JP2000192249A - Silicon steel sheet with insulating film excellent in corrosion resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silicon steel sheet with an insulating film excellent in corrosion resistance in the insulating film, particularly that in the flawed part and to provide a method for producing it. SOLUTION: The total of residual organic acid and the anions thereof contained in an insulating film baked on the surface of a silicon steel sheet and contg. a resin is controlled to <=0.05 wt.% to the coating weight of the insulating film expressed in terms of the amt. of oxalic anions. In the case of a chromic acid insulating film, preferably, the content of chromic acid and the salt thereof in the insulating film is controlled to 30 to 80 wt.% expressed in terms of chromic acid, the content of bivalent or trivalent metallic oxide and/or hydroxide is controlled to 5 to 40 wt.%, and the content of the organic resin is controlled to 5 to 30 wt.%. As for the method for producing it, preferably, a silicon steel sheet coated and baked with a treating agent contg. an organic reducing agent is washed by water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical steel sheet used for an iron core of a transformer or a rotating machine used for industrial electrical equipment, and more particularly to an electrical steel sheet with an insulating film having excellent corrosion resistance and a method of manufacturing the same.

[0002]

2. Description of the Related Art Magnetic steel sheets are used as iron core materials for electric equipment such as motors and transformers. The iron core for electrical equipment is made by punching out an electromagnetic steel sheet with an insulating coating into a predetermined shape.
After lamination, they are assembled by welding or swaging.
In some cases, the magnetic steel sheet after punching is subjected to strain relief annealing for improving magnetic properties.

[0003] The coating for electrical steel sheets must have excellent punching properties, weldability, and corrosion resistance in addition to excellent electrical insulation to suppress eddy current loss.

[0004] Insulating coatings for non-oriented electrical steel sheets are mainly composed of dichromate and organic resin having good punching properties (No. 155, 1 sponsored by the Iron and Steel Institute of Japan).
56th Nishiyama Memorial Technical Lecture "Recent Advances in Soft Magnetic Materials"
Published July 1, 1995 (p. 181).

[0005] Generally, an electromagnetic steel sheet is coated with an insulating film by a steel maker to be manufactured as a coil, and then turned into a product through a slitting step, a punching step, a welding / caulking step, a cutting step, and the like at a customer. In the meantime, strain relief annealing for improving magnetic properties may be performed, and the one subjected to the strain relief annealing is called a semi-processed product, and the one not subjected to the strain relief annealing is called a full process product.

As described above, since the electrical steel sheet goes through a number of steps until commercialization, the insulating film on the surface of the steel sheet may have scratches or handling scratches (hereinafter, simply referred to as scratches). When the coil is handled under high temperature and humidity,
Rust may occur based on those flaws.

[0007] A conventional film mainly composed of a dichromate and an organic resin has a problem that the corrosion resistance of the flaw is inferior. One of the causes is insufficient baking of the film. That is, when a treatment agent containing hexavalent chromium is applied to reduce insoluble trivalent chromium, baking must be performed at a relatively high temperature. However, if the baking temperature is excessively increased (for example, 300 ° C. or higher). In addition, a part of the organic resin is thermally decomposed to cause yellowing of appearance, swelling and the like, and the adhesiveness is reduced, so that the baking temperature cannot be too high. Further, high-temperature baking has problems such as an increase in energy cost, a decrease in production speed, and a burden on equipment.

As a countermeasure against this, for example, Japanese Patent Laid-Open No. 6-101
No. 057, the insulating film is made of an organic resin, Al, Mg,
An electromagnetic steel sheet with an insulating film containing a chromate of Ca and Zn and defining the surface roughness of the film and the shape of the projections of the coarse organic resin emulsion is disclosed. Punching property before and after strain relief annealing, weldability, sticking It is said to have excellent properties, lubricity, scratch resistance, corrosion resistance and the like.

JP-A-10-128903 discloses an electromagnetic steel sheet with an insulating film which can be produced at a relatively low temperature by incorporating an organic resin, silica and an alkali metal oxide into the insulating film.

