JP2003034880A - Method for forming insulation film superior in adhesiveness on surface of grain-oriented electrical steel sheet, and method for manufacturing grain- oriented electrical steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an insulation film superior in adhesion to the surface of a grain-oriented electrical steel sheet. SOLUTION: The method for forming an insulation film by applying a predetermined coating liquid, on the surface of a grain-oriented electrical steel in which forsterite is inhibited to generate or is removed, is characterized by the surface and the coating liquid, which have such properties that the contact angle of the droplet of the coating liquid against the surface is 0-25 degree, when the droplet is dropped on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating coating having excellent adhesion on the surface of a grain-oriented electrical steel sheet.

[0002]

2. Description of the Prior Art Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and it is basically important that they have excellent magnetic properties such as magnetic flux density and iron loss value, and especially energy loss is reduced. Therefore, a material with low iron loss is required.

As a means for reducing iron loss, in addition to methods such as reduction of plate thickness, increase of Si content in steel, improvement of crystal orientation, etc., a method of applying tension to the steel sheet is effective. Is. As a method for applying tension to a steel sheet, a coating film made of a material having a smaller thermal expansion coefficient than that of the steel sheet is currently provided. For example, in the final annealing process that also serves as a secondary recrystallization that finally aligns the crystal orientation and the purification of the steel sheet, the oxide on the steel sheet surface reacts with the annealing separator applied to the steel sheet surface, and mainly forsterite is produced. A coating film as a component is formed, and this coating film exerts a large tension on the steel sheet and is effective in reducing iron loss. In order to further increase the tension effect, it is common to apply a low thermal expansion coating as an overcoat on the forsterite coating to obtain a product.

However, in recent years, a method of magnetically smoothing the surface of a steel sheet has been developed. One of the methods is to intentionally suppress the formation of a forsterite coating in the finishing annealing step, or after removing the formed forsterite coating, finish the surface of the forsterite coating smoothly. It is becoming clear that it is recognized.

For example, Japanese Examined Patent Publication (Kokoku) No. 52-24499 discloses a method in which after surface finishing and purification, a surface product is removed by pickling, and then chemical polishing or electrolytic polishing is performed to obtain a mirror surface state. Further, Japanese Patent Laid-Open No. 5-43943 discloses a method of removing the forsterite coating film and then performing thermal etching in H ₂ at 1000 to 1200 ° C.

The reason why the iron loss is reduced by such surface treatment is that the pinning sites that hinder the domain wall movement near the surface of the steel sheet are reduced in the magnetization process.

[0007] Incidentally, reduce hysteresis losses as "magnetically smooth surface" is generally intended to be expressed by an arithmetic mean roughness R _a as defined in JIS B 0601, it is represented by only the so-called surface roughness Instead, as disclosed in Japanese Examined Patent Publication No. 4-72920, it is known that it is necessary to add the surface state by the crystal orientation enhancement treatment of electrolyzing in a halogenated aqueous solution after removing the surface product. ing.

At present, a tension imparting type insulating coating applied to a grain-oriented electrical steel sheet having a forsterite coating is mainly composed of a phosphate of Al or an alkaline earth metal and colloidal silica, chromic anhydride or chromate. In many cases, it is formed by applying the treatment liquid described above and baking.

[0009] The tension-type insulating coating forms an inorganic coating film represented by colloidal silica, which has a smaller coefficient of thermal expansion than a steel sheet, at high temperature, and utilizes the difference in thermal expansion between the base steel and the insulating coating to obtain a normal temperature. In the above, tension is applied to the steel sheet, and this coating has a large effect of applying tension to the steel sheet and is effective in reducing iron loss. For example,
The forming method is disclosed in Japanese Patent Publication No. 53-28375 or Japanese Patent Publication No. 56-52117.

It is necessary for the tension-applying insulating coating to have a higher adhesion to the substrate as the film having a higher tension applied to the steel plate is necessary to prevent the film from peeling off, and forsterite finish annealing. When the coating is present on the surface of the steel sheet, there is no problem because sufficient adhesion is obtained, but when the finish annealing coating of forsterite type is not present on the surface of the steel sheet by performing surface smoothing treatment such as mirror finishing. However, it was not possible to form a film having good adhesion on the surface of the steel sheet.

