Insulating coating treatment liquid for grain-oriented electrical steel sheet, and method for producing grain-oriented electrical steel sheet

Abstract

A method for producing an insulating coating treatment solution for a grain-oriented electrical steel sheet, the method comprising: an adjustment step for adding a Na compound to colloidal silica and adjusting the Na2O / SiO2 ratio, which is the mass% of the Na amount in terms of Na2O and the Si amount in terms of SiO2, in the colloidal silica to 0.5-10%; and a mixing step for mixing the colloidal silica, the Na2O / SiO2 ratio of which has been adjusted, with a metal phosphate salt of one or more metals selected from among Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of an insulating coating treatment liquid for grain-oriented magnetic steel sheets, and a manufacturing method of grain-oriented magnetic steel sheets using the insulating coating treatment liquid manufactured by the method. BACKGROUND

[0002] Grain-oriented magnetic steel sheets are steel sheets mainly used as cores of transformers and the like. Generally, two-layer surface coatings are formed on such grain-oriented magnetic steel sheets, the two-layer surface coatings being a forsterite layer (also referred to as a primary coating) formed in high-temperature final annealing, and a phosphate coating formed by sintering after applying a treatment liquid having a phosphate or the like as a main component to the steel sheet at the time of hot leveling.

[0003] The phosphate coating is required in order to impart electrical insulation to the grain-oriented magnetic steel sheet and reduce eddy current loss to improve iron loss. In addition to the insulation, various properties such as corrosion resistance, heat resistance, slidability, adhesion, and the like are required for the phosphate coating. This is in order to smoothly perform various manufacturing processes when the grain-oriented magnetic steel sheet is processed to make a core of a transformer or the like. For example, in the case where the phosphate coating is poor in heat resistance, slidability, and adhesion, the phosphate coating peels off at the time of stress relief annealing in the manufacture of the core, and sometimes the original insulation of the phosphate coating cannot be exerted or the steel sheets cannot be smoothly stacked and workability deteriorates.

[0004] Further, as important properties of the insulating coating of the grain-oriented magnetic steel sheet, imparting tension to the steel sheet can be cited. In the case where tension is imparted to the steel sheet, by making it easy for the magnetic domain wall to move, it is possible to improve the iron loss of the grain-oriented magnetic steel sheet. By imparting tension, it is also possible to reduce magnetostriction (one of the main causes of noise in a transformer).

[0005] In order to improve each of the above properties of the grain-oriented magnetic steel sheet, specifically, technologies disclosed in Patent Documents 1 to 9, for example, have been developed and researched.

[0006] For example, Patent Document 1 discloses the following: after forming a forsterite coating on the surface of a steel sheet after final annealing, an insulating coating treatment liquid having a specific composition is applied, and then sintering is performed. According to the technology disclosed in Patent Document 1, an insulating coating having high tension is formed on the surface of the steel sheet, and it is possible to reduce the iron loss and magnetostriction of the grain-oriented magnetic steel sheet.

[0007] In addition, Patent Document 2 discloses the following method: after applying a treatment liquid containing ultrafine particulate colloidal silica having a particle diameter of 8 μm or less, a first phosphate, and a chromate in a specific ratio to a steel sheet, sintering is performed. According to the technology disclosed in Patent Document 2, it is possible to maintain high tension of the insulating coating, and further improve the lubricity of the coating.

[0008] Furthermore, Patent Document 3 discloses the following technology: a technology for forming a high-tensile insulating film on the surface of an oriented electromagnetic steel sheet by quantitatively attaching an insulating film mainly composed of phosphate, chromate and colloidal silica with a glass transition temperature of 950°C to 1200°C.

[0009] According to the technologies disclosed in Patent Documents 1-3, it is possible to form insulating films with exceptionally superior coating properties and improved coating tension. However, the technologies disclosed in Patent Documents 1-3 all contain chromate as a chromium compound in the insulating film. In recent years, with increasing attention to environmental issues, there have been calls to ban or restrict the use of compounds such as lead, chromium, and cadmium.

[0010] Therefore, techniques for forming good insulating films without the aforementioned chromium compounds were investigated. However, insufficient tension imparted to the steel sheet became a problem when using insulating films without chromium compounds.

