene terephthalate, allowing a minimum value (Emin) of Young's modulus in the planar direction of a film to be a specified value or above. SOLUTION: A polyester film for a capacitor is polyester constituting a polyethylene terephthalate as a main component. A telephthalic acid is used as a dicarboxylic acid component, and as a diol component, an ethylene glycol is used as a main component for polymerization. The polyester film is manufactured by a biaxial stretching method considering a mechanical characteristics, electric characteristics, and productivily. The minimum value (Emin) of Young's modulus in the planar direction of the film must be 4.5 Gpa or above. The polyester film is used for a capacitor as a metalized polyester film wherein such metal layer as of Al, Zn, Mg, and Sn is provided st least on one surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a capacitor, and more particularly to a polyester film containing polyethylene terephthalate as a main component which is suitably used as a dielectric of a capacitor. The present invention relates to a polyester film containing polyethylene terephthalate as a main component and a film capacitor using the same.

[0002]

2. Description of the Related Art Conventionally, polyester films have been widely used as dielectrics for capacitors because of their excellent mechanical properties, heat resistance and electrical properties.

[0003] When a polyester film is used as a dielectric of a capacitor, it is usually wound together with a metal foil to form a compact shape, or wound into a metallized polyester film having a metal layer provided on the surface of the polyester film in advance. Alternatively, after forming the element by laminating, pressing, impregnating with insulating oil, embedding in resin or housing in a case are performed, and aging at a certain temperature to stabilize electric characteristics (mainly capacitance). It is also common to be done.

[0004] When a polyester film is used as a dielectric of a capacitor as described above, the polyester film is subjected to various thermal and mechanical stresses until the completion of the capacitor. As a result, in some cases, the completed capacitor may have lower capacitor characteristics than expected due to the excellent insulation resistance and withstand voltage inherent as a material of the polyester film. In addition, it goes without saying that if the electrical properties of the polyester film itself are inferior, the capacitor properties deteriorate. A capacitor with such deteriorated capacitor characteristics will be disposed of as a rejected product by electrical inspection.If the rejection rate increases, not only does the manufacturing cost increase, but also the capacitor shipped as a passed product. However, there is a high possibility that a species that potentially reduces the function is inherent, and it may be difficult to say that the capacitor is excellent in safety.

[0005] As a recent trend, if an abnormality occurs in a product after shipment, the manufacturer is increasingly liable, so that the capacitor manufacturer has to deal with it by strengthening the electrical inspection. As a result, a vicious circle such as an increase in the rejection rate at the time of manufacturing is increasing.

[0006] Under these circumstances, on the other hand, for the purpose of cost reduction, capacitor manufacturers constantly improve the conditions of the capacitor manufacturing process. For example, in a press process after winding a reel under the manufacturing conditions of a wound capacitor, a press temperature is set high or a press pressure is set high. Setting the press temperature and pressure to a high value not only has the advantage that the time required for the process can be shortened, but also results in a defective product (for example, the shape after the press is distorted due to insufficient press). However, there is an effect of reducing the ratio of non-defective or non-defective products whose shape after pressing is not stable after the next step).

However, if severe pressing conditions are used in view of the film, the defective rate of the shape after pressing can be reduced, but the completed capacitors having deteriorated withstand voltage and insulation resistance are drastically increased. In addition, since thermal stress is applied during aging for stabilizing electric characteristics, there is a problem that insulation resistance and withstand voltage deteriorate.

That is, a polyester film used as a dielectric of a capacitor is required to have no deterioration in withstand voltage and insulation resistance of a completed capacitor.

In order to solve such a problem, Japanese Patent Laid-Open Publication No.
Japanese Patent No. 753 discloses a polyester film for a capacitor dielectric, which has a high F5 value in the longitudinal direction, suppresses elongation due to tension at the time of winding because the number of protrusions on the film surface is specified, and is excellent in winding property and crushing property. Have been.

Japanese Patent Application Laid-Open No. 57-22021 also discloses that the F5 value in the longitudinal direction is high, the elongation due to tension at the time of winding is suppressed by containing specific crosslinked polymer particles, and the film is stretched at the time of film forming stretching. There is disclosed a polyester film for a capacitor dielectric which does not decrease the withstand voltage or the CR value because the destruction of the particles can be suppressed.

