ELECTRICAL STEEL SHEET

Abstract

An electrical steel sheet has an insulating coating on a steel sheet surface. The insulating coating includes one or more selected from an inorganic salt, an oxide, and an organic resin. The insulating coating includes the inorganic salt and/or the oxide in an amount of 50% or more by mass in total based on the total mass of the insulating coating. The insulating coating has a fluorine concentration ranging from 2 ppm to 130 ppm. The insulating coating is free of a chromium compound. The insulating coating of this electrical steel sheet has excellent coating compatibility.

Claims

1. An electrical steel sheet having an insulating coating on a steel sheet surface, wherein the insulating coating comprises one or more selected from an inorganic salt, an oxide and an organic resin, wherein the insulating coating contains, based on a total mass of the insulating coating, 50% or more by mass in total of: the inorganic salt and/or the oxide, has a fluorine concentration ranging from 2 ppm to 130 ppm, and is free of a chromium compound.

2. The electrical steel sheet according to claim 1, wherein the insulating coating contains, based on a total mass of the insulating coating, 50% or more by mass in total of: a metal phosphate, and; one selected from, or a mixture or a copolymer of two or more selected from an acrylic resin, an epoxy resin, and a polyester resin.

3. The electrical steel sheet according to claim 1, wherein the insulating coating contains, based on a total mass of the insulating coating, 50% or more by mass in total of: the oxide, and; one selected from, or a mixture or a copolymer of two or more selected from an acrylic resin, an epoxy resin, and a polyester resin.

4. The electrical steel sheet according to claim 2, wherein the insulating coating contains, based on a total mass of the insulating coating, 50% or more by mass in total of: 100 parts by mass of the metal phosphate including one or more metal elements selected from aluminum, zinc, calcium, cobalt, strontium, zirconium, titanium, nickel, barium, magnesium and manganese, and; 1 to 50 parts by mass of one selected from, or a mixture or a copolymer of two or more selected from the acrylic resin, the epoxy resin, and the polyester resin.

5. The electrical steel sheet according to claim 3, wherein the insulating coating contains, based on a total mass of the insulating coating, 50% or more by mass in total of: 100 parts by mass of the oxide including one or more selected from colloidal silica, zinc oxide, calcium oxide, cobalt oxide, zirconium oxide, titanium oxide and magnesium oxide and; 1 to 100 parts by mass of one selected from, or a mixture or a copolymer of two or more selected from the acrylic resin, the epoxy resin, and the polyester resin.

Description

EXAMPLE

[0081] Firstly, a non-oriented electrical steel sheet was prepared which contained, by mass, Si: 2.4%, Al: 0.3%, Mn: 0.5%, and the balance: Fe and impurities and which had a sheet thickness of 0.35 mm.

[0082] Next, metal phosphate solutions were prepared using an orthophosphoric acid as metal phosphate in the following manner. Hydroxides, oxides, or carbonates of metals, e.g., Mg(OH).sub.2 and Al(OH).sub.3, were each dissolved in water together with the orthophosphoric acid so as to obtain a metal phosphate concentration of 40% by mass, and each solution was mixed and stirred.

[0083] In addition, as the inorganic salt or oxide, fine particles of titanium oxide, magnesium oxide, and zirconium hydroxide (mass average particle size of less than 1 jam) (commercial products) and aluminum surface modified 30 mass % colloidal silica with an average particle size of 15 nm (commercial product) were used. These inorganic salts or oxides were each dispersed in water so as to obtain a concentration of 40% by mass, and thereby inorganic solutions were prepared. It is believed that the hydroxide (zirconium hydroxide) was partially converted to an oxide (zirconium oxide) as a result of heating for application and drying.

[0084] As for the organic resins, the following 4 types of 40 mass % emulsions were used.

[0085] (1) Acrylic Resin

[0086] An emulsion of an acrylic resin formed by copolymerizing 30% by mass of methyl methacrylate, 10% by mass of 2-hydroxyethyl methacrylate, 30% by mass of n-butyl acrylate, 10% by mass of a styrene monomer, and 20% by mass of isobutyl acrylate (2) Epoxy Resin

[0087] An emulsion of a carboxyl group modified epoxy resin formed by modifying bisphenol A with triethanolamine and reacting it with succinic anhydride

[0088] (3) Polyester Resin

[0089] An emulsion of a carboxyl group-containing polyester resin formed by copolymerizing 35% by mass of dimethyl terephthalate and 35% by mass of neopentyl glycol and then graft polymerizing the copolymer with 15% by mass of fumaric acid and 15% by mass of trimellitic anhydride

[0090] Furthermore, as the fluorine-containing compound, compounds listed in Table 1 were each added and mixed so as to obtain a fluorine concentration shown in Table 1.

