Title of invention: Coating liquid for forming an insulating film for grain-oriented electrical steel sheet, manufacturing method of grain-oriented electrical steel sheet, and grain-oriented electrical steel sheet.
Technical field
[0001]
　The present invention relates to a coating liquid for forming an insulating film for grain-oriented electrical steel sheets, a method for manufacturing grain-oriented electrical steel sheets, and grain-oriented electrical steel sheets.
　The present application claims priority based on Japanese Patent Application No. 2018-061745 filed in Japan on March 28, 2018, the contents of which are incorporated herein by reference.
Background technology
[0002]
　The grain-oriented electrical steel sheet has a crystal structure whose main orientation is the (110) [001] orientation, and is usually a steel sheet containing 2% by mass or more of Si. Its main use is for iron core materials such as transformers, and in particular, materials with low energy loss during transformation, that is, materials with low iron loss are required.
[0003]
　The typical manufacturing process of grain-oriented electrical steel sheets is as follows. First, a slab containing 2% by mass to 4% by mass of Si is hot-rolled to annead the hot-rolled plate. Next, cold rolling is performed once or twice or more with an intermediate annealing in between to obtain the final plate thickness, and decarburization annealing is performed. After that, an annealing separator mainly composed of MgO is applied and final finish annealing is performed. As a result, a crystal structure having the (110) [001] orientation as the main orientation is developed, and a finish annealing film mainly composed of Mg 2 SiO 4 is formed on the surface of the steel sheet . Finally, the coating liquid for forming the insulating film is applied and baked, and then shipped.
[0004]
　Conventionally, various coating liquids for forming an insulating film on a grain-oriented electrical steel sheet have been known (see, for example, Patent Documents 1 to 10).
Prior art literature
Patent documents
[0005]
Patent Document 1: Japanese Patent Application Laid-Open No. 48-0393338
Patent Document 2
: Japanese Patent Application Laid-Open No. 54-143737 Patent Document 3: Japanese Patent Application Laid-Open No. 2000-169972
Patent Document 4: Japanese Patent Application Laid-Open No. 2000- 178760 Japanese
Patent Document 5: International Publication No. 2015/11503
Patent Document 6: Japanese Patent Application Laid-Open No. 06-065754
Patent Document 7: Japanese Patent Application Laid-Open No. 06-065755
Patent Document 8: Japanese Patent Application Laid-Open No. 2010- 043293 JP
Patent Document 9: Japanese Patent 2010-037602 JP
Patent Document 10: Japanese Patent 2017-075358 JP
Outline of the invention
Problems to be solved by the invention
[0006]
　It was found that the grain-oriented electrical steel sheet has the property of improving iron loss by applying tension to the steel sheet. Therefore, by forming an insulating film made of a material having a coefficient of thermal expansion smaller than that of the steel sheet at a high temperature, tension is applied to the steel sheet, and iron loss can be improved.
[0007]
　The insulating film obtained by baking a coating solution composed of colloidal silica, primary phosphate and chromic acid disclosed in Patent Document 1 is excellent in various film properties such as tension.
　However, the coating liquid for forming the above insulating film contains hexavalent chromium, and an insulating film having excellent various film characteristics such as tension can be obtained without containing such hexavalent chromium. The development of a coating liquid for forming an insulating film of an electromagnetic steel sheet is expected.
[0008]
　For example, Patent Documents 2 to 5 describe a coating liquid for forming an insulating film of a directional electromagnetic steel plate, which is mainly composed of colloidal silica and primary phosphate and uses other additives instead of chromic acid. ing.
　However, further improvement is desired from the viewpoint of film tension in the insulating film obtained by the coating liquid for forming an insulating film which does not contain chromic acid and uses an additive other than chromic acid. In addition, many of the additives used in these techniques are more expensive than chromic acid.
[0009]
　On the other hand, the coating liquids for forming an insulating film described in Patent Documents 6 and 7 are formed of a mixture of alumina sol and boric acid. The film tension of the insulating film formed by baking this coating solution is larger than that of the insulating film obtained by baking the coating solution composed of colloidal silica, primary phosphate and chromic acid. can get.
　However, there is still room for further improvement in this insulating film from the viewpoint of corrosion resistance, and many of the alumina sol used as a raw material are expensive.
[0010]
　Therefore, the present inventors have focused on powder of hydrous silicate (clay mineral) as a substance whose raw material can be obtained at a relatively low cost and which has a possibility of obtaining a large film tension after baking.
