JP2019033207A - Film for film capacitor and film capacitor using the same - Google Patents

Abstract

To provide a film for a film capacitor and film capacitor using the same which have relatively high relative dielectric constant and good heat resistance, realize miniaturization of the film capacitor and improvement of heat resistance, and can contribute to energy saving and environmental response.SOLUTION: There is provided a film for a film capacitor containing a cellulose resin and an ester plasticizer. The molecular weight of the ester plasticizer is preferably 150 to 1000. Further, the film preferably includes an inorganic filler. There is also provided a film capacitor using the film for a film capacitor.SELECTED DRAWING: None

Description

  The present invention relates to a film for a film capacitor having high insulation properties and a film capacitor using the same.

  In recent years, power devices have been used in hybrid / electric vehicles, wind power / solar power generation, industrial equipment, etc. that contribute to energy savings. Among them, inverters using film capacitors that are advantageous in terms of high withstand voltage and high output The demand for film capacitors has been increasing due to the fact that film capacitors occupy a large percentage of the inverter due to the recent increase in capacity.

  Furthermore, with the expansion of application of SiC devices, there is also a demand for higher heat resistance of film capacitors in order to cope with an increase in heat generation temperature of peripheral components.

  To reduce the size of the film capacitor, there is a reduction in the film thickness. Currently, polyethylene terephthalate (PET), polypropylene (PP) and other engineering plastic materials are the mainstream for film capacitors. Among them, PP has a relative dielectric constant of 2.2 and is relatively high as an organic film material. Excellent workability and most frequently used.

  The main film thickness used for film capacitors is 5 to 6 μm. To reduce the size, products with a thickness of 2 to 4 μm are currently being developed, contributing to the miniaturization of film capacitors. Yes.

  It is effective to use a film having a high relative dielectric constant as a technique for downsizing the film capacitor, which is different from the film thinning. Since the volume of the capacitor is inversely proportional to the dielectric constant of the film used, by doubling the relative dielectric constant of the film, if the dielectric breakdown potential gradient is the same, the volume of the film capacitor is halved with the same capacitance. Will be calculated.

Polyvinylidene fluoride resin (dielectric constant 6-8) is a film with a high relative dielectric constant. In extrusion film molding, it is difficult to obtain a thin film, and it is dissolved using a solvent and coated on a film substrate. Thus, the solvent is evaporated to form a film (for example, Patent Documents 1 and 2). A film having a high dielectric constant can be obtained by film formation by this coating method, but polyvinylidene fluoride resin is inferior in heat resistance.
There are various types of film materials as materials other than polyvinylidene fluoride resin. Among them, synthetic resins such as acrylic resin, melamine resin, alkyd resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, and cellulose resin are processed. The film material formed is mainly mentioned.

  Among them, cellulose resin is a high-performance resin as a film. Although there are differences depending on the resin skeleton and the amount of modification, the relative permittivity is as high as 3 to 7, and the heat resistance is also high compared to other materials. And high heat resistance are possible.

International Publication No. 2015/064327 International Publication No. 2011/089948

  There are many methods for forming a film, such as coating and extrusion stretching, but considering mass productivity and cost reduction, it is considered that film formation by stretching is preferable.

  However, since the cellulose resin has a high melting point, it takes time to dissolve the varnish in the coating process in the production process, and it is difficult to mass-produce and produce a thin film of 2 μm because the stretchability is poor in the extrusion drawing. There is a problem. In addition, there is also a problem that it is fundamentally difficult to produce an ultra-thin film with a thickness of 2 μm with high accuracy by the coating method.

  In view of the above circumstances, the present invention has a relatively high dielectric constant, good heat resistance, and can be used as a cellulose film for film capacitors, such as hybrid / electric vehicles, wind / solar power generation, industrial equipment, etc. An object of the present invention is to provide a film capacitor film and a film capacitor using the film capacitor that can realize a reduction in size and an improvement in heat resistance of the film capacitor used in the manufacturing process and contribute to energy saving and environmental measures.

  As a result of intensive studies in view of the above background, in the cellulose resin film composition, by adding a plasticizer, in the film formation by the extrusion stretching process, the stretchability can be improved, and the production of a film having a flat and good handling property is possible. I came to find that it would be possible.

