Aggregated particles and composition

Abstract

The present invention provides boron nitride particles that exhibit good spreadability of the composition when included in the composition. [Solution] Aggregated particles containing primary boron nitride particles, wherein when observed with a scanning electron microscope (SEM), the number of primary particles in any 1 μm × 1 μm area in the SEM image is 2 or more.

Description

Technical Field

[0001] The present invention relates to agglomerated particles and compositions.

Background Art

[0002] Boron nitride has lubricity, high thermal conductivity, insulation properties, etc., and is widely used in solid lubricants, release agents for molten gases and aluminum, fillers for heat dissipation materials, and the like.

[0003] As boron nitride particles that utilize the lubricity and high thermal conductivity characteristics of boron nitride, Patent Document 1 describes flaky boron nitride fine particles with a small diameter / thickness ratio (aspect ratio), having a submicron size, and having high purity and high crystallinity. Further, Patent Document 2 describes submicron spherical boron nitride fine particles with high sphericity. Also, Patent Document 3 describes spherical boron nitride particles that can provide a resin composition with excellent fluidity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a composition containing boron nitride particles is used in paints, cosmetics, etc., it is required that the composition has high spreading properties, and thus further improvement of boron nitride particles is desired.

[0006] The present invention aims to provide boron nitride particles that exhibit good spreadability of the composition when included in the composition, and a composition containing said boron nitride particles. [Means for solving the problem]

[0007] The present invention includes the following embodiments.

[0008] [1] Aggregated particles containing primary boron nitride particles, wherein when observed with a scanning electron microscope (SEM), the number of primary particles in any 1 μm × 1 μm area in the SEM image is two or more.

[0009] [2] The aggregated particles are the aggregated particles described in [1], wherein the primary particles are attached to each other.

[0010] [3] The aggregated particle according to [1] or [2], wherein the primary particle is spherical.

[0011] [4] The aggregated particles according to any one of [1] to [3], wherein the average particle size (volume-based cumulative diameter (D50)) of the primary particles is 0.01 to 1.0 μm.

[0012] [5] The aggregated particles according to any one of [1] to [4], wherein the average circularity of the aggregated particles is 0.6 to 0.9.

[0013] A composition comprising aggregated particles as described in any of [6], [1], to [5].

[0014] [7] The composition according to [6], which is a paint composition or a cosmetic composition. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide boron nitride particles that, when included in a composition, exhibit good spreadability of the composition, and a composition containing said boron nitride particles. [Brief explanation of the drawing]

[0016] [Figure 1] This is an image of a scanning electron microscope (SEM) showing an example of the agglomerated particles according to this embodiment.

Mode for Carrying Out the Invention

[0017] [Agglomerated Particles] The agglomerated particles according to this embodiment are agglomerated particles containing primary particles of boron nitride, and when observed with a scanning electron microscope (SEM), the number of the primary particles within an arbitrary range of 1 μm × 1 μm in the SEM image is 2 or more.

[0018] The agglomerated particles according to this embodiment have, when observed with a SEM, the number of primary particles within an arbitrary range of 1 μm × 1 μm in the SEM image being 2 or more, and are formed by the aggregation of a large number of fine primary particles of boron nitride. Therefore, when the composition containing the agglomerated particles is stretched and spread, the agglomerated particles are easily dispersed as fine primary particles while being easily broken up, and the spreading property is good. As will be described later, since the composition has excellent spreading property, it can be suitably used as a composition for paints or a composition for cosmetics. In this specification, the "primary particles" mean solid particles having boundaries between particles that are recognized as the minimum unit of particles and cannot be further divided finely. Particles in a form where a plurality of about 2 to 10 primary particles are chemically bonded are also included in the primary particles.

[0019] The agglomerated particles according to this embodiment have, when observed with a SEM, the number of primary particles within an arbitrary range of 1 μm × 1 μm in the SEM image being 2 or more, preferably 5 or more, more preferably 8 or more, and even more preferably 10 or more. The upper limit of the range of the number of the primary particles is not particularly limited, but for example, it can be 100 or less.

