JPS5844744B2 - Method for forming a tension-applied top insulating film that does not contain chromium oxide on grain-oriented silicon steel sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an insulating top coat applied to the surface of a grain-oriented silicon steel plate having a forsterite coating.
In particular, the present invention provides chromic anhydride, dichromate, etc.
A method for forming a tension-applied insulating film using a coating treatment solution that does not contain valent chromium.

In recent years, large distribution transformers have been installed in urban areas as the demand for electricity increases, and the noise generated from them has become a problem as pollution.

It is known that the main cause of noise in transformers is the magnetostriction of the grain-oriented silicon steel plate used as the iron core material.

In order to reduce the noise of transformers, it is necessary to reduce the magnetostriction of grain-oriented silicon steel sheets, and an industrially effective means for this purpose is to apply tension to the steel sheets with a low thermal expansion top insulation coating. It is.

When manufacturing the iron core of a transformer from grain-oriented silicon steel sheets, compressive stress is inevitably applied to the steel sheets during operations such as shearing and assembly, which increases magnetostriction and iron loss.

If tension is applied to the steel plate in advance by applying an insulating film with low thermal expansion to the surface of the steel plate, increases in magnetostriction and iron loss due to such compressive stress can be suppressed.

In particular, in the case of recently developed high magnetic flux density grain-oriented silicon steel (RG-H, manufactured by Kawasaki Steel Corporation, product name) in which the axis of easy magnetization is very well aligned in the rolling direction, the effect of tension is large. Are known.

Conventional methods for forming a top insulating coating that imparts tension to a steel plate include, for example, using colloidal silica and aluminum phosphate, as disclosed in Japanese Patent Application Laid-Open No. 53-28043, or US Pat. No. 3,985,583; Obtained by applying and baking a coating treatment solution containing one or more selected from chromic anhydride, chromate, and dichromate to a primary phosphate solution of magnesium phosphate. Ru.

By these methods, a tension-applied coating with low thermal expansion that improves magnetostrictive properties and iron loss can be obtained, but chromic anhydride, which is blended in the coating treatment solution as an essential component,
Chromate and dichromate contain hexavalent chromium and are harmful to the human body.

The purpose of blending such anhydrous chromic acids is to improve the moisture absorption resistance, adhesion, and fusion resistance during strain relief annealing of the coating, but it is necessary to improve the moisture absorption resistance, adhesion, and fusion resistance during stress relief annealing of the coating. The workplace was contaminated with hexavalent chromium during processing operations, making it impossible to ensure safety and health at the manufacturing site.

Furthermore, it has been considered that the coating may peel off during processing of the grain-oriented silicon steel sheet, such as slitting or shearing, thereby contaminating the workplace with droplets containing chromium.

For example, a U.S. patent describes a method of forming an insulating top coat on a grain-oriented silicon steel sheet using a coating treatment solution that does not contain chromic anhydride, chromate, or dichromate (hereinafter simply referred to as chromic anhydride). As disclosed in No. 3940291, a method has been proposed in which a treatment solution obtained by mixing MgO, phosphoric acid, and sulfuric acid or nitric acid is applied and baked, but depending on this method, tension cannot be applied to the steel plate. I can't.

The present inventor has conducted extensive studies on a method of forming a tension-applied, pollution-free top insulating film on grain-oriented silicon steel sheets that improves magnetostrictive properties and iron loss using a coating treatment solution that does not contain chromic anhydride. As a result, 7 to 60 parts of magnesium phosphate [calculated as Mg (H2P 04 ) 2] was added to 20 parts by weight of colloidal silica with 5i02 content.
Parts by weight, Mg, At, Mn! After applying a coating treatment solution containing a total amount of 8 to 40 parts by weight of one or more selected from among the respective sulfates of Zn to a grain-oriented silicon steel sheet having a forsterite coating. It has been newly discovered that a tension-applied top insulating film with excellent moisture absorption resistance and adhesion can be formed by baking at a temperature of 300° C. or higher.

Next, the present invention will be explained in detail.

The surface coating of a grain-oriented silicon steel sheet usually consists of a crystalline forsterite coating formed during high-temperature finish annealing and a phosphate-based overcoat insulating coating applied thereon.

The grain-oriented silicon steel sheet used here is a steel sheet that is easily magnetized in the rolling direction (tto) (oo
1] Refers to a unidirectionally oriented silicon steel sheet that has a secondary recrystallized structure consisting of force positions.

Tension due to the surface coating is generated during the cooling process of heat treatment due to the difference in thermal expansion coefficient between the steel sheet and the coating.

