JP6017925B2 - Biaxially oriented film for electrical insulation - Google Patents

Description

  The present invention relates to a biaxially oriented film for electrical insulation, and more particularly to a biaxially oriented film for electrical insulation having excellent film forming properties.

  Films such as polypropylene, polystyrene, and polyester are used as electrical insulating films such as film capacitors. Moreover, the film capacitor is manufactured by a method in which these films and a metal thin film such as aluminum are overlapped, wound or stacked.

In recent years, in automotive applications, the range of use of film capacitors has been expanded not only in the cab, but also in the engine room. In addition to electrical characteristics, film capacitors suitable for use at higher temperatures are required. ing.
Therefore, in order to increase the heat resistance of the film capacitor, a polyethylene naphthalene dicarboxylate film has been studied. Further, Patent Document 1 discloses polyethylene naphthalene diene as a film for a film capacitor having high heat resistance and excellent withstand voltage characteristics. A biaxially stretched polyester film comprising a mixture of carboxylate and syndiotactic polystyrene and having a dielectric breakdown voltage at room temperature of around 450 V / μm and a heat resistant temperature of about 120 ° C. is disclosed.

Moreover, in order to improve the dielectric breakdown strength of thermoplastic resin films, such as polyester, adding antioxidants, such as hindered phenol, is examined (patent document 2 etc.).
On the other hand, a mixture of polyester and syndiotactic polystyrene is not sufficiently compatible, and it is difficult to form a thin film. A film is desired.

JP 2005-213351 A JP 2011-093984 A

  An object of the present invention is to provide a biaxially oriented film for electrical insulation, which is a film having an excellent withstand voltage characteristic composed of a mixture of polyester and polystyrene, and is excellent in film forming property even if it is thin.

  As a result of intensive studies to solve the above problems, the present inventors have used polyester and polystyrene together with a styrene-maleic acid half ester copolymer that has not been conventionally studied as a compatibilizer for these polymers. As compared with the conventional polyester / polystyrene-based polyester film for electrical insulation, the present invention has been completed by finding that the film is made of a mixture of polyester and polystyrene, but has excellent film-forming properties even when thin.

That is, according to the present invention, an object of the present invention is a biaxially oriented film comprising polyester, polystyrene, and a styrene-maleic acid half ester copolymer, and the content of the polyester is 10% based on the weight of the film. % To 90% by weight, the polystyrene content is 5% to 85% by weight, the styrene-maleic acid half ester copolymer content is 0.01% to 10% by weight, It is achieved by a biaxially oriented film for electrical insulation having a molar ratio expressed by styrene / maleic acid calculated from styrene and maleic anhydride, which is a monomer component of a styrene -maleic acid half ester copolymer, of 1 to 8. The

  Moreover, the biaxially oriented film for electrical insulation of the present invention is a preferred embodiment. The biaxially oriented film further contains an antioxidant, and the content of the antioxidant is 0.001% by weight or more and 5% by weight based on the film weight. %, The polyester contains 50% by weight or more of polyethylene naphthalene dicarboxylate or polyethylene terephthalate based on the weight of the polyester, the styrene is syndiotactic polystyrene, and the film is based on the weight of the film. The polyphenylene ether is contained in the range of 1% by weight to 30% by weight, the polyphenylene ether is an unmodified polyphenylene ether and an acid-modified polyphenylene ether, and the content of the acid-modified polyphenylene ether is 10% based on the film weight. Encompasses be within the scope of the following, it film thickness is 0.5μm or more 20μm or less, it is or motor insulation film capacitors, also those comprising at least any one.

  According to the present invention, the biaxially oriented film for electrical insulation according to the present invention is a film made of a mixture of polyester and polystyrene, but has excellent film-forming properties even when thin, and has good withstand voltage characteristics. It is suitably used for electrical insulation films such as film capacitors.

The present invention will be described in detail below.
<Biaxially oriented film for electrical insulation>
The biaxially oriented film for electrical insulation of the present invention is a biaxially oriented film containing polyester, polystyrene and a styrene-maleic acid half ester copolymer, and the content of the polyester is 10% based on the weight of the film. % To 90% by weight, the polystyrene content is 5% to 85% by weight, and the styrene-maleic acid half ester copolymer content is 0.01% to 10% by weight.
By using a styrene-maleic acid half ester copolymer together with polyester and polystyrene, the film-forming property is excellent even with a thin wall, compared to a polyester film for electrical insulation made of a mixture of conventional polyester and syndiotactic polystyrene. Hereinafter, each resin will be described in detail.

<Polyester>
The biaxially oriented film of the present invention contains polyester within a range of 10% by weight to 90% by weight based on the weight of the film, preferably 20% by weight to 80% by weight, more preferably 30% by weight. It is 70 weight% or less, More preferably, it is 50 weight% or more and 70 weight% or less. Further, as described later as a preferred embodiment of the present invention, when further containing an antioxidant or polyphenylene ether, the content of the polyester is adjusted so that the total amount thereof is 100% by weight within the above range. Good.
When the content of the polyester is less than the lower limit, the content of polystyrene used in combination is relatively increased, resulting in poor film formation stability. On the other hand, if the polyester content exceeds the upper limit, the content of polystyrene used in combination is relatively reduced, and the heat resistance and voltage resistance characteristics cannot be improved up to the target temperature range of the present invention.

