KR100939314B1 - Coating solution for forming insulating film on the isotropic electromagnetic iron steel and method for the forming insulating film, using the coating solution - Google Patents

Abstract

The present invention relates to a coating composition for forming a non-oriented electrical steel sheet insulation coating having excellent continuous roll coating workability, and a method for forming an insulating coating using the same, with respect to 100 g of chromic anhydride (CrO3) in calcium dichromate salt consisting of chromic anhydride and calcium oxide. Preparing an organic and inorganic mixed coating liquid by adding 1 to 5 g of ethanolamine, 14 to 72 g of water-soluble solid acrylic resin, 22 to 63 g of ethylene glycol, and 4 to 13 g of powdery silica having an average particle size of 4 μm or less; Applying the prepared organic and inorganic mixed coating liquid to the surface of the non-oriented electrical steel sheet so that a dry film thickness is in a range of 0.5 to 2.3 μm per one side; The non-oriented continuous roll coating workability is characterized by comprising the step of forming an insulating film by heating annealing for 13 to 72 seconds in an electric furnace maintained at a temperature of 360 ° C ~ 790 ° C coated with the dry coating Provided is an insulating film forming method using a coating composition for forming an electrical steel sheet.

As described above, the present invention provides a coating composition for forming an insulating film, and by appropriately controlling the conditions for forming an insulating film using the same, it is stable for a long time while maintaining excellent film appearance and insulation properties such as excellent coating appearance which cannot be obtained alone. There is an effect that the coating workability can be obtained.

Electrical steel, insulation film, coating composition, water soluble acrylic resin, ethylene glycol

Description

COATING SOLUTION FOR FORMING INSULATING FILM ON THE ISOTROPIC ELECTROMAGNETIC IRON STEEL AND METHOD FOR THE FORMING INSULATING FILM, USING THE COATING SOLUTION}

The present invention relates to a coating composition for forming an insulating non-oriented electrical steel sheet having excellent continuous roll coating workability, and a method for forming an insulating coating using the same. More specifically, a small amount of ethanolamine and an acrylic resin in a calcium dichromate salt having a strong acidity and After adding ethylene glycol and powdery silica to prepare insulating coating-forming coating composition, non-oriented electrical steel sheet insulation film with excellent roll roll workability that can be applied continuously and stably for a long time. The present invention relates to a coating composition for forming and a method for forming an insulating coating using the same.

In general, non-oriented electrical steel sheets used as iron cores for electric machines such as small electric motors and transformers are provided to demand after forming an insulating film on the surface thereof to suppress eddy currents and minimize power loss.

Coil-oriented non-oriented electrical steel sheet, which is available on demand, is usually SRA (Stress Relief Annealing), automatic lamination, welding processing for the purpose of punching and stress relief annealing, which are made into a predetermined shape by a mold. We will carry out a series of work to shape the core. Therefore, the insulation film is required to improve the work productivity due to the no peeling of the formed film during the stress relief heat treatment carried out at high temperature and heat resistance to maintain the intrinsic electrical insulation.

In addition, a beautiful appearance is required in consideration of the fact that the coating process for forming the insulation film is a finishing process for finally providing electrical steel products to demand. In addition, it is required to have excellent adhesion, weldability, corrosion resistance, continuous roll coating workability, and the like.

The coating composition for forming an insulating film requiring such characteristics is classified into three types of organic, inorganic, and organic-inorganic mixtures, and is formed by continuously supplying a treatment liquid to the surface of an electrical steel sheet, and then applying and drying.

Among them, the organic-inorganic mixed composition has both the advantages of the inorganic coating composition and the advantages of the organic coating composition.

The present invention relates to a method of forming an organic and inorganic composite insulating film composed of chromate and a water-soluble solution type acrylic resin on a non-oriented electrical steel sheet, and more particularly, continuous roll coating on the surface of electrical steel sheet. The present invention relates to an insulating coating treatment solution having excellent workability and an insulating coating manufacturing method using the same.

A study on the coating composition for forming an insulating coating which can secure the advantages of the inorganic coating composition and the organic coating composition at the same time has been conducted. As a part of the research, the present inventors and the like described in Korean Patent Application No. 1986-9847 I suggested it together.

While the coating composition disclosed in Korean Patent Application No. 1986-9847 shows good general coating properties of inorganic and organic mixed compositions, zinc oxide, calcium oxide, and magnesium oxide, which are divalent metal oxides in chromic anhydride solution, At least one type of solution added and dissolved up to the composition ratio to the solution is used. Since the pH value of the dichromic acid salt solution exhibits a strong acidity of 1 or less, the gelation reaction is easy in a short time when a resin or an organic reducing agent is added to the dichromic acid salt solution. Has the drawback that occurs.