Furthermore, Japanese Patent Application Laid-Open No. 3-246814 discloses that the sum of F5 values in the longitudinal direction and the transverse direction is high, and by containing specific crosslinked polymer particles, elongation due to tension during winding is suppressed. There is disclosed a polyester film for a capacitor dielectric having excellent reversibility and crushability.

Further, JP-A-2-251538 and JP-A-2-252226 disclose a method of regulating the birefringence of a film so as to strengthen the film in the longitudinal direction and to wind the film by including specific particles. There is disclosed a polyester film for a capacitor which suppresses elongation due to tension at the time and is excellent in winding property and crushing property.

Furthermore, Japanese Patent Application Laid-Open No. 2-207517 discloses that the birefringence of the film, the F5 value in the longitudinal direction and the heat shrinkage are specified to suppress the elongation due to the tension at the time of winding, and to improve the winding property and crushing. A polyester film for a capacitor having excellent properties is disclosed.

However, as proposed in these films, in a film that adopts a stretching method that simply strengthens the longitudinal direction of the film and suppresses elongation with respect to tension, heat is higher than the glass transition temperature of the film, such as the pressing temperature. When it is added, it cannot be pressed uniformly because there is no elongation enough to cause moderate thermal deformation, it is not possible to suppress the defective rate of the pressed shape, many defective products with poor dielectric loss occur, and productivity decreases Was causing it.

[0015] On the other hand, at present, the miniaturization of capacitors,
From the viewpoints of increasing capacitance and reducing costs, there is a strong demand for thinner dielectrics. As an advantage of thinning, for example, for a capacitor element having a rated voltage of 500 V and a capacitance of 0.1 μF using a 5.0 μm polyester film as a dielectric, if the thickness of the polyester film to be a dielectric is 4.5 μm, an electrostatic Since the capacitance is inversely proportional to the thickness of the dielectric, manufacturing a capacitor element having the same capacitance reduces the volume of the capacitor element by 19%.
Can be reduced. On the other hand, when a capacitor element having the same volume is manufactured, the capacitance becomes 1.2.
Can be doubled. However, there is a disadvantage that the rated voltage of 500 V cannot be guaranteed because the withstand voltage is reduced by thinning.

As described above, in order to realize a thinner polyester film serving as a dielectric, it is required to improve the withstand voltage to compensate for a decrease in the withstand voltage due to the thinner film. In order to improve the withstand voltage, it is necessary to improve the withstand voltage of the polyester film before processing into a capacitor, and it is necessary that the withstand voltage does not easily decrease due to thermal stress or mechanical stress during processing of the capacitor There is.

For the purpose of improving the voltage resistance,
No. 66394, JP-A-53-120167,
JP-A-55-21157, JP-A-55-2282
No. 6, JP-A-55-158609,
7-119923, JP-A-62-259304, JP-A-63-61028, JP-A-63-1
No. 41308, JP-A-63-255909,
JP-A-63-316419, JP-A-64-121
7, JP-A-1-117309 and JP-A-2-117.
In 272713 gazette, there is a proposal for a film having a specific surface structure by specific particles or coating,
JP-A-53-147774 proposes to change the heat setting temperature on the front and back of the film.
Japanese Patent No. 107610 proposes a polyester film for a capacitor in which workability and electrical characteristics are compatible by defining the average refractive index of the film, the F5 value in the longitudinal direction, and the degree of plane orientation.

However, the techniques proposed in these publications are:
It has not been possible to achieve both a reduction in the defect rate of the insulation resistance and an improvement in the withstand voltage.

[0019]

SUMMARY OF THE INVENTION The inventors of the present invention have ascertained that a polyester film having a specific mechanical strength can improve the withstand voltage of the film, and can improve the insulation resistance and the withstand voltage of a capacitor obtained as a product. Have been found to be difficult to reduce.

It is an object of the present invention to provide a polyester film capable of improving the withstand voltage of the film and reducing the deterioration of the insulation resistance and the withstand voltage of a capacitor manufactured under severe conditions.

