JP2008127460A - Biaxially oriented polypropylene film for capacitor, and metallized film and capacitor by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene film for a capacitor, while holding dimensional stability, heat resistance and rigidity as similar to conventional articles, improving insulation breakdown strength and excellent in both handling property and electric voltage-withstanding characteristic, and also a metallized film and capacitor by using the polypropylene film. <P>SOLUTION: This polypropylene film contains the polypropylene and an ion-containing polymer. The metallized film and capacitor by using the same are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biaxially oriented polypropylene film and a metallized polypropylene film for capacitors, which have extremely high dielectric breakdown strength, that is, extremely excellent withstand voltage characteristics. Further, the capacitor is suitable for use under a small size, large capacity and high rated voltage. It is about.

  Polypropylene films are widely used for industrial and packaging applications because they have excellent moisture resistance, transparency, and surface gloss and can be supplied at low cost. In addition, since polypropylene has excellent electrical characteristics (voltage resistance characteristics, dielectric loss, etc.) compared to other polymers, its biaxially oriented film is particularly widely used for electrical applications. In particular, the demand for capacitors as dielectrics is large, and the growth is remarkable.

  In recent years, biaxially oriented polypropylene films have attracted more attention as inverters of various electrical facilities, lighter, thinner, smaller, and larger capacities of capacitors have progressed, and thinning of the films has been accelerated.

  However, as the biaxially oriented polypropylene film becomes thinner, handling properties (for example, slipperiness is moderately good when the film is wound, and no winding slip or wrinkle occurs) and workability (for example, metallization) In such a case, there is a tendency that properties such as elongation, wrinkle, and whitening of the film do not occur), and these improvements are required.

  As a technique for improving the handling property of the biaxially oriented polypropylene film, a technique for improving the slipperiness by roughening at least one surface of the film is representative. Moreover, it is important from the viewpoint of improving the characteristics of the capacitor element to appropriately roughen the film surface. As this surface roughening method, for example, a mechanical surface roughening method such as an embossing method or a sandblasting method, a chemical surface roughening method such as chemical etching using a solvent, or a different polymer such as polyethylene is mixed with polypropylene. Examples thereof include a method of roughening by stretching a sheet and biaxially orienting, and a method of roughening by stretching and biaxially orienting a sheet containing β crystals (see, for example, Patent Document 1). . Of these, the biaxially oriented polypropylene film for capacitors should be biaxially oriented by stretching a sheet with β crystals formed on the surface from the viewpoints of roughness density control, heat resistance, withstand voltage characteristics, environmental friendliness, etc. The surface roughening method (hereinafter sometimes abbreviated as β crystal method) is mainly applied.

In roughening by the β crystal method, a melt-extruded polypropylene is wound around a metal drum and cooled and solidified to produce a sheet containing β crystals in addition to α crystals on the surface (near). β crystal in the process of biaxial stretching by crystal modification (the crystal density 0.922 g / cm ³⁾ of the α crystal (crystal density 0.936g / cm ^3), thereby forming irregularities on the film surface by these density differences crude Faces and provides slipperiness. Roughening by the β crystal method is based on the raw material properties of the polypropylene used (crystallinity, viscosity, etc.), cooling rate when cooling and solidifying on a metal drum (controllable by drum temperature, drum rotation speed, etc.), biaxial stretching conditions It is known that it can be controlled by (magnification, temperature, etc.) (for example, see Non-Patent Document 1).

  On the other hand, at the time of capacitor element production, the electrode is inserted into the film by stacking it with an electrode such as a separately prepared metal foil or paper or plastic film metallized on both sides, or by installing a metal layer on the film by metallization, After winding, heat treatment is performed at a constant temperature. At this time, it is necessary to remove the form-retaining property and air between the film layers by appropriately shrinking the film by heat and generating tightening of the element. If this thermal shrinkage is too large, the element may be deformed, resulting in a decrease in the capacitor capacity and destruction of the element. If it is too small, the winding is insufficiently tightened. In some cases, the device was destroyed. Therefore, the biaxially oriented polypropylene film for capacitors is required to have a reasonably low heat shrinkage rate.

  In addition, conventional film capacitors have been designed using thicker films with a margin in withstand voltage characteristics. However, as described above, with the progress of lighter, thinner, smaller and larger capacities, the film has become thinner. In the polypropylene film for capacitors, the film itself is highly regarded as having high dielectric breakdown strength, excellent reliability, and excellent heat resistance. In particular, high dielectric breakdown strength is often the most basic and maximum required characteristic.

To date, various proposals have been made to improve the handling property, workability, voltage resistance, heat resistance, and heat shrinkage properties of biaxially oriented polypropylene films for capacitors. For example, by setting the crystallinity obtained from mesopentad fraction, ash content, and film density within a specific range, the withstand voltage characteristics, heat resistance, and vapor deposition processability improved polypropylene film for heat and voltage resistant capacitors (for example, , Patent Document 2), the product of the ash content of the film and the internal haze within a specific range to improve the withstand voltage characteristics (for example, see Patent Document 3), the heptane index of the specific range A biaxially stretched polypropylene film that is roughened by the above β crystal method so that the 10-point average roughness, centerline roughness, and maximum roughness are in a specific range and improved handling properties (for example, patents) Reference 4), non-deposited surface and chromium plating after metal deposition on one side of polypropylene film When the coefficient of static friction with the applied metal plate at 80 ° C. is 0.8 or less and the content of the additive having a melting point of 130 ° C. or less is 4,000 ppm by weight or less, the slipperiness with the roll is reduced. Resin selected from a polypropylene film for capacitor deposition (see, for example, Patent Document 5) with good and improved deposition processability, a polypropylene resin, and a terpene resin substantially free of double bonds or polar groups. At least one resin layer mixed with a specific composition of at least one of the above, and by setting the center line average surface roughness of at least one side to a specific range, the insulation defects are reduced, the withstand voltage characteristics are improved, and in the long-term durability A capacitor-use polypropylene film having improved safety characteristics (see, for example, Patent Document 6) is known.
Japanese Examined Patent Publication No. 56-11963 (first page, first paragraph, lines 29-35) JP-A-8-294962 (second page, first paragraph, second to sixth lines) JP 9-139323 A (2nd page, 1st paragraph, 2nd to 6th lines) JP 11-147962 A (2nd page, 1st paragraph, lines 2 to 24) Japanese Patent No. 2663594 (1st page, 1st paragraph, 2nd to 7th lines) Japanese Patent Laid-Open No. 11-162779 (second page, first paragraph, lines 2 to 10) M. Fujiyama et al., “Journal of Applied Polymer Science”, 36, 1988, p. 985-1048

  However, in conventional films such as Patent Documents 1 to 5 and Non-Patent Document 1, it is difficult to achieve both handling properties and withstand voltage characteristics. Generally, even if the films have the same thickness, the greater the roughness of the film surface, the lower the dielectric breakdown strength. However, the smaller the surface roughness, the worse the slipperiness of the film and the lower the handling properties. As described above, the required characteristics with respect to the withstand voltage characteristics of the film are increasing year by year. On the other hand, since a thinner film is required, it is necessary to improve the handling property. One solution has been to reduce the surface roughness and improve the withstand voltage characteristics to the level at which practical minimum handling properties can be maintained in the conventional films described above. There was also a limit.

  In the conventional β crystal method, the raw material characteristics and film forming conditions are controlled mainly from the viewpoint of improving the withstand voltage characteristics and stable film forming. For this reason, in order to obtain a uniform rough surface with good handling properties, the amount of β crystal contained in the unstretched sheet is mainly controlled by controlling the cooling rate of the molten resin. That is, in order to obtain a rough surface, an appropriate amount of β crystal is formed on the surface (near) of the unstretched sheet by setting a high drum temperature when the molten resin is wound around a metal drum and slowing down the cooling rate (slow cooling). Needed to be generated. However, if the cooling rate at this time is too slow (drum temperature is too high), insulation defects such as voids are generated inside the film after biaxial stretching, and the withstand voltage characteristics may be significantly deteriorated.

  Also, the thinner the film, the more difficult it is to balance handling properties and withstand voltage characteristics at a high level. In order to thin the film after biaxial stretching, it is necessary to thin the unstretched sheet unless biaxial stretching is performed at a high stretching ratio at which film formation is not stable. If the unstretched sheet is thin, the adhesion to the metal drum is deteriorated during the production of the sheet, and uneven adhesion to the drum may occur. In addition, when the unstretched sheet becomes thin, the cooling rate of the sheet tends to increase, and coupled with the occurrence of uneven adhesion, the generation efficiency of β crystals deteriorates. The thinner the film, the rougher the surface of the film, and the smoother it becomes. There was a trend. In addition, the higher the drum temperature in order to compensate for the decrease in β crystal generation efficiency when thinned, the more voids are generated inside the film after biaxial stretching, and the withstand voltage characteristics tend to deteriorate. It was.

  In Patent Document 6, although a specific resin is mixed to reduce insulation defects and improve the withstand voltage characteristics, the thermal shrinkage rate at a high temperature is high and the dimensional stability is inferior. .

