JPH08250373A - Polyester film for capacitor - Google Patents

Abstract

PURPOSE: To provide a polyester film, which excels in adhesion with an electrode metal layer, provides high electric characteristics and moisture/heat resistance characteristics when it is used as the dielectric of a metallized film capacitor and improves the long-term reliability of the capacitor. CONSTITUTION: A biaxially oriented polyester film for a capacitor is provided with a 0.05-1.0μm thick coat layer composed of water soluble or water dispersing resin at least on one plane, has a refractive index (nα) of 1.490 or higher in the film thickness direction, a plane orientability (ΔP) of over 0.170 and a Young's modulus of 5.0GPa or more in the film longitudinal direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially oriented polyester film for capacitors. Specifically, the present invention is
The present invention relates to a biaxially oriented polyester film for a capacitor dielectric, which has excellent adhesion to an electrode metal layer and provides high electrical properties and resistance to moist heat.

[0002]

BACKGROUND OF THE INVENTION Biaxially oriented polyester films have various properties such as mechanical properties, heat resistance, electrical properties, and chemical resistance in a well-balanced manner, and have good cost performance. Because of its superiority, it is widely used as an industrial material for magnetic tape, packaging, plate making, and the like. Among them, for capacitors, demand for capacitors manufactured from a polyester film, which can be miniaturized, is rapidly increasing as electric devices are miniaturized.

Particularly in recent years, with the development of electronic devices and the like, there is a demand for higher performance of such polyester films for capacitors. First, it is necessary that the electrical properties of the polyester film are good. For example, it is necessary that the withstand voltage characteristics are good and that there are no insulation defects. In particular, when the film is thin, foreign matter may be present on the film, and unevenness in thickness may result in poor insulation. Further, it is required that the basic characteristics such as the dielectric constant and the dielectric loss as a capacitor dielectric are good. Moreover, it is necessary that these characteristics are good and change little in a wide temperature range from normal temperature to high temperature. That is, it is also necessary that such electrical characteristics are stable for a long period of time even under conditions of high temperature and high humidity, and that so-called long-term wet-heat resistance stability is good.

The metal vapor-deposited polyester film has a drawback in that the adhesiveness between the base film and the vapor-deposited metal, particularly in a high temperature and high humidity environment, that is, the so-called moisture and heat resistance, is poor, so that the conventional capacitor is not used. Despite being covered with epoxy resin to a sufficient thickness, when it is stored under high temperature and high humidity for a long time, moisture permeates at the interface between the base film and the evaporated metal, which causes electrostatic discharge due to corrosion of the evaporated electrode. There are problems such as a large decrease in capacity, and there is a need for improved moisture and heat resistance of capacitors in terms of long-term stability.

As a countermeasure for this, there is a method in which a low-viscosity epoxy resin is applied under reduced pressure instead of being applied in the atmosphere, and the resin is permeated deep inside the capacitor element due to the pressure difference from the atmospheric pressure. However, this low-viscosity epoxy resin foams under reduced pressure, adheres to the lead wires, and when soldering a capacitor element to a printed wiring board, it is easy to cause a serious failure such as no soldering, and overvoltage is applied. The self-healing effect is also poor when it is applied, and the withstand voltage characteristic of the capacitor deteriorates.

Japanese Patent Publication No. 2-59612 discloses a capacitor made of a film having a coating layer of vinylidene chloride, and Japanese Patent Publication No. 2-59613 discloses coating using a melamine and / or urea resin as an essential component. A capacitor made of a film having layers is disclosed as a capacitor having excellent wet heat resistance. However, even if the resin composition described in the above publication is used, the performance of the capacitor is not always sufficiently maintained in a humid heat environment. For example, even if the decrease in electrostatic capacity is suppressed in a moist heat atmosphere of 40 ° C., the electrostatic capacity is rapidly decreased in a moist heat atmosphere of 60 ° C. or higher.

In order to solve such a problem, a method of using a polyester film provided with a coating layer has been proposed, but even in that case, there are some problems. That is, when the thickness of the coating layer is thinner than the film thickness, the influence on the electrical characteristics of the film is small and the problem is not significant, but when the thickness of the polyester film is thin, the ratio of the thickness of the coating layer to the whole is Therefore, the influence of the characteristics of the coating layer must be taken into consideration. For example, characteristics such as withstand voltage and dielectric loss usually have a problem that they adversely affect a coating material having a structure containing many polar groups.

Further, in order to obtain more advanced characteristics,
It is necessary to consider the influence of damage given to the film in the process of depositing metal on the film. That is, in the usual metal vapor deposition process, vapor deposition is performed between the unwinding and winding of the film, so that the film is thermally damaged under tension. It is necessary that the film retains excellent properties and does not deteriorate the capacitor properties even when it is exposed to severe mechanical and thermal conditions in the vapor deposition process.

