Insulation coating composition for electrical steel sheet, electrical steel sheet, and manufacturing method therefor

Abstract

According to one embodiment of the present invention, an insulation coating composition for an electrical steel sheet comprises: 100 parts by weight of metal phosphate; 33-110 parts by weight of nanosilica having a particle diameter of 1-50 nm; 45-325 parts by weight of microsilica having a particle diameter of 0.5-50 μm; 28-215 parts by weight of nitrate; 10-100 parts by weight of a boron compound; and 8-110 parts by weight of a chromium compound.

Description

Electrical steel sheet insulation film composition, electrical steel sheet, and method for manufacturing the same

[0001] One embodiment of the present invention relates to an electrical steel sheet insulation coating composition, an electrical steel sheet, and a method for manufacturing the same. Specifically, the present invention relates to an electrical steel sheet insulation coating composition, an electrical steel sheet, and a method for manufacturing the same, wherein the components of the insulation coating composition are appropriately combined so that the coating does not separate even in a high-temperature and high-humidity environment and also has an excellent tensile strength-providing effect.

[0002] Electrical steel is used as a material for transformers, motors, and electrical equipment. Unlike general carbon steel, which prioritizes workability and mechanical properties, it is a functional product that prioritizes electrical properties. Required electrical properties include low core loss, high magnetic flux density, permeability, and space factor.

[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 the abnormal grain growth phenomenon called secondary recrystallization to obtain the Goss texture ({110} <001> This is an electrical steel sheet with excellent magnetic properties in the rolling direction by forming a grain structure (grain texture) throughout the steel sheet. Non-oriented electrical steel sheet is an electrical steel sheet with uniform magnetic properties in all directions on the rolled sheet.

[0004] Meanwhile, the formation of an insulating film is a process corresponding to the final manufacturing process of the product, and in addition to the electrical properties that usually suppress the generation of eddy currents, it requires continuous punching workability to suppress the wear of the mold when forming a core by stacking multiple layers after punching into a predetermined shape, sticking resistance to prevent adhesion between the steel sheets after the SRA process to remove the processing stress of the steel sheets and restore the magnetic properties, and surface adhesion. In addition to these basic characteristics, excellent coating workability and solution stability that can be used for a long time after mixing are also required. The coating solutions used for this purpose include chromic acid-based chrome coating and phosphate-based phosphate coating.

[0005] These coatings offer excellent corrosion resistance. However, they are vulnerable to weathering and stickiness. Poor weathering resistance and stickiness can lead to adhesion problems when uncoiling the coil. Furthermore, various defects in the steel sheet can cause surface stains.

[0006] One embodiment of the present invention provides an electrical steel sheet insulation coating composition, an electrical steel sheet, and a method for manufacturing the same. Specifically, by appropriately combining the components of the insulation coating composition, the present invention provides an electrical steel sheet insulation coating composition that does not separate even in a high-temperature and high-humidity environment and has excellent tensile strength-providing effect, an electrical steel sheet, and a method for manufacturing the same.

[0007] An insulating film composition for electrical steel according to one embodiment of the present invention comprises 100 parts by weight of metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 μm, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of boron compound, and 8 to 110 parts by weight of chromium compound.

[0008] The metal phosphate may include one or more of Mg, Ca, Ba, Sr, Zn, and Al.

[0009] The nitrate may include one or more of 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).

[0010] The nitrate may include two or more of 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).

[0011] The boron compound may include at least one of borax and boric acid.

[0012] The chromium compound may include one or more of chromate, chromate, and dichromate.

[0013] Nano silica and micro silica can each have a pH of 8 to 12.

[0014] Silica can have a pH of 8 to 12.

[0015] An electrical steel sheet according to one embodiment of the present invention includes an electrical steel sheet substrate and an insulating film positioned on a surface of the electrical steel sheet substrate, and the insulating film includes 100 parts by weight of a metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 ㎛, 28 to 215 parts by weight of a nitrate, 10 to 100 parts by weight of a boron compound, and 8 to 110 parts by weight of a chromium compound.

[0016] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention comprises the steps of preparing an electrical steel sheet substrate; applying an insulating film composition to a surface of the electrical steel sheet substrate; and heat-treating the electrical steel sheet substrate, wherein the insulating film composition comprises 100 parts by weight of a metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 μm, 28 to 215 parts by weight of a nitrate, 10 to 100 parts by weight of a boron compound, and 8 to 110 parts by weight of a chromium compound.

