JPH11260662A - Polypropylene film for oil-impregnated capacitor and capacitor constituted of the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the breakdown voltage and thermal resistance, by making mesopentad separation ratio at least a specified value, and making percentage of thermal contraction in the longitudinal direction and percentage of thermal contraction in the widthwise direction at most specified values. SOLUTION: Mesopentad separation ratio of a polypropylene film is set at least about 98.0%. Percentage of thermal contraction in the longitudinal direction is set at most 3.0%, and percentage of thermal contraction in the widthwise direction is set at most 1.0%. In the polypropylene film, cyclic epoxy araldite such as 3,4-epoxycyclohexylmethyl and 3,4-epoxycyclohexanecarboxylate is contained at least about 0.005 wt.% and at most about 0.060 wt.%. The film is formed by using a tenter method or an inflation method. As a result, a polypropylene film excellent in withstand voltage and thermal resistance is manufactured, and an oil-impregnated capacitor excellent in long term stability is manufactured by using the above film at least as a part of dielectrics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene film for an oil-impregnated capacitor having excellent heat and withstand voltage and durability, and an oil-impregnated capacitor using the film at least as a part of a dielectric.

[0002]

2. Description of the Related Art A polypropylene film is widely used as a dielectric material or an insulator material in electrical applications because of its excellent electrical characteristics. Above all, the range of use as a dielectric material for capacitor applications is wide, and the demand for the material is growing remarkably.

When a capacitor using such a polypropylene film is subjected to a long-term power application test, the dielectric strength characteristics of the polypropylene film are reduced with the lapse of time, and eventually the capacitor is destroyed. Generally, the life of a capacitor is considered in consideration of the influence of internal discharge of the capacitor. In particular, a power capacitor used at a high voltage has a large demand.

[0004] For this reason, in power capacitors, a prescription for suppressing this internal discharge by impregnating with insulating oil has been adopted. At this time, in order to secure a sufficient oil layer between the dielectric layers or between the dielectric and the electrode, the film and paper are wound together to form a dielectric, or the surface of the dielectric film or the electrode is made uneven to secure the oil layer. Methods and improvements in the properties of the oil itself have been proposed.

[0005]

However, these prior arts are not always sufficient to meet the demands for further improving the life characteristics and reliability of capacitors.

Accordingly, an object of the present invention is to improve the heat and withstand voltage and durability of a polypropylene film used as a dielectric and to provide a capacitor having excellent long-term stability.

[0007]

In order to achieve the above object, the polypropylene film for an oil-impregnated capacitor of the present invention has a mesopentad fraction of 98.0% or more and a heat shrinkage in the length direction of 3. 0% or less, and the heat shrinkage in the width direction is 1.0% or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the mesopentad fraction of a polypropylene film needs to be 98.0% or more. When the meso pentad fraction is less than 98.0%, not only the withstand voltage but also the heat resistance, which is one of the important characteristics for capacitors often used at high temperatures, deteriorates. It is preferably at least 98.5%, more preferably at least 99.0%.

Further, the heat shrinkage in the length direction of the polypropylene film of the present invention must be 3.0% or less.
If it exceeds 3.0%, the tightness of the winding of the capacitor element under high temperature becomes strong, and the film itself swells in the thickness direction, and the film and the interlayer between the film and the electrode become narrow, and a sufficient oil layer cannot be secured. In addition, the corona discharge cannot be suppressed and the withstand voltage durability of the capacitor is impaired. Preferably,
2.8% or less, more preferably 2.5% or less.

The thermal shrinkage in the width direction of the polypropylene film of the present invention must be 1.0% or less. 1.
If it exceeds 0%, the film width is widened relative to the electrode width, and the margin for securing the withstand voltage characteristics of the capacitor provided at both ends of the capacitor element becomes narrow at high temperatures. Occurs.
Preferably it is 0.8% or less, more preferably 0.1%.
5% or less.

[0011] The polypropylene film of the present invention preferably contains 0.005 wt% or more and 0.060 wt% or less of cyclic epoxy araldite.
When the content is 0.005 wt% or more, the effect of suppressing the deterioration of the withstand voltage characteristics is sufficiently exhibited. On the other hand, if the content exceeds 0.060 wt%, the cyclic epoxy araldite bleeds out from the film surface during film production, adheres to the roll surface in the film production process, and may adhere again to the film. More preferably, the content is 0.005 wt% or more and 0.050 wt% or less.

