JP2002164250A - Polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film for a capacitor which is superior in thermal characteristics. SOLUTION: The film is a biaxially oriented film which is mainly composed of polyethylene-2, 6-naphthalenedicarboxylate. The lengthwise thermal distortion factor RMD (T) of a film at a temperature T deg.C is defined as RMD (T)= [LMD (T)-LMD (35)]/LMD (35)}×100(%), based on a length LMD (t) in a lengthwise direction (MD) of a film at temperature t deg.C. The lengthwise thermal distortion factor RMD (150) of a film at a temperature 150 deg.C is defined as -1.5%<=RMD (150)<=0.0%. The number of fly speak, whose average diameter exceeds 60 μm, is 20 pieces/m2 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyester film for a capacitor.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electric and electronic devices, there has been a demand for miniaturization and large capacity of capacitors. I have. In response to such demands, in a film capacitor, a film as a dielectric is made thinner (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). And the reduction of pinholes present in films have been studied.

As described above, in the case of a film capacitor, although it is necessary to reduce the thickness of a dielectric film, workability in the process of processing the capacitor accompanying the thinning of the film (metal deposition as an electrode on the film, slit, element, etc.) For example, in order to avoid the deterioration of the winding, etc., see JP-A-10-29423.
No. 7 proposes adding specific inert fine particles as a lubricant to a polyethylene-2,6-naphthalenedicarboxylate film.

[0004]

However, although both thinning of the film and excellent workability in the processing step of the capacitor have been realized, the insulating properties caused by additives (particularly lubricants) contained in the film have been realized. In some cases, failure occurred, and the film was still insufficient as a capacitor film. Further, the temperature and pressure of the hot press after the winding of the capacitor element tend to be increased, and the insulation resistance and withstand voltage as the element may be lower than that of the film alone.

The present invention solves the above-mentioned problems of the prior art,
An object of the present invention is to obtain a biaxially stretched film containing polyethylene-2,6-naphthalenedicarboxylate as a main component and having excellent insulation properties and processability, particularly a film suitable for a dielectric of a film capacitor.

[0006]

SUMMARY OF THE INVENTION Polyethylene-2,6-
A biaxially oriented film containing naphthalene dicarboxylate as a main component, and based on a length LMD (t) of the film at a temperature t ° C., a longitudinal thermal strain rate of the film at a temperature T ° C. RMD (T), R
MD (T) = ｛[LMD (T) −LMD (35)] / L
When defined by MD (35) ％ × 100 (%), the longitudinal thermal distortion rate RMD (150) of the film at a temperature of 150 ° C. is −1.5% ≦ RMD (150) ≦
0.0%, and the number of fly specs having an average diameter exceeding 60 μm is not more than 20 pieces / m ² .

[Polyethylene-2,6-naphthalenedicarboxylate] A conventional polyester film for a capacitor is a polyethylene terephthalate film. This polyethylene terephthalate film is 80
The dielectric loss tangent increases in a temperature range of not less than ° C, and there is a possibility that thermal runaway occurs due to self-heating due to dielectric loss. Therefore, the upper limit of the operating temperature of the capacitor is suppressed to about 80 ° C.

On the other hand, in the present invention, the polyester film for a capacitor contains polyethylene-2,6-naphthalenedicarboxylate as a main component. Polyethylene-
For 2,6-naphthalenedicarboxylate, the increase in dielectric loss tangent is from around 120 ° C. Therefore, the upper limit of the operating temperature is about 120 ° C. Therefore, at high temperatures, capacitors of polyethylene-2,6-naphthalenedicarboxylate film are used. In addition, polyethylene-2,6-naphthalenedicarboxylate has a relatively small dielectric constant (2.9: 3.1), which appears to be disadvantageous for miniaturization, but has a high potential for reducing the thickness. However, polyethylene-2,6-naphthalenedicarboxylate is advantageous. The present invention is primarily directed to capacitors for such applications.

In the polyethylene-2,6-naphthalenedicarboxylate, the main dicarboxylic acid component is naphthalenedicarboxylic acid, and the main glycol component is
Ethylene glycol. Here, examples of the naphthalenedicarboxylic acid include -2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and the like. Naphthalenedicarboxylic acid is preferred.

In the present invention, "polyethylene-2,
"Containing a 6-naphthalenedicarboxylate as a main component" means that at least 90 mol% of all repeating units in the polymer component as a component of the film are ethylene-
It means a 2,6-naphthalenedicarboxylate unit. More preferably, it is 95 mol%.

The polymer constituting the film of the present invention may be composed of a copolymer or a mixture containing polyethylene-2,6-naphthalenedicarboxylate as a main component. Is 90 mol% or more of all repeating units, and it is sufficient that insulation properties, mechanical properties and thermal dimensional stability can be secured without extremely losing the original properties of the polyethylene-2,6-naphthalenedicarboxylate film.

