KR870002146B1 - Manufacturing method of epoxy electrical insulation - Google Patents

Abstract

A varnish is prepd. by mixing 100 wt. parts of bisphenol-A type epoxy resin(having mol. wt. 1,000-10,000), nitrile 1-10 wt. parts, mixt. of dicyandiamide and dihydrazid 5-15 wt. parts, imidazol cpds. with MeEt-ketone/methyl cellosolve solvent. This varnish is coated onto metal article by sand blast, vulcanization at 90deg.C for 15min and 140deg.C for 1hr. The surfacetreated metal article is inserted into moldings (mixt. of epoxy resin, acid anhydrousvulcanining agent and silica tampings) for the manufacture of electrical insulations.

Description

Method of manufacturing epoxy electric insulator

1 is a cross-sectional view of a molded article for measuring the tensile strength.

2 is a cross-sectional view of a molded article for measuring the thermal shock strength.

Where ① is the bracket

② is a cured epoxy resin.

The present invention relates to a method for producing an epoxy electrical insulator, which is molded and used in a state of inserting an insulator, a bushing, or the like. In particular, to provide a method for manufacturing an epoxy electrical insulator having improved tensile strength and thermal shock resistance of a molded article. It is for.

The cured product of the epoxy resin is light, has excellent mechanical and electrical properties, and is easy to design and form, compared to conventional magnetic materials, and has been widely applied as an electric insulator such as insulator and bushing. In particular, with the recent trend toward miniaturization and weight reduction of heavy electric equipment products, the amount of use and the application range of epoxy electric insulators are rapidly increasing. As these applications expand, epoxy electrical insulators have been applied to large, high-pressure heavy electric machines, and the demand for durability and reliability of heavy electric machines has become more stringent. For epoxy electric insulators, higher levels of tensile strength and thermal shock resistance are achieved. This became required.

However, in the case of epoxy electric insulator, fine separation occurs at the interface between hardened metal and epoxy resin due to temperature change and mechanical external force during use, or, in severe cases, cracks start at the interface between hardened metal and epoxy hardened material. There is a problem of destruction.

This problem arises from the difference in coefficient of thermal expansion between the bracket and the epoxy cured product and the lack of adhesion, which is a fatal defect in the durability and reliability of the heavy electric machine.

Conventionally, in order to solve this problem, a method of maintaining the thermal expansion coefficient of the cured product at a level similar to the thermal expansion coefficient by increasing the content of the inorganic filler of the epoxy resin and mechanically processing the adhesive surface with the epoxy resin of the bracket A method of increasing the illuminance of the light has been used.

However, when the thermal expansion coefficient of the cured epoxy resin is lowered by increasing the content of the filler, the mechanical properties, particularly the tensile strength and the impact strength of the cured product are reduced depending on the type of epoxy resin, which may adversely affect adhesion to the root bulb. There is a concern that the method of increasing the roughness of the bracket surface by mechanical treatment is insufficient to improve the adhesive force and the thermal shock resistance.

In the present invention, in order to solve this problem, the varnish based on the epoxy resin is applied to the adhesive surface with the epoxy cured product of the bracket, and then a coating film is formed through a curing process. Molding was made by insert molding.

In this case, the coating film formed on the bonding surface between the metal fittings and the epoxy resin contributes to the improvement of the adhesive strength of the hardened material of the metal fittings and epoxy resin, and the tensile stress and the thermal shock resistance of the molded article are alleviated by alleviating the interfacial stress caused by the difference in thermal expansion coefficient of the two materials. It turns out that the improvement of is possible.

In particular, it has been found that the varnish containing a mixture of an epoxy resin, nitrile rubber dicyandiamide and dihydrazide as a curing agent exhibits a high effect on the adhesion and interfacial stress relaxation that can satisfy the required level. .

