JP2022062529A - Coating agent for tension film formation for grain-oriented electromagnetic steel sheet, manufacturing method of the same, and manufacturing method of grain-oriented electromagnetic steel sheet using the same - Google Patents

Abstract

To provide a simple method for improving a rust-prevention property of a grain-oriented electromagnetic steel sheet having an aluminum borate coating.SOLUTION: A coating agent of which solid content concentration is 5-40 mass% is used, where 1-50 mass% of a solid content contains a fine particle that has an average gain size of 0.1-0.7 μm and is composed of an aluminum borate crystal of which (220) plane spacing is 0.525-0.535 nm, and a rest of an aluminum compound and a boron compound, of which a mole ratio of Al to B is in a range of 1.9-2.1. The coating agent is applied to a steel sheet for which finish annealing is complete, and is dried. The steel sheet is annealed to obtain a grain-oriented electromagnetic steel sheet.SELECTED DRAWING: None

Description

The present invention relates to a coating agent for forming a tension film of a grain-oriented electrical steel sheet, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

The grain-oriented electrical steel sheet is characterized by having a crystal structure having {110} <001> as the main orientation. Electrical steel sheets are mainly used as iron core materials for transformers, and in particular, materials with small iron loss are required in order to reduce energy loss. Since iron alloys containing iron and silicon have a large magnetocrystalline anisotropy, when an external tension is applied, the magnetic domain is subdivided, and the eddy current loss, which is the main element of iron loss, can be reduced. In particular, it is known that applying tension to a grain-oriented steel sheet containing 5% or less of silicon is effective in reducing the iron loss of the grain-oriented electrical steel sheet. This tension is applied by the coating formed on the surface.

Patent Document 1 discloses a grain-oriented electrical steel sheet having a film mainly composed of aluminum borate crystals on its surface as a grain-oriented electrical steel sheet having a film that generates a particularly high tension.

In order for a certain film to become a high-tensile film, it is required that the Young's modulus of the film is high and the coefficient of thermal expansion is small. Generally, crystals have a higher Young's modulus than amorphous. The film made of aluminum borate has a higher Young's modulus than the conventional amorphous film made of silica and phosphate because the main constituent is crystalline. Since the film made of aluminum borate has a sufficiently low coefficient of thermal expansion, it is possible to obtain high tension in combination with the effect of Young's modulus.

However, since the technique of Patent Document 1 has a weak rust preventive effect as compared with the insulating coating currently used, it is necessary to improve this point.

In order to improve such a problem, Patent Document 2 discloses a method of two-layer coating of an aluminum borate coating and a current coating. Patent Document 3 discloses a base treatment before forming an aluminum borate film by electroless nickel plating. Patent Document 4 discloses a method of applying a rust preventive component on an aluminum borate film. Patent Document 5 proposes an aluminum borate coating component containing a rust preventive component.

Japanese Unexamined Patent Publication No. 6-65754 Japanese Unexamined Patent Publication No. 9-272982 Japanese Unexamined Patent Publication No. 9-279358 Japanese Unexamined Patent Publication No. 8-277474 Japanese Unexamined Patent Publication No. 9-256164

The technique of Patent Document 2 has a problem that the cost increases as the number of processes increases and the space factor deteriorates. The techniques of Patent Document 3 and Patent Document 4 also have a problem of increased cost due to an increase in processes. The technique of Patent Document 5 has a problem that it is difficult to overcome problems such as a decrease in tension due to a rust preventive component.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a simple method for improving the rust prevention property of a grain-oriented electrical steel sheet having an aluminum borate film to which a high tension is applied.

The present inventors considered that the problem of rust resistance in the aluminum borate film could be solved by suppressing the unreacted boron contained in the film, and investigated a method for reducing the unreacted boron. As a result, it was found that it is effective to add fine particles of aluminum borate for promoting crystallization of aluminum borate into the coating agent for forming an aluminum borate film.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) The average particle size of aluminum borate crystals having a solid content concentration of 5 to 40% by mass and (220) interplanar spacing of 0.525 to 0.535 nm is 0.1 to 0.7 μm. Directionality characterized by containing 1 to 50% by mass of fine particles in the solid content and containing an aluminum compound and a boron compound in the balance in the range of 1.9 to 2.1 in the molar ratio Al / B of Al and B. A coating agent for forming a tension film on electromagnetic steel sheets.