  The polyester in the present invention is a polymer obtained by polycondensation of a diol and a dicarboxylic acid, and polyethylene terephthalate and polyethylene naphthalene dicarboxylate are preferably exemplified, and polyethylene naphthalene dicarboxylate is particularly preferable from the viewpoint of withstand voltage characteristics at high temperatures. Polyethylene-2,6-naphthalenedicarboxylate is preferred. When polyethylene naphthalene dicarboxylate is used as the polyester and syndiotactic polystyrene is used as the polystyrene, the long-term heat resistance can be enhanced.

  The polyester in the present invention preferably contains 50% by weight or more of polyethylene naphthalene dicarboxylate or polyethylene terephthalate based on the weight of the polyester, more preferably 70% by weight or more, still more preferably 80% by weight or more, particularly preferably 90%. % By weight or more, particularly preferably 95% by weight or more. In addition to other types of polyesters exemplified as polyesters other than the main component, other known polyester resins may be used.

Further, the polyester in the present invention may be a homopolymer or a copolyester, and in the case of a copolyester, 80% by mole or more of ethylene naphthalene dicarboxylate or ethylene terephthalate is based on all repeating units of the polyester. Preferably, it is 90 mol% or more, and particularly preferably 95 mol% or more. In the case of a copolymerized polyester, the following copolymer components include diol components such as diethylene glycol and neopentyl glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, and the like. It is preferable to use components other than the main component from among dicarboxylic acid components.

  It is preferable to use a titanium compound as a polymerization catalyst during the production of the polyester, and among these, a titanium compound that is soluble in the polyester is preferable. Here, the titanium compound soluble in the polyester means an organic titanium compound, specifically, tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraphenyl titanate or a partial hydrolyzate thereof, titanyl ammonium oxalate, oxalic acid. Examples thereof include compounds exemplified by titanyl potassium and titanium trisacetylacetonate, and products obtained by reacting the above titanium compounds with aromatic polycarboxylic acids such as trimellitic anhydride or anhydrides thereof. Among these, tetrabutyl titanate and titanium trimellitic acid are preferable. Trimellitic acid titanium is a compound obtained by reacting trimellitic anhydride with tetrabutyl titanate.

  The polyester in the present invention is produced by a conventionally known method, for example, a method in which a dicarboxylic acid and a diol and, if necessary, a copolymerization component are esterified, and then a reaction product obtained is polycondensed to form a polyester. be able to. Alternatively, these raw material monomer derivatives may be transesterified, and then the resulting reaction product may be subjected to a polycondensation reaction to obtain a polyester.

<Polystyrene>
The biaxially oriented film of the present invention contains polystyrene in the range of 5 wt% to 85 wt% based on the weight of the film, preferably 20 wt% to 60 wt%, more preferably 20 wt%. It is more than 45 weight%, More preferably, it is 20 weight% or more and 40 weight% or less. Further, when the antioxidant or polyphenylene ether is further included as described later as a preferred embodiment of the present invention, the polystyrene content is adjusted so that the total amount thereof is 100% by weight within the above range. Good.
By including polystyrene in the film, the withstand voltage characteristic of the film can be improved and the dielectric loss tangent can be reduced. By improving the dielectric loss tangent of the film, self-heating by polyester can be further reduced when used for electrical insulation.

Polyester and polystyrene are poorly compatible, and attempts to increase the polystyrene content sometimes resulted in a decrease in handling properties such as film-forming properties in a thin film thickness range. In the present invention, styrene-malein together with polyester and polystyrene. By adding the acid half ester copolymer, a large amount of polystyrene can be added even in a thin film, and the withstand voltage characteristic and the dielectric loss tangent can be further improved.
When the content of polystyrene is less than the lower limit, the effect of improving the withstand voltage characteristic and the dielectric loss tangent characteristic is hardly exhibited, and when the content of polystyrene exceeds the upper limit, a styrene-maleic acid half ester copolymer is added. In the range where the film thickness is thin, the film forming property is lowered.

  Examples of the polystyrene used together with the polyester in the present invention include homopolymers and copolymers composed of styrene derivatives such as styrene and poly (alkylstyrene). In addition, various polystyrenes such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene can be used. Among these, syndiotactic polystyrene is particularly preferable from the viewpoint of heat resistance.

The syndiotactic polystyrene in the present invention is a polystyrene whose stereochemical structure has a syndiotactic structure, and is used as a general term for a polystyrene-based polymer having a syndiotactic structure. In general, tacticity is measured by a nuclear magnetic resonance method ( ¹³ C-NMR method) using isotope carbon, and an abundance ratio of a plurality of consecutive constitutional units, for example, a dyad in the case of two, a triad in the case of three, In the case of five, it can be indicated by a pentad or the like. The syndiotactic polystyrene in the present invention is a polystyrene having a tacticity of 75% or more, preferably 85% or more for dyad, and 30% or more, preferably 50% or more for pentad.

  As such syndiotactic polystyrene, polystyrene having a syndiotactic structure, poly (alkylstyrene), poly (halogenated styrene), poly (alkoxystyrene), poly (phenylstyrene), poly (vinylstyrene), poly (vinylnaphthalene) Or a polymer in which a part of these benzene rings is hydrogenated, a mixture thereof, or a copolymer containing these structural units.

Examples of poly (alkyl styrene) include poly (methyl styrene), poly (ethyl styrene), poly (propyl styrene), and poly (butyl styrene).
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, polystyrene having a syndiotactic structure, poly (p-methylstyrene), poly (m-methylstyrene) or poly (p-tertiarybutylstyrene) is preferably exemplified.
The copolymerization component of the copolymerized syndiotactic polystyrene is preferably 0.1 mol% or more and 10 mol% or less based on all repeating units. The lower limit value of the copolymer component is more preferably 1 mol%, still more preferably 3 mol%, particularly preferably 5 mol%.

