JP2018156965A - Insulating film for capacitor, and film capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an insulating film for a capacitor, such as a cellulose film for a film capacitor, which has a high relative dielectric constant, a high insulating property, and high intensity and causes no foaming nor whitening, which enables materialization of downsizing of the film capacitor as used in a hybrid electric vehicle, a wind power/solar photovoltaic generation, industry equipment, etc., and which can make contribution to energy saving, and environmental measures; and the film capacitor using the insulating film.SOLUTION: An insulating film for a capacitor comprises cellulose resin, of which the total light transmittance is 85% or more and a film thickness is 10 μm or less. The insulating film preferably comprises an inorganic filler. It is preferred that the cellulose resin be one having a part of a hydroxyl group subjected to modification of any of acetylation, propionylation, and butyrylation. A film capacitor is arranged by using the insulating film for a capacitor.SELECTED DRAWING: None

Description

  The present invention relates to a highly transparent insulating film for a capacitor and a film capacitor using the same.

  In recent years, inverters for hybrid / electric vehicles, wind / solar power generation, industrial equipment, etc. that contribute to energy saving have been equipped with film capacitors that are advantageous in terms of high voltage resistance and high output. In recent years, the capacity of inverters has been increased, and the occupation ratio of film capacitors to the volume of inverters has increased. Thus, there is a demand for miniaturization of film capacitors.

  One means for reducing the size of the film capacitor is to make the film thinner. Currently, polyethylene terephthalate (PET), polypropylene (PP), and other engineering plastic materials are the mainstream as film for film capacitors. Above all, PP has a relatively high dielectric constant of 2.2 and is a relatively high organic film material. It is excellent in processability for film formation and is most often used.

  The main film thickness used for film capacitors is 5 to 6 μm, and products with a thickness of 3 to 4 μm are currently at the forefront of miniaturization. However, there is a limit to the reduction in thickness because the withstand voltage characteristic is lowered as a contradiction characteristic and the performance of the capacitor is lowered.

  Another policy for miniaturizing film capacitors is to increase the dielectric constant of the film used. It is known that the capacitor volume is inversely proportional to the dielectric constant of the film to be used, and by doubling the relative dielectric constant of the film, it is estimated that the volume of the film capacitor is halved with the same capacitance.

  There are various film materials, and among them, film materials obtained by processing synthetic resins such as acrylic resins, melamine resins, alkyd resins, urethane resins, epoxy resins, polyethylene resins, polypropylene resins, and cellulose resins are mainly mentioned.

  Among them, although the cellulose resin has a difference depending on the resin skeleton and the amount of modification, the relative dielectric constant is as high as 3 to 7, and since it has a high strength compared with other resins, in the film capacitor manufacturing process, particularly in the winding process. It has a high manufacturing margin and is a useful material. Cellulose resin is a synthetic resin made from a natural material, and contributes to the environment without causing the recent depletion of petroleum resources or environmental degradation.

  Examples of practical use of the cellulose film include a support film for a photographic negative film, but there is no practical example of application to a film capacitor.

  The processing method of a cellulose film is obtained by coating and drying a varnish obtained by dissolving a cellulose solid resin in a solvent, and a film is obtained by adding a part of a phosphorus plasticizer (for example, see Patent Document 1). . There is an example in which a mixed system of acetone and ether is used as the solvent, and the film thickness is in the range of several tens μm to several hundreds μm.

Japanese Unexamined Patent Publication No. 07-032391

  Films for film capacitor applications have been made thinner to increase the capacity of capacitors, and films with a thickness of several μm have been put into practical use as products. When thin film coating is applied to the cellulose film using the varnish shown in the above example, the solvent volatilization occurs abruptly in the heat-drying process, so foaming occurs and the film surface is uneven, and the film whitens due to light scattering. . The surface irregularities cause a decrease in insulation and a decrease in capacitance in the capacitor characteristics, and therefore it is necessary to reduce, preferably eliminate.

