METHOD FOR PRODUCING INSULATING COATING TREATMENT LIQUID FOR GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR PRODUCING GRAIN-ORIENTED ELECTRICAL STEEL SHEET

Abstract

This method for producing an insulating film treatment liquid for grain-oriented electromagnetic steel sheet comprises: an adjustment step in which an Na compound is added to colloidal silica, and the ratio of the Na content in terms of Na2O in the colloidal silica to the Si content in terms of SiO2, i.e., Na2O / SiO2, is adjusted to 0.5-10% in mass%; and a mixing step in which the colloidal silica with the adjusted Na2O / SiO2 ratio and a phosphate metal salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr are mixed together.

Description

METHOD FOR PRODUCING INSULATING COATING TREATMENT LIQUID FOR ELECTRICAL STEEL SHEETS Grain Oriented and Method for Producing Grain Oriented Electrical Steel Sheet TECHNICAL FIELD

[0001] The present invention relates to a method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet and a method for producing a grain-oriented electrical steel sheet by applying the insulating coating treatment liquid produced by the aforementioned method. PRIOR ART

[0002] Grain-oriented electrical steel sheets are steel sheets used primarily as iron cores in transformers and similar equipment. Typically, a two-layer surface coating is formed on this grain-oriented electrical steel sheet: a forsterite layer (also called the primary coating), which is formed during final annealing at high temperature; and a phosphate coating, which is formed by baking after the application of a treatment liquid composed mainly of phosphate during the thermal leveling of the steel sheet.

[0003] Phosphate coatings are needed to provide electrical insulation to grain-oriented electrical steel sheets and to improve iron loss by reducing eddy current loss. In addition to insulation, several other properties, such as corrosion resistance, heat resistance, lubricity, and adhesion, are also required for the phosphate coating. This is to facilitate various production processes when grain-oriented electrical steel sheets are processed to produce iron cores for transformers and other devices. For example, if the phosphate coating has low heat resistance, lubricity, or adhesion, the coating of Petition 870250082380, dated 12 / 09 / 2025, page 7 / 39 2 / 24 Phosphate may flake off during stress-relief annealing in the production of the iron core, which prevents the phosphate coating from exhibiting its original insulating properties or worsens processability, since the steel sheets cannot be stacked homogeneously.

[0004] Furthermore, an important property of the insulating coating of grain-oriented electrical steel sheets is that it applies tension to the steel sheets. When tension is applied to the steel sheets, the iron loss of the grain-oriented electrical steel sheets can be improved, facilitating the movement of the magnetic wall. The tension can also reduce magnetostriction (a major cause of noise in transformers).

[0005] In order to improve the various properties of grain-oriented electrical steel sheets as described above, specifically, technologies such as those described in Patent Documents 1 to 9 below have been researched and developed.

[0006] For example, Patent Document 1 describes that an insulating coating treatment liquid having a specific composition consisting mainly of aluminum phosphate, chromate, and colloidal silica is applied to the forsterite film formed on the surface of the steel sheet after final annealing and then subjected to baking. According to the technology described in Patent Document 1, a high-voltage insulating coating is formed on the surface of the steel sheet, thereby reducing iron loss and magnetostriction of the grain-oriented electrical steel sheet.

[0007] In addition, Patent Document 2 describes a method of applying a treatment liquid containing ultrafine colloidal silica particles with a particle diameter of 8 μm or less, primary phosphate and chromate in specific proportions to a sheet of Petition 870250082380, dated 12 / 09 / 2025, page 8 / 39 3 / 24 steel, followed by baking the sheet. According to the technology described in Patent Document 2, the high voltage of the insulating coating can be maintained and, in addition, the lubricity of the coating can be improved.

[0008] Furthermore, Patent Document 3 describes a technology for forming a high-voltage insulating coating on the surface of a grain-oriented electrical steel sheet by applying a specific amount of an insulating coating composed mainly of phosphate, chromate, and colloidal silica with a glass transition point of 950°C to 1200°C.

[0009] According to the technologies described in the Documents of Patents 1 to 3 above demonstrate the possibility of forming an insulating coating with significantly improved coating properties and enhanced coating voltage. However, all technologies described in Patent Documents 1 to 3 contain chromate, a chromium compound, in the insulating coating. In recent years, with a focus on environmental issues, there have been social demands to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0010] For this reason, technologies that allow the formation of effective insulating coatings without the aforementioned chromium compounds have been investigated. However, a problem with insulating coatings without chromium compounds is that they do not provide sufficient tension to the steel sheet.

