Annealing separator manufacturing method, annealing separator, and grain-oriented electrical steel sheet

Abstract

To provide a preparation method for annealing separating agent and the annealing separating agent, and a directional electromagnetic steel plate.SOLUTION: An annealing separating agent obtained by a method according to the present invention is high in purity, excellent in dispersibility and adhesion strength, and can form a uniform and fine forsterite layer on a surface of a directional electromagnetic steel plate. The preparation method for an annealing separating agent comprises: process step (1): mixing and reacting magnesium oxide and an ammonium salt solution to prepare a magnesium salt solution and ammonia, and then reacting the refined magnesium salt solution with ammonia to obtain magnesium hydroxide; process step (2): curing a part of the resulting magnesium hydroxide at a high temperature of 155-230°C, and curing the other part of the resulting magnesium hydroxide at a low temperature of 10-100°C; and process step (3): mixing and sintering the magnesium hydroxide cured under said conditions to obtain magnesium oxide for the annealing separating agent..SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an annealing separator, an annealing separator, and a grain-oriented electrical steel sheet. The annealing separator obtained by this method has high purity, excellent dispersibility, and adhesive strength, and is capable of forming a uniform and dense forsterite layer on the surface of a grain-oriented electrical steel sheet. [Background technology]

[0002] The manufacturing process for grain-oriented electrical steel generally involves hot rolling, annealing, cold rolling, and recrystallization annealing (decarburization annealing) of steel billets (steel ingots) with adjusted composition, followed by final annealing. During the above manufacturing process, the final annealing is performed at a high temperature of over 1200°C, so an annealing separator primarily composed of MgO is typically applied to prevent adhesion between the wound steel rolls.

[0003] In addition to the above functions, the MgO in the annealing separator reacts with the SiO2 oxide layer precipitated on the steel sheet surface during recrystallization annealing (decarburization annealing) to form a forsterite layer. At the same time, the final annealing process also suppresses the growth of precipitates known as inhibitors of iron crystal growth (e.g., AlN, MnS, TiN, Si3N4, TiC, etc.). This is crucial for forming a forsterite layer with a uniform thickness. The forsterite layer provides tension to the steel sheet surface, reduces core loss, improves magnetic properties, and provides insulation to the steel sheet. Furthermore, in a subsequent process, a phosphate-based insulating layer is applied to the formed forsterite layer, which acts as an adhesive to tightly bond it to the steel substrate. Therefore, annealing separators are extremely important in the production of electrical steel sheets.

[0004] Various methods and technologies have been proposed for annealing separators. Specifically, for example, Patent Document 1 discloses a technology for smoothing the surface of a base steel sheet, enhancing the tension of the steel sheet surface, and significantly reducing iron loss. However, the material in Patent Document 1 contains elements that are detrimental to reaction activity.

[0005] Patent Document 2 discloses a manufacturing technology for an annealing separator that mixes 2 to 40 parts by mass of an alkaline earth metal. This improves the performance of the formed forsterite layer by adjusting the physical properties and components of MgO, and also promotes the decomposition of SiO2 by adding chlorides, thereby preventing the formation of silicate compounds. However, it cannot be said that Patent Document 2 completely achieves its intended purpose.

[0006] Patent Document 3 discloses a technology related to an annealing separator with high cohesive properties. This technology is a technology for producing aggregated fine particles of MgO. However, in the manufacturing process of grain-oriented electrical steel sheets, it is necessary to reduce the content of moisture and O2 as much as possible. However, aggregated fine particles of MgO tend to cause trace amounts of water to remain, which is disadvantageous for manufacturing high-quality grain-oriented electrical steel sheets.

[0007] Patent Document 4 discloses a non-forsterite annealing separator. This patent document relates to a coating of a suspension containing alumina as the main component. However, moisture remains in the alumina coating, which causes an oxide layer to form on the surface of the steel sheet during high-temperature annealing.

[0008] Patent Document 5 discloses an annealing separator containing 0.04 to 0.30 mass% boron and containing 55 to 95% of boron with a coordination number of 4. The proportion of boron with a coordination number of 4 is controlled by adjusting the sintering temperature, drying time, and moisture absorption, thereby improving the performance of grain-oriented electrical steel sheets. However, there is a contradiction between the tetracoordinated boron element described in Patent Document 5 and the principle of forsterite formation, and it is unlikely that the expected effect will be fully achieved.

[0009] Patent Document 6 describes a method for producing a sintered body containing 0.04 to 0.15 mass% boron element, 0.05 mass% or less chlorine element, and having a Blaine specific surface area of ​​2.0 × 10 3 ~7.0×10 3 m 2 However, the Blaine method specific surface area is based on the specific surface area of ​​cement and the specific surface area of ​​0.2 to 0.6 m according to the Chinese national standard (GB / T 8074-2008). 2 This method is only applicable to the measurement of various powdery materials in the range of 1 / g, such as fly ash, granulated blast furnace slag powder, etc. The method is not applicable to the measurement and characterization of porous and ultrafine powdery materials such as annealing separators.

[0010] In Patent Document 7, seawater is used as a magnesium source, calcium hydroxide is used as an alkali source, and highly aggregated magnesium hydroxide synthesized at low temperature (50°C for 20 hours) is used as a precursor, and the Blaine particle size and BET particle size ratio R Blaine / R BET The document discloses a technology for an annealing separator with aggregates having a specific surface area between 3.0 and 5.5. However, as mentioned above, the Blaine method specific surface area measurement has a large error for porous fine particles such as magnesium oxide for annealing separators, making it unsuitable. Therefore, values ​​obtained using such a method are not reliable. Furthermore, according to the document, if the agglomeration degree of magnesium oxide is lower than 3, the reaction is too fast and the material is not suitable as a separator. This point also contradicts common knowledge. If the particle size of the primary particles is appropriately large, the material can be applied to grain-oriented electrical steel sheets even if the agglomeration degree is low. Conversely, if the particle size of the primary particles is small, the agglomeration degree is low, and the reactivity of magnesium oxide, i.e., the reaction rate, can be effectively controlled by appropriately adjusting the calcination temperature of the magnesium oxide. Therefore, from a technical standpoint, the document is also inappropriate.

[0011] Furthermore, some annealing separator products currently on the market have the problem of "seat bumps," i.e., slight depressions at the top and bottom ends of the coil.

[0012] As described above, there is still a demand for an annealing separator having sufficient performance. At present, there is no annealing separator having sufficiently satisfactory performance. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Special Publication No. 52-24499 [Patent Document 2] Japanese Patent Application Publication No. 64-62476 [Patent Document 3] PCT / JP01 / 09354 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-268450 [Patent Document 5] Japanese Patent Application Publication No. 2017-128773 [Patent Document 6] Japanese Patent Application Laid-Open No. 2017-179459 [Patent Document 7] PCT / JP2017 / 010691 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made in view of the above-mentioned problems existing in the prior art, and its object is to provide a method for producing an annealing separator, an annealing separator, and a grain-oriented electrical steel sheet. The annealing separator obtained by this method has high purity, excellent dispersibility (suspension ability), and adhesive strength, and is capable of forming a uniform and dense forsterite layer on the surface of a grain-oriented electrical steel sheet. As a result, a grain-oriented electrical steel sheet with excellent insulating and electromagnetic properties can be obtained. [Means for solving the problem]

[0015] The present inventors have conducted extensive research and have found that by subjecting a magnesium hydroxide precursor for producing an annealing separator to high-temperature aging and low-temperature aging, it is possible to control the physical properties of the resulting annealing separator, and to obtain an annealing separator that is highly pure and has excellent dispersibility (suspendability) and adhesion strength, thereby completing the present invention.