[0020] Incidentally, the number of the primary particles can be measured by the following method. A mixture of the agglomerated particles, the main agent, and the curing agent of an epoxy resin (trade name: EpoxiCure2, manufactured by Buehler) is cured to obtain a resin cured product. Ion milling is performed on the resin cured product to expose a cross-section, and the cross-section is observed with a scanning electron microscope (trade name: Regulus, manufactured by Hitachi High-Technologies Corporation). Using the observed image at 20,000 times magnification, image analysis is performed with image analysis software ImageJ by the following method. First, an arbitrary 1 μm × 1 μm square range containing the agglomerated particles is cut out from the image. Next, the cut-out image is subjected to median processing (2 pixels) and binarized using Otsu's method to measure the number of particles. This measurement is performed 4 times, and the average value is taken as the number of primary particles within the range of 1 μm × 1 μm.

[0021] In the agglomerated particles according to the present embodiment, it is preferable that the primary particles contained in the agglomerated particles are attached to each other. Since the primary particles of boron nitride are attached to each other, the agglomerated particles are more excellent in easy collapsibility than particles in which the primary particles are firmly bonded to each other. Therefore, the composition containing the agglomerated particles is more excellent in spreading property. "The primary particles of boron nitride are attached to each other" means that the primary particles of boron nitride are physically attached to each other without passing through a binder resin or an oily component. The fact that they are attached without passing through a binder resin or an oily component can be confirmed by, for example, the fact that no spectrum derived from a resin used as a binder or the like is detected when analyzed using an infrared absorption spectrum measurement method, or the fact that no component derived from a resin or the like is confirmed from the agglomerated particles by the TG-GC / MS method.

[0022] Furthermore, in this specification, "easily disintegrating" means that the aggregated particles have the property of being easily disintegrated. "Easily disintegrating property" may include, for example, the deformation of the aggregated particles with a smaller compressive load when compressed with a nanointender. It may also include the disintegration of the aggregated particles into primary particles by homogenizing treatment. Such "easily disintegrating aggregated particles" are easily obtained, for example, when the primary particles of boron nitride include spherical primary particles. Alternatively, they can be easily obtained by obtaining primary particles of boron nitride and then processing them by the spray drying method or recovery and drying method described later to prepare a crude aggregate of the primary particles.

[0023] More specifically, when aggregated particles are compressed in a nanointender at a loading rate of 0.0015 to 0.015 mN / sec, if the compression load at which the deformation rate of the aggregated particles reaches 70% is 0.03 to 3 mN, then the aggregated particles can be said to be "easily disintegrating". Alternatively, when treated with a homogenizer at a frequency of 20 kHz and a maximum oscillator output of 200 W or more, if 80% or more by mass of the aggregated particles (preferably 85% or more by mass, more preferably 90% or more by mass, and even more preferably 95% or more by mass) disintegrates down to primary particles, then the aggregated particles can be said to be "easily disintegrating".

[0024] The primary particles contained in the aggregated particles according to this embodiment are preferably spherical. The spherical shape of the primary particles reduces the contact area between particles, resulting in superior ease of disintegration. Therefore, compositions containing these aggregated particles exhibit superior spreadability. Furthermore, the spherical shape of the primary particles leads to superior dispersibility in solvents and resins. Whether or not the primary boron nitride particles contained in the aggregated particles are spherical can be determined, for example, by observing the aggregated particles with an electron microscope, as shown in Figure 1. "Spherical" means that the shape of each primary particle is observed to be circular or rounded. Alternatively, "spherical" may mean that the average circularity is 0.8 or higher.

[0025] The average circularity of the primary particles is preferably 0.8 or higher, more preferably 0.85 or higher, and even more preferably 0.87 or higher. The upper limit of the average circularity of the primary particles is not particularly limited, but may be, for example, 1 or less, or 0.95 or less.

