Insulating coating treatment solution for grain-oriented electrical steel sheet and method for manufacturing 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

[Technical Field]

[0001] The present invention relates to a method for producing an insulating coating solution for grain-oriented electrical steel sheets, and a method for producing grain-oriented electrical steel sheets using the insulating coating solution produced by the method. [Background technology]

[0002] Grain-oriented electrical steel sheets are steel sheets that are primarily used as iron cores for transformers, etc. Such grain-oriented electrical steel sheets typically have two surface coating layers: a forsterite layer (also called a primary coating) that is formed during high-temperature finish annealing, and a phosphate coating that is formed by applying a treatment solution containing phosphate as the main component and then baking it during heat flattening of the steel sheet.

[0003] Phosphate coatings are required to provide grain-oriented electrical steel sheets with electrical insulation and to reduce eddy current loss and improve core loss. Phosphate coatings are also required to have various other properties in addition to insulation, such as corrosion resistance, heat resistance, slipperiness, and adhesion. This is necessary to facilitate various manufacturing processes when grain-oriented electrical steel sheets are processed into iron cores for transformers and other devices. For example, if the heat resistance, slipperiness, and adhesion of a phosphate coating are poor, the phosphate coating may peel off during stress relief annealing in the manufacturing of the iron core, preventing the phosphate coating from exhibiting its inherent insulating properties or hindering smooth lamination of steel sheets, resulting in poor workability.

[0004] Furthermore, an important characteristic of the insulating coating of grain-oriented electrical steel sheets is the ability to apply tension to the steel sheets. Applying tension to steel sheets facilitates domain wall motion, thereby improving the iron loss of grain-oriented electrical steel sheets. Applying tension can also reduce magnetostriction (one of the main causes of noise in transformers).

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

[0006] For example, Patent Document 1 discloses that an insulating coating treatment solution containing a specific composition of aluminum phosphate, chromate, and colloidal silica as its main components is applied to a forsterite coating formed on the surface of a steel sheet after finish annealing, and then baked. The technology disclosed in Patent Document 1 allows an insulating coating with high tensile strength to be formed on the surface of the steel sheet, thereby reducing the iron loss and magnetostriction of the grain-oriented electrical steel sheet.

[0007] Patent Document 2 discloses a method in which a treatment solution containing ultrafine colloidal silica particles with a particle size of 8 μm or less, primary phosphate, and chromate in specific proportions is applied to a steel sheet and then baked. The technology disclosed in Patent Document 2 makes it possible to maintain the high tensile strength of the insulating coating and further improve the lubricity of the coating.

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

[0009] The techniques disclosed in Patent Documents 1 to 3 above made it possible to form insulating coatings with significantly superior coating properties and improved coating tension. However, all of the techniques disclosed in Patent Documents 1 to 3 contain chromate, a chromium compound, in the insulating coating. In recent years, with increasing attention being paid to environmental issues, there has been a social demand to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0010] Therefore, research has been conducted into technologies that can form good insulating coatings without containing the above-mentioned chromium compounds. However, the problem with insulating coatings that do not contain chromium compounds is that they do not impart sufficient tension to the steel sheet.

[0011] As a method for solving the above-mentioned problems, for example, Patent Document 4 discloses a method for treating an insulating coating on a grain-oriented electrical steel sheet, which involves baking at 300°C or higher a treatment solution containing 20 parts by weight of colloidal silica (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 sulfates selected from the group consisting of sulfates of Mg, Al, Fe, Co, Ni, and Zn.

[0012] Furthermore, Patent Document 5 discloses a technology relating to a coating agent for forming a film that contains a mixture of boric acid and alumina sol and an organic solvent that is compatible with water, and that has the effect of imparting tension to grain-oriented electrical steel sheets.

[0013] Patent Document 6 discloses a technology in which a surface treatment agent for grain-oriented electrical steel sheet contains primary phosphates of Al, Mg, and Ca and colloidal silica, and further contains one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al. Patent Document 6 also lists formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as examples of organic acid salts.