　For example, Patent Document 8 discloses a coating liquid composed of a hydrous silicate powder and a primary phosphate. Further, Patent Document 9 discloses a coating liquid composed of a hydrous silicate powder, a primary phosphate and colloidal silica. Further, Patent Document 10 discloses a coating liquid composed of kaolin, which is a kind of hydrous silicate, and lithium silicate. The insulating film obtained by baking the coating liquids described in these documents has a film tension equal to or higher than that obtained by baking the coating liquid composed of colloidal silica, primary phosphate and chromic acid. Be done. Further, the obtained grain-oriented electrical steel sheet has excellent iron loss.
　However, there is still room for further improvement in the insulating film made of these coating liquids from the viewpoint of water resistance and corrosion resistance of the insulating film.
[0011]
　Therefore, an object of the present invention is to produce a grain-oriented electrical steel sheet which can form an insulating film having excellent corrosion resistance and has further excellent iron loss while not using a chromium compound or reducing the amount used. It is possible to manufacture grain-oriented electrical steel sheets with excellent corrosion resistance and excellent iron loss while not using coating liquids and chromium compounds for forming insulating film for grain-oriented electrical steel sheets or reducing the amount used. A method for producing a grain-oriented electrical steel sheet that can be produced, and an object of the present invention are to provide a grain-oriented electrical steel sheet that does not use or reduces the amount of chromium compound, has excellent corrosion resistance, and has excellent iron loss.
Means to solve problems
[0012]
　The means for solving the above problems include the following aspects.
(1) The coating liquid according to one aspect of the present invention is a coating liquid for forming an insulating film for a directional electromagnetic steel plate,
　and is one of a solvent and a layered clay mineral powder having a
　specific surface area of ​​20 m 2 / g or more.
Alternatively, it is characterized by containing two or more kinds .
(2) The coating liquid according to (1) above may have
　a specific surface area of ​​150 m 2 / g or less of the layered clay mineral powder .
(3) The coating liquid according to (1) or (2) above
　is one or more powders in which the layered clay mineral powder is selected from the group consisting of kaolin, talc, and pyrophyllite. You may.
(4) The coating liquid according to any one of (1) to (3) above
　may contain an inorganic dispersant of more than 0% by mass and 20% by mass or less with respect to the layered clay mineral powder.
(5) In the coating liquid according to (4) above, the
　inorganic dispersant is one or more selected from the group consisting of sodium diphosphate, sodium hexametaphosphate, sodium silicate, and potassium silicate. May be good.
(6) The coating liquid according to any one of (1) to (5) above is
　The content of the chromium compound may be 4% by mass or less with respect to the layered clay mineral powder.
[0013]
(7) The method for manufacturing a directional electromagnetic steel sheet according to one aspect of the present invention is for the directional electromagnetic steel sheet according
　to any one of (1) to (6) above , with respect to the base material of the directional electromagnetic steel sheet. It is characterized by including a step of applying a coating liquid for forming an insulating film and a step
　of baking the base material after coating at a temperature of 600 ° C. or higher and 1000 ° C. or lower to form an insulating film.
And.
[0014]
(8) oriented electrical steel sheet according to one embodiment of the present invention,
　the base material,
　and an insulating film provided on a surface of the base material
a grain-oriented electrical steel sheet having the
　said insulating coating,
　　SiO 2 It is characterized by containing 1 or 2 types of Al 2 O 3 and Mg O , and
　　having a porosity of 10% or less.
(9) The grain-oriented electrical steel sheet according to (8) above is one type in which the
　insulating film is further selected from the group consisting of Fe 2 O 3 , Na 2 O, K 2 O, and P 2 O 5. It may contain two or more kinds.
(10) In the grain-oriented electrical steel sheet according to (8) or (9)
　above, the content of the chromium compound in the insulating film may be 4% by mass or less with respect to the dehydration product of the layered clay mineral. ..
The invention's effect
[0015]
　According to the present invention, it is possible to form an insulating film having excellent corrosion resistance while not using a chromium compound or reducing the amount used, and to produce a grain-oriented electrical steel sheet having further excellent iron loss. A coating liquid for forming an insulating film for an electromagnetic steel sheet is provided. Further, there is provided a method for producing a grain-oriented electrical steel sheet, which can produce a grain-oriented electrical steel sheet having excellent corrosion resistance and further excellent iron loss while not using a chromium compound or reducing the amount used. Further, a grain-oriented electrical steel sheet having excellent corrosion resistance and further excellent iron loss while using no chromium compound or reducing the amount used is provided.
A brief description of the drawing
[0016]
FIG. 1 is an image showing a cross-sectional structure of an insulating film coated and baked with a dispersion liquid containing a layered clay mineral powder of Comparative Example 2 (specific surface area 15 m 2 / g).