(2) The method for producing a coating agent for forming a tension film of a directional electromagnetic steel plate according to the above (1), wherein an aluminum compound and a boron compound are 1.9 to 2.1 in a molar ratio of Al / B of Al / B. A mixture containing the above range is prepared, the above mixture is fired at 800 to 1000 ° C. to synthesize aluminum borate powder, and the obtained aluminum borate powder is pulverized (220) with a surface spacing of 0.525. A directional electromagnetic steel plate comprising a step of obtaining fine particles having an average particle diameter of 0.1 to 0.7 μm composed of aluminum borate crystals having a diameter of about 0.535 nm and adding the obtained fine particles to a solvent. A method for manufacturing a coating agent for forming a tension film.

(3) A method for manufacturing a grain-oriented electrical steel sheet, in which the coating agent for forming a tension film of the grain-oriented electrical steel sheet according to (1) is applied and dried on the steel sheet that has been finish-baked, and then the dew point is 0 to 40. Manufacture of grain-oriented electrical steel sheets characterized by heat treatment at 750 to 1000 ° C. for 20 seconds or longer in an atmosphere at ° C., containing 0 to 30% by volume of hydrogen and having one or both of nitrogen and an inert gas remaining. Method.

According to the present invention, a coating agent for forming a tension film of a grain-oriented electrical steel sheet which has sufficient rust resistance and can easily form an aluminum borate film having a high tension, a method for producing the same, and a borate using the same. It is possible to provide a method for manufacturing a grain-oriented electrical steel sheet on which an aluminum acetate film is formed.

Hereinafter, the present invention will be described in detail based on a preferred embodiment of the present invention.

First, a coating agent for forming a tension film of grain-oriented electrical steel sheets according to the present embodiment (hereinafter, also simply referred to as “coating agent”) will be described.

(Examination of the present inventor)
As a grain-oriented electrical steel sheet, a steel sheet having an aluminum borate coating having a high tension-imparting effect is known on the surface of a steel sheet having a so-called glass film on the surface which has been subjected to secondary recrystallization annealing. The glass film is a film composed of an oxide mainly composed of forsterite crystals (Mg ₂ SiO ₄ ) having a thickness of about several μm.

Normally, this coating has fine defects, and it is considered that the steel sheet is not covered with forsterite at this defect. That is, it is presumed that there are places where the steel sheet is exposed and is in direct contact with the aluminum borate film due to defects in the glass film, and in such places, iron elutes when the aluminum borate film contains water, causing rust. Will be done.

In order to prevent the occurrence of rust in such a mechanism, it is conceivable to prevent the pH at which iron elutes on the surface of the steel sheet. The present inventors have investigated a method for improving rust resistance by a method in which the pH of the steel sheet surface is not set to the pH at which iron elutes. The idea is as follows.

The present inventors presumed that the pH at which iron elutes on the surface of the steel sheet is due to the presence of boric acid in the coating film, and that boric acid is produced due to the following causes.

The ratio of aluminum to boron in the coating agent for forming an aluminum borate film according to the prior art is such that the amount of boron is larger than the stoichiometric composition of Al ₄ B ₂ O ₉ which is aluminum borate. The reason for this is that if the ratio of aluminum to boron is the stoichiometric composition of aluminum borate, the temperature at which aluminum borate crystals are formed becomes extremely high, and it is necessary to set the temperature to a very high temperature in the film forming process. Is. Therefore, in the prior art, Al / B is made smaller than the stoichiometric composition of aluminum borate so that aluminum borate crystals can be formed at about 850 ° C.

Boron that is larger than the stoichiometric composition is considered to remain as boric acid in the film even after the film is baked. When a steel sheet with a film in which boric acid remains is exposed to a moist atmosphere, the boric acid present in the film absorbs moisture to form an acidic environment, and iron is dissolved at the interface between the aluminum boric acid film and the steel sheet. Is filled and it is estimated that rust will occur. Therefore, in order to improve the rust resistance, it is considered that excess boric acid should be eliminated.

Since boric acid has a high vapor pressure at high temperature, excess boric acid may be vaporized and removed from the coating film by heat treatment at high temperature. In fact, rust resistance is significantly improved when a coating agent having a composition having a larger amount of boron than the stoichiometric composition of aluminum borate is baked at about 1200 ° C. However, in order to carry out actual production by this method, heat treatment at a high temperature of about 1200 ° C. is required, and in order to avoid plastic deformation of the plate, which is a problem when continuous heat treatment is performed at a high temperature of about 1200 ° C. Technology development is required. Therefore, when a coating agent having a composition having a higher amount of boron than the stoichiometric composition of aluminum borate is used, it is currently feasible as a production technique to eliminate excess boric acid from the film after baking. Not.