  When syndiotactic polystyrene is used, its molecular weight and molecular weight distribution are not particularly limited, but those having a weight average molecular weight of 10,000 or more are preferred, and those having 50,000 or more are more preferred. When the weight average molecular weight is less than 10,000, the effect of improving the withstand voltage characteristics may not be sufficient, and the film forming property may be deteriorated.

<Compatibilizer>
The biaxially oriented film for electrical insulation of the present invention contains a certain amount of polystyrene together with polyester, and uses a styrene-maleic acid half ester copolymer as a compatibilizing agent in order to obtain excellent film forming properties even with a thin film. There is a feature in the point.

The styrene-maleic acid half ester copolymer in the present invention is obtained by adding an alcohol to a controlled molar ratio copolymer obtained by using a predetermined amount of styrene and maleic anhydride as monomer components, and esterifying the copolymer. The resulting maleic acid-derived copolymer component has a chemical structure of monoester and monocarboxylic acid groups.
In the present invention, the molar ratio represented by styrene / maleic acid of the styrene-maleic acid half ester copolymer is calculated based on the molecular weight of styrene and maleic anhydride as monomer components, and is represented by styrene / maleic acid. The molar ratio is 1 or more and 8 or less, preferably 1 or more and 3 or less, more preferably 1 or more and 2 or less.
The present inventors are examining various agents as a compatibilizing agent for polyester and polystyrene, and in studying low molecular weight compounds or thermoplastic resins having a solubility parameter (SP value) intermediate between polyester and polystyrene. This time, the copolymer component containing maleic anhydride as a monomer component has a chemical structure of a monoester and a monocarboxylic acid group, and the molar ratio represented by styrene / maleic acid is controlled within a specific range. It has been found that the dispersibility of the island phase can be greatly increased, a large amount of island phase components can be added even in a thin film, and the stretchability is greatly improved.

  The content of the styrene-maleic acid half ester copolymer is in the range of 0.01% by weight to 10% by weight based on the film weight, and the lower limit of the content of the styrene-maleic acid half ester copolymer. Is more preferably 0.1% by weight, still more preferably 0.5% by weight. The upper limit of the content of the styrene-maleic acid half ester copolymer is preferably 5.0% by weight, more preferably 3.0% by weight.

<Polyphenylene ether>
The biaxially oriented film for electrical insulation of the present invention can further contain polyphenylene ether in the range of 1 wt% to 30 wt% based on the film weight.
A known compound can be used as such polyphenylene ether. Specific examples of unmodified polyphenylene ether among polyphenylene ethers include poly (2,3-dimethyl-6-ethyl-1,4-phenylene ether), poly (2- Methyl-6-chloromethyl-1,4-phenylene ether), poly (2-methyl-6-hydroxyethyl-1,4-phenylene ether), poly (2-methyl-6-n-butyl-1,4- Phenylene ether), poly (2-ethyl-6-isopropyl-1,4-phenylene ether), poly (2-ethyl-6-n-propyl-1,4-phenylene ether), poly (2,3,6- Trimethyl-1,4-phenylene ether), poly [2- (4′-methylphenyl) -1,4-phenylene ether], poly (2-bromo-6-phenyl-1,4-phenylene ether), poly (2-methyl-6-phenyl-1,4-phenylene ether), poly (2-phenyl-1,4-phenylene ether), poly (2-chloro-1,4-phenylene ether), poly (2-methyl-1,4-phenylene ether), poly (2-chloro-6-ethyl-1,4-phenylene ether), poly (2-chloro -6-bromo-1,4-phenylene ether), poly (2,6-di-n-propyl-1,4-phenylene ether), poly (2-methyl-6-isopropyl-1,4-phenylene ether) , Poly (2-chloro-6-methyl-1,4-phenylene ether), poly (2-methyl-6-ethyl-1,4-phenylene ether), poly (2,6-dibromo-1,4-phenylene ether) Enylene ether), poly (2,6-dichloro-1,4-phenylene ether), poly (2,6-diethyl-1,4-phenylene ether), poly (2,6-dimethyl-1,4-phenylene) Ether).
Among polyphenylene ethers, specific examples of the acid-modified polyphenylene ether include those in which at least a part of the substituents of the polyphenylene ether are substituted with carboxylic acid, fumaric acid, maleic anhydride and the like.

When the biaxially oriented film of the present invention further contains polyphenylene ether, the glass transition temperature of the film can be increased. For example, when a capacitor is produced, the blocking resistance is improved.
Moreover, the compatibility between polyester and polystyrene can be further increased by using acid-modified polyphenylene ether as polyphenylene ether within a range of 10% by weight or less, or by using acid-modified polyphenylene ether in combination with unmodified polyphenylene ether. Further, the film can be made thinner.

The content of polyphenylene ether is preferably 2% by weight or more and 25% by weight or less, more preferably 3% by weight or more and 20% by weight or less. When only unmodified polyphenylene ether is used as the polyphenylene ether, the content is the same as described above.
Moreover, when using polyphenylene ether in this invention, it is preferable to use together unmodified polyphenylene ether and acid-modified polyphenylene ether, and it is preferable to adjust so that the total amount may become above-mentioned content. In such a case, the content of the acid-modified polyphenylene ether is preferably within a range of 10% by weight or less based on the film weight, more preferably 2 to 7% by weight, and further preferably 2 to 5% by weight.

