JP2009235321A - High insulation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high insulation film excellent in electrical properties, heat resistance, easy handling such as windability and processability. <P>SOLUTION: The high insulation film is a biaxially stretched film mainly composed of a syndiotactically structured polystyrene-based polymer containing inactive micro-particles having an average particle size of not less than 0.2 μm and not larger than 3.0 μm and a relative standard deviation of the particle size of not larger than 0.5 and an antioxidant. Specific orientation in structure gives the biaxially stretched film a refractive index in the thickness direction of not less than 1.6050 and not more than 1.6550. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a highly insulating film. More specifically, the present invention relates to a highly insulating film having good electrical characteristics and heat resistance and having a particularly high breakdown voltage.

  A stretched film made of a syndiotactic polystyrene resin composition is a film excellent in heat resistance, chemical resistance, hot water resistance, dielectric properties, electrical insulation, and the like, and is expected to be applied to various applications. In particular, it is used as an insulator for capacitors because of its excellent dielectric properties and high electrical insulation and heat resistance. For example, Patent Documents 1 to 4 propose syndiotactic polystyrene biaxially stretched films for capacitors.

Japanese Patent Laid-Open No. 3-124750 Japanese Patent Laid-Open No. 6-80793 JP 7-156263 A JP-A-8-28396

  However, although the syndiotactic polystyrene film disclosed in Patent Documents 1 to 4 can be used as an insulator of a capacitor, for example, it has higher performance than a capacitor mounted on a recent hybrid car. For such a capacitor, a film excellent in electrical characteristics such as dielectric breakdown voltage and heat resistance is required.

  In addition, for the purpose of improving the capacitance of the capacitor or reducing the size of the capacitor, further thinning is required as a film to be an insulator. End up. Therefore, even if the film thickness is reduced, there is a demand for a film that is superior in handling properties so that productivity in the film manufacturing process is not lowered and it can be adapted to the capacitor manufacturing speed required in recent years.

  The present invention has been made to solve the above-described problems, and its purpose is to provide a highly insulating film excellent in handling properties such as electrical characteristics, heat resistance, winding property and workability. is there.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have a specific orientation structure in a syndiotactic polystyrene-based biaxially stretched film containing a specific inert fine particle and an antioxidant. The inventors have found that a highly insulating film having a high dielectric breakdown voltage and excellent heat resistance and handleability can be obtained, and the present invention has been achieved.

  That is, the present invention is a biaxially stretched film comprising a styrene polymer having a syndiotactic structure as a main component, having an average particle size of 0.2 μm or more and 3.0 μm or less, and a relative standard deviation of the particle size of 0. 5 or less inert fine particles A are contained in an amount of 0.01% by mass or more and 1.5% by mass or less, an antioxidant is contained in an amount of 0.1% by mass or more and 8% by mass or less, and the refractive index in the thickness direction is 1.6050. It is the highly insulating film which is 1.6550 or less.

  Further, in the present invention, the average particle diameter is 0.01 μm or more and 0.5 μm or less, the average particle diameter is 0.2 μm or more smaller than the average particle diameter of the inert fine particles A, and the relative standard deviation of the particle diameter is 0. .5 or less inert fine particle B is contained in an amount of 0.05% by mass or more and 2.0% by mass or less, and the inert fine particle A is a spherical particle having a particle size ratio of 1.0 or more and 1.3 or less, The inert fine particles A are spherical polymer resin particles, the inert fine particles A are spherical silica particles, and the inert fine particles B are spherical silica particles having a particle size ratio of 1.0 to 1.3. In addition, the thermal decomposition temperature of the antioxidant is 250 ° C. or higher, and the film thickness is 0.4 μm or more and less than 6.5 μm. A film can be obtained.

  According to the present invention, a highly insulating film having excellent electrical characteristics, heat resistance, and handleability can be obtained. In particular, a highly insulating film having a high breakdown voltage can be obtained. Therefore, the highly insulating film obtained by the present invention can be suitably used as an insulator of a capacitor.

  The highly insulating film of the present invention is a biaxially stretched film mainly composed of a styrene polymer described later. Moreover, the highly insulating film of the present invention contains fine particles described later and an antioxidant. Hereafter, each structural component which comprises the highly insulating film of this invention is demonstrated.

<Styrene polymer>
The styrenic polymer in the present invention is a styrenic polymer having a syndiotactic structure, that is, the side chain phenyl groups and substituted phenyl groups are alternately opposite to the main chain formed from carbon-carbon bonds. It has a three-dimensional structure located in the direction. In general, tacticity is quantified by nuclear magnetic resonance ( ¹³ C-NMR) with isotope carbon, and the abundance ratio of a plurality of consecutive constitutional units, for example, dyad in the case of two, triad in the case of three, In the case of five, it can be indicated by a pentad or the like. In the present invention, the syndiotactic styrenic polymer is 75% or more, preferably 85% or more, or 30% or more, preferably 50%, of racemic pentad (rrrr) in racemic diad (r). Polystyrene, poly (alkyl styrene), poly (halogenated styrene), poly (alkoxy styrene), poly (vinyl benzoate) having the above syndiotacticity, or a part of these benzene rings are hydrogenated A polymer, a mixture thereof, or a copolymer containing these structural units is designated. Here, as poly (alkylstyrene), poly (methylstyrene), poly (ethylstyrene), poly (propylstyrene), poly (butylstyrene), poly (phenylstyrene), poly (vinylnaphthalene), poly ( Vinyl styrene), poly (acenaphthylene), and the like. Examples of poly (halogenated styrene) include poly (chlorostyrene), poly (bromostyrene), and poly (fluorostyrene). Examples of poly (alkoxystyrene) include poly (methoxystyrene) and poly (ethoxystyrene). Among these, particularly preferable styrenic polymers include polystyrene, poly (p-methylstyrene), poly (m-methylstyrene), poly (p-tertiarybutylstyrene), poly (p-chlorostyrene), poly (M-chlorostyrene), poly (p-fluorostyrene), and a copolymer of styrene and p-methylstyrene.

  Furthermore, in the case of using the styrene polymer in the present invention as a copolymer containing a copolymer component, as its comonomer, in addition to the styrene polymer monomer as described above, ethylene, propylene, butene, Examples thereof include olefin monomers such as hexene and octene, diene monomers such as butadiene and isoprene, cyclic diene monomers, and polar vinyl monomers such as methyl methacrylate, maleic anhydride, and acrylonitrile.

The weight average molecular weight of the styrenic polymer is preferably 1.0 × 10 ⁴ or more and 3.0 × 10 ⁶ or less, more preferably 5.0 × 10 ⁴ or more and 1.5 × 10 ⁶ or less, particularly preferably at 1.1 × 10 ⁵ or more 8.0 × 10 ⁵ or less. By setting the weight average molecular weight to 1.0 × 10 ⁴ or more, it is possible to obtain a film having excellent strength and elongation properties and further improved heat resistance. Moreover, when the weight average molecular weight is 3.0 × 10 ⁶ or less, the stretching tension is in a suitable range, and breakage or the like hardly occurs during film formation.