[0016] Specifically, the present invention provides the following: 1. A step (1) of mixing and reacting magnesium oxide with an ammonium salt solution to prepare a magnesium salt solution and ammonia, and then reacting the purified magnesium salt solution with the ammonia to obtain magnesium hydroxide; a step (2) of high-temperature aging a portion of the obtained magnesium hydroxide at 155 to 230°C and low-temperature aging another portion of the obtained magnesium hydroxide at 10 to 100°C; and (3) mixing the magnesium hydroxides aged under the respective conditions and calcining the mixture to obtain magnesium oxide, which is used as an annealing separator.

[0017] 2. The magnesium oxide in step (1) is obtained by lightly burning magnesium hydroxide derived from natural brucite, magnesite, magnesium carbonate, basic magnesium carbonate, seawater, or bittern, 2. The method according to 1, wherein the ammonium salt in step (1) is any one of ammonium nitrate, ammonium sulfate, and ammonium chloride.

[0018] 3. The manufacturing method according to 1 or 2, wherein the high-temperature aging is carried out by heating at a temperature of 160 to 180°C for 120 to 180 minutes, and the low-temperature aging is carried out by heating at a temperature of 50 to 90°C for 120 to 180 minutes.

[0019] 4. The production method according to any one of 1 to 3, wherein the ratio of the high-temperature aged magnesium hydroxide to the low-temperature aged magnesium hydroxide is 1:8 to 8:1 by mass of magnesium hydroxide.

[0020] 5. The method of any one of 1 to 4, wherein the firing temperature is 820 to 1150°C.

[0021] 6. The manufacturing method according to any one of 1 to 5, further comprising mixing the calcined magnesium oxide obtained in step (3) with 0 to 25 wt% of inactive magnesium oxide and / or 0 to 10 wt% of titanium dioxide, based on the weight of the calcined magnesium oxide.

[0022] 7. The sodium content is 20 to 50 ppm. The sedimentation coefficient S is 0.90 or more, An annealing separator that has an adhesion strength of 80% or more after application to the surface of steel plate and contains mainly magnesium oxide.

[0023] 8. The annealing separator according to 7, wherein the average pore diameter of the annealing separator is 45 to 100 nm.

[0024] 9. The annealing separator according to 7 or 8, wherein the ratio of CAA 70% / CAA 40% in the aqueous solution of the annealing separator at 30°C is in the range of 1.8 to 4.0.

[0025] 10. The annealing separator according to any one of 7 to 9, further containing at least one of the following based on the weight of the magnesium oxide: B: 500-1300 ppm; Cl: 100-350 ppm; CaO: 0.2-0.6 wt%; SiO2: 0.2~5.0wt%; TiO2: 0 to 10.0 wt%; or Inert magnesium oxide: 0-25.0 wt%.

[0026] 11. The annealing separator according to any one of 7 to 10, wherein the particles of the annealing separator have an average particle size of 0.5 to 5.0 μm.

[0027] 12. A grain-oriented electrical steel sheet having a forsterite layer on the surface, obtained by using the annealing separator according to any one of 7 to 11.

[0028] 13. A step (1) of mixing and reacting magnesium oxide with an ammonium nitrate solution to prepare a magnesium nitrate solution and ammonia, purifying and purifying the magnesium nitrate solution, recovering and concentrating the ammonia to obtain aqueous ammonia, and then reacting the purified magnesium nitrate solution with the aqueous ammonia to obtain magnesium hydroxide; a step (2) of high-temperature aging a part of the obtained magnesium hydroxide by heating it at a temperature of 160 to 180°C for 120 to 180 minutes, and low-temperature aging another part of the obtained magnesium hydroxide by heating it at a temperature of 50 to 90°C for 120 to 180 minutes; and (3) mixing the magnesium hydroxides aged under the respective conditions in a mass ratio of 1:8 to 8:1 with respect to magnesium hydroxide, followed by firing at 860 to 1050°C to obtain magnesium oxide, which is then used as an annealing separator.

[0029] 14. The sodium content is 20 to 50 ppm. The sedimentation coefficient S is 0.90 or more, The adhesive strength after application to the steel plate surface is 80% or more, An annealing separator having an average pore diameter of 45 to 100 nm and containing mainly magnesium oxide. [Effects of the Invention]

[0030] The annealing separator obtained by the method of the present invention has high purity, excellent dispersibility (suspendability) and adhesive strength, and is capable of forming a uniform and dense forsterite layer on the surface of grain-oriented electrical steel sheet, thereby enabling the production of grain-oriented electrical steel sheet with excellent insulating and electromagnetic properties. [Brief explanation of the drawings]

[0031] [Figure 1] 1 shows an electrophotograph of the annealing separator prepared in Example 4 of the present invention taken by a field emission scanning electron microscope (FE-SEM, 100,000 magnifications). [Figure 2] 1 is a curve showing the average pore size measurement of the annealing separator of Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] [Method of manufacturing annealing separator] The method for producing the annealing separator of the present invention includes the following steps. Step (1): Magnesium oxide and an ammonium salt solution are mixed and reacted to prepare a magnesium salt solution and ammonia. Next, the purified magnesium salt solution is reacted with ammonia to obtain magnesium hydroxide. Step (2): A portion of the obtained magnesium hydroxide is aged at a high temperature of 155 to 230°C, and another portion of the obtained magnesium hydroxide is aged at a low temperature of 10 to 100°C. Step (3): The magnesium hydroxides aged under the above conditions are mixed and calcined to obtain magnesium oxide, which is used as an annealing separator (hereinafter, sometimes referred to as "magnesium oxide for annealing separator").

[0033] The manufacturing method of the present invention purifies raw material magnesium oxide through a chemical reaction to obtain a highly pure raw material. This is then reacted to obtain a magnesium hydroxide precursor. The obtained magnesium hydroxide precursor is then subjected to high-temperature aging and low-temperature aging, respectively, and the high-temperature aged magnesium hydroxide and the low-temperature aged magnesium hydroxide are mixed and fired, thereby controlling the physical properties of the resulting magnesium oxide for an annealing separator. This makes it possible to obtain an annealing separator that is highly pure, has excellent dispersibility (suspensionability), and adhesion strength, and is capable of forming a uniform, dense forsterite layer on the surface of grain-oriented electrical steel sheet. Furthermore, grain-oriented electrical steel sheet with excellent insulating and electromagnetic properties can be produced.

[0034] In the production method of the present invention, the magnesium oxide source is not particularly limited, and commonly used magnesium oxide sources known in the art can be used. For example, magnesium oxide obtained by lightly burning magnesium hydroxide derived from seawater or bittern can be used. However, from the standpoint of availability and purity, lightly burned magnesium oxide obtained by lightly burning raw materials such as natural brucite, magnesite, magnesium carbonate, and basic magnesium carbonate (e.g., 4MgCO3·Mg(OH)2·4H2O or Mg5(CO3)4(OH)2·4H2O) can also be used. Among these, natural brucite, magnesite, and basic magnesium carbonate sources are widely available and have high magnesium oxide contents. Therefore, high-content magnesium oxide can be obtained by simple light burning (calcination at 800 to 1000°C) using these materials as raw materials. Furthermore, lightly burning the raw material can remove hydroxide ions and carbonate ions from the raw ore, thereby obtaining magnesium oxide raw material with a certain activity.