<Antioxidant>
The biaxially oriented film for electrical insulation of the present invention preferably contains an antioxidant in addition to polyester, polystyrene and styrene-maleic acid half ester copolymer. Further, by containing an antioxidant, high withstand voltage characteristics can be obtained at both room temperature and a high temperature range of 130 to 160 ° C.

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.
The antioxidant in the present invention is particularly preferably a primary antioxidant and particularly preferably a phenolic antioxidant from the viewpoint that it is excellent in corrosion resistance and can further enhance the effect of improving the dielectric breakdown voltage.
Moreover, it is preferable that the antioxidant in this invention is 250 degreeC or more in the thermal decomposition temperature. When the thermal decomposition temperature is too low, the antioxidant itself is thermally decomposed during melt extrusion, which may contaminate the film forming process and may cause the film to be colored. 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 higher the thermal decomposition temperature of the antioxidant is preferable, but the upper limit of the thermal decomposition temperature may be about 500 ° C. in consideration of the film forming temperature, the post-processing temperature, the use temperature, and the like.

  The melting point of the antioxidant in the present invention is preferably 90 ° C. or higher. When 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. Thereby, the supply of the polymer becomes unstable, and the thickness unevenness of the film may be reduced. 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 to the polymer tends to decrease. Thereby, the addition effect of antioxidant may be expressed 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.

  Specific examples of phenolic antioxidants include pentaerythritol tetrakis [3- (3,5-di-t-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 Preferred examples include -diylbis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionamide] (manufactured by Ciba Specialty Chemicals: trade name IRGANOX 1098).

The content of the antioxidant used in the biaxially oriented film for electrical insulation of the present invention is preferably 0.001 wt% or more and 5 wt% or less, more preferably 0.1 wt% based on the weight of the film. % To 2% by weight, more preferably 0.5% to 1.5% by weight.
When the content of the antioxidant is less than the lower limit, the further improvement of the withstand voltage characteristics may not be sufficient. On the other hand, even if an antioxidant is added in excess of the upper limit, further withstand voltage characteristics may not be obtained, and film formation stability may be lowered and process contamination may occur.

<Film thickness>
The film thickness of the biaxially oriented film for electrical insulation of the present invention is preferably from 0.5 μm to 300 μm, more preferably from 1 μm to 50 μm, still more preferably from 1 μm to 10 μm, particularly preferably from 2 μm to 5 μm. is there. The film thickness can be appropriately selected according to various uses for which electrical insulation characteristics are required. For example, when used for a film capacitor, the thinner film thickness is preferable.

<Film-forming properties>
The biaxially oriented film for electrical insulation of the present invention is a blend system of incompatible polymers with each other, and when the volume fraction of polyester is large, a sea-island structure in which polyester is a continuous phase and polystyrene is an island phase in the film When the volume fraction of polystyrene is large, a sea-island structure is formed in the film with polystyrene as the continuous phase and polyester as the island phase.
If the island-phase resin is not sufficiently dispersed in the sea-phase resin in the case of such a sea-island structure, fracture is likely to occur from the interface of the sea-island phase during biaxial stretching, and film-forming properties are reduced. The biaxially oriented film for electrical insulation of the present invention can sufficiently disperse the island phase in the sea phase by using a styrene-maleic acid half ester copolymer as a compatibilizing agent. The film property can be improved as compared with the prior art. The particle size of the island phase is preferably 5 μm or less, more preferably 2 μm or less when measured with a cross section of the unstretched film.

<Withstand voltage characteristics>
When the biaxially oriented film for electrical insulation of the present invention contains the polyester, polystyrene, and styrene-maleic acid half ester copolymer, a higher withstand voltage characteristic than that of a single polyester can be obtained.
Furthermore, the biaxially oriented film for electrical insulation of the present invention can have high withstand voltage characteristics at both room temperature and a high temperature range of 130 to 160 ° C. by containing an antioxidant together with the above composition.
Specifically, the biaxially oriented film for electrical insulation of the present invention preferably has a dielectric breakdown voltage of 500 V / μm or more at 25 ° C., more preferably 550 V / μm or more, particularly preferably 600 V / μm or more. It is. A higher dielectric breakdown voltage of the film at 25 ° C. is preferable because the reliability when used as these electrical insulating materials is high, but the upper limit is 800 V / μm at most due to the nature of the resin material. 750 V / μm or less.
As a specific example of the withstand voltage characteristics in the high temperature range, the dielectric breakdown voltage of the film at 150 ° C. is preferably 450 V / μm or more, more preferably 500 V / μm or more, and particularly preferably 550 V / μm or more. is there. The upper limit of the dielectric breakdown voltage of the film at 150 ° C. is at most 750 V / μm and further 700 V / μm or less due to the characteristics of each resin.

<Heat resistance>
The biaxially oriented film for electrical insulation of the present invention has improved long-term heat resistance in a high temperature range as compared with conventional polyester films. For example, IEC60216 is known as a heat resistance index for maintaining a dielectric breakdown voltage for a long time at a high temperature. It is preferable that the heat resistance in the range of 130 to 160 ° C. is obtained with respect to the heat resistant temperature based on the temperature index. Such heat resistance is achieved by using syndiotactic polystyrene as the polystyrene used with the polyester.
Excellent long-term heat resistance in the high-temperature region as well as the above-mentioned withstand voltage characteristics, so it can be used for applications including high-temperature and high-voltage use that were difficult to apply with conventional polyester resins. It can be used as a film capacitor for environmentally friendly vehicles such as cars.

