Magnesium oxide

Abstract

Provided is magnesium oxide.　The magnesium oxide satisfies a relaxation time of at most 1,000 milliseconds in TD-NMR at 40ºC when being made into an aqueous dispersion containing 16 g of the magnesium oxide per 100 g of water.

Description

Magnesium oxide

[0001] This invention relates to magnesium oxide, etc.

[0002] Magnesium oxide is being considered for use in various fields, one example being as an annealing separating agent (Patent Document 1, etc.).

[0003] International Publication No. 2019 / 065645

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

[0005] One way to use magnesium oxide is as a dispersion (slurry). For example, in applications such as the aforementioned annealing separating agent, it is used (applied) as a dispersion to form a coating film or layer.

[0006] The inventors of the present invention investigated magnesium oxides used in such dispersion forms and found that some magnesium oxides tended to produce clumps (lumps).

[0007] Such clumps, if used as is, can cause problems (for example, they may adhere to the coated surface as coarse particles, leading to uneven coating, reduced adhesion, and decreased performance of the desired magnesium oxide function in the coated surface). On the other hand, these clumps can potentially be eliminated or removed by separation by sieving or crushing by physical means (e.g., homodispersing), but this requires a separate process for elimination or removal, which can lead to a decrease in work efficiency and productivity.

[0008] Therefore, it is desirable to minimize the formation of clumps, but simply using magnesium oxide with a low proportion of large particles for dispersion may not solve the problem of clump formation, making the solution extremely difficult.

[0009] Under these circumstances, the inventors, after diligent research, discovered that certain physical properties affect the formation of clumps, and that the formation of clumps can be suppressed by adjusting or selecting the values ​​of these physical properties. Further research led to the completion of the present invention.

[0010] That is, the present invention relates to the following inventions and the like. [1] Magnesium oxide, when it is a water dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water, the relaxation time (relaxation time T ２ , transverse relaxation time, spin-spin relaxation time) of TD-NMR at 40 °C is 1000 milliseconds or less. [2] Magnesium oxide, when it is a water dispersion containing magnesium oxide at a ratio of 16 g per 100 g of water, the relaxation time of TD-NMR at 40 °C is 1000 milliseconds or less, and the BET specific surface area is 300 m ２ / g or less. [3] The magnesium oxide according to [1] or [2], wherein the relaxation time is 750 milliseconds or less. [4] The magnesium oxide according to any one of [1] to [3], wherein the relaxation time is 700 milliseconds or less. [5] The magnesium oxide according to any one of [1] to [4], wherein the relaxation time is 1 millisecond or more. [6] The magnesium oxide according to any one of [1] to [5], wherein the relaxation time is 10 milliseconds or more. [7] The magnesium oxide according to any one of [1] to [6], wherein the BET specific surface area is 200 m ２ / g or less. [8] The magnesium oxide according to any one of [1] to [7], wherein the BET specific surface area is 150 m ２ / g or less. [9] The magnesium oxide according to any one of [1] to [8], wherein the BET specific surface area is 0.1 m ２ / g or more.

[10] The magnesium oxide according to any one of [1] to [9], wherein the BET specific surface area is 1 m ２ / g or more.

[11] The magnesium oxide according to any one of [1] to

[10] , wherein the relaxation time is 1 to 800 milliseconds and the BET specific surface area is 0.1 to 250 m ２ / g.

[12] The magnesium oxide according to any one of [1] to

[11] , wherein the relaxation time is 3 to 750 milliseconds and the BET specific surface area is 0.3 to 200 m ２ / g.

[13] The magnesium oxide according to any one of [1] to

[11] , wherein the relaxation time is 5 to 700 milliseconds and the BET specific surface area is 0.5 to 160 m ２Magnesium oxide as described in any of [1] to

[12] , wherein the amount is / g.

[14] Relaxation time is 10 to 680 milliseconds and BET specific surface area is 0.8 to 150 m². ２ Magnesium oxide as described in any of [1] to

[13] , wherein the amount is / g.

[15] Relaxation time is 15 to 650 milliseconds and BET specific surface area is 1 to 135 m². ２ Magnesium oxide as described in any of [1] to

[14] , wherein the amount is / g.

[16] Relaxation time is 20 to 600 milliseconds and the BET specific surface area is 2 to 100 m². ２ Magnesium oxide as described in any of [1] to

[15] , wherein the amount is / g.

[17] Relaxation time is 28 to 580 milliseconds and BET specific surface area is 3 to 92 m². ２Magnesium oxide according to any one of [1] to

[16] , wherein the amount is / g.

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

[17] , wherein the D50 particle size is 0.01 to 100 μm.

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

[18] , wherein when the D10 particle size is D10 (μm) and the D90 particle size is D90 (μm), the value of (D90 - D10) / 2 is 50 or less.

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

[19] , wherein the D50 particle size is 0.1 to 50 μm, and when the D10 particle size is D10 (μm) and the D90 particle size is D90 (μm), the value of (D90 - D10) / 2 is 30 or less.

[21] The magnesium oxide according to any one of [1] to

[20] , 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.

[22] The magnesium oxide according to any one of [1] to

[21] , comprising calcium, boron, phosphorus, fluorine, sulfur, and chlorine.

