Magnesium oxide

Abstract

Magnesium oxide is provided. When magnesium oxide is dispersed in water at a ratio of 16 g of magnesium oxide per 100 g of water, the relaxation time of TD-NMR at 40°C satisfies 1000 milliseconds or less.

Description

[Technical Field]

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

[0002] Magnesium oxide is being considered for use in various fields, and one of these applications is as an annealing separator (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 065645 Summary of the Invention [Problem to be solved by the invention]

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

[0005] As described above, magnesium oxide is used in applications such as annealing separators and for forming paint films (coating films) and films (layers).

[0006] The present inventors have furthered their research into magnesium oxide for such applications and have found that magnesium oxide has problems such as the inability to form a good coating film (e.g., a uniform coating film) on the coating object (e.g., steel plate) (e.g., there are areas where the coating film does not adhere), and problems with the coating formed by baking (annealing, etc.) after application (e.g., large unevenness or numerous defects in the coating).

[0007] In response to this problem, the inventors have investigated ways such as adjusting the viscosity of the dispersion liquid (slurry) to be coated, but even with the same viscosity, the problem may not be solved in some cases, and solving the problem has been extremely difficult.

[0008] Under these circumstances, the present inventors conducted extensive research and found that specific physical properties completely different from viscosity and the like affect the coatability and film formation, and that by adjusting or selecting the values ​​of these physical properties, it is possible to form a good coating or film. After further research, the present inventors have completed the present invention.

[0009] That is, the present invention relates to the following inventions. [1] Magnesium oxide, when dispersed in water at a ratio of 16 g of magnesium oxide per 100 g of water (or a 13.8 mass % aqueous dispersion), exhibits TD-NMR relaxation times (relaxation time T2, transverse relaxation time, spin-spin relaxation time) of 1,000 milliseconds or less at 40°C. [2] [1] The magnesium oxide according to [1], which has a relaxation time of 600 milliseconds or less. [3] The magnesium oxide according to [1] or [2], which has a relaxation time of 500 milliseconds or less. [4] The magnesium oxide according to any one of [1] to [3], which has a relaxation time of 250 milliseconds or less. [5] The magnesium oxide according to any one of [1] to [4], which has a relaxation time of 200 milliseconds or less. [6] The magnesium oxide according to any one of [1] to [5], which has a relaxation time of 1 millisecond or longer. [7] The magnesium oxide according to any one of [1] to [6], which has a relaxation time of 10 milliseconds or longer. [8] The magnesium oxide according to any one of [1] to [7], which has a relaxation time of 20 milliseconds or more (for example, 30 milliseconds or more). [9] The magnesium oxide according to any one of [1] to [8], which has a relaxation time of 1 to 600 milliseconds.

[10] The magnesium oxide according to any one of [1] to [9], which has a relaxation time of 10 to 500 milliseconds.

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

[10] , which has a relaxation time of 20 to 250 milliseconds (for example, 30 to 250 milliseconds, 20 to 223 milliseconds).

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

[11] , which has a relaxation time of 40 to 150 milliseconds.

[13] BET specific surface area is 200m 2 The magnesium oxide according to any one of [1] to

[12] , wherein the magnesium oxide has a molecular weight of 1 / g or less.

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

[13] , having a D50 particle size of 100 μm or less.

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

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

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

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

[0010]

[17] BET specific surface area is 200m 2 / g or less, The D50 particle size is 100 μm or less, In the cumulative particle size distribution, when the particle size at 16% is D16 (μm) and the particle size at 84% is D84 (μm), the value of (D84-D16) / 2 is 30 μm or less (for example, 0.01 to 30 μm), The magnesium oxide according to any one of [1] to

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

[18] Relaxation times are between 10 and 500 milliseconds. BET specific surface area is 200m 2 / g or less, The D50 particle size is 100 μm or less, In the cumulative particle size distribution, when the particle size at 16% is D16 (μm) and the particle size at 84% is D84 (μm), the value of (D84-D16) / 2 is 30 μm or less (for example, 0.01 to 30 μm), The magnesium oxide according to any one of [1 to

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

[19] The relaxation time is between 20 and 250 milliseconds (e.g., between 30 and 250 milliseconds, between 20 and 223 milliseconds), BET specific surface area is 3 to 100 m 2 / g, The D50 particle size is 0.2 to 30 μm, In the cumulative particle size distribution, when the particle size at 16% is D16 (μm) and the particle size at 84% is D84 (μm), the value of (D84-D16) / 2 is 15 μm or less, The magnesium oxide according to any one of [1] to

[18] , which has a viscosity of 5 to 800 mPa s at 20°C when prepared as an aqueous dispersion containing 16 g of magnesium oxide per 100 g of water (a 13.8 mass% aqueous dispersion).

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

[19] , which contains calcium, boron, phosphorus, fluorine and chlorine. [twenty one] The magnesium oxide according to any one of [1] to

[20] , containing 0.01 to 5 mass% of calcium as calcium oxide (CaO), 0.001 to 0.5 mass% of boron, 0.001 to 1 mass% of phosphorus, 0.001 to 1 mass% of fluorine, and 0.001 to 1 mass% of chlorine. [twenty two] The magnesium oxide according to any one of [1] to

[21] , which is used as an annealing separator. [twenty three] The magnesium oxide according to any one of [1] to

[22] , for use in (forming a coating on) an electrical steel sheet (for example, a grain-oriented electrical steel sheet). [twenty four] A dispersion (slurry, aqueous dispersion, etc.) containing magnesium oxide according to any one of [1] to

[23] . [twenty five] An annealing separator containing the magnesium oxide according to any one of [1] to

[23] .