[0017] The heat treatment step can be performed at a temperature of 700 to 1000°C for 10 to 300 seconds.

[0018] According to one embodiment of the present invention, the composition has excellent durability in high temperature and high humidity environments, extreme corrosion resistance, and excellent heat resistance at very high temperatures for processability such as stress relief annealing (SRA).

[0019] According to one embodiment of the present invention, it has an excellent tension-giving effect.

[0020] Figure 1 is a schematic diagram of a cross-section of an electrical steel sheet according to one embodiment of the present invention.

[0021] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, 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.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0023] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0024] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0026]

[0027] An insulating film composition for electrical steel according to one embodiment of the present invention comprises 100 parts by weight of metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 ㎛, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of boron compound, and 8 to 110 parts by weight of chromium compound.

[0028] Below, each component is described in detail. In one embodiment of the present invention, "parts by weight" refers to the relative weight ratio based on 100 parts by weight of metal phosphate, and is based on the solid content of each component. "Solid content" refers to the weight of each component when dried in a state free of volatile matter such as solvent. Specifically, assuming a heat treatment process during the formation of an insulating film, it refers to the remaining weight after heat treatment.

[0029]

[0030] Metal phosphate acts as a binder in an insulating film composition. If the metal phosphate is not contained in an appropriate amount, the adhesiveness of the insulating film may be poor or the tension may not be sufficient. Metal phosphate can be manufactured by a manufacturing process in which a metal oxide is added to pure phosphoric acid (H3PO4) and reacted. To improve the adhesiveness of the metal phosphate, boric acid may be additionally added during the reaction process and maintained for 3 hours or more to induce a condensation reaction between the metal phosphate and boric acid. This condensation reaction product can also be used in place 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 of the metal phosphate and boric acid. The manufactured metal phosphate is strongly acidic.

[0031] The metal phosphate may be added to the composition using a solution having a solids content of 50 to 70 wt%. If the solids content in the solution is too low, free phosphoric acid may increase within the metal phosphate, resulting in surface moisture absorption after the metal phosphate is manufactured. If the solids content is too high, the excess solids compared to pure phosphoric acid may result in poor reaction and precipitation.

[0032] The metal phosphate and the metal oxide may include various metals without limitation. Specifically, the metal of the metal phosphate and the metal oxide may include at least one of Mg, Ca, Ba, Sr, Zn, and Al. More specifically, the metal phosphate may include at least one of monobasic magnesium phosphate (Mg(H2PO4)2) and monobasic aluminum phosphate (Al(H2PO4)3). More specifically, it may include monobasic magnesium phosphate (Mg(H2PO4)2) and monobasic aluminum phosphate (Al(H2PO4)3). In this case, the metal phosphate may include 10 to 90 parts by weight of monobasic aluminum phosphate and 10 to 90 parts by weight of monobasic magnesium phosphate based on the total 100 parts by weight. If too little monobasic aluminum phosphate is included, the tensile strength improvement effect by the addition of monobasic aluminum phosphate may not be sufficient. When too much monobasic aluminum phosphate is added, the Al component may increase the crystallization of silica, which may cause cracks in the insulating film. Specifically, the metal phosphate may include, based on the solid content, 20 to 80 parts by weight of monobasic aluminum phosphate and 20 to 80 parts by weight of monobasic magnesium phosphate, and more specifically, 30 to 70 parts by weight of monobasic aluminum phosphate and 30 to 70 parts by weight of monobasic magnesium phosphate, per 100 parts by weight of the total.

[0033] An insulating film composition for electrical steel sheet according to one embodiment of the present invention contains 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm.

[0034] Nano silica is a necessary component for reducing iron loss by imparting tensile strength to steel sheets. If too little nano silica is included, it is difficult to achieve the full tensile strength effect. If too much nano silica is included, problems with stickiness or solution stability may arise. More specifically, 35 to 100 parts by weight of nano silica may be included for every 100 parts by weight of metal phosphate.

[0035] Nano silica can contain basic and acidic properties, and more specifically, can contain basic properties. Including basic nano silica can be advantageous in terms of the stability of the insulation film composition and can improve the storage properties of the solution. Basic nano silica can have a pH of 8 to 12. The pH of nano silica can be measured in sol form.

[0036] In one embodiment of the present invention, in addition to nano-silica, micro-silica is also included, and nano-silica and micro-silica can be distinguished by particle size. Nano-silica refers to silica having a particle size ranging from 1 to 50 nm. In one embodiment of the present invention, the particle size can be measured using a Zeta Potential particle sizer. More specifically, nano-silica refers to silica having a particle size ranging from 3 to 30 nm.

