JPS6249721B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for forming an insulating coating on electrical steel sheets, and is based on the results of research developed to improve moisture-resistant adhesion, which is required for electrical steel sheets used in applications such as large-scale water turbine generators, along with corrosion resistance and electrical insulation. It is to be disclosed. Generally, there are many properties required for the insulation coating of electrical steel sheets, such as electrical insulation (interlayer resistance), adhesion, corrosion resistance, punchability, and weldability. The types of insulating coatings currently in practical use are roughly divided into phosphate-based or chromate-based inorganic coatings, chromate-resin-based semi-organic coatings, and resin-based organic coatings. All of these coatings are insufficient for electromagnetic steel sheets used in large power generators, etc. High electrical insulation, corrosion resistance, and adhesion are particularly important for the insulation coating of electromagnetic steel sheets used in large water turbine generators. With inorganic films and semi-organic films, it is generally difficult to uniformly and thickly coat the film at high speed, and it is extremely difficult to ensure an interlayer resistance of 100 Ωcm ² /sheet. Furthermore, even if thick coating is possible, the adhesion of the film is very poor. On the other hand, if a resin coating is used, it is easy to obtain high interlayer insulation by coating it thickly, but the corrosion resistance is insufficient. Therefore, the inventors investigated an insulating coating with excellent interlayer insulation, corrosion resistance, and moisture-resistant adhesion, and found that after applying a phosphate coating as an undercoat to the surface of an electrical steel sheet containing 2 to 4% by weight of Si. ,
It has been found that the desired film can be obtained by processing with a water-soluble resin consisting mainly of polyester resin and blended with melamine resin. First, the phosphate-based treatment solution used to form the base film is an aqueous solution of one or more phosphates such as magnesium, zinc, calcium, and aluminum. Forms a salt film. Chromic acid or boric acid may be added to this phosphate solution. If the dry film thickness of the base film is thinner than 0.3 μm, sufficient corrosion resistance will not be obtained even if a top coat resin film is applied.
Further, if the thickness is greater than 1.0 μm, the adhesion of the coating will be poor and peeling of the coating will easily occur during punching. In order to apply the dry film to a thickness of 0.3 to 1.0 μm, the specific gravity of the treatment liquid may be changed and the steel plate may be uniformly treated using a grooved rubber roll or a spray method. As for the baking conditions, it is sufficient to bake at 400 to 700°C for a short time. Next, regarding the top coat resin film, since organic solvent-based resins have safety and hygiene problems and handling problems, we decided to use a water-soluble resin in this invention. The adhesion of the coating, that is, the moisture-resistant adhesion, is significantly affected.
In this regard, resins containing many polar groups such as OH groups and COOH groups, such as alkyd resins, absorb water when exposed to high humidity.
Due to the swelling of the coating, the adhesion strength of the coating decreases. Therefore, as a result of various studies to create a resin film with few polar groups and good moisture-resistant adhesion, we decided to create a water-soluble resin film with a weight ratio of polyester resin and melamine resin in the range of 85/15 to 65/35. It has been found that the resin described below is optimal. Table 1 shows various properties of coatings treated with various blending ratios of polyester resin and melamine resin on phosphate coatings. Treatment conditions Material Non-oriented silicon steel sheet (Si3%) (1) Phosphate-based coating Treatment liquid 6% monomagnesium phosphate - 1.5%
Chromic anhydride - 2%, aluminum nitrate based Baking 450°C x 60 seconds Film thickness 0.5μm (2) Resin coating Water-soluble resin: polyester resin/melamine resin blending ratio changed as shown in Table 1 Baking 450 ℃×70 seconds Film thickness total 5μm

