Magnesium oxide dispersion, its manufacturing method and magnesium oxide thin film

Abstract

To provide a magnesium oxide dispersion liquid that enables a magnesium oxide thin film to be uniformly deposited over the entire substrate.SOLUTION: A magnesium oxide dispersion liquid includes magnesium oxide particles with a crystallite diameter of less than 35 nm, methanol and / or ethanol, and a non-vicinal polyhydric alcohol. Relative to the total amount of the magnesium oxide dispersion liquid, the content of the magnesium oxide particles is 1-25.0 mass%, the content of the methanol or ethanol is 50-98.5 mass%, and the content of the non-vicinal polyhydric alcohol is 0.5-49.0 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a magnesium oxide dispersion, a method for producing the same, and a magnesium oxide thin film. [Background technology]

[0002] Magnesium oxide thin films are used as dielectric protection layers in AC-type PDPs (alternating current plasma display panels), insulating films in MRAM (magnetoresistive memory) and TMR elements (tunneling magnetoresistive elements), and moisture adsorption layers in organic EL elements and barrier films. These magnesium oxide thin films are generally manufactured by vapor deposition methods such as electron beam evaporation, sputtering, and CVD. However, because vapor deposition methods involve film formation in a vacuum, they require vacuum equipment such as a vacuum chamber and a vacuum pump, making the manufacturing facilities large-scale.

[0003] On the other hand, a coating method is known as a method that allows film formation at normal pressure. The coating method involves coating a substrate with a dispersion of magnesium oxide particles or an intermediate that can be obtained by post-treatment to form a film. This method has the advantage of not requiring a vacuum device and of being faster in film formation speed than vapor deposition methods. For this reason, dispersions for forming magnesium oxide thin films have been proposed.

[0004] Patent Document 1 describes a method for dispersing magnesium oxide particles in a range of 0.05 to 20 mass % in a monohydric alcohol having 3 to 5 carbon atoms, and a volume cumulative particle diameter D of the magnesium oxide particles measured by a dynamic light scattering method. 50 A magnesium oxide particle dispersion having a particle size in the range of 5 to 100 nm is described.

[0005] Patent Document 2 discloses a method for producing a dispersion liquid in which magnesium oxide particles are dispersed in a polar organic solvent in an amount ranging from 0.05 to 20% by mass relative to the total amount of the dispersion liquid, and the volume cumulative particle diameter D of the magnesium oxide particles measured by a dynamic light scattering method is 50 is in the range of 5 to 20 nm, and D 10 / D 90A magnesium oxide particle dispersion liquid having a σ of 0.3 or more is described.

[0006] Patent Document 3 discloses a method in which magnesium oxide particles are dispersed in a range of 1 to 40% by mass in a monohydric alcohol having 1 to 5 carbon atoms, and the volume cumulative particle diameter D of the magnesium oxide particles measured by dynamic light scattering is 1000 μm or more. 50 The document discloses a magnesium oxide particle dispersion liquid having a particle size in the range of 5 to 90 nm, the water content of which is 9000 mass ppm or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-225240 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-137695 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-114178 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the monohydric alcohol dispersions used in Patent Documents 1 to 3 require a short drying time, and when the magnesium oxide dispersion is subjected to spin coating at a slow rotation speed to form a thick film, the coating liquid dries before it can wet and spread, which is a problem in that a magnesium oxide thin film cannot be formed uniformly over the entire substrate. An object of the present invention is to provide a magnesium oxide dispersion capable of forming a magnesium oxide thin film uniformly over the entire surface of a substrate, a method for producing the magnesium oxide dispersion, and the magnesium oxide thin film. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have found that by using a mixed solvent of methanol and / or ethanol with a non-vicinal polyhydric alcohol as a high-boiling point solvent, it is possible to control the drying time and obtain a magnesium oxide dispersion that does not undergo gelation and exhibits strong adhesion when applied to form a film, thereby completing the present invention. Here, gelation refers to the phenomenon in which the viscosity of a magnesium oxide dispersion increases over time and the fluidity is lost.