  In view of the above circumstances, the present invention is a cellulose film for a film capacitor having a high relative dielectric constant, high insulation, and high strength without foaming whitening, and is used in hybrid / electric vehicles, wind / solar power generation, industrial equipment, etc. It is an object of the present invention to provide a capacitor insulating film and a film capacitor using the same, which can realize miniaturization of the film capacitor to be made and contribute to energy saving and environmental measures.

  As a result of intensive studies in view of the present background, the inventors have invented that it is extremely useful to apply a film having a high light transmittance to a film capacitor. A film having a high light transmittance has high transparency, and according to observation with an electron microscope or the like, there are almost no irregularities on the coated surface of the film, the dielectric strength characteristics are high, and the film strength is also high. Furthermore, by using a smooth film with small irregularities on the film surface for the capacitor, the porosity existing in the film capacitor element after winding can be reduced, which contributes to an increase in the capacity of the capacitor.

That is, the present invention relates to the following.
(1) An insulating film for a capacitor containing a cellulose resin having a total light transmittance of 85% or more and a film thickness of 10 μm or less.
(2) The insulating film for capacitors according to (1), further containing an inorganic filler.
(3) The insulating resin for a capacitor according to (1) or (2), wherein the cellulose resin is one in which a hydroxyl group is partially modified by acetylation, propionylation, or butyrylation.
(4) The insulating film for capacitors according to (2) or (3), wherein the inorganic filler has a spherical shape or a scale shape and includes at least one of them.
(5) The insulating film for capacitors according to (4), wherein the spherical filler contains either titanium oxide (rutile) or alumina.
(6) The scale-shaped filler is an insulating film according to (4), which contains either mica or boron nitride.
(7) An insulating film for a capacitor obtained by applying pressure and heat treatment to the insulating film for a capacitor according to any one of (1) to (6).
(8) A film capacitor using the capacitor insulating film according to any one of (1) to (7).

  The insulating film for a capacitor having a high light transmittance according to the present invention is a cellulose film for a film capacitor having a high relative dielectric constant, high insulation, and high strength, such as a hybrid / electric vehicle, wind / solar power generation, industrial equipment, etc. The film capacitor used in this can be miniaturized, contributing to energy saving and environmental friendliness.

  Hereinafter, although the form for implementing this invention is demonstrated, the example shown below is an example and this invention is not limited to this.

  As the cellulose resin used in the present embodiment, it is preferable to use a resin obtained by esterifying a part of the hydroxyl groups generally possessed by acetylation, propylylation (propionylation), butyrylation, or the like. When the hydroxyl group is not modified by acylation or alkylation, the processability is lowered due to low solubility in a solvent, and it tends to be difficult to form a film. The amount of modification and the functional group to be modified are not particularly limited, but the greater the modification amount, the better the processability, and the longer the alkyl chain of the modified functional group, the better the solubility in a solvent. The molecular weight is not particularly limited, but the number average molecular weight is preferably in the range of 10,000 to 100,000, more preferably in the range of 20,000 to 80,000. When it is 10,000 or more, the film strength is sufficiently high, and when it is 100,000 or less, the solubility in a solvent is good and the processability is good. The number average molecular weight can be measured using gel permeation chromatography using polystyrene as a standard sample.

  The three-dimensional structure of the cellulose resin used in the present embodiment is not particularly limited.

The insulating film for capacitors of this embodiment may contain an inorganic filler. When inorganic fillers are classified by shape, there are spherical fillers that define an aspect ratio in the range of 1 to 1.5, and flat scale-shaped fillers that specify an aspect ratio in the range of 2 to 10, both or one of them. Can be included.
The aspect ratio can be obtained by measuring the minor axis and major axis of the primary particles by electron microscope observation and quantifying from the division (major axis / minor axis). In the present specification, the aspect ratio is an average value obtained by measuring 30 particles.