The present invention is as follows.
(1) A film capacitor film containing a cellulose resin and an ester plasticizer.
(2) The film capacitor film as described in Item 1, wherein the ester plasticizer has a molecular weight of 150 to 1,000.
(3) The film for a film capacitor according to Item 1 or 2, wherein the ester plasticizer has a structure in which a divalent or trivalent acid and a monovalent alcohol are ester-bonded.
(4) Content of ester plasticizer is a film for film capacitors as described in any one of 1-3 which are 1-20 mass% with respect to a cellulose resin.
(5) Furthermore, the film for film capacitors as described in any one of 1-4 whose inorganic filler is contained.
(6) The film for a film capacitor according to any one of 1 to 5, wherein the cellulose resin is one in which at least a part of a hydroxyl group is modified by any one of acetylation, propylation, and butyrylation.
(7) The film for film capacitors as described in 5 or 6, wherein the inorganic filler is a scaly shape.
(8) The film capacitor film according to item 7, wherein the scale-like inorganic filler is mica.
(9) The film according to any one of 1 to 8, wherein the film thickness is 10 μm or less.
(10) The film for a film capacitor according to any one of 1 to 9, which has been thinned by a stretching method.
(11) A film capacitor using the film for a film capacitor according to any one of 1 to 10.

  The film for a film capacitor obtained by the present invention has a high relative dielectric constant, good heat resistance, and can be used as a cellulose film for a film capacitor, such as a hybrid / electric vehicle, wind / solar power generation, industrial equipment, etc. The film capacitor used in this system can be reduced in size and improved in heat resistance, 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 group generally possessed by acetylation, propylation, butyrylation, or the like. When the hydroxyl group is not modified by alkylation or the like, the processability is lowered such as 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 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 the solvent. The number average molecular weight is not limited, but is preferably in the range of 20,000 to 100,000, more preferably in the range of 30,000 to 80,000. If it is less than 20000, the film strength is lowered, and if it exceeds 100000, the solubility in a solvent is lowered, and the workability is lowered.

The specific example of the cellulose resin used for this embodiment is shown.
As cellulose acetate, the Eastman Chemical company make and brand name: CA-398-3, CA-398-6, CA-398-10, CA-398-30 is mentioned, for example. Examples of cellulose acetate propionate include Eastman Chemical Co., Ltd., trade names: CAP-504-0.2, CAP-482-0.5, and CAP-482-20. As cellulose acetate butyrate, for example, manufactured by Eastman Chemical Co., Ltd., trade names: CAB-551-0.01, CAB-551-0.2, CAB-553-0.4, CAB-531-1, CAB-500 -5, CAB-381-0.1, CAB-381-0.5, CAB-381-2, CAB-381-20, CAB-381-20BP, CAB-321-0.1, CAB-171-15 Is mentioned.

  The film for a film capacitor of the present invention contains an ester plasticizer. The ester plasticizer has an ester group and is preferably formed from a divalent or trivalent acid and a monovalent alcohol. Examples of the acid include phthalic acid, adipic acid, phosphoric acid, and trimellitic acid.

  The molecular weight of the ester plasticizer is preferably in the range of 150 to 1000, and more preferably in the range of 200 to 500. If the molecular weight is less than 150, the plasticizer component volatilizes from the film during the production process, and the original characteristics may not be exhibited. If the molecular weight exceeds 1000, the stretchability tends to decrease. The molecular weight is the molecular weight when the structure of the plasticizer is known, and a divalent or trivalent acid or monovalent alcohol is a mixture of a plurality, and the obtained plasticizer has a plurality of molecular weights. In the specification, all are number average molecular weights.

In addition, the number average molecular weight in this specification can be measured by general gel permeation chromatography (GPC). The measurement conditions are described below.
〔Measurement condition〕
Pump: L-6000 (trade name, manufactured by Hitachi, Ltd.)
Column: TSKgel G4000HHR + G3000HHR + G2000HXL (manufactured by Tosoh Corporation, trade name (“TSKgel” is a registered trademark))
Column temperature: 40 ° C
Elution solvent: Tetrahydrofuran (without chromatographic stabilizer, Wako Pure Chemical Industries, Ltd.)
Sample concentration: 5 g / L (tetrahydrofuran soluble component)
Injection volume: 100 μL
Flow rate: 1.0 mL / min Detector: Differential refractometer RI-8020 (trade name, manufactured by Tosoh Corporation)
Molecular weight calibration standard: Standard polystyrene data processor: GPC-8020 (trade name, manufactured by Tosoh Corporation)

  Moreover, it is preferable that 1-20 mass% of ester plasticizers are included with respect to a cellulose resin, and it is more preferable that 3-15 mass% is included. If it is less than 1% by mass, the stretchability tends to be poor, and if it exceeds 20% by mass, the strength of the film decreases, and the film tends to become dense and easily break when stretched.