TABLE-US-00001 TABLE 1 Metal phosphate solution Fluorine-containing or inorganic solution Organic resin compound Ratio Ratio Ratio Fluorine [part by [part by [part by concentration Compound mass] Compound mass] Compound mass] (ppm) Inventive Al(H.sub.2PO.sub.4).sub.3 100 Acrylic 20 A 10 25 Example 1 Resin Inventive Mn(H.sub.2PO.sub.4).sub.2 100 Acrylic 40 A 20 3 Example 2 Resin Inventive Al(H.sub.2PO.sub.4).sub.3 + 100 Acrylic 5 C 30 45 Example 3 Ni(H.sub.2PO.sub.4).sub.2 Resin (70:30) Inventive Al(H.sub.2PO.sub.4).sub.3 + 100 C 30 36 Example 4 colloidal silica (80:20) Inventive TiO.sub.2 100 Polyester 70 B 30 130 Example 5 Resin Inventive Colloidal silica 100 Epoxy 60 E 40 97 Example 6 Resin Inventive Zr(OH).sub.2 + 100 Acrylic 20 F 10 6 Example 7 colloidal silica Resin Inventive TiO.sub.2 + Zr(OH).sub.2 100 Acrylic 30 D 10 9 Example 8 (20:80) Resin Inventive MgO + TiO.sub.2 100 Acrylic 50 D 20 24 Example 9 (50:50) Resin Comparative Al(H.sub.2PO.sub.4).sub.3 100 Acrylic 30 Example 1 Resin Comparative Al(H.sub.2PO.sub.4).sub.3 + 100 Epoxy 60 A 100 240 Example 2 Zn(H.sub.2PO.sub.4).sub.2 Resin (50:50) Comparative Acrylic 100 B 30 56 Example 3 Resin Comparative Al(H.sub.2PO.sub.4).sub.3 100 B 50 220 Example 4 Reference Magnesium 100 Acrylic 30 Example chromate Resin

[0091] In Table 1, the letters A to F represent the following fluorine-containing compounds and the symbol - indicates that no such compound was used.

[0092] A: vinylidene fluoride-hexafluoropropylene

[0093] B: tetrafluoroethylene-vinyl ether low copolymer

[0094] C: salt of perfluorobutanesulfonic acid

[0095] D: perfluoroalkyl polyether low polymer

[0096] E: fluorine-modified silicone

[0097] F: chlorotrifluoroethylene low polymer

[0098] In Table 1, the metal ion fractions are mass fractions and the contents of the organic resins and the fluorine-containing compounds are based on the solids content.

[0099] Treatment solutions having mixing ratios shown in Table 1 were each applied to the surface of the electrical steel sheet having the composition described above, and baking was performed at drying temperatures shown in Table 2, so as to prepare electrical steel sheets of Examples 1 to 9, Comparative Examples 1 to 4, and Reference Example. A roll coater method was employed for the application of the treatment solution to the surface of the electrical steel sheet, and the amount of roll pressure and others were adjusted so as to obtain an insulating coating thickness of approximately 0.8 m. The drying was performed using a radiation furnace. The end-point sheet temperatures and the baking times were adjusted so that the end-point sheet temperatures were within a range of 200 to 360 C. and the baking times were within a range of 10 to 60 seconds, depending on the samples.

[0100] The fluorine concentration was analyzed by a combustion-ion chromatography method. The measurement was made by an analysis technique in accordance with a JIS method (JIS K0102) and using a commercially available ion chromatograph.

[0101] In the following, the method for evaluating the produced samples will be described in detail.

[0102] The insulating properties were evaluated as follows based on interlayer resistances measured in accordance with a JIS method (JIS C2550): less than 5 .Math.cm.sup.2/sheet as ; 5 or more.Math.cm.sup.2/sheet and less than 10 .Math.cm.sup.2/sheet as ; 10 or more.Math.cm.sup.2/sheet and less than 50 .Math.cm.sup.2/sheet as O; and 50 or more .Math.cm.sup.2/sheet as . As for the insulating properties, samples evaluated as or O were determined to be acceptable.