  Spherical fillers include silica, alumina, titanium oxide (rutile), etc., but titanium oxide (rutile) or alumina is suitable for the effect of increasing the dielectric constant in forming a composite film with resin. (Rutile) is particularly preferred. As scale-shaped filler, there are many natural mica, synthetic mica, boron nitride, talc and the like. By dispersing the scale-shaped filler in the film, it is theoretically possible to improve the dielectric strength characteristics of the film by the maze effect. In addition, natural mica is suitable for achieving the effect of increasing the dielectric constant of the film as well as the spherical filler.

  When adding an inorganic filler, the addition amount is preferably in the range of 0.1 to 50% by volume, more preferably 10 to 30% by volume. When the content is 0.1% by volume or more, the effect of improving the withstand voltage characteristics is sufficient, and when the content is 50% by volume or less, a decrease in strength due to embrittlement of the film can be suppressed.

  The film of the present embodiment is prepared by dissolving the cellulose resin or cellulose resin and filler in a solvent for the cellulose resin using a solvent, dispersing the filler in the solvent, varnishing, and forming a predetermined film thickness on the substrate. It is produced by a method of coating so that the solvent is dried to form a film. Conventional equipment can be used without limitation as equipment for producing the varnish. Further, the base material to be coated is not particularly limited, but in general, it is directly applied to a plastic film such as polyethylene terephthalate (PET) or a metal support surface such as a steel belt or a metal drum to obtain an independent film. You can also. Moreover, adhesiveness with the insulating film for a capacitor | condenser of this invention is controllable by performing the surface treatment to the base-material surface.

  The solvent for varnishing is not particularly limited, but when using a filler with high solubility of cellulose resin, it is necessary to use a solvent with good filler dispersibility in order to obtain stable coating properties and film characteristics. preferable. Examples of the solvent include acetone, ethyl acetate, butyl acetate, cyclohexanone, ethyl lactate, N-methylpyrrolidone, and γ-butyrolactone. The solid content of the varnish is not particularly limited, but the solid content is adjusted so that the viscosity can be applied by a predetermined coating method.

  In addition, the capacitor insulating film of the present embodiment includes a surface conditioner such as a leveling agent and an antifoaming agent represented by silicon and acrylic, a silane coupling agent, a dispersant, a compatibilizing agent, and a thermoplastic agent. Various additives such as these can also be included.

  Although a film having a high transmittance can be produced even with a single film after coating produced with the above contents, in particular, in the production of a thin film having a thickness of 10 μm or less, irregularities are easily generated on the film surface, and the transmittance is high. There is a tendency to decrease. As a further improvement method, it has been found that applying heat press (pressurization / heat treatment) to the coated film is effective. Specifically, a hand press system is effective at the laboratory level, and a calender roll press and a belt press system are effective at the mass production level, both of which are accompanied by heating.

The heating temperature in the hot press is preferably not less than the glass transition point (Tg) of the cellulose resin. The general glass transition point of the cellulose resin varies depending on the type of modification and the molecular weight, but is generally in the range of 170 to 250 ° C. However, the thin film is not limited to this, and the effect is exhibited even by hot pressing at a temperature lower than the glass transition point. Specifically, hot pressing is performed at a temperature of 80 to 200 ° C, more preferably 140 to 180 ° C.
As a result, the unevenness of the film surface that occurred in the film before pressing is reduced, the light transmittance is improved even in a film that is originally transparent, and the film that is cloudy or translucent is also transparent in appearance. The light transmittance is improved.

  The film capacitor using this film has high film strength, so the workability in the winding process during film capacitor manufacture is improved, the drive voltage is improved due to the improved insulation, and the film surface unevenness is small. As a result, an improvement in capacitance can be achieved. As a result, it is possible to reduce the size of the film capacitor and contribute to energy saving.

  Examples of the present invention are shown below. In addition, the Example shown here is an example to the last, and this invention is not limited to these.

