JPH11170464A - Biaxially orientated polyester film for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress especially the deterioration of a capacity to the minimum possible extent through imparting the high degree of electrical properties and humidity/heat resisting characteristics by using a water-soluble or a water- dispersible resin as the principal component of a coated layer and adding a specific quantity of rust preventive to the resin. SOLUTION: Polyester is supplied to an extruder to be extruded in the form of a sheet. Next, the sheet is quenched using a cooling roll under a joining method by applying static electricity to obtain an amorphous sheet. This sheet is stretched in the longitudinal direction. In addition, a coating solution obtained by adding 9 wt.% of oxazoline compound, in terms of the solid concentration of a coating component and 0.001-3 wt.% of acetyleneglycol ethylene oxide adduct, in terms of the solid concentration of a coating component as a rust preventive, to an aqueous dispersion of copolymer (aromatics) polyurethane, is applied to both faces of a uniaxially stretched film thus obtained. Next, the film is stretched crosswise to obtain the biaxially orientated polyester film with a coated layer as thick as 0.005-0.5 μm and with a film thickness of 1.0-15 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyester film for a capacitor dielectric. More specifically, the present invention improves the withstand voltage, the moisture and heat resistance by improving the adhesion between the base film and the deposited metal, and reduces the capacitance decrease under high temperature and high humidity. And a biaxially oriented polyester film.

[0002]

2. Description of the Related Art Polyester films typified by polyethylene terephthalate have been widely used as substrate films for capacitors because of their excellent mechanical properties, heat resistance and electrical properties. However, with the development of various electronic devices and the like in recent years, higher characteristics of polyester films have been achieved. As one of the requirements for the improvement of the characteristics, there is a requirement for long-term stability to wet heat. That is, the metal-deposited polyester film has a drawback that the adhesiveness between the base film and the deposited metal, particularly the adhesiveness in a high-temperature and high-humidity environment, that is, the so-called wet heat-resistant adhesiveness, is poor. Therefore, when the capacitor is placed under high temperature and high humidity, there is a problem that moisture permeates at the interface between the base film and the vapor-deposited metal, and the capacitance of the capacitor decreases with time.In terms of long-term stability, There is a need for such improved wet heat resistance.

JP-A-60-115214 discloses a film capacitor having a vinylidene chloride coating layer, and JP-A-60-115214 discloses a coating capacitor containing melamine and / or urea resin as an essential component. Film capacitors each having a layer are disclosed as capacitors having excellent resistance to moist heat. However, even when the resin composition described in the above-mentioned publication is used, the performance of the capacitor is not always sufficiently maintained in a wet heat environment.

[0004] That is, when a capacitor is used under high temperature and high humidity, corrosion occurs in the deposited metal, and the area of the electrode is reduced, which causes a problem that the capacitance of the capacitor is reduced. This problem has been alleviated to some extent by forming a coating layer on the film to increase the adhesion to the deposited metal and to prevent the intrusion of oxygen and moisture, but it is not complete and further improvement is desired.

In addition, during the production of a capacitor,
In the step of contacting the film with a solvent, or the step of mechanically applying a force such as winding, pressing or laminating, the coating layer may be damaged, causing a problem that the electrical characteristics are deteriorated. That is, when the coating layer has a mechanically insufficient strength, is brittle, or has poor solvent resistance, excellent capacitor characteristics cannot be obtained.

[0006] In particular, the recent development of various electronic devices has been remarkable, and the demand for advanced electrical characteristics required for capacitors and their long-term reliability, especially the long-term stability of the capacitor performance to wet heat resistance, has further increased. Accordingly, there is an increasing demand for improving the characteristics of a film used as a dielectric.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an effect of providing excellent adhesion to an electrode metal layer, excellent heat resistance and solvent resistance, and an effect of preventing corrosion of a deposited metal. Polyester that has high electrical properties and moisture and heat resistance when used as a dielectric of metal-deposited film capacitors, and can especially suppress the capacity reduction and contribute to long-term reliability improvement of capacitors It is an object of the present invention to provide a film.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned problems, and as a result, have found that a polyester film having a coating layer containing a rust preventive agent has excellent moisture-heat resistance with a metal-deposited thin film. It has been found that a capacitor element using this metal-deposited polyester film has excellent electrical properties and wet heat resistance, and has completed the present invention.

That is, the gist of the present invention is that a thickness of 0.00
A biaxially oriented polyester film having a total thickness of 1.0 to 15 μm having a coating layer of 5 to 0.5 μm on at least one side, wherein the coating layer is mainly composed of a water-soluble or water-dispersible resin, and contains a rust inhibitor. The biaxially oriented polyester film for a dielectric material of a metal-deposited film capacitor characterized by containing 0.001 to 3% by weight.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyester in the present invention refers to a polyester comprising an aromatic dicarboxylic acid component and an alkylene glycol component, and preferably 80% by mole or more of the constituent unit is ethylene terephthalate, and 80% by mole or more of the constituent unit is ethylene terephthalate. Either polyethylene naphthalate, which is ethylene naphthalate, or poly-1,4-cyclohexane dimethylene terephthalate, in which 80 mol% of the constituent units are 1,4-cyclohexane dimethylene terephthalate. Further, it may be a copolymer containing components other than the above components,
Such components include, for example, diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, 1,
Examples thereof include diol components such as 4-butanediol, dicarboxylic acid components such as isophthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, and sebacic acid; and oxymonocarboxylic acids such as oxybenzoic acid and ester-forming derivatives thereof. be able to. Also, 2
A mixture of two or more polyesters may be used.

