Method for producing processing liquid for forming insulating coating on sheet of anisotropic electrical steel and method for producing sheet of anisotropic electrical steel

Abstract

FIELD: producing of anisotropic electrical steel.SUBSTANCE: method for producing a processing liquid for forming an insulating coating on a sheet of anisotropic electrical steel and a method for forming an insulating coating on said sheet. Process for regulating the composition of colloidal silicon dioxide is carried out, in which potassium hydroxide and / or potassium chloride are added to colloidal silicon dioxide to bring the K2O / SiO2 ratio to 0.5-10%. Then, mixing is carried out between colloidal silicon dioxide having an adjusted ratio of K2O / SiO2 and a metal phosphate in which the metal is selected from one or more metals from among Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr. The said method for forming an insulating coating includes applying the above-mentioned processing liquid to the surface of a sheet of anisotropic electrical steel and firing the said sheet coated with the said processing liquid, forming an insulating coating. During the firing process, the holding temperature is 800-1000°C, and the holding time is 10-60 s.EFFECT: provides an insulating coating on an anisotropic electrical steel sheet with improved surface tension and improved resistance to moisture absorption.2 cl, 1 dwg, 5 tbl

Description

Field of technology

[0001] The present invention relates to a method for producing a processing liquid for forming an insulating coating on an anisotropic electrical steel sheet and a method for producing an anisotropic electrical steel sheet by applying the processing liquid obtained by the above method for forming an insulating coating.Background of the invention

[0002] Anisotropic electrical steel sheets are steel sheets mainly used as the iron core of transformers and the like. Generally, such anisotropic electrical steel sheets are coated with two layers of surface coating: a forsterite layer (also called a "primary coating"), which is formed during high-temperature final annealing; and a phosphate coating, which is formed by baking after applying a processing liquid mainly consisting of phosphate during thermal straightening of the steel sheet.

[0003] Phosphate coatings are required to impart electrical insulation to anisotropic electrical steel sheets and improve magnetic losses by reducing eddy current losses. In addition to insulation, the phosphate coating is also required to have various other properties, such as corrosion resistance, heat resistance, lubricity, and adhesion. This is necessary to simplify various manufacturing processes when anisotropic electrical steel sheets are processed to produce iron cores for transformers and other devices. For example, if the phosphate coating has poor heat resistance, lubricity, or adhesion, the phosphate coating may peel off during stress-relief annealing during iron core production, preventing the phosphate coating from exhibiting its original insulating properties or impairing workability because the steel sheets cannot be laid flat on top of each other.

[0004] Furthermore, an important property of the insulating coating of the anisotropic electrical steel sheet is that it applies tension to the steel sheets. When tension is applied to the steel sheets, the magnetic losses of the anisotropic electrical steel sheets can be improved by facilitating the movement of magnetic domain walls. Tension can also reduce magnetostriction (one of the main causes of noise in transformers).

[0005] In order to improve various properties of the anisotropic electrical steel sheets as described above, in particular, technologies 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 a treatment liquid for forming an insulating coating with a specific composition, mainly consisting of aluminum phosphate, chromate, and colloidal silica, is applied to a forsterite film formed on the surface of a steel sheet after final annealing, and then annealed. According to the technology disclosed in Patent Document 1, a high-tension insulating coating is formed on the surface of the steel sheet, thereby reducing magnetic loss and magnetostriction of the anisotropic electrical steel sheet.

[0007] Furthermore, Patent Document 2 discloses 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 steel sheet, followed by calcining the sheet. According to the technology disclosed in Patent Document 2, high tension of the insulating coating can be maintained, and the lubricity of the coating can also be improved.

[0008] In addition, Patent Document 3 discloses a technology for forming a high-tension insulating coating on the surface of an anisotropic electrical steel sheet by applying a specific amount of an insulating coating mainly composed of phosphate, chromate, and colloidal silica, with a glass transition point of 950-1200°C.