[23] The magnesium oxide according to any one of [1] to

[22] , 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, sulfur in the proportions of 0.01 to 5% by mass, and chlorine in the proportions of 0.001 to 1% by mass.

[24] The magnesium oxide according to any one of [1] to

[23] for use in paints or annealing separating agents.

[25] The magnesium oxide according to any one of [1] to

[23] for use in electrical steel sheets.

[26] A dispersion containing magnesium oxide as described in any of [1] to

[25] .

[27] A paint containing magnesium oxide as described in any of [1] to

[25] .

[28] An annealing separating agent containing magnesium oxide as described in any of [1] to

[25] .

[0011] The present invention provides magnesium oxide (specific magnesium oxide). When such magnesium oxide is used in a dispersion (slurry), it can efficiently suppress the formation of clumps.

[0012] Therefore, magnesium oxide according to one embodiment of the present invention may be suitably used in applications where it is applied and used as a dispersion, and is particularly useful in applications where it is applied or forms a film, such as an annealing separating agent, in applications for electrical steel sheets [for example, in applications where a film (forsterite layer) is formed on electrical steel sheets], and as a paint.

[0013] Using it in this way makes it easier to achieve good coating properties (applicability). For example, it can effectively suppress unevenness (color variation) and missed spots on the coating target (steel plate, etc.), resulting in 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 with a slurry (dispersion), unevenness and incomplete adhesion tend to occur, especially when using a slurry with many clumps. However, with magnesium oxide according to one embodiment of the present invention, good coating performance can be achieved even when coating with a slurry. Coating performance can affect the function of the formed film (coating film, coating film), and therefore, good coating performance is highly useful in that it can contribute to the efficient performance or realization of that 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 is formed by firing a slurry containing many lumps, an uneven coating may be formed, such as one with large inconsistencies. Furthermore, such uneven coatings can 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, as described above. Depending on its application (for example, in annealing separation applications), magnesium oxide undergoes, for example, a coating film formation step and a film formation (film formation by firing) step. Therefore, in applications that undergo both of these steps, magnesium oxide according to this yet another aspect of the present invention is particularly useful.

[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) ２ It has specific values ​​in terms of transverse relaxation time and spin-spin relaxation time.

[0021] Such relaxation time may be selected from a range of, for example, 1000 milliseconds (ms) or less (e.g., 900 milliseconds or less), and is usually 800 milliseconds or less (e.g., 780 milliseconds or less), preferably 750 milliseconds or less (e.g., 720 milliseconds or less), more preferably 700 milliseconds or less (e.g., 680 milliseconds or less), and particularly 650 milliseconds or less (e.g., 620 milliseconds or less).

[0022] The relaxation time may be a smaller value, for example, 600 milliseconds or less (for example, 580 milliseconds or less), or 550 milliseconds or less (for example, 520 milliseconds or less, 500 milliseconds or less, 480 milliseconds or less, 450 milliseconds or less, 420 milliseconds or less, 400 milliseconds or less, 380 milliseconds or less, 350 milliseconds or less, 320 milliseconds or less, 300 milliseconds or less, 280 milliseconds or less, 270 milliseconds or less, 250 milliseconds or less, 240 milliseconds or less, 230 milliseconds or less, 220 milliseconds or less, 210 milliseconds or less, 200 milliseconds or less, 190 milliseconds or less, 180 milliseconds or less, 170 milliseconds or less). It can also be set to less than a second, less than 165 milliseconds, less than 160 milliseconds, less than 155 milliseconds, less than 150 milliseconds, less than 148 milliseconds, less than 145 milliseconds, less than 140 milliseconds, less than 135 milliseconds, less than 130 milliseconds, less than 125 milliseconds, less than 120 milliseconds, less than 115 milliseconds, less than 110 milliseconds, less than 105 milliseconds, less than 100 milliseconds, less than 95 milliseconds, less than 90 milliseconds, less than 85 milliseconds, less than 80 milliseconds, less than 75 milliseconds, less than 70 milliseconds, less than 65 milliseconds, less than 60 milliseconds, less than 55 milliseconds, less than 50 milliseconds, less than 45 milliseconds, less than 40 milliseconds, etc.

[0023] 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), and especially 20 milliseconds or more (e.g., 22 milliseconds or more), and 25 milliseconds or more (e.g., 28 milliseconds or more, 30 milliseconds or more, more than 30 milliseconds, 32 milliseconds or more, 35 milliseconds or more, 38 milliseconds or more, 40 milliseconds or more, 42 milliseconds or more, 4 It can be set to 5 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, 65 milliseconds or more, 68 milliseconds or more, 70 milliseconds or more, 72 milliseconds or more, 75 milliseconds or more, 78 milliseconds or more, 80 milliseconds or more, 82 milliseconds or more, 85 milliseconds or more, 88 milliseconds or more, 90 milliseconds or more, 92 milliseconds or more, 95 milliseconds or more, 98 milliseconds or more, 100 milliseconds or more, 102 milliseconds or more, 105 milliseconds or more, 108 milliseconds or more, 110 milliseconds or more, 112 milliseconds or more, 115 milliseconds or more, 118 milliseconds or more, 120 milliseconds or more, etc.

[0024] Furthermore, the relaxation time can 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 being able to suppress the formation of clumps very well [and furthermore, to achieve 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.