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

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

[0016] Furthermore, Patent Document 9 discloses an aqueous composition for coating grain-oriented electrical steel, which contains aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and / or phosphate anions, colloidal silicon dioxide, and optionally iron cations. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 48-39338 [Patent Document 2] Japanese Patent Publication No. 61-41778 [Patent Document 3] Japanese Patent Application Publication No. 11-071683 [Patent Document 4] Japanese Patent Application Publication No. 54-143737 [Patent Document 5] Japanese Patent Application Publication No. 7-278828 [Patent Document 6] Japanese Patent Application Laid-Open No. 2000-178760 [Patent Document 7] Japanese Patent Application Laid-Open No. 2010-13692 [Patent Document 8] International Publication No. 2017 / 057513 [Patent Document 9] Special Publication No. 2022-519691 Summary of the Invention [Problem to be solved by the invention]

[0018] These proposals have improved the application of tension to steel sheets. However, previous research by the present inventors has revealed that insulation coatings that do not contain chromium compounds also suffer from poor moisture absorption resistance. None of the above techniques has achieved the same level of moisture absorption resistance as conventional coatings containing chromic acid, and there is still room for improvement.

[0019] The insulating coating of grain-oriented electrical steel sheets must be able to apply a large tension to the surface of the steel sheet, and must also have good moisture absorption resistance and good productivity.

[0020] The present invention has been made to solve the above problems, and has an object to provide a method for producing an insulating coating treatment solution for grain-oriented electrical steel sheets that has good moisture absorption resistance and good productivity even when it does not contain chromate, and a method for producing grain-oriented electrical steel sheets that uses the insulating coating treatment solution produced by this method. [Means for solving the problem]

[0021] The gist of the present invention is as follows.

[0022] (1) A method for producing an insulating coating treatment solution for grain-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of: adding a Na compound to colloidal silica to adjust the NaO / SiO ratio, in mass %, of the amount of Na in terms of NaO and the amount of Si in terms of SiO in the colloidal silica to 0.5% or more and 10% or less; and mixing the colloidal silica having the adjusted NaO / SiO ratio with a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr.

[0023] (2) Another embodiment of the present invention provides a method for producing grain-oriented electrical steel sheet, comprising: a coating step of applying an insulating coating treatment liquid to the surface of a steel sheet; and a baking step of baking the insulating coating treatment liquid to form an insulating coating, wherein the insulating coating treatment liquid is an insulating coating treatment liquid for grain-oriented electrical steel sheet produced by the method described in (1) above, and the baking soaking temperature in the baking step is 800 to 1000°C, and the soaking holding time is 10 to 60 seconds. [Effects of the Invention]

[0024] According to the present invention, grain-oriented electrical steel sheets having excellent moisture absorption resistance and productivity can be stably obtained. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram showing the relationship between the Na2O / SiO2 ratio of colloidal silica and the amount of moisture absorption. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present inventors have investigated methods for improving the moisture absorption resistance of insulating coatings that do not contain chromium compounds. First, they wondered whether the moisture absorption resistance could be improved by adjusting the crystallization temperature of colloidal silica. Here, it is known that the crystallization temperature of colloidal silica can be lowered by adding sodium hydroxide to colloidal silica.

[0027] Therefore, the inventors evaluated the moisture absorption resistance of an insulating coating using colloidal silica to which sodium hydroxide had been added in advance. For comparison, a similar study was also conducted on a case in which sodium chloride had been added.

[0028] The results of the preliminary experiments that led to the present invention will now be described.

[0029] A 0.23 mm thick grain-oriented electrical steel sheet that had been finish-annealed and manufactured by a known method was sheared to a width of 60 mm and a length of 300 mm. The annealing separator adhering to the surface was removed by rinsing with water, and the resulting sheet was used as the base material. Next, sodium hydroxide or sodium chloride was added to the colloidal silica, and the Na2O / SiO2 ratio in the colloidal silica was adjusted to fall within the range of 0.2 to 11%, producing 11 types of colloidal silica. The "Na2O / SiO2 ratio" is the percentage (%) obtained by quantifying the amount of Na in terms of Na2O (hereinafter referred to as "Na2O amount," unit: mass%) and the amount of Si in terms of SiO2 (hereinafter referred to as "SiO2 amount," unit: mass%) contained in the colloidal silica, and then dividing the Na2O amount by the SiO2 amount.

