Electrical steel sheet insulating coating composition, electrical steel sheet and method for manufacturing the same

Abstract

An insulating coating composition for electrical steel sheets according to an embodiment of the present invention comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate and feldspar.

Description

Technical Field

[0001] One embodiment of the present invention relates to an insulating coating composition for electrical steel sheets, an electrical steel sheet, and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an insulating coating composition for electrical steel sheets, an electrical steel sheet, and a method for manufacturing the same. By appropriately combining the components of the insulating coating composition, the coating will not separate even in high-temperature and high-humidity environments, and it exhibits excellent shielding and tension imparting effects in the high-frequency region. Background Technology

[0002] Electrical steel sheets are used as materials for transformers, motors, and electrical equipment. Unlike ordinary carbon steel, which emphasizes machinability such as mechanical properties, electrical steel sheets are functional products that prioritize electrical properties. The required electrical properties include low iron loss, high magnetic flux density, high magnetic permeability, and high fill power.

[0003] Electrical steel sheets are further divided into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. Grain-oriented electrical steel sheets utilize an abnormal grain growth phenomenon known as secondary recrystallization to form a Gaussian texture in the overall steel sheet ({110}). <001> (Texture), thus possessing good magnetic properties in the rolling direction. Non-oriented electrical steel sheet is an electrical steel sheet with uniform magnetic properties in all directions of the rolled sheet.

[0004] On the other hand, the insulating coating formation process is equivalent to the final manufacturing process of the product. Besides the electrical properties that typically suppress eddy current generation, it also requires continuous punching workability to suppress die wear during the stacking of multiple cores after being punched into a predetermined shape, anti-adhesion properties to prevent adhesion between the core steel plates after the SRA process (which eliminates processing stress in the steel plates to restore magnetic properties), and surface adhesion. In addition to these basic characteristics, the coating solution is also required to have excellent coating operability and long-term solution stability after preparation. Coating solutions used for these purposes include chromic acid-based chromium coating solutions and phosphate-based phosphate coating solutions.

[0005] Such coating solutions exhibit excellent corrosion resistance. However, they are susceptible to weathering damage and can become sticky. If the weather resistance is weak and the coating is sticky, the wound stock may experience adhesion between the coating layers during unwinding. Additionally, surface blemishes may develop due to defects in various steel plates. Summary of the Invention

[0006] (a) Technical problems to be solved One embodiment of the present invention aims to provide an insulating coating composition for electrical steel sheets, an electrical steel sheet, and a method for manufacturing the same. Specifically, one embodiment of the present invention aims to provide an insulating coating composition for electrical steel sheets, an electrical steel sheet, and a method for manufacturing the same, wherein by appropriately combining the components of the insulating coating composition, the coating will not separate even in high-temperature and high-humidity environments, and it exhibits excellent shielding and tension imparting effects in high-frequency regions.

[0007] (II) Technical Solution An insulating coating composition for electrical steel sheets according to an embodiment of the present invention comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate and feldspar.

[0008] An insulating coating composition for electrical steel sheets according to an embodiment of the present invention may further comprise 1 to 10 parts by weight of pigment.

[0009] The pigment may contain one or more oxides of Mn, Fe and Cu.

[0010] Metal phosphates can contain one or more of Mg, Ca, Ba, Sr, Zn, and Al.

[0011] Nitrates may contain one or more of the following: aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3).

[0012] Nitrates can contain two or more of the following: aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3).

[0013] Boron compounds may include one or more of borax and boric acid.

[0014] The boron compound comprises one or more of methylboronic acid and propenylboronic acid.

[0015] The pH of silica can be between 8 and 12.

[0016] The shielding agent may contain two or more of dolomite, talc, carbonate, and feldspar.

[0017] According to an embodiment of the present invention, an electrical steel sheet comprises an electrical steel sheet substrate and an insulating film located on the surface of the electrical steel sheet substrate. The insulating film comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate, and feldspar.

[0018] A method for manufacturing an electrical steel sheet according to an embodiment of the present invention includes: a step of preparing an electrical steel sheet substrate; a step of coating an insulating coating composition onto the surface of the electrical steel sheet substrate; and a step of heat-treating the electrical steel sheet substrate, wherein the insulating coating composition comprises 100 parts by weight of a metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of a nitrate, 10 to 50 parts by weight of a boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate, and feldspar.

[0019] The heat treatment step can be carried out at a temperature of 700 to 1000°C for 10 to 300 seconds.

