Insulating coating composition, oriented electrical steel sheet comprising same, and method for producing oriented electrical steel sheet

Abstract

The present invention relates to a coating composition for a grain-oriented electrical steel sheet, a grain-oriented electrical steel sheet comprising the same, and a method for manufacturing the grain-oriented electrical steel sheet, the coating composition for a grain-oriented electrical steel sheet according to one embodiment of the present invention may comprise a phosphate salt, silica, a nitrate salt, and an oxidizing agent, the silicon dioxide comprises 50 to 400 parts by weight of solid matters, the ratio of the silicon dioxide solid matters to the phosphate solid matters is 0.3 to 3.9, and the oxidant comprises 0.5 to 10.0 parts by weight of solid matters based on 100 parts by weight of phosphate.

Description

Technical Field

[0001] The present invention relates to electrical steel sheets. More specifically, the present invention relates to an insulating coating composition, an oriented electrical steel sheet containing the composition, and a method for manufacturing the same. Background Art

[0002] Electrical steel sheets are products used as materials for transformers, motors, and electrical equipment. Different from ordinary carbon steels that emphasize workability such as mechanical properties, electrical steel sheets are functional products that emphasize electrical properties. The electrical properties required in the electrical steel sheets include low iron loss, high magnetic flux density, high magnetic permeability, and high duty ratio.

[0003] The electrical steel sheets are further divided into oriented electrical steel sheets and non-oriented electrical steel sheets. The oriented electrical steel sheets form a Goss texture ({110}<001> texture) in the entire steel sheet by using an abnormal grain growth phenomenon called secondary recrystallization, so that they have good magnetic properties in the rolling direction. In contrast, non-oriented electrical steel sheets are electrical steel sheets having uniform magnetic properties in all directions of the rolled sheet.

[0004] In order to ensure the stability of the oriented electrical steel sheets over time, it is important to ensure characteristics such as the surface roughness, gloss, and colorimetric uniformity of the insulating coating after insulation coating. For example, for the oriented electrical steel sheets, they have excellent durability in an extremely high-temperature and high-humidity environment, such as during SRA processing, and have a higher effect than conventional ones in an extremely corrosive environment, and need to ensure heat resistance at high temperatures.

[0005] The oriented electrical steel sheets have a conventional coating structure, which is composed of an MgO coating on the base material and an insulating coating on the upper surface. The insulating coating is usually composed of phosphates, silica, and nitrates.

[0006] Known general conditions for corrosion resistance are 5% NaCl, 60 °C, and 8 hours. In addition, for automotive parts used for a long time, the extreme conditions for corrosion resistance are 5% NaCl, 65 °C, and 100 hours during salt spray. General conditions for weather resistance are 72 hours under 98% moisture and 60 °C, but the extreme conditions for weather resistance are 100 hours under 98% moisture and 65 °C.

[0007] Generally, the insulating coating has excellent corrosion resistance, but has disadvantages of poor weather resistance and sticky adhesion on the surface. For such adhesion characteristics, problems may occur in terms of adhesiveness when coiling the coiled sheet.

[0008] Therefore, for the insulating coating, it is necessary to develop a chromium-free phosphate coating for grain-oriented electrical steel sheets in which the film and the material do not separate even in a high-humidity environment, and it is also necessary to develop an insulating coating composition to solve the problem of being susceptible to influence in a high-humidity environment due to the property of phosphate causing stickiness on the surface. Summary of the Invention

[0009] (I) Technical Problems to be Solved

[0010] The technical problem to be solved by the present invention is to provide an insulating film composition for grain-oriented electrical steel sheets, which contains a coating substance in which the film and the material do not separate even in a high-temperature and high-humidity environment.

[0011] Another technical problem to be solved by the present invention is to provide a grain-oriented electrical steel sheet coated with the insulating film composition having the aforementioned advantages.

[0012] Still another technical problem to be solved by the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet having the aforementioned advantages.

[0013] (II) Technical Solutions

[0014] An insulating film composition for grain-oriented electrical steel sheets according to an embodiment of the present invention may contain phosphate, silica, nitrate, and an oxidizing agent. Based on 100 parts by weight of the phosphate, the silica contains 50 to 400 parts by weight of solids, and the ratio of the silica solids to the phosphate solids is 0.3 to 3.9. Based on 100 parts by weight of the phosphate, the oxidizing agent contains 0.5 to 10.0 parts by weight of solids. In one embodiment, the nitrate may contain at least any one 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).

