JPS62227093A - Electrical steel sheet having excellent blankability and insulation resistance characteristic - Google Patents

Abstract

PURPOSE:To impart excellent blanking property and high insulation characteristic after annealing to an electrical steel sheet by mixing inorg. particles coated with a resin at a specific ratio with an aq. soln. contg. a chromic acid, phosphoric acid, the salts thereof and org. reducing agent, coating the mixture on the electrical steel sheet and baking the coating. CONSTITUTION:A paint is prepd. by mixing the inorg. particles such as BaSO4 coated with the org. resin with the aq. soln. which contains >=1 kinds among the chromic acid, phosphoric acid, and chromate and phosphate of Ca or Mg and the org. reducing agent and added with org. emulsion at need. The above- mentioned aq. soln. A (a kg, solid content nA%) and the inorg. particles B (b kg, weight ratio of the inorg. particles nb%) are so mixed to satisfy the conditions expressed by the mixing equation. Such paint is coated on the electrical steel sheet and is baked to form the coating. The inter-layer insulation characteristic of the film is thereby improved. The electrical steel sheet formed in the above-mentioned manner has the good blanking property and maintains the good insulation characteristic even after annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electrical steel sheet having an insulating coating formed thereon that has excellent punchability and excellent insulation resistance after annealing.

That is, the present invention involves adding melamine, epoxy, polyester, An electromagnetic steel sheet with excellent punchability and high insulation properties even after annealing, made by applying and baking a coating agent on the surface obtained by mixing inorganic particles coated with organic resins such as acrylic, polyethylene, and polypropylene. Regarding.

(Prior Art) Electromagnetic a-plates used as iron cores in transformers, morphs, etc. usually have an insulating coating on their surface in order to reduce eddy current loss. This coating is required to have excellent adhesion, punchability, heat resistance (seizure resistance), weldability, etc. in addition to insulation.

Insulating coatings on electrical steel sheets are broadly divided into two types: chromic acid-based inorganic coatings and organic coatings using acrylic resin, vinyl acetate resin, etc.

The former inorganic film is less susceptible to deterioration at high temperatures and is less prone to seizure and
The weldability is good, but the lubricity is poor, and when punching with a die (in some cases, die wear is severe, large burrs occur immediately, and the die must be replaced frequently.The latter organic coating is the opposite of this). Although it has good die punching properties, it has poor weldability and insufficient heat resistance.

Recently, we have been using a two-layer coating method in which an organic coating is formed on top of an inorganic coating, or a composite solution in which an organic resin emulsion is added to a mixed solution of chromic acid and phosphoric acid. A composite coating method that involves coating and baking has come into use, and various patent applications have been filed.

However, although the two-layer film method has good punchability because the upper layer is made of resin, it has the disadvantage of high costs because it requires coating and baking twice, and the film formed by the composite film method does not contain inorganic materials. Since it is an organic mixture, it is necessary to mix at least 20% (baked film weight ratio) of resin to improve punchability, but in that case, weldability is sacrificed, and as a result, weldability and Both the punching properties and the punching properties are somewhat inferior. Therefore, as a method that does not reduce weldability even if the amount of resin is increased, a method of imparting roughness to the surface of the steel plate (Japanese Patent Publication No.
6744), and a method of imparting roughness to the film (Japanese Patent Publications No. 49-19078, Japanese Patent Publications No. 48586-1982, and Japanese Patent Publication No. 55-21111).

Methods of imparting roughness to the film include (a) adding resin particles, (b) mechanically adding streaks to the film after painting, and (c) using special resin to create particles containing inorganic substances. An example of this method is to precipitate . However, these methods also have the following drawbacks. In other words, if roughness is given to mi, weldability will certainly improve, but the film thickness will naturally become uneven, leading to a decrease in punchability.Also, since the roughness is large, when stacking punched plates, it will be difficult to The product moment decreases.

