阅读说明：本技术 六方晶氮化硼粉末 (Hexagonal boron nitride powder ) 是由 中川由美 黑田尚臣 片山茂幸 锅岛诚司 宫口雅史 于 2019-08-02 设计创作，主要内容包括：本发明提供了一种光亮性优异的六方晶氮化硼粉末。在上述六方晶氮化硼粉末所包含的六方晶氮化硼颗粒中,具有相对于一次颗粒的晶体(1,0,0)面以110°～160°的角度弯折的结构的颗粒的个数比例为30％以上。(The invention provides hexagonal boron nitride powder with excellent brightness. The hexagonal boron nitride particles contained in the hexagonal boron nitride powder have a proportion of the number of particles having a structure bent at an angle of 110 ° to 160 ° with respect to the crystal (1,0,0) plane of the primary particles of 30% or more.)

1. A hexagonal boron nitride powder comprising hexagonal boron nitride particles, wherein the proportion of the number of particles having a structure bent at an angle of 110 DEG to 160 DEG with respect to the crystal (1,0,0) plane of the particles is 30% or more.

2. The hexagonal boron nitride powder according to claim 1, wherein the hexagonal boron nitride particles contained in the hexagonal boron nitride powder have a proportion of the number of particles having a structure bent at an angle of 110 ° to 130 ° with respect to the crystal (1,0,0) plane of the particles of 60% or more.

3. The hexagonal boron nitride powder of claim 1 or 2, wherein the ratio of the incident light angle: the full width at half maximum of the reflectance peak measured under the condition of 45 ° is 80 ° or less.

4. The hexagonal boron nitride powder according to any one of claims 1 to 3, having an average particle diameter of 6 to 100 μm.

5. The hexagonal boron nitride powder according to any one of claims 1 to 4, wherein the hexagonal boron nitride powder is a cosmetic hexagonal boron nitride powder.

Technical Field

The present invention relates to a hexagonal boron nitride powder, and more particularly to a hexagonal boron nitride powder which is excellent in brightness and can be preferably used as a material for cosmetics.

Background

Hexagonal boron nitride (h-BN) is a compound having a graphite-like layered structure in which hexagonal mesh-like layers composed of boron (B) and nitrogen (N) are laminated. Therefore, the usual hexagonal boron nitride particles have a flat plate-like (scaly) structure. Furthermore, no covalent bonds exist between layers within the particle, and the forces acting between the layers are only very weak van der waals forces. Therefore, a slight force can cause sliding between layers, and as a result, the hexagonal boron nitride powder has extremely excellent lubricity.

Further, hexagonal boron nitride is chemically stable and does not adversely affect the human body, and therefore, by effectively utilizing the above-mentioned lubricating properties, hexagonal boron nitride is widely used as an extender pigment for cosmetics excellent in "ductility" when applied to the skin surface (patent documents 1 and 2).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2013/065556;

patent document 2: international publication No. 2014/049956;

patent document 3: japanese patent laid-open No. 2001-011340;

patent document 4: jp 2010-163371 a.

Disclosure of Invention

Problems to be solved by the invention

However, depending on the use of the cosmetic, not only excellent lubricity but also excellent brightness may be required. Under such circumstances, for example, as described in patent documents 3 and 4, it has been proposed to add a glittering pigment such as a glass flake or a glittering agent to a cosmetic to impart glittering properties.

However, when the conventional hexagonal boron nitride powder and the glitter pigment are used in combination, there are the following problems: although the effect of imparting a smooth touch and gloss to the cosmetic can be maintained, the inherent glitter of the glitter pigment cannot be exhibited.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hexagonal boron nitride powder which has both a smooth texture and excellent glittering properties, which are characteristics of boron nitride powders, and which can obtain excellent glittering properties even when used in combination with a glittering pigment.

Means for solving the problems

The inventors of the present invention have focused attention on the shape of hexagonal boron nitride powder because the reason why the glitter is reduced when the glitter pigment is used in combination with the boron nitride powder is that light reflected by the glitter pigment interferes with light reflected by the hexagonal boron nitride powder. The present inventors have further studied to solve the above problems, and as a result, the following findings (1) and (2) were obtained.

(1) The boron nitride powder contains boron nitride particles having a structure bent at a specific angle, and the ratio of the particles is increased, whereby not only the glitter of the boron nitride powder but also the glitter when used in combination with a glitter pigment can be improved.