[0011] As a method for solving the aforementioned problems, for example, Patent Document 4 describes a method for treating an insulating coating for a grain-oriented electrical steel sheet in which a treatment liquid containing 20 parts by weight of colloidal silica in terms of SiO2 content, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid and 4 to 40 parts by weight in total of one or more types selected from Petition 870250082380, dated 12 / 09 / 2025, page 9 / 39 4 / 24 of sulfates of Mg, Al, Fe, Co, Ni and Zn is cooked at 300°C or more.

[0012] Furthermore, Patent Document 5 describes a technology relating to a coating agent for forming a coating containing a mixture of boric acid and alumina sol and a water-compatible organic solvent; this coating has a tension-inducing effect on grain-oriented electrical steel sheets.

[0013] Furthermore, Patent Document 6 describes a technology in which one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al are contained in a surface treatment agent for grain-oriented electrical steel sheets containing primary phosphates of Al, Mg, and Ca and colloidal silica. Additionally, formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate are exemplified as organic acid salts in Patent Document 6.

[0014] Furthermore, Patent Document 7 describes a technology in which, in an insulating coating treatment agent for grain-oriented electrical steel sheets containing phosphate and colloidal silica, the metallic components in the phosphate are a combination of specific proportions of divalent metallic elements, trivalent metallic elements and tetravalent or higher metallic elements.

[0015] Furthermore, Patent Document 8 describes a grain-oriented electrical steel sheet, including a steel sheet and an insulating coating containing: a first metallic phosphate which is a metallic phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni and Zn; a second metallic phosphate which is a metallic phosphate of one or more metals selected from Co, Mo, V, W and Zr; and colloidal silica.

[0016] In addition, Patent Document 9 describes an aqueous composition for coating grain-oriented electrical steel; a Petition 870250082380, dated 12 / 09 / 2025, page 10 / 39 5 / 24 composition contains aluminum cations; manganese cations; dihydrogen phosphate, hydrogen phosphate and / or phosphate anions; colloidal silica; and, optionally, iron cations. List of Prior Art Documents Patent Documents Patent Document 1: JP48-39338A Patent Document 2: JP61-41778A Patent Document 3: JP11-071683A Patent Document 4: JP54-143737A Patent Document 5: JP7-278828A Patent Document 6: JP2000-178760A Patent Document 7: JP2010-13692A Patent Document 8: WO2017-057513 A1 Patent Document 9: JP2022-519691A SUMMARY OF THE INVENTION Technical Problem

[0017] These proposals have improved the application of tension in steel sheets. However, the present inventors' research to date demonstrates that insulating coatings that do not contain a chromium compound also exhibit deterioration in terms of moisture absorption resistance. Even with all the techniques mentioned, it has not been possible to achieve the same level of moisture absorption resistance as conventional coatings containing chromic acid, and there is still room for improvement.

[0018] The insulating coating on grain-oriented electrical steel sheets must be able to impart a high voltage to the steel sheet surface. In addition, the insulating coating on grain-oriented electrical steel sheets must also exhibit good resistance to moisture absorption and good productivity. Petition 870250082380, dated 12 / 09 / 2025, page 11 / 39 6 / 24

[0019] The present invention was made to solve the aforementioned problems and its objectives are to provide a method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet that exhibits good resistance to moisture absorption and, moreover, good productivity even when chromate is not included and to provide a method for producing a grain-oriented electrical steel sheet by applying the insulating coating treatment liquid produced by the aforementioned method. Solution to the Problem

[0020] The essence of the present invention is as follows.

[0021] (1) A method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: an adjustment process in which a Na compound is added to colloidal silica to adjust the Na2O / SiO2 ratio in % by mass between the amount of Na in terms of Na2O and the amount of Si in terms of SiO2 in the colloidal silica to 0.5% or more and 10% or less, and a mixing process in which colloidal silica with the adjusted Na2O / SiO2 ratio and metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr are mixed.

[0022] (2) A method for producing an electrically oriented grain steel sheet according to another embodiment of the present invention includes: a coating process in which an insulating coating treatment liquid is applied to the surface of a steel sheet, and a baking process in which the insulating coating treatment liquid is baked to form an insulating coating. Petition 870250082380, dated 12 / 09 / 2025, page 12 / 39 7 / 24 wherein the insulating coating treatment liquid is the insulating coating treatment liquid for an oriented grain electrical steel sheet produced by the method described in (1) above, and wherein, in the baking process, the immersion temperature in baking is 800 to 1000°C and the immersion holding time is 10 to 60 seconds. Advantageous Effect of the Invention

[0023] According to the present invention, a grain-oriented electrical steel sheet with excellent moisture absorption resistance and productivity can be obtained in a stable manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 shows the relationship between the Na2O / SiO2 ratio of colloidal silica and the amount of moisture absorption. DESCRIPTION OF THE MODALITIES

[0025] The present inventors investigated methods for improving the moisture absorption resistance of insulating coatings that do not contain a chromium compound. Firstly, the present inventors questioned whether moisture absorption resistance could be improved by adjusting the crystallization temperature of colloidal silica. It is known that adding sodium hydroxide to colloidal silica reduces the crystallization temperature of colloidal silica.