[0010]

However, Japanese Patent Application Laid-Open No.
Even if the technology disclosed in Japanese Patent Application Laid-Open No. -101057 and Japanese Patent Application Laid-Open No. H10-128903 is used, in the process of commercializing the electrical steel sheet, the steel sheet may inevitably have flaws. In some cases, it may not have excellent flaw corrosion resistance.

[0011] In order to solve these problems of the prior art, an object of the present invention is to provide an electromagnetic steel sheet provided with an insulating film, which is excellent in the corrosion resistance of the insulating film, particularly the corrosion resistance of the flaws, and a method of manufacturing the same.

[0012]

Means for Solving the Problems The inventors of the present invention have made artificial steel sheets having a chromic acid-based insulating film provided with artificial flaws reaching the substrate and investigated the flaw corrosion resistance. It was found that there was a difference in corrosion resistance. When these samples were sorted by baking temperature, those with a high baking temperature (for example, 300 ° C. or higher) were noted to have good flaw corrosion resistance. It was found that there was little acid.
The evaluation of the corrosion resistance was further organized by the residual organic acid concentration.

FIG. 1 is a graph showing the relationship between the concentration (wt%) of the residual organic acid and its anion in the insulating film in terms of the amount of oxalate anion and the flaw corrosion resistance rating. As shown in the figure, when the amount of the residual organic acid is 0.05% or less, the corrosion resistance is almost good.

This residual organic acid is derived from an organic reducing agent.
Chromic acid and its salts, which are widely used for forming an insulating film on magnetic steel sheets, and an insulating film formed of an organic resin, use an organic reducing agent (hereinafter simply referred to as a trivalent chromium) to reduce hexavalent chromium in the treating agent to trivalent chromium. (Referred to as a reducing agent). As the reducing agent, alcohol compounds (ethylene glycol, methanol, glycerin, ethanol, 1,4-
Butanediol, 1,2,3,4-butanetetrol,
Polyethylene glycol) is frequently used.

During the baking, these reducing agents are oxidized in the order of alcoholic compound → organic acid → carbon dioxide + water, but some of them are not completely oxidized and may remain as organic acids. In addition, it remains in the insulating film and deteriorates the corrosion resistance of flaws.

The inventors have further confirmed that the residual organic acid can be removed by washing the magnetic steel sheet with water.

The present invention has been made based on the results and findings obtained as described above. The gist of the present invention is as follows: (1) and (2) electrical steel sheets with an insulating film; and (3) and (4) electrical steel sheets. Manufacturing method.

(1) The total amount of residual organic acids and / or their anions contained in the insulating film containing the resin baked on the surface of the magnetic steel sheet is 0.05% by weight of the amount of the oxalate anion adhered to the insulating film. An electromagnetic steel sheet with an insulating film having excellent corrosion resistance, characterized by the following.

(2) The insulating film contains at least one compound of chromic acid and salts thereof and dichromic acid and salts thereof in an amount of 30 to 80% by weight in terms of chromic acid, and a divalent or trivalent metal oxide and And / or 5 to 30% by weight of an organic resin containing one or a plurality of compounds selected from hydroxides, and having excellent corrosion resistance as described in the above item (1). Electrical steel sheet with insulating coating.

(3) A surface treatment agent in which the constituents of the insulating film are dissolved and dispersed is applied to the surface of the magnetic steel sheet, and baked to form an insulating film. Characterized in that the total amount of residual organic acids and / or their anions contained therein is 0.05% by weight or less of the amount of the attached insulating film in terms of the amount of oxalic acid anions. Production method.