Several methods have heretofore been proposed as a method for applying a tension-type coating to a surface without a forsterite coating, and further to a conditioned smooth surface. For example, JP-B-52-24499 discloses that after forming a thin metal plating film, there is also disclosed in JP-A-6-184762.
The publication discloses a method of applying a tension-applying coating solution and baking after forming a SiO ₂ thin film.

Further, Japanese Patent Publication No. 56-4150 discloses a method of forming a ceramic thin film by vapor deposition, sputtering, thermal spraying or the like, and Japanese Patent Publication No. 63-54767 discloses a nitride or carbide ceramic coating. Each of the methods for forming the above by ion plating or ion plantation is disclosed. In addition, Japanese Patent Fair 2-2
Japanese Patent No. 43770 discloses a method of directly forming a high-strength imparting type ceramic coating on the surface of a steel sheet by a so-called sol-gel method.

Although these methods were developed as methods for applying tension to a steel sheet having a smoothed surface,
It has not been put to practical use because it has some problems. In other words, the method of using a thin metal plating film as a base and coating the same has a problem that the adhesion of the film cannot be sufficiently obtained due to the smoothness of the plated surface, and a SiO ₂ thin film is formed. The method has a problem that the effect of improving iron loss cannot be sufficiently obtained, such as the effect of applying tension is poor.

In any of the methods for forming a ceramic coating made of a nitride, a carbide, or a combination thereof, the coefficient of thermal expansion of the ceramic coating is considerably lower than that of base iron, so that the tension effect due to the difference in thermal expansion coefficient is large. However, there was a problem in the bending adhesion between the base steel and the coating. Further, formation of a ceramic coating by vapor deposition, sputtering, thermal spraying, ion plating, or ion plantation is not only costly, but it is difficult to ensure uniformity when a large area is processed in large quantities.

Furthermore, although the sol-gel method can form a film by coating and baking as in the conventional case,
Since it is extremely difficult to form a sound film having a thickness of 0.5 μm or more, a large tension-providing effect cannot be brought, and the desired iron loss improving effect cannot be obtained.

Further, Japanese Patent Application Laid-Open No. 8-277475 proposes a coating liquid containing 90% or more by weight of aluminum phosphate in a phosphate and having excellent wettability. However, although it has excellent slipperiness and heat resistance, there is a problem in that it is inferior to that of a grain-oriented electrical steel sheet having a forsterite coating, because bending adhesion is not sufficiently obtained.

Therefore, it has been difficult at present to achieve both the technique of magnetically smoothing the surface to reduce the iron loss and the technique of reducing the iron loss by the tension imparting type coating.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming an insulating coating having excellent adhesion on the surface of grain-oriented electrical steel sheet.

[0019]

The present invention advantageously solves the above-mentioned problems of the prior art and is a manufacturing process capable of industrially producing a grain-oriented electrical steel sheet having an extremely low iron loss value at a low cost. Was made for the purpose of providing. Most of the conventional methods can be concentrated on a method of forming a base film having good adhesion between a smoothed surface and a tension-imparting film. In that case, it has been considered that it is more advantageous to increase the surface roughness of the undercoating film from the viewpoint of adhesion with the tension-imparting film.

The inventors have investigated in detail the relationship between the surface physical properties such as surface roughness and the adhesion of the coating type tension-imparting coating film. The present invention has been completed by finding that the contact angle with respect to is closely related to the bending adhesion of the coating.

The gist of the present invention is as follows. (1) In a method of forming a dielectric coating by applying a predetermined coating liquid on the surface of grain-oriented electrical steel from which the formation of forsterite is suppressed or the forsterite is removed, the surface and the coating liquid are the coating liquid. When the droplet is dropped on the surface, the contact angle of the droplet with respect to the surface is 0 to 25.
A method for forming an insulating coating film having excellent adhesion on the surface of a grain-oriented electrical steel sheet, which has a certain property.

(2) The surface and the coating liquid form an insulating coating having excellent adhesion on the surface of the grain-oriented electrical steel sheet according to (1), which has a property that the contact angle is 0 to 15 degrees. how to.