[0020] (III) Beneficial Effects According to one embodiment of the present invention, it exhibits excellent durability in high temperature and high humidity environments, extremely high corrosion resistance, and excellent heat resistance at temperatures with very high processability, such as stress-relief annealing (SRA).

[0021] According to one embodiment of the present invention, it has excellent shielding and tension imparting effects in a high-frequency magnetic field environment. Attached Figure Description

[0022] Figure 1 This is a schematic cross-sectional view of an electrical steel plate according to an embodiment of the present invention. Detailed Implementation

[0023] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a particular feature, domain, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, components, and / or groups.

[0025] If one part is described as being on top of another part, then other parts may exist directly on top of or in between. If one part is described as being directly on top of another part, then no other parts exist in between.

[0026] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0027] In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0028] An insulating coating composition for electrical steel sheets according to an embodiment of the present invention comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate and feldspar.

[0029] The components are described in detail below. In one embodiment of the present invention, parts by weight refers to the relative weight ratio based on 100 parts by weight of the metal phosphate, and based on the solids content of each component. Solids content refers to the weight of each component after drying to a state free of solvents and other volatiles, specifically the weight remaining after heat treatment assuming the formation of the insulating coating.

[0030] Metal phosphates act as binders in insulating coating compositions. If an adequate amount of metal phosphate is not included, the adhesion of the insulating coating deteriorates or it fails to achieve sufficient tension. Metal phosphates can be manufactured by reacting a metal oxide with pure phosphoric acid (H3PO4). To improve the adhesion of the metal phosphate, boric acid is further added during the reaction and maintained for at least 3 hours, thereby inducing a condensation reaction between the metal phosphate and boric acid. Alternatively, the condensation product can be used instead of the metal phosphate. In one embodiment of the invention, the metal phosphate comprises not only the metal phosphate but also the condensation product of the metal phosphate and boric acid. The manufactured metal phosphate is strongly acidic.

[0031] Metal phosphates can be added to the composition using a solution with a solid content of 50 to 70% by weight. If the solid content in the solution is too low, the free phosphoric acid in the metal phosphate will increase, potentially leading to surface hygroscopicity after metal phosphate production. Conversely, if the solid content is too high, it will be excessive relative to pure phosphoric acid, potentially causing poor reaction and precipitation.

[0032] The metal phosphate and metal oxide can contain various metals without limitation. Specifically, the metal in the metal phosphate and metal oxide can contain one or more of Mg, Ca, Ba, Sr, Zn, and Al. More specifically, the metal phosphate can contain one or more of magnesium phosphate (Mg(H2PO4)2) and aluminum phosphate (Al(H2PO4)3). More specifically, it can contain magnesium phosphate (Mg(H2PO4)2) and aluminum phosphate (Al(H2PO4)3). In this case, based on the solids, the metal phosphate can contain 10 to 90 parts by weight of aluminum phosphate and 10 to 90 parts by weight of magnesium phosphate relative to 100 parts by weight of the total. If the aluminum phosphate content is too low, the tensile strength improvement effect brought about by the addition of aluminum phosphate may be insufficient. When too much aluminum phosphate is added, the Al component will promote the crystallization of silica, which may cause cracking within the insulating coating. Specifically, based on the solid content, relative to a total of 100 parts by weight, the metal phosphate may contain 20 to 80 parts by weight of aluminum phosphate and 20 to 80 parts by weight of magnesium phosphate, more specifically, it may contain 30 to 70 parts by weight of aluminum phosphate and 30 to 70 parts by weight of magnesium phosphate.

[0033] An insulating coating composition for electrical steel sheets according to an embodiment of the present invention comprises 30 to 170 parts by weight of silicon dioxide relative to 100 parts by weight of metal phosphate.

[0034] Silica is a component required to impart tension to steel sheets to reduce iron loss. If the silica content is too low, it is difficult to achieve the desired tension effect on the steel sheet. If the silica content is too high, problems may occur with adhesion or solution stability. More specifically, silica comprises 35 to 160 parts by weight relative to 100 parts by weight of metal phosphate. More specifically, it may comprise 39 to 100 parts by weight.

[0035] Silica can contain both basic and acidic components, more specifically, basic components. The inclusion of basic silica is advantageous in terms of the stability of the insulating coating composition and can improve the shelf life of the solution. The pH of basic silica can be between 8 and 12. The pH of silica can be measured in sol form.