[0011]

[26] [1] to

[23] . A substrate (coated substrate) comprising a coating film (coating layer) containing magnesium oxide according to any one of [1] to

[23] {a substrate [e.g., a steel plate (base steel plate)] and a substrate [e.g., a steel plate (coated steel plate)], which is formed on the substrate (steel plate, etc.) and comprises a coating film (coating layer) containing magnesium oxide according to any one of [1] to

[23] .

[27]

[26] The substrate according to

[26] , wherein the substrate (substrate not provided with a coating film) has a water contact angle of 60° or less at 20°C.

[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 one of

[26] to

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

[30] A steel sheet provided with a coating containing the magnesium oxide according to any one of [1] to

[23] (the annealing separator according to

[25] ) [a coating of the magnesium oxide according to any one of [1] to

[23] (the annealing separator according to

[25] )] [a steel sheet (base steel sheet) and a coating formed on the steel sheet, containing the magnesium oxide according to any one of [1] to

[23] (a calcined product of magnesium oxide according to any one of [1] to

[23] ) (a steel sheet (coated steel sheet)].

[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 step of firing (firing step) a steel sheet [a steel sheet (base steel sheet) and a steel sheet (coated steel sheet) comprising a coating film (coating layer) containing magnesium oxide according to any one of [1] to

[23] (the annealing separator according to

[25] )].

[33] a step of applying a dispersion containing magnesium oxide according to any one of [1] to

[23] to a steel sheet (application step); The method for producing a steel plate according to

[30] or

[31] , which comprises at least a step of firing the steel plate provided with a coating film (coating layer) containing magnesium oxide obtained through the above step (firing step). [Effects of the Invention]

[0012] The present invention can provide magnesium oxide (specific magnesium oxide). Such magnesium oxide can be used in various applications, and is particularly useful for applications in which it is applied or a coating is formed, such as an annealing separator and for use in electrical steel sheets (e.g., for forming a coating (forsterite layer) on an electrical steel sheet).

[0013] One embodiment of the magnesium oxide of the present invention can have good coating properties. For example, it can efficiently suppress unevenness (shading) and adhesion leakage on a coating target (steel plate, etc.), and can achieve a highly uniform (relatively uniform) coating. Therefore, it is easy to efficiently coat the coating target (surface) without applying a thick coat.

[0014] According to the inventors' investigations, it appears that unevenness and leaks are particularly likely to occur when coating in a slurry form (dispersion liquid). However, with magnesium oxide according to one embodiment of the present invention, good coating properties can be exhibited or achieved even when coating in a slurry form. Coating properties can affect the function of the film (coating film, paint film) formed, and therefore good coating properties are highly useful in that they can contribute to the efficient performance or realization of the function.

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

[0016] According to the investigations of the present inventors, when a coating film (painted film) is baked to form a film, a non-uniform film, such as one with large unevenness, may be formed. Such non-uniform films may be observed even when the coating film is uniform (relatively uniform, or appears uniform).

[0017] However, with the magnesium oxide according to another embodiment of the present invention, such non-uniform film formation can be efficiently suppressed, and a good film can be formed.

[0018] Such uniformity of the coating may affect the function of the coating (for example, in applications as an annealing separator, problems may occur due to the non-uniformity of the formed forsterite layer). Therefore, good coating formation is highly useful in that it can contribute to the efficient exertion or realization of the function.

[0019] According to the magnesium oxide of yet another embodiment of the present invention, it is possible to achieve both good coatability and good film formation as described above. Depending on the application (e.g., in an annealing separation application), magnesium oxide undergoes, for example, a coating film formation step and a film formation step (film formation by firing) and therefore, in applications that undergo both of these steps, the magnesium oxide of yet another embodiment of the present invention is particularly useful. The magnesium oxide of the present invention can often achieve at least one of good coatability and good film formation, but magnesium oxide that can achieve both of these properties is particularly useful in some applications (for example, in annealing separation applications). DETAILED DESCRIPTION OF THE INVENTION

[0020] [Magnesium oxide] The magnesium oxide of the present invention, when dispersed in water, usually has specific values ​​for the relaxation time (relaxation time, relaxation time, relaxation time T2, transverse relaxation time, spin-spin relaxation time in TD-NMR) (time domain nuclear magnetic resonance) (pulse NMR, low field NMR). Such relaxation time may be selected, for example, from a range of about 1000 milliseconds (ms) or less (e.g., 800 milliseconds or less, 700 milliseconds or less, 600 milliseconds or less), and is 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 even more preferably 220 milliseconds or less (e.g., 210 milliseconds or less, 200 milliseconds or less, 190 milliseconds or less). The pulse width may be 100 milliseconds or less), particularly preferably 180 milliseconds or less (e.g., 170 milliseconds or less, 165 milliseconds or less, 160 milliseconds or less, 155 milliseconds or less, 150 milliseconds or less, 148 milliseconds or less), or 145 milliseconds or less (e.g., 140 milliseconds or less, 135 milliseconds or less, 130 milliseconds or less, 125 milliseconds or less, 120 milliseconds or less, 115 milliseconds or less, 110 milliseconds or less, 105 milliseconds or less, 100 milliseconds or less, 95 milliseconds or less, 90 milliseconds or less, 85 milliseconds or less, 80 milliseconds or less, 75 milliseconds or less, 70 milliseconds or less, 68 milliseconds or less, 67 milliseconds or less, etc.).