In order to give a large tension to the steel plate, it is preferable that the coefficient of thermal expansion of the coating is as small as possible.

According to the present invention, colloidal silica, which is a suspension of amorphous silica fine particles, is added to the coating liquid as an essential component in order to maintain the coating at low thermal expansion.

The type of colloidal silica is not necessarily limited in terms of Si02 content, pl (etc.), as long as uniform and stable compatibility with the other ingredients of the present invention can be obtained.

For example, commercially available colloidal silica Snowtex-0 (trade name, manufactured by Nissan Chemical Industries, Ltd., 5in2 content 20 wt%, pH 3-4) and Snowtex-30 (trade name, manufactured by Nissan Chemical Industries, Ltd., Si02 content 30w
t%, pH 9.5-105), etc. can be used.

The conventional method of forming a tensioned top insulating coating is as follows:
In addition to colloidal silica and chromic acid anhydride, aluminum phosphate or magnesium phosphate is blended as an essential ingredient.

The purpose of blending these non-acid salts is to form a film with good adhesion by reacting with the forsterite film.

According to the present invention, magnesium phosphate is blended as an essential component, but the reason for limiting to magnesium phosphate is as shown below.

A coating treatment solution consisting of various phosphate solutions of Mg, Ca, Sr, Ba, Fe, Zn, f/ and colloidal silica is applied to grain-oriented silicon steel sheets, resulting in various tension-added insulations. The magnetostrictive compressive stress characteristics of the coating were measured, and the magnitude of the tension exerted by the coating on the steel plate was investigated.

As a result, when colloidal silica and magnesium phosphate were used, the compressive stress characteristics of magnetostriction were improved.
Next was the case of using colloidal silica and aluminum phosphate.

Furthermore, as a result of a detailed comparison and study of the cases where magnesium phosphate and aluminum phosphate were used, it was found that when colloidal silica and aluminum phosphate were used, coating and baking were performed after the coating was applied, or the coating was applied after strain relief annealing. It has been found that a crystalline phase with high thermal expansion (for example, α-cristobalite) is precipitated in the steel sheet, thereby reducing the tension applied to the steel plate.

When colloidal silica and magnesium phosphate were used, precipitation of such a high thermal expansion crystalline phase was not observed.
No deterioration in the tension applied to the steel plate was observed even after strain relief annealing.

The difference in the crystallization behavior of the film during strain relief annealing when magnesium phosphate and aluminum phosphate are used is due to the presence of chromic anhydride as the third component or the water-soluble metal silica used in the present invention. The same result was obtained when an acid salt was added.

The above results indicate that magnesium phosphate is superior among various phosphates when forming a tension-applied top insulating film from colloidal silica and phosphate.

This is the reason why the present invention is limited to magnesium phosphate among various phosphates.

Furthermore, in the present invention, the amount of magnesium phosphate blended is 7 parts by weight based on the colloidal silica SiO2 content of 20 parts by weight.
~60 parts by weight (calculated as Mg (H2PO2)2)
The reason for limiting the range is that if it is less than 7 parts by weight, the reaction with the forsterite film will be insufficient and a film with poor adhesion will be formed. Since only a homogeneous film is formed, it is necessary to limit the amount of magnesium phosphate blended within the range of 7 to 60 parts by weight.

Magnesium phosphate applied to the present invention is Mg (H2
A solution of 11 J phosphate having a composition of PO4)2 M is preferred;
Magnesium phosphate solution containing 232-35 wt% Mg (H2PO4) (s, g, 1.32-1.35
) are commercially available.

Although colloidal silica and magnesium phosphate alone can be used to form an insulating top coat that can impart large tension to a steel plate, the coating has poor moisture absorption resistance and is completely impractical.

In other words, simply by leaving a silicon steel plate with this coating at room temperature, water vapor in the air will cause a moisture absorption pattern to appear on the coating surface, and as moisture absorption progresses further, the coating will appear to run, causing rust and reducing its commercial value. will be significantly reduced.

In the present invention, in order to improve the moisture absorption resistance of such a coating, in addition to colloidal silica and magnesium phosphate, one or two selected from sulfates of Mg, Ap, Mn, and Zn are added. The above ingredients are included as essential ingredients.

Mg, AI. The reason for limiting the use to Mn HZn sulfates is that there is nothing other than these sulfates that has been found to be effective in improving moisture absorption resistance and provide good film properties.

