Magnesium oxide

Abstract

Provided is a magnesium oxide.　This magnesium oxide, when being made into an aqueous dispersion containing the magnesium oxide at a proportion of 16 g per 100 g of water, exhibits a relaxation time satisfying 1000 milliseconds or less in TD-NMR at 40°C.

Description

Magnesium Oxide

[0001] The present invention relates to magnesium oxide and the like.

[0002] Magnesium oxide has been considered for use in various fields, and an annealing release agent is one of them (for example, Patent Document 1, etc.).

[0003] International Publication No. 2019 / 065645

[0004] An object of the present invention is to provide magnesium oxide and the like.

[0005] As described above, magnesium oxide is used for forming a coating film (coating membrane) or a film (layer) such as an annealing release agent.

[0006] When the present inventor studied magnesium oxide in such applications, it was found that depending on the magnesium oxide, a good coating film (for example, a uniform coating film) could not be formed on the coating target (such as a steel sheet) (for example, a site where the coating film does not adhere occurs), and there were problems such as difficulties in forming the film formed by baking (annealing, etc.) after coating (large unevenness or a large number of defects occur in the film).

[0007] In response to such problems, the present inventor studied, for example, adjusting the viscosity of the dispersion liquid (slurry) to be coated, but even with the same viscosity, etc., such problems could not be solved in some cases, and it was extremely difficult to solve the problems.

[0008] Under such circumstances, as a result of intensive studies, the present inventor found that specific physical properties, which are completely different from viscosity, etc., affect the coating property and film formation, and that by adjusting or selecting the values of the physical properties, a good coating film and film can be formed, etc. After further studies, the present invention was completed.

[0009] That is, the present invention relates to the following inventions, etc. [1] When a magnesium oxide-containing aqueous dispersion (or a 13.8 mass% aqueous dispersion) is prepared at a ratio of 16 g of magnesium oxide per 100 g of water, the relaxation time of TD-NMR at 40 °C (relaxation time T ,

[0009] , ,

[0008] , , ２ ,

[0007] ,

[0006] [1] Magnesium oxide having a relaxation time of 1,000 milliseconds or less (transverse relaxation time, spin-spin relaxation time). [2] Magnesium oxide according to [1], wherein the relaxation time is 600 milliseconds or less. [3] Magnesium oxide according to [1] or [2], wherein the relaxation time is 500 milliseconds or less. [4] Magnesium oxide according to any of [1] to [3], wherein the relaxation time is 250 milliseconds or less. [5] Magnesium oxide according to any of [1] to [4], wherein the relaxation time is 200 milliseconds or less. [6] Magnesium oxide according to any of [1] to [5], wherein the relaxation time is 1 millisecond or more. [7] Magnesium oxide according to any of [1] to [6], wherein the relaxation time is 10 milliseconds or more. [8] Magnesium oxide according to any of [1] to [7], wherein the relaxation time is 20 milliseconds or more (for example, 30 milliseconds or more). [9] Magnesium oxide according to any of [1] to [8], wherein the relaxation time is 1 to 600 milliseconds.

[10] Magnesium oxide according to any of [1] to [9], wherein the relaxation time is 10 to 500 milliseconds.

[11] Magnesium oxide according to any one of [1] to

[10] , wherein the relaxation time is 20 to 250 milliseconds (e.g., 30 to 250 milliseconds, 20 to 223 milliseconds).

[12] Magnesium oxide according to any one of [1] to

[11] , wherein the relaxation time is 40 to 150 milliseconds.

[13] Magnesium oxide with a BET specific surface area of ​​200 m ２ Magnesium oxide according to any one of [1] to

[12] , wherein the amount is less than or equal to / g.

[14] Magnesium oxide according to any one of [1] to

[13] , wherein the D50 particle size is 100 μm or less.

[15] Magnesium oxide according to any one of [1] to

[14] , wherein, in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less (for example, 0.01 to 30 μm).

[16] Magnesium oxide according to any one of [1] to

[15] , wherein when an aqueous dispersion (or 13.8 mass% aqueous dispersion) containing magnesium oxide at a ratio of 16 g per 100 g of water has a viscosity of 3000 mPa·s or less at 20°C.

[0010]

[17] BET specific surface area is 200 m２ Magnesium oxide as described in any of [1] to

[16] , wherein the amount is less than or equal to / g, the D50 particle size is 100 μm or less, and in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less (for example, 0.01 to 30 μm), and when an aqueous dispersion (or 13.8 mass% aqueous dispersion) containing magnesium oxide at a ratio of 16 g per 100 g of water has a viscosity of 3000 mPa·s or less at 20°C.

[18] The relaxation time is 10 to 500 milliseconds, and the BET specific surface area is 200 m ２ Magnesium oxide as described in any of [1] to

[17] , wherein the amount is less than or equal to / g, the D50 particle size is 100 μm or less, and in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less (for example, 0.01 to 30 μm), and when an aqueous dispersion (or 13.8 mass% aqueous dispersion) containing magnesium oxide at a ratio of 16 g per 100 g of water is prepared, the viscosity at 20°C is 3000 mPa·s or less.

[19] The relaxation time is 20 to 250 milliseconds (for example, 30 to 250 milliseconds, 20 to 223 milliseconds), and the BET specific surface area is 3 to 100 m ２Magnesium oxide according to any one of [1] to

[18] , wherein the amount is / g, the D50 particle size is 0.2 to 30 μm, and when the particle size that accounts for 16% of the cumulative particle size distribution is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 15 μm or less, and when an aqueous dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water (13.8 mass% aqueous dispersion) has a viscosity of 5 to 800 mPa·s at 20°C.

[20] Magnesium oxide according to any one of [1] to

[19] , comprising calcium, boron, phosphorus, fluorine, and chlorine.

[21] Magnesium oxide according to any one of [1] to

[20] , containing calcium as calcium oxide (CaO) in an amount of 0.01 to 5% by mass, boron in an amount of 0.001 to 0.5% by mass, phosphorus in an amount of 0.001 to 1% by mass, fluorine in an amount of 0.001 to 1% by mass, and chlorine in an amount of 0.001 to 1% by mass.

[22] Magnesium oxide according to any one of [1] to

[21] for use as an annealing separating agent.

[23] Magnesium oxide according to any one of [1] to

[22] for use on electrical steel sheets (e.g., grain-oriented electrical steel sheets) (to form a coating on electrical steel sheets).

[24] Dispersion (slurry, aqueous dispersion, etc.) containing magnesium oxide according to any one of [1] to

[23] .

[25] Annealing separating agent containing magnesium oxide according to any one of [1] to

[23] .

[0011]

[26] A substrate (coated substrate) having a coating film (coated layer) containing magnesium oxide as described in any of [1] to

[23] {a substrate [for example, a steel plate (base steel plate)] and a substrate [for example, a steel plate (coated steel plate)] having a coating film (coated layer) containing magnesium oxide as described in any of [1] to

[23] formed on the substrate (steel plate, etc.)}.

[27] The substrate according to

[26] , wherein the water contact angle of the substrate (substrate without a coating film) at 20°C is 60° or less.

[28] The substrate (coated substrate) according to

[26] or

[27] , wherein the substrate is a steel plate.

[29] A method for producing the substrate (coated substrate) according to any of

[26] to

[28] , comprising at least a step of applying a dispersion liquid containing magnesium oxide to the substrate (coating step).

[30] A steel sheet having a coating containing magnesium oxide (annealing separating agent) as described in any of [1] to

[23] [

[25] ] [[a coating of magnesium oxide (annealing separating agent) as described in any of [1] to

[23] ] [a steel sheet (a steel sheet with a coating formed thereon) comprising a steel sheet (base steel sheet) and a coating containing magnesium oxide (calcined product of magnesium oxide as described in any of [1] to

[23] ) formed on the steel sheet (a steel sheet with a coating formed thereon)].