Therefore, the present inventors have studied the formation of aluminum borate crystals at a low temperature without increasing the boron ratio. As a result, it was found that it is effective to add fine particles of aluminum borate crystals to the coating agent for forming an aluminum borate film. The reason why the formation temperature of the aluminum borate crystal is lowered by adding the fine particles of the aluminum borate crystal to the coating agent for forming the aluminum borate film is considered as follows.

When a coating agent of aluminum borate having a composition having a larger amount of boron than the stoichiometric composition is applied onto a steel sheet and dried, boric acid and alumina are in a mixed state. When the temperature is raised from this state, it is considered that boric acid and alumina react with each other to first form an amorphous phase of aluminum borate. If fine particles of aluminum borate crystals are present in advance in the system in which this reaction proceeds, aluminum borate crystals are likely to be formed with these as nuclei, and as a result, a tension film made of aluminum borate crystals can be formed at a low temperature. Presumed.

From the above, the mechanism by which the effect of the present invention is obtained is estimated as follows. That is, when baking a coating agent containing aluminum borate fine particles, aluminum borate crystals are formed in the coating film at a lower temperature than before, so that conventional coating is performed to lower the aluminum borate crystal formation temperature. It is possible to reduce the amount of boron that was added to the agent in excess. As a result, the amount of residual boric acid in the film after baking can be significantly reduced, so that the environment at the interface between the steel sheet and the film is no longer a condition for melting iron even in the presence of moisture.

<Applicant for forming grain-oriented electrical steel sheet coating>
Hereinafter, the coating agent for forming a tension film of a grain-oriented electrical steel sheet of the present invention will be described in detail.

The coating agent for forming a tension film of a directional electromagnetic steel plate of the present invention comprises aluminum borate crystals having a solid content concentration of 5 to 40% by mass and (220) interplanar spacing of 0.525 to 0.535 nm. Fine particles having an average particle size of 0.1 to 0.7 μm are contained in an amount of 1 to 50% by mass of the solid content, and an aluminum compound and a boron compound are contained in the balance. Includes in the range of 1. Here, the molar ratio Al / B of Al and B means the molar ratio of Al atom and B atom contained in the aluminum compound and the boron compound. The aluminum compound and the boron compound contained in the balance are an aluminum source such as aluminum oxide and a boron source such as boric acid, which will be described later, respectively.

There are several types of aluminum borate crystals. In the present invention, the additive particles capable of obtaining high tension by being contained in the coating agent for forming a tension film of a grain-oriented electrical steel sheet are crystals having a composition of Al _{4 B 2009} . This is an aluminum borate crystal having a plane spacing (220) of the strongest line in X-ray diffraction by a Cu target of 0.525 to 0.535 nm.

The (220) interplanar spacing of the added particles in the coating agent can be confirmed by X-ray diffraction with a Cu target of the powder obtained by drying the coating agent at about 100 ° C. The dried product of the coating agent contains boric acid and aluminum hydroxide in addition to the fine particles of aluminum borate, but since these diffraction lines are different from those of aluminum borate, the diffraction lines of the added aluminum borate fine particles are separated. can do.

The aluminum borate crystals are fine particles having an average particle diameter of 0.1 μm to 0.7 μm. If the size of the fine particles of the aluminum borate crystal is too large, the smoothness of the film will be problematic and the space factor after forming the tension film will decrease, which is not preferable. On the other hand, if the particle size is too small, it becomes difficult to disperse in the coating agent, the particles tend to aggregate in the coating agent, and it becomes difficult to obtain the effect of adding fine particles. Therefore, the average particle size of the fine particles to be added needs to be 0.1 to 0.7 μm.

It is convenient to calculate the particle size of the fine particles from the half-value width of the X-ray diffraction peak for the dried powder. This method is a method of estimating the crystal grain size t of the aluminum borate crystal using the Sherrer's formula shown in the formula (1).

Here, K: constant (0.9), λ: wavelength of X-ray (0.1542 nm), B: half-value width (rad), θ: peak position (°) in X-ray diffraction with a Cu target. ..