[0035] In the production method of the present invention, the ammonium salt to be reacted with magnesium oxide is not particularly limited, and examples thereof include a solution of ammonium nitrate, ammonium sulfate, or ammonium chloride, with ammonium nitrate being particularly preferred.

[0036] Furthermore, the manufacturing method of the present invention will be described below using an ammonium nitrate solution as an example.

[0037] Taking an ammonium nitrate solution as an example, the specific chemical reaction formula according to the manufacturing method of the present invention is as follows: MgO+2NH4NO3→ Mg(NO3)2+2NH3↑+H2O (1) Mg(NO3)2+2NH3·H2O → Mg(OH)2+2NH4NO3(2) Mg(OH)2 → MgO + H2O (3)

[0038] In the manufacturing method of the present invention, a magnesium hydroxide precursor is first produced. Specifically, magnesium oxide is dissolved in an ammonium nitrate solution, and the magnesium oxide and ammonium nitrate solution are mixed and reacted to prepare a magnesium nitrate solution and ammonia gas. The magnesium nitrate solution is purified by filtration to obtain a purified magnesium source. The purified magnesium nitrate solution is then reacted with aqueous ammonia to obtain magnesium hydroxide. The raw material magnesium oxide is purified by the chemical reactions represented by the above chemical reaction formulas (1) and (2), reducing its impurity content and producing magnesium hydroxide with extremely high purity. The aqueous ammonia can be obtained by recovering and concentrating the produced ammonia gas. Using the ammonia produced in this reaction as an alkali source allows it to be circulated within the system for repeated use, reducing raw material costs and contributing to the realization of industrialization.

[0039] In the production method of the present invention, the ammonium nitrate solution to be reacted with magnesium oxide may have a molar concentration of 0.5 to 8.0 mol / L, preferably 1.0 to 7.0 mol / L, and most preferably 1.5 to 6.0 mol / L.

[0040] In the production method of the present invention, magnesium oxide can be used in the form of a powder or a slurry. When used in the form of a slurry, its molar concentration may be 0.5 to 4.0 mol / L, preferably 0.8 to 3.8 mol / L, and more preferably 1.0 to 3.5 mol / L.

[0041] In the production method of the present invention, the reaction charge ratio between magnesium oxide and ammonium nitrate solution is not particularly limited. However, from the viewpoint of increasing the reaction rate and improving the production yield of the product, the molar ratio of ammonium nitrate to magnesium oxide may be 1.6 to 2.40, preferably 1.7 to 2.30, and most preferably 1.8 to 2.20. Specifically, for example, in industrial-scale production, magnesium oxide powder can be added to the ammonium nitrate solution at a rate of 1,000 to 1,200 kg / hour to achieve the above-mentioned molar ratio of ammonium nitrate to magnesium oxide. During the reaction between magnesium oxide and the ammonium nitrate solution, heat treatment can be performed, if necessary, to promote the reaction. The conditions for the heat treatment are not particularly limited, and heat treatment conditions commonly used in this field can be used. For example, heating can be performed under conditions of 90 to 140°C.

[0042] In the production method of the present invention, the magnesium nitrate solution obtained by the above reaction is filtered to remove unreacted magnesium oxide and other insoluble matter, thereby obtaining a high-purity magnesium nitrate solution as a magnesium source. The ammonia produced by the above reaction can be recovered with water and concentrated to, for example, 5 to 15.0 mol / L to be used as an alkali source.

[0043] In the production method of the present invention, the obtained magnesium nitrate solution is reacted with aqueous ammonia to obtain a magnesium hydroxide precursor. The mixing (reaction) temperature in this reaction is not particularly limited as long as it allows the reaction to proceed. For example, the reaction temperature may be 5 to 60°C. A reaction temperature within this range can avoid problems such as excessively high temperatures causing the product precursor to become too cohesive, which would affect the reactivity of the resulting annealing separator, or problems such as excessively low temperatures causing the reaction to proceed slowly, resulting in large energy consumption for controlling the reaction temperature and being disadvantageous for large-scale industrial production. The reaction temperature is more preferably 20 to 30°C, and even more preferably 25°C.

[0044] In the production method of the present invention, the magnesium hydroxide precursor is then aged. In conventional production methods, magnesium hydroxide precursors are generally produced at low temperatures, but low temperatures result in severe particle aggregation. In the present invention, a portion of the obtained magnesium hydroxide precursor is aged at high temperatures at 155 to 230°C, and the other portion is aged at low temperatures at 10 to 100°C. By using different temperatures for aging, the crystal growth and the degree of dispersion of the precursor particles of the two types of magnesium hydroxide precursors differ from each other, making it possible to control the physical properties of the resulting annealing separator.

[0045] As described above, conventional manufacturing methods generally produce magnesium hydroxide precursors at low temperatures, but at low temperatures, particle aggregation occurs severely, making it difficult to obtain particles with stable physical properties. In contrast, the present invention ages the magnesium hydroxide precursor at both low and high temperatures, and then mixes the two. This significantly reduces particle aggregation while also effectively controlling particle dispersibility and stability. This improves the contact between MgO and SiO2 when applied to steel sheets, facilitating the growth of a forsterite layer.

[0046] In the high-temperature aging, the magnesium hydroxide slurry can be heated at a temperature of 155 to 230°C for 120 to 600 minutes. This high-temperature aging allows the magnesium hydroxide precursor particles to grow sufficiently, improving the dispersibility of the precursor particles. The high-temperature aging temperature is preferably 155 to 200°C, more preferably 160 to 180°C. A high-temperature aging temperature higher than 230°C increases production costs and is unfavorable for large-scale industrial production. A high-temperature aging temperature lower than 155°C results in poor growth of the precursor particles. The high-temperature aging time is preferably 120 to 450 minutes, more preferably 120 to 240 minutes, and particularly preferably 120 to 180 minutes. High-temperature aging within the above time range further avoids the problems of insufficient growth of the precursor particles and the high dispersibility of the precursor particles, which is unfavorable for later sintering and also results in high energy consumption.

[0047] The low-temperature aging can be performed at a temperature of 10 to 100°C for 60 to 300 minutes. This low-temperature aging allows magnesium hydroxide to grow slowly and induces appropriate aggregation of primary particles. This is advantageous for subsequent sintering and improves productivity. The low-temperature aging temperature is preferably 30 to 90°C, more preferably 50 to 90°C. If the low-temperature aging temperature is higher than 100°C, the growth of magnesium hydroxide becomes rapid, the dispersibility of secondary particles becomes too high, and the degree of aggregation of secondary particles tends to decrease, making it difficult to control the pore size and sedimentation of the magnesium oxide produced subsequently. If the low-temperature aging temperature is lower than 10°C, cooling is required, resulting in excessively high energy consumption and being disadvantageous for large-scale industrial production. The low-temperature aging time is preferably 80 to 180 minutes, more preferably 120 to 180 minutes. By performing low-temperature aging within the above time range, problems such as difficulty in controlling dispersibility and excessive dispersibility of precursor particles can be further avoided.

