JP2002275640A - Method for producing silicon steel sheet deposited with insulation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a silicon steel sheet deposited with an insulation film in which the elution of Fe is suppressed, and whose appearance and film condition are made satisfactory even when an acidic water based coating film which does not substantially contain chromium compounds, and contains a resin and an inorganic colloid as components is applied and baked to a silicon steel sheet to deposit a thin insulation thin film thereon. SOLUTION: A water based coating solution of pH 2 to 7 containing a resin and an inorganic component is applied and baked to a silicon steel sheet to deposit an insulation film in which the amount of the film to be baked is <=2 g/m<2> , and the content of chromium is 0 to 1 mass% thereon. In this production method, the concentration of the solid contents in the water based coating solution is 10 to 30 mass%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrical steel sheet with an insulating coating, comprising forming an insulating coating by applying and baking an acidic aqueous coating liquid containing substantially no chromium to the electrical steel sheet. The present invention relates to a method for producing an electromagnetic steel sheet which can obtain an electromagnetic steel sheet which is excellent in heat resistance and capable of performing strain relief annealing.

[0002]

2. Description of the Related Art Insulating coatings on magnetic steel sheets used for motors, transformers, and the like are required to have various characteristics from the viewpoint of not only interlayer resistance but also convenience during working and storage. In addition, in order to improve the magnetic properties of electrical steel sheets,
In many cases, strain relief annealing is performed after the punching process. In this case, the strain relief annealing temperature (generally, 750 to 850 ° C.)
Degree). As described above, since the electromagnetic steel sheet is used in various applications, development of an electromagnetic steel sheet having various insulating coatings according to the application has been performed.

[0003] The insulating coating is made of (1) an inorganic coating which emphasizes weldability and heat resistance and can withstand strain relief annealing; and (2) a resin which can withstand strain relief annealing with the aim of achieving both punching properties and weldability. Semi-organic coatings contained, and (3) organic coatings that are used for special applications and cannot be subjected to strain relief annealing. Among these, the coatings containing inorganic substances of (1) and (2), which can withstand strain refining as a general-purpose product, and in particular, the chromate containing organic resin, which is a semi-organic coating of (2) The system-based insulating film is widely used because the punching property can be remarkably improved in the production of one coat and one bake as compared with the inorganic-based insulating film of (1).
For example, Japanese Patent Publication No. Sho 60-36476, a bichromate-based aqueous solution containing at least one divalent metal, vinyl acetate / VeoVa ratio as the organic resin to CrO ₃ 100 parts by weight of the aqueous solution is 90 A treatment liquid containing a resin emulsion having a ratio of / 10 to 40/60 in a proportion of 5 to 120 parts by weight of a resin solid content and an organic reducing agent in a proportion of 10 to 60 parts by weight is applied to the surface of a dough iron plate. A method for forming an insulating film on an electromagnetic steel sheet, characterized in that a film is obtained through a baking process according to (1).

On the other hand, in recent years, there has been a tendency for environmental awareness to increase, and there has been a demand for an insulating film containing less chromium compound or an insulating film containing no chromium compound at all in the manufacturing process of electromagnetic steel sheets or consumers. . For example, an insulating coating containing no resin and silica has been proposed as an insulating coating which does not contain a chromium compound and has good punching properties (Japanese Patent Laid-Open No. 10-34812, etc.).

[0005]

However, when a water-based coating liquid containing substantially no chromium compound, for example, a water-based coating liquid containing a resin and an inorganic colloid as components, is applied to an electromagnetic steel plate and baked, the water-based coating liquid becomes When it is acidic, there is a problem that the Fe component of the steel sheet is eluted to form an opaque film portion, and the appearance and the film state may be inferior. In particular, when an insulating film having a small film thickness is obtained, it often becomes a problem. On the other hand, there are many demands for using an acidic aqueous coating liquid due to the properties of the resin and the inorganic substance contained in the aqueous coating liquid.

