JPH10287984A - Method for producing unidirectional silicon steel sheet having aluminum borate coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a unidirectional silicon steel sheet in which iron loss is reduced by providing an aluminum borate coating on a surface of the steel sheet to impart a large tension to the steel sheet. SOLUTION: The surface of the silicon steel sheet after the finish annealing is completed,
Boric acid, the content of water of crystallization when dried at 100 ° C is Al
Boehmite sol that satisfies x ≦ 2.0 when expressed as ₂ O ₃ · xH ₂ O is at least 20% by weight in terms of oxide with respect to the whole aluminum oxide source, and water content of crystallization when dried at 100 ° C. Is coated with a boehmite sol that satisfies x ≧ 2.5 when expressed as Al ₂ O ₃ .xH ₂ O, and mixed with 20% or more of the same aluminum oxide source by weight in terms of oxide. By forming an aluminum borate film through a drying, gelling, baking and solidifying process, it is possible to apply a larger tension than a conventional film. Further, when the composition ratio of boric acid to boehmite sol is more than 12 to 40% by weight in terms of boron oxide, and boehmite sol in 60 to less than 88% by weight in terms of aluminum oxide, higher tension can be applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a unidirectional silicon steel sheet in which iron loss is reduced by providing an aluminum borate coating on the surface of the steel sheet to impart a large tension to the steel sheet.

[0002]

2. Description of the Related Art A grain-oriented silicon steel sheet is (100) [00
1], and is widely used as a magnetic iron core material. In particular, a material with small iron loss is required to reduce energy loss. To reduce the iron loss of a unidirectional silicon steel sheet containing 5% or less of silicon, it is effective to apply a tension to the steel sheet, and the iron loss can be effectively reduced by applying a tension up to about 1.5 kgf / mm ^2. It is known that it can be reduced. This tension is usually provided by a film formed on the surface.

Until now, the inventors have disclosed Japanese Patent Application Laid-Open No. 6-657.
No. 54, JP-A-6-65755, etc., a method of forming a new oxide film by applying a fine particle dispersion containing alumina sol and boric acid, drying and gelling, and baking, and the resulting aluminum oxide -We have proposed a boron oxide-based composite coating and an aluminum borate high tensile strength coating. It has been found that this coating can apply 1.5 to 2 times higher tension to the steel sheet than the conventional coating, and as a result, the magnetic properties of the steel sheet can be improved. Further, by using this manufacturing method, it is possible to secure good adhesion to a steel sheet without a primary coating, which can be expected to have a lower iron loss, and a steel sheet which has been subjected to mirror finishing.
Significant improvements in magnetic properties can be achieved.

However, in the course of research and development of this coating, the properties of the coating material which has not been studied so far, that is, the fine particle dispersion other than the components,
It has been found that the properties of the obtained coating such as adhesion to steel sheet and coating tension are greatly affected. Particularly important properties include the crystallinity in the b-axis direction of the alumina sol (boehmite sol) particles, in other words, the water content of crystallization, and the ratio of B ₂ O ₃ / Al ₂ O ₃ (composition ratio).