[0036] The average particle size of silica can range from 5 to 20 nm. If the average particle size of silica is too small, the condensation reaction is too fast, resulting in agglomeration and potentially causing color deviation defects on the surface. If the average particle size is too large, the surface area per unit mass becomes smaller, the condensation reaction is slower, and defects may also occur. More specifically, the average particle size of silica can range from 10 to 15 nm. In one embodiment of the invention, the particle size can be measured using a particle size analyzer (Zeta Potential), and the average particle size is the arithmetic mean.

[0037] Silica can be composed of at least one type of nanoparticles with different average particle sizes. Specifically, in order to form an insulating film with excellent coating properties, the silica can also be a mixture of at least one type of silica nanoparticles with different average particle sizes. In an insulating coating composition for electrical steel sheets according to an embodiment of the present invention, the nitrate comprises 20 to 105 parts by weight relative to 100 parts by weight of metal phosphate. The nitrate helps to improve corrosion resistance and weather resistance. Furthermore, the nitrate also acts as a dispersant to stably disperse the shielding functional agent described later in the insulating coating composition. Especially when used as an insulating coating for oriented electrical steel sheets, it is difficult to use organic dispersants, and the nitrate acts as a dispersant. If the nitrate content is too low, it is difficult to fully achieve the aforementioned effects. If the nitrate content is too high, there is a risk of fire. More specifically, the nitrate may comprise 25 to 100 parts by weight relative to 100 parts by weight of metal phosphate.

[0038] Nitrates may contain one or more of the following: aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3).

[0039] The nitrate may contain two or more of the following: aluminum nitrate (Al(NO3)3), cobalt nitrate (Co(NO3)2), calcium nitrate (Ca(NO3)2), strontium nitrate (Sr(NO3)2), zinc nitrate (Zn(NO3)2), manganese nitrate (Mn(NO3)2), magnesium nitrate (Mg(NO3)2), and silver nitrate (AgNO3). Containing two or more nitrates is beneficial for improving the shielding effect. More specifically, the nitrate may contain aluminum nitrate (Al(NO3)3) and magnesium nitrate (Mg(NO3)2). In this case, each may be contained in amounts of 10 to 50 parts by weight. More specifically, each may be contained in amounts of 13 to 50 parts by weight.

[0040] According to one embodiment of the insulating coating composition for electrical steel sheets, a boron compound comprises 10 to 50 parts by weight relative to 100 parts by weight of the metal phosphate. The boron compound, by imparting porosity to the insulating coating, can further improve the tensile strength of the insulating coating. If the boron compound content is too low, it is difficult to fully achieve the aforementioned effects. If the boron compound content is too high, gelation occurs, which may cause problems with solution stability. More specifically, the boron compound may comprise 12 to 30 parts by weight relative to 100 parts by weight of the metal phosphate.

[0041] Boron compounds may include one or more of borax and boric acid. Boric acid may include one or more of methylboronic acid and propenylboronic acid.

[0042] Borax is represented as Na2B4O7 and can contain borax decahydrate, borax pentahydrate, or anhydrous borax.

[0043] Boric acid is represented as H3BO3 and may include one or more of methylboronic acid and propenylboronic acid.

[0044] According to an embodiment of the present invention, the insulating coating composition for electrical steel sheets contains 50 to 150 parts by weight of a shielding agent relative to 100 parts by weight of a metal phosphate.

[0045] In one embodiment of the invention, the shielding agent improves insulation performance in ultra-high frequency environments and also contributes to uniform surface color. In this embodiment, the ultra-high frequency environment refers to the frequency band below 200 GHz. If the insulation performance is excellent, its application to grain-oriented electrical steel sheets helps improve electromagnetic wave shielding in the 50-70 Hz, especially 60 Hz, frequency band near transmission towers or high-voltage power line perimeters. If the content of the shielding agent is too low, the aforementioned effects cannot be fully realized. If too much shielding agent is added, the solution's lifespan may be shortened. More specifically, the shielding agent may contain 65 to 130 parts by weight, and more specifically, 100 to 125 parts by weight.

[0046] As a shielding agent, it may contain one or more of dolomite, talc, carbonates, and feldspar. These substances are known to be used in the cosmetics, coatings, and ceramics industries. Furthermore, by imparting surface roughness and relying on the crystal structure to scatter and block light, they achieve a uniform surface color. However, these substances are difficult to coat uniformly without the use of organic polymers or organic dispersants. In one embodiment of the invention, by simultaneously adding the aforementioned nitrates, the shielding agent can be coated uniformly.

