KR101110255B1 - Coating composition for forming insulation film, Method for manufacturing insulation film of grain-oriented electric steel sheet using it And Grain-oriented electric steel sheet therof - Google Patents

Abstract

The present invention relates to the formation of an insulating coating of a grain-oriented electrical steel sheet, and more particularly, to forming a coating composition for forming an insulating coating of electrical steel sheet having excellent coating tension and corrosion resistance without containing chromium or chromium oxide and forming an insulating coating of a grain-oriented electrical steel sheet using the same. The present invention relates to a grain-oriented electrical steel sheet having an insulating coating method and the coating composition.

The coating composition for forming an insulating film of the present invention for this purpose is 0.1 to 25 parts by weight based on nickel conversion of at least one selected from 25 to 300 parts by weight of silica, nickel or nickel compounds based on 100 parts by weight of phosphate , 0.1-10 parts by weight of boric acid is added, the grain-oriented electrical steel sheet has a coating tension of 0.35 ~ 1.00kg / mm ² formed of the coating composition, the insulating film forming method of the grain-oriented electrical steel sheet is the coating composition After the coating on the surface of the steel sheet so that the dry coating amount is 0.5 ~ 6.0g / m ² , the insulating film is formed by a two-step heat treatment performed by the second heat treatment temperature higher than the initial heat treatment temperature.

Oriented electrical steel, insulation coating, coating composition, hydroxyl group, silica

Description

Coated composition for forming insulation film, Method for manufacturing insulation film of grain-oriented with a coating composition for forming an insulating film with excellent coating properties, and a method for forming an insulating film of a grain-oriented electrical steel sheet using the same and a coating composition electric steel sheet using it And Grain-oriented electric steel sheet therof}

The present invention relates to the formation of an insulating coating of a grain-oriented electrical steel sheet, and more particularly, to a coating composition for forming an insulating coating of electrical steel, which does not contain chromium and has excellent coating properties to improve corrosion resistance, film tension, and adhesion to a material. The present invention relates to a method for forming an insulating coating of a grain-oriented electrical steel sheet and a grain-oriented electrical steel sheet having an insulating coating formed of a coating composition.

A grain-oriented electrical steel sheet is an electrical steel sheet having an aggregate structure of grain orientations arranged in the direction of (110) [001]. It has excellent magnetic properties in the rolling direction and is used as a core material for transformers, motors, generators, and other electronic devices. have.

In order to minimize the power loss of the oriented electrical steel sheet, an insulating film is formed on the surface of the electrical steel sheet, and the insulating film is basically a high electric insulation, excellent adhesion to the material, uniform color without appearance defects Should have In addition, in recent years, high magnetic flux density oriented electrical steel sheet has been commercialized, and the high tensile strength of the insulating film has been pursued, and it has been confirmed that the high tensile insulating film contributes to the improvement of the magnetic properties of the final product.

Various methods have been proposed to form a high tensile film. Currently commercialized oriented electrical steel sheet reduces iron loss by applying tensile stress to the steel sheet by using the difference in thermal expansion coefficient between the steel sheet and the insulating film formed on the base layer of the foliarite base. The effect is planned.

As a representative method of forming a conventional insulating film, Japanese Patent No. 2688147 and Japanese Patent No. 3098691 propose a technique of forming a high tensile oxide film on an electrical steel sheet using alumina sol and a mixture of boric acid. have. However, this does not fundamentally solve the problem of rust generated by the film deterioration by boric acid.

On the other hand, Japanese Patent Application Laid-Open No. 11-71683 proposes a method of improving the film tension by using colloidal silica having a high glass transition temperature, and in Korean Patent No. 0377566, a specific metal atom is formed on the base layer of the polesterite-based film. The formation of the first layer composed of hydrogen phosphate salt and silica induces an improvement in the adhesion between the foliarite base coating film and the insulating coating film, and a second layer containing aluminum borate as a main component is formed thereon. Proposes a technology that produces a tension effect. However, the coating liquid composition according to the prior art is inevitably added to the chromium oxide to improve the corrosion resistance, the situation is limited in view of the reality that the restrictions on the use of chromium in order to prevent environmental pollution.

