JP3379027B2 - Coating agent for forming a coating on grain-oriented electrical steel sheets - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention relates to film-forming coating agent of electrical steel sheet having excellent coating film tensioning effect. 2. Description of the Related Art In order to improve iron loss when used in a transformer or the like, an electromagnetic steel sheet is formed with a film having properties as an insulating material and capable of giving tension to the steel sheet depending on the application. It is common to do. 2. Description of the Related Art Conventionally, a method of manufacturing a magnetic steel sheet has been generally used in which a phosphate-based film is formed, and after baking, the steel sheet is tensioned to reduce iron loss. However, this phosphate-based coating has a low effect of imparting tension, and it is necessary to form a thick coating in order to apply a large tension in order to reduce iron loss. There was a case. JP-B-56-4150, JP-A-61-2
01732, JP-B-63-54767, JP-A-2-
Japanese Patent No. 21483 discloses a technique for forming a film by chemical vapor deposition or ion plating. These can form a film excellent in the effect of imparting tension, but have the disadvantage that the productivity is low and the cost is high because vacuum equipment is required. In contrast Japanese Patent Application No. 4-222849, the Japanese Patent Application No. Hei 4-two hundred twenty-two thousand eight hundred fifty forming method of coating is disclosed by a sol-gel method. [0004] [SUMMARY OF THE INVENTION The present invention, a coating agent having excellent formability of the <br/> film less oriented electrical steel sheet iron loss having an excellent coating tensioning effect It is intended to provide at low cost. SUMMARY OF THE INVENTION The present invention relates to a method for converting a boric acid and an alumina sol, or a compound which becomes a source of aluminum or boron or a soluble salt during baking, into Al ₂ O ₃ or B ₂ O.
₃ 1 to 50 wt terms and _{Al 2 O 3 / B 2 O} 3 mixture of 1-5 in the molar ratio, water-miscible there is, the organic solvent dissolving the salt. %, And the balance of the solid content consisting of water is 1 to 50 wt. Those related <br/> in% of the grain-oriented electrical steel sheet film-forming coating agent. [0006] The magnetic steel sheet coated and baked with this coating agent has a coating with few defects and an excellent effect of imparting tension, and has a low iron loss. The reason that the coating film of the present coating composition is excellent in the effect of imparting tension is due to the presence of aluminum oxide and aluminum borate in the coating film. In order to effectively apply stress to the magnetic steel sheet, it is sufficient that the product of the difference in thermal expansion coefficient between the steel sheet and the coating and the Young's modulus of the coating is large. Although the coefficient of thermal expansion and Young's modulus of aluminum borate are not clear, the effect of imparting tension is excellent when the coating contains aluminum oxide or aluminum borate. It is considered that this is because aluminum borate has a smaller thermal expansion coefficient and a higher Young's modulus than a steel sheet, as analogized from aluminum oxide and boron oxide. The coating composition also contains a water-soluble organic solvent,
It is excellent in suppressing defects when the coating agent dries. Although the mechanism is not clear, it is considered that the presence of the water-soluble organic solvent stabilizes the dissolution and dispersion of the salt or sol in the coating composition. The method for applying the coating composition of the present invention to a magnetic steel sheet can be applied to a method of applying a sol, for example, a simple method such as a dip method or a bar coater to form a sound film with few defects. . In addition, if this coating agent is applied and then baked at 500 to 1350 ° C. after drying, it is possible to form a film having a sufficient effect of imparting tension in a relatively short time of 1 hour or less. It is also excellent. The reason why the composition of the coating agent is limited as in claim 1 is that when the molar ratio in terms of Al ₂ O ₃ and B ₂ O ₃ is smaller than 1, the aluminum source is insufficient and sufficient tension is applied to the steel sheet. Can not be applied. Al ₂ O ₃ , B ₂ O ₃
If the molar ratio in terms of is larger than 5, the adhesion of the coating deteriorates, so that a sound coating cannot be obtained. In order to obtain a sound film with a more sufficient effect of applying tension,
Al ₂ O ₃ and B ₂ O ₃ are preferably converted to a molar ratio of A.
It is preferable that l ₂ O ₃ / B ₂ O ₃ is 1.5 to 4.5. What is called boric acid in the present invention is orthoboric acid,
It is a generic term for different forms of boric acid such as metaboric acid. Further, as the aluminum source, after applying the coating agent, supply aluminum at the time of baking, as long as it is a raw material that does not leave elements other than oxygen, regardless of its form, from the viewpoint of reactivity, sol or water-soluble Salts are desirable. For example, boehmite sol or alumina sol obtained by hydrolyzing metal alkoxide can be used. In addition, when a water-soluble organic solvent is contained in the coating agent, defects during drying of the coating film can be suppressed, but when the amount of the organic solvent is 1 wt. %, The effect is not obtained, and if the amount is too large, it becomes difficult to form a sound film rather than peeling off the film. Therefore, the amount of the organic solvent is limited to a maximum of 50 vol. The organic solvent may be any as long as it is compatible with water. For example, ethylene glycol, ethanol, glycerin and the like are suitable, but it is more preferable if the organic solvent can well dissolve the salt contained in the coating agent. The coating agent composed of these components has a solid content of 50 wt. % Or less, the viscosity and the like can be kept stable. However, in order to keep the coating composition stable for a long period of time, the solid content concentration is preferably 30 wt. % Is more desirable. On the other hand, if the solid content is too small, it becomes difficult to obtain a desired coating amount. % Or more is good. The reason for the above-mentioned baking conditions is as follows.