(3) A steel slab for a grain-oriented electrical steel sheet is hot-rolled, if necessary, hot-rolled sheet is annealed, and cold rolled once or a plurality of times with intermediate annealing to obtain a final sheet thickness. After performing recrystallization annealing, suppress the generation of forsterite in final finish annealing, or apply a prescribed coating solution on the surface of grain-oriented electrical steel sheet from which forsterite on the steel sheet surface after final finish annealing has been removed. In the method for producing a grain-oriented electrical steel sheet to be baked, the surface and the coating liquid have a property that the contact angle of the liquid droplet when the coating liquid is dropped onto the surface is 0 to 25 degrees. A method for producing a grain-oriented electrical steel sheet having excellent adhesiveness to an insulating coating.

(4) The surface and the coating liquid have a property that the contact angle is 0 to 15 degrees. The grain-oriented electrical steel sheet excellent in the adhesion of the insulating coating according to the above (3). Manufacturing method.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The cold-rolled sheet rolled to the final sheet thickness of 0.23 mm containing 3% Si was decarburized, primary recrystallization was annealed, and then an annealing separator containing MgO and lead chloride as the main components was applied, and the secondary recrystallization process was performed. Then, final annealing including the purification process was performed to obtain a finish annealed plate having a mirror surface state.

The finished annealed plate was dipped in a chemical polishing solution consisting of a mixed solution of H ₂ O ₂ and HF, or electrolytically polished in a NaCl aqueous solution to give a mirror-finished surface. As a comparison, a material that had been subjected to finish annealing as well as degreasing treatment was also prepared. 2 cc of a coating liquid in which the component composition was changed or various additives were mixed was dropped onto the surface, and the contact angle of the droplet was measured.

Here, the "contact angle" means an inner angle formed by the liquid surface and the solid surface, and this contact angle is measured by taking a photograph using an optical microscope from a direction parallel to the surface. It was performed by measuring the contact angle from the photographed image.

FIG. 1 shows the contact angles of droplets when various coating liquids were combined with various mirror-finished surfaces, and the coating liquids actually deposited by the combination had a coating amount of 4.0 g / m ² per surface. 3 is a graph showing the relationship with the bending adhesion of the coating when the coating is applied so that the coating is applied and then baked at 850 ° C. Here, the "flexural adhesion of the coating film" was evaluated by winding a sample around a round bar having various diameters and measuring the minimum diameter (mm) at which the coating film did not peel off.

Although the flexural adhesion of the coating depends on the type of coating liquid and the mirror surface treatment, a uniform evaluation can be made by measuring the contact angles of all combinations of coating liquid and surface. Speaking concretely, it has been found that the adhesion of the coating is better as the combination of the coating liquid and the surface having a smaller contact angle.

In the above-mentioned Japanese Patent Laid-Open Publication No. 8-277475, the wettability of the coating is good when the sample is completely covered with the coating liquid at the end of the drying immediately after the coating. Investigating the relationship between the contact angle and the coverage in detail, it is possible to coat almost the entire surface if the contact angle is about 30 degrees, but it must be said that the condition is insufficient for bending adhesion. I didn't get it.

It is considered that the contact angle depends not only on the wettability but also on the surface tension of the coating liquid, and is not simply the same index as the wettability.

The inventors have for the first time found that the contact angle has a bending point in the vicinity of 25 degrees, and that the bending adhesion is remarkably improved when the contact angle is 0 to 25 degrees. It is not clear why the contact angle of 0 to 25 degrees significantly improves the bending adhesion, but it is necessary to displace any adsorbate on the surface that cannot be removed even by pretreatment in the atmosphere. It is presumed that the coating solution is firmly bonded to the base steel itself.

Further, when the contact angle is further limited to a narrow range of 0 to 15 degrees, the bending adhesion does not have any further improving effect and seems to be saturated, but this is due to the buckling of the steel plate itself. By limiting the contact angle to a narrow range of 0 to 15 degrees, it is possible to completely prevent flaking due to coating, and in particular, significantly improve bending adhesion after stress relief annealing. Therefore, it is preferable.