In the case of a copolymer, the main component of the copolymer other than ethylene-2,6-naphthalenedicarboxylate is a copolymer component having 2 per molecule.
Compounds having two ester-forming functional groups can be used, such as oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, Dicarboxylic acids such as 4,4'-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid and diphenyletherdicarboxylic acid; p-oxybenzoic acid, p-oxyethoxybenzoic acid Oxycarboxylic acids such as propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanemethylene glycol, neopentyl glycol, and bisphenolsulfone; Oxide adducts, ethylene oxide adducts of bisphenol A, dihydric alcohols such as diethylene glycol, polyethylene oxide glycol and the like can be preferably used. 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.

The polyethylene-2,6-naphthalenedicarboxylate is obtained by blocking some or all of the terminal hydroxyl groups and / or carboxyl groups with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. Alternatively, it may be a copolymer of a tri- or higher functional ester-forming compound such as glycerin and pentaerythritol in a very small amount within a range where a substantially linear polymer can be obtained.

The polyester film for a capacitor of the present invention may be composed of a mixture of an organic polymer and polyethylene-2,6-naphthalenedicarboxylate as a main component. Polyethylene-2,6
-Naphthalenedicarboxylate preferably contains 90 mol% or more.

As such organic polymers, polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene 4,4'-tetramethylenediphenyldicarboxylate, polyethylene-2,7-naphthalenedicarboxylate, polytrimethylene-2, 6-naphthalenedicarboxylate, polyneopenthylene-2,6-naphthalenedicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate and the like can be mentioned. Among them, polyethylene isophthalate, polytrimethylene terephthalate, polytrimethylene-2,6-naphthalenedicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6
-Naphthalenedicarboxylate is preferred.

In the polyester film for a capacitor of the present invention, not only one kind but also two or more kinds of these organic polymers may be used in an amount of 10% by mole, preferably up to 5% by mole of the repeating units of polyethylene-2,6. -Can be used to form a mixture mixed with naphthalenedicarboxylate.

The production of such a mixture can be carried out 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 a reaction of dicarboxylic acid and glycol, or a conventionally known transesterification catalyst for converting a lower alkyl ester of dicarboxylic acid and glycol to glycol.
For example, after reacting with one or more compounds containing sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt, polymerization is carried out in the presence of a polymerization catalyst. Antimony trioxide, an antimony compound such as antimony pentoxide, a germanium compound represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or a partial hydrolyzate thereof, titanyl ammonium oxalate, Titanium compounds such as potassium titanyl oxalate and titanium trisacetylacetonate are exemplified.

When the polymerization is carried out via a transesterification reaction, trimethyl phosphate, triethyl phosphate,
Phosphorus compounds such as tri-n-butyl phosphate and orthophosphoric acid are added.
The content in 2,6-naphthalenedicarboxylate is 2
It is preferable from 0 to 100 ppm from the viewpoint of the thermal stability of the polyester.

The polyester may be formed into chips after melt polymerization and solid-phase polymerized under reduced pressure under heating or in an inert gas stream such as nitrogen.

The intrinsic viscosity of the polyester containing polyethylene-2,6-naphthalenedicarboxylate as a main component is preferably 0.40 dl / g or more and 0.90 dl / g or less. More preferably 0.43 to
0.85 dl / g, particularly preferably 0.45 to 0.80
dl / g. When the intrinsic viscosity is less than 0.40 dl / g, the film becomes brittle, and the film is likely to break during film formation. Further, it is not preferable because the film is likely to be broken during the transportation in the processing step of the capacitor. When the intrinsic viscosity of the film exceeds 0.90 dl / g, the intrinsic viscosity of the polymer needs to be considerably increased,
The usual synthesis method is not preferable because it takes a long time for polymerization and productivity is deteriorated.

[Thermal strain rate] Based on the length LMD (t) of the film in the machine direction (MD) at the temperature t ° C., the temperature T
Thermal distortion rate RMD (T) in the longitudinal direction of the film at ℃
RMD (T) = ｛[LMD (T) −LMD (3
5)] / 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, based on the film length at a temperature of 35 ° C., the thermal strain rate is defined by the degree of change in the film length that changes with temperature. The film of the present invention has a longitudinal thermal distortion rate RMD (150) at a temperature of 150 ° C. of -1.5% ≦ RMD (150).
≦ 0.0.

Here, the thermal distortion rate RMD at 150 ° C. (1
If the value of (50) is less than -1.5%, the film shrinks in the process of providing the metal layer on the surface of the film, and the flatness is reduced, so that the dielectric loss of the capacitor is deteriorated. On the other hand, if this value exceeds 0.0%, shape defects may occur during hot pressing, and the insulation resistance decreases.

In the present invention, based on the length LTD (t) of the film at the temperature t ° C. in the transverse direction (TD),
RTD in longitudinal direction of film at temperature T ° C
(T) is calculated as follows: RTD (T) = ｛[LTD (T) −LTD
(35)] / LTD (35)｝ × 100 (%), the thermal distortion rate RTD (150) in the transverse direction of the film at a temperature of 150 ° C. is −1.0% ≦ RT
It is preferable that D (150) ≦ 0.0%.

If this value is less than -1.0%, the film shrinks in the process of providing the metal layer on the surface of the film, and the capacitance may be insufficient. On the other hand, if the content exceeds 0.0%, after the metal layer is provided on the surface, the metal vapor-deposited film may be curled, and the yield may be reduced in the processing of the capacitor.