[0026] In this specification, the average circularity of primary particles refers to the value calculated as follows: For images of primary boron nitride particles (magnification: 10,000x, image resolution: 1280 x 1024 pixels) taken using a SEM, the projected area (S) and perimeter (L) of the primary boron nitride particles are calculated by image analysis using image analysis software (e.g., MacView, manufactured by Mountec). Using the projected area (S) and perimeter (L), the following formula is used: Circularity = 4πS / L 2 The circularity is determined according to the following method. The average value of the circularity obtained for 100 or more arbitrarily selected primary boron nitride particles is defined as the average circularity. Note that the average circularity of the primary boron nitride particles may be the same as the average circularity of the raw material boron nitride particles, as described later. For example, if the average circularity of the raw material boron nitride particles is 0.87, the average circularity of the primary boron nitride particles contained in the aggregated particles can also be set to 0.87.

[0027] In this embodiment, the average particle size (volume-based cumulative diameter (D50)) of the primary particles contained in the agglomerated particles is preferably 0.01 to 1.0 μm, more preferably 0.1 to 0.8 μm, and even more preferably 0.1 to 0.6 μm. When the D50 of the primary particles is within this range, the agglomerated particles exhibit superior disintegration properties, and the composition containing these agglomerated particles exhibits superior spreadability. The D50 of the primary particles can be measured using a laser diffraction / scattering particle size distribution analyzer (for example, Microtrac-Bell, product name "SYNC"). The particle size distribution can be measured after dispersing 0.1 g of the agglomerated particles in 80 mL of ethanol and performing a homogenizing treatment.

[0028] The average particle size (volume-based cumulative diameter (D50)) of the agglomerated particles according to this embodiment is preferably 1 to 50 μm, more preferably 5 to 40 μm, even more preferably 10 to 30 μm, and particularly preferably 15 to 25 μm. When the D50 of the agglomerated particles is within the above range, the agglomerated particles exhibit superior disintegration properties, and the composition containing the agglomerated particles exhibits superior spreadability. The D50 of the agglomerated particles can be measured using a laser diffraction / scattering particle size distribution analyzer (for example, Microtrac-Bell, product name "SYNC") without homogenizing treatment.

[0029] In this embodiment, the average circularity of the aggregated particles is preferably 0.6 to 0.9. In this embodiment, the average circularity of the aggregated particles is more preferably 0.7 to 0.9, and may be 0.75 to 0.85 or 0.80 to 0.85. In this embodiment, the average circularity of the aggregated particles may also be 0.77, 0.79, 0.80, 0.82, 0.84, or 0.90, and may be within a range where these are the upper or lower limits. When the average circularity of the aggregated particles is within the above range, the aggregated particles are rounder, and their dispersibility is higher when mixed with solvents, resins, etc. Therefore, the composition containing the aggregated particles and solvents, resins, etc. has superior spreadability.

[0030] In this specification, the average circularity of aggregated particles refers to the value calculated as follows: For images of aggregated particles taken using a SEM (magnification: 500x, image resolution: 1280 x 1024 pixels), the projected area (S) and perimeter (L) of the aggregated particles are calculated by image analysis using image analysis software (e.g., MacView, manufactured by Mountec). Using the projected area (S) and perimeter (L), the following formula is used: Circularity = 4πS / L 2 The circularity is determined according to the following method. The average value of the circularity obtained for 100 or more arbitrarily selected aggregated particles is defined as the average circularity.

[0031] [Method for producing aggregated particles] The method for producing aggregated particles according to this embodiment is not particularly limited, but for example, it can be produced by a method that includes a step of breaking down raw material boron nitride particles into primary particles (hereinafter also referred to as the first step) and a step of obtaining aggregated particles of the primary particles (hereinafter also referred to as the second step).