  A method for producing such a styrene polymer having a syndiotactic structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-187708. That is, in an inert hydrocarbon solvent or in the absence of a solvent, a styrene-based monomer (into the above-mentioned styrene-based polymer), using a titanium compound and a condensation product of water and an organoaluminum compound, particularly a trialkylaluminum, as a catalyst. It can be produced by polymerizing the corresponding monomer). Poly (halogenated alkylstyrene) is disclosed in JP-A-1-146912, and hydrogenated polymer is disclosed in JP-A-1-178505.

In the styrene polymer having a syndiotactic structure in the present invention, an appropriate amount of an additive such as a known antistatic agent can be blended if necessary. These blending amounts are preferably 10 parts by mass or less with respect to 100 parts by mass of the styrene polymer. If it exceeds 10 parts by mass, it tends to cause breakage during stretching, resulting in poor production stability.
Such a styrene polymer having a syndiotactic structure is remarkably superior in heat resistance as compared with a conventional styrene polymer having an atactic structure.

<Antioxidant>
In the present invention, when the biaxially stretched film containing the styrenic polymer as a main constituent contains a specific amount of an antioxidant, the electrical characteristics can be improved.

  Such an antioxidant may be either a primary antioxidant that captures the generated radicals to prevent oxidation, or a secondary antioxidant that decomposes the generated peroxides to prevent oxidation. Antioxidants include phenolic antioxidants and amine-based antioxidants, and secondary antioxidants include phosphorus-based antioxidants and sulfur-based antioxidants.

  Specific examples of the phenolic antioxidant include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, and 2-t-butyl-4-methoxy. Phenol, 3-t-butyl-4-methoxyphenol, 2,6-di-t-butyl-4- [4,6-bis (octylthio) -1,3,5-triazin-2-ylamino] phenol, n -Monophenol antioxidants such as octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2 , 2′-methylenebis (4-ethyl-6-tert-butylphenol), 4,4′-thiobis (3-methyl-6-tert-butylphenol), 4,4′-butylidenebis (3-methyl) 6-t-butylphenol), N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine, N, N′-hexane-1,6-diylbis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionamide], 3,9-bis [1,1-dimethyl-2- [β- (3-t-butyl-4-hydroxy-5] -Methylphenyl) propionyloxy] ethyl] 2,4,8,10-tetraoxaspiro [5.5] undecane and other bisphenol antioxidants, 1,1,3-tris (2-methyl-4-hydroxy- 5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, pentaerythritol tetrakis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], bis [3,3′-bis- (4′-hydroxy-3′-t-butylphenyl) butyric acid] glycol ester, 1,3,5-tris (3 ′, 5′-di-t-butyl-4′-hydroxybenzyl) -sec-triazine-2,4,6- (1H, 3H, 5H) trione, d-α- There may be mentioned polymer type phenolic antioxidants such as tocophenol.

Specific examples of amine-based antioxidants include alkyl-substituted diphenylamines.

  Specific examples of phosphorus antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenylditridecyl) phos. Phyto, octadecyl phosphite, tris (nonylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10- (3,5-di- t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, Tris (2,4-di-t-butylphenyl Phosphite, cyclic neopentanetetrayl bis (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetrayl bis (2,6-di-t-butyl-4-methylphenyl) phosphite 2,2′-methylenebis (4,6-di-t-butylphenyl) octyl phosphite and the like.

  Specific examples of the sulfur-based antioxidant include dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, pentaerythritol. Tetrakis (3-lauryl thiopropionate), 2-mercaptobenzimidazole, etc. can be mentioned.

  In view of the fact that the antioxidant in the present invention is particularly excellent in corrosion resistance and the effect of improving the dielectric breakdown voltage can be further enhanced, a primary antioxidant is preferable, and a phenol-based antioxidant is particularly preferable.

  The antioxidant in the present invention preferably has a thermal decomposition temperature of 250 ° C. or higher. If the thermal decomposition temperature is too low, the antioxidant itself is thermally decomposed at the time of melt extrusion, which tends to cause problems such as contamination of the process and yellowing of the polymer. From such a viewpoint, the thermal decomposition temperature of the antioxidant is more preferably 280 ° C. or higher, further preferably 300 ° C. or higher, and particularly preferably 320 ° C. or higher. The antioxidant in the present invention is preferably less susceptible to thermal decomposition and preferably has a higher thermal decomposition temperature, but in reality, the upper limit is about 500 ° C. or less.

  Moreover, it is preferable that melting | fusing point of the antioxidant in this invention is 90 degreeC or more. If the melting point is too low, the antioxidant melts faster than the polymer during melt extrusion, and the polymer tends to slip at the screw supply portion of the extruder. As a result, the supply of the polymer becomes unstable, and problems such as the uneven thickness of the film occur. From such a viewpoint, the lower limit of the melting point of the antioxidant is more preferably 120 ° C. or higher, further preferably 150 ° C. or higher, and particularly preferably 200 ° C. or higher. On the other hand, when the melting point of the antioxidant is too high, the antioxidant becomes difficult to melt during melt extrusion, and the dispersion in the polymer tends to be poor. Thereby, problems such as the effect of adding the antioxidant appear only locally. From such a viewpoint, the upper limit of the melting point of the antioxidant is preferably 300 ° C. or lower, more preferably 250 ° C. or lower, still more preferably 220 ° C. or lower, and particularly preferably 170 ° C. or lower.

  A commercial item can also be used as it is as the above antioxidant. Examples of commercially available products include pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (manufactured by Ciba Specialty Chemicals: trade name IRGANOX 1010), N, N′- Bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine (manufactured by Ciba Specialty Chemicals: trade name IRGANOX1024), N, N′-hexane-1,6-diylbis [ 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionamide] (manufactured by Ciba Specialty Chemicals: trade name IRGANOX 1098) is preferred.

  The highly insulating film of the present invention contains the above antioxidant in an amount of 0.1% by mass or more and 8% by mass or less based on the mass of the highly insulating film. By setting the content of the antioxidant within the above numerical range, the dielectric breakdown voltage is excellent. When the content of the antioxidant is too small, the effect of adding the antioxidant is not sufficient, the dielectric breakdown voltage tends to decrease, and the electrical characteristics are inferior. From such a viewpoint, the lower limit of the content of the antioxidant is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. On the other hand, when there is too much content, it exists in the tendency for antioxidant to aggregate in a film, there exists a tendency for the fault resulting from antioxidant to increase, and a dielectric breakdown voltage becomes low. From such a viewpoint, the upper limit of the content of the antioxidant is preferably 7% by mass or less, more preferably 5% by mass or less, and particularly preferably 3% by mass or less.