[0010] That is, the present invention provides a magnesium oxide dispersion containing magnesium oxide particles having a crystallite diameter of less than 35 nm, methanol and / or ethanol, and a non-vicinal polyhydric alcohol, wherein the magnesium oxide particles are contained in the ranges of 1 to 25.0 mass%, the methanol and / or ethanol in the range of 50 to 98.5 mass%, and the non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass%, relative to the total amount of the magnesium oxide dispersion.

[0011] The present invention also provides a method for producing a magnesium oxide dispersion, comprising the steps of calcining a magnesium compound or vapor-phase oxidizing metallic magnesium to obtain magnesium oxide particles having a crystallite diameter of less than 35 nm, and dispersing the magnesium oxide particles in methanol and / or ethanol and a non-vicinal polyhydric alcohol, wherein the magnesium oxide dispersion contains magnesium oxide particles in the ranges of 1 to 25.0 mass %, methanol and / or ethanol in the range of 50 to 98.5 mass %, and non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass %, relative to the total mass of the magnesium oxide dispersion.

[0012] The present invention further provides a method for producing a magnesium oxide dispersion, comprising the steps of calcining a magnesium compound or vapor-phase oxidizing metallic magnesium to obtain magnesium oxide particles having a crystallite size of less than 35 nm, and dispersing the magnesium oxide particles in methanol and / or ethanol and a non-vicinal polyhydric alcohol, wherein the dispersing step comprises a step of previously dispersing magnesium oxide and methanol and / or ethanol, and a step of further adding a non-vicinal polyhydric alcohol to obtain a magnesium oxide dispersion, and the magnesium oxide dispersion contains magnesium oxide particles in the ranges of 1 to 25.0 mass%, methanol and / or ethanol in the range of 50 to 98.5 mass%, and non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass%, relative to the total mass of the magnesium oxide dispersion.

[0013] The present invention also provides a magnesium oxide thin film composed of magnesium oxide having a crystallite diameter of less than 35 nm, obtained by coating the magnesium oxide dispersion liquid described above to form a film. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a magnesium oxide dispersion capable of forming a magnesium oxide thin film uniformly over the entire surface of a substrate, a method for producing the magnesium oxide dispersion, and the magnesium oxide thin film. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0016] The magnesium oxide dispersion of the present invention contains magnesium oxide particles having a crystallite size of less than 35 nm, methanol and / or ethanol, and a non-vicinal polyhydric alcohol. It may also contain a dispersant, binder, leveling agent, etc., as necessary. However, in order to obtain a high-purity magnesium oxide thin film, it is preferable for the dispersion to contain the essential components of magnesium oxide, monohydric alcohol, and polyhydric alcohol, but not the additives of dispersant, binder, leveling agent, etc. It is more preferable for the magnesium oxide dispersion of the present invention to consist only of magnesium oxide, monohydric alcohol, and polyhydric alcohol.

[0017] The crystallite size of the magnesium oxide particles is less than 35 nm, preferably 20 nm or less, and more preferably 15 nm or less, from the viewpoint of stabilizing the dispersion state of the magnesium oxide particles in the dispersion liquid for a long period of time and exhibiting adhesion during application. Although there are no particular restrictions on the lower limit of the crystallite size, making it smaller than necessary makes it difficult to produce magnesium oxide, so it is preferably 1 nm or more, more preferably 3 nm or more, and particularly preferably 5 nm or more.

[0018] The magnesium oxide particles generally have an average particle size in the range of 5 to 200 nm, preferably in the range of 10 to 150 nm, and more preferably in the range of 10 to 60 nm, from the viewpoint of maintaining the smoothness of the coating film.

[0019] Furthermore, in the present invention, methanol and / or ethanol are used. By using these monohydric alcohols, it becomes possible to exhibit adhesion during film formation by coating and to maintain the dispersion state for a long period of time.