As means for reducing the contact angle, it is essential to improve both the coating solution and the metal surface after finish annealing and a combination thereof.

Regarding the coating liquid, for example, in the case of a coating liquid mainly composed of phosphate and colloidal silica, phosphoric acid is added to increase the phosphoric acid ratio, which is the molar ratio of the metal element to the phosphate ion, to obtain the contact angle. Can be reduced. It is also effective to add an organometallic compound such as a surfactant or a silane coupling agent.

As a metal surface after finish annealing, a base metal surface obtained by simply removing an inorganic coating such as forsterite is effective, but if the surface is further smoothed, the contact angle of the coating solution decreases. It is more effective in reducing the iron loss value.

Regarding the smoothing treatment, the contact angle of the coating solution can be lowered by immersing it in an aqueous solution of halide or performing anodic electrolysis in an alkaline bath.
It was also found that a pretreatment of immersing in a coating liquid to be actually applied and performing cleaning while applying ultrasonic waves is also effective. Furthermore, the surface roughness should be minimized by thermal etching, chemical polishing, etc. to obtain a mirror-finished surface or a graining-like surface obtained by electrolytic orientation enhancement treatment in a halide aqueous solution. Is effective.

In any case, a very good bending adhesion can be obtained under the condition that the combination of the coating liquid and the surface state is essential and the contact angle between them is minimized.

Therefore, for example, when a silane coupling agent is added to the coating liquid, the coating liquid itself has a selective property for selecting a partner for the surface depending on the kind of the functional group of the silane coupling agent. Depending on the surface finishing condition, the change in the contact angle becomes larger, and the contact angle may decrease and the adhesion may be significantly improved. On the contrary, the contact angle may increase and the bending adhesion may deteriorate. .

The desirable component composition of the electromagnetic steel sheet according to the present invention will be described below.

As a component of the steel sheet used in the present invention, it is desirable to contain Si in an amount of 1.5 to 7.0 mass%. That is, Si is an effective component for increasing the electric resistance of the product and reducing the iron loss, but if the Si content exceeds 7.0 mass%, the hardness tends to be high and the manufacturing or processing tends to be difficult,
This is because if it is less than 1.5 mass%, transformation is likely to occur during final finish annealing and a stable secondary recrystallization structure cannot be obtained.

The crystal orientation can be further improved by including Al as an inhibitor element in the initial steel in an amount of 0.006 mass% or more, but the content is 0.06.
The Al content is preferably in the range of 0.006 to 0.06 mass% because the crystal orientation deteriorates again when the mass% is exceeded.

N has the same effect as Al, but if its content exceeds 100 ppm, swelling defects tend to occur, which is not preferable. Although the lower limit of the N content is not particularly specified, it can be said that it is economically difficult to industrially reduce it to 20 ppm or less. Further, the step of performing the nitriding treatment after the primary recrystallization annealing is also suitable.

If nitriding is not performed,
It is preferable to contain Se + S in the range of 0.01 to 0.06 mass%. In addition, 0.02 to precipitate as Mn compound.
It is more preferable to contain Mn of 0.2 mass%.
This is because if the content of each is too small, the precipitates that cause secondary recrystallization will be too small, and if it is too large, it will be difficult to form a solid solution before hot rolling.

When the nitriding treatment is not performed, Mn is not always necessary, but can be added as appropriate for the purpose of improving the ductility of steel.

In the steel, in addition to the above-mentioned elements, B, Bi, and B are added as inhibitor components suitable for the production of known grain-oriented electrical steel sheets.
Sb, Mo, Te, Sn, P, Ge, As, Nb, Cr, Ti, Cu, Pb, Zn
And In are known, and these elements can be contained alone or in combination.

Further, all the impurities such as C, S, and N have a harmful effect on the magnetic characteristics and particularly tend to deteriorate the iron loss. Therefore, C: 0.003 mass% or less, respectively.
It is preferable that S: 0.002 mass% or less and N: 0.002 mass% or less.

Next, a preferred example of the method for producing a grain-oriented electrical steel sheet to which the method for forming an insulating coating according to the present invention is applied will be described below as an example.