The method of improving the tensile strength and the thermal shock resistance of the insulating material by forming a coating film on the adhesive surface with the cured product of the bracket using such a varnish is generally applicable to all epoxy resin insulators containing the bracket. It is useful for the support insulator, the support insulator for the gas circuit breaker, and the bushing. In this case, the epoxy resin molding method is applicable to all known epoxy resin molding methods such as the main molding of the liquid resin and the compression molding of the powdery molding material.

In the present invention, the epoxy resin used for the production of varnish is a bisphenol A type epoxy resin prepared by the condensation reaction of known bisphenol-A and epichlorohydrin, and has a molecular weight in the range of 1,000 to 10,000 in terms of adhesive strength and thermal shock resistance. It is advantageous.

As a nitrile rubber mix | blended here, the copolymer of butadiene and acrylonitrile is used. The curing agent is a mixture of dicyandiamide and dihydrazide, which is advantageous for varnish pot life, coating properties, and the like.

The blending ratio for preparing varnish is 1 to 10 parts by weight of nitrile rubber and 100 to 2 parts by weight of the bisphenol-A epoxy resin mentioned above, and a mixture of dicyanamide and dihydrazide in a ratio of 9: 1 to 6: 4. After mixing 5 to 15 parts by weight, an imidazole series curing accelerator is added, and the viscosity of the varnish is adjusted by using a mixture of methyl ethyl ketox and methyl cellosolve as a solvent.

If it is out of the range of the above blending ratio, the effect on the relaxation of the adhesive force or interfacial stress is insufficient or there is a risk of adverse effects.

The coating film thickness of the coating surface of the metal fittings is appropriately 0.05 to 0.5 mm, and the problem that occurs when the coating film thickness is out of the range is the same as the case mentioned above.

The method of forming the coating film is not limited to a specific method, and a general spray coating and impregnation coating method may be applied.

In the following Examples, the application method and its effects of the present invention will be described in detail. However, the following examples do not limit the scope of the present invention.

EXAMPLE

100 parts by weight of a bisphenol-A epoxy resin having a molecular weight of 4,000 to 5,000, 5 parts by weight of nitrile rubber (brand name Perbunan N2818 NS, manufactured by Bayer, Germany), and a blending ratio of dicyanamide and isophthalic dihydride is 7: 3 ( 6 parts by weight of a curing agent) and 0.5 parts by weight of 2methyl 4ethylimidazole were added, and then a solvent, a mixture of methyl ethyl ketone and methyl cellosolve, was added thereto to prepare a varnish.

The varnish was applied to the surface of the air supply having a surface roughness of 5OB by sand blasting, and then cured at 90 ° C. for 15 minutes at 140 ° C. for 1 hour to form a 0.1 mm thick coating film. This surface-treated bracket is inserted into a mixture mixture for molding made of an epoxy resin acid anhydride hardener and a silica filler to prepare a tensile strength measuring member such as FIGS. 1 and 2 and a molded article for measuring thermal shock strength.

Tensile strength and thermal shock resistance tests were carried out using this molded article, and the results are shown in the "Table".

[Comparative Example]

Sandblasting of the same material as in Example was carried out to make the surface roughness to 50B, and then inserted into the same mold mixture as in Example to prepare a molded article as in Example.

The molded article was subjected to tensile strength and thermal shock resistance in the same manner and in the same manner as in Examples, and the results are shown in the "Table".

[table]

* -30 ℃ (2 hours → + 120 ℃ (2 hours) 10 times repetition

Claims (1)

100 parts by weight of a bisphenol-A epoxy resin having a molecular weight of 1,000 to 10,000, 1 to 10 parts by weight of nitrile rubber, 5 to 15 parts by weight of a mixture of dicyanamide and dihydra, and methyl ethyl ketone and methylcell to the imidazole compound. A method for producing an epoxy electrical insulator, comprising: forming a coating film on an epoxy resin cured product and an adhesive surface with a varnish prepared by mixing a mixture of sorbs, and inserting and molding the epoxy resin for molding.

Images