[0015] In one embodiment, the nitrate may contain at least 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). In one embodiment, based on 100 parts by weight of the phosphate, the nitrate may contain 5 to 100 parts by weight of solids. In one embodiment, the oxidizing agent may contain at least any one of HClO4, NaClO, NaClO4, KMnO4, NaIO4, OsO4, H2O2, and Ca(ClO)2.

[0016] An oriented electrical steel sheet according to another embodiment of the present invention may include an electrical steel sheet substrate and an insulating coating film located on the surface of the electrical steel sheet substrate. The insulating coating film includes phosphate, silica, nitrate, and an oxidizing agent. Based on 100 parts by weight of the phosphate, the silica includes 50 to 400 parts by weight of solids, and the ratio of the silica solids to the phosphate solids is 0.3 to 3.9. Based on 100 parts by weight of the phosphate, the oxidizing agent includes 0.5 to 10.0 parts by weight of solids.

[0017] A method for manufacturing an oriented electrical steel sheet according to still another embodiment of the present invention may include: a step of preparing an electrical steel sheet substrate, a step of coating an insulating coating composition on the surface of the electrical steel sheet substrate, and a step of curing the insulating coating composition. The insulating coating composition includes phosphate, silica, nitrate, and an oxidizing agent. Based on 100 parts by weight of the phosphate, the silica includes 50 to 400 parts by weight of solids, and the ratio of the silica solids to the phosphate solids is 0.3 to 3.9. Based on 100 parts by weight of the phosphate, the oxidizing agent includes 0.5 to 10.0 parts by weight of solids. The step of curing the insulating coating composition is carried out in the range of 800 to 900 °C for 30 seconds to 180 seconds.

[0018] In one embodiment, the step of coating the insulating coating composition on the surface of the electrical steel sheet substrate may include a step of adding phosphate and silica for miscibility, a step of adding nitrate to the miscible solution, and a subsequent step of adding an oxidizing agent. In one embodiment, the step of preparing the electrical steel sheet substrate may include: a step of preparing a steel billet, a step of heating the steel billet, a step of hot rolling the heated steel billet to manufacture a hot rolled steel sheet, a step of cold rolling the hot rolled steel sheet to manufacture a cold rolled steel sheet, a step of performing primary recrystallization annealing on the cold rolled sheet, a step of coating an annealing separating agent on the steel sheet after primary recrystallization annealing, and a step of performing secondary recrystallization annealing.

[0019] In one embodiment, the step of coating the annealing separating agent on the steel sheet after primary recrystallization annealing may include a step of coating the annealing separating agent in the range of 1 to 5 g / m 2 range. In one embodiment, the step of secondary recrystallization annealing may include a soaking step and a heating-up step. The soaking step may be carried out in the range of 650 to 750 °C, and the heating-up step may be carried out in the range of 1100 to 1250 °C.

[0020] In one embodiment, the heating step may be carried out at a heating rate in the range of 10 to 20 °C per hour (hr). In one embodiment, the soaking step may be carried out in a gas environment of two or more of hydrogen, nitrogen, and inert gas. In one embodiment, the heating step may be carried out in a hydrogen environment.

[0021] (III) Beneficial Effects

[0022] According to an embodiment of the present invention, an insulating coating composition can provide an insulating coating composition for grain-oriented electrical steel sheets. By adding an oxidizing agent for removing the hydrogen group of phosphates to the grain-oriented electrical steel sheets, it has excellent durability and extreme corrosion resistance in a high-temperature and high-humidity environment, and excellent heat resistance at a very high temperature with high processability such as SRA.

[0023] According to another embodiment of the present invention, a grain-oriented electrical steel sheet can provide a grain-oriented electrical steel sheet coated with the aforementioned insulating coating composition.

[0024] According to still another embodiment of the present invention, a method for manufacturing a grain-oriented electrical steel sheet having the aforementioned advantages can be provided. Detailed Embodiments

[0025] The terms first, second, third, etc. are used to describe each part, component, region, layer, and / or section, but these parts, components, regions, layers, and / or sections should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, or section described below can also be described as the second part, component, region, layer, or section.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless clearly indicated to the contrary in the context, the singular forms used herein are also intended to include the plural forms. The "including" used in the specification may specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, fields, integers, steps, actions, elements, and / or components.