[Table] From the above results, it can be seen that when the blending ratio of polyester resin/melamine resin is 100/0 or 90/10, the resulting film becomes sticky and easily attacked by solvents, and the corrosion resistance is not sufficient. If it is less than /60, the film will peel off during baking and no film will be formed, and if it is less than 60/40
At ~50/50, the adhesion of the film deteriorates. Polyester resin/melamine resin ratio is 85/15 to 65/35
It can be seen that the best coating performance is obtained when Next, in order to make the total thickness of both films 3 to 12 μm, it is sufficient to use a roll coater, etc. If the thickness is 3 μm or less, sufficient punchability and
Corrosion resistance and electrical insulation cannot be obtained, and 12μ
If it is thicker than m, the adhesion and space factor will decrease. Baking can be carried out at 400 to 700°C for a short time. The Si content of the electrical steel sheet used in the method of the present invention is 2 to 4% by weight. If the Si content is less than 2% by weight, it is not economical due to its electromagnetic properties as a magnetic steel sheet used in large-scale power generators, etc. If it exceeds 4% by weight, the plate will crack during rolling, making it difficult to commercialize the product.
It is necessary to use an electrical steel sheet containing ~4% by weight. Next, an example will be explained. Example 1 A phosphate treatment solution consisting of 6% monobasic magnesium phosphate - 2%, chromic anhydride - 2% aluminum nitrate was applied to the surface of a non-oriented silicon steel plate (Si 3%, plate thickness 0.5 mm). , baked at 450℃ for 60 seconds, 0.6μm
A thick film was formed. A water-soluble resin with a blending ratio of polyester resin/melamine resin of 80/20 is applied on top of this and baked at 400℃ for 70 seconds to give a total film thickness of 6μ.
I made it m. The resulting coating had excellent corrosion resistance, moisture-resistant adhesion, insulation, etc. On the other hand, Comparative Example 1, in which alkyd resin/melamine resin was used in the resin topcoat at a blending ratio of 80/20, had poor moisture-resistant adhesion and boiling water-resistant adhesion, and was not suitable for practical use. Example 2 On the surface of the same silicon steel plate as in Example 1, 8% monobasic aluminum phosphate - 1.5% and chromic anhydride - 2%
A phosphate treatment solution consisting of aluminum nitrate was applied and baked at 450°C for 60 seconds to form a film with a thickness of 0.7 μm. On top of this, a water-soluble resin with a polyester resin/melamine resin blending ratio of 70/30 is applied.
Bake for 70 seconds at ℃. The total thickness of both films is 8μm
It was hot. The resulting coating had excellent corrosion resistance, moisture-resistant adhesion, and insulation resistance. Comparative Example 2, in which an acrylic emulsion was used as the resin topcoat, had poor solvent resistance, film hardness, corrosion resistance, etc., and lost its gloss in the boiling water test. Comparative Example 3 In Example 1, which had only a phosphate-based coating, the interlayer resistance and corrosion resistance were very poor. Comparative Example 4 A treatment solution consisting of 8% magnesium chromate, 3% acrylic resin emulsion, and 0.5% ethylene glycol was applied to the same steel plate as in Example 1 and baked to obtain a coating with a thickness of 1.5 μm, but the interlayer resistance and corrosion resistance were poor. It was inferior. The characteristics of the above examples and comparative examples are summarized in Table 2.

【table】

[Table] As described above, according to the present invention, it is possible to easily form an insulating coating that can advantageously meet the severe requirements of electrical steel sheets used in applications such as large water turbine generators. Moreover, the film properties are appropriately improved.

Claims (1)

[Claims] 1. A phosphate-based treatment liquid is applied to the surface of an electrical steel sheet containing 2 to 4% by weight of Si and baked to form an amorphous film with a dry thickness of 0.3 to 1.0 μm as a base film. and a step of applying a water-soluble resin made of a mixture mainly composed of polyester resin and blended with melamine resin on the base film surface and baking it to form an insulating film with a total thickness of 3 to 12 μm. A method for forming an insulating film on an electrical steel sheet, characterized by forming a bond. 2 The water-soluble resin has a blending ratio of 85/15 to 85/15, which is expressed by the weight ratio of polyester resin and melamine resin.
65/35. The method according to claim 1.