Due to gelation, it is not possible to carry out coating work stably for a long time more than 1 day after starting supply of solution because it is caught in circulation equipment such as coating liquid supply pump, piping, etc. This results in a decrease in productivity.

An object of the present invention for solving the above problems is to add a small amount of ethanolamine to the calcium dichromate salt solution showing a strong acidity of less than 1 pH value of water-soluble type in calcium dichromate salt solution of which the pH value is increased to 4-5 (Solution Type) The coating process is stabilized for a long time after the start of solution supply by appropriately adjusting the component content and the mixing order of the insulating film forming treatment solution containing acrylic resin, ethylene glycol and powdery silica. To provide a coating composition for forming a non-oriented electrical steel sheet insulation coating excellent in continuous roll coating workability that can be carried out continuously.

Another object of the present invention is to provide a method for forming an insulating film using the coating composition for forming a non-oriented electrical steel sheet having excellent continuous roll coating workability by applying the coating composition to the non-oriented electrical steel sheet to stably form the insulating film. have.

In order to achieve the above object, the present invention is 1 to 5 g of ethanolamine, 14 to 72 g of water-soluble solid acrylic resin, and 22 to 63 g of ethylene glycol with respect to 100 g of chromic anhydride (CrO3) in calcium dichromate anhydride composed of chromic anhydride and calcium oxide. And it provides a coating composition for forming a non-oriented electrical steel sheet insulation coating excellent in continuous roll coating work, characterized in that the organic and inorganic mixed coating liquid prepared by adding 4 ~ 13g of powdery silica.

In addition, the present invention provides a coating composition for forming a non-oriented electrical steel sheet insulation coating excellent in continuous roll coating work, characterized in that the average particle size of the powdery silica is 4㎛ or less, wherein the calcium dichromate salt is the ethanolamine It is added to provide a coating composition for forming a non-oriented electrical steel sheet insulation coating excellent in continuous roll coating workability, characterized in that the pH value is maintained at 4-5.

On the other hand, the present invention is 1-5 g of ethanolamine, 14-72 g of water-soluble solid acrylic resin, 22-63 g of ethylene glycol, and an average particle size of 4 µm with respect to 100 g of chromic anhydride (CrO3) in calcium dichromate salt consisting of chromic anhydride and calcium oxide. Preparing an organic and inorganic mixed coating liquid by adding 4 to 13 g of powdery silica which is below;                     

Applying the prepared organic and inorganic mixed coating liquid to the surface of the non-oriented electrical steel sheet so that a dry film thickness is in a range of 0.5 to 2.3 μm per one side;

The non-oriented electrical excellent in continuous roll coating workability characterized in that it comprises a step of forming an insulating film by heating the electrical film coated with the dry film for 13 to 72 seconds in an electric furnace maintained at a temperature of 360 ℃ ~ 790 ℃ Provided is an insulating film forming method using a coating composition for forming a steel sheet insulating film.

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention is demonstrated in detail.

In the present invention, as a mineral component, a calcium dichromate solution having a pH value of 4-5 is added to a conventional calcium dichromate salt solution having a pH value of 1 or less and added with a small amount of ethanolamine.

After adding appropriate amount of water-soluble acrylic resin, ethylene glycol, and powdery silica, which are used as organic components, and appropriately controlling the manufacturing conditions of insulating film, chromate and acrylic resin are appropriately controlled. Along with the solidification of the film, it shows the effect of forming an excellent insoluble film that becomes a dense and beautiful film appearance. I knew it appeared.

Starting from the above point of view, the present invention is based on calcium dichromate salt solution of chromic anhydride and calcium oxide, with respect to 100 g of chromic anhydride (CrO3) in the metal salt solution, 1 to 5 g of ethanolamine and an acrylic water-soluble type (Solution Type). Coating for forming non-oriented electrical steel sheet having excellent continuous roll coating ability by adding 14-72g of resin, 22-63g of ethylene glycol, and 4-13g of powdery silica having an average particle size of 4 μm or less based on the weight of solids. The composition was prepared,

In addition, the present invention is a continuous composition consisting of applying the coating composition to the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.5 ~ 2.3㎛ per one side, and then heat-annealed for 13 to 72 seconds at 360 ℃ ~ 790 ℃ An insulating film forming method using a coating composition for forming a non-oriented electrical steel sheet insulating film having excellent roll coating workability was devised.

Hereinafter, the role and function of each component in the coating composition of the present invention will be described and the reason for numerical limitation will be described.

[Coating composition for insulating film formation]

As the dichromic acid metal salt solution of the present invention added in order to impart corrosion resistance to the film, a solution obtained by adding and dissolving calcium oxide, which is a divalent metal oxide, to a solution of calcium dichromate salt was dissolved in an aqueous solution of chromic acid.