[0020] The non-vicinal polyhydric alcohol refers to a polyhydric alcohol in which no hydroxyl group is bonded to each of two adjacent carbon atoms, and is particularly preferably one having 3 to 7 carbon atoms and a melting point of 25° C. or less. Examples of such non-vicinal polyhydric alcohols include 1,3-propanediol (melting point: −27° C.), 1,4-butanediol (melting point: 20° C.), 2-methyl-1,3-propanediol (melting point: 25° C. or less), 2,4-pentanediol (melting point: 25° C. or less), 1,5-pentanediol (melting point: −18° C.), 1,5-hexanediol (melting point: 25° C. or less), Examples include 2,5-hexanediol (melting point: 25°C or less), 2,4-dimethyl-2,4-pentanediol (melting point: 8°C), 2-methyl-2,4-pentanediol (melting point: -40°C), 3-methyl-1,5-pentanediol (melting point: 25°C or less), 1,7-heptanediol (melting point: 20°C), and 3-methyl-1,3-butanediol (melting point: -50°C). By using the above-mentioned non-vicinal polyhydric alcohol as a high-boiling point solvent, it is possible to control the drying time and obtain a magnesium oxide dispersion liquid that does not cause gelation.

[0021] The content of magnesium oxide particles in the magnesium oxide dispersion is preferably in the range of 1.0 to 25 mass%, more preferably in the range of 3 to 20 mass%, and even more preferably in the range of 5 to 15 mass%, which makes it possible to stabilize the dispersed state of the magnesium oxide particles in the magnesium oxide dispersion for a long period of time and to suppress gelation of the dispersion.

[0022] The content of methanol and / or ethanol in the magnesium oxide dispersion is 50.0 to 98.5 mass%, preferably 50.0 to 96.0 mass%, and more preferably 50 to 93.5 mass%, and the content of polyhydric alcohol in the magnesium oxide dispersion is 0.5 to 49.0 mass%, preferably 1.0 to 45.0 mass%, and more preferably 1.5 to 40.0 mass%, which makes it possible to suppress gelation of the dispersion and adjust the drying time over a wide range.

[0023] The magnesium oxide dispersion of the present invention can be produced as follows. First, a magnesium compound is calcined to obtain magnesium oxide particles with crystallites of less than 35 nm. Examples of suitable magnesium compounds include basic magnesium carbonate, magnesium carbonate, and magnesium hydroxide. In this case, the desired magnesium oxide particles can be obtained by dehydration or decarbonation. The magnesium oxide particles obtained by calcining the magnesium compound preferably have an MgO purity of 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more, after heating at 1000°C for 1 hour.

[0024] Magnesium oxide particles with crystallites of less than 35 nm obtained by a gas-phase oxidation method can also be used. Magnesium oxide particles produced by a gas-phase oxidation method generally have cubic primary particles and a high purity of 99.98% by mass or more. The gas-phase oxidation method is a method for obtaining magnesium oxide particles by contacting metallic magnesium vapor with oxygen to oxidize the metallic magnesium vapor.

[0025] Next, the magnesium oxide particles obtained as described above are mixed and dispersed with methanol and / or ethanol and a non-vicinal polyhydric alcohol to obtain a magnesium oxide dispersion. Mixing and dispersion can be carried out using, for example, a rocking mill, a paint shaker, a media mill, a wet jet mill, a roll mill disperser, an ultrasonic homogenizer, or the like. Note that the mixing and dispersion is carried out by applying energy to an extent that does not change the crystallite diameter of the magnesium oxide particles used as raw material. Therefore, although the average particle diameter may decrease before and after mixing and dispersion, there is no substantial change in the crystallite diameter.

[0026] The magnesium oxide dispersion of the present invention can also be produced as follows. First, magnesium oxide particles are obtained as described above. Next, the magnesium oxide particles are dispersed in methanol and / or ethanol, and then a non-vicinal polyhydric alcohol is added to the dispersion, followed by mixing and dispersion to obtain the desired magnesium oxide dispersion. As with the above, the mixing and dispersion is carried out by applying energy to an extent that does not change the crystallite size of the raw magnesium oxide particles. Therefore, although the average particle size may decrease before and after mixing and dispersion, there is no substantial change in the crystallite size.

