Aqueous dispersions, aerosol compositions, and aerosol products

Abstract

To provide an aqueous dispersion of hexagonal boron nitride particles that is applicable to metal substrates and molds, has excellent dispersion stability and heat resistance, and is less prone to generating air bubbles during stirring and coating processes. [Solution] The aqueous dispersion contains hexagonal boron nitride particles and layered silicate, with a volume-based 50% cumulative particle size (D50) of 1.0 to 5.0 μm as measured by laser diffraction and scattering, and a pH of 8 to 11.

Description

Technical Field

[0008] ,

[0001] The present invention relates to an aqueous dispersion containing hexagonal boron nitride particles, an aerosol composition, and an aerosol product.

Background Art

[0002] Hexagonal boron nitride is known as a material excellent in lubricity, mold release property, heat conductivity, heat resistance, corrosion resistance, and electrical insulation. A coating agent containing hexagonal boron nitride is used as a heat-resistant mold release agent for various metals and glasses by utilizing its corrosion resistance and mold release property. There are two types of coating agents containing hexagonal boron nitride: an organic solvent-based type and an aqueous (water-based) type. In recent years, due to environmental and safety aspects, the demand for aqueous coating agents has been increasing.

[0003] However, since hexagonal boron nitride has poor wettability, it is very difficult to disperse it in water. For this reason, various proposals have been made conventionally to disperse hexagonal boron nitride in water.

[0004] Patent Document 1 describes a dispersion liquid containing boron nitride nanosheets in which boron nitride nanosheets are highly dispersed in a superacid.

[0005] Patent Document 2 describes a dispersion liquid that is alkaline and contains hexagonal boron nitride, polydopamine, and a water-soluble polymer containing an amino group.

[0006] Patent Document 3 describes a method for producing a dispersion liquid in which ceramic fine particles (boron nitride fine particles) are dispersed in a dispersion medium of water in the presence of either or both of a polymer dispersant and a surfactant.

[0007] Patent Document 4 describes a boron nitride dispersant composed of a compound having a fluorene skeleton.

[0008] Patent Document 5 describes a boron nitride slurry for lubrication, which is obtained by dispersing boron nitride in an aqueous solution of a nonionic water-soluble cellulose ether and a polycarboxylate-based dispersant. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2015-196632 [Patent Document 2] Japanese Patent Publication No. 2022-164144 [Patent Document 3] WO2014 / 132445 [Patent Document 4] Japanese Patent Publication No. 2015-199064 [Patent Document 5] Japanese Patent Application Publication No. 08-127793 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the dispersion described in Patent Document 1 is strongly acidic, which means it cannot be used as a lubricant or mold release agent on metal substrates or molds, and it also has the problem of not being able to be filled into metal containers and used as an aerosol.

[0011] The dispersions described in Patent Documents 2 to 5 all contain organic compound dispersants or surfactants, which leads to the problem of insufficient heat resistance. Furthermore, when surfactants are used, there is a problem that bubbles tend to form during the stirring and coating processes.

[0012] The present invention has been made in view of the above points, and aims to provide an aqueous dispersion of hexagonal boron nitride particles that is applicable to metal substrates and molds, has excellent dispersion stability and heat resistance, and is less prone to generating bubbles during stirring and coating processes, as well as an aerosol composition and aerosol product containing this aqueous dispersion. [Means for solving the problem]

[0013] To solve the above problems, the following aqueous dispersions, aerosol compositions, and aerosol products are provided. [1] An aqueous dispersion of hexagonal boron nitride particles, It contains hexagonal boron nitride particles and layered silicates, has a volume-based 50% cumulative particle size (D50) of 1.0 to 5.0 μm as measured by laser diffraction and scattering, and has a pH of 8 to 11. Aqueous dispersion. [2] The aqueous dispersion of [1], wherein the content of the hexagonal boron nitride particles is 6 to 14% by mass, and the content of the layered silicate is 0.1 to 3% by mass. [3] An aqueous dispersion of the above [1] or [2], measured by laser diffraction and scattering, having a volume-based cumulative particle size distribution graph with frequency on the vertical axis and particle size on the horizontal axis, with a first peak appearing in the particle size range of 0.05 to 0.2 μm and a second peak appearing in the particle size range of 1 to 10 μm. [4] The layered silicate is a synthetic smectite, an aqueous dispersion of any of the [1] to [3] above. [5] An aqueous dispersion of any of the above [1] to [4] that does not contain organic dispersants or surfactants. [6] An aerosol composition comprising the aqueous dispersion of [1] and a propellant. [7] An aerosol product in which the aerosol composition of [6] is filled into an outer container. [Effects of the Invention]

