JP3847550B2 - Polyester film for capacitors - Google Patents

Description

【００８０】
【発明の効果】
本発明によれば、ポリエチレン−２，６−ナフタレンジカルボキシレートを主たる成分としてなる絶縁特性に優れ、加工性特に熱プレス時の特性低下のないコンデンサ用誘電体に好適なフィルムを提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester film for capacitors.
[0002]
[Prior art]
Capacitors are required to be smaller and have larger capacities along with recent miniaturization of electric and electronic devices, and also to improve insulation characteristics as the operating voltage range increases. In response to such demands, in a film capacitor, the film thickness as a dielectric is reduced (the capacitance per unit volume of the dielectric (film) is inversely proportional to the square of the film thickness, and the dielectric constant of the dielectric is And reduction of pinholes existing in the film have been studied.
[0003]
As described above, although it is necessary to reduce the film thickness of the dielectric film capacitor, workability in the capacitor processing process associated with the film thickness reduction (metal deposition as an electrode on the film, slit, element winding, etc.) In order to avoid this deterioration, Japanese Patent Application Laid-Open No. 10-294237 proposes to add specific inert fine particles as a lubricant to the polyethylene-2,6-naphthalenedicarboxylate film.
[0004]
[Problems to be solved by the invention]
However, although it has been possible to achieve both excellent film workability and excellent workability in the capacitor processing process, there may be cases where the insulation characteristics are poor due to additives (especially lubricants) contained in the film. It was still insufficient as a film. In addition, there is a tendency to increase the temperature and pressure of the hot press after winding the capacitor element, and the insulation resistance and withstand voltage as the element may be lower than those of the film alone.
[0005]
The present invention solves the above-mentioned problems of the prior art, and is suitable for a biaxially stretched film excellent in insulating properties and workability mainly comprising polyethylene-2,6-naphthalenedicarboxylate, particularly a dielectric film capacitor. The purpose is to obtain a film.
[0006]
[Means for Solving the Problems]
A biaxially oriented film mainly composed of polyethylene-2,6-naphthalenedicarboxylate, The film is manufactured by the simultaneous biaxial stretching method and subjected to the longitudinal relaxation treatment, Based on the length LMD (t) in the longitudinal direction (MD) of the film at the temperature t ° C., the thermal strain rate RMD (T) in the longitudinal direction of the film at the temperature T ° C.
RMD (T) = {[LMD (T) -LMD (35)] / LMD (35)} × 100 (%)
When the thermal strain rate RMD (150) in the longitudinal direction of the film at a temperature of 150 ° C. is defined as -1. 0 % ≦ RMD (150) ≦ 0.0%, The film thickness is 0.3 to 10 μm, The number of fly specs with an average diameter exceeding 60 μm is 20 / m ² It is characterized by the following.
[0007]
[Polyethylene-2,6-naphthalenedicarboxylate]
The conventional polyester film for capacitors was a polyethylene terephthalate film. In this polyethylene terephthalate film, the dielectric loss tangent increases in a temperature range of 80 ° C. or higher, and there is a possibility that self-heating occurs due to dielectric loss and thermal runaway occurs. For this reason, the upper limit of the use temperature as a capacitor | condenser is restrained to about 80 degreeC.
[0008]
On the other hand, the polyester film for capacitors in the present invention contains polyethylene-2,6-naphthalenedicarboxylate as a main component. In polyethylene-2,6-naphthalenedicarboxylate, the increase in dielectric loss tangent is from around 120 ° C. Therefore, the upper limit of the use temperature is about 120 ° C. Therefore, polyethylene-2,6-naphthalenedicarboxylate film capacitors are used at high temperatures. In addition, the dielectric constant of polyethylene-2,6-naphthalenedicarboxylate is slightly small (2.9: 3.1), which seems disadvantageous for miniaturization at first glance, but the potential for reducing the thickness is high. However, polyethylene-2,6-naphthalenedicarboxylate is advantageous. The present invention is mainly directed to capacitors for such applications.
[0009]
In the polyethylene-2,6-naphthalene dicarboxylate, the main dicarboxylic acid component is naphthalene dicarboxylic acid, and the main glycol component is ethylene glycol. Here, examples of naphthalenedicarboxylic acid include -2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and the like. Among these, -2,6- Naphthalenedicarboxylic acid is preferred.
[0010]
In the present invention, “having polyethylene-2,6-naphthalenedicarboxylate as a main component” means that at least 90 mol% of all repeating units are ethylene-2,6-naphthalene in the constituent components of the polymer that is a component of the film. Means a carboxylate unit. More preferably, it is 95 mol%.
[0011]
The constituent component of the polymer which is a component of the film of the present invention may be a copolymer or a mixture mainly composed of polyethylene-2,6-naphthalene dicarboxylate, and ethylene-2,6-naphthalene dicarboxylate is completely repeated. It is 90 mol% or more of the unit, and it is sufficient that the original properties of the polyethylene-2,6-naphthalene dicarboxylate film are not extremely lost and the insulating properties, mechanical properties, and thermal dimensional stability can be ensured.