[0025] The specific relaxation time may be, for example, 0.1 to 1000 milliseconds (e.g., 1 to 800 milliseconds), preferably 3 to 750 milliseconds (e.g., 5 to 700 milliseconds), more preferably 10 to 680 milliseconds (e.g., 15 to 650 milliseconds), and particularly preferably 20 to 600 milliseconds (e.g., 28 to 580 milliseconds).

[0026] This relaxation time effectively suppresses the formation of clumps [and furthermore, it makes it easier to improve the coatability and film-forming properties (especially coatability and film-forming properties)].

[0027] 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 primarily affect the wettability or affinity between the particle interface and the solvent. Specifically, a higher proportion of bound solvent (shorter relaxation time) leads to greater wettability or affinity, which in turn makes it easier to disperse (aggregate) the particles in the dispersion. Thus, the relaxation time affects the ease of particle dispersion, and by keeping the relaxation time from being too long, the dispersibility of the particles can be improved, and the formation of clumps can be efficiently suppressed. In terms of suppressing clump 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 suppress clump formation at a high level. The reason for this is unclear, but it is thought that if there is too much constrained solvent (the relaxation time becomes too short), the surface state and aggregation state of magnesium oxide change at a microscopic level, affecting the dispersibility of the particles.

[0028] Furthermore, perhaps due to the excellent dispersibility (suppression of clump formation) mentioned above, when applied and used as a dispersion, it efficiently reflects (exhibits) good coatability and film-forming properties (and even the functions of magnesium oxide). The following reasons are thought to be the cause of this.

[0029] As mentioned above, 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.

[0030] 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.

[0031] 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).

[0032] The aqueous dispersion is not particularly limited, but for example, one prepared by the method described below can be used for measurement immediately [for example, within 10 minutes after preparation (for example, within 5 minutes, within 3 minutes, or within 1 minute 30 seconds)].

[0033] 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.)].

[0034] The relaxation time is not particularly limited, but can be adjusted by, for example, the composition and physical properties of the magnesium hydroxide used as a raw material for magnesium oxide production (e.g., the type and proportion of impurities or trace elements in the magnesium hydroxide, BET specific surface area, particle size, etc.) and the calcination conditions of the magnesium hydroxide (calcination temperature, calcination 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 small particle size, or by lowering the calcination temperature.

[0035] Furthermore, by combining magnesium oxides with different relaxation times, it is possible to obtain magnesium oxide with a desired relaxation time (adjust the relaxation time) (the same applies to physical properties other than relaxation time, etc.).

[0036] Magnesium oxide (magnesium oxide particles, particulate magnesium oxide) usually satisfies a specific relaxation time, as described above, but it may also possess (satisfy) other physical properties (other than relaxation time).

[0037] For example, the BET specific surface area of ​​magnesium oxide is 300 m². ２ / g or less (for example, 250m) ２ You may choose from a range of approximately 1 / g or less, and 200m ２ / g or less (for example, 180m) ２ / g or less, 160m ２ (less than or equal to / g), preferably 150m ２ / g or less (for example, 140m) ２ / g or less, 135m ２ / g or less, 130m ２ / g or less, 125m ２ (less than or equal to / g), more preferably 120m ２ / g or less (for example, 115m) ２ / g or less, 110m ２ / g or less, 105m ２ (less than / g), especially 100m ２ / g or less (for example, 95m) ２ / g or less, 92m ２ It may be less than or equal to 90m ２ / g or less (for example, 85m) ２ / g or less, 82m ２ / g or less, 80m ２ / g or less, 78m ２ / g or less, 75m ２ / g or less, 72m ２ / g or less, 70m ２ / g or less, 68m ２ / g or less, 65m ２ / g or less, 62m ２ / g or less, 60m ２ / g or less, 58m ２ / g or less, 55m ２ / g or less, 52m ２ / g or less, 50m ２ / g or less, 48m ２ / g or less, 45m ２ / g or less, 42m ２ / g or less, 40m ２ / g or less, 38m ２ / g or less, 35m ２ / g or less, 32m ２ / g or less, 30m ２ / g or less, 28m ２ / g or less, 25m ２ It may also be (e.g., less than / g), etc.

[0038] The lower limit of the BET specific surface area of ​​magnesium oxide is, for example, 0.1 m². ２ / g or more (for example, 0.2m) ２ / g or more, 0.3m ２ / g or more, 0.5m ２ / g or more, 0.8m ２ You may choose from a range of approximately (1 m) or more. ２ / g or more (for example, 1.2m) ２ / g or more, 1.5m２ / g or more, 1.8 m ２ / g or more), preferably 2 m ２ / g or more (for example, 2.2 m ２ / g or more, 2.5 m ２ / g or more, 2.8 m ２ / g or more), more preferably 3 m ２ / g or more (for example, 3.2 m ２ / g or more, 3.5 m ２ / g or more, 3.8 m ２ / g or more) may be sufficient, 4 m ２ / g or more (for example, 4.2 m ２ / g or more, 4.5 m ２ / g or more, 4.8 m ２ / g or more, 5 m ２ / g or more, 5.5 m ２ / g or more, 6 m ２ / g or more, 6.5 m ２ / g or more, 7 m ２ / g or more, 7.5 m ２ / g or more, 8 m ２ / g or more, 10 m ２ / g or more, 12 m ２ / g or more, 15 m ２ / g or more, 18 m ２ / g or more, 20 m ２ / g or more) etc. can also be used.