[31] The steel sheet according to

[30] , which is an electrical steel sheet (for example, a grain-oriented electrical steel sheet).

[32] A method for producing a steel sheet according to

[30] or

[31] , comprising at least a firing step (firing step) of a steel sheet having a coating (coating layer) containing magnesium oxide according to any one of [1] to

[23] (annealing separating agent according to

[25] ).

[33] A method for producing a steel sheet according to

[30] or

[31] , comprising at least a step (coating step) of applying a dispersion liquid containing magnesium oxide according to any one of [1] to

[23] to a steel sheet (coating step), and firing the steel sheet having a coating (coating layer) containing magnesium oxide obtained through this step (firing step).

[0012] The present invention provides magnesium oxide (specific magnesium oxide). Such magnesium oxide can be used in a variety of applications, and is particularly useful for coating or forming films, such as an annealing separating agent and for electrical steel sheet applications [for example, for forming a film (forsterite layer) on electrical steel sheets].

[0013] One embodiment of the magnesium oxide of the present invention can provide good coating properties (applicability). For example, it can efficiently suppress unevenness (color variation) and incomplete adhesion on the coating target (steel plate, etc.), achieving a highly uniform (relatively uniform) coating (application). Therefore, it is easy to efficiently coat the coating target (surface) without having to apply a thick coat.

[0014] According to the inventors' research, when coating in slurry form (dispersion), unevenness and incomplete adhesion tend to occur. However, with magnesium oxide according to this embodiment of the present invention, good coating properties can be achieved even when coating in slurry form. Coating properties can affect the function of the formed film (coating film, coating film), and therefore, good coating properties are highly useful in that they can contribute to the efficient performance or realization of said function.

[0015] In another embodiment of the magnesium oxide of the present invention, a good coating can be formed after firing (annealing, etc.). For example, after firing, unevenness (shading) and defects in the coating formed on the object to be coated (steel plate, etc.) can be efficiently suppressed, and a highly uniform (relatively uniform) coating can be formed.

[0016] According to the inventors' research, when a coating film (paint film) is formed by firing, a non-uniform film may be formed, such as one with large inconsistencies. Furthermore, such non-uniform films may be observed even when the coating film is uniform (relatively uniform, seemingly uniform).

[0017] However, according to another embodiment of the present invention, magnesium oxide can efficiently suppress such uneven film formation and form a good film.

[0018] The uniformity of such a coating can affect its function (for example, in annealing separation agent applications, problems can arise due to the non-uniformity of the forsterite layer formed), and therefore, good coating formation is highly useful in that it can contribute to the efficient performance or realization of the said function.

[0019] According to yet another aspect of the present invention, magnesium oxide can achieve both good coating properties and good film formation. Depending on its application (for example, in annealing separation applications), magnesium oxide undergoes a coating film formation process and a film formation (film formation by firing) process. Therefore, in applications that undergo both of these processes, magnesium oxide according to this yet another aspect of the present invention is particularly useful. While the magnesium oxide of the present invention can often achieve at least one of good coating properties and good film formation, magnesium oxide that can achieve both is particularly useful in certain applications (for example, in annealing separation applications).

[0020] [Magnesium Oxide] The magnesium oxide of the present invention, when normally dispersed in water, exhibits the following characteristics: TD-NMR (Time-Domain Nuclear Magnetic Resonance) (pulsed NMR, low-field NMR) relaxation time (TD-NMR relaxation time, relaxation time, relaxation time T) ２The relaxation time (transverse relaxation time, spin-spin relaxation time) has a specific value. Such relaxation times may be selected from a range of, for example, 1000 milliseconds (ms) or less (e.g., 800 milliseconds or less, 700 milliseconds or less, 600 milliseconds or less), and are usually 500 milliseconds or less (e.g., 450 milliseconds or less, 400 milliseconds or less), preferably 350 milliseconds or less (e.g., 320 milliseconds or less, 300 milliseconds or less, 280 milliseconds or less, 270 milliseconds or less), more preferably 250 milliseconds or less (e.g., 240 milliseconds or less, 230 milliseconds or less, 223 milliseconds or less), and more preferably 220 milliseconds or less (e.g., 210 milliseconds or less, 200 milliseconds or less, 190 milliseconds or less). The time is less than or equal to a millisecond), and is particularly preferably less than or equal to 180 milliseconds (for example, less than or equal to 170 milliseconds, less than or equal to 165 milliseconds, less than or equal to 160 milliseconds, less than or equal to 155 milliseconds, less than or equal to 150 milliseconds, less than or equal to 148 milliseconds), and can also be less than or equal to 145 milliseconds (for example, less than or equal to 140 milliseconds, less than or equal to 135 milliseconds, less than or equal to 130 milliseconds, less than or equal to 125 milliseconds, less than or equal to 120 milliseconds, less than or equal to 115 milliseconds, less than or equal to 110 milliseconds, less than or equal to 105 milliseconds, less than or equal to 100 milliseconds, less than or equal to 95 milliseconds, less than or equal to 90 milliseconds, less than or equal to 85 milliseconds, less than or equal to 80 milliseconds, less than or equal to 75 milliseconds, less than or equal to 70 milliseconds, less than or equal to 68 milliseconds, less than or equal to 67 milliseconds, etc.).

[0021] The lower limit of the relaxation time is not limited, but may be, for example, 0.1 milliseconds (ms) or more (e.g., 0.5 milliseconds or more, 1 millisecond or more, 2 milliseconds or more, 3 milliseconds or more), 5 milliseconds or more (e.g., 8 milliseconds or more), preferably 10 milliseconds or more (e.g., 12 milliseconds or more), more preferably 15 milliseconds or more (e.g., 18 milliseconds or more), more preferably 20 milliseconds or more (e.g., 22 milliseconds or more), particularly 25 milliseconds or more (e.g., 28 milliseconds or more), particularly preferably 30 milliseconds or more (e.g., more than 30 milliseconds, 32 milliseconds or more), and may be 35 milliseconds or more (e.g., 38 milliseconds or more, 40 milliseconds or more, 42 milliseconds or more, 45 milliseconds or more, 48 milliseconds or more, 50 milliseconds or more, 52 milliseconds or more, 55 milliseconds or more, 58 milliseconds or more, 60 milliseconds or more, 62 milliseconds or more, 64 milliseconds or more, 65 milliseconds or more, 66 milliseconds or more, 67 milliseconds or more, etc.).

[0022] Furthermore, the relaxation time can also be set to a range that appropriately combines the lower and upper limits of the above range (the same applies to the description of the range below). In particular, from the viewpoint of easily achieving extremely good coating properties and film formation properties (or even both), a relaxation time that is neither too small (too short) nor too large (too long) may be selected.

[0023] The specific relaxation time may be, for example, 0.1 to 1000 milliseconds (e.g., 1 to 800 milliseconds), preferably 3 to 600 milliseconds (e.g., 5 to 550 milliseconds), more preferably 8 to 500 milliseconds (e.g., 10 to 480 milliseconds), more preferably 12 to 280 milliseconds (e.g., 15 to 260 milliseconds), particularly preferably 20 to 250 milliseconds (e.g., 25 to 240 milliseconds, 30 to 230 milliseconds, 25 to 200 milliseconds, 30 to 185 milliseconds, 20 to 223 milliseconds), or 32 to 180 milliseconds (e.g., 35 to 170 milliseconds, 38 to 160 milliseconds, 40 to 155 milliseconds, 42 to 148 milliseconds), etc.

[0024] By allowing such a relaxation time, it is easier to improve the applicability and film-forming properties of magnesium oxide (especially applicability and film-forming properties).