  The object of the present invention is to solve the above-mentioned problems, and is to provide a biaxially oriented polypropylene film that retains dimensional stability and heat resistance at the same level as conventional products and has significantly enhanced dielectric breakdown strength. . It is preferable to provide a biaxially oriented polypropylene film in which more uniform and dense irregularities are formed on the surface and insulation defects are reduced as compared with a conventional β crystal method film. That is, it is to provide a biaxially oriented polypropylene film that is extremely excellent in handling properties and withstand voltage characteristics.

  As a result of intensive studies, the present inventors have found that the above-described problem can be achieved mainly by the following configuration.

  That is, the biaxially oriented polypropylene film for capacitors of the present invention is characterized by containing polypropylene and an ion-containing polymer.

  Further, as a preferred embodiment, the edge breaking strength (BDV) at 25 ° C. is 650 V / μm or more, the film thickness by the micrometer method is 5 μm or less, and the center line average of both sides of the film The ratio (Rmax / Ra) of the surface roughness (Ra) to the maximum surface roughness (Rmax) is 8 to 15, and the thermal contraction rate in the longitudinal direction at 120 ° C. of the film is 0.5 to 4.5. A metallized polypropylene film in which a metal layer is provided on at least one side of the polypropylene film, a biaxially oriented polypropylene film for a capacitor, or a capacitor using at least a part of the metallized polypropylene film. is there.

  The polypropylene film of the present invention has extremely high dielectric breakdown strength while maintaining dimensional stability, rigidity, and heat resistance at the same level as in the past, and is excellent in both handling characteristics and withstand voltage characteristics, which are contradictory characteristics. Also, unlike conventional films using the simple β crystal method, there is no extreme smoothing tendency when thinned, and uniform and dense irregularities with few coarse protrusions are formed appropriately on both surfaces of the film. Therefore, handling characteristics can be maintained even if the thickness is reduced. Furthermore, since the surface irregularities are uniform and dense, and there are fewer insulation defects such as voids generated during biaxial stretching than in the prior art, it is possible to suppress a decrease in the withstand voltage characteristics as the thickness decreases. Moreover, since there are few voids, there are few tears in film forming seen as it becomes thin, and productivity can be hold | maintained even if it makes a film thin.

  From the above, the polypropylene film of the present invention has excellent handling properties in the case of metallization and capacitor element production, for example, as a highly reliable polypropylene film excellent in withstand voltage characteristics and used for capacitor applications. Application is expected.

  The biaxially oriented polypropylene film for capacitors of the present invention (hereinafter sometimes simply referred to as a polypropylene film or a film) is preferably composed mainly of polypropylene. In the present invention, this is defined as that the film contains 70% by weight or more of a propylene monomer component with respect to all the polymers constituting the film. If polypropylene is the main component, a capacitor film having a high dielectric breakdown strength, excellent withstand voltage characteristics and low loss can be obtained when a capacitor element is used. The content of the propylene monomer is more preferably 80% by weight or more, and still more preferably 85% by weight or more based on the total amount of monomers of all the polymers constituting the film.

  The polypropylene used for the polypropylene film of the present invention is preferably composed mainly of polypropylene, but is a polymer obtained by copolymerizing propylene and a monomer component of an unsaturated hydrocarbon other than propylene within a range not to impair the purpose of the present invention. It may be a polymer, a polymer obtained by copolymerizing propylene and an unsaturated hydrocarbon monomer component other than propylene may be blended, or an unsaturated hydrocarbon monomer component other than propylene. (Co) polymers may be blended. Examples of the monomer component constituting such a copolymer component or blend include, for example, ethylene, propylene (in the case of a copolymer blend), 1-butene, 1-pentene, 3-methylpentene-1, 3 -Methylbutene-1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl -2-norbornene and the like.

  In addition, the polypropylene used for the polypropylene film of the present invention, from the viewpoint of economy, when producing scrap film and other films produced when producing the film of the present invention within a range not impairing the characteristics of the present invention. The generated waste film may be collected and used.

  The raw material properties of polypropylene used in the film of the present invention are not particularly limited. For example, if the raw material properties as shown below are present, the material has further excellent withstand voltage properties, good sliding properties, and excellent handling properties. It is preferable because the film can be excellent in dimensional stability, rigidity, heat resistance, and workability.

  The melt index (MI) of the polypropylene used for the polypropylene film of the present invention is preferably in the range of 0.5 to 30 g / 10 minutes from the viewpoint of film forming properties and film properties after film formation. If the MI is less than 0.5 g / 10 min, there may be problems such as an increase in filtration pressure during melt extrusion or a long time for replacement of the extrusion raw material, and the dimensional stability of the resulting film ( (Heat shrinkage rate) may deteriorate. When MI exceeds 30 g / 10 minutes, the thickness unevenness of the film obtained may become large, and problems, such as surface roughness becoming small, may arise. In order to make MI into the above range, a method of adjusting the average molecular weight, molecular weight distribution, etc. according to the polymerization conditions at the time of polypropylene polymerization is preferably used. MI is more preferably 1 to 20 g / 10 min, and further preferably 1.5 to 10 g / min.

The mesopentad fraction (mmmm) of the polypropylene used for the polypropylene film of the present invention is preferably in the range of 92 to 99.2%. Here, mmmm is an index that directly reflects the isotactic three-dimensional structure in polypropylene. Moreover, mmmm here is the average value computed by the method shown in the detailed description of the following measuring method from each spectrum derived from the methyl group obtained by ¹³ C-NMR as shown below. If the mmmm is less than 92%, the dimensional stability, heat resistance, and rigidity of the resulting film will be reduced, resulting in poor workability, poor handling, and markedly reduced voltage resistance. As it may not be practical. If mmmm exceeds 99.2%, the film forming property may be significantly reduced. In order to set mmmm within the above range, a catalyst composition (solid catalyst, external electron donor) at the time of polypropylene polymerization, a method of adjusting the purity thereof, and the like are preferably used. mmmm is more preferably 94 to 99%, further preferably 95 to 98.5%, and most preferably 96 to 98.5%.

  It is preferable that the isotactic index (II) of the polypropylene used for the polypropylene film of the present invention is in the range of 92 to 99.5%. When the II is less than 92%, the dimensional stability and rigidity of the resulting film are lowered, the workability is lowered, the handling property is lowered, and the withstand voltage characteristic is significantly lowered. It may not be tolerable. When II exceeds 99.5%, the film forming property may be remarkably deteriorated. In order to make II within the above range, a method using a polypropylene having a moderately low ratio of a boiling low n-heptane soluble low molecular weight component of polypropylene or a so-called atactic component having low stereoregularity is preferably used. II is more preferably 94 to 99.3%, still more preferably 95 to 99%, and most preferably 96 to 99%.

  The polypropylene ash used in the polypropylene film of the present invention is preferably 50 ppm or less. In the polymerization process of polypropylene, it is common to use a compound containing a metal as a catalyst. At this time, the catalyst residue can be evaluated from the amount of the metal oxide after the resin is completely burned, and this is defined as ash. When the ash content exceeds 50 ppm, the withstand voltage characteristic of the resulting film is lowered, and the dielectric breakdown strength may be lowered when a capacitor is used. The ash content of the polypropylene film of the present invention is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 1 ppm or more, for example, from the viewpoint of productivity during polypropylene polymerization. In order to make the ash content within the above range, a method of reducing the catalyst residue of the polypropylene to be used is most preferably used. In addition, it is important that the ash content of the obtained film itself is low, and in the film forming process, contamination (contamination of deteriorated products or foreign matters at the time of melt extrusion of polypropylene, contamination of foreign matters at the time of film formation, winding, slitting, It is also preferable to suppress as much as possible contamination of foreign contaminants during raw material recovery. The ash content of polypropylene is more preferably 40 ppm or less, further preferably 30 ppm or less, and most preferably 20 ppm or less.

  Next, the polypropylene film of the present invention contains an ion-containing polymer. Here, when the film of the present invention is a film having a multilayer structure of two or more layers, it is necessary that at least one layer thereof contains polypropylene and an ion-containing polymer, which is mainly composed of polypropylene and contains an ion-containing polymer. It is preferable. By dispersing the ion-containing polymer in polypropylene, the dielectric breakdown strength of the polypropylene film can be increased, that is, excellent voltage resistance characteristics can be imparted. This is presumably because some inhibitory action acts on the charge transfer in the film by adding the ion-containing polymer. In addition, for example, if an ion-containing polymer having a melting point lower than the stretching temperature at the time of producing a film is selected as described below, insulation defects such as voids generated during biaxial stretching can be reduced. The characteristics can be further improved. In this case, since the sheet tends to be in close contact with the metal drum during the production of the unstretched sheet, the cooling rate of the molten resin and thus the β crystal fraction in the unstretched sheet can be easily controlled, and the film is uniform on both surfaces. In addition, it is possible to improve the handling properties by forming dense irregularities and imparting excellent slipperiness. In addition, even when the film is thin, it has a high dielectric breakdown strength, reduces insulation defects, maintains adhesion to the metal drum during film formation, and can form uniform and precise irregularities on both surfaces. The ratio of the insulation defects such as surface irregularities to the total thickness can be reduced, and excellent voltage resistance characteristics can be maintained.