[0039] The specific BET specific surface area of magnesium oxide is, for example, 0.1 to 300 m ２ / g (for example, 0.2 to 250 m ２ / g), preferably 0.3 to 200 m ２ / g (for example, 0.4 to 180 m ２ / g), more preferably 0.5 to 160 m ２ / g (for example, 0.8 to 150 m ２ / g), even more preferably 1 to 135 m ２ / g (for example, 1.2 to 120 m ２ / g), particularly 1.5 to 110 m ２ / g (for example, 2 to 100 m ２ / g, 2 to 95 m ２ / g, 2 to 92 m ２ / g, 2.2 to 100 m ２ / g, 2.5-100m ２ / g, 2.8-92m ２ / g, 3-100m ２ / g, 3-92m ２ / g, 4-100m ２ / g, 5-100m ２ / g, 2-80m ２ / g, 2.5-70m ２ / g, 3-60m ２ / g, 2-50m ２ / g, 3-40m ２ / g, 3-30m ２ / g, 3-25m ２ / g, 4-30m ２ / g, 5-25m ２ (e.g., / g) may also be used.

[0040] By keeping the BET specific surface area from being too large, it is easier to efficiently suppress the formation of clumps. This is presumed to be because it may make it easier to suppress the aggregation of particles. Similarly, by keeping the BET specific surface area from being too small, it is easier to efficiently suppress the formation of clumps. This is presumed to be because it may make it easier to suppress the sedimentation and accumulation of particles. Furthermore, it appears that the formation of clumps can be suppressed even more efficiently when magnesium oxide satisfies the above-mentioned BET specific surface area in combination with the specific relaxation time mentioned above.

[0041] Furthermore, as mentioned above, by keeping the BET specific surface area not too large (or even too small), it is 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 (or even a protective film).

[0042] 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.

[0043] 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).

[0044] The D50 particle size of magnesium oxide [D50 volume diameter, particle size at which the cumulative particle size distribution becomes 50%, particle size at which the cumulative particle size distribution (cumulative curve) becomes 50% (volume particle diameter)] may be selected from a range of, for example, 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), 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.

[0045] 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.

[0046] 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., 0.6 to 4 μm).

[0047] The magnesium oxide of the present invention can suppress the formation of clumps regardless of the D50 particle size (average particle size) by satisfying the aforementioned relaxation time (and furthermore, the BET specific surface area). In particular, according to the inventors' research, considering that clump formation generally becomes more likely as the D50 particle size decreases, the present invention can be said to be extremely useful in suppressing the formation of clumps in magnesium oxide with a relatively small D50 particle size as described above.

[0048] 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.

[0049] While the particle size is not particularly limited, it can be efficiently adjusted through methods such as grinding conditions (methods) and classification operations.

[0050] The particle size distribution of magnesium oxide (particles) may also be based on the cumulative diameter. When the D10 particle diameter [D10 volume diameter, particle size at which the cumulative particle size distribution becomes 10%, the particle size at which 10% occurs in the cumulative particle size distribution (cumulative curve) (volume particle diameter)] of magnesium oxide (particles) is D10 (μm) and the D90 particle diameter [D90 volume diameter, particle size at which the cumulative particle size distribution becomes 90%, the particle size at which 90% occurs in the cumulative particle size distribution (cumulative curve) (volume particle diameter)] is D90 (μm), then the value of (D90 - D10) / 2 is 100 μm or less (for example, 80 μm). The range can be selected from approximately m or less, or 60 μm or less, and may be 50 μm or less (for example, 45 μm or less), preferably 40 μm or less (for example, 35 μm or less), more preferably 30 μm or less (for example, 28 μm or less), even more preferably 25 μm or less (for example, 22 μm or less), particularly preferably 20 μm or less (for example, 18 μm or less), and may also be 15 μm or less (for example, 12 μm or less, 10 μm or less), etc.

[0051] The lower limit of (D90-D10) / 2 may be selected from a range of, for example, 0.01 μm or more (e.g., 0.02 μm or more), preferably 0.03 μm or more (e.g., 0.04 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), even more preferably 0.2 μm or more (e.g., 0.25 μm or more), particularly preferably 0.3 μm or more (e.g., 0.35 μm or more), and so on. It may also be μm or larger (for example, 0.5 μm or larger, 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, 2.9 μm or larger, 3 μm or larger), etc.

[0052] The specific value of (D90 - D10) / 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).

[0053] Furthermore, the above value of (D90 - D10) / 2 can also be considered the standard deviation (μm) of magnesium oxide (particles) [it is a pseudo-standard deviation (μm)].

[0054] The magnesium oxide of the present invention can suppress the formation of clumps regardless of the particle size distribution by satisfying the aforementioned relaxation time (and furthermore, the BET specific surface area). In particular, according to the inventors' studies, considering that clumps tend to form more easily as the particle size distribution [(D90 - D10) / 2] becomes smaller, the present invention can be said to be extremely useful in suppressing the formation of clumps in magnesium oxide exhibiting a relatively small particle size distribution as described above.