[0025] The reason for this is not entirely clear, but the following reasons can be assumed. First, in a dispersion, the solvent in contact with or adsorbed to the particles (bound solvent) and the bulk liquid (solvent in a free state not in contact with the particle surface) respond differently to changes in the magnetic field, and therefore have different relaxation times. Consequently, even in dispersions containing seemingly identical particles (at the same concentration), particles with a higher proportion of bound solvent will have shorter relaxation times. Here, the bound solvent is thought to affect the wettability or affinity between the particle interface and the solvent, and consequently, the wettability or affinity between the coating target (surface) and the particles after coating. Specifically, a higher proportion of bound solvent (shorter relaxation time) leads to greater wettability or affinity, and consequently, the particles adhere more easily to the coating target (and are less likely to detach). Thus, the relaxation time affects how easily particles adhere to the coating target (coating ability), and by keeping the relaxation time from being too long, it is possible to efficiently achieve good coating ability.

[0026] On the other hand, the confined solvent is also recognized as being related to the ease of particle dispersion (aggregation), and consequently, when undergoing post-coating or post-adhesion treatment (heat treatment, etc.), it is thought to affect the ease of dispersion (aggregation) between the particles and the target surface after coating or adhesion. Specifically, it is thought that if there is a large amount of confined solvent (short relaxation time), the particles will be less likely to aggregate on the target surface after coating or adhesion (and consequently, unevenness, film defects, separation, etc. will be less likely to occur). In terms of coatability and film formation, it is advantageous to keep the relaxation time from being too long, and in particular, selecting a relaxation time that is not too short makes it easier to achieve extremely good coatability and film formation. The reason for this is not clear, but it is thought that if there is too much confined solvent (the relaxation time becomes too short), the surface state and aggregation state of magnesium oxide will change at a microscopic level, affecting coatability and film formation.

[0027] Thus, it can be inferred that relaxation time is related to coatability and film-forming properties, and consequently, that selecting the appropriate relaxation time can efficiently achieve good coatability and film-forming properties. In particular, relaxation time seems to be related to both coatability and film-forming properties, and it can be inferred that selecting an appropriate (well-balanced) relaxation time can lead to the achievement (combination) of good coatability and good film-forming properties.

[0028] The relaxation time can be measured in an aqueous dispersion (slurry) of magnesium oxide. The proportion (concentration) of magnesium oxide (magnesium oxide particles, magnesium oxide powder, particulate magnesium oxide, powdered magnesium oxide) in the aqueous dispersion (suspension) used to measure the relaxation time may be, for example, 16 g (or 13.8 mass%) per 100 g of water, and the temperature of the aqueous dispersion may be a predetermined temperature (for example, 40°C). Typically, the relaxation time may be the value (relaxation time) measured when an aqueous dispersion containing magnesium oxide at a predetermined proportion (e.g., 16 g per 100 g of water) is measured at a predetermined temperature (e.g., 40°C).

[0029] The aqueous dispersion is not particularly limited, but can be prepared, for example, by the method described below [and used for measurement as soon as possible [for example, within 10 minutes after preparation (for example, within 5 minutes, within 3 minutes, or within 1 minute 30 seconds)].

[0030] Furthermore, the measurement conditions (calculation conditions) for the relaxation time are not particularly limited, but for example, it may be measured under the conditions described later. The measurement may also be performed promptly on the prepared aqueous dispersion [for example, within 10 minutes after preparation (e.g., within 5 minutes, 3 minutes, 1 minute 30 seconds, etc.)].

[0031] The relaxation time is not particularly limited. For example, it can be adjusted according to the composition and physical properties of magnesium hydroxide, which is a raw material for producing magnesium oxide (e.g., the types and proportions of impurities or trace elements in magnesium hydroxide, BET specific surface area, particle size, etc.), and the firing conditions of magnesium hydroxide (firing temperature, firing time, etc.). For example, if other conditions are the same, the relaxation time can be reduced by using magnesium hydroxide with a large BET specific surface area or a small particle size, or by lowering the firing temperature.

[0032] Also, by combining magnesium oxides with different relaxation times, magnesium oxide with a desired relaxation time can be obtained (the relaxation time can be adjusted) (the same applies to physical property values other than the relaxation time below).

[0033] Magnesium oxide (magnesium oxide particles, particulate magnesium oxide) usually only needs to satisfy a specific relaxation time as described above, but may further have (satisfy) other (other than the relaxation time) physical property values

[0034] For example, the BET specific surface area of magnesium oxide is preferably selected from the range of 300 m ２ / g or less (e.g., 250 m ２ / g or less), more preferably 200 m ２ / g or less (e.g., 180 m ２ / g or less), preferably 150 m ２ / g or less (e.g., 120 m ２ / g or less), more preferably 100 m ２ / g or less (e.g., 80 m ２ / g or less), even more preferably 70 m ２ / g or less (e.g., 60 m ２ / g or less), particularly preferably 50 m ２ / g or less (e.g., 40 m ２ / g or less), and may even be 38 m ２ / g or less (e.g., 35 m ２ / g or less, 32 m ２ / g or less, 30 m ２ / g or less), etc.

[0035] The lower limit of the BET specific surface area of ​​magnesium oxide is, for example, 0.1 m². ２ / g or more (for example, 0.3m) ２ / g or more, 0.5m ２ You may choose from a range of approximately (1 m) or more. ２ / g or more (for example, 1.5m) ２ ( / g or more), preferably 2m ２ / g or more (for example, 2.5m) ２ ( / g or more), more preferably 3m ２ / g or more (for example, 3.5m) ２ ( / g or more), more preferably 4m ２ / g or more (for example, 4.5m) ２ ( / g or more), particularly preferably 5m ２ / g or more (for example, 6m ２ / g or more, 7m ２ It may be around 8m (or more / g), ２ / g or more (for example, 10m ２ / g or more, 12m ２ / g or more, 15m ２ / g or more, 18m ２ (or more than / g) etc. may also be acceptable.

[0036] The specific BET specific surface area of ​​magnesium oxide is, for example, 0.1 to 300 m². ２ / g (for example, 1 to 200m) ２ ( / g), preferably 2 to 150 m ２ / g (for example, 2.5 to 120m) ２ ( / g or more), more preferably 3 to 100 m ２ / g (for example, 3.5 to 80m) ２ / g), more preferably 4 to 70m ２ / g (for example, 4.5 to 60 m) ２ / g), particularly preferably 5 to 50m ２ / g (for example, 7-40m) ２ It may be around 8-38 m / g. ２ / g (for example, 10-35m) ２ / g, 12-32m ２ / g, 15-30m ２ (e.g., / g) may also be used.

[0037] By keeping the BET specific surface area neither too large nor too small, it becomes easier to suppress the deterioration of magnesium oxide (such as moisture absorption), resulting in excellent handling properties and making it easier to efficiently obtain a good coating (and even a protective film).

[0038] The method for measuring the BET specific surface area is not particularly limited, but it can be measured according to, for example, JIS Z 8830, and specifically, it can be determined by the single-point method as shown in the examples below.

[0039] The BET specific surface area is not particularly limited, but can be efficiently adjusted by factors such as the composition of magnesium hydroxide used as a raw material for magnesium oxide production (e.g., the types and proportions of impurities or trace elements in the magnesium hydroxide), the calcination conditions of the magnesium hydroxide (calcination temperature, calcination time, etc.), and the pulverization conditions (method).

[0040] The D50 particle size of magnesium oxide (D50 volume diameter, particle size at which the cumulative particle size distribution is 50%) may be selected from a range of approximately 300 μm or less (e.g., 250 μm or less, 200 μm or less, 150 μm or less), preferably 100 μm or less (e.g., 80 μm or less), preferably 50 μm or less (e.g., 40 μm or less), more preferably 30 μm or less (e.g., 20 μm or less), even more preferably 15 μm or less (e.g., 12 μm or less), and particularly preferably 10 μm or less (e.g., 8 μm or less), and may also be 5 μm or less (e.g., 4 μm or less, 3.5 μm or less, 3.2 μm or less, 3 μm or less), etc.