[0026] Therefore, the present inventors evaluated the moisture absorption resistance of insulating coatings produced with colloidal silica previously supplemented with sodium hydroxide. For comparison, a similar study was also carried out with the addition of sodium chloride.

[0027] The results of the preliminary experiments that led to the present invention are described below.

[0028] Final annealed grain-oriented electrical steel sheets, 0.23 mm thick, produced by a method Petition 870250082380, dated 12 / 09 / 2025, page 13 / 39 8 / 24 known sheets were sheared to a width of 60 mm and a length of 300 mm, and the annealing separator adhered to the surface was removed by washing, and the resulting sheets were used as base metals. Then, sodium hydroxide or sodium chloride was added to the colloidal silica, and the Na2O / SiO2 ratio in the colloidal silica was adjusted within a range of 0.2 to 11% to prepare 11 types of colloidal silica. Note that the Na2O / SiO2 ratio is a percentage (%) obtained by quantifying the amount of Na in terms of Na2O (hereinafter referred to as the amount of Na2O, unit: % by mass) and the amount of Si in terms of SiO2 (hereinafter referred to as the amount of SiO2, unit: % by mass) contained in the colloidal silica, respectively, and by dividing the amount of Na2O by the amount of SiO2.

[0029] Next, an insulating coating treatment liquid, consisting of 60 parts by mass of primary aluminum phosphate and 40 parts by mass of colloidal silica, was applied to both sides of the above-prepared base metals using a roller coating machine, so that the amount of coating after baking was 4.5 g / m2 per side. They were then baked at a temperature of 850°C for 30 seconds.

[0030] For comparison, an insulating coating treatment liquid consisting of 50 parts by mass of primary aluminum phosphate, 40 parts by mass of colloidal silica (Na2O / SiO2 ratio = 1.2%) and 10 parts by mass of chromic anhydride was applied similarly to the base metal and baked.

[0031] The resulting steel sheet was used as a test specimen to evaluate its resistance to moisture absorption. First, the specimen was placed in a thermo-hydrostat (temperature: 50°C, humidity: 90%) for one week, and the difference in weight before and after treatment in the thermo-hydrostat was determined. The difference Petition 870250082380, dated 12 / 09 / 2025, page 14 / 39 9 / 24 of the quantified weight was divided by the area of ​​both sides of the test specimen, 0.036 m2, which was defined as the amount of moisture absorption (unit: g / m2), and the resistance to moisture absorption was evaluated using the amount of moisture absorption as an index.

[0032] Figure 1 shows the results of the above evaluation, organizing the relationship between the amount of moisture absorption and the Na2O / SiO2 ratio. As shown in Figure 1, the steel sheet with a coating containing chromium has a small Na2O / SiO2 ratio; the amount of moisture absorption is 0.1 g / m2 or less, and almost no moisture is absorbed. In contrast, in the case of steel sheets with a coating that does not contain chromium, in the region where the Na2O / SiO2 ratio is less than 0.5%, the amount of moisture absorption exceeds 1.0 g / m2, which is large, and sufficient resistance to moisture absorption is not achieved. However, in regions where the Na2O / SiO2 ratio is high, especially where the Na2O / SiO2 ratio is 0.5% or more, the amount of moisture absorption is 1.0 g / m2 or less, regardless of whether sodium hydroxide or sodium chloride is used.Furthermore, in the region where the Na2O / SiO2 ratio is 5.0% or more, almost no moisture is absorbed and good moisture absorption resistance, equivalent to that of steel, is exhibited in the sheet coated with a chromium-containing coating. On the other hand, when the Na2O / SiO2 ratio exceeds 10%, it has been confirmed that the dispersibility of colloidal silica deteriorates, resulting in an uneven appearance after baking.

