JPS6257713B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for forming a low-expansion insulating film on the surface of a thin silicon steel plate having a thickness of 0.20 mm or less. (Prior art) It is well known that applying tension to the surface of a silicon steel plate or reducing the thickness of the silicon steel plate reduces iron loss and has a positive effect on magnetism. In addition to research into methods of forming insulating films for this purpose, many attempts have been made to reduce the board thickness. Conventionally, in the production of silicon steel sheets, a cold-rolled steel strip rolled to the final thickness is decarburized and annealed in an atmosphere consisting of hydrogen and steam to form SiO ₂ and iron oxide on the surface of the steel strip. By applying an annealing separator mainly composed of MgO on the generated layer, and then winding the steel strip and final annealing it at a temperature range of 1100 to 1300℃, forsterite (2MgO・SiO ₂ ) is formed. An insulating film is formed whose main component is (For example, Special Publication No. 59-11670, etc.)
At this time, the tension applied to the silicon steel sheet is applied by the insulation film by the temperature difference between the annealing temperature and the temperature at which the silicon steel sheet is used, since the expansion coefficient of the insulation film is smaller than that of the silicon steel sheet. (Problem to be solved by the invention) However, the 2MgO・SiO ₂ formed here has an expansion coefficient of about 13, for example, of a silicon steel plate containing 3.2% Si.
Since there is only a slight difference between ×10 ^-6 °C ^-1 and 10 × 10 ^-6 °C ^-1 , an additional external force was applied to the silicon steel plate, which had already been coated with an insulating film, to create tension. In this case, only a small tension is applied compared to the limit tension at which iron loss can be improved, and an insulating film with a lower expansion coefficient is required. The thickness of the 2MgO.SiO ₂ insulating film formed is approximately 2 μm on one side of the currently manufactured 0.3 mm thick silicon steel plate. As the thickness of the silicon steel sheet becomes thinner, the decarburization annealing time becomes shorter and the amount of _SiO2 concentrated in the silicon steel sheet decreases, resulting in less 2MgO and SiO formed during final annealing. ₂
The insulation film becomes thinner, but the thickness of the silicon steel plate is 0.20.
If it is less than mm, it becomes difficult to form a homogeneous and strong film, and therefore the magnetic properties deteriorate. It is presumed that the reason for the inability to obtain a homogeneous film is that when powder is used as an insulating film forming material, the particle size of the particles becomes large, or the primary particles agglomerate to form coarse secondary particles. (Means for Solving the Problems) According to the present invention, an organic solvent solution containing one or more metal alkoxides is applied to a silicon steel plate, and moisture in the atmosphere is absorbed to remove some of the dissolved metal ions or By hydrolyzing the entire material, a fine sol or gel-like homogeneous film of metal oxide is obtained, which is then annealed, so even when the thickness of silicon steel sheet becomes thinner, it can be reduced to a thickness in the range of 0.1 to 1.0 μm. Expandable oxide or composite oxide insulating films can be easily obtained, and silicon steel sheets with extremely excellent magnetic properties can be obtained. Metal alkoxides are represented by the general formula M(OR) _o , where M is a metal element and R is hydrogen or an alkyl group. Metal alkoxide is
It is soluble in alcohols such as CH ₃ OH, C ₂ H ₅ OH, C ₃ H ₇ OH, and C ₄ H ₉ OH, and organic solvents such as C ₆ H ₆ , and is usually used after being dissolved and diluted in alcohol. Although the rate of hydrolysis of metal ions in metal alkoxides differs depending on the type of metal element, it is possible to adjust the rate of hydrolysis by adding H ₂ O or HCl to the alcohol solution of metal alkoxides, and if two or more types of Even from a solution containing metal alkoxides, a uniform mixture of metal oxides can be simultaneously precipitated without segregation. Metal alkoxide applied to the surface of a silicon steel sheet absorbs moisture from the atmosphere during the drying process, is hydrolyzed, and precipitates fine hydroxides or direct oxides to form a thin film in a sol or gel state. When multiple metal alkoxides are contained, it is possible to mix them until the metal atoms become almost uniform in the solution stage by refluxing, and this uniformity can also be ensured during hydrolysis and precipitation, so that the atomic arrangement becomes crystalline. 400~
It has the characteristic of crystallizing at temperatures as low as 700℃. The thickness of the metal oxide layer formed as an insulating film on the silicon steel plate can be adjusted to 0.1 to 1.0 μm depending on the concentration of the metal alkoxide, the viscosity of the solution, and the coating operation. The viscosity of the solution can be adjusted by adding _H2O , glycerin, or hydroxylpropylcellulose (HPC).
It can be adjusted within a wide range by adjusting the thickening agent. Zircon (ZrO ₂・SiO ₂ , 5×10 ^-6 ℃
^-1 ), β-spodiumene (Li ₂ O・Al ₂ O ₃・
4SiO ₂ , 0.9×10 ^-6 ℃ ^-1 ), β-eucryptite (Li ₂ O・Al ₂ O ₃・2SiO ₂ , -0.6×10 ^-6 ℃ ^-1 ),
Examples include compositions such as 95wt%SiO ₂ -5wt%TiO ₂ . Here, the numbers in parentheses indicate the expansion rate. Therefore, the metal alkoxide used in the present invention is
Desirable materials include Zr, Si, Li, Al, Ti, and Mg. Conventionally, insulating coatings were created by applying MgO as an annealing separator to steel sheets after decarburization annealing, and then applying MgO as an annealing separator.
An insulating film whose main component is 2MgO・SiO ₂ has been obtained. However, depending on the material applied to the silicon steel sheet to obtain a predetermined tension, metallurgically desirable properties such as the degree of desulfurization, denitrification, decarburization, and secondary recrystallization grain size after final annealing of the silicon steel sheet may not be obtained. There are cases. In such cases, first coat with a material that provides the desired metallurgical properties, perform final annealing, then remove the oxide film that has been formed by pickling, etc. An insulating film can be formed by applying a solution containing a seed or two or more metal alkoxides, drying, and annealing. In this case, a reaction involving diffusion of atoms or molecules of the silicon steel sheet is not necessarily necessary, and the reaction between the silicon steel sheet surface and the coating,
Since it is only necessary to obtain the necessary adhesive strength between the produced oxide film, it is possible to perform firing in a non-reducing atmosphere where strong adhesive strength can be obtained with the silicon steel plate surface.
Continuous firing is also possible by lowering the firing temperature or shortening the firing time. However, care must be taken as firing at a temperature higher than the previous finish annealing may change the metallurgical structure. A solution containing a metal alkoxide is applied to the surface of a silicon steel sheet and dried to obtain a film of metal oxide or metal hydroxide, and then a high melting point oxide powder such as ZrO ₂ or MgO is applied in the form of a slurry on top of it. After being attached by coating or electrostatic coating, it can be rolled up into a coil shape and annealed for finishing. Powders such as ZrO ₂ or MgO applied later or electrostatically prevent fusion between silicon steel plates during annealing, and can be easily removed by washing with water or light pickling after annealing. When MgO is used, since MgO has a large affinity for S, it also has the effect of removing S from the silicon steel sheet. (Example) Example 1 A 0.12 mm thick silicon steel plate containing 0.05 wt% C and 3.2 wt% Si was continuously annealed at 820°C for 2.5 minutes in an atmosphere consisting of 75% hydrogen and the balance nitrogen (dew point 45°C). It was decarburized. The following treatment solution was applied to the decarburized silicon steel sheet, and after drying in the atmosphere, hydrogen was heated at 15℃/hr to 75%
%, the temperature was raised to 1180°C in an atmosphere consisting of 25% nitrogen, and annealing was performed at 1180°C for 20 hours in an atmosphere containing 100% hydrogen.
After cooling, the thickness and magnetism of the insulating film were measured. Coating agent Zirconium isopropoxide (Zr(i-
_OC3H7 ) ₄ ), _magnesium ethoxide (Mg
(OC ₂ H ₅ ) ₂ ) and lithium ethoxyoxide (LiOC ₂ H ₅ ) in an atomic ratio of Zr:Mg:Li = 85:10:5, and ZrO ₂ of each Zr, Mg, and Li atom. , MgO, and Li ₂ O were mixed to give a weight of 5%, and the viscosity of the solution was adjusted to 20 cp by adding hydroxylpropyl cellulose (HPC). 5% magnesium isopropoxide (Mg(i-
OC ₃ H ₇ ) ₂ ) only ethanol solution. An aqueous solution of MgO powder containing 5% by weight of MgO, which has traditionally been used as an annealing separator for silicon steel sheets. Table 1 shows the measurement results of magnetism and film thickness.