[0012]
In the case of a copolymer, a compound having two ester-forming functional groups in the molecule can be used as a copolymerization component constituting the copolymer other than the main component ethylene-2,6-naphthalenedicarboxylate, Examples of such compounds include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindandicarboxylic acid, 2, 7-naphthalenedicarboxylic acid, tetralin dicarboxylic acid, decalin dicarboxylic acid, dicarboxylic acid such as diphenyl ether dicarboxylic acid; oxycarboxylic acid such as p-oxybenzoic acid, p-oxyethoxybenzoic acid; or propylene glycol, trimethylene glycol, Te Preferably used are dihydric alcohols such as tramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, ethylene oxide adduct of bisphenol sulfone, ethylene oxide adduct of bisphenol A, diethylene glycol, polyethylene oxide glycol, etc. it can. These compounds can be used alone or in combination of two or more. Of these, preferably, the acid component is isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid, and the glycol component is trimethylene glycol or hexamethylene. It is an ethylene oxide adduct of glycol, neopentyl glycol, and bisphenol sulfone.
[0013]
In addition, polyethylene-2,6-naphthalenedicarboxylate may be one in which a terminal hydroxyl group and / or a carboxyl group is partially or entirely blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Alternatively, it may be copolymerized within a range in which a substantially linear polymer is obtained with a trifunctional or higher functional ester-forming compound such as glycerin and pentaerythritol.
[0014]
Furthermore, the polyester film for capacitors of the present invention may be composed of a mixture in which an organic polymer is mixed in addition to the main component polyethylene-2,6-naphthalenedicarboxylate. Polyethylene-2,6-naphthalenedicarboxylate is preferably contained in an amount of 90 mol% or more.
[0015]
Polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene 4,4′-tetramethylene diphenyl dicarboxylate, polyethylene-2,7-naphthalene dicarboxylate, polytrimethylene-2,6-naphthalene as such organic polymer Examples include dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene dicarboxylate, and the like. Polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalenedicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate Is preferred.
[0016]
These organic polymers are not only one type but also two or more types, in the polyester film for capacitors of the present invention, polyethylene-2,6-naphthalene, up to 10 mol%, preferably up to 5 mol%, of the polymer repeating unit. It can be used to be a mixture mixed with a carboxylate.
[0017]
Such a mixture can be produced by a generally known method for producing a polyester composition. The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low polymerization degree polyester by reaction of dicarboxylic acid and glycol, or a lower alkyl ester of dicarboxylic acid and glycol are conventionally known transesterification catalysts, such as sodium , Potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and a compound containing two or more kinds of cobalt-containing compounds, followed by polymerization in the presence of a polymerization catalyst. As a polymerization catalyst, antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or a partial hydrolyzate thereof, titanyl ammonium oxalate, Examples include titanium compounds such as potassium titanyl oxalate and titanium trisacetylacetonate.
[0018]
When the polymerization is performed via a transesterification reaction, a phosphorus compound such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, or normal phosphoric acid is added for the purpose of deactivating the transesterification catalyst before the polymerization reaction. However, the content of polyethylene-2,6-naphthalenedicarboxylate as a phosphorus element is preferably 20 to 100 ppm from the viewpoint of thermal stability of the polyester.
[0019]
Polyester can also be chipped after melt polymerization and solid state polymerization can be performed under reduced pressure by heating or in an inert gas stream such as nitrogen.
[0020]
The intrinsic viscosity of the polyester mainly composed of polyethylene-2,6-naphthalenedicarboxylate is preferably 0.40 dl / g or more and 0.90 dl / g or less. More preferably, it is 0.43-0.85 dl / g, Most preferably, it is 0.45-0.80 dl / g. When the intrinsic viscosity is less than 0.40 dl / g, the film becomes brittle, and breakage tends to occur when the film is formed. Further, it is not preferable because the film is easily broken during conveyance of the capacitor processing step. On the other hand, if the intrinsic viscosity of the film exceeds 0.90 dl / g, it is necessary to make the intrinsic viscosity of the polymer considerably high, and the normal synthesis method is not preferable because it takes a long time for polymerization and deteriorates the productivity.
[0021]
[Thermal strain rate]
Based on the length LMD (t) of the film in the machine direction (MD) at the temperature t ° C., the thermal strain rate RMD (T) in the machine direction at the temperature T ° C. is calculated as RMD (T) = {[LMD (T ) −LMD (35)] / LMD (35)} × 100 (%). Here, LMD (35) is the length in the machine direction (MD) of the film at a temperature of 35 ° C. That is, in the present invention, the thermal strain rate is defined by the degree of change in the film length that changes with temperature, with the film length at a temperature of 35 ° C. being the reference. The film of the present invention is characterized in that the thermal strain rate RMD (150) in the longitudinal direction of the film at a temperature of 150 ° C. is −1.5% ≦ RMD (150) ≦ 0.0.
[0022]
Here, when the thermal strain rate RMD (150) at 150 ° C. is less than −1.5%, the film shrinks in the process of forming a metal layer on the surface of the film, and the planarity is lowered. Gets worse. On the other hand, if this value exceeds 0.0%, shape defects may occur during hot pressing, resulting in a decrease in insulation resistance.
[0023]
And in this invention, based on length (TD) of the horizontal direction (TD) of the film in temperature t degree C, the film in temperature T degree C side Film at a temperature of 150 ° C. when the thermal strain rate RTD (T) in the direction is defined by RTD (T) = {[LTD (T) −LTD (35)] / LTD (35)} × 100 (%) It is preferable that the thermal strain rate RTD (150) in the lateral direction is −1.0% ≦ RTD (150) ≦ 0.0%.
[0024]
If this value is less than -1.0%, the film may shrink in the process of forming a metal layer on the surface of the film, and the capacitance may be insufficient. On the other hand, if it exceeds 0.0%, the metal deposited film may be curled after a metal layer is provided on the surface, which may reduce the yield in the processing of the capacitor.