  The above antioxidants may be used individually by 1 type, and may use 2 or more types together. When two or more types are used in combination, an embodiment using two or more types of primary antioxidants may be used, an embodiment using two or more types of secondary antioxidants may be used, or one or more types of primary antioxidants and 1 Two or more kinds of secondary antioxidants may be used in combination. For example, it can be expected to prevent both primary oxidation and secondary oxidation by using two types of antioxidants, a primary antioxidant and a secondary antioxidant, in combination. In the present invention, an embodiment in which a primary antioxidant is used alone or an embodiment in which two or more kinds of primary antioxidants are used is preferable from the viewpoint that the effect of improving the dielectric breakdown voltage can be further increased. An embodiment using a single antioxidant or an embodiment using two or more phenolic antioxidants is preferred.

<Inert fine particles A>
The highly insulating film of the present invention contains inert fine particles A having an average particle diameter and a relative standard deviation of the particle diameter in a specific numerical range.

  The average particle diameter of the inert fine particles A in the present invention is 0.2 μm or more and 3.0 μm or less. By making the average particle diameter of the inert fine particles A within the above numerical range, the film can have good air evacuation performance while maintaining a high dielectric breakdown voltage, and has high insulation properties with excellent winding properties. A film can be obtained. When the average particle diameter of the inert fine particles A is too small, sufficient air detachability tends not to be obtained, and the winding property is inferior. On the other hand, when it is too large, the size of voids in the film tends to increase, and the dielectric breakdown voltage becomes low. From such a viewpoint, the average particle diameter of the inert fine particles A is preferably 0.25 μm to 2.0 μm, more preferably 0.4 μm to 1.6 μm, and particularly preferably 1.0 μm to 1.2 μm. It is.

  Further, the inert fine particles A in the present invention have a relative standard deviation of the particle size of 0.5 or less. By setting the relative standard deviation of the particle diameter within the above numerical range, the height of the projection on the film surface becomes uniform, and a highly insulating film excellent in winding property can be obtained. Further, coarse particles and coarse protrusions are reduced, and a highly insulating film excellent in dielectric breakdown voltage can be obtained. From such a viewpoint, the relative standard deviation of the particle diameter of the inert fine particles A is preferably 0.4 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.

  Furthermore, the inert fine particles A in the present invention are preferably spherical particles having a particle size ratio of 1.0 or more and 1.3 or less. The particle size ratio is more preferably 1.0 or more and 1.2 or less, and particularly preferably 1.0 or more and 1.1 or less. When the particle size ratio is in the above numerical range, the effect of improving the winding property and the effect of improving the dielectric breakdown voltage can be further increased.

  The highly insulating film of the present invention contains the inert fine particles A as described above in an amount of 0.01% by mass to 1.5% by mass in 100% by mass of the highly insulating film. By containing the inert fine particles A in an amount in the above numerical range, the film can be handled easily while maintaining a high dielectric breakdown voltage. When the content of the inert fine particles A is too small, the air release property tends to be inferior, and the winding property is inferior. On the other hand, when the amount is too large, the film surface tends to become too rough, and thus the abrasion resistance of the film surface tends to deteriorate, resulting in inferior dielectric breakdown voltage. In particular, in a capacitor application, the space factor tends to increase. From such a viewpoint, the content of the inert fine particles A is preferably 0.05% by mass or more and 1.0% by mass or less, more preferably 0.1% by mass or more and 0.5% by mass or less, and particularly preferably 0% by mass. It is 2 mass% or more and 0.4 mass% or less.

The inert fine particles A as described above may be organic fine particles or inorganic fine particles. Examples of organic fine particles include polymer resin particles such as polystyrene resin particles, silicone resin particles, acrylic resin particles, styrene-acrylic resin particles, divinylbenzene-acrylic resin particles, polyester resin particles, polyimide resin particles, and melamine resin particles. Can be mentioned. Among these, silicone resin particles and polystyrene resin particles are particularly preferable from the viewpoint of excellent slipperiness and abrasion resistance. Such polymer resin particles are preferably spherical as described above, that is, spherical polymer resin particles are preferred. Among these, spherical silicone resin particles and spherical polystyrene resin particles are particularly preferable from the viewpoint of superior slipperiness and abrasion resistance. Examples of inorganic fine particles include (1) silicon dioxide (including hydrates, silica sand, quartz and the like); (2) alumina in various crystal forms; and (3) a silica containing 30% by mass or more of SiO ₂ component. Acid salts (eg amorphous or crystalline clay minerals, aluminosilicates (including calcined and hydrated), warm asbestos, zircon, fly ash, etc.); (4) oxidation of Mg, Zn, Zr and Ti (5) Sulfates of Ca and Ba; (6) Phosphate of Li, Ba, and Ca (including monohydrogen and dihydrogen salts); (7) Benzoic acid of Li, Na, and K (8) terephthalate of Ca, Ba, Zn, and Mn; (9) titanate of Mg, Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co, and Ni; ) Ba and Pb chromate; (11) carbon (e.g. Carbon black, graphite, etc.); (12) glass (for example, glass powder, glass beads, etc.); (13) carbonates of Ca and Mg; (14) fluorite; (15) spinel oxide. Of these, calcium carbonate particles and silica particles are preferable, and silica particles are particularly preferable from the viewpoint of excellent slipperiness and abrasion resistance. Such inorganic fine particles are preferably spherical as described above, and spherical silica particles are particularly preferred from the viewpoint of superior slipperiness and abrasion resistance.

<Inert fine particles B>
In addition to the inert fine particles A, the highly insulating film of the present invention preferably includes an inert fine particle B having an average particle size and a relative standard deviation of the particle size in a specific numerical range.

  The average particle diameter of the inert fine particles B in the present invention is 0.01 μm or more and 0.5 μm or less. By setting the average particle diameter of the inert fine particles B within the above numerical range, it is possible to obtain an appropriate slip property and to enhance the winding property. When the average particle diameter of the inert fine particles B is too small, the slipping property tends to be low, and the effect of improving the winding property is low. On the other hand, if it is too large, the height of the low protrusions on the film surface tends to be too high, thereby making the slipping property too high, and the effect of improving the winding property is low, such as the end face being liable to be displaced during winding. Become. Furthermore, the wear resistance tends to deteriorate, and the effect of improving the dielectric breakdown voltage is reduced. From such a viewpoint, the average particle diameter of the inert fine particles B is preferably 0.05 μm to 0.5 μm, more preferably 0.08 μm to 0.4 μm, and particularly preferably 0.1 μm to 0.3 μm. It is.

  The average particle diameter of the inert fine particles B is preferably 0.2 μm or less smaller than the average particle diameter of the inert fine particles A. By setting the difference between the average particle diameter of the inert fine particles A and the average particle diameter of the inert fine particles B as described above, high protrusions due to the inert fine particles A are scattered on the film surface. The air-removing property between them becomes good. At the same time, low protrusions due to the inert fine particles B are present, and the slipperiness between the films is improved. With these, when winding a film into a roll, the balance between air release and sliding is good, and it is possible to obtain a film roll with a good winding shape even if it is wound at a high speed. The effect can be increased. From such a viewpoint, the average particle diameter of the inert fine particles B is preferably 0.4 μm or more smaller than the average particle diameter of the inert fine particles A, more preferably 0.6 μm or smaller, and more preferably 0.8 μm or larger. Smaller embodiments are particularly preferred.

