Composition for forming insulating coating on electrical steel sheet, electrical steel sheet, and method for manufacturing electrical steel sheet

Abstract

The present invention provides an insulating coating composition for an electrical steel sheet, an electrical steel sheet, and a method for producing an electrical steel sheet, which can improve the insulating properties and tensile properties of an insulating coating and maintain high tensile properties even after stress relief annealing. [Solution] The composition for forming an insulating coating on an electrical steel sheet according to the present invention contains 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 3 to 150 parts by weight of a carbon structure, 3 to 150 parts by weight of an oxide containing two or more of Al, Si, Mg, and Fe in a total amount of 3 to 150 parts by weight, and 50 to 250 parts by weight of silica, with the carbon structure and oxide being 20 to 150 parts by weight in total.

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a composition for forming an insulating coating on an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the electrical steel sheet. More specifically, one embodiment of the present invention relates to a coating composition for forming an insulating coating on an electrical steel sheet, an electrical steel sheet, and a method for manufacturing the electrical steel sheet, which contains a carbon structure and an oxide in addition to a main component based on metal phosphate and silica, thereby improving the insulating properties and tensile properties of the insulating coating, while maintaining high tensile properties even after stress relief annealing, and imparting a beautiful color to the insulating coating, thereby dramatically increasing the surface yield rate of mass-produced products. [Background technology]

[0002] Grain-oriented electrical steel sheets generally contain a large amount of silicon and have a texture in which the grains are aligned in the 110

[0001] direction. They exhibit excellent magnetic properties in the rolling direction. It is known that these magnetic properties can be further improved by reducing the iron loss of grain-oriented electrical steel sheets and improving their insulation properties. Currently available grain-oriented electrical steel sheets aim to reduce iron loss by applying tensile stress to the steel sheet by utilizing the difference in thermal expansion coefficients between the steel sheet and the insulating coating (secondary coating) formed on a forsterite-based base coating (primary coating). In relation to this, active research is being conducted into the formation of a high-tensile insulating coating on the surface of grain-oriented electrical steel sheets as a method for reducing iron loss.

[0003] The primary coating of grain-oriented electrical steel sheet is a forsterite (2MgO SiO2) layer formed by a reaction between silicon oxide (SiO2) produced on the surface of the material during the primary recrystallization decarburization annealing process and magnesium oxide (MgO), used as an annealing separator. This primary coating formed during high-temperature annealing should preferably have a uniform color and no external defects. Functionally, it prevents fusion between sheets in the coiled state and applies tensile stress to the material due to the difference in thermal expansion coefficients between the material and the primary coating, thereby improving the core loss of the material.

[0004] However, the most important characteristic of a primary coating is that it has a uniform color and no defects on the surface of the material. Commercially produced products are manufactured in large coils, making it extremely difficult to maintain uniform coating properties along the entire length of the coil. In commercially produced coil-shaped grain-oriented electrical steel sheets, the amount of hydrated water released varies depending on the coil position and location, making it impossible to avoid the occurrence of bare spots or oxidation defects. In particular, secondary coatings formed with conventional phosphate-based tension coating agents have poor shielding properties due to their high transparency, exposing defects in the primary coating underneath the secondary coating. Therefore, in mass production, exposed defective areas are removed before shipping, resulting in a lower yield and higher product unit prices.

[0005] Coils that have been coated with the secondary tensile coating are supplied in hoop form after being slit to the desired size by transformer manufacturers, and are manufactured into stacked core transformers or wound core transformers depending on the application. In order to improve efficiency when manufacturing transformers, inter-plate insulation is very important, and generally, increasing the coating thickness improves insulation, but reduces no-load loss, which can ultimately result in a decrease in transformer efficiency.

[0006] To solve these problems and maximize coating properties such as film tension and insulation, the coating agent needs to incorporate an insoluble substance into the coating. However, the insoluble substance is not widely used due to technical issues such as reduced illuminance and gloss, as well as the generation of voids within the coating after formation. Therefore, there is a need for a colored secondary coating product that can mask oxidation defects that occur in the primary coating and has excellent insulation properties even at thin coating thicknesses. However, conventional coating agents for grain-oriented electrical steel sheets are unable to meet these requirements, and commercialization technology is needed to address this issue. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a composition for forming an insulating coating on an electrical steel sheet, an electrical steel sheet, and a method for producing the same, specifically, a composition for forming an insulating coating on an electrical steel sheet that contains a metal phosphate, silica-based main components, and also a carbon structure and an oxide, an electrical steel sheet, and a method for producing the same. [Means for solving the problem]

[0008] A composition for forming an insulating coating on an electrical steel sheet according to one embodiment of the present invention comprises 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 3 to 150 parts by weight of a carbon structure, 3 to 150 parts by weight of an oxide containing two or more of Al, Si, Mg, and Fe in a total amount of 3 to 150 parts by weight, and 50 to 250 parts by weight of silica, with the carbon structure and the oxide in a total amount of 20 to 150 parts by weight.