[0011] As a method to solve the above problems, for example, Patent Document 4 discloses an insulating coating treatment method for oriented electromagnetic steel sheets that sinter a treatment solution at a temperature above 300°C. The treatment solution contains the following components: 20 parts by weight of colloidal silicon dioxide based on SiO2 content, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid, and a total of 4 to 40 parts by weight of one or more sulfates selected from Mg, Al, Fe, Co, Ni and Zn.

[0012] In addition, Patent Document 5 discloses a technology for a coating agent for coating formation, wherein the coating agent for coating formation contains a mixture of boric acid and alumina sol, and an organic solvent that is compatible with water, and has the effect of imparting tension to oriented electromagnetic steel sheets.

[0013] Furthermore, Patent Document 6 discloses the following technique: a surface treatment agent for oriented electromagnetic steel sheets containing Al, Mg, Ca monophosphate and colloidal silica, comprising one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B and Al. In addition, Patent Document 6 exemplifies formate, acetate, oxalate, tartrate, lactate, citrate, succinate and salicylate as organic acid salts.

[0014] In addition, Patent Document 7 discloses the following technology: in an insulating coating treatment agent for oriented electromagnetic steel sheets containing phosphate and colloidal silica, the metal component in the phosphate is set as a combination of divalent metal elements, trivalent metal elements and metal elements with a valence of four or more in a specific ratio.

[0015] In addition, Patent Document 8 discloses an oriented electromagnetic steel sheet comprising an insulating film and a steel sheet, wherein the insulating film contains: a first metal phosphate salt as a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni and Zn; a second metal phosphate salt as a metal phosphate salt of one or more metals selected from Co, Mo, V, W and Zr; and colloidal silicon dioxide.

[0016] Furthermore, Patent Document 9 discloses an aqueous composition for coating oriented electromagnetic steel sheets, comprising: aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and / or anions of phosphate, colloidal silica, and optionally iron cations.

[0017] Prior art literature

[0018] Patent documents

[0019] Patent Document 1: Japanese Patent Application Publication No. 48-39338

[0020] Patent Document 2: Japanese Patent Application Publication No. 61-41778

[0021] Patent Document 3: Japanese Patent Application Publication No. 11-071683

[0022] Patent Document 4: Japanese Patent Application Publication No. 54-143737

[0023] Patent Document 5: Japanese Patent Application Publication No. 7-278828

[0024] Patent Document 6: Japanese Patent Application Publication No. 2000-178760

[0025] Patent Document 7: Japanese Patent Application Publication No. 2010-13692

[0026] Patent Document 8: International Publication No. 2017 / 057513

[0027] Patent Document 9: Japanese Patent Publication No. 2022-519691 Summary of the Invention

[0028] The technical problem that the invention aims to solve

[0029] According to these methods, the tension imparted to the steel sheet is improved. However, according to the research conducted by the inventors to date, it is known that moisture resistance also deteriorates in the case of insulating coatings that do not contain chromium compounds. Regardless of which of the above techniques is used, the moisture resistance has not reached the same level as existing coatings containing chromic acid, leaving room for improvement.

[0030] The insulating coating of oriented electromagnetic steel sheets must be able to impart high tension to the surface of the steel sheet. In addition, the insulating coating of oriented electromagnetic steel sheets also requires good moisture resistance and high productivity.

[0031] The present invention was made to solve the above-mentioned problems, and its object is to provide a method for manufacturing an insulating coating treatment liquid for oriented electromagnetic steel sheets that has good moisture resistance and thus good productivity even without the presence of chromate, and a method for manufacturing oriented electromagnetic steel sheets using the insulating coating treatment liquid manufactured by the method.

[0032] Technical means for solving technical problems

[0033] The main points of this invention are as follows.

[0034] (1) A method for manufacturing an insulating coating treatment liquid for oriented electromagnetic steel sheets according to an embodiment of the present invention includes: an adjustment step of adding a Na compound to colloidal silica and adjusting the Na2O / SiO2 ratio (in mass % of Na converted to Na2O and Si converted to SiO2) in the colloidal silica to 0.5% or more and 10% or less; and a mixing step of mixing the colloidal silica with the adjusted Na2O / SiO2 ratio with a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr.