FIG. 2 is an image showing a cross-sectional structure of an insulating film coated and baked with a dispersion liquid containing a layered clay mineral powder of Example 2 (specific surface area 50 m 2 / g).
FIG. 3 is an explanatory diagram for explaining a method for measuring porosity.
Mode for carrying out the invention
[0017]
　Hereinafter, an example of the embodiment of the present invention will be described.
[0018]
　In the present specification, the numerical range represented by using "-" means a range including the numerical values ​​before and after "-" as the lower limit value and the upper limit value.
　In the present specification, the term "process" is used not only as an independent process but also as a term as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. included.
　In addition, it is obvious that each element of the following embodiments can be combined.
[0019]
A coating liquid for forming an insulating film for a directional electromagnetic steel sheet according to the
　present embodiment (hereinafter, also simply referred to as "coating liquid for forming an insulating film"). Contains a layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more and a solvent such as water.
[0020]
　Conventionally, when a coating liquid containing a layered clay mineral powder in a solvent is applied and baked to form an insulating film of a directional electromagnetic steel plate, a coating liquid containing only a single layered clay mineral powder as a solid content is a dense film. It was not easy to form. Therefore, a coating liquid to which a binder such as primary phosphate or lithium silicate is added is applied to the surface of the base material of the grain-oriented electrical steel sheet and baked at a predetermined temperature to obtain an insulating film. Such an insulating film can obtain a film tension equal to or higher than that obtained by baking a coating liquid containing colloidal silica, primary phosphate and chromic acid.
[0021]
　However, according to the study by the present inventors, it has been found that the grain-oriented electrical steel sheet having an insulating film thus produced has room for further improvement from the viewpoint of corrosion resistance. It was also found that the coating liquid containing the layered clay mineral powder and the binder increased in viscosity with time even at room temperature and may gel.
[0022]
　The present inventors have prepared an insulating film in which a coating liquid in which a powder of a layered clay mineral having a specific surface area of ​​20 m 2 / g or more is dispersed in a solvent does not add the above binder or reduces the amount used. It has been found that it is easy to form and that a film tension equal to or higher than that of an insulating film obtained by baking a coating solution containing colloidal silica, primary phosphate and chromic acid can be obtained.
　Then, the present inventors can form an insulating film having excellent corrosion resistance and can produce a grain-oriented electrical steel sheet having further excellent iron loss even if a chromium compound is not used or the amount used is reduced. I found.
[0023]
　The coating liquid according to the present embodiment does not have to contain a binder (for example, primary phosphate, lithium silicate, water-soluble lithium salt, etc.) substantially, and the binder is not added or the amount used is reduced. However, the insulating film can be easily formed.
　The coating liquid according to the present embodiment does not contain a binder and may be composed of a layered clay mineral powder and a solvent. As a result, the effect of improving the water resistance of the film after baking can be obtained. Further, when phosphoric acid or phosphate is used as the binder, the coating liquid tends to gel, but when the binder is not contained, this gelation can be suppressed.
[0024]
　Further, it is preferable that the coating liquid according to the present embodiment does not substantially contain a chromium compound (chromic acid, hexavalent chromium, etc.). Specifically, the content of the chromium compound is preferably 4 parts by mass or less with respect to 100 parts by mass of the layered clay mineral powder. The content of the chromium compound is more preferably 2 parts by mass or less, still more preferably 1 part by mass or less, and particularly preferably 0 parts by mass with respect to 100 parts by mass of the layered clay mineral powder.
[0025]
　Further, it is preferable that the grain-oriented electrical steel sheet according to the present embodiment also contains substantially no chromium compound in its insulating film. Specifically, the content of the chromium compound is preferably 4 parts by mass or less with respect to 100 parts by mass of the dehydration product of the layered clay mineral. The content of the chromium compound is more preferably 2 parts by mass or less, still more preferably 1 part by mass or less, and particularly preferably 0 parts by mass with respect to 100 parts by mass of the dehydrated product of the layered clay mineral.
[0026]
　Hereinafter, each material constituting the coating liquid according to the present embodiment will be described.
[0027]
(Layered clay mineral powder) The
　layered clay mineral powder has a 1: 1 silicate layer represented by the composition formula X 2-3 Si 2 O 5 (OH) 4 and a composition formula X 2-3 (Si, Al) 4. The 2: 1 silicate layer represented by O 10 (OH) 2 (X is Al, Mg, Fe, etc.) has a laminated structure, either alone or mixed. The layers of the layered structure may contain at least one of water molecules and ions.