[0009] According to the technologies disclosed in Patent Documents 1-3 above, it was possible to form an insulating coating with significantly improved coating properties and coating tension. However, all the technologies disclosed in Patent Documents 1-3 contain chromate, a chromium compound, in the insulating coating. In recent years, with increased attention to environmental issues, there has been a growing demand in society to ban or restrict the use of compounds of elements such as lead, chromium, and cadmium.

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

[0011] As a method for solving the above problems, for example, Patent Document 4 discloses a processing method for forming an insulating coating on an anisotropic electrical steel sheet, in which a processing liquid containing 20 parts by mass of colloidal silicon dioxide in terms of the SiO2 content, 10-120 parts by mass of aluminum phosphate, 2-10 parts by mass of boric acid and 4-40 parts by mass in total of one or more types selected from sulfates of Mg, Al, Fe, Co, Ni and Zn is calcined at 300°C or higher.

[0012] In addition, Patent Document 5 discloses a technology related to a coating agent for forming a coating that contains a mixture of boric acid and aluminum oxide sol and a water-compatible organic solvent; such a coating has a tension-imparting effect on anisotropic electrical steel sheets.

[0013] In addition, Patent Document 6 discloses 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 anisotropic electrical steel sheets containing primary phosphates of Al, Mg, and Ca and colloidal silicon dioxide. In addition, Patent Document 6 cites formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as examples of the organic acid salts.

[0014] In addition, Patent Document 7 discloses a technology in which, in a processing agent for forming an insulating coating on anisotropic 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 four or more.

[0015] Furthermore, Patent Document 8 discloses an anisotropic electrical steel sheet including a steel sheet and an insulating coating that contains: a first metal phosphate that is a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni and Zn; a second metal phosphate that is a metal phosphate of one or more metals selected from Co, Mo, V, W and Zr; and colloidal silicon dioxide.

[0016] In addition, Patent Document 9 discloses an aqueous coating composition for anisotropic electrical steel; the composition contains aluminum cations; manganese cations; dihydrogen phosphate, hydrogen phosphate and / or phosphate anions; colloidal silicon dioxide; and optionally, iron cations.List of Prior Art DocumentsPatent Documents

[0017] 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 InventionTechnical Problem

[0018] These proposals have improved the application of tension to steel sheets. However, the present inventors' research to date has shown that insulating coatings that do not contain chromium compounds also suffer in terms of moisture absorption resistance. Even using all of the above technologies, it was impossible to achieve the same level of moisture absorption resistance as traditional coatings containing chromic acid, and there is still room for improvement.

[0019] The insulating coating on the anisotropic electrical steel sheet must be capable of imparting high tension to the steel sheet surface. Furthermore, the insulating coating on the anisotropic electrical steel sheet must also have good moisture absorption resistance and good performance.

[0020] The present invention was made in order to solve the above problems, and its objectives are to provide a method for producing a treatment liquid for forming an insulating coating on an anisotropic electrical steel sheet that exhibits good resistance to moisture absorption and, in addition, good performance even when chromate is not included, and to provide a method for producing an anisotropic electrical steel sheet by applying the treatment liquid obtained by the above method for forming an insulating coating. Problem Solving

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

[0022] (1) A method for producing a treatment liquid for forming an insulating coating on an anisotropic 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 mass% ratio 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 an adjusted K2O / SiO2 ratio and a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr are mixed.

