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

Abstract

Provided is an insulation coating treatment liquid for a grain-oriented electromagnetic steel sheet, the insulation coating treatment liquid containing a phosphoric acid metal salt of one or two or more metals selected from among Na, Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, and colloidal silica, wherein the Na2O / SiO2 ratio of the Na amount in mass % in terms of Na2O and the Si amount in mass % in terms of SiO2 in the insulation coating treatment liquid is 0.5% to 10%.

Description

1 / 26 INSULATING COATING TREATMENT LIQUID FOR GRAIN-ORIENTED ELECTRICAL STEEL SHEET, METHOD FOR PRODUCING THE SAME, AND METHOD FOR PRODUCING GRAIN-ORIENTED ELECTRICAL STEEL SHEET TECHNICAL FIELD

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

[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 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.

[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 870250082303, dated 12 / 09 / 2025, page 7 / 42 2 / 26 Phosphate can 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 870250082303, dated 12 / 09 / 2025, page 8 / 42 3 / 26 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 consisting 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 870250082303, dated 12 / 09 / 2025, page 9 / 42 4 / 26 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 metallic elements having a valence of tetravalent or more.

[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 870250082303, dated 12 / 09 / 2025, page 10 / 42 5 / 26 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 to steel sheets. However, the inventors' research to date has shown 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 870250082303, dated 12 / 09 / 2025, page 11 / 42 6 / 26

[0019] The present invention was made to solve the aforementioned problems and its objectives are to provide 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 a method for producing the same and to provide a method for producing a grain-oriented electrical steel sheet by applying the aforementioned insulating coating treatment liquid. Solution to the Problem

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

[0021] (1) An insulating coating treatment liquid for a grain-oriented electrical steel sheet according to an embodiment of the present invention includes metal phosphate of one or more metals selected from Na, Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr and colloidal silica, wherein the Na2O / SiO2 ratio in % by mass between the amount of Na in terms of Na2O and the amount of Si in terms of SO in the insulating coating treatment liquid is 0.5% or more and 10% or less.

[0022] (2) A method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet according to another embodiment of the present invention includes: an addition process in which a Na compound is added to metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr, and a mixing process in which colloidal silica and metal phosphate with the added Na compound are mixed to form a 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 insulating coating treatment liquid of 0.5% or more and 10%. Petition 870250082303, dated 12 / 09 / 2025, page 12 / 42 7 / 26 or less.

[0023] (3) 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 a 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 an electrically oriented grain steel sheet as 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

[0024] 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 DRAWING

[0025] Figure 1 shows the relationship between the Na2O / SiO2 ratio of the insulating coating treatment liquid and the amount of moisture absorption. DESCRIPTION OF THE MODALITIES

[0026] The results of the preliminary experiments that led to the present invention are described below.

[0027] 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 spacer adhered to the surface. Petition 870250082303, dated 12 / 09 / 2025, page 13 / 42 8 / 26 was removed by washing and the resulting sheets were used as base metals. Then, 1 to 20 parts by mass of sodium phosphate were added to 100 parts by mass of primary aluminum phosphate and then mixed with 70 parts by mass of colloidal silica to prepare 10 types of insulating coating treatment liquid. In this way, the Na2O / SiO2 ratio in the insulating coating treatment liquid was adjusted within a range of 0.6 to 10%. 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 insulating coating treatment liquid, respectively, and by dividing the amount of Na2O by the amount of SiO2.

[0028] Next, the insulating coating treatment liquid was applied to both sides of the base metals prepared above using a roller coating machine, so that the amount of coating after baking was 4.5 g / m2 per side. Then, the metals were baked at a temperature of 850°C for 30 seconds.

[0029] For comparison, an insulating coating treatment liquid (Na2O / SO2 ratio = 0.8%) consisting of 50 parts by mass of primary aluminum phosphate containing no Na, 40 parts by mass of colloidal silica and 10 parts by mass of chromic anhydride was applied similarly to the base metal and baked.

[0030] 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 870250082303, dated 12 / 09 / 2025, page 14 / 42 9 / 26 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.

[0031] 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.

[0032] However, in regions where the Na2O / SiO2 ratio is high, especially where the Na2O / SiO2 ratio is 0.5% or more, moisture absorption is 1.0 g / m2 or less. 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 chromium-coated sheet steel is exhibited. 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 foregoing, the present inventors considered the mechanism by which the Na2O / SiO2 ratio in a non-chromium insulating coating affects moisture absorption resistance as follows.