On the other hand, in the method (a) above, although there is little negative impact on punchability, the resin is melted during coating baking to improve the adhesion between the resin particles and the steel plate, so the required roughness can be stabilized. It is difficult to get it.

With method (b), the film becomes uneven, leading to a decrease in punchability and glabellar insulation (furthermore, because the film itself is thin, even if the streaks are formed, the surface roughness does not increase significantly. ,
Does not contribute much to improving weldability.

In method (c), the resin used is limited, and
It also has a negative effect on punching performance.

That is, the current situation is that an inexpensive film that has good punchability, weldability, statesking resistance, etc., has not yet been obtained.

The present inventors have previously found that when a treatment solution containing a conventional chromic acid solution mixed with one or both of a fluororesin emulsion and a polyethylene emulsion is used, a film formed by one application and baking can be obtained. However, it was discovered that a two-layer baked film was formed in which the resin floated on the surface layer and the lower layer had a high chromium concentration. In comparison, we proposed an insulating film with significantly superior punchability and weldability.

As described above, some composite coatings made of a mixture of one or two of chromic acid and phosphoric acid and an organic resin have a balance between punchability and weldability.

Therefore, by adding organic resin particles such as polyethylene to this composite coating and baking the coating, weldability was also improved. However, the insulation resistance after strain-relief annealing in any of the coatings significantly decreases due to the decomposition and scattering of the organic resin that makes up the coating during annealing, and the insulation resistance after annealing used as an actual product decreases significantly. It has the disadvantage of being low.

Therefore, the present inventors proposed adding inorganic particles with a particle size of 1 to 20/7 m to the above composite coating in order to improve these problems (Japanese Patent Application No. Sho-2), but the improvement was not achieved. The effect is still not enough.

(Means for Solving the Problems) In order to eliminate the above-mentioned conventional drawbacks, the present inventors conducted detailed studies regarding the insulation resistance after annealing, and found that the resistance between the H1 layers of the electrical steel sheet after annealing was It was found that the value is largely due to the insulation of the contact area between the eyebrows.

That is, when electromagnetic steel sheets are laminated, it has been found that it is important to reduce the area of the contact portion and increase the insulation of the contact portion.

As a result, it was found that by adding inorganic particles as fillers to the insulating coating and using the non-4m particle portions as contact points during lamination, high insulation properties could be maintained even after annealing.

Furthermore, in addition to high insulation properties, the inorganic filler must also have a certain level of strength, avoid damage during the manufacturing process of motors and transformers, and wear out dies during punching. It is required that there be no thermal decomposition during annealing.

Furthermore, stable production is possible in the insulation coating formation process, so
Good painting workability is also required.

Therefore, based on the results of previous research, the present inventors further investigated coating systems that meet these requirements, and found that chromic acid, phosphoric acid, their calcium or magnesium salts, and organic reducing agents Melamine,
The inventors have discovered that the above object can be achieved by coating and baking a paint obtained by mixing BaSO4 particles coated with an organic resin such as epoxy or polypropylene on an electrical steel sheet, and have completed the present invention.

Thus, the gist of the present invention is to use one or more of chromic acid, phosphoric acid, calcium chromates and phosphates, and magnesium chromates and phosphates as film-forming agents; and an aqueous solution (A) (a kg, solid content na%) containing an organic reducing agent, and inorganic particles (B) (b kg,
After mixing components A and B as shown in 1a, apply the non-Japanese particles (weight ratio n8%) onto an electrical steel sheet,
This is an electromagnetic steel sheet that is baked and has excellent punchability and insulation resistance.

If necessary, an organic resin emulsion may be added to the aqueous solution to form an inorganic-organic composite film.

(Function) Chromic acid, phosphoric acid, used for forming the composite film of the present invention,
and calcium or magnesium salts and organic reducing agents are already known.

That is, conventionally known chromic acids and their calcium and magnesium salts can be used.

Examples of such ROM compounds that improve the corrosion resistance and heat resistance of the film include Crys, KzCrtOt, and CaCrz07.
, NazCrtOq, MgCrz07, etc.