[0035] (2) Another embodiment of the present invention includes a method for manufacturing an oriented electromagnetic steel plate, comprising: a coating step of coating an insulating coating treatment liquid onto the surface of a steel plate; and a sintering step of sintering the insulating coating treatment liquid to produce an insulating coating, wherein the insulating coating treatment liquid is an insulating coating treatment liquid for oriented electromagnetic steel plates manufactured by the method described in (1) above, and the sintering homogenization temperature in the sintering step is 800 to 1000°C and the homogenization holding time is 10 to 60 seconds.

[0036] Invention Effects

[0037] According to the present invention, it is possible to reliably obtain oriented electromagnetic steel sheets with excellent moisture resistance and productivity. Attached Figure Description

[0038] Figure 1 This is a graph showing the relationship between the Na2O / SiO2 ratio and the moisture absorption of colloidal silica. Detailed Implementation

[0039] The inventors have investigated a method for improving moisture resistance in insulating films that do not contain chromium compounds. First, they considered whether moisture resistance could be improved by adjusting the crystallization temperature of colloidal silica. It is known that adding sodium hydroxide to colloidal silica lowers its crystallization temperature.

[0040] Therefore, the inventors evaluated the moisture resistance of the insulating film using colloidal silica with pre-added sodium hydroxide. Furthermore, for comparative purposes, the same study was conducted on the case with added sodium chloride.

[0041] The results of the preliminary experiments that led to the present invention will be described below.

[0042] Oriented electromagnetic steel sheets with a thickness of 0.23 mm, manufactured using known methods and finally annealed, are cut into 60 mm wide and 300 mm long sheets. The annealing separating agent adhering to the surface is removed by washing with water, and these sheets are then used as base materials. Next, sodium hydroxide or sodium chloride is added to colloidal silica to adjust the Na₂O / SiO₂ ratio within the range of 0.2% to 11%, producing 11 types of colloidal silica. Furthermore, the "Na₂O / SiO₂ ratio" is the percentage (%) obtained by dividing the amount of Na (converted to Na₂O, hereinafter referred to as "Na₂O amount"; unit: mass%) and the amount of Si (converted to SiO₂, hereinafter referred to as "SiO₂ amount"; unit: mass%) in the colloidal silica by the amount of SiO₂.

[0043] Then, for the prepared base material, an insulating coating treatment solution consisting of 60 parts by mass of aluminum dihydrogen phosphate and 40 parts by mass of colloidal silica is applied at a coating adhesion rate of 4.5 g / m² per side after firing. 2 The coating is applied to both sides using a roller coater. Then, it is sintered at 850°C for 30 seconds.

[0044] In addition, as a comparison, an insulating coating solution consisting of 50 parts by mass of aluminum dihydrogen phosphate, 40 parts by mass of colloidal silica (Na2O / SiO2 ratio = 1.2%), and 10 parts by mass of chromic anhydride was similarly applied to the base material and sintered.

[0045] The obtained steel plate was used as a test piece for moisture absorption resistance evaluation. First, the test piece was placed in a constant temperature and humidity bath (temperature 50℃, humidity 90%) for one week, and the weight difference before and after the temperature and humidity were quantified. Then, the quantified weight difference was divided by the area of ​​both sides of the test piece, 0.036 m². 2 The result obtained is defined as moisture absorption (unit: g / m³). 2The moisture absorption capacity is used as an indicator to evaluate the moisture absorption resistance.

[0046] The results of the above evaluation, which summarize the relationship between moisture absorption and the Na2O / SiO2 ratio, are shown below. Figure 1 .like Figure 1 As shown, in steel plates with a chromium-containing coating, the Na₂O / SiO₂ ratio is small, but the moisture absorption is 0.1 g / m³. 2 Below this point, almost no moisture absorption occurs. In contrast, in steel sheets with a chromium-free coating, moisture absorption exceeds 1.0 g / m³ in areas where the Na₂O / SiO₂ ratio is less than 0.5%. 2 However, in areas with a high Na₂O / SiO₂ ratio, especially those exceeding 0.5%, the moisture absorption is consistently 1.0 g / m³ regardless of whether sodium hydroxide or sodium chloride is used. 2 Furthermore, in regions where the Na2O / SiO2 ratio is 5.0% or higher, almost no moisture absorption is observed, achieving moisture resistance comparable to that of steel sheets with a chromium-coated film. On the other hand, it was confirmed that if the Na2O / SiO2 ratio exceeds 10%, the dispersion of colloidal silica deteriorates, resulting in uneven appearance after sintering.

