WO2026014048A1 - Method for producing grain-oriented electrical steel sheet and method for evaluating insulating film treatment solution - Google Patents

Abstract

The present invention produces a grain-oriented electrical steel sheet that is provided with a steel sheet and an insulating film disposed on the surface of the steel sheet by applying an insulating film treatment solution, which is used for forming an insulating film, on the surface of the steel sheet within X minutes from completion of the preparation of the insulating film treatment solution, and then performing baking. The ratio YX/Y5 of a yield value YX X minutes after completion of the preparation of the insulating film treatment solution to a yield value Y5 5 minutes after completion of the preparation of the insulating film treatment solution is not more than 8.00. Thus, the grain-oriented electrical steel sheet that is produced has an excellent appearance.

Description

Manufacturing method for grain-oriented electrical steel sheet and evaluation method for insulating coating treatment solution

The present invention relates to a method for manufacturing grain-oriented electrical steel sheets and a method for evaluating insulating coating treatment solutions.

Grain-oriented electrical steel sheet is a soft magnetic material used as the iron cores of transformers, generators, and other devices. It has a crystal texture in which the <001> orientation, the axis of easy magnetization of iron, is highly aligned in the rolling direction of the steel sheet. This texture is formed during the manufacturing process of grain-oriented electrical steel sheet through a finishing annealing (secondary recrystallization annealing) process that preferentially grows crystal grains with the {110} <001> orientation, known as the Goss orientation.

Such grain-oriented electrical steel sheets generally comprise a steel sheet and insulating coatings disposed on both sides of the steel sheet. The insulating coatings not only apply tension to the steel sheet to reduce the iron loss of the grain-oriented electrical steel sheet, but also provide the grain-oriented electrical steel sheet with properties such as insulation, workability, and rust resistance.
As such insulating coatings, for example, chromium-free insulating coatings have been proposed from the viewpoint of environmental conservation (Patent Documents 1 to 4).

Japanese Patent Application Laid-Open No. 2000-169972 JP 2017-137540 A Japanese Patent Application Laid-Open No. 2008-266743 Special table 2017-511840 publication

The insulating coating is formed, for example, by applying an insulating coating treatment solution containing phosphate, colloidal silica, etc. to the surface of a steel sheet (e.g., a secondary recrystallized sheet) using, for example, a roll coater, and then baking the applied solution.
At this time, the insulating coating treatment liquid may be applied to the steel sheet while it is being transported, but if the transport speed is too high, the resulting grain-oriented electrical steel sheet may have poor appearance.

The present invention was made in consideration of the above points, and aims to produce grain-oriented electrical steel sheets with excellent appearance.

As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention.
That is, the present invention provides the following [1] to [6].
[1] A method for producing a grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating disposed on a surface of the steel sheet, wherein an insulating coating treatment liquid used to form the insulating coating is applied to the surface of the steel sheet within X minutes from completion of preparation of the insulating coating treatment liquid, and baked, so that the ratio _YX / _Y5 of the yield value _YX after X minutes from completion of preparation of the insulating coating treatment liquid to the yield value _Y5 after 5 minutes from completion of preparation of the insulating coating treatment liquid satisfies 8.00 or less.
[2] The method for producing a grain-oriented electrical steel sheet according to [1] above, wherein the insulating coating treatment solution contains a phosphate containing at least one element selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al, and Mn, colloidal silica, and a metal compound containing a metal element, the content of the colloidal silica being 50 to 120 parts by mass, calculated as _SiO2 solid content, per 100 parts by mass of the solid content of the phosphate, and the content of the metal compound being 5 to 60 parts by mass, calculated as metal element, per 100 parts by mass of the solid content of the phosphate.
[3] The method for producing a grain-oriented electrical steel sheet according to the above [1] or [2], wherein the yield value _Y5 is 1.50 × 10 ^-5 N/cm ² or less.
[4] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3] above, wherein the consistency index 5 minutes after completion of preparation of the insulating coating treatment solution is 10.0 mPa s or less, and the flow index 5 minutes after completion of preparation of the insulating coating treatment solution is 0.80 or more and 1.20 or less.
[5] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [4] above, wherein the metal compound contains at least one metal element selected from the group consisting of Zn, Ba, Sr, Mn, Ca, V, Ti, Mg, Hf, Zr, and Nb.
[6] A method for evaluating an insulating coating solution used to form an insulating coating on a grain-oriented electrical steel sheet, the method comprising: applying the insulating coating solution to a surface of a steel sheet and baking the insulating coating to form the insulating coating; and determining that the appearance of the grain-oriented electrical steel sheet obtained is good if the ratio _Y180 / _Y5 of the yield value _{Y180 180} minutes after completion of preparation of the insulating coating solution to the yield value Y5 5 minutes after completion of preparation of the insulating coating solution is 8.00 or less.

