JPH0578855A - Composition for forming magnetic steel sheet insulating film and method therefor - Google Patents

Abstract

PURPOSE:To provide the insulating film forming composition not contg. a harmful matter such as chromium (VI) with the TIG weldability and insulating performance not deteriorated even if the film amt. is increased. CONSTITUTION:An aq. inorg. soln. contg. 100-350g/l of ammonium dihydrogen phosphate expressed in terms of P2O5 and an aq. synthetic resin emulsion at pH1-3 are mixed so that the ratio of the nonvolatile matter in the latter to the total amt. of both materials is controlled to 10-40wt.% to obtain an aq. composition, and 5-20 pts.wt. of a granular additive is admixed with 100 pts.wt. of the total nonvolatile matter to obtain a composition. This composition does not contain a harmful matter, the TIG weldability, etc., are not deteriorated, the pot life is long, the composition is easy to transport, workability is improved, and a film having various excellent characteristics is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention does not contain harmful components such as hexavalent chromium, and has TIG weldability, insulation, heat resistance,
The present invention relates to a composition for forming an electrical steel sheet insulating coating capable of obtaining an electrical steel sheet insulating coating having excellent adhesion and a method for forming an electrical steel sheet insulating coating.

[0002]

2. Description of the Related Art Heretofore, many techniques have been proposed for a composition for forming an insulating film of a magnetic steel sheet (hereinafter, may be simply referred to as a composition). The main constituents of these compositions are those containing chromate or phosphate as the main component in the old days, and in recent years chromate or phosphate, among which chromate is the main component of inorganic film-forming substances. There is a mixture of an inorganic aqueous solution containing an aqueous emulsion of an organic film-forming substance made of a specific synthetic resin, and an improved type thereof (see, for example, JP-A-1-298175). There are various drawbacks as follows.

First, the above conventional composition contains a large amount of hexavalent chromium, which is a pollution control substance, and there is a concern that it may affect the human body and pose a problem of environmental pollution. Therefore, regarding the former, it is necessary to take strict measures for safety and hygiene such as protective equipment so as not to adhere to the human body during mixing and stirring of the composition, painting work, and the like. Regarding the latter,
It is obligatory to carry out detoxification treatment for all the waste liquid, waste water, etc. generated by mixing and stirring the composition, painting work, etc., and it requires a great deal of treatment cost. There are also major economic problems. Further, in recent years, from the viewpoint of preventing environmental pollution, there is a tendency that restrictions on the use of these substances are tightened as in Europe and the United States.

Secondly, chromate has a particularly strong oxidizing property,
Since the dispersed state of the resin in the mixed aqueous emulsion becomes unstable, the pot life is short. In many cases, the mixed solution gels due to the aggregation of the resin within a few days or about 1 to 2 weeks after mixing, and thus the composition often becomes unusable during the coating operation. Although this point has been improved in recent years, it is still not sufficient.

Thirdly, since the pot life of the composition is short as described above, when the composition is used at a long distance, the inorganic aqueous solution and the synthetic resin aqueous emulsion are separately transported to the coating site. It is necessary to mix these just before use. Therefore, the transportation cost is high, the workability is poor, and the cost of the composition is high.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, does not contain harmful substances, and therefore there is little concern about environmental pollution, and detoxification treatment is unnecessary or mild, and pot life. It is an object of the present invention to provide an insulating film-forming composition having a long length, and an insulating film-forming composition that does not reduce the TIG weldability or the insulating property after annealing even if the amount of the film is increased.

[0007]

The inventors of the present invention firstly found that an inorganic compound which is less likely to cause environmental pollution and which was mixed with an appropriate amount of resin aqueous emulsion instead of chromate has good insulation. As a result of repeated searches for inorganic compounds that form a film, aluminum dihydrogen phosphate Al
It was clarified that (H ₂ PO ₄ ) ₃ is most suitable as an inorganic film-forming substance, and one of the present inventions was completed. That is,
One of the present invention is to add an inorganic aqueous solution containing aluminum dihydrogen phosphate in an amount of 100 to 350 g / l in terms of P ₂ O ₅ and a synthetic resin aqueous emulsion having a pH of 1 to 3 to a total of non-volatile substances. The amount of non-volatile matter in the latter is 10-4
The present invention relates to a composition for forming an electrical steel sheet insulating film, which comprises an aqueous liquid mixed so as to be 0 parts by weight (hereinafter, such an aqueous liquid may be referred to as a semi-organic aqueous liquid).