  Measurement method of film strength (tensile strength): The film is punched into a size of 3 mm wide and 60 mm long using a cutting device, and abrasive paper is attached to both ends of the test piece to prevent slipping, and a microforce precision test device is used. The tensile strength was measured.

  Measurement of film light transmittance: The total light transmittance of the film was measured using a haze meter (trade name: NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.). A white LED was used as the light source, and the measurement light flux was measured with a diameter of 10 mm.

  Measurement of film withstand voltage (dielectric breakdown voltage): Place a brass electrode on a film soaked in a fluorine-based inert liquid, and use a function generator and AC / DC high-voltage amplifier to maintain a constant voltage boost rate (100 VDC / sec) Then, voltage was applied until dielectric breakdown occurred. The voltage when the sample broke down was recorded, and the breakdown voltage gradient (V / μm, dielectric breakdown voltage) was calculated by dividing the breakdown voltage by the thickness of the sample.

(Comparative Example 1)
Preparation of the varnish was cellulose resin (trade name: CAB381-20, manufactured by Eastman Chemical Co., Ltd., cellulose acetate butyrate, butyryl group 37% by mass, acetyl group 13.5% by mass, hydroxyl group 1.8% by mass, melting point 195 Table 1 using ethyl acetate with ˜205 ° C., Tg 141 ° C. (catalog value)) and micafila (trade name: AB-25S, manufactured by Yamaguchi Mica, muscovite, average particle size 24 μm, scale shape) as a solvent Mixing was carried out at the indicated blending amount to make the varnish solid content 25% by volume. The produced varnish was applied to a release-treated PET film (trade name: A-53, manufactured by Teijin DuPont Films, Ltd.) using an applicator, and placed in an explosion-proof dryer set at 120 ° C. A 6 μm film was prepared.

Example 1
The film produced in Comparative Example 1 was hot pressed. The temperature of the press hot plate was set to 120 ° C., the press pressure was 10 MPa, and the press time was 5 minutes.

(Example 2)
A film was produced in the same manner as in Example 1 except that the temperature of the press hot plate was changed to 160 ° C. by the method described in Example 1.

(Example 3)
A film was produced in the same manner as in Example 1 except that the temperature of the press hot plate was 200 ° C. by the method described in Example 1.

Example 4
Preparation of the varnish was made of cellulose resin (trade name: CAP482-0.5, manufactured by Eastman Chemical Co., Ltd., cellulose acetate propionate, acetyl group 2.5% by mass, propionyl group 45% by mass, hydroxyl group 2.6% by mass, Melting point 188-210 ° C., Tg 142 ° C. (catalog value)) and micafila (trade name: AB-25S, manufactured by Yamaguchi Mica Co., Ltd.) using ethyl acetate as a solvent and mixing in the compounding amounts shown in Table 2, varnish The solid content was 25% by volume. The produced varnish was applied to a release-treated PET film (trade name: A-53, manufactured by Teijin DuPont Films, Ltd.) using an applicator, and placed in an explosion-proof dryer set at 120 ° C. A 6 μm film was prepared.

(Example 5)
The film produced in Example 4 was hot pressed. The temperature of the press hot plate was set to 120 ° C., the press pressure was 10 MPa, and the press time was 5 minutes.

(Example 6)
A film was produced in the same manner as in Example 5 except that the temperature of the press hot plate was changed to 160 ° C. by the method described in Example 5.

(Example 7)
A film was produced in the same manner as in Example 5 except that the temperature of the press hot plate was changed to 200 ° C. by the method described in Example 5.

(Example 8)
Preparation of the varnish is described in Table 3 using ethyl acetate with cellulose resin (trade name: CAB381-20, manufactured by Eastman Chemical Co.) and micafila (trade name: AB-25S, manufactured by Yamaguchi Mica Co., Ltd.) as a solvent. Mixing was carried out at a blending amount to make the varnish solid content 25% by volume. The produced varnish was applied to a release-treated PET film (trade name: A-53, manufactured by Teijin DuPont Films, Ltd.) using an applicator, and placed in an explosion-proof dryer set at 120 ° C. A 6 μm film was prepared.