As the cyclic epoxy araldite,
3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate, 2- (3 ', 4'-
Epoxycyclohexyl) -1,3-dioxane-5-
Spiro-3 ', 4'-epoxycyclohexane, 3,4
-Epoxy, 6, methylcyclohexyl adipate and the like.

The polypropylene film of the present invention preferably contains a phenolic antioxidant. The content is not particularly limited, but may be 0.02 wt.
% Or more and 0.60% by weight or less. 0.02wt%
If the amount is less than 0.60, the antioxidant effect may be insufficient.
If the content exceeds wt%, the insulation resistance may decrease.

The phenolic antioxidants used in the polypropylene film of the present invention include tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane and n-octadecyl-3 -(3 ', 5'-di-tert-butyl-
4'-hydroxyphenyl) propionate, 2,2
-Thio [diethylene-bis-3 (3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, 1,3,5 trimethyl-2,4,6-tris (3
5-di-tert-butyl-4-hydroxybenzyl) benzene, tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 4,
4'-thio-bis (3-methyl-6-tert-butyl-phenol), tris (2,4-di-tert-butylphenyl) phosphite and the like are exemplified, and two or more kinds may be used alone. May be used in combination, but among them, tetrakis [methylene-3] exhibiting good electric characteristics.
(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane or 1,3,5 trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) Benzene is preferred.

Further, the polypropylene film of the present invention may be obtained by a tenter method or an inflation method, and may be a single layer or a composite. The tenter method and the biaxial stretching are preferred from the viewpoint of the above.

The ash content of the polypropylene film of the present invention is preferably 30 ppm or less from the viewpoint of withstand voltage characteristics.

The specifications of the oil-impregnated capacitor made of the polypropylene film of the present invention are not particularly limited. For example, the dielectric may be wound together with the capacitor paper or only the film, or may be flat. It may be a shape or a round shape.

The center line surface roughness Ra of the film when wound together with the capacitor paper is preferably 0.10 μm or less on both sides from the viewpoint of withstand voltage characteristics. In consideration of the above, the center line surface roughness Ra of at least one surface of the film is preferably 0.04 μm or more and 0.70 μm or less.

The electrode used in the oil-impregnated capacitor made of the polypropylene film of the present invention is not particularly limited, and may be a metal foil such as an aluminum foil or a paper on which metal is deposited on both sides. Alternatively, an electrode may be directly formed on a film by a metal vapor deposition method or the like.

When an electrode is directly formed on a film by a metal vapor deposition method or the like, a surface treatment such as a corona discharge treatment is preferably performed on a surface of the film on which an electrode layer is to be provided.

The insulating oil used as the impregnating agent for the oil-impregnated capacitor is not particularly limited, and examples thereof include phenylxylylethane, alkylbenzene, isopropyl biphenyl, and vegetable oil. Silylethane is more preferred.

The film of the present invention may be used for a gas-filled condenser or a dry condenser other than the oil impregnated type.

Next, an example of a preferred method for producing a film and a capacitor according to the present invention will be described, but the present invention is not particularly limited thereto.

A polypropylene resin having a mesopentad fraction of 98.0% or more is supplied to an extruder at a temperature of 220 to 270 ° C., melted, extruded into a sheet shape from a slit T die, and extruded at a temperature of 20 to 95 ° C. It is cooled and solidified by a cooling roll at a temperature. Next, it is stretched 3 to 6 times in the length direction at a temperature of 100 to 150 ° C. Next, the film is stretched 6 to 12 times in the width direction at a temperature of 140 to 165 ° C. At this time, the lower the stretching temperature, the higher the heat shrinkage. Then 140
Heat treatment is performed at a temperature of 165 ° C. The lower the heat treatment temperature, the higher the heat shrinkage. The thus obtained polypropylene film is wound up by a winder.

Next, the measurement method and the evaluation method used in the present invention will be described.