[0033] Based on the above experimental results, the present inventors have discovered that, in an insulating coating treatment liquid containing metallic phosphate and colloidal silica, it is possible to impart high resistance to moisture absorption by limiting the Na2O / SiO2 ratio in the colloidal silica to 0.5% or more and 10% or less, thereby promoting the insulating coating formation reaction. Petition 870250082380, dated 12 / 09 / 2025, page 15 / 39 10 / 24

[0034] As mentioned above, it is known that the addition of sodium hydroxide to colloidal silica reduces the crystallization temperature of colloidal silica; however, in the present experiment, no change in the crystallization temperature was observed when sodium chloride was added to the colloidal silica. It is considered that the improvement in moisture absorption resistance is not due to the reduction in the crystallization temperature of colloidal silica, as conventional knowledge suggests, but rather to a factor: the addition of sodium itself improves moisture absorption resistance. Method for Producing Liquid Insulating Coating for Grain Oriented Electrical Steel Sheet

[0035] This section describes the configuration of the method for producing the insulating coating treatment liquid for a grain-oriented electrical steel sheet (hereinafter simply referred to as insulating coating treatment liquid) according to the present embodiment and the reasons for its limitations.

[0036] The method for producing the insulating coating treatment liquid of the present embodiment includes an adjustment process to adjust the colloidal silica composition and a mixing process to mix the colloidal silica and the metallic phosphate.

[0037] In the adjustment process, a Na compound is added to the colloidal silica to adjust the Na2O / SiO2 ratio in % by mass between the amount of Na2O and the amount of SiO2 in the colloidal silica. This should be between 0.5% or more and 10% or less. If the Na2O / SiO2 ratio is less than 0.5%, the effect of promoting the insulating coating formation reaction is small, resulting in insufficient moisture absorption resistance. On the other hand, if the Na2O / SiO2 ratio exceeds 10%, the dispersibility of the colloidal silica deteriorates, resulting in an inferior appearance after baking. The Na2O / SiO2 ratio is preferably 1% or more, more preferably 3% or more, and even Petition 870250082380, dated 12 / 09 / 2025, p. 16 / 39 11 / 24 more preferably, 5% or more. The Na2O / SiO2 ratio is preferably 8% or less, more preferably 7% or less, and even more preferably 6% or less.

[0038] There is no specific limitation as to the method of adjusting the Na2O / SiO2 ratio of colloidal silica to 0.5% or more and 10% or less; however, for example, a method of pre-adding sodium hydroxide and / or sodium chloride to the colloidal silica may be used. From the point of view of increasing the pH of the insulating coating treatment liquid and thus improving the dispersibility of the colloidal silica, it is preferable to add sodium hydroxide.

[0039] The size of the colloidal silica (silica particles) used in the present embodiment is not particularly limited; however, the average particle diameter (average primary particle diameter) is preferably from 4 to 35 nm. If the average particle diameter of the colloidal silica is less than 4 nm, the colloidal silica tends to aggregate and the stability of the insulating coating treatment liquid may deteriorate or the insulating coating may become porous with large gaps, reducing the adhesion of the insulating coating, which is undesirable. On the other hand, if the average particle diameter of the colloidal silica is greater than 35 nm, the colloidal silica becomes less reactive and the mixture of phosphate as a binder and colloidal silica may not be sufficient or cracks may appear in the insulating coating to reduce adhesion, which is undesirable.

[0040] It is even more preferable that the maximum limit of the average particle diameter of colloidal silica be defined as 31 nm, 22 nm, 18 nm or 12 nm, since smaller colloidal silica particle diameters form denser coatings and increase coating stress. Furthermore, it is even more preferable that the surface of the colloidal silica be chemically treated with aluminum. The average particle diameter (primary average particle diameter) of colloidal silica may Petition 870250082380, dated 12 / 09 / 2025, page 17 / 39 12 / 24 can be determined, for example, by converting the specific surface area measured using the BET adsorption method (according to JIS Z8830 standard).

[0041] In the mixing process, colloidal silica, whose components were adjusted in the adjustment process, and metal phosphate are mixed. The aforementioned metal phosphate is a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr. It is preferable that the metal phosphate be a metal phosphate of one or more metals selected from Al, Mg, Ni, V, and W. This is because, by selecting these phosphates, a level and uniform appearance can be obtained under a wide variety of cooking conditions. In the mixing process, it is preferable not to actively add chromates, taking environmental concerns into account.

[0042] In the method for producing an insulating coating treatment liquid according to the present embodiment, the ratio of metallic phosphate and colloidal silica is not particularly limited. Provided that the Na2O / SiO2 ratio in the colloidal silica is 0.5% or more and 10% or less, the insulating coating of the grain-oriented electrical steel sheet using the insulating coating treatment liquid produced by the method of the present embodiment exhibits excellent properties. The following are examples of preferred values.