[0011] The polyester film of the present invention is intended to improve the slipperiness of the film and improve the workability.
It is preferable to form protrusions on the surface, and for that purpose, it is preferable to include particles in the film within a range that does not deteriorate the characteristics of the capacitor described below. Examples of such particles include calcium carbonate, calcium phosphate, silica, titanium oxide, alumina, kaolin, talc, zeolite, barium sulfate, calcium fluoride, lithium fluoride and other inorganic particles, calcium oxalate, crosslinked polymer particles and other organic particles. So-called precipitated particles obtained by depositing particles and a metal component contained as a catalyst or the like are included.

The average particle size of the particles is usually 0.001 to 5 μm
, Preferably in the range of 0.01 to 3 μm, more preferably 0.1 to 2 μm, and the particle content in the film is usually 0.01 to 5% by weight, preferably 0.05 to 2% by weight.
%, More preferably 0.1 to 1% by weight. When the average particle size is less than 0.001 μm or the particle content is less than 0.01%, the effect of improving the handleability of the film tends to be insufficient. On the other hand, when the average particle size exceeds 5 μm or when the amount of added particles exceeds 5% by weight, electric characteristics such as withstand voltage characteristics tend to decrease.

As additives other than the above-mentioned projection-forming agent, if necessary, antistatic agents, stabilizers, lubricants, crosslinking agents, antiblocking agents, antioxidants, coloring agents, light blocking agents, ultraviolet rays An absorbent or the like may be contained within a range that does not deteriorate the capacitor characteristics. The coating layer of the film of the present invention can be provided by applying a coating liquid containing a water-soluble or water-dispersible resin as a solid component and containing a specific amount of a rust inhibitor.

The resin constituting the coating layer includes polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, and the like. Examples thereof include polyurethane-based resins and copolymers and mixtures of these resins. Among these, the most preferred coating resin is a polyurethane resin, and when a polyurethane resin is used, extremely high adhesiveness and long-term wet heat resistance can be obtained. Hereinafter, this polyurethane resin will be described in detail.

The polyurethane resin as used in the present invention refers to a high molecular compound having a urethane bond in the polymer main chain, and is composed of a polyol, a polyisocyanate, a chain extender, a crosslinking agent and the like. Examples of polyols include polyoxyethylene glycol, polyoxypropylene glycol, polyoxypropylene triol, polyethers such as polyoxytetramethylene glycol, polyethylene adipate, polyethylene butylene adipate, polypropylene adipate, polyhexylene adipate, poly Examples include polyesters such as caprolactone, acrylic polyols, and castor oil.

Examples of polyisocyanates include tolylene diisocyanate, phenylene diisocyanate,
4,4'-diphenylmethane diisocyanate, 1,5
-Aromatic diisocyanates such as naphthalene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, 4,
Examples include aliphatic diisocyanates such as 4'-dicyclohexylmethane diisocyanate and isophorone diisocyanate.

Examples of the chain extender or the crosslinking agent include ethylene glycol, propylene glycol, butanediol, hexanediol, diethylene glycol, trimethylolpropane, glycerin, hydrazine, ethylenediamine, diethylenetriamine, 4,4'-diaminodiphenylmethane, 4'-diaminodicyclohexylmethane, water and the like.

The coating layer of the film of the present invention preferably contains an aromatic polyurethane in which the above-mentioned isocyanate component is aromatic, and similarly contains an aliphatic polyurethane in which the isocyanate component is aliphatic. More preferred. The proportion of the aromatic polyurethane in the coating layer is preferably 10% by weight or more, more preferably 20 to 90% by weight, and most preferably 30 to 80% by weight. If the content of the aromatic polyurethane is small, desired capacitor characteristics may not be obtained. The proportion of the aliphatic polyurethane in the coating layer is usually 90%.
% By weight, preferably in the range of 10-80% by weight, most preferably 20-70% by weight. By containing the aliphatic polyurethane, the hydrolysis resistance of the coating layer is improved, and the wet heat resistance of the capacitor is improved.

At the time of synthesizing the polyurethane, an aromatic isocyanate and an aliphatic isocyanate can be used in combination. That is, a polyurethane having two or more kinds of polyisocyanates of aromatic isocyanate and aliphatic isocyanate in one molecule can also be preferably used. The polyurethane-based coating agent used in the present invention is a coating agent using water as a medium, but may contain an organic solvent as an auxiliary without departing from the gist of the present invention. In order to use water as a medium, a coating agent forcibly dispersed with a surfactant or the like may be used, but a hydrophilic nonionic component such as a polyether or a cationic agent such as a quaternary ammonium salt is preferable. It is a self-dispersible coating agent having a group, and more preferably a water-soluble or water-dispersible coating agent having an anionic group. A water-soluble or water-dispersible coating agent having an anionic group is a compound having an anionic group bonded to a resin by copolymerization, grafting, or the like,
It is appropriately selected from sulfonic acid, carboxylic acid, phosphoric acid and salts thereof.