For example, if nitrates are added to these metals in addition to sulfates, the moisture absorption resistance of the coating will be improved, but only a whitish coating with poor uniformity will be obtained.

Figure 1 shows a solution of magnesium phosphate (s, g, 1.35) containing 35 wt% as Mg(H4F 04)2 for 100 parts by weight of colloidal silica containing 2 wt% as SiO□. Manganese sulfate (MnS) was added to the treatment solution containing 70 parts by weight.
04.4H20) in a range of 0 to 50 parts by weight, water was added to adjust the specific gravity to 1.16, and a coating treatment solution was applied onto a grain-oriented silicon steel plate having a forsterite coating with a thickness of 2 microns on one side. FIG. 2 is a diagram showing the relationship between the water resistance of a film obtained by applying the film to form a thin film and baking it in a nitrogen atmosphere at 800° C. for 1 minute and the amount of manganese sulfate.

The water resistance test of the film in the present invention was conducted as follows.

The silicon steel plate having the above-mentioned coating was sheared into three 50 x 50 mm test pieces, and the three test pieces were immersed and boiled in distilled water at 100°C for 25 minutes to elute P from the coating surface. The amount was quantitatively analyzed to quantitatively compare the water resistance of the coatings.

As is clear from Figure 1, the water resistance of the film was significantly improved by adding manganese sulfate, and colloidal silica 5I
By adding 8 parts by weight or more of manganese sulfate to 20 parts by weight of 02 content, the elution amount of P is 100μ, 97
It decreases to about 150-.

If a film has this level of water resistance, its moisture absorption resistance will be improved to the extent that it will not absorb moisture or rust even if exposed to an atmosphere with a dew point of 50°C for more than 100 hours, and will have moisture absorption resistance that does not cause any practical problems. It becomes a coating with

Figure 1 shows an example of manganese sulfate (MnSO4・4F■2o), but M n SO,i・4H2
Examples of sulfates that improve moisture absorption resistance other than 0 include Mg5O, 7H20, A12(SO4)316~
18H20, MnSO4'H20, ZnSO4''7H2
Examples include 0.

Even if these sulfates are used alone or in combination of two or more, a film with excellent moisture absorption resistance can be obtained.

The lower limit of the preferred amount of sulfate used alone or when two or more types of sulfates are combined is determined by conducting a water resistance test of a film similar to that shown in Figure 1, and determining the colloidal silica Si02 content. It was determined to be 8 parts by weight compared to 20 parts by weight.

In addition, the -L limit value of the preferred blending amount was determined by limiting it within a range that does not deteriorate the coating appearance and space factor.

That is, when the colloidal silica 5iO7 content exceeds 40 parts by weight with respect to 20 parts by weight, the uniformity of the resulting film becomes poor, the surface becomes rough, and the space factor decreases.

For the above reasons, in the present invention, Mg, Al, M
The amount of one or more selected from among the sulfates of Zn and Zn is limited to 8 to 40 parts by weight.

In the present invention, in addition to these sulfates, other water-soluble salts such as nitrates, chlorides, acetates, etc. may be added in small amounts as long as they do not deteriorate the coating properties.

In addition, in order to improve the adhesion resistance of the interlayer coating during strain relief annealing, Sio2? High melting point oxide fine powder such as A1203, for example, Aeros i l-200, A obtained by high temperature hydrolysis of vaporized chloride as disclosed in JP-A No. 52-25296.
It is also within the scope of the present invention to blend a small amount of oxide fine powder such as Luminium Oxide G (both trade names of Nippon Aerosil).

Figure 2 shows a phosphoric acid coating obtained by the conventional method of forming an overcoat insulating coating without using chromic anhydride containing hexavalent chromium, disclosed in U.S. Pat. The magnetostrictive compressive stress characteristics of the grain-oriented silicon steel sheet with the resulting coating are shown.

Curve a shows the magnetostrictive compressive stress characteristics of a silicon steel sheet having only a forsterite film before the coating is applied.

Curves b and b' are shown in U.S. Patent No. 394,029, respectively.
The application and baking of the Mg0-IJ acid-based coating treatment solution disclosed in No. 1 is applied to a silicon steel plate having a subsequent coating,
The magnetostrictive compressive stress characteristics measured after strain relief annealing was performed in a nitrogen atmosphere at 800° C. for 3 hours are shown.