[0021]

In order to achieve the above object, a polyester film for a capacitor of the present invention comprises:
A biaxially oriented film containing polyethylene terephthalate as a main component, characterized in that the minimum value (Emin) of the in-plane Young's modulus of the film is 4.5 GPa or more.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with preferred embodiments. The polyester of the polyester film in the present invention is a polyester having polyethylene terephthalate as a main component,
More specifically, terephthalic acid is used as a dicarboxylic acid component, and polycondensation can be obtained using ethylene glycol as a main component as a diol component. Here, the main component means that the total amount of terephthalic acid and ethylene glycol constituting polyethylene terephthalate is 90% by weight or more, and if it is 10% by weight or less, the third component is copolymerized or blended. It may be. As the copolymerization component, a dicarboxylic acid component other than terephthalic acid and a diol component other than ethylene glycol are preferably used.

The dicarboxylic acid component used as the copolymerization component includes isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, trimethyladipic acid, sebacic acid, malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, pimerin Acid, 2,2-dimethylglutaric acid,
Azelaic acid, fumaric acid, maleic acid, itaconic acid,
1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalic acid, diphenic acid, 4,4′-
Oxybenzoic acid, 2,5-naphthalenedicarboxylic acid and the like can be used. Of these, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid,
Diphenylethanedicarboxylic acid is preferred.

The diol component used for copolymerization includes diethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentane. Diol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 2,4-dimethyl-2-
Ethylhexane-1,3-diol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 3-methyl-1,5 -Pentanediol,
2,2,4-trimethyl-1,6-hexanediol, 1,
2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 4,4′-thiodiphenol, bisphenol A, 4,4'-methylenediphenol, 4,4 '-(2
-Norbornylidene) diphenol, 4,4'-dihydroxybiphenol, o-, m-, and p-dihydroxybenzene, 4,4'-isopropylidenephenol, 4,4'-isopropylidenebis (2,6-dichlorophenol ) 2,5-Naphthalenediol, p-xylenediol, cyclopentane-1,2-diol, cyclohexane-1,2-diol, cyclohexane-1,
4-diol and the like can be used. Of these, propylene glycol, tetramethylene glycol, and cyclohexanedimethanol are preferred.

In addition to the dicarboxylic acid component and the diol component, oxycarboxylic acids such as p-oxybenzoic acid and the like may be copolymerized. Further, these have a linear structure, but form a trivalent or higher valent ester. Branched polyesters can also be formed using the components.

Examples of the blend include homopolyesters other than polyethylene terephthalate, copolymerized polyesters, polycarbonate resins, acrylic resins, polyolefin resins and the like.

The intrinsic viscosity of the polyester used in the present invention is preferably 0.5 dl / g or more, more preferably 0.55 dl / g or more, in terms of withstand voltage and mechanical properties for use in a capacitor. It is also preferable from the viewpoint of properties.

Inert particles may be added to the polyester used in the present invention. Examples of the inert particles include silica,
Examples include inorganic fillers such as alumina, calcium carbonate, calcium phosphate, barium sulfate, magnesium oxide, zinc oxide, and titanium oxide, and organic polymer particles (for example, crosslinked polystyrene particles and acrylic particles).

If necessary, flame retardants, heat stabilizers, plasticizers, antioxidants, ultraviolet absorbers, antistatic agents, pigments,
Organic lubricants such as fatty acid esters and waxes may be blended, or two or more of these may be used in combination.

The polyester film in the present invention needs to be biaxially stretched from the viewpoint of mechanical properties, electrical properties and productivity.

As the method of biaxial stretching, any of an inflation simultaneous biaxial stretching method, a stenter simultaneous biaxial stretching method, and a stenter sequential biaxial stretching method may be employed. From the viewpoint of the properties, a stenter sequential biaxial stretching method and a stenter simultaneous biaxial stretching method are preferred.