[0032] (Boron nitride particles as raw material) Commercially available boron nitride particles can be used as the raw material, but it is preferable to manufacture them using the following method, for example, as described in Patent Document 2. Specifically, first, a borate ester with a molar ratio of ammonia / boric acid ester of 1 to 10 is reacted with ammonia in an inert gas stream at 750°C or higher for 30 seconds or less. Examples of borate esters include trimethyl borate. Next, the mixture is heat-treated at 1,000 to 1,600°C for 1 hour or more in an atmosphere of ammonia gas or a mixed gas of ammonia gas and an inert gas. Here, the bulk density of the raw material boron nitride particles during the heat treatment is 0.25 g / cm³. 3 The following steps make it easier to obtain spherical primary particles. The bulk density can be calculated by dividing the weight of the raw material boron nitride particles by the volume occupied by the raw material boron nitride in the heat treatment crucible. Furthermore, the particles are calcined at 1,800 to 2,200°C for 0.5 hours or more under an inert gas atmosphere. This yields the raw material boron nitride particles.

[0033] The volume-based cumulative diameter (D50) of the raw material boron nitride particles, evaluated by laser diffraction scattering, may be 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more, and may be 1 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less. The D50 is preferably, for example, 0.01 to 1.0 μm, and more preferably 0.3 to 0.8 μm.

[0034] The raw material boron nitride particles are preferably spherical. The average circularity of the raw material boron nitride particles is preferably 0.8 or higher, more preferably 0.85 or higher, and even more preferably 0.87 or higher. The upper limit of the range of the average circularity is not particularly limited, but may be 1 or less, or 0.95 or less. The average circularity of the raw material boron nitride particles can be measured by the same method as the average circularity of the primary boron nitride particles described above.

[0035] (First step) In this step, the boron nitride particles of the raw material are broken down into primary particles. Preferably, this step includes a step of dispersing the boron nitride particles of the raw material in a liquid containing cavitation bubbles. By dispersing the boron nitride particles of the raw material in a liquid containing cavitation bubbles, the expansion and contraction force due to the pressure difference of the bubbles generated by cavitation makes it easier for the aggregated boron nitride particles of the raw material to break down into primary particles. Therefore, by including this step, aggregated particles with superior ease of disintegration can be obtained, and the composition containing these aggregated particles has superior spreadability. This step may also be a step in which 80% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 100% by mass of the boron nitride particles of the raw material are broken down into primary particles.

[0036] In this specification, "cavitation bubbles" refers to bubbles that are generated when a liquid vaporizes under low pressure. Cavitation bubbles can be generated using commercially available devices that produce cavitation bubbles by reducing pressure or by using ultrasound to induce foaming in a liquid. It is preferable to use a commercially available powder suction continuous dissolution and dispersion device as such a device, and it is particularly preferable to perform a process that generates cavitation bubbles by circulating the liquid. Powder suction continuous dissolution and dispersion devices generally have a mechanism that generates flow velocity using a stirring blade. The rotation speed of the stirring blade is preferably 2000 to 10000 rpm, more preferably 4000 to 9000 rpm, even more preferably 4500 to 8000 rpm, and particularly preferably 5000 to 8000 rpm. The rotation speed may also be 6000 to 7200 rpm.

[0037] The cavitation bubble generation process is preferably performed 50 times or more, more preferably 100 times or more, and even more preferably 150 times or more, based on the number of cavitation processes calculated from the rotation speed (rpm) and discharge rate of the device's stirring blades.

[0038] (Second step) In this step, aggregated particles of the primary particles obtained in the first step are obtained. This step preferably includes a step of spray-drying the primary particles (hereinafter described as the "spray-drying method"), or a step of recovering the primary particles from the liquid (the liquid containing cavitation bubbles) and then drying them (hereinafter described as the "recovery and drying method").