If the amount of fine particles of aluminum borate crystals in the coating agent is too small, the effect of lowering the temperature at which aluminum borate crystals are formed cannot be obtained. On the other hand, if the amount is too large, a smooth tension film cannot be obtained, and the space factor of the product decreases. Therefore, the amount of the fine particles of the aluminum borate crystal in the solid content is set to 1 to 50% by mass. The solid content includes aluminum sources such as aluminum oxide and boron sources such as boric acid, in addition to the fine particles of aluminum borate crystals.

The amount of the fine particles in the solid content can be determined from the amount of boron in the precipitate when the coating agent is allowed to stand after the solid content of the coating agent is first determined. The solid content of the coating agent is determined according to the formula (2).

Solid content (g) = A + B ... (2)
Here A: Aluminum oxide reduced mass (g) of the aluminum source
B: Orthoboric acid reduced mass (g) of boron source

The fine particles in the present invention are considered to have a stoichiometric composition of aluminum borate Al ₄ B ₂ O ₉ . Therefore, the amount of fine particles in the solid content in the coating agent can be calculated from the amount of boron in the precipitate, the molar mass of aluminum borate, and the solid content of the initial coating agent. The calculation method is as follows.

First, the coating agent to be analyzed is divided into two equal parts. The coating agent in one container is dried, the amounts of boron and aluminum contained in the residue are determined by chemical analysis or the like, and the number of moles thereof is p (mol) and q (mol), respectively.

The coating agent in the other container collects the precipitate and determines the amount of aluminum borate fine particles contained therein. Since it is necessary to collect the entire amount of the precipitate, carefully discard the supernatant after standing and collect the remaining precipitate. When standing, add about 10% by mass of an inorganic acid to the coating before standing so that gelation of the coating does not occur. Nitric acid or hydrochloric acid is used as the inorganic acid. By adding the inorganic acid, the alumina source such as alumina sol in the coating agent aggregates and the dispersed state deteriorates, but it does not affect the analysis of the amount of boron in the precipitate.

In this method, it is necessary to sufficiently eliminate the boric acid component in the coating agent other than boron contained in the fine particles. Boron other than fine particles is water-soluble boric acid, so if a large amount of boric acid dissolved in the supernatant or boric acid precipitated in the precipitate is present, it will be contained in the precipitate dried for analysis. A large amount of boric acid remains, and the amount of fine particles in the solid content cannot be accurately measured. Therefore, after discarding the supernatant, pure water having a volume of 3 times or more the volume of the precipitate containing water remaining is added, the mixture is sufficiently stirred, and then the mixture is allowed to stand again, and the operation of discarding the supernatant is repeated 5 times. By performing such an operation, the amount of boric acid remaining in the solid content can be sufficiently reduced.

Let r (mol) be the number of moles of boron contained in the precipitate obtained as described above. Since boric acid contained in the coating agent is sufficiently removed by performing the supernatant disposal work 5 times or more, it can be considered that r is derived from boron of aluminum borate fine particles.

The ratio of aluminum borate fine particles in the solid content is determined as follows.

Assuming that the orthoboric acid equivalent amount X (g) of boron other than the aluminum borate fine particles contained in the dried residue and the aluminum oxide equivalent amount Y (g) of aluminum, X = (pr) from p and q, respectively. × 59.8
Y = {(q-r × 2) / 2} × 102
Will be. In the above formula, 59.8 is the molecular weight of orthoboric acid, and 102 is the molecular weight of aluminum oxide.

Assuming that the weight of the aluminum borate fine particles in the precipitate is Z (g), the ratio M (mass%) of the aluminum borate fine particles in the solid content is Z = (r / 2) × 146.5.
M = Z × 100 / (X + Y + Z)
Will be. Here, 146.5 is the molecular weight of aluminum borate (Al ₄ B ₂ O ₉ ).

As described above, the ratio of aluminum borate fine particles in the solid content can be determined.

The solid content concentration of the entire coating agent to which fine particles are added has an appropriate range as in the known technique, and if it is too low, bumping or the like occurs during drying, causing film defects and reducing the tension of the film. On the other hand, if it is too high, the stability of the coating agent is lowered and gelation is likely to occur. With such a coating agent, a film having many defects is formed and the tension is lowered. Therefore, the solid content concentration needs to be between 5 and 40% by mass. Here, the solid content concentration is defined according to the formula (3).

Solid content concentration (mass%) = {(W _AB + W _Al + W _B ) x 100} / (W _AB + W _Al + W _B + W _W ) ... (3)
here
W _AB : Mass of aluminum borate fine particles
W _Al : Aluminum oxide reduced mass of aluminum source
_WB : Orthoboric acid reduced mass of boron source
W _W : Moisture content of the coating agent.