The present invention has been made to solve the above problems. That is, the present invention does not substantially contain a chromium compound, and when an acidic water-based coating liquid containing a resin and an inorganic colloid as a component is applied to an electromagnetic steel sheet and baked to form a thin insulating film, Fe is eluted. It is an object of the present invention to provide a method for producing an electrical steel sheet with an insulating coating, in which the appearance and the state of the coating are suppressed and the appearance and the state of the coating are improved.

[0007]

The present inventors have found that when the coating liquid contains a chromium compound, even if the coating liquid is acidic, chromium forms a passive film and Fe elution hardly occurs. It was considered that when the coating liquid did not substantially contain a chromium compound, Fe elution would occur because of no such effect. Further, in the case of an electromagnetic steel sheet, since plating for rust prevention is not performed unlike a normal surface-treated steel sheet,
It is difficult to obtain a good coating by suppressing elution. And
The above problem is particularly remarkable when obtaining a thin insulating film, when the time from application to baking is long, or when applying and baking with coke as a fuel using coke gas, which is widely used in ironworks, as a fuel. It turned out that.

Further, the inventor of the present invention has made intensive studies in order to solve the above-mentioned problems which occur when an insulating coating having a small thickness is obtained by using an acidic aqueous coating liquid. As a result, when the time from coating to baking is long due to the convenience of the apparatus, the reaction time between the coating solution and the steel sheet is prolonged and oxidation is easy to proceed. It has been found that oxidation easily proceeds due to SO ₂ gas or the like which is generated when combustion is performed. The present inventor has considered that essentially the same occurs in these two oxidation mechanisms. That is, it was considered that when the insulating film was thin, the exchange of oxygen in the coating liquid was large, and the oxidation reaction was more likely to proceed. And the present inventor:
The inventors have found that the above oxidation reaction can be suppressed by setting the solid content concentration of the aqueous coating liquid to a specific range, and completed the present invention.

That is, according to the present invention, an electromagnetic steel sheet is coated with a water-based coating solution containing a resin and an inorganic component and having a pH of 2 to 7 and baked.
The coating baking amount is 2 g / m ² or less and the chromium content is 0 to
A method for producing an electrical steel sheet with an insulating coating, wherein an insulating coating of 1% by mass is formed, wherein the solid concentration of the aqueous coating liquid is 1%.
A method for producing an electrical steel sheet with an insulating coating, characterized in that the content is 0 to 30% by mass.

It is preferable that the aqueous coating solution has a pH of 3 to 6.

The resin is preferably supplied as an aqueous resin, and the inorganic component is preferably supplied as an inorganic colloid.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, an electromagnetic steel plate (electric iron plate) is used as a starting material. The electromagnetic steel sheet used in the present invention is not particularly limited.

The aqueous coating solution used in the present invention contains a resin and an inorganic substance and has a pH of 2 to 7.

The aqueous coating liquid used in the present invention is a coating liquid containing water as a solvent. Therefore, other solvents may be contained in addition to water. The embodiment of the aqueous coating liquid used in the present invention is not particularly limited, and examples thereof include an emulsion (emulsion), a dispersion, and an aqueous solution.

The resin contained in the aqueous coating solution used in the present invention is not particularly limited.
Alkyd resin, polyolefin resin, styrene resin, vinyl acetate resin, epoxy resin, phenol resin, urethane resin, and melamine resin are exemplified. These may be used alone or in combination of two or more. The resin preferably has a glass transition point of 30 to 150 ° C. The resin is preferably supplied as an aqueous resin in view of the dispersibility of the coating liquid. The aqueous resin can be in the form of an emulsion, dispersion, or water-soluble. The shape, particle size, emulsifier, protective colloid, charge and the like of the particles are not particularly limited, and can be selected according to the resin and the application.

The inorganic component contained in the water-based coating solution used in the present invention is not particularly limited, and examples thereof include silica, alumina, titanium oxide and antimony oxide. These may be used alone or in combination of two or more. The inorganic component is preferably supplied to the aqueous coating liquid as an inorganic colloid. For example, colloidal silica, alumina sol, and titanium oxide sol can be used.

