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 coating film treatment liquid for a grain-oriented electromagnetic steel sheet includes: an adjustment step of adding a K compound to colloidal silica, and adjusting a K2O / SiO2 ratio in mass% between the K amount in terms of K2O in the colloidal silica and the Si amount in terms of SiO2 to 0.5% to 10%; and a mixing step of mixing the colloidal silica in which the K2O / SiO2 ratio has been adjusted, without adding a chromic acid salt, and a metal phosphate salt(s) of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr.

Description

[001] The present invention relates to a method for producing 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. PREVIOUS TECHNIQUE

[002] 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 these grain-oriented electrical steel sheets: a forsterite layer (also called the primary coating), which is formed during final high-temperature annealing; 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.

[003] 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 re Petition 870250083133, dated 09 / 16 / 2025, page 7 / 39 2 / 24 Phosphate coating can peel 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 steel sheets cannot be stacked homogeneously.

[004] 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).

[005] 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.

[006] 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.

[007] Furthermore, 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 cha Petition 870250083133, dated 09 / 16 / 2025, page 8 / 39 3 / 24 pa of 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.

[008] 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.

[009] According to the technologies described in Patent Documents 1 to 3 above, it was possible to form an insulating coating with several much greater coating properties and with improved coating voltage. However, all the technologies described in Patent Documents 1 to 3 contain chromate, a chromium compound, in the insulating coating. In recent years, with the 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 S1O2 content, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid is used. Petition 870250083133, dated 09 / 16 / 2025, page 9 / 39 4 / 24 and 4 to 40 parts by weight in total of one or more types selected from sulfates of Mg, Al, Fe, Co, Ni and Zn is baked 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 salts of organic acids 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. Furthermore, formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate are exemplified as salts of organic acids 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 a with Petition 870250083133, dated 09 / 16 / 2025, page 10 / 39 5 / 24 aqueous position for coating grain-oriented electrical steel; the composition contains aluminum cations; manganese cations; dihydrogen phosphate, hydrogen phosphate and / or phosphate anions; colloidal silica; and optionally, iron cations. List of State of the 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 870250083133, dated 09 / 16 / 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 K compound is added to colloidal silica to adjust the K2O / SiO2 ratio in % by mass between the amount of K in terms of K2O 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 having the adjusted K2O / 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 a grain-oriented electrical 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 870250083133, dated 09 / 16 / 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 K2O / 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 the moisture absorption resistance could be improved by adjusting the crystallization temperature of colloidal silica. It is known that the addition of sodium hydroxide to colloidal silica reduces the crystallization temperature of colloidal silica.

[0026] In previous studies, the present inventors evaluated the moisture absorption resistance of insulating coatings made with colloidal silica to which sodium hydroxide had been previously added. In addition, the inventors focused on potassium, which has properties similar to those of sodium, and wondered if the crystallization temperature of colloidal silica could be reduced by adding potassium hydroxide to the colloidal silica.

[0027] Therefore, the present inventors evaluated the resistance to Petition 870250083133, dated 09 / 16 / 2025, page 13 / 39 8 / 24 moisture absorption of insulating coatings produced using colloidal silica with added potassium hydroxide. For comparison, a similar study was also conducted with the addition of potassium chloride.

[0028] The results of the preliminary experiments that led to the present invention are described below.

[0029] Final annealed grain-oriented electrical steel sheets, 0.23 mm thick, produced by a known method, were sheared to a width of 60 mm and a length of 300 mm, and the annealing separator adhering to the surface was removed by washing and the resulting sheets were used as base metals. Then, potassium hydroxide or potassium chloride was added to colloidal silica and the K2O / S1O2 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 K2O / SiO2 ratio is a percentage (%) obtained by quantifying the amount of K in terms of K2O (hereinafter referred to as the amount of K2O, 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 colloidal silica, respectively, and by dividing the amount of K2O by the amount of SiO2.

[0030] 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.

[0031] For comparison, an insulating coating treatment liquid consisting of 50 parts by mass of aluminum phosphate Petition 870250083133, dated 09 / 16 / 2025, page 14 / 39 9 / 24 primary, 40 parts by mass of colloidal silica (K2O / S1O2 ratio = 1.2%) and 10 parts by mass of chromic anhydride was applied similarly to the base metal and baked.

[0032] The resulting steel sheet was used as a test specimen to evaluate moisture absorption resistance. First, the test specimen was placed in a thermo-hydrostat (temperature: 50°C, humidity: 90%) for one week, and the weight difference before and after treatment in the thermo-hydrostat was determined. The quantified weight difference 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 moisture absorption resistance was evaluated using the amount of moisture absorption as an index.