[0014] The aqueous dispersion of the present invention is applicable to metal substrates and molds, exhibits excellent dispersion stability and heat resistance, and suppresses the generation of bubbles during stirring and coating processes. The aqueous dispersion of the present invention can form a coating film with good flatness and adhesion when applied using a brush or similar tool. Furthermore, the aerosol composition and aerosol product of the present invention can form a coating film with good flatness and adhesion when sprayed with the aqueous dispersion of the present invention. [Brief explanation of the drawing]

[0015] [Figure 1] It is a figure showing the powder X-ray diffraction pattern of the hexagonal boron nitride powder raw material of Comparative Example 1. [Figure 2] It is a figure showing the particle size distribution diagram of the aqueous dispersion liquid A of the hexagonal boron nitride particles of Comparative Example 1. [Figure 3] It is a figure showing the optical microscope photograph of the coating film A of Comparative Example 1. [Figure 4] It is a figure showing the X-ray diffraction pattern of the powder obtained by natural drying of the aqueous dispersion liquid B of the hexagonal boron nitride particles of Example 1. [Figure 5] It is a figure showing the particle size distribution diagram of the aqueous dispersion liquid B of the hexagonal boron nitride particles of Example 1. [Figure 6] It is a figure showing the optical microscope photograph of the coating film B of Example 1. [[ID=IP19]] [Figure 7] It is a figure showing the particle size distribution diagram of the aqueous dispersion liquid C of the hexagonal boron nitride particles of Example 2. [Figure 8] It is a figure showing the optical microscope photograph of the coating film C of Example 2.

MODE FOR CARRYING OUT THE INVENTION

[0016] Hereinafter, an embodiment of the aqueous dispersion liquid, aerosol composition, and aerosol product of the present invention will be described.

[0017] <Aqueous dispersion liquid> The aqueous dispersion liquid of the hexagonal boron nitride particles of the present invention contains hexagonal boron nitride particles and layered silicate.

[0018] The hexagonal boron nitride particles as raw materials may have a volume-based 50% cumulative particle diameter (D50) measured by the laser diffraction / scattering method of 1.0 to 5.0 μm. The identification of hexagonal boron nitride can be carried out by confirming that there are no attribution peaks other than hexagonal boron nitride in the X-ray diffraction of the sample powder.

[0019] The content of hexagonal boron nitride particles in the aqueous dispersion is preferably 6 to 14% by mass. When the content of hexagonal boron nitride particles is within this range, the aqueous dispersion has an appropriate viscosity, as well as good dispersion stability and coating properties. From this viewpoint, the content of hexagonal boron nitride particles in the aqueous dispersion is more preferably 6 to 12% by mass, and even more preferably 9 to 11% by mass.

[0020] The layered silicate should be dispersible in water and form a stable colloidal dispersion. Its type is not particularly limited, but it is preferably smectite (natural or synthetic smectite). Smectites include bentonite, montmorillonite, saponite, byderite, hectorite, stevensite, soaconite, and nontronite. The layered silicate may be one or more of these smectites.

[0021] Furthermore, it is preferable that the layered silicate is a high-purity layered silicate with few impurities. For this reason, it is preferable that the layered silicate is a high-purity layered silicate chemically synthesized by hot water treatment. Many such high-purity layered silicates are commercially available. Examples of commercially available layered silicates include "Kunipia" or "Smecton" manufactured by Kunimine Industries Co., Ltd., and "LAPONITE RD" or "LAPONITE-S 482" manufactured by Big Chemie Japan Co., Ltd.