In the present invention, the thermal distortion rate RMD (210) and the RTD (210) at a temperature of 210 ° C. are -3.5%
≤RMD (210) ≤ 0.0% and -3.5% ≤ RT
More preferably, D (210) ≦ 0.0%. 2
Thermal distortion rate RMD at 10 ° C. (210) or RTD (2)
10) is less than -3.5% or more than 0.0%,
At the time of metallikon (spraying the electrode metal on both end surfaces of the element), the deformation of the film may result in poor contact and insufficient capacity.

[Aspect Ratio of 5% Strain Intensity] In the present invention, the ratio of the 5% strain intensity in the longitudinal direction of the film to the 5% strain intensity in the transverse direction of the film, that is, the 5% strain intensity in the longitudinal direction is defined as the transverse direction. It is preferable that the value divided by the 5% strain strength is 0.90 or more and 1.40 or less. This ratio is 0.90
If it is less than 1, it tends to elongate in the machine direction during processing, and if it exceeds 1.40, the thermal strain rate R at 150 ° C. in the machine direction (MD)
MD (150) may be less than -1.5%, which is not preferable.

[Fly Specification] The film of the present invention comprises:
The number of fly specs whose average diameter exceeds 60 μm is 20
Pieces / m ² or less. It is more preferably at most 15 / m ² , particularly preferably at most 10 / m ² . Here, fly specs are generated from additives (lubricants, etc.) and foreign substances contained in the resin as nuclei, and are formed from portions (voids) in which the film thickness of the resin constituting the nucleus and the film formed around the nuclei is reduced. It is composed. The average diameter is the average of the major axis and minor axis of the fly specification.

If the fly specification is large, the range of thin resin film thickness is widened, so if there is a sudden change in tension or sudden heating during the film formation, slitting to an appropriate width, or a processing step of the capacitor, etc. The film is torn due to stress concentration in the film, and the insulation performance is reduced. In addition, even when the film is not torn, the insulating performance tends to decrease because the thickness of the resin film is small. In addition, the fly specs which significantly lower the insulation performance have an average diameter of more than 60 μm, and if the frequency of occurrence exceeds 20 / m ² , the insulation performance as a dielectric of the capacitor becomes insufficient.

In order to keep the number of large fly specs in the above range, a filter having a wire diameter of 15 μm
Average opening of stainless steel fine wire 10-40
It is preferable to filter with a nonwoven fabric type filter having a thickness of μm, preferably 15 to 35 μm. Filter opening is 40
If it exceeds μm, there is no effect of reducing coarse particles in the molten polymer, while if the opening is less than 10 μm, clogging of the filter is liable to occur, which makes industrial practical use difficult.
There are other filters using a network structure or a sintered metal, but there are problems such as a shorter life and a slightly lower filtration efficiency as compared with a non-woven filter. further,
In order to more effectively keep the number of large-sized fly specs in the above range, it is preferable to add the lubricant itself to the polymer after previously filtering the lubricant with a filter having a predetermined opening.

[Surface Roughness (Ra)] The polyester film for a capacitor of the present invention preferably has a center line average roughness (Ra) of 40 to 80 nm, more preferably 45 to 80 nm, particularly preferably 50 to 80 nm. 77 nm. If the center line average roughness (Ra) is less than 40 nm, the film has poor slipperiness and air bleeding property, making it extremely difficult to wind the film around a roll. In addition, the element has poor crushing properties during hot pressing. In some cases, a defective shape or a decrease in insulation resistance may occur. Poor shape is due to poor slipperiness,
This is a phenomenon in which the crush trace at the center of the element does not become linear but causes distortion, or a dumbbell-shaped cavity remains at both ends of the crush 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 size or to increase the amount of the lubricant. In addition, since the frequency of breakage in film formation increases, productivity significantly decreases. Also, the dielectric breakdown voltage of the capacitor decreases.

[Thickness] The thickness of the polyester film for a capacitor 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. is there. When the thickness of the film is less than 0.3 μm, the film is extremely thin, so that rupture frequently occurs during film formation, and film formation is difficult. Further, when the thickness of the film exceeds 10 μm, a sufficient resin thickness can be maintained even if a fly specification exists, so that a phenomenon of lowering the insulation properties does not occur, and there is no problem of lowering the insulation strength by pressing, and the present invention Not eligible.

[Density] The polyester film for a capacitor of the present invention has a density of 1.340 to 1.361 g / cm ^3.
It is preferable that More preferably, 1.345
1.357 g / cm ³ . The density is 1.340 g / c
If it is less than m ^3, it may cause variations in capacitor performance and cause a reduction in processing yield, which is not preferable. On the other hand, if it exceeds 1.361 g / cm ³ , 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.

[Additives] The polyester film of the present invention may contain additives such as lubricants, stabilizers, flame retardants and the like. At the time of film production, processing, in order to improve the runnability and handling during use, in order to improve the slipperiness of the film, a small percentage of inert fine particles such as inorganic particles, organic particles, and crosslinked polymer particles are contained. Is preferred.

Examples of the 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, Examples thereof include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, and lithium fluoride.