[0028]
　Layered clay minerals are typically kaolin (or kaolinite) (Al 2 Si 2 O 5 (OH) 4 ), talc (Mg 3 Si 4 O 10 (OH) 2 ), and pyrophyllite (Al). 2 Si 4 O 10 (OH) 2 ) can be mentioned. Most of the layered clay mineral powders are refined and pulverized naturally occurring layered clay minerals. As the layered clay mineral powder, one or more of kaolin powder, talc powder, and pyrophyllite powder may be used because they are industrially readily available. The layered clay mineral powder may be used in combination.
[0029]
　The layered clay mineral powder used in the present embodiment has a specific surface area of ​​20 m 2 / g or more, preferably 40 m 2 / g or more.
　Further, although not particularly limited , it is preferable that the specific surface area of ​​the layered clay mineral powder is 150 m 2 / g or less. When the specific surface area of ​​the layered clay mineral powder is less than this range, the stability (viscosity stability) of the dispersion liquid can be easily maintained by adding the dispersant.
　The specific surface area of ​​the layered clay mineral powder is measured by the method of JIS Z 8830: 2013.
[0030]
(Specific surface area 20 m 2 production of / g or more layered clay mineral powder)
　The layered clay mineral powder, which is commercially available in industrial applications specific surface area 20 m 2 it is difficult to obtain more than a / g. Therefore, for example, by subjecting a commercially available product to a pulverization treatment, a layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more can be obtained.
[0031]
　As the crushing means, a ball mill, a vibration mill, a bead mill, a jet mill and the like are effective. In these pulverization treatments, either dry pulverization in which the powder is pulverized or wet treatment in which layered clay mineral powder is dispersed in water or alcohol is effective.
　Since the specific surface area of ​​each of the various crushing means increases with the crushing time, it is possible to obtain a clay mineral powder having a required specific surface area and a dispersion liquid thereof by controlling the crushing time.
[0032]
　In the case of the wet pulverization treatment, if the specific surface area of ​​the layered clay mineral powder is increased to 20 m 2 / g or more by pulverization, the viscosity of the dispersion liquid increases and gels, which may interfere with the pulverization treatment. The increase in viscosity during the pulverization treatment can be suppressed by adding a dispersant.
　However, if an organic dispersant is added, it may be decomposed and carbonized at the time of baking the insulating film and carburized in the grain-oriented electrical steel sheet. Therefore, an inorganic dispersant is preferable. Examples of inorganic dispersants include polyphosphate and water glass. Specific examples of the former include sodium diphosphate and sodium hexametaphosphate. Specific examples of the latter include sodium silicate and potassium silicate.
[0033]
　The amount of these inorganic dispersants added is preferably suppressed to 20% by mass or less with respect to the layered clay mineral powder. By setting the addition amount of the inorganic dispersant to 20% by mass or less, the change in the film composition after baking is suppressed, and a higher film tension can be easily obtained.
　The amount of the inorganic dispersant added is more preferably 1% by mass or more.
　In the case of the dry pulverization treatment, it is not necessary to add the dispersant at the time of pulverization.
[0034]
(Method for preparing coating liquid) In
　the preparation of the coating liquid for forming an insulating film according to the present embodiment , layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more is added to a solvent such as water, and if necessary, other coating liquids are added. It is obtained by adding an additive and mixing and stirring. The layered clay mineral powder used may be used alone or in combination of two or more. When a layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more is prepared by a dry pulverization treatment, it may thicken or gel after mixing with a solvent such as water. At the time of preparation, it is effective to add the above-mentioned inorganic dispersant in a range of 20% by mass or less with respect to the layered clay mineral powder.
[0035]
　As the solvent used for the coating liquid, in addition to water, for example, alcohols such as ethyl alcohol, methyl alcohol and propyl alcohol can be used as a supplement. As the solvent used for the coating liquid, it is desirable to use water having no flammability.
[0036]
　The concentration of the layered clay mineral powder in the coating liquid for forming the insulating film is not particularly limited as long as it can be applied to the grain-oriented electrical steel sheet. The concentration (solid content concentration) of the layered clay mineral powder in the coating liquid for forming an insulating film is preferably, for example, 5.0% by mass to 50.0% by mass, more preferably 10.0% by mass to 30.0% by mass. %.
[0037]
　When a small amount of other additives is contained, for example, the content of the other additives is often 3% by mass or less with respect to the total solid content of the coating liquid for forming an insulating film according to the present embodiment, and 1% by mass. It may be as follows. Examples of other additives include, for example, a surfactant that prevents the coating liquid from repelling on the steel sheet.
[0038]

　Next, the method of manufacturing grain-oriented electrical steel sheet according to the present embodiment will be described.