[0025]
In the present invention, thermal strain rates RMD (210) and RTD (210) at a temperature of 210 ° C. are −3.5% ≦ RMD (210) ≦ 0.0% and −3.5% ≦ RTD (210 ) ≦ 0.0% is more preferable. If the thermal strain rate RMD (210) or RTD (210) at 210 ° C. is less than −3.5% or more than 0.0%, the metallicon (electrode metal is sprayed on both end faces of the element) may cause deformation of the film. It may result in poor contact and insufficient capacity.
[0026]
[Aspect ratio of 5% strain strength]
In the present invention, the ratio of the 5% strain strength in the longitudinal direction of the film to the 5% strain strength in the transverse direction of the film, that is, the value obtained by dividing the 5% strain strength in the longitudinal direction by the 5% strain strength in the transverse direction is 0.00. It is preferable that it is 90 or more and 1.40 or less. If this ratio is less than 0.90, it tends to stretch in the machine direction during processing, and if it exceeds 1.40, the thermal strain rate RMD (150) at 150 ° C. in the machine direction (MD) is less than −1.5%. This is not preferable.
[0027]
[Fly spec]
In the film of the present invention, the number of fly specs having an average diameter exceeding 60 μm is 20 / m. ² You need to be: More preferably 15 / m ² Below, particularly preferably 10 pieces / m ² It is as follows. Here, fly specs are generated from additives (lubricants, etc.) contained in the resin and foreign matter as the core, and from the part (void) where the film thickness of the resin constituting the core and the film formed around it is reduced (void) It is composed. The average diameter is the average of the major axis and minor axis of the fly spec.
[0028]
If this fly spec is large, the range of thin resin film will spread, so stress concentration will occur when there is sudden tension fluctuation or rapid heating during film formation, slitting to an appropriate width, capacitor processing process, etc. As a result, the film is broken and the insulation performance is lowered. Even when the film does not break, the insulation performance tends to decrease because the resin film is thin. In addition, the fly spec that significantly reduces the insulation performance has an average diameter of more than 60 μm, and the presence frequency is 20 / m 2. ² If it exceeds, the insulation performance as the dielectric of the capacitor will be insufficient.
[0029]
In order to keep the large number of fly specs within the above range, filter with a nonwoven fabric type filter having an average opening of 10 to 40 μm, preferably 15 to 35 μm made of stainless steel fine wire with a wire diameter of 15 μm or less as a filter during film formation. Is preferred. When the opening of the filter exceeds 40 μm, there is no effect of reducing coarse particles in the molten polymer. On the other hand, when the opening is less than 10 μm, the filter is likely to be clogged, and industrial practical application is difficult. There are other filters using a network structure, sintered metal, etc., but there are problems such as short life and slightly inferior filtration efficiency compared to non-woven type filters. Furthermore, in order to make the number of fly specs having a large size more effectively within the above range, it is preferable to add the lubricant itself into the polymer after being filtered through a filter having a predetermined mesh size.
[0030]
[Surface roughness (Ra)]
The polyester film for capacitors of the present invention preferably has a center line average roughness (Ra) of 40 to 80 nm, more preferably 45 to 80 nm, and particularly preferably 50 to 77 nm. When the center line average roughness (Ra) is less than 40 nm, the slipperiness and air release property of the film are poor, it is very difficult to wind the film on a roll, and the crushing property of the element is poor during hot pressing. In some cases, shape defects and insulation resistance may be reduced. The defective shape is caused by a poor sliding property, and the crushing trace at the center of the element is not linear but is distorted, or the dumb-shaped cavities remain at both ends of the crushing trace. Further, in order for the center line average roughness (Ra) to exceed 80 nm, it is necessary to add a lubricant having a large particle diameter or increase the amount of the lubricant, but the thickness of the polyester film for capacitors of the present invention is thin. In addition, since the frequency of breakage in film production increases, productivity is significantly reduced. In addition, the dielectric breakdown voltage of the capacitor decreases.
[0031]
[Thickness]
The thickness of the capacitor polyester film of the present invention is preferably 0.3 to 10 μm, more preferably 0.4 to 7.0 μm, and particularly preferably 0.5 to 5.0 μm. When the thickness of the film is less than 0.3 μm, the film is very thin, so that the film is frequently broken and is difficult to form. In addition, when the thickness of the film exceeds 10 μm, a sufficient resin thickness can be maintained even if fly specs exist, so that a phenomenon of deterioration of insulation characteristics does not occur, there is no problem of reduction in dielectric strength due to press, and Not subject.
[0032]
[density]
The polyester film for capacitors of the present invention has a density of 1.340 to 1.361 g / cm. ^Three It is preferable that More preferably 1.345 to 1.357 g / cm ^Three It is. Density is 1.340 g / cm ^Three If it is less than that, it will cause variation in capacitor performance and cause a decrease in processing yield, which is not preferable. 1.361 g / cm ^Three If it exceeds 1, the crystallinity becomes too high and the toughness of the film is lost, so that the frequency of breakage during film transport and slit processing increases.
[0033]
[Additive]
The polyester film of the present invention can contain additives such as lubricants, stabilizers, flame retardants and the like. A small amount of inert fine particles such as inorganic particles, organic particles, and crosslinked polymer particles are included in order to impart slipperiness to the film for the purpose of improving runnability and handling properties during film production, processing, and use. It is preferable.
