JP2017036373A - Insulation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation film that is excellent in winding property and insulation breakdown voltage, and is low in film long-sized direction (MD) thermal shrinkage.SOLUTION: An insulation film is characterized in: having a styrenic polymer having a syndiotactic structure as a main constituent component; containing inactive fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less by 2.0 mass% or less; and when subjected to a heating treatment at 150°C for 30 minutes in a state of no tension, the thermal shrinkage in the film long-sized direction and the short-sized direction is 2% or less, respectively.SELECTED DRAWING: None

Description

  The present invention relates to an insulating film. More specifically, the present invention relates to an 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.

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. In such a capacitor, a film excellent in electrical characteristics such as breakdown voltage and heat resistance is required.
In addition, in order to improve the capacitance of the capacitor or to reduce the size of the capacitor, it is required to further reduce the film thickness as 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.

  In response to this problem, Patent Document 5 discloses a syndiotactic polystyrene film containing a specific inert fine particle and an antioxidant and having a specific refractive index. However, the syndiotactic polystyrene film disclosed in Patent Document 5 has a problem in that the thermal shrinkage in the machine direction (MD) of the film is high.

Japanese Patent Laid-Open No. 3-124750 Japanese Patent Laid-Open No. 6-80793 JP 7-156263 A JP-A-8-28396 JP 2013-241626 A

  An object of the present invention is to provide an insulating film that is excellent in winding property and dielectric breakdown voltage and has a low heat shrinkage rate in the longitudinal direction (longitudinal direction, MD) of the film.

According to the present invention, the following insulating films are provided.
1. A styrene polymer having a syndiotactic structure as a main constituent component, containing 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less,
An insulating film characterized in that, when heat treatment is performed at 150 ° C. for 30 minutes in a tensionless state, the thermal shrinkage rate in the long direction and the short direction of the film is 2% or less, respectively.
2. A styrenic polymer-containing composition containing 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less, comprising a styrene polymer having a syndiotactic structure as a main constituent, An insulating film produced by biaxial stretching.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in winding property and a dielectric breakdown voltage, and can provide the insulating film with the low heat shrinkage rate of the longitudinal direction (longitudinal direction, MD) of a film.

The first insulating film of the present invention comprises a syndiotactic styrene polymer as a main component, and contains 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less. When the heat treatment is performed at 150 ° C. for 30 minutes in a tensionless state, the heat shrinkage rate in the long direction and the short direction of the film is 2% or less, respectively.
The second insulating film of the present invention comprises a styrene polymer having a syndiotactic structure as a main constituent, and contains 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less. An insulating film produced by simultaneously biaxially stretching a styrene polymer-containing composition.

The first insulating film of the present invention is a film obtained by simultaneously biaxially stretching the styrene polymer-containing composition of the second insulating film of the present invention. Therefore, the longitudinal direction of the film corresponds to each of the longitudinal direction, MD, MD direction, and the machine axis direction, and the short direction is perpendicular to the transverse direction, TD, TD direction, the machine axis direction, and the thickness direction. Corresponds to each of the directions.
Hereinafter, both the first insulating film of the present invention and the second insulating film of the present invention are collectively referred to as “the insulating film of the present invention”.

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 thinned (thinned), there is a problem that handling properties such as wrinkling of the film easily occurs and the film easily breaks. In addition, as the film is made thinner, the added particles easily fall off, and the dielectric breakdown voltage is lowered due to the dropping of the added particles. In the insulating film of the present invention, in a syndiotactic polystyrene biaxially stretched film containing specific inert fine particles, excellent winding even when the film is thinned by simultaneous biaxial stretching as the stretching method. And the dielectric breakdown voltage can be exhibited, and the thermal shrinkage rate in the machine direction (MD) of the film can be kept low.
Hereafter, each component of the composition which manufactures the insulating film of this invention, the manufacturing method of a film, and the characteristic of a film are demonstrated. In addition, the component and its quantity which comprise an insulating film respond | correspond with a composition.

<Styrene polymer>
The styrenic polymer contained in the composition for producing the insulating film of the present invention is a styrenic polymer having a syndiotactic structure, that is, phenyl that is a side chain with respect to the main chain formed from carbon-carbon bonds. It has a three-dimensional structure in which groups and substituted phenyl groups are alternately positioned in opposite directions.
In general, tacticity is quantified by nuclear magnetic resonance (13C-NMR) with isotope carbon, and the abundance ratio of a plurality of consecutive structural units, for example, dyad for two, triad for three, In the case of a piece, it can be indicated by a pentad or the like.

  In the present invention, the styrenic polymer having a syndiotactic structure is, for example, 75% or more, preferably 85% or more, or 30% or more, preferably 50%, of racemic pentad (rrrr) in racemic diad (r). % Polystyrene having a syndiotacticity of at least, poly (alkyl styrene), poly (aryl styrene), poly (alkylene styrene), poly (halogenated styrene), poly (alkoxy styrene), poly (vinyl benzoate), Or the polymer in which some of these benzene rings were hydrogenated, these mixtures, or the copolymer containing these structural units is said. The styrenic polymer of the present invention includes poly (vinyl naphthalene) and poly (acenaphthylene).

Examples of the poly (alkylstyrene) include poly (methylstyrene), poly (ethylstyrene), poly (propylstyrene), poly (butylstyrene), and the like.
Examples of the poly (aryl styrene) include poly (phenyl styrene).
Examples of the poly (alkylene styrene) include poly (vinyl styrene).
Examples of the poly (halogenated styrene) include poly (chlorostyrene), poly (bromostyrene), poly (fluorostyrene) and the like.
Examples of the poly (alkoxystyrene) include poly (methoxystyrene) and poly (ethoxystyrene).
Particularly preferred styrenic polymers include polystyrene, poly (p-methylstyrene), poly (m-methylstyrene), poly (p-tertiarybutylstyrene), poly (p-chlorostyrene), poly (m-chloro). Styrene), poly (p-fluorostyrene), and copolymers of styrene and p-methylstyrene.