[0039] <Spray drying method> This process preferably includes a step of spray-drying the primary particles. When this process includes a step of spray-drying the primary particles, coarse aggregates of the primary particles are obtained, and at the same time, the coarse aggregates are broken down, and the desired aggregated particles are obtained. Coarse aggregates of primary particles refer to clumps of boron nitride particles that naturally aggregate during the drying process of boron nitride particles that have been broken down into primary particles, and coarse aggregates are larger aggregates than aggregated particles.

[0040] Spray drying is preferably carried out by spray drying a dispersion containing primary boron nitride particles, and it is more preferable to use the dispersion after the cavitation treatment described above. The solvent for the dispersion may be water, a liquid consisting only of an organic solvent such as ethanol, or a mixed solution of water and an organic solvent. The viscosity of the dispersion at 25°C is preferably 1 to 10 Pa·s, and more preferably 1 to 100 mPa·s. When the viscosity of the dispersion is within the above range, better spraying is possible during spray drying, and the desired aggregated particles are more easily obtained.

[0041] There are no particular limitations on the method for drying a dispersion by spray drying. For example, the method may involve introducing droplets of the dispersion into the heating section of a spray drying apparatus, heating and drying the dispersion in the heating section, evaporating and drying the dispersion medium, and obtaining a spray-dried product which is a dried droplet of the dispersion.

[0042] The spray drying apparatus used for spray drying is not particularly limited, and known apparatuses can be suitably used. Examples of spray drying apparatuses include those manufactured by Okawara Seisakusho Co., Ltd. (model number CL-8i), Pris Co., Ltd. (model number SB39), and Yamato Scientific Co., Ltd. (model number DL410).

[0043] The drying temperature when drying by spray drying is preferably 100 to 200°C, and more preferably 100 to 150°C. A drying temperature within this range makes it easier to obtain the desired aggregated particles.

[0044] The spray mechanism used in spray drying can be one of the following: a two-fluid nozzle, a one-fluid pressurized nozzle, a three-fluid nozzle, a four-fluid nozzle, an ultrasonic nozzle, or a centrifugal sprayer. Depending on the selected spray mechanism, various parameters such as the liquid flow rate, gas flow rate, supply gas pressure, and rotation speed can be adjusted to perform spray drying.

[0045] <Recovery and drying method> As an alternative to the spray-drying method described above, this process preferably includes a step of obtaining coarse aggregates by recovering primary particles from a liquid containing cavitation bubbles and then drying them, and a step of dissolving the coarse aggregates. By recovering primary particles from the liquid and then drying them, it is easier to obtain coarse aggregates that are aggregated to a degree that makes them easy to dissolve in the subsequent dissolving process. The primary particles can be recovered from the liquid containing cavitation bubbles by filtration. The recovered primary particles can be dried by drying them in a commercially available dryer or oven. Here, it is preferable to dry them at a temperature of 100 to 150°C. When the drying temperature is within this range, surface tension due to liquid crosslinking between primary particles acts and aggregation is more likely to occur. The step of dissolving the coarse aggregates can be carried out, for example, by applying an external force to the coarse aggregates.

[0046] When obtaining coarse agglomerates by the recovery and drying method described above, it is preferable that this step further includes a step of further breaking up the coarse agglomerates by sieving them. Commercially available metal mesh sieves or nylon sieves can be used as sieves. By sieving with a sieve of a desired mesh size, it becomes easier to obtain agglomerates of a desired particle size. The mesh size is preferably 1000 μm or less, more preferably 850 μm or less, and even more preferably 750 μm or less.

[0047] In the method for producing the boron nitride particles, coarse aggregates, and aggregated particles of the raw materials, the liquid used in production may be a liquid consisting only of an organic solvent such as ethanol, a mixed solution of water and an organic solvent, or a liquid consisting only of water. In the case of a mixed solution of water and an organic solvent, the water content in the mixed solution is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0048] [Composition] The composition according to this embodiment contains the aggregated particles according to this embodiment. Because the aggregated particles according to this embodiment provide good spreadability to the composition when included in the composition, the composition according to this embodiment has excellent spreadability. For this reason, the composition according to this embodiment can be, for example, a paint composition, a cosmetic composition, etc. The paint composition can be an outdoor paint and / or an indoor paint. Examples of cosmetic compositions include powder cosmetics and liquid cosmetics. Depending on its application, the composition according to this embodiment may also contain, for example, resins, solvents, etc., in addition to the aggregated particles according to this embodiment. The content ratio of the aggregated particles according to this embodiment in the composition according to this embodiment is not particularly limited and can be arbitrarily adjusted within a range of, for example, 1 to 99% by mass, depending on the application of the composition and the required physical properties. [Examples]