(2) By adding one or both of an alkali metal carbonate and an alkaline earth metal carbonate to a raw material for producing a boron nitride powder and producing a hexagonal boron nitride powder under specific conditions, a hexagonal boron nitride powder satisfying the above condition (1) can be produced.

The present invention has been completed based on the above findings, and its main contents are as follows.

1. A hexagonal boron nitride powder comprising hexagonal boron nitride particles, wherein the proportion of the number of particles having a structure bent at an angle of 110 DEG to 160 DEG with respect to the crystal (1,0,0) plane of the particles is 30% or more.

2. The hexagonal boron nitride powder according to 1, wherein the hexagonal boron nitride particles contained in the hexagonal boron nitride powder have a proportion of the number of particles having a structure bent at an angle of 110 ° to 130 ° with respect to the crystal (1,0,0) plane of the particles of 60% or more.

3. The hexagonal boron nitride powder according to 1 or 2 above, wherein the ratio of the incident light angle: the full width at half maximum of the reflectance peak measured under the condition of 45 ° is 80 ° or less.

4. The hexagonal boron nitride powder according to any one of the above 1 to 3, wherein the average particle diameter is 6 to 100 μm.

5. The hexagonal boron nitride powder according to any one of claims 1 to 4, wherein the hexagonal boron nitride powder is a cosmetic hexagonal boron nitride powder.

Effects of the invention

The hexagonal boron nitride powder of the present invention has excellent glittering properties in addition to the lubricity of the hexagonal boron nitride powder, and therefore can be used very preferably as a material for cosmetics.

Drawings

Fig. 1 is a schematic view showing an example of the shape of a particle according to an embodiment of the present invention.

Detailed Description

[ bending particle ratio ]

In the present invention, it is important that the number ratio of particles having a structure in which the particles are bent at an angle of 110 ° to 160 ° with respect to the crystal (1,0,0) plane of the particles (hereinafter referred to as "bent particle ratio") in the hexagonal boron nitride particles contained in the hexagonal boron nitride powder is 30% or more. When the bending particle ratio is less than 30%, sufficient brightness cannot be obtained. Therefore, the bent particle ratio is 50% or more, preferably 70% or more, and more preferably 80% or more. On the other hand, the upper limit of the bent particle ratio is not particularly limited, and may be 100%. However, when the bending particle ratio exceeds 90%, the effect is saturated, and thus the bending particle ratio may be 90% or less. The above bending grain ratio can be measured by the method described in examples. Hexagonal boron nitride powder satisfying the above conditions can be produced by the following production method.

In the hexagonal boron nitride particles contained in the hexagonal boron nitride powder, the number ratio of particles having a structure in which the particles are bent at an angle of 110 ° to 130 ° with respect to the crystal (1,0,0) plane of the particles (hereinafter referred to as "2 nd bent particle ratio") is preferably 60% or more. The 2 nd bent particle ratio can be increased by, for example, increasing the amount of the additive in the manufacturing method described below.

[ length of bent portion ]

The length of the bent portion in the particle having a structure bent at an angle of 110 ° to 160 ° with respect to the crystal (1,0,0) plane of the particle is not particularly limited, and is preferably 3 μm or more. This is because when it is less than 3 μm, there is no effect of bending. Here, the "length of the bent portion" refers to an average distance from a vertex of the bend to one end surface near the vertex in the bent outer side surface when the particle is observed under a microscope.

For example, as shown in fig. 1(a), when the particle has 1 bend at an angle of 110 ° to 160 °, the length L of the bent portion is preferably 3 μm or more. In this case, it is also preferable that the average distance from the apex of the bend to the one end surface distant from the apex is 3 μm or more.

Further, as shown in fig. 1(b), when the particles are bent at an angle of 110 ° to 160 ° at 2, the length L of the bent portion closest to the bend of one end face is preferably set to be the length L of the bent portion₁And a length L of the bent portion of the bend closest to the other end face₂At least one of them is 3 μm or more, and preferably both are 3 μm or more.

In addition, as described below, since the bending of the above-described particles occurs when crystal growth in the (100) plane is inhibited by impurities, the bending angle is theoretically determined. However, since the angle varies depending on various industrial factors, the bending angle is set to 110 ° to 160 °.