[0048] The above-mentioned chemical reactions (1) to (2) and low-temperature aging and high-temperature aging can be carried out using a reactor such as a general high-pressure reactor used in this field depending on the specific circumstances, and treatments such as cooling, heating, or stirring can be carried out as necessary.

[0049] In the production method of the present invention, the high-temperature aged magnesium hydroxide and the low-temperature aged magnesium hydroxide are then mixed and the mixture is calcined. In the above mixing, the ratio of the high-temperature aged magnesium hydroxide to the low-temperature aged magnesium hydroxide is 1:8 to 8:1, preferably 1:5 to 2:1, and most preferably 1:5 to 1:2, by mass of magnesium hydroxide. By controlling the ratio of the two within the above range, the physical properties of the resulting annealing separator can be controlled, and particle distribution, aggregation, sedimentation, and coatability can be improved. If the ratio of the two is outside the above range, the content of aggregate particles may be too low or too high, which may disrupt the balance of the particle composition and make it impossible to optimize the physical properties of the separator.

[0050] After mixing the high-temperature aged magnesium hydroxide and the low-temperature aged magnesium hydroxide, the mixed magnesium hydroxide can be further heat-treated at 100°C or less as needed before firing.

[0051] The calcination temperature may be 820 to 1150°C, preferably 840 to 1100°C, and more preferably 860 to 1050°C. By controlling the calcination temperature within this range, magnesium oxide with better activity, cohesiveness, and dispersibility (suspensionability) can be obtained. Within the above temperature range, it is possible to avoid problems such as excessively high reaction activity resulting in an excessively high water content, and problems such as the activity of the resulting magnesium oxide being too low, resulting in low suspension stability and difficulty in acting on the annealing separator, making it difficult to form a satisfactory forsterite layer. Calcination can be carried out in a rotary kiln, such as a direct-fired rotary kiln.

[0052] According to the production method of the present invention, magnesium oxide having high purity and excellent dispersibility (suspendability) and adhesion strength can be obtained as an annealing separator.

[0053] The annealing separator obtained by the above method mainly contains magnesium oxide. The magnesium oxide content may be 99.5 wt% or more. The annealing separator also contains approximately 20 to 50 ppm of sodium. The low sodium content of the annealing separator is one of the features of the present invention. The above method makes it possible to reduce the content of impurities contained in raw materials and sodium introduced during the reaction process. The low sodium content can also be used as an indicator of the purity of the annealing separator of the present invention.

[0054] The manufacturing method of the present invention also allows for control of the pore size of the resulting annealing separator. The average pore size of the annealing separator may be 45 to 100 nm. By having such appropriate physical properties, the amount of residual moisture in the annealing separator can be optimized, and the residual moisture in the annealing separator after application and firing can be reduced to a low level, thereby enabling a satisfactory forsterite layer to be obtained.

[0055] The magnesium oxide obtained by the calcination process can be used as an annealing separator as is. However, to further improve the properties of the annealing separator, various trace elements can be added as auxiliary or additive agents before the calcination process, as needed. Examples of trace elements include calcium (Ca), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), silicon (Si), cobalt (Co), zinc (Zn), nickel (Ni), copper (Cu), strontium (Sr), and aluminum (Al). These trace elements can be added or present in various forms, such as oxides, salts, and acids. For example, when calcium is added, calcium oxide, hydroxide, carbonate, nitrate, sulfate, silicate, and phosphate salts can be used. When phosphorus is added, common salts such as phosphoric acid, metaphosphoric acid, phosphonic acid, and phosphonous acid, as well as alkali metal salts, alkaline earth metal salts, and ammonium salts of these substances, can be used. When boron is added, boric acid, alkali metal borates, ammonium borates, alkali metal metaborates, boron dioxide, etc. can be used. When sulfur is added, sulfuric acid, sulfurous acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts can be used. When fluorine is added, magnesium fluoride, etc. can be used. When chlorine is added, magnesium chloride, etc. can be used. When silicon is added, alkali metal silicates, alkaline earth metal silicates, and colloidal silicas can be used.

[0056] Furthermore, by further adding 0 to 25 wt% of inactive magnesium oxide and / or 0 to 10 wt% of titanium dioxide to the annealing separator obtained by calcination, the annealing separator can exhibit even better properties. Inactive magnesium oxide is magnesium oxide that has been calcined at a high temperature exceeding the range of the present invention. Because the calcination temperature is too high, the reactivity is at least partially lost.

[0057] Although the manufacturing method of the present invention has been described above using ammonium nitrate solution as an example, it will be understood that the above description can also be applied to the other ammonium salts mentioned above.

[0058] More specifically, in one embodiment of the present invention, the method for producing the annealing separator includes: Step (1): Magnesium oxide and ammonium nitrate solution are mixed and reacted to prepare magnesium nitrate solution and ammonia. The magnesium nitrate solution is purified and the ammonia is recovered and concentrated to produce aqueous ammonia. Next, the purified magnesium nitrate solution is reacted with aqueous ammonia to obtain magnesium hydroxide. Step (2): A portion of the obtained magnesium hydroxide is heated at a temperature of 160 to 180°C for 120 to 180 minutes for high-temperature aging, and another portion of the obtained magnesium hydroxide is heated at a temperature of 50 to 90°C for 120 to 180 minutes for low-temperature aging. Step (3): The magnesium hydroxides aged under the above conditions are mixed in a mass ratio of 1:8 to 8:1 and fired at 860 to 1050°C to obtain magnesium oxide, which is used as an annealing separator.

[0059] [Annealing separator] The annealing separator of the present invention can be produced by the above-mentioned method, but the production method of the annealing separator of the present invention is not limited to the above-mentioned method. The annealing separator of the present invention will be described in detail below.

[0060] The annealing separator of the present invention has high purity and is excellent in dispersibility (suspendability) and adhesive strength. By using the annealing separator of the present invention, a uniform and dense forsterite layer can be formed on the surface of a grain-oriented electrical steel sheet. As a result, a grain-oriented electrical steel sheet with excellent insulating and electromagnetic properties can be obtained.

[0061] The annealing separator of the present invention may be composed of the above-mentioned magnesium oxide for an annealing separator of the present invention, or may mainly contain the magnesium oxide for an annealing separator of the present invention. In such cases, the content (purity) of the magnesium oxide for an annealing separator of the present invention may be 99.5 wt% or more, with the remainder being unavoidable impurities (e.g., Na).

[0062] As described above, the annealing separator of the present invention has high purity. Specifically, the annealing separator of the present invention has a low impurity content, particularly a low sodium (Na) content, and may have a sodium content of 20 to 50 ppm, for example. As described above, a low sodium content is one of the features of the present invention. The presence of an appropriate amount of sodium can lower the melting point of the oxide. This can promote the solid-phase reaction, which is advantageous for the formation of a forsterite layer. If the sodium content is lower than 20 ppm, the reaction promotion effect is not significant, while if the sodium content is higher than 50 ppm, the reaction rate becomes too fast, which is disadvantageous for the formation of a dense forsterite insulating layer. The sodium content is preferably 25 to 50 ppm, more preferably 35 to 45 ppm. The sodium in the annealing separator of the present invention is mainly derived from impurities contained in the raw materials and impurities introduced during the reaction. A low sodium content can also be used as an indicator of the purity of the annealing separator of the present invention.