  Here, the ion-containing polymer is a polymer having an ion-bonded cross-linked structure due to an ionic group in the side chain or main chain. The detailed definition of the polymer generally called “ionomer” is described in, for example, Shinichi Yano, “Physical properties and industrial application of ionomer”, chapters 1 and 3 of IPC (1989), etc. According to Ion-containing polymers are classified into side chain type, telechelic type, and ionene type depending on the form of introduction of ionic groups into the polymer into which ionic groups are introduced (referred to as “host polymer” in the above document). It is further classified according to the type of counter ion used for molecules and ionic groups. The ion-containing polymer used in the polypropylene film of the present invention is not particularly limited as long as the effects of the present invention are exhibited, but from the viewpoint of dispersibility in polypropylene, melt extrusion properties, etc., a side chain type ion-containing polymer should be used. Among them, it is preferable to use an ion-containing polymer such as ethylene-methacrylic acid or ethylene-acrylic acid.

  Specific examples of the ion-containing polymer preferably used for the polypropylene film of the present invention include, for example, “Surlyn” (type name: 9721, etc.) manufactured by DuPont, “High Milan” (type name) manufactured by Mitsui DuPont Polychemical Co., Ltd. : 1706), “Iotek” manufactured by ExxonMobil Chemical, and the like.

  The addition amount of the ion-containing polymer contained in the polypropylene film of the present invention is preferably 1 to 30% by weight with respect to the total amount of resin used in the film, and the above-described effects can be seen even when added in a small amount. When the addition amount of the ion-containing polymer is less than 1% by weight, the dielectric breakdown strength is decreased, the insulation defects of the obtained film are increased, the surface roughness is not obtained, and the handling characteristics of the film are May decrease. If the amount of the ion-containing polymer added exceeds 30% by weight, the dispersibility of the ion-containing polymer in polypropylene deteriorates, defects occur during extrusion, and the resulting film has heat resistance, dimensional stability and high temperature. In some cases, the volume resistance of the material may decrease more than necessary. The addition amount of the ion-containing polymer is more preferably 2 to 20% by weight, still more preferably 3 to 15% by weight.

  The polypropylene film of the present invention preferably has a dielectric breakdown strength (BDV; also referred to as a dielectric breakdown voltage) at 25 ° C. of 650 V / μm or more, and has a higher BDV than the conventional one by including an ion-containing polymer. It is. When the BDV at 25 ° C. is less than the above range, when the obtained film is a capacitor element, the withstand voltage characteristic is low and may not be practically used. This tendency tends to decrease as the micrometer film thickness decreases. strong. The BDV at 25 ° C. is more preferably 680 V / μm or more, further preferably 720 V / μm or more, and most preferably 750 V / μm or more. The BDV can be controlled mainly by the crystallinity of polypropylene, the type of ion-containing polymer to be added and the amount thereof added. In the present invention, for example, the mmmm and II of the polypropylene used are within the above range, and the ion-containing examples exemplified above It is preferable to use a polymer and make the addition amount into the above range. Note that the higher the BDV of the polypropylene film of the present invention at 25 ° C., the higher the BDV tends to be a highly reliable film with excellent withstand voltage characteristics when used as a capacitor element. However, for example, in order to balance the film forming property, handling property, and withstand voltage characteristics at a high level, it is preferably 1,200 V / μm or less. Further, for example, it is more preferable that it is within the range of the BDV obtained in the following examples because the above-described characteristics can be balanced at a higher level.

  The melting point of the ion-containing polymer is preferably 50 to 145 ° C. In addition, melting | fusing point here is the value measured in accordance with the following measuring method using the differential scanning calorimeter (DSC). When the melting point of the ion-containing polymer is less than 50 ° C., in the production process of the unstretched sheet, the sheet sticks to the casting drum, or the heat resistance, dimensional stability and volume resistance at high temperature of the resulting film deteriorate. There is. If the melting point of the ion-containing polymer exceeds 145 ° C., the polymer may be difficult to melt during the film production process, or insulation defects in the film may not be reduced. Moreover, it is difficult to form uniform and dense surface irregularities and to provide a surface roughness that is balanced between the front and back surfaces, resulting in a decrease in slipperiness and inferior handling properties. The melting point can be controlled by selecting the counter ion of the ion group of the ion-containing polymer and selecting the polymer skeleton structure. In order to obtain the above range, for example, selecting zinc, sodium ion, etc. It is preferable to select. The melting point of the ion-containing polymer is more preferably 60 to 140 ° C, still more preferably 70 to 135 ° C, and most preferably 80 to 120 ° C.

  In the polypropylene used for the polypropylene film of the present invention, for example, an antioxidant, a chlorine scavenger, a crystal nucleating agent, a heat stabilizer, a lubricant, an antiblocking agent, a viscosity modifier, a copper damage, as long as the object of the present invention is not impaired. You may mix well-known additives, such as an inhibitor.

  Among these, selection of the kind and addition amount of the antioxidant is important for the long-term heat resistance of the film. Antioxidants added to the polypropylene used in the polypropylene film of the present invention are phenols having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples of the antioxidant include various compounds. For example, 2,6-di-tert-butyl-p-cresol (BHT; molecular weight 220) and 1,3,5-trimethyl-2,4,6 -Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, “Irganox” 1330 manufactured by Ciba Geigy Co., Ltd .; molecular weight 775), or tetrakis [methylene-3 (3,5-di- t-butyl-4-hydroxyphenyl) propionate] methane (for example, “Irganox” 1010 manufactured by Ciba Geigy Co., Ltd .; molecular weight 1,178) is preferably used in combination. The addition amount of these antioxidants is preferably 0.03 to 1% by weight with respect to the total amount of polypropylene. When the addition amount of the antioxidant is less than 0.03% by weight, long-term heat resistance may be inferior when a capacitor element is formed. When the addition amount of the antioxidant exceeds 1% by weight, blocking may occur at a high temperature due to bleeding out of the antioxidant. The addition amount of the antioxidant is more preferably 0.05 to 0.9% by weight, still more preferably 0.1 to 0.8% by weight, based on the total amount of polypropylene.

  The polypropylene film of the present invention preferably has a film thickness by a micrometer method of 5 μm or less. The biaxially oriented polypropylene film of the present invention is characterized in that the film thickness is in the above-described range and has excellent handling properties and withstand voltage characteristics even if it is thin. When the film thickness of the polypropylene film of the present invention measured by the micrometer method exceeds 5 μm, the capacitance per volume may be reduced when a capacitor element is used, which may not be preferable. The film thickness can be controlled by the film forming conditions such as the discharge amount of the molten polymer in the extrusion process and the stretching ratio in the longitudinal / lateral stretching process. As the film thickness by the micrometer method of the polypropylene film of the present invention is thinner, the capacitance per unit volume in the case of a capacitor element per volume tends to be increased, and the film thickness by the micrometer method has a lower limit in particular. Although not provided, for example, from the viewpoint of stable film formation and subsequent processability, it is preferably 0.5 μm or more, more preferably 1 μm or more, and further preferably 1.5 μm or more. The film thickness by the micrometer method is more preferably 4 μm or less, further preferably 3.7 μm or less, still more preferably 3.3 μm or less, and most preferably 3.2 μm or less.

  The center line average surface roughness (Ra) of at least one surface of the polypropylene film of the present invention is preferably 0.03 to 0.3 μm. When Ra is less than 0.03 μm, the slipperiness of the film is lowered, and wrinkles may occur during film processing such as vapor deposition, resulting in poor handling properties. If Ra exceeds 0.3 μm, the film end face may be displaced in the film winding process during film formation, capacitor element production, etc., or the ratio of surface irregularities to the total thickness may increase and the withstand voltage characteristics may decrease. . The Ra can be controlled mainly by the crystallinity of the polypropylene used, the melting point of the ion-containing polymer and its addition amount, the production process, the production conditions of the unstretched sheet in the casting process, the stretching temperature, etc. In the casting process, the mmmm and II of the polypropylene used are within the above range, the melting point of the ion-containing polymer and the addition amount thereof are within the above range, and in the casting step, the temperature of the cast drum is set to 50 to 95 ° C. as follows (the drum is In one case, the longitudinal and transverse stretching temperatures are preferably 120 to 160 ° C. and 150 to 180 ° C., respectively, as described below. Ra is more preferably 0.04 to 0.2 μm, still more preferably 0.05 to 0.15 μm. Furthermore, it is preferable that Ra of both surfaces of a film satisfy | fill the said range from a viewpoint of coexistence of handling property and a withstand voltage characteristic.

  It is preferable that the maximum surface roughness (Rmax) of at least one surface of the polypropylene film of the present invention is 0.3 to 2 μm. When Rmax is less than 0.3 μm, the handling property is inferior and wrinkles are easily formed in the capacitor element manufacturing process, and the withstand voltage characteristics may be deteriorated due to the wrinkles. When Rmax exceeds 2 μm, the ratio of coarse protrusions increases, so when a capacitor element is used, air enters between the film layers, leading to deterioration of the element, and when a metal layer is formed on the film, there are pinholes in the metal layer. In some cases, the dielectric breakdown strength and device life may be reduced during high-temperature use, or charges may be concentrated when a voltage is applied, causing insulation defects. The Ra can be controlled mainly by the crystallinity of the polypropylene used, the melting point of the ion-containing polymer and its addition amount, the production process, the production conditions of the unstretched sheet in the casting process, the stretching temperature, etc. In the casting process, the mmmm and II of the polypropylene used are within the above range, the melting point of the ion-containing polymer and the addition amount thereof are within the above range, and in the casting step, the temperature of the cast drum is set to 50 to 95 ° C. as follows (the drum is In one case, the longitudinal and transverse stretching temperatures are preferably 120 to 160 ° C. and 150 to 180 ° C., respectively, as described below. Rmax is more preferably 0.4 to 1.7 μm, still more preferably 0.5 to 1.5 μm. Furthermore, it is preferable that Rmax of both surfaces of the film satisfy the above range.