[0041] The lower limit of the D50 particle diameter of magnesium oxide may be selected from a range of, for example, 0.01 μm or more (e.g., 0.03 μm or more), preferably 0.05 μm or more (e.g., 0.08 μm or more), preferably 0.1 μm or more (e.g., 0.15 μm or more), more preferably 0.2 μm or more (e.g., 0.25 μm or more), even more preferably 0.3 μm or more (e.g., 0.35 μm or more), particularly preferably 0.4 μm or more (e.g., 0.45 μm or more), and may also be 0.5 μm or more (e.g., 0.55 μm or more, 0.6 μm or more, 0.65 μm or more, 0.7 μm or more, 0.75 μm or more, 0.8 μm or more, 0.85 μm or more, 0.9 μm or more, 0.95 μm or more, 1 μm or more), and so on.

[0042] The specific D50 particle size of magnesium oxide may be, for example, 0.01 to 300 μm (e.g., 0.03 to 200 μm), preferably 0.05 to 100 μm (e.g., 0.1 to 50 μm), more preferably 0.2 to 30 μm (e.g., 0.25 to 20 μm), even more preferably 0.3 to 15 μm (e.g., 0.35 to 12 μm), particularly preferably 0.4 to 10 μm (e.g., 0.45 to 8 μm), or 0.5 to 5 μm (e.g., 0.7 to 3 μm).

[0043] By keeping the particle size neither too large nor too small, it becomes easier to obtain a good coating (or even a protective film) efficiently with excellent handling properties.

[0044] The method for measuring particle size (D50 particle size) is not particularly limited, but for example, it can be measured using a particle size distribution analyzer and determined as the volume-based particle size (volume particle size) in the obtained particle size distribution. Specifically, it may be determined as shown in the examples described below.

[0045] While the particle size is not particularly limited, it can be efficiently adjusted through methods such as grinding conditions (methods) and classification operations.

[0046] The particle size distribution of magnesium oxide (particles) may be based on the cumulative diameter. For example, in the cumulative particle size distribution (cumulative curve) of magnesium oxide (particles), if the particle size (volume particle diameter) that accounts for 16% is D16 (μm) and the particle size (volume particle diameter) that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 may be selected from a range of approximately 30 μm or less (e.g., 25 μm or less, 20 μm or less), preferably 18 μm or less (e.g., 16 μm or less), preferably 15 μm or less (e.g., 13 μm or less), more preferably 12 μm or less (e.g., 11 μm or less), even more preferably 10 μm or less (e.g., 9 μm or less), and particularly preferably 8 μm or less (e.g., 7.5 μm or less), and may also be 7 μm or less (e.g., 7 μm or less, 6.5 μm or less, 6.2 μm or less, 6 μm or less), etc.

[0047] The lower limit of (D84-D16) / 2 may be selected from a range of, for example, 0.01 μm or more (e.g., 0.03 μm or more), preferably 0.05 μm or more (e.g., 0.08 μm or more), more preferably 0.1 μm or more (e.g., 0.15 μm or more), more preferably 0.2 μm or more (e.g., 0.25 μm or more), even more preferably 0.3 μm or more (e.g., 0.35 μm or more), and particularly preferably 0.4 μm or more (e.g., 0.45 μm or more), etc. They may be present, and may be 0.5 μm or larger (for example, 0.6 μm or larger, 0.7 μm or larger, 0.8 μm or larger, 0.9 μm or larger, 1 μm or larger, 1.1 μm or larger, 1.2 μm or larger, 1.3 μm or larger, 1.4 μm or larger, 1.5 μm or larger, 1.6 μm or larger, 1.7 μm or larger, 1.8 μm or larger, 1.9 μm or larger, 2 μm or larger, 2.1 μm or larger, 2.2 μm or larger, 2.3 μm or larger, 2.4 μm or larger, 2.5 μm or larger, 2.7 μm or larger, 2.8 μm or larger), etc.

[0048] The specific value of (D84-D16) / 2 may be, for example, 0.01 to 30 μm (e.g., 0.05 to 20 μm), preferably 0.1 to 15 μm (e.g., 0.15 to 12 μm), more preferably 0.2 to 10 μm (e.g., 0.3 to 9 μm), even more preferably 0.4 to 8 μm (e.g., 0.45 to 7.5 μm), and particularly preferably 0.5 to 7 μm (e.g., 0.6 to 6.5 μm).

[0049] Furthermore, the above value of (D84 - D16) / 2 can also be considered the standard deviation (μm) of magnesium oxide (particles) [it is a pseudo-standard deviation (μm)].

[0050] By keeping the value of (D84 - D16) / 2 (particle size distribution, standard deviation, particle size variation) not too large (and also not too small), it becomes easier to obtain a good coating (and even a protective film) efficiently with excellent handling properties.

[0051] The value of (D84 - D16) / 2 (particle size distribution) is not particularly limited, but can be determined, for example, by measuring using a particle size distribution analyzer and determining it based on the obtained particle size distribution. Specifically, it may be determined as shown in the examples described later.

[0052] The particle size distribution [(D84 - D16) / 2 value, standard deviation] is not particularly limited, but can be efficiently adjusted by, for example, grinding conditions (method) or classification operations.

[0053] The viscosity of magnesium oxide when used as an aqueous dispersion (an aqueous dispersion of a predetermined concentration) may be selected from a range of approximately 5000 mPa·s or less (for example, 4500 mPa·s or less, 4000 mPa·s or less, 3500 mPa·s or less), 3000 mPa·s or less (for example, 2000 mPa·s or less), preferably 1500 mPa·s or less (for example, 1000 mPa·s or less), more preferably 800 mPa·s or less (for example, 500 mPa·s or less), even more preferably 300 mPa·s or less (for example, 250 mPa·s or less), particularly preferably 200 mPa·s or less (for example, 180 mPa·s or less), and may also be 150 mPa·s or less (for example, 140 mPa·s or less, 130 mPa·s or less, 120 mPa·s or less), etc.

[0054] The lower limit of the viscosity of magnesium oxide when it is used as an aqueous dispersion (an aqueous dispersion of a predetermined concentration) may be selected from a range of, for example, 0.1 mPa·s or more (for example, 0.3 mPa·s or more), preferably 0.5 mPa·s or more (for example, 1 mPa·s or more), preferably 2 mPa·s or more (for example, 3 mPa·s or more), more preferably 5 mPa·s or more (for example, 8 mPa·s or more), and even more preferably 10 mPa·s or more. For example, it may be 15 mPa·s or more), particularly preferably 20 mPa·s or more (for example, 25 mPa·s or more), and may also be 30 mPa·s or more (for example, 35 mPa·s or more, 40 mPa·s or more, 45 mPa·s or more, 50 mPa·s or more, 55 mPa·s or more, 60 mPa·s or more, 65 mPa·s or more, 70 mPa·s or more, 75 mPa·s or more, 80 mPa·s or more, 85 mPa·s or more), etc.

[0055] The viscosity of magnesium oxide in a specific aqueous dispersion (an aqueous dispersion of a predetermined concentration) may be selected from a range of approximately 0.1 to 5000 mPa·s (for example, 0.3 to 4000 mPa·s), preferably 0.5 to 3000 mPa·s (for example, 1 to 2000 mPa·s), preferably 2 to 1500 mPa·s (for example, 3 to 1000 mPa·s), and more preferably 5 to 800 mPa·s. For example, it may be around 8 to 500 mPa·s), more preferably 10 to 300 mPa·s (for example, 15 to 250 mPa·s), particularly preferably 20 to 200 mPa·s (for example, 25 to 180 mPa·s), and also 30 to 150 mPa·s (for example, 50 to 140 mPa·s, 60 to 130 mPa·s, 70 to 120 mPa·s, 85 to 130 mPa·s or more).