　The method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment is for forming an insulating film for grain-oriented electrical steel sheet on the base material of the grain-oriented electrical steel sheet, that is, the grain-oriented electrical steel sheet for which the final finish annealing process has been completed. It has a step of applying the coating liquid of No. 1 and a step of subjecting the base metal after coating to a baking process. The coating liquid is a coating liquid containing a layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more. An inorganic dispersant is added to this coating liquid as needed.
[0039]
(Base material of directional electromagnetic steel sheet (directional electromagnetic steel sheet after final finish annealing))
　The directional electromagnetic steel sheet after final finish annealing is coated with the above coating liquid (that is, the coating liquid for forming an insulating film according to the present embodiment). A directional electromagnetic steel sheet that serves as a base material before coating. The grain-oriented electrical steel sheet after final finish annealing is not particularly limited.
　Specifically, the grain-oriented electrical steel sheet used as a base material is, for example, a steel piece containing 2% by mass to 4% by mass of Si, which is hot-rolled, annealed by hot-rolling, and cold-rolled, and then decarburized. Anneal. After that, it is obtained by applying an annealing separator having an MgO content of 50% by mass or more and performing final finish annealing. The grain-oriented electrical steel sheet after final finish annealing does not have to have a finish annealing film.
[0040]
(Coating and baking treatment of coating liquid for forming an insulating film)
　After applying the coating liquid for forming an insulating film according to the present embodiment to a grain-oriented electrical steel sheet (base material) after final finish annealing, a baking treatment is performed.
　The amount of the coating liquid to be applied is not particularly limited, but the amount of the film after forming the insulating film is excellent in terms of film strength, space factor, corrosion resistance and water resistance, and further obtains an iron loss reduction effect. It is preferable to apply the coating in the range of 1 g / m 2 to 10 g / m 2 . More preferably, the coating amount of the coating solution, as the amount of film after the insulating film forming, 2 g / m 2 ~ 8 g / m 2 is. The coating amount after the baking treatment can be obtained from the mass difference before and after the insulating film is peeled off.
[0041]
　The method of applying the coating liquid for forming an insulating film to the grain-oriented electrical steel sheet after final finish annealing is not particularly limited. For example, a coating method using a coating method such as a roll method, a spray method, or a dip method can be mentioned.
[0042]
　After applying the coating liquid for forming an insulating film, baking is performed. Many layered clay mineral powders release structural water at a heating temperature of around 550 ° C. to form a film. Therefore, the baking temperature is preferably 600 ° C. or higher. On the other hand, when a baking temperature of more than 1000 ° C. is adopted, the grain-oriented electrical steel sheet is softened and easily distorted, so the baking temperature is preferably 1000 ° C. or less.
　When the baking temperature is low, it is preferable to take a long baking time. The preferable lower limit of the baking temperature is 700 ° C. or higher. The preferred upper limit of the baking temperature is 950 ° C. or lower. The baking time is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 120 seconds.
[0043]
　The heating method for performing the baking treatment is not particularly limited, and examples thereof include a radiant furnace, a hot air furnace, and induction heating.
[0044]
　The insulating film after the baking treatment becomes a dense film. The thickness of the insulating film is preferably 0.5 μm to 5 μm, more preferably 1 μm to 4 μm.
　The thickness of the insulating film after the baking treatment can be determined by observing a cross section including the thickness direction of the base material of the directional electromagnetic steel plate with an SEM (scanning electron microscope).
[0045]
　Through the above steps, the coating liquid for forming an insulating film according to the present embodiment has a large film tension, a film property having excellent corrosion resistance, and a grain-oriented electrical steel sheet having further excellent iron loss.
[0046]

　The grain-oriented electrical steel sheet according to this embodiment contains a base material of the grain-oriented electrical steel sheet and SiO 2 provided on the surface of the base material , and is selected from Al 2 O 3 and Mg O. It has an insulating film containing one or two of the above.
　Further, the insulating film may further contain one or more selected from Fe 2 O 3 , Na 2 O, K 2 O, and P 2 O 5 .
[0047]
　This insulating film is a dense film, and specifically, the porosity is 10% or less.
　In the directional electromagnetic steel sheet according to the present embodiment, since the insulating film has the above-mentioned structure, it is possible to obtain a dense insulating film while not containing the binder as described above or reducing the amount used. In addition, a film tension equal to or higher than that of an insulating film obtained by baking a coating solution containing colloidal silica, primary phosphate and chromic acid can be obtained.
　Further, even if a chromium compound is not used or the amount used is reduced, an insulating film having excellent corrosion resistance can be obtained, and a grain-oriented electrical steel sheet having further excellent iron loss can be obtained.
[0048]
　In the grain-oriented electrical steel sheet according to the present embodiment, the porosity of the insulating film is 10% or less. Preferably, the porosity of the insulating film is 5% or less, more preferably 1% or less.