[0022] Aqueous suspensions of layered silicates are weakly alkaline. Depending on the type and concentration of commercially available products, the pH value of an aqueous suspension of layered silicates is generally in the range of approximately 8 to 11.

[0023] The layered silicate content in the aqueous dispersion is preferably 0.1 to 3% by mass. When the layered silicate content is within this range, an appropriate viscosity is achieved, along with good dispersion stability and coatability. From this viewpoint, the layered silicate content in the aqueous dispersion is more preferably 0.5 to 1% by mass.

[0024] High-purity layered silicates have good affinity for water, and one of their characteristics is a property called "swelling," which allows them to incorporate water molecules between crystalline layers when dispersed in water, increasing the interlayer spacing. When a dispersion of layered silicates is vigorously stirred and shear force is applied, the interlayer distance between the stacked crystals increases due to the swelling property, allowing for uniform dispersion in water in the form of unit crystals. The layer planes of these unit crystals are negatively charged, while the end faces are positively charged. In water, the negatively charged layer planes and the positively charged end faces attract each other, forming a three-dimensional association structure of layer plane-end face bonds.

[0025] The water content in the aqueous dispersion is preferably 83 to 94% by mass.

[0026] The aqueous dispersion has a volume-based 50% cumulative particle size (D50), measured by laser diffraction and scattering, of 1.0 to 5.0 μm. When the D50 of the aqueous dispersion is within this range, it exhibits excellent dispersion stability, and the resulting coating film has excellent flatness and adhesion. If the D50 of the aqueous dispersion is less than 1.0 μm, re-aggregation is more likely to occur, which may lead to a decrease in the lubricity and release properties of the formed coating film. Furthermore, if the D50 of the aqueous dispersion exceeds 5.0 μm, the flatness and adhesion of the coating film may decrease. The D50 of the aqueous dispersion originates from the particle size distribution of hexagonal boron nitride particles in the aqueous dispersion.

[0027] In aqueous dispersions, if the particle size distribution pattern exhibits a bimodal characteristic, the dispersion stability and film flatness are further improved. Specifically, aqueous dispersions are preferably measured by laser diffraction / scattering, and in a volume-based cumulative particle size distribution graph with frequency (or relative particle amount based on volume) on the vertical axis and particle size on the horizontal axis, they have a first peak appearing in the particle size range of 0.05 to 0.2 μm and a second peak appearing in the particle size range of 1 to 10 μm. The peak top of the first peak is smaller than that of the second peak. The peak top is defined as the height on the vertical axis at a position where, when focusing on a certain particle size on the horizontal axis of the particle size distribution, the frequency (relative particle amount) (unit: %) is greater than either of the relative particle amounts (unit: %) of the adjacent particle sizes. Aqueous dispersions in which such a first and second peak are observed exhibit superior dispersion stability and film flatness.

[0028] The inventors of the present invention have discovered that, in the process of producing an aqueous dispersion of hexagonal boron nitride by grinding, the particle size distribution of a sample ground for a short time is unimodal (one peak), but by appropriately adjusting the grinding conditions such as the grinding time, the particle size distribution of the resulting aqueous dispersion of hexagonal boron nitride becomes bimodal (a first peak and a second peak appear).

[0029] The method for adjusting (or controlling) the particle size distribution of an aqueous dispersion (hexagonal boron nitride particles) is not particularly limited. For example, an aqueous dispersion of hexagonal boron nitride particles having a predetermined particle size distribution can be produced by grinding. Examples of grinding equipment include bead mills, planetary ball mills, ball mills, and jet mills. In one aspect of the present invention, hexagonal boron nitride particles with an adjusted particle size distribution by grinding may be used as raw materials and added to an aqueous solvent together with a layered silicate to produce an aqueous dispersion. In another aspect of the present invention, an aqueous dispersion of hexagonal boron nitride particles having a predetermined particle size distribution can also be produced by grinding the hexagonal boron nitride particles in an aqueous dispersion containing hexagonal boron nitride particles and a layered silicate by grinding.