According to the present invention, grain-oriented electrical steel sheets with excellent appearance can be manufactured.

[Findings Obtained by the Inventors]
The present inventors have made the following findings.

The insulating coating treatment liquid is typically applied to the surface of the steel sheet using a roll coater. It is then baked to form an insulating coating on the surface of the steel sheet.

When the insulating coating treatment liquid is applied to the surface of a steel sheet, if the viscosity of the insulating coating treatment liquid (viscosity at high shear rates) is high, the liquid surface (liquid surface of the insulating coating treatment liquid) between the steel sheet and the roll of the roll coater becomes unstable, making it likely that uneven application such as ribbing defects (streaky defects) will occur.
If baking is carried out while the coating is uneven, the resulting grain-oriented electrical steel sheet may have a poor appearance.

However, even if coating unevenness such as ribbing defects occurs, poor appearance can be suppressed if the viscosity (viscosity in the low shear rate range) of the insulating coating treatment solution applied to the surface of the steel sheet is low and the solution is sufficiently leveled and uniformed before baking.
That is, in order to obtain a good appearance, it is effective not only to improve the unevenness of the coating but also to improve the leveling properties of the insulating coating treatment solution.

Incidentally, the insulating coating treatment solution is prepared, for example, by mixing raw materials (phosphate, colloidal silica, etc.) in a preparation container. After preparation is complete, the insulating coating treatment solution is stored in a stationary state in the preparation container (or in a stirred state in a temporary storage container).
The stored insulating coating solution is then transferred by a pump or the like to a roll coater and applied to the surface of the steel sheet. In many cases, the insulating coating solution that overflows from the surface of the steel sheet and is not applied is recovered and transferred (circulated) to the roll coater again.
As described above, it has been found that a certain amount of time may pass between the completion of preparation of the insulating coating treatment solution and application, and that the viscosity characteristics may change during this time.

That is, even if the viscosity of the insulating coating solution in the low shear rate range is low immediately after preparation, it may increase over time from preparation to application. In this case, the applied insulating coating solution will not be sufficiently leveled before baking, and poor appearance cannot be prevented.
On the other hand, if the change in viscosity is small, the applied insulating coating treatment liquid will level off before baking, resulting in a good appearance.

The present invention was made based on the above findings and further investigations.
Next, a preferred embodiment of the present invention will be described.

[Method of manufacturing grain-oriented electrical steel sheet]
The method for manufacturing a grain-oriented electrical steel sheet of this embodiment is a method for manufacturing a grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating disposed on the surface of the steel sheet, and generally, is a method for forming an insulating coating by applying an insulating coating treatment liquid to the surface of the steel sheet and baking it.
The following description also includes an explanation of the method for evaluating the insulating coating treatment solution.

<Steel plate>
The steel sheet used in this embodiment is, for example, a secondary recrystallized sheet (finish annealed sheet) having a forsterite coating formed on the surface.
The secondary recrystallized plate is produced, for example, as follows.

First, a steel slab having the above-mentioned component composition (steel composition) is obtained from molten steel produced by a conventionally known refining process by using a continuous casting method or an ingot making-blooming rolling method.
The steel slab is hot-rolled to obtain a hot-rolled sheet, which is then annealed as necessary and then cold-rolled once or twice or more times with intermediate annealing to obtain a cold-rolled sheet of the final thickness.
Next, the cold-rolled sheet is subjected to primary recrystallization annealing and decarburization annealing, after which an annealing separator containing MgO as a main component is applied, and the sheet is subjected to finish annealing (secondary recrystallization annealing) to form a forsterite coating.
In this way, a secondary recrystallized plate having a forsterite coating on the surface is obtained.

The steel sheet has a chemical composition (steel composition) containing, for example, C: 0.001 to 0.10%, Si: 1.0 to 5.0% (preferably 2.0 to 5.0%), sol. Al: 0.003 to 0.050%, N: 0.001 to 0.020%, at least one element selected from the group consisting of S and Se: 0.001 to 0.05%, and the balance consisting of Fe and unavoidable impurities.
In addition, "%" in the component composition means "% by mass" unless otherwise specified.

