JPH02205006A - Metallized film capacitor - Google Patents

Abstract

PURPOSE:To obtain a metallized film capacitor excellent in moisture resistance even in simple sheathing by forming a specified ethylene terephthalate-ethylene isophthalate copolymer (PEI) layer onto at least one surface of a biaxially oriented PET film and metallizing the upper section of the copolymer layer so as to acquire a specific surface resistance value. CONSTITUTION:PET contains a not less than 90mol% ethylene terephthalate unit. PEI represents a copolymer including a 10-25mol% ethylene isophthalate unit, an effect regarding dampproof performance at the time of usage as a capacitor is reduced in 10mol% or less, and the fraction defective of breakdown is increased in 25mol% or more. It is favorable that 0.01<=PEI layer/PET layer<=0.4 holds at the ratio of the thickness of the PET layer and the PEI layer on one side. A metallic film layer formed on the PEI layer of a laminated film mainly comprising aluminum is preferable, and 0.5-5OMEGA/square are required as the surface resistance value of the metallic film layer. The metallic film layer is used as an electrode, the laminated film is employed as a main dielectric, and a metallized film capacitor is manufacture through a known method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metallized film capacitor used in electronic equipment, information equipment, and the like.

[Prior Art] Conventionally, capacitors in which a biaxially oriented polyethylene terephthalate film is used as a dielectric and a vapor-deposited thin film mainly composed of aluminum formed on the surface of the dielectric are used as metallized polyester film capacitors. ing. However, when this type of capacitor is used for a long time under high temperature and high humidity, the electrodes made of thin metal films are oxidized by oxygen and moisture in the atmosphere and lose their conductivity, which impairs their function as a capacitor (humidity resistance It had the disadvantage of being inferior.

In order to improve this drawback, Japanese Patent Laid-Open No. 62-190827 and other publications have proposed strengthening the exterior for the purpose of preventing moisture from entering the capacitor element.

[Problem to be solved by the invention] However, on the other hand, there is also a strong demand for miniaturization of capacitors, and the above-mentioned conventional technology goes against this demand. This was something that was not traditionally available to customers.

An object of the present invention is to solve these problems and provide a metallized film capacitor that has superior moisture resistance even with a simpler exterior than conventional capacitors.

[Means for Solving the Problems] In order to solve the above objects, the present invention provides at least one side of a biaxially oriented film of polyethylene terephthalate,
The main dielectric is a laminated film with a layer (PEI layer) made of ethylene terephthalate/ethylene isophthalate copolymer copolymerized with ethylene isophthalate units in a range of 10 to 25 mol%, and a surface resistance layer is formed on the PE layer. The main feature of the capacitor is a metallized film capacitor characterized by having a metal film layer having a value of 0°5 to 5Ω/□ as an electrode.

Polyethylene terephthalate (hereinafter referred to as "FP") in the present invention
(abbreviated as ET) is one in which ethylene terephthalate units account for 90 mol% or more. In other words, other molecular units such as ethylene adipate, alkylene glycol, etc. may be copolymerized within a range not exceeding 10 mol%. This PET contains known additives,
For example, inorganic fine particles, anti-coloring agents, etc. may be added. □The biaxially oriented PET film of the present invention is obtained by forming the above-mentioned PET into a film and stretching it in biaxial directions to orient it.

The ethylene terephthalate/ethylene isophthalate copolymer of the present invention has 10 ethylene isophthalate units.
It is a copolymer consisting of mol % or more, preferably 12 mol % or more, and if it is smaller than this value, the effect on moisture resistance when used in a capacitor is small. Further, it is necessary that the ethylene isophthalate unit content is 25 mol % or less, and if it exceeds the second value, the defective rate due to dielectric breakdown will increase when used as a capacitor. This ethylene terephthalate/ethylene isophthalate copolymer (hereinafter abbreviated as PEI) may contain a known refueling agent such as inorganic fine particles, color inhibitor, etc.

Alternatively, it may be oriented in biaxial directions.

The melting point of the PEI is preferably 190°C or higher, more preferably 200°C or higher. The average surface roughness of the PEI layer of the present invention is preferably 0°01 to 0.10 μm1.
More preferably, it is 0.02 to 0.07 μm. Also,
The inorganic fine particles in PEI have an average particle size of 0.1 to 0.6.
Particles with a size of μm range from 0.05 to 0. The content is preferably 5%.