[0027] If a part is described as being on another part, it may be directly on the other part or there may be other parts therebetween. When a part is described as being directly on another part, there are no other parts therebetween.

[0028] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0029] In addition, unless otherwise specifically stated, % represents weight %, and 1 ppm is 0.0001 weight %.

[0030] In one embodiment of the present invention, further comprising an additional element means that the additional element replaces the remaining iron (Fe), and the replacement amount is equivalent to the addition amount of the additional element.

[0031] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention belongs can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0032] The insulating coating composition for grain-oriented electrical steel sheets according to one embodiment of the present invention may include phosphates, silica, nitrates, and oxidants. The phosphate is a metal phosphate and can satisfy M(H2PO4) or M(HPO4). The M may include Mg, Al, Zn, Ca, or a combination thereof. For example, it may be a phosphate in which M includes Mg and Al.

[0033] The silica is an essential component to reduce iron loss by imparting tension to the steel sheet. In addition, the phosphate acts as an adhesive for the silica, thereby improving the film-forming property of the coating and the adhesion of the coating film. In one embodiment, the silica may be an alkaline or acidic substance.

[0034] In one embodiment, based on 100 parts by weight of the phosphate, the silica may include 50 to 400 parts by weight of solids. Specifically, based on 100 parts by weight of the phosphate, the silica may include 80 to 200 parts by weight, more specifically may include 135 to 180 parts by weight, and even more specifically may include 145 to 160 parts by weight.

[0035] If the range of the silica exceeds the upper limit value, it can be confirmed that there are poor effects in terms of adhesiveness or solution stability. If the range of the silica exceeds the lower limit value, there is a problem of insufficient effect of imparting tension to the steel sheet.

[0036] In one embodiment, the silica may have an average particle size in the range of 5 to 20 nm. If the average particle size of the silica exceeds the upper limit value of the range, the surface area per unit mass decreases, the condensation reaction rate becomes slower, and in order to increase the reaction rate, it is necessary to increase the heat treatment temperature, so there is an uneconomical problem. If the average particle size of the silica exceeds the lower limit value of the range, the condensation reaction rate is relatively fast, resulting in a coagulation phenomenon, and there is a problem of causing color deviation defects on the surface.

[0037] In one embodiment, the silica may be composed of at least one nanoparticle having a different average particle size. Specifically, for the silica, in order to form an insulating film having excellent film-forming characteristics, at least one or more silica nanoparticles having different average particle sizes may also be mixed and used.

[0038] In one embodiment, the ratio of the silica solid content to the phosphate solid content may be 0.3 to 3.9. Specifically, the ratio may be 0.5 to 2.0. Since the silica and the phosphate are mixed in the ratio, when manufacturing an electrical steel sheet, the adhesion to the base material is excellent, and the advantages of excellent heat resistance, weather resistance, and corrosion resistance can be exhibited.

[0039] For the ratio, if the proportion of the phosphate is too high, there is a problem of reduced durability in a high-temperature and high-humidity environment. If the proportion of the silica is too high, there is a problem of reduced adhesion to the base material.

[0040] The nitrate may be a component that plays a role due to corrosion resistance and weather resistance. In one embodiment, the nitrate may include any one 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).

[0041] In one embodiment, based on 100 parts by weight of the phosphate, the nitrate may include 5 to 100 parts by weight of the solid content. Specifically, based on 100 parts by weight of the phosphate, the nitrate may include 15 to 80 parts by weight of the solid content, more specifically, it may include 20 to 60 parts by weight of the solid content, even more specifically, it may include 22 to 51 parts by weight of the solid content, and even more specifically, it may include 22 to 28 parts by weight.

[0042] If the content of the nitrate exceeds the upper limit value of the range, there is a risk of fire. If the content of the nitrate exceeds the lower limit value of the range, there is a problem of weather resistance.

[0043] The oxidizing agent can function as an additive for removing hydrogen groups (H) from phosphates such as M(H2PO4) or M(HPO4). For the oxidizing agent, by removing the hydrogen groups from the phosphate, it can function to react with phosphates such as M(H2PO4) or M(HPO4) having sticky properties to remove H and form M(PO4) without sticky properties.