Furthermore, phosphoric acid or calcium and magnesium salts of phosphoric acid include IhPO4, K3PO4, KzH
PO4, KL PO4, Ca1lPO4, Ca(HzP
O4) tlMgs (PGact, Mg1lPQa, etc.) can be used alone or in combination of two or more to improve the adhesion of the film.Also, for the purpose of improving the seizure resistance of the film, one of AQ or Af2 compounds can be used. One species or two or more species can be used.

In addition, examples of hydroxides that improve liquid stability and film-forming properties include Ca(OR)*, Mg(Oll)t, 1Zn(O
H)z, AQ(OH)i, etc., and further oxides such as CaO, MgO1ZnO, NiO, HsBOz, etc. may be used alone or in combination of two or more.

The a reducing agent is one that reduces and precipitates chromic acid (salt) or phosphoric acid (salt) to promote film formation, and -i may be ethylene glycol, etc., and oxycarboxylic acid, etc. may be added in some cases. .

Next, the inorganic particles must have properties such as being insoluble in acids, having excellent heat resistance, and being difficult to deform. Preferred examples include Ba5O, clay, and clay. This is not so hard that it impedes punching properties, nor is it so strong that it can be scratched and damaged during work (it is appropriate).

The shape of the aluminous particles is preferably close to spherical to some extent, but there is no problem even if rod-shaped, dice-shaped, etc. particles are mixed therein. However, tabular grains such as mica are less preferred. The average particle size of the inorganic particles is 0.5 to 1.0 in thickness.
In order to obtain surface roughness by having part of the particles protrude from the .mu.m-sized film, the appropriate thickness is about 1 to 20 .mu.m, preferably about 3 to 10 .mu.m. The amount of inorganic particles added is 5 to 40% of the baked film.
The volume percentage is appropriate. If it is less than 5% by volume, it will be less effective in improving weldability, and if it exceeds 40% by volume, it will have an adverse effect on punchability.

By adding inorganic particles in this way, a stable surface roughness is obtained and weldability is improved. Surface roughness can also be controlled by changing the particle size of the particles. Also, unlike organic particles, they are inorganic particles, so
This also leads to a reduction in gas-generating components and improves the interlayer insulation of the film.

-C, it is said that adding inorganic particles to the coating reduces the punchability, but according to the present invention, the particles are further stably suspended in the coating system for forming a composite coating. are coated with organic resins such as melamine, epoxy, polyester, acrylic, polyethylene, and polypropylene.

The coating method may be any suitable method, such as kneading inorganic particles in a resin and then re-pulverizing them, or dispersing the inorganic particles in a dispersion medium and precipitating the organic resin on the surface of the resin. .

The inorganic particles obtained in this way have a low particle specific gravity and are close to composite film-forming paints, or have various functionalities such as hydrophilic groups -OB and -COO11, ester groups, and amine groups on their surfaces. Since it has a group, it has good dispersibility in the water-soluble paint and can extremely facilitate workability in the coating process.

More preferably, the resin coverage is 1 to 200 parts by weight based on 8 parts by weight of the inorganic particles. This is because if the resin coverage is too small, the dispersibility in the water-soluble paint will be reduced, which is not practical, and if it exceeds 200 parts, the insulation resistance after annealing will drop significantly and no effect will be seen.

As described above, the composite coating according to the present invention in which inorganic particles coated with an organic resin are added has better punchability than conventional composite coatings or coatings in which organic resin particles are added. Even after that, the inorganic particles control the insulation resistance, making it possible to maintain extremely good insulation properties.

As already mentioned, there are inorganic and inorganic/organic coatings for the coated electrical steel sheet according to the present invention, but the inorganic + organic coating format contains various organic coatings in addition to the aforementioned chromic acid, phosphoric acid, etc. Emulsions can be added.