[0103] As for the adhesion, each steel sheet sample, with an adhesive tape attached thereto, was wound around metal bars of 10 mm, 20 mm, and 30 mm in diameter and then the adhesive tape was peeled off from each steel sheet sample, and evaluations were made based on the occurrence of delamination in the insulating coatings. Samples that did not have delamination in the insulating coating at the curvature of 10 mm were evaluated as 10 mm OK, samples that did not have delamination in the insulating coating at the curvature of 20 mm were evaluated as 20 mm OK, samples that did not have delamination in the insulating coating at the curvature of 30 mm were evaluated as 30 mm OK, and samples that had delamination in the insulating coating at the curvature of 30 mm were evaluated as 30 mm OUT. As for the adhesion, samples evaluated as 10 mm OK, 20 min OK, or 30 mm OK were determined to be acceptable.

[0104] Corrosion resistance in wet environments was evaluated in accordance with a JIS salt spray test (JIS Z2371). Firstly, a 5% NaCl aqueous solution was allowed to drop naturally onto each sample for 1 hour in an atmosphere at 35 C., and thereafter the sample was subjected to 5 cycles of holding, with one cycle including 3 hours of holding at a temperature of 60 C. and a moisture content of 40% and 3 hours of holding at a temperature of 40 C. and a moisture content of 95%. Subsequently, the area of rust was evaluated by a 10-point evaluation. The evaluation criteria are as follows. As for the corrosion resistance, samples evaluated as 7 or higher were determined to be acceptable.

[0105] 10: No rust forming

[0106] 9: Very slight rust forming (area fraction of not more than 0.1%)

[0107] 8: Area fraction of rust=more than 0.1% and not more than 0.25%

[0108] 7: Area fraction of rust=more than 0.25% and not more than 0.50%

[0109] 6: Area fraction of rust=more than 0.50% and not more than 1%

[0110] 5: Area fraction of rust=more than 1% and not more than 2.5%

[0111] 4: Area fraction of rust=more than 2.5% and not more than 5%

[0112] 3: Area fraction of rust=more than 5% and not more than 10%

[0113] 2: Area fraction of rust=more than 10% and not more than 25%

[0114] 1: Area fraction of rust=more than 25% and not more than 50%

[0115] As for the powder coating compatibility, firstly, a commercially available low temperature cure polyester powder coating solution was sprayed onto each sample using a tribo gun so as to obtain an average coating thickness of 50 m, and each sample was heat cured at 160 C. for 15 minutes. Subsequently, each coated sample was subjected to salt spraying over 100 hours and then a cross-cut adhesion test was conducted to evaluate the powder coating compatibility. In the cross-cut adhesion test, samples in which the powder coating did not delaminate were evaluated as , samples in which the powder coating slightly delaminated were evaluated as O, samples in which the powder coating partially delaminated but adhered were evaluated as , and samples in which the powder coating was corroded and had blistering were evaluated as . As for the powder coating compatibility, samples evaluated as or O were determined to be acceptable.

[0116] As for the electrodeposition coating, firstly, a surface pretreatment was performed using a commercially available degreasing solution, and then, a high weatherability electrodeposition coating solution of epoxy-acrylic type was applied onto each sample in a bath at 25 C. so as to obtain an average coating thickness of 20 m. The coated samples were rinsed with water to clean off an excess of the coating composition and then heat dried at 160 C. for 20 minutes. Subsequently, each coated sample was subjected to salt spraying over 80 hours and then a cross-cut adhesion test was conducted to evaluate the electrodeposition coating compatibility. In the cross-cut adhesion test, samples in which the electrodeposition coating did not delaminate were evaluated as , samples in which the electrodeposition coating slightly delaminated were evaluated as O, samples in which the electrodeposition coating partially delaminated but adhered were evaluated as , and samples in which the electrodeposition coating was corroded and had blistering were evaluated as . As for the electrodeposition coating compatibility, samples evaluated as or O were determined to be acceptable.

[0117] As for aqueous coating compatibility, firstly, a commercially available acrylic resin aqueous coating composition was sprayed to obtain an average coating thickness of 10 m, and then the coating was dried at room temperature and visually evaluated. Samples in which the aqueous coating was glossy and uniform were evaluated as 5, samples in which the aqueous coating was glossy but slightly less uniform were evaluated as 4, samples in which the aqueous coating was less uniform but was totally applied were evaluated as 3, samples in which the aqueous coating was less uniform and partially thin were evaluated as 2, and samples in which the aqueous coating was entirely non-uniform were evaluated as 1. As for the aqueous coating compatibility, samples evaluated as 3 or higher were determined to be acceptable.