[0027] The magnesium oxide dispersion liquid can be advantageously used as a raw material when producing a magnesium oxide thin film by a coating method. That is, a magnesium oxide thin film can be produced by coating the magnesium oxide dispersion liquid on a substrate and drying it. Methods that can be used to coat the magnesium oxide dispersion liquid on a substrate include spin coating, dipping, spraying, bar coating, roll coating, curtain coating, gravure printing, silk screen printing, and inkjet printing.

[0028] The magnesium oxide thin film formed by the coating method using a magnesium oxide dispersion is a film-like aggregate of magnesium oxide particles. Therefore, the crystallite diameter of the magnesium oxide thin film is similar to that of the raw material magnesium oxide. In other words, the magnesium oxide thin film formed by the coating method using the magnesium oxide dispersion of the present invention is crystalline. Here, crystalline means that a magnesium oxide peak, for example, at 2θ=43°, is observed in X-ray diffraction measurement, and does not preclude the inclusion of other substances. [Example]

[0029] Example 1 25 g of basic magnesium carbonate (average particle size: 8.2 μm, crystallite size: 21.2 nm) was placed in an alumina crucible and calcined in a box-type electric heating furnace at 600°C for 90 minutes to obtain magnesium oxide powder (average particle size: 6.9 μm, crystallite size: 10.0 nm). Next, 6.0 g of magnesium oxide powder (crystallite diameter 10.0 nm), 54.0 g of methanol, and 100 g of zirconia spherical media (Nikkato Corporation, zirconia ball YTZ-0.1, diameter: 0.1 mm) were placed in a 100 mL polypropylene bottle and the bottle was capped. The mixture was then dispersed by shaking at 50 Hz for 4 hours using a rocking mill (RM-05, Seiwa Giken Co., Ltd.). After dispersion, the media was separated by decantation. To 10.0 g of the dispersed solution, 0.3 g of 1,3-propanediol was added and mixed for 1 minute to prepare a magnesium oxide dispersion. The dispersion liquid obtained was evaluated as follows and the results are shown in Table 1.

[0030] Example 2 A dispersion was prepared in the same manner as in Example 1, except that the amount of 1,3-propanediol was changed to 0.5 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0031] Example 3 A dispersion was prepared in the same manner as in Example 1, except that the amount of 1,3-propanediol was changed to 1.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0032] Example 4 A dispersion was prepared in the same manner as in Example 1, except that the amount of 1,3-propanediol was changed to 2.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0033] Example 5 A dispersion was prepared in the same manner as in Example 1, except that the amount of 1,3-propanediol was changed to 3.3 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0034] Example 6 A dispersion was prepared in the same manner as in Example 1, except that the amount of 1,3-propanediol was changed to 5.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0035] Example 7 A dispersion was prepared in the same manner as in Example 1, except that 0.3 g of 1,5-pentanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 1.

[0036] Example 8 A dispersion was prepared in the same manner as in Example 7, except that the amount of 1,5-pentanediol was changed to 0.5 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0037] Example 9 A dispersion was prepared in the same manner as in Example 7, except that the amount of 1,5-pentanediol was changed to 1.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0038] Example 10 A dispersion was prepared in the same manner as in Example 7, except that the amount of 1,5-pentanediol was changed to 2.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0039] Example 11 A dispersion was prepared in the same manner as in Example 7, except that the amount of 1,5-pentanediol was changed to 3.3 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0040] Example 12 A dispersion was prepared in the same manner as in Example 7, except that the amount of 1,5-pentanediol was changed to 5.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0041] Example 13 A dispersion was prepared in the same manner as in Example 3, except that the amount of magnesium oxide powder was 12.0 g and the amount of methanol was 48.0 g. The obtained dispersion was evaluated as follows and the results are shown in Table 1.