In order to impart water solubility to the resin, it is generally preferred that the counter ion of the anionic group be an alkali metal. However, in the present invention, the counter ion is preferably used in order to highly satisfy the wet heat resistance of the capacitor. The ion is preferably selected from amine-based onium ions containing ammonium ions. The amount of the anionic group of the water-soluble or water-dispersible resin having an anionic group is preferably in the range of 0.05 to 5% by weight. If the amount of anionic group is less than 0.05% by weight, the water solubility or dispersibility of the polyester resin may be poor. If the amount of anionic group exceeds 5% by weight, the water resistance of the coating layer may be poor, Moisture absorption causes the films to adhere to each other, or reduces the moisture and heat resistance.

On the other hand, in the present invention, the rust inhibitor to be contained in the coating layer refers to a substance having an effect of reducing the corrosion rate in an environment where metal corrodes. In particular,
For example, use is made of a compound capable of realizing 70% or more, preferably 75% or more, more preferably 80% or more in the range of 0.01 to 1.0% by weight of the rust inhibitor added, as defined below. can do. The corrosion inhibition rate as used herein refers to the weight loss of steel after being immersed in a 5% aqueous solution of hydrochloric acid at 25 ° C. for 72 hours, and from the results when the rust inhibitor was added to the aqueous solution and when it was not added. It is calculated using the following equation.

[0022]

(Equation 2)

Here, a indicates the weight reduction of the steel when the rust inhibitor is not added, and b indicates the weight reduction of the steel when the rust inhibitor is added. When calculating the a value and the b value, 20 samples of the same type and the same shape of steel are prepared, and 10 points are randomly selected and processed to obtain the average value. In each case, the weight of the aqueous hydrochloric acid solution is at least 100 times the weight of the steel.

Since the effect of the rust inhibitor is not always large when the amount added is large, the amount added to the aqueous solution in this test is arbitrarily changed in the range of 0.01 to 1.0% by weight, % Can be used if a corrosion inhibition rate of at least% is obtained. When the addition of 1.0% by weight or more is required, the amount of the rust inhibitor required in the coating layer is too large when actually used, which may cause deterioration of the electric characteristics.

The rust preventive includes a water-soluble rust preventive, an oil-soluble rust preventive, and a vaporizable rust preventive. In the present invention, the water-soluble or oil-soluble rust preventive has an affinity for water. Is preferred. Examples of rust inhibitors include naphthenic acid, abietic acid,
Soaps of a carboxylic acid such as oleic acid or dimer acid with a metal or an amine, in which case the metal is sodium,
Examples of amines such as potassium, calcium and barium include rosinamine, dodecylamine, cyclohexylamine and the like. Further, fatty acid partial esters such as sorbitan and pentaerythritol, sulfonates such as petroleum sulfonate and dinonylnaphthalene sulfonate, octaethylbenzene sulfonate, alkyl phosphates, alkanolamides, imidazolines, amine derivatives such as quinoline, and alkylamines Examples include ethylene oxide, propylene oxide adducts, acetylene glycol, and ethylene oxide adducts thereof.
Among these, in addition to the effect of corrosion prevention, in the point of being able to highly satisfy the coating suitability in the coating process, in the present invention,
Most preferably, acetylene glycol or its ethylene oxide adduct is used.

In order not to lower the electrical characteristics of the capacitor, the content of the metal component in the rust inhibitor is preferably small, and the content of the metal component is preferably 5% by weight or less, more preferably 1% by weight or less. Most preferably, it is 0.5% by weight or less. The content of the rust inhibitor in the present invention with respect to the coating layer is in the range of 0.001 to 3% by weight. 0.0
If the amount is less than 01% by weight, the effect of preventing corrosion of the metal deposited layer is insufficient, while if it exceeds 3% by weight, there arises a problem that the adhesion between the metal deposited layer and the coating layer becomes insufficient. The lower limit of the rust inhibitor content is preferably 0.01% by weight, more preferably 0.1% by weight, and the upper limit is preferably 1% by weight.
More preferably, it is 0.5% by weight.

As a method of using a rust preventive agent to prevent corrosion of the deposited metal, for example, a method of incorporating a rust preventive agent into a film can be considered. However, in this case, the total amount of the rust preventive agent in the interelectrode dielectric increases because the effective amount of the rust preventive agent is present in the film, which may adversely affect the electrical characteristics. Therefore, addition to a coating layer that is present only on the surface is a preferred method.

Further, the coating layer of the film of the present invention preferably contains a crosslinking agent in order to improve the solvent resistance. Examples of such a cross-linking agent include compounds such as an epoxy-based, isocyanate-based, aziridine-based, melamine-based, oxazoline-based, silane-coupling agent, and titanium-coupling agent. Oxazoline-based crosslinking agents are preferred. The oxazoline-based cross-linking agent refers to a compound containing an oxazoline ring acting as a cross-linking component in the structural formula, but has an affinity for components constituting the coating layer, a film-forming property, a reactivity, a base film or a metal deposition layer From the viewpoint of adhesiveness to the polymer, those having an oxazoline ring as a side chain of the polymer are preferred. As such a polymer, an acrylic polymer is particularly preferred in terms of reactivity and the like. Although the molecular weight of the oxazoline compound is not particularly limited, it is generally in the range of 1,000 to 100,000, and the content of the oxazoline ring in the compound is usually 1 to 3.
0% by weight. The oxazoline compound is preferably water-soluble or water-dispersible.