The polyester film in the present invention is used for the purpose of improving the withstand voltage of the film and reducing the deterioration of the insulation resistance of the manufactured capacitor and improving the withstand voltage which are the main objects of the present invention. It is necessary that the minimum value (Emin) of the Young's modulus in the direction is 4.5 GPa or more. Emin measures Young's modulus not only in the longitudinal direction (MD) and the width direction (TD) but also in all directions in the film plane, and defines the minimum value as Emin. Emin is the mechanical strength in the weakest direction in the plane of the film as defined, and Emin may be smaller than the MD and TD directions depending on the film forming method and the like. In the present invention, E
It has been found that min controls the withstand voltage of the film, the insulation resistance and the withstand voltage of the capacitor. If Emin is less than 4.5 GPa, the withstand voltage of the film and the insulation resistance and withstand voltage of the capacitor deteriorate. Emin is more preferably 5.0 GPa or more. The method of setting Emin to 4.5 GPa or more is not particularly limited, but a film forming method in which the draw ratio is increased as much as possible, a film forming method in which the film is not excessively stretched in one direction in a longitudinal direction or a width direction of the film, and a film width direction. In the case where there is physical property unevenness in the width direction of the formed film, it is preferable to use the central part or to use them in combination.

In the present invention, from the viewpoints of insulation resistance and withstand voltage, the plane orientation coefficient fn represented by the following formula (1) is set to 0.1.
It is preferably from 165 to 0.18. Plane orientation coefficient f
When n is less than 0.165, insulation resistance and withstand voltage are insufficient, and when the plane orientation coefficient fn exceeds 0.18, tearing occurs frequently during the production of the polyester film, and the productivity is reduced.
A more preferred range of the plane orientation coefficient fn is 0.169 to
0.178. fn = (nMD + nTD) / 2-nZD (1) (Here, nMD, nTD, and nZD are the refractive indexes in the longitudinal direction, width direction, and thickness direction of the film, respectively.)

The polyester film of the present invention has a birefringence Δ represented by the following formula (2) in order to improve the withstand voltage.
n is preferably -0.02 to 0.03. Δn = nMD−nTD (2) (where nMD and nTD are the refractive indices in the longitudinal direction and the width direction of the film, respectively.) When the birefringence Δn is out of the above range, the balance of the orientation of the polymer chains. May be greatly distorted, and the withstand voltage may decrease or the insulation resistance may deteriorate. A more preferable range of the birefringence Δn is −0.015 to 0.02.

It is preferable to age the polyester film obtained in the present invention at 40 to 80 ° C. from the viewpoint of further stabilizing the insulation resistance and the withstand voltage. The reason for this is not clear, but is presumed to be that aging relaxes the free volume of the amorphous chains in the film and reduces insulation defects. Aging time is 1
0 hours or more is preferable in terms of improving insulation resistance, and more preferably 24 hours or more.

The polyester film of the present invention preferably has an endothermic peak at 70 to 120 ° C. when measured by a differential scanning calorimeter. The endothermic peak is 40
This is because the effect of the heat treatment can be confirmed thermally because the heat treatment appears at a temperature of about 80 ° C. for 10 hours or more. In addition, it is preferable that the heat quantity at the endothermic peak is 0.05 to 1 J / g because the insulation resistance and the withstand voltage of the capacitor are further improved. If the heat quantity at the endothermic peak is less than 0.05 J / g, the insulation resistance and the withstand voltage may not be improved, and 1 J / g
When the ratio exceeds, the flatness of the polyester film may be deteriorated, so that the winding property is deteriorated, and it becomes difficult to prepare a capacitor element. The calorific value of the endothermic peak is more preferably 0.1 to 0.8 J / g.

The surface of the polyester film of the present invention is
The center line average surface roughness Ra is preferably from 10 to 90 nm, more preferably from 20 to 80 nm, from the viewpoints of handleability, slipperiness, anti-blocking properties, pressability of the capacitor element, withstand voltage, and self-heel property.

The polyester film of the present invention is preferably used for a capacitor as a metalized polyester film having a metal layer provided on at least one side in order to maximize the effect of improving the insulation resistance of the present invention. In a foil-wound capacitor using the polyester film of the present invention together with a metal foil as a winding capacitor, the insulation resistance may be stable even without using the polyester film of the present invention.

The method for providing a metal layer on at least one surface of the polyester film of the present invention includes, but is not particularly limited to, a vacuum deposition method and a sputtering method. However, a vacuum evaporation method is preferably employed from the viewpoint of economy. In the vacuum deposition method, a metal from an evaporation source is deposited on a polyester film adhered to a cooling roll in a vacuum to form a metal layer on the polyester film.