[0009] The carbon structure may include one or more of natural graphite, synthetic graphite, carbon black, carbon nanotubes, carbon fiber, and graphene.

[0010] The oxide containing two or more of Al, Si, Mg, and Fe may include one or more of montmorillonite, kaolinite, illite, talc, and chlorite.

[0011] The silica may have an average particle size of 7 to 20 nm.

[0012] The composition for forming an insulating coating on an electrical steel sheet according to one embodiment of the present invention may further include 2 to 10 parts by weight of chromium oxide.

[0013] An electrical steel sheet according to one embodiment of the present invention includes an electrical steel sheet substrate and an insulating coating located on a surface of the electrical steel sheet substrate, the insulating coating including 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 3 to 150 parts by weight of a carbon structure, 3 to 150 parts by weight of a total of an oxide containing two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica, and the carbon structure and the oxide can be included in a total of 20 to 150 parts by weight.

[0014] The insulating coating may have a surface roughness (Ra) of 0.5 μm or less and a coating transparency of 20% or less.

[0015] The insulating coating can consist of, in weight percent, 6.0 to 45% P, 11 to 80% Si, 0.5 to 10% Cr, 0.1 to 35% of one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn, 1 to 40% C, and the remainder being O and unavoidable impurities.

[0016] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention includes the steps of preparing an electrical steel sheet substrate, applying the composition for forming an insulating coating according to claim 1 to the surface of the electrical steel sheet substrate, and performing a heat treatment.

[0017] The method may further include storing the composition for forming an insulating coating at a temperature of 10 to 30° C. before the coating step.

[0018] At the coating stage, the composition for forming an insulating coating is applied at a rate of 0.5 to 6.0 g / m 2 It can be applied over a range.

[0019] In the heat treatment step, the heat treatment can be performed at 550 to 900°C for 10 to 50 seconds. [Effects of the Invention]

[0020] A composition for forming an insulating coating on an electrical steel sheet according to one embodiment of the present invention can improve the coating tension and insulating properties of an insulating coating, while at the same time maintaining high coating tension properties even after stress relief annealing (SRA). It can also impart beautiful luminance to the insulating coating, thereby imparting excellent gloss and beautiful color, thereby dramatically increasing the surface yield rate of mass-produced products. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of a cross section of an electrical steel sheet according to an embodiment of the present invention. FIG. [Figure 2] 1 is a photograph of a cross section of the electrical steel sheet produced in Example 1 taken with a scanning electron microscope (SEM). [Figure 3] 1 is a photograph of a cross section of the electrical steel sheet produced in Comparative Example 8 taken with a scanning electron microscope (SEM). DETAILED DESCRIPTION OF THE INVENTION

[0022] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0023] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0024] When a moiety is referred to as being "on" another moiety, it means that it is directly on top of the other moiety, or there may be other moieties between them. In contrast, when a moiety is referred to as being "directly on" another moiety, there may be no other moieties between them. Also, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001 wt%. In one embodiment of the present invention, the term "further containing an additional element" means that an additional amount of the additional element is contained in place of the remaining iron (Fe) or oxygen (O).

[0025] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not to be construed as having an ideal or very formal meaning unless defined.

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily understand and practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0027] A composition for forming an insulating coating on an electrical steel sheet according to one embodiment of the present invention contains 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 10 to 150 parts by weight of a carbon structure, 10 to 150 parts by weight in total of an oxide containing two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica.

[0028] Each component will be described in detail below. In one embodiment of the present invention, parts by weight refer to the relative weight ratio based on 100 parts by weight of metal phosphate and are based on the solid content of each component. The solid content refers to the weight of each component when it is dried to a state free of volatiles such as solvents. Specifically, it refers to the weight remaining after heat treatment, assuming a heat treatment process during the formation of an insulating coating. The metal phosphate acts as a binder in the composition for forming an insulating coating. If the metal phosphate is not included in the appropriate amount, the insulating coating may have poor adhesion or may not be able to obtain sufficient tension.