The content of the oxazoline-based crosslinking agent is as follows:
The content of the oxazoline ring with respect to the total solid content in the coating solution is preferably 0.1 to 5% by weight. When the content of the oxazoline ring is less than 0.1% by weight, the effect of improving the strength and solvent resistance of the coating layer tends to be insufficient. If the solvent resistance is insufficient, when it comes into contact with solvents in the capacitor manufacturing process,
The coating layer is deformed, and the vapor deposition layer is damaged, and the electric characteristics are deteriorated. On the other hand, if it exceeds 5% by weight, the coating layer becomes brittle, and cracks may occur in the coating layer during the capacitor manufacturing process or during use, which may cause problems such as deterioration of electrical characteristics. The oxazoline ring content is preferably in the range of 0.2 to 3% by weight, more preferably 0.5 to 2% by weight.

The thickness of the coating layer of the film of the present invention is 0.1.
005 to 0.5 μm, preferably 0.01 to 0.5 μm.
The range is 2 μm. It is necessary to reduce the thickness of the coating layer in order to reduce the size of the capacitor. In addition, the thickness is 0.
If it exceeds 5 μm, the electrical characteristics, particularly the dielectric loss characteristics, are undesirably deteriorated. On the other hand, if the thickness of the coating layer is 0.0
If the thickness is less than 05 μm, it is difficult to obtain a uniform coating layer, so that uneven coating is likely to occur on the product, which is inappropriate.

The coating layer of the film of the present invention contains silica as inorganic fine particles in order to improve sticking property and sliding property.
Silica sol, alumina, alumina sol, zirconium sol, kaolin, talc, calcium carbonate, calcium phosphate, titanium oxide, barium sulfate, carbon black,
Molybdenum sulfide, antimony oxide sol, etc., as organic fine particles, polystyrene, polyethylene, polyamide,
It may contain polyester, polyacrylate, epoxy resin, silicone resin, fluorine resin and the like.

Further, if necessary, an antifoaming agent, a coating improver, a thickener, an antistatic agent, an organic lubricant, an organic polymer particle, an ultraviolet absorber, a foaming agent, a dye, a pigment and the like are applied. It may be contained in the liquid. As a method of applying the above-mentioned coating solution to a polyester film, there is a reverse roll coater, a tar gravure coater, a rod coater, an air doctor coater, or other coats described in "Coating System", written by Yuji Harasaki, Maki Shoten, 1979. A method of applying a coating solution outside the process of producing a biaxially stretched polyester film using an apparatus, and more preferably, a method of applying a coating solution within the process of producing a film. As a method of applying in the film manufacturing process, a method of applying a coating solution to a polyester unstretched film, sequentially or simultaneously biaxially stretching, applying to a uniaxially stretched polyester film, and further perpendicularly to a uniaxial stretching direction. Or a method in which the film is applied to a biaxially stretched polyester film and further stretched in the transverse and / or longitudinal directions.

The center line average roughness (Ra) of the surface of the coating layer formed as described above is preferably 0.005 to 5.
0.5 μm, more preferably 0.01 to
0.3 μm, particularly preferably 0.02 to
The range is 0.1 μm. If Ra is less than 0.005 μm, the slipperiness of the film may be insufficient. on the other hand,
If Ra exceeds 0.5 μm, the surface may be too rough and the withstand voltage characteristics and the wet heat resistance may be deteriorated.

The total thickness of the film of the present invention is 1.0 to 1
5 μm, preferably 2.0 to 12 μm, more preferably 3.0 to 10 μm. In order to produce a small, high-performance capacitor, the film needs to be thin. However, when the total thickness is less than 1.0 μm, the proportion of the thickness of the coating layer becomes relatively large. It is not preferable because the improvement effect is not sufficient and it becomes difficult to form a coating layer having a uniform thickness. On the other hand, if the total thickness exceeds 15 μm, a high-quality, small-sized capacitor cannot be obtained. The total thickness in the present invention refers to the total thickness of the film including the coating layer.

As described above, the moisture-heat resistance can be improved by providing a coating layer on the film. However, when the shrinkage characteristic of the film is within the specific range specified in the present invention, the long-term moisture-heat resistance is further enhanced. Is achieved. That is, when the shrinkage in the longitudinal direction of the film simultaneously satisfies the following expressions (2) and (3), excellent characteristics can be obtained.

[0036]

Equation 3] _{-1.0% <S 150 <+ 2.5} % (2) -1.0% <S 180 <+ 3.5% (3) ( In the formula, S _150, S _180, respectively 150 ° C, 1
4 shows the shrinkage of the film at 80 ° C. (Positive values indicate shrinkage, negative values indicate elongation.)

If the shrinkage in the longitudinal direction of the film is larger than the above range, the dimensional stability of the film is inferior. There is. On the other hand, when the shrinkage ratio shows a negative value and elongates beyond the above range, the electrical characteristics of the capacitor may be deteriorated. Although the cause is not necessarily clear, the cooling can and the film are brought into contact with each other so that the film is not damaged by the heat received at the time of vapor deposition. Adhesion becomes insufficient, causing sagging and wrinkles. This is considered to be a cause of deterioration of the electric characteristics.