[0030] When using hexagonal boron nitride particles with an adjusted particle size distribution as a raw material, the 50% cumulative particle diameter (D50) of the hexagonal boron nitride particles, measured by laser diffraction and scattering, can be adjusted to be between 1.0 and 5.0 μm. Furthermore, an aqueous dispersion of hexagonal boron nitride exhibiting a bimodal particle size distribution can be prepared, for example, by mixing two types of hexagonal boron nitride particles with different particle sizes.

[0031] The aqueous dispersion is alkaline, with a pH of 8-11. Given the aforementioned content of hexagonal boron nitride particles and layered silicates, the pH of the aqueous dispersion falls within this range. Therefore, this aqueous dispersion is applicable to metal substrates and molds.

[0032] Other components may be appropriately added to the aqueous dispersion as long as they do not impair the effects of the present invention. Examples of other components include inorganic nanoparticles. It is preferable that the aqueous dispersion does not contain organic dispersants and surfactants. In this case, the aqueous dispersion has excellent heat resistance because it does not use organic dispersants and surfactants. Also, because the aqueous dispersion does not use surfactants, the generation of bubbles is suppressed during the stirring and coating processes. When inorganic nanoparticles are added to the aqueous dispersion, the 50% cumulative particle size (D50) of the volume, as measured by laser diffraction and scattering of the aqueous dispersion, should be adjusted to be between 1.0 and 5.0 μm.

[0033] In the aqueous dispersion of the present invention, hexagonal boron nitride particles are stably dispersed in water using a layered silicate. As a result, the aqueous dispersion exhibits excellent dispersion stability, heat resistance, coating performance, film flatness, and adhesion.

[0034] The aqueous dispersion of the present invention can form a coating film of boron nitride particles by applying it to an object using methods such as a brush, spatula, roller, bar coater, applicator, dipping, or spray gun. This coating film has excellent flatness and adhesion.

[0035] The mechanism of dispersion stability in aqueous dispersions is thought to be as follows: The surface charge distribution of anisotropic hexagonal boron nitride particles is uneven, with no charge on the plate-like surfaces and charge concentrated at the edges. Measurement of the zeta potential of hexagonal boron nitride particles in water confirmed that it was negative, so it can be inferred that the edges of the hexagonal boron nitride particles are negatively charged. When hexagonal boron nitride particles and layered silicates coexist in water, the edges of the hexagonal boron nitride particles and the edges of the layered silicates connect due to attraction between positive and negative charges. Since the layered surfaces of the layered silicate crystals carry the same charge (negative), it is presumed that the aggregation of hexagonal boron nitride particles together with the layered silicates is suppressed due to repulsion between charges. In other words, layered silicates, which are highly compatible with water and dispersed in water as nanosheet-like unit crystals, play a role as a dispersant for hexagonal boron nitride particles.

[0036] As described above, the aqueous dispersion of the present invention is applicable to metal substrates and molds, eliminates the need for organic dispersants and surfactants, offers excellent dispersion stability and heat resistance, and suppresses the generation of bubbles during stirring and coating processes. Furthermore, the coating film of hexagonal boron nitride particles formed using the aqueous dispersion of the present invention exhibits high flatness and good adhesion to the substrate, making it suitable for use as a heat-resistant lubricant or mold release agent when applied to metal surfaces. Specifically, the aqueous dispersion of the present invention can be applied to high-temperature environments (in air, above 500°C) where mineral oil, silicone oil, molybdenum disulfide, or graphite cannot be used. In addition, the aqueous dispersion of the present invention can be used in a wide range of fields, such as a mold release agent for grinding wheel sintering and aluminum mold castings, a mold release agent for carbon molds in plasma discharge sintering, and protection of the inner surface of crucibles. Moreover, the aqueous dispersion of the present invention can be used in various applications that take advantage of the high insulating and thermal conductivity of hexagonal boron nitride. The aqueous dispersion of the present invention can be used, for example, as a white paint that reflects sunlight, for surface coating of air conditioner outdoor units.