Aluminum dihydrogen phosphate is
It has a composition of l ₂ O ₃ · 3P ₂ O ₅ · 6H ₂ O, is dehydrated by heating and is stabilized as Al ₂ O ₃ · 3P ₂ O ₅ , and is firmly bonded to the base steel. Aluminum to M
Addition of chemical substances such as gO, H ₃ BO ₃ and CaO accelerates the hardening of the film and improves the heat resistance.
Focusing on such an advantage, the following results were obtained by studying the composition of the inorganic aqueous solution in which aluminum dihydrogen phosphate was dissolved for use as the main component of the inorganic film-forming substance.

The concentration of aluminum dihydrogen phosphate is P ₂
The amount in terms of O ₅ is 100 to 350 g / l. When the concentration of aluminum dihydrogen phosphate is less than 100 g / l, the resulting coating cannot firmly bond to the base steel, so the original performance of the insulation coating cannot be exhibited, and the heat resistance of the insulation coating is improved. MgO, H ₃ BO ₃ added for
Solubility of chemical substances such as, etc. decreases significantly, and it is not possible to add these required amounts. Moreover, when the concentration of aluminum dihydrogen phosphate exceeds 350 g / l, the insulating coating cannot be formed uniformly, but this is because the drying of the insulating coating is generally performed at a high temperature of 250 to 500 ° C. for a short time. It is considered that the dehydration reaction rapidly progresses and adversely affects the uniform formation of the film.

As the synthetic resin aqueous emulsion mixed with the inorganic aqueous solution, homopolymers of acrylic type, styrene type, alkyd type, phenol type, vinyl acetate type, epoxy type monomers and copolymers thereof are used. 20-50% by weight of resin (nonvolatile) in emulsions
However, the pH of the aqueous emulsion is 1
~ 3. This is because the pH of the inorganic aqueous solution is adjusted to 1 to 3, and the pH of the synthetic resin aqueous emulsion is
If the value exceeds 3, the dispersion state of the synthetic resin becomes unstable after mixing with the inorganic aqueous solution and the gelation is promoted. The mixed amount of the synthetic resin aqueous emulsion is in the range of 10 to 40% by weight of the nonvolatile matter of the synthetic resin aqueous emulsion with respect to the total amount of the nonvolatile matter of both the inorganic aqueous solution and the synthetic resin aqueous emulsion. The reason for this is
This is because when the amount of the non-volatile matter mixed in the synthetic resin aqueous emulsion is less than 10% by weight, sufficient coating properties such as insulation and punchability cannot be obtained, and when it exceeds 40% by weight, the TIG weldability deteriorates.

The insulating film obtained by coating and heating the composition thus obtained is a smooth film (hereinafter sometimes referred to as a smooth film). However, in the case of a smooth coating, the TIG weldability deteriorates when the coating amount exceeds about 2 g / m ² . Therefore, in order to improve this point in the case of a large coating amount by the space effect, a preferable particulate additive was searched for. That is, by adding this particulate additive, an uneven coating (hereinafter, also referred to as an uneven coating) is formed, and when electromagnetic steel sheets are laminated and their end faces are TIG-welded, they are placed between the sheets. The decomposition gas generated by TIG welding is to be diffused through the minute gaps formed by the uneven coating.

As such a particulate additive, those satisfying the following conditions are preferable. Those that uniformly disperse in the insulating film to form preferable irregularities, those that easily disperse when added and mixed in a semi-organic aqueous solution and do not easily precipitate and solidify, chemically between semi-organic aqueous solution Stable and does not adversely affect the insulation film properties. As a result of various searches for particulate additives based on such criteria, the following was found: polymethylmethacrylate (PMM)
A) Crosslinked resin particles and polyacrylonitrile (PA
It was found that crosslinked resin particles such as N) -based crosslinked resin particles, hollow glass beads, and mica powder having specific average particle diameters satisfy the above conditions and give good results. Completed the investigation.