If the baking temperature is lower than 500 ° C., it is difficult to sufficiently react the alumina and boric acid, and the adhesion is poor.
It is not possible to obtain a film excellent in the effect of imparting tension. If the baking temperature is high, it is advantageous for forming a film, but if the baking temperature is too high, it is not economical, and the baking temperature is preferably set to 1350 ° C, more preferably 1200 ° C or less. The effects of the present invention will be specifically described in the following examples. (Example 1) Alumina sol and boric acid were mixed with Al ₂ O ₃ and B ₂ O.
_The ratio was 1.8: 1 in terms of ₃ and dispersed and dissolved in distilled water. % Of ethylene glycol to reduce the solid content to 3 wt. % Was used as a coating agent, which was applied to a 0.2 mm-thick grain-oriented electrical steel sheet having a finish-annealed forsterite film, dried, and hydrogen was added at 20%.
Baking was performed in a nitrogen atmosphere containing vol.%. The coating amount is 4 g / m ^{2 on} one side, and the baking temperature and time are 950 ° C. for 10 minutes. As a result, the adhesion is good,
A film having a high iron loss improving effect by a tension imparting effect was obtained. (Example 2) A commercially available alumina sol and boric acid were dissolved in distilled water at a ratio of 1.8: 1 in terms of Al ₂ O ₃ and B ₂ O ₃ , and 10 wt. % Of ethylene glycol to reduce the solid content to 3 wt. % Was used as a coating agent. The surface of a grain-oriented electrical steel sheet having a thickness of 0.2 mm having a finish-annealed forsterite coating is treated in a mixed solution of sulfuric acid and hydrofluoric acid, and the coating agent is applied as a sample with the forsterite coating removed, It was dried and baked in a nitrogen atmosphere containing 20 vol.% Of hydrogen.
The coating amount is 4 g / m ^{2 on} one side, and the baking temperature and time are 950 ° C. for 10 minutes. As a result, a coating film having good adhesion and a high iron loss improving effect by a tension imparting effect was obtained. Example 3 Aluminum sec-butoxide was hydrolyzed with distilled water heated to 90 ° C., and the resulting precipitate was peptized with nitric acid.
This was dispersed and dissolved in distilled water at a ratio of 2.5: 1 in terms of ₂ O ₃ and B ₂ O ₃ , and 20 wt. % Of ethylene glycol to reduce the solid concentration to 10 wt. % Is used as a coating agent, which is applied to a 0.2 mm thick grain-oriented electrical steel sheet having a finish-annealed forsterite film, dried, and baked in a nitrogen atmosphere containing 20 vol.% Of hydrogen. Was. The coating amount is 4 g / m ^{2 on} one side, and the baking temperature and time are 950 ° C. for 10 minutes. As a result, a coating film having good adhesion and a high iron loss improving effect by a tension imparting effect was obtained. Comparative Example 1 Aluminum phosphate was 30 wt.
%, A coating agent consisting of water in the balance is applied to a 0.2 mm-thick grain-oriented electrical steel sheet having a finish-annealed forsterite film, dried, and baked in a nitrogen atmosphere containing 20 vol.% Of hydrogen. Was. The coating amount is 4 g / m ^{2 on} one side, and the baking temperature and time are 950 ° C. for 10 minutes. The obtained film was amorphous aluminum phosphate. Table 1 shows the effect of imparting tension at this time as Comparative Example 1. [Table 1] Comparative Example 2 Alumina sol and boric acid were converted to Al ₂
This was dispersed and dissolved in distilled water at a ratio of 5.5: 1 in terms of O ₃ and B ₂ O ₃ to obtain a coating material having a solid content of 9%. It was applied to a 0.2 mm-oriented magnetic steel sheet, dried, and baked in a nitrogen atmosphere containing 20 vol.% Of hydrogen. The coating amount is 4 g / m ^{2 on} one side, and the baking temperature and time are 950 ° C. for 10 minutes. The resulting coating had penetrating defects. According to the present invention, there is provided a coating material for coating a grain-oriented electrical steel sheet having a coating excellent in a tension imparting effect, and an iron loss due to a tension imparting effect on the electromagnetic steel sheet is improved. Has a great industrial effect.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuichi Yamazaki 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division (72) Inventor Takeo Nagashima 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology (56) References JP-A-6-65754 (JP, A) JP-B-46-18603 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00 -22/86

Claims (1)

(57) [Claims 1] A mole ratio of boric acid and alumina sol, or boron or a compound serving as an aluminum source or a soluble salt at the time of baking, in terms of Al ₂ O ₃ and B ₂ O ₃ , is represented by A.
a mixture of _{l 2 O 3 / B 2 O} 3 is 1 to 5, compatible with water Ri <br/> Oh, the organic solvent dissolving the salt 1 to 50 wt. % Included
The concentration of the solid content consisting of water is 1 to 50 wt. % Coating material for forming a coating on grain-oriented electrical steel sheets.