  In addition, the inert fine particle B in the present invention has a relative standard deviation of the particle size of 0.5 or less from the same viewpoint as the aforementioned inert fine particle A. The relative standard deviation of the particle diameter of the inert fine particles B is preferably 0.4 or less, more preferably 0.3 or less, and particularly preferably 0.2 or less.

  Further, the inert fine particles B in the present invention are preferably spherical particles having a particle size ratio of 1.0 or more and 1.3 or less, more preferably 1.0, from the same viewpoint as the aforementioned inert fine particles A. It is 1.2 or more and particularly preferably 1.0 or more and 1.1 or less.

  The high-insulating film of the present invention preferably includes 0.05 to 2.0% by mass of the inert fine particles B as described above in 100% by mass of the highly-insulating film. By containing the inert fine particles B in an amount in the above numerical range, the effect of improving the handleability of the film can be enhanced while maintaining a high dielectric breakdown voltage. When the content of the inert fine particles B is too small, the slipping property tends to be low, and the effect of improving the winding property is low. On the other hand, when it is too much, the frequency of voids in the film tends to increase, and the effect of improving the dielectric breakdown voltage becomes low. In addition, the slipping property tends to be too high, and the effect of improving the winding property such as end face misalignment during winding is reduced. From such a viewpoint, the content of the inert fine particles B is more preferably 0.1% by mass or more and 1.0% by mass or less, further preferably 0.1% by mass or more and 0.5% by mass or less, particularly preferably. It is 0.1 mass% or more and 0.3 mass% or less.

  As the inert fine particles B as described above, organic fine particles and inorganic fine particles similar to the aforementioned inert fine particles A can be used. Among these, inorganic fine particles are preferable, and calcium carbonate particles and silica particles are preferable, and silica particles are particularly preferable from the viewpoint of excellent slipperiness and abrasion resistance. Such inorganic fine particles are preferably spherical as described above, and spherical silica particles are particularly preferred from the viewpoint of superior slipperiness and abrasion resistance.

  The inert fine particles A and the inert fine particles B used in the present invention are not limited in the method of inclusion as long as they are contained in the final film. For example, a method of adding or precipitating in an arbitrary process during polymerization of a styrene monomer, and a method of adding in an arbitrary process of melt extrusion can be mentioned. Moreover, in order to disperse these fine particles effectively, a dispersant, a surfactant or the like can be used.

  In the present invention, as a particularly preferable embodiment of the inert fine particle A and the inert fine particle B, an embodiment using spherical silica particles can be exemplified, but even in such a case, the average particle in each particle can be exemplified. In the particle size distribution curve, the two types of particles can be clearly distinguished because the diameters are in specific numerical ranges that do not overlap each other and the relative standard deviation of the particle size of each particle is small. It shows a particle size peak, that is, the inactive fine particles A and the inactive fine particles B can be clearly distinguished. In addition, when the two particle size peaks overlap each other at the base portion to form a valley portion, the particle size peak is decomposed into two particle size peaks with a point indicating a minimum value in the valley portion as a boundary.

<Other additives>
The highly insulating film of the present invention basically comprises a styrenic polymer having the above-mentioned syndiotactic structure, an antioxidant, inert fine particles A and inert fine particles B. In order to improve physical properties, surface properties and the like, other resin components can be contained.

  Examples of other resin components that can be contained include styrene polymers having an atactic structure, styrene polymers having an isotactic structure, polyphenylene ether, styrene-maleic anhydride copolymer, and the like. It is easily compatible with other styrenic polymers, is effective in controlling crystallization when creating a preform for stretching, the stretchability is improved, the stretching conditions are easily controlled, and the mechanical properties are excellent. Preferably, it is preferable because a film can be obtained. Among these, when a styrenic polymer having an atactic structure and / or an isotactic structure is contained, a styrene polymer having a syndiotactic structure is preferably used. The content ratio of these compatible resin components is preferably 40 parts by mass or less, more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, with respect to 100 parts by mass of the syndiotactic styrene polymer. What should I do? When the content ratio of the compatible resin component exceeds 40 parts by mass, the effect of improving the heat resistance, which is an advantage of the styrenic polymer having a syndiotactic structure, is lowered.

Among the other resin components that can be contained, examples of resins that are incompatible with the styrenic polymer having a syndiotactic structure include polyolefins such as polyethylene, polypropylene, polybutene, and polypentene, polyethylene terephthalate, and polybutylene terephthalate. , Polyesters such as polyethylene naphthalate, polyamides such as nylon 6 and nylon 6,6, polythioethers such as polyphenylene sulfide, polycarbonate, polyacrylate, polysulfone, polyetheretherketone, polyethersulfone, polyimide, Teflon (registered trademark), etc. Resin other than the compatible resin, such as a vinyl halide polymer, an acrylic polymer such as polymethyl methacrylate, polyvinyl alcohol, and the like, and further includes the compatible resin. Crosslinked resins. Since these resins are incompatible with the syndiotactic styrene polymer of the present invention, they can be dispersed in an island shape in the syndiotactic styrene polymer when contained in a small amount. It is effective for giving a moderate gloss after stretching or improving the slipperiness of the surface. The content ratio of the incompatible resin component is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less with respect to 100 parts by mass of the syndiotactic styrene polymer. . Moreover, when the temperature used as a product is high, it is preferable to contain a relatively heat-resistant incompatible resin component.
Furthermore, additives such as an antistatic agent, a colorant, and a weathering agent can be added within a range that does not impair the object of the present invention.

<Film characteristics>
The highly insulating film of the present invention has a refractive index in the thickness direction of 1.6050 or more and 1.6550 or less. The refractive index in the thickness direction is preferably 1.6100 or more and 1.6400 or less, more preferably 1.6130 or more and 1.6380 or less, and particularly preferably 1.6150 or more and 1.6360 or less. By setting the refractive index in the thickness direction within the above numerical range, the dielectric breakdown voltage can be increased. Further, the frequency of film breakage in the film manufacturing process is reduced, and productivity can be improved. When the refractive index in the thickness direction is too high, the frequency of film breakage in the film production process tends to increase, and the productivity of the film decreases. On the other hand, if it is too low, the dielectric breakdown voltage tends to be low, and the electrical characteristics are poor. In addition, the frequency of film breakage in the capacitor manufacturing process increases, and the productivity of the capacitor decreases. Furthermore, the thickness unevenness of the film tends to deteriorate, and it becomes difficult to obtain a capacitor with stable quality.

