JPH0715857B2 - Polyester film for external capacitors - Google Patents

Description

The present invention relates to a novel polyester film for capacitors. More specifically, the present invention relates to a polyester laminated composite film for capacitors which does not require an exterior.

[Prior Art] Conventionally, as a packaging method for a polyester film capacitor, a resin dip coating or a resin molding coating in which a capacitor element is wrapped in a resin by dipping or molding, or an adhesive tape is wrapped around the outside of the capacitor element and then sealed with a resin. In general, a tape wrap exterior for stopping, a metal case exterior for enclosing and sealing a capacitor element in a container made of metal or resin, and a resin case exterior are generally adopted.

[Problems to be Solved by the Invention] However, polyester film capacitors are now widely used for electronic devices and other applications, and VTRs, audio devices capacitors, etc. are being further reduced in size and weight, but they are used as the exterior. The accompanying increase in size and weight has become non-negligible, and the conventional externally mounted capacitor cannot sufficiently satisfy such requirements.

Further, in the case of using the resin, the coating or dipping of the resin and the drying and curing of the resin are repeated, so that there is a drawback that the processing step becomes long.

An object of the present invention is to provide a capacitor and an insulating polyester film with an exterior function, thereby reducing the size of the capacitor and omitting the exterior process without deteriorating the electrical characteristics.

[Means for Solving Problems] The present invention is a composite film in which a thermal adhesive layer (B) is laminated on at least one surface of a polyester base layer (A),
The polyester base layer (A) and the thermal adhesive layer (B) satisfy the following formula (I), and relates to a polyester film for an exterior capacitor.

1000 ≦ (Tg1 + Tg2) × (Tm1−Tm2) ≦ 9500 ……… (I) Where, Tg1: glass transition temperature of base layer (A) Tg2: glass transition temperature of thermal bonding layer (B) Tm1: base layer ( A) Melting point Tm2: Thermal adhesive layer (B) melting point The polyester base layer in the present invention is selected from ethylene terephthalate, butylene terephthalate, ethylene naphthalate and arylate, and the unit thereof is 70 mol%.
The above, preferably 80 mol% or more. Of course, various dicarboxylic acid components (eg, isophthalic acid, adipic acid, etc.) or diol components (eg, diethylene glycol, polyethylene glycol, neopentyl glycol, etc.) may be copolymerized within the above range. Further, it may be a polymer blend of two or more kinds of the above polyesters or a copolymerized product by an exchange reaction. Among these, a polyester film layer containing polyethylene terephthalate as a main component is particularly preferably used from the viewpoints of balance of electric characteristics, strength, cost performance and the like.

On the other hand, the thermal adhesive layer of the present invention includes a film layer mainly composed of a thermoplastic polymer having excellent electrical properties such as polyester, polypropylene, polyolefin, polyamide, and polycarbonate. From the viewpoint, polyester is preferably used. In particular, polyester having a solubility parameter similar to that of the base layer is suitable.

Further, in any of the plastic base layer or the heat-adhesive layer, titanium oxide, calcium carbonate, calcium silicate, barium titanate, calcium sulfate, barium sulfate, calcium phosphate, for the purpose of improving slipperiness and electrical characteristics, if desired. Inorganic particles such as aluminum oxide, magnesium oxide, silica, kaolinite, talc, mica and zeolite can be added.

The polyester base layer (A) and the thermal adhesive layer (B) of the present invention need to satisfy the following thermal characteristic formula (I). That is, 1000 ≦ (Tg1 + Tg2) × (Tm1−Tm2) ≦ 9500 (I) where Tg1: glass transition temperature of base layer (A) Tg2: glass transition temperature of thermal bonding layer (B) Tm1: base Melting Point Tm2 of Layer (A): Melting Point of Thermal Adhesive Layer (B) More preferably, 3000 ≦ (Tg1 + Tg2) × (Tm1−Tm2) ≦ 8000.

In the formula (I), if (Tg1 + Tg2) × (Tm1-Tm2) (hereinafter, referred to as thermal characteristic parameter) is less than 1000,
Non-uniform adhesion between capacitor element layers causes deterioration of capacitance, insulation resistance and dielectric loss tangent due to moisture absorption in the outside air.
If it exceeds, the durability of the element interlayer adhesive portion is insufficient, and it is adversely affected by environmental temperature changes, ultraviolet rays, harmful gases and the like.

The laminated composite of the polyester base layer and the heat-adhesive layer in the present invention can achieve the purpose by composite film formation by co-extrusion, lamination of the base film and the heat-adhesive film, or coating of the heat-adhesive polymer on the surface of the base film. It is possible to use a laminate of two or more layers having a heat-adhesive layer on at least one side, but 2-3 layers are more preferable from the viewpoint of enhancing the surface adhesive force, and the thickness of the surface adhesive layer is the adhesive force and the electrical characteristics. From the point of, 0.5 to 5 μm is suitable.

The capacitor according to the present invention that does not require an outer package can be manufactured by, for example, the following method, but is not limited thereto. That is, in the conventional metal foil piece polyester film capacitor, the polyester film and the aluminum foil are wound up at the same time, taped, hot-pressed, further cured with epoxy resin for undercoating, and then again cured. After finishing resin coating and curing are repeated, the product is marked and marked. On the other hand, when the polyester film for a capacitor of the present invention which does not require an exterior is used, a capacitor element obtained by simultaneously winding the film of the present invention and an aluminum foil is used at a temperature of 150 to 210 ° C., which is higher than that of the conventional one, and a pressure area is 1 ~ 50kg / c
A product can be obtained by marking after hot pressing for 50 to 250 seconds while applying a pressure of m ² .