[0021] The lower limit of the relaxation time is not limited, and 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), and particularly preferably 30 milliseconds or more (e.g., more than 30 milliseconds, 32 milliseconds or more), or 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] The relaxation time may be set to a range that is an appropriate combination of the lower limit and upper limit of the above range (the same applies to the ranges hereinafter). In particular, from the viewpoint of easily achieving extremely good coating properties and film-forming properties (and even achieving both), a relaxation time that is not too small (not too short) and not too large (not too long) may be selected.

[0023] Specific examples of the relaxation time include 0.1 to 1000 milliseconds (e.g., 1 to 800 milliseconds), preferably 3 to 600 milliseconds (e.g., 5 to 550 milliseconds), further preferably 8 to 500 milliseconds (e.g., 10 to 480 milliseconds), more preferably 12 to 280 milliseconds (e.g., 15 to 260 milliseconds), and 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), and may be 32 to 180 milliseconds (e.g., 35 to 170 milliseconds, 38 to 160 milliseconds, 40 to 155 milliseconds, 42 to 148 milliseconds).

[0024] By setting the relaxation time in this range, it is easy to improve the coating properties and film-forming properties (particularly, the coating properties and film-forming properties) of magnesium oxide.

[0025] The reason for this is not clear, but the following reasons are assumed. First, in a dispersion, the solvent in contact with or adsorbed to the particles (bound solvent) and the bulk liquid (free solvent not in contact with the particle surface) respond differently to changes in the magnetic field, and also have different relaxation times. Therefore, even in a dispersion containing seemingly identical particles (at the same concentration), the more bound solvent there is in the particles, the shorter the relaxation time will be. Here, it is thought that the bound solvent first affects the wettability or affinity between the particle interface and the solvent, and ultimately, when applied, the wettability or affinity between the particle and the surface to be applied (surface). Specifically, it is thought that if there is a large amount of bound solvent (shorter relaxation time), the wettability or affinity will be greater, and in turn, the particles will be more likely to adhere to the coating target (less likely to fall off). In this way, the relaxation time affects the ease with which particles adhere to the coating target (coating property), and it is thought that by not making the relaxation time too long, it is possible to efficiently achieve good coating property.

[0026] On the other hand, the bound solvent is also recognized to be related to the ease of dispersion (aggregation) of particles, and in turn, when undergoing treatment (heat treatment, etc.) after application or deposition, it is thought to affect the ease of dispersion (aggregation) between the particles and the treatment target (surface) after the application or deposition. Specifically, it is thought that if there is a large amount of bound solvent (shorter relaxation time), the particles will be less likely to aggregate on the object to be treated after the coating or attachment (and thus less likely to cause unevenness, film defects, separation, etc.). In terms of coatability and film-forming properties, it is advantageous to not make the relaxation time too long, but selecting a relaxation time that is not too short makes it easier to achieve extremely good coatability and film-forming properties. The reason for this is unclear, but it is thought that if too much solvent is bound (if the relaxation time is too short), the surface condition and aggregation state of the magnesium oxide change at a microscopic level, affecting coatability and film-forming properties.

[0027] Thus, it can be inferred that the relaxation time is related to the coatability and film-forming properties, and that by selecting the relaxation time, it can be efficiently realized good coatability and film-forming properties. In particular, it can be inferred that the relaxation time is related to both the coatability and film-forming properties, and that selecting an appropriate (well-balanced) relaxation time can lead to the realization (achievement) 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 for measuring such relaxation times 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 a value (relaxation time) measured at a predetermined temperature (e.g., 40°C) for an aqueous dispersion (containing magnesium oxide at a predetermined ratio, e.g., 16 g per 100 g of water).

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

[0030] The relaxation time may be measured under any of the conditions described below, but may be calculated under any of the conditions described below. The measurement may also be performed promptly after preparation of the aqueous dispersion (for example, within 10 minutes (e.g., within 5 minutes, 3 minutes, or 1 minute 30 seconds)).

[0031] The relaxation time is not particularly limited, but can be adjusted, for example, by the composition and physical properties of magnesium hydroxide, which is a raw material for producing magnesium oxide (for example, 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 shortened by using magnesium hydroxide with a larger BET specific surface area or a smaller particle size, or by lowering the firing temperature, etc.

[0032] 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 property values ​​other than the relaxation time hereinafter).

[0033] As described above, magnesium oxide (magnesium oxide particles, particulate magnesium oxide) generally only needs to satisfy a specific relaxation time, but may also have (satisfy) other physical properties (other than the relaxation time).

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

[0035] The lower limit of the BET specific surface area of ​​magnesium oxide is, for example, 0.1 m 2 / g or more (e.g., 0.3m 2 / g or more, 0.5m 2 / g or more), and 2 / g or more (e.g., 1.5m 2 / g or more), preferably 2m 2 / g or more (e.g., 2.5m 2 / g or more), more preferably 3m 2 / g or more (e.g., 3.5m 2 / g or more), and even more preferably 4m 2 / g or more (e.g., 4.5m 2 / g or more), particularly preferably 5m 2 / g or more (e.g., 6m 2 / g or more, 7m 2 / g or more), and 2 / g or more (e.g., 10m 2 / g or more, 12m 2 / g or more, 15m 2 / g or more, 18m 2 / g or more).

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

[0037] By ensuring that the BET specific surface area is not too large (or even too small), it is easier to prevent the magnesium oxide from deteriorating (by absorbing moisture, etc.), and it is easier to efficiently obtain a good coating film (or even a coating) with excellent handleability.