[0044] In one embodiment, the oxidizing agent may include at least any one of HClO4, NaClO, NaClO4, KMnO4, NaIO4, OsO4, H2O2, Ca(ClO)2. For the oxidizing agent, as described above, it may include a substance that removes hydrogen groups by oxidizing the phosphate.

[0045] In one embodiment, based on 100 parts by weight of the phosphate, the oxidizing agent may include 0.5 to 10.0 parts by weight of solids. Based on 100 parts by weight of the phosphate, the oxidizing agent may include 0.8 to 5.0 parts by weight, and more specifically, may include 1.0 to 3.0 parts by weight. By including the oxidizing agent within the aforementioned range, there is an advantage of reducing the adhesiveness exhibited by the phosphate.

[0046] If the content of the oxidizing agent exceeds the upper limit value of the range, it may have a poor effect in terms of adhesion resistance and solution stability. If the content of the oxidizing agent is less than the lower limit value of the range, there is a problem that the advantage of reducing adhesiveness brought about by adding the oxidizing agent cannot be exhibited.

[0047] In one embodiment, the silica may be an acidic substance. When an alkaline substance is used as the silica, there are problems of instability of the phosphate and the nitrate and gelation phenomenon.

[0048] The grain-oriented electrical steel sheet according to another embodiment of the present invention includes a electrical steel sheet substrate and an insulating coating film located on the surface of the electrical steel sheet substrate. The insulating coating film includes a phosphate, silica, nitrate, and an oxidizing agent, and the detailed descriptions of the phosphate, silica, nitrate, and oxidizing agent are the same within the range not conflicting with the content of the aforementioned insulating coating composition.

[0049] A method for manufacturing a grain-oriented electrical steel sheet according to still another embodiment of the present invention includes: a step of preparing a electrical steel sheet substrate, a step of coating an insulating coating composition on the surface of the electrical steel sheet substrate, and a step of curing the insulating coating composition.

[0050] The steps of preparing the base of the electrical steel sheet may include: the step of preparing a steel billet, the step of heating the steel billet, the step of hot rolling the heated steel billet to manufacture a hot-rolled steel sheet, the step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet, the step of performing primary recrystallization annealing on the cold-rolled sheet, the step of coating an annealing separating agent on the steel sheet after primary recrystallization annealing, and the step of performing secondary recrystallization annealing.

[0051] The step of heating the steel billet may heat the steel billet to a temperature below 1300 °C. If the steel billet is heated within the aforementioned temperature range, the columnar crystal structure of the steel billet can be prevented from growing coarsely, thereby preventing cracks in the sheet during the hot rolling process. Specifically, the step of heating the steel billet may heat to a temperature of 1050 to 1300 °C.

[0052] Then, the heated steel billet is hot rolled, whereby a hot-rolled steel sheet can be manufactured. The hot rolling temperature is not limited. As an example, hot rolling can be ended at a temperature below 950 °C.

[0053] In one embodiment, after the step of manufacturing the hot-rolled steel sheet, the step of annealing the hot-rolled steel sheet may be performed. The step of annealing the hot-rolled steel sheet can homogenize the non-uniform fine structure and precipitates of the hot-rolled steel sheet. Specifically, the step of annealing the hot-rolled steel sheet may be performed within a temperature range of 800 to 1300 °C.

[0054] Then, the step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet may be performed. The cold rolling step may be a single cold rolling or may be two or more cold rollings including intermediate annealing.

[0055] Then, the step of performing primary recrystallization annealing on the cold-rolled steel sheet may be performed. At this time, the step of primary recrystallization annealing may include a decarburization step and a nitriding step. The decarburization step and the nitriding step may be performed without regard to order. For example, the nitriding step may be performed after the decarburization step, or the decarburization step may be performed after the nitriding step.

[0056] In one embodiment, the step of simultaneously performing decarburization annealing and nitriding treatment on the cold-rolled steel sheet obtained by cold rolling to cause primary recrystallization may be included. Specifically, the decarburization step and the nitriding step may be performed simultaneously. The nitriding step is for nitriding the inside of the steel sheet and is a step of introducing nitrogen ions into the steel sheet and is a step for precipitating precipitates such as (Al, Si, Mn)N or AlN, which are grain growth inhibitors. Through the nitriding step, nitriding can be performed until the nitrogen content of the grain-oriented electrical steel sheet is 0.01% or less.