[0029] Metal phosphates can be prepared by adding a metal oxide to pure phosphoric acid (H3PO4) and reacting them. To improve the adhesion of the metal phosphate, a condensation reaction between the metal phosphate and boric acid can be induced by adding boric acid during the reaction and maintaining the reaction for at least 3 hours. This condensation reaction product can be used instead of the metal phosphate. In one embodiment of the present invention, the metal phosphate includes not only the metal phosphate but also the condensation reaction product between the metal phosphate and boric acid. The prepared metal phosphate is highly acidic.

[0030] The metal phosphate can be added to the composition using a solution with a solid content of 50 to 70 wt %. If the solid content in the solution is too low, free phosphoric acid increases in the metal phosphate, which can cause surface moisture absorption after the metal phosphate is produced. If the solid content is too high, the excess solid content compared to pure phosphoric acid can cause poor reaction and precipitation.

[0031] The metal phosphate and metal oxide may contain various metals without limitation. Specifically, the metals of the metal phosphate and metal oxide may include one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn. More specifically, the metal phosphate may include one or more of monomagnesium phosphate (Mg(H2PO4)2) and monoaluminum phosphate (Al(H2PO4)3). More specifically, the metal phosphate may include monomagnesium phosphate (Mg(H2PO4)2) and monoaluminum phosphate (Al(H2PO4)3). In this case, the metal phosphate may contain 10 to 40 parts by weight of monoaluminum phosphate and 60 to 90 parts by weight of monomagnesium phosphate per 100 parts by weight of the total solids content. If the amount of monoaluminum phosphate is too low, the tensile strength improvement effect of the addition of the monoaluminum phosphate may be insufficient. If the amount of monoaluminum phosphate is too high, the Al component may increase silica crystallization, causing cracks in the insulating coating. Specifically, the metal phosphate may contain 15 to 35 parts by weight of aluminum monophosphate and 65 to 85 parts by weight of magnesium monophosphate, and more specifically, 20 to 30 parts by weight of aluminum monophosphate and 70 to 80 parts by weight of magnesium monophosphate, based on the total 100 parts by weight of the solid content.

[0032] An insulating coating composition according to one embodiment of the present invention contains 3 to 150 parts by weight of carbon structures per 100 parts by weight of metal phosphate. The carbon structures are added to improve the shielding properties and coating tension of the coating. Here, improving shielding properties means lowering transparency to enhance color and shielding performance. Furthermore, improving coating tension means utilizing the low thermal expansion coefficient of the carbon structures to lower the thermal expansion coefficient of the coating formed, thereby applying tensile stress to the substrate. If the carbon structures are included in an excessively low amount, while there is an advantage in that almost no voids are generated within the coating after coating formation, the coating color may be light and transparency may be high, significantly reducing the shielding effect. Furthermore, the tension applied to the substrate by the coating is so weak that the iron loss improvement effect due to the coating tension cannot be expected. If the carbon structures are included in an excessively high amount, the solid fraction in the composition may be high, which may cause aggregation and sedimentation between the carbon structures. Furthermore, voids may form at the carbon structure interfaces after coating formation, significantly reducing the coating tension and insulating properties. Therefore, specifically, the carbon structure is contained in an amount of 10 to 150 parts by weight per 100 parts by weight of the metal phosphate.

[0033] The carbon structure may include one or more of natural graphite, artificial graphite, carbon black, carbon nanotubes, carbon fibers, and graphene, and may specifically include carbon black.

[0034] The carbon structure has an average grain size of 10 1 nm~10 6 nm. More specifically, 10 1 ~10 3 The average particle size of the carbon structure can be as small as 100 nm. If the average particle size of the carbon structure is too small, it is difficult to disperse uniformly in the solution due to the electrostatic attraction of the particles themselves, and if the average particle size is too large, it is difficult to achieve proper performance due to rapid sedimentation in the solution. The average particle size can be measured by dispersing particles in a solution and using a laser scattering method.

[0035] An insulating coating composition according to one embodiment of the present invention contains 3 to 150 parts by weight of oxides containing two or more of Al, Si, Mg, and Fe per 100 parts by weight of metal phosphate. The oxides are added to improve the shielding properties and coating tension of the coating. Here, improving shielding properties means lowering transparency to enhance color and shielding performance. Improving coating tension means utilizing the low thermal expansion coefficient of the oxide to lower the thermal expansion coefficient of the coating formed and impart tensile stress to the substrate. If the oxide content is too low, there is the advantage that almost no voids are generated within the coating after coating formation, but the coating color may be light and transparency may be high, significantly reducing the shielding effect. Furthermore, the tension applied to the substrate by the coating is so slight that the coating tension cannot be expected to improve iron loss. If the oxide is included in an excessive amount, the solid content in the composition will be high, which may cause aggregation and sedimentation between the oxides, and after the coating is formed, voids may form at the oxide interface, which may significantly reduce the coating tension and insulating properties. Therefore, specifically, the oxide should be included in an amount of 10 to 150 parts by weight per 100 parts by weight of the metal phosphate.

