JPH0158803B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulated wire that has characteristics suitable for use in oil-filled transformers and is inexpensive to manufacture. Generally speaking, insulated wires for oil-filled transformers need to have excellent resistance to insulating oil since they come into contact with insulating oil, and they also need to have minimal deterioration of insulation properties due to hydrolysis when a small amount of water gets mixed into the insulating oil. This is required. Conventionally, so-called polyvinyl formal copper wire has been used in which a polyvinyl formal insulating paint is coated and baked on the surface of the copper wire in order to impart the above characteristics. However, polyvinyl formal insulating paint becomes extremely viscous when the concentration of non-volatile components (mainly resin components) in the paint is high, so it is necessary to set the concentration low when applying it. Generally, a thick copper wire of 1 mm or more is used as an insulated wire for an oil-filled transformer, and therefore the insulating layer also needs to have a thickness of about 35 to 60 μm. For this reason, in order to form an insulating layer of the required thickness using polyvinyl formal insulating paint, a time-consuming and labor-intensive method of repeating coating and baking more than 10 times is usually adopted. The disadvantage was that the manufacturing cost was high. Furthermore, the polyvinyl formal insulating paint itself was expensive. In addition, polyvinyl formal electric wire has relatively excellent insulating oil resistance properties, but it does not have enough resistance to deterioration of the insulation layer due to hydrolysis when a small amount of water is mixed in the insulating oil, especially at high temperatures. The results are not satisfactory, and there is still room for improvement. This invention was made to eliminate the above-mentioned conventional drawbacks, and is an insulated wire for oil-filled transformers that has a simpler manufacturing process, is lower in cost, and has superior performance compared to conventional polyvinyl formal copper wires. is intended to provide. That is, in the insulated wire according to the present invention, as shown in the drawings, an insulating coating layer 2 on the surface of a conductor 1 such as a round wire or a rectangular wire is coated with a lower layer 3 by coating and baking a liquid acrylic insulating paint containing a specific resin component. and an upper layer 4 formed by coating and baking a liquid polyvinyl formal insulating paint. The above-mentioned acrylic insulating paint is generally much cheaper than polyvinyl formal insulating paint, and is characterized by a small increase in viscosity even when the concentration of nonvolatile matter is increased. Therefore, by setting the concentration high, the lower layer 3 that occupies part or the main part of the insulating coating layer 2 can be formed by one coating and baking process, and at the same time, the polyvinyl formal insulation for forming the upper layer 4 can be formed. Since coating and baking of the paint only needs to be done once or several times, the material cost and manufacturing cost of the insulating coating layer 2 are greatly reduced. The thickness of such an insulating coating layer 2 is preferably about 35 to 60 μm, and the thickness of the upper layer 4 is about 2 to 60 μm.
Approximately 10μm is good, especially 5μm in terms of characteristics and manufacturing.
Before and after is best. The acrylic insulating paint used to form the lower layer 3 has resin components of 50 to 80 mol% of acrylonitrile or/and methacrylonitrile, 2 to 5 mol% of a glycidyl compound such as glycidyl methacrylate or allyl glycidyl ether, and styrene and α.
- Consisting of a copolymer with a monomer containing other compounds having double bonds such as methylstyrene, methyl methacrylate, ethyl acrylate, N-butyl methacrylate, methacrylic acid, acrylic acid, etc., especially in water dispersion. Type acrylic paints are preferred. However, if the nitrile compound and glycidyl compound in the monomer components are each less than the above range, the general properties, especially the thermal properties, of the obtained electric wire will deteriorate, and if the nitrile compound is too large, Similarly, the general properties are insufficient, and when the amount of glycidyl compound is too large, the mechanical properties of the obtained wire are deteriorated. On the other hand, for forming the upper layer 4, various commercially available liquid polyvinyl formal insulation paints can be used. By the way, when applying and baking acrylic insulating paint to the conductor surface by electrodeposition, it is common to first bake at a low temperature to form a film by volatilizing the solvent, and then to complete the curing reaction to completely harden the paint film. Secondary baking at high temperature is required to achieve this.
When this acrylic paint layer is used as a lower layer and a polyvinyl formal insulation paint layer is formed on top of it, the lower layer is cured by baking this upper layer. When using paint, when baking the upper layer at a baking temperature suitable for polyvinyl formal insulation paint, the lower layer acrylic insulation paint becomes semi-cured, or insufficiently cured, and conversely, when selecting a baking temperature that is sufficient for the lower layer curing. The upper polyvinyl formal insulating paint layer became overcured, resulting in paint film deterioration, and in any case, sufficient characteristics could not be obtained as an insulated wire for an oil-filled transformer. However, as in the present invention, the resin component of the lower layer acrylic insulating paint is 50 to 80 mol% of (meth)acrylonitrile and 2 to 5 mol% of a glycidyl compound.
When using a product having a specific composition consisting of a copolymer of and another double bond-containing compound, the above-mentioned acrylic insulation paint of the lower layer can be baked at a relatively low baking temperature suitable for the polyvinyl formal insulation paint of the upper layer. is sufficiently cured, and therefore it is possible to provide sufficient characteristics as an insulated wire for an oil-filled transformer. Hereinafter, the present invention will be specifically explained with reference to Examples. Table 1 below shows the monomers of the acrylic insulating paint used to form the lower layer 4 of the insulation coating layer 3 in the insulated wire A of the first embodiment and the insulated wire B of the second embodiment according to the present invention. Indicates the ingredients.