  The polypropylene film of the present invention preferably has a ratio of Rmax and Ra and Rmax / Ra of 8 to 15 for both surfaces. Here, since Rmax / Ra is the ratio of the height of the coarse protrusion to the average height of the unevenness on the surface, it can be considered as a measure for the uniformity of the unevenness on the film surface. When Rmax / Ra is less than 8, the handling property is inferior and the capacitor element is easily wrinkled, and the breakdown strength may be lowered due to the wrinkle. When Rmax / Ra exceeds 15, the ratio of coarse protrusions increases, so that air easily enters between the laminated film layers at the time of producing the capacitor element, the capacitor element is likely to deteriorate, or the metal layer is formed when the film is metalized. In some cases, a hole or the like is generated, and the element life of the obtained capacitor is reduced. The Rmax / Ra can be controlled mainly by the melting point and addition amount of the ion-containing polymer used. In the present invention, for example, it is preferable that the Rmax / Ra be within the above-mentioned range, for example. Rmax / Ra on both sides of the film is more preferably 9 to 14, still more preferably 9.5 to 13.5, and most preferably 10 to 13.

  The heat shrinkage rate in the vertical direction at 120 ° C. of the polypropylene film of the present invention is preferably 0.5 to 4.5%. In addition, the heat shrinkage rate in the vertical direction at 120 ° C. here refers to the shrinkage rate in the vertical direction of the film when heated at 120 ° C. for 15 minutes under a load of 3 gf. If the thermal shrinkage in the vertical direction at 120 ° C. is less than the above range, winding will be insufficient when producing capacitor elements, which will adversely affect shape retention and capacity change rate, and voids will be formed between the element layers. In some cases, the deterioration of the capacitor element proceeds. In addition, if the thermal contraction rate in the vertical direction at 120 ° C. exceeds the above range, the tightening at the time of manufacturing the capacitor element is too large, the element is deformed, the capacity of the capacitor is decreased due to an increase in internal stress, and the element is further destroyed. May occur. The heat shrinkage rate can be controlled mainly by the crystallinity of the polypropylene used, the amount of ion-containing polymer added, the heat setting conditions (temperature, relaxation rate) after transverse stretching, etc. In the present invention, mmmm and II of the polypropylene used. Is within the above range, the addition amount of the ion-containing polymer is preferably within the above range, and the transverse heat setting temperature and relaxation rate are preferably 150 to 180 ° C. and 1% or more as follows. The thermal contraction rate in the longitudinal direction at 120 ° C. is more preferably 1 to 3.8%, further preferably 1.2 to 3.5%, and most preferably 1.4 to 3.2%.

  The F2 value in the longitudinal direction at 25 ° C. of the polypropylene film of the present invention is preferably 35 MPa or more. Here, the F2 value in the vertical direction means that a sample cut out in a size of 15 cm in the vertical direction and 1 cm in the horizontal direction is used as a sample when the elongation is 2% when the original length is 50 mm and the tensile speed is 300 mm / min. Such stress. If the F2 value in the longitudinal direction at 25 ° C. is less than 35 MPa, the tensile strength of the film is insufficient, and in particular, when the film is thinned, it may be stretched due to processing tension. The F2 value can be controlled mainly by the crystallinity of the polypropylene used, the amount of ion-containing polymer added, the stretching conditions (temperature, magnification) in the longitudinal direction, etc. In the present invention, the mmmm and II of the polypropylene used are within the above ranges. The addition amount of the ion-containing polymer is preferably in the above range, and the stretching temperature and the stretching ratio in the longitudinal direction are preferably 120 to 160 ° C. and 4.2 to 6 times as follows. The longitudinal F2 value at 25 ° C. is more preferably 37 MPa or more, and further preferably 40 MPa or more. The metalized polypropylene film of the present invention preferably satisfies the above range.

  The polypropylene film of the present invention is biaxially oriented. By biaxially orienting, the resulting film can be further improved in heat resistance, withstand voltage characteristics, and handling properties, and can be made into a thinner film, that is, a capacitor having a larger capacitance per unit volume. In addition, as a biaxial orientation method, either a simultaneous biaxial stretching method or a sequential biaxial stretching method may be used, but a sequential biaxial stretching method is preferable from the viewpoint of device expandability.

  Here, the orientation state of the film (non-orientation, uniaxial orientation, or biaxial orientation) is described in, for example, Kiyoichi Matsumoto et al., “Journal of the Fiber Society”, Vol. 26, No. 12, 1970, p. 537-549; Kiyoichi Matsumoto, “Making a film”, Kyoritsu Shuppan (1993), p. 67-86; Seizo Okamura et al., “Introduction to Polymer Chemistry (Second Edition)”, Kagaku Dojin (1981), p. As described in 92-93, etc., X-rays were incident on the film from three directions (in general, through incidence (in the longitudinal direction (longitudinal direction, MD) and lateral direction (width direction, TD) of the film)). Incident perpendicular to the surface to be formed), End incident (incident to the surface formed in the transverse direction / thickness direction of the film), Edge incidence (incident to the surface formed in the longitudinal direction / thickness direction of the film) Discriminated from the X-ray diffraction photograph. That is, the non-oriented sheet gives a Debye-Scherrer ring having substantially the same intensity in the X-ray diffraction photographs in any direction, and the longitudinally uniaxially oriented film shows the same in the X-ray diffraction photographs at the end incidence. A Debye-Scherrer ring having an intensity can be obtained, and a biaxially oriented film can obtain a diffraction image with nonuniform diffraction intensity reflecting the orientation in X-ray diffraction photographs in any direction. This determination method is performed as a method known to those skilled in the art, although corrections and the like are added as the apparatus and the method evolve.

  The electrode when the polypropylene film of the present invention is used for a capacitor element may be a metal foil or a paper or plastic film that is metallized on both sides, and is a metal that is installed by metallizing at least one side of the film of the present invention. Although it may be a layer and is not particularly limited, for example, from the viewpoints of lightness, thinness, small size, and large capacity, a metal layer provided by metallization is preferable. In this case, examples of the metal to be used include at least one metal selected from zinc, tin, silver, chromium, aluminum, copper, nickel and the like, but are not particularly limited.

  When a metal layer is disposed (metallized) on at least one surface of the polypropylene film of the present invention, it is preferable to perform corona discharge treatment on the film surface to further improve the adhesion to the metal layer. As the atmospheric gas during the corona discharge treatment, air, oxygen, nitrogen, carbon dioxide, or a mixed system of nitrogen / carbon dioxide is preferable. From the viewpoint of economy, the corona discharge treatment is particularly preferred in the air. Also, flame (flame) treatment, plasma treatment, etc. are preferable from the viewpoint of improving adhesion to the metal layer.

  Examples of the method for metallizing the film include a vacuum deposition method, a sputtering method, an ion beam method, and the like, and are not particularly limited. For example, the vacuum deposition method is more preferable from the viewpoints of productivity and economy.

  In general, examples of the vacuum deposition method include a crucible method and a wire method, and are not particularly limited. However, for example, an EB gun method with a small defect occurrence rate on a metal layer is more preferable.

  In the present invention, the film resistance value of the metallized film is preferably 1 to 40Ω / □. If the film resistance is less than 1 Ω / □, the metal layer is thick, so that so-called heat loss occurs during vapor deposition, and defects such as whitening and perforation may occur in the film. When the membrane resistance value exceeds 40Ω / □, the capacitance change may be large when a capacitor element is used. The film resistance value can be controlled by the composition of the metal layer and the thickness of the metal layer. The membrane resistance value is more preferably 1.2 to 30Ω / □.

  In the present invention, the specifications of the margin formed on the metallized film (the portion without the metal layer provided on the surface on which the metal layer is formed for the purpose of electrical insulation) are various specifications including a fuse mechanism in addition to the normal type. Things can be adopted according to the purpose. Also, the method for forming these margins is not particularly limited. For example, a tape method or an oil method may be used.

  In addition, the structure and form of the capacitor using the polypropylene film of the present invention as a dielectric material are not particularly limited. For example, it may be a dry type, an impregnation type with an insulating oil, a round type or a flat press type. In particular, it may be particularly preferable for a flat capacitor application that undergoes a flattening press process in which wrinkles tend to enter, because it exhibits excellent handling properties and workability.

  When the polypropylene film of the present invention is used for an oil-impregnated capacitor, any insulating oil can be used as long as it has electrical insulation properties. For example, polychlorinated biphenyls, paraffins, naphthenes can be used. Or, mineral oils made of aromatic hydrocarbons, polybutene, rapeseed oil, or silicone oil can be used. These oils can be used alone or in combination, and various additives can be added to these oils. You can also Preferred insulating oils include phenyl xylyl ethane and monoisopropyl biphenyl, which have low viscosity and excellent gas absorption.