Of these, the ratio (composition ratio) of B ₂ O ₃ / Al ₂ O ₃ is described in JP-A-6-306628, JP-A-7-207424, and JP-A-7-278.
No. 831 discloses a range of 0.1 to 5 by mole ratio as a desirable value. One sol particle is disclosed in JP-A-5-226134 and JP-A-6-226134.
JP-287765, JP-A-8-283958, and the like only disclose the rules regarding the particle size. Regarding the crystallinity of the sol or the water of crystallization contained therein, examples disclosed so far are as follows. Absent. Further, hitherto, a single-property boehmite has usually been used as a starting material, and no example in which boehmite having different properties is mixed and used has been disclosed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a grain-oriented silicon steel sheet having an aluminum borate coating film which is excellent in adhesion and gives a greater tension.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a silicon steel sheet having been subjected to finish annealing, in which boric acid and water of crystallization when dried at 100 ° C. are expressed as Al ₂ O ₃ .xH ₂ O. The boehmite sol satisfying x ≦ 2.0 is at least 20% by weight in terms of oxide with respect to the whole aluminum oxide source, and the crystal water content when dried at 100 ° C. is A
A fine particle dispersion containing boehmite sol that satisfies x ≧ 2.5 when expressed as l ₂ O ₃ .xH ₂ O is similarly mixed in an amount of 20% or more in terms of oxide with respect to the whole aluminum oxide source, and coated. The gist of the present invention is a method for producing a unidirectional silicon steel sheet, wherein an aluminum borate film is formed through drying, gelling, baking, and solidifying steps.
Further, the unidirectionality is characterized in that the composition ratio of boric acid to boehmite sol is more than 12 to 40% by weight in terms of boron oxide, and boehmite sol in 60 to less than 88% by weight in terms of aluminum oxide. The gist is a method for manufacturing a silicon steel sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a grain-oriented silicon steel sheet according to the present invention is characterized in that a fine particle dispersion containing two or more kinds of boehmite sols having different crystallization water contents and boric acid is subjected to finish annealing (2).
The coating is applied to a silicon steel sheet which has been subjected to a subsequent recrystallization annealing, dried, gelled, and then baked and solidified to form an oxide film on the surface. Two or more boehmite sols having different crystallization water contents are defined as boehmite sols in which the crystallization water content when dried at 100 ° C. satisfies x ≦ 2.0 when expressed as Al ₂ O ₃ .xH ₂ O. , And the water of crystallization when dried at 100 ° C. is Al ₂ O ₃ .xH ₂ O
In this case, a boehmite sol satisfying x ≧ 2.5 as an essential component is used as an essential component, and may further include a boehmite sol satisfying 2.0 <x <2.5 that does not satisfy the above properties.

According to the study by the inventors, boehmite having relatively good crystallinity in the b-axis direction, that is, having a relatively small content of crystallization water, has excellent adhesion to a steel sheet, and has a strong crystal. It has little change with time and has excellent stability even when dispersed as a sol. On the other hand, b
Boehmite, which has low crystallinity in the axial direction and has a relatively large crystallinity content, has a large viscosity dependence on the environment such as temperature or trace components in the sol state. It is easy to adjust the viscosity to the most preferable one, and generally, a high coating tension tends to be obtained.

Although the reason for this is under study, in the case of the latter boehmite, water or a small amount of additive is easily taken into the hydrogen bonding layer having a weak bonding force in the b-axis direction, which is a cause of a large amount of water of crystallization. It is presumed that this is because the properties, for example, the liquid viscosity, are easily changed according to the environment, and when boric acid (ion) is taken in, the reactivity with the aluminum component is improved and a greater tension is obtained.

The above advantages can be maximized by mixing both of them in a predetermined amount or more. The range of good crystalline boehmite in which these effects can be obtained is such that the content of water of crystallization when dried at 100 ° C. is x ≦ 2.0 when expressed as Al ₂ O ₃ .xH ₂ O.
And preferably x ≦ 1.8
It is. On the other hand, the range of low crystallinity boehmite and crystal water content when dried at 100 ° C., Al ₂
A boehmite sol that satisfies x ≧ 2.5 when expressed as O ₃ .xH ₂ O, preferably x ≧ 2.7, and more preferably x ≧ 3.0.

The mixing ratio is such that boehmite sol having good crystallinity and low crystallization water content is contained in an amount of 20% or more, preferably 30% or more in terms of oxide relative to the whole aluminum oxide source, resulting in poor crystallinity. The weight ratio of the boehmite sol having a large crystal water content to the total aluminum oxide source is preferably 20% or more in terms of oxide. If the mixing ratio exceeds this range and the amount of boehmite sol having a small content of crystallization water is too small, a film having poor adhesion may be formed, and a problem may occur in the stability of the coating solution. On the other hand, if the amount of boehmite having a large amount of crystallization water is too small, the viscosity of the fine particle dispersion may be too low, and it may be difficult to control the amount of adhered particles.

Although the adhesion varies greatly depending on the base steel sheet, the above values can ensure the adhesion to almost all unidirectional silicon steel sheets. Further, the present invention is characterized in that a boehmite sol having the above properties is used in a mixture of a predetermined amount or more, and boehmite having other properties, that is, boehmite having 2.0 <x <2.5 may be contained at a maximum of 60%. No problem.

Since the value of x in the present invention varies depending on the drying and heating conditions, it is determined by the following method. The powdery material is dried at 100 ° C. to remove the adsorbed water on the surface, and the already dispersed one is dried at 100 ° C. to remove the solvent. Then 700 ° C
As described above, the sample is heated to a temperature at which no weight change occurs, and the weight change before and after the heating is measured. The value of x is calculated from the weight loss ratio. The value of x at this time depends on the drying time at 100 ° C. and the heating time at 700 ° C. or more, and is preferably a value obtained by applying an infinite drying time and heating time. However, according to the inventors' investigation, drying is performed for 50 hours or more, and heating is performed for 3 hours even at 700 ° C., for example.
Since the value of x becomes almost constant at 0 minutes or more, the value measured and calculated at these times can be substituted.