Recent development of various electronic devices is remarkable,
The demand for long-term reliability required for capacitors, especially long-term resistance to moisture and heat resistance, is further increasing. Therefore, the required characteristics of the film used for the dielectric of the capacitor having such high reliability have become more severe. Moreover, there is a strong demand for miniaturization of capacitors accompanying the miniaturization of electric equipment products in recent years, and it is indispensable to reduce the thickness of the film used as the dielectric, and it is necessary to improve the overall characteristics including the influence of the coating layer described above. It is needed.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, a polyester film having a coating layer, the film satisfying a requirement for a specific orientation, and mechanically It has been found that when the strength is high, high electrical properties and wet heat resistance can be satisfied at the same time, and excellent properties as a capacitor dielectric are achieved, and the present invention has been completed.

That is, the gist of the present invention is that the thickness of the water-soluble or water-dispersible resin on at least one surface is 0.005.
It has a coating layer of μm to 1.0 μm, the refractive index (nα) in the thickness direction of the film is less than 1.490, and the degree of plane orientation (Δ
P) exceeds 0.170, and the Young's modulus in the longitudinal direction of the film is 5.0 GPa or more.

The present invention will be described in detail below. The polyester constituting the film of the present invention is a polyester obtained by using aromatic dicarboxylic acid or its ester and glycol as main starting materials, and 80% or more of repeating structural units are ethylene terephthalate units or ethylene-2,6- Refers to polyesters with naphthalate units. Further, other third component may be contained as long as it does not deviate from the above range. Examples of the aromatic dicarboxylic acid component of the third component include, for example, terephthalic acid and 2,6-naphthalenedicarboxylic acid, as well as isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxy). Benzoic acid etc.) and the like can be used. As the glycol component, other than ethylene glycol, for example, one kind or two or more kinds of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used.

The intrinsic viscosity of the polyester is usually 0.45 or more, preferably 0.50 to 1.0, more preferably 0.52 to 0.80. When the intrinsic viscosity is less than 0.45, there arises a problem that productivity during film production is lowered and mechanical strength of the film is lowered. On the other hand, it is preferable that the intrinsic viscosity does not exceed 1.0 from the viewpoint of melt extrusion stability of the polymer.

The polyester film of the present invention contains particles in the polyester for the purpose of preventing the occurrence of scratches on the film during the production of the film and imparting slipperiness to the film so as to improve the handling property. Are preferably formed. Examples of such particles include calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, inorganic particles such as molybdenum sulfide, crosslinked polymer particles, oxalic acid. Examples thereof include organic particles such as calcium, and precipitated particles generated during polyester polymerization.

The average particle size of the particles contained in the film of the present invention is preferably 0.005 to 5.0 μm, more preferably 0.01 to 3.0 μm. If the average particle size exceeds 5.0 μm, there is a tendency that problems arise such that the insulating property is deteriorated due to the roughening of the surface, or the particles fall off from the film surface to cause an insulating defect. Also,
If the average particle diameter is less than 0.005 μm, the formation of protrusions may be insufficient, which may cause scratches on the surface of the film or reduce the handleability of the film.

The particle content is based on polyester.
Usually 0.01 to 5.0% by weight, preferably 0.05 to
2.0% by weight, more preferably 0.1 to 1.5% by weight
Is. When the particle content is less than 0.01% by weight, the projections on the film surface are insufficient and the slipperiness tends to be insufficient. On the other hand, if the content of particles exceeds 5.0% by weight, the particles may easily fall off, or the particles may aggregate to form coarse protrusions, causing problems such as insulation defects.

Two or more kinds of such particles may be mixed in the film, or particles of the same kind but having different particle diameters may be mixed. In any case, it is preferable that the average particle diameter of all the particles contained in the film and the total content thereof satisfy the above-mentioned ranges. In the production of polyester containing particles, the particles may be added during the polyester synthesis reaction or may be added directly to the polyester. When it is added during the synthesis reaction, a method of adding it as a slurry in which particles are dispersed in ethylene glycol or the like at any stage of polyester synthesis is preferable. On the other hand, when it is directly added to the polyester, a method of adding and mixing to the polyester as a dried particle or as a slurry dispersed in water or an organic solvent having a boiling point of 200 ° C. or less using a twin-screw kneading extruder is preferable. . It should be noted that the particles to be added may be subjected to treatments such as crushing, dispersing, classifying, and filtering, if necessary.

As a method for controlling the content of particles, a master raw material containing a high concentration of particles is prepared by the above-described method, and the master raw material is diluted with a raw material containing substantially no particles at the time of film formation. A method of adjusting the particle content is effective. Further, as an additive other than the above-mentioned protrusion forming agent, if necessary, an antistatic agent, a stabilizer, a lubricant, a cross-linking agent, an antiblocking agent, an antioxidant, a colorant, a light blocking agent, an ultraviolet absorber, etc. May be contained within a range that does not deteriorate the capacitor characteristics.