  Although the specific example of the plasticizer which can be used by this embodiment is shown below, this invention is not limited to these. One type can also be used, but two or more types may be included. The molecular weights described below are values obtained by calculating the sum of atomic weights from the number of atoms constituting the molecular formula, and are not actually measured values by GPC.

Bis (2-ethylhexyl) adipate (abbreviation DOA, molecular weight 370.57, boiling point 335 ° C.)
Diisobutyl adipate (abbreviation DI4A, molecular weight 258.35, boiling point 293 ° C.)
Acetyl tributyl citrate (abbreviation ATBC, molecular weight 402.48, boiling point 173 ° C.)
Dodecanedioic acid bis (2-ethylhexyl) (abbreviation DODN, molecular weight 454.73, boiling point 267 ° C.)
Dibutyl sebacate (abbreviation DBS, molecular weight 314.46, boiling point 180 ° C. (3 mmHg))
Dibutyl phthalate (abbreviation DBP, molecular weight 278.35, boiling point 340 ° C.)
Diethyl phthalate (abbreviation DEP, molecular weight 222.24, boiling point 295 ° C)
Dimethyl phthalate (abbreviation DMP, molecular weight 194.18, boiling point 283 ° C)
Triphenyl phosphate (abbreviation TPP, molecular weight 326.28, boiling point 244 ° C. (10 mmHg))
Tricresyl phosphate (abbreviation TCP, molecular weight 368.36, boiling point 265 ° C. (10 mmHg))

The film for a film capacitor of this embodiment may contain an inorganic filler. When classifying inorganic fillers by shape, spherical particles that have an aspect ratio in the range of 1 to 1.5 and flat scale particles that have the same aspect ratio in the range of 2 to 10 (scale shape, aspect ratio; grain Diameter / thickness) and can include both or either.
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.

  Natural mica and synthetic mica are suitable for increasing the dielectric constant of the film.

  When adding an inorganic filler, the addition amount is in the range of 0.1 to 50% by volume, and more preferably 10 to 30% by volume. If it is less than 0.1% by volume, there is no effect of improving the relative dielectric constant or withstand voltage characteristics, and if it exceeds 50% by volume, the film becomes brittle and the film strength tends to decrease.

  When adding an inorganic filler to the film for a film capacitor of the present embodiment, by using a coupling agent, the affinity between the resin and the filler interface is increased, and the stretchability can be improved.

  Although the specific example of the coupling agent which can be used by this embodiment is shown below, this invention is not limited to these. One type can be used, but two or more types may be included.

  As coupling agents, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3 , 4-epoxycyclohexyl) ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3-amino Propyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptotriethoxysilane, 3-ureidopropyltriethoxysilane, propyltrimethoxysilane, propyltrie Kishishiran, hexyl trimethoxysilane, hexyl triethoxysilane, decyl trimethoxysilane, decyl triethoxysilane, dodecyl trimethoxy silane, a dodecyloxy triethoxy silane and the like.

  The addition amount of the coupling agent is preferably in the range of 0.1 to 3.0% by mass and more preferably in the range of 0.3 to 1.5% by mass with respect to the filler mass. If the added amount is less than 0.1% by mass, the dispersibility of the filler is lowered, and the dispersibility deterioration due to the aggregation of the filler becomes remarkable. If it exceeds 3.0% by mass, the film strength is lowered, and the film is densely packed during stretching. Tends to occur and tends to break.

  The film for film capacitor of the present embodiment is a method in which the above resin, plasticizer or filler is mixed and varnished in a solvent, coated on a substrate so as to have a predetermined film thickness, and the solvent is dried to form a film. Can be produced. Conventional equipment can be used without limitation as equipment for producing the varnish. The substrate to be coated is not particularly limited, but in general, it is applied directly to the surface of a plastic support such as polyethylene terephthalate (PET) or a metal support such as a steel belt or a metal drum, and is used as an independent film. It can also be obtained. In addition, by performing surface treatment on the surface of the substrate, the adhesiveness with the film for film capacitor of the present embodiment can be controlled when the film is made independent as a single film. This coating film can also be processed into a desired film thickness by stretching.