Depending on the sol used, the above-mentioned weight reduction is not always caused only by water (H ₂ O), but may include contributions from sol stabilizers, impurities and the like. Is difficult to distinguish between
In the present invention, apparently, the values calculated on the assumption that they are all based on water of crystallization are used. Boehmite is customarily referred to as boehmite, pseudoboehmite, amorphous, etc. depending on its crystallinity or water content. For example, when the value of x is 2.5 or more, it is almost amorphous and amorphous. However, in this specification, they are unified with boehmite (crystal) without particular distinction.

As the boehmite used in the present invention, either a commercially available one or a uniquely synthesized one can be suitably used. In order to further clarify the present invention, the representative brands of commercially available boehmite sols are described below. First, as the boehmite sol of x ≦ 2.0, AS-520 (manufactured by Nissan Chemical Industries, Ltd.), AS-520
2, AS-3 (all manufactured by Catalyst Kasei Co., Ltd.), 23N4-2
0,23N4-80 (all are Vista brands manufactured by Condea). On the other hand, representative examples of the boehmite sol having x ≧ 2.5 include AS-100 and AS-200.
(All manufactured by Nissan Chemical Industries, Ltd.). In the case of a synthetic product, a boehmite sol having a desired crystallinity and crystallinity content can be prepared by controlling the starting material, reaction temperature, time, pH, aging time, and the like. Any boehmite sol that can be used can be used without any problem.

In the production method of the present invention, two kinds of boehmite sols having different properties are used as essential components. However, the raw materials used are not necessarily two kinds, and three kinds may be used as long as the conditions of the present invention are satisfied. Alternatively, a mixture of more than them may be used. There is no problem in blending a commercial product and a synthetic product at the same time.

B ₂ contained in the fine particle dispersion as a coating liquid
The ratio of O ₃ / Al ₂ O ₃ (composition ratio) is 12% by weight.
/ 88 to 40/60 (however, the combination of 12/88 is not included). Conventionally, this ratio is 0.1-5 in molar ratio, ie about 6 / 94-7 in weight ratio.
A range of 8/22 is disclosed as being preferred. Although the conventional disclosure range is quite wide, studies by the inventors have shown that within this range, a film having well-balanced properties such as film tension and adhesion can be obtained. However, as a result of diligent studies by the inventor, it has been found that when a boehmite sol having the properties of the present invention is used, a coating film having extremely excellent properties can be obtained particularly in the composition range of the present invention. In the case of following the embodiment of the present invention, if the composition ratio exceeds this range and the amount of B ₂ O ₃ is small, the effect of improving the iron loss cannot be sufficiently obtained because the film tension becomes small. On the other hand, if there is too much B ₂ O ₃ , the excess from the stoichiometric composition will remain as unreacted substances,
Water resistance and corrosion resistance may be reduced, or a film having poor heat resistance and sticking resistance may be formed. More preferred B ₂
The ratio of O ₃ / Al ₂ O ₃ is more than 20 / less than 80/40/60, more preferably more than 26 / less than 74 by weight.
36/64.

The fine particle dispersion of the present invention may contain a small amount of additives in addition to the above-mentioned boehmite sol and boric acid. Examples of commonly used additives include silicon oxide precursor compounds, transition metal compounds, alkali / alkaline earth metal compounds, rare earth element compounds, acids such as inorganic acids and organic acids, and ammonia, depending on the purpose. The amount can be added.

The fine particle dispersion as described above is mixed with 5% or less of S
The surface of the silicon steel sheet which has been subjected to finish annealing containing i is applied by a conventionally known method such as a coater such as a roll coater, a dipping method, a spraying method, or an electrophoresis method. The application method is not particularly limited, and an optimum method may be selected according to the properties of the liquid. The term “finished annealing-completed steel sheet” as used herein refers to (1) finish annealing performed in the process of manufacturing a conventionally known unidirectional magnetic steel sheet, and a forsterite-like film generated in the process is formed on the surface. steel sheet,
(2) a steel sheet obtained by immersing the above-mentioned forsterite-based coating and the interfacial oxide layer formed by immersion in an acid, and (3) flattening and annealing the steel sheet obtained in the above (2) in hydrogen. Steel plates, or steel plates that have been polished such as chemical polishing or electrolytic polishing, (4) alumina powder that is inert to film formation, or a conventionally known annealing separator containing a small amount of additives such as chlorides As used herein, refers to a steel sheet or the like that has been subjected to finish annealing under conditions that do not produce a forsterite-based annealed film.