[0037] The aqueous dispersion of the present invention can be used to create a coating film by, for example, spraying it in a mist using an airbrush with compressed air. Furthermore, the aqueous dispersion of the present invention can be made into an aerosol form (spray can) for easy application.

[0038] <Aerosol compositions and aerosol products> The aerosol composition of the present invention comprises the aqueous dispersion of the hexagonal boron nitride particles of the present invention described above, and a propellant.

[0039] Examples of propellants include liquefied petroleum gas, dimethyl ether (DME), carbon dioxide, nitrogen, nitrous oxide, and fluorinated hydrocarbons. In the aerosol composition, the mass ratio of propellant (b) to aqueous dispersion (a) ((b) / (a)) is, for example, 0.8 to 1.6, preferably 1 to 1.2. By keeping the mass ratio of propellant (b) to aqueous dispersion (a) within this range, it is possible to properly aerosolize the aqueous dispersion (a).

[0040] The aerosol composition may contain an appropriate amount of water-soluble organic solvent, provided that it does not affect the dispersion stability. This makes it possible to shorten the drying time of the coating film. Examples of organic solvents include ethanol, 2-propanol, methanol, and ascent.

[0041] Aerosol compositions may contain various other additives, to the extent that they do not affect safety. Examples of additives include extreme pressure agents, lubricity enhancers such as friction and wear inhibitors, rust inhibitors, antioxidants, corrosion inhibitors, defoamers, hard cake inhibitors, and settling inhibitors.

[0042] Furthermore, the aerosol product of the present invention is filled with an aerosol composition in an outer container (pressure-resistant container). As a specific example of the product, an aerosol product comprising a hexagonal boron nitride particle aqueous dispersion, a propellant, a pressure-resistant container body, and a spray unit attached to the top of the container body can be exemplified. When using the product, a push button provided on the outside of the aerosol product is pressed down, and the aerosol composition inside the container body is sprayed through the spray nozzle.

[0043] The aqueous dispersions, aerosol compositions, and aerosol products of the present invention are not limited to the embodiments described above. [Examples]

[0044] The present invention will be described below with reference to examples, but the aqueous dispersions, aerosol compositions, and aerosol products of the present invention are not limited in any way to the following examples.

[0045] <1> Analytical measurement methods and conditions The presence or absence of changes in the crystalline structure of the raw material, boron nitride powder, and its pulverization process was confirmed by powder X-ray diffraction. The particle size distribution was measured by laser diffraction and scattering. The surface condition of the coating film was observed using an optical microscope. The details of the various analytical and measurement methods and conditions performed in this invention are as follows.

[0046] (1) Powder X-ray diffraction The raw material, boron nitride powder, was placed on a glass sample plate and used as the measurement sample. In the case of a dispersion, the powder obtained by air drying in a glass dish was placed on a glass sample plate and used as the measurement sample. A powder X-ray diffractometer (RINT-Ultima+ type) manufactured by Rigaku Corporation was used. The details of the measurement conditions are as follows. X-ray: Cu / 40 kV / 30 mA Counting time / scan speed: 2 deg / min Goniometer: Ultima+ Horizontal Goniometer Sampling width: 0.02 deg Scan axis: 2θ / θ Scanning range: 10-80 degrees Longitudinal limiting slit: 10 mm Entrance slit: 1° Light-receiving slit 1:1° Light-receiving slit 2: 0.3 mm Detector: Scintillation counter Scan mode: Continuous

[0047] (2) Measurement of particle size distribution An appropriate amount of dispersion was dropped into the stirring tank of a laser diffraction / scattering particle size distribution analyzer, and measurements were performed using a circulating method. A particle size distribution analyzer (LA-950V2 model) manufactured by Horiba, Ltd. was used. The details of the measurement conditions are as follows. Dispersion medium: Purified water Circulation speed: 7 Refractive index of dispersion medium: 1.333 Sample refractive index: 1.740 Particle size standard: volume Number of repetitions: 15

[0048] (3) Observation using an optical microscope The surface condition of the coating film was observed using a Keyence VHX-2000 video microscope. The lens used for observation was a ZS20.