  In the case of using a copolymer component containing a copolymer component in a styrene polymer, the comonomer includes olefin monomers such as ethylene, propylene, butene, hexene and octene in addition to the above-mentioned styrene polymer monomer; Examples include 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 having a syndiotactic structure 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 1.1 × 10 ⁵ or more and 8.0 × 10 ⁵ or less.
By setting the weight average molecular weight of the styrenic polymer having a syndiotactic structure to 1.0 × 10 ⁴ or more, it is possible to obtain a film having excellent high elongation properties and further improved heat resistance. Further, 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.

  In the present invention, the composition for producing an insulating film has a syndiotactic styrene polymer as a main constituent component. Here, the “main constituent component” is the largest of all components contained in the composition. It means that it is a component (in mass%). Preferably it is 50 mass% or more, More preferably, it contains 80 mass% or more.

  Such a styrenic polymer having a syndiotactic structure can be produced by a known method, and is disclosed, for example, in JP-A-62-187708. Specifically, in an inert hydrocarbon solvent or in the absence of a solvent, a styrene monomer (the above styrenic monomer) is prepared by using a titanium compound and a condensation product of water and an organoaluminum compound, particularly trialkylaluminum, as a catalyst. It can be produced by polymerizing a monomer corresponding to the polymer. Poly (halogenated alkylstyrene) is disclosed in JP-A-1-146912, and hydrogenated polymer is disclosed in JP-A-1-178505.

<Inert fine particles>
The composition for producing the insulating film of the present invention contains inert fine particles having an average particle diameter of 0.2 μm or more and 3.0 μm or less.
By setting the average particle size of the inert fine particles within the above numerical range, the air can be easily removed while maintaining a high dielectric breakdown voltage, and an insulating film excellent in winding property is obtained. be able to.
If the average particle size of the inert fine particles is too small, sufficient air repellency tends not to be obtained, resulting in poor rollability of the resulting film. On the other hand, when it is too large, the size of voids in the obtained film tends to increase, and the dielectric breakdown voltage becomes low. From such a viewpoint, the average particle diameter of the inert fine particles is preferably 0.25 μm to 2.0 μm, more preferably 0.4 μm to 1.6 μm, and particularly preferably 0.8 μm to 1.2 μm. is there.

  The inert fine particles preferably 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 protrusion on the film surface becomes uniform, and an insulating film excellent in winding property can be obtained. Further, coarse particles and coarse protrusions are reduced, and an insulating film having an excellent dielectric breakdown voltage can be obtained. From such a viewpoint, the relative standard deviation of the particle diameter of the inert fine particles is more preferably 0.4 or less, still more preferably 0.3 or less, and particularly preferably 0.2 or less.

  The inert fine particles are preferably spherical particles having a particle size ratio of 1.0 to 1.3. 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, it is possible to further increase the winding effect and the dielectric breakdown voltage.

In the composition used for producing the insulating film of the present invention, the content of the inert fine particles is 2.0% by mass or less. Similarly, the content of inert fine particles in the insulating film is 2.0% by mass or less.
By containing the inert fine particles in an amount in the above numerical range, the handleability of the resulting film can be improved while maintaining a high dielectric breakdown voltage. When the amount is too large, the surface of the obtained film tends to be too rough, and thus the abrasion resistance of the film surface tends to be deteriorated, 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 in the composition is preferably 0.05% by mass or more and 1.8% by mass or less, more preferably 0.1% by mass or more and 1.5% by mass or less, particularly Preferably they are 0.2 mass% or more and 1.0 mass% or less.
Since the composition used for manufacturing the insulating film usually does not contain a component that disappears by heating, such as a solvent, the content of the inert fine particles in the composition is the content of the inert fine particles in the insulating film as it is.

The inert fine particles may be organic fine particles or inorganic fine particles.
Examples of the 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; Examples include benzoates of Li, Na, and K; terephthalates of Ca, Ba, Zn, and Mn. 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 polymer resin particles, and spherical silicone resin particles and spherical polystyrene resin particles are particularly preferable from the viewpoint of superior slipperiness and abrasion resistance.

Examples of the inorganic fine particles include (1) silicon dioxide (including hydrate, silica sand, quartz, etc.); (2) alumina in various crystal forms; (3) silicate containing 30% by mass or more of SiO ₂ component. (For example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.); (4) oxides of Mg, Zn, Zr, and Ti; (5) Sulfates of Ca and Ba; (6) Phosphates of Li, Ba, and Ca (including monohydrogen and dihydrogen salts); (7) Mg, Ca, Ba, Zn, Cd, Pb , Sr, Mn, Fe, Co, and Ni titanates; (8) Ba and Pb chromates; (9) Carbon (eg, carbon black, graphite, etc.); (10) Glass (eg, glass powder, (11) Charcoal of Ca and Mg) Acid salts; (12) fluorite; (13) spinel oxides and the like. 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 inorganic fine particles, and spherical silica particles are particularly preferable from the viewpoint of being superior in terms of slipperiness and abrasion resistance.

<Antioxidant>
The composition for producing the insulating film of the present invention may contain an antioxidant.
When the insulating film contains 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, 2-t-butyl-4- Methoxyphenol, 3-tert-butyl-4-methoxyphenol, 2,6-di-tert-butyl-4- [4,6-bis (octylthio) -1,3,5-triazin-2-ylamino] phenol, monophenol antioxidants such as n-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-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, pentaerythritol tetrakis [3- ( 3,5-di-tert-butyl-4-hydroxyphenyl) propionate], bis [3,3′-bis- (4′-hydroxy-3′-tert-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-tocophenol And polymer type phenolic antioxidants such as
Specific examples of the amine-based antioxidant include alkyl-substituted diphenylamine.

  Specific examples of the phosphorus antioxidant include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenylditridecyl). Phosphite, 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-butylphenol Phosphite, cyclic neopentanetetraylbis (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,6-di-t-butyl-4-methylphenyl) Examples thereof include phosphite and 2,2′-methylenebis (4,6-di-t-butylphenyl) octyl phosphite.

  Specific examples of the sulfur-based antioxidant include dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, penta Examples include erythritol tetrakis (3-lauryl thiopropionate) and 2-mercaptobenzimidazole.