[0036] The oxide containing two or more of Al, Si, Mg, and Fe may include one or more of montmorillonite, kaolinite, illite, talc, and chlorite. More specifically, montmorillonite (Montmorillonite, M x (Al 4-x Mg x )SiO 20 Oxides containing two or more of Al, Si, Mg, and Fe have a lower thermal expansion coefficient than oxides containing only one of them (e.g., Al2O3), and therefore have the advantage of increasing coating tension and improving iron loss.

[0037] Oxides containing two or more of Al, Si, Mg and Fe have an average particle size of 10 2 nm~10 5nm. If the average particle size of the oxide is too small, it is difficult to disperse uniformly in the solution due to the electrostatic attraction of the particles themselves, and if the average particle size is too large, it is difficult to achieve optimal performance due to rapid sedimentation in the solution. The average particle size can be measured by dispersing particles in a solution and using laser scattering.

[0038] The oxide's component ratios among Al, Si, Mg, and Fe are important. Based on the total weight of Al, Si, Mg, and Fe in the oxide particles (100%), the oxide particles can contain 15-45 wt% Al, 40-70 wt% Si, 0.1-5 wt% Mg, and 1-10 wt% Fe. The reason for limiting the major components in the oxide as described above is that excessively low Al content in the oxide particles results in a low coating modulus, making it impossible to achieve the desired coating tension. Excessive Al content increases electrical conductivity, resulting in poor coating insulation. Excessively low Si content in the particles results in a difference in thermal expansion coefficients, making it impossible to achieve the desired coating tension. Excessive Si content increases coating hardness, significantly reducing the workability of the material.

[0039] If the Mg content is too low, the affinity between the water and oxide in the coating solution decreases, resulting in less uniform dispersion of the oxide in the coating solution. If the Mg content is too high, the film's elastic modulus decreases, preventing the film from achieving improved tension. Furthermore, if the Fe content is too low, the heat resistance of the film decreases. If the Fe content is too high, the specific gravity of the oxide increases, accelerating its settling and reducing the corrosion resistance of the film. More specifically, the oxide particles can contain 20-40 wt% Al, 45-65 wt% Si, 0.5-3 wt% Mg, and 3-7 wt% Fe, based on the total weight of Al, Si, Mg, and Fe (100%). The oxide can also contain Ca and K.

[0040] The oxide content must be adjusted by adjusting the total amount with the carbon structure. Specifically, the total amount of the carbon structure and oxide may be 20 to 170 parts by weight per 100 parts by weight of the metal phosphate. More specifically, the total amount of the carbon structure and oxide may be 30 to 150 parts by weight. The carbon structure and oxide act similarly in terms of forming voids in the coating, and the total amount must be adjusted.

[0041] Silica increases the strength and hardness of the coating itself through an intramolecular network reaction when the coating dries after coating, thereby applying tension to the material. Various silicas can be used without restriction, including commercially available colloidal silica. More specifically, basic colloidal silica can be used. Generally, tension coating agents for grain-oriented electrical steel sheets are prepared by mixing chromium oxide, which reinforces corrosion resistance after coating formation, with solid silica, which adjusts the illuminance and applicability of the coating.

[0042] Silica may be included in an amount of 50 to 250 parts by weight per 100 parts by weight of the metal phosphate. If too little silica is added, the tensile strength-improving effect of silica addition cannot be fully achieved. If too much silica is added, the amount of metal phosphate is relatively reduced, which may result in poor adhesion of the insulating coating. Specifically, silica may be included in an amount of 100 to 200 parts by weight per 100 parts by weight of the metal phosphate, and more specifically, silica may be included in an amount of 125 to 175 parts by weight per 100 parts by weight of the metal phosphate. Here, parts by weight refer to the relative weight based on the metal phosphate.

[0043] During the drying process of the coating, silica undergoes a condensation reaction due to a chain reaction of silica as shown in Reaction Formula 1 below, forming a network structure such as -(HO-Si-O-Si)-n.

[0044] [Reaction Scheme 1] -(HO-Si-OH-) n +-(HO-Si-OH-) n =-(HO-Si-O-Si-) n +H2O (1)

[0045] However, if silica alone is used, an excessively uniform network structure is formed, which limits the denseness of the coating. Therefore, there is a limit to the adhesion between the electrical steel sheet substrate and the insulating coating and the corrosion resistance it can provide. To compensate for these insufficient physical properties, metal phosphate or metal phosphate and chromium oxide can be used.