The present invention provides PE on at least one side of the PET film.
It is a laminated film made by laminating I films, and the ratio of the thickness of the PET layer to the PEI layer on one side is 0.01≦PEI layer/P
It is preferable that the ET layer≦0.4. If it is smaller than this range, the moisture resistance effect will be small, and if it is larger than this range, the dielectric breakdown voltage will decrease.

The present invention requires that a metal film layer be provided on the PEI layer of the laminated film. The metal film layer preferably contains aluminum as a main component in terms of moisture resistance and adhesive strength, and a small amount of metal such as zinc or copper may be attached within a range that does not impair the properties of aluminum. Here, the term "aluminum is the main component" means that the aluminum layer has a thickness of 100A or more.

The surface resistance value of the metal film layer of the present invention is 0. '5~5Ω/□
and preferably 1 to 4Ω/Rose.

If it is larger than this range, the thickness of the metal film will be too small and it will be difficult to produce a moisture-resistant effect.On the other hand, if it is smaller than this range, the thickness of the metal film will be too thick and self-heal will not be effective easily, which is undesirable.

The metallized film capacitor of the present invention is one in which the metal film layer is used as an electrode, the laminated film is used as the main dielectric material, the capacitor is wound or laminated, and then subjected to heat pressing, metallization, cutting, and voltage treatment. Of course, a metallized film capacitor may be formed by overlaying another dielectric material, such as a PET film, on the gold film layer. Alternatively, a wound capacitor may be made by sandwiching an aluminum foil and using the foil as the other electrode.

Next, a method for manufacturing the metallized film capacitor of the present invention will be explained.

The laminated film may be manufactured by any method such as coextrusion/extrusion, extrusion, lamination, coating, etc., but coextrusion is preferred. The PET and PEI pellets are each fed into separate extruders and melt extruded at 270-300°C, and the respective melts are combined in a T-shaped nozzle to form a two-layer PET/PEI sheet. This sheet is 80-10
After stretching 3 to 4 times in the longitudinal direction at 0'C and cooling once,
Stretch 3 to 4 times in the axial direction at 80 to 110°C. After stretching,
It is preferred to heat set the film, which is usually 1
60°C to 240°C, preferably 180°C to 23°C
It is usually carried out for 1 to 20 seconds at a temperature of 0°C. The thickness of the laminated film is preferably 0.5 to 25 μm. The heat-set laminated film is cooled to room temperature and 10% is applied to the surface of the PEI layer.
-2 to 1O-6T.

At a pressure of rr, apply the metal that will become the electrode to the entire surface of the film, or with a margin of 0.5 to 5 Ω using tape.
Vacuum evaporate to a thickness of /□. In the thus-formed vapor-deposited film, if the entire surface is vapor-deposited, a margin portion is created using a laser beam or the like, and microslits are performed. The microslit films are rolled or laminated into capacitor elements and heat pressed, metallized, and voltage treated by known methods to form metallized film capacitors. This metallized film capacitor is optionally lead wired,
The product is finished with a thermosetting resin exterior.

[Effects of the Invention] The present invention creates a capacitor by vapor depositing a metal on the PEI layer of a PET/PEI laminated film to have a specific surface resistance value.
It is presumed that the growth state of the deposited film is different from that in the case of simply depositing on a PET layer, and is denser. This seems to be the reason why the adhesion of the deposited film improved and the rate of change in capacitance decreased. It also has the advantage of having a low defective rate due to dielectric breakdown, which is a problem when used in capacitors.

[Method for measuring properties and evaluating effects] (1) Adhesion of vapor deposited film The vapor deposited film before being rolled or laminated was immersed in a constant temperature bath at 65° C. for 15 minutes, and the degree of disappearance of the vapor deposited film was observed. The evaluation criteria are as follows.

○: There is no change in the deposited film △: The deposited film has slightly changed ×: The deposited film has almost disappeared (2) Capacitance change rate Metalized film capacitor (capacitance C = 1° 5μF)
A DC voltage of 35 V was applied at 50°C and 95% RH. The amount of change in capacitance after 2000 hours is Δ
C, and the capacitance change rate (ΔC/C) (%) was measured.

(3) Defective rate of capacitors For 100 metallized film capacitors, DC 120 V was applied per 1 μm of film thickness using an instantaneous step-up method, and the number of capacitors that suffered dielectric breakdown was directly defined as the defective rate (%). In other words, if 10 out of 100 capacitors have dielectric breakdown, the defective rate is 10%. Note that the value of this defective rate is generally 3
% or less, preferably 2% or less, it would be difficult to put it into practical use.