(4) At least one compound selected from chromic acid and salts thereof or dichromic acid and salts thereof, and one or more compounds selected from oxides and / or hydroxides of divalent or trivalent metals By applying an insulating film surface treating agent containing a compound of, an organic resin emulsion, and an organic reducing agent to the surface of the magnetic steel sheet, forming an insulating film by baking, and then washing the magnetic steel sheet with water, An electromagnetic steel sheet with an insulating film having excellent corrosion resistance, characterized in that the total amount of residual organic acids and / or anions thereof contained in the insulating film is 0.05% by weight or less of the amount of the oxalate anion in terms of the amount of the oxidized anion. Manufacturing method.

Here, the conversion method of the organic acid and its anion to the amount of oxalate anion is carried out as follows.

The coating amount of the insulating film is A ₀ (g / m ² ),
The amount of the organic acid (including its anion) measured by liquid chromatography or the like is defined as A ₁ (g / m ² ). Assuming that the molecular weight of the organic acid is M and the acid value of the organic acid is x, the oxalate anion content Y (%) in the insulating film is as follows: Y = (A ₁ / A ₀ ) ｛88 / (M−x) ｝ (X / 2) × 100 = 44 × / (M−x) × (A ₁ / A ₀ ) × 100 (%)

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The surface of a magnetic steel sheet provided with an insulating film having excellent corrosion resistance and a method for producing the same according to the present invention will be described in detail below.

(A) Electromagnetic Steel Sheet Base Material The electromagnetic steel sheet used in the present invention may be a normal electromagnetic steel sheet.
Si may be added to ensure electromagnetic characteristics. The type of the magnetic steel sheet may be any of non-directional, unidirectional and bidirectional. Before applying a surface treatment agent for forming a uniform and beautiful insulating film, pretreatment such as pickling, alkali cleaning, or brushing may be performed.

(B) Insulating Film The insulating film of the magnetic steel sheet of the present invention contains an organic resin, and the total content of residual organic acids and / or anions thereof is 0.05% by weight of the amount of the insulating film adhered in terms of oxalate anions. The following is assumed.

The organic resin has the effect of improving the punching property of the magnetic steel sheet and enhancing the scratch resistance.

The conversion to the amount of oxalate anions is for evaluating the total equivalent of these acid values, although various organic reducing agents are converted into organic acids having various acid numbers during the decomposition process.

If the total content of the residual organic acids and / or their anions exceeds 0.05% by weight of the amount of the insulating film adhered in terms of oxalate anions (hereinafter referred to as the total amount of anions), there is a flaw reaching the base iron. When the magnetic steel sheet is exposed to a humid atmosphere, it rusts or corrodes. The lower limit of the total amount of anions is not particularly limited, and the smaller the better, the more the amount is desirably reduced.

The adhesion amount of the insulating film is usually 0.1 to 5.0 g.
/ M ² . The electrical steel sheet provided with the insulating coating of the present invention can be applied to any electrical steel sheet provided with an insulating coating, such as a chromium-based coating or a resin + silica-based non-chromium-based coating.

Hereinafter, an application example of a chromium-based film (a film composed of chromic acid and its salt or dichromic acid and its salt, metal oxide and organic resin) to an electromagnetic steel sheet will be described.

The components of the insulating film include (a) at least one compound selected from chromic acid and salts thereof or dichromic acid and salts thereof, and (b) oxides or hydroxides of divalent or trivalent metals. One or more compounds,
(c) an organic resin. Further, the treating agent used for forming the film contains an organic resin emulsion and further contains a reducing agent. Hereinafter, each component will be described in detail.

(A) Chromic acid and its salt or dichromic acid and its salt Chromic acid and its salt or dichromic acid and its salt include not only chromic acid represented by CrO ₃ but also Al, Mg,
Chromates such as Ba, Ca, Zn and the like or dichromates can be used.

The content of chromic acid and its salt or dichromic acid and its salt is preferably 30 to 80% by weight in terms of chromic acid. If the content is less than 30% by weight, the corrosion resistance and insulation performance of the insulating film are insufficient. Upper limit of 8
If it exceeds 0% by weight, the corrosion resistance is saturated, and the film properties may deteriorate due to shrinkage during dehydration. Preferably, it is 45 to 70% by weight.