[0023] (2) A method for producing an anisotropic electrical steel sheet according to another embodiment of the present invention includes: a coating process in which a processing liquid for forming an insulating coating is applied to the surface of a steel sheet, and a baking process in which the processing liquid for forming an insulating coating is baked to form an insulating coating, wherein said processing liquid for forming an insulating coating is a processing liquid for forming an insulating coating on an anisotropic electrical steel sheet obtained by the method described in item (1) above, and wherein in the baking process, the baking holding temperature is 800-1000°C and the holding time is 10-60 seconds. Advantageous effects of the invention

[0024] According to the present invention, anisotropic electrical steel sheet with excellent moisture absorption resistance and performance can be stably obtained.Brief description of the drawings

[0025] Fig. 1 shows the relationship between the K2O / SiO2 ratio of colloidal silicon dioxide and the moisture absorption value. Description of embodiments of the invention

[0026] The present inventors investigated methods for improving the moisture absorption resistance of insulating coatings that do not contain chromium compounds. Initially, the inventors questioned whether moisture absorption resistance could be improved by controlling the crystallization temperature of colloidal silica. It is known that adding sodium hydroxide to colloidal silica lowers its crystallization temperature.

[0027] In previous studies, the present inventors evaluated the moisture absorption resistance of insulating coatings made using colloidal silica to which sodium hydroxide had been added. Furthermore, the inventors focused on potassium, which has properties similar to sodium, and examined whether the crystallization temperature of colloidal silica could be lowered by adding potassium hydroxide to the colloidal silica.

[0028] Therefore, the present inventors evaluated the moisture absorption resistance of insulating coatings made using colloidal silica pre-dosed with potassium hydroxide. For comparison, a similar study was also conducted with the addition of potassium chloride.

[0029] The following describes the results of preliminary experiments leading to the creation of the present invention.

[0030] Anisotropic electrical steel sheets with a thickness of 0.23 mm, produced by a known method after final annealing, were cut into pieces 60 mm wide and 300 mm long. The annealing separator adhering to the surface was removed by washing. The resulting sheets were used as base metals. Potassium hydroxide or potassium chloride was then added to the colloidal silica, and the K2O / SiO2 ratio in the colloidal silica was adjusted within the range of 0.2-11%, producing 11 types of colloidal silica. It should be noted that the "K2O / SiO2 ratio" is a percentage (%) obtained by quantifying the amount of K in terms of K2O (hereinafter referred to as "amount of K2O", unit: mass%) and the amount of Si in terms of SiO2 (hereinafter referred to as "amount of SiO2", unit: mass%) contained in colloidal silicon dioxide, respectively, and dividing the amount of K2O by the amount of SiO2.

[0031] Then, a treatment liquid for forming an insulating coating composed of 60 parts by mass of primary aluminum phosphate and 40 parts by mass of colloidal silica was applied to both sides of the base metals prepared above using a roller coating device so that the coating amount after baking became 4.5 g / m 2 per side. They were then fired at 850°C for 30 seconds.

[0032] For comparison, a treatment liquid for forming an insulating coating consisting of 50 parts by weight of primary aluminum phosphate, 40 parts by weight of colloidal silicon dioxide (K2O / SiO2 ratio= 1.2%) and 10 parts by weight of chromium anhydride was similarly applied to the base metal and fired.

[0033] The resulting steel sheet was used as a test specimen to evaluate its resistance to moisture absorption. First, the test specimen was placed in a thermohygrostat (temperature: 50°C, humidity: 90%) for one week, and the weight difference before and after treatment in the thermohygrostat was determined. The quantitative difference in weight was divided by the area of ​​both sides of the test specimen, 0.036 m. 2 , which was taken as the value of moisture absorption (unit: g / m 2 ), and the water absorption resistance was evaluated using the water absorption value as an indicator.

[0034] Fig. 1 shows the results of the above evaluation, demonstrating the relationship between the moisture absorption value and the K2O / SiO2 ratio. As shown in Fig. 1, the chromium-plated steel sheet has a small K2O / SiO2 ratio; the moisture absorption value is 0.1 g / m 2or less, and almost no moisture is absorbed. In contrast, in the case of steel sheets with a chromium-free coating, in the region where the K2O / SiO2 ratio is less than 0.5%, the moisture absorption value exceeds 1.0 g / m3. 2 , which is large, and sufficient resistance to moisture absorption is not achieved. However, in areas where the K2O / SiO2 ratio is large, especially where the K2O / SiO2 ratio is 0.5% or more, the moisture absorption value is 1.0 g / m 2 Regardless of whether potassium hydroxide or potassium chloride is used, the K2O / SiO2 ratio is 5.0% or less. Furthermore, in the region where the K2O / SiO2 ratio is 5.0% or more, moisture absorption is almost nonexistent, achieving good moisture absorption resistance equivalent to that of a chromium-plated steel sheet. On the other hand, when the K2O / SiO2 ratio exceeds 10%, it has been confirmed that the dispersity of colloidal silica deteriorates, resulting in an uneven appearance after firing.