The steel sheet composition may further contain at least one element selected from the group consisting of Cu: 0.01-0.2%, Ni: 0.01-0.5%, Cr: 0.01-0.5%, Sb: 0.01-0.1%, Sn: 0.01-0.5%, Mo: 0.01-0.5%, and Bi: 0.001-0.1%.

The steel sheet may further contain at least one element selected from the group consisting of B: 0.001-0.01%, Ge: 0.001-0.1%, As: 0.005-0.1%, P: 0.005-0.1%, Te: 0.005-0.1%, Nb: 0.005-0.1%, Ti: 0.005-0.1%, and V: 0.005-0.1%.

<Insulating coating treatment liquid>
The insulating coating treatment solution used in this embodiment contains phosphate and colloidal silica, and preferably further contains a metal compound containing a metal element.

Phosphate
The phosphate preferably contains at least one element selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al and Mn.
Examples of phosphates include magnesium phosphate, calcium phosphate, barium phosphate, strontium phosphate, zinc phosphate, aluminum phosphate, and manganese phosphate. Hereinafter, for example, magnesium phosphate will also be referred to as "Mg phosphate" (the same applies to other phosphates).
As the phosphate, monophosphate (biphosphate) is easily available and is therefore preferred.

Colloidal silica
The content of colloidal silica is, for example, 30 parts by mass or more in terms of _SiO2 solid content per 100 parts by mass of the phosphate solid content, and is preferably 50 parts by mass or more, and more preferably 60 parts by mass or more, because this provides an insulating coating that has excellent moisture absorption resistance.
The content of colloidal silica is, for example, 150 parts by mass or less in terms of _SiO2 solid content per 100 parts by mass of the phosphate solid content, and is preferably 120 parts by mass or less, and more preferably 100 parts by mass or less, because this provides an insulating coating having excellent moisture absorption resistance.

《Metal compounds》
When forming a chromium-free insulating coating, it is preferable for the insulating coating treatment solution to contain a metal compound, from the viewpoints of ensuring good moisture absorption resistance and corrosion resistance and increasing the tension (applied tension) that the insulating coating imparts to the steel sheet.
The metal element contained in the metal compound is an element other than Cr, and from the viewpoint of moisture absorption resistance, etc., it is preferably at least one element selected from the group consisting of Zn, Ba, Sr, Mn, Ca, V, Ti, Mg, Hf, Zr, and Nb.
The metal compound is, for example, a metal oxide, a metal nitride or a metal nitrate.
Specific examples of _{metal compounds include TiO2, ZrO2, HfO2, MgO, ZnO, Nb2O5, V2O5 , TiN , ZrN , BaO} , Ba( _NO3 ) ₂ , Sr( _NO3 ) ₂ , MnO, and CaO.

The content of the metal compound, calculated as the metal element, is, for example, 2 parts by mass or more per 100 parts by mass of the solid content of the phosphate. In order to provide an insulating coating that has excellent moisture absorption resistance and can impart a high tension, the content is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more.
The content of the metal compound is, for example, 80 parts by mass or less in terms of metal element relative to 100 parts by mass of the solid content of the phosphate, and is preferably 60 parts by mass or less, and more preferably 40 parts by mass or less, because this makes it easier to suppress an increase in viscosity of the insulating coating treatment solution.

The metal compound may be in the form of particles (powder), for example.
The particle size of the metal compound will be described later.

<Dispersant>
The insulating coating treatment solution may further contain a dispersant, which will be described later.

《Chromium compounds》
The insulating coating treatment solution is preferably so-called chromium-free, that is, does not contain chromium compounds such as chromic anhydride (chromium trioxide), chromates, or dichromates.
Specifically, the content of the chromium compound is preferably 1.0 part by mass or less, more preferably 0.10 part by mass or less, and even more preferably 0.01 part by mass or less, calculated as chromium element (Cr) per 100 parts by mass of the solid content of the phosphate.

<Preparation and application of insulating coating treatment solution>
<<Application within X minutes after completion of blending and ratio _YX / _Y5 >>
In this embodiment, the above-described insulating coating treatment solution is prepared and applied to the surface of the steel sheet within X minutes after the preparation is completed.
At this time, the ratio _YX / _Y5 of the yield value YX _X minutes after the completion of preparation of the insulating coating solution to the yield value Y5 ₅ minutes after the completion of preparation of the insulating coating solution satisfies 8.00 or less.
When the above conditions are satisfied, the viscosity (viscosity at low shear rates) of the insulating coating treatment solution applied to the surface of the steel sheet is low and sufficient leveling occurs before baking, resulting in a good appearance. From the viewpoint of obtaining a better appearance, the ratio _YX / _Y5 is preferably 5.00 or less, more preferably 4.50 or less, and even more preferably 3.00 or less.