Curve C shows the concentration of Mg (H2P
O4) 235 wt% magnesium monophosphate solution was added to 60 parts by weight, magnesium sulfate (MgS04.7H20
) and 5 parts by weight of zinc sulfate (ZnSO4.7H20) were applied and baked at 800°C for 1 minute in a nitrogen atmosphere, resulting in a coating with a thickness of 2 microns on one side. Curve C also shows the magnetostrictive compressive stress characteristics after strain relief annealing.

As is clear from FIG. 2, the film obtained by the present invention, which does not use chromic acid anhydride, has magnetostrictive compressive stress properties that are significantly superior to those obtained by the conventional method.

This is because the coating of the present invention imparts strong tension to the steel plate.

When assembling the iron core of a transformer, compressive stress is inevitably applied to the steel plates, increasing magnetostriction and causing noise in the transformer.

If a grain-oriented silicon steel sheet having a tension-applied coating formed according to the present invention is used as a core material of a transformer, it is possible to reduce transformer noise.

Furthermore, since the present invention does not use a coating treatment solution containing harmful hexavalent chromium, it is possible to make the top coat non-polluting and ensure occupational safety and health at the manufacturing site.

By the method of the present invention described above, a pollution-free tension-added top insulating coating with excellent moisture absorption resistance and magnetostriction properties can be obtained without using chromic anhydride, chromate, or dichromate containing hexavalent chromium. is obtained.

In addition to moisture absorption resistance and magnetostrictive properties, the coating of the present invention has excellent features such as a beautiful appearance, good adhesion, high interlayer resistance and space factor.

The coating treatment liquid used in the present invention is applied to a steel plate after adjusting its specific gravity to 1.05 to 1.30,
It is preferable to apply the coating amount to the steel plate so that the coating thickness after baking is 1 to 3 microns on one side.

According to the present invention, a steel plate coated with a coating treatment liquid is baked at a temperature of 300° C. or higher to form a topcoat film.

Since the film of the present invention will not be formed if the baking temperature is lower than 300°C, it is necessary to limit the baking temperature to 300°C or higher.

Next, the present invention will be explained with reference to examples.

Example 3 Grain-oriented silicon steel plate containing 3% Si (thickness 0.30Tt
After forming a forsterite film on the surface of 771) by final annealing, unreacted separation agent of MgO was removed by water washing, and a 60 x 280 size test piece was sheared from the adjacent position of the coil for flattening. Seven types of coating materials were prepared by applying strain relief annealing.

A coating treatment solution having the composition shown in Table 1 was applied to the surface of these silicon steel plates using a grooved rubber roll, and then heated to SOO℃.
Baked for 1 minute in a nitrogen atmosphere.

The thickness of the film after baking was 2 microns on one side.

Table 2 shows the results of investigating the characteristics of these coated silicon steel sheets.

As is clear from the investigation results in Table 2, the compressive stress characteristics of magnetostriction of the coatings of Examples 1 to 4 obtained by the method of the present invention are very good, and the deterioration of magnetostriction due to increase in compressive stress is slight. It can be seen that the coating gives a large tension to the steel plate.

Furthermore, the moisture absorption resistance of the coatings of Examples 1 to 4 was good, and they did not absorb moisture or develop rust even after being exposed to an atmosphere with a dew point of 50°C for more than 100 hours, and the analysis value of the amount of P eluted from the coating surface was also good. It can be seen that a film with excellent moisture absorption resistance can be formed without using chromic anhydride, chromate, or dichromate containing low and harmful hexavalent chromium.

On the other hand, the moisture absorption resistance of the coatings of Comparative Examples 1 and 2 consisting only of colloidal silica and magnesium phosphate is not good.

Further, as shown in Comparative Example 3, the conventional method of forming an overcoat film from a coating treatment solution that does not contain hexavalent chromium results in only a film that is less effective in improving magnetostrictive compressive stress characteristics.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the amount of manganese sulfate blended and the amount of P eluted from the coating surface, and Figure 2 is a graph of U.S. Patent No. 394029.
FIG. 1 is a diagram showing the compressive stress characteristics of magnetostriction of coatings obtained by No. 1 and the present invention.

Claims (1)

[Claims] 1 colloidal silica SiO2 content of 20 parts by weight,
7 to 60 parts by weight of magnesium phosphate (calculated as Mg (H2PO2)2), Mg, A7, Mn
A coating treatment solution containing a total of 8 to 40 parts by weight of one or more selected from the respective sulfates of Zn was applied to a grain-oriented silicon steel sheet having a forsterite coating. A method for forming a tension-applied overcoat insulating film that does not contain chromium oxide on a grain-oriented silicon steel sheet, which is then baked at a temperature of 300° C. or higher.