[0035] Based on the above experimental results, the inventors of the present invention found that, in a processing liquid for forming an insulating coating containing a metal phosphate and colloidal silica, it is possible to ensure high resistance to moisture absorption by limiting the K2O / SiO2 ratio in the colloidal silica to 0.5% or more and 10% or less and thereby promoting the reaction of forming an insulating coating.

[0036] As mentioned above, this experiment was based on the idea that adding potassium hydroxide to colloidal silica could lower the crystallization temperature of colloidal silica; however, in this experiment, no change in the crystallization temperature was observed when potassium chloride was added to colloidal silica. It is believed that the improvement in moisture absorption resistance is not due to the lowering of the crystallization temperature of colloidal silica, but rather to the fact that the addition of potassium itself improves the moisture absorption resistance. <Method for producing a processing liquid for forming an insulating coating on anisotropic electrical steel sheet>

[0037] This section describes the configuration of a method for producing a processing liquid for forming an insulating coating on an anisotropic electrical steel sheet (hereinafter simply referred to as "processing liquid for forming an insulating coating") according to the present embodiment and the reasons for its limitations.

[0038] The method for producing a processing liquid for forming an insulating coating according to the present embodiment includes an adjustment process for adjusting the composition of colloidal silicon dioxide and a mixing process for mixing colloidal silicon dioxide and a metal phosphate.

[0039] In the adjustment process, a K compound is added to colloidal silica to adjust the K2O / SiO2 ratio (by mass%) between the amount of K2O and the amount of SiO2 in the colloidal silica to 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 weak, resulting in insufficient moisture absorption resistance. On the other hand, if the K2O / SiO2 ratio exceeds 10%, the dispersity of the colloidal silica deteriorates, resulting in poorer appearance after firing. The K2O / SiO2 ratio is preferably 1% or more, more preferably 3% or more, and still more preferably 5% or more. The K2O / SiO2 ratio is preferably 8% or less, more preferably 7% or less, and still more preferably 6% or less.

[0040] There are no specific limitations on the method for adjusting the K2O / SiO2 ratio of colloidal silica to 0.5% or more and 10% or less; however, for example, a method of adding potassium hydroxide and / or potassium chloride to the colloidal silica in advance can be used. From the viewpoint of raising the pH of the treatment liquid for forming the insulating coating and thereby improving the dispersion of the colloidal silica, it is preferable to add potassium hydroxide. Potassium permanganate can also be added to the colloidal silica in advance. However, potassium permanganate is a strong oxidizing agent and is highly reactive, so its use is not preferable from a safety viewpoint. Therefore, it is preferable to exclude potassium permanganate as the K compound.

[0041] The size of the colloidal silica (silicon dioxide particles) used in the present embodiment is not particularly limited; however, the average particle diameter (average primary particle diameter) is preferably 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 processing liquid for forming the insulating coating may deteriorate, or the insulating coating may become porous with large gaps, reducing the adhesion of the insulating coating, which is undesirable. On the other hand, if the average particle diameter of the colloidal silica is more than 35 nm, the colloidal silica becomes less reactive, and the mixing of the phosphate as a binder and the colloidal silica may not be sufficient, or cracks may appear in the insulating coating, reducing the adhesion, which is undesirable.