  In order to set the refractive index in the thickness direction within the above range, it is achieved by employing a manufacturing method as described later. That is, the preferred refractive index in the thickness direction in the present invention is such that the stretching ratio of the film is in a specific numerical range to be described later, and in the stretching step, the film is stretched in the direction perpendicular to the uniaxial direction that is carried out after the uniaxial stretching. In the stretching, the stretching temperature is divided into a plurality of stages, and a specific temperature difference is set between the first stage temperature and the final stage temperature.

  The highly insulating film of the present invention preferably has a film thickness of 0.4 μm or more and less than 6.5 μm. More preferably, it is 0.4 μm or more and less than 6.0 μm, and particularly preferably 0.5 μm or more and less than 3.5 μm. By setting the film thickness within the above numerical range, a capacitor having a high capacitance can be obtained.

  It is generally well known that a film used as an insulator of a capacitor is preferable to have a thinner film thickness because the capacitance of the capacitor is higher. However, when the film thickness is actually reduced (thinned), wrinkles are easily formed on the film, the film is easy to break, the handling property is lowered, and the added particles are easily dropped. Since problems such as lowering the breakdown voltage and lowering the absolute value of the dielectric breakdown voltage occur due to the thin film thickness, it is essential to balance them. The present invention provides a highly insulating film having a novel structure having an antioxidant and specific particles by a manufacturing method described later so that the above-mentioned problem does not occur even when the film thickness is reduced. .

  The highly insulating film of the present invention preferably has a center line average surface roughness Ra of at least one surface of 7 nm or more and 89 nm or less. By making the center line average surface roughness Ra within the above numerical range, the effect of improving the winding property can be enhanced. Moreover, blocking resistance improves and the external appearance of a roll can be made favorable. When the center line average surface roughness Ra is too low, the slipping property tends to be too low, and the effect of improving the winding property is lowered. On the other hand, if it is too high, the slipping property tends to be too high, and the effect of improving the winding property, such as end face misalignment at the time of winding, becomes low. From such a viewpoint, the lower limit of the center line average surface roughness Ra is preferably 11 nm or more, more preferably 21 nm or more, and particularly preferably 31 nm or more. The upper limit of the center line average surface roughness Ra is more preferably 79 nm or less, still more preferably 69 nm or less, and particularly preferably 59 nm or less.

  In the highly insulating film of the present invention, it is preferable that the 10-point average roughness Rz of at least one surface is 200 nm or more and 3000 nm or less. By setting the 10-point average roughness Rz within the above numerical range, the effect of improving the winding property can be increased. When the 10-point average roughness Rz is too low, the air release property tends to be low when the film is wound as a roll, and the effect of improving the winding property such that the film is liable to skid is reduced. In particular, when the film thickness is thin, the film loses its elasticity, so that the air release property tends to be further lowered, and the effect of improving the winding property is further reduced. On the other hand, when the 10-point average roughness Rz is too high, the number of coarse protrusions tends to increase, and the effect of improving the dielectric breakdown voltage is reduced. From such a viewpoint, the lower limit of the 10-point average roughness Rz is more preferably 600 nm or more, further preferably 1000 nm or more, and particularly preferably 1250 nm or more. Further, the upper limit of the 10-point average roughness Rz is more preferably 2600 nm or less, further preferably 2250 nm or less, and particularly preferably 1950 nm or less.

<Film production method>
The high-insulating film of the present invention can be obtained by a method that has been conventionally known or accumulated in the industry, except for some special manufacturing methods. Hereinafter, the production method for obtaining the highly insulating film of the present invention will be described in detail.

  First, a resin composition in which a predetermined amount of an antioxidant is blended with a syndiotactic styrene polymer is heated and melted to prepare an unstretched sheet. Specifically, the resin composition is heated and melted at a temperature not lower than the melting point (Tm, unit: ° C.) and not higher than (Tm + 70 ° C.), extruded into a sheet, cooled and solidified to obtain an unstretched sheet. The intrinsic viscosity of the obtained unstretched sheet is preferably in the range of 0.35 to 0.9 dl / g. Next, this unstretched sheet is stretched biaxially. Stretching may be performed simultaneously in the machine direction (machine axis direction) and the transverse direction (direction perpendicular to the machine axis direction), or may be sequentially stretched in an arbitrary order. For example, in the case of sequential stretching, first, in a uniaxial direction (glass transition temperature of resin composition (Tg, unit: ° C.)-10 ° C.) to (Tg + 70 ° C.) or less, 2.7 times or more and 4.8 times or less. , Preferably 2.9 times or more and 4.4 times or less, more preferably 3.1 times or more and 4.0 times or less, and then Tg or more (Tg + 80 ° C.) or less in a direction perpendicular to the uniaxial direction. The film is stretched at a ratio of 2.8 times to 4.9 times, preferably 3.0 times to 4.5 times, more preferably 3.2 times to 4.1 times at temperature.

  In the stretching in the direction perpendicular to the uniaxial direction, the crystallization is progressed in the previous stretching, so that the stretching becomes difficult and the film is easily broken during film formation. In particular, when a thin film having a film thickness of about 3 μm is formed, breakage easily occurs particularly in a region where the draw ratio is 3.2 times or more.

  As a result of examining this measure, it has been found that it is effective to set the stretching speed within a specific numerical range in stretching in the direction perpendicular to the uniaxial direction. That is, if the stretching speed is too high, the higher-order structure change of the molecule due to stretching cannot follow the speed of the shape change of the film due to stretching, and the higher-order structure is likely to be distorted. It tends to occur. On the other hand, if the film is too slow, crystallization of the film precedes in the course of stretching, and variations in stretching stress may occur, and stretching spots and thickness spots are likely to occur, thereby easily causing breakage. From such a viewpoint, the lower limit of the stretching speed is preferably 500% / min or more, more preferably 1000% / min or more, still more preferably 2000% / min or more, and particularly preferably 4000% / min or more. The upper limit of the stretching speed is preferably 30000% / min or less, more preferably 15000% / min or less, further preferably 9000% / min or less, and particularly preferably 6000% / min or less.

  Further, as another effective means, in the stretching in the direction perpendicular to the uniaxial direction, the stretching temperature is not made constant, but is divided into a plurality of stages, and the temperature at the first stage temperature and the final stage temperature. It turned out to be effective to make a difference. The lower limit of the temperature difference is preferably 4 ° C. or higher, more preferably 7 ° C. or higher, more preferably 12 ° C. or higher, and more preferably 15 ° C. or higher. preferable. The upper limit of the temperature difference is preferably 49 ° C. or less, more preferably 39 ° C. or less, further preferably 29 ° C. or less, and particularly preferably 20 ° C. or less. If the temperature difference is too large, film breakage tends to occur. Moreover, it exists in the tendency for the uneven thickness of the film after extending | stretching to worsen. Thus, by setting the temperature difference between the first stage and the final stage within the above numerical range, it is possible to achieve a high draw ratio, which has been difficult in the past in the production of a film having a thin film thickness. A good film can be obtained.