[0043] The colloidal silica content in the insulating coating treatment liquid, in terms of SiO2, is preferably from 25.0 to 65.0% by mass of the total mass of the insulating coating treatment liquid in terms of solids content. If the colloidal silica content in the insulating coating treatment liquid is less than 25.0% by mass, the coating tension of the insulating coating may not be sufficient, which is undesirable.If the colloidal silica content in the insulating coating treatment liquid exceeds 65.0% by mass, the adhesion of the insulating coating may decrease, which is undesirable. Petition 870250082380, dated 12 / 09 / 2025, p. 18 / 39 13 / 24 The colloidal silica content in the insulating coating treatment liquid is, more preferably, 27.0% by mass or more, and even more preferably, 35.0% by mass or more, 40.0% by mass or more, or 45.0% by mass or more in terms of the solids content relative to the total mass of the insulating coating treatment liquid. The colloidal silica content in the insulating coating treatment liquid is, more preferably, 58.0% by mass or less, even more preferably 55.0% by mass or less, or even more preferably, 50.0% by mass or less.

[0044] Furthermore, the insulating coating treatment liquid according to the present embodiment is mainly composed of metallic phosphate and colloidal silica, and is used to form a phosphate coating. Therefore, the metallic phosphate content in the insulating coating treatment liquid in terms of solids content is preferably from 28.0 to 75.0% by mass of the total mass of the insulating coating treatment liquid in terms of solids content.

[0045] In the above mixing process, inorganic compounds, including various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments and barium titanate, may be additionally mixed. However, the content of components other than colloidal silica and phosphate in the insulating coating treatment liquid in terms of solids content 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, based on the total mass of the insulating coating treatment liquid in terms of solids content.

[0046] Furthermore, as mentioned above, it is preferable not to actively add chromate, and the chromate content in the insulating coating treatment liquid should not exceed the level of impurities. Specifically, the chromate content in the treatment liquid of Petition 870250082380, dated 12 / 09 / 2025, p. 19 / 39 14 / 24 insulating coating, in terms of CrÜ3, should preferably be 0.1% by mass or less of the total mass of the insulating coating treatment liquid in terms of solids content.

[0047] In the above mixing process, a compound containing Si and / or Na may be additionally mixed in. In this case, however, the ratio of Na2O / SiO2 contained in the insulating coating treatment liquid after mixing is preferably 0.5% or more and 10% or less.

[0048] In the method for producing an insulating coating treatment liquid according to the present embodiment, the analysis of the Na2O / SiO2 ratio in colloidal silica is carried out as follows. The amount of Na contained in the colloidal silica is measured by atomic absorption spectrophotometry and converted to the amount of Na2O. The amount of Si contained in the colloidal silica is determined by an elemental analysis method, such as ICP, and converted to the amount of SiO2. Then, the Na2O / SiO2 ratio can be calculated from the obtained amounts of Na2O and SiO2 and expressed as a percentage. Method for Producing Grain-Oriented Electrical Steel Sheet

[0049] The method for producing a grain-oriented electrical steel sheet according to the present embodiment is described below. The method for producing a grain-oriented electrical steel sheet (treatment method with an insulating coating) of the present embodiment includes a coating process in which an insulating coating treatment liquid is applied to the surface of the steel sheet and a baking process in which the insulating coating treatment liquid is baked. By means of baking, an insulating coating is formed.

[0050] In the method for producing a grain-oriented electrical steel sheet according to the present embodiment, the steel sheet on Petition 870250082380, dated 12 / 09 / 2025, page 20 / 39 15 / 24 The insulating coating formed on which the sheet is applied can be a common grain-oriented electrical steel sheet with a forsterite film or a grain-oriented electrical steel sheet without a forsterite film. In both cases, after final annealing followed by rinsing to remove excess annealing separator, the grain-oriented electrical steel sheet is pickled in a sulfuric acid bath or similar and then rinsed in water. After the steel sheet surface is cleaned and activated in this way, an insulating coating treatment liquid is applied to the steel sheet during the coating process. The grain-oriented electrical steel sheet coated with the insulating coating treatment liquid is then subjected to a baking process under the conditions described below to form an insulating coating on the surface.

[0051] In the baking process, the grain-oriented electrical steel sheet coated with the insulating coating treatment liquid is heated to the baking immersion temperature, held at the baking immersion temperature, and then cooled. The baking immersion temperature (°C) is the temperature of the sheet reached during the baking process (maximum sheet temperature) and should be 800°C or higher and 1000°C or lower. If the baking immersion temperature is lower than 800°C, the insulating coating may not impart sufficient tension to the steel sheet. Conversely, if the baking immersion temperature exceeds 1000°C, cracks may appear in the insulating coating, resulting in a decrease in coating tension, insulation properties, etc., and defects may also appear in the steel sheet. The baking immersion temperature is more preferably 850°C or higher and 950°C or lower.