Of these antioxidants, primary antioxidants are preferred, and phenolic antioxidants are particularly preferred from the viewpoint that they are more excellent in corrosion resistance and can further improve the dielectric breakdown voltage.
In addition, an antioxidant may be used individually by 1 type and may use 2 or more types together. When two or more kinds of antioxidants are used in combination, an aspect using two or more kinds of primary antioxidants may be used, an aspect using two or more kinds of secondary antioxidants may be used, and one or more kinds of primary oxidations may be used. An inhibitor and one or more secondary antioxidants may be used in combination. For example, it can be expected that both primary oxidation and secondary oxidation are prevented 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.

The antioxidant 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 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.

  The melting point of the antioxidant is preferably 90 ° C. or higher. 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 there is a possibility that problems such as deterioration in thickness unevenness of the film may 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, there is a possibility that 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.

  As the antioxidant, a commercially available product can be used as it is. Examples of commercially available products include pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (BASF, trade name: IRGANOX 1010), N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine (manufactured by BASF: trade name IRGANOX1024), N, N′-hexane-1,6-diylbis [3- (3,5-di -T-butyl-4-hydroxyphenyl) propionamide] (manufactured by BASF: trade name IRGANOX 1098) and the like are preferred.

The insulating film of the present invention preferably contains an antioxidant in an amount of 0.1% by mass or more and 8% by mass or less based on the mass of the composition for producing the insulating film. By setting the content of the antioxidant within the range, the dielectric breakdown voltage can be improved.
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. 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.

<Polyphenylene ether resin>
The composition for producing the insulating film of the present invention may contain a polyphenylene ether resin in order to improve moldability, mechanical properties, surface properties and the like in addition to the syndiotactic styrene polymer.
Preferred examples of the polyphenylene ether resin include aromatic polyethers such as polyphenylene ether and polyetherimide represented by the following formula, polycarbonate, polyacrylate, polysulfone, polyethersulfone, and polyimide. An amorphous polymer is particularly preferable. Of these resin components, polyphenylene ether is particularly preferred.

  The polyphenylene ether resin in the composition for producing the insulating film is preferably blended in an amount of 5 parts by weight to 48 parts by weight, preferably 8 parts by weight or more, based on 100 parts by weight of the syndiotactic styrene polymer. 11 parts by mass or more is more preferable, and 20 parts by mass or more is particularly preferable. Moreover, when there are many compounding quantities of polyphenylene ether-type resin, it exists in the tendency for the crystallinity of the styrene polymer of a syndiotactic structure to fall easily, and it exists in the tendency for the heat resistance improvement effect of a film to become low. From such a viewpoint, the upper limit of the content of the polyphenylene ether resin is preferably 45 parts by mass or less, more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

<Other resin components>
In order to increase the dielectric breakdown voltage of the insulating film, the composition for producing the insulating film may contain other resin components in addition to the above-mentioned syndiotactic styrene polymer and polyphenylene ether resin. Other resin components include a resin component that is compatible with a syndiotactic styrenic polymer and an incompatible resin component.
In addition, the composition which manufactures an insulating film normally does not contain a solvent.

Examples of other resin components that are compatible with the syndiotactic styrene polymer include atactic styrene polymers, isotactic styrene polymers, and styrene-maleic anhydride copolymers. . These resin components are easily compatible with styrene polymers with a syndiotactic structure, and are effective in controlling crystallization when producing a preform for stretching, improving the stretchability thereafter, and controlling stretching conditions. Can be easily obtained, and a film having excellent mechanical properties 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 blending 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. That's fine. When the blending ratio of the compatible resin component exceeds 40 parts by mass, the effect of improving the heat resistance, which is an advantage of the styrene polymer having a syndiotactic structure, is lowered.

Other resin components that are incompatible with the syndiotactic styrenic polymer include polyesters such as polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polybutylene terephthalate (PBT) resin; polyethylene, polypropylene, polybutene Polyolefins such as polypentene, polyamides such as nylon 6 and nylon 6,6, halogenated vinyl polymers such as Teflon (registered trademark), acrylic polymers such as polymethyl methacrylate, polyvinyl alcohol, etc. The resin which becomes can be illustrated preferably. Among these, from the viewpoint that the dielectric breakdown voltage can be further increased, polyester is preferable, and polyethylene terephthalate (PET) resin and polyethylene naphthalate (PEN) resin are more preferable. Among these, polyethylene terephthalate (PET) resin is particularly preferable.
When a small amount of the incompatible resin component is blended, it can be dispersed in an island shape in a styrenic polymer having a syndiotactic structure to give a moderate gloss after stretching or to improve the surface slipperiness. It is effective for.
The blending 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 styrene polymer having a syndiotactic structure. . Moreover, when the temperature used as a product is high, it is preferable to mix | blend the incompatible resin component with comparatively heat resistance.

Furthermore, known additives such as antistatic agents, colorants, weathering agents and the like can be added as long as the object of the present invention is not impaired.
As for the compounding quantity of an additive, 10 mass parts or less are preferable with respect to 100 mass parts of styrene-type polymers. If it exceeds 10 parts by mass, it tends to cause breakage during stretching, resulting in poor production stability.
For example, heat resistance can be improved by blending an antistatic agent as an additive.

<Insulating film manufacturing method>
The insulating film of the present invention is a film obtained by simultaneously biaxially stretching the above-described styrenic polymer-containing composition. An unstretched sheet is produced using the styrene-based polymer-containing composition, and the unstretched sheet is simultaneously It can be manufactured by axial stretching.

The unstretched sheet is obtained by heating and melting a resin composition containing a predetermined amount of inert fine particles and an antioxidant and the like in a syndiotactic styrene polymer, and extruding it into a sheet, followed by cooling and solidifying. Can be made. Here, the heating and melting temperature is preferably a melting point (Tm, unit: ° C) or more and (Tm + 70 ° C) or less of the resin composition.
The intrinsic viscosity of the obtained unstretched sheet is preferably in the range of 0.35 to 0.9 dl / g.