The aluminum oxide equivalent mass of the aluminum source means to replace the raw material as the aluminum source with the mass of the amount of aluminum oxide such that the molar amount of aluminum contained in aluminum oxide (Al ₂ O ₃ ) is equal. Similarly, the reduced orthoboric acid-equivalent mass of the boron source means to replace the raw material as the boron source with the mass of orthoboric acid such that the molar amount of boron contained in orthoboric acid (H ₃ BO ₃ ) is equal. ..

The amount of aluminum borate fine particles in the solid content is calculated by the formula (4).

Amount of fine particles of aluminum borate in solid content (wt%) = W _AB x 100 / (W _AB + W _Al + W _B ) ... (4)

The ratio of boron to aluminum other than fine particles in the coating agent in the present invention needs to be a smaller amount of boron than in the prior art, and good results are obtained when Al / B is between 1.9 and 2.1. can get. If Al / B is too small, the amount of excess boric acid in the film increases and rust resistance becomes poor, while if it is too large, sufficient tension cannot be obtained.

<Manufacturing method of coating agent for forming tension film of grain-oriented electrical steel sheet>
The coating agent for forming a tension film of a grain-oriented electrical steel sheet has (220) fine particles of aluminum borate having a surface spacing of 0.525 to 0.535 nm, and has the above-mentioned solid content concentration of Al / B. It may be added to the solvent.

(220) Fine particles of aluminum borate having a surface spacing of 0.525 to 0.535 nm can be obtained by synthesizing aluminum borate powder and then pulverizing the powder with a ball mill or the like. The method for obtaining the aluminum borate powder is obtained by drying and firing a sol having the same composition as that of a coating agent of a known technique for forming an aluminum borate film.

The firing temperature needs to be a temperature sufficient for forming aluminum borate crystals, and a minimum of 800 ° C. is required. When the temperature is high, there is no particular problem in obtaining aluminum borate crystals, but since it tends to be difficult to pulverize into fine particles, the upper limit is set to 1000 ° C.

In the sol for obtaining fine particles, in order to suppress the formation of excess boric acid, the Al / B of the sol should be in the range of 1.9 to 2.1 as in the coating agent for the aluminum borate coating in the present invention. There is a need to. If this value is too large, the formation of aluminum borate crystals is insufficient as in the case of the coating film, and if it is too small, excess boric acid increases and the rust resistance of the aluminum borate film using the excess boric acid becomes inferior.

Hereinafter, each component and the like contained in the coating agent will be described in detail.

(Aluminum source)
The aluminum source of the coating agent comprises aluminum oxide and / or an aluminum oxide precursor compound. The aluminum oxide precursor compound is not particularly limited as long as it can form aluminum oxide in the formed aluminum borate film, and is, for example, aluminum oxide represented by Al ₂ O ₃ · mH ₂ O such as boehmite. Examples thereof include hydrates and aluminum hydroxide, and one of these can be used alone or in combination of two or more.

The aluminum source may be dispersed in the coating agent, or may be dissolved in the coating agent. Usually, the aluminum source is dispersed in the coating. The aluminum source is preferably in the form of particles so that it can be stably dispersed in the coating agent. In this case, the volume-based average particle size (D50) of the aluminum source by the laser diffraction / scattering method is, for example, 0.005 μm or more and 1.0 μm or less, preferably 0.015 μm or more and 0.7 μm or less.

The aluminum source may be in the form of a sol and may be added to the coating agent. By using such a fine particle dispersion system called a sol, an aluminum borate film that is thin, uniform, and has good adhesion can be obtained. Examples of such sol include alumina sol, boehmite sol and the like. Boehmite sol and alumina sol are particularly suitable in terms of workability, price, and the like.

(Boron source)
Examples of the boron source of the coating agent include boron oxo acids (boric acid) such as orthoboric acid, metaboric acid, and tetraboric acid, and boron oxide represented by B ₂ O ₃ , and one of these is used alone. Or two or more types can be used in combination. Of these, orthoboric acid represented by H ₃ BO ₃ is preferable from the viewpoint of workability and cost.

The coating agent according to the present embodiment has less boron source than the aluminum source as compared with the conventional one. Specifically, the coating agent contains an aluminum source and a boron source so that Al / B has an Al / B ratio of 1.9 to 2.1 in terms of molar ratio. This can be realized by including fine crystals of aluminum borate in the coating agent, which is a feature of the present invention, to obtain an effect that aluminum borate crystals are sufficiently formed without excessive inclusion of boron. It is a thing. If the amount of boron source is too small, sufficient tension cannot be obtained, while if the amount of boron source is too large, rusting occurs due to deterioration of the water resistance of the aluminum borate film.