[0046] The silica may be colloidal silica having an average particle size in the range of 7 to 20 nm. The composition may be prepared using a solution of silica having a solid fraction of 25 to 35 wt%. If the solid fraction is too low, the insulating properties may be reduced. If the solid fraction is too high, the compatibility of the coating may be reduced after preparation. More specifically, the solid fraction may be 28 to 32 wt%.

[0047] Silica is Na + The content can be 0.1 to 1.0 wt%. + If the content is too low, the density of the coating may decrease. + If the content is too high, the increase in cations in the coating agent can cause problems with inter-component compatibility. + The content may be 0.3 to 0.7 wt%. The silica solution containing silica may have a pH of 9.5 to 10.5. If the pH is too low or too high, the pH difference between components other than silica in the coating composition may be too great, resulting in phase separation. More specifically, the pH may be 9.5 to 10.0.

[0048] The viscosity of silica may be 3.5 to 6.5 cp. If the viscosity is too low, problems may occur with the application of the coating composition. If the viscosity is too high, the composition may thicken over time and cause aging problems. More specifically, the viscosity may be 4 to 6 cp. The viscosity may be measured using a Brookfield viscometer at 20°C based on a 30% by weight silica solution.

[0049] The specific gravity of silica may be 1.1 to 1.3. If the specific gravity is too low, it may be difficult to control the amount of coating composition applied. If the specific gravity is too high, sedimentation may occur after the coating agent is prepared. More specifically, the specific gravity may be 1.15 to 1.25.

[0050] Chromium oxide may be added to enhance the corrosion resistance of the insulating coating. When chromium oxide is added, it may be included in an amount of 2 to 10 parts by weight per 100 parts by weight of metal phosphate. If the amount of chromium oxide is too small, the corrosion resistance enhancement effect may be insufficient and it may be difficult to properly perform the role of neutralizing silica, as described below. If the amount of chromium oxide is too large, the viscosity of the coating agent may increase rapidly. Specifically, chromium oxide may be included in an amount of 2 to 8 parts by weight per 100 parts by weight of metal phosphate, and more specifically, chromium oxide may be included in an amount of 4 to 6 parts by weight per 100 parts by weight of metal phosphate.

[0051] In addition to the above-mentioned components, the composition for forming an insulating coating may further include a solvent. The solvent facilitates application of the composition and uniformly disperses the components. The amount of solvent is not particularly limited, but may be 100 to 1,000 parts by weight per 100 parts by weight of the metal phosphate. The method for producing the composition for forming an insulating coating is not particularly limited, but the following methods may be used.

[0052] The method may include the steps of simultaneously adding metal oxide and powder (two or more oxides and a carbon structure) to phosphoric acid (H3PO4), heating and mixing to prepare a first composition containing metal phosphate and powder, and mixing silica and, if necessary, chromium oxide into the first composition. At this time, the mixing ratio can be the same as the solid content ratio described above, so redundant description will be omitted.

[0053] Each step will be described in detail below. If the powder is added after the reaction between phosphoric acid and metal oxide, the viscosity of the metal phosphate increases rapidly after the metal phosphate is produced, and even if the powder is introduced and mixed at this stage, the powder will not be uniformly dispersed within the metal phosphate, resulting in a phenomenon in which the particles aggregate with each other.

[0054] In one embodiment of the present invention, a metal oxide and a powder are simultaneously added to phosphoric acid to cause a reaction between the phosphoric acid and the metal oxide. Since the reaction has not yet progressed and the phosphoric acid has a low viscosity, the powder is added. As a result, a very uniform phosphoric acid / powder mixed phase is formed due to the flow induced by stirring, and the mixture gradually progresses to a uniform metal phosphate / powder mixed phase with a higher viscosity, thereby improving the dispersibility of the powder in the coating composition and significantly improving the shielding properties of the coating.

[0055] In the step of preparing the first composition, the heating temperature may be 80° C. or higher. If the heating temperature is too low, the powder may not form a uniform mixed phase in the metal phosphate even when stirred, and the particles may aggregate together. Silica and optionally chromium oxide may then be added to and mixed with the first composition.

[0056] The silica and chromium oxide and their contents have been described in relation to the composition for forming an insulating coating on an electrical steel sheet, and therefore, a duplicated description will be omitted.

[0057] Silica becomes basic and metal phosphate becomes acidic, and when they are mixed, a temporary gelation phenomenon occurs due to the significant pH difference between the two components, which prevents the formation of a dense coating. In one embodiment of the present invention, chromium oxide is used as a buffer to neutralize the silica.