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

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

[0040] The D50 particle size of the magnesium oxide (D50 volume diameter, particle size at which the cumulative particle size distribution is 50%) may be selected from a range of, for example, about 300 μm or less (e.g., 250 μm or less, 200 μm or less, 150 μm or less), and may be about 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), or may 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 size of magnesium oxide may be selected from a range of, for example, about 0.01 μm or more (e.g., 0.03 μm or more), 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), or may 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), etc.

[0042] A 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), and particularly preferably 0.4 to 10 μm (e.g., 0.45 to 8 μm), or may be 0.5 to 5 μm (e.g., 0.7 to 3 μm).

[0043] By ensuring that the particle size is not too large (or even too small), it is easy to efficiently obtain a good coating film (or even a film) with excellent handling properties.

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

[0045] The particle size is not particularly limited, but can be easily and efficiently adjusted by, for example, the pulverization conditions (method), classification operation, etc.

[0046] The particle size distribution of the magnesium oxide (particles) may be based on cumulative diameter. For example, in the cumulative particle size distribution (cumulative curve) of magnesium oxide (particles), when the particle size (volume particle size) at 16% is D16 (μm) and the particle size (volume particle size) at 84% is D84 (μm), the value of (D84-D16) / 2 may be selected from a range of about 30 μm or less (e.g., 25 μm or less, 20 μm or less), or may be about 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), particularly preferably 8 μm or less (e.g., 7.5 μm or less), or may 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, for example, from a range of about 0.01 μm or more (e.g., 0.03 μm or more), and is 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), and particularly preferably 0.4 μm or more (e.g., 0.45 μm or more). or may be 0.5 μm or more (e.g., 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, 1 μm or more, 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm or more, 1.5 μm or more, 1.6 μm or more, 1.7 μm or more, 1.8 μm or more, 1.9 μm or more, 2 μm or more, 2.1 μm or more, 2.2 μm or more, 2.3 μm or more, 2.4 μm or more, 2.5 μm or more, 2.7 μm or more, 2.8 μm or more), etc.

[0048] A 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] The above value of (D84-D16) / 2 can also be said to be the standard deviation (μm) of magnesium oxide (particles) [a pseudo standard deviation (μm)].

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

[0051] The value of (D84-D16) / 2 (particle size distribution) is not particularly limited, but can be determined, for example, by performing measurement using a particle size distribution meter and based on the obtained particle size distribution, and specifically, can be determined as in the examples described later.

[0052] The particle size distribution [(D84-D16) / 2 value, standard deviation] is not particularly limited, but can be easily and efficiently adjusted by, for example, the pulverization treatment conditions (method), classification operation, etc.

[0053] The viscosity of magnesium oxide when made into an aqueous dispersion (aqueous dispersion of a predetermined concentration) may be selected from a range of, for example, about 5000 mPa·s or less (e.g., 4500 mPa·s or less, 4000 mPa·s or less, 3500 mPa·s or less), or may be 3000 mPa·s or less (e.g., 2000 mPa·s or less), preferably 1500 mPa·s or less (e.g., 1000 mPa·s or less), more preferably 800 mPa·s or less (e.g., 500 mPa·s or less), even more preferably 300 mPa·s or less (e.g., 250 mPa·s or less), particularly preferably about 200 mPa·s or less (e.g., 180 mPa·s or less), or may be 150 mPa·s or less (e.g., 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 made into an aqueous dispersion (aqueous dispersion of a predetermined concentration) may be selected from a range of, for example, about 0.1 mPa·s or more (e.g., 0.3 mPa·s or more), and is 0.5 mPa·s or more (e.g., 1 mPa·s or more), preferably 2 mPa·s or more (e.g., 3 mPa·s or more), more preferably 5 mPa·s or more (e.g., 8 mPa·s or more), and even more preferably 10 mPa·s or more (e.g., 10 mPa·s or more). It may be particularly preferably about 20 mPa·s or more (e.g., 25 mPa·s or more), or may be 30 mPa·s or more (e.g., 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 when it is made into a specific aqueous dispersion (aqueous dispersion of a predetermined concentration) may be selected from the range of, for example, about 0.1 to 5000 mPa·s (e.g., 0.3 to 4000 mPa·s), and is preferably 0.5 to 3000 mPa·s (e.g., 1 to 2000 mPa·s), preferably 2 to 1500 mPa·s (e.g., 3 to 1000 mPa·s), and more preferably 5 to 800 mPa·s ( For example, it may be about 8 to 500 mPa·s), even more preferably about 10 to 300 mPa·s (for example, 15 to 250 mPa·s), and particularly preferably about 20 to 200 mPa·s (for example, 25 to 180 mPa·s), or it may be about 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 ensuring that the viscosity is not too high (or even too low), it is easy to efficiently obtain a good coating film (or even a film) with excellent handling properties.

[0057] The 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 such viscosity measurement 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). The viscosity can be measured using a viscometer (such as a BII type viscometer). Typically, the viscosity may be the value (viscosity) obtained by measuring an aqueous dispersion (containing magnesium oxide at a predetermined ratio) at a predetermined ratio [e.g., 16 g (or 13.8 mass%) per 100 g of water] at a predetermined temperature (e.g., 20°C) using a viscometer (e.g., BII-type viscometer), and specifically, may be measured (determined) as in the examples described below.

[0058] The viscosity is not particularly limited, but can be easily and efficiently adjusted by, for example, the BET specific surface area, particle size, and the like. The viscosity of magnesium oxide when used can also be adjusted by additives such as viscosity adjusters (thickeners, viscosity reducers), but adjusting the viscosity of magnesium oxide (aqueous dispersion) can make it possible to eliminate the use of such additives or reduce the amount of additives used, which can ultimately lead to the formation of good coating films or films.