In response to the recent strengthening of environmental regulations, studies are being actively conducted to improve coating properties of chromium-free insulating films.

In the case of non-oriented electrical steel sheet, a method of inducing a barrier effect by introducing phosphate or colloidal silica to reinforce corrosion resistance and adhesion deterioration caused by removing chromium from the insulating coating has been actively proposed. However, none of the chromium-free coatings of non-oriented electrical steel sheets mainly composed of phosphate or colloidal silica do not completely solve the problem of the corrosion resistance of the sticky or colloidal silica of phosphate.

As a chromium-free tension coating agent for oriented electrical steel sheets, a method of introducing colloidal silica modified with Fe, Al, Ga, Ti, etc., as disclosed in Japanese Patent No. 2007-23329, but in Korean Unexamined Patent Publication No. 2008-0025733 As described above, a method of improving the corrosion resistance and the film tension by introducing oxides such as Fe, Co, and Cu has been proposed. However, in the former case, the process of modifying colloidal silica by reacting with Fe, Al, etc. is quite complicated, which is disadvantageous in terms of manufacturing cost and its effect is not sufficient, so it is difficult to be implemented in the industry. However, the introduced oxides are to improve the film density and film tension incidentally by simply preventing the free phosphoric acid generated when the coating is dried, so as to satisfy the high corrosion resistance and film tension level required in recent high-quality oriented electrical steel sheets. There is a limit.

As such, no technology for commercializing a chromium-free coating agent that satisfies all of the excellent coating properties such as high film tension, corrosion resistance, adhesion, and surface gloss required for high-quality grain-oriented electrical steel sheet has not been proposed.

The present invention has been made to solve all the problems of the prior art as described above, it does not contain chromium, it is environmentally friendly and has excellent corrosion resistance, adhesion, compatibility and high film tension coating composition for forming an electrical steel sheet and the same It is an object of the present invention to provide a method for forming an insulating coating of a grain-oriented electrical steel sheet and a coating-oriented electrical steel sheet having an insulating coating.

In order to solve the above problems, the coating composition for forming an electrical steel sheet according to the present invention may include at least one selected from 25 to 300 parts by weight of silica, nickel or a nickel compound based on solids based on 100 parts by weight of phosphate, based on nickel conversion amount. 0.1 to 25 parts by weight and 0.1 to 10 parts by weight of boric acid is added to the composition, characterized in that it improves the film tension and corrosion resistance without adding chromium or chromium oxide.

It is preferable that the said nickel compound consists of nickel hydroxide.

The oriented electrical steel sheet excellent in the film tension and corrosion resistance of the present invention for solving the above problems is 25 to 300 parts by weight of silica, nickel or nickel hydroxide in terms of solids based on 100 parts by weight of phosphate An insulation coating is formed of a coating composition added by adding 0.1 to 25 parts by weight as a standard, and the coating tension of the insulation coating is 0.35 to 1.00 kg / mm ² .

The phosphate may be in the form of a mixture of at least two or more selected from monobasic aluminum phosphate, monobasic magnesium phosphate or zinc monophosphate.

The silica is preferably made of nanoparticles having an average particle diameter of 1 nm or more and 100 nm or less having a hydroxyl group on the surface.

The coating composition is more preferably formed by adding 0.1 to 40 parts by weight of cobalt hydroxide relative to 100 parts by weight of phosphate.

The method for forming an insulating film of a grain-oriented electrical steel sheet having excellent film tension and corrosion resistance of the present invention for solving the above problems is at least one selected from 25 to 300 parts by weight of silica, nickel or nickel hydroxide based on 100 parts by weight of phosphate solids The coating composition formed by adding 0.1-25 parts by weight based on the nickel conversion amount was applied to the surface of the steel sheet so that the dry coating amount was 0.5 to 6.0 g / m ² , and the latter heat treatment temperature was lower than the initial heat treatment temperature. Characterized in that the insulating film is formed by a two-step heat treatment carried out at a high level.