(B) Divalent or trivalent metal oxide or hydroxide Divalent or trivalent metal oxide or hydroxide neutralizes chromic acid (or dichromic acid) to form an organic resin. Has the effect of stabilizing As the divalent or trivalent metal oxide, oxides and hydroxides of Al, Mg, Ba, Ca, Zn and the like can be used. Generally, Mg salts are often used. The content of the divalent or trivalent metal oxide or hydroxide is desirably 5 to 40% by weight.
If the lower limit is less than 5% by weight, the stability of the treating agent may be lost. If it exceeds the upper limit of 40% by weight, the dissolved hydroxide may precipitate due to a change in temperature. Preferably, it is 15 to 30% by weight.

(C) Organic Resin As the organic resin, any of epoxy-based, melamine-based, phenol-based, polyester-based, acrylic-based, acryl-styrene-based, vinyl acetate-based, silicon-based, and fluorine-based resins can be used. Further, two or more kinds may be used in combination.

Further, in addition to the above substances, boric acid, borate, colloidal alumina and colloidal silica may be contained for the purpose of improving heat resistance. Organic resin content is 5-3
It is desirably 0% by weight. If the lower limit is less than 5% by weight, desired punching properties and adhesion of the coating may be deteriorated. If the content exceeds the upper limit of 30% by weight, blowholes may be generated during welding. Preferably 10
20% by weight.

In general, the thickness of the insulating film is preferably 0.1 to 5.0 g / m ^{2 in} terms of the amount deposited on one side. 0.1g /
If it is less than m ^2, the insulation between the laminated magnetic steel sheets will be insufficient, and if it exceeds 5.0 g / m ² , the lamination volume of the magnetic steel sheets will increase and the magnetic properties will decrease.

Next, a method of manufacturing the magnetic steel sheet with an insulating film according to the present invention will be described. (a) Organic resin-containing treating agent The treating agent containing an organic resin to be applied to the magnetic steel sheet of the present invention is preferably one based on an aqueous emulsion. 0.05 to 1.0 μm as the particle size of the organic resin emulsion
It is preferable to use one adjusted to about m, more preferably 0.1 to 0.5 μm. If the particle size is too large, the stability in the processing solution is insufficient, and a problem may occur during coating. On the other hand, an emulsion having a small particle size is difficult to obtain industrially, and even if it is obtained, it is disadvantageous in terms of cost.

In the case of forming a chromic acid-based film, the content of each component in the treating agent is controlled by the oxidation of chromic acid and salts thereof, divalent or trivalent metals, excluding the solvent (water) and a reducing agent described below. What is necessary is just to use the processing agent which contains each component of a thing and / or a hydroxide, and resin in the compounding ratio equivalent to the said film component.

(B) Reducing agent in treating agent Chromic acid and its salt or dichromic acid and its salt according to the method of the present invention, from oxide (or hydroxide) of divalent or trivalent metal and organic resin It is necessary to use a water-based treating agent containing the above three types of substances and further include a reducing agent for reducing hexavalent chromium to trivalent chromium. If hexavalent chromium remains in the insulating film, the moisture resistance and corrosion resistance deteriorate.

Chromic acid in the treating agent becomes dichromic acid when the pH is 6 or less. Usually, the treatment is usually carried out with an acidic solution having a pH of 6 or less, so that it is considered that dichromic acid and salts thereof are formed. In the following description, chromic acid is collectively referred to as chromic acid and bichromic acid.

As the reducing agent, an ordinary alcohol compound can be used. Examples include ethylene glycol, methanol, glycerin, ethanol, 1,4-butanediol, 1,2,3,4-butanetetrol, polyethylene glycol and the like. The addition amount of the reducing agent, the amount of chromium chromic acid contained in the chromic acid and its salts (CrO ₃₎ per 100 parts by weight in terms of 10 to 100
Parts by weight, and more preferably 15 to 60 parts by weight. The corrosion resistance of the insulating film to be formed is preferably such that the residual organic acid and its anion are small. Therefore, it is preferable to reduce the amount of the reducing agent in the treating agent in consideration of the baking temperature, the facility capacity, and the like.