[0055] Furthermore, by keeping the value of (D90 - D10) / 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.

[0056] The values ​​of D10 and D90 are not particularly limited, but for example, they can be determined as volume-based particle diameters (volume particle diameters) based on the particle size distribution obtained by measuring using a particle size distribution analyzer, and specifically, they may be determined as shown in the examples described later.

[0057] While the particle size distribution is not particularly limited, it can be efficiently adjusted by, for example, the grinding conditions (methods) or classification operations.

[0058] 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.

[0059] 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.

[0060] 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).

[0061] The magnesium oxide of the present invention can suppress the formation of clumps regardless of viscosity by satisfying the aforementioned relaxation time (and BET specific surface area). In particular, by keeping the viscosity not too high (and not too low), as described above, the formation of clumps can be suppressed even more efficiently. Furthermore, by keeping the viscosity not too high (and not too low), it is easy to obtain a good coating (and even a film) efficiently with excellent handling properties.

[0062] 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.

[0063] 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.

[0064] 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).

[0065] 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).

[0066] Magnesium oxide may contain these impurities individually or in combination of two or more.

[0067] 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, if it contains elements selected from calcium, boron, phosphorus, fluorine, and chlorine, the proportion of calcium is 5% by mass or less of magnesium oxide (total magnesium oxide including impurities) as calcium oxide (CaO) (for example, 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 5% by mass, 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), and the proportion of boron is acid The amount of magnesium oxide is 1% by mass or less (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, 0.15% 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 amount of phosphorus is 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, 0.001 to 0.5% by mass, 0.01 to 0.3% by mass, 0.03 to 0 25% by mass, 0.05-0.2% by mass), fluorine content is 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, 0.001-0.5% by mass, 0.01-0.3% by mass, 0.005-0.15% by mass, 0.01-0.1% by mass), sulfur content is 5% by mass or less of magnesium oxide (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 The amount of chlorine may be less than or equal to mass%, 0.01 to 5% by mass, 0.01 to 3% by mass, 0.05 to 2% by mass, 0.1 to 2.5% by mass, or 0.2 to 1% by mass), and the amount of chlorine may be less than or equal to 1% by mass of magnesium oxide (for example, less than or equal to 0.8% by mass, less than or equal to 0.5% by mass, less than or equal to 0.4% by mass, less than or equal to 0.3% by mass, less than or equal to 0.2% by mass, less than or equal to 0.001 to 0.5% by mass, less than or equal to 0.01 to 0.3% by mass, less than or equal to 0.15% by mass, less than or equal to 0.005 to 0.1% by mass, less than or equal to 0.01 to 0.09% by mass, or less than or equal to 0.01 to 0.07% by mass), etc.

[0068] 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.

[0069] 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.

[0070] Magnesium oxide is typically in particulate form (powder, granules, pulverized material, or powder). 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.

[0071] 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).

[0072] Magnesium hydroxide (magnesium hydroxide subjected to or used in the calcination process) may have physical properties (BET specific surface area, particle size, etc.) similar to those of magnesium oxide, and may contain impurities. The magnesium hydroxide is not particularly limited and may be synthesized by conventional methods or derived from seawater or magnesium chloride.

[0073] 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).

[0074] These 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.).

[0075] 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)].

[0076] 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.).

[0077] 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.).

[0078] [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.

[0079] In particular, the magnesium oxide of the present invention is suitable for applications where magnesium oxide is applied or used in the form of a dispersion (slurry) because it easily suppresses the formation of clumps (lumps, coarse particles). Examples of such applications include coating and film formation. In particular, perhaps due to the suppression of clump formation, using such a dispersion makes it easier to achieve good coating properties and film formation properties, making it suitable for such applications.

[0080] Examples of such applications include paints and annealing separators.

[0081] 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.

[0082] 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.

[0083] The present invention also includes such dispersions.

[0084] 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.

[0085] 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).

[0086] 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).

[0087] 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.

[0088] The present invention includes a coating object (a coating object) having such a magnesium oxide coating layer (coating film) (a coating layer formed thereon).

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.).

[0096] 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).

[0097] 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.).

[0098] 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.).

[0099] 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.

[0100] 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.

[0101] 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.).

[0102] 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)].

[0103] 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).

[0104] 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).

[0105] 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.

[0106] The various physical properties and characteristics were measured and evaluated as follows.

[0107] Relaxation time Relaxation time (Relaxation time T ２The 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).

[0108] 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.

[0109] 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

[0110] 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).

[0111] Particle Size (D10, D50, D90) 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. The mixture was then dispersed using an ultrasonic generator (UD-201 model) manufactured by Tommy Seiko Co., Ltd. for 3 minutes to prepare a dispersion. The obtained dispersion was measured using a particle size analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.) (measured by laser diffraction) to obtain the volume-based D10, D50, and D90 particle sizes. The measurement conditions were: solvent refractive index: 1.36, particle permeability: transparent, particle refractive index: 1.73, and particle shape: non-spherical.

[0112] Viscosity: 800 mL of 20°C water and 128 g of the 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 (20°C) of the obtained slurry was then measured using a BII type viscometer (manufactured by Toki Sangyo Co., Ltd.) with rotor No. 2 or rotor No. 3 [only for the sample in Example 11 (magnesium oxide)] and a rotation speed of 60 rpm.