As the evaporation source, a boat type of resistance heating system, a crucible type by radiation or high frequency heating,
There is a method using electron beam heating, but there is no particular limitation.

The metals used for this deposition are Al, Z
Metals such as n, Mg and Sn are preferred, but Ti, In,
Cr, Ni, Cu, Pb, Fe and the like can also be used. These metals have a purity of 99% or more, preferably 99.5%.
% Or more, processed into a granular, rod, tablet, wire or crucible shape.

In this case, aluminum is particularly preferred in terms of productivity and cost. Aluminum is deposited on at least one side to provide an aluminum metal layer. At this time, for example, nickel, copper Other metal components such as gold, silver, chromium, zinc, etc. can also be deposited.

Next, the method for producing the polyester film of the present invention will be described, but the present invention is not necessarily limited thereto. First, polyester as a raw material is melt-extruded by an extruder, cooled on a cooling roll to a temperature lower than the glass transition point, cast, heated to a temperature higher than the glass transition point, and then stretched 2.8 to 7.5 times in the longitudinal direction. After further preheating to a temperature range of 120 ° C. from the Tg of the base polyester with a stenter, stretched in the width direction 3 to 12 times, and, if necessary, a temperature lower than the melting point of the base polyester while relaxing.
Preferably, it is manufactured by heat-setting at a temperature in the range of 200 to 250 ° C and winding. In order to keep the minimum value (Emin) of the Young's modulus in the in-plane direction of the film within the range of the present invention, the film may be stretched in several steps in the longitudinal direction, or may be stretched in the width direction and then stretched again. A method of stretching in the width direction and the width direction is preferably used.

The film thus obtained can be laminated or wound by a known method to obtain a film capacitor. To illustrate a wound film capacitor,
Aluminum is vacuum deposited on both sides of the film to be metallized. At this time, vapor deposition is performed in a stripe shape having a margin portion running in the longitudinal direction (the vapor deposition is performed so that the patterns on the front surface and the back surface are alternately shifted). Next, insert a blade in the center of each vapor deposition section on the front side and the center of each margin section and slit it, on a tape-like take-up reel such that the front side has a margin on one side and the back side has a margin on the opposite side. I do. The obtained reel and one laminated film which are not metallized are superposed and wound in a width direction such that the metallized film protrudes from the laminated film to obtain a wound body. A core material is removed from the wound body and pressed, metallicon is sprayed on both end surfaces to form external electrodes, and a lead wire is welded to the metallicon to obtain a wound capacitor element.

The method of measuring and evaluating the characteristic values in the present invention are as follows. (1) The minimum value of the Young's modulus in the in-plane direction of the film (Emi
n) The Young's modulus in 6 directions was measured 20 times at intervals of 30 ° with respect to the MD direction of the film using an Instron type tensile tester based on JIS-Z1702 (23 ° C.,
65% RH), the average value in each direction was calculated, and the minimum value was defined as Emin. .

(2) Plane orientation coefficient fn, birefringence Δn In accordance with the method specified in JIS-K7105, the refractive index in the longitudinal direction, the width direction and the thickness direction is measured using an Abbe refractometer with sodium D line as a light source. Measured (each n
MD, nTD, nZD). Here, the mounting liquid was measured using methylene iodide at 25 ° C. and 65% RH. Next, the plane orientation coefficient fn was calculated by the following equation (3), and the birefringence Δn was calculated by the following equation (4). Plane orientation coefficient fn = (nMD + nTD) / 2-nZD (3) Birefringence Δn = nTD−nMD (4)

(3) Measurement by Differential Scanning Calorimeter As a differential scanning calorimeter, DS manufactured by Seiko Denshi Kogyo KK
C (RDC220), using a disk station (SSC / 5200) manufactured by the company as a data analyzer, about 10 mg of a film sample was mounted on an aluminum pan, and the temperature was raised from room temperature at a rate of temperature increase of 40 ° C./min. At this time
It was confirmed whether an endothermic peak was observed at 120 ° C.
The calorific value was calculated from the peak area for the endothermic peak observed. The peak area is the area from the baseline to the absorption side by increasing the temperature, and is the area from the point at which the temperature begins to shift to the end position by a straight line, and the area A is determined. Was. Under the same conditions, measurement was performed with In (indium) weighed to the same weight as the film sample, the area B was obtained, and the calorific value of the endothermic peak was obtained by the following equation. Endothermic peak calorific value (J / g) = 28.5 x A / B