(1) Mesopentad fraction (mmmm) A sample was dissolved in o-dichlorobenzene / benzene-D6, and JNM-GX27 manufactured by JEOL Ltd. (JEOL) was dissolved.
0 device, at a resonance frequency of 67.93 MHz and ¹³ C-
NMR was measured. Regarding the assignment of the obtained spectrum and the calculation of the pentad fraction, see T.W. The method performed by Hayashi et al. [Polymer, 29, 138 (198)
8)], m
Each peak was assigned with the mmm peak as 21.885 ppm, the peak area was determined, and the ratio to the total peak area derived from the methyl group was expressed as a percentage.

Measurement solvent: o-dichlorobenzene (90 w
t%) / benzene-D6 (10 wt%) Measurement temperature: 120 to 130 ° C. Resonance frequency: 67.93 MHz Pulse width: 10 μsec (45 ° pulse) Pulse repetition time: 7.091 sec Data point: 32K Integration frequency: 8168 Measurement mode : Noise decoupling

(2) Heat shrinkage rate According to JIS-C-2330.

(3) Heat and voltage resistance of the capacitor A polypropylene film is slit at a width of 100 mm, and a capacitor paper having the same width as the slit film is used as a dielectric by a combination of film / paper / film and has a thickness of 6 mm.
An aluminum foil having a width of 80 mm was used as an electrode and wound by an element winding machine to form a capacitor element.
%, Fixed in a metal case, impregnated with insulating oil phenylxylylethane, sealed and filled with a capacitance of 0.1%.
Create a 2 μF capacitor. Set this capacitor to 65
After applying an electric current for 1,000 hours at an AC voltage of 2.7 KV in an ambient temperature of ° C., the number of insulation defects of the polypropylene film obtained by unwinding the capacitor and the polypropylene film that was not subjected to the electric power were measured. The increase in the number of insulation defects was investigated.

The insulation defects were measured by sandwiching a polypropylene film as a sample between a metallized film as a test electrode and a copper flat plate and applying a DC voltage of 6 KV for 1 minute to count the number of breaks (the number of defects). The sample area was 1.0 m ² .

(4) Insulation Resistance The completed capacitors after impregnation were measured before and after the application of power for 1000 hours in accordance with EIAJ RC-3666A. However, the measurement temperature was 80 ° C.

(5) Swellability of Film The thickness (t ₁ ) of the film unwound from the capacitor is measured by the method of JIS C-2330 (however, the number is one), and the thickness of the film before making the capacitor is measured. The rate of increase with respect to the height (t ₀ ) was examined. Increase rate (%) = (t ₁ / t ₀ ) × 100

Next, the present invention will be described based on examples.

[0034]

EXAMPLES Example 1 As an antioxidant, tetrakis [methylene-3 (3,5-
Di-tert-butyl-4-hydroxyphenyl) propionate] methane with a content of 0.05 w
at t%, the mesopendat fraction is 99.0%,
A polypropylene resin to which 0.04 wt% of 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate was added was supplied to an extruder at a temperature of 250 ° C., melted, and extruded into a sheet from a slit T die. It was cooled and solidified by a cooling roll at a temperature of 40 ° C. Next, it is stretched 5 times in the length direction at a temperature of 135 ° C.
Then, it is stretched 10 times in the width direction at a temperature of 160 ° C.
Heat treatment was performed at a temperature of 50 ° C. The thus obtained polyprofin film was wound up with a winder.

The film had a thickness of 22 μm, a heat shrinkage in the length direction of 2.0%, and a heat shrinkage in the width direction of 0.3%. The content of 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate in this film was 0.010% by weight.

This polypropylene film is 100 m wide.
m, and a capacitor paper having the same width as the slit film is made into a dielectric by a combination of film / paper / film, and an aluminum foil having a thickness of 6 μm and a width of 80 mm is wound as an electrode by an element winding machine to form a capacitor element. After fixing by pressing at a clamping rate of 115%, the sheet is placed in a metal case and dried in vacuum at a temperature of 40 ° C. for 16 hours.
Phenylxylylethane at a temperature of 2 ° C. and impregnated to form a capacitor having a capacitance of 0.2 μF.