  Next, an example of producing the polypropylene film of the present invention by biaxial stretching and an example of a method for producing a metallized film and a capacitor using the obtained film will be described below. It is not limited to.

  A resin in which an ion-containing polymer is mixed with polypropylene is prepared. At this time, the mixing method of these resins may be a dry blend method in which chips of each raw material are mixed in a specific composition as they are in order to keep foreign matters mixed during melt extrusion to a minimum, and dispersion of ion-containing polymers in polypropylene may be used. From the viewpoint of properties, a master batch method may be used in which both are heated and melt-kneaded at a specific concentration in advance in an extruder, extruded into a gut shape, passed through a chip cutter, and the resulting chips are used. Moreover, you may add additives, such as above-mentioned antioxidant, according to the objective in this case. The ion-containing polymer is preferably sufficiently dried from the viewpoint of stable discharge of the melt-extruded polymer and prevention of defects during extrusion.

  According to the above method, polypropylene and ion-containing polymer are added and mixed, supplied to a single screw extruder, melted at a temperature of 200 to 260 ° C., passed through a filtration filter, extruded from a slit die, and then cooled to a metal drum for cooling. It is wound and cooled and solidified into a sheet to obtain an unstretched sheet. The extrusion temperature is preferably lower even within the above temperature range from the viewpoint of preventing defects during extrusion, as long as there are no other problems such as filtration pressure and unstretched sheet thickness.

  In the process of cooling and solidifying the molten polymer by winding it around the metal drum, it is important to adjust the temperature of the metal drum and slow down the cooling rate of the molten polymer from the viewpoint of controlling the surface roughness after biaxial stretching. At this time, the number of the cooling metal drums may be one, or two or more may be continuously installed, and the cooling rate may be controlled by passing them through. For example, it is preferable that the cast drum temperature in the case of one cooling metal drum be 50 to 95 ° C. When the drum temperature is less than 50 ° C., since there are few β crystals generated in the unstretched sheet, the surface of the resulting biaxially oriented film is smoothed, the desired slip property cannot be obtained, and the handling property may be inferior. . When the drum temperature exceeds 95 ° C., the biaxial stretching property is deteriorated, film formation may become unstable, and the withstand voltage characteristic may be deteriorated. The drum temperature is preferably 60 to 90 ° C. In addition, the above drum temperature condition is merely an example, and the cooling rate of the molten polymer varies depending on the metal drum diameter, the number of drums, the drum temperature, the drum peripheral speed, etc., and preferable voltage resistance characteristics and surface roughness are obtained. It is known to those skilled in the art to design these as described.

  In addition, the polypropylene film of the present invention is characterized in that the adhesion of the molten polymer to the metal drum is good in the cooling and solidifying step, and even if the film is thinned, the adhesion unevenness hardly occurs. In order to improve the adhesion to the substrate, a known method such as an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, or the like is preferably used. Any of them may be used, but it is preferable to use an air knife method because the flatness is good and the surface roughness can be controlled by the temperature of the blown air.

  Next, the obtained unstretched sheet is biaxially stretched to be biaxially oriented. Examples of the biaxial stretching method include a sequential biaxial stretching method and a simultaneous biaxial stretching method, and any of them may be used. A case where the sequential biaxial stretching method is used will be described below. First, the unstretched sheet is preheated by passing it through a roll maintained at a temperature of 120 to 160 ° C., then the sheet is maintained at a temperature of 120 to 160 ° C. and passed between rolls with a difference in peripheral speed, and effective in the longitudinal direction. The film is stretched at a magnification of 4.2 to 6 and immediately cooled to room temperature. At this time, it may be preferable to perform the longitudinal stretching in at least two stages from the viewpoint of improving the rigidity in the longitudinal direction and suppressing surface defects. Moreover, in the cooling process after longitudinal stretching, it is preferable from the viewpoint of dimensional stability in the longitudinal direction to provide relaxation in the longitudinal direction to such an extent that the thickness unevenness of the film does not deteriorate.

  Then, this longitudinally stretched film is guided to a tenter type stretching machine, preheated at a temperature of 150 to 180 ° C., and stretched at an effective magnification of 7 to 12 times in the transverse direction at a temperature of 150 to 180 ° C. Further, from the viewpoint of improving dimensional stability, the film is heat-fixed at 150 to 180 ° C. while being relaxed by 1% or more in the lateral direction and cooled.

  If necessary, the metallized surface of the film is subjected to a corona discharge treatment in air, nitrogen, carbon dioxide gas or a mixed atmosphere thereof from the viewpoint of improving adhesion to the metal, and wound using a winder.

Next, the obtained film was loaded into a vacuum deposition apparatus in which the inside was kept in a high vacuum state with a degree of vacuum of 10 ⁻⁴ Torr or less, the film was run, and the metal according to the purpose exemplified above was heated and melted to evaporate. And a metal layer is formed so as to have a film resistance value of 1 to 40Ω / □ by agglomerating and depositing on the corona discharge treated surface of the film. At this time, oil is applied to the metallized surface of the film using a gravure coater or the like in order to form an insulating groove portion according to the purpose, and a so-called margin is appropriately formed so that the oil-applied portion is not evaporated. It doesn't matter. In addition, the metal resistance of the metal layer is not increased so much that the capacitance change when the capacitor element is made larger than necessary, and the end metallicon when the capacitor element is made lower than necessary to make the capacitor element. In order not to increase the contact resistance and deteriorate the current resistance characteristics of the capacitor, the film resistance value of the metal layer is inclined so that the film resistance value of only the metallicon contact part at the time of capacitor fabrication is lowered and the rest is increased. The so-called heavy edge method, which is metallized, is also preferably employed.

  Aging the obtained metallized film at a temperature of 40 to 60 ° C. is preferable because the film structure (preferably crystallinity) is stabilized and the adhesion between the metal layer and the film tends to be improved. In this case, the aging time is preferably 12 hours or more, more preferably 24 hours or more from the viewpoint of improving the adhesion of the metal layer.

  The obtained metallized film is slit to a desired dimension to form a two-reel pair of vapor deposition reels for making a capacitor element. After that, it is wound into an element shape, heat-pressed and formed into a flat shape, for example, the end is metal sprayed (metallicon process), the lead terminal is taken out, and impregnated with insulating oil as exemplified above if necessary Then, the capacitor is made through the exterior.

  Here, at least one metal (or alloy) selected from aluminum, copper, zinc, tin, solder, or the like may be used as the sprayed metal used in the metallicon process, and in particular, a metal having a melting temperature of 100 to 200 ° C. It is preferable to use (or an alloy) because uneven spraying tends to be reduced and the current resistance characteristics of the obtained capacitor tend to be improved. In addition, this process is referred to as so-called two-layer spraying, in which a metal having a good electrical adhesion with the metal layer on the film surface is sprayed on the first layer, and then a metal that easily adheres the lead wire is sprayed thereon. This method is also preferably adopted.

[Measurement method of characteristic values]
The terms and measurement methods used in the present invention are collectively described below.
(A) Determination of orientation by X-ray diffraction photograph The orientation state of the film is determined from an X-ray diffraction photograph in which X-rays are incident on the film from the following three directions.

Through incidence: incident perpendicular to the surface formed in the longitudinal direction (longitudinal direction, MD) and lateral direction (width direction, TD) of the film End incident: incident perpendicular to the surface formed in the lateral direction / thickness direction of the film Edge incidence: incidence perpendicular to the surface formed in the longitudinal direction / thickness direction of the film Note that the samples were aligned in the same direction, adjusted to a thickness of about 1 mm, cut out to a width of about 1 mm, and subjected to measurement. In addition, when it is difficult to distinguish between the vertical and horizontal directions of the film, it is simply assumed that one direction in the film plane is the vertical direction, and the direction perpendicular to the vertical direction is measured as the horizontal direction of the film.

  X-ray diffraction photographs were measured by the imaging plate method under the following conditions.

X-ray generator: Rigaku Denki Co., Ltd. 4036A2 type X-ray source: CuKα ray (using Ni filter)
Output: 40Kv, 20mA
Slit system: 1mmφ pinhole collimator Imaging plate: FUJIFILM BAS-SR
Shooting conditions: camera radius 40 mm, exposure time 5 minutes.

  Here, the non-orientation, uniaxial orientation, and biaxial orientation of the film are described in, for example, Kiyoichi Matsumoto et al., “Journal of the Textile Society”, Vol. 26, No. 12, 1970, p. 537-549; Kiyoichi Matsumoto, “Making a film”, Kyoritsu Shuppan (1993), p. 67-86; Seizo Okamura et al., “Introduction to Polymer Chemistry (Second Edition)”, Kagaku Dojin (1981), p. As described in 92-93, etc., it can be determined according to the following criteria.