That is, according to another aspect of the present invention, an inorganic aqueous solution containing aluminum dihydrogen phosphate in an amount of 100 to 350 g / l in terms of P ₂ O ₅ and a synthetic resin aqueous emulsion having a pH of 1 to 3 are prepared. An average particle diameter of 5 μm to 15 μm is added to an aqueous liquid mixed so that the latter nonvolatile matter is 10 to 50% by weight with respect to the total amount of the nonvolatile matter of both. The present invention relates to a composition for forming an electrical steel sheet insulating film, which is characterized in that 5 to 20 parts by weight of crosslinked resin particles are added and mixed. Yet another invention is
Instead of the crosslinked resin particles, the average particle size is 5 μm to 1
5 μm hollow glass beads or average particle size of 15 to 50
It is formed by adding and mixing μm mica powder.

If the resin particles to be added to and mixed with the semi-organic aqueous liquid have a normal linear structure, the heat resistance and acid resistance are inferior, so that a crosslinked structure is used. Hollow glass beads are preferred as the glass beads. This is because the hollow one is lighter and does not precipitate and solidify in the semi-organic aqueous liquid to maintain the dispersed state. It was also found that mica powder also practically satisfies the above conditions.

The average particle size of each particulate additive for forming appropriate irregularities on the insulating film is preferably in the range of 5 μm to 15 μm for the crosslinked resin particles and the glass beads. If the average particle size of each of these particulate additives is less than 5 μm, sufficient unevenness is not formed after coating and heating. If it exceeds 15 μm, TIG weldability and insulation are improved, but the space factor is reduced. However, the mica powder has a fold-out flaky shape and is slightly different from the above-mentioned two kinds of particles. As a result of various examinations, the average particle size in the case of mica powder was 15 μm to 50 μm.
It has been found that the range of is appropriate. In the case of the uneven coating, the decomposed gas is easily released as described above. Therefore, the addition amount of the synthetic resin aqueous emulsion may be increased to 40 parts by weight when the particulate additive is not added and mixed up to 40 parts by weight. The decrease in TIG weldability does not pose a practical problem.

The amount of the particulate additive added and mixed is preferably 5 to 20 parts by weight with respect to 100 parts by weight of all the non-volatile matters in the semi-organic aqueous liquid. If the amount of the particulate additive added and mixed is less than 5 parts by weight, unevenness will not be formed densely on the surface of the insulating film after coating and heating, and if it exceeds 20 parts by weight, the coating workability will deteriorate and the economy will be poor.

A method of forming an insulating film on a magnetic steel sheet using the composition for forming an insulating film having the above-described composition will be described. After applying the composition for forming an insulating film to a magnetic steel sheet by an appropriate means such as a roll coater,
An insulating film is formed by heating at a temperature of 500 ° C. When the composition does not contain a particulate additive and forms a smooth film, the amount of the film is adjusted to be in the range of 0.5 g to 2.0 g / m ² , and the composition contains a particulate additive. In the case of forming a concave-convex film, the amount of the film should be in the range of 0.5 g to 6.0 g / m ² .

[0018]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples. Each insulating film forming composition was prepared according to the composition shown in Table 1. In common with any of the above compositions, each aluminum dihydrogen phosphate aqueous solution contains MgO of 30 g / l and H for the purpose of improving the curing degree and heat resistance of the insulating film.
₃ BO ₃ 50 g / l and nonionic surfactant 0.3
Added to each concentration of g / l.

Each of the prepared insulating film-forming compositions was used to coat a magnetic steel sheet by a roll coating method,
An insulating film was formed by heating and drying in a hot air drying oven at an ambient temperature of 350 ° C. for 90 seconds. The amount of coating was adjusted by the pressure of the roll and the concentration of the insulating coating composition. The coating properties of the above-prepared insulating coating composition during coating are observed, the surface condition of the resulting coating is observed, and the coating amount is measured, as well as the space factor, adhesion, interlayer resistance, punching workability. , TIG weldability was evaluated.