Examples of the organic salt particles include terephthalate salts of calcium oxalate, calcium, barium, zinc, manganese, magnesium and the like.

Examples of the crosslinked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, and homopolymers or copolymers of vinyl monomers of acrylic acid or methacrylic acid. In addition, polytetrafluoroethylene, silicone Organic fine particles such as resin, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin are also used.

The average particle diameter of these lubricants is 0.1 μm.
It is preferably from m to 5 μm. 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. 0.1
If it is less than μm, the effect of improving the slipperiness is small, so that it is necessary to make the added concentration extremely high. 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 falling off of particles are increased, which is not preferable.

In the present invention, the "average particle diameter" of the inert fine particles means the "equivalent spherical diameter" of the particles at a point of 50% by weight of all the measured particles. The “equivalent spherical diameter” means the diameter of an imaginary sphere (ideal sphere) having the same volume as a particle, and can be calculated from the particle by an electron microscope or by a measurement using a normal sedimentation method.

The total amount of inert fine particles added is 0.05% by weight.
Not less than 3% by weight, more preferably not less than 0.08% by weight and not more than 2.5% by weight, preferably not less than 0.1% by weight and not more than 2.0% by weight.
The following are 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, breakage increases in the film production process, which is not preferable.

The inert fine particles to be added to the film may be a single component selected from those exemplified above, or a multi-component containing two or more than three components. In particular, the polyester film for a capacitor of the present invention particularly preferably contains calcium carbonate and plate-like aluminum silicate among the above examples.

The polyester film of the present invention may contain a nucleating agent, an antioxidant, a heat stabilizer, a lubricating agent, a flame retardant, an antistatic agent, a polysiloxane, etc., depending on the application.

The timing of adding the inert fine particles and other additives is not particularly limited as long as it is a stage before forming the polyethylene-2,6-naphthalenedicarboxylate into a film. For example, it may be added at the polymerization stage. Also, it may be added at the time of film formation. From the viewpoint of uniform dispersion, it is preferable to add the compound in ethylene glycol at a high concentration during polymerization to prepare a master chip, and dilute the mixture with a non-added chip.

[Calcium Carbonate Particles] The calcium carbonate particles, which are inert fine particles particularly preferably added to the polyester film for a capacitor of the present invention, have an average particle diameter of 0.2 from the viewpoint of the slipperiness and air bleeding property of the film. ~ 5 μm
Is preferably 0.3 to 4 μm, more preferably 0.5 to 3 μm. Further, the addition amount of the calcium carbonate particles is preferably 0.03 to 2% by weight, more preferably 0.05 to 2% by weight.
To 1.5% by weight, particularly preferably 0.1 to 1% by weight.

As the calcium carbonate used in the present invention,
Although not particularly limited, calcite crystals such as precipitated limestone, chalk, and precipitated calcium carbonate generated from limestone by a chemical method, and algo obtained by reacting lime milk with carbon dioxide gas at high temperature. Knight crystals, vaterite crystals and combinations thereof are exemplified. Heavy calcium carbonate (calcite crystal) obtained by pulverizing limestone mechanically can also be used.

[Plate-like aluminum silicate particles] The aluminum silicate particles, which are inert fine particles, which are particularly preferably added to the polyester film for a capacitor of the present invention, preferably have an average particle diameter of 0.1 to 2 µm. ,
More preferably, it is 0.3 to 1.7 μm,
It is particularly preferable that the thickness be 1.5 μm. Further, the addition amount is preferably 0.03 to 1% by weight from the viewpoint of the slipperiness of the film and the handleability in the manufacturing process of the capacitor.
More preferably 0.06 to 0.8% by weight,
It is particularly preferred that the content is 0.1 to 0.7% by weight.

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 a naturally occurring kaolin mineral. Further, the kaolin clay may have been subjected to a purification treatment such as washing with water.

[Coarse Particles] Polyester for Capacitor of the Present Invention
Coarse particles present in the steal film have a maximum diameter of 35.
The number of objects exceeding μm is 10 / m^TwoMust be
Is preferred. More preferably 8 pieces / m^TwoLess preferred
Or 5 pieces / m^TwoIt is as follows. The film of the present invention
Calcium carbonate particles or plate-like aluminum silicate
Care must be taken when chromium is contained. Maximum diameter 35
The number of coarse particles exceeding μm is 10 / m ^TwoOver, coarse
Frequent parts where the thickness of resin around large particles is thin
Insufficient insulation performance as a capacitor dielectric
Therefore, it is not preferable.

[Variation in Thickness] In the polyester film for a capacitor of the present invention, the variation in thickness at an arbitrary position is preferably 25% or less, more preferably 20% or less, particularly preferably, to the film thickness. 15% or less. If the variation in the thickness with respect to the thickness of the film exceeds 25%, it is not preferable because when the multilayer film is used as a dielectric thin film of a capacitor, the variation in the thickness causes a variation in the performance as a capacitor.