[0059] Magnesium oxide may contain impurities (components other than magnesium oxide) within a range that does not impair the effects of the present invention. In particular, depending on the manner in which magnesium oxide is used, it may be preferable for the magnesium oxide to contain a moderate amount of impurities. For example, when a magnesium oxide coating is formed through firing, the impurities can adjust (control) the reaction (for example, the forsterite coating formation reaction), leading to efficient and good coating formation. The impurities may be derived from the raw material (magnesium hydroxide) or components (catalyst, etc.) used or mixed in the manufacturing process.

[0060] 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), other metals (zinc, cobalt, nickel, copper), etc. Note that such elements (atoms) may be contained in magnesium oxide as compounds (e.g., oxides, etc.).

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

[0062] When magnesium oxide contains such impurities, the proportion of the impurities is not particularly limited as long as it is within a range that does not impair the effects of the present invention. For example, when an element selected from calcium, boron, phosphorus, fluorine, and chlorine is contained, the proportion of calcium as calcium oxide (CaO) is 5% by mass or less of the 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 is 1% by mass or less of the 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 is 1% by mass or less of the magnesium oxide (e.g., 0. 8% by mass or less, 0.5% by mass or less, 0.4% by mass or less, 0.001~0.5% by mass, 0.01~0.3% by mass, 0.03~0.25% by mass, 0.05~0.2% 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, 0.001~0.5% by mass, 0.01~0.3% by mass, 0.00 The proportion of chlorine may be 1 mass% or less of the magnesium oxide (for example, 0.8 mass% or less, 0.5 mass% or less, 0.4 mass% or less, 0.3 mass% or less, 0.2 mass% or less, 0.001 to 0.5 mass%, 0.01 to 0.3 mass%, 0.15 mass% or less, 0.005 to 0.1 mass%, 0.01 to 0.09 mass%, 0.01 to 0.07 mass%), etc.

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

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

[0065] Magnesium oxide is usually in the form of particles (granules, powder, pulverized material, powder). The shape of the particles is not particularly limited, and may be spherical (approximately spherical), plate-like, or the like. The particles may be primary particles or secondary particles.

[0066] The method for producing the 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 to be subjected to or used in the calcination treatment) may have the same physical properties (BET specific surface area, particle size, etc.) as the magnesium oxide described above, and may contain impurities.

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

[0069] Such physical property values ​​and the types and proportions of impurities may be adjusted according to the desired physical property values ​​(relaxation time, physical property values ​​other than relaxation time, etc.) of magnesium oxide.

[0070] In the firing step, firing conditions can be appropriately selected. For example, the firing temperature may be 400°C or higher [e.g., 500 to 1700°C, preferably 550°C or higher (e.g., 600 to 1500°C)], and the firing time may be 0.1 hours or longer [e.g., 0.2 to 24 hours, preferably 0.5 hours or longer (e.g., 1 to 12 hours)].

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

[0072] After the firing step (the magnesium oxide obtained through the firing step), if necessary, a pulverization treatment or a classification treatment (sieving, etc.) may be carried out. The conditions for these treatments [such as the intensity of crushing, the type or form of the screen or sieve (screen diameter, opening, mesh, etc.)] can be selected as appropriate and may be adjusted according to the desired physical properties of magnesium oxide (such as relaxation time and physical properties other than relaxation time).

[0073] [Dispersion liquid, usage, etc.] The magnesium oxide of the present invention can be used for a variety of purposes without any particular limitations.

[0074] Among these, magnesium oxide often has good coating properties and film-forming properties, and is therefore suitable for use in such applications involving coating or film formation.

[0075] An example of such an application is as an annealing separator.

[0076] The annealing separator may contain magnesium oxide (may consist of magnesium oxide). Such an annealing separator may contain (or consist of) only magnesium oxide as the annealing separation component (solid content), or may contain other components (such as elements or atoms corresponding to the above-mentioned impurities or their compounds) as necessary. In such cases, the proportion of magnesium oxide in the annealing separator (solid content) may be, for example, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, 95 mass% or more, 99 mass% or more, etc.

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

[0078] The present invention also includes such dispersions.

[0079] The solvent may vary depending on the application, but examples thereof include water and aqueous solvents [hydrophilic solvents or water-soluble solvents, for example, organic solvents such as alcohols (e.g., lower alcohols such as methanol and ethanol)]. In general, solvents containing at least water may be preferably used.

[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 may be 100% by mass (water only).

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

[0082] As described above, magnesium oxide (or an annealing separator, etc.) can be used for coating purposes. In such a case, the magnesium oxide forms a coating layer (film, paint film, coating film) on the object to be coated.

[0083] The present invention includes an object to be coated that is provided with such a coating layer (coating film) of magnesium oxide (on which a coating layer is formed).

[0084] The material of the object to be coated (base, substrate) can be selected depending on the application, and examples include metal, glass, plants (wood, etc.), resin, etc.

[0085] The shape of the object to be coated (base, substrate) can also be selected depending on the application, etc., and may be any of a one-dimensional shape (e.g., a rod), a two-dimensional shape [e.g., a plate (film, sheet), a cloth (woven fabric, nonwoven fabric, etc.)], a three-dimensional shape (e.g., the shape of various molded products, etc.), etc.

[0086] Specific examples of the coating target (base, substrate) 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 coating can be formed by baking after coating.