The lower limit of the ratio _Yx / _Y5 is not particularly limited.
However, if the ratio _Yx / _Y5 is too low, the viscosity of the applied insulating coating treatment solution will decrease excessively before baking, and the desired amount of insulating coating may not be obtained.
Therefore, the ratio _Yx / _Y5 is preferably 0.10 or greater, more preferably 0.50 or greater, and even more preferably 1.00 or greater.

X minutes is, for example, 180 minutes.
For example, when the ratio _Y180 / _Y5 of the yield value _Y180 180 minutes after the completion of preparation of the insulating coating treatment solution to the yield value Y5 ₅ minutes after the completion of preparation of the insulating coating treatment solution satisfies the above range (e.g., 8.00 or less), it may be determined that a good appearance is obtained.

How to calculate the yield value
The yield value of the insulating coating solution is determined as follows.
First, the shear stress τ of the insulating coating treatment liquid (liquid temperature: 20°C) is measured using a Brookfield viscometer at a shear rate γ in the range of 13.2 to 330.0 ^s-1 , and then fitted to the Herschel-Bulkley equation "τ = _τ0 + ^kγn " ( _τ0 : yield value, k: consistency index, n: flow index).
In this manner, "Y ₅ ," which is the yield value (τ ₀ ) 5 minutes after the completion of preparation, and "Y _{X ,} " which is the yield value (τ ₀ ) X minutes after the completion of preparation, are determined for the insulating coating treatment solution.

<<Yield value Y ₅ 5 minutes after synthesis is complete>>
The yield value of the insulating coating treatment solution itself is not particularly limited.
However, if the yield value _Y5 5 minutes after the completion of preparation is too high, it may be difficult to apply the insulating coating treatment solution itself. Therefore, the yield value _Y5 5 minutes after the completion of preparation is preferably 3.00×10 ⁻⁵ N/cm ² or less, more preferably 2.50×10 ⁻⁵ N/cm ² or less, even more preferably 2.00×10 ⁻⁵ N/cm ² or less, and particularly preferably 1.50×10 ⁻⁵ N/cm ² or less.
On the other hand, the yield value _Y5 5 minutes after the completion of mixing is, for example, 0.05×10 ⁻⁵ N/cm ² or more, and may be 0.10×10 ⁻⁵ N/cm ² or more.

<<K 5 minutes after the compounding is complete>>
The consistency index k 5 minutes after the completion of mixing is, for example, 18.0 mPa·s or less, preferably 16.0 mPa·s or less, more preferably 14.0 mPa·s or less, even more preferably 12.0 mPa·s or less, and particularly preferably 10.0 mPa·s or less.
On the other hand, the viscosity k 5 minutes after the completion of preparation is, for example, 1.0 mPa·s or more, and may be 1.5 mPa·s or more.

<<n 5 minutes after the compounding is complete>>
The flow index (n) 5 minutes after the completion of the blending is, for example, 1.20 or less, preferably 1.10 or less, and more preferably 1.00 or less.
On the other hand, n 5 minutes after the completion of blending is, for example, 0.60 or more, may be 0.70 or more, and is preferably 0.80 or more.

《Definition of Synthesis and Synthesis Completion》
Generally, the blending is carried out by placing raw materials (phosphoric acid, colloidal silica, etc.) in a blending vessel and mixing them.
Specifically, blending refers to the process of adding raw materials (including dispersants), mixing the raw materials, and performing general operations aimed at improving the uniformity and dispersibility of the mixed liquid obtained by mixing the raw materials (for example, the dispersion process described below).
Completion of compounding means the point at which such compounding is completed.

Furthermore, after the blending is complete, other tasks (post-blending tasks) are carried out, such as transferring the insulating coating treatment liquid from the blending container to the temporary storage container; stirring the insulating coating treatment liquid in the temporary storage container; transferring the insulating coating treatment liquid from the blending container or temporary storage container to the coater; circulating the insulating coating treatment liquid; and applying the insulating coating treatment liquid using a coater. However, such post-blending tasks are not included in blending.

In some cases, the insulating coating solution is diluted with water after preparation to adjust the amount of the insulating coating to be formed, etc. In this case, a correction formula is prepared in advance, and the yield values ( _Y5 , _YX ) of the insulating coating solution before dilution are calculated using the correction formula.