[0033] Figure 1 shows the results of the above evaluation, organizing the relationship between the amount of moisture absorption and the K2O / SiO2 ratio. As shown in Figure 1, the steel sheet with a coating containing chromium has a small K2O / 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 having a coating that does not contain chromium, in the region where the K2O / 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 K2O / SiO2 ratio is high, especially where the K2O / SiO2 ratio is 0.5% or more, the amount of moisture absorption is 1.0 g / m2 or less, regardless of whether potassium hydroxide or potassium chloride is used.Furthermore, in the region where the K2O / SiO2 ratio is 5.0% or more, almost no moisture is absorbed and there is good resistance to moisture absorption, equivalent to that of steel sheet coated with [the material]. Petition 870250083133, dated 09 / 16 / 2025, page 15 / 39 A 10 / 24 coating containing chromium is shown. On the other hand, when the K2O / S1O2 ratio exceeds 10%, it has been confirmed that the dispersibility of colloidal silica deteriorates, resulting in an uneven appearance after baking.

[0034] 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 K2O / SiO2 ratio in the colloidal silica to 0.5% or more and 10% or less, thereby promoting an insulating coating formation reaction.

[0035] As mentioned above, this experiment was based on the idea that adding potassium hydroxide to colloidal silica could lower the crystallization temperature of the colloidal silica; however, in the present experiment, no change in crystallization temperature was observed when potassium 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 the colloidal silica, but rather to a factor: the addition of potassium itself improves moisture absorption resistance. Method for Producing Liquid Insulating Coating for Grain Oriented Electrical Steel Sheet

[0036] This section describes the configuration of the method for producing 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.

[0037] 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. Petition 870250083133, dated 09 / 16 / 2025, page 16 / 39 11 / 24 to mix the colloidal silica and metallic phosphate.

[0038] In the adjustment process, a K compound is added to the colloidal silica to adjust the K2O / SiO2 ratio. The mass percentage ratio between the amount of K2O and the amount of SiO2 in the colloidal silica should be 0.5% or more and 10% or less. If the K2O / 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 K2O / SiO2 ratio exceeds 10%, the dispersibility of the colloidal silica deteriorates, resulting in an inferior appearance after baking. The K2O / SiO2 ratio is preferably 1% or more, more preferably 3% or more, and even more preferably 5% or more. The K2O / SiO2 ratio is preferably 8% or less, more preferably 7% or less, and even more preferably 6% or less.

[0039] There is no specific limitation as to the method of adjusting the K2O / SiO2 ratio of colloidal silica to 0.5% or more and 10% or less; however, for example, a method of pre-adding potassium hydroxide and / or potassium chloride to 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 colloidal silica, it is preferable to add potassium hydroxide. It is also possible to add potassium permanganate to colloidal silica beforehand. However, potassium permanganate is a strong oxidizing agent and is highly reactive, therefore its use is not preferable from a safety point of view. Therefore, it is preferable to exclude potassium permanganate as a K compound.

[0040] The size of the colloidal silica (silica particles) used in the present embodiment is not particularly limited; however, the average particle diameter (average diameter of the primary particle) is, Petition 870250083133, dated 09 / 16 / 2025, p. 17 / 39 Ideally, the average particle size should be 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. Conversely, 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, reducing adhesion, which is undesirable.

[0041] It is even 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 (average primary particle diameter) of colloidal silica can be determined, for example, by converting the specific surface area measured by the BET adsorption method (according to JIS Z8830).

[0042] 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, once these phosphates are selected, a level and uniform appearance can be obtained under a wide variety of baking conditions. In the mixing process, it is preferable not to actively add chromates, taking into account the issues surrounding the process. Petition 870250083133, dated 09 / 16 / 2025, page 18 / 39 13 / 24 biennial.

[0043] 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 K2O / 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.

[0044] 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. 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 solids content relative to the total mass of the insulating coating treatment liquid.The colloidal silica content in the insulating coating treatment liquid is, most 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.

[0045] 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 coating Petition 870250083133, dated 09 / 16 / 2025, page 19 / 39 14 / 24 phosphate content. Therefore, the metallic phosphate content in the insulating coating treatment liquid in terms of H2PO4 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.

[0046] 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.

[0047] 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 insulating coating treatment liquid, in terms of CrOs, should preferably be 0.1% by mass or less of the total mass of the insulating coating treatment liquid in terms of solids content.

[0048] In the above mixing process, a compound containing Si and / or K may be additionally mixed in. In this case, however, the K2O / SiO2 ratio contained in the insulating coating treatment liquid after mixing is preferably 0.5% or more and 10% or less.