In order to highly satisfy the above-mentioned characteristics, S
₁₅₀ further -0.5 + 2.0% in the range, S ₁₈₀ is preferably a further -0.5 + 2.5% range. In addition to the shrinkage characteristics of the film, the film has a Young's modulus in the longitudinal direction of 4.5 GPa or more, preferably 5.0 GPa or more.
When it is GPa or more, higher moist heat resistance can be obtained. That is, in the step of performing metal vapor deposition on a film, the film is unwound and vapor-deposited while running under a certain tension. Therefore, if the film does not have sufficient strength, that is, Young's modulus, against the tension, the film cannot withstand the tension, and will be greatly damaged by heat generated by vapor deposition. According to the knowledge of the present inventors, when such damage is received, the uniformity of the vapor-deposited film is reduced in the same manner as the requirement for the shrinkage characteristics described above, and thus the yield during the production of the capacitor is reduced or obtained. The electrical characteristics and wet heat resistance of the capacitor are reduced. If the Young's modulus in the longitudinal direction of the film is in the above range,
Such electrical characteristics and wet heat resistance are highly satisfied.

Next, the method for producing the film of the present invention will be specifically described. The polyester raw material is supplied to the extrusion device,
It is melt-extruded at a temperature equal to or higher than the melting point of the polyester and extruded as a molten sheet from a slit die. Next, the molten sheet is quenched and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

The electrostatic application adhesion method is generally such that a linear electrode is provided on the upper surface of a sheet in a direction perpendicular to the flow of the sheet, and a DC voltage of about 5 to 10 kV is applied to the electrode to statically apply the sheet. This is a method of giving a charge and improving the adhesion to the drum. In addition, the liquid application adhesion method is a method of improving the adhesion between the drum and the sheet by uniformly applying the liquid to the entire or a part of the surface of the rotary cooling drum (for example, only the part in contact with both ends of the sheet). It is. In the present invention, both may be used as needed.

The sheet thus obtained is stretched in the biaxial direction to form a film. By setting the stretching and heat treatment conditions in an appropriate range, the shrinkage characteristics characteristic of the film of the present invention can be achieved. . Specifically, the biaxial stretching conditions are as follows. The unstretched sheet is first stretched in the first axial direction so that its birefringence (Δn) becomes 0.06 or more, preferably 0.08 or more. The stretching temperature range is 70 to 150 ° C., the stretching magnification is 2.5 to 6 times, and the desired birefringence is obtained by appropriately combining the temperature and the magnification. Stretching can be performed in one step or two or more steps. Next, the second axis direction, that is, once cooled the uniaxially oriented film below the glass transition point in the direction orthogonal to the first axis direction, or without cooling, for example, preheated to a temperature range of 80 to 150 ° C., 2.5 to 5 times at the same temperature, preferably 3.0 to 4.5
The film is stretched twice to obtain a biaxially oriented film.

It is preferable that the stretching in the first axial direction is performed in two or more steps because good thickness uniformity can be achieved. Further, a method of further stretching in the longitudinal direction after the transverse stretching is possible, but in any case, it is preferable to set the total stretching ratio in the longitudinal direction to 3.5 times or more. The film thus obtained is heated at 180 ° C. to 240 ° C. for 1 second to 5 minutes.
The heat treatment is performed in a temperature range of 200C, preferably in a temperature range of 200C to 240C. At this time, re-stretching may be performed in the longitudinal direction, the lateral direction, or both directions during or after the heat treatment step.

In order to obtain the above-mentioned specific range of shrinkage characteristics, 3-30%, preferably 5-20% in the longitudinal or transverse direction or both directions in the heat treatment step during film production.
%, A method in which the film is subjected to off-line thermal relaxation under low tension, and the like are preferably used. Although shrinkage characteristics are improved by using a method of increasing the heat treatment temperature during film production, using such a method,
It is not preferable because the electrical characteristics, particularly the dielectric loss characteristics, of the polyester film deteriorate. Specifically, when the heat treatment temperature exceeds 240 ° C., the film density becomes too high, and high electrical characteristics cannot be obtained. On the other hand, if the temperature is lower than 180 ° C., the heat shrinkage of the film becomes large, causing dimensional changes in the step of receiving heat during the production of the capacitor, thereby deteriorating the productivity of the capacitor and deteriorating the capacitor characteristics such as withstand voltage. Occurs. In any case, in the present invention, a specific shrinkage property is achieved by heat treatment while relaxing the film.

As a method for providing the coating layer of the present invention, in particular, a coating solution is applied to a uniaxially stretched polyester film stretched in the first axial direction by a roll stretching method, and is appropriately dried or not dried. A method in which the uniaxially stretched film is immediately stretched in the second axial direction and heat-treated is preferred.
According to this method, the coating layer can be dried simultaneously with the stretching, and the thickness of the coating layer can be reduced according to the stretching ratio, and the uniformity of the thickness is improved. Can also be made very strong. A film which is advantageous in terms of cost and is suitable as a substrate for a capacitor dielectric can be produced at low cost.

The coating layer in the present invention may be provided on only one side of the polyester film, but is preferably provided on both sides. When the coating is applied to only one surface, a coating layer other than the coating solution of the present invention may be formed on the opposite surface as needed to impart other properties to the polyester film of the present invention.

The film may be subjected to a chemical treatment or a discharge treatment before application in order to improve the coating property and adhesion of the coating agent to the film. It is particularly preferable to perform the corona discharge treatment in terms of treatment efficiency, cost, and simplicity of the treatment. Also,
In order to improve the adhesiveness, coatability, and the like of the coating layer of the biaxially stretched polyester film of the present invention, the coating layer may be subjected to a discharge treatment after the formation of the coating layer.