Glass transition temperature and melting point to be used in the thermal characteristic parameters of the present invention uses fiber, according to the technology of polymer Measurement (Fiber Society of Japan) Differential scanning calorimeter (DSC), a sample 10 mg N ₂
After heating to the melting point + 25 ° C at a heating rate of 16 ° C / min in the air flow
It is a value measured by a second run which is rapidly cooled at 50 ° C. and heated again.

[Examples] The present invention will be described in more detail by the following examples.

Example 1 Polyethylene terephthalate (Tg1 = 80) having an intrinsic viscosity of 0.65
(° C, Tm1 = 256 ° C) as the inner layer, and laminated on both sides with a thermal adhesive layer of polyethylene terephthalate ([η] = 0.63, Tg2 = 76 ° C, Tm2 = 211 ° C) copolymerized with 17.5 mol% of isophthalic acid. The film extruded from the die was stretched at 90 ° C. in the longitudinal direction by 3.3 times and in the transverse direction by 3.4 times. Then heat-treated at 180 ℃, the total thickness is 6.0μm, and the thickness of the thermal adhesive layer is 1.0
A composite film having a thermal property parameter of 7020 was obtained in μm. The obtained 3-layer laminated composite film was wound with 7 mm width of aluminum foil with 4 mm width of micro slits, and then integrally molded at 200 ° C. for 60 seconds while applying a pressure of 1 kg / cm ^{2 in} the hot pressing process. We obtained a DC capacitor with a rated capacity of 1000pF without any external packaging. Compared to the conventional resin-dipped exterior product, this capacitor not only has a 75% higher volume, but also eliminates the exterior process, resulting in a 1 / 4th of the length of the capacitor manufacturing process.
I was able to Also, dielectric breakdown strength, electric capacity,
The electrical characteristics of insulation resistance and its durability were also superior to those of conventional exterior capacitors.

Comparative Example 1 A single-layer film having a thickness of 6.0 μm and containing only the copolymerized polyethylene terephthalate used for the exterior of Example 1 was formed by the same method. When a capacitor without a sheath was manufactured under the same conditions as in Example 1, the crystal of polyethylene terephthalate and the fine structure of the orientation region were deteriorated by hot pressing, and the electrical characteristics of the film capacitor were deteriorated.

Comparative Example 2 Polyethylene terephthalate copolymerized with 2 mol% of isophthalic acid as the heat-bonding layer of Example 1 ([η] = 0.65, Tg
2 = 79 ℃, Tm2 ＝ 251 ℃)
In the non-packaged capacitor using the 95 composite film, the adhesion between the element layers was non-uniform and the seal with the outside air was incomplete, so the electrostatic capacity and insulation resistance deteriorated significantly when the temperature and humidity were high.

Comparative Example 3 Polyethylene terephthalate copolymerized with 30 mol% of isophthalic acid as the heat-bonding layer of Example 1 ([η] = 0.63, Tg
2 = 71 ° C., Tm2 = 179 ° C.) and the film was formed under the same conditions as in Example 1 except that heat treatment was performed at 150 ° C.
627 composite films were obtained. The adhesive seal part of the exterior capacitor using this film is
The durability against harmful gas was small and the short-circuit failure rate was high after long-term use.

Example 2 Polybutylene terephthalate ([η] = 0.89, as a heat-bonding layer on both surfaces of the polyester base layer shown in Example 1,
(Tg1 = 35 ° C., Tm1 = 225 ° C.) was composited by a coextrusion method, and after forming a film under the same conditions as in Example 1, a capacitor was also processed under the same conditions. The obtained non-packaged capacitor was compact and lightweight and had excellent electrical characteristics.

Example 3 Isophthalic acid 1 was applied onto a polyethylene terephthalate film ([η] = 0.64, Tg1 = 80 ° C., Tm1 = 256 ° C.) having a thickness of 4 μm so that the coating thickness after drying was 1.5 μm.
A water-soluble polyester copolymerized with 2.5 mol% and 12.5 mol% of sulfonic acid sodium salt is coated on one side as a thermal adhesive layer, dried in hot air at 130 ° C, and has a total thickness of 5.5 μm and a thermal characteristic parameter of 9372, which is a laminated composite film. Got Further, when this film was processed into a capacitor having a rated capacity of 10,000 pF under the same conditions as in Example 1, changes in electric capacity and insulation resistance were small, and there were few failures and high reliability.

[Advantages of the Invention] By using the composite film according to the present invention, it is possible to easily obtain a miniaturized, non-packaged capacitor, and such a capacitor has a fluctuation in insulation resistance, a capacitance in a high temperature and high humidity atmosphere, and a dielectric breakdown. Minimal changes in strength, dielectric loss tangent, and insulation resistance, resulting in extremely few failures. Further, since the exterior process can be omitted, the space that is substantially occupied by the capacitor manufacturing process can be reduced, and the productivity can be greatly improved and the cost can be reduced.

Claims (1)

[Claims] 1. A composite film in which a thermal adhesive layer (B) is laminated on at least one side of a polyester base layer (A), the polyester base layer (A) and the thermal adhesive layer (B).
Satisfies the following formula (I): A polyester film for a non-exterior capacitor. 1000 ≦ (Tg1 + Tg2) × (Tm1−Tm2) ≦ 9500 ……… (I) Where, Tg1: glass transition temperature of base layer (A) Tg2: glass transition temperature of thermal bonding layer (B) Tm1: base layer ( Melting point of A) Tm2: Melting point of thermal bonding layer (B)