《Mixing temperature》
One method for controlling the ratio _Yx / _Y5 of the insulating coating treatment solution within the above range is to lower the preparation temperature.
The blending temperature refers to the temperature of the raw materials and the temperature of the mixed liquid (insulation coating treatment liquid) obtained by mixing the raw materials.

In general, raw materials such as phosphate and colloidal silica consist of liquids with different pH values. When the raw materials are mixed, the pH of the mixture passes near the isoelectric point of each raw material, causing them to aggregate, resulting in the formation of precipitates and gelation, which can increase the yield value of the mixture.

By maintaining the compounding temperature at a low temperature, the formation of precipitates and the occurrence of gelation can be suppressed, and the ratio _Yx / _Y5 can be controlled within the above-mentioned range.
Specifically, the blending temperature is preferably 13° C. or lower, more preferably 10° C. or lower, and even more preferably 7° C. or lower. There is no particular lower limit to the blending temperature, but the blending temperature may be, for example, 0° C. or higher, or 3° C. or higher.

Distributed Processing
From the viewpoint of controlling the yield value _Y5 5 minutes after the completion of blending within a suitable range, it is preferable to carry out a dispersion treatment on the raw materials (mixture) charged into the blending vessel.
The dispersion treatment is preferably carried out using a homogenizer such as an ultrasonic homogenizer. Commercially available homogenizers include the Sonicmix manufactured by Mitsui Electric Seiki Co., Ltd., the Ultrasonic Processor atomizer manufactured by F.T. Associates, Inc., and the high-efficiency industrial ultrasonic generator (UIP1000, etc.) manufactured by Hielscher.

The intensity of the dispersion treatment (treatment intensity) is expressed as a value calculated by the following formula: treatment output (unit: W) x treatment time (unit: h) ÷ treatment liquid volume (unit: L).
Specifically, when dispersion treatment is carried out, the treatment intensity is preferably 2 Wh/L or more, more preferably 4 Wh/L or more, while the treatment intensity is preferably 12 Wh/L or less, more preferably 8 Wh/L or less.

<<Addition of dispersant>>
From the viewpoint of adjusting the consistency index (k) 5 minutes after the completion of mixing to a suitable range, it is preferable to add a dispersant as a raw material. The dispersant reduces the viscosity of the insulating coating treatment solution and suppresses re-aggregation of colloidal silica and the like, thereby controlling the ratio _Yx / _Y5 within the above range.

Dispersants include cationic surfactants, anionic surfactants, and nonionic surfactants, with cationic surfactants being preferred. This is because, in the insulating coating treatment solution, the particle surfaces of the metal compounds mentioned above are negatively charged, and it is believed that cationic surfactants are likely to be adsorbed onto these surfaces.

As cationic surfactants, quaternary ammonium salt types are preferred because of their low foaming properties. Commercially available quaternary ammonium salt cationic surfactants include SN Dispersant 4215 manufactured by San Nopco and Adekamin 4DAC-85 manufactured by ADEKA.

The content of dispersant in the insulating coating treatment solution is, for example, 0.3 parts by mass or more, preferably 0.7 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 1.5 parts by mass or more, and particularly preferably 2.0 parts by mass or more, per 100 parts by mass of the phosphate solids content.

On the other hand, if the dispersant content is too high, the ratio _YX / _Y5 may become too low. Therefore, the content of the dispersant in the insulation coating treatment solution is, for example, 5.0 parts by mass or less, preferably 4.0 parts by mass or less, more preferably 3.5 parts by mass or less, and even more preferably 3.0 parts by mass or less.

If the dispersant is diluted with a solvent, the dispersant content refers to the amount excluding the solvent.

<Particle size of metal compound>
From the viewpoint of adjusting the flow index n (5 minutes after the completion of the preparation) to a suitable range, it is preferable to control the particle size of the metal compound.
When the particle size of the metal compound is appropriately small, the non-Newtonian fluidity of the insulating coating treatment solution becomes prominent, and the flow index (n) becomes smaller or larger than 1.
Furthermore, if the particle size of the metal compound is too large, the reactivity between the insulating coating treatment liquid and the steel sheet during baking is insufficient, which tends to result in insufficient moisture absorption resistance and imparted tension to the insulating coating.