[0056] By maintaining a viscosity that is neither too high nor too low, it becomes easier to obtain a good coating (or even a protective film) efficiently with excellent handling properties.

[0057] Viscosity can be measured in an aqueous dispersion (slurry) of magnesium oxide. The proportion (concentration) of magnesium oxide (magnesium oxide particles, magnesium oxide powder, particulate magnesium oxide, powdered magnesium oxide) in the aqueous dispersion (suspension) used for measuring viscosity may be, for example, 16 g (or 13.8 mass%) per 100 g of water, and the temperature of the aqueous dispersion may be a predetermined temperature (for example, 20°C). Viscosity can be measured using a viscometer (such as a BII-type viscometer). Typically, the viscosity may be the value (viscosity) obtained when measuring an aqueous dispersion (containing magnesium oxide in a predetermined proportion) at a predetermined temperature (such as 20°C) using a viscometer (such as a BII-type viscometer) at a predetermined temperature (such as 20°C), and specifically, it may be measured (determined) as shown in the examples described later.

[0058] Viscosity is not particularly limited, but can be efficiently adjusted by, for example, the BET specific surface area or particle size. While the viscosity when using magnesium oxide can also be adjusted by additives such as viscosity modifiers (thickeners, dethickeners), adjusting the viscosity of the magnesium oxide (aqueous dispersion) can eliminate the need for such additives or reduce their usage, ultimately leading to better coating and film formation.

[0059] Magnesium oxide may contain impurities (components other than magnesium oxide) as long as they do not impair the effects of the present invention. In particular, depending on the manner in which magnesium oxide is used, it may be preferable to contain an appropriate amount of impurities. For example, when forming a magnesium oxide film by calcination, impurities can adjust (control) the reaction (e.g., forsterite film formation reaction), leading to efficient and good film formation. The impurities may originate from the raw materials (magnesium hydroxide) or components used or introduced in the manufacturing process (such as catalysts).

[0060] Examples of such impurities (elements, atoms) include alkali metals (e.g., sodium, potassium), alkaline earth metals (e.g., calcium, strontium), boron, aluminum, silicon, titanium, phosphorus, sulfur, halogens (e.g., fluorine, chlorine), and other metals (zinc, cobalt, nickel, copper). These elements (atoms) may also be present in magnesium oxide as compounds (e.g., oxides).

[0061] Magnesium oxide may contain these impurities individually or in combination of two or more.

[0062] If magnesium oxide contains such impurities, the proportion is not particularly limited as long as it does not impair the effects of the present invention. For example, when an element selected from calcium, boron, phosphorus, fluorine, and chlorine is included, the proportion of calcium as calcium oxide (CaO) should be 5% by mass or less of magnesium oxide (total magnesium oxide including impurities) (e.g., 4% by mass or less, 3% by mass or less, 2.5% by mass or less, 2% by mass or less, 1.5% by mass or less, 1% by mass or less, 0.01 to 3% by mass, 0.05 to 2% by mass, 0.1 to 2.5% by mass, 0.2 to 1% by mass), the proportion of boron should be 1% by mass or less of magnesium oxide (e.g., 0.8% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.15% by mass or less, 0.001 to 0.5% by mass, 0.005 to 0.3% by mass, 0.01 to 0.25% by mass, 0.02 to 0.2% by mass), and the proportion of phosphorus should be 1% by mass or less of magnesium oxide (e.g., 0. 8% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.001 to 0.5% by mass, 0.01 to 0.3% by mass, 0.03 to 0.25% by mass, 0.05 to 0.2% by mass), the proportion of fluorine is 1% by mass or less of Si (for example, 0.8% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.001 to 0.5% by mass, 0.01 to 0.3% by mass, 0.00 The amount of chlorine may be 5 to 0.15% by mass, 0.01 to 0.1% by mass, and the proportion of chlorine may be 1% by mass or less of magnesium oxide (for example, 0.8% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.001 to 0.5% by mass, 0.01 to 0.3% by mass, 0.15% by mass or less, 0.005 to 0.1% by mass, 0.01 to 0.09% by mass, 0.01 to 0.07% by mass), etc.

[0063] The proportion (and detection) of such impurities can be detected or measured by conventional or known methods depending on the type of impurity (element, atom), etc. For example, it may be measured (and detected) (determined) as shown in the examples described below.

[0064] The purity of magnesium oxide may be, for example, 80% by mass or more, preferably 85% by mass or more, more preferably 90% by mass or more, particularly 95% by mass or more, or even 100% by mass. If the magnesium oxide contains impurities, the upper limit of the purity of the magnesium oxide may be, for example, 99.999% by mass, 99% by mass, 95% by mass, 90% by mass, 85% by mass, etc.

[0065] Magnesium oxide is typically in particulate form (granular, powder, pulverized, or powdery). However, the particle shape is not particularly limited and may be spherical (approximately spherical), plate-shaped, etc. Furthermore, the particles may be primary or secondary particles.

[0066] The method for producing magnesium oxide of the present invention is not particularly limited, but for example, it may be produced by at least a calcination step in which magnesium hydroxide is calcined (heat treated) (the produced product may be used as the magnesium oxide of the present invention).

[0067] Magnesium hydroxide (magnesium hydroxide subjected to or used in calcination treatment) may have physical properties (BET specific surface area, particle size, etc.) similar to those of magnesium oxide mentioned above, and may contain impurities.

[0068] The range of physical properties (BET specific surface area, particle size, etc.), the type and proportion of impurities may be the same as those described above for magnesium oxide (magnesium oxide may be replaced with magnesium hydroxide).

[0069] Such physical properties, as well as the types and proportions of impurities, may be adjusted according to the desired physical properties of magnesium oxide (relaxation time, other physical properties, etc.).

[0070] In the firing process, firing conditions can be selected as appropriate. For example, the firing temperature may be 400°C or higher [for example, 500 to 1700°C, preferably 550°C or higher (for example, 600 to 1500°C)], and the firing time may be 0.1 hours or more [for example, 0.2 to 24 hours, preferably 0.5 hours or more (for example, 1 to 12 hours)].

[0071] The firing conditions may be adjusted in combination with the characteristics of the magnesium hydroxide subjected to firing (physical properties, type and proportion of impurities), according to the desired physical properties of the magnesium oxide (relaxation time, physical properties other than relaxation time, etc.).

[0072] After the calcination process (of the magnesium oxide obtained through the calcination process), grinding and classification (such as sieving) may be performed as needed. The conditions for these processes [grinding intensity, type or form of screen or sieve (screen diameter, mesh size, etc.)] can be selected as appropriate and adjusted according to the desired physical properties of the magnesium oxide (relaxation time, other physical properties, etc.).

[0073] [Dispersion, Uses, etc.] The uses of magnesium oxide of the present invention are not particularly limited and can be used for a variety of purposes.

[0074] In particular, magnesium oxide often possesses good applicability and film-forming properties, making it suitable for use in applications involving coating or film formation.

[0075] One example of such an application is an annealing separation agent.

[0076] The annealing separation agent only needs to contain magnesium oxide (it only needs to be composed of magnesium oxide). Such an annealing separation agent may contain only magnesium oxide as its annealing separation component (solid content) (it may be composed only of magnesium oxide), or it may contain other components as needed (elements or atoms or compounds thereof corresponding to the aforementioned impurities). In such cases, the proportion of magnesium oxide in the annealing separation agent (solid content) may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, etc.

[0077] Furthermore, magnesium oxide (and other components) may be dispersed (or suspended) in a solvent [as a dispersion (suspension, slurry)] when used for various purposes such as annealing separation agents.

[0078] The present invention also includes such dispersions.

[0079] Suitable solvents include, depending on the application, water, aqueous solvents [hydrophilic solvents or water-soluble solvents, such as organic solvents like alcohols (e.g., lower alcohols such as methanol and ethanol)], but generally, solvents containing at least water may be preferred.