(4) Melting point 10 mg of the sample was set in a DSC, and the temperature was raised at a rate of 20° C./min, and the temperature corresponding to the top of the endothermic peak accompanying melting was defined as the melting point.

(5) Average surface roughness Measured using a stylus surface roughness meter according to the method specified in J I 5-B-0601. Note that the cutoff is 0.25 mm and the measurement length is 4 mm.

(6) Surface resistance value Measured using OHM-METER manufactured by Toyo Metallizing ■.

[Examples] Hereinafter, the present invention will be described in more detail based on Examples. However, the present invention is not limited to the following examples.

Example I PET pellets (melting point 260°C, average particle size 0°3 μm)
PEI copolymerized with 85 mol% terephthalic acid and 15 mol% isophthalic acid as the acid component and 100% ethylene glycol as the diol component (contains 0.1% by weight of dry silica) (with a melting point of 215°C and an average particle size of 0.1%). The pellets (containing 0.10% of 2 μm dry silica) were each fed into a separate extruder and melt extruded at 290°C, and the respective melts were combined in a T-shaped nozzle to form PET/PEI. A sheet consisting of two layers was made. This sheet was stretched 3.2 times in the longitudinal direction at 85°C and 3.3 times in the width direction at 95°C.
Heat treatment was performed at 0° C. for 5 seconds to obtain a laminated film having a PET layer 1, 5 μm thick, and a PEI layer 0.4 μm thick. The average surface roughness of the PEI layer was 0.05 μm. PE of this laminated film
Aluminum was deposited on the surface of the I layer to a thickness of 2Ω/□ in terms of surface resistance. One pair of this vapor-deposited film was wound, heat-pressed, treated with methacrylate, lead wire material, voltage treated, and packaged to form a metallized film capacitor. The evaluation results of this metallized film capacitor are shown in Table 1, and the results showed that the adhesion of the deposited film, the capacitance change rate, and the defective rate of the capacitor showed good results.

Comparative Example 1 A metallized film capacitor was manufactured under the same manufacturing conditions as in Example 1, except that the surface resistance value of aluminum was set to 5.5Ω/□.

Table 1 shows the adhesion strength of the deposited film, the capacitance change rate, and the failure rate of the capacitor. As is clear from Table 1, the adhesion of the deposited film and the rate of change in capacitance were poor.

Comparative Example 2 PEI copolymerized with 6 mol% isophthalic acid (melting point 247
A metallized film capacitor was manufactured under the same manufacturing conditions as in Example 1, except that the temperature (°C) was used.

Table 1 shows the adhesion strength of the deposited film, the capacitance change rate, and the failure rate of the capacitor. As is clear from Table 1, the adhesion of the deposited film and the rate of change in capacitance were poor.

Comparative Example 3 PEI copolymerized with 30 mol% isophthalic acid (melting point 18
A metallized film capacitor was manufactured under the same manufacturing conditions as in Example 1, except that a temperature of 5° C.) was used.

Table 1 shows the adhesion strength of the deposited film, the capacitance change rate, and the failure rate of the capacitor. As is clear from Table 1, although the adhesion of the deposited film and the capacitance change rate are excellent, the capacitor failure rate is abnormally high, making it unusable.

Comparative Example 4 Only the PET pellets of Example 1 were melt-extruded at 280°C to produce a single layer sheet. This sheet was treated in the same manner as in Example 1 to obtain a 3 μm film to produce a metallized film capacitor.

Table 1 shows the adhesion strength of the deposited film, the capacitance change rate, and the failure rate of the capacitor. As is clear from Table 1, the adhesion of the deposited film and the rate of change in capacitance were poor.

Claims (2)

[Claims] (1) One ethylene isophthalate unit is added to at least one side of a biaxially oriented polyethylene terephthalate film.
A layer consisting of ethylene terephthalate/ethylene isophthalate copolymer copolymerized in the range of 0 to 25 mol% (P
1. A metallized film capacitor characterized in that a laminated film provided with an EI layer is used as a main dielectric, and a metal film layer having a surface resistance value of 0.5 to 5 Ω/□ is provided on the PEI layer as an electrode. (2) The metallized film capacitor according to claim 1, wherein the metal film layer contains aluminum as a main component.