The polyester film of the present invention may have a multi-layer structure as long as the finally obtained properties satisfy the constitution of the present invention. Further, in the film of the present invention, a coating layer is provided on the surface of the film in order to enhance the adhesiveness with the vapor-deposited metal. Examples of the coating material that constitutes the coating layer include resins such as polyester, polyamide, polystyrene, polyacrylate, polycarbonate, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyvinyl alcohol, polyurethane, and the like. Examples thereof include polymers and mixtures. The most preferable coating resin among these is a polyurethane resin. When a polyurethane resin is used, it is possible to obtain extremely high adhesiveness and long-term wet heat resistance stability. Hereinafter, the coating layer made of the polyurethane resin will be described in detail.

The polyurethane coating layer in the present invention comprises
It is obtained by applying a coating solution containing an aromatic polyurethane, preferably a coating solution containing an aromatic polyurethane and an aliphatic polyurethane, and then drying. The proportion of the aromatic polyurethane in the coating layer is usually 20% by weight or more, preferably 30 to 90% by weight, more preferably 30 to 8% by weight.
It is in the range of 0% by weight. If the proportion of aromatic polyurethane in the coating layer is low, desired capacitor characteristics may not be obtained.

The proportion of the aliphatic polyurethane in the coating layer is usually 80% by weight or less, preferably 10 to 70% by weight, more preferably 20 to 70% by weight.
By using the aliphatic polyurethane, the hydrolysis resistance of the coating layer is improved and the long-term wet heat resistance is improved. The following polyols, polyisocyanates, chain extenders, cross-linking agents and the like can be exemplified as components constituting the polyurethane in the present invention.

Examples of polyols include polyoxyethylene glycol, polyoxypropylene glycol, polyoxypropylene triol, polyethers such as polyoxytetramethylene glycol, polyethylene adipate, polyethylene-butylene adipate, polypropylene adipate and polyhexene. Examples include xylene adipate, polyesters such as polycaprolactone, acrylic polyols, castor oil, and the like.

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,
Aliphatic diisocyanates such as 4′-dicyclohexylmethane diisocyanate and isophorone diisocyanate can be mentioned. Examples of chain extenders or crosslinkers include ethylene glycol, propylene glycol,
Butanediol, hexanediol, diethylene glycol, trimethylolpropane, glycerin, hydrazine, ethylenediamine, diethylenetriamine, 4,
4'-diaminodiphenylmethane, 4,4'-diaminodicyclohexylmethane, water and the like can be mentioned.

The aromatic polyurethane in the present invention means
The above-mentioned polyisocyanate component is a polyurethane in which the polyisocyanate component is aromatic, and similarly, the aliphatic polyurethane is a polyurethane in which the polyisocyanate component is aliphatic. Aromatic polyisocyanates and aliphatic polyisocyanates are often used together during the synthesis of polyurethane,
Polyurethanes having two or more kinds of polyisocyanates of aromatic polyisocyanate and aliphatic polyisocyanate in one molecule can also be particularly preferably used.

The polyurethane in the present invention is preferably a coating agent using water as a medium for safety and hygiene, but within a range not exceeding the gist of the present invention, an organic agent as an auxiliary agent for a water-soluble or water-dispersible resin is used. It may contain a solvent. When water is used as a medium, it may be a coating agent forcibly dispersed with a surfactant or the like, but is preferably a hydrophilic nonion component such as polyethers or a cationic agent such as a quaternary ammonium salt. A self-dispersion type coating agent having a group, and more preferably a water-soluble or water-dispersible coating agent having an anionic group. The water-soluble or water-dispersible coating agent having an anionic group is a compound having a compound having an anionic group bound to a resin by copolymerization or grafting, and sulfonic acid, carboxylic acid, phosphoric acid and their It is appropriately selected from salts and the like.

In order to impart water solubility to the resin, the counter ion of the anionic group is preferably an alkali metal ion, but from the viewpoint of the heat and humidity resistance of the capacitor described later, the counter ion of the anionic group is an ammonium ion. It is preferable to select from amine-based onium ions containing The amount of the anionic group in the water-soluble or water-dispersible coating agent having the anionic group is preferably in the range of 0.05 to 8% by weight. When the amount of the anionic group is less than 0.05% by weight, the water solubility or water dispersibility of the resin may be poor, and the amount of the anionic group is 8%.
When the content is more than 5% by weight, the water resistance of the undercoat layer after coating may be poor, moisture absorption may cause the films to stick to each other, or the wet heat resistance may be deteriorated.