[Production conditions] The polyester film of the present invention is a biaxially stretched film containing polyethylene-2,6-naphthalenedicarboxylate as a main component. This biaxially stretched film is melted at a temperature higher than its melting point by a usual method, for example, extruded from a die slit onto a casting drum adjusted to a temperature of about 60 ° C., and then tightly cooled and solidified to obtain an unstretched film. The unstretched film can be produced by biaxially stretching in the longitudinal and transverse directions, heat setting, and, if necessary, relaxing in the longitudinal and / or transverse directions. The stretching of the film is performed by a known roll type longitudinal stretching machine, infrared heating longitudinal stretching machine, tenter crib type transverse stretching machine, a multi-stage stretching machine which performs these stretchings in a plurality of stages, a tubular stretching machine, and an oven type longitudinal stretching machine. And a simultaneous biaxial stretching machine, etc., but are not particularly limited. In the present invention, it is necessary to control the thermal distortion rate at 150 ° C. in the longitudinal direction of the film to a small value, and simultaneous biaxial stretching is preferable.

Next, the method for producing the polyester film of the present invention will be described in detail, but is not necessarily limited thereto. First, production by the simultaneous biaxial stretching method will be described. As a longitudinal stretching mechanism of the simultaneous biaxial stretching machine, there are a conventional type of a screw type in which a clip is placed on a groove of a screw to increase a clip interval, and a pantograph type in which a pantograph is used to increase a clip interval. These have problems such as a low film-forming speed and difficulty in changing conditions such as a draw ratio. However, when such equipment is already possessed, it can be used in the present invention. On the other hand, in recent years, a simultaneous biaxial tenter of a linear motor type has been developed, and has attracted attention due to its high film forming speed.
The simultaneous biaxial stretching of the linear motor system can solve these problems at once. Therefore, when a new simultaneous biaxial stretching machine is introduced, it is preferable to use equipment of this type. Also, simultaneous biaxial stretching does not use a longitudinal stretching roller as in sequential biaxial stretching, and thus has the advantage of reducing scratches on the film surface. In addition, in the sequential biaxial stretching, the surface of the benzene ring or naphthalene ring of the polyester tends to be parallel to the film surface, the refractive index nz in the thickness direction is small, the tear propagation resistance is small, and the layer is easily peeled.
This is improved with simultaneous biaxial stretching. In addition, there is a structure that can be relaxed longitudinally in the heat fixing region, and the thermal strain rate in the longitudinal direction at 150 to 210 ° C. can be reduced. Since these characteristics are consistent with the required characteristics of the capacitor film of the present invention, it is preferable to employ simultaneous biaxial stretching in the present invention.

Simultaneous biaxial stretching in the present invention refers to stretching in order to simultaneously orient the film in the machine direction and transverse direction. The film is conveyed while holding both ends of the film with clips using a simultaneous biaxial stretching machine. Refers to the operation of stretching in the vertical and horizontal directions. 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 is sufficient if there is a portion where the stretching in the longitudinal direction and the stretching in the transverse direction are simultaneously stretched temporally.Therefore, after stretching in the transverse direction or the longitudinal direction independently first, the longitudinal direction and the transverse direction are combined. A method of simultaneous stretching, a method of further stretching independently in the horizontal or vertical direction after simultaneous biaxial stretching, and the like are also included in the scope of the present invention.

In order to produce the polyester film of the present invention, after containing predetermined inactive fine particles, it is melted at, for example, a normal extrusion temperature, that is, a temperature not lower than the melting point temperature (hereinafter referred to as Tm) and not higher than (Tm + 70) ° C. The extruded film 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 at 170 ° C. for about 6 hours, extrusion temperature is around 300 ° C., and cooling drum surface temperature is 60 ° C.
It is about. The ratio of the thickness of the end portion and the center portion of the unstretched film (the thickness of the end portion / the thickness of the center portion) is desirably 1 or more and 10 or less, preferably 1 or more and less than 5, and more preferably 1 or more. , Less than 3. If the ratio of the thickness is less than 1 or more than 10, film breakage or clip detachment frequently occurs, which is not preferable.

Next, the unstretched film is guided to a simultaneous biaxial stretching machine by gripping both ends of the film with clips, and in a preheating zone, (glass transition temperature Tg-40 of polyester) to (Tg + 50) ° C. After heating in (Tg-10) to (Tg-10) to (Tg-10)
g + 70) ° C., area magnification 10 to 40 times (vertical magnification 2 to 6)
X) at the same time. Further, if necessary, the melting point of the polyester (Tm-120) to (Tm
-10) In the temperature range of -10 ° C, simultaneous biaxial stretching may be performed at an area magnification of 2 to 5 times in one step or in two or more steps. Subsequently, heat fixing is performed in a temperature range of (Tm-70) to (Tm) ° C., and if necessary, while performing heat fixing or in a cooling process after heat fixing, preferably 100 to 245.
The relaxation treatment is performed in the vertical and horizontal directions in a temperature range of ° C., 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, the film is subjected to relaxation treatment in the longitudinal and transverse directions while performing heat setting, and then cooled to room temperature and wound up to obtain a desired simultaneous biaxial polyester film. Incidentally, in the present invention, in order to impart surface properties of the film, for example, in order to impart easy adhesion, easy lubricity, release properties, antistatic properties, in the process before or after simultaneous biaxial stretching, polyester It is also preferable to coat a coating agent on the surface of the film.