[0052] The immersion holding time (seconds) indicates the time the cooking temperature is maintained at the immersion level. The Petition 870250082380, dated 12 / 09 / 2025, page 21 / 39 16 / 24 The immersion holding time should be 10 seconds or more. If the immersion holding time is less than 10 seconds, the baking of the insulating coating is insufficient and the moisture absorption resistance may deteriorate (the amount of moisture absorption may increase). The immersion holding time is desirably 20 seconds or more. On the other hand, the immersion holding time should be 60 seconds or less. If the immersion holding time is greater than 60 seconds, not only does the moisture absorption resistance hardly change, but excessive crystallization of the insulating coating may cause cracking and reduce the coating's tensile strength. The immersion holding time is more preferably 45 seconds or less to achieve the necessary and sufficient coating properties.

[0053] The type of steel sheet to which the above insulating coating treatment is applied is not limited. The reason is that the main characteristic of the grain-oriented electrical steel sheet of the present embodiment is the composition of the insulating coating and the effects of the insulating coating of the grain-oriented electrical steel sheet of the present embodiment, namely, the ability to impart high voltage to the surface of the steel sheet; good adhesion, corrosion resistance and productivity; and good moisture absorption resistance, even when chromate is not included, can be achieved regardless of the type of steel sheet.

[0054] Preferably, the aforementioned insulating coating treatment can be applied to grain-oriented electrical steel sheets, such as those produced using the technology described, for example, in document JP7-268567A, thus enabling an additional effect of reducing iron loss. The above insulating coating treatment can further reduce iron loss by applying the above insulating coating treatment specifically to a Petition 870250082380, dated 12 / 09 / 2025, page 22 / 39 17 / 24 grain-oriented electrical steel sheet containing at least C: 0.005% or less and Si: 2.5 to 7.0% by mass and optionally containing other alloying elements within ranges that do not compromise the properties (e.g., Mn: 0 to 1.0%, Al: 0 to 0.03%, N: 0.01% or less, P: 0.01% or less and S: 0.01% or less) and the balance of Fe and impurities and having an average grain size of 1 to 10 mm and an average angle of 8° or less between the crystal orientation (110)

[001] and the rolling direction.

[0055] Although there is no specific limit to the amount of insulating sheathing of the grain-oriented electrical steel sheet produced by the grain-oriented electrical steel sheet production method according to the present embodiment, an amount of sheathing of 2.0 to 7.0 g / m2 is suitable. If the amount of insulating sheathing is less than 2.0 g / m2, it becomes difficult to impart high voltage to the grain-oriented electrical steel sheet, and the insulation properties and corrosion resistance of the grain-oriented electrical steel sheet may also deteriorate, which is undesirable. On the other hand, if the amount of insulating sheathing is greater than 7.0 g / m2, the space factor of the grain-oriented electrical steel sheet may decrease, resulting in deterioration of the transformer characteristics, which is undesirable.The amount of coating for the insulating sheathing is preferably 3.0 g / m2 or more, and even more preferably 4.0 g / m2 or more. The amount of coating for the insulating sheathing is preferably 6.0 g / m2 or less, and even more preferably 5.0 g / m2 or less. EXAMPLE.

[0056] Next, the effects of one embodiment of the present invention will be described in more concrete detail by means of examples. The conditions in the examples are exemplary conditions adopted. Petition 870250082380, dated 12 / 09 / 2025, p. 23 / 39 18 / 24 to confirm the feasibility and effects of the present invention, and the present invention is not limited to such exemplary conditions. Various conditions may be employed in the present invention, provided they do not depart from the essence of the present invention and achieve its objective.

[0057] A plate containing, in % by mass, C: 0.082%, Si: 3.25%, A mixture of Mn: 0.084%, Al solution: 0.026%, N: 0.0088%, P: 0.008%, and S: 0.023%, with the remainder being Fe and impurities, was melted, heated to 1150°C, and subjected to hot rolling to prepare a hot-rolled steel sheet with a thickness of 2.6 mm. The hot-rolled steel sheet was then annealed as needed and cold-rolled one or more times with intermediate annealing to obtain a cold-rolled steel sheet with a final thickness of 0.23 mm. The cold-rolled steel sheet underwent decarburizing and nitriding annealing in an atmosphere containing ammonia during the temperature reduction step. Known conditions were used in the processes, from plate heating to nitriding.