[0030] Then, an insulating coating solution consisting of 60 parts by mass of primary aluminum phosphate and 40 parts by mass of colloidal silica was applied to the previously prepared base material so that the coating amount after firing was 4.5 g / m per side. 2 The coating was applied to both sides using a roll coater so that the coating was as follows: Then, the coating was baked at a temperature of 850°C for 30 seconds.

[0031] For comparison, an insulating coating solution 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 similarly applied to the base material and baked.

[0032] The obtained steel sheet was used as a test piece to evaluate moisture absorption resistance. First, the test piece was placed in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week, and the weight difference before and after constant temperature and humidity was quantified. The quantified weight difference was then compared to the area of ​​both sides of the test piece (0.036 m). 2 The moisture absorption amount (unit: g / m 2 ) and the moisture absorption resistance was evaluated using the moisture absorption amount as an index.

[0033] The relationship between the moisture absorption amount and the Na2O / SiO2 ratio based on the above evaluation results is summarized in Figure 1. As shown in Figure 1, the moisture absorption amount of the steel sheet with a chromium-containing coating was 0.1 g / m2, even though the Na2O / SiO2 ratio was small. 2 In contrast, in the case of steel sheets coated with a chromium-free coating, the moisture absorption amount was 1.0 g / m in the region where the Na2O / SiO2 ratio was less than 0.5%. 2 However, in the region where the Na2O / SiO2 ratio is large, especially in the region where the Na2O / SiO2 ratio is 0.5% or more, the moisture absorption amount is 1.0 g / m3 regardless of whether sodium hydroxide or sodium chloride is used. 2Furthermore, when the Na2O / SiO2 ratio was 5.0% or more, there was almost no moisture absorption, and the same excellent moisture absorption resistance as steel sheets coated with a chromium-containing coating was obtained. On the other hand, when the Na2O / SiO2 ratio exceeded 10%, the dispersibility of the colloidal silica deteriorated, and it was confirmed that unevenness occurred in the appearance after baking.

[0034] Based on the above experimental results, the inventors discovered that in an insulating coating treatment solution containing metal phosphate and colloidal silica, it is possible to impart high moisture absorption resistance by limiting the Na2O / SiO2 ratio in the colloidal silica to between 0.5% and 10%, thereby accelerating the insulating coating formation reaction.

[0035] As mentioned above, it is known that adding sodium hydroxide to colloidal silica lowers the crystallization temperature of colloidal silica, but in the experiments of the present invention, no change in the crystallization temperature was observed even when sodium chloride was added to colloidal silica.From this, it is thought that the lowering of the crystallization temperature of colloidal silica, as derived from conventional knowledge, does not improve the moisture absorption resistance, but rather that the addition of sodium itself improves the moisture absorption resistance for some reason.

[0036] <Method of manufacturing an insulating coating treatment solution for grain-oriented electrical steel sheets> The configuration of the method for producing an insulating coating solution for grain-oriented electrical steel sheets (hereinafter simply referred to as "insulating coating solution") according to this embodiment and the reasons for the limitations thereon will be described.

[0037] The method for producing the insulating coating treatment solution according to this embodiment includes a preparation step of adjusting the components of colloidal silica, and a mixing step of mixing the colloidal silica and the metal phosphate.

[0038] In the adjustment process, a Na compound is added to the colloidal silica to adjust the Na2O / SiO2 ratio (by mass %) of the Na2O and SiO2 content in the colloidal silica to 0.5% to 10%. 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 a poor appearance after firing. 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 also preferably 8% or less, more preferably 7% or less, and even more preferably 6% or less.

[0039] The method for adjusting the Na2O / SiO2 ratio in the colloidal silica to 0.5% or more and 10% or less is not particularly limited, but for example, sodium hydroxide and / or sodium chloride may be added to the colloidal silica in advance. From the viewpoint of increasing the pH of the insulating coating treatment solution and improving the dispersibility of the colloidal silica, adding sodium hydroxide is preferred.