[0034] Na2O is known as a Lattice Modifier: NWM that significantly alters the properties of glass when incorporated Petition 870250082303, dated 12 / 09 / 2025, page 15 / 42 10 / 26 rado a vidros como a phosphate. It is believed that the Na compound has the property of softening the glass, but it is believed that sodium strengthens the phosphate network structure, significantly improving resistance to moisture absorption.

[0035] Based on the experimental results above, 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 insulating coating treatment liquid to 0.5% or more and 10% or less, thereby strengthening the phosphate network structure that constitutes the insulating coating. Liquid Insulating Coating for Grain Oriented Electrical Steel Sheet

[0036] This section describes the configuration of 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.

[0037] The insulating coating treatment liquid of the present embodiment includes metal phosphate of one or more metals selected from Na, Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr and colloidal silica. 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, when these phosphates are selected, a level and uniform appearance can be obtained under a wide variety of baking conditions. As described below, it is preferable to add sodium phosphate as a Na compound and, therefore, the insulating coating treatment liquid of the present embodiment preferably contains a Na metal phosphate. Petition 870250082303, dated 12 / 09 / 2025, page 16 / 42 11 / 26

[0038] The Na2O / SiO2 ratio in the insulating coating treatment liquid of the present embodiment is 0.5% or more and 10% or less. If the Na2O / SiO2 ratio is less than 0.5%, the effect of strengthening the phosphate network structure that constitutes the insulating coating is small, resulting in insufficient moisture absorption resistance. On the other hand, if the Na2O / SiO2 ratio exceeds 10%, the appearance after baking deteriorates. The Na2O / SiO2 ratio is preferably 1% or more, more preferably 3% or more, and even 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.

[0039] In the present embodiment, the analysis of the Na2O / SiO2 ratio in the insulating coating treatment liquid is performed as follows. The amount of Na contained in the insulating coating treatment liquid is measured by atomic absorption spectrophotometry and converted to the amount of Na2O. The amount of Si contained in the insulating coating treatment liquid 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 Insulating Coating Treatment Liquid for Grain-Oriented Electrical Steel Sheet

[0040] This section describes the configuration of the method for producing an insulating coating treatment liquid according to the present embodiment and the reasons for its limitations.

[0041] The method for producing an insulating coating treatment liquid of the present embodiment includes an addition process for adding a Na compound to the metal phosphate and a mixing process for mixing the colloidal silica and the metal phosphate. Petition 870250082303, dated 12 / 09 / 2025, page 17 / 42 12 / 26

[0042] In the addition process, a Na compound is added to the metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr. It is preferable to add sodium phosphate as a Na compound.

[0043] One possible method for adding Na to the insulating coating treatment liquid is to add a Na compound beforehand to the colloidal silica. However, adding a Na compound to colloidal silica carries the risk of colloidal silica clumping. Therefore, in the present embodiment's method for producing an insulating coating treatment liquid, a Na compound is added beforehand to the metal phosphate.

[0044] In the mixing process, colloidal silica and metallic phosphate with the Na compound added during the addition process are mixed. Then, the Na2O / SiO2 ratio in % by mass between the amount of Na2O and the amount of SO2 in the insulating coating treatment liquid is adjusted to 0.5% or more and 10% or less. The reason why the Na2O / SiO2 ratio is set within the above range is as described above and therefore will not be repeated in this document.

[0045] Furthermore, provided that the Na2O / SO2 ratio of the insulating coating treatment liquid is within the above range, a compound containing Si and / or Na may be added later in the mixing process. For example, a Na compound may be added prior to the colloidal silica. In this case, for example, a method of prior addition of sodium hydroxide and / or sodium chloride to the colloidal silica may be used. In the mixing process, it is preferable not to actively add chromates, considering environmental concerns.

[0046] 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 870250082303, dated 12 / 09 / 2025, page 18 / 42 13 / 26 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 its adhesion, 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, reducing adhesion, which is undesirable.

[0047] 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 (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).

[0048] 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 insulating coating treatment liquid is 0.5% or more and 10% or less, the insulating coating of a 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. Petition 870250082303, dated 12 / 09 / 2025, page 19 / 42 14 / 26

[0049] 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.

[0050] Furthermore, the insulating coating treatment liquid according to the present embodiment consists mainly 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.

[0051] 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 coating treatment liquid Petition 870250082303, dated 12 / 09 / 2025, page 20 / 42 15 / 26 insulation 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.