(4) Intrinsic Viscosity The value calculated from the following equation based on the solution viscosity measured in orthochlorophenol at 25 ° C. was used. That is, ηsp / C =
[Η] + 2K [η] C (where ηsp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml), and K is the Huggins constant (0.3
43)) Solution viscosity and solvent viscosity were measured with an Ostwald viscometer.

(5) Center line average surface roughness Ra was measured according to JIS-B6010.

(6) Withstand Voltage of Film The dielectric breakdown voltage was measured at DC according to JIS-2110. An aluminum foil electrode with a thickness of 100 μm and 10 cm square was used as the cathode, and a 25 mmφ, 500 g brass electrode was used as the anode. A film was sandwiched between the electrodes, and the voltage was applied at a rate of 100 V / sec using a high voltage DC power supply manufactured by Kasuga. , 10
It was assumed that the dielectric breakdown occurred when a current of not less than mA flowed. The average value of the 30 measurements was taken as the withstand voltage of the film.

(7) Insulation resistance 1000 capacitor samples of 0.1 μF
In an atmosphere of 65 ° C. and 65% RH, measured as 1 minute value at an applied voltage of 500 V using a super insulation resistance meter 4329A manufactured by YHP, and a capacitor sample having an insulation resistance of less than 5000 MΩ is judged as defective according to the following criteria. did. In the present invention, ◎, △, and △ were evaluated as acceptable. Less than 10 defective products: ◎ 10 or more and less than 20 defective products: ○ 20 or more and less than 50 defective products: △ 50 or more defective products: ×

(8) Withstand Voltage With respect to 1000 capacitor samples, a voltage of 1
The voltage is applied while increasing the voltage at a rate of 00 V / sec, and a voltage (breakdown voltage) at the time when a dielectric breakdown occurs in the capacitor and a current of 5 mA or more flows is measured. The obtained breakdown voltage was converted per unit thickness of the polyester film used as the dielectric, and the withstand voltage was calculated as an average value of 1,000 capacitor samples. When the capacity of the capacitor is large and a current of 5 mA or more flows only by the charging current, the current value is set to an appropriate value that can separate the charging current and the breakdown current. In the present invention, a capacitor with a withstand voltage of 450 V / μm or more was accepted.

[0053]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Comparative Example 1 As a polyester of a polyester film, polyethylene terephthalate, an ethylene terephthalate homopolycondensate having an intrinsic viscosity of 0.65 to which 0.1% of agglomerated silica having an average particle diameter of 1.1 μm was added, was dried at 180 ° C. under vacuum. Thereafter, the mixture was supplied to an extruder, melted at 285 ° C., discharged from a T-die, cooled and solidified by a cooling drum at 25 ° C., and an undrawn sheet was prepared. 95 ℃
, Stretched 3.0 times in the longitudinal direction, stretched 3.5 times in the width direction at 110 ° C, and stretched 5 times in the width direction at 220 ° C.
After the heat treatment, the film (2 m in width and 5 μm in width) was wound up. The center portion of the film in the width direction was slit to a width of 0.5 m to obtain a polyester film.

Next, aluminum was vacuum-deposited on one surface of the obtained polyester film so that the surface resistance was 2 Ω / □. At that time, vapor deposition was carried out in a stripe shape having a margin portion running in the longitudinal direction (repeated of 58 mm in width of the vapor deposition portion and 2 mm in width of the margin portion). Next, a blade was inserted into the center of each vapor deposition section and the center of each margin section, and slit to form a tape-shaped take-up reel having a total width of 30 mm and a left or right margin of 1 mm.