[ full Width at half maximum of reflectance peaks ]

The above hexagonal boron nitride powder was measured by a variable angle photometer at an incident light angle: the full width at half maximum of the reflectance peak measured under the condition of 45 ° is preferably 80 ° or less, and more preferably 60 ° or less. By setting the full width at half maximum to 80 ° or less, the brightness of the hexagonal boron nitride powder can be improved. This is considered because reflection of reflected light at a narrow angular width is perceived as stronger reflection of light than reflection (scattering) of reflected light at a wide angle. The lower limit of the full width at half maximum is not particularly limited, and may be usually 10 ° or more. The full width at half maximum can be measured by the method described in examples using a variable angle photometer.

[ average particle diameter ]

The hexagonal boron nitride powder preferably has an average particle diameter of 6 to 100 μm. When the average particle size is less than 6 μm, hexagonal boron nitride powder forms an extremely dense film when applied to the skin, and therefore, when other glittering pigments such as glass flakes are used in combination, the glittering properties of the glittering pigment are impaired. Further, increasing the average particle diameter also contributes to increasing the bent particle ratio. Therefore, the average particle diameter is preferably 6 μm or more. Further, by setting the average particle diameter to 15 μm or more, the light reflection per 1 particle becomes more remarkable, and as a result, the glitter can be further improved. Therefore, the average particle diameter is more preferably 15 μm or more. On the other hand, if the average particle size is 100 μm or less, the adhesiveness to the skin can be further improved. Therefore, the average particle diameter is preferably 100 μm or less, and more preferably 50 μm or less. The average particle size refers to the average particle size of the primary particles, and can be measured by the method described in examples. The average particle diameter can be controlled by the conditions (heating temperature, treatment time, etc.) in the 2-time heating.

[ proportion of coarse particles ]

In the hexagonal boron nitride powder of the present invention, the proportion of particles having a particle diameter of 200 μm or more (hereinafter referred to as "coarse particle proportion") is preferably 0.5% by mass or less. Coarse particles having a particle diameter of 200 μm or more are aggregated particles in which a plurality of particles are adhered, and by setting the proportion of such coarse particles to 0.5 mass% or less, the rough feel when applied to the skin can be further reduced. The proportion of the coarse particles can be controlled by selecting the pulverization method and the classification method.

[ apparent thickness ]

In the hexagonal boron nitride powder of the present invention, it is preferable that the apparent thickness of the particles constituting the hexagonal boron nitride powder is 0.5 to 3.0 μm. When the apparent thickness is 0.5 μm or more, the brightness can be further improved. On the other hand, if the apparent thickness is 3.0 μm or less, the rough feeling when applied to the skin can be further reduced. The apparent thickness can be controlled by adjusting the heat treatment conditions during production. The apparent thickness is an average value of apparent thicknesses observed under a microscope field of view. The apparent thickness can be measured by the method described in examples.

[ average aspect ratio ]

In order to further improve the smoothness of the hexagonal boron nitride powder, the hexagonal boron nitride powder preferably has an average aspect ratio (length of the particles/thickness of the particles) of 5 to 30. The aspect ratio is an average value of the aspect ratios of the respective particles obtained by observing the particles constituting the hexagonal boron nitride powder with an electron microscope. As the major axis and the thickness of the particles when calculating the aspect ratio of each particle, the apparent major axis and the apparent thickness under a microscope field of view can be used.

[ production method ]

The hexagonal boron nitride powder of the present invention can be produced by sequentially performing the following treatments (1) to (6), without any particular limitation. Hereinafter, each process will be specifically described.

(1) Mixing

(2) 1 st heating

(3) Cooling down

(4) 2 nd heating

(5) Pulverizing

(6) Washing with water and drying

(1) Mixing

First, it will be used to produce hexagonal boron nitrideThe raw materials of the powder are mixed with additives. As the raw materials, a boron compound as a boron source and a nitrogen compound as a nitrogen source are used. As the boron compound, boric acid and boron oxide (B) are used₂O₃) One or both of them. In addition, the boron compound may further contain boron carbide. As the nitrogen compound, one or both of urea and a urea compound are used. As the urea compound, for example, one or both of dicyandiamide and melamine can be used. As the above-mentioned additive, Na selected from the group consisting of Na₂CO₃、K₂CO₃、MgCO₃、CaCO₃、BaCO₃1 or 2 or more of MgO, CaO and BaO. It is considered that by using the above additive, crystal growth of the (100) plane is inhibited, and as a result, boron nitride particles having a bent structure are generated.