<Dielectric properties>
In the biaxially oriented film for electrical insulation of the present invention, the dielectric loss tangent (Tan δ) of the film at 150 ° C. is preferably 0.010 or less.
Further, the biaxially oriented film for electrical insulation of the present invention contains polystyrene, so that the effect of improving the dielectric constant and dielectric loss tangent is exhibited as compared with polyester alone. Specifically, the dielectric constant at 25 ° C. is 2. It is preferably 5 or more and less than 3.0, and more preferably 2.6 or more and 2.9 or less. Also, good dielectric properties at high temperatures are achieved by using syndiotactic polystyrene among polystyrene, and the film dielectric loss tangent at 150 ° C. is preferably 0.006 or less.
By having such dielectric properties, it is excellent in suppressing self-heating, and therefore can be used as an insulating film for a film capacitor that is required to suppress self-heating at high temperatures.

<Slipperiness>
Since the biaxially oriented film for electrical insulation of the present invention is composed of the above-mentioned composition, the slipperiness of the thin film can be enhanced without containing a lubricant in the film. Specifically, the biaxially oriented film for electrical insulation of the present invention has a coefficient of static friction in the range of 0.60 to 1.0 even without containing a lubricant, and more preferably 0.60 to 0.00. 90. Moreover, when a lubricant is not contained in the film, there is also an effect that a decrease in withstand voltage characteristics in a high temperature region is less than when a lubricant is added.

  Further, the biaxially oriented film for electrical insulation of the present invention may contain particles, and when added, spherical crosslinked polymer resin particles having an average particle size of 0.1 μm to 3.0 μm based on the weight of the film. It is preferable to contain 0.01 wt% or more and 1.0 wt% or less, more preferably 0.05 wt% or more and 0.5 wt% or less. On the other hand, in the present invention, due to the characteristics of the composition, since it has good slipperiness even without including a lubricant, the effect of further improving slipperiness by adding particles tends to be small.

<Coating layer>
The biaxially oriented film for electrical insulation of the present invention may further be provided with a coating layer on one side or both sides of the film. The coating layer preferably contains 1 to 50% by weight of at least one selected from the group consisting of wax, silicone compound and fluorine compound based on the weight of the coating layer.

When the coating layer contains at least one of these compounds, the adhesive strength with the metal layer laminated via the coating layer is weakened, and a short circuit occurs when a breakdown occurs in a defective portion of the film. The nearby metal layer is easily scattered by the electric current, and self-recovery (self-healing) superior to that of the prior art can be obtained.
On the other hand, when the coating layer does not contain these compounds, since the coating layer does not have sufficient peelability, the adhesive strength with the metal layer cannot be weakened, and a dielectric breakdown occurs in the defective part of the film, resulting in a short circuit. When the state is reached, the metal layer in the vicinity thereof cannot be easily scattered, and sufficient self-recovering property may not be exhibited.

<Film manufacturing method>
The biaxially oriented film of the present invention can be formed using a known sequential biaxial stretching method or simultaneous biaxial stretching method, and the method is not particularly limited.
In addition, when using an antioxidant, the addition timing may be any of the polymer polymerization stage, the master chip manufacturing stage, the resin composition blending stage, and the resin composition charging stage. Well, these methods may be combined.

  As a film forming method using a sequential stretching method, a resin composition is supplied to an extruder, formed into a sheet form from a T die, and cooled and solidified with a cooling drum having a surface temperature of 10 to 60 ° C., for example, by roll heating or infrared heating. Heat and stretch in the longitudinal direction to obtain a longitudinally stretched film. The longitudinal stretching temperature is preferably higher than the glass transition point (Tg) of the composition, more preferably 20 to 40 ° C. higher than Tg. The longitudinal draw ratio may be appropriately adjusted according to the requirements of the intended use, but is preferably 2.5 times or more and 5.0 times or less, more preferably 3.0 times or more and 4.5 times or less.

Subsequently, transverse stretching is performed, and the transverse stretching treatment starts at a temperature 20 ° C. or more higher than the glass transition point (Tg) of the composition and is performed while raising the temperature to a temperature lower by 120 to 30 ° C. than the melting point (Tm) of the polyester. . The maximum transverse stretching temperature is preferably a temperature lower by (100 to 40) ° C. than Tm.
The transverse draw ratio may be appropriately adjusted according to the requirements of the application to be used, but is preferably 2.5 times or more and 5.0 times or less, more preferably 3.0 times or more and 4.5 times or less.

Thereafter, heat-fixing and heat-relaxation treatments are sequentially performed as necessary to obtain a biaxially oriented film. Such treatment is performed while the film is running.
When providing a coating layer further, the method of apply | coating in a film extending process is mentioned. In this case, the coating solution is preferably used in the form of an aqueous coating solution. The solid content concentration of the aqueous coating solution is usually 20% by weight or less, preferably 1 to 10% by weight.

<Application>
Since the biaxially oriented film of the present invention has excellent withstand voltage characteristics and heat resistance, it can be suitably used as a film for electrical insulation, and specifically, film capacitors, wedge materials, slot materials, etc. It can be used as a base film for electrical insulation applications such as motor insulation members, flexible printed circuit boards, and flat cables.

Among these electrical insulation applications, for example, a film capacitor is obtained by winding or laminating a laminated film in which a metal layer is laminated on one side or both sides of the biaxially oriented film of the present invention.
The flexible printed circuit board is obtained by laminating a metal layer made of copper foil or conductive paste on at least one surface of the biaxially oriented film of the present invention, and forming a fine circuit pattern on the metal layer.
Motor insulating members such as wedge materials and slot materials can be obtained by subjecting the biaxially oriented film of the present invention to deformation processing using a punch with an R.