Each of the left and right margins of the reel thus obtained was wound one on top of another to obtain a capacitor element having a capacitance of 0.1 μF. This capacitor element is heated at 130 ° C., at a temperature and pressure of 20 kg / cm ² for 5 minutes.
Pressed for minutes. Metallicon is sprayed on both ends to form external electrodes, lead wires are welded to the metallicon, and the exterior is cured with epoxy resin to form a wound capacitor.
Aged at 100 ° C. for 12 hours. Thereafter, the capacitor was subjected to a voltage treatment for 30 seconds at a direct current of 800 V for 30 seconds, and the polarity of the electrodes applied to the two lead wires was reversed once more to evaluate the capacitor again. Table 1 shows the evaluation results of the film and the capacitor.

Example 1 The stretching in the longitudinal direction was doubled at 120 ° C.
° C and stretched 2.5 times, then stretched in the width direction by 9
A polyester film and a capacitor were produced in the same manner as in Comparative Example 1 except that the film was stretched 4 times at 0 ° C. Table 1 shows the evaluation results of the film and the capacitor.

Example 2 The polyester film wound up in Example 1 was aged at 60 ° C. for 48 hours to produce a polyester film and a capacitor. Table 1 shows the evaluation results of the film and the capacitor.

Example 3 The stretching in the longitudinal direction was doubled at 120 ° C.
° C and stretched 2.7 times, and then stretched in the width direction by 9 times.
A polyester film and a capacitor were produced in the same manner as in Comparative Example 1, except that the film was stretched 4 times at 0 ° C. and heat-treated at 210 ° C. while relaxing 5% in the width direction. Table 1 shows the evaluation results of the film and the capacitor.

Example 4 Except that the stretched polyester film was stretched 3.8 times at 90 ° C. in the longitudinal direction and stretched 4 times at 110 ° C. in the width direction, and the wound polyester film was aged at 60 ° C. for 8 hours. Produced a polyester film and a capacitor in the same manner as in Comparative Example 1. Table 1 shows the evaluation results of the film and the capacitor.

Comparative Example 2 A polyester film and a capacitor were prepared in the same manner as in Comparative Example 1 except that the heat treatment was performed at 235 ° C. while relaxing 5% in the width direction. Table 1 shows the evaluation results of the film and the capacitor.

Comparative Example 3 The stretching in the longitudinal direction was stretched 1.8 times at 110 ° C., further cooled to 85 ° C. and stretched 2.8 times, and then the stretching in the width direction was stretched 3.8 times at 90 ° C. Stretched, 5% in width direction at 210 ° C
After heat treatment while relaxing, a polyester film and a capacitor were produced in the same manner as in Comparative Example 1 except that the wound film was slit to a width of 0.5 m from the end.
Table 1 shows the evaluation results of the film and the capacitor.

Comparative Example 4 A polyester film and a capacitor were produced in the same manner as in Comparative Example 3 except that the heat treatment was performed at 220 ° C. while relaxing 5% in the width direction. Table 1 shows the evaluation results of the film and the capacitor.

[0063]

[Table 1]

[0064]

According to the polyester film for a capacitor of the present invention, the polyester film is excellent in the withstand voltage, the insulation resistance and the withstand voltage when the capacitor is used, and thus a highly safe capacitor can be obtained. Further, a polyester film which is thinner than a conventional one can be used as a dielectric of the capacitor.

Continued on the front page F-term (reference) 4F210 AA24 AE01 AG01 AG03 AH33 QC05 QC06 QD04 QD16 QG01 QG18 QW12 5E001 AB03 AB04 AC04 AC09 AE00 AE04 AF03 AH03 AJ01 AJ02 5E082 AB03 AB05 BC35 EE07 EE27 EE24 EE24 FG36 FG48 FG54 GG04 HH48 JJ04 JJ22 JJ25 MM22 MM24 MM27 PP10

Claims (4)

[Claims] 1. A polyester film for a capacitor, comprising: a biaxially oriented film containing polyethylene terephthalate as a main component, wherein a minimum value (Emin) of an in-plane Young's modulus of the film is 4.5 GPa or more. . 2. The polyester film for a capacitor according to claim 1, wherein the heat shrinkage in the longitudinal direction of the film is less than 3% and the heat shrinkage in the width direction is less than 2%. 3. The polyester film for a capacitor according to claim 1, wherein a metal layer is provided on at least one surface of the film. 4. A film capacitor using the polyester film for a capacitor according to claim 1.