[0049] In the method for producing an insulating coating treatment liquid according to the present embodiment, the analysis of the K2O / SiO2 ratio in colloidal silica is carried out as follows Petition 870250083133, dated 09 / 16 / 2025, page 20 / 39 15 / 24 form. The amount of K contained in colloidal silica is measured by atomic absorption spectrophotometry and converted to the amount of K2O. The amount of Si contained in colloidal silica is determined by an elemental analysis method, such as ICP, and converted to the amount of SiO2. Then, the K2O / SiO2 ratio can be calculated from the obtained amounts of K2O and SiO2 and expressed as a percentage. Method for Producing Grain-Oriented Electrical Steel Sheet

[0050] The following is a method for producing a grain-oriented electrical steel sheet according to the present embodiment. 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.

[0051] In the method for producing a grain-oriented electrical steel sheet according to the present embodiment, the steel sheet on which the insulating coating is formed 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 surface of the steel sheet 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 coating treatment liquid Petition 870250083133, dated 09 / 16 / 2025, page 21 / 39 16 / 24 insulation is then subjected to a baking process under the conditions described below to form an insulating coating on the surface.

[0052] 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.

[0053] The immersion holding time (seconds) indicates the holding time at the immersion temperature during baking. 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. Conversely, 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. Petition 870250083133, dated 09 / 16 / 2025, page 22 / 39 17 / 24 and reduce coating tension. The immersion holding time is preferably 45 seconds or less to achieve the necessary and sufficient coating properties.

[0054] 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.

[0055] 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 making it possible to obtain 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 an oriented grain electrical steel sheet containing at least C: 0.005% or less and Si: 2.5 to 7.0% by mass and optionally also 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 8o or less between the crystal orientation (110)

[001] and the rolling direction.

[0056] Although there is no specific limit to the amount of insulation coating on electrical steel sheet Petition 870250083133, dated 09 / 16 / 2025, page 23 / 39 18 / 24 oriented grain produced by means of the method of producing oriented grain electrical steel sheet according to the present embodiment, a coating quantity of 2.0 to 7.0 g / m2 is suitable. If the coating quantity of the insulating sheath is less than 2.0 g / m2, it becomes difficult to impart high voltage to the oriented grain electrical steel sheet, and the insulation properties and corrosion resistance of the oriented grain electrical steel sheet may also deteriorate, which is undesirable. On the other hand, if the coating quantity of the insulating sheath is greater than 7.0 g / m2, the space factor of the oriented grain electrical steel sheet may decrease, resulting in the deterioration of the transformer characteristics, which is undesirable. The coating quantity of the insulating sheath 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

[0057] 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 examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to such examples of 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.

[0058] A plate containing, in mass %, C: 0.082%, Si: 3.25%, 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 sheet of Petition 870250083133, dated 09 / 16 / 2025, page 24 / 39 Hot-rolled 19 / 24 steel 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.

[0059] 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.

[0060] 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. Table 1 Treatment Liquid No. Insulating Coating Treatment Liquid Metallic Phosphate Colloidal Silica Chromate Inorganic Compound Metal Metal Proportion (molar ratio) Content (% by mass sa) K2O / SiO2 Ratio (%) Content (% by mass sa) Amount of SiO2 (% by mass) Amount of Na2O (% by mass) Amount of K2O (% by mass) Content (% by mass) Type Content (% by mass) A1 Al 100 74.8 0.5 25.2 25.0 0.08 0.13 - - - A2 Al 100 72.4 2 27.6 27.0 0.09 0.54 - - - A3 Al 100 63.8 3 36.2 35.0 0.14 1.1 - - - A4 Al 100 52.6 5 47.4 45.0 0.19 2.3 - - - A5 Al 100 46.8 6 53.2 50.0 0.23 3.0 - - - A6 Al 100 37.2 8 62.8 58.0 0.19 4.6 - - - A7 Al 100 28.3 10 71.7 65.0 0.21 6.5 - - - A8 Al 100 47.4 5 50.6 48.0 0.20 2.4 - Boric acid 2.0 Petition 870250083133, dated 09 / 16 / 2025, page 25 / 39 20 / 24 Insulating Coating Treatment Liquid Treatment Liquid No. Metal Phosphate Colloidal Silica Chromate Inorganic Compound Metal Metal Proportion (molar ratio) Content (% by mass sa) K2O / SiO2 Ratio (%) Content (% by mass sa) Amount of SiO2 (% by mass) Amount of Na2O (% by mass) Amount of K2O (% by mass) Content (% by mass) Type Content (% by mass) Borate A9 Al 100 47.4 5 50.6 48.0 0.18 2.4 - 2.0 Sodium Oxide A10 Al 100 47.4 5 50.6 48.0 0.17 2.4 - 2.0 Titanium Oxide A11 Al 100 47.5 5 50.5 48.0 0.14 2.4 Molybdenum Titana- 2.0 A12 Al 100 47.4 5 50.6 48.0 0.18 2.4 - to 2.0 Al / Fe barium A13 80 / 20 49.4 5 50.6 48.0 0.20 2.4 - - - A14 Al / Mg 80 / 20 49.4 5 50.6 48.0 0.18 2.4 - - - A15 Al / Mn 80 / 20 49.4 5 50.6 48.0 0.17 2.4 - - - A16 Al / Ni 80 / 20 49.4 5 50.6 48.0 0.22 2.4 - - - A17 Al / Zn 80 / 20 49.4 5 50.6 48.0 0.20 2.4 - - - A18 Al / Co 80 / 20 49.4 5 50.6 48.0 0.20 2.4 - - - A19 Al / Mo 80 / 20 49.4 5 50.6 48.0 0.18 2.4 - - - A20 Al / V 80 / 20 49.4 5 50.6 48.0 0,21 2.4 - - - A21 Al / W 80 / 20 49.4 5 50.6 48.0 0.18 2.4 - - - A22 Al / Zr 80 / 20 49.4 5 50.6 48.0 0.20 2.4 - - - a1 Al 100 51.6 0.4 48.4 48.0 0.22 0.20 - - - a2 Al 100 46.1 12 53.9 48.0 0.15 5.8 - - - a3 Al 100 41.7 0.2 48.3 48.0 0.16 0.10 10.0 - -, Petition 870250083133, dated 09 / 16 / 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