[0034]
Inorganic particles include calcium carbonate, porous silica, spherical silica, kaolin (plate-like aluminum silicate), talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, Examples thereof include silicon oxide, titanium oxide, zirconium oxide, and lithium fluoride.
[0035]
Examples of the organic salt particles include calcium oxalate, terephthalate such as calcium, barium, zinc, manganese, and magnesium.
[0036]
Examples of the cross-linked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, acrylic monomers or homopolymers of vinyl monomers such as methacrylic acid, polytetrafluoroethylene, silicone resin, benzoguanamine. Organic fine particles such as resins, thermosetting epoxy resins, unsaturated polyester resins, thermosetting urea resins, and thermosetting phenol resins are also used.
[0037]
The average particle size of these lubricants is preferably 0.1 μm or more and 5 μm or less. The average particle size is more preferably 0.15 μm or more and 4 μm or less, and particularly preferably 0.2 μm or more and 3 μm or less. If the thickness is less than 0.1 μm, the effect of improving the slipperiness is small, so it is necessary to make the concentration of addition very high, and it is not preferable because breakage increases in the film production process. On the other hand, when the thickness exceeds 5 μm, not only is the number of breaks increased in the film production process, but also pinholes due to particle dropout are increased, which is not preferable.
[0038]
In the present invention, the “average particle diameter” of the inert fine particles means the “equivalent spherical diameter” of the particles at the point of 50% by weight of the total particles measured. The “equivalent sphere diameter” means the diameter of an imaginary sphere (ideal sphere) having the same volume as the particle, and can be obtained by calculation from the measurement of the particle by an electron microscope or a normal sedimentation method.
[0039]
The total amount of inert fine particles added is 0.05% by weight or more and 3% by weight or less, more preferably 0.08% by weight or more and 2.5% by weight or less, and 0.1% by weight or more and 2.0% by weight or less. Particularly preferred. If it is less than 0.05% by weight, the improvement of the slipperiness is insufficient, and if it exceeds 3% by weight, it is not preferable because breakage increases in the film production process.
[0040]
The inert fine particles to be added to the film may be a single component selected from those exemplified above, or may be a multiple component including two components or three or more components. In particular, in the polyester film for capacitors of the present invention, it is particularly preferable to contain calcium carbonate and plate-like aluminum silicate among the above examples.
[0041]
The polyester film of the present invention can be blended with a crystal nucleating agent, an antioxidant, a heat stabilizer, a lubricant, a flame retardant, an antistatic agent, a polysiloxane, and the like depending on the application.
[0042]
There is no particular limitation on the addition timing of the inert fine particles and other additives as long as it is a stage until the film formation of polyethylene-2,6-naphthalenedicarboxylate, and it may be added, for example, in the polymerization stage. You may add in the case of. From the standpoint of uniform dispersion, it is preferable to add it to ethylene glycol and add it at a high concentration during polymerization to form a master chip and dilute with an additive-free chip.
[0043]
[Calcium carbonate particles]
The calcium carbonate particles, which are inert fine particles that are particularly preferably added to the polyester film for capacitors of the present invention, preferably have an average particle size of 0.2 to 5 μm from the viewpoint of film slipperiness and air release. More preferably, it is 0.3-4 micrometers, and it is especially preferable that it is 0.5-3 micrometers. The amount of calcium carbonate particles added is preferably 0.03 to 2% by weight, more preferably 0.05 to 1.5% by weight, and particularly preferably 0.1 to 1% by weight.
[0044]
The calcium carbonate used in the present invention is not particularly limited, but limestone produced in nature, chalk (chalk), and calcite crystals such as precipitated calcium carbonate produced from limestone by a chemical method, lime milk at high temperature Examples thereof include argonite crystals, vaterite crystals obtained by reacting carbon dioxide gas, and combinations thereof. Heavy calcium carbonate (calcite crystal) obtained by pulverizing limestone into a machine cake can also be used.
[0045]
[Plate-like aluminum silicate particles]
It is preferable that the average particle diameter of the aluminum silicate particles, which are inert fine particles added particularly preferably in the polyester film for capacitors of the present invention, is 0.1 to 2 μm, and 0.3 to 1.7 μm. Is more preferable, and 0.5 to 1.5 μm is particularly preferable. Further, the addition amount is preferably 0.03 to 1% by weight, more preferably 0.06 to 0.8% by weight from the viewpoint of film slipperiness and handleability in the capacitor manufacturing process, Particularly preferred is 0.1 to 0.7% by weight.
[0046]
The plate-like aluminum silicate in the present invention refers to an aluminosilicate, and is not particularly limited, and examples thereof include kaolin clay made of kaolin mineral produced naturally. Furthermore, kaolin clay may be subjected to a purification treatment such as washing with water.
[0047]
[Coarse particles]
Coarse particles present in the polyester film for capacitors of the present invention have a maximum diameter of more than 10 μm / m. ² The following is preferable. More preferably 8 pieces / m ² Below, particularly preferably 5 pieces / m ² It is as follows. In the film of the present invention, special attention is required when calcium carbonate particles or plate-like aluminum silicate is contained. The number of coarse particles exceeding the maximum diameter of 35 μm is 10 / m ² Exceeding the ratio is not preferable because the frequency of the portion where the thickness of the resin around the coarse particles is reduced increases and the insulating performance as the dielectric of the capacitor is insufficient.