[0087] The water contact angle (water contact angle) of at least the applied (coated) portion (surface, etc.) of the application target is not particularly limited, but may be 150° or less (e.g., 120° or less), preferably 100° or less (e.g., 80° or less), more preferably 60° or less (e.g., 55° or less, 50° or less, 45° or less), etc., particularly from the viewpoint of the application property of the magnesium oxide (or dispersion). 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 at a predetermined temperature (for example, 20° C.). The water contact angle can be measured by a conventional method, and specifically, it may be determined as in the examples described later.

[0089] The metal plate (steel plate) can be selected depending on the application, etc., and may be, for example, a silicon steel plate [steel plate containing silicon (silicon component)].

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

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

[0092] When a silicon steel sheet or the like is used, a forsterite layer (or a coating containing the forsterite layer) can be efficiently formed through a firing (annealing) treatment. The steel sheet on which the coating (forsterite layer, etc.) is formed can be suitably used (applied) as an electromagnetic steel sheet (grain-oriented electromagnetic steel sheet, etc.).

[0093] The coating method can be selected depending on the application, etc., but for example, a dispersion (suspension) containing magnesium oxide (annealing separator) may be applied to the coating target (steel sheet, etc.).

[0094] The coating method is not particularly limited and may be a conventional method depending on the application, etc. After coating, drying treatment may be carried out as necessary.

[0095] The amount of magnesium oxide (or solid content) to be applied to the object to be applied can be selected depending on the application, etc., and is, for example, 0.1 to 5000 g / m 2 , preferably 1 to 500 g / m 2 , and more preferably 10 to 150 g / m 2 It may be to some extent.

[0096] The object to be coated having the coating layer (magnesium oxide coating layer) may be subjected to a firing treatment (or heat treatment, annealing treatment, etc.).

[0097] By the firing treatment, a coating of magnesium oxide [or a coating derived from magnesium oxide (annealing separator), for example, a forsterite layer (a coating containing a forsterite layer) (forsterite coating, glass coating)] is formed.

[0098] The present invention includes a coating object (such as a steel sheet) that is provided with such a coating (i.e., has a coating formed thereon). Such a coating object can be used for various purposes depending on the type of steel sheet, and can be suitably used, for example, as an electrical steel sheet (such as a grain-oriented electrical steel sheet).

[0099] In the firing treatment, firing conditions can be selected depending on the application, etc. For example, the firing temperature may be 800°C or higher [e.g., 900 to 1700°C, preferably 900°C or higher (e.g., 1000 to 1500°C)], and the firing time may be 0.5 hours or longer [e.g., 1 to 48 hours, preferably 2 hours or longer (e.g., 3 to 24 hours)]. The firing treatment may also be carried out in an inert atmosphere (for example, under nitrogen). [Example]

[0100] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications can be made by those skilled in the art within the technical spirit of the present invention.

[0101] The measurements and evaluations of various physical properties and characteristics were carried out as follows.

[0102] Relaxation time The relaxation times (relaxation time T2, transverse relaxation time, spin-spin relaxation time) were measured immediately after the preparation of the aqueous dispersion (slurry) (before the magnesium oxide precipitated over time). Specifically, the aqueous dispersion was prepared and measured as follows. 100 mL of water and a stir bar (length 35 mm x diameter 8 mm, manufactured by Sanplatec Co., Ltd., PTFE stir bar (SA) type, product 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 had reached 40°C, 16 g of sample (magnesium oxide) was added to the beaker [i.e., the sample was added in a ratio of 16 g (13.8 mass%) per 100 g of water] and stirred for 3 minutes to obtain an aqueous dispersion. After stirring was stopped, the obtained aqueous dispersion was quickly placed in a sample (glass) tube and set (inserted) into the following apparatus (TD-NMR), and measurement was carried out at 40° C. The time from stopping stirring to starting measurement was approximately 1 minute 30 seconds (the time from stopping stirring to finishing measurement was approximately 2 minutes 30 seconds).

[0103] Equipment (TD-NMR): Bruker Japan Minispec mq20 The analysis was performed using the attached 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 (shown) below. Observed Objects: 1 H nucleus Measurement method: CPMG method Scans:1 Recycle Delay: 2 seconds 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 Homolog. Limit: 0.5 ms Desired Magnet Temp.: 40℃ NMR Frequency Base Freq.:20MHz NMR Frequency Freq.Offset:-50kHz Monoexponential Curve Fitting:on Phase Cycling: off

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

[0106] Particle size (D50) and particle size distribution [(D84-D16) / 2] 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 Japan Alcohol Sales Co., Ltd.). The mixture was ultrasonically dispersed for 3 minutes using an ultrasonic generator (UD-201) manufactured by Tomy Seiko Co., Ltd. to prepare a dispersion. The resulting dispersion was measured (by laser diffraction) using a particle size distribution analyzer (Microtrac HRA manufactured by Nikkiso Co., Ltd.) to obtain the volume-based D50 particle size and the (D84-D16) / 2 value [calculated from the particle size distribution (by software)]. The measurement conditions were as follows: solvent refractive index: 1.36, particle transmittance: transmission, particle refractive index: 1.73, particle shape: non-spherical.

[0107] viscosity A 2000 mL beaker was charged with 800 mL of water at 20°C and 128 g of sample (16 g of sample per 100 g of water), and the mixture was stirred at 300 rpm for 3 minutes to obtain a dispersion (slurry). The viscosity of the resulting slurry (20°C) was 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 amount Cl: Quantitative determination was carried out by mercuric thiocyanate absorption spectrophotometry. B: Quantitated using ICP-AES. The determination was carried out by chelate titration using CaO:EDTA. P: Quantitatively determined by vanadomolybdic acid spectrophotometry. F: Quantitatively determined using lanthanum-alizarin complexone spectrophotometry in accordance with JIS K 0102:2019 (industrial wastewater testing method).