[0037] Nano silica may have an average particle size ranging from 5 to 20 nm. If the average particle size of the silica is too small, the condensation reaction rate may be rapid, causing agglomeration and color deviation defects on the surface. If the average particle size is too large, the surface area per unit mass may be small, slowing down the condensation reaction rate and causing defects. More specifically, the silica may have an average particle size ranging from 10 to 15 nm. In one embodiment of the present invention, the average particle size is an arithmetic mean.

[0038] An insulating film composition for an electrical steel sheet according to one embodiment of the present invention contains 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 ㎛.

[0039] Micro-silica, along with nano-silica, is a necessary component for reducing iron loss by imparting tension to the steel sheet. If nano-silica or micro-silica alone is included, the tension-imparting effect of the insulation film may be reduced. If too little micro-silica is included, it is difficult to sufficiently impart tension to the steel sheet. If too much micro-silica is included, problems with stickiness or solution stability may occur. More specifically, 50 to 300 parts by weight of micro-silica may be included for every 100 parts by weight of metal phosphate.

[0040] Micro silica may contain basic and acidic properties, and more specifically, may contain basic properties. Including basic micro silica may be advantageous in terms of the stability of the insulation film composition and may improve the storage properties of the solution. Basic micro silica may have a pH of 8 to 12. The pH of micro silica can be measured by grinding silica into nano-sized silica and then preparing it in a sol form.

[0041] In one embodiment of the present invention, micro silica refers to silica having a particle size in the range of 0.5 to 50 μm. More specifically, it refers to silica having a particle size in the range of 1 to 10 μm.

[0042] Micro silica may have an average particle size ranging from 1 to 20 μm. If the average particle size is too large, the condensation reaction rate may be slow. More specifically, micro silica may have an average particle size ranging from 5 to 10 μm.

[0043]

[0044] An insulating coating composition for electrical steel sheets according to one embodiment of the present invention contains 28 to 215 parts by weight of nitrate per 100 parts by weight of metal phosphate. Nitrate contributes to improving corrosion resistance and weather resistance. In addition, it also functions as a dispersant to stably disperse boron compounds and chromium compounds, which will be described later, within the insulating coating composition. In particular, when used as an insulating coating for grain-oriented electrical steel sheets, it is difficult to use an organic dispersant, and nitrate functions as a dispersant. If too little nitrate is included, it is difficult to sufficiently achieve the aforementioned role. If too much nitrate is included, there is a risk of fire. More specifically, 30 to 200 parts by weight of nitrate is included per 100 parts by weight of metal phosphate.

[0045] The nitrate may include one or more of 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).

[0046] The nitrate may include two or more of 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). When two or more nitrates are included, it is advantageous in terms of improving corrosion resistance and weather resistance. More specifically, the nitrate may include aluminum nitrate (Al(NO3)3) and magnesium nitrate (Mg(NO3)2). In this case, each may be included in an amount of 10 to 150 parts by weight. More specifically, each may be included in an amount of 15 to 100 parts by weight.

[0047] An insulating coating composition for electrical steel sheets according to one embodiment of the present invention comprises 10 to 100 parts by weight of a boron compound relative to 100 parts by weight of a metal phosphate. The boron compound imparts porosity to the insulating coating, thereby further improving the tensile strength of the insulating coating. If too little of the boron compound is included, it is difficult to sufficiently achieve the aforementioned role. If too much of the boron compound is included, gelation may occur, causing problems in terms of solution stability. More specifically, the composition may comprise 20 to 70 parts by weight of a boron compound relative to 100 parts by weight of a metal phosphate. More specifically, the composition may comprise 25 to 50 parts by weight of a boron compound relative to 100 parts by weight of a metal phosphate.

[0048] The boron compound may include at least one of borax and boric acid. The boric acid may include at least one of methylboronic acid and propenylboronic acid.

[0049] Borax is represented by the symbol Na2B4O7 and may include Borax Decahydrate, Borax Pentahydrate, or Borax (Anhydrous).

[0050] Boric acid is represented by H3BO3 and may contain one or more of methylboronic acid and propenylboronic acid.