[0058] FIG. 1 shows a schematic cross-sectional view of an electrical steel sheet 100 according to one embodiment of the present invention. As shown in FIG. 1, the electrical steel sheet 100 according to one embodiment of the present invention includes an electrical steel sheet substrate 10 and an insulating coating 20 disposed on the electrical steel sheet substrate 10. The electrical steel sheet substrate 10 can be a general non-oriented or grain-oriented electrical steel sheet without restriction. Since one embodiment of the present invention is mainly configured by forming an insulating coating 20 of a special composition on the electrical steel sheet substrate 10, a detailed description of the electrical steel sheet substrate 10 will be omitted. The components of the grain-oriented electrical steel sheet substrate will now be described.

[0059] The grain-oriented electrical steel sheet substrate contains 2.0 to 7.0 wt% silicon (Si), 0.020 to 0.040 wt% aluminum (Al), 0.01 to 0.20 wt% manganese (Mn), 0.01 to 0.15 wt% phosphorus (P), 0.01 wt% or less (excluding 0%) carbon (C), 0.005 to 0.05 wt% N, and 0.01 to 0.15 wt% antimony (Sb), tin (Sn), or a combination thereof, with the balance being Fe and other unavoidable impurities. The description of each component of the grain-oriented electrical steel sheet substrate 10 is the same as that generally known, so a detailed description will be omitted.

[0060] A metal oxide layer (base coating layer, primary coating) formed by reaction between the grain-oriented electrical steel sheet substrate and the insulating coating during the secondary recrystallization process and the annealing separator and the oxide layer of the steel sheet may exist between the grain-oriented electrical steel sheet substrate and the insulating coating. An example of a metal oxide layer is a forsterite layer. It is possible for the formation of the metal oxide layer to be suppressed or removed during the manufacturing process of the grain-oriented electrical steel sheet, resulting in contact between the grain-oriented electrical steel sheet substrate and the insulating coating.

[0061] The thickness of the insulating coating 20 may be 1 to 10 μm. If the insulating coating 20 is too thin, it is difficult to ensure appropriate insulation. If the insulating coating 20 is too thick, the space factor may be low. In one embodiment of the present invention, appropriate insulation can be ensured even when a thin insulating coating 20 is formed. More specifically, the thickness of the insulating coating 20 may be 2 to 5 μm.

[0062] The insulating coating 20 can maintain the solid components and content ratios of the insulating coating composition described above. Specifically, the insulating coating 20 can include 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 10 to 150 parts by weight of a carbon structure, 10 to 150 parts by weight of an oxide containing two or more of Al, Si, Mg, and Fe in total, and 50 to 250 parts by weight of silica. The reasons for limiting each component and its content are the same as those described for the composition described above, so a repeated explanation will be omitted.

[0063] The insulating coating 20 may contain both the carbon structure and oxide. By containing both the carbon structure and oxide, the insulating coating exhibits excellent defect shielding and excellent coating tensile strength and excellent insulating properties before and after SRA due to the oxide's low thermal expansion coefficient and heat resistance. The insulating coating 20 may have a surface roughness (Ra) of 0.5 μm or less. If the surface roughness of the insulating coating is too high, the space factor increases during lamination of materials for transformer manufacturing, which can result in reduced transformer efficiency.

[0064] The insulating coating 20 may have a coating transparency of 20% or less. Coating transparency is measured by reflectometry and is defined as the ratio of the absolute intensity of the reflected light (Ir) to the intensity of the incident light (Ii) on the specimen (Ir / Ii), or the reciprocal of (1 / Rabs). That is, coating transparency 1 / Rabs = Ir / Ii. If the coating has high transmittance and most of the incident light is reflected, the coating transparency approaches 100%. Conversely, if the coating has low transmittance and most of the incident light is absorbed or scattered by the coating, the coating transparency approaches 0%. If the coating transparency is 20% or less, the coating is opaque, and external light incident from the outside is mostly absorbed or scattered by the coating, making it impossible to distinguish the original color of the specimen underneath, resulting in excellent shielding effects. On the other hand, if the coating transparency exceeds 20%, the opacity is poor and the original color of the specimen beneath the coating cannot be discerned, which makes it impossible to achieve the object of the present invention. Specifically, the coating transparency may be 19% or less, and more specifically, 10% or less.

[0065] The insulating coating may contain, in weight percent, 6.0 to 45% P, 11 to 80% Si, 0.5 to 10% Cr, 0.1 to 30% of one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn, 1 to 40% C, and the remainder being oxygen and unavoidable impurities.