[0042] It is also preferable that the upper limit of the average particle diameter of the colloidal silica be set to 31 nm, 22 nm, 18 nm, or 12 nm, since colloidal silica particles with smaller diameters form denser coatings and increase the coating tension. 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 the colloidal silica can be determined, for example, by conversion from the specific surface area measured by the BET adsorption method (according to JIS Z8830).

[0043] The mixing process involves mixing colloidal silica, the components of which have been adjusted, and a metal phosphate. Said 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 for the metal phosphate to 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 flat and uniform appearance can be achieved under a wide range of firing conditions. It is preferable not to intentionally add chromates during the mixing process, taking into account environmental concerns.

[0044] In the method for producing a processing liquid for forming an insulating coating according to the present embodiment, the ratio of metal phosphate to 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 an anisotropic electrical steel sheet using the processing liquid for forming an insulating coating obtained by the method of the present embodiment exhibits excellent properties. Examples of preferred values ​​are given below.

[0045] The content of colloidal silicon dioxide in the insulating coating processing liquid, calculated as SiO2, is preferably 25.0-65.0% by mass based on the total mass of the insulating coating processing liquid in terms of solids content. If the content of colloidal silicon dioxide in the insulating coating processing liquid is less than 25.0% by mass, the tension of the insulating coating may be insufficient, which is undesirable. If the content of colloidal silicon dioxide in the insulating coating processing liquid exceeds 65.0% by mass, the adhesion of the insulating coating may decrease, which is undesirable. The content of colloidal silicon dioxide in the processing liquid for forming the insulating coating is preferably 27.0 wt% or more, and even more preferably 35.0 wt% or more, 40.0 wt% or more, or 45.0 wt%.% or more based on the solids content, relative to the total weight of the processing liquid for forming the insulating coating. The content of colloidal silicon dioxide in the processing liquid for forming the insulating coating is preferably 58.0% by weight or less, even more preferably 55.0% by weight or less, or even more preferably 50.0% by weight or less.

[0046] Furthermore, the insulating coating forming treatment liquid according to the present embodiment is mainly composed of metal phosphate and colloidal silica and is used to form a phosphate coating. Therefore, the metal phosphate content in the insulating coating forming treatment liquid, calculated as H2PO4, is preferably 28.0-75.0% by mass of the total mass of the insulating coating forming treatment liquid, calculated as a solid content.

[0047] In the above-mentioned mixing process, inorganic compounds including various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments and barium titanate may be further mixed in. However, the content of components other than colloidal silicon dioxide and phosphate in the processing liquid for forming an insulating coating, in terms of the solid 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 processing liquid for forming an insulating coating, in terms of the solid content.

[0048] In addition, as mentioned above, it is preferable not to intentionally add chromate, and the chromate content in the insulating coating treatment liquid is preferably no more than the impurity level. Specifically, the chromate content in the insulating coating treatment liquid, calculated as CrO3, is preferably 0.1% by mass or less of the total mass of the insulating coating treatment liquid, calculated as solids.

[0049] In the above mixing process, a compound containing Si and / or K may be further mixed in. In this case, however, the ratio of K2O / SiO2 contained in the processing liquid for forming the insulating coating after mixing is preferably 0.5% or more and 10% or less.

[0050] In the method for producing a processing liquid for forming an insulating coating according to the present embodiment, the K2O / SiO2 ratio in colloidal silica is analyzed as follows. The amount of K contained in the colloidal silica is measured by atomic absorption spectrophotometry and converted into the amount of K2O. 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. Afterwards, the K2O / SiO2 ratio can be calculated from the obtained amounts of K2O and SiO2 and expressed as a percentage. <Method for producing anisotropic electrical steel sheet>

[0051] Next, a method for producing an anisotropic electrical steel sheet according to the present embodiment is described. The method for producing an anisotropic electrical steel sheet (a processing method for forming an insulating coating) according to the present embodiment includes a coating process in which a processing liquid for forming an insulating coating is applied to the surface of a steel sheet, and a baking process in which the processing liquid for forming an insulating coating is baked. The baking process forms an insulating coating.

