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 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

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 the steel sheet exhibits excellent defect shielding and tension imparting effects. 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 the steel sheet exhibits excellent defect shielding and tension imparting effects.

[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 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

[0008] An insulating coating composition for electrical steel sheets according to an embodiment of the present invention may further comprise 5 to 100 parts by weight of pigment.

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

[0010] It may further contain 30 to 300 parts by weight of boron compound.

[0011] Boron compounds may include one or more of borax and boric acid.

[0012] Metal phosphates can contain one or more of Mg, Ca, Ba, Sr, Zn, and Al.

[0013] 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).

[0014] 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).

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

[0016] 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 comprising 100 parts by weight of metal phosphate, 30 to 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

[0017] 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-treating the electrical steel sheet substrate, wherein the insulating film composition comprises 100 parts by weight of a metal phosphate, 30 to 300 parts by weight of silica, 30 to 300 parts by weight of a nitrate, 30 to 300 parts by weight of feldspar, and 30 to 300 parts by weight of talc.

[0018] The heat treatment step can be carried out at a temperature of 700 to 1000°C for 10 to 300 seconds.

[0019] (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).

[0020] According to one embodiment of the present invention, it has the effect of shielding defects in steel plates and imparting tension. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of an electrical steel plate according to an embodiment of the present invention. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

[0028] 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.

[0029] Metal phosphates act as adhesives 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.

[0030] 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.

[0031] 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.

[0032] An insulating coating composition for electrical steel sheets according to an embodiment of the present invention comprises 30 to 300 parts by weight of silicon dioxide relative to 100 parts by weight of metal phosphate.

[0033] Silica is a component required to impart weather resistance and corrosion resistance to steel plates. If the silica content is too low, it will be difficult to fully achieve the desired weather resistance and corrosion resistance. If the silica content is too high, problems may occur in terms of adhesion or solution stability. More specifically, the silica content is 30 to 300 parts by weight relative to 100 parts by weight of metal phosphate. More specifically, it can be 50 to 250 parts by weight. More specifically, it can be 100 to 230 parts by weight.

[0034] 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.

[0035] 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.

[0036] 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. According to an embodiment of the insulating coating composition for electrical steel sheets, the nitrate comprises 30 to 300 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 feldspar and talc (described later) in the insulating coating composition, thereby ensuring the overall opacity of the steel sheet. 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 50 to 250 parts by weight relative to 100 parts by weight of metal phosphate. More specifically, it may comprise 100 to 200 parts by weight.

[0037] 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).

[0038] 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 weather resistance and corrosion resistance. 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 200 parts by weight. More specifically, each may be contained in amounts of 15 to 100 parts by weight.

[0039] According to one embodiment of the insulating coating composition for electrical steel sheets, feldspar comprises 30 to 300 parts by weight relative to 100 parts by weight of metal phosphate. Feldspar is a framework silicate mineral, and more specifically, may comprise albite and orthoclase. Feldspar plays a role in improving corrosion resistance in the insulating coating composition. If the feldspar content is too low, it is difficult to obtain sufficient corrosion resistance. If the feldspar content is too high, problems may occur regarding solution stability. More specifically, it may comprise 50 to 250 parts by weight. More specifically, it may comprise 100 to 230 parts by weight.

[0040] According to one embodiment of the present invention, an insulating coating composition for electrical steel sheets contains 30 to 300 parts by weight of talc relative to 100 parts by weight of metal phosphate. Talc (Talcum) is a magnesium-containing silicate mineral, represented as H₂Mg₃(SiO₃)₄ or Mg₃Si₄O. 10 (OH)₂. Talc plays a role in improving opacity in the insulating coating composition. If the talc content is too low, it is difficult to achieve sufficient opacity and to shield defects present in the steel sheet. If the talc content is too high, problems may occur with solution stability. More specifically, it may contain 50 to 250 parts by weight. More specifically, it may contain 100 to 230 parts by weight.

[0041] In one embodiment of the invention, the color may differ from existing products due to the addition of feldspar and talc. To compensate for this, pigment may be further added. The pigment may be added in the form of 5 to 100 parts by weight. More specifically, it may contain 10 to 75 parts by weight. More specifically, it may contain 20 to 50 parts by weight.

[0042] The pigment is not particularly limited, but may contain oxides of one or more of Mn, Fe, and Cu. More specifically, it may contain oxides of Mn, Fe, and Cu.

[0043] According to one embodiment of the present invention, the insulating coating composition for electrical steel sheets may further contain 30 to 300 parts by weight of a boron compound relative to 100 parts by weight of a 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 composition may contain 50 to 250 parts by weight of a boron compound relative to 100 parts by weight of a metal phosphate. More specifically, the composition may contain 10 to 200 parts by weight of a boron compound.