[0047] Dolomite, also known as malachite, has the chemical formula CaMg(CO3)2. Talc, a magnesium-containing silicate mineral, is represented as H2Mg3(SiO3)4 or Mg3Si4O. 10 (OH)2. Carbonates are salts containing carbonate ions (CO3). 2- The carbonate compounds may specifically include one or more of magnesium carbonate, barium carbonate, and calcium carbonate. Feldspar is a framework silicate mineral, and more specifically may include albite and orthoclase. More specifically, talc may be included as a shielding agent.

[0048] As a shielding agent, it may contain two or more of dolomite, talc, carbonates, and feldspar. Using two or more shielding agents can further enhance the shielding effect. More specifically, the shielding agent may contain talc and feldspar, in which case each may contain 25 to 70 parts by weight. More specifically, each may contain 30 to 65 parts by weight.

[0049] On the other hand, in one embodiment of the invention, the color may differ from existing products due to the addition of a shielding agent; therefore, pigments can be further added to compensate for this. The pigments can be added in amounts of 1 to 10 parts by weight. More specifically, they can comprise 2 to 5 parts by weight.

[0050] The pigment is not particularly restricted, but may contain oxides of one or more of Mn, Fe, and Cu. More specifically, it may contain oxides of Mn, Fe, and Cu.

[0051] In addition to the aforementioned components, the composition for forming an insulating film may further include a solvent. The solvent serves to facilitate coating of the composition and to ensure uniform dispersion of the components. There is no particular limitation on the amount of solvent, but it may be from 100 parts by weight to 1000 parts by weight relative to 100 parts by weight of the metal phosphate.

[0052] Figure 1 A schematic cross-sectional view of an electrical steel sheet 100 according to an embodiment of the present invention is shown. Figure 1 As shown, an electrical steel sheet 100 according to an embodiment of the present invention includes an electrical steel sheet substrate 10 and an insulating coating 20 located on the electrical steel sheet substrate 10.

[0053] The electrical steel sheet substrate 10 can be made of general non-oriented or oriented electrical steel sheet without limitation. In one embodiment of the invention, the main component is the formation of an insulating film 20 of special composition on the electrical steel sheet substrate 10, therefore a detailed description of the electrical steel sheet substrate 10 is omitted.

[0054] The composition of the grain-oriented electrical steel sheet matrix is ​​explained below.

[0055] The grain-oriented electrical steel sheet matrix may contain silicon (Si): 2.0 to 7.0 wt%, aluminum (Al): 0.020 to 0.040 wt%, manganese (Mn): 0.01 to 0.20 wt%, phosphorus (P): 0.01 to 0.15 wt%, carbon (C): less than 0.01 wt% and excluding 0%, N: 0.005 to 0.05 wt%, and antimony (Sb), tin (Sn), or combinations thereof, with the balance containing Fe and other unavoidable impurities. The description of the 10 components of the grain-oriented electrical steel sheet matrix is ​​the same as that generally known, and therefore detailed descriptions are omitted.

[0056] Between the grain-oriented electrical steel sheet substrate and the insulating coating, a metal oxide layer (base coating, primary coating) can exist, formed through a reaction with the annealing release agent and the oxide layer of the steel sheet during secondary recrystallization. An example of this metal oxide layer could be a magnesium olivine layer. Alternatively, the formation of the metal oxide layer can be suppressed or removed during the manufacturing process of the grain-oriented electrical steel sheet, allowing direct contact between the grain-oriented electrical steel sheet substrate and the insulating coating.

[0057] The thickness of the insulating film 20 can be from 0.5 to 10 μm. If the insulating film 20 is too thin, it is difficult to ensure proper insulation. If the insulating film 20 is too thick, the fill power may be reduced. In one embodiment of the invention, proper insulation can be ensured even when a thin insulating film 20 is formed. More specifically, the thickness of the insulating film 20 can be from 1 to 5 μm.

[0058] The insulating coating 20 comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding agents selected from dolomite, talc, carbonate, and feldspar. The insulating coating may be substantially the same as the solid components in the aforementioned insulating coating composition.

[0059] A method for manufacturing an electrical steel sheet according to an embodiment of the present invention includes: a step of preparing an electrical steel sheet substrate; a step of coating an insulating film composition onto the surface of the electrical steel sheet substrate; and a step of heat treatment.

[0060] The electrical steel plate substrate and the insulating coating composition have been described in detail above, so a repeat description is omitted.

[0061] As an example, the substrate of an electrical steel sheet can be manufactured as follows.