The coating liquid in the present invention contains an isocyanate compound as a cross-linking agent in order to improve the adhesion (blocking property), water resistance, solvent resistance and mechanical strength of the coating layer,
Contains epoxy compounds, amine compounds, aziridine compounds, silane coupling agents, titanium coupling agents, zirco-aluminate coupling agents, peroxides, heat and photoreactive vinyl compounds and photosensitive resins. May be.

Further, in order to improve the stickiness and slipperiness, silica, silica sol, alumina, alumina sol, zirconium sol, kaolin, talc, calcium carbonate, calcium phosphate, titanium oxide, as inorganic fine particles in the coating layer,
Barium sulfate, carbon black, molybdenum sulfide, antimony oxide sol, etc. are used as organic fine particles such as polystyrene, polyethylene, polyamide, polyester, polyacrylic ester, epoxy resin, silicone resin,
It may contain a fluororesin or the like. Further, if necessary, it may contain a defoaming agent, a coating property improving agent, a thickener, an antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment and the like. .

The content of alkali metal in the coating solution is preferably 1000 ppm or less, more preferably 500 ppm or less, and particularly preferably 200 ppm or less, based on the solid content of the coating solution. When the content of the alkali metal in the coating solution is high, the wet heat resistance of the capacitor tends to be poor. It is difficult to avoid mixing of alkali metal as an impurity in the coating liquid in the preparation process from the raw material synthesis for industrial production. In addition, tap water or groundwater is often used as the commercially available coating agent. Furthermore, it is general that an alkali metal is used as a counter ion of the hydrophilic functional group of the anionic resin preferably used in the present invention in order to make the resin water-soluble. Therefore, a desired coating liquid may be obtained by performing deionization treatment as needed.

A reverse roll coater, a gravure coater, a rod coater, an air doctor coater or the like described in "Coating Method" by Yuji Harasaki, Maki Shoten, issued in 1979, can be used to apply the above-mentioned coating liquid to a polyester film. Other coating devices can be used. The coating layer may be provided in the film production process or may be applied after the film production. In particular, the method of coating in the film manufacturing process is preferable from the viewpoint of uniformity of coating thickness and production efficiency.

As a method of coating in the film production process, a coating solution is applied to a polyester unstretched film and biaxially stretched sequentially or simultaneously, or a uniaxially stretched polyester film is coated, and then uniaxially stretched. There is a method of stretching in a direction perpendicular to the direction, or a method of coating on a biaxially stretched polyester film and further stretching in a transverse and / or longitudinal direction.

The thickness of the coating layer is 0.005 to 1.0 μm.
And preferably in the range of 0.01 to 0.5 μm. The thickness of the coating layer is preferably thin in view of the demand for miniaturization of the capacitor. Especially the coating layer thickness is 1.0μ
If it exceeds m, the electrical characteristics may be deteriorated, which is not preferable. On the other hand, when the thickness of the coating layer is less than 0.005 μm, coating unevenness and coating loss occur.

The coating layer formed as described above preferably has a water droplet contact angle of 60 ° or more. If the water droplet contact angle is less than 60 °, the water-resistant adhesion with the metal vapor deposition film may be poor. Therefore, it is preferable to appropriately change the amount of hydrophilic groups, the amount of emulsifiers, and the amount of hydrophilic compounds of the coating agent. The center line average roughness (Ra) of the coating layer surface formed as described above is preferably in the range of 0.005 to 0.5 μm, and more preferably in the range of 0.01 to 0.3 μm. , Particularly preferably in the range of 0.02 to 0.1 μm. When Ra is less than 0.005 μm, the slipperiness of the film may be insufficient. On the other hand, Ra is 0.5 μm
If it exceeds, the surface may be too rough and the withstand voltage characteristics and the moist heat resistance characteristics may deteriorate.

As described above, the wet heat resistance can be improved by providing a coating layer on the film, but when the orientation property of the film provided with such a coating layer is within a specific range,
A high degree of moist heat resistance is achieved. That is, when the refractive index (nα) in the thickness direction of the film is less than 1.490 and the plane orientation degree (ΔP) exceeds 0.170, excellent properties can be obtained. The degree of plane orientation is such that the refractive index in the main orientation direction of the film is nγ, the refractive index in the direction orthogonal to the main orientation direction is nβ,
When the refractive index in the thickness direction is nα, it is given by the following formula.

[0035]

## EQU1 ## When ΔP = (nγ + nβ) / 2−nα nα and ΔP satisfy such conditions, the film itself and the coating layer have good thickness uniformity, and the film is less damaged by heat received during metal deposition. Therefore, it is considered that the obtained moist heat resistance becomes extremely high. In order to further enhance the effect of the present invention, nα
Is preferably less than 1.487 and ΔP is preferably 0.1.
The range is 73 or more.