[0049] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The number of primary particles within a range of 1 μm × 1 μm, the average particle size of the primary particles (volume-based cumulative diameter (D50)), the average circularity of the aggregated particles, and the evaluation of spreadability were performed by the following methods.

[0050] [Measurement of the number of primary particles within a 1 μm × 1 μm area] A mixture of aggregated particles and the main component and curing agent of epoxy resin (product name: EpoxiCure2, manufactured by Bueher) was cured to obtain a resin cured product. The resin cured product was subjected to ion milling to expose the cross-section, which was observed with a scanning electron microscope (product name: Regulus, manufactured by Hitachi High-Tech Corporation). The observed image at 20,000x magnification was used for image analysis using the image analysis software ImageJ in the following manner. First, an arbitrary 1 μm × 1 μm square area containing aggregated particles was cropped from the image. Next, the cropped image was subjected to median processing (2 pixels), binarized using Otsu's formula, and the number of particles was measured. This measurement was performed four times, and the average value was taken as the number of primary particles in the 1 μm × 1 μm area.

[0051] [Measurement of average particle size of aggregated particles (volume-based cumulative diameter (D50))] The average particle size (volume-based cumulative diameter (D50)) of aggregated particles was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell, product name "SYNC").

[0052] [Measurement of the average circularity of aggregated particles] Images of aggregated particles (magnification: 500x, image resolution: 1280 x 1024 pixels) taken using a SEM (product name: Regulus, Hitachi High-Tech Corporation) were analyzed using image analysis software (Mountec Corporation, product name: MacView) to calculate the projected area (S) and perimeter (L) of the aggregated particles. Using the projected area (S) and perimeter (L), the following formula was used: Circularity = 4πS / L 2 The circularity was determined according to the following method. The average value of the circularity obtained for 100 or more arbitrarily selected aggregated particles was defined as the average circularity.

[0053] [Evaluation of potential for expansion and growth] The spreadability of aggregated particles was evaluated using a multi-functional static friction measuring instrument (manufactured by Trinity-Lab, product name "TL-201Ts") as follows. (1) A sample (aggregated particles) with a sample weight of 5.2 mg ± 0.3 mg and a sample size of 5 mmφ × 0.5 mmt was placed on a 3 cm × 15 cm BioSkin (manufactured by Viewlux Co., Ltd., product name "5T#10"). (2) A tactile contactor having a surface structure that mimics a human fingerprint (contact area: 1.5 cm²) 2 The device was placed on top of the sample, and a 0.49 N weight load (equivalent to the pressure applied to a human fingertip during a sensory test) was placed on top of the measurement unit. After that, it was confirmed that the level indicator on the measurement unit was horizontal. (3) The spread distance of the sample was measured when the lower table was moved 100 mm at a speed of 10 mm / sec. The spread distance was defined as the distance to which the line of the sample (white powder) was visible to the naked eye. A longer spread distance indicates higher spreadability.