[0052] In the method for producing an anisotropic electrical steel sheet according to the present embodiment, the steel sheet on which the insulating coating is formed may be a normal anisotropic electrical steel sheet with a forsterite film or an anisotropic electrical steel sheet without a forsterite film. In any case, after final annealing and subsequent rinsing to remove excess annealing separator, the anisotropic electrical steel sheet is pickled in a sulfuric acid bath or the like and then rinsed in water. After the surface of the steel sheet is cleaned and activated in this manner, a treatment liquid is applied to the steel sheet to form an insulating coating during the coating process.The anisotropic electrical steel sheet coated with a treatment liquid to form an insulating coating is then subjected to a baking process under the conditions described below to form an insulating coating on its surface.

[0053] In the baking process, the anisotropic electrical steel sheet coated with a processing liquid to form an insulating coating is heated to the baking soaking temperature, held at the baking soaking temperature, and then cooled. The baking soaking temperature (°C) is the sheet temperature reached during the baking process (the maximum sheet temperature), and should be 800°C or higher and 1000°C or lower. If the baking soaking temperature is less than 800°C, the insulating coating may not impart sufficient tension to the steel sheet. On the other hand, if the baking soaking temperature exceeds 1000°C, cracks may appear in the insulating coating, resulting in a decrease in the coating tension and insulating properties, and defects may also appear on the steel sheet. The holding temperature during firing is preferably 850°C or higher and 950°C or lower.

[0054] The holding time during soaking (seconds) indicates the holding time at the soaking temperature during baking. The holding time during soaking should be 10 seconds or more. If the holding time during soaking is less than 10 seconds, the baking of the insulating coating is insufficient, and the moisture absorption resistance may deteriorate (the moisture absorption value may increase). The holding time during soaking is preferably 20 seconds or more. On the other hand, the holding time during soaking should be 60 seconds or less. If the holding time during soaking exceeds 60 seconds, not only will the moisture absorption resistance remain unchanged, but excessive crystallization of the insulating coating may cause cracks and reduce the coating tension. In order to achieve the required and sufficient coating properties, the holding time during soaking is preferably 45 seconds or less.

[0055] The type of steel sheet to which the above-mentioned treatment for forming the insulating coating is applied is not limited. This is because the main feature of the anisotropic electrical steel sheet of the present embodiment is the composition of the insulating coating. The insulating coating effects of the anisotropic electrical steel sheet of the present embodiment, namely, the ability to impart high tension to the surface of the steel sheet; good adhesion, corrosion resistance, and performance; and good resistance to moisture absorption, even when chromate is not included, can be achieved regardless of the type of steel sheet.

[0056] Preferably, the above-mentioned treatment for forming an insulating coating can be applied to anisotropic electrical steel sheets such as those produced using the technology disclosed in, for example, JP7-268567A, which can achieve an additional effect of reducing magnetic loss.The above-mentioned treatment for forming an insulating coating can further reduce magnetic loss by applying the above-mentioned treatment for forming an insulating coating, in particular, to an anisotropic electrical steel sheet containing at least C: 0.005% or less and Si: 2.5-7.0% by weight and, optionally, further containing other alloying elements within ranges that do not deteriorate properties (for example, Mn: 0-1.0%, Al: 0-0.03%, N: 0.01% or less, P: 0.01% or less and S: 0.01% or less), and the rest is Fe and impurities, and having an average grain size of 1-10 mm and an average angle of 8° or less between the crystallographic orientation (110)

[001] and the rolling direction.