The coating composition is a mixture of at least two selected from monobasic aluminum phosphate, monobasic magnesium phosphate or zinc monophosphate, and has a hydroxyl group on the surface, and the silica nanoparticles and nickel hydroxide having an average particle diameter of 1 nm or more and 100 nm or less. It is preferable to be comprised by the compounding procedure to introduce.

The two-step heat treatment is particularly preferably performed by heat treatment for 10 seconds to 10 minutes at a low temperature of less than 800 ℃, then heat treatment for 30 seconds to 10 minutes at a high temperature of 800 ℃ or more.

According to the present invention, nickel hydroxide forms strong hydrogen bonds with silica nanoparticles composed of hydroxyl groups at low temperatures, and thus has excellent compatibility and compatibility, and at high temperatures, solid and dense ones are formed through reactions between silica nanoparticles. The adhesion between the material and the film can be improved.

In addition, according to the present invention can obtain a higher tension imparting ability than the conventional insulating film, it is possible to produce high-quality oriented electrical steel sheet having excellent corrosion resistance by an environmentally friendly technology that does not contain chromium.

Hereinafter, the present invention will be described in detail.

The coating composition of the present invention is a chromium-free coating material that can exhibit excellent coating properties without containing chromium, and can be used as a coating material for forming an insulating film such as a grain-oriented electrical steel sheet without restriction due to environmental regulations.

In the case of the chromium-based coating material, hexavalent chromium ion (Cr ⁶⁺ ) reacts with water present in the coating material when the film is dried to convert it into chromic acid (H ₂ CrO ₄ ), and again, chromic acid (H ₂ CrO ₄ ) is present in the steel sheet. By reacting with (Fe) to produce iron oxide (FeO) it is made to react with iron oxide (FeO) and metal phosphate. This action is possible due to the two hydroxyl groups (Hydroxy group, -OH) present in the chromic acid (H ₂ CrO ₄ ), which helps to improve the adhesion between the steel sheet and the coating material and consequently improves the film tension. In addition, hexavalent chromium ion (Cr ⁶⁺⁾ is a film reaction excessively produced iron oxide (FeO) to 3 are sometimes reduced to chromium ions (Cr ^3+), and a reduced 3 by a condensation reaction of the chromium ions (Cr ³⁺⁾ It increases the density, which greatly affects the corrosion resistance. In addition, chromium oxide improves surface properties by suppressing the generation of free phosphoric acid, which causes poor wetting after drying the film. Therefore, when chromium oxide is excluded from the coating material, it is very difficult to secure the coating properties such as film adhesion, film tension, and corrosion resistance.

On the other hand, silica is widely used because of its excellent film tension. However, when silicon dioxide (SiO ₂ ) is used, surface quality variation occurs due to poor dispersion in water used as a solvent of the coating material. It is not compatible with the metal phosphate used, causing gelation. In this case, the addition of chromium oxide prevents gelation when the two components are mixed, and allows the coating material to have a stable liquid phase. Therefore, the reduced compatibility of silica and metal phosphate, which is generated when chromium oxide is excluded from the coating material, is a major factor that makes the coating material difficult to manufacture.

Therefore, the present invention proposes the following technique to solve problems such as film tension, corrosion resistance and compatibility degradation when using a chromium-free coating material chromium oxide is excluded.

First, the problem of reduction of surface gloss and corrosion resistance in coating materials including metal phosphate is solved by introducing nickel hydroxide, and the problem of degradation of surface absorption is solved by introducing cobalt hydroxide. .

Second, using silica nanoparticles composed of hydroxyl groups on the surface, strong hydrogen bonds with metal phosphates are formed, resulting in improved compatibility and compatibility between solution components. Of course, it also makes a great contribution to improving the adhesion of metal phosphates, which ultimately results in excellent film tension.

Third, in order to secure excellent solution stability after the coating material is prepared, the order of the ingredients is differentiated. At least one selected from the acidic monobasic aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) or monobasic magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) or zinc monophosphate (Zn (H ₂ PO ₄ ) ₂ ) By introducing silica nanoparticles whose surface is composed of hydroxyl groups in a form in which two or more are mixed, it is to ensure mutual compatibility between the components of the coating agent, that is, compatibility. Therefore, in the present invention, the compounding order of the metal phosphate, silica nanoparticles, and nickel hydroxide (Ni (OH) ₂ ) is specifically used to improve storage stability.