The simultaneous biaxial stretching of the unstretched sheet is to simultaneously stretch the unstretched sheet in the long direction (machine axis direction) and the short direction (direction perpendicular to the machine axis direction).
In the simultaneous biaxial stretching, the stretching temperature is set to a glass transition temperature (Tg, unit: ° C.)-10 ° C.) or higher and (Tg + 70 ° C.) lower than the resin composition, and the draw ratio is, for example, 2.7 times or higher. 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 can be carried out by stretching in each of the long direction and the short direction.
The lower limit of the stretching speed in the simultaneous biaxial stretching is preferably 500% / min or more, more preferably 1000% / min or more, further 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.

In the above-mentioned simultaneous biaxial stretching, the stretching temperature is not made constant, but the stretching temperature is raised in multiple stages as the stretching progresses, and a temperature difference is created between the first stage stretching temperature and the final stage stretching temperature. And preferred.
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 particularly preferably 15 ° C. or higher. 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 in the numerical range, it is possible to achieve a high draw ratio, which has been difficult in the past, in the production of a film with a thin film thickness. A film with good spots can be obtained.

The simultaneously biaxially stretched film may be heat-set in a temperature range of (Tg + 70 ° C.) to Tm. The heat setting temperature is, for example, 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, particularly when a film having a thin film thickness is produced, film breakage tends to occur, and the thickness unevenness may be deteriorated.
Dimensional stability can be improved by performing relaxation treatment for 3 seconds to 60 seconds and 1% to 10% at a temperature lower than the heat setting temperature by 20 ° C. to 90 ° C. as necessary after the heat setting.

  As the apparatus for carrying out the simultaneous biaxial stretching, any of an incremental pitch screw type, a linear motor type, a link type, and an individual clip driving type can be used.

<Characteristics of insulating film>
The 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 thickness of the insulating film within the numerical range, a capacitor having a high capacitance can be obtained.

The 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 of at least one surface of the insulating film within the 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.

The insulating film of the present invention preferably has a 10-point average roughness Rz of at least one side of 200 nm to 3000 nm.
By making 10-point average roughness Rz of an insulating film into the said numerical range, the improvement effect of winding property can be made high. When the 10-point average roughness Rz is too low, the air release property tends to be low when the film is wound up as a roll, and the effect of improving the winding property such as the film being liable to skid may be 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 may be 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.

The heat shrinkage rate of the insulating film of the present invention is 150 ° C. × 30 minutes under no tension, in the long direction (machine axis direction) and in the short direction (direction perpendicular to the machine axis direction and the thickness direction), respectively. 2.0% or less.
When the thermal shrinkage is in the above numerical range, blocking that occurs during the processing of the capacitor (e.g., vapor deposition) can be suppressed, and a capacitor having excellent quality can be easily obtained. On the other hand, if the thermal shrinkage rate becomes too large, blocking tends to occur during the processing of the capacitor (e.g., vapor deposition), and it tends to be difficult to obtain a good product. From such a viewpoint, the heat shrinkage rate at 150 ° C. × 30 minutes is more preferably 1.0% or less in both the vertical and horizontal directions, further preferably 0.5% or less, and particularly preferably 0%.
In order to achieve the above heat shrinkage rate, the stretching method is simultaneous biaxial stretching. In addition, it is more preferable to set the heat setting temperature within the range described below. When the heat setting temperature is increased, the heat shrinkage rate tends to decrease. Moreover, the numerical range of the said heat shrinkage rate can be achieved more effectively by performing a heat relaxation process at the time of heat setting or a subsequent process.

  The insulating film of the present invention preferably has a dielectric breakdown voltage (BDV) at 120 ° C. of 320 V / μm or more. The fact that the dielectric breakdown voltage is in the above numerical range means that the dielectric breakdown voltage is excellent even at a high temperature. The breakdown voltage is more preferably 400 V / μm or more, and further preferably 420 V / μm or more.

When the insulating film of the present invention contains 80% by mass or more of a syndiotactic styrene polymer contained in the composition, the refractive index in the thickness direction of the simultaneously biaxially stretched film is 1.5800 or more and 1.6550 or less. It is preferable that By setting the refractive index in the thickness direction within the above numerical range, the dielectric breakdown voltage can be further increased. In addition, the frequency of film breakage in the film manufacturing process is reduced, and productivity is easily improved. From such a viewpoint, the refractive index in the thickness direction is preferably 1.620 or less, more preferably 1.615 or less, and particularly preferably 1.610 or less. On the other hand, when the refractive index in the thickness direction is too low, the dielectric breakdown voltage tends to be low.
Further, the insulating film of the present invention increases the frequency of film breakage in the capacitor manufacturing process, and the productivity of the capacitor tends to decrease. Furthermore, the thickness unevenness of the film tends to deteriorate, and it becomes difficult to obtain a capacitor with stable quality. From such a viewpoint, the refractive index in the thickness direction is preferably 1.590 or more, more preferably 1.595 or more, and particularly preferably 1.600 or more.
The refractive index in the thickness direction of the insulating film can be measured, for example, at 23 ° C. and 65% RH using an Abbe refractometer using sodium D-line (589 nm) as a light source.

The insulating film of the present invention preferably has a humidity expansion coefficient αh in the short direction (lateral direction, TD direction) of the film in the range of 0.1 × 10 ^{−6 to} 13 × 10 ⁻⁶ /% RH. More preferable αh is in the range of 0.5 × 10 ^{−6 to} 11 × 10 ⁻⁶ /% RH, and particularly preferably in the range of 0.5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ /% RH.
In order to make αh smaller than the lower limit, the film forming property may be lowered. On the other hand, when the upper limit is exceeded, the film stretches due to a change in humidity, and when used in a film capacitor, the capacitor characteristics may not be sufficient in applications where a high humidity environment is required, such as an automobile engine room.