[0080] In such a solvent, the proportion of water may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, etc., or it may be 100% by mass (water only).

[0081] In the dispersion (suspension, slurry), the proportion (concentration) of magnesium oxide (or solid content) can be selected according to the application, etc., but for example, it may be 1% by mass or more (e.g., 2 to 50% by mass), preferably 3% by mass or more (e.g., 5 to 45% by mass), and more preferably 10% by mass or more (e.g., 11 to 35% by mass).

[0082] Magnesium oxide (or annealing separating agents, etc.) can be used for coating purposes, as described above. In such cases, magnesium oxide forms a coating layer (film, coating film) on the surface to be coated.

[0083] The present invention includes a coating object (a coating object) having such a magnesium oxide coating layer (coating film) (a coating layer formed thereon).

[0084] The material of the coating target (base, substrate) can be selected according to the application, etc., and examples include metal, glass, plants (wood, etc.), resin, etc.

[0085] The shape of the coating target (base, substrate) can also be selected according to the application, and may be one-dimensional (e.g., rod-shaped), two-dimensional (e.g., plate-shaped (film, sheet-shaped), cloth-shaped (woven fabric, non-woven fabric-shaped), etc.), or three-dimensional (e.g., various molded product shapes).

[0086] Specific examples of coating targets (bases, substrates) include metal plates [e.g., steel plates (steel billets, steel materials)], glass plates, resin plates, wood (wooden boards), and nonwoven fabrics. For coating targets such as metal plates, a magnesium oxide film can also be formed by firing after coating.

[0087] In the object to be coated, the water contact angle of at least the coated portion (surface, etc.) is not particularly limited, but especially from the viewpoint of the applicability of the magnesium oxide (or dispersion), it may be 150° or less (for example, 120° or less), preferably 100° or less (for example, 80° or less), and more preferably 60° or less (for example, 55° or less, 50° or less, 45° or less), etc. The lower limit of the water contact angle may be 0° or more, 5° or more, 10° or more, 15° or more, 20° or more, 25° or more, etc.

[0088] The water contact angle may be a value obtained at a predetermined temperature (for example, 20°C). The water contact angle can be measured by conventional methods, and specifically may be determined as shown in the examples described later.

[0089] The metal sheet (steel sheet) can be selected according to the application, but for example, silicon steel sheet [steel sheet containing silicon (silicon component)] may also be used.

[0090] Furthermore, the silicon steel sheet may be a steel sheet on which a silicon oxide film (silica film) has been formed. Such a steel sheet can be obtained through a decarburization treatment. The steel sheet used for the decarburization treatment may be one manufactured using a steel billet (silicon steel billet) by a known method (for example, through rolling, annealing, etc.).

[0091] In silicon steel sheets, the silicon content may be, for example, 0.1% by mass or more (for example, 0.3 to 15% by mass, or 1 to 10% by mass).

[0092] By using silicon steel sheets, a forsterite layer (or a coating containing it) can be efficiently formed through a firing (annealing) process. The steel sheet with the coating (forsterite layer, etc.) formed on it can be suitably used (applied) as electrical steel sheets (grain-oriented electrical steel sheets, etc.).

[0093] The coating method can be selected according to the application, but for example, a dispersion (suspension) containing magnesium oxide (annealing separating agent) may be applied to the object to be coated (steel plate, etc.).

[0094] The application method is not particularly limited and can be any conventional method depending on the application. Furthermore, drying treatment may be performed after application if necessary.

[0095] The amount of magnesium oxide (or solid content) applied to the surface can be selected according to the application, for example, 0.1 to 5000 g / m². ２ Preferably 1 to 500 g / m ２ More preferably 10 to 150 g / m ２ It can be to a certain extent.

[0096] A coating object (a coating object) equipped with a coating layer (a magnesium oxide coating layer) may be subjected to a firing treatment (or heat treatment, annealing treatment, etc.).

[0097] The firing process forms a magnesium oxide coating [or a coating derived from magnesium oxide (annealing separating agent), such as a forsterite layer (or a coating containing forsterite) (forsterite coating, glass coating)].

[0098] The present invention includes a coating-equipped object (such as a steel sheet) having such a coating (a coating has been formed on it). Such a coating-equipped object can be used for various applications depending on the type of steel sheet, and can be suitably used as, for example, an electrical steel sheet (such as a grain-oriented electrical steel sheet).

[0099] Furthermore, the firing conditions can be selected according to the application. For example, the firing temperature may be 800°C or higher [for example, 900 to 1700°C, preferably 900°C or higher (for example, 1000 to 1500°C)], and the firing time may be 0.5 hours or more [for example, 1 to 48 hours, preferably 2 hours or more (for example, 3 to 24 hours)]. In addition, the firing process may be carried out under an inert atmosphere (for example, under nitrogen).

[0100] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples, and many modifications are possible within the technical concept of the present invention by those with ordinary skill in the art.

[0101] The various physical properties and characteristics were measured and evaluated as follows.

[0102] Relaxation time Relaxation time (Relaxation time T ２ The lateral relaxation time and spin-spin relaxation time were measured immediately after the preparation of the aqueous dispersion (slurry) (before the magnesium oxide settled over time). Specifically, the aqueous dispersion was prepared and measured as follows: 100 mL of water and a stirring bar (35 mm in length x 8 mm in diameter, manufactured by Sanplatec Co., Ltd., PTFE stirring bar (SA) type, part number: 19015) were placed in a 300 mL glass beaker, and stirring was started at 600 rpm using a hot stirrer. After confirming that the water temperature reached 40°C, 16 g of the sample (magnesium oxide) was added to the beaker [i.e., 16 g of the sample (13.8 mass%) was added per 100 g of water], and the mixture was stirred for 3 minutes to obtain an aqueous dispersion. After stopping the stirring, the obtained aqueous dispersion was immediately placed in a sample (glass) tube and set up (inserted) in the following apparatus (TD-NMR), and measurements were taken at 40°C. The time from the cessation of stirring to the start of measurement was approximately 1 minute and 30 seconds (the time from the cessation of stirring to the end of measurement was approximately 2 minutes and 30 seconds).

[0103] Instrument (TD-NMR): Minispec mq20, manufactured by Bruker Japan Ltd. The analysis was performed using the instrument's included software, "the minispec Software." The software automatically fitted the raw data and calculated the relaxation time.

[0104] The measurement conditions (TD-NMR setting conditions) are described (displayed) below. Observation target: １H nuclear measurement method: CPMG method Scans: 1 Recycle Delay: 2 s Dummy Shots: 0 Detection Mode: complex 90°-180°Pulse Separation: 1 tau Total number of acquired echoes: 5000 Number of not Fitted Echoes: 0 90°Pulse Length: 2.8μs 180°Pulse Length: 5.82μs Detection Angle: 168° Magnetic Field Steps: 536 Rec. Dead Time: 0.0054 ms Field Homog. Limit: 0.5 ms Desired Magnet Temp.: 40℃ NMR Frequency Base Freq.: 20MHz NMR Frequency Freq.Offset: -50 kHz Monoexponential Curve Fitting: on Phase Cycling: off

[0105] Samples pretreated at approximately 130°C for approximately 30 minutes under a nitrogen gas atmosphere were measured using the nitrogen gas adsorption method (single-point method) in accordance with JIS 8830 (Method for measuring the specific surface area of ​​powders (solids) by gas adsorption) with a Macsorb HM Model-1208 (manufactured by MOUNTECH).

[0106] Particle size (D50) and particle size distribution [(D84 - D16) / 2 value] Approximately 0.1 g of the sample powder was placed in a 100 mL glass beaker and added to 50 mL of Solmix A-7 manufactured by Nippon Alcohol Sales Co., Ltd. Then, the mixture was dispersed for 3 minutes using an ultrasonic generator (UD-201 model) manufactured by Tommy Seiko Co., Ltd. to prepare a dispersion. The obtained dispersion was measured (measured by laser diffraction) using a particle size analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.) to obtain the volume-based D50 particle size and the (D84 - D16) / 2 value [value calculated from the particle size distribution (calculated by software)]. The measurement conditions were solvent refractive index: 1.36, particle permeability: transparent, particle refractive index: 1.73, and particle shape: non-spherical.