Non-orientation: Debye-Scherrer ring having substantially uniform intensity is obtained in X-ray diffraction photographs in any direction. Longitudinal uniaxial orientation: Debye-Scherrer ring having substantially uniform intensity in X-ray diffraction photographs of End incidence. Obtained biaxial orientation: A diffraction image in which the diffraction intensity is not uniform, which reflects the orientation in X-ray diffraction photographs in any direction, is obtained.
(A) Dielectric breakdown strength (BDV)
Measured based on JIS C 2110 (1994). Using a 100 μm thick, 10 cm square aluminum foil electrode for the lower electrode and a brass 8 mmφ electrode for the upper electrode, sandwiching a film between them, using a DC high voltage stabilizing power source manufactured by Kasuga Electric Co., Ltd., 100 V / sec. A voltage was applied while boosting at a speed, and the case where current flowed 10 mA or more was assumed to be dielectric breakdown. Dielectric breakdown is obtained by dividing the voltage at that time by the film thickness in the vicinity of the measurement point (an electric micrometer manufactured by Anritsu Electric Co., Ltd., digital display K351C, plunger type detector K-402B, JIS B 7536 (1982)). The strength (V / μm) was taken as an average value measured at 30 points.
(C) Micrometer method film thickness (MMV)
The micrometer method film thickness (MMV, unit: μm) was measured according to 7.4.1.1 of JIS C 2330 (2001).
(D) Centerline average surface roughness (Ra), maximum surface roughness (Rmax)
Based on JIS B 0601 (2001), it measured using the stylus type surface roughness meter. In addition, it calculated | required from the following conditions using the high precision thin film level | step difference measuring device (model: ET-30HK) and a three-dimensional roughness analyzer (type: SPA-11) by Kosaka Laboratory.
-Stylus scanning direction: Film lateral direction-Measurement mode: Stylus type (STYLUS)
・ Processing mode: 8 (ROUGHNESS)
・ Measurement length: 1mm
-Stylus diameter: Conical 0.5μmR
・ Load: 16mg
・ Cutoff: 250μm
・ Number of measurement lines: 30 ・ Scanning speed: 100 μm / second ・ Pitch: 4 μm in the X direction, 10 μm in the Y direction
・ SLOPE COMP: ON
・ GAIN: × 1
Measurement area: 0.2988 mm ²
Standard area: 0.1 mm ²
In the measurement, a roughness curve was recorded using a recorder as appropriate. The conditions at that time are as follows.
-X / Y-axis direction recording magnification: 100 times-Z-axis direction magnification: 10,000 times (If the magnification of the roughness curve is too large on the recorder, it may be appropriately 5,000 times)
・ Recorder speed: 40μm / sec ・ Y recording pitch: 2mm
At this time, the centerline average surface roughness (Ra) is determined by extracting a portion of the measurement length L from the roughness curve, setting the centerline of this extracted portion as the X axis, the vertical direction as the Y axis, and the roughness curve as y = When expressed by f (x), it is a value obtained by the following formula (unit: μm).

   The maximum surface roughness (Rmax) is the distance between two straight lines when the measured length L is extracted from the roughness curve and the maximum and minimum values are sandwiched between two straight lines parallel to the average line. It is obtained (unit: μm).

The same measurement was performed five times for each sample while changing the measurement location, and the average value of the obtained values was calculated to be Ra (μm) and Rmax (μm) of the polypropylene film.
(E) Longitudinal heat shrinkage at 120 ° C. With the measurement direction as the longitudinal direction, the film is sampled to a test length of 260 mm and a width of 10 mm, and a mark is put at a position of 200 mm as the original dimension (L0). A load of 3 g is applied to the lower end of the sample, heat treated for 15 minutes in a hot air circulating oven at 120 ° C., then taken out to room temperature, and the length (L1) marked on the sample is measured. Under the present circumstances, the thermal contraction rate of the vertical direction in 120 degreeC is calculated | required by following Formula (unit:%). The same measurement was performed five times for each sample, and the average value of the obtained values was calculated and used as the thermal contraction rate in the vertical direction at 120 ° C. of the sample.

Longitudinal heat shrinkage (%) at 120 ° C. = 100 × (L0−L1) / L0
(F) Melt index (MI)
The measurement was performed under conditions M (230 ° C., 2.16 kgf) according to JIS Z 7210 (1999).
(Ki) Mesopentad fraction (mmmm)
Polypropylene is extracted with n-heptane at a temperature of 60 ° C. or lower for 2 hours to remove impurities and additives in the polypropylene, and then dried under reduced pressure at 130 ° C. for 2 hours or more as a sample. The sample was dissolved in a solvent, and the mesopentad fraction (mmmm) was determined under the following conditions using ¹³ C-NMR (unit:%).
Measurement conditions and apparatus: DRX-500 manufactured by Bruker
・ Measurement nucleus: ¹³ C nucleus (resonance frequency: 125.8 MHz)
・ Measured concentration: 10% by weight
Solvent: benzene: heavy orthodichlorobenzene = 1: 3 mixed solution (volume ratio)
・ Measurement temperature: 130 ℃
・ Spin rotation speed: 12Hz
NMR sample tube: 5 mm tube Pulse width: 45 ° (4.5 μs)
・ Pulse repetition time: 10 seconds ・ Data point: 64K
・ Number of conversions: 10,000 times ・ Measurement mode: complete decoupling
Analysis conditions LB (line broadening factor) was set to 1 to perform Fourier transform, and the mmmm peak was set to 21.86 ppm. Peak splitting is performed using WINIT software (manufactured by Bruker). At that time, peak splitting is performed as follows from the peak on the high magnetic field side, soft automatic fitting is performed, peak splitting is optimized, and mmmm and ss (mmmm spinning sideband peak) The sum of the peak fractions is defined as the mesopentad fraction (mmmm).
(1) mrrm
(2) (3) rrrm (divided as two peaks)
(4) rrrr
(5) mrmm + rmrr
(6) mmrr
(7) mmmr
(8) ss (mmmm spinning sideband peak)
(9) mmmm
(10) rmmr.
The same measurement was performed 5 times on the same sample, and the average value of mmmm obtained was defined as mmmm of the sample.
(G) Isotactic index (II)
Polypropylene is extracted with n-heptane at a temperature of 60 ° C. or lower for 2 hours to remove impurities and additives in the polypropylene. Thereafter, it is dried under reduced pressure at 130 ° C. for 2 hours. A sample of weight W (mg) is taken from this, placed in a Soxhlet extractor and extracted with boiling n-heptane for 12 hours. Next, this sample was taken out, thoroughly washed with acetone, dried under reduced pressure at 130 ° C. for 6 hours, then cooled to room temperature, measured for weight W ′ (mg), and determined by the following formula.

II (%) = (W '/ W) x 100 (%)
The same measurement was performed 5 times for the same sample, and the average value of the obtained II was taken as II of the sample.
(H) Ash content It was measured according to 6.3.5 of JIS C 2330 (1995). A sample having an initial weight Wo (g) was put in a platinum crucible, and first burned sufficiently with a gas burner, and then completely ashed by treatment in an electric furnace at 800 ° C. for 1 hour. The weight of the obtained ash W1 (g ) And measured by the following formula.

Ash content (ppm) = 1,000,000 × (W1 / Wo) / Wo
(K) Melting point A resin sample of 5 mg in weight is enclosed in an aluminum pan and loaded into a thermal analyzer RDC220 manufactured by Seiko Instruments Inc., heated from 30 ° C. to 280 ° C. at a rate of 20 ° C./min, and held for 5 minutes. To do. Next, the temperature is lowered from 280 ° C. to 30 ° C. at 20 ° C./minute, held for 5 minutes, and then heated from 30 ° C. to 280 ° C. at 20 ° C./minute. From the calorimetric curve obtained in the second temperature raising process, the peak of the endothermic peak accompanying melting of the crystal was defined as the melting point (Tm) (unit: ° C.) using the built-in program of the company's thermal analysis system SSC5200.
(F) Longitudinal F2 value at 25 ° C. The F2 value in the vertical direction at 25 ° C. is 65% RH using a film strong elongation measuring device (AMF / RTA-100) manufactured by Orientec Co., Ltd. Measured at A sample was cut into a size of 15 cm in the vertical direction and 1 cm in the horizontal direction, stretched at an original length of 50 mm, and a tensile speed of 300 mm / min, and the stress applied to the sample with respect to an elongation of 2% was measured as an F2 value (unit: MPa). . The same measurement was performed five times for each sample, and the average value of the obtained values was calculated to obtain the F2 value in the vertical direction at 25 ° C. of the sample.
(Sa) Membrane resistance Based on the four-probe method shown in JIS K 7194 (1994), a low resistivity meter (Loresta-GP, MCP-T600 manufactured by Mitsubishi Chemical Corporation) and a four-probe probe (ASP probe) The surface resistivity (unit: Ω / □) was measured for the surface on the metal layer side. The surface resistivity referred to here is represented by the following formula based on the definition of 5.13 of JIS K 6911 (1995).

  Surface resistivity (Ω / □) = R × RCF.