The humidity expansion coefficient αh in the TD direction of the insulating film can be calculated from the following equation.
αt = {(L ₆₀ −L ₄₀ ) / (L ₄₀ × ΔT)} + 0.5 × 10 ⁻⁶
L ₄₀ : Sample length at 40 ° C. (mm)
L ₆₀ : sample length at 60 ° C. (mm)
ΔT: 20 (= 60-40) ° C.
0.5 × 10 ⁻⁶ : Temperature expansion coefficient of quartz glass

The insulating film of the present invention preferably has a temperature expansion coefficient αt in the TD direction in the range of −10 × 10 ⁻⁶ to + 15 × 10 ⁻⁶ / ° C. Preferred αt is in the range of −8 × 10 ⁻⁶ to + 10 × 10 ⁻⁶ / ° C., particularly −5 × 10 ⁻⁶ to + 5 × 10 ⁻⁶ / ° C.
When αt is smaller than the lower limit, the film shrinks, while when it exceeds the upper limit, the film expands due to temperature change. When used as a film capacitor, capacitor characteristics are required for applications that require a high-temperature environment such as an automobile engine room. May not be enough.

The temperature expansion coefficient αt in the width direction of the insulating film can be calculated from the following equation.
αh = (L ₇₀ −L ₃₀ ) / (L ₃₀ × ΔH)
Sample length (mm) when L _{30 is} 30% RH
Sample length when L _{70 is} 70% RH (mm)
ΔH: 40 (= 70-30)% RH

The insulating film of the present invention preferably has a Young's modulus in the MD and TD directions of 5 GPa or more. If either of them has a Young's modulus smaller than the lower limit, the mechanical properties when used in a film capacitor may not be sufficient, and deformation may occur due to changes in temperature and humidity.
The sum of the Young's modulus in the MD direction and the TD direction is preferably at most 22 GPa. When the sum of the Young's modulus in the MD direction and the Young's modulus in the TD direction exceeds the upper limit, the draw ratio becomes excessively high during film formation, the film breaks frequently, and the product yield may be remarkably deteriorated. A preferable upper limit of the sum of Young's modulus in the MD direction and the TD direction is 20 GPa or less, and further 18 GPa or less.

  The Young's modulus of the insulating film is obtained by cutting the film into a sample width of 10 mm and a length of 15 cm, pulling it with an Instron type universal tensile tester at a tensile speed of 10 mm / min and a chart speed of 500 mm / min with a chuck spacing of 100 mm. It can be calculated from the tangent of the rising part of the load-elongation curve.

  The insulating film of the present invention has the absolute value (Δn) of the difference between the minimum refractive index (Nx) in the plane direction of the film and the refractive index (Ny) perpendicular to the direction indicating the refractive index of Nx. However, 0.025 or less is preferable. When ΔN is 0.25 or less, physical properties in the surface direction of the film are balanced, fine wrinkles due to shrinkage spots, deterioration of flatness, and the like can be suppressed, and heat resistance can be further improved. From these viewpoints, ΔN is more preferably 0.020 or less, further preferably 0.018 or less, and particularly preferably 0.015 or less.

The insulating film of the present invention preferably has a storage elastic modulus (E ′) at 120 ° C. measured at a frequency of 10 Hz by dynamic viscoelasticity measurement of 600 MPa or more. When the storage elastic modulus (E ′) at 120 ° C. is in the above numerical range, the mechanical properties of the film under a high temperature environment are excellent. When the storage elastic modulus at 120 ° C. is too low, mechanical properties (breaking strength, breaking elongation, etc.) tend to decrease when used at high temperatures. From such a viewpoint, the storage elastic modulus at 120 ° C. is more preferably 650 MPa or more, further preferably 700 MPa or more, and particularly preferably 750 MPa or more.
The insulating film of the present invention preferably has a storage elastic modulus (E ′) at 150 ° C. measured at a frequency of 10 Hz by dynamic viscoelasticity measurement of 370 MPa or more. It can be said that the higher the storage elastic modulus (E ′) at 150 ° C., the better the heat resistance. From these viewpoints, the storage elastic modulus (E ′) at 150 ° C. is more preferably 400 MPa or more, further preferably 430 MPa or more, and particularly preferably 460 MPa or more.

  The insulating film of the present invention preferably has a peak temperature of loss elastic modulus (E ″) measured at a vibration frequency of 10 Hz by dynamic viscoelasticity measurement of 120 ° C. or more and 150 ° C. or less. The peak temperature of the loss elastic modulus (E ″) being moderately high means that the temperature at which molecular motion begins to become active when the insulating film is heated is moderately high. Therefore, the heat resistance as a film tends to increase. From such a viewpoint, the peak temperature of the loss elastic modulus (E ″) is more preferably 125 ° C. or higher, further preferably 130 ° C. or higher, and particularly preferably 135 ° C. or higher. On the other hand, the fact that the peak temperature of the loss elastic modulus (E ″) is too high has the combined effect that the molecular motion is less active, and the stretching stress during stretching becomes high. Sometimes breaks easily occur. From such a viewpoint, the peak temperature of the loss elastic modulus (E ″) is more preferably 145 ° C. or less, and further preferably 140 ° C. or less.

The insulating film of the present invention preferably has a dielectric loss tangent (tan δ) of 0.0015 or less at 120 ° C. and a frequency of 1 kHz. When the dielectric loss tangent (tan δ) at 120 ° C. is large, when the film is used at a high temperature (for example, 120 ° C.) for a long time, it tends to self-heat and tends to be damaged. From such a viewpoint, the dielectric loss tangent (tan δ) at 120 ° C. is more preferably 0.0012 or less, further preferably 0.0009 or less, and particularly preferably 0.0006 or less.
The dielectric loss tangent can be calculated by using dielectric loss imperfection using a sample prepared according to JIS C 2151.

In the insulating film of the present invention, the plane orientation coefficient (ΔP) based on the refractive index of the film is −0.027 or less. In the insulating film of the present invention, the more negative the plane orientation coefficient, the more the molecular chain is oriented in the film plane direction. Surprisingly, the plane orientation coefficient (ΔP) is not more than the upper limit. By going, the heat resistance seen by the below-mentioned shear stress can be improved. From such a viewpoint, the upper limit of the plane orientation coefficient is preferably −0.029 or less, more preferably −0.030 or less, still more preferably −0.032 or less, and particularly preferably −0.033 or less.
On the other hand, the lower limit of the plane orientation coefficient (ΔP) is not particularly limited, but the frequency of film breakage in the film production process, particularly in the stretching process tends to increase, and the productivity of the film tends to decrease. From such a viewpoint, the lower limit of the plane orientation coefficient (ΔP) is preferably −0.045 or more, more preferably −0.040 or more, further preferably −0.039 or more, and −0.038 or more. Particularly preferred.