The proposed technique as described above will be described in more detail with specific examples.

Recently, the improvement of the magnetic properties by the high tension of the insulating film has become an important factor in accordance with the trend of high-quality oriented electrical steel sheet. In the final process, the oriented electrical steel sheet undergoes the final process of insulation coating and planarization annealing. The heat-expanded material undergoes annealing after insulation coating, and then shrinks again when cooled. Will interfere. Therefore, by increasing the difference in thermal expansion coefficient between the base material and the coating material it is possible to improve the film tension. However, there is a limit in forming a high tension coating film simply by the difference in thermal expansion coefficient between the base material and the coating material.

Accordingly, the present invention is to provide a strong coating tension by forming a dense coating layer by a chain reaction by forming a strong hydrogen bond between the solution components. In order to form such a dense coating layer, a material that improves adhesion by reacting with silica and metal phosphate is required. In the present invention, by using nickel hydroxide having good compatibility with metal phosphate and silica nanoparticles having a hydroxyl group on the surface thereof, This is to solve this problem.

Silica nanoparticles constituting the coating composition for forming an insulating film of the present invention has a surface is composed of a hydroxyl group to form a hydrogen bond with the metal phosphate has the effect of improving the solution stability and the film tension. In addition, since the surface area of the silica nanoparticles is very large, when the heat treatment at 800 ℃ or more, the condensation reaction proceeds quickly to form a very solid and dense coating has the advantage of excellent insulation properties.

The coating composition for forming an insulating film of the present invention is characterized in that nickel or a nickel compound is added alone or in a mixed state to 100 parts by weight of phosphate in order to suppress corrosion and impart gloss of a magnetic material.

In this case, when nickel metal is introduced alone, it is difficult to react with silica and phosphate at low temperature during drying. Therefore, nickel hydroxide in which the outside of the particle is substituted with a hydroxyl group is used rather than adding nickel metal alone. Excellent at

The coating composition for forming an insulating coating of the present invention improves the absorption problem caused by chromium removal by adding cobalt hydroxide (Co (OH) ₂ ). Cobalt is preferably a metal having an ability to improve absorptivity, but when a simple cobalt metal is introduced, cobalt hydroxide in which the outside of the particle is substituted with a hydroxyl group is difficult to react with silica and phosphate at low temperature during drying.

The coating composition for forming an electrical steel sheet insulation coating according to the present invention is based on a solid content based on 100 parts by weight of phosphate 25 to 300 parts by weight of silica, 0.1 to 25% by weight based on nickel conversion of at least one selected from nickel or nickel compounds It has a composition to add.

The phosphate used in the coating composition was magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) or aluminum monophosphate (Al (H ₂ PO ₄ ) ₃ ) or zinc phosphate (Zn (H ₂ PO ₄ ) ₂ ). ) Alone or at least two or more selected from them may be in a mixed form.

When the total weight of the coating material is 100 g, the dosage of the coating composition is suitably 30 to 60 g. If less than 30g, the adhesive strength of the coating material is lowered, the film tension is lowered, if more than 60g is introduced because wetting (Sticky) by free phosphoric acid can be induced.

Silica acts to impart tensile stress to the material by forming a ceramic layer having a low coefficient of thermal expansion during heat treatment of the insulating coating, and the amount of the silica is preferably added in an amount of 25 to 300 g with respect to 100 g of phosphate based on solid content. When the amount of silica is less than 25g, it is unable to form an appropriate ceramic layer and thus does not impart sufficient tensile stress to the material. When the amount of silica is more than 300g, the solid content is increased in the coating material, resulting in a problem that the surface quality of the steel sheet is degraded. Therefore, the present invention is to limit the silica content in the range of 25 ~ 300g compared to 100g of phosphate.