[0057] For the step of primary recrystallization annealing, heat treatment can be carried out within the range of annealing temperature from 800 to 950 °C. If the range of the annealing temperature exceeds the upper limit value, the recrystallized grains grow coarsely, resulting in a decrease in the driving force for grain growth. Therefore, there is a problem that stable secondary recrystallization cannot be formed. If the range of the annealing temperature exceeds the lower limit value, there is a problem of excessive time consumption during decarburization.

[0058] The step of primary recrystallization annealing can be carried out in an environment of nitrogen, hydrogen, and their mixed gases. For example, the gas environment can be an ammonia gas environment. The gas environment can be a moist environment or a dry environment.

[0059] After the step of primary recrystallization annealing, an annealing release agent can be coated on the steel plate. For example, as the annealing release agent, an annealing release agent with a main component of MgO can be used. In one embodiment, in the step of coating the annealing release agent, the coating amount of the annealing release agent can be 1 to 5 g / m 2 Range.

[0060] If the coating amount of the annealing release agent exceeds the upper limit value of the range, there is a problem of affecting secondary recrystallization. If the coating amount of the annealing release agent exceeds the lower limit value of the range, there is a problem of difficulty in smoothly forming a coating film.

[0061] The step of performing secondary recrystallization annealing is to form a {110}<001> texture through secondary recrystallization, and to endow insulation and remove impurities that damage magnetic properties through the oxide layer formed during primary recrystallization annealing and the vitreous coating film formed by the reaction of MgO.

[0062] In one embodiment, the step of secondary recrystallization annealing can include a soaking step and a heating-up step. The soaking step can be carried out within the range of 650 to 750 °C, and the heating-up step can be carried out within the range of 1100 to 1250 °C. If the temperature range is exceeded, there is a problem of difficulty in forming an appropriate coating film.

[0063] In one embodiment, the heating-up step can be carried out at a heating-up rate within the range of 10 to 20 °C / hour. Specifically, the heating-up rate can be within the range of 13 to 17 °C / hour.

[0064] If the heating-up rate exceeds the upper limit value of the range, there is a problem of decomposition of the phosphate resulting in decomposition of the coating film. If the heating-up rate exceeds the lower limit value of the range, there is a problem of poor curing of silicon dioxide resulting in poor corrosion resistance and weather resistance.

[0065] In one embodiment, the soaking step may be carried out in an environment of at least two or more of hydrogen, nitrogen, and inert gas. In one embodiment, the heating step may be carried out in a hydrogen environment. Specifically, as a method of secondary recrystallization annealing, a mixed gas of nitrogen and hydrogen is maintained in the heating step before secondary recrystallization occurs to protect the nitride as a grain growth inhibitor, so that secondary recrystallization can develop smoothly. After secondary recrystallization is completed, it is maintained in a 100% hydrogen environment for a long time in the soaking step to remove impurities.

[0066] In one embodiment, the step of coating the surface of the electrical steel sheet substrate with the insulating coating composition includes: a step of adding phosphate and silica for miscibility; a step of adding nitrate to the miscible solution; and a subsequent step of adding an oxidant. The phosphate, the silica, the nitrate, and the oxidant are the same within the range not conflicting with the content described in the foregoing insulating coating composition.

[0067] In one embodiment, the step of curing the insulating coating material may be carried out in a temperature range of 800 to 900 °C. If it exceeds the upper limit value of the temperature range, there is a problem of deterioration in the weather resistance and corrosion resistance of the insulating film. If it exceeds the lower limit value of the temperature range, the curing of the silica sol does not occur, and problems may occur in terms of corrosion resistance and weather resistance.

[0068] In one embodiment, the step of curing the insulating coating material may be carried out within a time of 30 to 240 seconds. Specifically, the time may be 45 to 180 seconds.

[0069] If it exceeds the upper limit value of the time, there is a problem of phosphate decomposition. If it exceeds the lower limit value of the time, there is a problem of poor corrosion resistance and weather resistance due to non-curing.

[0070] Hereinafter, specific embodiments of the present invention will be described. However, the following embodiments are only specific embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0071] Experimental Examples 1 to 8

[0072] To manufacture the insulating film composition for the grain-oriented electrical steel sheet of the present invention, an aluminum and magnesium phosphate solution with 67% of the phosphate solid content dissolved is prepared, and then a colloidal silica solution with 30% of the solid content dissolved as shown in Table 1 below is added for miscibility.