  The plane orientation coefficient ΔP of the insulating film can be calculated by ΔP = (Nx + Ny) / 2−Nz. Here, Nx is the minimum refractive index in the surface direction, the refractive index in the direction orthogonal to the refractive index is (Ny), and the refractive index (Nz) in the thickness direction.

<Coating layer>
The insulating film of the present invention preferably has a coating layer having a water contact angle of 85 ° or more and 120 ° or less on at least one surface thereof. By having such a coating layer, the dielectric breakdown voltage can be increased. It is considered that the presence of a thin coating layer between the insulating film and the electrode can alleviate charge concentration and improve the dielectric breakdown voltage. In addition, if there is a coating layer that is a thin layer with a surface energy smaller than that of the insulating film, even if a discharge occurs, the coating layer peels off from the insulating film, preventing the dielectric insulating film from being destroyed, and as a result It is considered that the dielectric breakdown voltage is improved. That is, in the present invention, when the water contact angle on the surface of the coating layer is in the above numerical range, the coating layer peels off from the film at the same time as voltage is applied and discharge occurs, and only the peeled coating layer is destroyed, It is considered that the breakdown voltage is improved as a result without being broken.

  If the water contact angle of the coating layer is too low, the coating layer is difficult to peel off from the film even if a discharge occurs, and since the peeling is incomplete, the dielectric breakdown of the coating layer is induced and the dielectric breakdown of the film occurs. The effect of improving the breakdown voltage due to the coating layer cannot be obtained. Moreover, when the water contact angle of the coating layer is in the above range, it is possible to improve the slipping property and improve the winding property, and it is also possible to improve the heat resistance as seen by shear stress described later.

  From such a viewpoint, the water contact angle on the surface of the coating layer is preferably 86 ° or more, more preferably 88 ° or more, still more preferably 90 ° or more, and particularly preferably 95 ° or more. On the other hand, when the water contact angle is high, the coating layer tends to be peeled off from the insulating film. Therefore, even when a discharge occurs, only the peeled coating layer is easily broken and the insulating film is hardly broken down. However, if the water contact angle on the surface of the coating layer becomes too high, the adhesiveness with the metal layer formed on the capacitor becomes low, and particularly when the water contact angle exceeds 120 °, the adhesion with the metal layer is reduced. It tends to be inferior in performance and difficult to function as a capacitor. From such a viewpoint, the water contact angle on the surface of the coating layer needs to be 120 ° or less, preferably 115 ° or less, more preferably 110 ° or less, and further preferably 105 ° or less.

  In order to achieve the value of the surface water contact angle as described above, for example, a component that can reduce the surface energy after forming the coating layer, such as a wax component, a silicone component, or a fluorine component, is contained in the coating layer. Good. Moreover, the water contact angle in the coating layer surface can also be adjusted by adjusting these content and the thickness of a coating layer. Preferably, it is an embodiment in which the components described later are contained in the content described later. Of the wax component, silicone component, and fluorine component, the wax component and silicone component are particularly preferred.

The type of the coating layer is not particularly limited as long as the above-described water contact angle on the surface is achieved, but at least one selected from the group consisting of a wax component, a silicone component, and a fluorine component is used with respect to the mass of the coating layer. And it is preferable to contain 41 to 94 mass%.
The content here refers to the total content of the wax component, the silicone component, and the fluorine component in the coating layer. When the coating layer contains at least one of these components in the above content, the surface energy of the coating layer can be easily made smaller than the surface energy of the film, and the water contact angle on the surface of the coating layer can be reduced. The numerical range can be achieved more easily. When the content is too small, the water contact angle tends to be difficult to increase. From such a viewpoint, the content of the above components is more preferably 51% by mass or more, and particularly preferably 65% by mass or more. On the other hand, if the content is large, the contact angle tends to increase, so that it tends to be preferable from the viewpoint of peeling of the coating layer, but if it is too much, it becomes difficult to form a uniform coating layer, for example, Defects in the coating layer such as missing coating are likely to occur, or the coating layer is easily peeled off from the film, and these improve the dielectric breakdown voltage improvement effect.
In addition, when manufacturing a capacitor, the releasability of the coating layer is too high and the metal layer easily peels off, and the metal layer is easily detached during processing into a capacitor such as winding, resulting in a defective capacitor. May occur. From such a viewpoint, the content is more preferably 90% by mass or less, and particularly preferably 85% by mass or less.

(Wax component)
Examples of the wax component include synthetic waxes such as polyolefin waxes and ester waxes, and natural waxes such as carnauba wax, candelilla wax and rice wax.
Examples of polyolefin waxes include polyethylene wax and polypropylene wax. Examples of ester waxes include ester waxes composed of aliphatic monocarboxylic acids having 8 or more carbon atoms and polyhydric alcohols, and specific examples thereof include sorbitan tristearate, pentaerythritol triplet. Nate, glycerin tripalmitate and polyoxyethylene distearate are exemplified.
Among these waxes, it is preferable to use a polyolefin wax because the contact angle of the coating layer is easily satisfied. Particularly preferred is polyethylene wax.
In addition, the wax is preferably water-soluble or water-dispersible from the viewpoint of exhibiting good dispersibility in the coating layer and thereby improving the dielectric breakdown voltage.

(Silicone component)
The silicone component is preferably a silicone composition mainly formed from a silicone compound having a reactive group. Here, “mainly” means, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more in the silicone component. By setting it as such an aspect, the improvement effect of a dielectric breakdown voltage can be made high.
In addition, although the silicone compound which does not have a reactive group may be contained in a silicone component, when the content is too much (for example, in the case of 30 mass% or more in a silicone component), a vapor deposition layer It is difficult to form and cannot be evaluated as a capacitor. Therefore, the silicone compound having no reactive group is preferably 20% by mass or less, more preferably 10% by mass or less, in the silicone component.