The film of the present invention can be produced by ordinary sequential biaxial stretching. As described above, the unstretched film of polyethylene-2,6-naphthalenedicarboxylate obtained by a known method is used at 120 to 180 ° C, more preferably at 1 to 180 ° C.
The film is stretched in the longitudinal direction at 25 to 170 ° C, particularly preferably 130 to 160 ° C, by a roll-type longitudinal stretching machine at 3.0 to 5.0 times, more preferably 3.3 to 4.6 times. Although an infrared heating type vertical stretching machine may be used, a roll type vertical stretching machine is more preferable, especially when a thin film is stretched, because it is advantageous to uniformly heat the entire film. In order to easily stretch in the longitudinal stretching, it is preferable to perform the stretching in multiple stages by dividing the stretching into a plurality of times. After longitudinal stretching, 120-1 in the stenter
It is stretched in the transverse direction at 80 ° C, more preferably at 125 to 170 ° C, particularly preferably at 130 to 160 ° C, 3.0 to 4.5 times, more preferably 3.5 to 4.3 times, and 195 to 250 times.
C., more preferably at a temperature of 205 to 245 ° C. for 0.3 to 50 seconds, and then a heat relaxation treatment in the longitudinal and / or transverse direction at a relaxation rate of 0.5 to 15% to obtain a desired heat relaxation treatment. A polyester film can be obtained. In addition, you may use the multi-stage extending | stretching which divides extending | stretching of a horizontal direction into several steps.

The polyester film of the present invention is used as a dielectric for 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, the operating temperature is higher. It is preferably applied to film capacitors used in high places. In particular, a rectifier circuit which is closer to a heat source than before due to miniaturization of electric and electronic equipment, and a circuit of an electric component installed around an engine or in a vehicle as an electric component of an automobile, are preferably used because the use environment temperature becomes high. Further, it is preferably applied as a film for a capacitor which is required to have a withstand voltage characteristic under a high voltage and a stabilization of a capacitance under a high frequency, such as a transformer circuit of a hybrid car, an electric vehicle, an electronic exchange, etc. .

[0056]

The present invention will be further described with reference to the following examples.
The present invention is not limited only to the following examples unless the gist is changed. The measurement methods and definitions of various physical property values and characteristics in the present invention are as follows.

(1) Calculation of Component Amount (Mole Ratio of Main Component, Copolymer Component) of Polyethylene-2,6-naphthalenedicarboxylate A film sample was measured with a solvent (CDCl ₃ : CF ₃ COO).
(D = 1: 1), and then subjected to ¹ H-NMR measurement, and calculated from the integration ratio of the obtained signals.

(2) Thermal strain rate Measurement module TMA / SS manufactured by Seiko Electronic Industry Co., Ltd.
Using a model 120C and the company's thermal analysis system SSC / 5200H as a data analyzer, a film sample is sampled into a long strip in the machine direction (MD) with a width of 4 mm, and a constant load of 2.0 MPa is applied in the machine direction. In this state, the temperature is raised from room temperature at a rate of 5 ° C./min. Then, at 35 ° C., 150 ° C., and 210 ° C., the length of the film is measured, and the thermal distortion rate RMD in the longitudinal direction is calculated by the above formula. Also, the thermal distortion rate R in the transverse direction (TD)
TD conforms to the above except that a long sample is cut in the horizontal direction (TD).

(3) Fly Spec, Coarse Particles (3-1) Fly Spec
Observe and mark the fly specs present in the measurement area 1 m ² by magnifying it twice. Further, each fly spec is observed with an optical microscope, and the average diameter including the nuclei of the fly spec and the voids generated around the nucleus, that is, (major diameter / short diameter) / 2, is counted, and the number of those exceeding 60 μm is counted. .

(3-2) Coarse Particles Using a universal projector, the surface of the film was magnified 50 times with transmitted illumination and a measurement area of 1 m ² was observed. The maximum diameter of the particles existing in the film was 35 μm. The number of particles exceeding.

(4) 5% strain strength (F5 value) The film was cut into a sample having a width of 10 mm and a length of 150 mm, the chuck was set to 100 mm, and the tensile speed was 100 mm / min, and the chart speed was 500 mm / min. Pull with device. The MD and TD directions were measured, and the strength at 5% elongation was read from the obtained load-elongation curve, and divided by the original cross-sectional area to obtain a 5% strain strength (N / mm ² ).
And The F5 value in the MD direction is divided by the F5 value in the TD direction to calculate the aspect ratio.

(5) Surface roughness (center line average roughness: Ra) The center line average roughness (Ra) is a value defined by JIS B0601. In the present invention, using a non-contact type three-dimensional roughness meter (ET-30HK manufactured by Kosaka Laboratories), a semiconductor laser having a wavelength of 780 nm, an optical stylus having a beam diameter of 1.6 μm, a measurement length (Lx) of 1 mm, and a sampling pitch of 2 μm , Cutoff 0.25 mm, thickness direction magnification 10,000 times, plane direction magnification 200 times, number of scanning lines 100 (Ly = 0.2 mm)
Measure the protrusion profile of the film surface under the conditions of
Calculate the surface roughness (Ra).