[0040] The size of the colloidal silica (silica particles) used in this embodiment is not particularly limited, but the average particle size (average primary particle size) is preferably 4 to 35 nm. If the average particle size of the colloidal silica is less than 4 nm, the colloidal silica tends to aggregate, which may reduce the stability of the insulating coating treatment solution, or the insulating coating may become porous with large gaps, reducing the adhesiveness of the insulating coating. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the reactivity of the colloidal silica may decrease, which may result in insufficient mixing of the phosphate binder with the colloidal silica, or cracks may occur in the insulating coating, reducing the adhesiveness.

[0041] Furthermore, since the smaller the particle size of the colloidal silica, the denser the coating film formed and the higher the coating tension, it is more preferable that the upper limit of the average particle size of the colloidal silica is 31 nm, 22 nm, 18 nm, or 12 nm. Furthermore, it is more preferable that the surface of the colloidal silica is chemically treated with aluminum. The average particle size (average primary particle size) of the colloidal silica can be determined, for example, by conversion from the specific surface area measured by the BET adsorption method (in accordance with JIS Z8830).

[0042] In the mixing step, colloidal silica whose components have been adjusted in the adjusting step and a metal phosphate are mixed. The 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. The metal phosphate is preferably a phosphate of one or more metals selected from Al, Mg, Ni, V, and W. This is because selecting these phosphates results in a flat, uniform appearance over a wide range of baking conditions. In consideration of environmental issues, it is preferable not to actively add chromate to the mixing step.

[0043] In the method for producing an insulating coating solution according to this embodiment, the ratios of metal phosphate and colloidal silica are not particularly limited. As long as the Na2O / SiO2 ratio in the colloidal silica is between 0.5% and 10%, the insulating coating of grain-oriented electrical steel sheets produced using the insulating coating solution according to this embodiment will exhibit excellent properties. Preferred values ​​are listed below.

[0044] The content of colloidal silica in the insulating coating treatment solution, calculated as SiO2, is preferably 25.0 to 65.0 mass% based on the total mass of the insulating coating treatment solution in terms of solids. A colloidal silica content of less than 25.0 mass% is undesirable because the insulating coating may not have sufficient coating tension. A colloidal silica content of more than 65.0 mass% is undesirable because the adhesiveness of the insulating coating may be reduced. Furthermore, the colloidal silica content in the insulating coating treatment solution is more preferably 27.0 mass% or more, more preferably 35.0 mass% or more, 40.0 mass% or more, or 45.0 mass% or more, based on the total mass of the insulating coating treatment solution in terms of solids. The colloidal silica content in the insulating coating treatment solution is more preferably 58.0 mass% or less, even more preferably 55.0 mass% or less, and even more preferably 50.0 mass% or less.

[0045] The insulating coating treatment solution according to this embodiment is primarily composed of metal phosphate and colloidal silica and is used to form a phosphate coating. Therefore, the content of metal phosphate in the insulating coating treatment solution, calculated as solid content, is preferably 28.0 to 75.0 mass % of the total mass of the insulating coating treatment solution, calculated as solid content.

[0046] In the mixing step, various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate may also be mixed in. However, the content of components other than colloidal silica and phosphate in the insulation coating treatment solution, calculated as solids, 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 insulation coating treatment solution calculated as solids.

[0047] As mentioned above, it is preferable not to actively add chromate, and the content of chromate in the insulation coating treatment solution is preferably at or below the impurity level. Specifically, the content of chromate in the insulation coating treatment solution, calculated as CrO, is preferably 0.1 mass % or less relative to the total mass of the insulation coating treatment solution calculated as solids.

[0048] In the mixing step, a compound containing Si and / or Na may be further mixed in. However, in this case, it is preferable that the Na2O / SiO2 ratio contained in the insulating coating treatment solution after mixing is 0.5% or more and 10% or less.

[0049] In the method for producing an insulating coating treatment solution according to this embodiment, the Na2O / SiO2 ratio in the colloidal silica is analyzed as follows. The amount of Na contained in the colloidal silica is measured by atomic absorption spectrometry and converted into 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 into the amount of SiO2. The Na2O / SiO2 ratio can be calculated from the obtained amounts of Na2O and SiO2 and then expressed as a percentage.