  In the process of performing stretching in the direction perpendicular to the uniaxial direction, in order to set a temperature difference between the first stage and the final stage, the zone inlet (first stage) and outlet (final stage) in one stretching zone The temperature difference may be given by or two or more continuous drawing zones having different temperatures may be provided, and the temperature difference may be given by the first drawing zone (first stage) and the last drawing zone (final stage). Good. Here, the zone indicates one area divided by a shutter or the like in a tenter or the like. In any case, it is preferable to further divide between the first stage and the final stage, and to increase the temperature in a gradient from the first stage toward the final stage. For example, when two or more continuous stretching zones having different temperatures are used, it is preferable to further provide one or more stretching zones between the first stretching zone and the last stretching zone, and one or more stretching zones are provided. More preferably. Setting the total number of stretching zones to 13 or more is disadvantageous in terms of equipment costs. For example, when the film is stretched in the width direction, a value obtained by dividing the film width immediately after leaving the final stage by the film width immediately before entering the first stage may be a target draw ratio. It is preferable to increase the film width in an inclined manner, and it is particularly preferable to increase the film width linearly. In the case where the machine direction and the transverse direction are drawn simultaneously, the drawing temperature is similarly divided into a plurality of stages, and a temperature difference is provided between the first stage temperature and the final stage temperature.

  In the present invention, these means can be preferably exemplified as means for achieving the preferred refractive index in the thickness direction in the present invention. Furthermore, according to these means, even if the film thickness is reduced, breakage hardly occurs. Therefore, these means can be preferably exemplified as means for achieving a preferable film thickness in the present invention. In the present invention, it is preferable to employ at least one of the above-described stretching speed mode and stretching temperature mode, but it is more preferable to employ both modes, and the stretching process is stable. It becomes easy to achieve the preferable refractive index and preferable film thickness in the present invention.

  Next, heat setting is performed at a temperature of (Tg + 70 ° C.) to Tm. The heat setting temperature is 200 ° C. or higher and 260 ° C. or lower, preferably 220 ° C. or higher and 250 ° C. or lower, and more preferably 230 ° C. or higher and 240 ° C. or lower. When the heat setting temperature is too high, film breakage is likely to occur particularly when a film having a thin film thickness is produced, and the thickness unevenness is deteriorated. If the relaxation treatment is performed at a temperature lower by 20 ° C. to 90 ° C. than the heat setting temperature as necessary after the heat setting, the dimensional stability is improved.

  Next, the present invention will be described in more detail with reference to examples and comparative examples. Various characteristic values in the examples were measured and evaluated by the following methods.

(1) Average particle size and particle size ratio of particles (1-1) Average particle size and particle size ratio of powder The powder is dispersed on the sample stage so that the individual particles do not overlap as much as possible, and gold sputtering is performed. A gold thin film deposited layer is formed on the surface with a thickness of 200 to 300 mm using an apparatus, and observed at 10,000 to 30,000 times using a scanning electron microscope, and at least 1000 pieces are manufactured with Luzex 500 manufactured by Japan Regulator Co., Ltd. The area equivalent particle diameter (Di), major axis (Dli) and minor axis (Dsi) of the particles were determined.

(1-2) Average particle size and particle size ratio of particles in film A sample film piece is fixed to a sample stage for a scanning electron microscope, and a sputtering device (JIS-1100 type ion sputtering device) manufactured by JEOL Ltd. is used. The film surface was subjected to an ion etching treatment for 10 minutes under the conditions of 0.25 kV and 1.25 mA under a vacuum of 0.13 Pa. Furthermore, gold sputtering was performed with the same apparatus, and observation was performed at 10,000 to 30,000 times using a scanning electron microscope, and the area equivalent particle size (at least 1000 particles) was measured with Luzex 500 manufactured by Japan Regulator Co., Ltd. Di), major axis (Dli) and minor axis (Dsi) were determined.

For the average particle size and particle size ratio of the powder, the values obtained from the above item (1-1), and for the average particle size and particle size ratio of the particles in the film, The number n of particles was used, and the number average value of the area equivalent particle diameter (Di) was defined as the average particle diameter (D).

Moreover, the particle size ratio was calculated as Dl / Ds from the average value of the major axis (Dl) and the average value of the minor axis (Ds) obtained from the following formula.

(2) Relative standard deviation of particle size of particles The relative standard deviation of powder was determined in the above item (1-1), and the relative standard deviation of particles in the film was determined in the above item (1-2). It calculated | required by the following formula from the area equivalent particle diameter (Di) and average particle diameter (D) of particle | grains.

(3) Surface roughness of film (3-1) Centerline average surface roughness (Ra)
Measurement length (Lx) 1 mm, sampling pitch 2 μm, cut-off using a non-contact type three-dimensional roughness meter (Kosaka Laboratories, ET-30HK) with a semiconductor laser with a wavelength of 780 nm and an optical probe with a beam diameter of 1.6 μm The protrusion profile on the film surface is measured under the conditions of 0.25 mm, thickness direction enlargement magnification of 10,000 times, lateral direction enlargement magnification of 200 times, and the number of scanning lines of 100 (thus, the measurement length Ly in the Y direction is 0.2 mm). . When the roughness curved surface was represented by Z = f (x, y), the value obtained by the following formula was defined as the center line average surface roughness (Ra, unit: nm) of the film.

(3-2) 10-point average roughness (Rz)
In the projection profile on the film surface obtained by the above (3-1), take 5 points from the higher peak (Hp) and 5 points from the lower valley (Hv), and calculate the 10-point average roughness by the following formula: (Rz, unit: nm) was determined.

(4) Thermal contraction rate The thermal contraction rate (unit:%) of the film in 30 minutes in the atmosphere of 150 degreeC in the tension | tensile_strength state was calculated | required.

(5) Refractive index The refractive index (nZ) in the thickness direction was measured at 23 ° C. and 65% RH using an Abbe refractometer using sodium D line (589 nm) as a light source.

(6) Dielectric breakdown voltage (BDV)
It was measured according to the method shown in JIS C 2151. Using a DC withstand voltage tester in an atmosphere of 23 ° C. and 50% relative humidity, the upper electrode is a brass cylinder with a diameter of 25 mm, the lower electrode is an aluminum cylinder with a diameter of 75 mm, and the pressure is increased at a pressure increase rate of 100 V / second. The voltage (unit: V) when the film was broken and short-circuited was read. The obtained voltage was divided by the film thickness (unit: μm) to obtain a dielectric breakdown voltage (unit: V / μm).
The measurement was performed 41 times, and the median value of 21 was taken as the measured value of the dielectric breakdown voltage, except for the larger 10 and the smaller 10.
Measurements at 100 ° C. and 120 ° C. were performed by setting electrodes and samples in a hot air oven, connecting to a power source with a heat-resistant cord, and starting pressurization 1 minute after the oven was put in.