Known resin emulsions used in such composite films include emulsions of acrylic resins, styrene resins, vinyl acetate resins, and copolymers thereof, but in the present invention, polyethylene or fluororesin emulsions are particularly preferably used. .

Fluorocarbon resins and polyethylene resins are both nonpolar substances with small solubility parameters, and therefore have poor wettability with steel plates and chromate films. On the other hand, the chromate film has good wettability with *+i, and the chromate film tends to separate into the lower layer and the resin into the upper layer. ES the film surface
When measured using CA (photoelectron spectroscopy), it is found that the fluororesin and polyethylene are easily separated on the surface of the film.

By adding a small amount of polyethylene and fluorine resin,
Very good lubricity can be obtained.

Organic emulsions such as fluororesin emulsions and polyethylene emulsions can be used alone or in combination. In addition, compared to other non-polar emulsions, the tendency for separation is particularly large, so even if small amounts of other resins such as acrylic resin, polymer vinyl chloride, vinyl acetate, etc. are added for the purpose of improving corrosion resistance, the effects of the present invention will not be maintained. It's not something. The reason for determining the amount of resin emulsion by weight is 5 to 60%, because if it is less than 5%, it will affect the relative punchability, and if it exceeds 60%, it will affect the weldability. This is because both properties are experimentally good within this range.

A more suitable range is that the amount of polyethylene emulsion is 20 to 40% by weight and the amount of fluororesin emulsion is 5 to 20% by weight.

The blending ratio of component A and component B is 0.00 according to the above formula.
1 to 1.5, but if it is outside the above range, including when the above-mentioned organic emulsion is blended into component A, the initial objective of the present invention will not be achieved.

Next, the present invention will be explained in more detail with reference to Examples.

Example To prepare film-forming agent A, 120 g of CrO+
.

11, 430 g of PO and Ca (O
ff) Dissolve t 60g in ion-exchanged water, l kg
And so. To this aqueous solution, 200 g of Boncoat manufactured by Dainippon Ink [resin temperature (9124), non-explosion 1 minute 55%] was added as an organic resin emulsion. The solid content in the obtained liquid mixture was 28 wt%, and this was designated as component A.

On the other hand, the average particle size 110L coated with melamine resin
The barium sulfate particles of No. 1 (BaSOa weight ratio 50%) were used as component B.

Next, both of the above components A and B are mixed in various ratios, and the resulting coating liquid is applied to the surface of the electrical steel sheet as a dry film of 2 g/r+ per side. It was roll coated so that it became, and it was hardened in the baking oven for 1 minute so that the steel plate temperature would be 250 degreeC.

For comparison, only component A was applied and cured under the same conditions. Comparative experiments were also conducted on coating liquids in which Component B was mixed in an amount exceeding the scope of the present invention.

The electromagnetic steel sheet thus obtained was used for punching, and the interlayer resistance after annealing at 750°C was measured.

The results are shown in Table 1 below. As can be seen from the results in Table 1, the electromagnetic steel sheet provided with the coating according to the present invention had punchability of 800,000 times or more and good glabellar resistance. on the other hand,
If the amount of component B added is too large, the punching property will be greatly deteriorated, and if component B is not added, the interlayer resistance will be extremely low.

Note that no particularly significant difference was observed even when no organic emulsion was used as a coating component (Example 4).

Claims (2)

[Claims] (1) An aqueous solution containing one or more of chromic acid, phosphoric acid, calcium chromate and phosphate, and magnesium chromate and phosphate as a film forming agent, and an organic reducing agent ( A) (akg, solid content n
_A%) and inorganic particles (B) coated with organic resin (bkg,
Inorganic particle weight ratio n_B%) as a mixing formula: 0.001≦(n_B・b)/(n_A・
a) After mixing components A and B so that ≦1.5,
An electromagnetic steel sheet with excellent punchability and insulation resistance, made by coating and baking on an electromagnetic steel sheet. (2) adding an organic resin emulsion to the aqueous solution;
An electrical steel sheet according to claim 1.