[0107] Viscosity: 800 mL of 20°C water and 128 g of sample (16 g of sample per 100 g of water) were placed in a 2000 mL beaker and stirred at 300 rpm for 3 minutes to obtain a dispersion (slurry). The viscosity of the obtained slurry (at 20°C) was then measured using a BII type viscometer (manufactured by Toki Sangyo Co., Ltd.) with rotor No. 2 and a rotation speed of 60 rpm.

[0108] Impurity levels were determined as follows: Cl: Quantified by mercury thiocyanate spectrophotometric method. B: Quantified using ICP-AES. CaO: Quantified by chelation titration using EDTA. P: Quantified by vanadomolybdate spectrophotometric method. F: Quantified in accordance with JIS K 0102:2019 (Test methods for factory wastewater) using lanthanum-alizarin complexone spectrophotometric method.

[0109] Using a water contact angle meter (CA-X model, manufactured by Kyowa Interface Science Co., Ltd.), 2 μL of pure water was dropped at 20°C, and the contact angle (θ / 2 method) was measured after 5 seconds.

[0110] A dispersion (slurry) prepared in the same manner as that used for measuring the relaxation time of the coating properties was applied using a bar coater to a coating target (substrate) measuring 40 cm wide x 60 cm long at a rate of 111 g / m². ２ The coating was applied and dried in a dryer at 105°C. After that, the coating film was visually inspected and evaluated according to the following criteria.

[0111] ◎: The paint film is applied to the entire surface and no variations in shade are observed. 〇: The paint film is applied to the entire surface, but there are slight variations in shade (approximately 20% of the surface area is uneven). ×: There are areas where the paint film is not applied.

[0112] Steel plates (water contact angle 45°) and glass plates (water contact angle 30°) were used as the materials to be coated.

[0113] The steel sheet was manufactured as follows: A slab (iron slab) containing trace elements including at least silicon (for example, Si: 3.25 mass%, C: 0.045 mass%, Mn: 0.070 mass%, Al: 80 mass ppm, N: 40 mass ppm, and S: 20 mass ppm) was heated to 1200°C and then hot-rolled to obtain a 2.2 mm thick hot-rolled sheet. This hot-rolled sheet was then hot-rolled and annealed at 1000°C for 30 seconds to remove surface scale. Next, it was cold-rolled in a tandem rolling mill to a final sheet thickness of 0.30 mm. Subsequently, primary recrystallization annealing, which also served as decarburization annealing, was performed by holding it at a soaking temperature of 850°C for 90 seconds to allow silica (SiO₂) to form on the surface. ２ A steel sheet was obtained in which an oxide film mainly composed of ) was formed.

[0114] The coating was formed three times, and the evaluation was the same each time.

[0115] A dispersion (slurry) prepared in the same manner as that used for measuring the relaxation time of film formation was applied to a 40 cm wide x 60 cm long steel plate (the steel plate prepared and used as described above) using a bar coater at a rate of 111 g / m². ２ The coating was applied and dried in a dryer at 105°C to form a coating film. The steel sheet with the coating film formed in this way was wound into a coil, and the coil was placed vertically and fired (annealed) in a nitrogen atmosphere at 1200°C at 25°C / hour to form a protective film. The formed film was visually inspected and evaluated according to the following criteria.

[0116] ◎: The coating is formed over the entire surface with no unevenness observed. 〇: The coating is formed over the entire surface, but there is some unevenness (approximately 20% of the surface area) or there are some pinpoint defects (approximately 3 or fewer). ×: The coating is uneven and there are more than 3 pinpoint defects.

[0117] The coating was formed three times, and the evaluation was the same each time.

[0118] <Example 1> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​36 m² ２A magnesium hydroxide powder with a D50 particle size of 1.0 μm, containing 0.01% Cl, 0.08% B, 0.08% P, 0.3% CaO, and 0.003% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 830°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). Subsequently, the powder was ground twice using a bantam mill (AP-B type, screen diameter 3 mm, manufactured by Hosokawa Micron Corporation) to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 10 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 27 m². ２ The particle size of the D50 was 0.8 μm, the value of (D84-D16) / 2 was 5.2 μm, and the viscosity was 100 mPa·s. The magnesium oxide contained impurities in amounts corresponding to the raw material (magnesium hydroxide) [approximately 50% (0.005%) Cl, approximately 80% (0.0024%) F, and 100% (substantially 100%) B, P, and CaO, etc.] (the same applies hereafter). The obtained magnesium oxide was then evaluated for its coating properties and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0119] <Example 2> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​35 m² ２ A magnesium hydroxide with a D50 particle size of 1.0 μm, containing 0.01% Cl, 0.07% B, 0.10% P, 0.2% CaO, and 0.010% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 900°C for 3 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 15 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 25 m². ２The particle size of the D50 was 0.8 μm, the value of (D84 - D16) / 2 was 3.5 μm, and the viscosity was 90 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0120] <Example 3> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​56 m² ２ A magnesium hydroxide powder with a D50 particle size of 1.2 μm, containing 0.01% Cl, 0.11% B, 0.20% P, 0.5% CaO, and 0.003% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 900°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 30 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 20 m². ２ The particle size of the D50 was 1.2 μm, the value of (D84 - D16) / 2 was 2.4 μm, and the viscosity was 70 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0121] <Example 4> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​15 m² ２ A magnesium hydroxide with a D50 particle size of 3.0 μm, containing 0.05% Cl, 0.08% B, 0.10% P, 0.3% CaO, and 0.010% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 820°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 42 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 27 m². ２The particle size of the D50 was 2.7 μm, the value of (D84 - D16) / 2 was 2.8 μm, and the viscosity was 110 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0122] <Example 5> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​23 m² ２ A magnesium hydroxide with a D50 particle size of 1.0 μm, containing 0.04% Cl, 0.07% B, 0.08% P, 0.3% CaO, and 0.005% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 850°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 64 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 20 m². ２ The particle size of the D50 was 1.0 μm, the value of (D84 - D16) / 2 was 5.9 μm, and the viscosity was 85 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0123] <Example 6> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​11 m² ２ A magnesium hydroxide powder with a D50 particle size of 4.0 μm, containing 0.01% Cl, 0.07% B, 0.12% P, 0.3% CaO, and 0.010% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 850°C for 3 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 67 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 24 m². ２The particle size of the D50 was 3.0 μm, the value of (D84 - D16) / 2 was 5.2 μm, and the viscosity was 115 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0124] <Example 7> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​19 m² ２ A magnesium hydroxide with a D50 particle size of 1.1 μm, containing 0.05% Cl, 0.08% B, 0.08% P, 0.2% CaO, and 0.010% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 870°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 148 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 19 m². ２ The particle size of the D50 was 0.9 μm, the value of (D84 - D16) / 2 was 4.1 μm, and the viscosity was 90 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0125] <Example 8> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​19 m² ２ A magnesium hydroxide with a D50 particle size of 3.7 μm, containing 0.05% Cl, 0.09% B, 0.10% P, 0.2% CaO, and 0.020% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 900°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 185 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 15 m². ２The particle size of the D50 was 3.8 μm, the value of (D84 - D16) / 2 was 4.0 μm, and the viscosity was 65 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0126] <Example 9> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​11 m² ２ A magnesium hydroxide with a D50 particle size of 3.8 μm, containing 0.05% Cl, 0.07% B, 0.12% P, 0.3% CaO, and 0.020% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 820°C for 3 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 223 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 26 m². ２ The particle size of the D50 was 3.7 μm, the value of (D84 - D16) / 2 was 6.1 μm, and the viscosity was 70 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0127] <Example 10> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​12 m² ２ A magnesium hydroxide with a D50 particle size of 4.0 μm, containing 0.05% Cl, 0.09% B, 0.09% P, 0.2% CaO, and 0.010% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 930°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 260 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 17 m². ２The particle size of the D50 was 3.9 μm, the value of (D84 - D16) / 2 was 3.0 μm, and the viscosity was 70 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0128] <Example 11> Magnesium oxide (powder) was prepared as follows: Magnesium hydroxide (powder) with a BET specific surface area of ​​9 m² ２ A magnesium hydroxide powder with a D50 particle size of 0.8 μm, containing 0.05% Cl, 0.08% B, 0.10% P, 0.2% CaO, and 0.015% F was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 950°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). After that, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 478 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 14 m². ２ The values ​​were as follows: 1 / g, D50 particle size 1 μm, (D84-D16) / 2 value 4.2 μm, and viscosity 30 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0129]