Preferred examples of the silicone compound include polydimethylsiloxane in which the methyl group may be substituted with another alkyl group, phenyl group, or the like. By using this, the effect of improving the dielectric breakdown voltage is further increased. be able to.
Preferred reactive groups of the silicone compound include hydrogen groups, vinyl groups (including vinyl alkyl groups such as allyl groups), hydroxyl groups, and the like.
As the silicone compound having a reactive group, polydimethylsiloxane having any of the above-described reactive groups is particularly preferable. In the polydimethylsiloxane having such a reactive group, the reactive group has two or more reactive groups in the molecule and is usually directly bonded to a silicon atom. Then, due to heat applied at the time of forming the coating layer, preferably using a catalyst such as platinum or palladium, an addition reaction occurs in the hydrogen group and the vinyl group, or a condensation reaction occurs in the hydrogen group and the hydroxyl group, and curing is performed. Reaction occurs to form a crosslinked structure, resulting in a silicone composition.

The silicone compound may be a mixture of silicone compounds having different types of reactive groups. Such a silicone compound preferably has a molecular weight of 1,000 to 500,000. If it is less than 1000, the cohesive force of the coating film may be reduced and the coating layer may be easily lost. If it exceeds 500,000, the viscosity becomes high and handling may be difficult.
From the viewpoint of easy handling of the coating liquid for forming the coating layer and good dispersibility in the coating layer, thereby enhancing the effect of improving the dielectric breakdown voltage, the silicone compound and polydimethylsiloxane are water-soluble or It is preferably water-dispersible.

The silicone compound is preferably used in combination with a silane coupling agent. Such a silane coupling agent is a silane compound having a hydrolyzable group directly bonded to a silicon atom, preferably having a reactive group.
The silane compound having the reactive group has a hydrolyzable group directly bonded to a silicon atom, and is a reaction selected from an organic group containing an amino group, an organic group containing an epoxy group, and an organic group containing a carboxylic acid group It is preferable to use one containing at least one type of functional group. The hydrolyzable group is an organic group that generates a silanol group by hydrolysis and reaction, such as an alkoxy group or a halogen group, such as a methoxy group or an ethoxy group.

  For example, as a specific example of the reactive group of the silane compound, the organic group containing an amino group includes a primary aminoalkyl such as a 3-aminopropyl group, a 3-amino-2-methyl-propyl group, and a 2-aminoethyl group. Examples thereof include organic groups having primary and secondary amino groups such as a group, N- (2-aminoethyl) -3-aminopropyl group, and N- (2-aminoethyl) -2-aminoethyl group. Examples of the organic group containing an epoxy group include glycidoxyalkyl groups such as γ-glycidoxypropyl group, β-glycidoxyethyl group, γ-glycidoxy-β-methyl-propyl group, and 2-glycidoxycarbonyl-ethyl. And a glycidoxycarbonylalkyl group such as a 2-glycidoxycarbonyl-propyl group. Examples of organic groups that generate silanol groups by hydrolysis include alkoxy groups such as methoxy group, ethoxy group, butoxy group, and 2-ethylhexyloxy group, β-methoxyethoxy group, β-ethoxyethoxy group, and butoxy-β-ethoxy group. Such as alkoxy-β-ethoxy group, acetoxy group, propoxy group and the like, N-alkylamino group such as methylamino group, ethylamino group and butylamino group, N, N-dialkylamino group such as dimethylamino group and diethylamino group And heterocyclic groups containing nitrogen such as imidazole group and pyrrole group.

  Preferred silane coupling agents include those having three methoxy groups as hydrolyzable groups, γ-glycidoxypropyl groups as reactive groups, and three ethoxy groups bonded as hydrolyzable groups. And those having a γ-glycidoxypropyl group as a reactive group. By adding such a silane coupling agent, the crosslinking density of the silicone compound thin film can be increased. When the coating film rigidity is increased, breakage of the film due to discharge can be further suppressed, and the dielectric breakdown characteristics are improved.

(Fluorine component)
Examples of the fluorine component include a polymer using a fluoroethylene monomer and a polymer using a fluorinated alkyl (meth) acrylate monomer.
Examples of (co) polymers using fluoroethylene monomers include (co) polymers such as tetrafluoroethylene, trifluoroethylene, difluoroethylene, monofluoroethylene, and difluorodichloroethylene.

(Other additives)
The coating layer may further contain additives such as a surfactant, a crosslinking agent, and a lubricant.
The surfactant is used for the purpose of increasing the wettability of the coating liquid for forming the coating layer on the film or improving the stability of the coating liquid. For example, polyoxyethylene-fatty acid ester, sorbitan fatty acid Examples include anionic and nonionic surfactants such as esters, glycerin fatty acid esters, fatty acid metal soaps, alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. It is preferable that 1-60 mass% of surfactant is contained on the basis of the mass of an application layer.

By adding a crosslinking agent, the cohesive force of the coating layer can be improved, which is preferable.
Examples of the crosslinking agent include epoxy compounds, oxazoline compounds, melamine compounds, and isocyanate compounds, and other coupling agents can also be used. It is preferable that the addition amount of a crosslinking agent is 5-30 mass% on the basis of the mass of an application layer.

  For the purpose of further improving the handleability of the insulating film or preventing blocking between the films, fine particles inert to the components forming the coating layer can be added to the coating layer. . Such fine particles are preferably organic or inorganic inert fine particles, such as calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, silica particles, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, melamine resin particles, crosslinked particles. Examples thereof include silicone resin particles.

The thickness of the coating layer is preferably 0.005 to 0.5 μm, more preferably 0.005 to 0.2 μm, and still more preferably 0.02 to 0.1 μm as the thickness after drying.
By setting the thickness of the coating layer in the above range, when peeling and causing dielectric breakdown, larger voltage energy can be lost, and the effect of improving the dielectric breakdown voltage can be enhanced. When the thickness of the coating layer is less than the lower limit value, the effect of improving the dielectric breakdown voltage may not be sufficiently exhibited. Moreover, even if the thickness of the coating layer is increased to an extent that exceeds the upper limit value, a further effect of improving the dielectric breakdown voltage may not be obtained.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples and comparative examples.