[0058] An annealing separator consisting mainly of MgO was applied to the decarburized annealed sheet after the decarburized annealing described above and allowed to dry. The decarburized annealed sheet coated with the annealing separator was subjected to final annealing at 1200°C for 20 hours.

[0059] Next, the excess annealing separator was rinsed off with a scrubber and then the insulating coating treatment liquids, with the components adjusted as shown in Table 1, were applied and baked under the conditions shown in Table 2 to form the insulating coatings. Petition 870250082380, dated 12 / 09 / 2025, page 24 / 39 Table 1 Liquid Insulating Coating Treatment Liquid Metallic Phosphate Colloidal Silica Chromate Inorganic Treatment Compound No.Metal proportion (molar ratio) Content (% by mass) Na2O / SiO2 ratio (%) Content (% by mass) Amount of SiO2 (% by mass) Amount of Na2O (% by mass) Content (% by mass) Type Content (% by mass) A1 Al 100 74.9 0.5 25.1 25.0 0.13 - - - A2 Al 100 72.5 2 27.5 27.0 0.54 - - - A3 Al 100 64.0 3 36.1 35.0 1.1 - - - A4 Al 100 52.7 5 47.3 45.0 2.3 - - - A5 Al 100 47.0 6 53.0 50.0 3.0 - - - A6 Al 100 37.4 8 62.6 58.0 4.6 - - - A7 Al 100 28.5 10 71.5 65.0 6.5 - - - A8 Al 100 47.6 5 50.4 48.0 2.4 - Boric acid 2.0 A9 Al 100 47.6 5 50.4 48.0 2.4 - Sodium borate 2.0 A10 Al 100 47.6 5 50.4 48.0 2.4 - Titanium dioxide 2.0 A11 Al 100 47.6 5 50.4 48.0 2.4 - Molybdenum oxide 2.0 A12 Al 100 47.6 5 50.4 48.0 2.4 - Barium titanate 2.0 A13 Al / Fe 80 / 20 49.6 5 50.4 48.0 2.4 - - - A14 Al / Mg 80 / 20 49.6 5 50.4 48.0 2.4 - - - A15 Al / Mn 80 / 20 49.6 5 50.4 48.0 2.4 - - -. 19 / 24 Petition 870250082380, dated 12 / 09 / 2025, page 25 / 39 Liquid Insulating Coating Treatment Liquid Metal Phosphate Colloidal Silica Chromate Inorganic Treatment Compound No. Metal Metal Proportion (Molar Ratio) Content (% by mass) Na2O / SiO2 Ratio (%) Content (% by mass) SiO2 Amount (% by mass) Na2O Amount (% by mass) Content (% by mass) Type Content (% by mass) A16 Al / Ni 80 / 20 49.6 5 50.4 48.0 2.4 - - - A17 Al / Zn 80 / 20 49.6 5 50.4 48.0 2.4 - - - A18 Al / Co 80 / 20 49.6 5 50.4 48.0 2.4 - - - A19 Al / Mo 80 / 20 49.6 5 50.4 48.0 2.4 - - - A20 Al / V 80 / 20 49.6 5 50.4 48.0 2.4 - - - A21 Al / W 80 / 20 49.6 5 50.4 48.0 2.4 - - - A22 Al / Zr 80 / 20 49.6 5 50.4 48.0 2.4 - - - a1 Al 100 51.8 0.4 48.2 48.0 0.20 - - - a2 Al 100 46.2 12 53.8 48.0 5.8 - - - a3 Al 100 41.9 0.2 48.1 48.0 0.10 10.0 - - 20 / 24 Petition 870250082380, dated 12 / 09 / 2025, page 26 / 39 21 / 24 Table 2 Production Method No. Cooking Process Immersion Temperature Holding Time (°C) (s) B1 800 30 B2 1000 30 B3 850 10 B4 850 60 B5 850 30 B6 870 30 B7 950 30 b1 750 30 b2 1050 30 b3 850 5 b4 850 90 Amount of Moisture Absorption

[0060] The amount of moisture absorption of the resulting grain-oriented electrical steel sheet with an insulating coating was measured using the method described above. Appearance

[0061] The appearance of the insulating coating after baking was evaluated. The appearance of the insulating coating after baking was evaluated by visual inspection based on the presence or absence of cloudiness in the insulating coating. A cloud-free area of ​​less than 10% of the coating surface was classified as Very Good, from 10% to less than 20% was classified as Good, and 20% or more was classified as Poor. When the cloudy sample surface was observed using a SEM, small cracks were found in the coating. Therefore, the occurrence of cracks is considered to cause diffuse reflection of light, which causes the sample to be observed as cloudy.