[0066] Phosphorus (P) may be contained in the insulating coating at 6.0 to 45 wt %. Phosphorus (P) may originate from metal phosphates in the insulating coating composition or may diffuse from the electrical steel sheet substrate 10. If the phosphorus (P) ratio is too high, the coating may become sticky after formation. If the phosphorus (P) ratio is too low, the coating may have poor adhesion. More specifically, P may be contained at 18 to 23 wt %.

[0067] Silicon (Si) may be contained in the insulating coating at 11 to 80 wt %. Silicon (Si) may originate from silica or oxides in the insulating coating composition, or may diffuse from the electrical steel sheet substrate 10. If the silicon (Si) ratio is too high, the coating may be too hard and its workability may be reduced, while if the silicon (Si) ratio is too low, the coating tension effect of silicon may be reduced. More specifically, silicon (Si) may be contained at 20 to 45 wt %.

[0068] Chromium (Cr) may be contained in the insulating coating at 0.5 to 10 wt %. Chromium (Cr) may originate from chromium oxide in the insulating coating composition or may diffuse from the electrical steel sheet substrate 10. If the chromium (Cr) ratio is too high, the viscosity of the coating agent may increase, which may cause problems with application. If the chromium (Cr) ratio is too low, problems may occur with reduced corrosion resistance. More specifically, chromium (Cr) may be contained at 1.5 to 2.3 wt %.

[0069] Carbon (C) may be contained in the insulating coating at 1 to 40 wt %. Carbon (C) may originate from carbon structures in the insulating coating composition or may diffuse from the electrical steel sheet substrate 10 during the insulating coating formation process. If the carbon (C) ratio is too high, problems may occur, such as ash remaining on the surface after the coating is formed. If the carbon (C) ratio is too low, problems may occur, such as increased transparency of the coating, resulting in reduced shielding properties. More specifically, carbon (C) may be contained at 3 to 40 wt %.

[0070] The remainder comprises oxygen (O). Specifically, the oxygen content may be 35 to 75% by weight. The insulating coating may further comprise 0.1 to 35% of one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn.

[0071] The aforementioned Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn can be derived from metal phosphates added to the insulating coating composition. Adding Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn within the aforementioned ranges can further improve adhesion. More specifically, the insulating coating composition can contain 20 to 33 wt % of one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn.

[0072] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of applying a composition for forming an insulating coating onto an electrical steel sheet substrate, and drying the steel sheet to which the composition for forming an insulating coating has been applied to form an insulating coating.

[0073] First, the insulating coating composition is applied to an electrical steel sheet substrate. The electrical steel sheet substrate and the insulating coating composition are the same as those described above, so a repeated explanation will be omitted. The insulating coating composition before application can be maintained at a temperature of 10 to 30°C. If the temperature is lower than the above range, the viscosity increases, making it difficult to control a uniform application amount. If the temperature is too high, the gelation phenomenon of the insulating coating composition may be accelerated, resulting in a deterioration in surface quality. More specifically, the insulating coating composition before application can be maintained at a temperature of 15 to 25°C.

[0074] When applying the insulating coating composition, the amount of application is 0.5 to 6.0 g / m 2 If the amount of coating is too large, the insulating coating will become too thick, which may result in poor adhesion to the steel sheet and poor space factor in the electrical steel sheet product. If the amount of coating is too small, the tension provided by the insulating coating may be weak. More specifically, the amount of coating should be 1.0 to 5.0 g / m. 2 It could be.

[0075] The drying step may involve heating at 550-900°C for 10-50 seconds. Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereto, but is defined only by the scope of the claims below.

[0076] Experimental example: Confirmation of characteristics by metal type

[0077] Grain-oriented electrical steel sheets (300 x 60 mm) containing 3.1% Si by weight and having a finish-annealed primary coating with a thickness of 0.23 mm were prepared as test materials. An insulating coating composition containing the ingredients listed in Table 1 below and 100 g of water was prepared. When producing the phosphate, metal oxide and powder (composite oxide and carbon structure) were simultaneously added to phosphoric acid and stirred under a heated state of 80°C or higher to produce the metal phosphate, after which chromium oxide and colloidal silica were added and mixed. The produced insulating coating composition was applied to the test material at a concentration of 4 g / m 2 After coating, the coating was dried at 850°C for 30 seconds to prepare a test specimen. The physical properties of the test specimens prepared in this manner were measured and are shown in Table 3 below, and the composition of the insulating coating formed on the test specimens was summarized in Table 2 below.