[0073] Then, add a nitrate solution in which 50% of a solid substance such as aluminum nitrate or magnesium nitrate equivalent to the conversion coating substance having the content shown in Table 1 below is miscible. Then, add an oxidizing agent in which 50% of a solid substance such as HClO4, NaClO, and NaClO4 having the content shown in Table 1 below is miscible to produce an insulating coating composition solution having the components shown in Table 1 below. Coat the produced insulating coating composition solution on a steel plate treated with MgO. Then, after drying at 700 to 950 °C for 30 to 240 seconds, evaluate the adhesiveness, weather resistance, heat resistance, corrosion resistance, and solution stability.

[0074] For the adhesiveness, weather resistance, heat resistance, corrosion resistance, and solution stability, evaluation is carried out by the method described below.

[0075] <Evaluation method>

[0076] Evaluate the adhesion resistance

[0077] The adhesion resistance is used to evaluate the degree of non-stickiness. Using a sphere diameter of 12.7 mm, a pressing load of 50 N, a rotation speed of 50 rpm, a rotation radius of 15 mm, and a slip distance of 200 m (Test 1), in order to compare the wear amount according to the slip distance, change the rotation radius to 10 mm and the slip distance to 10 m under the same load and rotation speed as in Test 1, and evaluate the adhesion by the friction coefficient. At this time, for the friction coefficient, it is calculated by the frictional force relative to the vertical load (frictional force / vertical load). When the friction coefficient is good and lower than 0.4, it is expressed as "qualified (OK)", and when the friction coefficient is poor and higher than or equal to 0.4, it is expressed as "poor (NG)".

[0078] Evaluate the coatability

[0079] By visual evaluation, when there are no spots and it is good, it is expressed as "qualified", and when there are spots and it is bad, it is expressed as "poor".

[0080] Evaluate the weather resistance

[0081] Evaluate the weather resistance under the conditions of 98% moisture, 60 °C, and 72 hours. When it is good, it is expressed as "qualified", and when it is bad, it is expressed as "poor".

[0082] Evaluate the heat resistance

[0083] For the heat resistance evaluation, heat at 560 °C under the conditions of 20% hydrogen and 80% nitrogen for 2 hours. Then, confirm that it reaches 5B or more through the CROSS-HATCH CUT test.

[0084] If the test result is 5B or more, it is good and expressed as "qualified", and if the test result is less than 5B, it is bad and expressed as "poor".

[0085] Evaluation of corrosion resistance

[0086] A salt spray test with 5% NaCl, 100% RH, 65 °C for 8 hours was carried out.

[0087] Evaluation of solution stability

[0088] Dissolve a coated plate with a size of 2x2 CM in 100 ml of 10% NaOH, and then filter. The substance that remains undissolved and exists in powder form is PO4. After measuring the weight of the powder remaining on the filter paper, if there is powder, it can be determined that HPO4 has been removed by the oxidant.

[0089] Cl tracing method: After dissolving a coating with a size of 2x2 CM in 100 mL of 10% NaOH, if there is a Cl component in the solution, it can be considered that Cl has been added.

[0090] [Table 1]

[0091]

[0092] From the above Table 1, when comparing Experimental Example 1 with Experimental Examples 2 to 4, in the case of further adding oxidants such as oxidants HClO4, NaClO or NaClO4, good adhesion resistance, weather resistance, corrosion resistance and solution stability have been confirmed. In the case of not adding the said oxidant, poor adhesion resistance, weather resistance and corrosion resistance have been confirmed. In addition, for Experimental Examples 5 to 8, compared with Experimental Examples 1 to 4, the difference is that magnesium nitrate is used as the nitrate instead of aluminum nitrate. It has been confirmed that even if magnesium nitrate is used as the said nitrate instead of aluminum nitrate, the same effect is obtained.

[0093] Specifically, by adding the said oxidant, the amino group can be removed by an oxidant such as M(H2PO4) or M(HPO4) through the following reaction formula.

[0094] [Reaction formula]

[0095] 2M X (HPO4) Y + NaClO → H2O + NaCl + M X (PO4) Y

[0096] According to the said reaction formula, with the removal of the amino group from the phosphate, good adhesion resistance has been confirmed.