[0052] 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 CrO3, should preferably be 0.1% by mass or less of the total mass of the insulating coating treatment liquid in terms of solids content. Method for Producing Grain-Oriented Electrical Steel Sheet

[0053] 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. Through baking, an insulating coating is formed.

[0054] 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 electrical steel sheet Petition 870250082303, dated 12 / 09 / 2025, page 21 / 42 16 / 26 grain-oriented steel is pickled in a sulfuric acid bath or similar and then rinsed with 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.

[0055] 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.

[0056] 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 absorption of Petition 870250082303, dated 12 / 09 / 2025, page 22 / 42 17 / 26 humidity may increase). The immersion holding time is ideally 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 can cause cracking and reduce the coating's tensile strength. The immersion holding time is preferably 45 seconds or less to achieve the necessary and sufficient coating properties.

[0057] 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 resistance to moisture absorption, even without the addition of chromate, can be achieved regardless of the type of steel sheet.

[0058] Preferably, the above-mentioned 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 a grain-oriented 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%, Petition 870250082303, dated 12 / 09 / 2025, page 23 / 42 18 / 26 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.

[0059] Although there is no specific limit to the amount of insulating sheathing of the grain-oriented electrical steel sheet produced by the method of producing a grain-oriented electrical steel sheet 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 apply 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

[0060] Next, the effects of one embodiment of the present invention will be described in more concrete detail by means of examples. The conditions presented in the examples are exemplary conditions adopted 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 Petition 870250082303, dated 12 / 09 / 2025, p. 24 / 42 19 / 26 achieve the objective of the present invention.

[0061] A plate containing, in % by mass, C: 0.082%, Si: A sheet of steel, composed of 3.25% iron, 0.084% Mn, 0.026% Al solution, 0.0088% N, 0.008% P, and 0.023% S, with the remainder being iron 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 required 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 decarburization 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.

[0062] 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.

[0063] 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. Note that the amount of Na2O in the metal phosphate was adjusted by adding sodium phosphate. Table 1 Liquid of Insulating Coating Treatment Liquid Metallic Phosphate Colloidal Silica Chromate Inorganic Compound Ratio Petition 870250082303, dated 12 / 09 / 2025, page 25 / 42 20 / 26 Treatment No. Metal Proportion of metal (molar ratio) Content (% by mass) Amount of Na? (% by mass) Content (% by mass) Amount of SiO2 (% by mass) Amount of Na2O (% by mass) Content (% by mass) Type Content (% by mass) Na2Q / SiO2 (%) A1 Al 100 71.9 0.04 28.1 28.0 0.10 - - - 0.5 A2 Al 100 73.6 0.12 26.4 26.0 0.40 - - - 2 A3 Al 100 73.7 0.48 26.3 26.0 0.30 - - - 3 A4 Al 100 51.8 2.2 48.2 48.0 0.20 - - - 5 A5 Al 100 39.6 2.6 60.4 60.0 0.40 - - - 5 A6 Al 100 33.7 2.8 66.3 66.0 0.30 - - - 5 A7 Al 100 69.8 1.6 30.2 30.0 0.20 - - - 6 A8 Al 100 68.5 2.3 31, 31.3 0.20 - - - 8 A9 Al 100 67.8 3.0 32.2 32.0 0.20 - Acid - 10 A10 Al 100 53.8 2.0 44.2 44.0 0.20 Borate 2.0 5 A11 Al 100 53.8 2.0 44.2 44.0 0.20 - Sodium Oxide 2.0 5 A12 Al 100 53.8 2.0 44.2 44.0 0.20 - Titanium Oxide 2.0 5 A13 Al 100 53.8 2.0 44.2 44.0 0.20 - Molybdenum 2.0 5 Petition 870250082303, dated 12 / 09 / 2025, p. 26 / 42 21 / 26 A14 Al 100 80 / 53.8 2.0 44.2 44.0 0.20 - Barium Titanate 2.0 5 Al / A15 Fe 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A16 Al Mg / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A17 Al Mn / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A18 Al Ni / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A19 Al Zn / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A20 Al Co / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A21 Al Mo / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A22 Al V / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A23 Al W / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 A24 Al Zr / 80 / 20 51.8 2.2 48.2 48.0 0.20 - - - 5 a1 Al 100 67.4 0.03 32.6 32.5 0.10 - - - 0.4 a2 Al 100 64.5 3.7 35.5 35.0 0.50 - - - 12 a3 Al 100 60.0 0.01 30.1 30.0 0.05 10.0 - - 0.2 Table 2 Production Method No. Cooking Process Immersion Temperature Holding Time (°C) (s) B1 800 30 B2 1000 30 Petition 870250082303, dated 12 / 09 / 2025, page 27 / 42 22 / 26 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 Moisture Absorption Quantity

[0064] 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

[0065] 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.