[0057] Although there is no specific limit on the amount of insulation coating applied to the anisotropic electrical steel sheet produced by the method for producing the anisotropic electrical steel sheet according to the present embodiment, the amount of coating is 2.0-7.0 g / m 2 is suitable. If the applied amount of insulating coating is less than 2.0 g / m 2 , it becomes difficult to impart high tension to the anisotropic electrical steel sheet, and the insulating properties and corrosion resistance of the anisotropic electrical steel sheet may also deteriorate, which is undesirable. On the other hand, if the applied amount of insulating coating exceeds 7.0 g / m 2 , the fill factor of the anisotropic electrical steel sheet may decrease, leading to deterioration in transformer performance, which is undesirable. The applied amount of insulation coating is preferably 3.0 g / m. 2or more, and even more preferably 4.0 g / m 2 or more. The applied amount of the insulating coating is preferably 6.0 g / m 2 or less, and even more preferably 5.0 g / m 2 or less. Examples

[0058] Next, the effects of an embodiment of the present invention will be described in more detail through examples. The conditions in the examples are examples of conditions used to confirm the feasibility and effects of the present invention, and the present invention is not limited to these example conditions. Various conditions can be used in the present invention, provided that they do not deviate from the essence of the present invention and achieve the purpose of the present invention.

[0059] A slab containing, in mass%, C: 0.082%, Si: 3.25%, Mn: 0.084%, sol. Al: 0.026%, N: 0.0088%, P: 0.008% and S: 0.023%, and the balance is Fe and impurities, was cast, heated to 1150°C and hot rolled to prepare a hot-rolled steel sheet with a thickness of 2.6mm. The hot-rolled steel sheet was then annealed if necessary and cold rolled once or more times with intermediate annealing to obtain a cold-rolled steel sheet with a final thickness of 0.23mm. The cold-rolled steel sheet was subjected to decarburization annealing and nitriding in an ammonia-containing atmosphere during the temperature reduction step. Known conditions were used in these processes, from slab heating to nitriding.

[0060] Annealing separator, mainly composed of MgO, was applied to the decarburization-annealed sheet after the decarburization annealing process described above and left to dry. The decarburization-annealed sheet coated with the annealing separator was then subjected to a final annealing at 1200°C for 20 hours.

[0061] After this, the excess annealing separator was washed off with a scrubber, and then the insulating coating forming treatment liquids with the components adjusted as shown in Table 1 were applied and fired under the conditions shown in Table 2 to form insulating coatings.

[0062] Table 1 Processing fluid No. Processing liquid for forming an insulating coating Metal phosphate Colloidal silicon dioxide Chromate Inorganic compound Metal Metal ratio (molar ratio) Content (wt.%) K2O / SiO2 ratio (%) Content (wt.%) Amount of SiO2 (wt.%) Amount of Na2O (wt.%) Amount of K2O (wt.%) Content (wt.%) Type Content (wt.%) 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 A9 Al 100 47,4 5 50,6 48,0 0,18 2,4 Sodium borate 2,0 A10 Al 100 47,4 5 50,6 48,0 0,17 2,4 Titanium oxide 2,0 A11 Al 100 47,5 5 50,5 48,0 0,14 2,4 Molybdenum oxide 2,0 A12 Al 100 47,4 5 50,6 48,0 0,18 2,4 Barium titanate 2,0 A13 Al / Fe 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 - -

[0063] Table 2 Production method No. The firing process Holding temperature Holding time (°C) (seconds) 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 [Moisture absorption value]

[0064] The moisture absorption value of the resulting anisotropic electrical steel sheet with insulating coating was measured using the above method.[Appearance]

[0065] The appearance of the insulating coating after firing was assessed. The appearance of the insulating coating after firing was judged by visual inspection based on the presence or absence of haze on the insulating coating. A clear area of ​​less than 10% of the coating surface was rated "Very Good," 10% to less than 20% was rated "Good," and 20% or more was rated "Poor." When the surface of the hazed specimen was observed using an SEM, fine cracks were found in the coating. Therefore, it is believed that the cracks are caused by diffuse light reflection, which causes the specimen to appear hazy.

[0066] The results of these evaluations are shown in Tables 3-5.