In the case of forming an electrode by metal evaporation when manufacturing a capacitor using the film of the present invention, the metal to be evaporated includes aluminum, palladium, zinc, nickel, indium, tin, chromium, titanium and the like. However, a particularly preferred metal is aluminum. The thickness of the metal deposited film is preferably in the range of 1 to 200 nm, and the method of vapor deposition is generally vacuum deposition, but may be electroplating, sputtering or the like. In addition, the metal deposition layer may be provided on both sides of the polyester film. After the metal deposition, a surface treatment of the deposited metal layer or a coating treatment with another resin may be performed.

Two metal-deposited polyester films obtained in this manner are superposed and wound (including winding of a double-sided metal-deposited polyester film and another film including the polyester film of the present invention), or a large number of sheets. Laminated to make a capacitor element, according to the usual method,
For example, a capacitor can be formed by hot pressing, taping, metallikon, voltage treatment, sealing of both ends, attachment of a lead wire, and the like, but of course, the capacitor is not limited to these.

[0049]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “parts” means “parts by weight”. (1) Intrinsic viscosity of polymer [η] (dl / g) 1 g of polymer is phenol / tetrachloroethane = 50
/ 50 (weight ratio) in 100 ml of a mixed solvent.
Measured in ° C. (2) Average particle size (μm) of particles Particle size distribution measuring device (SA-CP) manufactured by Shimadzu Corporation
Integrated volume fraction 5 in equivalent spherical distribution measured by type 3)
The particle size of 0% was defined as the average particle size.

(3) Film Thickness (μm) Approximately 100 films are cut into a square of 10 cm × 10 cm, and the weight is measured. Then count the number,
The film thickness is calculated from the film density, the total film area and the weight.

[0051]

(Equation 4)

(4) Shrinkage The film cut out to a width of 30 mm and a length of 50 cm was heat-treated in an oven set at a predetermined temperature for 3 minutes without tension. From the dimensions of the film before and after heat treatment,
The shrinkage (%) at 0 ° C. and 180 ° C. was calculated.

[0053]

(Equation 5)

(5) Center line average roughness (Ra) (μm) It was determined as follows using a surface roughness measuring instrument (SE-3F) manufactured by Kosaka Laboratory Co., Ltd. That is, a portion of the reference length L (2.5 mm) is extracted from the film cross-sectional curve in the direction of the center line, and the center line of the extracted portion is the x-axis, and the direction of the vertical magnification is the y-axis. When represented by f (x), the value given by the following equation was represented by [μm]. The center line average roughness was obtained by calculating ten cross-sectional curves from the surface of the sample film, and expressing the average value of the center line average roughness of the sampled portion obtained from these cross-sectional curves. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08.
mm.

[0055]

(Equation 6)

(6) Film density (g / cm ³ ) Measured by a density gradient tube method using a mixed solution of n-heptane and carbon tetrachloride. The measurement was performed at a temperature of 25 ° C. (7) Young's modulus (GPa) Tensile tester Intesco Model 20 manufactured by Intesco Corporation
The measurement was performed in a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH using a Model 01. That is, length 300m
The sample film having a width of 25 mm and a width of 25 mm is pulled at a strain rate of 10% / min, and is calculated by the following equation using the first straight line portion of the tensile stress-strain curve.

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E = Δσ / Δε (where E is the tensile modulus, Δσ is the stress difference between the two points on the straight line due to the original average cross-sectional area, and Δε is the strain difference between the same two points. )

The thickness of the film for determining the average sectional area was determined by a gravimetric method. That is, 10cm × 10
The total weight of 100 pieces of the film cut into a square of cm was measured and calculated using the density of the film.

(8) Solvent Resistance of Coating Layer A liquid bisphenol A type epoxy resin used as a curing agent was applied to a surface of an aluminum vapor-deposited film at a thickness of 0.5 μm in the production of a capacitor described later.
The film was treated at 100 ° C. for 30 minutes under no tension, and the shape change of the film surface was observed with a microscope. The following evaluation was made based on the state of the surface shape change due to the erosion of the coating layer. Rank A: Almost no change in surface shape was observed. Rank B: 10% or less of the area changed in shape. Rank C: The shape changed in a portion exceeding 10% as an area.

(9) Heat Resistance of Coating Layer The aluminum vapor-deposited film in the production of a capacitor described below was heat-treated in an oven at a predetermined temperature under no tension for 10 minutes. The film surface after the heat treatment was observed with a microscope, and the shape change of the coating layer surface was observed. Rank A: Almost no change in surface shape was observed even after heat treatment at 120 ° C. Rank B: A heat treatment at 120 ° C. causes cracks on the surface and fine irregularities. Rank C: Cracks are formed on the surface or fine irregularities are generated by heat treatment at 100 ° C. or less.

(10) Evaluation of electrical characteristics Withstand voltage characteristics Measurement was performed according to JIS C-2319. That is, using a 10 kV DC withstand voltage tester, 23 ° C., 50%
Under an atmosphere of RH, the voltage was increased at a rate of 100 V / sec, and the voltage when the film was broken and short-circuited was read.