The evaluation method of each of the above characteristics is as follows. Paintability: Roll coated on a magnetic steel sheet at a line speed of 30 to 150 m / min, and evaluated by the appearance after coating. ○: Good coating finish △: Some streak unevenness is observed (occurs when the particle size of the particulate additive is large or when the addition amount is excessive) ×: Streak unevenness is significant (particulate additive Occurs when the particle size is large or the amount added is too large)

Surface state of the film: The state of occurrence of surface defects such as swelling (due to dehydration condensation reaction) on the surface after coating and drying was observed with a 10 times magnifier and judged. ◯: No surface defects were found Δ: Some surface defects were found ×: Significant surface defects

Adhesion: A test piece was wound around a round bar having a radius of 5 mm, and the peeled state of the film was observed with a loupe of 10 times. ◯: No peeling of the coating △: Slight peeling of the coating was observed ×: Significant peeling of the coating

Interlayer resistance: Measured by the method of JISC2550.

Punching workability: Expressed by the maximum number of punching times when the burr height of the punching sample when continuous punching was carried out under the following conditions was 50 μm or less. Stroke: 500 strokes / minute, Mold: SKD-1
1, punching diameter: diameter 5mm, punching oil: light oil, press machine: high-speed automatic press manufactured by Mitsui Seiki Co., Ltd.

TIG Weldability: The degree of blowhole generation after TIG welding under the following conditions was evaluated. Welding current: 100 AMP, Electrode diameter: 2.4 mmφ, Core pressure:
50 kg / cm ² , welding speed: 100 cm / min, welding machine: TIG welding machine manufactured by Osaka Transformer Co., Ltd. ○: blowholes are not observed △: blowholes are slightly observed ×: blowholes are remarkable

Space factor: Measured by the method of JISC2550.

Pot life: The viscosity of the composition after bathing was measured, and the viscosity (aging) after leaving this composition for 1 month was measured and evaluated as follows. ◯: Almost no thickening observed Δ: Slight thickening observed ×: Significant thickening The obtained results are shown in Table 2.

[0028]

[Table 1]

Note) 1) Amount equivalent to P ₂ O ₅ 2) Weight% of non-volatile matter of the former with respect to total amount of non-volatile matter of both synthetic resin aqueous emulsion and aqueous solution of aluminum dihydrogen phosphate 3) PMMA: PMMA-based crosslinked resin Particle PAN: PA
N-based crosslinked resin particles 4) Parts by weight based on 100 parts by weight of all non-volatile substances in the semi-organic aqueous solution 5) Methyl methacrylate-butyl acrylate-styrene copolymer resin

[0030]

[Table 2]

From Table 2, according to the present invention, by using the aqueous solution of aluminum dihydrogen phosphate as the main component of the inorganic coating film-forming substance, the coatability and the film-forming state after heating are good, and moreover, in general. It can be seen that it has excellent insulating film characteristics. In particular, the uneven coating is remarkably excellent in TIG weldability and insulation. That is, even if the amount of the coating film is about 3 to 6 g / m ^2, no blowholes are observed during welding, and the formation of irregularities significantly improves the insulating property.

In Examples 9 and 14, since the coating is a thick film, the adhesion is slightly inferior, but the electromagnetic steel sheets are often used by laminating punched cores, which is not a practical problem. .. On the other hand, when the concentration of aluminum dihydrogen phosphate in the aqueous solution is small as shown in Comparative Examples outside the scope of the present invention (Comparative Example 1), the coating film after heating is not sufficiently cured and the adhesion is remarkably poor. .. On the contrary, if the concentration of aluminum dihydrogen phosphate in the aqueous solution is too high as in Comparative Example 2, the surface condition of the coating after heating is significantly deteriorated.
It is considered that this is because the dehydration condensation reaction by heating rapidly progresses.

When the amount of the synthetic resin aqueous emulsion added is insufficient as in Comparative Example 3, the punching property, the insulating property and the adhesive property are poor and the insulating film properties required for practical use are not satisfied. On the contrary, when the addition amount of the synthetic resin aqueous emulsion is too large (Comparative Example 4), the generated amount of decomposed gas at the welding temperature is large, and since the coating has no unevenness, the TIG weldability is poor.