[0049]
　The porosity of the insulating film (the area ratio of the pores contained in the insulating film) is measured by the following method. First, as shown in FIG. 3, a backscattered electron image of a cross section of the insulating film is obtained by SEM. Performs binarization processing using image processing software such as Image-Pro with respect to the image, the area A of the cross-section excluding the area of the voids (pores) from the binary image C obtaining (example of FIG. 3 In, A C = 197Myuemu 2 ).
　Further, the area A of the cross section including the area of ​​the voids (pores) is obtained from the image filled with the voids of the binarized image (A = 260 μm 2 in the example of FIG. 3 ).
　Then, the porosity F, F = 1-A C calculated from / A (in the example of FIG. 3, F = 1-197 / 260 = 24.1%).
　The insulating film of one grain-oriented electrical steel sheet is observed by SEM (magnification of 5000 times) to obtain five images, and the porosity is calculated for each image by the above method. The average value of these is calculated and used as the porosity of the insulating film.
[0050]
　The insulating film of the directional electromagnetic steel sheet according to the present embodiment contains SiO 2 and one or two selected from Al 2 O 3 and Mg O , and further contains Fe 2 O 3 , Na 2 O, and the like. It may contain one or more selected from K 2 O and P 2 O 5 .
　The insulating film having a porosity of 10% or less is coated with a coating liquid for forming the insulating film for grain-oriented electrical steel sheets according to the present embodiment, and is baked at a temperature of 600 ° C. or higher and 1000 ° C. or lower. Can be formed by
[0051]
　Here, SiO 2 contained in the insulating film formed by the above method ; one or two selected from Al 2 O 3 and Mg O ; and Fe 2 O 3 , Na 2 O, K 2 O, and P 2 One or more constituents selected from O 5 are dehydrated products of layered clay minerals and inorganic dispersants.
[0052]
　The dehydration product of the layered clay mineral contained in the insulating film is preferably a dehydration product of one or more layered clay minerals selected from kaolin, talc, and pyrophyllite. Dehydration products of kaolin approximate molar ratio of 1: 2 of Al 2 O 3 and SiO 2 is composed of, dehydration product of talc approximate molar ratio of 3: 4 of MgO and SiO 2 is composed of, dehydration of pyrophyllite The product is composed of Al 2 O 3 and SiO 2 having a molar ratio of approximately 1: 4 . However, since layered clay minerals are naturally produced, the molar ratio varies by about 10% and may contain Fe 2 O 3 as an impurity .
[0053]
　In the present embodiment, an inorganic dispersant may be added to the coating liquid for forming the insulating film for the directional electromagnetic steel plate, but these are also dehydrated after baking to become anhydrous, and often dehydration of layered clay minerals. Reacts with the product. The insulating film contains a dehydration product derived from an inorganic dispersant of more than 0% by mass and 20% by mass or less with respect to the dehydration product of the layered clay mineral, or a reaction product with the dehydration product derived from the layered clay mineral. May be good.
　As the inorganic dispersant, the above-mentioned ones described in the section of the coating liquid can be mentioned as similarly suitable ones. For example, sodium diphosphate and sodium hexametaphosphate, which are a kind of inorganic dispersant, are composed of Na 2 O and P 2 O 5 after baking . In the case of sodium silicate, it is composed of Na 2 O and SiO 2 . In the case of potassium silicate, it is composed of K 2 O and SiO 2 .
[0054]
　Although preferred embodiments of the present invention have been described, the present invention is not limited to the above. The above is an example, and any material having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same action and effect is the technique of the present invention. It is included in the target range.
Example
[0055]
　Hereinafter, the present invention will be specifically described by exemplifying examples, but the present invention is not limited thereto.
[0056]
(Example A)
　First, commercially available fine powders of kaolinite, talc, and pyrophyllite (specific surface areas are all 10 m 2 / g) were prepared and pulverized by various means shown in Table 1 below. When the dispersant was added, the dispersant was added at the time of preparing the water slurry before the treatment in the wet pulverization, and at the time of adjusting the coating liquid after the pulverization in the dry pulverization. After the pulverization treatment, the specific surface area of ​​the layered clay mineral powder was measured by the method of JIS Z 8830: 2013.
[0057]
　Using the above layered clay mineral powder, a coating liquid having the composition shown in Table 1 was prepared. In order to confirm the stability of the coating liquid, a part of the preparation liquid was collected and left at room temperature for 2 days and nights, and then the state of the coating liquid (presence or absence of gelation) was observed. The coating liquid shown in Example 13 is an example containing two types of layered clay mineral powder.