Of the above-mentioned inorganic components, silica is preferred. In particular, alumina-treated silica (silica surface coated with alumina) and / or alumina-containing silica are preferred from the viewpoint of excellent colloidal stability in an acidic aqueous coating liquid.

The water-based coating liquid used in the present invention is used for forming an insulating film having a chromium content of 0 to 1% by mass as described later, and therefore contains substantially no chromium compound. It is. Further, the aqueous coating liquid used in the present invention may contain additives such as a rust preventive for further improving the performance of the coating. When the additive is contained, the total amount of the inorganic substance in the coating liquid is reduced to 10% in order to secure the performance after the strain relief annealing.
It is preferably from 3 to 300 parts by mass with respect to 0 parts by mass.

The aqueous coating solution used in the present invention has a pH of 2 or more and a pH of 7 or less. This is because in the above range, the Fe component of the steel sheet described above is eluted, and the appearance and the state of the coating film are deteriorated. Further, since this problem is likely to occur when the aqueous coating liquid has a pH of 6 or less, the present invention is suitably used when the aqueous coating liquid has a pH of 6 or less. It is preferable that the aqueous coating liquid has a pH of 3 or more, since the dispersibility becomes particularly excellent.

The present invention is characterized in that the aqueous coating solution used in the present invention has a solid content of 10 to 30% by mass. Here, the “solid content concentration” is a ratio of the mass of the coating liquid excluding components volatilized at the time of coating and baking such as water and an organic solvent to the mass of the entire coating liquid. When the solid content concentration of the water-based coating liquid is 10% by mass or more, elution of Fe can be suppressed, an insulating film excellent in appearance and film state can be obtained, and the uniformity of the film thickness after baking is also very high. Does not deteriorate. On the other hand, if the solid content concentration of the water-based coating solution is too high, there is a problem that the viscosity increases and foaming easily occurs, or precipitation tends to occur, and the appearance and the film state, and the film thickness after baking Is also degraded. When the solid content concentration of the aqueous coating solution is 30% by mass or less, such a problem does not occur.

In the method for producing a magnetic steel sheet with an insulating coating according to the present invention, the above-mentioned water-based coating solution is applied and baked on the magnetic steel sheet, and the baked amount of the coating is 2 g / m ² or less and the chromium content is 0 to 1. An insulating coating having a mass% is formed.

In the present invention, a pretreatment can be performed on the steel sheet before coating and baking. The pretreatment for the steel sheet may or may not be performed. The pretreatment of the steel sheet is not particularly limited, and examples thereof include a degreasing treatment using an alkali or the like; and a pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, or the like.

An untreated steel sheet or a steel sheet which has been subjected to the above pretreatment is subjected to coating and baking. In the present invention, the method of coating and baking is not particularly limited, and coating and baking methods generally used industrially can be used. Examples of the coating method include a roll coater method, a flow coater method, a spray method, and a knife coater method. Examples of the printing method include hot air, infrared, and induction heating printing methods.

In the present invention, the baking amount of the coating is 2 g / m
² or less. This is because when the film thickness is so thin that the baking amount of the film is 2 g / m ² or less, the appearance and the state of the film are likely to be deteriorated due to the elution of Fe. When the baking amount of the coating exceeds ² g / m ² , the adhesion of the coating is reduced, and the coatability may be reduced such as blistering during drying at a high temperature. The coating baking amount is preferably 1.8 g / m ² or less. Further, the baking amount of the coating is 0.05 g / m ^2.
It is preferable that this is the case. If the adhesion amount is less than 0.05 g / m ² , the thickness of the coating becomes uneven and the base iron is easily exposed, and the sticking property and the boiling steam exposure property may be insufficient. More preferably, the coating baking amount is 0.1 g / m ² or more.