(6) Density The density is measured by a floating gradient method at 25 ° C. in a density gradient tube using an aqueous solution of calcium nitrate.

(7) Film Thickness, Thickness Variation The thickness of the film is 10 cm long × 10 cm wide from an arbitrary position.
Fifty cm samples are collected at intervals of 10 cm or more both vertically and horizontally. The thicknesses (μm) T1, T2... T50 of each sample are defined as width (cm) and length (c).
m), the weight (g), and the density (g / cm ³ ) are calculated by the following formula, and the average thickness Tav of 50 samples is further determined to be the film thickness. Further, the difference between the maximum thickness Tmax and the minimum thickness Tmin among the above-mentioned 50 samples is obtained, and the ratio to the average thickness Tav is calculated by the following formula to obtain the thickness variation. Thickness T (μm) = [weight / (width × length × density)] × 100
00 Average thickness Tav (μm) = (T1 + T2 +... + T50)
/ 50 thickness variation (%) = [(Tmax−Tmin) / average thickness Tav] × 100

(8) Average particle size of inert fine particles CP-50 type centrifugal particle size analyzer (Centrifugal P, manufactured by Shimadzu Corporation)
The measurement is performed using an article size analyzer. From the integrated curve of the particles of each particle size and its abundance calculated based on the obtained centrifugal sedimentation curve, 50% by weight was obtained.
And read the value as the average particle size ("Granularity measurement technology", published by Nikkan Kogyo Shimbun, p.2, 1975).
42-247).

(9) Film-forming property of the film When the biaxially stretched film was continuously formed for 24 hours, the state of film formation was observed and evaluated according to the following criteria. ：: The number of breaks was 0 times / 24 hours, and extremely stable film formation was possible. ：: The number of breaks is 1 to 3 times / 24 hours, and stable film formation is possible. ×: The number of breaks is 4 or more / 24 hours, and the film formation is unstable.

(10) Film Roll Winding The film roll was wound on a roll with a width of 550 mm and a length of 10,000 m, and was observed at the time of film formation / slitting and after vapor deposition in capacitor processing. evaluated. ：: No wrinkles or misalignment on the surface observed by naked eyes at the time of film formation / slitting and after vapor deposition, and the wound appearance is good. ×: Wrinkles, winding deviations, etc. on the surface were observed during film formation / slit and / or visual observation after vapor deposition, and the winding appearance was poor.

(11) Insulation Resistance 200 capacitor samples of 0.1 μF were placed at 23 ° C. for 6 hours.
In an atmosphere of 5% RH, the value was measured as a 1-minute value at an applied voltage of 500 V using a super insulation resistance meter 4329A manufactured by YHP, and a capacitor sample having an insulation resistance of less than 5000 MΩ was judged as defective and judged according to the following criteria. In the present invention, ○ and △ were accepted. ：: Less than 4 defectives △: 4 or more and less than 10 defectives ×: 10 or more defectives

(12) Breakdown voltage (BDV) Measured according to the method shown in JIS C 2318, and n =
The minimum value of 200 was taken as the 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.

[Example 1] 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol were used as transesterification catalysts using 0.03 part of manganese acetate tetrahydrate, and a lubricant having an average particle diameter of 1.0 µm was used. Kaolin clay particles (plate-like aluminum silicate particles) having 0.45% by weight of calcium carbonate particles and an average particle diameter of 0.7 μm were added to 0.1%.
The mixture was added so as to contain 30% by weight and transesterified according to a conventional method. Then, 0.023 part of trimethyl phosphate was added to substantially terminate the transesterification reaction.

Then, 0.024 part of antimony trioxide was added, and a polymerization reaction was carried out by a conventional method at a high temperature and a high vacuum to obtain polyethylene-2, having an intrinsic viscosity of 0.62 dl / g.
6-naphthalenedicarboxylate (PEN Tg = 1
21 ° C.). After drying this PEN polymer at 170 ° C. for 5 hours, it was supplied to an extruder and melted at a temperature of 295 ° C.
, And filtered through a nonwoven fabric filter having an average opening of 30 µm made of a stainless steel fine wire having a wire diameter of 14 µm, extruded through a die slit, and then cooled and solidified on a casting drum to prepare an unstretched film.

The unstretched film was introduced into a simultaneous biaxial stretching machine, preheated at 140 ° C., and simultaneously held at 145 ° C. by 4.5 times in the machine direction and 4.2 times in the transverse direction with clips. Stretched. Thereafter, 3% longitudinal relaxation was given while heat setting 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.

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 was 2 Ω / □. At that time, vapor deposition was carried out in a stripe shape having a margin portion running in the longitudinal direction (repeated of 58 mm in width of the vapor deposition portion and 2 mm in width of the margin portion). Next, direct current 8
A voltage process of applying 00V to the entire width of the film is performed, and a blade is inserted into the center of each vapor deposition section and the center of each margin section to slit the entire width 30 having a margin of 1 mm to the left or right.
mm tape-shaped take-up reel.