(Silicon oxide and silicon oxide precursor)
The coating agent may contain known silicon oxide and / or silicon oxide precursors for the purpose of improving the adhesion of the aluminum borate film. The silicon oxide and / or the silicon oxide precursor contributes to the formation of a vitreous network in the aluminum borate film and contributes to the improvement of the adhesion of the obtained aluminum borate film.

The silicon oxide is not particularly limited, but various known silicon oxides can be used. In particular, colloidal silica has excellent dispersibility in the coating agent.

Further, examples of the silicon oxide precursor include compounds capable of forming silicon oxide, for example, silane compounds. The silane compound is not particularly limited, and examples thereof include alkoxysilanes such as tetraethoxysilane and other silicon oxide precursors, and one of these may be used alone or in combination of two or more. can. Alternatively, a pre-hydrolyzed part of these silane compounds may be used.

(solvent)
The coating agent contains a solvent. The solvent functions not only as a solvent for decomposing each component but also as a dispersion medium for dispersing each component.

The solvent is not particularly limited, and examples thereof include water, alcohol-based solvents, ketone-based solvents, ether-based solvents, hydrocarbon-based solvents, and the like, and one of these may be used alone or in combination of two or more. Can be done. Water is preferable from the viewpoint of workability, defect suppressing effect during drying, and excellent dispersibility and solubility of each component.

According to the coating agent according to the present embodiment described above, the rust resistance is excellent and the tension applying effect to the steel sheet is high without causing the problem of cost due to the increase process and the problem of deterioration of space factor or decrease in tension. A coating agent is obtained, which can be used to form an aluminum borate film having sufficient rust resistance and high tension.

<Manufacturing method of grain-oriented electrical steel sheet>
The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described below. The method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment includes a step of forming an aluminum borate film by using the coating agent for forming a tension film of the grain-oriented electrical steel sheet according to the present embodiment described above.

(Preparation of base steel plate)
First, a base steel sheet for forming an aluminum borate film is prepared. As the base steel sheet, for example, (1) a steel sheet in which a forsterite primary film is formed on the surface by finish annealing by a conventionally known method, (2) a primary film and an incidentally formed inside. Steel sheet obtained by immersing the oxide layer in acid to remove it, (3) Steel sheet obtained by flattening and annealing in a hydrogen-containing atmosphere, or steel sheet obtained by polishing such as chemical polishing or electrolytic polishing. Or (4) Apply a conventionally known annealing separator to which an alumina powder or the like, which is inactive to film formation, or a trace additive such as chloride is added, and perform finish annealing under conditions that do not form a primary film. It suffices to prepare a steel sheet that has been subjected to finish annealing, such as a steel sheet whose surface has been flattened by the method (3). The preparation of the base steel sheet may be before or after the preparation of the coating agent described below.

(Preparation of coating agent for forming tension film on grain-oriented electrical steel sheet and formation of aluminum borate film)
Next, a coating agent for forming a tension film of grain-oriented electrical steel sheets is prepared by the above-mentioned method. The obtained coating agent is used to form an aluminum borate film on the surface of the steel sheet. The aluminum borate film can be formed by applying a coating agent to the surface of the steel sheet and then drying and baking.

The coating on the surface of the steel sheet can be performed by a conventionally known method such as a coater such as a roll coater, a dip method, spray spraying or electrophoresis.

An aluminum borate film is formed on the surface of the steel sheet by drying the steel sheet after applying the coating agent and then baking the steel sheet. The baking can be performed, for example, at a temperature of 750 ° C. or higher. When the baking temperature is 750 ° C., the applied precursor may not become an oxide, and since the baking temperature is low, sufficient tension is not developed, which is not preferable. The baking temperature is preferably 750 ° C. or higher and 1000 ° C. or lower, and more preferably 800 ° C. or higher and 1000 ° C. or lower.

The baking time is 20 seconds or more. If the baking time is shorter than this, aluminum borate crystals are not sufficiently produced, and the tension of the film after baking cannot be sufficiently obtained. On the other hand, even if the baking time is long, there is no particular effect, but since the heat treatment time is only long and no new effect can be obtained, the baking time is preferably 120 seconds or less.