  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 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.

  As another method for forming a film, it can also be obtained by solid kneading without solvent, forming a film by extrusion, and stretching the film to a desired film thickness.

  When solid kneading, a blended material such as cellulose resin and plasticizer is premixed in advance with a Henschel mixer, etc., and a biaxial kneader or the like is used to uniformly mix the materials at a desired size with a pelletizer. Pelletize. Even in a system to which a filler is added, solid kneading can be performed using the same equipment. It is possible to uniformly mix the resin by heating while kneading to a temperature range where the resin melts. In the production of the film of this embodiment, the range of 180 to 250 ° C. was a preferable kneading temperature.

  The pellets obtained by the biaxial kneader are formed into a film with a desired film thickness through a T die by an extruder. Although a film thickness is decided by the target film thickness after extending | stretching and the extending | stretching rate of a film, a thick film can be produced in the range of 20-500 micrometers. The film width obtained by T-die extrusion almost depends on the T-die width. Although there is no restriction | limiting in T die width | variety, it can determine with the extending | stretching rate of a film, and the film thickness after extending | stretching. The film extruded from the T die is wound up while passing through a cooling roll. When winding, the film thickness can be controlled by changing the winding speed while winding in one axis direction.

  The film obtained by T-die extrusion is stretched to a desired film thickness by a stretching machine. As the stretching machine, generally available equipment can be used, and a uniaxial stretching machine or a biaxial stretching machine can be used. The biaxial stretching machine may be any equipment for stretching one axis at a time or biaxial stretching at the same time. During stretching, the film is heated to a predetermined temperature. In the film for a film capacitor of the present embodiment, a good stretched film could be produced in the range of 140 to 180 ° C. If the temperature is lower than 140 ° C., the resin does not soften, and the film has a low stretching rate and the film is likely to break. It tends to occur. A stretched film is produced with a desired film thickness by setting the film thickness and stretch ratio of the film before stretching, and the stretched film is taken out after cooling.

  In consideration of mass productivity, the film for film capacitor of this embodiment can be produced in a roll state by unwinding the heated pre-stretched film, chucking the end, stretching, and winding after cooling. Also in this case, a stretched film can be produced with a desired film thickness by setting the film thickness of the pre-stretch film and the stretch ratio.

  Although a film capacitor can be produced even with a single film produced as described above, in particular, in a thin film having a thickness of 10 μm or less, irregularities are present on the film surface, which adversely affects the capacitor characteristics. As a method for improving this, it is effective to apply a heat press. 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.

It is preferable that the heating temperature in the heating press be equal to or higher than the glass transition point 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 most is in the range of 80 to 200 ° C. However, in the case of a thin film, this is not the case, and the effect is exhibited even by a hot press at a temperature lower than the glass transition point. Specifically, the hot pressing is performed at a temperature of 60 to 200 ° C., more preferably 120 to 180 ° C.
Thereby, the unevenness | corrugation of the film surface which had generate | occur | produced with the film before a press reduces, and transparency also increases externally.

  Since the film for film capacitor of the present invention has sufficient film strength in capacitor production, the workability in the winding process at the time of manufacturing the film capacitor is improved, and since the relative dielectric constant of the film is high, Miniaturization is possible, heat resistance is high, and capacitors can be used at high ambient temperatures, contributing to energy savings.

  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.

  Measuring method of film strength: The film is punched into a size of 3 mm wide and 60 mm long using a cutting device, and abrasive paper is pasted on both ends of the test piece to prevent slipping, and tensile strength is measured using a microforce precision testing device. It was measured.

  Film appearance: The film appearance was visually evaluated for transparency.

  Measurement of film 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 at a constant pressure increase rate (100 Vdc / sec). Voltage was applied until. The voltage when the sample broke down was recorded, and the breakdown voltage was divided by the thickness of the sample to calculate the dielectric breakdown voltage (unit: V / μm).

  Measurement of relative dielectric constant: A film on which gold was deposited was sandwiched between dielectric characteristic measurement terminals (trade name: 16451B, manufactured by Agilent), the electrostatic capacity was measured with an LCR meter, and the relative dielectric constant of the film was calculated. The measurement frequency was 1 KHz (25 ° C.).