[0042] Example 14 A dispersion was prepared in the same manner as in Example 3, except that the calcination conditions for basic magnesium carbonate were 950°C and 60 minutes to obtain magnesium oxide powder (average particle size: 5.7 µm, crystallite size: 30.0 nm). The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0043] Example 15 A commercially available magnesium oxide powder produced by a gas phase oxidation method (500A manufactured by Ube Material Industries, Ltd., average particle size 4.4 μm, crystallite size: 31.9 nm) was used, and a dispersion was prepared in the same manner as in Example 3, except that the calcination step was omitted. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0044] Example 16 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 2-methyl-1,3-propanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0045] Example 17 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 2-methyl-2,4-pentanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 1.

[0046] Example 18 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 3-methyl-1,3-butanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows, and the results are shown in Table 1.

[0047] Example 19 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 3-methyl-1,5-pentanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 1.

[0048] Comparative Example 1 25 g of basic magnesium carbonate (average particle size: 8.2 μm, crystallite size: 21.2 nm) was placed in an alumina crucible and calcined in a box-type electric heating furnace at 600°C for 90 minutes to obtain magnesium oxide powder (average particle size: 6.9 μm, crystallite size: 10.0 nm). Next, 6.0 g of magnesium oxide powder (crystallite diameter 10.0 nm), 54.0 g of methanol, and 100 g of zirconia spherical media (Nikkato Corporation, zirconia ball YTZ-0.1, diameter: 0.1 mm) were placed in a 100 mL polypropylene bottle and the bottle was capped. The mixture was then shaken at 50 Hz for 4 hours using a rocking mill (RM-05, Seiwa Giken Co., Ltd.) to perform a dispersion treatment. After the dispersion treatment, the media was separated by decantation to obtain a magnesium oxide dispersion. The dispersions obtained were evaluated as follows and the results are shown in Table 2.

[0049] Comparative Example 2 A dispersion was prepared in the same manner as in Comparative Example 1, except that no methanol was used and 54.0 g of 1,3-propanediol was used and dispersion treatment was carried out using a rocking mill. The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0050] Comparative Example 3 A dispersion was prepared in the same manner as in Example 1, except that 1.0 g of 1,2-ethanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 2.

[0051] Comparative Example 4 A dispersion was prepared in the same manner as in Comparative Example 3, except that the amount of 1,2-ethanediol was changed to 2.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0052] Comparative Example 5 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 1,2-propanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 2.

[0053] Comparative Example 6 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of 1,2-pentanediol was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 2.

[0054] Comparative Example 7 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of propylene glycol monomethyl ether acetate (PGMEA) was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0055] Comparative Example 8 A dispersion was prepared in the same manner as in Example 1, except that 2.0 g of tetradecane was used instead of 0.3 g of 1,3-propanediol. The obtained dispersion was evaluated as follows and the results are shown in Table 2.

[0056] Comparative Example 9 A dispersion was prepared in the same manner as in Example 3, except that the amount of magnesium oxide powder was 18.0 g and the amount of methanol was 42.0 g. The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0057] Comparative Example 10 A dispersion was prepared in the same manner as in Example 3, except that the calcination conditions for basic magnesium carbonate were 950°C and 180 minutes to obtain magnesium oxide powder (average particle size: 5.7 µm, crystallite size: 35.0 nm). The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0058] Comparative Example 11 A dispersion was prepared in the same manner as in Comparative Example 1, except that no methanol was used and 54.0 g of 1-butanol was used and dispersion treatment was carried out using a rocking mill. The obtained dispersion was evaluated as follows, and the results are shown in Table 2.