[0097] Experimental Examples 9 to 17

[0098] In Table 2 below, except that the components of the insulating coating composition for grain-oriented electrical steel sheets were controlled within the content ranges shown in Table 2 below and aluminum nitrate was used as the nitrate and HClO4 was used as the oxidizing agent, the insulating coating composition was manufactured by the same method as in Experimental Examples 1 to 8 and evaluated.

[0099] [Table 2]

[0100]

[0101] Referring to Table 2 above, as described in Experimental Examples 9 to 12, when HClO4 as the oxidizing agent was added, compared with Experimental Example 13 where the oxidizing agent was not added, it had adhesiveness resistance, thus confirming that it was not sticky. In addition, when the oxidizing agent was added in excess, it was confirmed that the solution stability was poor as described in Experimental Example 12. In addition, when comparing Experimental Examples 9 to 11 with Experimental Examples 14 to 17, since the content of silica was too high and when the ratio of phosphate to silica exceeded the target ratio of the present invention, poor adhesiveness resistance or solution stability was confirmed.

[0102] Experimental Examples 18 to 26

[0103] For Experimental Examples 18 to 26, except that the components of the insulating coating composition for grain-oriented electrical steel sheets were controlled within the content ranges shown in Table 3 below, the insulating coating composition was manufactured by the same method as in Experimental Examples 1 to 8 and evaluated.

[0104] [Table 3]

[0105]

[0106] Referring to Table 3 above, when HClO4 as the oxidizing agent was added as described in Experimental Examples 18 to 20, compared with Experimental Example 22 where the oxidizing agent was not added, Experimental Example 22 had adhesiveness resistance and it was confirmed that it was not sticky. In addition, when the oxidizing agent was added in excess beyond the ratio of phosphate to silica of the present invention as described in Experimental Examples 23 to 26, poor adhesiveness resistance or solution stability was confirmed.

[0107] Experimental Examples 27 to 36

[0108] For Experimental Examples 27 to 36, except that the components of the insulating coating composition for grain-oriented electrical steel sheets were controlled within the content ranges shown in Table 4 below and magnesium nitrate was added together with aluminum nitrate as the nitrate and HClO4 was used as the oxidizing agent, the insulating coating composition was manufactured by the same method as in Experimental Examples 1 to 9 and evaluated.

[0109] [Table 4]

[0110]

[0111] Referring to Table 4 above, for Experimental Examples 29, 31, 32, 34, and 35, when magnesium nitrate and aluminum nitrate are added simultaneously as nitrates and HClO4 is included as an oxidizing agent, good adhesion resistance has been confirmed compared to Experimental Example 33 containing the said oxidizing agent. In addition, as described in Experimental Examples 27 and 28, when the content of the oxidizing agent is too much or too little, poor adhesion resistance or solution stability has been confirmed. In addition, in Experimental Example 30, the total amount of magnesium nitrate and aluminum nitrate is 1 g, and when the content of the nitrate is too little, poor adhesion resistance has been confirmed. In addition, as described in Experimental Example 36, when the content of the oxidizing agent is too much, poor adhesion resistance and solution stability have been confirmed.

[0112] Experimental Examples 37 to 47 - Curing Temperature Test

[0113] The following Table 5 evaluates the adhesion resistance, weather resistance, and corrosion resistance of the insulating coating composition for grain-oriented electrical steel sheets with the same components when the curing temperature and curing time are adjusted as shown in Table 4 below.

[0114] [Table 5]

[0115]

[0116] Referring to Table 5 above, among the curing conditions, for Experimental Examples 38 to 40 where the curing temperature is within the scope of the present invention, good adhesion resistance, weather resistance, and corrosion resistance have been confirmed compared to Experimental Examples 37 and 41 where the curing temperature exceeds the scope of the present invention. It has been confirmed from Experimental Examples 42 to 47 that for Experimental Examples 42 to 45 where the curing time is within the scope of the present invention, the adhesion resistance, weather resistance, and corrosion resistance are good, but for Experimental Examples 46 and 47 where the curing time exceeds the scope of the present invention, at least one of the adhesion resistance, weather resistance, and corrosion resistance is poor.

[0117] The present invention is not limited to the said embodiments and / or examples and can be manufactured in various different ways. Those of ordinary skill in the technical field to which the present invention pertains can understand that the present invention can be implemented in other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above embodiments and / or examples are exemplary in all aspects and not restrictive.