[0054] [Example 1] The raw material, boron nitride particles, were prepared using the following procedure. (1) A reaction tube (quartz tube) placed in a resistance heating furnace was heated to 1150°C. Trimethyl borate was introduced into the reaction tube by passing nitrogen gas through it. Subsequently, ammonia gas was directly introduced into the reaction tube. The molar ratio of the amount of ammonia introduced to the amount of trimethyl borate introduced (ammonia / trimethyl borate) was set to 1.8. Trimethyl borate and ammonia were reacted to obtain a precursor of boron nitride particles (white powder). (2) The obtained boron nitride particle precursor was placed in a boron nitride crucible set up in a resistance heating furnace, and nitrogen gas and ammonia gas were introduced into the reaction tube separately at flow rates of 10 L / min and 15 L / min, respectively. The reaction tube was heated at 1500°C for 5 hours to obtain a second precursor. (3) The obtained second precursor was placed in a boron nitride crucible and heated in an induction heating furnace under a nitrogen atmosphere at 2000°C for 5 hours to obtain the raw material boron nitride particles. The bulk density of the boron nitride particles in the crucible was 0.2 g / cm³. 3 That was the case.

[0055] The volume-based cumulative diameter (D50) of the raw material boron nitride particles, evaluated by laser diffraction scattering, was 0.62 μm, and the average circularity was 0.87.

[0056] The boron nitride particles, the raw material, were mixed with 1000cc of deionized water to a concentration of 10% by weight. The resulting aqueous solution was subjected to cavitation treatment using a continuous powder suction dissolution and dispersion apparatus (Jet Paster, model number: JPSS, manufactured by Nippon Spindle Co., Ltd.). The cavitation treatment conditions were 150 treatment cycles and a rotation speed of 7200 rpm. The "number of treatment cycles" refers to the number of times the treatment solution passes through the impeller, calculated from the rotation speed (rpm) and discharge volume per rotation of the continuous powder suction dissolution and dispersion apparatus. After cavitation treatment, the liquid was filtered and dried to recover the boron nitride particles. The drying temperature was 120°C.

[0057] The recovered boron nitride particles were mixed with deionized water to a concentration of 10% by weight to form a slurry. The liquid was filtered through filter paper with a pore size of 0.2 μm and then dried to collect a cake-like coarse aggregate. The obtained coarse aggregate was then gently broken up by hand using a scraper on a nylon mesh and passed through a 20-mesh nylon sieve to obtain aggregated particles.

[0058] For the obtained aggregated particles, the number of primary particles within a 1 μm × 1 μm area, the average particle size of the aggregated particles (volume-based cumulative diameter (D50)), and the average circularity of the aggregated particles were measured using the method described above. Furthermore, the spreadability was evaluated using the same method. The results are shown in Table 1. In the measurement of the number of primary particles within a 1 μm × 1 μm area, it was confirmed that the obtained aggregated particles were adhered to each other and that these primary particles were spherical.

[0059] [Comparative Example 1] For GR50 (trade name, manufactured by DCEI), a commercially available aggregated particle containing primary boron nitride particles, the number of primary particles, the average particle size (volume-based cumulative diameter (D50)), and the average circularity of the aggregated particles were measured within a 1 μm × 1 μm area using the method described above. Furthermore, the spreadability was evaluated using the same method. The results are shown in Table 1. In the measurement of the number of primary particles within a 1 μm × 1 μm area, it was confirmed that the primary particles of GR50 were not adhering to each other and that the primary particles were flaky.

[0060] [Table 1]

Claims

1. Aggregated particles containing primary boron nitride particles, wherein, when observed with a scanning electron microscope (SEM), the number of primary particles within any 1 μm × 1 μm area in the SEM image is two or more.

2. The aggregated particles according to claim 1, wherein the aggregated particles are formed by the primary particles adhering to each other.

3. The aggregated particle according to claim 1 or 2, wherein the primary particle is spherical.

4. The aggregated particle according to any one of claims 1 to 3, wherein the average particle size (volume-based cumulative diameter (D50)) of the primary particles is 0.01 to 1.0 μm.

5. The aggregated particle according to any one of claims 1 to 4, wherein the average circularity of the aggregated particle is 0.6 to 0.

9.

6. A composition comprising aggregated particles according to any one of claims 1 to 5.

7. The composition according to claim 6, which is a paint composition or a cosmetic composition.

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