Furthermore, in addition to having such orientation properties, when the density of the film is less than 1.3980 g / cm ³ , preferably less than 1.3960 g / cm ³ , the electrical properties of the film, such as dielectric constant and dielectric loss properties, are Even if the coating layer contains a large number of polar groups and may deteriorate the electrical characteristics, the electrical characteristics of the film as a whole will be excellent, which is preferable.

In addition to such film orientation conditions, the Young's modulus in the longitudinal direction of the film must be 5.0 GPa or more, and preferably 5.5 GPa or more. When such conditions are satisfied, a high degree of resistance to moist heat can be obtained. That is, in the step of performing metal vapor deposition on the film, the film is unwound and vapor-deposited while running while applying a constant tension. Therefore, if the film does not have sufficient strength against such tension, that is, Young's modulus, the film cannot withstand the tension and is greatly damaged by the heat of vapor deposition. According to the knowledge of the present inventors, when such damage is caused, the heat-resistant dimensional stability of the vapor-deposited film is lowered, so that the yield at the time of manufacturing the capacitor is reduced, and the electrical characteristics and wet heat resistance of the obtained capacitor are reduced. Will decrease. When the Young's modulus of the film in the longitudinal direction is within the range of the present invention, such electric characteristics and wet heat resistance are highly satisfied.

In addition to this, when the Young's modulus in the longitudinal direction of the film at 100 ° C. is 1.0 GPa or more, preferably 1.2 GPa or more, it is less likely to be damaged by the heat during the vapor deposition, so that the electrical characteristics of the capacitor are improved. And the heat and humidity resistance is further highly satisfied. Further, the film of the present invention preferably has a longitudinal shrinkage of less than 2.0% after being treated at 120 ° C. for 30 minutes, and is 1.5%.
% Is more preferable. When the heat shrinkage ratio in the longitudinal direction is large, the film undergoes dimensional changes in the process of receiving heat during the manufacturing of the capacitor, which causes problems such as deterioration of productivity and shortening of the life of the capacitor. Next, the method for producing the film of the present invention will be specifically described.

The polyester raw material is fed to the extruder,
It is melt extruded at a temperature equal to or higher than the melting point of polyester and extruded as a molten sheet from a slit-shaped die. Next, the molten sheet is rapidly cooled and solidified on the rotary cooling drum so as to have a temperature not higher than the glass transition temperature to obtain a substantially non-oriented sheet in an amorphous state. In this case, in order to improve the flatness of the sheet, it is preferable to enhance the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid coating adhesion method is preferably adopted.

The electrostatic application contact method referred to here is usually a method in which a linear electrode is placed on the upper surface of the sheet in a direction orthogonal to the flow of the sheet, and a DC voltage of about 5 to 10 kV is applied to the electrode. This is a method of imparting an electrostatic charge to the sheet to improve the adhesion to the drum. In addition, the liquid application contact method is a method for improving the adhesion between the drum and the sheet by uniformly applying the liquid to the whole or part of the surface of the rotary cooling drum (for example, only the portions that contact both ends of the sheet). Is. In the present invention, both may be used together if necessary.

In the present invention, the thus-obtained sheet is biaxially stretched to form a film, which is a feature of the film of the present invention by setting the stretching and heat treatment conditions in appropriate ranges. Orientation and Young's modulus can be achieved. To describe the biaxial stretching conditions in detail, the unstretched sheet is first stretched in the first axial direction so that the birefringence (Δn) is 0.06 or more, preferably 0.08 or more. The stretching temperature range is 70 to 150 ° C., the stretching ratio is 2.5 to 6 times, and the desired birefringence is obtained by appropriately combining the temperature and the stretching ratio. The stretching can be performed in one step or in two or more steps. Next, in the second axial direction, that is, in the direction orthogonal to the first axial direction, the uniaxially oriented film is once cooled below the glass transition point, or is preheated to a temperature range of, for example, 80 to 150 ° C. without cooling, 2.5 ~ under almost the same temperature
The film is stretched 5 times, preferably 3.0 to 4.5 times to obtain a biaxially oriented film.

It is preferable to carry out the stretching in the first axial direction in two or more steps because good thickness uniformity can be achieved. A method in which the film is transversely stretched and then re-stretched in the longitudinal direction is also possible, but in any case, it is preferable to set the total stretching ratio in the longitudinal direction to 3.0 times or more. The film thus obtained is heat-treated for 1 second to 5 minutes under an elongation of 30%, a limited shrinkage, or a constant length. At this time, re-stretching may be performed in the longitudinal direction, the transverse direction, or both directions within or after the heat treatment step.