The steel adjusted to the predetermined composition is usually subjected to slab heating and then hot rolled into a hot rolled coil. When the heating temperature of this slab is set to a high temperature of 1300 ° C. or higher. The temperature may be as low as 1250 ° C. or lower, but any temperature may be used in the present invention. Further, in recent years, a method of directly performing hot rolling after continuous casting without performing slab heating has been developed, but this method can be applied even when hot rolling is performed by this method.

The hot-rolled steel sheet is subjected to hot-rolled sheet annealing as required, and is once cold-rolled or is subjected to a plurality of rolling operations with intermediate annealing interposed therebetween to obtain a final cold-rolled sheet. These rollings may be so-called warm rolling aiming at dynamic aging, or interpass aging aiming at static aging.

The steel sheet after the final cold rolling also serves as decarburization annealing.
The secondary recrystallization annealing is performed, and the secondary recrystallization treatment is performed by the final finish annealing to obtain the orientation. When the final finish annealing is performed, usually, an annealing separator is applied after the primary recrystallization annealing to form an oxide film, but the composition of this pure annealing separator is adjusted to adjust the composition on the surface of the steel sheet. It is also possible to suppress the formation of an oxide film.

Even if the steel sheet thus obtained is irradiated with a laser or a plasma flame for the purpose of further reducing iron loss and the magnetic domains are subdivided, there is no problem with the adhesion of the insulating coating. Further, since the magnetic domains are subdivided at any stage of the production process of the grain-oriented electrical steel sheet of the present invention, it is effective as means for further reducing iron loss to form grooves at a constant interval on the surface by etching or tooth profile rolls. Is. The grain-oriented electrical steel sheet produced by the above method is subjected to the smoothing treatment and the insulating coating as described above.

[0053]

[Example (1)] A steel slab containing 3% Si was hot-rolled, and cold-rolled to a final thickness of 0.23 mm by two cold rolling processes with intermediate annealing. After refining charcoal and primary recrystallization, using an annealing separator containing 0.3 mass% nickel chloride with respect to MgO, while forming a groove for magnetic domain refinement while suppressing the formation of forsterite film Then, secondary recrystallization was performed to obtain a grain-oriented electrical steel sheet having a mirror surface. The surface condition of the obtained grain-oriented electrical steel sheet was changed by only degreasing with sodium carbonate, immersing in a coating liquid to be applied, or washing while applying ultrasonic waves.

An aqueous solution prepared by adding 15 parts by weight of potassium dichromate and colloidal silica to magnesium monophosphate containing 100 parts by weight of phosphate group (P0 ₄ ) of phosphate in the grain-oriented electrical steel sheet is used as a base composition. Phosphoric acid or aminopropyltriethoxysilane was mixed as a coating liquid of the above, and the mixture was applied with a roll coater and baked at 800 ° C. to form a film having an adhesion amount of about 4.0 g / m ² . At the same time, 2 cc of the coating liquid was dropped on the surface of each steel sheet, and the contact angle was measured. The adhesion between the coating and the steel plate is the minimum diameter of the round bar (m) where the sample is wrapped around the round bar with various diameters and the coating does not peel off.
Evaluated by The film appearance was evaluated by visual inspection of the coating. These results are collectively shown in Table 1.

[0055]

[Table 1]

As is clear from the evaluation results shown in Table 1,
Steel plates Nos. 1 to 4, which are comparative examples manufactured under conditions outside the scope of the method of the present invention, have a contact angle of more than 25 degrees and do not have sufficient bending adhesion, whereas the method of the present invention. It is understood that the steel sheets Nos. 5 to 8 which are the examples manufactured by using the above have a small contact angle of 25 degrees or less and are excellent in bending adhesion.

Further, when the bending adhesion after strain relief annealing at 800 ° C. for 3 hours was evaluated, it was found that the steel sheets Nos. 7 and 8 were rounded without peeling of the coating even after strain relief annealing at 800 ° C. for 3 hours. The minimum diameter of each rod is as small as 30 mm or less, and it has both heat resistance and bending adhesion.