Therefore, the particle size of the metal compound is, for example, 1.50 μm or less, preferably 1.20 μm or less, more preferably 1.00 μm or less, and even more preferably 0.80 μm or less.
On the other hand, the particle size of the metal compound is, for example, 0.01 μm or more, preferably 0.03 μm or more, and more preferably 0.05 μm or more.

Particle size is the 50% particle size (median diameter) on a volume basis, determined using laser diffraction/scattering methods.

The above-mentioned dispersion treatment, addition of a dispersant, and control of the particle size of the metal compound do not affect only the yield value, k (Consistency Index), and n (Flow Index) independently, but affect multiple factors.
The above description has been given by listing factors that have a particularly large influence.

<Application method>
When applying the insulating coating treatment liquid to the surface of the steel sheet, it is preferable to apply the insulating coating treatment liquid to the surface of the steel sheet using a roll coater while transporting the steel sheet.
In this case, the conveying speed of the steel plate is, for example, 100 mpm (m/min) or more, preferably 200 mpm or more, and may be 300 mpm or more.

Before applying the insulating coating solution, the surface of the steel sheet may be pickled using phosphoric acid or similar.

<Baking of insulating coating treatment liquid>
After the insulating coating treatment liquid is applied to the surface of the steel sheet, the surface is dried as needed, and then baked to form an insulating coating. Planarization annealing may also be performed in conjunction with baking.
The baking temperature is preferably 600 to 1000°C, more preferably 700 to 930°C, and even more preferably 800 to 860°C. The baking atmosphere is preferably an inert gas atmosphere such as a nitrogen gas atmosphere. The baking time is preferably 1 to 300 seconds, preferably 5 to 200 seconds, and more preferably 10 to 100 seconds.

The amount of the insulating coating formed on both sides is, for example, 2.0 to 12.0 g/ ^m2 , and preferably 4.0 to 10.0 g/ ^m2 .

[Grain-oriented electrical steel sheet]
The grain-oriented electrical steel sheet obtained by the manufacturing method of this embodiment has excellent appearance, with poor appearance being suppressed.
Furthermore, in order to obtain grain-oriented electrical steel sheets with excellent magnetic properties, the tension (applied tension) applied to the steel sheet by the insulating coating is preferably 10.0 MPa or more, and the iron loss W _17/50 is preferably 0.88 W/kg or less.
Furthermore, in the obtained grain-oriented electrical steel sheet, the amount of phosphorus elution is preferably 150 μg/150 cm ² or less, and more preferably 100 μg/150 cm ² or less, because this provides excellent moisture absorption resistance.
The methods for measuring the applied tension, iron loss, and amount of phosphorus elution will be described later (see Examples below).

The present invention will be specifically explained below using examples. However, the present invention is not limited to the examples described below.

[Test 1]
<Manufacturing of grain-oriented electrical steel sheets>
A secondary recrystallized steel sheet (finish annealed steel sheet) having a thickness of 0.23 mm was prepared as a steel sheet. The surface of the prepared steel sheet was pickled with phosphoric acid.
The raw materials (phosphate, colloidal silica, and metal compound) were then charged into the mixing vessel and mixed to prepare an insulating coating treatment solution (solvent: pure water, specific gravity: 1.150) having the component composition shown in Table 1 below, at the mixing temperature shown in Table 1 below.

As the phosphate, primary phosphate was used, and as the colloidal silica, Snowtex N (manufactured by Nissan Chemical Industries, Ltd.) was used.
The particle size of the metal compounds was in the range of 0.05 to 0.60 μm.
No dispersion treatment or addition of a dispersant was carried out.

In Table 1 below, the content of phosphate means the content of the solid content of phosphate (unit: parts by mass).
The content of colloidal silica means the content (unit: parts by mass) converted to SiO ₂ solid content relative to 100 parts by mass of the solid content of the phosphate.
The content of the metal compound means the content (unit: parts by mass) converted to the metal element relative to 100 parts by mass of the solid content of the phosphate.
The same applies to [Test 2] described later.

For each prepared insulating coating solution, the yield value _Y5 was determined 5 minutes after preparation was completed, and the yield value _Y180 was determined 180 minutes after preparation was completed, according to the method described above. Furthermore, the ratio of the yield value _Y180 to the yield value _Y5 , _Y180 / _Y5 , was calculated. The results are shown in Table 1 below.

The Brookfield LVDV3T digital viscometer was used as the Brookfield viscometer. The insulation coating treatment liquid at a liquid temperature of 20°C was placed in the small-volume sample adapter of the Brookfield viscometer, and the shear stress τ was measured at 18 points using an SC4-18 spindle at a shear rate γ of 13.2 to 330.0 s ^-1 . During the measurements, the temperature of the insulation coating treatment liquid was maintained at 20°C using a water-cooled jacket.