[0051] An insulating coating composition for electrical steel sheets according to one embodiment of the present invention comprises 8 to 110 parts by weight of a chromium compound relative to 100 parts by weight of a metal phosphate. The chromium compound contains chromium (Cr) within the compound and serves to form a uniform coating by improving dispersion stability. In addition, the chromium compound has the advantage of enabling stable operation in an insulation coating process. If the chromium compound is contained in too little amount, sufficient weather resistance and corrosion resistance cannot be obtained. If the chromium compound is contained in too much amount, gelation occurs, resulting in a decrease in corrosion resistance. More specifically, the composition comprises 10 to 100 parts by weight of a chromium compound relative to 100 parts by weight of a metal phosphate.

[0052] The chromium compound may include one or more of chromate, chromate, and dichromate.

[0053] Chromic acid is CrO3, H2CrO4, H2Cr2O7, H2Cr3O 10 , H2Cr4O 13 It can be displayed as etc.

[0054] As the chromate and dichromate, for example, it may include a chromate or dichromate containing Na, K, Mg, Ca, Mn, Mo, Zn, or Al. When two or more types of chromium compounds are included, the combined amount may be included within the above-mentioned range.

[0055]

[0056] In addition to the aforementioned components, the composition for forming an insulating film may further include a solvent. The solvent facilitates application of the composition and helps uniformly disperse the components. The amount of the solvent is not particularly limited, but may range from 100 to 1,000 parts by weight per 100 parts by weight of the metal phosphate.

[0057]

[0058] Fig. 1 shows a schematic diagram of a cross-section of an electrical steel plate (100) according to one embodiment of the present invention. As shown in Fig. 1, the electrical steel plate (100) according to one embodiment of the present invention includes an electrical steel plate substrate (10) and an insulating film (20) positioned on the substrate (10) of the electrical steel plate.

[0059] The electrical steel plate substrate (10) can be a general non-oriented or oriented electrical steel plate without limitation. In one embodiment of the present invention, the main configuration is to form an insulating film (20) of a special composition on the electrical steel plate substrate (10), so a detailed description of the electrical steel plate substrate (10) is omitted.

[0060] In addition, the components of the directional electrical steel plate substrate are explained as follows.

[0061] The grain-oriented electrical steel substrate contains 2.0 to 7.0 wt% of silicon (Si), 0.020 to 0.040 wt% of aluminum (Al), 0.01 to 0.20 wt% of manganese (Mn), 0.01 to 0.15 wt% of phosphorus (P), 0.01 to 0.15 wt% or less of carbon (C) (excluding 0%), 0.005 to 0.05 wt% of nitrogen, and 0.01 to 0.15 wt% of antimony (Sb), tin (Sn), or a combination thereof, and the remainder may contain iron and other unavoidable impurities. Since the description of each component of the grain-oriented electrical steel substrate (10) is the same as generally known, a detailed description is omitted.

[0062] Between the grain-oriented electrical steel substrate and the insulating film, a metal oxide layer (base coating layer, primary film) may exist, which is formed by a reaction between the annealing separator and the oxide layer of the steel sheet during the secondary recrystallization process. An example of a metal oxide layer may be a forsterite layer. During the manufacturing process of grain-oriented electrical steel, it is possible to suppress the formation of the metal oxide layer or remove the metal oxide layer so that the grain-oriented electrical steel substrate and the insulating film are in contact.

[0063] The thickness of the insulating film (20) may be 0.5 to 10 μm. If the thickness of the insulating film (20) is too thin, it is difficult to secure adequate insulation. If the thickness of the insulating film (20) is too thick, the space factor may be reduced. In one embodiment of the present invention, even if the insulating film (20) is formed with a thin thickness, adequate insulation can be secured. More specifically, the thickness of the insulating film (20) may be 1 to 5 μm.

[0064] The insulating film (20) contains 100 parts by weight of metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 μm, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of boron compound, and 8 to 110 parts by weight of chromium compound. The insulating film may be substantially the same as the solid component in the aforementioned insulating film composition. In particular, the particle size of nano silica and micro silica is maintained even within the insulating film (20), and when a sufficient area is analyzed using an electron microscope, the content of nano silica and micro silica can be measured.

[0065]

[0066] 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 an insulating film composition to the surface of the electrical steel sheet substrate; and performing a heat treatment.

[0067] Since the electrical steel plate substrate and insulating film composition have been described in detail above, redundant descriptions will be omitted.

[0068] For example, the substrate of an electrical steel plate can be manufactured as follows.