[0061] 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

[0062] 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.

[0063] The results of these evaluations are presented in the Tables Petition 870250083133, dated 09 / 16 / 2025, page 27 / 39 22 / 24 beautiful 3 to 5. Table 3 Test No. Treatment Liquid No. Production Method No. Property Evaluation Moisture Absorption Amount (g / m2) Appearance after cooking C1 A1 B5 0.96 good C2 A2 B5 0.41 good C3 A3 B5 0.06 good C4 A4 B5 0.04 very good C5 A5 B5 0.04 very good C6 A6 B5 0.05 good C7 A7 B5 0.04 good C8 A8 B5 0.05 very good C9 A9 B5 0.06 very good C10 A10 B5 0.05 very good C11 A11 B5 0.04 very good Example of the Invention C12 A12 B5 0.05 very good C13 A13 B5 0.05 very good C14 A14 B5 0.04 very good C15 A15 B5 0.05 very good C16 A16 B5 0.06 very good C17 A17 B5 0.05 very good C18 A18 B5 0.04 very good C19 A19 B5 0.06 very good C20 A20 B5 0.04 very good C21 A21 B5 0.05 very good C22 A22 B5 0.05 very good c1 a1 B5 1.10 good c2 a2 B5 0.03 bad Comparative Example c3 a3 B5 0.01 good Petition 870250083133, dated 09 / 16 / 2025, pp. 28 / 39 23 / 24 Table 4 Test No. Treatment Liquid No. Production Method No. Property Evaluation Moisture Absorption Amount (g / m2) Appearance after cooking D1 A4 B1 0.07 good D2 A4 B2 0.04 good D3 A4 B3 0.82 good Example of the Invention D4 A4 B4 0.04 good D5 A4 B5 0.03 very good D6 A4 B6 0.04 very good D7 A4 B7 0.03 good d1 A4 b1 1.29 good d2 A4 b2 0.04 poor Example d3 A4 b3 1.41 good Comparative d4 A4 b4 0.05 poor 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) K2O / SiO2 Ratio (%) Average Particle Diameter (nm) Content (% by mass) SiO2 Amount (% by mass) Na2O Amount (% by mass) K2O Amount (% by mass) E1 E2 E3 E4 E5 E6 B5 Al 49.4 5 4 50.6 48.0 0.21 2.4 - 0.04 very good Example of the Invention B5 Al 49.4 5 12 50.6 48.0 0.22 2.4 - 0.05 very good B5 Al 49.4 5 18 50.6 48.0 0.20 2.4 - 0.04 good B5 Al 49.4 5 22 50.6 48.0 0.21 2.4 - 0.03 good B5 Al 49.4 5 31 50.6 48.0 0.22 2.4 - 0.05 good B6 Al 49.4 5 35 50.6 48.0 0.20 2.4 - 0.04 good

[0064] As can be seen in Tables 3 to 5, in the examples of the invention, the method for producing the insulating coating treatment liquid met the specified ranges of the present invention. Petition 870250083133, dated 09 / 16 / 2025, pp. 29 / 39 24 / 24 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.

[0065] 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

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 K compound is added to colloidal silica to adjust the K2O / SiO2 ratio in % by mass between the amount of K in terms of K2O 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 having the adjusted K2O / 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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