Each of the left and right margins of the reel thus obtained was wound one on top of another, and a capacitor element having a capacitance of 0.1 μF was obtained. 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 external electrodes, and a lead wire was welded to the metallicon and cured as an exterior with epoxy resin to form a wound capacitor. Table 1 shows the evaluation results as capacitors. Dielectric breakdown voltage of 270
V / μm and high insulation resistance. It is also particularly excellent in film forming properties.

Example 2 An unstretched film was prepared in the same manner as in Example 1, except that the amount of inert particles to be added was as shown in Table 1. This film is stretched 1.8 times in the longitudinal direction (longitudinal direction) at 135 ° C., stretched twice in the longitudinal direction at 145 ° C. (longitudinal stretching ratio 3.6 times), and stretched in the transverse direction (width direction at 140 ° C.). ), And then successively biaxially stretched 3.6 times.
The film was heat-set at 2 ° C. for 3 seconds to obtain a biaxially oriented film having a thickness of 3.0 μm and wound up on a roll. The film alone was evaluated, and a capacitor element was prepared and evaluated in the same manner as in Example 1. Table 1 shows the results. Dielectric breakdown voltage is 260V
/ Μm, and has excellent insulation resistance characteristics.

Comparative Example 1 A film was formed in the same manner as in Example 1 except that the average aperture of the melt filter was set to 50 μm, and a capacitor element was prepared and evaluated. Table 1 shows the results. Many fly specifications and low dielectric breakdown voltage.

[Comparative Example 2] The heat setting temperature was set to 200 for each zone.
As C, no longitudinal relaxation was given. Otherwise, Example 1
A film was formed in the same manner as described above to prepare and evaluate a capacitor element. Table 1 shows the results. The thermal strain rate in the vertical direction at 150 ° C. was large on the negative side, and the shape of the capacitor was often defective.

Comparative Example 3 In Example 2, the stretching conditions shown in Table 1 were changed. 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 positive side, and the insulation resistance is low.

[0079]

[Table 1]

[0080]

According to the present invention, polyethylene-2,6
-It is possible to provide a film suitable for a dielectric for a capacitor which is excellent in insulation properties containing naphthalene dicarboxylate as a main component and which does not cause deterioration in workability, especially in hot pressing.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C08K 7/00 C08L 67/02 C08L 67/02 B29K 67:00 // B29K 67:00 105: 16 105: 16 B29L 7:00 B29L 7:00 H01G 4/24 321C (72) Inventor Makoto Iida 3-37-19 Koyama, Sagamihara-shi, Kanagawa F-term in the Sagamihara Research Center, Teijin Limited 4F071 AA45 AB21 AB26 AB30 AE17 AF61 AH15 BA01 BB06 BB08 BC01 BC17 4F210 AA26 AB16 AG01 AH33 QC05 QC06 QC07 QD04 QD16 QG01 QG18 4J002 CF081 DE236 DJ007 FD016 FD017 GQ01 5E082 AA05 AB04 BC35 EE07 EE24 FG37 FG24 FG22 FG37 PP08 PP09 PP10

Claims (7)

[Claims] 1. A biaxially oriented film containing polyethylene-2,6-naphthalenedicarboxylate as a main component, and has a temperature based on a length LMD (t) of the film at a temperature t ° C. in a machine direction (MD). The longitudinal thermal distortion rate RMD (T) of the film at T ° C. is expressed as RMD (T) =
｛[LMD (T) -LMD (35)] / LMD (3
5) The longitudinal thermal distortion rate RMD of the film at a temperature of 150 ° C., as defined by に よ っ て × 100 (%).
(150) is -1.5% ≦ RMD (150) ≦ 0.0
%, And the number of fly specs having an average diameter of more than 60 μm is 20 / m ² or less. 2. A film in a transverse direction (T) at a temperature t ° C.
D) Based on the length LTD (t), the longitudinal thermal distortion rate RTD (T) of the film at the temperature T ° C.
(T) = ｛[LTD (T) −LTD (35)] / LTD
(35) When defined by｝ × 100 (%),
Thermal distortion rate RT in the transverse direction of the film at a temperature of 150 ° C.
D (150) is -1.0% ≦ RTD (150) ≦ 0.
The polyester film for a capacitor according to claim 1, wherein the content is 0%. 3. A thermal distortion rate RMD (21) at a temperature of 210 ° C.
0) and RTD (210) are -3.5% ≦ RMD (21
0) ≦ 0.0%, and −3.5% ≦ RTD (210) ≦
The polyester film for capacitors according to claim 1 or 2, wherein the content is 0.0%. 4. The ratio of the longitudinal 5% strain intensity of the film to the transverse 5% strain intensity of the film is 0.90.
4. The ratio is not less than 1.40 and not more than 1.40.
The polyester film for a capacitor according to any one of the above. 5. An aluminum silicate particle containing 0.03 to 2% by weight of calcium carbonate particles having an average particle size of 0.2 to 5 μm and a plate-like aluminum silicate particle having an average particle size of 0.1 to 2 μm.
5. The composition according to claim 1, wherein the content is from 0.3 to 1% by weight.
The polyester film for a capacitor according to any one of the above. 6. The method 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 / m ² or less. A polyester film for a capacitor as described in Crab. 7. The polyester film for a capacitor according to claim 1, wherein the film is produced by a simultaneous biaxial stretching method.