[0118] As for the appearance, samples whose insulating coating was glossy, smooth, and uniform were evaluated as 5, samples whose insulating coating was glossy but slightly less uniform were evaluated as 4, samples whose insulating coating was somewhat glossy and smooth but less uniform were evaluated as 3, samples whose insulating coating was less glossy, somewhat less smooth, and less uniform were evaluated as 2, and samples whose insulating coating was less glossy, less uniform, and less smooth were evaluated as 1. As for the appearance, samples evaluated as 4 or higher were determined to be acceptable.

[0119] As for the thermal resistance, after the electrical steel sheet was subjected to stress relief annealing at 750 C. for 2 hours in a nitrogen atmosphere, the surface thereof was rubbed with a gauze measuring 2 mm30 mm at a loading of 100 gf (approximately 0.98 N), and then evaluations were made based on the occurrence of delamination in the insulating coating. Samples that did not have delamination after rubbing with the gauze were evaluated as 5, samples that had slight delamination were evaluated as 4, samples that had apparent delamination were evaluated as 3, samples that had severe delamination were evaluated as 2, and samples that had delamination even without rubbing with the gauze were evaluated as 1. As for the thermal resistance, samples evaluated as 4 or higher were determined to be acceptable.

[0120] The above results of evaluations of the electrical steel sheets are summarized in Table 2.

TABLE-US-00002 TABLE 2 Electro- Powder deposition Aqueous Insulating Corrosion coating coating coating Thermal Test No. properties Adhesion resistance compatibility compatibility compatibility Appearance resistance Inventive 20 mm OK 10 5 5 5 Example 1 Inventive 20 mm OK 10 5 5 5 Example 2 Inventive 20 mm OK 10 4 4 5 Example 3 Inventive 20 mm OK 7 4 5 5 Example 4 Inventive 20 mm OK 9 3 4 4 Example 5 Inventive 20 mm OK 7 3 5 4 Example 6 Inventive 20 mm OK 8 5 4 4 Example 7 Inventive 20 mm OK 9 5 4 5 Example 8 Inventive 30 mm OK 7 5 4 5 Example 9 Comparative 20 mm OK 7 X 5 3 4 Example 1 Comparative 30 mm OUT 8 2 4 4 Example 2 Comparative 30 mm OK 2 3 2 4 Example 3 Comparative 30 mm OUT 9 2 5 4 Example 4 Reference 20 mm OK 8 5 5 5 Example

[0121] Reference to the results shown in Table 2 clarifies the advantageous effects of the present invention.

[0122] The results in Table 2 demonstrate that Examples 1 to 9 of the present invention have excellent powder coating compatibility, electrodeposition coating compatibility, and aqueous coating compatibility. The results also demonstrate that Examples 1 to 9 of the present invention have excellent insulating properties, adhesion, corrosion resistance, appearance, and thermal resistance, in addition to excellent powder coating compatibility, electrodeposition coating compatibility, and aqueous coating compatibility. Specifically, it is seen that Examples 1 to 9 have insulating properties, adhesion, corrosion resistance, powder coating compatibility, electrodeposition coating compatibility, aqueous coating compatibility, appearance, and thermal resistance that are comparable to or better than those of Reference Example, which includes a chromium compound-containing insulating coating.

[0123] On the other hand, with regard to Comparative Examples 1 to 4, most of them have low powder coating compatibility, electrodeposition coating compatibility, and aqueous coating compatibility, and none of them are excellent in all the categories of insulating properties, adhesion, corrosion resistance, powder coating compatibility, electrodeposition coating compatibility, appearance, and thermal resistance.

[0124] Specifically, it is seen that Comparative Example 1, which does not include a fluorine-containing compound, has low powder coating compatibility and electrodeposition coating compatibility, and also does not have a good appearance. Furthermore, it is seen that Comparative Example 2, which has a fluorine concentration higher than the range of the present invention, has low powder coating compatibility, electrodeposition coating compatibility, and aqueous coating compatibility and also has low adhesion. Furthermore, it is seen that Comparative Example 3, which does not contain an inorganic salt or oxide, or, a metal phosphate, has poor corrosion resistance and appearance. Furthermore, it is seen that Comparative Example 4, which does not include an organic resin, has low powder coating compatibility, electrodeposition coating compatibility, and aqueous coating compatibility, and also has low adhesion.

[0125] As described in the foregoing, the electrical steel sheet according to the embodiment of the present invention shows good coating compatibility for powder coating, electrodeposition coating, and aqueous coating for production of laminate iron cores, and the insulating coating shows good properties for the electrical steel sheet.

[0126] In the foregoing description, a preferred embodiment of the present invention has been described in detail, but the present invention is not limited to such examples. It will be apparent that those having general knowledge in the field to which the present invention belongs may find various alternations and modifications within the scope of the technical ideas described in the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention.