JP2008184631A - Electromagnetic steel sheet having insulation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic steel sheet which is superior in corrosion resistance against salt spray and has an insulation film formed from a chromate thereon. <P>SOLUTION: This electromagnetic steel sheet is manufactured by applying a coating liquid containing, for instance, magnesium chromate onto the surface of an electromagnetic steel sheet, baking it, and dipping the steel sheet in a treatment liquid containing phosphoric acid. The electromagnetic steel sheet having thus formed insulation film thereon is superior in stampability, and besides, has improved corrosion resistance against salt spray. At this time, the insulation film contains Cr and P which have a mole ratio of P/Cr=0.010 to 0.50. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrical steel sheet having an insulating coating made of chromate and a method for producing the same.

Insulating coatings on electrical steel sheets used for motors, transformers and the like are required to have not only interlayer resistance but also various characteristics. For example, convenience during processing, storage, stability during use, and the like. Furthermore, since electromagnetic steel sheets are used for various applications, various insulating coatings have been developed according to the applications.
For example, when a magnetic steel sheet is subjected to punching, shearing, bending, etc., the magnetic properties are deteriorated due to residual strain. Therefore, in order to recover the deteriorated magnetic characteristics, strain relief tempering is often performed at about 750 to 850 ° C. In this case, the insulating coating must withstand strain relief annealing.

  Insulating coatings are (1) inorganic coating (in principle not including organic resin) that can withstand strain relief annealing with emphasis on weldability and heat resistance, and (2) strain relief annealing with the aim of achieving both punchability and weldability. It is roughly classified into three types: a semi-organic film containing an organic resin that is resistant to (3), and an organic film that cannot be subjected to strain relief annealing for special applications. Among these, as a general-purpose product, it is a film containing the inorganic substances (1) and (2) that can withstand strain relief annealing, and both contain a chromium compound in the film. In particular, the chromate-based insulating coating containing the organic resin in the type (2) is widely used because punchability can be remarkably improved as compared with the inorganic insulating coating.

For example, Patent Document 1 discloses that a dichromate-based aqueous solution containing at least one divalent metal has a vinyl acetate / veova (TM) ratio of 90/10 to 100 parts by weight of CrO ₃ in an aqueous solution. A resin emulsion having a ratio of 40/60 is blended in a proportion of 5 to 120 parts by weight in terms of resin solids and 10 to 60 parts by weight of an organic reducing agent to form a coating liquid. There is described an electrical steel sheet having an electrical insulating coating that is applied to the surface of a (steel sheet) and formed through a conventional baking process.

However, although an insulating coating using chromate generally exhibits high corrosion resistance, it may be insufficient in a severe salt spray environment.
Japanese Patent Publication No. 60-36476

  In view of the above circumstances, an object of the present invention is to provide an electrical steel sheet having an insulating coating made of chromate, which is excellent in salt spray corrosion resistance.

The inventors of the present invention have intensively studied to solve the above problems. As a result, the following knowledge was obtained.
After applying and baking a coating solution containing chromate as a main component on the surface of the magnetic steel sheet, phosphoric acid and / or phosphate treatment causes the phosphoric acid compound and Cr to react, resulting in a very stable Cr phosphate. Form. And the barrier property of a film increases by this Cr phosphate, and corrosion resistance improves.

The present invention has been made based on the above findings, and the gist thereof is as follows.
An electrical steel sheet having an insulating coating formed by applying phosphoric acid and / or phosphate treatment after applying and baking a coating liquid mainly composed of chromate on the surface of the electrical steel sheet,
The electrical steel sheet having an insulating coating, wherein the insulating coating contains Cr and P in a molar ratio of P / Cr = 0.0.10 to 0.50.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical steel sheet which has an insulating film excellent in salt spray corrosion resistance is obtained. And since the insulating coating of this invention has chromate as a main component, it can be said that it is excellent in punching property, and can be used widely including uses, such as a motor and a transformer, and is industrially useful invention.

The present invention is described in detail below.
The electrical steel sheet of the present invention is an electrical steel sheet having an insulating coating formed by applying and baking a coating solution containing chromate as a main component on the surface of the electrical steel sheet and then performing phosphoric acid and / or phosphate treatment.
In the present invention, “having chromate as a main component” means that about 50 mass% or more (total solid content mass ratio) of chromate is contained in the coating solution.

First, the electrical steel sheet used in the present invention will be described.
The electromagnetic steel plate (also referred to as an electric iron plate) before forming a coating that can be used in the present invention is any steel plate (iron plate) adjusted to obtain a desired magnetic property by changing the specific resistance. A steel plate having a composition may be used and is not particularly limited.
For example, increasing the specific resistance is effective for improving the iron loss, so that at least one selected from Si, Al, Mn, Cr, P, Ni, Cu and the like, which are specific resistance improving components, is necessary. It is preferable to add them accordingly. The content of these elements may be determined according to the desired magnetic properties, but Si: about 5% by mass or less (including no addition, the same applies hereinafter), Al: about 3% by mass or less, Mn: about 1. 0% by mass or less, Cr: about 5% by mass or less, P: about 0.5% by mass or less, Ni: about 5% by mass or less, and Cu: about 5% by mass or less are common.
A typical electrical steel sheet is obtained by adding 0.1% by mass or more of Si, but Si: 0.05% by mass or more is preferable for a low-grade product.
Further, in order to improve magnetic properties, at least one or more selected from an inhibitor forming element or segregating element such as Mn, Se, S, Al, N, Bi, B, Sb, Sn, etc. should be added as necessary. Can do. Addition as an inhibitor forming element usually contains a total of 0.5% by mass or less of these elements.
The balance other than the above is iron and inevitable impurities. Examples of the impurity include C, N, O, and a small amount of S that is less effective as an inhibitor. Although it is better that these impurities are small, if not a high-grade product, C may be contained in an amount of about 0.02 to 0.05% by mass.
Moreover, the plate | board thickness of the electromagnetic steel plate of this invention is not specifically limited. It is preferably about 0.02 to 1.0 mm which is a normal thickness. Further, it is usually a flat shape, but may be a curved shape depending on the purpose.
In addition, the surface of the electrical steel sheet on which the insulating film is formed may be subjected to any pretreatment such as degreasing treatment with alkali, pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc., or untreated as manufactured. May be the surface.
Furthermore, although it is not always necessary to form the third layer between the insulating coating and the surface of the ground iron, it may be formed as necessary. For example, in a normal manufacturing method, a metal oxide metal oxide film may be formed between the insulating film and the metal iron surface, but it may be possible to omit the trouble of removing this.

Next, the insulating coating of the present invention applied to the surface of the steel plate will be described.
The insulating coating of the present invention contains Cr and P in a molar ratio of P / Cr = 0.0.10 to 0.50.

Cr Compound The insulating coating applied to the electrical steel sheet of the present invention contains a Cr compound. Examples of the Cr compound include Mg salt, Al salt, and Ca salt. After applying a coating solution containing these Mg, Al, and Ca dichromates, heat-baking is performed with a reducing agent such as ethylene glycol as necessary to form a coating.

P Compound The insulating coating applied to the steel sheet of the present invention contains a specific amount of P compound. Examples of the P compound include phosphoric acid, phosphoric acid Mg, phosphoric acid Al, and phosphoric acid Ca. Phosphoric acid is particularly preferred, and can take forms such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid. Such a P compound is contained in the insulating coating by applying and baking a coating solution containing chromate on the surface of the magnetic steel sheet and then performing phosphoric acid and / or phosphate treatment. Some of these phosphoric acid and phosphate react with the Cr compound to form Cr phosphate. This Cr phosphate is formed by a reduction reaction and is usually Cr (III). At the time when the chromate is baked, a part of the chromium hydroxide may be in the form of chromium, or if the baking is insufficient, a part of the Cr contained in the insulating film may take the form of Cr (VI). Phosphoric acid and / or phosphate treatment is performed, and a phosphoric acid compound and Cr react with each other in contact or coexistence to form very stable Cr phosphate. This is considered to increase the barrier properties of the coating and improve the corrosion resistance. Phosphoric acid or phosphoric acid components such as Mg phosphate, Al phosphate, and Ca phosphate can also form Cr phosphate.

The method of phosphoric acid and / or phosphate treatment is not particularly limited, but the method of dipping the phosphoric acid and / or phosphate-containing treatment liquid after applying and baking chromate, the treatment liquid The method of coating with a spray, a coater, etc. is mentioned. By these treatments, Cr phosphate is formed on the surface layer of the insulating coating. Further, baking and washing with water can be performed.
By such phosphoric acid and / or phosphate treatment performed after chromate baking, the phosphoric acid component adheres to the surface layer or is unevenly distributed on the surface layer, and is the outermost layer portion that is important for the barrier properties of the coating Can be effectively converted to Cr phosphate.

  In the present invention, Cr and P contained in the insulating coating in the present invention are set to have a molar ratio of P / Cr of 0.010 to 0.50. If it is less than 0.010, the reaction to Cr phosphate is reduced, and the effect of improving corrosion resistance cannot be expected. On the other hand, if it exceeds 0.50, the coating is easily peeled off by excess phosphoric acid or phosphate. More preferably, it is 0.020-0.40.

  Such a molar ratio P / Zr can be calculated from the added weight at the time of preparation, or the abundance ratio may be obtained by fluorescent X-rays or the like.

  From the above, the present invention can provide the desired properties, but in addition to the above-mentioned inclusions, it can contain a resin and an additive for the following purposes within a range not impairing the effects of the present invention.

Resin In the insulating coating of the present invention, a resin can be added within a range not impeding the effects of the present invention. In general, it is preferably in a state dispersed in a chromate film. As the resin, polyolefin resin such as polyethylene and polypropylene, polyester resin, alkyd resin, styrene resin, vinyl acetate resin, epoxy resin, phenol resin, polyester resin, urethane resin, melamine resin, etc. A combined aqueous resin (emulsion, dispersion, water-soluble) can be mentioned. The addition amount is preferably 30% or less in terms of the total solid content.

Additives In order to further improve the performance and uniformity of the coating, the insulating coating of the present invention is optionally provided with a surfactant (nonionic, cationic, anionic surfactant; silicone surfactant; acetylenic diol). ), Rust preventives (amine and non-amine rust preventives, etc.), boric acid, silane coupling agents (amino silane, epoxy silane, etc.), lubricants (wax etc.), alumina sol, silica sol, iron sol, titania sol, It is preferable to contain organic and inorganic additives such as oxide sols such as tin sol, cerium sol, antimony sol, tungsten sol and molybdenum sol. As these additives, known additives that are applied to conventionally known chromate-based insulating coatings can be used.
When these additives are used, in order to maintain sufficient film characteristics, it is preferable that the content is about 10% by mass or less based on the total solid mass of the insulating film of the present invention.

Next, the manufacturing method of the electrical steel sheet which has an insulating film of this invention is demonstrated.
The pretreatment of the electrical steel sheet used as the starting material of the present invention is not particularly defined. Untreated or alkaline degreasing treatment, pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid or the like is preferably applied.
And the coating liquid which has chromate as a main component is apply | coated on this steel plate. Next, the electrical steel sheet coated with the coating solution is baked. Thereafter, a predetermined amount of phosphoric acid and / or phosphate is applied (attached) onto the surface of the electrical steel sheet, and an insulating film is formed on the surface of the electrical steel sheet by performing phosphoric acid and / or phosphate treatment.
As a method for applying the insulating coating, a method using various facilities such as a roll coater, a flow coater, a spray, a knife coater, and a bar coater, which are generally used industrially, can be applied. In addition, a hot air method, an infrared heating method, an induction heating method, or the like, which is usually performed, is also possible for the baking method.
The baking temperature may be at a normal level, but it should be 200 ° C. or higher and 350 ° C. or lower in order to sufficiently reduce the chromate (200 ° C. or higher) and avoid thermal decomposition of the resin (350 ° C. or lower). Is preferred. A more preferable range is 250 ° C. or higher and 300 ° C. or lower.

Insulating coating weight per unit area The insulating coating weight (including the basis weight by phosphoric acid treatment) is not particularly limited, but is preferably 0.01 g / m ² or more per side. The basis weight is preferably 5 g / m ² or less. If it is less than 0.01 g / m < ² >, corrosion resistance and insulation may be insufficient. On the other hand, if it exceeds 5 g / m ² , workability in coating may be deteriorated. More preferably, it is 0.1 g / m ² or more and 3.0 g / m ² or less. Even more preferably, it is 0.2 g / m ² or more and 2.5 g / m ² or less.

The weight per unit area, that is, the total solid mass in the insulating coating of the present invention can be measured by a weight method in which only the coating is dissolved with hot alkali or the like and measured from the weight change before and after dissolution. Further, when the basis weight is small, measurement may be performed using fluorescent X-rays. In this case, it is preferable to calculate the basis weight using a calibration curve created using the alkali peeling method.
In addition, the insulating coating of the present invention is preferably on both surfaces of the steel sheet, but depending on the purpose, only one surface may be used. That is, depending on the purpose, only one surface may be applied, and the other surface may be another insulating coating, or the other surface may not be provided with an insulating coating.

Hereinafter, although the effect of the present invention is concretely explained based on an example, the present invention is not limited to these examples.
First, as the electrical steel sheet, a full process electrical steel sheet containing steel components containing Si: 0.25% by mass, Mn: 0.25% by mass, and Al: 0.25% by mass and subjected to finish annealing with a thickness of 0.5 mm was used. A coating solution containing chromate shown in Table 1 was applied to the surface of the electrical steel sheet and baked at 300 ° C. Then, the phosphoric acid (salt) process which dips a steel plate to the processing liquid containing the phosphoric acid or phosphate shown in Table 1 was performed, and the surplus processing liquid was squeezed with a ringer and dried to obtain a test material.
The obtained test material (electrical steel sheet having an insulating coating) was dissolved in boiling 50% NaOH, and the basis weight of the insulating coating was measured by the above-described weight method. The weight per unit area (including those by phosphoric acid treatment) was 1.0 g / m ² in total per side.
Moreover, with respect to the electrical steel sheet having the insulating coating obtained as described above, the following coating properties were measured and evaluated. The results obtained are shown in Table 1 together with the experimental conditions, and the results of Examples 1 to 11 and Comparative Examples 1 to 7 in Table 1 are shown in FIG.

<Corrosion resistance>
The salt spray test evaluated. The conditions are 5% NaCl, temperature 35 ° C. The state of occurrence of rust was visually judged, and the quality of the corrosion resistance was judged by the test time in which rust generation was 5% or less.
(Criteria)
A: 24 hr or more B; 12 hr or more and less than 24 hr C; 7 hr or more and less than 12 hr D; 3 hr or more and less than 7 hr In Table 1 and FIG. 1, A: A, B: O, C: Δ, D: x.

<Adhesion>
Evaluation was made with a cello tape (registered trademark) peel test. Cellotape (registered trademark) was applied to the surface of the insulating coating, bent to 10 mmΦ, and then peeled off, and the state of the insulating coating was visually determined.
(Criteria)
A: No peeling B: 20% or less peeling C; 20% or more peeling 40% or less D; 40% peeling or less In Table 1, A: ◎, B: ○, C: Δ, D: × As shown.

  As is clear from Table 1 and FIG. 1, the examples of the present invention are excellent in both corrosion resistance and adhesion. In particular, it can be seen that the above-described characteristics are further improved in the present invention example in which P / Cr is in a suitable range. On the other hand, in the comparative example, either corrosion resistance or adhesion is inferior.

  In addition to punchability, it also has excellent performance in terms of corrosion resistance, so it is expected to be used in various applications, mainly in motors and transformers.

It is a figure which shows the relationship between P / Cr, corrosion resistance, and adhesiveness. (Example 1)

Claims (1)

An electrical steel sheet having an insulating coating formed by applying phosphoric acid and / or phosphate treatment after applying and baking a coating liquid mainly composed of chromate on the surface of the electrical steel sheet,
The electrical steel sheet having an insulating coating, wherein the insulating coating contains Cr and P in a molar ratio of P / Cr = 0.0.10 to 0.50.

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