Comparative Example 5 Even if unevenness was formed on the film
As described above, when the addition amount of the particulate additive (PMMA-based crosslinked resin particles) is less than the range of the present invention, the density of forming irregularities is low and the TIG weldability is poor. Further, in Comparative Example 6, since the glass beads have a large average particle diameter, the coatability during coating is poor, a uniform film is not formed, and the adhesion is poor. For Comparative Examples 1, 2, and 6, the properties such as interlayer resistance were not measured because the adhesion of the coating and the surface condition of the coating were extremely poor. From the above examples and comparative examples, it can be seen that an excellent insulating film for electromagnetic steel sheets is formed within the scope of the present invention.

[0035]

Industrial Applicability As described in detail above, the composition for forming an electrical steel sheet insulating film according to the present invention is used as a main component of an inorganic film-forming substance in the prior art as chromate or phosphate, especially chromic acid. In contrast to the case where a salt was used, aluminum dihydrogen phosphate was used, and one invention was constituted so as to be composed of an aqueous liquid obtained by mixing an inorganic aqueous solution in which this was dissolved and a synthetic resin aqueous emulsion, Furthermore, in addition to the above-mentioned constitution, by constituting another invention by adding and mixing a particulate additive, the electromagnetic steel sheet insulating film forming composition according to the present invention contains hexavalent chromium which is a harmful substance. Since there is no concern about safety and hygiene, the detoxification treatment of waste liquid, washing water, etc.
Economically easy.

Furthermore, aluminum dihydrogen phosphate does not impair the dispersion stability of the resin in an aqueous emulsion, unlike chromate salts, thus prolonging pot life and allowing transport as a composition, From the standpoint of workability as well, it is superior to conventional insulating film forming compositions. Moreover, the obtained film is not only excellent in film properties such as adhesion and interlaminar resistance, but the one in which particulate additives are added and mixed can obtain an insulating film excellent in TIG weldability even when the amount of film is increased. Can be done. As described above, the industrial value of the present invention having various advantages is extremely great.

Claims (8)

[Claims] 1. An inorganic aqueous solution containing 100 to 350 g / l of aluminum dihydrogen phosphate in terms of P ₂ O ₅ and a synthetic resin aqueous emulsion having a pH of 1 to 3 are added to the total amount of non-volatile substances. In contrast, the latter non-volatile matter is 10-4
A composition for forming an insulating film of a magnetic steel sheet, which comprises an aqueous liquid mixed so as to be 0% by weight. 2. An inorganic aqueous solution containing aluminum dihydrogen phosphate in an amount of 100 to 350 g / l in terms of P ₂ O ₅ and a synthetic resin aqueous emulsion having a pH of 1 to 3 are added to the total amount of non-volatile substances. In contrast, the latter non-volatile matter is 10-5
An aqueous solution mixed so as to be 0% by weight has an average particle diameter of 5 μm to 15 with respect to 100 parts by weight of all the non-volatile matters in the aqueous solution.
A composition for forming an insulating film of a magnetic steel sheet, characterized by comprising 5 to 20 parts by weight of crosslinked resin particles having a size of 5 μm. 3. The composition for forming an electrical steel sheet insulating coating according to claim 2, wherein the crosslinked resin particles are polymethylmethacrylate-based crosslinked resin particles. 4. The composition according to claim 2, wherein the crosslinked resin particles are polyacrylonitrile-based crosslinked resin particles. 5. The composition according to claim 2, wherein 5 to 20 parts by weight of hollow glass beads having an average particle diameter of 5 μm to 15 μm are added and mixed instead of the crosslinked resin particles. Composition for forming a steel sheet insulating film. 6. The electromagnetic steel sheet according to claim 2, wherein 5 to 20 parts by weight of mica powder having an average particle diameter of 15 μm to 50 μm is added and mixed in place of the crosslinked resin particles. Insulating film forming composition. 7. The electromagnetic steel sheet insulating film forming composition according to claim 1 is applied to an electromagnetic steel sheet and heated at a temperature of 250 to 500 ° C. to form a smooth insulating film of 0.5 to 2.0 g / m ^2. A method of forming an electrical steel sheet insulating film, which is characterized in that 8. The electromagnetic steel sheet insulating film forming composition according to claim 2 is applied to an electromagnetic steel sheet and heated at a temperature of 250 to 500 ° C. to form a concave-convex insulating film. A method for forming an electrical steel sheet insulating film, which comprises forming the insulating film in the range of 5 to 6.0 g / m ² .