[0066] The results of these evaluations are presented in Tables 3 to 5. Table 3 Liquid Test Method Property Evaluation Petition 870250082303, dated 12 / 09 / 2025, page 28 / 42 23 / 26 Treatment No. Production No. Moisture Absorption Amount Appearance after cooking (g / m2) C1 A1 B5 0.96 good Example of the Invention C2 A2 B5 0.58 good C3 A3 B5 0.32 good C4 A4 B5 0.03 very good C5 A5 B5 0.03 very good C6 A6 B5 0.04 very good C7 A7 B5 0.05 very good C8 A8 B5 0.04 good C9 A9 B5 0.06 good C10 A10 B5 0.04 very good C11 A11 B5 0.05 very good C12 A12 B5 0.04 very good C13 A13 B5 0.06 very good C14 A14 B5 0.04 very good C15 A15 B5 0.03 very good C16 A16 B5 0.04 very good good C17 A17 B5 0.06 very good C18 A18 B5 0.03 very good C19 A19 B5 0.04 very good C20 A20 B5 0.05 very good C21 A21 B5 0.04 very good C22 A22 B5 0.03 very good C23 A23 B5 0.04 very good C24 A24 B5 0.06 very good c1 a1 B5 1.18 good Comparative Example c2 a2 B5 0.02 bad c3 a3 B5 0.01 good Petition 870250082303, dated 12 / 09 / 2025, page 29 / 42 24 / 26 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 0.03 good Example of Invention D3 A4 B3 0.78 good D4 A4 B4 0.04 good D5 A4 B5 0.05 very good D6 A4 B6 0.04 very good D7 A4 B7 0.05 good d1 A4 b1 1.31 good Example d2 A4 b2 0.04 bad d3 A4 b3 1.42 good Comparative d4 A4 b4 0.05 bad Petition 870250082303, dated 12 / 09 / 2025, pages 30 / 42 Table 5 Test No. Production Method No. Insulating Coating Treatment Liquid Property Evaluation Metal Phosphate Colloidal Silica Chromate Na2O / SiO2 Ratio (%) Moisture Absorption Amount (g / m2) Appearance after Baking Metal Content (% by mass) Na2O Amount (% by mass) Average Particle Diameter (nm) Content (% by mass) SiO2 Amount (% by mass) Na2O Amount (% by mass) E1 B5 Al 51.8 2.2 4 48.2 48.0 0.21 - 5 0.04 very good Example of the Invention E2 B5 Al 51.8 2.2 12 48.2 48.0 0.22 - 5 0.05 very good E3 B5 Al 51.8 2.2 18 48.2 48.0 0.20 - 5 0.04 good E4 B5 Al 51.8 2.2 22 48.2 48.0 0.21 - 5 0.05 good E5 B5 Al 51.8 2.2 31 48.2 48.0 0.22 - 5 0.06 good E6 B6 Al 51.8 2.2 35 48.2 48.0 0.20 - 5 0.05 good 25 / 26 Petition 870250082303, dated 12 / 09 / 2025, pp. 31 / 42 26 / 26

[0067] As can be seen in Tables 3 to 5, in the examples of the invention, the insulating coating treatment liquid 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 example of the invention exhibited good resistance to moisture absorption and excellent coating appearance.

[0068] In contrast, in the comparative examples, at least one item in the 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. Petition 870250082303, dated 12 / 09 / 2025, pages 32 / 42

Claims

1 / 2 CLAIMS 1. Insulating coating treatment liquid for a grain-oriented electrical steel sheet, characterized in that it comprises: metallic phosphate of one or more metals selected from Na, Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr and colloidal silica, wherein 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 insulating coating treatment liquid is 0.5% or more and 10% or less.

2. A method for producing an insulating coating treatment liquid for a grain-oriented electrical steel sheet, characterized in that it comprises: an addition process in which a Na compound is added to the metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr, and a mixing process in which the colloidal silica and the metal phosphate with the added Na compound are mixed to form a Na2O / SiO2 ratio in % by mass between an amount of Na in terms of Na2O and an amount of Si in terms of SO2 in the insulating coating treatment liquid of 0.5% or more and 10% or less.

3. 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, 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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