However, the method for preparing and blending the calcium dichromate salt is not limited to the present invention. In order to improve the stability of the organic-inorganic mixed solution on the premise of using the generally prepared calcium dichromate salt, ethanolamine is added to the calcium dichromate salt solution. It contains 1-5 g with respect to 100 g of chromic anhydride in it.

If less than 1g, the pH value of calcium dichromate salt does not increase sufficiently to 2 or less. When aqueous resins and ethylene glycol are added, coagulation occurs easily due to gelation, and when added in excess of 5 g, the pH value is increased. The effect is not so small that the stability of the liquid is not improved any more, and sedimentation occurs, which impairs the coating properties such as adhesion. Therefore, it is effective to make an appropriate amount of 1 to 5 g.

The acid-soluble acrylic resin of the water-soluble solution type serves to increase the adhesion to the material and give flexibility to the film.

In other words, the aqueous solution-type acrylic resin synthetically prepared without using an emulsifier is poor in appearance when the surface is roughly added in an amount of 14 g / g by weight when the resin is solid with respect to 100 g of CrO3 in the inorganic composition (calcium dichromate salt) in the treatment liquid. This results in insufficient film adhesion, and thus does not have an organic resin addition effect. When the content is added in excess of 72 g, weldability and heat resistance deterioration appear, so that 14 g to 72 g is an appropriate amount.

When the organic reducing agent ethylene glycol added in the role of reducing chromium hexavalent to chromium trivalent rapidly and stably annealing is added to less than 22 g of CrO3 in the inorganic composition (calcium dichromate salt), the amount of residual chromium hexavalent in the film is large. The presence of the yellowish brown surface is poor, and when added in excess of 63g, the treatment solution is easily gelled, so that the stability of the solution may be defective.

Powdered silica, which gives an effect of showing excellent insulating properties of the coating, is less than 4 g with respect to 100 g of CrO3 in the inorganic composition (calcium dichromate salt), and the effect of improving the insulation is insufficient. Insufficient solution stability due to the precipitation of silica added within the solution leads to an uneven insulation after the coating treatment. Therefore, an appropriate amount of addition is preferably 4 to 13 g.

Since the average particle size of the powdered silica shows good insulation effect even at ultrafine particles of about 1 μm, a specific lower limit is not specified, but when the average particle size exceeds 4 μm, problems with solution stability arise.

[Insulation film formation method using coating composition for insulation film formation]

The resin-chromic acid composite coating composition prepared as described above is applied to the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.5 to 2.3 μm per one side, and then annealed for 13 to 72 seconds in the temperature range of 360 ° C to 790 ° C. Inorganic-organic mixed coating which shows characteristics to be provided as insulation coating of non-oriented electrical steel such as insulation property, adhesion, corrosion resistance, weldability, etc., continuously roll coating and processing for a long time more than one day It can be obtained by liquid circulation.

One of the factors that determine the appearance of the film is the relationship between annealing temperature and time. When the annealing temperature is lower than 360 ° C, a large amount of chromium hexavalent is present in the film to facilitate moisture absorption, and the surface color is also yellowish brown, which is poor.

On the other hand, when it is higher than 790 ℃, the annealing temperature becomes difficult because it is difficult to control the annealing temperature, resulting in non-uniform reduction, and it is difficult to control the surface quality such as the appearance defects easily. Preferably limited to a temperature range of 790 ° C.

If the annealing time is shorter than 13 seconds, a large amount of chromium hexavalent is present in the film, so that the moisture is easily absorbed, and the color of the surface tends to be yellowish brown. It is preferable that the annealing time is limited to 13 to 72 seconds because there is a problem of appearing yellowish brown.

Even if the film is formed after the roll is applied to meet the above annealing conditions, if the thickness of the dry film by the method of the present invention is less than 0.5 μm, the required insulation and corrosion resistance cannot be obtained and the surface color is almost the same as that of the small support plate. As a result, it is a factor that avoids the user from the demand price.

When the thickness of the dry film exceeds 2.3μm, it is preferable to limit the dry film thickness so as to be in the range of 0.5 to 2.3μm per one side because it lowers the welding characteristics and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The coating composition for forming an insulating film having the composition as shown in Table 1 was applied to the surface of the non-oriented electrical steel sheet (containing 0.37% of Si) having a thickness of 0.49 mm uniformly and continuously, under the conditions of heating annealing as shown in Table 1 below. Insulation coatings were formed, respectively. Comparative example showing poor surface color of yellowish brown due to insufficient reducing effect by using less organic reducing agent ethylene glycol in coating composition, Comparative example showing repellency and reddish brown surface appearance with less resin, and by annealing treatment Comparative example showing the appearance of carbonized damage, comparative example showing easy hygroscopicity with a large amount of remaining chromium 6 in the film due to insufficient annealing treatment conditions, both appearance was poor and was excluded from the film evaluation.