The coating on the outermost surface of the unidirectional silicon steel sheet of the present invention is formed so as not to exceed 2% of the thickness of the steel sheet on one side. When the thickness of the coating exceeds 2% of the thickness of the steel sheet, the effect of reducing the iron loss by the application of the tension is substantially constant and is in a saturated region, and the space factor is reduced due to the thick coating.

The coated steel sheet is dried to cause gelation, and thereafter, is finally baked and solidified at 500 to 1200 ° C. in a reducing atmosphere containing an inert gas or hydrogen to obtain boron and boron. An insulating film made of aluminum oxide is formed. Baking in an oxidizing atmosphere is not preferable because the steel sheet may be oxidized.
In particular, a steel sheet having no primary coating is sensitive to atmospheric oxidation, and is preferably baked in an atmosphere with a controlled oxygen potential. In addition, if the surface or the interface with the coating is slightly damaged by oxidation, and unevenness occurs, the characteristics of the steel sheet whose surface is smoothed to reduce iron loss will be markedly deteriorated. It is preferable to set conditions. When the baking temperature is lower than 500 ° C., it is highly possible that the decomposition of boehmite in the gel is insufficient and the gel does not become an oxide, but remains an incomplete film. Also, 1
When the temperature exceeds 200 ° C., it is not economical, although there is no particular inconvenience. More preferably, 700-1200 ° C
Within this range, a good film having excellent adhesion and film tension can be obtained.

[0023]

【Example】

(Example 1) Alumina sol in which x = 1.6 (the AS
-520), alumina sol where x = 3.2 (the AS
-200), a commercially available boric acid reagent was blended in the ratio shown in Table 1, and distilled water was added as necessary to prepare a fine particle dispersion for coating. This is made to have a smooth surface without a forsterite film and a thickness of 0.2% containing 3.2% of Si.
The coating was applied to a unidirectional silicon steel sheet with a roll coater such that the coating thickness after baking was about 2 μm per side.

Then, immediately after a drying and gelling step, finally, 850 in an N ₂ atmosphere containing 75 vol% of H _2.
C. for 30 seconds to form an aluminum borate coating, thereby producing a unidirectional silicon steel sheet having an insulating coating.
Table 1 also shows the properties of the obtained unidirectional silicon steel sheet and the aluminum borate coating on the surface.

The adhesion of the coating film was evaluated by conducting a winding test around a 20 mmφ cylinder at an angle of 180 ° and evaluating the peeling condition. The water resistance was evaluated by measuring the weight change of the test material immersed in boiling distilled water for 60 minutes, and evaluating the magnitude of the weight reduction ratio with respect to the amount of the immersed coating. The evaluation criteria for water resistance were acceptable if the weight loss was less than 1 wt%. The film tension was measured from the size of the warpage of the steel sheet from which the film on one side was removed, and was defined as the average value of 10 test materials. Similarly, B8 and W17 / 50 were averaged values of 10 test materials.

[0026]

[Table 1]

From Table 1, it is deviated from the scope of the present invention that x ≦
Comparative Examples 1 and 2 having a large amount of boehmite of 2.0
In the above, the film tension, the magnetic properties are poor values,
Conversely, Comparative Examples 3 and 4, which are compositions having a large amount of boehmite with x ≧ 2.5, have extremely poor adhesion. On the other hand, the method of the present invention, that is, an aluminum borate coating formed by applying and baking a fine particle dispersion in which a boehmite sol having controlled crystallinity and a water content is blended in a predetermined ratio or more has an adhesion property and a water resistance. sex,
It can be seen that the unidirectional silicon steel sheet formed with this coating is excellent in any of the coating tensions and has achieved a remarkably low iron loss.