The insulating coating obtained according to the present invention has a chromium content of 0 to 1% by mass. Here, “chromium content” refers to the Cr of hexavalent chromium compound contained in the insulating coating.
It is a mass ratio with respect to the whole insulating coating in conversion. When the chromium content is large, there is no problem that the appearance and the film state are inferior due to the elution of Fe. However, when the chromium content is too large, the load on the environment is increased in the manufacturing process of the electromagnetic steel sheet. The present invention results from Fe elution in the manufacture of insulating films that are substantially free of chromium compounds, i.e., either containing no chromium compounds or containing only a small amount of chromium compounds. The purpose of the present invention is to solve the problems of appearance and film state, and the chromium content is set in the above range.
Therefore, in the present invention, chromium in the insulating coating is an optional component and may not be contained at all,
It may be contained at a concentration of 1% by mass or less.

According to the method for producing an electromagnetic steel sheet with an insulating coating of the present invention, the appearance and coating state of the obtained insulating coating are excellent. As described above, when an acidic water-based coating liquid substantially containing no chromium compound is applied to an electromagnetic steel sheet and baked to obtain a thin insulating coating, the Fe component of the steel sheet is eluted and an opaque coating is formed. There is a problem that a portion may be generated and the appearance and the state of the film may be inferior. In particular, this problem was remarkable when the time from application to baking was long, and when baking was performed with a coke gas open flame. This is because, in an acidic aqueous coating liquid containing substantially no chromium compound, the passivation effect of chromium is not exhibited, so that Fe of the steel sheet is easily eluted.

Conventionally, when a thin insulating film having a thickness of about ² g / m ² or less is applied and baked, a coating liquid is applied to prevent contact seizure between a coating roll or the like and a steel plate and to ensure uniformity of the film thickness. Was adjusted to about several mass%. The present inventors have conducted intensive studies on a method for suppressing the Fe elution reaction, and as a result, surprisingly found that the solid content concentration of the water-based coating liquid has a significant effect on the Fe elution reaction, leading to the present invention. It is. That is, in the present invention, by making the solid content concentration of the aqueous coating liquid 10% by mass or more, the elution of Fe is suppressed, and the appearance and the state of the film are improved.
The uniformity of the film thickness after baking was also ensured. In the present invention, the mechanism by which the elution of Fe is suppressed when an aqueous coating solution having a solid content of 10% by mass or more is used
It is considered that the elution reaction, that is, the amount of water required for the generation of rust is reduced. Conversely, when the solid concentration is low and the amount of water is large, the contact time with water, that is, the reaction time with water becomes longer, and it is considered that the Fe elution reaction itself proceeds rapidly.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. 1. Manufacture of Electrical Steel Sheet with Insulating Coating (Example 1) After an electromagnetic steel sheet having a thickness of 0.5 mm, a width of 150 mm and a length of 300 mm was alkali-degreased, the epoxy resin and colloidal silica (alumina-treated silica) shown in Table 1 were used. A coating solution having a solid content concentration of 10% by mass and having a pH of 4.0 (solid mass ratio: epoxy resin / colloidal silica =
(50/50) was applied with a roll coater. Thereafter, propane gas direct baking was performed so that the ultimate plate temperature was 200 ° C., and the mixture was allowed to cool to form a coating containing an epoxy resin and alumina-treated silica, thereby obtaining an electrical steel sheet with an insulating coating.

(Examples 2 to 14 and Comparative Examples 1 to 14)
Coating liquid components (resin and inorganic components), solid concentration of coating liquid,
An electromagnetic steel sheet with an insulating coating was obtained in the same manner as in Example 1, except that the pH of the coating solution and the amount of the baked film were as shown in Table 1. However, in Comparative Example 2, the solid content concentration of the coating solution was too high, and uniform application was not possible. Also,
In Comparative Examples 13 and 14, the coating liquid was in a poorly dispersed state and could not be applied.