[0058]
　A grain-oriented electrical steel sheet (B8 = 1.93T) having a thickness of 0.23 mm and having a finish-annealed film that has been final-annealed is prepared, and the coating liquid having the composition shown in Table 1 is subjected to an insulating film amount after baking. The coating was applied using a roll coater so as to have a concentration of 5 g / m 2 , dried, and then annealed at 850 ° C. for 30 seconds.
[0059]
　The composition of the coating liquid of the reference example in Table 1 is as follows.
　・ Colloidal silica 20% by mass aqueous dispersion: 100 parts
　by mass ・ Aluminum 50% by mass aqueous solution: 60 parts
　by mass ・ Chromic anhydride: 6 parts by mass
[0060]
　The film characteristics, magnetic properties, water resistance and corrosion resistance of the obtained grain-oriented electrical steel sheet with an insulating film were evaluated. Moreover, the porosity of the insulating film was measured by the above-mentioned method.
　The results are shown in Table 1. The evaluation method of each evaluation shown in Table 1 is as follows.
[0061]
(Film tension) The
　film tension is calculated from the warp of the steel sheet that occurs when one side of the insulating film is peeled off. The specific conditions are as follows.
　The insulating film on only one side of the electromagnetic steel sheet is removed with an alkaline aqueous solution. After that, the film tension is calculated from the warp of the electromagnetic steel sheet by the following formula.
　Formula: Film tension = 190 x plate thickness (mm) x plate warpage (mm) / {plate length (mm)} 2 [MPa]
[0062]
(Iron loss)
　Measure according to the method described in JIS C 2550-1 (2011). Specifically, it is measured as an iron loss (W 17/50 ) per unit mass under the conditions of an amplitude of the measured magnetic flux density of 1.7 T and a frequency of 50 Hz .
[0063]
(Water resistance)
　Water resistance was evaluated by the amount of elution film. The test piece was immersed in boiling water for 1 hour, and the weight change of the test piece before and after the immersion was determined and used as the elution film amount. Table 1 shows the film elution rate (%), which is the ratio of the elution film amount to the insulation film formation amount. The smaller the film elution rate (%), the better the water resistance.
[0064]
(Corrosion resistance)
　Corrosion resistance was evaluated by JIS Z 2371 (salt spray test). The results are shown in Table 1 as the rust area ratio (%) after the test. The smaller the rust area ratio (%), the better the corrosion resistance.
[0065]
[table 1]

[0066]
　In Table 1, the abbreviations for layered clay mineral powder, the abbreviation for the crushing method, and the abbreviation for the dispersant name are as follows.
　K: Kaolinite
　T: Talc
　P: Pyrophyllite
[0067]
　JM: Jet mill (dry type)
　BD: Ball mill (dry type)
　BW: Ball mill (wet type)
　BM: Bead mill (wet type)
[0068]
　SDP: Sodium
　diphosphate SHMP: Sodium hexametaphosphate
　SS: Sodium silicate
　PS: Potassium silicate
[0069]
　As shown in Table 1, when a coating liquid containing a layered clay mineral powder having a specific surface area of ​​20 m 2 / g or more is applied and baked by pulverization, the film tension is large, the iron loss reduction effect is large, and water resistance and corrosion resistance are large. Is extremely good. That is, it can be seen that the performance equal to or higher than that of the film when the coating liquid containing the chromium compound shown in the reference example is used can be obtained.
[0070]
　Further, the coating liquid having a large specific surface area tends to gel and the workability of the coating liquid tends to deteriorate. However, by increasing the dispersant concentration in response to the increase in the specific surface area, from Examples 9 to 11 and Example 12. It can be seen that viscosity stability can be maintained.
　However, if a dispersant for preventing gelation of the dispersion liquid is added in an amount of more than 20% by mass as in Example 12, the film composition is affected, and even if a layered clay mineral powder having a large specific surface area is used, the film tension Tends to cause deterioration. Therefore, it can be seen that it is preferable to set the upper limit of the dispersant addition to 20% by mass.
[0071]
　As shown in Examples 4 and 8, when the specific surface area exceeds 150 m 2 / g and the amount of the dispersant added is suppressed to 20% by mass or less, the coating liquid tends to gel and it is difficult to apply with a simple coating facility. Become. However, this can be achieved by using a coating facility for high-viscosity liquids such as die coat.
[0072]
　Here, FIGS. 1 and 2 show the results of observing the cross sections of the grain-oriented electrical steel sheets provided with the insulating coatings of Comparative Example 2 and Example 2 by SEM (JSM7000 manufactured by JEOL Ltd.). In FIGS. 1 and 2, 11 and 21 represent an insulating film, and 12 and 22 represent a finish annealing film (hereinafter, reference numerals are omitted).