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

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

[0111] ◎: The coating is completely adhered and no shading is visible. 〇: The coating is completely coated, but there is some variation in shading (approximately up to 20% of the surface area). ×: There are some areas where the coating film is not adhered.

[0112] The coating targets used were a steel plate (water contact angle: 45°) and a glass plate (water contact angle: 30°).

[0113] The steel sheets were prepared as follows. A slab (iron slab) containing trace elements including at least silicon (e.g., 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 a temperature of 1200°C and hot-rolled to a 2.2 mm thick hot-rolled sheet. This hot-rolled sheet was subjected to hot-rolled sheet annealing at a temperature of 1000°C for 30 seconds to remove surface scale. Next, it was cold-rolled using a tandem rolling mill to a final thickness of 0.30 mm. Subsequently, it was subjected to primary recrystallization annealing, which also served as decarburization annealing, by holding at a soaking temperature of 850°C for 90 seconds, to obtain a steel sheet on which an oxide film mainly composed of silica (SiO2) was formed on the surface.

[0114] The coating film formation was carried out three times, and the evaluation was the same each time.

[0115] Film forming property A dispersion (slurry) prepared in the same manner as that prepared for the measurement of the relaxation time was applied to a steel plate (prepared and used above) measuring 40 cm in width and 60 cm in length using a bar coater at a rate of 111 g / m 2 The steel sheet on which the coating film was formed was wound into a coil, and the coil was placed vertically and subjected to a baking treatment (annealing treatment) in a nitrogen atmosphere up to 1200°C at 25°C / hour to form a coating film. The formed coating film was visually inspected and evaluated according to the following criteria.

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

[0117] The film formation was carried out 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 ​​36m 2 / g, D50 particle size of 1.0 μm, Cl 0.01%, B 0.08%, P 0.08%, CaO 0.3%, F 0.003% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 830° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the mixture was pulverized twice using a Bantam Mill (Hosokawa Micron Corporation, AP-B type, screen diameter 3 mm) to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 10 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 27 m 2 / g, D50 particle size was 0.8 μm, (D84-D16) / 2 was 5.2 μm, and viscosity was 100 mPa·s. The magnesium oxide contained impurities in amounts corresponding to those of the raw material (magnesium hydroxide): approximately 50% (0.005%) Cl, approximately 80% (0.0024%) F, 100% (substantially 100%) B, P, CaO, etc. (hereinafter the same). The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation 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 ​​35m 2 / g, D50 particle size of 1.0 μm, Cl 0.01%, B 0.07%, P 0.10%, CaO 0.2%, F 0.010% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 900° C. for 3 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured and found to be 15 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured and found to have a BET specific surface area of ​​25 m 2 / g, D50 particle size was 0.8 μm, (D84-D16) / 2 value was 3.5 μm, and viscosity was 90 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation 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 ​​56m 2 / g, D50 particle size of 1.2 μm, Cl 0.01%, B 0.11%, P 0.20%, CaO 0.5%, F 0.003% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 900° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 30 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 20 m 2 / g, D50 particle size was 1.2 μm, (D84-D16) / 2 value was 2.4 μm, and viscosity was 70 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation 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 ​​15m 2 / g, D50 particle size of 3.0 μm, Cl 0.05%, B 0.08%, P 0.10%, CaO 0.3%, F 0.010% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 820° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 42 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 27 m 2 / g, the D50 particle size was 2.7 μm, the (D84-D16) / 2 value was 2.8 μm, and the viscosity was 110 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0122] <Example 5> Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 23m 2 / g, D50 particle size of 1.0 μm, Cl 0.04%, B 0.07%, P 0.08%, CaO 0.3%, F 0.005% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 850° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured and found to be 64 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured and found to have a BET specific surface area of ​​20 m 2 / g, D50 particle size was 1.0 μm, (D84-D16) / 2 value was 5.9 μm, and viscosity was 85 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0123] Example 6 Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 11m 2 / g, D50 particle size of 4.0 μm, Cl 0.01%, B 0.07%, P 0.12%, CaO 0.3%, F 0.010% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 850° C. for 3 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 67 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 24 m 2 / g, D50 particle size was 3.0 μm, (D84-D16) / 2 value was 5.2 μm, and viscosity was 115 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0124] Example 7 Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 19m 2 / g, D50 particle size of 1.1 μm, Cl 0.05%, B 0.08%, P 0.08%, CaO 0.2%, F 0.010% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 870° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured and found to be 148 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured and found to have a BET specific surface area of ​​19 m 2 / g, D50 particle size was 0.9 μm, (D84-D16) / 2 value was 4.1 μm, and viscosity was 90 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0125] Example 8 Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 19m 2 / g, D50 particle size of 3.7 μm, Cl 0.05%, B 0.09%, P 0.10%, CaO 0.2%, F 0.020% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 900° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured and found to be 185 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured and found to have a BET specific surface area of ​​15 m 2 / g, D50 particle size was 3.8 μm, (D84-D16) / 2 value was 4.0 μm, and viscosity was 65 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0126] Example 9 Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 11m 2 / g, D50 particle size of 3.8 μm, Cl 0.05%, B 0.07%, P 0.12%, CaO 0.3%, F 0.020% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 820° C. for 3 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured and found to be 223 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured and found to have a BET specific surface area of ​​26 m 2 / g, D50 particle size was 3.7 μm, (D84-D16) / 2 value was 6.1 μm, and viscosity was 70 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0127] Example 10 Magnesium oxide (powder) was prepared as follows. As magnesium hydroxide (powder), the BET specific surface area is 12m 2 / g, D50 particle size of 4.0 μm, Cl 0.05%, B 0.09%, P 0.09%, CaO 0.2%, F 0.010% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 930° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 260 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 17 m 2 / g, the D50 particle size was 3.9 μm, the (D84-D16) / 2 value was 3.0 μm, and the viscosity was 70 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation 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 ​​9m 2 / g, D50 particle size of 0.8 μm, Cl 0.05%, B 0.08%, P 0.10%, CaO 0.2%, F 0.015% were used (prepared). 100 g of this magnesium hydroxide was placed in an alumina crucible and fired at 950° C. for 2 hours using an electric furnace (manufactured by Koyo Lindberg Co., Ltd.). Thereafter, the same pulverization treatment as in Example 1 was carried out to obtain magnesium oxide (powder). The relaxation time of the obtained magnesium oxide was measured to be 478 milliseconds. In addition, various physical properties of the obtained magnesium oxide were measured to find that the BET specific surface area was 14 m 2 / g, D50 particle size was 1 μm, (D84-D16) / 2 value was 4.2 μm, and viscosity was 30 mPa·s. The magnesium oxide thus obtained was evaluated for its coatability and film-forming properties by the methods described above. The physical properties of magnesium oxide and their evaluation are summarized in Table 1.