Claims

1. An insulating coating composition for grain-oriented electrical steel sheets, comprising: Phosphate; Silica; Nitrate; and Oxidant, Based on 100 parts by weight of the phosphate, the silica contains 50 to 400 parts by weight of solids, The ratio of the silica solids to the phosphate solids is 0.3 to 3.9, Based on 100 parts by weight of the phosphate, the oxidant contains 0.5 to 10.0 parts by weight of solids.

2. The insulating coating composition for grain-oriented electrical steel sheets according to claim 1, wherein The nitrate contains at least any one 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).

3. The insulating coating composition for grain-oriented electrical steel sheets according to claim 2, wherein The nitrate contains at least 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).

4. The insulating coating composition for grain-oriented electrical steel sheets according to claim 1, wherein Based on 100 parts by weight of the phosphate, the nitrate contains 5 to 100 parts by weight of solids.

5. The insulating coating composition for grain-oriented electrical steel sheets according to claim 1, wherein The oxidant contains at least any one of HClO4, NaClO, NaClO4, KMnO4, NaIO4, OsO4, H2O2, and Ca(ClO)2.

6. A grain-oriented electrical steel sheet, comprising: A base of electrical steel sheet; and An insulating coating on the surface of the base of the electrical steel sheet, The insulating coating contains phosphate, silica, nitrate, and oxidant, Based on 100 parts by weight of phosphate, the silica contains 50 to 400 parts by weight of solids, The ratio of the silica solids to the phosphate solids is 0.3 to 3.9, Based on 100 parts by weight of the phosphate, the oxidant contains 0.5 to 10.0 parts by weight of solids.

7. A method for manufacturing a grain-oriented electrical steel sheet, comprising: A step of preparing a base of electrical steel sheet; A step of coating an insulating coating composition on the surface of the base of the electrical steel sheet; and A step of curing the insulating coating composition, The insulating coating composition contains phosphate, silica, nitrate, and oxidant, Based on 100 parts by weight of phosphate, the silica contains 50 to 400 parts by weight of solids, the ratio of the silica solids to the phosphate solids is 0.3 to 3.9, and based on 100 parts by weight of the phosphate, the oxidant contains 0.5 to 10.0 parts by weight of solids, The step of curing the insulating coating composition is carried out at a temperature in the range of 800 to 900 °C for 30 seconds to 180 seconds.

8. The method for manufacturing an oriented electrical steel sheet according to claim 7, wherein, The step of coating the insulating coating composition on the surface of the electrical steel sheet substrate includes: a step of adding phosphate and silica for miscibility; a step of adding nitrate to the miscible solution; and a subsequent step of adding an oxidant.

9. The method for manufacturing an oriented electrical steel sheet according to claim 7, wherein, The step of preparing the electrical steel sheet substrate includes: A step of preparing a steel billet; A step of heating the steel billet; A step of hot rolling the heated steel billet to manufacture a hot rolled steel sheet; A step of cold rolling the hot rolled steel sheet to manufacture a cold rolled steel sheet; A step of performing primary recrystallization annealing on the cold rolled sheet; A step of coating an annealing release agent on the steel sheet after primary recrystallization annealing; and A step of performing secondary recrystallization annealing.

10. The method for manufacturing an oriented electrical steel sheet according to claim 9, wherein, The step of coating the annealing release agent on the steel sheet after primary recrystallization annealing includes the step of coating the annealing release agent in a range of 1 to 5 g / m 2 2.

11. The method for manufacturing an oriented electrical steel sheet according to claim 9, wherein, The step of secondary recrystallization annealing includes a soaking step and a heating-up step, The soaking step is carried out in the range of 650 to 750 °C, and the heating-up step is carried out in the range of 1100 to 1250 °C.

12. The method for manufacturing an oriented electrical steel sheet according to claim 11, wherein, The heating-up step is carried out at a heating rate in the range of 10 to 20 °C / hour.

13. The method for manufacturing an oriented electrical steel sheet according to claim 11, wherein, The soaking step is carried out in a gas environment of two or more of hydrogen, nitrogen, and inert gas.

14. The method for manufacturing an oriented electrical steel sheet according to claim 11, wherein, The heating-up step is carried out in a hydrogen environment.

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