Various characteristic values in the examples were measured and evaluated by the following methods.
(1) Average particle diameter of fine particles The powder was dispersed on the sample stage so that the individual particles would not overlap as much as possible, and a gold thin film deposition layer was formed on the surface with a thickness of 200 to 300 mm by a gold sputtering apparatus. The deposited layer was observed at 10,000 to 30,000 times using a scanning electron microscope, and the area equivalent particle diameter (Di) was determined for at least 100 fine particles. The obtained numerical value was applied to the following formula to calculate the average particle size.

(2) Stretchability At the time of film formation, the breaking frequency per 10,000 m was evaluated according to the following criteria.
A: The number of breaks is 0 times per 10,000 m of film formation. B: The number of breaks is 1 to 4 times per 10,000 m film formation. C: The number of breaks is 5 times or more per 10,000 m film formation.

(3) Roll appearance The appearance of the roll obtained when the film was wound into a roll of 600 mm width and 6000 m at a speed of 95 m / min was evaluated according to the following criteria.
A: There are no convex points on the roll surface and good B: There are 1 or more and less than 5 convex points on the roll surface C: There are 5 or more and less than 10 convex points on the roll surface D: There are 10 or more convex points on the roll surface

(4) Winding deviation Rolling deviation obtained when the film was wound into a roll of 600 mm width and 6000 m at a speed of 95 m / min was evaluated according to the following criteria.
A: End face deviation at the roll end face is less than 0.5 mm, Good B: End face deviation at the roll end face is from 0.5 mm to less than 1 mm C: End face deviation at the roll end face is from 1 mm to less than 2 mm D: End face deviation at the roll end face 2mm or more

(5) Film surface roughness (Ra)
For the surface roughness, the center line average roughness Ra was measured using a confocal laser microscope.

(6) Thermal contraction rate The thermal contraction rate (unit:%) of the long direction (MD) and short direction (TD) of the film in 30 minutes in the atmosphere of 150 degreeC in the state of no tension was each calculated | required.

(7) Dielectric breakdown voltage 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.

Example 1
With respect to 99% by mass of syndiotactic polystyrene (made by Idemitsu Kosan Co., Ltd .: trade name Zalec) having an MFR of 9 measured at 300 ° C. and a 1.2 kg load, an antioxidant (made by BASF: trade name IRGANOX 1010) is used. 0.5% by mass of 0.5% by mass of aluminosilicate particles (manufactured by Mizusawa Chemical: trade name AMT-08L (average particle size 0.8 μm)) was blended to obtain a resin mixture. The obtained mixture was melt-kneaded at an extrusion temperature of 300 ° C. with a 35 mmφ biaxial kneader to obtain pellets. The pellets were supplied to a 75 mmφ single screw extruder, melted at 300 ° C., extruded from a sheet forming die slit, and cooled and solidified on a casting drum cooled to 40 ° C. to obtain an unstretched sheet.
This unstretched sheet is introduced into a simultaneous biaxial stretching machine, and stretched at 110 ° C. and stretched at 5,000% / min in the long direction (machine axis direction) and the short direction (machine axis and perpendicular direction), respectively. 3. Stretched 3 times. Thereafter, the film was heat-fixed at 240 ° C. for 6 seconds. At that time, 3% relaxation treatment was performed in each of the vertical and horizontal directions to obtain a stretched film having a thickness of 3 μm and wound into a roll.
The properties of the obtained stretched film were evaluated. The results are shown in Table 1. In the examples of the present application, since the resin mixture does not contain a component that disappears by heating and stretching such as a solvent, the content of the inert fine particles in the resin mixture is equal to the content of the inert fine particles in the obtained film. It becomes.

Example 2-5 and Comparative Example 1-2
A stretched film was produced in the same manner as in Example 1 except that fine particles were used in the types and addition amounts shown in Table 1 and the stretching conditions shown in Table 1 were used, and the characteristics were evaluated. The results are shown in Table 1.
In Table 1, the fine particles of Example 2-5 and Comparative Example 1 were compared using the same aluminosilicate particles (Mizusawa Chemical: trade name AMT-08L (average particle size 0.8 μm)) as in Example 1. In Example 2, aluminosilicate particles (manufactured by Mizusawa Chemical Co., Ltd., trade name: AMT-50 (average particle size: 5.0 μm)) were used as fine particles.

Comparative Example 3
An unstretched sheet was produced in the same manner as in Example 1.
The obtained unstretched sheet was stretched 3.3 times in the long direction (machine axis direction) at 110 ° C., then led to the tenter, and then 3.3 times in the short direction (direction perpendicular to the machine axis direction). Stretched. At that time, the drawing speed in the short direction was set to 5000% / min. The stretching temperature in the short direction was 120 ° C. Thereafter, heat fixing and 3% relaxation treatment were performed at 240 ° C. for 9 seconds to obtain an insulating film having a thickness of 3.0 μm and wound into a roll.
The characteristics of the obtained stretched film were evaluated in the same manner as in Example 1. The results are shown in Table 1.

  The insulating film of the present invention can be suitably used as a capacitor insulator. In particular, it can be suitably used as an insulator for a capacitor mounted on a hybrid car or the like and exposed to a relatively high temperature environment.

Claims (2)

A styrene polymer having a syndiotactic structure as a main constituent component, containing 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less,
An insulating film characterized in that, when heat treatment is performed at 150 ° C. for 30 minutes in a tensionless state, the thermal shrinkage rate in the long direction and the short direction of the film is 2% or less, respectively.   A styrenic polymer-containing composition containing 2.0% by mass or less of inert fine particles having an average particle size of 0.2 μm or more and 3.0 μm or less, comprising a styrene polymer having a syndiotactic structure as a main constituent, An insulating film produced by biaxial stretching.