On the other hand, in the case of the comparative example showing a strong acidity of calcium dichromate salt solution of less than 1 by adding a small amount of ethanolamine and a comparative example with an excess of ethanolamine and an excess of powdered silica added, Precipitation and gelation of the liquid began to occur, and the appearance of the coating appeared to be visually stained and streaked by the naked eye after 1 hour of continuous application. Therefore, the further treatment was omitted for these coating compositions.

Film characteristics of the electrical insulating film formed as described above were measured, and the measurement results are shown in Table 2 below.

RA SRA (Stress Relief Annealing): The electrically insulating coating material was heat-treated at 750 ° C for 2 hours in a dry 100% N2 gas atmosphere.

⑵ Insulation was evaluated by the received current value (Amps.) When the current of 0.5V, 1.0A was applied under 300PSI pressure.

⑶ Adhesion (mmψ) was evaluated as the minimum arc diameter without film peeling when the specimen was bent 180 ° after being annealed around an annular rod with an arc of 10, 20, 30 to 100 mmψ after annealing.

식 Corrosion resistance was shown by visual observation of rust on the surface after 8 hours of salt spray test (5% NaCl, 35 ℃).

⑸ Weldability: Appearance and blow hole formation in the weld bead after TIG welding (welding current: 150A, electrode: pure-W (3.2㎜), electrode gap: 0.35㎜, welding speed: 15㎜ / sec.) Was evaluated by visual observation.                     

⑹ Film peelability was expressed by the presence or absence of adhered coating material that appeared when the adhesive tape (polypropylene) was attached to the coating surface after SRA.

The results of the present invention will be described below based on Table 1 and Table 2.

Inventive examples (a, b) satisfying the conditions of the present invention exhibited excellent properties required as a coating such as roll coating continuous workability (more than 24 hours) and appearance characteristics, insulation, adhesion, corrosion resistance, weldability, film peelability, etc. .

On the other hand, in the case of Comparative Examples (1 to 3) in which the addition range of the coating composition was improperly applied or improperly applied and annealed, compared to the invention examples (a, b), it was required as a film such as insulation, corrosion resistance, weldability, film peeling property, etc. The characteristics have fallen.

That is, the comparative example (1) containing excess resin in the coating composition exhibited low heat resistance in which the coating film was peeled off after welding and stress relief annealing, and the comparative example (2) in which the insulating film was treated with a thick film also had weldability and heat resistance. Appeared poorly.

In addition, in the case of Comparative Example 2, in which powdery silica was not added but a thin film was formed, insulation and corrosion resistance were poor.

As described above, the present invention is a main component of the calcium dichromate solution and the aqueous solution type acrylic resin in which the pH value is increased to 4 to 5 by adding a small amount of ethanolamine to the conventional calcium dichromate salt solution having a pH value of 1 or less. Excellent coating appearance which cannot be obtained by these components alone by appropriately controlling the component content and insulating film forming conditions of the treatment solution for forming an insulating film in which an appropriate amount of powdery silica and ethylene glycol are added to the inorganic and organic mixed composition. It is effective in obtaining stable coating workability for a long time while maintaining the film-specific properties such as insulation.

Claims (4)

Organic, prepared by adding 1-5 g of ethanolamine, 14-72 g of water-soluble solid acrylic resin, 22-63 g of ethylene glycol, and 4-13 g of powdered silica, to 100 g of chromic anhydride (CrO3) in a calcium dichromate salt consisting of chromic anhydride and calcium oxide. It consists of inorganic mixed coating liquid, The calcium dichromate salt coating composition for forming a non-oriented electrical steel sheet having excellent continuous roll coating workability, characterized in that the ethanolamine is added to maintain a pH value of 4 ~ 5. The method of claim 1, The powdery silica is a coating composition for forming a non-oriented electrical steel sheet insulation coating excellent in continuous roll coating work, characterized in that the average particle size of 4㎛ or less. delete To 100 g of chromic anhydride (CrO3) in a calcium dichromate salt consisting of chromic anhydride and calcium oxide, 1 to 5 g of ethanolamine, 14 to 72 g of water-soluble solid acrylic resin, 22 to 63 g of ethylene glycol, and 4 to 13 g of powdered silica are added. Preparing a mixed coating liquid; Applying the organic and inorganic mixed coating liquid to the surface of the non-oriented electrical steel sheet such that a dry film thickness is in a range of 0.5 to 2.3 µm per side; Forming an insulating film by heating and annealing the electrical steel sheet coated with the organic and inorganic mixed coating liquid for 13 to 72 seconds in an electric furnace maintained at a temperature of 360 ° C to 790 ° C. The calcium dichromate salt is an insulating film forming method using a coating composition for forming a non-oriented electrical steel sheet excellent in continuous roll coating work, characterized in that the ethanolamine is added to maintain a pH value of 4 ~ 5.