  Among such electrical insulation applications, the biaxially oriented film of the present invention has excellent withstand voltage characteristics and heat resistance up to a higher temperature range than conventional ones. It is suitably used as an insulating film for film capacitors for environmentally friendly vehicles such as cars.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean weight% and weight%, respectively.

(1) Composition analysis
Measurement was performed using ¹ H-NMR or ¹³ C-NMR.

(2) Content of Antioxidant 20 mg of the obtained film sample was dissolved in a mixed solvent of deuterated trifluoroacetic acid: deuterated chloroform = 1: 1, and measured with 256 times using a 600 M ¹ H-NMR apparatus. Then, the content of the antioxidant was determined.
In the measurement, for example, in the case of N, N′-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide], tert-butyl-4- The peak intensity due to hydrogen due to the hydrocarbon chain between the hydroxyphenyl and the amide bond was measured. Based on the NMR measurement results, when the stabilizer reacted with the resin, the content converted to the original stabilizer was determined. In addition, if a polymer and an unreacted stabilizer are mixed with a stabilizer that has reacted with a polymer and a plurality of peak positions are detected even when focusing on the same hydrocarbon chain, the content is calculated from the total value of them. Asked.
Similarly, for other phenolic antioxidants, the peak intensity caused by the hydrogen of interest was measured, and the content was determined from the total value of the antioxidants contained in the film while confirming the reaction state with the resin. .

(3) Particle content After dissolving the resin and selecting a solvent that does not dissolve the particles and dissolving the sample, the particles were centrifuged from the resin and measured from the ratio (wt%) of the particles to the sample weight.

(4) Film thickness Film thickness was measured at 30 g of needle pressure using an electronic micrometer (trade name “K-312A type” manufactured by Anritsu Co., Ltd.).

(5) Dielectric breakdown voltage i) Dielectric breakdown voltage at 20 ° C. Using the obtained biaxially oriented film, in accordance with the plate electrode method in the DC test described in JIS standard C2151, ITS-manufactured by Tokyo Seiden Co., Ltd. Using 6003, measurement was performed at a boosting rate of 0.1 kV / sec, and the voltage at the time of breakdown was measured as a dielectric breakdown voltage.
Measurement was performed at n = 50, and the average value was taken as the dielectric breakdown voltage. The measurement was performed at room temperature of 20 ° C.

ii) Dielectric breakdown voltage at 150 ° C. With respect to the dielectric breakdown voltage at 150 ° C., using the obtained film sample, the specimen size is 10 cm × 10 cm, electrode shape; spherical shape of upper electrode Φ20 mm, lower electrode 100 mm × 100 mm × 100 μm thickness (made of stainless steel), pressurization speed: DC 0.1 kV / sec, test atmosphere in silicon oil (JIS c2320 insulating oil compatible product), test apparatus: withstand voltage tester TOS 5101 (manufactured by Kikusui Electronics Co., Ltd.) Then, n = 3 was measured at a temperature of 150 ° C., and the average value was obtained.

(6) Heat resistance Using the obtained film, the relationship between the half-life time of the dielectric breakdown voltage and the temperature was Arrhenius plotted according to the temperature index of IEC60216, and the temperature that could withstand 20000 hours was obtained.

(7) Dissipation factor (tan δ)
Using the obtained film sample, aluminum deposition was performed in accordance with JIS C2151, set in a thermostatic bath (Ando Electric Co., Ltd., T0-9 type), 10 ° C. pitch and LCR meter in the range of 30-200 ° C. ( HEWLETT PACKAD 4284A) was used to determine the dielectric loss tangent (tan δ) at 1 KHz and 150 ° C. Moreover, the dielectric constant at 25 ° C. was determined based on the measurement results.

(8) Film-forming property The composition was supplied to an extruder, and the film-forming property in the film-forming step of the film was evaluated according to the following criteria.
◯: There is no problem of cutting or the like when forming a film, and the film can be continuously formed for 12 hours or more by setting the draw ratio to 10.5 times or more in terms of area magnification.
X: Inferior to continuous film-forming property, and when the draw ratio is 10.5 times or more in terms of area magnification, film formation can be performed only in a very short time.

(9) Winding Form of Film Roll The winding form after winding the film on a roll with a width of 700 mm and a length of 10,000 m was observed at the time of film formation and slitting and evaluated according to the following criteria.
○: There is no surface wrinkle, winding deviation, etc. by visual observation during film formation and slitting, and the winding shape is good.
X: Wrinkles on the surface, winding deviation, etc. were confirmed by visual observation at the time of film formation and slitting, and the winding shape was poor.

(10) Coefficient of static friction A glass plate fixed on the lower side of two films overlaid with the obtained film is placed, and the film on the lower side of the laminated film (the film in contact with the glass plate) is placed on a low-speed roll. Taking up (about 10 cm / min), a detector is fixed to one end of the upper film (opposite to the take-up direction of the lower film) to detect the tensile force at the start of the film / film. The thread used at that time has a weight of 0.1 kg and a lower area of 100 cm ² .
The static friction coefficient (μs) was obtained from the following equation.
μs = (Tensile force kg at start) / (Load 0.1 kg)
When the static friction coefficient of the film exceeds 1.0, the slipperiness is extremely lowered, and wrinkles and defects are likely to occur when the film is wound into a roll.

(11) Surface roughness Measured using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022) at a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ). The center plane average roughness (Ra) was determined by the surface analysis software MetroPro built in the roughness meter, and this was defined as the surface roughness (Ra). The measurement was performed 10 times while changing the measurement location, and the average value thereof was defined as the center plane average roughness (Ra).