[0113] Impurity levels: Cl: Determined by mercury thiocyanate spectrophotometry. B: Determined using ICP-AES. CaO: Determined by chelation titration using EDTA. P: Determined by vanadomolybdate spectrophotometry. F: Determined using lanthanum-alizarin complexone spectrophotometry in accordance with JIS K 0102:2019 (Testing methods for factory wastewater). S: Determined using ICP-AES.

[0114] Sieve Passability (1) 400 mL of water and 32 g of magnesium oxide (MgO) were placed in a 5 L poly jug, and stirring was started at 300 rpm. After 10 seconds, the remaining 400 mL of water was added, and stirring was performed at 800 rpm for 5 minutes to form a slurry. A dissolving type stirring blade with a diameter of 60 mm was used for stirring. (2) After stirring was completed, the slurry was passed through a sieve with a mesh size of 150 μm. The 5 L poly jug was also washed with approximately 2 L of water, and the washings were passed through the same sieve. The mesh size of 150 μm is sufficiently large compared to the D50 particle size (and even D90 particle size) of the magnesium oxide (powder) used. (3) Four minutes after the end of stirring, a shower of water at a flow rate of 100 mL / second was poured over the sieve to wash away the slurry, leaving only clumps. The shower faucet used had a diameter of 60 mm, a hole size of 1 mm, and 137 holes. The distance between the faucet and the mesh part of the sieve was set to approximately 4 cm, and the sieve was rotated for 20 to 60 seconds while washing. (4) After washing, the sieve residue (magnesium oxide remaining on the sieve) was collected, and alcohol was applied and it was dried in a 120°C dryer for 30 minutes or more. (5) After drying, the mass (g) of the sieve residue was measured, and the sieve passability was evaluated according to the following criteria.

[0115] A: Mass of sieved material is less than 0.1g B: Mass of sieved material is 0.1g or more and less than 1g C: Mass of sieved material is 1g or more and less than 3g D: Mass of sieved material is 3g or more and less than 6g E: Mass of sieved material is 6g or more and less than 10g F: Mass of sieved material is 10g or more and less than 15g G: Mass of sieved material is 15g or more and less than 20g H: Mass of sieved material is 20g or more and less than 25g I: Mass of sieved material is 25g or more

[0116] 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.

[0117] 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.

[0118] ◎: The paint film is applied evenly across the entire surface, and no variations in shade are observed. 〇: The paint film is applied evenly across 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.

[0119] Steel plates (water contact angle 45°) and glass plates (water contact angle 30°) were used as the materials to be coated.

[0120] 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.

[0121] The coating was formed three times, and the evaluation was the same each time.

[0122] 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.

[0123] ◎: 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.

[0124] The coating was formed three times, and the evaluation was the same each time.