In this case, the silica is preferably made of nanoparticles having an average particle diameter of 1 ~ 100nm. When the average particle diameter of silica exceeds 100 nm, the surface area per unit mass increases, so that the condensation reaction rate is low, and it is uneconomical to increase the heat treatment temperature in order to increase the reaction rate. The lower limit of the average particle diameter of silica was set to 1 nm because the particle diameters of the silica nanoparticles used as the examples of the present invention were all 1 nm or more, and sufficient condensation reaction rate could be obtained by only making the silica average particle diameter of 1 nm or more. to be. On the other hand, in order to obtain an insulating film having excellent coating properties, it is also possible to use a mixture of two or more kinds of silica nanoparticles having different average particle diameters.

Nickel or nickel compound added in the present invention is preferably added in 0.1 to 25g (nickel conversion amount) based on 100g of phosphate. If the amount is less than 0.1g based on nickel, it is difficult to form a proper hydrogen bond in the drying process, so that the effect of imparting gloss and corrosion resistance is insufficient, and when it is added more than 25g, the fraction of nickel in the coating material is increased to change the color of the coating surface. Cause. Nickel hydroxide is suitable as the nickel compound, and it is more preferable to add nickel hydroxide having excellent reactivity upon drying with silica and phosphate rather than nickel metal. Therefore, the coating composition for forming an insulating film according to the present invention is most preferably added to the nickel hydroxide of 0.1 ~ 25g compared to 100g of phosphate on the basis of nickel conversion.

It is preferable to add 0.1-10 g of boric acid (H ₃ BO ₃ ) to the metal phosphate solution based on 100 g of phosphate solids. When boric acid is added below 10g, it is difficult to form a proper condensation reaction with magnesium, alumina or zinc present in the phosphate, and when added above 10g, precipitation occurs due to excessive addition. 0.1-10g is determined to be added.

Cobalt hydroxide is preferably added in order to improve the surface absorption, and when 0.1 to 40g is added in a solid weight ratio to 100g of a phosphate solution, it may contribute to improvement of physical properties.

The grain-oriented electrical steel sheet according to the present invention is formed by adding at least one selected from 25 to 300 parts by weight of silica, nickel or nickel hydroxide, based on solids, based on 100 parts by weight of phosphate, and adding 0.1 to 25 parts by weight based on the amount of nickel. The coating composition is applied to form an insulating coating, and the insulating coating is characterized by having a high coating tension of 0.35 ~ 1.00kg / mm ² . Since the coating composition of the insulating film formed on the surface of the grain-oriented electrical steel sheet is the same as described above, overlapping descriptions will be omitted. The coating tension is a value based on the application amount of the coating composition to 4.0 g / m ² as in the following examples, and when converted in relation to the coating amount (film tension / coating amount) × 100 ≧ 8.7 × 10 Satisfying ⁹ is a preferable condition.

Insulating film forming method of the grain-oriented electrical steel sheet according to the present invention is based on the solid content based on 100 parts by weight of phosphate 25 to 300 parts by weight of silica, at least one selected from nickel or nickel hydroxide 0.1 to 25% by weight After coating the coating composition, which is added by addition, to the surface of the steel sheet so that the dry coating amount is 0.5 to 6.0 g / m ² , the insulation coating is carried out by a two-step heat treatment performed after the latter heat treatment temperature is higher than the initial heat treatment temperature. To form. The coating composition may be formed by adding 0.1 to 40 parts by weight of cobalt hydroxide and 0.1 to 10 parts by weight of boric acid with respect to 100 parts by weight of phosphate, and redundant description of the added composition and its amount is omitted.

In the present invention, after mixing at least two or more selected from aluminum monophosphate, magnesium monophosphate or zinc monophosphate, and having a hydroxyl group on the surface and introducing a silica nanoparticle and nickel hydroxide having an average particle diameter of 1nm or more and 100nm or less. A coating composition is formed according to the mixing procedure to ensure compatibility. By forming the coating composition in such a mixing sequence, storage stability is ensured so that there is no problem even when stored for 10 hours or more.

The two-step heat treatment is preferably performed by heat treatment for 10 seconds to 10 minutes at a low temperature of less than 800 ℃, heat treatment for 30 seconds to 10 minutes at a high temperature of 800 ℃ or more.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on an Example. This is for illustrating the present invention, and the present invention is not limited to the specific embodiments.