[0050] <Method of manufacturing grain-oriented electrical steel sheets> Next, a method for manufacturing a grain-oriented electrical steel sheet according to this embodiment will be described. The method for manufacturing a grain-oriented electrical steel sheet according to this embodiment (insulating coating method) includes a coating step of applying an insulating coating treatment liquid to the surface of the steel sheet, and a baking step of baking the insulating coating treatment liquid. The insulating coating is formed by baking.

[0051] In the method for producing a grain-oriented electrical steel sheet according to this embodiment, the steel sheet on which an insulating coating is formed may be a grain-oriented electrical steel sheet having a normal forsterite coating, or may be a grain-oriented electrical steel sheet without a forsterite coating. Regardless of which steel sheet is used, after finish annealing, the grain-oriented electrical steel sheet undergoes water washing to remove excess annealing separator, followed by pickling in a sulfuric acid bath or the like, and then water washing. This cleans and activates the surface of the steel sheet, and then an insulating coating treatment solution is applied to the steel sheet in the application step. The grain-oriented electrical steel sheet to which the insulating coating treatment solution has been applied is subjected to a baking step under the conditions described below, thereby forming an insulating coating on the surface.

[0052] In the baking process, the grain-oriented electrical steel sheet coated with the insulating coating treatment solution is heated to a baking soaking temperature, maintained at the baking soaking temperature, and then cooled. The baking soaking temperature (°C) refers to the sheet temperature (maximum sheet temperature) reached in the baking process, and must be 800°C or higher and 1000°C or lower. If the baking soaking temperature is lower than 800°C, the insulating coating may not be able to impart sufficient tension to the steel sheet. On the other hand, if the baking soaking temperature is higher than 1000°C, cracks may occur in the insulating coating, reducing the coating tension and insulating properties, and scratches may also occur on the steel sheet. The baking soaking temperature is more preferably 850°C or higher and 950°C or lower.

[0053] The soaking time (seconds) indicates the time required to maintain the temperature at the baking temperature. A soaking time of 10 seconds or more is required. If the soaking time is less than 10 seconds, the insulating coating may not be baked properly, resulting in a deterioration in moisture absorption resistance (increased moisture absorption). A soaking time of 20 seconds or more is desirable. On the other hand, the soaking time should be 60 seconds or less. If the soaking time exceeds 60 seconds, not only will there be almost no change in moisture absorption resistance, but excessive crystallization of the insulating coating may occur, leading to cracks and a decrease in coating tension. A soaking time of 45 seconds or less is more preferable, as this provides sufficient coating properties.

[0054] The type of steel sheet to be treated with the insulating coating is not particularly limited. The grain-oriented electrical steel sheet according to this embodiment is characterized primarily by the configuration of the insulating coating, and the effects of the insulating coating of the grain-oriented electrical steel sheet according to this embodiment, namely, the ability to impart large tension to the surface of the steel sheet, good adhesion, corrosion resistance, and productivity, and even if the coating does not contain chromate, good moisture absorption resistance, can be achieved regardless of the type of steel sheet.

[0055] Preferably, the above-mentioned insulating coating treatment is applied to grain-oriented electrical steel sheets manufactured using the technology disclosed in, for example, Japanese Patent Laid-Open Publication No. 7-268567, thereby achieving a further reduction in iron loss. Specifically, the above-mentioned insulating coating treatment is applied to grain-oriented electrical steel sheets containing, by mass, at least 0.005% or less of C and 2.5 to 7.0% of Si, and optionally containing other alloying elements (e.g., 0 to 1.0% of Mn, 0 to 0.03% of Al, 0.01% or less of N, 0.01% or less of P, and 0.01% or less of S) within ranges that do not impair the properties, with the balance being Fe and impurities, an average grain size of 1 to 10 mm, and an average angle between the (110)

[0001] crystal orientation and the rolling direction of 8° or less.