In the present invention, the film density is 1.3.
Less than 980 g / cm ³ , preferably 1.3960 g / c
It is desirable to be less than m ^3, and since the above characteristics are satisfied, the temperature of the above-mentioned heat treatment step is appropriately selected. The heat treatment temperature depends on the stretching conditions, but is preferably 180 to 2
The temperature is 40 ° C, more preferably 200 to 225 ° C. When the heat treatment temperature exceeds 240 ° C., the film density becomes too high, and high electrical characteristics may not be obtained. On the other hand, if the temperature is less than 180 ° C., the heat shrinkage rate of the film becomes large, causing a dimensional change in the process of receiving heat during the manufacturing of the capacitor and deteriorating the productivity of the capacitor.
Problems such as deterioration of capacitor characteristics such as withstand voltage may occur.

As the method for providing the coating layer of the present invention, in particular, the coating solution is applied to a uniaxially stretched polyester film stretched in the first axial direction by a roll stretching method, and the coating solution is appropriately dried or not dried. A method in which a uniaxially stretched film is immediately stretched in the second axis direction and heat treated is preferable.
According to this method, the coating layer can be dried at the same time as stretching, the thickness of the coating layer can be thinned according to the stretching ratio, and the uniformity of the thickness can be improved. The adhesiveness with can also be made extremely strong. It is also advantageous in terms of cost, and a film suitable as a substrate for a capacitor dielectric can be manufactured at low cost.

When applying by this method,
The thickness of the obtained coating layer is preferably 0.005 μm or more.
0.5 μm, more preferably 0.01 μm to 0.2 μm
m. If it is attempted to form a coating layer having a thickness of more than 0.5 μm by this method, a large amount of heat is required to dry the coating layer, which causes stretching unevenness, which is not preferable. On the other hand, it is not preferable to provide a coating layer having a thickness of 0.005 μm or less, because coating unevenness and coating dropout easily occur.

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. In addition, when coated on only one surface, a coating layer other than the coating layer in the present invention may be formed on the opposite surface, if necessary, to impart other properties to the polyester film of the present invention. In addition, in order to improve the coating property and the adhesive property of the coating agent on the film, the film may be subjected to a chemical treatment or a discharge treatment before the coating. Corona discharge treatment is particularly preferable in terms of treatment efficiency, cost, and ease of treatment. Further, in order to improve the adhesiveness, coatability, etc. of the coating layer of the biaxially stretched polyester film of the present invention, the coating layer may be subjected to discharge treatment after the coating layer is formed.

In the present invention, the metal to be vapor-deposited is
Aluminum, palladium, zinc, nickel, gold, silver,
Copper, indium, tin, chromium, titanium and the like can be mentioned, but a particularly preferable metal is aluminum. Note that the above metals include metal oxides. The thickness of the metal vapor deposition film is preferably in the range of 10 to 5000Å, and the vapor deposition method is generally a vacuum vapor deposition method, but may be an electroplating method, a sputtering method, or the like. The metal vapor deposition layer may be provided on both sides of the polyester film. Further, the surface treatment of the vapor-deposited metal layer or the coating treatment with another resin may be performed after the metal vapor deposition.

Two metal-deposited polyester films thus obtained are superposed and wound (including a double-sided metal-deposited polyester film and another film including the polyester film of the present invention) or a large number of sheets The capacitor element can be formed by laminating and heat-pressing, taping, metallikon, voltage treatment, both end surface sealing, lead wire attachment, etc. can be performed according to a conventional method to obtain a capacitor, but not limited to these. Absent.
From the viewpoint of long-term reliability of the capacitor, the capacitor according to the present invention has a temperature of 60 ° C. and a humidity of 95% RH at 100% while applying a DC voltage of 60 V / μm between its electrodes.
It is preferable that the rate of change in capacitance after standing for 0 hour is -10 to 10%.

[0049]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The evaluation methods in the examples are as follows. In Examples and Comparative Examples, "part" means "part by weight".

(1) Intrinsic viscosity of polymer [η] (d
1 / g) 1 g of polymer is phenol / tetrachloroethane = 50
Dissolved in 100 ml of a mixed solvent of 50/50 (weight ratio),
It was measured at 30 ° C. (2) Average particle size (μm) Centrifugal sedimentation type particle size distribution measuring device (SA-CP, manufactured by Shimadzu Corporation)
Equivalent spherical distribution measured by type 3) 5
The particle size of 0% was taken as the average particle size.

(3) Center line average roughness (Ra) (μm) The roughness was determined as follows using a surface roughness measuring device (SE-3F) manufactured by Kosaka Laboratory Ltd. That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-section curve in the direction of the center line, and the center line of the extracted portion is taken as the x-axis, and the direction of longitudinal magnification is taken as 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 represented by the average value of the center line average roughness of the extracted portions obtained from the 10 section curves obtained from the surface of the sample film. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08.
mm.