[Table] Example 2 An insulating film material was applied to the surface of the steel plate after decarburization annealing shown in Example 1 by dipping it in the coating agent shown below and pulling it up, and after drying in the atmosphere, the seizing between the steel plates was prevented. 5 by electrostatic coating of MgO powder for
After coating on one side at a ratio of g/m ² , it was wound up into a coil shape, placed in a finish annealing furnace, and finish annealed in the same manner as in Example 1. Electrostatically painted by washing with water after annealing
MgO powder was removed. Film thickness 0.6μ on silicon steel plate surface
A ZrO ₂ / SiO ₂ insulating film with a large m is formed, and the magnetic properties were measured: B ₁₀ (Tesla) 1.92, W
A good result of 〓(w/Kg) 0.39 was obtained. Coating agent: Ethanol solutions of each of Zr(i-OC ₃ H ₇ ) ₄ and LiOC ₂ H with an atomic ratio of Zr:Li = 95:5, Zr, Li
They were mixed so that the weight of ZrO ₂ and Li ₂ O in terms of atoms was 5%. The viscosity of the solution was the same as in Example 1.
Adjusted to 20cp. Example 3 Using the silicon steel plate used in Example 1, the conventional MgO shown in Example 1 was coated with 2MgO・SiO ₂
A silicon steel plate on which a quality insulation film was formed was immersed in a mixed solution of sulfuric acid and hydrofluoric acid, the insulation film was removed by pickling, and the insulation film was washed with water and dried. The following treatment solution was applied to the silicon steel sheet from which the insulation film had been removed, and after drying in the atmosphere, the annealing temperature was 1180°C, the same as in Example 1, and 100% nitrogen was added.
Annealed in atmosphere for 30 minutes. After cooling, the thickness and magnetism of the insulating film were measured.

【table】 The magnetic measurement results are shown in comparison with those of Example 1.

【table】

【table】

Claims (1)

[Scope of Claims] 1. An insulating film made of a metal oxide is formed by applying an organic solvent solution containing one or more metal alkoxides to the surface of a silicon steel plate with a thickness of 0.20 mm or less, drying and annealing. 1. A method for forming an insulating film on a silicon steel sheet, the method comprising forming an insulating film on a silicon steel plate. 2 After removing the film made of metal oxides formed on the surface of a silicon steel plate with a thickness of 0.20 mm or less during the annealing process, an organic solvent solution containing one or more metal alkoxides is applied to the surface of the silicon steel plate. A method for forming an insulating film on a silicon steel sheet, comprising forming an insulating film made of a metal oxide by annealing after drying. 3. A method for forming an insulating film on a silicon steel sheet according to claim 1 or 2, which uses metal alkoxides of Zr, Si, Li, Al, Ti, and Mg.