(12) Average dispersed particle size of island phase An unstretched film was cut into a film length direction of 2 mm and a width direction of 2 cm, fixed to an embedded capsule, and then embedded with an epoxy resin (Epomount manufactured by Refine Tech Co., Ltd.). The embedded sample was cut perpendicularly to the film width direction with a microtome (“ULTRACUT” (registered trademark) UCT manufactured by Leica Microsystems) to form a thin film slice having a thickness of 5 nm.
The cross section of the unstretched film was observed at a magnification of 10,000 using a transmission electron microscope (S-4300, manufactured by Hitachi High-Technologies Corporation), and the equivalent circle diameter was calculated from the area of the island phase. The island phase was measured at 20 points, and the average dispersed particle size of the island phase was determined from the average value.

(13) Maximum possible draw ratio The maximum draw ratio (area ratio) that allows continuous film formation for 12 hours or more.

[Example 1]
2,6-naphthalenedicarboxylic acid dimethyl ester (hereinafter sometimes referred to as NDC) 100 parts, ethylene glycol (hereinafter sometimes referred to as EG) 60 parts and titanium compound (trimellitic acid titanium is the amount of titanium element) Was added to a SUS container and subjected to a transesterification reaction while raising the temperature from 140 ° C. to 240 ° C., then the reaction mixture was transferred to a polymerization reactor, and the temperature was raised to 295 ° C. The polycondensation reaction was performed under the following high vacuum to obtain polyethylene-2,6-naphthalenedicarboxylate having an intrinsic viscosity of 0.60 dl / g.
Obtained polyethylene-2,6-naphthalene dicarboxylate, syndiotactic polystyrene (manufactured by Idemitsu Kosan Co., Ltd., XAREC, 60ZC (trade name)), unmodified polyphenylene ether (manufactured by Mitsubishi Engineering Plastics Co., Ltd., PX-100L) (Trade name)), styrene-maleic acid half ester copolymer (manufactured by CRAY VALLEY, SMA 1440 trade name), styrene / maleic acid = 1 (mole / mole)), and phenolic antioxidant “Irganox (registered trademark) ) 1098 "(N, N'-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamide]) (mp 156-161 ° C), and as particles Using silicone resin particles, the composition ratios shown in Table 1 are obtained. Prepare the fat composition, after 6 hours drying at 170 ° C., was supplied to an extruder heated to 300 ° C..

After melt-kneading with an extruder, the unstretched film formed into a sheet form from a 290 ° C. die and cooled and solidified with a cooling roll is guided to a roll group heated to 140 ° C., and stretched in the longitudinal direction (longitudinal direction). The film is cooled with a roll group of 60 ° C., and then guided to a tenter while holding both ends of the longitudinally stretched film with clips, and a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to a maximum transverse stretching temperature of 150 ° C. ). Then, after heat fixing in a tenter at 210 ° C. for 5 seconds and further performing thermal relaxation at 200 ° C. in the lateral direction by 1%, the film is uniformly cooled and cooled to room temperature to form a biaxially oriented film having a thickness of 5 μm. Obtained. The properties of the obtained film are shown in Table 2. Table 2 shows the maximum draw ratio (area ratio) obtained from the draw ratio in the longitudinal direction and the draw ratio in the transverse direction and capable of continuous film formation for 12 hours or more.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example had a heat resistance as high as 145 ° C. even though it was a polyester-based film. Moreover, film-forming property was also stable compared with the comparative example which does not contain a compatibilizing agent, and the comparative example using another compatibilizing agent.

[Example 2]
A biaxially oriented film having a thickness of 5 μm was obtained in the same manner as in Example 1 except that the contents of polyethylene naphthalene dicarboxylate, syndiotactic polystyrene, and unmodified polyphenylene ether were changed to the amounts shown in Table 1. The properties of the obtained film are shown in Table 2.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example obtained heat resistance as high as 145 ° C. while being a film mainly composed of polyethylene naphthalene dicarboxylate. Moreover, the film forming property was also stable.

[Example 3]
The content of polyethylene naphthalene dicarboxylate and unmodified polyphenylene ether was changed to the amount shown in Table 1, and fumaric acid-modified polyphenylene ether (CX-1 (trade name) manufactured by Idemitsu Kosan Co., Ltd.) was further used as acid-modified polyphenylene ether. A biaxially oriented film having a thickness of 2 μm was obtained in the same manner as in Example 1 except that the amount shown in Table 1 was used. The properties of the obtained film are shown in Table 2.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example had a heat resistance as high as 150 ° C. despite being a film mainly composed of polyethylene naphthalene dicarboxylate. Moreover, the film forming property was also stable.

[Example 4]
A biaxially oriented film having a thickness of 2 μm was obtained in the same manner as in Example 3 except that the contents of polyethylene naphthalene dicarboxylate, syndiotactic polystyrene, and unmodified polyphenylene ether were changed to the amounts shown in Table 1. The properties of the obtained film are shown in Table 2.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example had a heat resistance as high as 150 ° C. despite being a film mainly composed of polyethylene naphthalene dicarboxylate. In addition, the dielectric properties were improved and the film-forming property was stable.