The above-mentioned (a) treating agent and (b) reducing agent are applied to a magnetic steel sheet and baked. Baking temperature is usually 150
３００300 ° C. and the baking time is about 20-180 s.

(C) Method of Reducing Organic Acids and Anions Residual in Insulating Film In the case of forming an insulating film composed of chromic acid and its salt and an organic resin, an insulating film treating agent is applied to a magnetic steel sheet and then baked. In many cases, a baking temperature and time sufficient to completely reduce hexavalent chromium in the film to trivalent chromium cannot be secured. In that case, chromium can be sufficiently reduced by adding a reducing agent in an amount larger than the reducing equivalent of chromic acid and a salt thereof. At this time, the easily soluble hexavalent chromium in the film is reduced to the hardly soluble trivalent chromium, and the corrosion resistance in a humid atmosphere is secured. However, since the organic acid and its anion that have not been sufficiently oxidized remain in the film, the corrosion resistance of the flaw often deteriorates.

After baking the film, the film is washed with water to remove organic acids and anions thereof in the film, thereby improving corrosion resistance. By setting the total amount of the residual organic acids and their anions contained in the insulating film to 0.05% by weight or less of the coating amount in terms of the amount of oxalate anions, the corrosion resistance, particularly the flaw portion corrosion resistance, is remarkably improved.

The electrical steel sheet provided with the insulating coating at a high temperature is usually subjected to a cooling treatment. In the method of the present invention, it is desirable to carry out a water washing treatment with a high-temperature water in order to reduce the amount of residual organic acids and their anions. This is because the solubility of the organic acid and its anion in water is generally higher at higher temperatures, and the organic acid and its anion can be efficiently removed.

In the actual manufacturing process, the temperature T of the washing water is used.
(° C.) and the washing time t (s) are expressed by the following equation (1) and
It is preferable to be within the range satisfying the expression (2). If the ratio is out of this range, the effect of washing with water will be saturated, but the production speed will decrease and the equipment cost will increase. 15 ≦ 3T ≦ 300-t (1) 0.5 ≦ t ≦ 180 (2)

[0049]

EXAMPLES (Example 1) A treating agent having the components shown in Table 1 was prepared, and the amount of adhering after baking was 0.9 g / m ^{2 on the} surface of a non-oriented electrical steel sheet containing 0.1% by weight of Si. 0.5 in film thickness
μm). After that, steel plate maximum temperature 2
After baking for 30 seconds in the range of 00 ° C to 280 ° C, a water washing treatment was performed under the conditions shown in Table 2.

[0050]

[Table 1]

The corrosion resistance test and the measurement of the amount of the residual organic acid and the anion thereof in the film were performed as follows.

(A) Corrosion resistance test Five flaws having a length of 50 mm reaching the base steel were attached to the steel sheet surface after baking using a cutter knife, and the steel sheet was heated at 50 ° C. and a humidity of 95% R.
The sample was exposed to a constant temperature and humidity chamber adjusted to H for 300 hours, and the number of rusts generated on the surface was counted using a 10-fold loupe. The average value was calculated and the corrosion resistance of the flaws was evaluated as follows, and the evaluation of ◎ and お よ び was evaluated as good.

◎ 0 rusts, ○ 1 to 10 rusts, △ 11 to 30 rusts, 31 to 50 rusts, xx 51 or more rusts .

(B) Method of measuring residual organic acids and their anions in the coating film 100 pieces of 100 mm square test pieces were immersed in a glass beaker containing 1 liter of water heated to 70 ° C. for 24 hours. Was measured by liquid chromatography. The measurement results were converted to oxalate anions for each organic acid, and the total amount was determined.

The column of organic acid in the film shown in Table 2 is the value of the residual organic acid and its anion in terms of the amount of oxalate anions (total amount of anions). Is expressed by a value (% by weight) divided by the total amount of the coating. Here, the total amount of coating film is calculated as follows.