[0059] [Table 1]

[0060] [Table 2]

[0061] ◇Crystallite size evaluation method The sample was measured under the following conditions, and the broadening of the diffraction peak due to the instrument was corrected using an alumina sintered plate as a standard sample. The crystallite diameter was calculated from the half-width of the X-ray diffraction peak in the obtained X-ray diffraction pattern using the following method. Magnesium oxide: (200) plane Basic magnesium carbonate: (110) face (conditions) X-ray diffractometer (Bruker AXS NEW D8 ADVANCE), X-ray source: CuKα (Ni filter), tube voltage: 40 kV, tube current: 40 mA, detector: 1D semiconductor high-speed detector LynxEye, divergence slit: 0.30 degrees, step size: 0.015 degrees, counting time: 0.65 seconds / step Scherrer method L=Kλ / (βcosθ) L: Crystallite diameter K: Scherrer constant (0.9) λ: wavelength (1.5418 Å) (X-ray source: CuKα (using Ni filter)) β: Half width θ: Bragg angle

[0062] ◇Method for measuring the average particle size of basic magnesium carbonate and raw magnesium oxide powder Measurement was carried out using a laser diffraction scattering method (Microtrac Bell, MT-3000EXII) under the following conditions. (conditions) After the sample was placed in ethanol, it was dispersed for 3 minutes at 40 W using the built-in ultrasonic disperser as a pretreatment. After that, the particle size distribution was measured to determine the average particle size based on number. ◇Method for measuring the average particle size of magnesium oxide dispersion The volume-based average particle size was determined by dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments) under the following conditions: Dispersions using monohydric alcohols and non-vicinal polyhydric alcohols were diluted 10 times with the monohydric alcohol used before measurement. (conditions) Measurement cell: Polystyrene (10mm x 10mm x 45mm) Sample parameters (MgO) RI: 1.735 Absorption: 0.000 Dispersion medium parameters: Methanol (temperature: 25.0℃, viscosity: 0.5476cP, RI: 1.326) Ethanol (temperature: 25.0℃, viscosity: 1.2000cP, RI: 1.361) Temperature: 25.0℃ Equilibrium time: 0 seconds Measurement angle: 173° Backscatter(NIBS default) Measurement time: Automatic Number of measurements: 3 Measurement interval setting: 0 seconds

[0063] ◇Method for measuring semi-hardening drying time of magnesium oxide dispersion 1.5 g of the magnesium oxide dispersion was dropped onto a 50 mm borosilicate glass (D263Teco, 50 × 50 mm, t0.7 mm), and the glass was rotated at 100 rpm for 3 seconds using a spin coater (1H-DX2, Mikasa Corporation), then accelerated to 1,000 rpm over 5 seconds, and rotated at 1,000 rpm for 5 seconds, after which it was decelerated over 3 seconds and stopped. Drying was carried out at room temperature (24.5°C, 50% RH) as specified in JIS K5600-1-1, and the time from the point at which spin coating stopped until the product reached a semi-hardened, dry state was measured and categorized as follows: "30 seconds or less (indicated as "<30")," "more than 30 seconds but not more than 60 seconds (indicated as "30-60")," "more than 60 seconds but not more than 180 seconds (indicated as "60-180")," "more than 180 seconds but not more than 300 seconds (indicated as "180-300")," and "longer than 300 seconds (indicated as "300<")."

[0064] ◇Adhesion evaluation method 1.5 g of magnesium oxide dispersion was dropped onto borosilicate glass (D263Teco, 50 x 50 mm, t0.7 mm, manufactured by SCHOTT) and spun at 100 rpm for 5 seconds using a spin coater (1H-DX2, manufactured by Mikasa Corporation). The spin coater was then accelerated to 1,000 rpm over 10 seconds and spun at 1,000 rpm for 10 seconds. The spin coater then decelerated and stopped over 5 seconds. After stopping the spin coater, the glass was left to stand for 1 minute, and then heated at 100°C for 15 minutes to completely dry it. Adhesion was evaluated by applying an 18mm wide tape (Nichiban Cellotape (registered trademark) conforming to the JIS-K5600 adhesion test) conforming to the cross-cut test and cross-cut test to the coated thin film and then peeling it off. A rating of ◎ indicates that no magnesium oxide adhered to the adhesive surface of the tape, a rating of ○ indicates that the adhesion area was less than half, and a rating of × indicates that the adhesion area was more than half.