Change in capacitance (manufacture of capacitor) A capacitor was manufactured and evaluated as follows. That is, the resistance of a vacuum chamber was set to 10 ⁻⁴ Torr by using a resistance heating type metal deposition apparatus on the film surface.
Aluminum was deposited to a thickness of 45 nm as follows.
At that time, vapor deposition was performed in a stripe shape having a margin portion in the longitudinal direction of the polyester film (the width of the vapor deposition portion was 8 mm,
The width of the margin part is 1 mm repeatedly). The obtained vapor-deposited polyester film was slit into a 4.5 mm width tape having a left or right margin of 0.5 mm width. Each of the obtained left margin and right margin vapor-deposited polyester films, one by one, was wound together to obtain a wound body. At this time, the two films were wound while being shifted so that the vapor deposition portion protruded by 0.5 mm in the width direction. The wound body is heated at 140 ° C. and a pressure of 50 kg / cm ² for 5 hours.
Pressed for minutes. After applying a lead wire after spraying metallikon on both end surfaces of the wound body after pressing, impregnated layer with liquid bisphenol A type epoxy resin, and a minimum thickness of 0.5 mm by heating and melting the powdery epoxy resin. An exterior was formed to obtain a film capacitor having a capacitance of 0.1 μF.

(Measurement of Change in Capacitance) While applying a DC voltage of 60 V / μm between the electrodes of the obtained capacitor, the capacitor was allowed to stand for 1000 hours in an atmosphere of a temperature of 70 ° C. and a humidity of 95% RH. Was determined as a reference value. That is, the value obtained by subtracting the initial capacitance from the capacitance after 1000 hours was divided by the initial capacitance and expressed as a percentage.

AC Withstand Voltage A 1 kHz AC voltage was applied between the electrodes of the capacitor obtained above, and the time t until dielectric breakdown occurred was measured. The same measurement was performed by changing the applied voltage V, and the relationship between V and t was plotted. The applied voltage at t = 15 hours was defined as the AC withstand voltage. The value of the AC withstand voltage at 100 ° C. and 25
The values at ° C. were compared and evaluated according to the following criteria. Rank A: Even at 100 ° C., the decrease in AC withstand voltage is small and good. Rank B: AC withstand voltage is slightly lowered at 100 ° C., but there is no practical problem. Rank C: The AC withstand voltage at 100 ° C. is greatly reduced, and there is a practical problem.

Example 1 (Synthesis of polyurethane for coating layer) Terephthalic acid 665
Parts, 635 parts of isophthalic acid, 1,4-butanediol 4
A polyester polyol was obtained using 60 parts and 470 parts of neopentyl glycol as starting materials.
20 parts and 270 parts of dimethylolpropionic acid were added to obtain a carboxyl group-containing polyester polyol. 160 parts of tolylene diisocyanate was added to 1900 parts of this polyester polyol to obtain an aromatic polyester polyurethane solution. The solvent was removed while adding the obtained solution to an aqueous ammonia solution to obtain an aqueous dispersion of an aromatic polyester polyurethane (A).

(Production of film raw material polyester) 100 parts of dimethyl terephthalate, ethylene glycol 60
And 0.09 part of calcium acetate monohydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out a transesterification reaction.
The temperature was raised to ° C. to substantially complete the transesterification reaction.
Next, 0.3 parts of silica particles having a particle diameter of 1.2 μm were added as an ethylene glycol slurry. After adding the slurry, further add 0.06 parts of phosphoric acid and 0.09 parts of antimony trioxide.
4 parts were added, the reaction system was gradually reduced in pressure, the temperature was raised, and the polycondensation reaction was performed for 4 hours to obtain a polyester (a) having an intrinsic viscosity of 0.66.

(Production of Polyester Film) The polyester (a) was dried by a conventional method and supplied to an extruder.
It was melted at 0 ° C., extruded into a sheet, and quenched on a cooling roll using an electrostatic contact method to obtain an amorphous sheet. The obtained sheet was stretched 3.8 times in the longitudinal direction at 80 ° C. using a roll stretching method. In the obtained uniaxially stretched film, the above-mentioned aqueous dispersion of the copolymerized polyurethane was coated with Epocross K2020E (manufactured by Nippon Shokubai Co., Ltd.) as an oxazoline compound at a solid concentration of 9% by weight as an application component, and an acetylene glycol ethylene oxide adduct ( A coating solution containing 0.9% by weight as a coating component solid content concentration of trade name: Surfynol 440) was applied to both sides of the film, and then the film was guided to a tenter, and 4.1 times at 110 ° C. in the horizontal direction. The film was stretched and heat-treated at 230 ° C. while relaxing 7% in the transverse direction to obtain a biaxially oriented polyester film having a coating layer thickness of 0.05 μm and a film thickness of 6.0 μm. In this case, the oxazoline ring content based on the solid content in the coating solution was 1.1% by weight. Further, the corrosion prevention rate of the rust preventive was 82%. As shown in Table 1 below, the metal-deposited film capacitor prepared using the obtained film was a metal-deposited polyester film capacitor having excellent withstand voltage characteristics, a small decrease in capacitance, and excellent in wet heat resistance.

Comparative Example 1 A biaxially oriented polyester film having a thickness of 5 μm was obtained in the same manner as in Example 1 except that the coating solution was not applied. The capacitor made by using the obtained film was inferior in moisture-heat resistance as compared with Example 1.