[0129] [Table 1]

[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 approximately the same, the evaluation results are completely different, indicating that relaxation time has a significant effect on coatability. In particular, it was found that extremely good coating properties can be achieved by setting the relaxation time to be neither too large nor too small.

[0131] It was also found that the relaxation time had a significant effect on film formation. In particular, it was found that extremely good film-forming properties can be achieved by setting the relaxation time to be neither too long nor too short (in particular, it becomes easier to achieve both extremely good coating properties and film-forming properties).

[0132] Example 12 The coating properties of each of the magnesium oxides obtained in Examples 1 to 7 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°), and the same trends were observed.

[0133] Example 13 The magnesium oxide obtained in Example 1 and the magnesium oxide obtained in Example 7 were mixed at a mass ratio of 1:1, and the relaxation time was measured to be 75 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 24 m 2 / g, D50 particle size was 0.9 μm, (D84-D16) / 2 value was 4.6 μm, and viscosity was 90 mPa·s. The obtained magnesium oxide was evaluated for its coatability and film-forming ability on steel sheets by the above-mentioned methods, and the coatability on steel sheets was rated "A", and the film-forming ability was rated "A".

[0134] Example 14 The magnesium oxide obtained in Example 2 and the magnesium oxide obtained in Example 3 were mixed in a mass ratio of 6:4, and the relaxation time was measured to be 20 milliseconds. Furthermore, various physical properties of the obtained magnesium oxide were measured, and the BET specific surface area was 23 m 2 / g, D50 particle size was 1.0 μm, (D84-D16) / 2 value was 2.9 μm, and viscosity was 70 mPa·s. The obtained magnesium oxide was evaluated for its coatability and film-forming ability by the above-mentioned methods. The coatability to steel plate was "good", the coatability to glass plate was "excellent", and the film-forming ability was "good". [Industrial Applicability]

[0135] According to the present invention, it is possible to provide magnesium oxide etc. Such magnesium oxide can be suitably used in applications where it is subjected to coating (and further firing), for example, as an annealing separator etc.

Claims

1. Magnesium oxide, which, when dispersed in water at a ratio of 16 g of magnesium oxide per 100 g of water, exhibits a TD-NMR relaxation time of 10 to 478 milliseconds at 40°C.

2. Magnesium oxide, which, when dispersed in water at a ratio of 16 g of magnesium oxide per 100 g of water, exhibits a TD-NMR relaxation time of 20 to 223 milliseconds at 40°C.

3. When an aqueous dispersion containing magnesium oxide is prepared in a proportion of 16 g per 100 g of water, the relaxation time of TD-NMR at 40°C is 10 to 478 milliseconds, Magnesium oxide having a D50 particle size of 0.01 to 300 μm.

4. When an aqueous dispersion containing magnesium oxide is prepared in a proportion of 16 g per 100 g of water, the relaxation time of TD-NMR at 40°C is 10 to 478 milliseconds, Magnesium oxide in which, in a cumulative particle size distribution, the value of (D84-D16) / 2 is 30 μm or less, where D16 (μm) is the particle size that accounts for 16% and D84 (μm) is the particle size that accounts for 84%.

5. The magnesium oxide according to any one of claims 1 to 4, for use as an annealing separator.

6. The magnesium oxide according to any one of claims 1 to 4, for use in an electrical steel sheet.

7. An annealing separator containing the magnesium oxide according to any one of claims 1 to 4.

8. A substrate provided with a coating film containing the magnesium oxide according to any one of claims 1 to 4.

9. The substrate according to claim 8, wherein the substrate has a water contact angle of 60° or less at 20°C.

10. The substrate of claim 8 , wherein the substrate is a steel plate.

11. A method for producing the substrate according to claim 8, comprising at least the step of applying a dispersion containing magnesium oxide to the substrate.

12. A steel sheet provided with a coating containing the magnesium oxide according to any one of claims 1 to 4.

13. The steel sheet according to claim 12, which is an electrical steel sheet.

14. A method for producing the steel sheet according to claim 12, comprising at least a step of firing the steel sheet provided with the coating film containing magnesium oxide according to any one of claims 1 to 4.

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