[0078] Corrosion resistance measurement method: The rust area of ​​the specimen was evaluated after immersing it in a 5% by weight NaCl solution at 35°C for 8 hours. Coating tension measurement method: The insulating coating on one side of the specimen was removed, and the remaining insulating coating on the surface was bent in one direction with tensile stress applied. The force required to bend the specimen was measured to evaluate the coating tension of the insulating coating. Franklin insulation measurement: The storage current value was measured when a current of 1.0 A was passed through an input of 0.5 V under 300 PSI pressure.

[0079] Impedance insulation measurement: Using KCl as the electrolyte solution, Pt as the counter electrode, and Ag / AgCl as the reference, the real part of the impedance resistance measurement was calculated. When measuring resistance, both terminals were measured 100 mm apart for all specimens. Coating transparency measurement: As mentioned above, the coating transparency was measured using reflectometry. Coating solution uniformity: Immediately after the solution was made, the powder dispersion state within the solution was judged as good / bad. Presence or absence of voids within the coating: Observed using a focused ion beam scanning electron microscope.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] As can be seen from Tables 1 to 3, in the examples where the carbon structure and composite oxide were appropriately contained, it was confirmed that the insulation property, film shielding property, presence or absence of voids, corrosion resistance, and coating tension were all improved in all composition systems. On the other hand, it was confirmed that the comparative examples where the constituent components were not appropriately contained were inferior in terms of insulation property, film shielding property, presence or absence of voids, corrosion resistance, and coating tension.

[0084] 2 and 3, it can be seen that the insulating coating is densely formed without any voids in the case of Example 1 shown in Fig. 2. In the case of Comparative Example 8 shown in Fig. 3, it can be seen that multiple voids, represented by dark areas, are formed in the insulating coating.

[0085] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting.

Claims

1. 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn; 3 to 150 parts by weight of carbon structure, an oxide containing two or more of Al, Si, Mg, and Fe in a total amount of 3 to 150 parts by weight; and containing 50 to 250 parts by weight of silica, A composition for forming an insulating coating on an electrical steel sheet, comprising the carbon structure and the oxide in a total amount of 20 to 150 parts by weight.

2. 2. The composition for forming an insulating coating for electrical steel sheet according to claim 1, wherein the carbon structure comprises at least one of natural graphite, artificial graphite, carbon black, carbon nanotubes, carbon fiber, and graphene.

3. 2. The composition for forming an insulating coating on an electrical steel sheet according to claim 1, wherein the oxide containing two or more of Al, Si, Mg, and Fe includes one or more of montmorillonite, kaolinite, illite, talc, and chlorite.

4. 2. The composition for forming an insulating coating on an electrical steel sheet according to claim 1, wherein the silica has an average particle size of 7 to 20 nm.

5. The composition for forming an insulating coating on an electrical steel sheet according to claim 1, further comprising 2 to 10 parts by weight of chromium oxide.

6. an electrical steel substrate, and an insulating coating located on a surface of the electrical steel sheet substrate, the insulating coating comprises 100 parts by weight of a metal phosphate containing one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, 3 to 150 parts by weight of a carbon structure, 3 to 150 parts by weight in total of an oxide containing two or more of Al, Si, Mg, and Fe, and 50 to 250 parts by weight of silica; The electrical steel sheet comprises the carbon structure and the oxide in a total amount of 20 to 150 parts by weight.

7. 7. The electrical steel sheet according to claim 6, wherein the insulating coating has a surface roughness (Ra) of 0.5 μm or less and a coating transparency of 20% or less.

8. 7. The electrical steel sheet according to claim 6, wherein the insulating coating contains, in weight %, 6.0 to 45% P, 11 to 80% Si, 0.5 to 10% Cr, 0.1 to 35% of one or more of Al, Mg, Co, Ca, Sr, Ba, Zn, Fe, and Mn, 1 to 40% C, and the remainder being O and unavoidable impurities.

9. preparing an electromagnetic steel sheet substrate; applying the insulating coating composition according to claim 1 to a surface of the electrical steel sheet substrate; and A method for manufacturing an electrical steel sheet, comprising a heat treatment step.

10. The method for manufacturing an electrical steel sheet according to claim 9, further comprising storing the insulating coating composition at a temperature of 10 to 30° C. before the coating step.

11. In the step of applying, the composition for forming an insulating coating is applied at a rate of 0.5 to 6.0 g / m ２ The method for producing an electrical steel sheet according to claim 9, wherein the coating is applied within a range.

12. The method for manufacturing an electrical steel sheet according to claim 9, wherein the heat treatment is performed at 550 to 900°C for 10 to 50 seconds.

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