After the capacitor was subjected to an AC voltage of 2.7 KV for 1000 hours in an atmosphere temperature of 65 ° C., the number of insulation defects in the polypropylene film obtained by unwinding the capacitor and the polypropylene film not subjected to the power supply were determined as follows:
The insulation resistance and the thickness were measured, and the increase in the number of insulation defects, the change in the insulation resistance, and the rate of increase in the thickness after the application of electricity were examined. The insulation defects were measured by sandwiching a polypropylene film as a sample between a metallized film as a test electrode and a copper flat plate and applying a DC voltage of 6 KV for 1 minute to count the number of breaks (the number of defects). The sample area is 1.0m ²
And Table 1 shows the results.

The number of broken pieces was 0, which was the same as that of the uncharged film. The thickness increase rate was 3.8%. Also, the insulation resistance was stable and high before and after the voltage application.

Example 2 The same as Example 1 except that a polypropylene resin having a mesopentad fraction of 98.0% was used. The heat shrinkage in the length direction of the film was 2.2%, and the heat shrinkage in the width direction was 0.3%. Table 1 shows the results.

The number of destroyed films was 3 while the number of films not charged was 0. The rate of thickness increase is 5.1
%Met. Also, the insulation resistance was stable and high before and after the application of power.

Example 3 The same as Example 1 except that the stretching temperature in the width direction was 155 ° C. and the heat treatment temperature was 145 ° C. The heat shrinkage in the length direction of the film was 2.9%, and the heat shrinkage in the width direction was 0.8%. Table 1 shows the results.

The number of destroyed films was 5 while the number of films not charged was 0. The thickness increase rate is 7.7
%Met. Also, the insulation resistance after the application of electricity was slightly lower than that before the application of electricity, but there was no practical problem.

Example 4 Example 1 was repeated except that the content of tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane was 0.50 wt%.
Same as Table 1 shows the results.

The number of destroyed films was 3 while the number of films which did not charge was 0. The rate of thickness increase is 3.7
%Met. In addition, the insulation resistance was slightly lower before and after the application of power, but there was no practical problem.

Example 5 Same as Example 1 except that 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate was not added. Table 1 shows the results.

The number of broken films was 7 in contrast to one film that was not charged. The rate of thickness increase is 3.7
%Met. In addition, the insulation resistance after the application of electricity was slightly lower than that before the application of electricity, but there was no practical problem.

Example 6 Same as Example 1 except that 0.080 wt% of 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate was added. The content of 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate in this film is 0.050
wt%. Table 1 shows the results.

The number of destroyed films was one while the number of films which did not charge was zero. The rate of thickness increase is 3.7
%Met. Also, the insulation resistance was stable and high before and after the application of power.

However, 3,4 epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate adhered to the roll in the process during the production of the film, and there was some concern about the long-term continuous production.

Comparative Example 1 The same as Example 1 except that a polypropylene resin having a mesopentad fraction of 94.0% was used. Table 1 shows the results.

The number of destroyed films was one where no power was applied, but increased to 15 after the power application, which was a problem in practical use. The thickness increase rate was 7.1%. In addition, the insulation resistance after power application was much lower than that before power application.

Comparative Example 2 The temperature for stretching in the length direction was 130 ° C., the temperature for stretching in the width direction was 150 ° C., and the heat treatment temperature was 140 ° C.
Same as Example 1 except that the temperature was changed to ° C. The thermal shrinkage in the length direction of this film is 3.7%, and the thermal shrinkage in the width direction is 1.3%.
Met. Table 1 shows the results.

The number of destructed films was 0, which was not charged, and deteriorated to 11 after charging. The thickness increase rate was 13.2%. Also, the insulation resistance after the application of electricity was lower than that before the application of electricity.

[0054]

[Table 1]

[0055]

The polypropylene film for an oil-impregnated capacitor of the present invention is excellent in heat resistance, withstand voltage and durability, and by using the oil-impregnated capacitor, a capacitor excellent in long-term stability can be obtained.

Claims (3)

[Claims] (1) a mesopentad fraction of 98.0% or more;
A polypropylene film for an oil-impregnated capacitor, wherein the heat shrinkage in the length direction is 3.0% or less and the heat shrinkage in the width direction is 1.0% or less. 2. The cyclic epoxy araldite is 0.005 watts.
2. The polypropylene film for an oil-impregnated capacitor according to claim 1, wherein the content is at least t% and at most 0.060 wt%. 3. An oil-impregnated capacitor characterized by using the polypropylene film for an oil-impregnated capacitor according to claim 1 at least as a part of a dielectric.