  Determination of stretching ratio: Using a biaxial stretching machine, stretching was performed so that the film thickness after stretching was 3 to 7 μm, and the results of measuring the maximum value of the stretching ratio at which the film did not break or have defects in 100% units were measured. Adopted. The apparatus was IMC-18B2 (manufactured by Imoto Seisakusho Co., Ltd., trade name), and the stretching was performed in the range of 140 to 180 ° C. The film size before stretching was 50 mm × 50 mm, and the effective film size after chucking the four corners was 38 mm × 38 mm.

  The film production process is described below. The composition and the results of property evaluation are summarized in Table 1.

(Example 1): Cellulose resin (trade name: CAP482-20, cellulose acetate propionate (acetyl content; 1.3% by mass, propionyl content; 48% by mass, Tg; 147 ° C.), manufactured by Eastman Chemical Co., Ltd. ) And a plasticizer (DOA (bis (2-ethylhexyl) adipate, manufactured by Taoka Chemical Co., Ltd.)), Micafila (trade name: Somasif ME-100, hydrophilic swellable mica, average particle size 3 to 7 μm, Katakura Corp. Agri Co., Ltd.) and a coupling agent (trade name: KBM-3063, hexyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) are mixed using a Henschel mixer in the blending amounts shown in Table 1 and mixed in a twin-screw kneader. The resin was pelletized by a pelletizer and charged again into the single-screw kneader, and the T-die was controlled. Out and thick film by molding. The thick film subjected to stretching treatment by biaxial stretching machine to obtain a thin film having a thickness of 3 to 7 [mu] m.

(Example 2): A film was obtained by the same operation except that the plasticizer of Example 1 was changed to DODN (bis (2-ethylhexyl) dodecanedioate, manufactured by Taoka Chemical Co., Ltd.).

(Example 3): A film was obtained by the same operation except that the plasticizer of Example 1 was changed to TPP (triphenyl phosphate).

(Comparative Example 1): A film was obtained by the same operation except that the plasticizer of Example 1 was not added.

(Example 4): Cellulose resin (trade name: CAP482-20, manufactured by Eastman Chemical Co., Ltd.) and plasticizer (DOA, manufactured by Taoka Chemical Industry Co., Ltd.) using the Henschel mixer in the blending amounts shown in Table 1. The mixture was mixed, charged into a twin-screw kneader, and kneaded while controlling the discharged resin temperature at 200 ° C. The resin pelletized by the pelletizer was again put into a uniaxial kneader and formed into a thick film by T-die extrusion. The thick film was stretched by a biaxial stretching machine to obtain a thin film having a thickness of 3 to 7 μm.

(Example 5): A film was obtained by the same operation except that the plasticizer of Example 4 was changed to DODN (Taoka Chemical Industries, Ltd.).

Example 6 A film was obtained by the same operation except that the plasticizer of Example 4 was changed to TPP.

(Comparative Example 2) A film was obtained by the same operation except that the plasticizer of Example 4 was not added.

  As shown in Table 1, both the filler-added system (Comparative Example 1, Examples 1 to 3) and the filler-free system (Comparative Example 2 and Examples 4 to 6) improve the stretchability by adding the plasticizer. When the DOA was used as the plasticizer, the stretch ratio was the highest. In addition, the breakdown voltage and the relative dielectric constant tended to improve as the stretchability improved.

Claims (11)

  A film for a film capacitor containing a cellulose resin and an ester plasticizer.   The film for a film capacitor according to claim 1, wherein the ester plasticizer has a molecular weight of 150 to 1,000.   The film for a film capacitor according to claim 1 or 2, wherein the ester plasticizer has a structure in which a divalent or trivalent acid and a monovalent alcohol are ester-bonded.   The film for a film capacitor according to any one of claims 1 to 3, wherein the content of the ester plasticizer is 1 to 20% by mass with respect to the cellulose resin.   Furthermore, the film for film capacitors as described in any one of Claims 1-4 containing an inorganic filler.   The film for a film capacitor according to any one of claims 1 to 5, wherein the cellulose resin is one in which at least a part of a hydroxyl group is modified by any one of acetylation, propylation, and butyrylation.   The film for a film capacitor according to claim 5 or 6, wherein the inorganic filler has a scale shape.   The film for a film capacitor according to claim 7, wherein the scale-shaped inorganic filler is mica.   The film capacitor film according to any one of claims 1 to 8, wherein the film thickness is 10 µm or less.   The film for a film capacitor according to any one of claims 1 to 9, wherein the film is thinned by a stretching method.   The film capacitor using the film for film capacitors as described in any one of Claims 1-10.