[0044] Boron compounds may include one or more of borax and boric acid.

[0045] Borax is represented as Na2B4O7 and can contain borax decahydrate, borax pentahydrate, or anhydrous borax.

[0046] Boric acid is represented as H3BO3 and may include one or more of methylboronic acid and propenylboronic acid.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The composition of the grain-oriented electrical steel sheet matrix is ​​explained below.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The insulating coating 20 comprises 100 parts by weight of metal phosphate, 30 to 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar, and 30 to 300 parts by weight of talc. The insulating coating may be substantially the same as the solid components in the aforementioned insulating coating composition. The insulating coating 20 may further comprise pigments and boron compounds. In one embodiment of the invention, the insulating coating 20 is opaque, thus shielding defects such as iron mounds present on the steel plate. Furthermore, by applying tension to the steel plate, the iron loss characteristics of the steel plate can be improved.

[0055] 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.

[0056] The electrical steel plate substrate and the insulating coating composition have been described in detail above, so a repeat description is omitted.

[0057] As an example, the substrate of an electrical steel sheet can be manufactured as follows.

[0058] 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. 2 If 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.

[0059] 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.

[0060] The atmosphere during heat treatment can be a nitrogen atmosphere.

[0061] 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.

[0062] Example 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.

[0063] 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 in the same amount was added, followed by the addition of feldspar, talc, anhydrous borax, and pigments, ultimately producing the insulating coating composition.

[0064] 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.

[0065] Weather resistance, corrosion resistance, solution stability, coatability, opacity, and tensile strength were evaluated using the following methods and are summarized in Table 2.

[0066] Evaluation of weather resistance Weather resistance is evaluated under conditions of 98% moisture content, 60℃, and 72 hours. Good weather resistance is indicated as "OK" and poor weather resistance is indicated as "NG".

[0067] Evaluation of corrosion resistance A salt spray test was conducted for 8 hours at 5% NaCl, 100 RH, and 65℃. A good result was indicated as "OK" and a bad result as "NG".

[0068] Evaluate solution stability A 2x2cm coated plate was dissolved in 100mL of 10% NaOH and then filtered. The substance that did not dissolve but remained as powder was PO4. After measuring the weight of the powder remaining on the filter, if powder was present, it could be determined that HPO4 had been removed by the oxidizing agent.

[0069] Cl tracking method: After dissolving a 2x2cm coating in 100mL of 10% NaOH, if Cl is present in the solution, it can be considered that Cl has been added.

[0070] Evaluation of coating properties When evaluated by the naked eye, a condition without blemishes is considered "OK" and a condition with blemishes is considered "NG".

[0071] Evaluation of tension Place the specimen on the ground and mark the highest point where it bends and rises from the ground. Measure the distance between the highest point and the specimen's initial position before bending, and input this distance as the maximum bending length (H). Then, measure as follows. The tension value is 8 x 10. -6The above indicates that it is qualified (OK), and the tension value is less than 8 x 10. -6 When this occurs, it is indicated as non-compliant (NG).

[0072] σ = E / (1-ν) x T 2 / 3t x 2H / I 2 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 opacity: Measured using an opacity-shade reflectometer. A value of 35 or higher is considered acceptable (OK), and a value less than 35 is considered unacceptable (NG).

[0073] Table 1 Table 2 As shown in Tables 1 and 2, when the insulating coating composition is appropriately included, excellent weather resistance, corrosion resistance, solution stability, coatability, opacity, and tensile strength are simultaneously observed. On the other hand, when the insulating coating composition is not appropriately included, some properties are found to deteriorate.

[0074] 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.

[0075] [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 300 parts by weight of silicon dioxide 30 to 300 parts by weight of nitrates Feldspar 30 to 300 parts by weight, and Talc, 30 to 300 parts by weight.

2. The insulating coating composition for electrical steel sheets according to claim 1, wherein, The insulating coating composition further comprises 5 to 100 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 insulating coating composition further comprises 30 to 300 parts by weight of a boron compound.

5. The insulating coating composition for electrical steel sheets according to claim 4, wherein, The boron compound includes one or more of borax and boric acid.

6. 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.

7. 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.

8. 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.

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

10. 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 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

11. 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 300 parts by weight of silica, 30 to 300 parts by weight of nitrate, 30 to 300 parts by weight of feldspar and 30 to 300 parts by weight of talc.

12. The method for manufacturing electrical steel sheet according to claim 11, 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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