Here, R is a resistance (unit: Ω), and RCF is a resistivity correction coefficient for the shape, size, and measurement position of the sample. Since the surface resistivity changes reflecting the thickness of the metal layer, it is used as an index value of the thickness of the metal layer placed on the film surface in the present invention. The same measurement was performed five times for each sample by changing the measurement position, and the average value of the obtained surface resistivity was calculated and used as the film resistance value of the sample.
(I) Surface wetting tension (mN / m)
It measured according to 7.4.13 of JIS C 2330 (2001).
(S) Effective stretch ratio An unstretched film extruded from a slit-shaped base, wound around a metal drum (cast drum) and cooled and solidified into a sheet, each side of a square having a length of 1 cm square has a longitudinal direction and a width of the film. After engraving so as to be parallel to the direction, the film was stretched and wound, and the length (cm) of the resulting film was measured, and this was taken as the effective stretch ratio in the machine direction and the transverse direction.
(C) Insulation defect test Based on 6.3.10 of JIS C 2330 (1995), 100 test pieces were produced, and a speed of 100 V / sec was used using a DC high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd. A voltage was applied while boosting at, and the number of test pieces destroyed at a voltage of 150 V or less was determined as the number of insulation defects (films) for a film having a thickness of 6 μm or less on which the reference voltage was not described. In addition, what can be practically used as a polypropylene film for a capacitor | condenser is a thing of (circle) and (triangle | delta).

○: The number of insulation defects is 2 or less △: The number of insulation defects is 3 to 5 or less ×: The number of insulation defects is 6 or more (So) Handling property, workability The film is loaded into a vacuum evaporation machine manufactured by ULVAC, and corona When aluminum was vapor-deposited on the treated surface so as to have a film resistance of 15Ω / □, a T-shaped margin and a normal margin were formed. Next, the T-type margin product and the normal margin product 1-to-2 reel were wound around to produce 100 capacitor elements with a capacity of 100 μF. The winding conditions at the time of element winding are as follows.
-Winding machine: KAW-4L manufactured by Minato Seisakusho
-Winding speed: 2,000 rpm
・ Tension: 600gf
The obtained capacitor element was measured for wrinkles and deviations, and the wrinkle generation rate (%) and deviation generation rate (%) were measured from the ratio to 100 elements. What can be practically used as a capacitor element has a wrinkle occurrence rate and a deviation occurrence rate of 5% or less. Here, the appearance of the wound element was visually observed, and an element in which wrinkles having a length of 10 mm or more were confirmed in two or more places was assumed to be wrinkled, and an element in which an end face deviation of 2 mm or more was confirmed was displaced. Measured as having occurred. Moreover, the element by which the wrinkles and deviation | shift were confirmed simultaneously by the said reference | standard is measured to both.
(T) Element dielectric breakdown strength Ten capacitor elements with no wrinkles or deviations selected from the above (So) are selected and heated for 6 hours in a flattened state at a temperature of 110 ° C. and a pressure of 0.4 MPa. After the treatment, metallicon and lead terminals were attached. The device was packaged with an epoxy resin to produce a capacitor with a capacity of 100 μF. A voltage is applied to the capacitor element maintained at 105 ° C. in a hot-air circulating oven while increasing the voltage at a rate of 100 V / sec using a DC high-voltage stabilized power source manufactured by Kasuga Electric Co., Ltd., and a current of 10 mA or more flows. In this case, the element was assumed to have a dielectric breakdown. The voltage at this time was obtained, and the average value of the voltage measured for 10 elements was converted to the micrometer method film thickness to obtain the element dielectric breakdown strength (V / μm).

  The present invention will be described based on examples. In order to obtain a film having a desired thickness, the rotational speed of the extruder and the peripheral speed of the cooling drum were adjusted to predetermined values unless otherwise specified. Further, unless otherwise specified, it was confirmed that the obtained film was biaxially oriented by the method of measurement method (a). Furthermore, unless otherwise specified, metal vapor deposition was performed on the surface in contact with the drum when the film was produced by melt extrusion of the resin and winding it around a metal drum to produce an unstretched sheet.

(Example 1)
A known homopolypropylene having a melt index (MI) of 4 g / 10 min, a mesopentad fraction (mmmm) of 96.8%, an isotactic index (II) of 98.5%, and an ash content of 14 ppm (the above-mentioned BHT, "Irganox" 1010 each containing 3,000 ppm and calcium stearate 50 ppm) 90% by weight, and Mitsui-DuPont Polychemical Co., Ltd. "High Milan" 1706 (dried) as an ion-containing polymer at a ratio of 10% by weight Add and mix, feed to a single screw extruder, melt at 240 ° C, pass through a 35 µm cut filtration filter, extrude from a slit-shaped die, and wrap around a metal drum with a surface temperature of 80 ° C at an air temperature of 30 ° C using an air knife To form a sheet.

  The unstretched sheet is preheated through a group of rolls maintained at 135 ° C., passed between rolls maintained at 140 ° C. and provided with a difference in peripheral speed, stretched 5 times in the longitudinal direction, and immediately cooled to room temperature. Subsequently, this longitudinally stretched film was introduced into a tenter, preheated at 165 ° C., stretched 10 times in the transverse direction at 160 ° C., and then heat-set at 160 ° C. while giving 8% relaxation in the width direction. One side (the surface in contact with the cooling drum when producing an unstretched sheet) was corona discharge treated in air so that the wetting tension was 40 mN / m, wound up with a winder after cooling, and film thickness (MMV method) ) Was 3.0 μm to obtain a biaxially oriented polypropylene film.

  The obtained biaxially oriented polypropylene film was loaded into a vacuum deposition machine, and aluminum was deposited on the corona-treated surface so as to have a film resistance of 15Ω / □. At this time, vapor deposition was performed by an oil margin method so that T-type margins having a width of 0.7 mm in the vertical direction, a width of 0.4 mm in the horizontal direction, and an interval of 16 mm were formed on the film after slitting. Similarly, a normal margin product was produced. The obtained T-shaped margin product and normal margin product were each slit into a width of 100 mm, and these were wound as a pair to produce a capacitor element.

  Tables 1 and 2 collectively show the raw material composition, characteristic values, and evaluation results of the metallized film and capacitor element of the obtained biaxially oriented film. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 2)
In Example 1, a biaxially oriented polypropylene film having an MMV of 3.0 μm, produced under the same conditions except that the surface temperature of the metal drum was raised to 90 ° C., a metallized film produced from the film, and a capacitor element Was taken as Example 2.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 3)
In Example 1, as a polypropylene, a known homopolypropylene having MI of 4.8 g / 10 min, mmmm of 98.2%, II of 99.0%, and ash content of 17 ppm (2,500 ppm of the above-described BHT, “ A biaxially oriented polypropylene film having an MMV of 3.2 μm and a metallized film and a capacitor produced under the same conditions except that Irganox “1330 is contained at 2,000 ppm and calcium stearate is contained at 50 ppm) The device was referred to as Example 3.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

Example 4
Known homopolypropylene having a melt index (MI) of 3.5 g / 10 min, mmmm of 96.0%, II of 97.0%, and ash content of 12 ppm (“Irganox” 1010 described above is 4,500 ppm, calcium stearate Is added to and mixed with 40% by weight of “Himiran” 1650 (dried) made by Mitsui DuPont Polychemical Co., Ltd. as an ion-containing polymer, and supplied to a twin screw extruder at 220 ° C. It was melt-extruded into a gut shape, passed through a 20 ° C. water bath, cooled, cut to 3 mm length with a chip cutter, and then dried under reduced pressure at 50 ° C. for 8 hours. 25% by weight of the obtained chip and 75% by weight of the above-mentioned homopolypropylene were mixed, supplied to a single screw extruder, melted at 240 ° C., passed through a 35 μm cut filter, extruded from a slit die, and surface temperature of 80 ° C. The metal drum was wound at an air temperature of 40 ° C. using an air knife and formed into a sheet shape.

  This unstretched sheet was preheated through a roll group maintained at 132 ° C., passed between rolls maintained at 138 ° C. and provided with a peripheral speed difference, stretched 5 times in the longitudinal direction, and immediately cooled to room temperature. Subsequently, this longitudinally stretched film was introduced into a tenter, preheated at 165 ° C., stretched 10 times in the transverse direction at 160 ° C., and then heat-set at 160 ° C. while giving 9% relaxation in the width direction. One side (the surface in contact with the cooling drum when producing an unstretched sheet) was subjected to corona discharge treatment in the air so that the wetting tension was 40 mN / m, wound up with a winder after cooling, and the MMV was 3.3 μm. A biaxially oriented polypropylene film was obtained.

  The obtained biaxially oriented polypropylene film was subjected to aluminum vapor deposition and element winding in the same manner as in Example 1 to produce a metallized film and a capacitor element.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 5)
In Example 4, a biaxially oriented polypropylene having an MMV of 3.3 μm was produced under the same conditions except that the amount of the chip containing the ion-containing polymer supplied to the single screw extruder was 37.5% by weight. A film, a metallized film produced from the film, and a capacitor element were taken as Example 5.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 6)
In Example 4, a biaxially oriented polypropylene having an MMV of 3.3 μm was produced under the same conditions except that the amount of the chip containing the ion-containing polymer supplied to the single screw extruder was 12.5% by weight. A film, a metallized film produced from the film, and a capacitor element were taken as Example 6.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 7)
A raw material having the same composition as that of Example 1 was supplied to a single screw extruder, melted at 240 ° C., passed through a 35 μm cut filter, extruded from a slit die, and air was applied to a metal drum having a surface temperature of 80 ° C. using an air knife. It was wound at a temperature of 25 ° C. and formed into a sheet shape.