(7) Stretchability Judgment was made as follows according to the number of breaks that occurred while a biaxially stretched film was formed into 1 million meters.
Stretchability ◎: Less than 1 break per 100,000 m of film formation Stretchability ○: 1 to less than 2 breaks per 100,000 m of film formation Stretchability Δ: Break per 100,000 m film formation 2 times to less than 4 times Stretchability ×: 100,000 m per film formation, breakage 4 times to less than 8 times Stretchability XX: 8 times or more per 100,000 m film formation

(8) Winding property In the film manufacturing process, the film is wound up into a 9000 m roll with a width of 500 mm at a speed of 140 m / min, and the roll shape obtained and the end face shift at the end face of the roll are rated as follows. did.
[Rolling appearance]
A: There are no pimples on the surface of the roll, and the winding shape is good.
B: There are 1 to 4 pimples (protruding bulges) on the surface of the roll, and the winding shape is almost good.
C: There are 4 or more and less than 10 pimples (protruding bulges) on the surface of the roll, and the wound form is somewhat poor, but it can be used as a product.
D: There are 10 or more pimples (protruding protrusions) on the surface of the roll, the winding shape is poor, and it cannot be used as a product.
[Edge misalignment]
A: The end face deviation at the end face of the roll is less than 0.5 mm, which is good.
○: The end face deviation at the end face of the roll is 0.5 mm or more and less than 1 mm, which is almost good.
(Triangle | delta): The end surface shift | offset | difference in a roll end surface is 1 mm or more and less than 2 mm, and although it is a little inferior, it can be used as a product.
X: The end face deviation at the end face of the roll is 2 mm or more, which is inferior and cannot be used as a product.
XX: The end face shift increases during roll winding, and a 9000 m roll cannot be created.

(9) Pyrolysis temperature Measured at a temperature increase rate of 10 ° C./min in an air atmosphere using a differential thermothermal gravimetric simultaneous measurement apparatus (manufactured by Seiko Denshi Kogyo Co., Ltd .: trade name TG / DTA220). / The temperature at which the weight starts to change from the weight change curve was determined by the tangential method and was defined as the thermal decomposition temperature (unit: ° C).

(10) Glass transition temperature and melting point About 10 mg of sample was sealed in an aluminum pan for measurement, and attached to a differential calorimeter (TA Instruments, trade name: DSC2920 Modulated), at a rate of 25 ° C. to 20 ° C./min. The glass transition temperature (unit: ° C) and the melting point (unit: ° C) were measured by raising the temperature to 300 ° C.

[Example 1]
As an antioxidant, pentaerythritol tetrakis [3] was added to 99.0 parts by mass of polystyrene, which was observed to have a weight average molecular weight of 3.0 × 10 ⁵ and an almost complete syndiotactic structure by ¹³ C-NMR measurement. -(3,5-di-t-butyl-4-hydroxyphenyl) propionate] (manufactured by Ciba Specialty Chemicals: trade name IRGANOX 1010) (melting point 120 ° C., thermal decomposition temperature 335 ° C.) 0.5 part by mass (obtained) And 0.5% by mass based on the mass of the highly insulating film to be obtained), and as inert fine particles A, spherical silica particles having an average particle size of 1.1 μm, a relative standard deviation of 0.15, and a particle size ratio of 1.08 0.3 parts by mass (made by Nippon Shokubai Co., Ltd .: trade name Sea Hoster KE) (0.3% by mass based on the mass of the resulting highly insulating film), As inert fine particles B, 0.2 part by mass of spherical silica particles having an average particle size of 0.3 μm, a relative standard deviation of 0.16, and a particle size ratio of 1.08 (manufactured by Nippon Shokubai Co., Ltd .: trade name Sea Hoster KE) And 0.2 mass% based on the mass of the resulting highly insulating film).
The obtained resin mixture was dried at 130 ° C. for 7 hours, then fed to an extruder, melted at 290 ° C., extruded from a die slit, cooled and solidified on a casting drum cooled to 20 ° C., and an unstretched sheet was Created.

  This unstretched sheet was stretched 3.2 times in the longitudinal direction (machine axis direction) at 114 ° C., subsequently led to a tenter, and then stretched 3.3 times in the transverse direction (direction perpendicular to the machine axis direction). At that time, the stretching speed in the transverse direction was set to 5000% / min. The stretching temperature in the transverse direction was 102 ° C. for the first stage and 119 ° C. for the final stage. Thereafter, the film was heat-fixed at 235 ° C. for 9 seconds, and further subjected to a 4% relaxation treatment in the lateral direction while cooling to 180 ° C. to obtain a highly insulating film having a thickness of 3.0 μm and wound into a roll. The characteristics of the obtained highly insulating film are shown in Table 1.

[Examples 2 to 4, Comparative Examples 1 and 2]
A highly insulating film having a thickness of 3.0 μm was obtained in the same manner as in Example 1 except that the content of the antioxidant was as shown in Table 1, and wound into a roll. The characteristics of the obtained highly insulating film are shown in Table 1. In addition, the amount of polystyrene was adjusted so that the whole would be 100 parts by mass.

[Example 5]
As an antioxidant, N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine (manufactured by Ciba Specialty Chemicals: trade name IRGANOX1024) (melting point 210 ° C. Except for using a thermal decomposition temperature of 275 ° C., a highly insulating film having a thickness of 3.0 μm was obtained in the same manner as in Example 2 and wound into a roll. The characteristics of the obtained highly insulating film are shown in Table 1.

According to Examples 1 to 5 and Comparative Examples 1 and 2, knowledge of the type of antioxidant and its content can be obtained.
The highly insulating films obtained in Examples 1 to 4 having an appropriate antioxidant content have good stretchability and winding property, have high dielectric breakdown voltage, and are suitable as insulators for capacitors. It was.

In addition, the highly insulating film obtained in Example 5 using an antioxidant different from the above Examples 1 to 4 also has good stretchability and winding property, high dielectric breakdown voltage, and capacitor insulator. It was suitable as.
On the other hand, the highly insulating film obtained in Comparative Example 1 containing no antioxidant had good stretchability and winding property, but had a low dielectric breakdown voltage and low performance as a capacitor insulator. It was unsatisfactory as an insulator for a hybrid vehicle capacitor.

  In addition, as can be seen from Comparative Example 2, when the content of the antioxidant is too large, defects such as formation of voids due to aggregation of the antioxidant tend to occur, or the dielectric breakdown voltage tends to decrease. It was observed. As a result, the highly insulating film obtained in Comparative Example 2 could not be used as a capacitor insulator.

[Example 6]
Spherical silica particles having an average particle size of 0.27 μm, a relative standard deviation of 0.16, and a particle size ratio of 1.08 as 98.6 parts by mass of polystyrene, as inert fine particles A (made by Nippon Shokubai Co., Ltd., trade name: Sea Hoster) KE) was 0.4 parts by mass (0.4% by mass based on the mass of the resulting highly insulating film), and the thickness was the same as in Example 2 except that the inert fine particles B were not added. A highly insulating film of 3.0 μm was obtained and wound into a roll. Table 2 shows the characteristics of the obtained highly insulating film.