[0062] Prepare a steel slab. In the next step, the steel slab is heated. At this time, the slab can be heated using a low-temperature slab method at a temperature below 1200°C. Next, the heated steel slab is hot-rolled to produce a hot-rolled sheet. Subsequently, the produced hot-rolled sheet can be hot-rolled and annealed. Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. A single cold rolling or two or more cold rolling processes including intermediate annealing can be performed. Next, the cold-rolled sheet undergoes a recrystallization annealing. This recrystallization annealing step can include simultaneous decarburization annealing and nitriding annealing, or a step including decarburization annealing followed by nitriding annealing. Next, an annealing release agent is applied to the surface of the recrystallized annealed steel sheet. The amount of annealing release agent applied can be 1 to 5 g / m². 2If the amount of annealing release agent applied is too small, the coating formation may not proceed smoothly. If the amount of annealing release agent applied is too large, it may affect secondary recrystallization. Therefore, the amount of annealing release agent applied can be adjusted within the aforementioned range. Next, the steel sheet coated with the annealing release agent is subjected to secondary recrystallization annealing. During secondary recrystallization annealing, the primary homogenization temperature can be 650 to 750°C, and the secondary homogenization temperature can be 1100 to 1250°C. The heating rate can be controlled at 15°C / hour (hr) in the heating zone. Furthermore, for the gas atmosphere, up to the primary homogenization step, it can be carried out in an atmosphere containing 20 to 30% by volume nitrogen and 70 to 80% by volume hydrogen. The secondary homogenization step can be carried out in a 100% hydrogen atmosphere for 15 hours followed by furnace cooling.

[0063] In the heat treatment step, the heat treatment temperature can be between 700 and 1000°C. If the temperature is too low, the time required to form the insulating coating will be too long, and the operability of continuous processing may deteriorate. If the temperature is too high, the heat resistance and resistance to bluing due to cracking may decrease. More specifically, the heat treatment temperature can be between 750 and 950°C. The heat treatment time can be between 10 and 300 seconds. More specifically, the heat treatment time can be between 30 and 180 seconds.

[0064] The atmosphere during heat treatment can be a nitrogen atmosphere.

[0065] In the following sections, preferred embodiments of the present invention, comparative examples thereof, and evaluative examples thereof will be described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0066] Example 1 Grain-oriented electrical steel sheet (300) was prepared as the test material. The plate is 60mm thick, contains 3.1% Si by weight, has a thickness of 0.23mm, and has a single coating after final annealing.

[0067] The components were mixed according to the proportions shown in Table 1 below to prepare an insulating coating composition. First, alkaline colloidal silica (average particle size of 15 nm) was added to a phosphate solution containing 50 parts by weight of aluminum phosphate and 50 parts by weight of magnesium phosphate and mixed. Subsequently, a nitrate solution containing aluminum nitrate and magnesium nitrate was added, followed by the addition of a shielding functional agent and anhydrous borax, ultimately producing the insulating coating composition.

[0068] The prepared solution was prepared at 3.1 g / mm 2 The coating is applied to both sides of the electrical steel sheet and heat-treated at 850°C for 45 seconds to form an insulating film with a thickness of 1 μm.

[0069] The weather resistance, corrosion resistance, solution stability, coating property, heat resistance adhesion, and ultra-high frequency insulation were evaluated by the following methods and summarized in Table 2.

[0070] Evaluating weather resistance The weather resistance was evaluated under the conditions of 98% moisture, 60 °C, and 72 hours. When it was good, it was indicated as "Qualified (OK)", and when it was bad, it was indicated as "Unqualified (NG)".

[0071] Evaluating corrosion resistance The salt spray test was carried out at 5% NaCl, 100% RH, and 65 °C for 8 hours. When it was good, it was indicated as "Qualified", and when it was bad, it was indicated as "Unqualified".

[0072] Evaluating solution stability A coated plate with a size of 2x2 cm was placed in 100 mL of 10% NaOH to dissolve, and then filtered with a filter. The substance that did not dissolve and existed in the form of powder was PO4. After measuring the weight of the residual powder on the filter, if there was powder, it could be determined that HPO4 was removed by the oxidant.

[0073] Cl tracing method: After dissolving a coated film with a size of 2x2 cm in 100 mL of 10% NaOH, if there is Cl component in the solution, it can be regarded as Cl being added.

[0074] Evaluating coating property After visually evaluating, when there were no scars and it was good, it was indicated as "Qualified", and when there were scars and it was bad, it was indicated as "Unqualified".