  The obtained unstretched sheet was introduced into a pantograph simultaneous biaxial stretching machine and preheated at 170 ° C., and simultaneously stretched at 165 ° C. 8 times in the machine direction and 7 times in the transverse direction, and then 5% in the machine direction. The film was heat-set at 160 ° C. while giving a relaxation of 8% in the direction, and then subjected to corona discharge treatment in air so that the wet tension was 40 mN / m on one side of the film. A biaxially oriented polypropylene film of 4 μm was obtained.

  The obtained biaxially oriented polypropylene film was subjected to aluminum vapor deposition and element winding in the same manner as in Example 1 to produce a metallized film and a capacitor element.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 8)
A biaxially oriented polypropylene film having an MMV of 7.5 μm produced under the same conditions as in Example 1 except that the thickness of the unstretched sheet was changed, and a metallized film and a capacitor element produced from the film were produced in Example 8. It was.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

Example 9
A biaxially oriented polypropylene film having an MMV of 2.5 μm produced under the same conditions as in Example 1 except that the thickness of the unstretched sheet was changed, and a metallized film and a capacitor element produced from the film were produced in Example 9. It was.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Example 10)
In Example 4, as a polypropylene, a known homopolypropylene having an MI of 3 g / 10 min, an mmmm of 94.5%, an II of 96%, and an ash content of 15 ppm (3,000 ppm of the above-mentioned BHT, “Irganox” 1010 Example 5 Example of Biaxially Oriented Polypropylene Film with MMV of 4.5 μm, Metallized Film, and Capacitor Element Prepared under the Same Conditions except that 5,000 ppm and 50 ppm of calcium stearate were used) It was set to 10.

  The results are shown in Tables 1 and 2. The obtained film had extremely high dielectric breakdown strength and was excellent in withstand voltage characteristics. In addition, since the surface has few coarse protrusions and uniform unevenness is formed on the front and back of the film, the handling property at the time of vapor deposition is excellent. Further, the excellent withstand voltage characteristics were maintained even after the capacitor element was fabricated.

(Comparative Example 1)
In Example 1, a biaxially oriented polypropylene film having an MMV of 3.0 μm and a metallized film produced from the film were produced under the same conditions except that a homopolypropylene alone was used without adding an ion-containing polymer. The capacitor element was Comparative Example 1.

  The results are shown in Tables 1 and 2. The obtained film did not have few insulation defects, had low dielectric breakdown strength, and was inferior in withstand voltage characteristics. Moreover, the obtained film had spotted unevenness due to uneven contact with the metal drum on the surface. Moreover, the surface roughness of the film front and back was unbalanced, and the roughness of one surface was small. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior.

(Comparative Example 2)
In Comparative Example 1, the surface temperature of the metal drum was raised to 90 ° C. and produced under the same conditions except that the metal drum was stretched 5 times and 11 times in the longitudinal direction and subsequently in the transverse direction. An oriented polypropylene film, a metallized film produced from the film, and a capacitor element were used as Comparative Example 2.

  The results are shown in Tables 1 and 2. The obtained film had extremely low dielectric breakdown strength due to a large amount of insulation defects, and was extremely inferior in withstand voltage characteristics. In addition, winding misalignment occurred sporadically during the vapor deposition process, and the handling property was poor. Furthermore, the withstand voltage characteristics of the capacitor element were also greatly inferior.

(Comparative Example 3)
In Example 3, a biaxially oriented polypropylene film having an MMV of 3.2 μm and a metallized film produced from the film were produced under the same conditions except that a homopolypropylene alone was used without adding an ion-containing polymer. The capacitor element was designated as Comparative Example 3.

  The results are shown in Tables 1 and 2. The obtained film did not have few insulation defects, had low dielectric breakdown strength, and was inferior in withstand voltage characteristics. Moreover, the obtained film had spotted unevenness due to uneven contact with the metal drum on the surface. Moreover, the surface roughness of the film front and back was unbalanced, and the roughness of one surface was small. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior.

(Comparative Example 4)
In Example 4, a biaxially oriented polypropylene having an MMV of 3.3 μm was produced under the same conditions except that a homopolypropylene simple substance was directly supplied to a single screw extruder without adding an ion-containing polymer to form a film. A film, a metallized film produced from the film, and a capacitor element were used as Comparative Example 4.

  The results are shown in Tables 1 and 2. The obtained film did not have few insulation defects, had low dielectric breakdown strength, and was inferior in withstand voltage characteristics. Moreover, the obtained film had spotted unevenness due to uneven contact with the metal drum on the surface. Moreover, the surface roughness of the film front and back was unbalanced, and the roughness of one surface was small. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior.

(Comparative Example 5)
In Comparative Example 1, a known homopolypropylene having a MI of 4.3 g / 10 min, a mmmm of 99.5%, an II of 99.6%, and an ash content of 13 ppm as polypropylene (2,000 ppm of the above-described BHT, “ A biaxially oriented polypropylene film produced under the same conditions except that Irganox “1010 was contained at 2,000 ppm and calcium stearate was contained at 35 ppm) was used as Comparative Example 5.

  The results are shown in Tables 1 and 2. The film was broken during the film formation, and a satisfactory film could not be obtained.

(Comparative Example 6)
In Comparative Example 1, a biaxially oriented polypropylene film having an MMV of 7.5 μm produced under the same conditions except that the thickness of the unstretched sheet was changed, a metallized film produced from the film, and a capacitor element were compared with Comparative Example 6. It was.

  The results are shown in Tables 1 and 2. Although the obtained film had practically necessary handling properties and withstand voltage characteristics, the dielectric breakdown strength was low and the withstand voltage characteristics were inferior. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior. In addition, since the film is thick, the capacitor element becomes large, which is clearly unsuitable for downsizing.

(Comparative Example 7)
In Comparative Example 1, a biaxially oriented polypropylene film having an MMV of 2.5 μm produced under the same conditions except that the thickness of the unstretched sheet was changed, and a metallized film and a capacitor element produced from the film were compared with Comparative Example 7. It was.

  The results are shown in Tables 1 and 2. The resulting film had a large and non-uniform surface roughness and voids, or a large amount of insulation defects, low dielectric breakdown strength, and poor withstand voltage characteristics. Moreover, the obtained film had spotted unevenness due to uneven contact with the metal drum on the surface. Moreover, the surface roughness of the film front and back was unbalanced, and the roughness of one surface was small. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior.

(Comparative Example 8)
In Example 4, MMV produced under the same conditions was 3.3 μm except that “Escollet” 5320 manufactured by Tonex Co., Ltd. was used as a hydrogenated petroleum resin containing no polar group instead of an ion-containing polymer. An axially oriented polypropylene film, a metallized film produced from the film, and a capacitor element were used as Comparative Example 8.

  The results are shown in Tables 1 and 2. The obtained film had few insulation defects but low dielectric breakdown strength and inferior withstand voltage characteristics. Moreover, the obtained film had spotted unevenness due to uneven contact with the metal drum on the surface. Moreover, the surface roughness of the film front and back was unbalanced, and the roughness of one surface was small. Further, the withstand voltage characteristics of the capacitor element after winding the element were inferior.

  From Tables 1 and 2, the polypropylene film of the present invention, which contained an ion-containing polymer, was able to increase the dielectric breakdown strength as compared with the case where it was not added, and was excellent in the withstand voltage characteristics. In addition, because the melting point of the polymer is sufficiently lower than the stretching temperature and it melts during the film forming process, the insulation breakdown strength is also due to extremely few insulation defects and the formation of uniform irregularities with few coarse protrusions. This is thought to be part of the increase.

  Moreover, even if the film was thinned, the unstretched sheet could be brought into close contact with the drum in the casting process. From this, it was possible to form a uniform unevenness with few coarse protrusions balanced on the front and back of the film, and it was superior in handling property during vapor deposition as compared with the conventional product.

  In addition, even if the film was thin, there was no significant decrease in withstand voltage characteristics as seen in conventional products, and these excellent characteristics could be controlled by the amount of ion-containing polymer added, film forming conditions, etc. .

  In addition, the capacitor element using the polypropylene film of the present invention was excellent in withstand voltage characteristics.

  When the polypropylene film of the present invention is a metallized film, it exhibits excellent adhesion with the metal layer, and when stretched, it exhibits excellent film forming properties with few voids. There is a possibility that it can be used as a metallizing film with few defects and excellent gas barrier properties.

Claims (7)

A biaxially oriented polypropylene film for a capacitor comprising polypropylene and an ion-containing polymer. The biaxially oriented polypropylene film for a capacitor according to claim 1, wherein the dielectric breakdown strength (BDV) at 25 ° C. is 650 V / μm or more. The biaxially oriented polypropylene film for a capacitor according to claim 1 or 2, wherein the thickness of the film by a micrometer method is 5 µm or less. 4. The capacitor according to claim 1, wherein the ratio (Rmax / Ra) of the center line average surface roughness (Ra) to the maximum surface roughness (Rmax) is 8 to 15 on both surfaces of the film. Biaxially oriented polypropylene film. The biaxially oriented polypropylene film for a capacitor according to any one of claims 1 to 4, wherein the film has a longitudinal heat shrinkage of 0.5 to 4.5% at 120 ° C. A metallized polypropylene film obtained by providing a metal layer on at least one surface of the biaxially oriented polypropylene film according to claim 1. The capacitor | condenser which uses the biaxially oriented polypropylene film in any one of Claims 1-5, or the metallized polypropylene film of Claim 6 for at least one part.