[0130] As is clear from the results in Table 1, even when physical properties such as BET specific surface area, D50 particle size, and viscosity are similar, the evaluations are completely different, indicating that relaxation time greatly affects coatability. In particular, it was found that extremely good coatability can be achieved by using a relaxation time that is neither too long nor too short.

[0131] Furthermore, it was found that relaxation time significantly affects film formation. In particular, it was found that by using a relaxation time that is neither too long nor too short, extremely good film formation can be achieved (especially, it becomes easier to achieve both extremely good coatability and film formation).

[0132] <Example 12> For each of the magnesium oxides obtained in Examples 1 to 7, the coating properties were evaluated using the same method as above, except that the coating target was changed to a resin plate (made of acrylic resin, water contact angle 80°). Similar trends were observed.

[0133] <Example 13> When magnesium oxide obtained by mixing the magnesium oxide obtained in Example 1 and the magnesium oxide obtained in Example 7 in a mass ratio of 1:1 was prepared, the relaxation time was measured to be 75 milliseconds. Furthermore, when various physical properties of the prepared magnesium oxide were measured, the BET specific surface area was 24 m². ２ The particle size of the D50 was 0.9 μm, the value of (D84 - D16) / 2 was 4.6 μm, and the viscosity was 90 mPa·s. The obtained magnesium oxide was then evaluated for its applicability to steel plates and film formation properties using the method described above. The applicability to steel plates was "◎" and the film formation properties were "◎".

[0134] <Example 14> The relaxation time of magnesium oxide obtained by mixing the magnesium oxide obtained in Example 2 and the magnesium oxide obtained in Example 3 in a mass ratio of 6:4 was measured to be 20 milliseconds. Furthermore, when various physical properties of the obtained magnesium oxide were measured, the BET specific surface area was 23 m². ２ The particle size of the D50 was 1.0 μm, the value of (D84 - D16) / 2 was 2.9 μm, and the viscosity was 70 mPa·s. The obtained magnesium oxide was then evaluated for its coatability and film-forming properties using the method described above. The coatability on steel plates was "〇", the coatability on glass plates was "◎", and the film-forming properties were "〇".

[0135] The present invention provides magnesium oxide and the like. Such magnesium oxide can be suitably used for applications involving coating (and even firing), such as as an annealing separating agent.

Claims

1. Magnesium oxide, when prepared as an aqueous dispersion containing 16 g of magnesium oxide per 100 g of water, exhibits a TD-NMR relaxation time of 1000 milliseconds or less at 40°C.

2. The magnesium oxide according to claim 1, wherein the relaxation time is 600 milliseconds or less.

3. The magnesium oxide according to claim 1, wherein the relaxation time is 500 milliseconds or less.

4. The magnesium oxide according to claim 1, wherein the relaxation time is 250 milliseconds or less.

5. The magnesium oxide according to claim 1, wherein the relaxation time is 200 milliseconds or less.

6. Magnesium oxide according to claim 1, wherein the relaxation time is 1 millisecond or more.

7. The magnesium oxide according to claim 1, wherein the relaxation time is 10 milliseconds or more.

8. Magnesium oxide according to claim 1, wherein the relaxation time is 20 milliseconds or more.

9. Magnesium oxide according to claim 1, wherein the relaxation time is 1 to 600 milliseconds.

10. Magnesium oxide according to claim 1, wherein the relaxation time is 10 to 500 milliseconds.

11. The magnesium oxide according to claim 1, wherein the relaxation time is 20 to 250 milliseconds.

12. The magnesium oxide according to claim 1, wherein the relaxation time is 40 to 150 milliseconds.

13. BET specific surface area is 200 m² ２ The magnesium oxide according to claim 1, wherein the amount is less than or equal to / g.

14. The magnesium oxide according to claim 1, wherein the D50 particle size is 100 μm or less.

15. In the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less, according to claim 1, the magnesium oxide.

16. The magnesium oxide according to claim 1, wherein when an aqueous dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water has a viscosity of 3000 mPa·s or less at 20°C.

17. BET specific surface area is 200 m² ２ The magnesium oxide according to claim 1, wherein the amount is less than or equal to / g, the D50 particle size is 100 μm or less, and in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less, and when an aqueous dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water is prepared, the viscosity at 20°C is 3000 mPa·s or less.

18. Relaxation time is 10-500 milliseconds, and BET specific surface area is 200 m². ２ The magnesium oxide according to claim 1, wherein the amount is less than or equal to / g, the D50 particle size is 100 μm or less, and in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 30 μm or less, and when an aqueous dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water is prepared, the viscosity at 20°C is 3000 mPa·s or less.

19. Relaxation time is 20–250 milliseconds, and BET specific surface area is 3–100 m². ２ The magnesium oxide according to claim 1, wherein the amount is / g, the D50 particle size is 0.2 to 30 μm, and in the cumulative particle size distribution, when the particle size that accounts for 16% is D16 (μm) and the particle size that accounts for 84% is D84 (μm), the value of (D84 - D16) / 2 is 15 μm or less, and when an aqueous dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water is prepared, the viscosity at 20°C is 5 to 800 mPa·s.

20. Magnesium oxide according to claim 1, comprising calcium, boron, phosphorus, fluorine, and chlorine.

21. The magnesium oxide according to claim 1, containing calcium as calcium oxide (CaO) in the proportions of 0.01 to 5% by mass, boron in the proportions of 0.001 to 0.5% by mass, phosphorus in the proportions of 0.001 to 1% by mass, fluorine in the proportions of 0.001 to 1% by mass, and chlorine in the proportions of 0.001 to 1% by mass.

22. Magnesium oxide according to claim 1, for use as an annealing separating agent.

23. Magnesium oxide according to claim 1, for use in electrical steel sheets.

24. A dispersion containing magnesium oxide according to any one of claims 1 to 23.

25. An annealing separating agent containing magnesium oxide according to any one of claims 1 to 23.

26. A substrate comprising a coating film containing magnesium oxide as described in any one of claims 1 to 23.

27. The substrate according to claim 26, wherein the water contact angle of the substrate at 20°C is 60° or less.

28. The base material according to claim 26, wherein the base material is a steel plate.

29. A method for producing the substrate according to claim 26, comprising at least the step of applying a dispersion containing magnesium oxide to the substrate.

30. A steel sheet having a coating containing magnesium oxide as described in any one of claims 1 to 23.

31. The steel sheet according to claim 30, which is an electrical steel sheet.

32. A method for producing a steel sheet according to claim 30, comprising at least a step of firing a steel sheet having a coating film containing magnesium oxide according to any one of claims 1 to 23.

33. A method for producing a steel sheet according to claim 30, comprising at least the steps of: applying a dispersion containing magnesium oxide according to any one of claims 1 to 23 to a steel sheet; and firing the steel sheet having a magnesium oxide coating obtained through this step.

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