[0063] The annealing separator of the present invention has a sedimentation coefficient S, defined by the following formula, of 0.90 or more. S=(100-V) / 100 Here, V represents the volume (unit: ml) of the supernatant after leaving 100 ml of a 10 wt % annealing separator dispersion to stand for 1 hour. For example, if the volume of the supernatant is 15 ml, V is 15.

[0064] A specific method for measuring the sedimentation coefficient may be, for example, as follows. After uniformly dispersing the 10 wt% annealing separator dispersion, immediately take out 100 ml of the dispersion, place it in a 100 ml measuring cylinder, and leave it for a predetermined time. Next, calculate the sedimentation coefficient according to the above formula.

[0065] By having a sedimentation coefficient within the above range, the annealing separator of the present invention has good and stable dispersibility and sedimentation properties, exists in a very stable state, and is not prone to aggregation. When applied as a coating solution, the annealing separator of the present invention can maintain a good dispersion state suitable for application for a long period of time, reduce coating unevenness in the resulting coating layer, and improve the uniformity of the forsterite layer.

[0066] Furthermore, the annealing separator of the present invention has an adhesion strength of 80% or more after being applied to the surface of a steel sheet, as defined by the following formula:

[0067] Adhesion strength = [(weight of steel sheet after polishing - weight of steel sheet before coating) / weight of steel sheet before polishing - weight of steel sheet before coating] x 100%

[0068] By having the above-mentioned adhesion strength, the annealing separator of the present invention has high adhesion strength and strong bonding with the steel sheet, making it difficult to separate from the steel sheet, thereby achieving the effect of promoting good reaction during the manufacturing process of grain-oriented electrical steel sheet. If the adhesion strength is less than 80%, the forsterite layer formed after the final annealing treatment may become non-uniform, which may affect the quality and appearance of the grain-oriented electrical steel sheet. The adhesion strength is preferably 85% or more, more preferably 88% or more. For more specific methods for measuring adhesion strength, please refer to the Examples section.

[0069] Furthermore, the average pore diameter of the annealing separator powder of the present invention may be 45 to 100 nm. By having such a pore diameter, the residual moisture in the annealing separator can be optimized, and the residual moisture in the annealing separator after coating and sintering can be reduced to a low level, thereby obtaining a satisfactory forsterite coating layer. The average pore diameter is more preferably 45 to 75 nm.

[0070] Furthermore, the CAA 70% / CAA 40% ratio of the annealing separator at 30°C is within the range of 1.8 to 4.0. CAA activity is based on the reaction rate between magnesium oxide particles and acid, i.e., citric acidity (CAA). CAA is measured by mixing a 0.4 N citric acid solution at a predetermined temperature (e.g., 30°C) with phenolphthalein as an indicator, adding a final reaction equivalent of magnesium oxide, and stirring the mixture until the citric acid solution becomes neutral. CAA can be used as an activity evaluation index for annealing separators for grain-oriented electrical steel sheets. By having a CAA 70% / CAA 40% ratio within the range of 1.8 to 4.0, the annealing separator has appropriate and good reactivity and can achieve good coating properties. Specifically, the CAA 70% of the annealing separator may be 90 to 360 seconds, and the CAA 40% may be 50 to 90 seconds.

[0071] Furthermore, the average particle size of the annealing separator is 0.5 to 5.0 μm. By having such an average particle size, the annealing separator can be appropriately aggregated, thereby obtaining good coating properties.

[0072] As described above, in the production process of the annealing separator of the present invention, various trace elements can be added as auxiliary agents or additives before the calcination, as needed. In this case, the annealing separator of the present invention can further contain one or more of the following trace elements: calcium (Ca), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), silicon (Si), cobalt (Co), zinc (Zn), nickel (Ni), copper (Cu), strontium (Sr), and aluminum (Al). The contents in the following specific description are based on the weight of magnesium oxide for the annealing separator of the present invention.

[0073] The content of B may be 500 to 1300 ppm. The presence of B can lower the melting point of the oxide and promote the reaction, but if the content of B is too high, it accelerates the sintering of magnesium oxide, affects the diffusion of magnesium oxide particles into the SiO2 layer, and causes defects such as pits on the steel sheet surface.

[0074] The Cl content may be 100 to 350 ppm. Cl can appropriately lower the melting point of the mixed oxide, thereby promoting the reactivity of the annealing separator. However, if the Cl content is lower than the above lower limit, the effect is not significant, and if it exceeds the above upper limit, the oxidation reaction of the substrate is promoted, impairing the formation of highly adhesive forsterite.

[0075] Regarding CaO, the Ca content may be 0.2-0.6 wt%. An appropriate amount of Ca in the form of CaO forms a rough interface between the substrate and the insulating layer, thereby improving the adhesion of the coating layer, but if the content is too high, it will cause quality problems.

[0076] Regarding SiO2, the Si content may be 0.2 to 5.0 wt%. SiO2 has a low melting point, and Si present in the form of SiO2 can promote solid-state reactions and inhibit reactions between other divalent metals and the SiO2 layer.

[0077] The annealing separator of the present invention may further contain appropriate amounts of Al in the form of Al2O3 and P in the form of P2O3. The tensile strength of the spinel compound formed by Al2O3 is twice that of forsterite, thereby improving the adhesion of the coating layer and the magnetic properties of the product. The contents of Al2O3 and P2O3 may be 0.1 to 3 wt%.

[0078] Furthermore, the amount of other trace elements that may be contained in the annealing separator of the present invention is generally controlled to 0.5 wt% or less. If the content is too high, these metal oxides compete with magnesium to form silicates other than magnesium, which is unfavorable to the formation of forsterite and ultimately affects the performance of the grain-oriented electrical steel sheet.

[0079] The annealing separator of the present invention may further contain titanium dioxide and / or inert magnesium oxide, which may be added after the calcination. The inert magnesium oxide is magnesium oxide that has been calcined at a high temperature exceeding the range of the present invention. The calcination temperature is too high, and the magnesium oxide loses at least part of its reactivity.

[0080] The amount of titanium dioxide added may be 0 to 10.0 wt%. During the annealing process, titanium dioxide releases an appropriate amount of oxygen, contributing to the formation of a uniform and dense forsterite layer. At the same time, Ti 3+ It diffuses into the SiO2 layer together with magnesium, improving the tensile strength of the insulating layer and improving physical properties such as core loss. If the titanium dioxide content is too high, Ti +4 Ti +3 During the transition process, excessive free oxygen is generated, causing defects such as blackening on the surface of the grain-oriented electrical steel sheet.

[0081] The amount of inert magnesium oxide added may be 0 to 25.0 wt%. Adding inert magnesium oxide can strengthen the bonding strength between the formed forsterite insulating layer and the substrate. This is because inert magnesium oxide only partially participates in the reaction and undergoes little change itself, thereby alleviating the adverse effect of a large difference in the expansion coefficient between the formed forsterite layer and the substrate. Therefore, when inert magnesium oxide is added, the proportions of the other auxiliary agents described above can be increased according to the proportion of inert magnesium oxide added, thereby maintaining the above content range for all magnesium oxides.

[0082] The annealing separator of the present invention has high purity, excellent dispersibility (suspendability) and adhesive strength, and is capable of forming a uniform and dense forsterite layer on the surface of grain-oriented electrical steel sheet, thereby enabling the production of grain-oriented electrical steel sheet with excellent insulating and electromagnetic properties.