[0048]
[Thickness variation]
In the polyester film for capacitors of the present invention, the variation in thickness at an arbitrary position is preferably 25% or less, more preferably 20% or less, and particularly preferably 15% or less with respect to the film thickness. When the thickness variation with respect to the thickness of the film exceeds 25%, it is not preferable that the capacitor is thinly used as a dielectric thin film because it causes variation in the performance as a capacitor due to the variation in thickness.
[0049]
[Production conditions]
The polyester film of the present invention is a biaxially stretched film mainly composed of polyethylene-2,6-naphthalenedicarboxylate. This biaxially stretched film is obtained by an ordinary method, for example, the polymer is melted at a melting point or higher and extruded from a die slit onto a casting drum adjusted to a temperature around 60 ° C. to be closely cooled and solidified to obtain an unstretched film. This unstretched film can be produced by biaxially stretching in the longitudinal and lateral directions, then heat setting, and if necessary, relaxing treatment in the longitudinal and / or lateral directions. For film stretching, known roll type longitudinal stretching machines, infrared heating longitudinal stretching machines, tenter crib type transverse stretching machines, multistage stretching machines, tubular stretching machines, oven type longitudinal stretching machines that perform these stretching processes in multiple stages. Although it can be performed using a simultaneous biaxial stretching machine or the like, it is not particularly limited. In the present invention, the thermal strain rate at 150 ° C. in the machine direction of the film needs to be controlled to a small value, and simultaneous biaxial stretching is preferred.
[0050]
Next, although the manufacturing method of the polyester film of this invention is described in detail, it is not necessarily limited to this. First, production by the simultaneous biaxial stretching method will be described. The longitudinal stretching mechanism of the simultaneous biaxial stretching machine includes a conventional screw system that extends a clip interval by placing a clip in a screw groove and a pantograph method that expands a clip interval using a pantograph. These have the problems that the film forming speed is slow and it is not easy to change the conditions such as the draw ratio. However, when such equipment is already owned, it can be used in the present invention. On the other hand, in recent years, a linear motor type simultaneous biaxial tenter has been developed and attracts attention because of its high film-forming speed. Linear motor type simultaneous biaxial stretching can solve these problems all at once. Therefore, it is preferable to use this type of equipment when newly introducing a simultaneous biaxial stretching machine. In addition, simultaneous biaxial stretching has an advantage in that scratches on the film surface are reduced because a longitudinal stretching roller is not used unlike sequential biaxial stretching. In addition, in sequential biaxial stretching, the surface of the benzene ring or naphthalene ring of the polyester is likely to be parallel to the film surface, the refractive index nz in the thickness direction is small, the tear propagation resistance is small, and layer peeling is likely to occur. Simultaneous biaxial stretching improves this. Moreover, there exists a thing of the structure which can be longitudinally relaxed in a heat setting area | region, and can reduce the thermal strain rate of the longitudinal direction of 150-210 degreeC. Since these characteristics match the required characteristics of the capacitor film of the present invention, it is preferable to employ simultaneous biaxial stretching in the present invention.
[0051]
In the present invention, simultaneous biaxial stretching is stretching for simultaneously giving orientation in the machine direction and transverse direction of the film, using a simultaneous biaxial stretching machine, and transporting while holding both ends of the film with clips, An operation of stretching in the longitudinal direction and the transverse direction. Here, the longitudinal direction of the film is the longitudinal direction of the film, and the lateral direction is the width direction of the film. Of course, it suffices if there is a portion in which the stretching in the machine direction and the transverse direction are stretched at the same time in time, and therefore, after stretching first in the transverse direction or the longitudinal direction, the longitudinal direction and the transverse direction are separated. A method of stretching simultaneously, a method of further stretching in the transverse direction or the longitudinal direction after simultaneous biaxial stretching, and the like are also included in the scope of the present invention.
[0052]
In order to produce the polyester film of the present invention, after containing predetermined inert fine particles, it was melt extruded at a normal extrusion temperature, that is, a melting point temperature (hereinafter referred to as Tm) to (Tm + 70) ° C. or less. The film-like melt is quenched on the surface of the rotary cooling drum to obtain an unstretched film having an intrinsic viscosity of 0.40 to 0.90 dl / g. Taking polyethylene-2,6-naphthalenedicarboxylate as an example, drying is performed at 170 ° C. for about 6 hours, the extrusion temperature is around 300 ° C., and the surface temperature of the cooling drum is about 60 ° C. The ratio of the thickness between the edge and the center of the unstretched film (the thickness of the edge / the thickness of the center) is desirably 1 or more and 10 or less, preferably 1 or more and less than 5, more preferably 1 or more. 3 or less. If the thickness ratio is less than 1 or exceeds 10, film tearing or clip detachment frequently occurs, which is not preferable.
[0053]
Next, the unstretched film was guided to the simultaneous biaxial stretching machine by gripping both ends of the film with clips, and heated to (Tg + 50) ° C. to (Tg + 50) ° C. in the preheating zone. Thereafter, simultaneous biaxial stretching is performed at (Tg−10) to (Tg + 70) ° C. at an area magnification of 10 to 40 times (longitudinal times 2 to 6 times) in one step or multiple steps including two or more steps. In addition, if necessary, after that, in the temperature range of (polyester melting point Tm-120) to (Tm-10) ° C., in one step or in multiple steps of two or more steps, the area magnification is 2 to 5 times simultaneously. It may be stretched. Subsequently, heat setting is performed in a temperature range of (Tm-70) to (Tm) ° C., and if necessary, while performing heat setting or in the cooling process from heat setting, a temperature range of preferably 100 to 245 ° C. The relaxation treatment is performed in the vertical and horizontal directions, preferably in the range of 1 to 10% in each direction. In the case of polyethylene-2,6-naphthalenedicarboxylate, the preheating temperature is preferably about 140 ° C., the stretching temperature is about 145 ° C., and the heat setting temperature is preferably about 240 ° C. If necessary, relaxation treatment is performed in the longitudinal and lateral directions while heat setting, and the film is then cooled to room temperature and wound to obtain the desired simultaneous biaxial polyester film. In the present invention, in order to impart the surface characteristics of the film, for example, in order to impart easy adhesion, slipperiness, releasability, and antistatic properties, the polyester may be used before or after the simultaneous biaxial stretching. It is also preferable to coat the coating on the surface of the film.