[0047] Based on the above experimental results, the inventors have discovered that by limiting the ratio of Na2O / SiO2 in colloidal silica to 0.5% to 10% in an insulating coating treatment solution containing metal phosphate salts and colloidal silica, the formation reaction of the insulating coating is promoted, thereby imparting high moisture resistance.

[0048] Furthermore, as mentioned above, it is known that adding sodium hydroxide to colloidal silica lowers its crystallization temperature. However, in the experiments of this invention, no change in crystallization temperature was observed even when sodium chloride was added to silica. Therefore, it is believed that the decrease in crystallization temperature of colloidal silica derived from previous insights did not improve moisture resistance, but rather that the addition of sodium itself improved moisture resistance for some reason.

[0049] <Manufacturing Method of Insulating Coating Treatment Liquid for Oriented Electromagnetic Steel Sheets>

[0050] This document describes the structure and rationale for the limitation of the manufacturing method of the insulating coating treatment liquid for oriented electromagnetic steel sheets (hereinafter referred to as "insulating coating treatment liquid") according to this embodiment.

[0051] The method for manufacturing the insulating coating treatment liquid in this embodiment includes an adjustment step of adjusting the composition of colloidal silica and a mixing step of mixing colloidal silica and metal phosphate salt.

[0052] In the adjustment process, a Na compound is added to the colloidal silica to adjust the Na2O / SiO2 ratio (mass percentage of Na2O and SiO2 in the colloidal silica) to 0.5% to 10%. When the Na2O / SiO2 ratio is less than 0.5%, the promoting effect on the formation reaction of the insulating coating is small, resulting in insufficient moisture resistance. On the other hand, if the Na2O / SiO2 ratio exceeds 10%, the dispersibility of the colloidal silica deteriorates, and the appearance after sintering deteriorates. The Na2O / SiO2 ratio is preferably 1% or more, more preferably 3% or more, and even more preferably 5% or more. Furthermore, the Na2O / SiO2 ratio is preferably 8% or less, more preferably 7% or less, and even more preferably 6% or less.

[0053] Furthermore, there are no particular limitations on the method used to ensure that the Na₂O / SiO₂ ratio in the colloidal silica is 0.5% to 10%. For example, a method of pre-adding sodium hydroxide and / or sodium chloride to the colloidal silica can be used. From the viewpoint of increasing the pH of the insulating coating treatment solution and improving the dispersibility of the colloidal silica, the addition of sodium hydroxide is preferred.

[0054] The size of the colloidal silica (silica particles) used in this embodiment is not particularly limited, but an average particle size (average primary particle size) of 4 to 35 nm is preferred. If the average particle size of the colloidal silica is less than 4 nm, the colloidal silica may easily agglomerate, resulting in poor stability of the insulating coating treatment solution, or the insulating coating may become a porous coating with large gaps, reducing the adhesion of the insulating coating, which is therefore undesirable. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the colloidal silica may lack reactivity, resulting in insufficient mixing of the phosphate as a binder with the colloidal silica, or the insulating coating may crack, reducing its adhesion, which is also undesirable.

[0055] Furthermore, smaller particle size of colloidal silica leads to a denser coating, which improves coating tension. Therefore, the upper limit of the average particle size of colloidal silica is preferably set to 31 nm, 22 nm, 18 nm, or 12 nm. Moreover, it is further preferred that the surface of the colloidal silica is chemically treated with aluminum. Additionally, the average particle size (average primary particle size) of the colloidal silica can be calculated, for example, from the specific surface area measured using the BET adsorption method (according to JIS Z8830).