[0062] The results of these evaluations are presented in Tables 3 to 5. Petition 870250082380, dated 12 / 09 / 2025, page 27 / 39 Table 3 Test No. Treatment Liquid No. Production Method No. Property Evaluation Moisture Absorption Amount (g / m2) Appearance C1 A1 B5 0.98 good C2 A2 B5 0.42 good C3 A3 B5 0.05 good C4 A4 B5 0.03 very good C5 A5 B5 0.05 very good C6 A6 B5 0.04 good C7 A7 B5 0.05 good C8 A8 B5 0.06 very good C9 A9 B5 0.05 very good C10 A10 B5 0.06 very good Example of Invention C11 A11 B5 0.05 very good C12 A12 B5 0.04 very good C13 A13 B5 0.04 very good C14 A14 B5 0.05 very good C15 A15 B5 0.04 very good C16 A16 B5 0.04 very good C17 A17 B5 0.04 very good C18 A18 B5 0.05 very good C19 A19 B5 0.05 very good C20 A20 B5 0.04 very good 22 / 24 Petition 870250082380, dated 12 / 09 / 2025, pp. 28 / 39 Test No. Treatment Liquid No. Production Method No. Property Evaluation Moisture Absorption Amount (g / m2) Appearance C21 A21 B5 0.04 very good C22 A22 B5 0.06 very good d a1 B5 1.20 good Comparative Example c2 a2 B5 0.02 poor c3 a3 B5 0.01 good Table 4 Test No. Treatment Liquid No. Production Method No. Property Evaluation Moisture Absorption Amount (g / m2) Appearance after cooking D1 A4 B1 0.08 good D2 A4 B2 0.03 good D3 A4 B3 0.80 good D4 A4 B4 0.03 good Example of the Invention D5 A4 B5 0.04 very good D6 A4 B6 0.04 very good D7 A4 B7 0.04 good d1 A4 b1 1.30 good d2 A4 b2 0.03 poor Comparative Example d3 A4 b3 1.40 good d4 A4 b4 0.04 poor 23 / 24 Petition 870250082380, dated 12 / 09 / 2025, pp. 29 / 39 Table 5 Test No. Production Method No. Insulating Coating Treatment Liquid Property Evaluation Metal Phosphate Colloidal Silica Chromate Moisture Absorption Amount (g / m2) Appearance after baking Metal Content (% by mass) Na2O / SiO2 Ratio (%) Average Particle Diameter (nm) Content (% by mass) SiO2 Amount (% by mass) Na2O Amount (% by mass) E1 B5 Al 49.6 5 4 50.4 48.0 2.4 - 0.05 very good Example of the Invention E2 B5 Al 49.6 5 12 50.4 48.0 2.4 - 0.05 very good E3 B5 Al 49.6 5 18 50.4 48.0 2.4 - 0.05 good E4 B5 Al 49.6 5 22 50.4 48.0 2.4 - 0.04 good E5 B5 Al 49.6 5 31 50.4 48.0 2.4 - 0.04 good E6 B6 Al 49.6 5 35 50.4 48.0 2.4 - 0.05 good

[0063] As can be seen in Tables 3 to 5, in the examples of the invention, the method for producing the liquid of The 24 / 24 insulating coating treatment met the specified ranges of the present invention, and the grain-oriented electrical steel sheet on which the insulating coating was formed using the insulating coating treatment liquid of the invention example exhibited good moisture absorption resistance and excellent coating appearance.

[0064] In contrast, in the comparative examples, at least one item in the method for producing an insulating coating treatment liquid was outside the scope of the present invention and the moisture absorption resistance or appearance of the insulating coating of the grain-oriented electrical steel sheet was inferior.

Claims

CLAIMS 1. A method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet, characterized in that it comprises: an adjustment process in which a Na compound is added to colloidal silica to adjust the Na2O / SiO2 ratio in % by mass between the amount of Na in terms of Na2O and the amount of Si in terms of SiO2 in the colloidal silica to 0.5% or more and 10% or less, and a mixing process in which the colloidal silica with the adjusted Na2O / SiO2 ratio and metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr are mixed.

2. Method for producing a grain-oriented electrical steel sheet, characterized in that it comprises: a coating process in which an insulating coating treatment liquid is applied to the surface of a steel sheet, and a baking process in which the insulating coating treatment liquid is baked to form an insulating coating, wherein the insulating coating treatment liquid is the insulating coating treatment liquid for a grain-oriented electrical steel sheet produced by the method as defined in claim 1, and wherein, in the baking process, the immersion temperature in the baking process is 800 to 1000°C and the immersion holding time is 10 to 60 seconds.

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