(Example 2) A boehmite sol where x = 1.5 (above 23N4-80), a sol obtained by dispersing and peptizing boehmite synthesized in a laboratory (x = 4.5), and a commercially available boric acid reagent were used. It was blended in the proportions shown in Table 2 and subjected to a dispersion treatment by adding distilled water to prepare a fine particle dispersion for coating. This was applied to a 0.2-mm-thick forged unidirectional silicon steel sheet having a forsterite-type primary coating containing 3.2% of Si, and the coating thickness after baking was about 2 μm per side. Was applied by a roll coater so that

Then, immediately after passing through a drying and gelling step, finally in an N ₂ atmosphere containing 3 vol% of H ₂ ,
C. for 30 seconds to form an aluminum borate coating, thereby producing a unidirectional silicon steel sheet having an insulating coating.
Coating adhesion, water resistance, coating tension, and B8 of steel sheet
W17 / 50 was evaluated in the same manner as in Example 1, and is also shown in Table 2.

[0030]

[Table 2]

From Table 2, it can be seen that an aluminum borate film having good properties is formed at any of the compounding amounts. In particular, the method of claim 2 of the present invention, that is, using a controlled boehmite sol, B ₂ O ₃ / Al ₂ O ₃ ratio exceeds 12/8
The aluminum borate coating formed by applying and baking a fine particle dispersion adjusted to less than 8 to 40/60 is excellent in all of adhesiveness, water resistance, and coating tension. It can be seen that the silicon steel sheet achieves remarkably low iron loss.

Example 3 The powdery boehmite sol 23N4-80 used in Example 2, the alumina sol AS-200 used in Example 1, and a commercially available boric acid reagent were blended in the proportions shown in Table 3 and distilled. Water was added for dispersion treatment to prepare a fine particle dispersion for coating. This was applied to a 0.2-mm thick unidirectional silicon steel sheet having a smooth surface without a forsterite coating and containing 3.2% of Si so that the coating thickness after baking was about 2 μm per side. It was applied with a roll coater.

Then, immediately after a drying and gelling step, finally, 850 in an N ₂ atmosphere containing 75 vol% of H _2.
C. for 30 seconds to form an aluminum borate coating, thereby producing a unidirectional silicon steel sheet having an insulating coating.
Coating adhesion, water resistance, coating tension, and B8 of steel sheet
W17 / 50 was evaluated in the same manner as in Example 1.
Also described in 3-2).

[0034]

[Table 3]

[0035]

[Table 4]

From Table 3, it can be seen that the compositions of Comparative Examples 1, 2, 4 and 6 which have a large amount of boehmite sol with x = 1.5 outside the range of the present invention have insufficient film tension and good magnetic properties. Not obtained. Further, the compositions of Comparative Examples 3, 5, 7, and 8 having a large amount of boehmite sol with x = 3.2 have poor adhesion. The method of the present invention, namely, controlled crystallinity, the aluminum borate coating formed by applying and baking a fine particle dispersion using a boehmite sol having a water content is excellent in adhesion, water resistance, and coating tension. also oriented silicon steel sheet formed with the coating is remarkably low iron loss has been achieved, B ₂ O _3, in particular the claims 2
It can be seen that particularly good results were obtained when the ratio was adjusted to / Al ₂ O ₃ .

[0037]

The grain-oriented silicon steel sheet according to the production method of the present invention exhibits good magnetic properties by having an aluminum borate coating on the surface that imparts a greater tension than conventional coatings, as well as adhesion and water resistance. Also excellent in chemical stability such as properties. In addition, the method for producing a grain-oriented silicon steel sheet of the present invention is a method of coating and baking, which is the same as a conventional method of forming a film. The industrial effect is enormous from the viewpoints of performance and versatility.

Claims (2)

[Claims] Claims: 1. A finish-annealed silicon steel sheet surface
Boric acid, the content of water of crystallization when dried at 100 ° C is Al
Boehmite sol that satisfies x ≦ 2.0 when expressed as ₂ O ₃ · xH ₂ O is at least 20% by weight in terms of oxide with respect to the whole aluminum oxide source, and water content of crystallization when dried at 100 ° C. Is coated with a boehmite sol that satisfies x ≧ 2.5 when expressed as Al ₂ O ₃ .xH ₂ O, and mixed with 20% or more of the same aluminum oxide source by weight in terms of oxide. A method for producing a unidirectional silicon steel sheet, comprising forming an aluminum borate film through a drying, gelling, baking and solidifying process. 2. The composition ratio of boric acid to boehmite sol is more than 12 to 40% by weight in terms of boron oxide and 60 to less than 88% by weight in terms of aluminum oxide. 2. The method for producing a unidirectional silicon steel sheet according to 1.