[0052]

[Equation 2]

(4) Degree of plane orientation (ΔP) and refractive index in thickness direction (nα) Using an Abbe refractometer manufactured by Atago Optical Co., Ltd., the maximum value nγ of refractive index in the film plane and the refractive index in the direction perpendicular thereto nβ,
Further, the refractive index nα in the film thickness direction was measured, and the plane orientation degree ΔP was calculated from the following equation. The measurement of the refractive index was performed at 23 ° C. using sodium D line.

[0054]

(Equation 3)

(5) Film Density (g / cm ³ ) The density was measured by a density gradient tube method using a mixed solution of n-heptane and carbon tetrachloride. The measurement temperature was 25 ° C. (6) Young's modulus (GPa) Intesco Co., Ltd. Tensile tester Intesco Model 20
The measurement was performed using a 01 model in a room controlled at a temperature of 23 ° C. and a humidity of 50% RH. That is, the length is 300m
A sample film of m, 25 mm wide is pulled at a strain rate of 10% / min and is calculated by the following equation using the first linear part of the tensile stress-strain curve.

[0056]

[Equation 4] E = Δσ / Δε (In the above equation, E is the tensile elastic modulus, Δσ is the stress difference due to the original average cross-sectional area between two points on the straight line, and Δε is the strain difference between the same two points.) The thickness of the film when determining the average cross-sectional area was determined by the gravimetric method. That is, the total weight of 100 films cut into a square of 10 cm × 10 cm was measured and calculated using the density of the film.

(7) Water Droplet Contact Angle (°) The contact angle between the sample film and distilled water under a temperature of 23 ° C. and a humidity of 50% RH was measured by a contact angle meter (CA-DT manufactured by Kyowa Interface Science Co., Ltd.). -A type). The contact angle is
A total of 6 points were measured with 2 points on the left and right and 3 points on the number of samples, and the average value was calculated as the contact angle. The diameter of the water droplets was 2 mm, and 1
The number after a minute was read.

(8) Analysis of alkali metal ions Li, Na, K, Rb, Cs and Fr were quantified by a calibration curve method using an atomic absorption spectrometer (Spectro AA) manufactured by Varian.

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

(Ii) Change in capacitance (manufacture of capacitor) A capacitor was manufactured and evaluated as follows. That is, a resistance heating type metal vapor deposition apparatus was used on the film surface, and the pressure in the vacuum chamber was adjusted to 10 ⁻⁴ Torr.
As described below, aluminum was vapor-deposited to a thickness of 450Å.
At that time, the polyester film was vapor-deposited in a stripe shape having a margin portion in the longitudinal direction (width of vapor deposition portion 8 mm,
Repeated width of the margin is 1 mm). The obtained vapor-deposited polyester film was slit into a tape shape having a width of 4.5 mm having a margin portion having a width of 1 mm on the left or right. Each of the obtained vapor-deposited polyester films of the left margin and the right margin was wound together to obtain a wound body. At this time, the two films were shifted and wound so that the vapor deposition portion protruded 0.5 mm each in the width direction. The wound body was pressed at a temperature of 140 ° C. and a pressure of 50 kg / cm 2 for 5 minutes. After spraying metallikon on both end surfaces of the rolled body after pressing and applying a lead wire, liquid bisphenol A
A type epoxy resin impregnated layer and a powdered epoxy resin were heat-melted to form an outer package having a minimum thickness of 0.5 mm to obtain a film capacitor having a capacitance of 0.1 μF.

(Measurement of Capacitance Change) 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 temperature 60 ° C. and humidity 95% RH to obtain the initial capacitance. The rate of change in electrostatic capacitance was determined with the reference value as. 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.

(Iii) AC Withstanding Voltage An AC voltage of 1 kHz was applied between the electrodes of the capacitor obtained above, and the time t until the dielectric breakdown occurred was measured. The same measurement was performed while changing the applied voltage V, the relationship between V and t was plotted, and the applied voltage at t = 15 hours was defined as the AC withstand voltage. The value of such AC withstanding voltage at 100 ° C and 25
The values at ° C were compared and evaluated according to the following criteria. Rank A: Decrease in AC withstand voltage is small even at 100 ° C. Good Rank B: Decrease in AC withstand voltage at 100 ° C, but practically no problem Rank C: Decrease in AC withstand voltage is large at 100 ° C There's a problem

Example 1 (Synthesis of Polyurethane) A polyester polyol was obtained from 660 parts of terephthalic acid, 635 parts of isophthalic acid, 472 parts of 1,4-butanediol and 447 parts of neopentyl glycol as starting materials, and 321 parts of adipic acid. And 268 parts of dimethylolpropionic acid were added to obtain a carboxyl group-containing polyester polyol. 1880 parts of this polyester polyol was mixed with 1 part of tolylene diisocyanate.
60 parts were added to obtain an aromatic polyester polyurethane solution. The solvent was removed while introducing the obtained solution into an aqueous ammonia solution to obtain an aromatic polyester polyurethane water dispersion (A). On the other hand, an aliphatic polyester polyurethane water dispersion (B) was obtained in the same manner as above except that 4,4′-dicyclohexylmethane diisocyanate was used instead of tolylene diisocyanate.