[Example (2)] A steel slab containing 3% Si was hot-rolled, hot-rolled sheet was annealed, and cold-rolled once to a final thickness of 0.23 mm. After forming etching grooves at intervals of 5 mm for magnetic domain refinement treatment, decarburization, and primary recrystallization annealing, a final pure annealed plate was obtained by applying a pure separation agent containing MgO as a main component and containing chromium chloride. . As an additional treatment, the crystal orientation enhancement treatment by electrolysis in NaCl aqueous solution and chemical polishing with hydrofluoric acid and hydrogen peroxide solution were performed to magnetically smooth the surface. The coating composition of the obtained steel sheet was changed in the same manner as in Example (1), and the coating appearance, adhesion and the contact angle were evaluated, and the results are summarized in Table 2.

[0059]

[Table 2]

As is clear from the evaluation results of Table 2, the steel sheets Nos. 1 to 4 as the comparative examples have a contact angle of more than 25 degrees and a sufficient bending adhesion is not obtained. Steel plate numbers 5 to 8 which are examples manufactured using the inventive method
It can be seen that each of them has a small contact angle of 25 degrees or less and is excellent in bending adhesion.

Further, when the bending adhesion after strain relief annealing at 800 ° C. for 3 hours was evaluated, it was 80 for steel plate No. 8.
Even after strain relief annealing at 0 ° C for 3 hours, the minimum diameter of the round bar that does not cause peeling of the coating is as small as 20 mm, and it is possible to have both heat resistance and bending adhesion.

[0062]

INDUSTRIAL APPLICABILITY The insulating coating forming method of the present invention can form an insulating coating having excellent adhesion to the surface of a smoothed grain-oriented electrical steel sheet having no coating formed by finish annealing. As a result, sufficient tension can be applied to the steel sheet, and as a result, it is possible to provide a grain-oriented electrical steel sheet with low iron loss.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a contact angle of a droplet when various coating liquids are combined with various mirror-finished surfaces and bending adhesion of a formed coating film.

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[Procedure amendment]

[Submission date] July 30, 2001 (2001.7.3)
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

Further, since impurities such as C and S all have a harmful effect on the magnetic properties and particularly tend to deteriorate iron loss, C: 0.003 mass% or less and S: 0.002, respectively.
It is preferable that the content is not more than mass%.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) H01F 1/18 H01F 1/18 (72) Inventor Mitsumasa Kurosawa 1 Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture F) Term at Mizushima Works, Kawasaki Steel Co., Ltd. MA00 PA04 PA10 TA04 TA08 5E041 AA02 BC01 BC08 CA02 NN05

Claims (4)

[Claims] 1. A method for forming an insulating coating by applying a predetermined coating liquid on the surface of grain-oriented electrical steel from which the formation of forsterite is suppressed or the forsterite is removed, wherein the surface and the coating liquid are the coating liquid. An insulating coating having excellent adhesion on the surface of a grain-oriented electrical steel sheet, which has a property that when the liquid is dropped onto the surface as a droplet, the contact angle of the droplet with respect to the surface is 0 to 25 degrees. How to form. 2. The method for forming an insulating coating having excellent adhesion on the surface of a grain-oriented electrical steel sheet according to claim 1, wherein the surface and the coating liquid have a property that the contact angle is 0 to 15 degrees. . 3. A steel slab for grain-oriented electrical steel is hot-rolled,
If necessary, hot-rolled sheet annealing is performed, and cold rolling is performed once or multiple times with intermediate annealing sandwiched to obtain the final sheet thickness, and after primary recrystallization annealing, generation of forsterite is suppressed in final finish annealing. Or, in the method for producing a grain-oriented electrical steel sheet, wherein a predetermined coating liquid is applied and baked on the surface of the grain-oriented electrical steel sheet from which forsterite on the steel sheet surface after final finish annealing is applied, the surface and the coating fluid are , A grain-oriented electrical steel sheet having excellent adhesiveness to an insulating coating, which has a property that a contact angle of a droplet with respect to the surface is 0 to 25 degrees when the coating liquid is dropped on the surface. Manufacturing method. 4. The production of a grain-oriented electrical steel sheet having excellent adhesiveness to an insulating coating according to claim 3, wherein the surface and the coating liquid have a property that the contact angle is 0 to 15 degrees. Method.