The atmosphere at the time of baking is preferably an atmosphere containing 0 to 30% by volume of hydrogen and the balance being one or both of nitrogen and the inert gas. Specifically, a nitrogen gas atmosphere, an inert gas atmosphere such as argon, a nitrogen-argon mixed atmosphere, a reducing atmosphere such as a nitrogen-hydrogen mixed atmosphere, and the like are preferable. An atmosphere containing excessive air or oxygen is not preferable because it may excessively oxidize the steel sheet. Further, even if the ratio of hydrogen exceeds 30% by volume, there is no particularly harmful effect, but even if the amount of hydrogen increases, there is no particular effect, and the cost of hydrogen gas only increases, so the upper limit is set to 30% by volume. ..

Good results can be obtained when the dew point of the atmospheric gas is 0 to 40 ° C.

As described above, a grain-oriented electrical steel sheet having an aluminum borate film having a sufficient rust preventive effect and tension can be manufactured.

Hereinafter, the present invention will be described in more detail based on examples, but the examples shown below are merely examples of the present invention, and the present invention is not limited to such examples.

[Example 1]
A commercially available boric acid reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) are mixed in the amounts shown in Table 1, distilled water is added thereto, and the grains shown in Table 1 are further added. Fine particles of aluminum borate crystals having a diameter and (220) interplanar spacing of 0.525 to 0.535 nm were added in the amounts shown in Table 1 and sufficiently stirred to prepare a slurry to be a coating agent. ..

The fine particles of the aluminum borate crystal used here are weighed using aluminum oxide and boric acid with a composition of Al / B = 2.0 and mixed sufficiently, and this is mixed in the air at 900 ° C. for 1 hour. After heat treatment with, it was pulverized with an alumina ball mill using pure water as a medium. The slurry after pulverization was spray-dried, pulverized into primary particles by a jet mill, and then classified into target particle diameters by a cyclone.

The obtained slurry was applied to a unidirectional silicon steel sheet (with a glass coating) having a thickness of 0.23 mm and containing 3.2% of Si and having a finish annealing of 4 g / m ² . This was dried at an atmospheric atmosphere temperature of 100 ° C. for 60 seconds, then heated to 800 ° C., and baked at this temperature with a soaking time of 100 seconds to form an insulating film. The atmosphere at the time of baking was a nitrogen atmosphere containing 10% hydrogen, and the dew point was 30 ° C.

Rust resistance, film tension, and space factor were measured for the obtained sample.

For rust resistance, a 50 mm square sample is exposed to an atmosphere with a temperature of 50 ° C and a relative humidity of 98% for 48 hours, and it is visually confirmed whether or not there is rust. If there is no rust, the rust resistance is good. Therefore, it was rated as "good", and if there was rust, it was rated as "bad".

The coating tension was calculated from the bending of the steel plate generated at each side of the aluminum borate coating of the sample having a width of 30 mm and a length of 300 mm. An aqueous sodium hydroxide solution was used to remove the insulating film, and the obtained tension was a tension that did not include the glass film. Here, if the film tension is 12 MPa or more, it is judged to be high tension and “good”, and if it is less than 12 MPa, it is judged to be “bad”.

The space factor was measured by the method of JISC2550-5, and 97.5% or more was regarded as "good" and less than 97.5% was regarded as "bad".

From the results in Table 1, it was confirmed that in the examples, a film having rust resistance, a good space factor, and a high tension was obtained.

[Example 2]
A commercially available boric acid reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) are mixed in the amounts shown in Table 2, distilled water is added thereto, and the grains shown in Table 2 are further added. Fine particles of aluminum borate crystal having a diameter and (220) interplanar spacing of 0.525 to 0.535 nm are added in the amounts shown in Table 2 and sufficiently stirred to serve as a coating agent. Was produced. The fine particles of the aluminum borate crystal used here were produced in the same manner as in Example 1.

The obtained slurry is applied to a unidirectional silicon steel plate (with a glass coating) having a thickness of 0.23 mm and containing 3.2% of Si and having a glass coating, so that the coating mass after annealing is 4 g / m ² . Was applied to. This was dried at an atmospheric atmosphere temperature of 100 ° C. for 60 seconds, then heated to 800 ° C., and baked at this temperature with a soaking time of 100 seconds. The atmosphere at the time of baking was a nitrogen atmosphere containing 10% hydrogen, and the dew point was 30 ° C.

Rust resistance, film tension, and space factor were measured for the obtained sample. These evaluation methods were the same as in Example 1.