[0054]
The film of the present invention can also be produced by ordinary sequential biaxial stretching. As described above, an unstretched film of polyethylene-2,6-naphthalenedicarboxylate obtained by a known method is stretched in the machine direction at 120 to 180 ° C, more preferably 125 to 170 ° C, particularly preferably 130 to 160 ° C. The film is stretched 3.0 to 5.0 times, more preferably 3.3 to 4.6 times with a roll type longitudinal stretching machine. An infrared heating type longitudinal stretching machine may be used, but in particular, when a thin film is stretched, a roll type longitudinal stretching machine is preferred because it is advantageous for heating the entire film uniformly. In order to stretch easily by longitudinal stretching, it is preferable to divide the stretching into a plurality of times and perform multi-stage stretching. After longitudinal stretching, it is further 120 to 180 ° C., more preferably 125 to 170 ° C., particularly preferably 130 to 160 ° C., and 3.0 to 4.5 times in the transverse direction, more preferably 3.5 to 4.3. Double-stretched, heat-treated at 195 to 250 ° C., more preferably 205 to 245 ° C. for 0.3 to 50 seconds, and then heat relaxed in the range of 0.5 to 15% in the longitudinal and / or transverse direction A desired polyester film can be obtained by performing the treatment. In addition, you may use multistage extending | stretching which divides | segments extending | stretching of a horizontal direction into several steps.
[0055]
The polyester film of the present invention is used as a dielectric of a film capacitor. However, since the glass transition temperature of the dielectric film is higher than that of a conventional polyester (polyethylene terephthalate) film capacitor, it is used in a place where the use environment temperature is higher. It is preferably applied to the film capacitor used. In particular, a rectifier circuit closer to a heat source than in the past due to miniaturization of electric / electronic devices, and a circuit of electrical components installed around an engine or in a vehicle as electrical components of an automobile are preferably used because the use environment temperature becomes high. Moreover, it is preferably applied as a film for a capacitor that requires a withstand voltage characteristic under a high voltage and a capacity stabilization under a high frequency, such as a transformer circuit, a current conversion circuit, etc. of a hybrid car, an electric vehicle, an electronic exchange, etc. .
[0056]
【Example】
Hereinafter, the present invention will be further described by way of examples. However, the present invention is not limited to the following examples unless the gist thereof is changed. In addition, the measurement methods and definitions of various physical property values and characteristics in the present invention are as follows.
[0057]
(1) Calculation of component amount of polyethylene-2,6-naphthalenedicarboxylate (main component molar ratio, copolymer component molar ratio)
Film sample is measured with solvent (CDCl _Three : CF _Three After dissolving in COOD = 1: 1) ¹ An H-NMR measurement is performed, and calculation is performed with the integration ratio of each obtained signal.
[0058]
(2) Thermal strain rate
Using Seiko Electronics Industry's measurement module TMA / SS120C type and the company's thermal analysis system SSC / 5200H type as a data analysis device, the film sample is sampled into a strip shape that is 4 mm wide and long in the machine direction (MD). The temperature is increased from room temperature at a temperature increase rate of 5 ° C./min with a constant load of 2.0 MPa in the vertical direction. And at 35 degreeC, 150 degreeC, and 210 degreeC, the length of a film is measured and the thermal strain rate RMD of the vertical direction is computed by the above-mentioned formula. The thermal strain rate RTD in the horizontal direction (TD) is the same as that described above except that a long sample is cut in the horizontal direction (TD).
[0059]
(3) Fly specs, coarse particles
(3-1) Fly spec
The film surface is magnified 50 times with polarized light transmission using a universal projector, and the measurement area is 1m. ² Observe and mark fly specs present in Furthermore, each fly spec is observed with an optical microscope, and the average diameter including the fly spec nucleus and voids generated around the fly spec is obtained, that is, (major axis + minor axis) / 2, and the number of those exceeding 60 μm is counted. .
[0060]
(3-2) Coarse particles
Using a universal projector, the film surface is magnified 50 times with transmitted illumination, and the measurement area is 1 m. ² The number of particles having a maximum diameter exceeding 35 μm was counted among the particles present in the film.
[0061]
(4) 5% strain strength (F5 value)
The film is cut into a sample width of 10 mm and a length of 150 mm, pulled between chucks by 100 mm, and pulled by an Instron type universal tensile tester at a pulling speed of 100 mm / min and a chart speed of 500 mm / min. Measure in both MD and TD directions, read the strength at 5% elongation from the obtained load-elongation curve, and divide by the original cross-sectional area to obtain 5% strain strength (N / mm ² ). The aspect ratio is calculated by dividing the F5 value in the MD direction by the F5 value in the TD direction.