[0069] Prepare a steel slab. In the next step, the steel slab is heated. At this time, the slab can be heated at 1,200℃ or lower using the low-temperature slab method. Next, the heated steel slab is hot-rolled to produce a hot-rolled sheet. Thereafter, the manufactured hot-rolled sheet can be hot-rolled and annealed. Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Cold rolling can be performed once, or two or more cold rollings including intermediate annealing can be performed. Next, the cold-rolled sheet is subjected to primary recrystallization annealing. At this time, the step of primary recrystallization annealing of the cold-rolled sheet can include a step of simultaneously decarburization annealing and nitriding annealing the cold-rolled sheet, or a step of nitriding annealing after decarburization annealing. Next, an annealing separator is applied to the surface of the recrystallization-annealed steel sheet. The amount of the annealing separator applied is 1 to 5 g / m. 2 can be. If the amount of the annealing separator applied is too small, the film formation may not occur smoothly. If the amount of the annealing separator applied is too large, it may affect the secondary recrystallization. Therefore, the amount of the annealing separator applied can be adjusted within the aforementioned range. Next, the steel sheet to which the annealing separator has been applied is subjected to secondary recrystallization annealing. During the secondary recrystallization annealing, the primary soaking temperature can be 650 to 750°C, and the secondary soaking temperature can be 1100 to 1250°C. The temperature section of the temperature increase section can be controlled at a condition of 15°C / hr. In addition, the gas atmosphere can be performed in an atmosphere containing 20 to 30% by volume of nitrogen and 70 to 80% by volume of hydrogen until the first soaking stage, and can be maintained in a 100% hydrogen atmosphere for 15 hours and then furnace cooling can be performed in the second soaking stage.

[0070] During the heat treatment step, the heat treatment temperature may range from 700 to 1000°C. If the temperature is too low, the time required for the insulating film to form may be too long, which may deteriorate the continuous processing workability. If the temperature is too high, heat resistance and blueing resistance may be reduced due to cracking. More specifically, the heat treatment temperature may range from 750 to 950°C. The heat treatment time may range from 10 to 300 seconds. More specifically, it may range from 30 to 180 seconds.

[0071] The atmosphere during heat treatment may be a nitrogen atmosphere.

[0072]

[0073] Hereinafter, preferred embodiments of the present invention, comparative examples thereof, and evaluation examples thereof will be described. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0074]

[0075] Example

[0076] Grain-oriented electrical steel sheets (300*60mm) containing Si: 3.1% by weight and having a primary coating annealed to a thickness of 0.23mm were prepared as test materials.

[0077] An insulating film composition was prepared by mixing the components in the ratios summarized in Table 1 below. First, basic colloidal nano silica (particle size ranging from 5 nm to 20 nm, average particle size 15 nm) and basic micro silica (particle size ranging from 1 ㎛ to 2 ㎛, average particle size 1.5 ㎛) were added to a phosphate solution containing 50 parts by weight of aluminum phosphate and 50 parts by weight of magnesium phosphate and mixed. Thereafter, a nitrate solution containing equal amounts of aluminum nitrate and magnesium nitrate was added, followed by the addition of anhydrous borax and chromic acid (CrO3) to finally prepare an insulating film composition.

[0078] The prepared solution was applied to both sides of the electrical steel sheet at a concentration of 3.1 g / mm 2The coating was applied and heat-treated at 850°C for 45 seconds to form an insulating film with a thickness of 1 μm.

[0079] The weather resistance, corrosion resistance, solution stability, and tension were evaluated using the following methods and summarized in Table 2.

[0080]

[0081] Weatherability evaluation

[0082] The weather resistance was evaluated under the conditions of 98% moisture, 60℃, and 72 hours, and was marked as “OK” if good and “NG” if bad.

[0083]

[0084] Corrosion resistance evaluation

[0085] A salt spray test was performed at 5% NaCl, 100 RH, 65 ℃, for 8 hours. If good, it was marked as “OK”, and if bad, it was marked as “NG”.

[0086]

[0087] Solution stability evaluation

[0088] Dissolve 100 ml of 10% NaOH in a 2x2 cm coating plate and filter. The substance that remains as a powder is PO4. Weigh the powder remaining on the filter. If it remains, it can be determined that HPO4 has been removed by the oxidizing agent.

[0089] Cl tracing method: Dissolve 100 mL of 10%NaOH, 2x2 CM size coating, and if Cl component is present in the solution, it can be seen that Cl has been added.