2. Evaluation (1) Dispersion state of coating liquid The dispersion state of the used coating liquid was visually evaluated. The results of the evaluation are shown in Table 1 by the following symbols. ：: Uniformly dispersed Δ: Slightly aggregated and thickened ×: Gelled by aggregation

(2) Adhesion of Coating After adhering the cellophane tape to the coating surface of the magnetic steel sheet provided with an insulating coating, the coating was peeled off, and it was visually observed whether or not the coating was peeled off, and the adhesion of the coating was evaluated. The results of the evaluation are shown in Table 1 by the following symbols. ：: Not peeled off △: Slightly peeled ×: Peeled

(3) Appearance / Coating State The time from the application by the roll coater to the start of baking was changed to 15 seconds, 30 seconds, and 60 seconds to manufacture an electromagnetic steel sheet with an insulating coating, and Fe elution was performed. The appearance and the presence or absence of deterioration of the film state were evaluated by visual observation. The results of the evaluation are shown in Table 1 by the following symbols. ：: good (colorless and transparent film was obtained) △: slightly bad (opaque part and discoloration were slightly observed) ×: bad (many spotted opaque parts were seen and ugly) ×× : Very bad (the entire surface of the film was opaque and clearly poor)

As is evident from Table 1, the manufacturing methods of the magnetic steel sheet with an insulating coating of the present invention (Examples 1 to 14) are all excellent in the appearance and coating state of the obtained magnetic steel sheet with an insulating coating. I understand. On the other hand, when the solid content concentration of the aqueous coating liquid is too low (Comparative Examples 3 to 7 and 10 to 1
2) is inferior in appearance and film state because Fe is eluted. Further, when the solid content concentration of the aqueous coating liquid is too high (Comparative Examples 1 and 2), the adhesion of the coating is poor or the coating cannot be applied uniformly. When the coating baking amount is too large, the adhesion of the coating is inferior (Comparative Examples 8 and 9). When pH is too low (Comparative Examples 13 and 14)
Cannot be applied because of poor dispersion of the coating liquid.

[0034]

[Table 1]

[0035]

[Table 2]

In Table 1, "Epoxy / Silica" in the column of the insulating coating is epoxy resin / colloidal silica = 50/5.
Acrylic / silica means an acrylic resin / colloidal silica = 50/50 (mass ratio of solid content) using a coating solution of 0 (mass ratio of solid content). Means the resulting coating. The column of “Chromium in coating” indicates the content in terms of Cr when the coating further contains magnesium dichromate as an inorganic component.

[0037]

According to the method for producing an electrical steel sheet with an insulating coating of the present invention, an acidic aqueous coating liquid substantially containing no chromium compound is applied to the electrical steel sheet and baked to form a thin insulating coating. In addition, it is possible to obtain an insulating coating of an electrical steel sheet having excellent appearance and coating state.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C21D 9/46 501 C21D 9/46 501B C23C 22/50 C23C 22/50 H01F 1/16 H01F 1/16 A (72) Inventor Masaki Kono 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. (Without address) Inside the Mizushima Works, Kawasaki Steel Co., Ltd. Kawasaki Steel Co., Ltd. Mizushima Works in the F-term (reference) 4D075 CA13 CA18 CA23 CA38 CA48 DA06 DB03 EA06 EA10 EA13 EB13 EB14 EB19 EB22 EB32 EB33 EB36 EB38 EB53 EB56 EC01 4F100 AA01B AA20H AA22B AB03A AK01B AK53 BA02 CA23 GB51 JA13B JB05B JG04B JG06A JM10B YY00B 4K026 AA03 AA22 BB05 CA13 CA39 CA41 DA02 DA06 DA16 EB11 4K033 RA03 TA03 5E041 AA02 BC08 CA02 HB14 NN05

Claims (3)

[Claims] An aqueous steel coating solution containing a resin and an inorganic component and having a pH of 2 to 7 is applied and baked on an electromagnetic steel sheet, and the amount of baked film is 2 g.
/ M ² or less and a chromium content of 0 to 1% by mass, which is a method for producing an electrical steel sheet with an insulating film, wherein the solid content of the aqueous coating solution is 10 to 30% by mass. A method for producing an electrical steel sheet with an insulating coating, characterized in that: 2. The method according to claim 1, wherein the aqueous coating solution has a pH of 3 to 6. 3. The method according to claim 1, wherein the resin is supplied as an aqueous resin, and the inorganic component is supplied as an inorganic colloid.