[Examples 7 to 9]
High insulation having a thickness of 3.0 μm as in Example 6 except that the average particle size, relative standard deviation, particle size ratio, and content of the spherical silica particles as the inert particles A are as shown in Table 2. A conductive film was obtained and wound into a roll. Table 2 shows the characteristics of the obtained highly insulating film. In addition, the amount of polystyrene was adjusted so that the whole would be 100 parts by mass.

[Example 10]
Spherical silica particles having an average particle size of 0.5 μm, a relative standard deviation of 0.15, and a particle size ratio of 1.08, as 98.4 parts by mass of polystyrene, and inert fine particles A (made by Nippon Shokubai Co., Ltd .: trade name Sea Hoster) KE) 0.1 parts by mass (based on the mass of the resulting highly insulating film 0.1% by mass), and as inert fine particles B, an average particle size of 0.1 μm, a relative standard deviation of 0.17, 0.5 parts by mass of spherical silica particles having a particle size ratio of 1.07 (manufactured by Nippon Shokubai Co., Ltd .: trade name Seahoster KE) (0.5% by mass based on the mass of the resulting highly insulating film) A highly insulating film having a thickness of 3.0 μm was obtained in the same manner as in Example 2 except that was incorporated into a roll. Table 2 shows the characteristics of the obtained highly insulating film.

[Examples 11 and 12]
Average particle size, relative standard deviation, particle size ratio, content of spherical silica particles as inert particles A, and average particle size, relative standard deviation, particle size ratio, content of spherical silica particles as inert particles B Was obtained in the same manner as in Example 10, except that a highly insulating film having a thickness of 3.0 μm was obtained and wound into a roll. Table 2 shows the characteristics of the obtained highly insulating film. In addition, the amount of polystyrene was adjusted so that the whole would be 100 parts by mass.

[Example 13]
As inert fine particles A, 0.3 part by mass of spherical silicone resin particles having an average particle size of 1.3 μm, a relative standard deviation of 0.14, and a particle size ratio of 1.10 (based on the mass of the resulting highly insulating film is 0 A high insulating film having a thickness of 3.0 μm was obtained in the same manner as in Example 2 except that 3 wt% was used. Table 2 shows the characteristics of the obtained highly insulating film.

According to Example 2 and Examples 6 to 13, knowledge about the aspect of the inert particle A and the aspect of the inert particle B can be obtained.
The high insulating films obtained in Examples 2 and 6 to 13 in which the inert particles contained are proper have good stretchability and winding property, high dielectric breakdown voltage, and as a capacitor insulator. It was suitable.

[Comparative Example 3, Example 14]
A highly insulating film having a thickness of 3.0 μm was obtained in the same manner as in Example 2 except that the film forming conditions were as shown in Table 3, and wound into a roll. Table 3 shows the characteristics of the obtained highly insulating film.

[Comparative Example 4]
In order to obtain a film having a refractive index in the thickness direction of approximately 1.6580, the film was formed in the same manner as in Example 2 except that the film forming conditions such as the stretching ratio in the longitudinal direction and the transverse direction were as shown in Table 3. As a result, film breakage occurred frequently, and a biaxially stretched film could not be obtained.

The knowledge concerning the refractive index in the thickness direction of the film can be obtained by Examples 2 and 14 and Comparative Examples 3 and 4.
The highly insulating films obtained in Examples 2 and 14 have a suitable refractive index in the thickness direction, and therefore have good stretchability and winding property, high dielectric breakdown voltage, and are suitable as an insulator for capacitors. Met.

On the other hand, the highly insulating film obtained in Comparative Example 3 had poor drawability and dielectric breakdown voltage because the draw ratio was low and the refractive index in the thickness direction of the film was too low.
In Comparative Example 4, the intended refractive index in the thickness direction was too high, and a highly insulating film could not be obtained.

Using the obtained highly insulating film, a capacitor was prepared as follows.
First, aluminum was vacuum deposited on one side of the film to a thickness of 500 mm. At that time, deposition was performed in the form of vertical stripes consisting of repetition of an 8 mm wide vapor deposition portion and a 1 mm wide non-deposition portion. The obtained vapor-deposited film is slit at the center in the width direction of the vapor-deposited portion and the non-vapor-deposited portion, and is formed into a 4.5 mm-wide tape shape consisting of a vapor-deposited portion with a width of 4 mm and a non-vapor-deposited portion with a width of 0.5 mm. A take-up reel. Next, the two reels were overlapped and wound so that the non-deposited portions were on the opposite end faces, respectively, to obtain a wound body, and then pressed at 150 ° C. and 1 MPa for 5 minutes. Metallicon was sprayed on both end faces of the wound body after pressing to form external electrodes, and lead wires were welded to the metallicon to form a wound film capacitor.

  The film capacitor using the highly insulating film obtained in Examples 1 to 14 was excellent in heat resistance and withstand voltage characteristics and exhibited excellent performance as a capacitor. Moreover, it was excellent in workability at the time of capacitor production.

  In particular, the film capacitors using the highly insulating films obtained in Examples 2, 3, 6, 8 to 10, 13, and 14 were particularly excellent in withstand voltage characteristics, and exhibited better performance as capacitors. .

Claims (9)

  A biaxially stretched film comprising a styrene polymer having a syndiotactic structure as a main component, and having an average particle size of 0.2 μm to 3.0 μm and a relative standard deviation of particle size of 0.5 or less Fine particles A contain 0.01 mass% or more and 1.5 mass% or less, antioxidant contains 0.1 mass% or more and 8 mass% or less, and the refractive index in the thickness direction is 1.6050 or more and 1.6550 or less. Is a highly insulating film.   The average particle diameter is 0.01 μm or more and 0.5 μm or less, the average particle diameter is 0.2 μm or more smaller than the average particle diameter of the inert fine particles A, and the relative standard deviation of the particle diameter is 0.5 or less. The highly insulating film according to claim 1, comprising 0.05% by mass or more and 2.0% by mass or less of active fine particles B.   The highly insulating film according to claim 1 or 2, wherein the inert fine particles A are spherical particles having a particle size ratio of 1.0 to 1.3.   The highly insulating film according to claim 3, wherein the inert fine particles A are spherical polymer resin particles.   The highly insulating film according to claim 3, wherein the inert fine particles A are spherical silica particles.   The highly insulating film according to any one of claims 1 to 5, wherein the inert fine particles B are spherical silica particles having a particle size ratio of 1.0 to 1.3.   The thermal decomposition temperature of antioxidant is 250 degreeC or more, The highly insulating film of any one of Claims 1-6.   The highly insulating film according to claim 1, wherein the film thickness is 0.4 μm or more and less than 6.5 μm.   The capacitor | condenser using the highly insulating film of any one of Claims 1-8.