[0075] Evaluating heat resistance adhesion For the evaluation of heat resistance adhesion, it was heated under the conditions of 560 °C, 20% hydrogen, and 80% nitrogen for 2 hours, and then the adhesion grade was confirmed to reach above 5B through the cross-cut (CROSS-HATCH CUT) test.

[0076] If the test result is above 5B, it is determined to be good and indicated as "Qualified"; if it is below 5B, it is determined to be bad and indicated as "Unqualified".

[0077] Evaluating tension The test piece was placed on the ground, and the highest point where the test piece bent and翘起 from the ground was marked. The distance between the highest point and the position of the test piece before bending was measured and input as the maximum bending part length (H). Then, it was measured as follows. The tension value was 8x10 -6 Above, it was indicated as qualified, and the tension value was less than 8x10 -6 When, it was indicated as unqualified.

[0078] σ = E / (1-ν) x T 2 / 3t x 2H / I2 σ = Coating tension (Kg / mm) ν = Poisson's ratio (0.3) t = Thickness after coating removal (mm) T = Thickness before coating removal (mm) H = Maximum bending length (mm) I = Length of test piece (mm) Evaluation of shielding Measurements were performed using ASTM D4953. First, a test piece with an outer diameter of 130 mm and an inner diameter of 70 mm was inserted between the upper and lower shielding chambers, and the shielding performance was measured using a network analyzer. Then, a test piece with an outer diameter of 130 mm was placed and measured using the same method. The difference between the first and second measurements was taken as the shielding rate, and the shielding performance was evaluated accordingly.

[0079] Table 1 Table 2 As shown in Tables 1 and 2, when the insulating coating composition is included in appropriate amounts, excellent weather resistance, corrosion resistance, solution stability, coatability, heat adhesion, tensile strength, and shielding properties can be confirmed simultaneously. On the other hand, when the insulating coating composition is not appropriately included, some properties can be confirmed to deteriorate.

[0080] This invention can be implemented in various different ways and is not limited to the embodiments described above. Those skilled in the art will understand that this invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

[0081] [Explanation of reference numerals in the attached figures] 100: Electrical steel sheet; 10: Electrical steel sheet substrate 20: Insulating film

Claims

1. An insulating coating composition for electrical steel sheets, comprising: 100 parts by weight of metal phosphate 30 to 170 parts by weight of silicon dioxide 20 to 105 parts by weight of nitrates 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding agents selected from dolomite, talc, carbonates and feldspar.

2. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The insulating coating composition further comprises 1 to 10 parts by weight of pigment.

3. The insulating coating composition for electrical steel sheets according to claim 2, wherein, The pigment contains one or more oxides of Mn, Fe and Cu.

4. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The metal phosphate contains one or more of Mg, Ca, Ba, Sr, Zn and Al.

5. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The nitrate contains one or more of the following: aluminum nitrate, cobalt nitrate, calcium nitrate, strontium nitrate, zinc nitrate, manganese nitrate, magnesium nitrate, and silver nitrate.

6. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The nitrate contains two or more of the following: aluminum nitrate, cobalt nitrate, calcium nitrate, strontium nitrate, zinc nitrate, manganese nitrate, magnesium nitrate, and silver nitrate.

7. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The boron compound includes one or more of borax and boric acid.

8. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The boron compound comprises one or more of methylboronic acid and propenylboronic acid.

9. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The silica has a pH of 8 to 12.

10. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The shielding agent contains two or more of the following: dolomite, talc, carbonate, and feldspar.

11. An electrical steel sheet, comprising: Electrical steel sheet substrate; and The insulating film located on the surface of the electrical steel plate substrate, The insulating coating comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding agents selected from dolomite, talc, carbonate, and feldspar.

12. A method for manufacturing an electrical steel sheet, comprising: Steps for preparing electrical steel plate substrate; The step of coating the insulating film composition onto the surface of the electrical steel plate substrate; and The step of heat treating the electrical steel plate substrate. The insulating coating composition comprises 100 parts by weight of metal phosphate, 30 to 170 parts by weight of silica, 20 to 105 parts by weight of nitrate, 10 to 50 parts by weight of boron compound, and 50 to 150 parts by weight of one or more shielding functional agents selected from dolomite, talc, carbonate, and feldspar.

13. The method for manufacturing electrical steel sheet according to claim 12, wherein, The heat treatment step is carried out at a temperature of 700 to 1000°C for 10 to 300 seconds.

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