[0065] ◇Temporal stability evaluation method 3 g of the prepared magnesium oxide dispersion was sealed in a glass screw vial (Maruem Co., Ltd., screw vial No. 3 (21 × 45)) and left to stand for 2 weeks at 25° C. After standing for 2 weeks, samples that had not undergone gelation or solid sedimentation were marked with an ◯, and samples that had undergone either were marked with an ×.

[0066] As is clear from Table 1, a magnesium oxide dispersion using magnesium oxide particles with a crystallite size of less than 35 nm, methanol as the monohydric alcohol, and a non-vicinal polyhydric alcohol as the polyhydric alcohol, in a range of 1 to 25.0 mass% of magnesium oxide particles, 50 to 98.5 mass% of methanol, and 0.5 to 49.0 mass% of the non-vicinal polyhydric alcohol, suppresses gelation and exhibits excellent stability over time. Furthermore, by delaying the drying time, it is possible to form a uniform and thick film. Furthermore, a coating film formed using this magnesium oxide dispersion exhibits excellent adhesion.

[0067] On the other hand, in Comparative Example 1, which does not use a polyhydric alcohol, adhesion and stability over time are good, but the drying time is fast, making it difficult to form a uniform thick film. Also, in Comparative Examples 2 and 11, which do not use methanol, stability over time and drying time can be reduced, but adhesion is poor. Furthermore, in Comparative Examples 3-8, which use a vicinal polyhydric alcohol or a solvent other than alcohol, Comparative Example 9, which contains more than 25% by mass of magnesium oxide, and Comparative Example 10, which uses a raw magnesium oxide with a crystallite diameter of 35 nm or more, stability over time is poor.

Claims

1. A magnesium oxide dispersion comprising magnesium oxide particles having a crystallite size of less than 35 nm, methanol and / or ethanol, and a non-vicinal polyhydric alcohol, A magnesium oxide dispersion comprising, relative to the total amount of the magnesium oxide dispersion, magnesium oxide particles in the ranges of 1 to 25.0 mass%, methanol and / or ethanol in the ranges of 50 to 98.5 mass%, and a non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass%,

2. 2. The magnesium oxide dispersion according to claim 1, wherein the non-vicinal polyhydric alcohol is a non-vicinal diol having 3 to 7 carbon atoms and a melting point of 25° C. or lower.

3. a step of calcining a magnesium compound or vapor-phase oxidizing metallic magnesium to obtain magnesium oxide particles having a crystallite size of less than 35 nm; A method for producing a magnesium oxide dispersion, comprising a step of dispersing the magnesium oxide particles in methanol and / or ethanol and a non-vicinal polyhydric alcohol, A method for producing a magnesium oxide dispersion, the magnesium oxide dispersion containing magnesium oxide particles in the ranges of 1 to 25.0 mass%, methanol and / or ethanol in the ranges of 50 to 98.5 mass%, and non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass%, relative to the total amount of the magnesium oxide dispersion.

4. calcining a magnesium compound or vapor-phase oxidizing metallic magnesium to obtain magnesium oxide particles having a crystallite size of less than 35 nm; A method for producing a magnesium oxide dispersion, comprising a step of dispersing the magnesium oxide particles in methanol and / or ethanol and a non-vicinal polyhydric alcohol, the dispersing step includes a step of dispersing magnesium oxide in methanol and / or ethanol in advance, and a step of further adding a non-vicinal polyhydric alcohol to obtain a magnesium oxide dispersion, A method for producing a magnesium oxide dispersion, the magnesium oxide dispersion containing magnesium oxide particles in the ranges of 1 to 25.0 mass%, methanol and / or ethanol in the ranges of 50 to 98.5 mass%, and non-vicinal polyhydric alcohol in the ranges of 0.5 to 49.0 mass%, relative to the total amount of the magnesium oxide dispersion.

5. A method for producing a magnesium oxide thin film, comprising applying the magnesium oxide dispersion liquid according to claim 1 or 2 to form a film, thereby obtaining a magnesium oxide thin film composed of magnesium oxide having a crystallite diameter of less than 35 nm.

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