[0083] More specifically, an annealing separator according to one embodiment of the present invention mainly contains magnesium oxide, has a sodium content of 20 to 50 ppm, a sedimentation coefficient S of 0.90 or more, an adhesion strength of 80% or more after application to a steel sheet surface, and an average pore diameter of 45 to 100 nm.

[0084] [Grain-oriented electrical steel sheet] By using the annealing separator described above, the grain-oriented electrical steel sheet of the present invention can be obtained, and the surface of the steel sheet has a forsterite layer obtained by using the annealing separator of the present invention.

[0085] The grain-oriented electrical steel sheet of the present invention can be produced by the following method. Silicon steel billets containing 2.5 to 4.5% silicon (Si) are hot-rolled, annealed, and cold-rolled by known methods to a predetermined thickness, and then decarburization annealing is performed in a humid atmosphere. During this process, an oxide film containing silica as a main component is formed on the surface of the steel sheet. Next, the annealing separator of the present invention is uniformly dispersed in water to obtain a slurry. The slurry is continuously applied to a steel sheet, baked, and then finish-annealed at 1200°C for about 20 hours, forming a forsterite layer (Mg2SiO4 film) on the surface of the steel sheet.

[0086] The grain-oriented electrical steel sheet of the present invention has excellent insulating and electromagnetic properties because it has a forsterite layer formed from the annealing separator of the present invention. [Example]

[0087] The present invention will be further described below with reference to Synthesis Examples, Examples, and Comparative Examples, although the present invention is not limited to these Synthesis Examples, Examples, and Comparative Examples.

[0088] First, the measurement method will be described.

[0089] 1. Measurement of average particle size 80 ml of ethanol was placed in a 100 ml beaker, and then 0.8 g of the dried annealing separator prepared in the following Examples and Comparative Examples was added thereto. The mixture was dispersed ultrasonically for 4 minutes, and then the average particle size of the annealing separator was measured using a laser diffraction / scattering particle size analyzer (product name: MT3000, manufactured by Nikkiso Co., Ltd.).

[0090] 2. Sedimentation Coefficient Measurement 900 ml of 10°C water was weighed into a 1000 ml beaker, and then 100 g of the dried annealing separator prepared in the following Examples and Comparative Examples was added. The mixture was dispersed for 60 minutes at 2000 rpm / min using an IKA RW20 digital stirrer (manufactured by IKA GmbH, Germany). 100 ml of the dispersion was immediately removed, placed in a 100 ml measuring cylinder, and allowed to stand for 1 hour. The sedimentation coefficient was then calculated according to the following formula: Sedimentation coefficient = (100-V) / 100 V: Volume of the supernatant (ml); 100: Volume of the measuring cylinder (ml)

[0091] In addition, for the sedimentation coefficient measurement, the sedimentation coefficient was measured after leaving the sample to stand for a total of 24 hours and used as a reference.

[0092] 3. Measurement of adhesion strength Steel plates were manufactured in the same manner as the steel plates for evaluation in the section "5. Evaluation of Forsterite Coating" below, except that the thickness was set to 0.5 mm. Steel plates measuring 150 mm x 80 mm x 0.5 mm were accurately weighed. 20 g of dried annealing separator prepared in the following Examples and Comparative Examples was accurately weighed and added to 150 ml of water at 20°C. The mixture was vigorously stirred and dispersed for 1 minute at 2000 rpm using an IKA RW20 digital stirrer (manufactured by IKA, Germany) to obtain a coating solution. The coating solution was applied to the steel plate of the known weight using a roll coater. The coated steel plate was then placed in a muffle furnace at 500°C and sintered for 30 seconds. After cooling and weighing, the steel plate was placed in a vibrating rotor (a rotary hammer-type vibrator manufactured by Iida Seisakusho Co., Ltd., Japan). 400 g of sea sand was then placed on the steel plate, which was then subjected to a vibrating and rotating treatment (polishing) for 30 seconds (rotation speed: 60 Hz / 290 rpm). The steel plates after treatment were weighed, and the adhesive strength was calculated according to the following formula: Four steel plates were measured, and the average value was taken as the adhesive strength. Adhesion strength = [(weight of steel sheet after polishing - weight of steel sheet before coating) / weight of steel sheet before polishing - weight of steel sheet before coating] x 100%

[0093] 4. Quantitative analysis of elements Quantitative analysis of relevant elements was carried out using a ZSX PrimusII X-ray fluorescence spectrometer manufactured by RIGAKU INDUSTRIAL Co., Ltd., Japan.

[0094] 5. Evaluation of forsterite coating Silicon steel billets for grain-oriented electrical steel sheets were hot-rolled and cold-rolled by known methods to a thickness of 0.23 mm, and then decarburization annealing was performed in a humid atmosphere (25% N + 75% H) to produce steel sheets for evaluation. The composition of the steel sheets before decarburization annealing was, in mass%, 3.2% Si, 0.06% C, 0.02% Mn, 100 ppm Al, 0.008% N, with the remainder being iron and unavoidable impurities.

[0095] The annealing separators obtained in the Examples and Comparative Examples were prepared into 100 g / L suspensions (slurries), and titanium dioxide was added to the suspensions so that the titanium dioxide content was 7 wt% of the total magnesium oxide contained in the annealing separator. The uniformly mixed slurry was hydrated in water at 10°C and then applied to annealed steel sheets, and the applied amount after drying on both sides of the steel sheets was 15 g / m. 2 After baking, the steel sheets were wound into rolls, annealed at 1200°C for 20 hours, and then flattened by hot drawing to produce finished steel sheets, which were evaluated as follows:

[0096] Coating evaluation: The state of the forsterite coating on the steel sheet surface of all rolls was observed with the naked eye. When all rolls were dark gray with no obvious color difference and the coating defects were less than 2% of the total area, it was evaluated as ⊚; when all rolls were dark gray with no obvious color difference and the coating defects were less than 2-4% of the total area, it was evaluated as ○; when the coating defects were 4-6% of the total area, it was evaluated as △; and when the coating defects were more than 6% of the total area, it was evaluated as ×.

[0097] Sheet shape evaluation: If the reactivity of the annealing separator is poor, a wavy coating will form on the edge of the steel sheet. The sheet shapes of all rolled steel sheets were observed with the naked eye, and if the length of the unevenness (wavy coating) on ​​the sheet surface at the edge in the longitudinal direction of the steel sheet was less than 2% of the length of the entire rolled steel sheet, it was evaluated as ◎; if the length of the unevenness on the sheet surface was less than 2 to 4% of the length of the entire rolled steel sheet, it was evaluated as ○; if the length of the unevenness on the sheet surface was 4 to 6% of the length of the entire rolled steel sheet, it was evaluated as △; and if the length of the unevenness on the sheet surface was more than 6% of the length of the entire rolled steel sheet, it was evaluated as ×.

[0098] 6. Evaluation of number of bending times From the finished steel plate obtained in the above section "5. Evaluation of forsterite coating", a steel plate measuring 20 cm x 20 cm x 0.23 mm was cut as a test piece, which was then manually bent in half at 90 degrees, and the number of times it could be bent until the coating began to fall off was calculated.