<Examples>

As a test material, a grain-oriented electrical steel sheet (300x60mm) containing a Si: 3.1% by weight and a thickness of 0.23 mm finished annealing was used as a test material, and the surface coated by drying for 30 seconds at 850 ° C was coated on the coating material. Due to the addition of tensile stress, the bending strength of the insulation film was evaluated by measuring the degree of warpage.

The SRA was heat-treated at 750 ° C for 2 hours in a dry 100% N ₂ gas atmosphere. The insulation was expressed as the received current value when a voltage of 0.5 V and a current of 1.0 A were passed under a 300 PSI pressure. Is shown as the minimum arc diameter without film peeling when bent 180 ° in contact with a 10, 20, 30 to 100 mm arc, and the film appearance is evaluated by observing the presence of streaks, luster, and the like. Corrosion resistance is assessed for 5 hours at 35 ° C and NaCl solution for 8 hours. In this test, it is excellent when the rust area is less than 5%, good when less than 20%, 20 to 50% slightly poor, 50 Above%, it was marked as bad.

The present inventors examined the inferior physical properties one by one when the coating material was unchromated. First, chromium oxide was removed from the coating material, and the silica nanoparticles and the metal phosphate were mixed at a weight ratio of 1: 2, and a coating composition containing nickel hydroxide, cobalt hydroxide, and boric acid was mixed thereto. For comparison, some experiments were carried out by mixing metal phosphate with colloidal silica and boric acid.

The metal phosphate and silica nanoparticles, nickel hydroxide, cobalt hydroxide, boric acid were classified according to the mixing order, and after stirring for 8 hours at room temperature to evaluate compatibility, the viscosity change of the solution was measured and the results are shown in Table 1. It was.

[Table 1]

As shown in Table 1, the gelation phenomenon was observed in the conventional example using colloidal silica and metal phosphate. On the other hand, the addition of nickel hydroxide and cobalt hydroxide could prevent the gelation phenomenon. This phenomenon is thought to be due to the stabilization of the hydroxyl groups on the surface of the silica nanoparticles, the hydroxyl groups of the metal phosphate, and the hydroxyl groups of nickel and cobalt to form strong hydrogen bonds with each other.

In addition, it was confirmed that the mixing order and compatibility of the coating composition are closely related. That is, in Examples 1 to 3, which are composed of silica nanoparticles having a hydroxyl group in phosphate and nickel hydroxide, the compatibility is excellent, whereas in Comparative Example 2 in which nickel, cobalt, phosphate, and boric acid are added to silica, You can see that the castle is falling.

From the results of Table 1, phosphate, boric acid, nickel hydroxide, cobalt hydroxide, and silica nanoparticles were adopted as basic components of the non-chromium-based tension coating material. The coating properties of the components of the silica nanoparticles composed of hydroxides of metal phosphate and nickel hydroxide, cobalt hydroxide and boric acid dissolved in the surface were evaluated, and the coating amount was adjusted to 4.0 g / m ² . The coated composition was heat-treated in a drying furnace having a temperature of 750 ° C. in one step for 10 seconds to 10 minutes, and then dried in a two-step heat treatment of 30 seconds to 10 minutes in a drying furnace having a temperature set to 900 ° C. in two steps. .

The film tension characteristics, corrosion resistance, and gloss according to metal phosphate, nickel hydroxide, cobalt hydroxide, boric acid, and silica nanoparticle components were measured and shown in Table 2.