【table】

[Table] Using the monomer mixture shown in the above table, using sodium laurate as a surfactant and potassium persulfate as a polymerization initiator, the mixture was heated at 60 to 70°C in a nitrogen stream.
Emulsion polymerization was carried out for 4 hours to prepare a water-dispersible acrylic insulation paint with a non-volatile content of 20% by weight. This insulating paint was electrodeposited on the surface of a copper wire with a diameter of 1.6 mm using a conventional method at a line speed of 6 m/min, and the coated wire was introduced into N,N'-dimethylformamide vapor and heated to 250°C. and then apply polyvinyl formal insulation paint (trade name: WM-447 manufactured by Hitachi Chemical Co., Ltd.) to this surface.
was coated once and baked at a temperature of 350°C to obtain insulated wires A to C in which the lower layer 3 of the insulating coating layer 2 had a thickness of 35 μm and the upper layer 4 had a thickness of 5 μm. On the other hand, for comparison, an insulated wire D was prepared in which an insulating layer with a thickness of 40 μm was formed in the same manner using only the water-dispersed acrylic insulating paint used in the first example.
Insulated wires E and E were each coated with the polyvinyl formal insulating paint used in the example and baked in a conventional manner to form an insulating layer of 40 μm thick. Regarding the above insulated wires A to E, dielectric breakdown voltage,
When the softening resistance and insulating oil resistance were tested, the results shown in Table 2 below were obtained. In addition, the insulating oil resistance is based on insulating paper containing about 2600 ppm of moisture per 400 ml of insulating oil.
30 g was sealed together with a wire test piece having a length of 30 cm, and the dielectric breakdown voltage after storage at the indicated temperature and number of days was expressed as a residual rate (%) with respect to the voltage before the packaging.

[Table] As is clear from the above table, the insulated wires A and B according to the present invention are more susceptible to deterioration of the insulation coating layer 2 when a small amount of water is mixed in the insulating oil, compared to the conventional polyvinyl formal wire E. In particular, the resistance under high temperatures is very good, and the resistance to softening is also excellent, and each characteristic is also improved even for electric wire D, which has an insulation coating layer made of acrylic insulation paint alone. In good condition. However, the electric wire C whose lower layer is formed of an acrylic insulating paint containing a resin component made of a copolymer that deviates from the monomer composition specified in the present invention has significantly poor softening resistance and is resistant to softening when water is mixed in. It can be seen that the insulating oil resistance is also insufficient. As described in detail above, the insulated wire of the present invention has a double layer: a lower layer formed by applying and baking a liquid acrylic insulating paint containing a specific resin component, and an upper layer formed by applying and baking a liquid polyvinylformer insulating paint. Because it has a coating layer, it has higher performance than an insulated wire for oil-filled transformers that has an insulation layer made by applying and baking each of the above insulating paints separately, and it also has a coating layer that can be used on a part or main part of the insulation coating layer. can be formed by applying and baking an inexpensive acrylic insulating paint once using electrodeposition coating, etc., and the amount of expensive polyvinyl formal insulating paint used can be reduced accordingly, reducing the material cost of the insulating coating layer. In addition, since the total number of times of coating and baking is only two, the manufacturing process is significantly simplified and the manufacturing cost is greatly reduced.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view of an insulated wire for an oil-filled transformer according to the present invention. 1... Conductor, 2... Insulating coating layer, 3... Lower layer, 4... Upper layer.

Claims (1)

[Claims] 1. On the conductor surface, (meth)acrylonitrile 50~
A lower layer made by coating and baking a liquid acrylic insulating paint containing a resin component consisting of a copolymer of 80 mol% glycidyl compound, 2 to 5 mol% glycidyl compound, and other compounds having double bonds, and a liquid polyvinyl formal insulating paint. An insulated wire for oil-filled transformers with a double insulation coating layer consisting of an upper layer that is coated and baked.