Example 9
The film produced in Example 8 was hot pressed. The temperature of the press hot plate was set to 120 ° C., the press pressure was 10 MPa, and the press time was 5 minutes.

(Example 10)
A film was produced in the same manner as in Example 9 except that the temperature of the press hot plate was changed to 160 ° C. by the method described in Example 9.

(Example 11)
A film was produced in the same manner as in Example 9 except that the temperature of the press hot plate was changed to 200 ° C. by the method described in Example 9.

(Example 12)
The varnish was prepared by mixing cellulose resin (trade name: CAB381-20, manufactured by Eastman Chemical Co., Ltd.) and ethyl acetate as a solvent in the blending amounts shown in Table 4 to make the varnish solid content 25% by volume. The produced varnish was applied to a release-treated PET film (trade name: A-53, manufactured by Teijin DuPont Films, Ltd.) using an applicator, and placed in an explosion-proof dryer set at 120 ° C. A 6 μm film was prepared.

(Example 13)
The film produced in Example 12 was hot pressed. The temperature of the press hot plate was set to 120 ° C., the press pressure was 10 MPa, and the press time was 5 minutes.

(Example 14)
A film was produced in the same manner as in Example 13 except that the temperature of the press hot plate was changed to 160 ° C. by the method described in Example 13.

(Example 15)
A film was produced in the same manner as in Example 13 except that the temperature of the press hot plate was changed to 200 ° C. by the method described in Example 13.

As shown in Tables 1 to 4, even in the case of an insulating film for a capacitor containing a cellulose resin having a film thickness of 10 μm or less, the filler addition system of Examples 1 to 11 has a decrease in filler filling amount. The light transmittance (total light transmittance) of the film is increased to 85% or more, and at the same time, the film strength and the dielectric breakdown potential gradient (dielectric breakdown voltage) are improved. Furthermore, from the results of Comparative Example 1 and Examples 1 to 15, the light transmittance (total light transmittance) of the film was improved to 85% or more regardless of the amount of filler added by the hot press treatment, and at the same time the film strength and insulation. The breakdown potential gradient is improved. The temperature at the time of hot pressing increases from 120 ° C. to 160 ° C. as the temperature increases, and the light transmittance (total light transmittance) improves, but when pressed at a temperature higher than 200 ° C., there is almost no change in transmittance. As a result of visual observation, yellowing, which was suggested to be due to thermal decomposition of the resin, was confirmed.
According to the present invention, an insulating film for a capacitor having a high relative dielectric constant without foaming whitening, a high insulating property (dielectric breakdown voltage) and a high strength (tensile strength) can be obtained. Contributes to downsizing.

Claims (8)

  An insulating film for a capacitor containing a cellulose resin having a total light transmittance of 85% or more and a film thickness of 10 μm or less.   Furthermore, the insulating film for capacitors of Claim 1 containing an inorganic filler.   The insulating film for a capacitor according to claim 1 or 2, wherein the cellulose resin has a hydroxyl group partially modified by any one of acetylation, propionylation, and butyrylation.   The insulating film for capacitors according to claim 2 or 3, wherein the inorganic filler has a spherical shape or a scale shape, and includes at least one of them.   The insulating film for capacitors according to claim 4, wherein the spherical filler contains either titanium oxide (rutile) or alumina.   The insulating film for capacitors according to claim 4, wherein the scale-shaped filler contains either mica or boron nitride.   An insulating film for a capacitor obtained by applying pressure and heat treatment to the insulating film for a capacitor according to claim 1.   The film capacitor using the insulating film for capacitors as described in any one of Claims 1-7.