From the results in Table 2, it was confirmed that in the examples, a film having rust resistance, a good space factor, and a high tension was obtained.

[Example 3]
A commercially available boric acid reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) were mixed in the amounts shown in Table 3, distilled water was added thereto, and the particle size was 0. Fine particles of aluminum borate crystal having an interplanar spacing of 0.525 to 0.535 nm at 4 μm are added in the amounts shown in Table 3 and sufficiently stirred to serve as a coating agent. Was produced.

For the fine particles of aluminum borate crystal used here, aluminum oxide and boric acid are weighed so that the Al / B value becomes the value shown in Table 3, and the firing temperature before crushing the aluminum borate fine particles is shown in Table 3. Other than the above, it was produced in the same manner as in Example 1. However, in Comparative Example 3-4, crushing was difficult because the firing temperature before crushing the aluminum borate fine particles was too high at 1200 ° C., and the particle size of the aluminum borate fine particles was 1.1 μm.

The obtained slurry is applied to a unidirectional silicon steel plate (with a glass coating) having a thickness of 0.23 mm and containing 3.2% of Si and having a glass coating, so that the coating mass after annealing is 4 g / m ² . Was applied to. This was dried at an atmospheric atmosphere temperature of 100 ° C. for 60 seconds, then heated to 800 ° C., and baked at this temperature with a soaking time of 100 seconds. The atmosphere at the time of baking was a nitrogen atmosphere containing 10% hydrogen, and the dew point was 30 ° C.

Rust resistance, film tension, and space factor were measured for the obtained sample. These evaluation methods were the same as in Example 1.

From the results in Table 3, it was confirmed that in the examples, a film having rust resistance, a good space factor, and a high tension was obtained.

[Example 4]
A commercially available boric acid reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) are mixed in the amounts shown in Table 4, and distilled water is added thereto, and the (220) surface spacing is further increased. Fine particles of aluminum borate crystal having a particle size of 0.525 to 0.535 nm and having the values shown in Table 4 are added so as to be in the amount shown in Table 4, and the mixture is sufficiently stirred to serve as a coating agent. Was produced. The fine particles of the aluminum borate crystal used here were produced in the same manner as in Example 1.

The obtained slurry is baked into a unidirectional silicon steel sheet (with a glass coating) having a thickness of 0.23 mm and containing 3.2% of Si and having a coating mass of 4 g / m ² . Applied. This was dried at an atmospheric atmosphere temperature of 100 ° C. for 60 seconds and then baked under the conditions shown in Table 4.

The rust resistance and film tension of the obtained sample were measured. These evaluation methods were the same as in Example 1.

From the results in Table 4, it was confirmed that in the examples, a film having rust resistance, a good space factor, and a high tension was obtained.

Claims (3)

Fine particles having an average particle size of 0.1 to 0.7 μm composed of aluminum borate crystals having a solid content concentration of 5 to 40% by mass and (220) interplanar spacing of 0.525 to 0.535 nm. Contains 1 to 50% by mass of solid content
A coating agent for forming a tension film of a directional electromagnetic steel plate, wherein the balance contains an aluminum compound and a boron compound in a molar ratio Al / B of Al and B in the range of 1.9 to 2.1. A method for manufacturing a coating agent for forming a tension film of a grain-oriented electrical steel sheet according to claim 1.
A mixture containing an aluminum compound and a boron compound in a molar ratio of Al / B in the range of 1.9 to 2.1 was prepared.
The above mixture is calcined at 800 to 1000 ° C. to synthesize aluminum borate powder.
The obtained aluminum borate powder was pulverized (220) to obtain fine particles having an average particle diameter of 0.1 to 0.7 μm composed of aluminum borate crystals having a plane spacing of 0.525 to 0.535 nm.
A method for producing a coating agent for forming a tension film of a grain-oriented electrical steel sheet, which comprises a step of adding the obtained fine particles to a solvent. It is a manufacturing method of grain-oriented electrical steel sheets.
The coating agent for forming a tension film of the grain-oriented electrical steel sheet according to claim 1 is applied and dried on the steel sheet that has been finish-annealed, and then dried.
A direction characterized by heat treatment at 750 to 1000 ° C. for 20 seconds or more in an atmosphere having a dew point of 0 to 40 ° C., containing 0 to 30% by volume of hydrogen, and the balance being one or both of nitrogen and an inert gas. Method of manufacturing a sex electromagnetic steel plate.