The prepared insulating coating solution was applied to the surface of the steel sheet within 180 minutes after the completion of the preparation (specifically, 180 minutes after the completion of the preparation). More specifically, the insulating coating solution was applied using a roll coater while the steel sheet was being conveyed at a conveying speed of 200 mpm.
Thereafter, baking (baking temperature: 850° C., baking time: 25 seconds, baking atmosphere: nitrogen atmosphere) was carried out to form an insulating coating (adhesion amount on both sides: 8.0 g/m ² ).
Thus, a grain-oriented electrical steel sheet was obtained.

<evaluation>
The grain-oriented electrical steel sheets thus obtained were subjected to the following tests to evaluate various properties. The results are shown in Table 1 below.

"exterior"
The surface condition of the obtained grain-oriented electrical steel sheet was visually observed, and if there were no ribbing defects, it was given an "A", and if there were ribbing defects, it was given a "B", which are recorded in the following Table 1. If it was given an "A", it was evaluated as having excellent appearance.

Grant Tension
For the obtained grain-oriented electrical steel sheets, the tension in the rolling direction (applied tension) applied to the steel sheets by the insulating coating was determined.
A test piece (30 mm in length in the direction perpendicular to the rolling direction × 280 mm in length in the rolling direction) was taken from the grain-oriented electrical steel sheet. One side of the test piece was masked with adhesive tape, and the insulating coating on the other side was removed using acid and alkali.
Next, one end of the test piece was fixed at 30 mm, and the remaining 250 mm was used as the "warpage measurement length," and the "amount of warpage" was measured, and the "applied tension" was calculated using the following formula. The "Young's modulus of the steel plate" was set to 132 GPa.
Applied tension [MPa] = Young's modulus of steel sheet [GPa] × thickness of steel sheet [mm] × amount of warpage [mm] ÷ (measured length of warpage [mm]) ² × 10 ³
The applied tension is preferably 10.0 MPa or more.

Iron loss W _17/50
Test pieces (width 30 mm×length 280 mm) were taken from the obtained grain-oriented electrical steel sheets, and the iron loss W _17/50 was determined using the test pieces taken in accordance with JIS C 2550.
The lower the iron loss W _17/50 is, the more excellent the magnetic properties can be evaluated. The iron loss W _17/50 is preferably 0.88 W/kg or less.

<Phosphorus elution amount>
Three test pieces (50 mm x 50 mm) were taken from the obtained grain-oriented electrical steel sheet.
The three test pieces were immersed in distilled water at 100°C and boiled for 5 minutes to elute phosphorus from the surface of the insulating coating of each test piece, and the amount of phosphorus eluted (unit: μg/150 cm ² ) was determined using an ICP emission spectrometer.
The lower the amount of phosphorus elution, the better the moisture absorption resistance can be evaluated. The amount of phosphorus elution is preferably 150 μg/150 cm ² or less, and more preferably 100 μg/150 cm ² or less.

<Summary of evaluation results>
As shown in Table 1 above, Nos. 1-3, 1-12 and 1-25, which had a ratio Y ₁₈₀ /Y ₅ of more than 8.00, had insufficient appearance.

In contrast, Nos. 1-1, 1-2, 1-4 to 1-11, 1-13 to 1-24, and 1-26 to 1-33, which had a ratio Y ₁₈₀ /Y ₅ of 8.00 or less, had good appearances.

Comparing Nos. 1-4 to 1-6, No. 1-5, which contained 110 parts by mass of colloidal silica, had a lower amount of phosphorus elution and better moisture absorption resistance than Nos. 1-4 and 1-6, which contained 40 parts by mass or 130 parts by mass of colloidal silica.

Furthermore, when comparing Nos. 1-7 to 1-9, it was found that the magnetic properties and moisture absorption resistance tended to improve as the content of the metal compound increased.
A similar tendency was observed in the comparison results between No. 1-10 and No. 1-13.

[Test 2]
<Manufacturing of grain-oriented electrical steel sheets>
A secondary recrystallized steel sheet (finish annealed steel sheet) having a thickness of 0.18 mm was prepared as a steel sheet. The surface of the prepared steel sheet was pickled with phosphoric acid.
The raw materials (phosphate, colloidal silica, metal compound, and optional dispersant) were then charged into the mixing vessel and mixed to prepare an insulating coating treatment solution (solvent: pure water) having the component composition shown in Table 2 below at a mixing temperature of 5°C.