[0056] In the mixing process, colloidal silica, whose composition has been adjusted in the conditioning process, is mixed with a metal phosphate salt. The metal phosphate salt is a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr. Furthermore, the metal phosphate salt is preferably a metal phosphate salt of one or more metals selected from Al, Mg, Ni, V, and W. This is because, with these phosphates, a flat and uniform appearance can be obtained under a wide range of sintering conditions. Considering environmental concerns, it is preferable not to actively add chromate during the mixing process.

[0057] In the method for manufacturing the insulating coating treatment solution of this embodiment, the ratio of metal phosphate salt to colloidal silica is not particularly limited. As long as the Na2O / SiO2 ratio contained in the colloidal silica is 0.5% to 10%, the insulating coating of the orientation-oriented electromagnetic steel sheet using the insulating coating treatment solution manufactured by the method of this embodiment exhibits excellent properties. Furthermore, preferred values ​​are shown below.

[0058] The content of colloidal silica in the insulating coating treatment solution, calculated as SiO2, is preferably 25.0 to 65.0% by mass relative to the total mass of the insulating coating treatment solution, calculated as solids. If the content of colloidal silica in the insulating coating treatment solution is less than 25.0% by mass, the coating tension of the insulating coating may become insufficient, which is undesirable. If the content of colloidal silica in the insulating coating treatment solution exceeds 65.0% by mass, the adhesion of the insulating coating may decrease, which is also undesirable. Furthermore, the content of colloidal silica in the insulating coating treatment solution is more preferably 27.0% by mass or more, more preferably 35.0% by mass or more, 40.0% by mass or more, or 45.0% by mass or more, calculated as solids relative to the total mass of the insulating coating treatment solution. The content of colloidal silica in the insulating coating treatment solution is more preferably 58.0% by mass or less, more preferably 55.0% by mass or less, and more preferably 50.0% by mass or less.

[0059] Furthermore, the insulating coating treatment solution of this embodiment is mainly composed of metal phosphate salts and colloidal silica, and is used to form a phosphate coating. Therefore, the content of metal phosphate salts in the insulating coating treatment solution, calculated as solids, relative to the total mass of the insulating coating treatment solution, is preferably 28.0 to 75.0% by mass.

[0060] In the above mixing process, various oxides such as titanium dioxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate may also be further mixed. However, the content of components other than colloidal silica and phosphate in the insulating coating treatment solution, calculated as solids, relative to the total mass of the insulating coating treatment solution, is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, even more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less.

[0061] Furthermore, as mentioned above, it is preferable not to actively add chromate, and the chromate content in the insulating coating treatment solution is preferably below the impurity level. Specifically, the chromate content in the insulating coating treatment solution, calculated as CrO3, is preferably 0.1% by mass or less relative to the total mass of the insulating coating treatment solution, calculated as solids.

[0062] In the above mixing process, compounds containing Si and / or Na may also be further mixed. However, in this case, it is preferable that the Na2O / SiO2 ratio in the mixed insulating coating solution is 0.5% to 10%.

[0063] In the method for manufacturing the insulating coating treatment liquid of this embodiment, the Na₂O / SiO₂ ratio in colloidal silica is analyzed by the following methods. The amount of Na contained in the colloidal silica is determined by atomic absorption spectrophotometry and converted to Na₂O. Furthermore, the amount of Si contained in the colloidal silica is determined by elemental analysis such as ICP and converted to SiO₂. The Na₂O / SiO₂ ratio is calculated based on the obtained Na₂O and SiO₂ amounts and can be expressed as a percentage.

[0064] <Manufacturing Method of Oriented Electromagnetic Steel Sheets>

[0065] Next, the manufacturing method of the oriented electromagnetic steel sheet according to this embodiment will be described. The manufacturing method of the oriented electromagnetic steel sheet (insulation coating treatment method) according to this embodiment includes a coating step of applying an insulation coating treatment liquid to the surface of the steel sheet, and a sintering step of sintering the insulation coating treatment liquid. An insulation coating is formed by sintering.