[0049] <2> Preparation of aqueous dispersions and coating films (1) Comparative Example 1 Starting materials For the hexagonal boron nitride, we used hexagonal boron nitride powder with a purity of 99% or higher, provided by Audec Co., Ltd. For the layered silicate, we used synthetic hectorite (product name: Smecton-SWN) manufactured by Kunimine Industries Co., Ltd.

[0050] Figure 1 shows the results of the powder X-ray diffraction measurement of the hexagonal boron nitride powder raw material. Only hexagonal boron nitride crystals were detected, and no other crystalline substances were detected. Furthermore, wavelength-dispersive X-ray fluorescence analysis confirmed that the purity of hexagonal boron nitride was 99% or higher. In addition, the particle size distribution was measured by laser diffraction and scattering, and the 50% volume cumulative particle size was 6.3 μm. The figure for the particle size distribution measurement results of the hexagonal boron nitride powder raw material is omitted, but it is almost the same as the analysis results of dispersion A in Comparative Example 1 (Figure 2) below.

[0051] 0.67 parts by weight of layered silicate was added to 100 parts by weight of purified water and stirred with a glass rod to disperse. After visually inspecting the mixture, it was almost completely dissolved and a clear liquid was obtained. Then, 11.11 parts by weight of boron nitride powder was added to prepare 500 g of composition. Next, the mixture was stirred with a propeller-type stirrer (RZR 2051) at a rotation speed of 100 rpm for 30 minutes to obtain aqueous dispersion A of hexagonal boron nitride particles.

[0052] Aqueous dispersion A was placed in a glass dish and allowed to air dry to obtain a powder, which was then measured by powder X-ray diffraction. The results showed that hexagonal boron nitride crystals were detected, and the intensity ratio of each diffraction peak was almost the same as that of the hexagonal boron nitride powder raw material.

[0053] Figure 2 shows the particle size distribution of aqueous dispersion A. The particle size distribution of aqueous dispersion A, measured by laser diffraction and scattering, was unimodal (one peak), and the 50% volume cumulative particle size was 6.3 μm. The pH of aqueous dispersion A, containing hexagonal boron nitride particles, was measured to be approximately 9.5.

[0054] A coating film A was prepared by applying an aqueous dispersion A onto a glass plate using an applicator and allowing it to air dry. The prepared coating film A was observed using an optical microscope. Figure 3 is an optical microscope image of coating film A. As shown in Figure 3, it was confirmed that coating film A did not have sufficient flatness and adhesion.

[0055] (2) Example 1 Aqueous dispersion A from Comparative Example 1 was ground using a bead mill under the following conditions to prepare aqueous dispersion B of hexagonal boron nitride particles. Equipment used: LMZ015 (manufactured by Ashizawa Finetech Co., Ltd.) Slurry input amount: 500g Bead diameter used: 0.5mm (zirconia material, manufactured by Nikkatoh Co., Ltd.) Amount of beads added: 520g Rotor peripheral speed: 10 m / s Processing time (device operating time): 90 minutes Cooling water temperature: 10℃

[0056] Figure 4 shows the X-ray diffraction pattern of the powder obtained by air-drying aqueous dispersion B in a glass dish. Only hexagonal boron nitride crystals were detected; no other crystalline substances were detected.

[0057] Figure 5 shows the particle size distribution results for aqueous dispersion B. The particle size distribution of aqueous dispersion B, measured by laser diffraction and scattering, is bimodal, with a first peak appearing in the particle size range of 0.05 to 0.2 μm and a second peak appearing in the particle size range of 1 to 10 μm, and it was confirmed that the 50% volume cumulative particle size is 3.1 μm.

[0058] Furthermore, the pH of aqueous dispersion B was measured to be approximately 9.5.

[0059] A coating film B was prepared by applying an aqueous dispersion B onto a glass plate using an applicator and allowing it to air dry. The prepared coating film B was observed using an optical microscope. Figure 6 is an optical microscope image of coating film B. It was confirmed that coating film B had particularly good flatness and adhesion.