[0090]

[0091] Tension evaluation

[0092] Place the specimen on the floor and mark the top point of the specimen's bend. Measure the distance between the top point and the specimen's position before bending, and enter this as the maximum bend length (H). Then, measure as follows:

[0093] σ = E / (1-ν) x T2 / 3t x 2H / I 2

[0094] σ = film tension (Kg / mm)

[0095] ν = Poisson's ratio (0.3)

[0096] t = thickness after coating removal (mm)

[0097] T = Thickness before coating removal (mm)

[0098] H = maximum bend length (mm)

[0099] I = specimen length (mm)

[0100]

[0101] (Parts by weight) Phosphate Nano Silica Micro Silica Nitrate Boron Compound Chromium Compound 110058100532612210035100532612310010010053261241003010053261251001201005326126100581003026127100581002002612810058100252612910058100230261210100585 0532612111005830053261212100584053261213100583505326121410058100532610151005810053261001610058100532651710058100532612019100581005351220100581005312012

[0102] Corrosion resistance growth strength (Mpa) Weather resistance Solution stability Classification 1 OK 5 OK 8 Example 2 OK 5 OK 8 Example 3 OK 5 OK 8 Example 4 OK 3 OK 8 Comparative example 5 OK 5 OK 30 Comparative example 6 OK 5 OK 8 Example 7 OK 5 OK 8 Example 8 OK 4 OK 8 Comparative example 9 OK 5 OK 10 Comparative example 10 OK 5 OK 8 Example 11 OK 5 OK 8 Example 12 OK 3 OK 8 Comparative example 13 OK 5 OK 20 Comparative example 14 OK 5 OK 8 Example 15 OK 5 OK 8 Example 16 NG 5 NG 8 Comparative example 17 NG 5 OK 8 Comparative example 19 NG 5 NG 8 Comparative example 19 OK 5 OK 30 Comparative example

[0103] As shown in Tables 1 and 2, when the components of the insulating film composition are included in an appropriate amount, it can be confirmed that weather resistance, corrosion resistance, solution stability, and tensile strength are simultaneously excellent. On the other hand, when the components of the insulating film composition are not included in an appropriate amount, it can be confirmed that some properties are inferior.

[0104]

[0105] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0106] [Explanation of symbols]

[0107] 100: Electrical steel sheet 10: Electrical steel sheet base

[0108] 20: Insulating film

Claims

100 parts by weight of metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 μm, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of a boron compound and An insulating film composition for electrical steel sheets containing 8 to 110 parts by weight of a chromium compound. In the first paragraph, The above metal phosphate is an insulating film composition for electrical steel sheets containing at least one of Mg, Ca, Ba, Sr, Zn, and Al. In the first paragraph, An insulating film composition for electrical steel, wherein the above nitrate comprises at least one of aluminum nitrate, cobalt nitrate, calcium nitrate, strontium nitrate, zinc nitrate, manganese nitrate, magnesium nitrate, and silver nitrate. In the first paragraph, An insulating film composition for electrical steel, wherein the above nitrate comprises two or more of aluminum nitrate, cobalt nitrate, calcium nitrate, strontium nitrate, zinc nitrate, manganese nitrate, magnesium nitrate, and silver nitrate. In the first paragraph, An insulating film composition for electrical steel sheets, wherein the above boron compound comprises at least one of borax and boric acid. In the first paragraph, The above chromium compound is an insulating film composition for electrical steel sheets containing at least one of chromic acid, chromate, and dichromate. In the first paragraph, The above nano silica and the above micro silica are each an insulating film composition for electrical steel sheets having a pH of 8 to 12. Electrical steel sheet substrate and Including an insulating film positioned on the surface of the electrical steel plate substrate, An electrical steel sheet wherein the insulating film comprises 100 parts by weight of metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 ㎛, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of boron compound, and 8 to 110 parts by weight of chromium compound. Step for preparing electrical steel plate substrate; A step of applying an insulating film composition to the surface of the electrical steel plate substrate; and Comprising a step of heat treating the electrical steel plate substrate, A method for manufacturing an electrical steel sheet, wherein the insulating film composition comprises 100 parts by weight of a metal phosphate, 33 to 110 parts by weight of nano silica having a particle size of 1 to 50 nm, 45 to 325 parts by weight of micro silica having a particle size of 0.5 to 50 ㎛, 28 to 215 parts by weight of nitrate, 10 to 100 parts by weight of a boron compound, and 8 to 110 parts by weight of a chromium compound. In Article 9, A method for manufacturing an electrical steel sheet, wherein the heat treatment step is performed at a temperature of 700 to 1000°C for 10 to 300 seconds.

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