TABLE 2

(Excellent: ◎, good: ○, moderate: △, poor: X)

From these results, it can be seen that silica nanoparticles improve the film tension, and nickel hydroxide improves surface gloss and corrosion resistance. In Examples 1 to 13, wherein the amount of silica nanoparticles added to 100 parts by weight of phosphate, which is the scope of the present invention, belongs to 25 to 300 parts by weight, (tension tension / coating amount) × 100 is 8.7 × 10 ⁹ or more (film tension 0.35 kg / mm) ² or more). In Comparative Example 5 in which the amount of silica nanoparticles added was 350 parts by weight, poor surface quality was observed. In addition, it was confirmed that the corrosion resistance and gloss of the nickel equivalent amount of nickel hydroxide in Examples 1 to 13 belonging to the range of 0.1 to 25 parts by weight of the present invention are good or above normal levels. In order to obtain more excellent corrosion resistance and gloss, it is preferable to add nickel hydroxide at least 0.7 parts by weight based on the nickel equivalent. In Comparative Example 3 having a nickel hydroxide amount of 30 parts by weight, the surface quality was observed to be poor due to the color change of the insulating coating, and in Example 11 having a nickel hydroxide amount of 25 parts by weight, the surface quality was found to be normal. In consideration of corrosion resistance, gloss and surface quality at the same time, it is more preferable to add nickel hydroxide in an amount of 0.7 to 5.6 parts by weight. 1 and 2 show the surface analysis results and corrosion resistance when the insulating film is formed from the coating composition of Example 1 compared with the chromium-based insulating film. 1 and 2, when the insulating film of the grain-oriented electrical steel sheet is formed of the coating composition according to the present invention, it can be seen visually that the surface quality and corrosion resistance are superior to the conventional chromium-based insulating film.

The method for forming an insulating film according to the present invention is based on the solid content based on 100 parts by weight of the phosphate as described above from 25 to 300 parts by weight of silica, at least one selected from nickel or nickel hydroxide 0.1 to 25% by weight based on the amount of nickel After the addition of the composition to be added to the surface of the grain-oriented electrical steel sheet so that the dry coating amount is in the range of 0.5 ~ 6.0g / m ² per side, and heat-treated for 10 seconds to 10 minutes at a low temperature of less than 800 ℃, 800 It is made by heat treatment for 30 seconds to 10 minutes at a high temperature of more than ℃.

The reason why the coating composition is applied so that the dry coating amount is in the range of 0.5 to 6.0 g / m ² per side is less than 0.5 g / m ^{2 in} the dry coating state of the coating composition, so that the insulation is lowered to perform a function as an insulating coating. This is because it is difficult, and when it exceeds 6.0g / m ² it is difficult to form a solid film due to the film drying problem due to over-coating and cracks due to the weight of the film.

The present inventors formulated and coated the coating composition of Example 1 of Table 2 in order to identify the heat treatment conditions to obtain a better film tension, and dried it under various conditions to measure the film properties, the results are shown in Table 3 is shown.

[Table 3]

From Table 3, after performing one step of drying at low temperature, two steps of drying at high temperature are performed.

It can be seen that the two-step heat treatment performed greatly contributes to the improvement of the film tension. That is, as in the scope of the present invention, the film tension is improved by a two-step heat treatment for 10 seconds to 10 minutes at a low temperature of less than 800 ℃, heat treatment for 30 seconds to 10 minutes at a high temperature of more than 800 ℃, which is a phosphate and hydroxyl group It is thought that the hydrogen bonding reaction between nickel, cobalt and silica nanoparticles composed of is influenced by the two-stage heat treatment conditions.

If the one-stage drying at low temperature is kept less than 10 seconds, the film formation is insufficient and the hygroscopicity remains. Therefore, the one-stage drying is performed for more than 10 seconds, and if it exceeds 10 minutes, the surface appearance is bad due to the film oxidation. The drying is carried out in less than 10 minutes. In addition, even when the two-stage drying at a high temperature is less than 30 seconds, the problem of insufficient film formation occurs, so it is preferable to set the one-stage drying time to 30 seconds or more, and perform the two-stage drying in excess of 10 minutes. In this case, since the surface appearance deteriorates due to the film oxidation, it is preferable to perform two-stage drying of 10 minutes or less.

1 is a photograph showing an electron microscope (SEM) analysis result of an insulating film formed of a conventional chromium-based insulating film and the coating composition of the present invention.

2 is a photograph showing the corrosion resistance of the conventional chromium-based insulating film and the insulating film formed of the coating composition of the present invention.