Total coating amount = (coating amount) × (test piece area) × (both sides) × (number) = 0.9 g / m ² × 1000
0mm ² × 2 × 100 sheets = 1.8g

[0057]

[Table 2]

As shown in the results in Table 2, excellent corrosion resistance was obtained by reducing the total amount of anions of residual organic acids (oxalic acid in this embodiment) in the coating to 0.05% or less of the coating weight. An electromagnetic steel sheet with an insulating film was obtained.

(Example 2) A treating agent having the components shown in Table 3 was prepared, and the adhesion amount after baking was 1.26 g / m ^{2 on the} surface of a non-oriented electrical steel sheet containing 0.1% by weight of Si. It was applied to a thickness of 0.7 μm).

[0060]

[Table 3]

Then, at the maximum temperature of the steel sheet of 240 ° C.,
After baking the treating agent for a period of 50 seconds, a water washing treatment was performed under the conditions shown in Table 4. A corrosion resistance test and a measurement of residual organic acids and anions thereof in the film of each test piece were performed. The measuring method is the same as the method of the first embodiment.

[0062]

[Table 4]

As shown in the results of Table 4, the corrosion resistance of the flaws is improved by increasing the baking time and keeping the amount of the reducing agent added to the treating agent low. Further, it was found that the corrosion resistance, especially the flaw portion corrosion resistance, was improved by performing the water washing treatment.

[0064]

By applying the magnetic steel sheet with an insulating film and the method of manufacturing the same according to the present invention, it is possible to improve the flaw corrosion resistance of a non-oriented magnetic steel sheet used in a full process, in particular, in which a processing flaw easily occurs. .

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total amount of residual organic acids and their anions in an insulating film, converted to oxalate anions, and the flaw corrosion resistance.

Continued on the front page F term (reference) 4K026 AA03 AA22 BA06 BB05 BB08 CA16 CA18 CA20 CA22 CA36 CA38 CA39 CA40 DA02 DA16 EB00 EB11 4K033 AA02 TA03

Claims (4)

[Claims] 1. The total amount of residual organic acids and / or anions thereof contained in an insulating film containing a resin baked on the surface of an electromagnetic steel sheet is 0.05% by weight or less of the amount of oxalate anions adhered to the insulating film. An electrical steel sheet with an insulating film having excellent corrosion resistance. 2. The insulating film according to claim 1, wherein said insulating film contains at least one compound selected from chromic acid and salts thereof and dichromic acid and salts thereof in an amount of 30 to 80% by weight in terms of chromic acid, and divalent or trivalent.
2. The composition according to claim 1, further comprising 5 to 40% by weight of one or more compounds selected from oxides and / or hydroxides of a multivalent metal and 5 to 30% by weight of an organic resin. 3. An electrical steel sheet with an insulating film with excellent corrosion resistance as described. 3. A surface treating agent in which the constituents of the insulating film are dissolved and dispersed are applied to the surface of the magnetic steel sheet, and baked to form the insulating film. The production of electrical steel sheets with an insulating film excellent in corrosion resistance, characterized in that the total of residual organic acids and / or anions thereof contained in the steel is not more than 0.05% by weight of the amount of the insulating film adhered in terms of the amount of oxalate anions. Method. 4. A compound selected from the group consisting of at least one compound selected from chromic acid and salts thereof and dichromic acid and salts thereof, and one or more compounds selected from oxides and / or hydroxides of divalent or trivalent metals. A compound, an organic resin emulsion, and an insulating film surface treating agent containing an organic reducing agent are applied to the surface of the magnetic steel sheet, and baked to form an insulating film. An electromagnetic steel sheet with an insulating film having excellent corrosion resistance, characterized in that the total of residual organic acids and / or anions thereof contained in the film is 0.05% by weight or less of the amount of the insulating film adhered in terms of the amount of oxalate anions. Production method.