[0125] <Example 1> Magnesium hydroxide (powder) with a BET specific surface area of ​​25 m² ２ A magnesium hydroxide mixture with a D50 particle size of 0.6 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.2% CaO, 0.009% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 800°C for 2 hours using an electric furnace (Koyo Lindbergh). Subsequently, the mixture was ground twice using a bantam mill (Hosokawa Micron AP-B type, screen diameter 3 mm) 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 50 m². ２The particle size of D10 was 0.3 μm, D50 was 0.6 μm, D90 was 4.2 μm, and the viscosity was 265 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0126] <Example 2> The magnesium oxide obtained in Example 1 and the magnesium oxide obtained in Example 4 (described below) were mixed in a ratio of 60 parts by mass and 40 parts by mass, respectively, to obtain magnesium oxide (powder mixture). The relaxation time of the obtained magnesium oxide was measured to be 20 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was found to be 39 m². ２ The particle size of D10 was 0.3 μm, D50 was 0.8 μm, D90 was 7.8 μm, and the viscosity was 80 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0127] <Example 3> Magnesium hydroxide (powder) with a BET specific surface area of ​​25 m² ２A magnesium hydroxide mixture was used (prepared) with a D50 particle size of 0.6 μm, containing 0.07% Cl, 0.09% B, 0.08% P, 0.2% CaO, 0.01% F, and 0.1% S. 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 700°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). Afterward, the same grinding process as in Example 1 was performed to obtain magnesium oxide (powder) A. The obtained magnesium oxide A, the magnesium oxide obtained in Example 5 (described later), and the magnesium oxide obtained in Example 8 (described later) were mixed in proportions of 15 parts by mass, 45 parts by mass, and 40 parts by mass, respectively, to obtain magnesium oxide (powder mixture). The relaxation time of the obtained magnesium oxide was measured to be 28 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 13 m². ２ The particle size of D10 was 0.5 μm, D50 was 3.5 μm, D90 was 18.4 μm, and the viscosity was 15 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0128] <Example 4> Magnesium hydroxide (powder) with a BET specific surface area of ​​23 m² ２ A magnesium hydroxide powder with a D50 particle size of 1.0 μm, containing 0.01% Cl, 0.11% B, 0.20% P, 0.5% CaO, 0.003% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 910°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 32 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 22 m². ２The particle size of D10 was 0.3 μm, D50 was 1.0 μm, D90 was 13.2 μm, and the viscosity was 70 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0129] <Example 5> Seawater and slaked lime in molar ratio Mg ２＋ : OH － The mixture was reacted in a ratio of 1:1.8 to obtain primary magnesium hydroxide. The obtained primary magnesium hydroxide was calcined at 1300°C for 2 hours, pulverized, and sieved through a 200-mesh sieve to obtain magnesium oxide powder. The obtained magnesium oxide powder was added to water at a liquid temperature of 80°C to a concentration of 15% by mass to obtain a magnesium hydroxide slurry. The obtained magnesium hydroxide slurry was dried to obtain a BET specific surface area of ​​24 m². ２ A magnesium hydroxide powder was obtained with a D50 particle size of 0.9 μm, containing 0.01% Cl, 0.07% B, 0.12% P, 0.3% CaO, 0.010% F, and 0.1% S. 100 g of the obtained magnesium hydroxide powder was placed in an alumina crucible and calcined at 800°C for 3 hours using an electric furnace (manufactured by Koyo Lindbergh). Afterward, 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 found to be 24 m². ２ The particle size of D10 was 0.3 μm, D50 was 0.9 μm, D90 was 9.8 μm, and the viscosity was 125 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0130] <Example 6> Magnesium hydroxide (powder) with a BET specific surface area of ​​23 m²２ A magnesium hydroxide powder with a D50 particle size of 1.0 μm, containing 0.04% Cl, 0.07% B, 0.08% P, 0.3% CaO, 0.005% F, and 0.3% S 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 78 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 D10 was 0.4 μm, D50 was 1.0 μm, D90 was 9.1 μm, and the viscosity was 85 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0131] <Example 7> Magnesium hydroxide (powder) with a BET specific surface area of ​​50 m² ２ A magnesium hydroxide mixture with a D50 particle size of 3.6 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.4% CaO, 0.020% F, and 0.2% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 550°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 93 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 134 m². ２The particle size of D10 was 1.9 μm, D50 was 3.7 μm, D90 was 6.8 μm, and the viscosity was 140 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0132] <Example 8> Magnesium hydroxide (powder) with a BET specific surface area of ​​19 m² ２ A magnesium hydroxide powder with a D50 particle size of 1.1 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.2% CaO, 0.009% F, and 0.4% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 880°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 100 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 21 m². ２ The particle size of D10 was 0.4 μm, D50 was 1.0 μm, and D90 was 6.9 μm. The viscosity was 90 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0133] <Example 9> Magnesium hydroxide (powder) with a BET specific surface area of ​​50 m² ２A magnesium hydroxide mixture was used (prepared) with a D50 particle size of 3.6 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.4% CaO, 0.020% F, and 0.2% S. 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 750°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). Afterward, 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 111 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was found to be 92 m². ２ The particle size of D10 was 1.7 μm, D50 was 3.5 μm, D90 was 6.5 μm, and the viscosity was 100 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0134] <Example 10> Magnesium hydroxide (powder) with a BET specific surface area of ​​50 m² ２ A magnesium hydroxide powder with a D50 particle size of 3.6 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.4% CaO, 0.020% F, and 0.2% S 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 169 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 52 m². ２ The particle size of D10 was 1.6 μm, D50 was 3.4 μm, and D90 was 6.2 μm, with a viscosity of 70 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0135] <Example 11> 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 0.06% Cl, 0.08% B, 0.10% P, 0.2% CaO, 0.020% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 560°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 160 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 150 m². ２ The particle size of D10 was 0.3 μm, D50 was 0.7 μm, D90 was 1.8 μm, and the viscosity was 990 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0136] <Example 12> Magnesium hydroxide (powder) with a BET specific surface area of ​​50 m² ２ A magnesium hydroxide mixture with a D50 particle size of 3.6 μm, containing 0.04% Cl, 0.08% B, 0.08% P, 0.4% CaO, 0.020% F, and 0.3% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 980°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 272 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 8 m². ２The particle size of D10 was 1.4 μm, D50 was 3.2 μm, D90 was 5.9 μm, and the viscosity was 30 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0137] <Example 13> 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 0.06% Cl, 0.08% B, 0.10% P, 0.2% CaO, 0.020% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 960°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 400 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 10 m². ２ The particle size of D10 was 0.3 μm, D50 was 1.1 μm, D90 was 1.9 μm, and the viscosity was 30 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0138] <Example 14> Magnesium chloride and sodium hydroxide are mixed in a molar ratio of Mg ２＋ : OH － The reaction was carried out in a ratio of 1:1.9, and cured in an autoclave at 180°C for 5 hours to obtain a magnesium hydroxide slurry. The obtained magnesium hydroxide slurry was dried to obtain a BET specific surface area of ​​9 m². ２A magnesium hydroxide powder was obtained with a D50 particle size of 0.8 μm, containing 0.06% Cl, 0.08% B, 0.10% P, 0.2% CaO, 0.020% F, and 0.1% S. 100 g of the obtained magnesium hydroxide was placed in an alumina crucible and calcined at 980°C for 2 hours using an electric furnace (manufactured by Koyo Lindbergh). Afterward, 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 518 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was found to be 5 m². ２ The particle size of D10 was 0.3 μm, D50 was 1.1 μm, D90 was 2.0 μm, and the viscosity was 30 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0139] <Example 15> 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 0.06% Cl, 0.08% B, 0.10% P, 0.2% CaO, 0.020% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 990°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 580 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 3 m². ２ The particle size of D10 was 0.3 μm, D50 was 1.0 μm, D90 was 2.0 μm, and the viscosity was 25 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve passability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0140] <Example 16> Magnesium hydroxide (powder) with a BET specific surface area of ​​9 m² ２ A magnesium hydroxide mixture containing 0.8 μm of D50 particles, 0.06% Cl, 0.08% B, 0.10% P, 0.2% CaO, 0.020% F, and 0.1% S was used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and calcined at 1000°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) B. The obtained magnesium oxide B and the magnesium oxide obtained in Example 10 were mixed in a ratio of 90 parts by mass and 10 parts by mass, respectively, to obtain magnesium oxide (powder mixture). The relaxation time of the obtained magnesium oxide was measured to be 646 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 16 m². ２ The particle size of D10 was 0.3 μm, D50 was 1.0 μm, D90 was 2.1 μm, and the viscosity was 25 mPa·s. The magnesium oxide contained impurities (Cl, B, P, CaO, F, S, etc.) in amounts corresponding to the raw material (magnesium hydroxide). The sieve permeability of the obtained magnesium oxide was then evaluated. The physical properties of the magnesium oxide and these evaluations are summarized in Table 1.