[Example 5]
Other than changing the type of styrene-maleic acid half-ester copolymer to one having a different styrene / maleic acid molar ratio (manufactured by CRAY VALLEY, SMA 2625 (trade name), styrene / maleic acid = 2 (mole / mole)) Performed the same operation as Example 1 to obtain a biaxially oriented film having a thickness of 5 μm. The properties of the obtained film are shown in Table 2.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example obtained heat resistance as high as 145 ° C. while being a film mainly composed of polyethylene naphthalene dicarboxylate. Compared with Example 1, the dispersed particle size was large, and compared with Example 1, the film-forming property was slightly reduced, but the film-forming property evaluation standard ○ was satisfied.

[Example 6]
The contents of polyethylene naphthalene dicarboxylate and syndiotactic polystyrene were changed to the amounts shown in Table 1, and fumaric acid-modified polyphenylene ether (CX-1 manufactured by Idemitsu Kosan Co., Ltd.) was used as acid-modified polyphenylene ether instead of unmodified polyphenylene ether. (Product name) was used in the same manner as in Example 1 except that the amount shown in Table 1 was used to obtain a biaxially oriented film having a thickness of 2 μm. The properties of the obtained film are shown in Table 2.
The film of this example had a high heat resistance as high as 140 ° C. while being a film mainly composed of polyethylene naphthalene dicarboxylate, in addition to having a high dielectric breakdown voltage at room temperature and in a high temperature region of 150 ° C. Moreover, the film forming property was also stable.

[Example 7]
A biaxially oriented film having a thickness of 2 μm was obtained by performing the same operation as in Example 3 except that the content of polyethylene naphthalene dicarboxylate was changed to the amount shown in Table 1 without using particles. The properties of the obtained film are shown in Table 2.
In addition to the high dielectric breakdown voltage in the high temperature region of room temperature and 150 ° C., the film of this example had a heat resistance as high as 150 ° C. despite being a film mainly composed of polyethylene naphthalene dicarboxylate. In addition, the dielectric properties were improved and the film-forming property was stable. Compared to the case of containing particles, an effect of particularly high dielectric breakdown strength at 150 ° C. was obtained.

[Comparative Example 1]
As a compatibilizing agent, instead of a styrene-maleic acid half ester copolymer, a styrene-maleic anhydride copolymer in which a copolymer component derived from maleic anhydride is not added with alcohol (manufactured by CRAY VALLEY, SMA1000 (trade name)) , Styrene / maleic acid ratio = 1 (mole / mole) was used, and the same operation as in Example 1 was carried out. The film breakage occurred frequently.

[Comparative Example 2]
Without using a styrene-maleic acid half ester copolymer, fumaric acid-modified polyphenylene ether (made by Idemitsu Kosan Co., Ltd., CX-1 (trade name)) was used as the acid-modified polyphenylene ether in the amount shown in Table 1, and accordingly polyethylene naphthalene Except that the content of dicarboxylate was changed to the amount shown in Table 1, the same operation as in Example 1 was performed. In the area magnification, which is the film forming property evaluation method of the present invention, the film forming property was poor. Film breakage occurred frequently.

[Comparative Example 3]
The same operation as in Example 1 was performed except that the content of the styrene-maleic acid half ester copolymer was changed to 15% by weight and the content of polyethylene naphthalene dicarboxylate was changed to the amount shown in Table 1 accordingly. As a result, film formation could not be performed due to a decrease in the molecular weight of the polymer.

[Comparative Example 4]
Example 1 except that the content of polyethylene naphthalenecarboxylate and syndiotactic polystyrene was changed to the amounts shown in Table 1 without using unmodified polyphenylene ether, styrene-maleic acid half ester copolymer, and antioxidant. When the same operation was performed, the film forming property was poor at the area magnification which is the film forming property evaluation method of the present invention, and film breakage occurred frequently.

  The biaxially oriented film for electrical insulation of the present invention is a film made of a mixture of polyester and polystyrene, but is thin and excellent in film-forming properties and has good withstand voltage characteristics. It is suitably used for insulating films.

Claims (8)

A biaxially oriented film comprising polyester, polystyrene and styrene-maleic acid half ester copolymer, wherein the polyester content is 10 based on the weight of the film
% By weight to 90% by weight, the polystyrene content is 5% by weight to 85% by weight, and the styrene-maleic acid half ester copolymer content is 0.01% by weight to 10% by weight, A molar ratio represented by styrene / maleic acid calculated from styrene and maleic anhydride, which is a monomer component of the styrene -maleic acid half ester copolymer, is 1 or more and 8 or less. Axially oriented film. The biaxially oriented film for electrical insulation according to claim 1, wherein the biaxially oriented film further comprises an antioxidant, and the content of the antioxidant is 0.001 wt% or more and 5 wt% or less based on the film weight. the film. The polyester comprises 50% by weight or more of polyethylene naphthalene dicarboxylate or polyethylene terephthalate based on the weight of the polyester.
A biaxially oriented film for electrical insulation as described in 1. The biaxially oriented film for electrical insulation according to any one of claims 1 to 3, wherein the styrene is syndiotactic polystyrene. The biaxially oriented film for electrical insulation according to any one of claims 1 to 4, wherein the film contains polyphenylene ether in a range of 1 wt% to 30 wt% based on the film weight. 6. The electrical insulating two-component film according to claim 5, wherein the polyphenylene ether is an unmodified polyphenylene ether and an acid-modified polyphenylene ether, and the content of the acid-modified polyphenylene ether is within a range of 10% by weight or less based on the film weight. Axially oriented film. The biaxially oriented film for electrical insulation according to claim 1, wherein the film thickness is 0.5 μm or more and 20 μm or less. The biaxially oriented film for electrical insulation according to any one of claims 1 to 7, which is used for film capacitors or motor insulation.