[0066] In the manufacturing method of the oriented electromagnetic steel sheet of this embodiment, the steel sheet with the insulating coating can be an oriented electromagnetic steel sheet with a conventional forsterite coating or an oriented electromagnetic steel sheet without a forsterite coating. Regardless of which type of steel sheet is used, after final annealing and washing to remove the remaining annealing separating agent, the oriented electromagnetic steel sheet undergoes pickling treatment using a sulfuric acid bath or similar method, followed by washing. This cleans and activates the surface of the steel sheet, and then, in the coating process, an insulating coating treatment liquid is applied to the steel sheet. The oriented electromagnetic steel sheet coated with the insulating coating treatment liquid is then subjected to a sintering process under the conditions described later to form an insulating coating on its surface.

[0067] In the sintering process, the oriented electromagnetic steel sheet coated with an insulating film treatment solution is heated to the sintering homogenization temperature, held at the sintering homogenization temperature, and then cooled. The sintering homogenization temperature (°C) represents the plate temperature reached (maximum plate temperature) in the sintering process, and needs to be between 800°C and 1000°C. If the sintering homogenization temperature is less than 800°C, the insulating film may not impart sufficient tension to the steel sheet. On the other hand, if the sintering homogenization temperature exceeds 1000°C, cracks may sometimes occur in the insulating film, the film tension may decrease, or the insulation performance may be reduced. In addition, defects may sometimes occur on the steel sheet. The sintering homogenization temperature is more preferably between 850°C and 950°C.

[0068] The soaking time (in seconds) represents the holding time at the sintering soaking temperature. The soaking time needs to be 10 seconds or more. If the soaking time is less than 10 seconds, the sintering of the insulating film is insufficient, and the moisture resistance may deteriorate (moisture absorption increases). Preferably, it is 20 seconds or more. On the other hand, the soaking time is 60 seconds or less. If the soaking time exceeds 60 seconds, not only is the moisture resistance almost unchanged, but sometimes excessive crystallization of the insulating film can cause cracking, reducing the film tension. A more preferable soaking time is 45 seconds or less, which allows for obtaining the necessary and sufficient properties of the film.

[0069] Furthermore, there is no particular limitation on the type of steel sheet for which the above-described insulating coating treatment is performed. This is because the main feature of the oriented electromagnetic steel sheet of this embodiment lies in the composition of the insulating coating. The effect of the insulating coating of the oriented electromagnetic steel sheet of this embodiment—namely, the ability to impart high tension to the surface of the steel sheet, good adhesion, corrosion resistance, and productivity, and good moisture resistance even without the presence of chromates—is independent of the type of steel sheet.

[0070] Preferably, for example, by performing the above-mentioned insulating coating treatment on an orientation-oriented electromagnetic steel sheet manufactured using the technology disclosed in Japanese Patent Application Publication No. 7-268567, it is possible to further reduce iron loss. Specifically, by performing the above-mentioned insulating coating treatment on the orientation-oriented electromagnetic steel sheet, it is possible to further reduce iron loss. The orientation-oriented electromagnetic steel sheet contains at least 0.005% or less of C and 2.5 to 7.0% of Si by mass, and may also contain other alloying elements (e.g., Mn: 0 to 1.0%, Al: 0 to 0.03%, N: less than 0.01%, P: less than 0.01%, and S: less than 0.01%) within a range that does not impair its properties. The remainder contains Fe and impurities, the average crystal grain size is 1 to 10 mm, and the average angle between the crystal orientation of (110)

[001] and the rolling direction is 8° or less.

[0071] There is no particular limitation on the amount of insulating film adhering to the oriented electromagnetic steel sheet manufactured by the method of this embodiment, which is 2.0 to 7.0 g / m². 2 This is appropriate. The coating adhesion amount of the insulating film is less than 2.0 g / m². 2 In certain situations, it is difficult to impart high tension to oriented electromagnetic steel sheets, and the insulation and corrosion resistance of the sheets may also decrease, making it undesirable. On the other hand, when the coating thickness of the insulating film exceeds 7.0 g / m²... 2 In such cases, the duty cycle of the oriented electromagnetic steel sheet decreases, potentially deteriorating transformer characteristics, therefore it is not preferred. A more preferable coating weight for the insulating film is 3.0 g / m². 2 The above, and more preferably 4.0 g / m 2 The above. More preferably, the coating weight of the insulating film is 6.0 g / m². 2 The following, and more preferably, is 5.0 g / m 2 the following.