Example 2 Aqueous dispersion of aliphatic polyester polyurethane in the same manner as in Example 1 except that 4,4'-dicyclohexylmethane diisocyanate was used in place of tolylene diisocyanate used in the preparation of polyester polyurethane for coating agent in Example 1. A body (B) was obtained. The coating agent used in Example 1 was 55 parts / 45 parts by weight as a solid content of the aromatic polyester polyurethane (A) and the aliphatic polyester polyurethane (B), and Epocross K2030E manufactured by Nippon Shokubai Co., Ltd. as the oxazoline compound. 5 for total solids
% By weight, and a coating solution containing 0.5 parts by weight of monobutyl phosphate as a rust preventive agent and 0.3 parts of cyclohexylamine ethylene oxide adduct was added. The relaxation rate in the process is 1
Except that it was set to 0%, the thickness was 5.1 in the same manner as in Example 1.
A μm biaxially oriented polyester film was obtained. In this case, the oxazoline ring content relative to the solid content in the coating solution is 0.1.
It was 62% by weight.

Example 3 A copolymerized polyester resin was produced as a coating agent as follows. That is, 30 parts of dimethyl terephthalate, 70 parts of dimethyl isophthalate, 15 parts of dimethyl sebacate,
Dimethyl-5-sulfoisophthalate sodium salt 6
And 80 parts of ethylene glycol as a starting material, and 0.04 part of manganese acetate tetrahydrate was added as a catalyst, and the mixture was heated and heated, and methanol was distilled off to carry out a transesterification reaction. It took 3 hours from the start of the reaction to raise the temperature to 230 ° C., thereby substantially terminating the transesterification reaction. Next, 0.01 part of phosphoric acid was added to the reaction product, and 0.04 part of antimony trioxide was further added to perform a polycondensation reaction.
After 4 hours, a copolymerized polyester having an intrinsic viscosity of 0.50 was obtained. A solution prepared by dissolving 20 parts of the obtained copolymerized polyester in 80 parts of tetrahydrofuran was mixed with water 180 under high-speed stirring.
After the addition, the mixture was heated to evaporate tetrahydrofuran to obtain an aqueous dispersion of copolymerized polyester (C). The obtained aqueous dispersion (C) and the polyester polyurethane dispersion (A) produced in Example 1 were mixed, and the weight ratio of the copolymerized polyester / aromatic polyester polyurethane was 30 parts / 70 parts as solids. And EPOXROS RS manufactured by Nippon Shokubai Co., Ltd. as an oxazoline compound.
500 in the same manner as in Example 2 except that the coating treatment was performed using a coating liquid containing 2.5% by weight of the total solid content and 1.5 parts by weight of sodium benzoate as a rust inhibitor. Coating thickness 0.05μm, film thickness 5.1μm
Was obtained. In this case, the oxazoline ring content based on the solid content in the coating solution was 0.62% by weight.

Example 4 In Example 2, a coating thickness of 0.04 μm and a film thickness of 5.1 μm were obtained in the same manner as in Example 1 except that the heat treatment temperature of the film was set at 200 ° C. and the relaxation treatment was not performed during the heat treatment. Was obtained. Example 5 A biaxially oriented polyester film having a coating layer thickness of 0.05 μm and a total film thickness of 6.0 μm was obtained in the same manner as in Example 1 except that the oxazoline compound was not contained in the coating layer. .

Comparative Example 2 The procedure of Example 1 was repeated, except that no rust inhibitor was added to the coating composition.
A biaxially oriented polyester film having a film thickness of 5.0 μm was obtained. Capacitors manufactured using this film are:
In the heat and humidity resistance, the capacitance was greatly reduced.

Comparative Example 3 The same procedure as in Example 2 was carried out except that the coating layer contained 5% by weight of a rust inhibitor.
A biaxially oriented film having a thickness of 5 μm and a film thickness of 5.1 μm was obtained. The capacitor manufactured using the film was slightly inferior in moisture heat resistance and AC withstand voltage.

Comparative Example 4 The total film thickness was 5.1 in the same manner as in Example 1, except that the thickness of the coating layer was changed to 0.8 μm.
A μm biaxially oriented film was obtained. A capacitor made using the obtained film had poor AC withstand voltage characteristics. Comparative Example 5 In Example 1, a film was formed with the thickness of the coating layer being 0.0005 μm.
A uniform coating layer could not be obtained. The capacitor using the film was poor in moist heat resistance.

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[Table 1]

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[Table 2]

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[Table 3]

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The film of the present invention has excellent adhesion to the electrode metal layer, heat resistance and solvent resistance, and has the effect of preventing corrosion of the deposited metal. In this case, the capacitor provides high electrical characteristics and moisture and heat resistance, and in particular, can suppress a decrease in capacity, thereby contributing to an improvement in long-term reliability of the capacitor, and has a high industrial value.

Claims (2)

[Claims] 1. A biaxially oriented polyester film having a total thickness of 1.0 to 15 μm having a coating layer of 0.005 to 0.5 μm on at least one side, wherein the coating layer is formed of a water-soluble or water-dispersible resin. Main component, 0.00% rust inhibitor
A biaxially oriented polyester film for a metal-deposited film capacitor dielectric, comprising 1 to 3% by weight. 2. The biaxial orientation for a metal-deposited film capacitor dielectric according to claim 1, wherein the rust inhibitor is a compound having a corrosion inhibition rate defined by the following formula (1) of 70% or more. Polyester film. (Equation 1) (In the above formula, a and b are 25% aqueous solution of hydrochloric acid,
° C., weight loss of steel after 72 hours immersion, a is
The weight loss of the steel when no rust inhibitor is added, and b indicates the weight loss of the steel when the rust inhibitor is added)