　As shown in FIG. 2, it was clarified that the insulating film of Example 2 was a dense film having extremely few voids. As shown in FIG. 2, since the insulating film of Example 2 is dense, it is considered that the film tension is excellent and the iron loss is improved.
[0073]
(Example B)
　Next, the results of evaluating the film characteristics and the magnetic characteristics by changing the baking temperature are shown.
　A coating liquid having the same composition as that of Example 2 was applied with a roll coater and dried by the same procedure as in Example 2 so that the amount of the insulating film after the baking treatment was 5 g / m 2 . Then, the baking process was performed by changing the baking temperature to the conditions shown in Table 2. The baking time is the same as in Example A. The results are shown in Table 2.
[0074]
　As shown in Table 2, it is considered that when the baking temperature is set to 600 ° C. or higher, the reaction between the hydrous silicate powder and the phosphoric acid proceeds sufficiently and a high film tension can be obtained. It can be seen that each example having a baking temperature of 600 ° C. or higher is excellent in film characteristics and magnetic characteristics.
[0075]
[Table 2]

[0076]
　Although suitable examples of the present invention have been described above, the present invention is not limited to these examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the ideas described in the claims, and these also naturally belong to the technical scope of the present invention. It can be understood as a thing.
Industrial applicability
[0077]
　According to the present invention, it is possible to form an insulating film having excellent corrosion resistance while not using a chromium compound or reducing the amount used, and to produce a grain-oriented electrical steel sheet having further excellent iron loss. A coating liquid for forming an insulating film for an electromagnetic steel sheet is provided. Further, there is provided a method for producing a grain-oriented electrical steel sheet, which can produce a grain-oriented electrical steel sheet having excellent corrosion resistance and further excellent iron loss while not using a chromium compound or reducing the amount used. Further, a grain-oriented electrical steel sheet having excellent corrosion resistance and further excellent iron loss while using no chromium compound or reducing the amount used is provided. Therefore, the present invention has high industrial utility value.
The scope of the claims
[Claim 1]
　A solvent,
　a specific surface area 20 m 2 and one or more / g or more layered clay mineral powder,
containing
coating solution for forming the oriented electrical steel sheet insulating coating, characterized in that.
[Claim 2]
The coating liquid for forming an insulating film for grain-oriented electrical steel sheets according to claim 1, 　wherein the specific surface area of ​​the layered clay mineral powder is 150 m 2 / g or less
.
[Claim 3]

The directional electromagnetic steel plate according to claim 1 or 2, 　wherein the layered clay mineral powder is one or more powders selected from the group consisting of kaolin, talc, and pyrophyllite . A coating liquid for forming an insulating film.
[Claim 4]
　The
insulating film for a directional electromagnetic steel plate according to any one of claims 1 to 3, which contains an inorganic dispersant of more than 0% by mass and 20% by mass or less with respect to the layered clay mineral powder. Coating liquid to do.
[Claim 5]

The directional electromagnetic steel plate according to claim 4, 　wherein the inorganic dispersant is one or more selected from the group consisting of sodium diphosphate, sodium hexametaphosphate, sodium silicate, and potassium silicate. Coating liquid for forming an insulating film.
[Claim 6]

To form the insulating film for a directional electromagnetic steel plate according to any one of claims 1 to 5 　, wherein the content of the chromium compound is 4% by mass or less with respect to the layered clay mineral powder. Coating liquid.
[Claim 7]
　The step of applying a coating liquid for forming the insulating film for grain-oriented electrical steel sheet according to any one of claims 1 to 6 to the base material of the grain-oriented electrical steel sheet, and the base material
　after coating. A method for producing a grain-oriented electrical steel sheet ,
which comprises a step of forming an insulating film by performing a baking process at a temperature of 600 ° C. or higher and 1000 ° C. or lower
.
[Claim 8]
　A
　grain-
oriented electrical steel sheet having a base material and an insulating film provided on the surface of the base material ,
　wherein the insulating film contains
　　SiO 2 , and is one or 2 of Al 2 O 3 and Mg O. A grain-containing
　　grain-
oriented electrical steel sheet having a porosity of 10% or less .
[Claim 9]
　8. The eighth aspect of the invention, wherein the insulating film further contains one or more selected from the group consisting of Fe 2 O 3 , Na 2 O, K 2 O, and P 2 O 5.
Directional electromagnetic steel plate.
[Claim 10]

The directional electromagnetic steel sheet according to claim 8 or 9, 　wherein the content of the chromium compound in the insulating film is 4% by mass or less with respect to the dehydration product of the layered clay mineral .