[0072] Example

[0073] Next, the effects of one embodiment of the present invention will be described in further detail with reference to the embodiments. However, the conditions in the embodiments are merely examples used to confirm the feasibility and effects of implementing the present invention, and the present invention is not limited to this single example. Various conditions can be used to achieve the purpose of the present invention as long as they do not depart from the spirit of the present invention.

[0074] A slab containing, by mass percent, 0.082% C, 3.25% Si, 0.084% Mn, 0.026% sol.Al, 0.0088% N, 0.008% P, and 0.023% S, with the remainder being Fe and impurities, is heated to 1150°C and hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.6 mm. This hot-rolled steel sheet is then subjected to hot-rolled annealing as needed, followed by a single cold rolling or multiple cold rolling processes with intermediate annealing, to produce a cold-rolled steel sheet with a final thickness of 0.23 mm. This cold-rolled steel sheet is then subjected to decarburization annealing and nitriding treatment, held in an ammonia-containing atmosphere during cooling. Furthermore, known conditions are applied from slab heating to nitriding treatment.

[0075] The decarburized annealed plates were coated with an annealing separating agent mainly composed of MgO and then dried. The decarburized annealed plates coated with the annealing separating agent were then subjected to a final annealing at 1200℃ for 20 hours.

[0076] Afterwards, the remaining annealing separator is removed by washing with a washing machine, and an insulating coating treatment solution with the composition shown in Table 1 is applied. The coating is then sintered under the conditions shown in Table 2 to form an insulating coating.

[0077] [Table 1]

[0078]

[0079] [Table 2]

[0080] Table 2

[0081]

[0082] [moisture absorption]

[0083] Based on the above method, the moisture absorption of the oriented electromagnetic steel sheet with insulating film obtained in this way was measured.

[0084] [Appearance]

[0085] In addition, the appearance of the sintered insulating film was evaluated. The appearance of the sintered insulating film was judged by visually observing whether there was any cloudiness. A surface area of ​​less than 10% without cloudiness was rated as "very good," 10% to less than 20% as "good," and more than 20% as "poor." Furthermore, when observing the surface of the cloudy samples using SEM, fine cracks were observed on the film. Therefore, it was believed that the cloudiness was due to light scattering caused by the cracks.

[0086] These evaluation results are shown in Tables 3-5.

[0087] [Table 3]

[0088] Table 3

[0089]

[0090] [Table 4]

[0091] Table 4

[0092] [Table 5]

[0093]

[0094] As can be seen from Tables 3 to 5, in the invention examples, the manufacturing method of the insulating coating treatment liquid meets the scope of the invention. The oriented electromagnetic steel sheet with insulating coating formed by using the insulating coating treatment liquid of the invention examples has good moisture resistance and excellent appearance.

[0095] In contrast, in the comparative example, at least one item of the method for manufacturing the insulating coating treatment liquid is outside the scope of the present invention, resulting in poor moisture resistance of the oriented electromagnetic steel sheet or poor appearance of the insulating coating.

Claims

1. A method for manufacturing an insulating coating treatment liquid for oriented electromagnetic steel sheets, comprising: An adjustment step involves adding a Na compound to colloidal silica to adjust the Na2O / SiO2 ratio (mass % of Na content converted to Na2O and Si content converted to SiO2) in the colloidal silica to a value between 0.5% and 10%. A mixing process that involves mixing colloidal silica with an adjusted Na2O / SiO2 ratio with a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr.

2. A method for manufacturing an orientation-oriented electromagnetic steel sheet, comprising: The coating process of applying an insulating coating solution to the surface of a steel plate; as well as The sintering process for producing an insulating coating by sintering the insulating coating treatment liquid. The insulating coating treatment liquid is an insulating coating treatment liquid for oriented electromagnetic steel sheets manufactured by the method described in claim 1. The sintering homogenization temperature in the sintering process is 800-1000℃, and the homogenization holding time is 10-60 seconds.

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