The phosphate used was monobasic phosphate. The colloidal silica used was Snowtex N (manufactured by Nissan Chemical Industries, Ltd.).

The dispersant used was a quaternary ammonium salt type cationic surfactant, specifically SN Dispersant 4215 manufactured by San Nopco (referred to as "SN4215" in Table 2 below) or Adekamin 4DAC-85 manufactured by ADEKA (referred to as "4DAC" in Table 2 below).
When no dispersant was added, a "-" is entered in the corresponding column in Table 2 below.

In some cases, a dispersion treatment was carried out using a high-efficiency industrial ultrasonic generator (UIP1000) manufactured by Hielscher, with 1,000 L of the mixed liquid obtained by mixing the raw materials circulated at a processing output of 10,000 W for various processing times (unit: h). The dispersion strength (unit: Wh/L) is shown in Table 2 below.
When the dispersion treatment was not carried out, "-" is entered in the corresponding column in Table 2 below.

The prepared insulation coating solution was subjected to the same test as in Test 1 to determine the yield value _Y5 5 minutes after preparation and the yield value _Y180 180 minutes after preparation. Furthermore, the ratio of the yield value _Y180 to the yield value Y5 _{, Y180} / _Y5 , was calculated. The results are shown in Table 2 below.
The consistency index (k) and flow index (n) 5 minutes after the completion of the blending are also shown in Table 2. In Table 2, the values are simply represented as "k" and "n".

The prepared insulating coating solution was applied to the surface of the steel sheet within 180 minutes after the completion of the preparation (specifically, 180 minutes after the completion of the preparation). More specifically, the insulating coating solution was applied using a roll coater while the steel sheet was being conveyed at a conveying speed of 300 mpm.
Thereafter, baking (baking temperature: 820° C., baking time: 30 seconds, baking atmosphere: nitrogen atmosphere) was carried out to form an insulating coating (adhesion amount on both sides: 6.5 g/m ² ).
Thus, a grain-oriented electrical steel sheet was obtained.

<evaluation>
The obtained grain-oriented electrical steel sheets were evaluated for various properties in the same manner as in Test 1. The results are shown in Table 2 below.

<Summary of evaluation results>
As shown in Table 2 above, all of No. 2-1 to No. 2-25, which had a ratio Y ₁₈₀ /Y ₅ of 8.00 or less, had good appearances, and also had good magnetic properties and moisture absorption resistance.

Claims (6)

A method for manufacturing a grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating disposed on a surface of the steel sheet, the method comprising:
An insulating coating treatment liquid used to form the insulating coating is applied to the surface of the steel sheet within X minutes from the completion of preparation of the insulating coating treatment liquid, and baked.
a ratio _YX / _{Y5 of a yield value YX at} X minutes after completion of preparation of the insulating coating solution to a yield value _Y5 at 5 minutes after completion of preparation of the insulating coating solution being 8.00 or less. the insulating coating treatment solution contains a phosphate containing at least one element selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al, and Mn, colloidal silica, and a metal compound containing a metal element;
The content of the colloidal silica is 50 to 120 parts by mass in terms of _SiO2 solid content relative to 100 parts by mass of the solid content of the phosphate,
2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the content of the metal compound is 5 to 60 parts by mass, calculated as metal element, per 100 parts by mass of the solid content of the phosphate. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein the yield value _Y5 is 1.50×10 ⁻⁵ N/cm ² or less. the consistency index of the insulating coating treatment solution is 10.0 mPa s or less 5 minutes after completion of preparation;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the flow index 5 minutes after completion of preparation of the insulating coating treatment solution is 0.80 or more and 1.20 or less. The method for producing grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the metal compound contains at least one metal element selected from the group consisting of Zn, Ba, Sr, Mn, Ca, V, Ti, Mg, Hf, Zr, and Nb. A method for evaluating an insulating coating treatment solution used to form an insulating coating on a grain-oriented electrical steel sheet, comprising:
The insulating coating treatment liquid is applied to the surface of the steel sheet and baked to form the insulating coating,
The method for evaluating an insulating coating solution determines that the appearance of the resulting grain-oriented electrical steel sheet is good if the ratio _Y180 / _Y5 of the yield value _{Y180 180} minutes after completion of preparation of the insulating coating solution to the yield value Y5 5 minutes after completion of preparation of the insulating coating solution satisfies 8.00 or less.