[0056] The coating weight of the insulating coating of the grain-oriented electrical steel sheet manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment is not particularly limited, but is preferably 2.0 to 7.0 g / m 2 The coating weight of the insulating coating is 2.0 g / m 2 If the coating weight of the insulating coating is less than 7.0 g / m, it becomes difficult to apply high tension to the grain-oriented electrical steel sheet, and the insulating properties and corrosion resistance of the grain-oriented electrical steel sheet may also be reduced, which is undesirable. 2 If the coating weight of the insulating coating exceeds 3.0 g / m, the space factor of the grain-oriented electrical steel sheet may decrease, which may result in deterioration of the transformer characteristics, which is not preferable. 2 More preferably, 4.0 g / m 2 The coating weight of the insulating coating is more preferably 6.0 g / m2 or less, more preferably 5.0 g / m 2 The following is the result. [Example]

[0057] Next, the effects of one embodiment of the present invention will be explained in more detail using examples, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0058] A slab containing, by mass%, 0.082% C, 3.25% Si, 0.084% Mn, 0.026% sol.Al, 0.0088% N, 0.008% P, and 0.023% S, with the balance being Fe and impurities, was cast, heated to 1150°C, and hot-rolled to a 2.6 mm thick hot-rolled steel sheet. This hot-rolled steel sheet was subjected to hot-rolled sheet annealing as necessary, followed by a single cold rolling or multiple cold rolling steps with intermediate annealing between them to obtain a cold-rolled steel sheet with a final thickness of 0.23 mm. This cold-rolled steel sheet was subjected to decarburization annealing and then nitriding treatment in an ammonia-containing atmosphere during cooling. Known conditions were used for the slab heating and nitriding treatments.

[0059] An annealing separator mainly composed of MgO was applied to the decarburized annealed sheet after the decarburization annealing described above and dried. The decarburized annealed sheet coated with the annealing separator was subjected to finish annealing at 1200°C for 20 hours.

[0060] Thereafter, excess annealing separator was removed by washing with water using a scrubber, and then an insulating coating treatment solution adjusted to the components shown in Table 1 was applied, followed by baking under the conditions shown in Table 2 to form an insulating coating.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Moisture absorption amount] The moisture absorption amount of the thus obtained grain-oriented electrical steel sheet with an insulating coating was measured according to the method described above.

[0064] [exterior] The appearance of the insulating coating after baking was also evaluated. The appearance of the insulating coating after baking was judged visually based on the presence or absence of cloudiness in the insulating coating. A non-cloudy area ratio of the coating surface of less than 10% was rated "Very Good," 10% to less than 20% was rated "Good," and 20% or more was rated "Poor." When the surface of the cloudy sample was observed using an SEM, fine cracks were found in the coating. Therefore, it is believed that the occurrence of cracks causes diffuse reflection of light, causing the sample to appear cloudy.

[0065] The evaluation results are shown in Tables 3 to 5.

[0066] [Table 3]

[0067] [Table 4]

[0068] [Table 5]

[0069] As can be seen from Tables 3 to 5, in the examples of the invention, the manufacturing method of the insulating coating treatment liquid satisfied the specified range 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 examples of the invention had good moisture absorption resistance and the appearance of the insulating coating was also excellent.

[0070] In contrast, in the comparative examples, at least one item in the method for producing the insulating coating treatment solution was outside the scope of the present invention, and the moisture absorption resistance of the grain-oriented electrical steel sheet or the appearance of the insulating coating was poor.

Claims

1. A method for producing an insulating coating treatment solution for grain-oriented electrical steel sheets, comprising: Adding a Na compound to colloidal silica, ２ The amount of Na converted into O and SiO ２ The amount of Si converted into Na in mass% ２ O / SiO ２ an adjusting step of adjusting the ratio to 0.5% or more and 10% or less; The Na ２ O / SiO ２ a mixing step of mixing the ratio-adjusted colloidal silica and a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, the content of chromate in the insulation coating treatment solution is 0.1% or less in terms of CrO 3 with respect to the total mass of the insulation coating treatment solution in terms of solid content; A method for manufacturing an insulating coating treatment solution for grain-oriented electrical steel sheets.

2. a coating step of coating an insulating coating treatment liquid on a surface of the steel sheet; a baking step of baking the insulating coating treatment solution to form an insulating coating, The insulating coating treatment solution is an insulating coating treatment solution for grain-oriented electrical steel sheets, which is produced by the method according to claim 1, In the baking step, the baking soaking temperature is 800 to 1000°C, and the soaking holding time is 10 to 60 seconds. Manufacturing method for grain-oriented electrical steel sheets.

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