[0060] Next, coating film B was heat-treated in an electric furnace at 800°C to 900°C for approximately 30 minutes in air. After cooling to room temperature, the heat-treated coating film B was observed using an optical microscope. The appearance of the heat-treated coating film B showed almost no change from before the heat treatment, confirming that it possesses excellent heat resistance.

[0061] Next, 30g of hexagonal boron nitride particle aqueous dispersion B and 50ml (33.5g) of dimethyl ether (DME) as a propellant were filled into a transparent pressure-resistant glass container to prepare an aerosol. The transparent pressure-resistant glass container was a 100ml capacity aerosol test bottle valve set product. The button on the prototype aerosol was pressed, and the contents were sprayed from a distance of 15cm from the glass plate to create a uniform coating on the glass plate surface. The prototype aerosol was confirmed to have no nozzle clogging and good stability over time.

[0062] (3) Example 2 Aqueous dispersion A of hexagonal boron nitride particles was pulverized under the same conditions as in Example 1, except that the processing time (operating time of the device) in the bead mill was changed to 10 minutes, to obtain aqueous dispersion C.

[0063] Figure 7 shows the particle size distribution of aqueous dispersion C. The particle size distribution of aqueous dispersion C, measured by laser diffraction and scattering, was unimodal (one peak), and the 50% cumulative volume particle size was confirmed to be 4.9 μm.

[0064] Furthermore, the pH of aqueous dispersion C was measured to be approximately 9.5.

[0065] A coating film C was prepared by applying an aqueous dispersion C onto a glass plate using an applicator and allowing it to air dry. The prepared coating film C was observed using an optical microscope. Figure 8 is an optical microscope image of coating film C. Coating film C was confirmed to have good flatness and adhesion.

[0066] (4) Comparison of dispersion stability of Comparative Example 1, Example 1 and Example 2 The dispersion stability of Comparative Example 1 (aqueous dispersion A), Example 1 (aqueous dispersion B), and Example 2 (aqueous dispersion C) was evaluated by test tube testing. Aqueous dispersions A to C of hexagonal boron nitride particles, prepared immediately, were placed in lidded test tubes, the lids were closed, and the tubes were left standing at room temperature. Changes in state were visually observed and evaluated according to the following criteria. ×: A small amount of supernatant appears within 1 day. △: A small amount of supernatant appears within 1 to 7 days. ○: A small amount of supernatant will appear within 7 to 14 days. ◎: No clear liquid has appeared even after 14 days.

[0067] Table 1 shows the dispersion stability of aqueous dispersions A to C of hexagonal boron nitride particles.

[0068] [Table 1]

[0069] Aqueous dispersions B and C have a volume-based 50% cumulative particle size (D50), measured by laser diffraction and scattering, of 1.0 to 5.0 μm. As shown in Table 1, aqueous dispersion C exhibited good dispersion stability, and aqueous dispersion B showed particularly excellent dispersion stability. On the other hand, aqueous dispersion A was found to have insufficient dispersion stability.

Claims

1. A aqueous dispersion of hexagonal boron nitride particles, It contains hexagonal boron nitride particles and layered silicate, and has a volume-based 50% cumulative particle size (D50) of 1.0 to 5.0 μm as measured by laser diffraction and scattering, and a pH of 8 to 11. Aqueous dispersion.

2. The content of the hexagonal boron nitride particles is 6 to 14% by mass, and the content of the layered silicate is 0.1 to 3% by mass. The aqueous dispersion according to claim 1.

3. In a volume-based cumulative particle size distribution graph measured by laser diffraction and scattering, with frequency on the vertical axis and particle size on the horizontal axis, there is a first peak appearing in the particle size range of 0.05 to 0.2 μm and a second peak appearing in the particle size range of 1 to 10 μm. The aqueous dispersion according to claim 1.

4. The layered silicate is synthetic smectite. The aqueous dispersion according to claim 1.

5. It does not contain organic dispersants or surfactants. The aqueous dispersion according to claim 1.

6. The aqueous dispersion and propellant according to claim 1, Aerosol composition.

7. The outer container is filled with the aerosol composition of claim 6. Aerosol products.

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