[0099] 7. Dew crystal evaluation From the finished steel sheets obtained in the above section "5. Evaluation of the Forsterite Coating," a 20 cm x 20 cm x 0.23 mm steel sheet was cut into test specimens, which were then visually inspected and the number of dew crystals counted. A specimen with 0 to 2 dew crystals was evaluated as ◎; a specimen with 3 to 4 dew crystals was evaluated as ○; a specimen with 5 to 7 dew crystals was evaluated as △; and a specimen with 7 or more dew crystals was evaluated as ×. Here, dew crystals refer to "small holes" (defects in the coating layer) with a diameter of 0.1 mm or more that can be observed with the naked eye on the surface of the finished steel sheet, and are caused by insufficient reaction between MgO and SiO2.

[0100] 8. Measurement of CAA 70% / CAM 40% 0.4N citric acid solution 1 x 10 -4 m 3 and an appropriate amount (2 x 10 -6 m 3 ) 2 × 10 -4 m 3 The solution was added to a beaker, the temperature was adjusted to 30°C, and the mixture was stirred at 700 rpm using a magnetic stirrer. At the same time, 40% or 70% of the final reaction equivalent of the annealing separator was added to the citric acid solution, and the time until the final reaction, i.e., the time until the citric acid was consumed and the solution became neutral, was measured. From this, the ratio of CAA 70% / CAA 40% was calculated.

[0101] 9. Measurement of Average Pore Diameter The average pore diameter of the annealing separators obtained in the examples and comparative examples was measured under the following conditions using a specific surface area / pore distribution measuring device (manufactured by Microtrack-Bell Corporation, model: BELSORP-max). Gas used: N2 Adsorption conditions: -196°C Pretreatment conditions: Heat at 105°C for 1 hour Analysis program: BJH

[0102] 10. Seat thrust measurement The presence or absence of the seating phenomenon is visually determined for the finished steel plate obtained in the above section "5. Evaluation of the forsterite coating." Specifically, seating refers to a depression caused by stress concentration at the edge, which is due to the difference in stress generated near the edge and in the middle of the steel plate during the cooling process of the finished steel plate.

[0103] Synthesis Examples, Examples and Comparative Examples

[0104] Preparation of magnesium hydroxide precursor In a reactor equipped with a stirrer, cooler, thermometer, and gas inlet, light-burned magnesium oxide powder (manufactured by Liaoning Haicheng Houying Group, calcined at 950°C, containing 92.9 wt% MgO, 2.39 wt% SiO2, 2.36 wt% CaO, 0.19 wt% Al2O3, and 0.55 wt% Fe2O3) was added to an aqueous solution of ammonium nitrate (manufactured by Henan Kaifeng Jinkai Chemical Co., Ltd.) at a molar ratio of NH4NO3 / MgO = 2 under heating at 100°C. The mixture was stirred, dissolving the light-burned magnesium oxide in the ammonium nitrate solution and reacting to produce a magnesium nitrate solution while releasing ammonia gas. The resulting ammonia gas was then added to water, recovered, and concentrated to 10.0 mol / L to serve as an alkali source. The resulting magnesium nitrate solution was collected by filtration and adjusted to 3.5 mol / L to serve as the magnesium source.

[0105] The above purified magnesium nitrate solution, ammonia water, and water were mixed at 25°C in a ratio of 1.46 mol Mg(NO3)2 (417.14 ml): 2.92 mol NH3·H2O (292.0 ml): 16.14 mol H2O (290.86 ml) to react the magnesium nitrate with ammonia, yielding a magnesium hydroxide slurry with a concentration of 85 g / L (1.46 mol / L).

[0106] The resulting magnesium hydroxide slurry was divided into two parts, one part was heated in a reactor at 70°C for 150 minutes and designated as part A, and the other part was heated in an autoclave at 160°C for 150 minutes and designated as part B.

[0107] Synthesis Example 1 The magnesium hydroxide in solution A was filtered, washed with water, and then re-dispersed in pure water. Appropriate amounts of CaCO3, B2O3, MgCl2, and SiO2 were added to the dispersion and stirred to disperse the magnesium oxide after firing so that the CaO content was 0.45 wt%, the B content was 0.075 wt%, the Cl content was 0.02 wt%, and the SiO2 content was 0.40 wt%.

[0108] The dispersion was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 1200°C for 240 minutes in an air atmosphere to obtain magnesium oxide. This was then pulverized in a hammer mill and designated Synthesis Example 1.

[0109] The obtained magnesium oxide powder of Synthesis Example 1 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, a sample of magnesium hydroxide was taken, and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0110] Synthesis Example 2 Liquids A and B were mixed in a mass ratio of 83.33%:16.67% magnesium hydroxide (i.e., the total of both was 100%, and the same applies below), then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized using a hammer mill and designated Synthesis Example 2.

[0111] The obtained magnesium oxide powder of Synthesis Example 2 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, the dispersed magnesium hydroxide was sampled and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0112] Synthesis Example 3 Liquids A and B were mixed in a mass ratio of 66.67%:33.33% magnesium hydroxide, then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized in a hammer mill and designated Synthesis Example 3.

[0113] The obtained magnesium oxide powder of Synthesis Example 3 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, the dispersed magnesium hydroxide was sampled and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0114] Synthesis Example 4 Liquids A and B were mixed in a mass ratio of 33.33%:66.67% magnesium hydroxide, then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized in a hammer mill and designated Synthesis Example 4.

[0115] The obtained magnesium oxide powder of Synthesis Example 4 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, the dispersed magnesium hydroxide was sampled and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0116] Synthesis Example 5 Liquids A and B were mixed in a mass ratio of 62.5%:37.5% magnesium hydroxide, then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized in a hammer mill and designated Synthesis Example 5.

[0117] The obtained magnesium oxide powder of Synthesis Example 5 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, the dispersed magnesium hydroxide was sampled and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0118] Synthesis Example 6 Liquids A and B were mixed in a mass ratio of 37.5%:62.5% magnesium hydroxide, then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized in a hammer mill and designated Synthesis Example 6.

[0119] The obtained magnesium oxide powder of Synthesis Example 6 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, the dispersed magnesium hydroxide was sampled and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0120] Synthesis Example 7 Magnesium oxide powder was produced according to the conditions in "Synthesis Example 1" except that the calcination was carried out at 940°C for 25 minutes, and this was designated Synthesis Example 7.

[0121] The obtained magnesium oxide powder of Synthesis Example 7 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, a sample of magnesium hydroxide was taken, and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0122] Synthesis Example 7 is an example in which only low-temperature aging was carried out.

[0123] Synthesis Example 8 Magnesium oxide powder was obtained according to the method of Example 2 of Patent Document 3 (PCT / JP01 / 09354), and this was designated as Synthesis Example 8.

[0124] Specifically, magnesite was fired in a rotary kiln at 1100°C for 1 hour to produce a powder with a BET specific surface area of ​​5.2 × 10 3 m 2 ·kg -1 This magnesium oxide was prepared in a slurry with a concentration of 2 mol kg -1 The mixture was then added to water so that the BET specific surface area was 7.5 × 10 3 m 2 ·kg -1 Magnesium hydroxide of Synthesis Example 8 was produced. The resulting mixture was then calcined in a rotary kiln at 980°C for 0.2 hours, 0.5 hours, 0.8 hours, and 2 hours, and then pulverized in an impact crusher to produce magnesium oxide particle aggregates with different calcination degrees. The four types of magnesium oxide particle aggregates were then mixed in a mixing ratio of 25:30:15:30 to produce the magnesium oxide particle aggregate of Synthesis Example 8.