Claims (15)

It is formed by adding 0.1 to 25 parts by weight of silica and 0.1 to 10 parts by weight of boric acid on the basis of nickel amount of at least one selected from 25 to 300 parts by weight of silica, nickel or nickel compounds based on 100 parts by weight of phosphate Coating composition for electrical insulation film formation with excellent film tension and corrosion resistance. The method according to claim 1, The nickel compound is nickel hydroxide, the coating composition for forming an electrical steel sheet excellent coating film corrosion resistance and corrosion resistance. The method according to claim 1 or 2, The silica is a coating composition for forming an electrical steel sheet excellent coating film and corrosion resistance, characterized in that having a hydroxyl group on the surface. The method according to claim 1 or 2, The silica is a coating composition for forming an insulating film of electrical steel with excellent film tension and corrosion resistance, characterized in that consisting of nanoparticles having an average particle diameter of more than 1nm 100nm. The method according to claim 1 or 2, The phosphate is a coating composition for forming an electrical steel sheet having excellent film tension and corrosion resistance, characterized in that the form of a mono aluminum phosphate, a first magnesium phosphate or a zinc phosphate alone or a mixture of at least two or more selected from them. . The method according to claim 1 or 2, The coating composition is a coating composition for forming an electrical steel sheet excellent coating film and excellent corrosion resistance, characterized in that the composition is added by adding 0.1 to 40 parts by weight of cobalt hydroxide with respect to 100 parts by weight of phosphate. delete It is formed by adding from 0.1 to 25 parts by weight of silica and from 0.1 to 10 parts by weight of boric acid based on nickel equivalent amount of at least one selected from 25 to 300 parts by weight, nickel or nickel hydroxide based on 100 parts by weight of phosphate Insulation coating is formed of a coating composition, the film is excellent tensile strength and corrosion-resistant electrical steel sheet, characterized in that the coating tension of 0.35 ~ 1.00kg / mm ² . The method according to claim 8, The silica has a hydroxyl group on the surface, the grain-oriented electrical steel sheet having excellent film tension and corrosion resistance, characterized in that consisting of nanoparticles of 1nm or more and 100nm or less. The method according to claim 8 or 9, The coating composition is a grain-oriented electrical steel sheet excellent in coating tension and corrosion resistance, characterized in that the composition is further added by 0.1 to 40 parts by weight of cobalt hydroxide relative to 100 parts by weight of phosphate. The method according to claim 8 or 9, The phosphate is a grain-oriented electrical steel sheet excellent in coating tension and corrosion resistance, characterized in that the form of a mixture of at least two or more selected from monobasic aluminum phosphate, monobasic magnesium phosphate or zinc monophosphate alone. The coating composition, which is formed by adding 25 to 300 parts by weight of silica, 0.1 to 25 parts by weight of nickel or nickel hydroxide, based on the amount of nickel, based on 100 parts by weight of phosphate, is dried. After the coating on the surface of the steel sheet to be 0.5 ~ 6.0g / m ² , the film tension and corrosion resistance characterized in that the insulating film is formed by a two-step heat treatment performed by the second heat treatment temperature higher than the initial heat treatment temperature Method of forming insulating film of excellent grain-oriented electrical steel sheet. The method according to claim 12, The coating composition is formed by adding 0.1 to 40 parts by weight of cobalt hydroxide and 0.1 to 10 parts by weight of boric acid with respect to 100 parts by weight of phosphate. The method according to claim 12, wherein the coating composition After mixing at least two or more selected from monobasic aluminum phosphate, monobasic magnesium phosphate or zinc monophosphate, and having a hydroxyl group on the surface thereof, silica nanoparticles having an average particle diameter of 1 nm or more and 100 nm or less are introduced. An insulating film forming method of a grain-oriented electrical steel sheet having excellent film tension and corrosion resistance, characterized by being formed by. The method of claim 12 or 13, wherein the two-step heat treatment After the heat treatment for 10 seconds to 10 minutes at a low temperature of less than 800 ℃, 30 seconds to 10 minutes heat treatment at a high temperature of 800 ℃ or more characterized in that the insulating film forming method of the oriented electrical steel sheet having excellent tensile strength and corrosion resistance.

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