[0141]

[0142] As is clear from the results in Table 1, even when physical properties such as D50 particle size and (D90-D10) / 2 are similar, the evaluations are completely different. This indicates that relaxation time and BET specific surface area (especially both relaxation time and BET specific surface area) have a significant influence on clump formation.

[0143] In particular, it was found that the formation of clumps can be suppressed to a high degree by using a relaxation time that is neither too long nor too short, and by using a BET specific surface area that is not too large (or even too small) (and by combining these factors).

[0144] <Examples 17-22> For each of the magnesium oxide samples obtained in Examples 4, 5, 6, 8, 13, and 14, the coating properties and film-forming properties were evaluated using the method described above. These evaluations are summarized in Table 2.

[0145]

[0146] As is clear from the results in Table 2, it was found that the occurrence and degree of clumping in the slurry (and consequently, the relaxation time, etc.) affects the coatability and film-forming properties.

[0147] <Example 23> For each of the magnesium oxides obtained in Examples 4, 5, 6, 8, 13, and 14, 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°). The results showed a similar trend.

[0148] The present invention provides magnesium oxide and the like. Such magnesium oxide can be used or applied in various applications, particularly in the form of a dispersion, for applications such as coating annealing separating agents.

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. When magnesium oxide is dispersed in an aqueous solution at a ratio of 16 g per 100 g of water, the TD-NMR relaxation time at 40°C is 1000 milliseconds or less, and the BET specific surface area is 300 m². ２ Magnesium oxide that is less than / g.

3. The magnesium oxide according to claim 1, wherein the relaxation time is 750 milliseconds or less.

4. The magnesium oxide according to claim 1, wherein the relaxation time is 700 milliseconds or less.

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

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

7. 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.

8. BET specific surface area is 150 m² ２ The magnesium oxide according to claim 1, wherein the amount is less than or equal to / g.

9. BET specific surface area is 0.1 m² ２ Magnesium oxide according to claim 1, wherein the amount is 1 / g or more.

10. BET specific surface area is 1 m² ２ Magnesium oxide according to claim 1, wherein the amount is 1 / g or more.

11. Relaxation time is 1 to 800 milliseconds, and BET specific surface area is 0.1 to 250 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

12. Relaxation time is 3 to 750 milliseconds, and BET specific surface area is 0.3 to 200 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

13. Relaxation time is 5 to 700 milliseconds, and BET specific surface area is 0.5 to 160 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

14. The relaxation time is 10 to 680 milliseconds, and the BET specific surface area is 0.8 to 150 m ２ / g, the magnesium oxide according to claim 1.

15. The relaxation time is 15 to 650 milliseconds, and the BET specific surface area is 1 to 135 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

16. Relaxation time is 20-600 milliseconds, and BET specific surface area is 2-100 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

17. Relaxation time is 28–580 milliseconds, and BET specific surface area is 3–92 m². ２ Magnesium oxide according to claim 1, wherein the amount is / g.

18. Magnesium oxide according to claim 1, wherein the D50 particle size is 0.01 to 100 μm.

19. When the D10 particle size is D10 (μm) and the D90 particle size is D90 (μm), the value of (D90 - D10) / 2 is 50 or less, according to claim 1.

20. The magnesium oxide according to claim 1, wherein the D50 particle size is 0.1 to 50 μm, and when the D10 particle size is D10 (μm) and the D90 particle size is D90 (μm), the value of (D90 - D10) / 2 is 30 or less.

21. 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.

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

23. 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, sulfur in the proportions of 0.01 to 5% by mass, and chlorine in the proportions of 0.001 to 1% by mass.

24. Magnesium oxide according to claim 1, for use in paints or annealing separating agents.

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

26. A dispersion containing magnesium oxide according to any one of claims 1 to 25.

27. A paint containing magnesium oxide according to any one of claims 1 to 25.

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

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