[0062]
(5) Surface roughness (centerline average roughness: Ra)
The center line average roughness (Ra) is a value defined by JISB0601. In the present invention, using a non-contact type three-dimensional roughness meter (ET-30HK manufactured by Kosaka Laboratory), a measurement length (Lx) of 1 mm and a sampling pitch of 2 μm using a semiconductor laser having a wavelength of 780 nm and an optical probe having a beam diameter of 1.6 μm. The protrusion profile on the film surface was measured under the conditions of a cutoff of 0.25 mm, a magnification in the thickness direction of 10,000 times, a magnification in the surface direction of 200 times, and the number of scanning lines of 100 (Ly = 0.2 mm). (Ra) is calculated.
[0063]
(6) Density
A density gradient tube using a calcium nitrate aqueous solution is used for measurement by a floatation method at 25 ° C.
[0064]
(7) Film thickness and thickness variation
50 samples of 10 cm in length and 10 cm in width are sampled at an interval of 10 cm or more in both the length and width from an arbitrary place on the formed film. The thickness (μm) T1, T2... T50 for each sample is defined as width (cm), length (cm), weight (g), density (g / cm). ^Three ) From the following equation, and the average thickness Tav of 50 samples is obtained to obtain the film thickness. Further, the difference between the maximum thickness Tmax and the minimum thickness Tmin in the above-mentioned 50 samples is obtained, and the ratio to the average thickness Tav is calculated by the following equation to obtain the thickness variation.
Thickness T (μm) = [weight / (width × length × density)] × 10000
Average thickness Tav (μm) = (T1 + T2 +... + T50) / 50
Thickness variation (%) = [(Tmax−Tmin) / average thickness Tav] × 100
[0065]
(8) Average particle size of inert fine particles
It is measured using a Shimadzu CP-50 type Centrifugal Particle Size Analyzer. The particle size corresponding to 50% by weight is read from the integrated curve of the particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is taken as the average particle size (“particle size measurement technique”). Nikkan Kogyo Shimbun, published 1975 pages 242-247).
[0066]
(9) Film formability
When the biaxially stretched film was formed continuously for 24 hours, the film formation state of the film was observed and evaluated according to the following criteria.
A: The number of breaks is 0 times / 24 hours, and extremely stable film formation is possible.
○: The number of breaks is 1 to 3 times / 24 hours, and stable film formation is possible.
X: The number of breaks was 4 times / 24 hours, and the film formation was unstable.
[0067]
(10) Roll form of film roll
After winding the film on a roll with a width of 550 mm and a length of 10,000 m, the wound shape was observed during film formation and slitting and after vapor deposition in capacitor processing, and evaluated according to the following criteria.
A: The film has a good winding shape with no wrinkles or winding deviations on the surface as observed with the naked eye both during film formation, slitting and after vapor deposition.
X: Wrinkles on the surface, winding deviation, etc. were confirmed by observation with the naked eye during film formation and slitting and / or after deposition, and the winding shape was poor.
[0068]
(11) Insulation resistance
Capacitors with an insulation resistance of less than 5000 MΩ were measured with 200 0.1 μF capacitor samples at 23 ° C. and 65% RH in a super insulation resistance meter 4329A manufactured by YHP as a 1-minute value at an applied voltage of 500 V. The sample was judged as a defective product according to the following criteria. In the present invention, ○ and Δ were acceptable.
○: Less than 4 defective products
Δ: 4 or more and less than 10 defective products
×: 10 or more defective products
[0069]
(12) Dielectric breakdown voltage (BDV)
It measured according to the method shown to JISC2318, and made the minimum value of n = 200 the dielectric breakdown voltage (BDV). In the present invention, the dielectric breakdown voltage is preferably 220 V / μm or more, and particularly preferably 240 V / μm or more.
[0070]
[Example 1]
100 parts of dimethyl 2,6-naphthalenedicarboxylate, 60 parts of ethylene glycol were used as a transesterification catalyst and 0.03 part of manganese acetate tetrahydrate was used as a lubricant, and 0.45% by weight of calcium carbonate particles having an average particle diameter of 1.0 μm Then, kaolin clay particles (plate-like aluminum silicate particles) having an average particle size of 0.7 μm were added so as to contain 0.30% by weight and subjected to transesterification according to a conventional method, and then trimethyl phosphate 0.023. The transesterification reaction was substantially completed by adding a portion.
[0071]
Subsequently, 0.024 part of antimony trioxide was added, and then a polymerization reaction was carried out in a conventional manner at high temperature and high vacuum to obtain polyethylene-2,6-naphthalenedicarboxylate (PEN Tg) having an intrinsic viscosity of 0.62 dl / g. = 121 ° C). This PEN polymer was dried at 170 ° C. for 5 hours, then supplied to an extruder, melted at a melting temperature of 295 ° C., filtered through a nonwoven fabric type filter having an average opening of 30 μm made of stainless steel fine wire having a wire diameter of 14 μm, After extruding from the slit, it was cooled and solidified on a casting drum to prepare an unstretched film.
[0072]
The unstretched film was introduced into a simultaneous biaxial stretching machine, preheated at 140 ° C., and stretched simultaneously at 145 ° C. while being held with a clip 4.5 times in the longitudinal direction and 4.2 times in the lateral direction. Then, 3% longitudinal relaxation was given while heat fixing at 200, 230, and 235 ° C. for 2 seconds in the first, second, and third heat setting zones, respectively, to obtain a biaxially oriented film having a thickness of 3.0 μm. Table 1 shows the physical properties and evaluation results of the biaxially oriented film.