[0125] The magnesium oxide powder obtained in Synthesis Example 8 was subjected to elemental analysis, and the magnesium oxide content at this time is shown in Table 1 as the MgO content before the addition of the auxiliary agent.

[0126] Synthesis Example 9 The magnesium hydroxide in Solution B was filtered, washed with water, and then redispersed in pure water. Appropriate amounts of CaCO3, B2O3, MgCl2, and SiO2 were added to the dispersion in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The resulting powder was then pulverized in a hammer mill and designated Synthesis Example 9.

[0127] The obtained magnesium oxide powder of Synthesis Example 9 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, a sample of magnesium hydroxide was taken, and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0128] Synthesis Example 9 is an example in which only high-temperature aging was carried out.

[0129] Synthesis Example 10 Liquids A and B were mixed at a mass ratio of 94.44%:5.56 wt% magnesium hydroxide, then dehydrated, washed with water, and redispersed in pure water. Next, CaCO3, B2O3, MgCl2, and SiO2 were added to the mixed liquid in the same proportions as in Synthesis Example 1. After stirring and dispersion, the mixture was dehydrated, washed with water, and dried. The dried powder was fired in a rotary kiln at 940°C for 25 minutes in an air atmosphere to obtain magnesium oxide. The mixture was then pulverized in a hammer mill and designated Synthesis Example 10.

[0130] The obtained magnesium oxide powder of Synthesis Example 10 was subjected to elemental analysis, and the results are shown in Table 1. Furthermore, before the addition of the above-mentioned auxiliary agent, a sample of magnesium hydroxide was taken, and similarly dehydrated, washed with water, dried, and fired. The obtained magnesium oxide was subjected to elemental analysis to measure its content, and the results are also shown in Table 1.

[0131] Example 1 The magnesium oxide powder of Synthesis Example 2 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 9:1, and the mixture was designated as Example 1. The blending ratio of Example 1 is shown in Table 2.

[0132] For the annealing separator of Example 1, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat contact were measured by the methods described above, and the results are shown in Table 3.

[0133] Example 2 The magnesium oxide powder of Synthesis Example 3 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 9:1, and the mixture was designated as Example 2. The blending ratio of Example 2 is shown in Table 2.

[0134] For the annealing separator of Example 2, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat contact were measured using the methods described above, and the results are shown in Table 3.

[0135] Example 3 The magnesium oxide powder of Synthesis Example 4 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 9:1, and the mixture was designated as Example 3. The blending ratio of Example 3 is shown in Table 2.

[0136] For the annealing separator of Example 3, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured by the above-mentioned methods, and the results are shown in Table 3.

[0137] Example 4 The magnesium oxide powder of Synthesis Example 5 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 8:2, and the mixture was designated Example 4. The blending ratio of Example 4 is shown in Table 2.

[0138] For the annealing separator of Example 4, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat contact were measured using the methods described above, and the results are shown in Table 3.

[0139] The annealing separator of Example 4 was photographed using a field emission scanning electron microscope (FE-SEM, 100,000 magnifications), and the resulting photograph is shown in FIG.

[0140] The pore size measurement curve of the annealing separator of Example 4 of the present invention is shown in FIG.

[0141] Example 5 The magnesium oxide powder of Synthesis Example 6 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 8:2, and the mixture was designated as Example 5. The blending ratio of Example 5 is shown in Table 2.

[0142] For the annealing separator of Example 5, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured using the methods described above, and the results are shown in Table 3.

[0143] Example 6 The magnesium oxide powder of Synthesis Example 3 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed in a mass ratio of 7.5:2.5, and the mixture was designated Example 6. The blending ratio of Example 6 is shown in Table 2.

[0144] For the annealing separator of Example 6, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat contact were measured using the methods described above, and the results are shown in Table 3.

[0145] Comparative Example 1 The magnesium oxide powder of Synthesis Example 7 and the magnesium oxide powder of Synthesis Example 1 were uniformly mixed at a mass ratio of 9:1, and the mixture was designated Comparative Example 1. The blending ratio of Comparative Example 1 is shown in Table 2.

[0146] For the annealing separator of Comparative Example 1, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured using the methods described above, and the results are shown in Table 3.

[0147] Comparative Example 2 The magnesium oxide powder of Synthesis Example 9 and the magnesium oxide powder of Synthesis Example 1 were mixed in a mass ratio of 9:1, and the mixture was designated Comparative Example 2. The blending ratio of Comparative Example 2 is shown in Table 2.

[0148] For the annealing separator of Comparative Example 2, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured using the methods described above, and the results are shown in Table 3.

[0149] Comparative Example 3 The magnesium oxide powder of Synthesis Example 8 was used as Comparative Example 3.

[0150] For the annealing separator of Comparative Example 3, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured using the methods described above, and the results are shown in Table 3.

[0151] Comparative Example 4 The magnesium oxide powder of Synthesis Example 10 and the magnesium oxide powder of Synthesis Example 1 were mixed at a mass ratio of 9:1, and the mixture was designated Comparative Example 4. The blending ratio of Comparative Example 4 is shown in Table 2.

[0152] For the annealing separator of Comparative Example 4, the average particle size, sedimentation coefficient, adhesion strength, forsterite coating, number of bending times, dew crystallization, CAA70% / CAM40% ratio, pore size, and seat projection were measured using the methods described above, and the results are shown in Table 3.

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3]

[0156] As can be seen from the above data, the annealing separator satisfying the present invention is excellent in all of the sedimentation coefficient, adhesion strength, forsterite film evaluation, number of bending times, dew crystal evaluation, and measurement of contact, and is therefore of great industrial value. In contrast, annealing separators outside the scope of the present invention do not satisfy the requirements in at least one of the sedimentation coefficient, adhesion strength, forsterite film evaluation, number of bending times, dew crystal evaluation, and measurement of contact, and are therefore inferior to the annealing separator of the present invention.

Claims

1. The sedimentation coefficient S is 0.90 or more, The average particle size is 0.5 to 5.0 μm, The average pore diameter is 45 to 100 nm, The purity of the magnesium oxide is 99.5 wt% or more, A method for producing a grain-oriented electrical steel sheet, comprising: dispersing magnesium oxide for an annealing separator, the magnesium oxide containing 500 to 1300 ppm of B, 100 to 350 ppm of Cl, and 0.2 to 0.6 wt % of CaO based on the weight of the magnesium oxide, in water to obtain a slurry; applying the slurry to a steel sheet; and performing finish annealing.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the magnesium oxide for an annealing separator has an adhesion strength of 80% or more after being applied to the surface of the steel sheet.

3. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the ratio of CAA 70% / CAA 40% in the magnesium oxide for the annealing separator is in the range of 1.8 to 4.

0.

4. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the magnesium oxide for an annealing separator has a Na content of 20 to 50 ppm.

5. The method for producing a grain-oriented electrical steel sheet according to claim 1, further comprising at least one of the following based on the weight of the magnesium oxide for an annealing separator: Yes ２ :0.2~5.0wt%; Titanium dioxide: greater than 0 wt % to 10.0 wt %; or Inactive magnesium oxide: greater than 0 wt % to 25.0 wt %.

6. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the magnesium oxide for an annealing separator has a structure in which a plurality of spherical particles are connected together, and is an overall hexagonal plate shape having a plurality of holes on the surface.

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