(Production of Polyester for Film Raw Material) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol
Part and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out an ester exchange reaction.
The temperature was raised to 0 ° C. to substantially complete the transesterification reaction. Next, 0.3 part of silica particles having a particle size of 1.3 μm was added as an ethylene glycol slurry. After addition of the slurry, 0.05 part of phosphoric acid and 0.
04 parts was added, the reaction system was gradually evacuated, the temperature was raised and the polycondensation reaction was carried out for 4 hours to obtain a polyester (a) having an intrinsic viscosity of 0.65.

(Production of Polyester Film) Polyester (a) was dried by an ordinary method and fed to an extruder.
It was melted at 0 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application contact method to obtain an amorphous sheet. The obtained sheet was stretched by a roll stretching method in the longitudinal direction at 85 ° C. for 2.6 times and then at 95 ° C. for 1.8 times. The resulting uniaxially stretched film was composed of 50 parts of the above-mentioned aromatic polyester polyurethane (A) (solid content weight, the same applies hereinafter) and 50 parts of the aliphatic polyester polyurethane (B), and a coating solution using water as a medium was applied to both sides of the film. The film, then guide the film to a tenter,
It was stretched 4.1 times at 2 ° C. and heat treated at 210 ° C. to obtain a biaxially stretched polyester film having a coating layer thickness of 0.04 μm and a base polyester film thickness of 4.5 μm.
The content of alkali metal in the coating liquid was 40 ppm of Na and 5.0 ppm of K in terms of solid content of the coating liquid, and other alkali metals were below the detection limit. The contact angle of water droplets on the coating layer was 63 °, and the center line average roughness (Ra) was 0.023 μm. The metal-evaporated film capacitor manufactured using the obtained film has excellent withstand voltage characteristics and little change in capacitance, as shown in Table 1 below.
It was a metal-deposited polyester film capacitor having excellent resistance to moisture and heat.

Comparative Example 1 A polyester film was obtained in the same manner as in Example 1 except that the coating liquid was not applied. The capacitor manufactured using the obtained film was inferior in wet heat resistance property as compared with Example 1.

Examples 2 to 5 Polyesters were prepared in the same manner as in Example 1 except that the coating treatment was carried out so that the ratio of the aromatic polyester polyurethane to the aliphatic polyester polyurethane of the coating agent in Example 1 was set to the composition shown in Table 1. I got a film.

Example 6 In Example 1, the content of sodium chloride in the coating agent was 2000 p of sodium as the solid content of the coating solution.
A polyester film was obtained in the same manner as in Example 1, except that the coating composition was the same as in Example 1 except that the coating liquid had pm and potassium of 10.0 ppm. The capacitor manufactured using the obtained film was slightly inferior in moist heat resistance property as compared with Example 1.

Comparative Example 2 A polyester film having a coating layer was obtained in the same manner as in Example 1 except that the heat treatment temperature after stretching in the transverse direction was 245 ° C. The capacitor manufactured using the obtained film was inferior in AC withstand voltage.

Comparative Example 3 In Example 1, the film stretching conditions were changed as follows. That is, the longitudinal stretching by the roll stretching method,
First, it was made 2.4 times at 85 ° C. and then 1.1 times at 75 ° C. After forming a coating layer, it was laterally stretched 4.5 times at 110 ° C. with a tenter and further heat-treated at 230 ° C. The composition of the coating agent was the same as in Example 1. The capacitor manufactured using the obtained film was inferior in AC withstand voltage. The results obtained above are summarized in Tables 1 to 3 below.

[0071]

[Table 1]

[0072]

[Table 2]

[0073]

[Table 3]

[0074]

EFFECT OF THE INVENTION The film of the present invention has excellent adhesion to the electrode metal layer, and when it is used as a dielectric for a metal-deposited film capacitor, it imparts a high degree of electrical characteristics and wet heat resistance.
It can contribute to the improvement of long-term reliability of the capacitor, and its industrial value is high.

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Claims (1)

[Claims] 1. A coating layer having a thickness of 0.005 to 1.0 μm made of a water-soluble or water-dispersible resin is provided on at least one side, and the refractive index (nα) in the thickness direction of the film is 1.4.
A biaxially oriented polyester film for capacitors, which has a surface orientation degree (ΔP) of less than 90, a surface orientation (ΔP) of more than 0.170, and a Young's modulus in the longitudinal direction of the film of 5.0 GPa or more.