[0067] Table 3 Test No. Processing fluid No. Production method No. Evaluation of properties Water absorption rate (g / m2) Appearance after firing C1 A1 B5 0,96 Fine Example of the invention C2 A2 B5 0,41 Fine C3 A3 B5 0,06 Fine C4 A4 B5 0,04 Very good C5 A5 B5 0,04 Very good C6 A6 B5 0,05 Fine C7 A7 B5 0,04 Fine 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 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 Fine Comparative example c2 a2 B5 0,03 Badly c3 a3 B5 0,01 Fine

[0068] Table 4 Test No. Processing fluid No. Production method No. Evaluation of properties Water absorption rate (g / m2) Appearance after firing D1 A4 B1 0,07 Fine Example of the invention D2 A4 B2 0,04 Fine D3 A4 B3 0,82 Fine D4 A4 B4 0,04 Fine D5 A4 B5 0,03 Very good D6 A4 B6 0,04 Very good D7 A4 B7 0,03 Fine d1 A4 b1 1,29 Fine Comparative example d2 A4 b2 0,04 Badly d3 A4 b3 1,41 Fine d4 A4 b4 0,05 Badly

[0069] Table 5 Test No. Production method No. Processing liquid for forming an insulating coating Evaluation of properties Metal phosphate Colloidal silicon dioxide Chromate Water absorption rate (g / m2) Appearance after firing Metal Content (wt.%) K2O / SiO2 ratio (%) Average particle diameter (nm) Content (wt.%) Amount of SiO2 (wt.%) Amount of Na2O (wt.%) Amount of K2O (wt.%) E1 B5 Al 49,4 5 4 50,6 48,0 0,21 2,4 - 0,04 Very good Example of the invention E2 B5 Al 49,4 5 12 50,6 48,0 0,22 2,4 - 0,05 Very good E3 B5 Al 49,4 5 18 50,6 48,0 0,20 2,4 - 0,04 Fine E4 B5 Al 49,4 5 22 50,6 48,0 0,21 2,4 - 0,03 Fine E5 B5 Al 49,4 5 31 50,6 48,0 0,22 2,4 - 0,05 Fine E6 B6 Al 49,4 5 35 50,6 48,0 0,20 2,4 - 0,04 Fine

[0070] As can be seen from Tables 3-5, in the examples of the invention, the method for producing the processing liquid for forming the insulating coating satisfied the specified ranges of the present invention, and the anisotropic electrical steel sheet on which the insulating coating was formed using the processing liquid for forming the insulating coating according to the example of the invention had good moisture absorption resistance and an excellent coating appearance.

[0071] On the contrary, in the comparative examples, at least one feature in the method for producing a processing liquid for forming an insulating coating was outside the scope of the present invention, and the moisture absorption resistance or the appearance of the insulating coating of the anisotropic electrical steel sheet was inferior.

Claims

1. A method for producing a treatment liquid for forming an insulating coating on an anisotropic electrical steel sheet, comprising a process for adjusting the composition of colloidal silicon dioxide, in which potassium hydroxide and / or potassium chloride are added to the colloidal silicon dioxide to bring the K2O / SiO2 ratio to 0.5-10%, wherein the K2O / SiO2 ratio is a percentage obtained by determining the amount of K in terms of K2O in mass percent and the amount of Si in terms of SiO2 in mass percent in the colloidal silicon dioxide and dividing the amount of K2O by the amount of SiO2, and a mixing process in which colloidal silicon dioxide having an adjusted K2O / SiO2 ratio and a metal phosphate are mixed, wherein the metal is selected from one or more metals from among Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr.

2. A method for forming an insulating coating on a sheet of anisotropic electrical steel, in which a processing liquid for forming an insulating coating, obtained by the method for producing a processing liquid for forming an insulating coating on a sheet of anisotropic electrical steel according to paragraph 1, is applied to the surface of the sheet of anisotropic electrical steel and the sheet of anisotropic electrical steel coated with said processing liquid is fired to form an insulating coating, wherein during the firing process the holding temperature is 800-1000°C, and the holding time is 10-60 s.

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