[0073]
Next, the obtained polyester film was treated at 70 ° C. for 24 hours one week after film formation, and then aluminum was vacuum-deposited on one side so that the surface resistance value was 2Ω / □. At that time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction (repetition of a vapor deposition portion width of 58 mm and a margin portion width of 2 mm). Next, a voltage treatment is applied to the vapor deposition film by applying a direct current of 800V to the entire width of the film, a blade is inserted into the center of each vapor deposition section and the center of each margin section and slit, and a tape with a width of 30 mm having a margin of 1 mm on the left or right. A take-up reel.
[0074]
The obtained reels of the left margin and the right margin were overlapped and wound one by one to obtain a capacitor element having a capacitance of 0.1 μF. This capacitor element was pressed at a temperature of 150 ° C. and a pressure of 196 MPa for 5 minutes. Metallicon was sprayed on both end surfaces to form an external electrode, and a lead wire was welded to the metallicon and cured with an epoxy resin as an exterior to obtain a wound capacitor. Table 1 shows the evaluation results of the capacitor. The dielectric breakdown voltage is as high as 270 V / μm, and the insulation resistance characteristics are also excellent. Moreover, it is excellent also in the film forming property of a film.
[0075]
[ Comparative Example 1 ]
An unstretched film was prepared in the same manner as in Example 1 with the amount of inert particles added as shown in Table 1. This film was stretched 1.8 times in the longitudinal direction (longitudinal direction) at 135 ° C., then stretched twice in the longitudinal direction at 145 ° C. (longitudinal stretching ratio: 3.6 times), and transverse direction (width direction) at 140 ° C. ) Was successively biaxially stretched 3.6 times, and then heat-fixed at 232 ° C. for 3 seconds to obtain a biaxially oriented film having a thickness of 3.0 μm and wound on a roll. A single film was evaluated, and a capacitor element was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. The dielectric breakdown voltage is as high as 260 V / μm, and the insulation resistance characteristics are also excellent.
[0076]
[Comparative example 2 ]
A capacitor element was prepared and evaluated in the same manner as in Example 1 except that the average aperture of the melt filtration filter was 50 μm. The results are shown in Table 1. Many fly specs and low breakdown voltage.
[0077]
[Comparative example 3 ]
The heat set temperature was set to 200 ° C. for each zone, and no longitudinal relaxation was given. Otherwise, a film was formed in the same manner as in Example 1, and a capacitor element was prepared and evaluated. The results are shown in Table 1. The thermal strain rate in the vertical direction at 150 ° C. was large on the negative side, and capacitor shape defects occurred frequently.
[0078]
[Comparative example 4 ]
Comparative Example 1 The stretching conditions were changed to those shown in Table 1. Table 1 shows the evaluation results of the film and the capacitor element. The thermal strain rate in the vertical direction at 150 ° C. is large on the plus side, and the insulation resistance is low.
[0079]
[Table 1]

[0080]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it is excellent in the insulation characteristic which uses polyethylene-2, 6-naphthalene dicarboxylate as a main component, and provides a film suitable for the dielectric material for capacitors which does not have the workability especially the characteristic fall at the time of a hot press. it can.

Claims (6)

A biaxially oriented film comprising polyethylene-2,6-naphthalenedicarboxylate as a main component, the film is produced by a simultaneous biaxial stretching method and subjected to a longitudinal relaxation treatment, and the film at a temperature of t ° C. Based on the length LMD (t) in the longitudinal direction (MD), the thermal strain rate RMD (T) in the longitudinal direction of the film at a temperature T ° C.
RMD (T) = {[LMD (T) -LMD (35)] / LMD (35)} × 100 (%)
When the thermal strain rate RMD (150) in the longitudinal direction of the film at a temperature of 150 ° C. is defined as -1. 0 % ≦ RMD (150) ≦ 0.0%, the film thickness is 0.3 to 10 μm, and the number of fly specs having an average diameter exceeding 60 μm is 20 pieces / m ² or less. Polyester film. Based on the length (TD) in the transverse direction (TD) of the film at the temperature t ° C., the thermal strain rate RTD (T) in the transverse direction of the film at the temperature T ° C.
RTD (T) = {[LTD (T) −LTD (35)] / LTD (35)} × 100 (%)
The thermal strain rate RTD (150) in the transverse direction of the film at a temperature of 150 ° C. is defined as −1.0% ≦ RTD (150) ≦ 0.0%. The polyester film for capacitors as described. Temperature thermal distortion RMD at 210 ° C. (210) and RTD (210), - 2.3% ≦ RMD (210) ≦ 0.0%, and -3.5% ≦ RTD (210) ≦ 0.0 The polyester film for capacitors according to claim 1, wherein the polyester film is a percentage.   4. The capacitor according to claim 1, wherein a ratio of 5% strain strength in the longitudinal direction of the film to 5% strain strength in the lateral direction of the film is 0.90 or more and 1.40 or less. Polyester film.   Contains 0.03 to 2% by weight of calcium carbonate particles having an average particle size of 0.2 to 5 μm, and further contains 0.03 to 1% by weight of plate-like aluminum silicate particles having an average particle size of 0.1 to 2 μm The polyester film for capacitors according to any one of claims 1 to 4, wherein: 6. The capacitor according to claim 1, wherein the number of coarse particles containing calcium carbonate particles and plate-like aluminum silicate particles and having a maximum diameter exceeding 35 μm is 10 particles / m ² or less. Polyester film .