(2) 1 st heating

Then, the mixed raw materials and additives are heated to a heating temperature of 600 to 1200 ℃ and held at the heating temperature for 1 hour or more (heating 1 st). The raw material is boron nitride (t-BN) having a turbostratic structure by the above-mentioned heating of the 1 st stage. When the heating temperature is less than 600 ℃, the reaction of the boron compound as a raw material with the nitrogen compound to form boron nitride having a turbostratic structure becomes insufficient, and as a result, the yield of the hexagonal boron nitride heated in the subsequent 2 nd heating is lowered. Further, as described below, when the heating temperature of the 1 st heating is less than 600 ℃, a hexagonal boron nitride powder having a bent particle ratio satisfying the conditions of the present invention cannot be obtained. On the other hand, when the above heating temperature is higher than 1200 ℃, the manufacturing cost increases, and therefore, it is not economically reasonable. The 1 st heating may be performed in an inert gas atmosphere, and for example, a nitrogen atmosphere may be used as the inert gas atmosphere.

Here, the "turbostratic structure" means a state of being completely uncrystallized. An X-ray diffraction pattern of boron nitride having a turbostratic structure obtained by X-ray diffraction shows a broad peak indicating complete amorphization, instead of a sharp peak of hexagonal boron nitride.

(3) Cooling down

After the 1 st heating, the obtained boron nitride powder having a turbostratic structure is temporarily cooled. The cooling method is not particularly limited, and air cooling can be generally used. Further, it is preferable to cool the boron nitride powder of the turbostratic structure to room temperature in the above cooling.

(4) 2 nd heating

Next, the cooled boron nitride powder is heated to a heating temperature (heating temperature No. 2) of 1500 to 2300 ℃ in an inert gas atmosphere, and is held at the heating temperature for 2 hours or more (heating No. 2). The crystallization of boron nitride proceeds by the above-mentioned heating of the 2 nd stage, and boron nitride (t-BN) having a turbostratic structure is converted into hexagonal boron nitride (h-BN).

It is important that the average temperature increase rate of the 2 nd heating is 20 ℃/min or less. When the temperature increase rate is 20 ℃/min or less, the occurrence of bending and crystal growth due to the presence of an additive added to the raw material can be promoted, and a hexagonal boron nitride powder satisfying the conditions of the bending particle ratio specified in the present invention can be obtained. The average temperature increase rate of the 2 nd heating is preferably 10 ℃/min or less.

In order to produce the boron nitride of the present invention, it is very important to perform the 1 st heating in a state where the additive is mixed in the raw material. The reason for this is considered to be as follows, for example.

As described above, in the heating of 1 st, the boron compound as a raw material reacts with the nitrogen compound to produce boron nitride having a turbostratic structure. In this case, when an additive is added to the raw material, "ammonium borate containing an additive component (e.g., Ca)" is generated in addition to boron nitride having a turbostratic structure. By the presence of the "ammonium borate containing an additive component or the like", the occurrence of bending and crystal growth in the 2 nd heating can be promoted, and as a result, the bent grain ratio can be increased. Further, by adding the additive in advance before the 1 st heating, the raw material and the additive are melt-mixed, and therefore, the occurrence of bending and crystal growth in the 2 nd heating can be promoted.

Therefore, in order to finally obtain hexagonal boron nitride powder having a bent particle ratio of 30% or more, it is necessary to add an additive in advance before the 1 st heating. For example, when the additive is added after the 1 st heating and then the 2 nd heating is performed, the transition from the turbostratic boron nitride to the hexagonal boron nitride is performed in a state where "ammonium borate or the like containing an additive component" does not exist, and therefore the bent grain ratio cannot be made 30% or more.

Further, when the heating temperature of the 1 st heating is less than 600 ℃, boron nitride having a turbostratic structure cannot be sufficiently obtained in the 1 st heating. As a result, in the heating of the 2 nd stage, the formation reaction of hexagonal boron nitride by crystallization of boron nitride having a turbostratic structure did not proceed sufficiently, and therefore, it was not possible to obtain hexagonal boron nitride powder having a bent grain ratio of 30% or more.

(5) Pulverizing

The hexagonal boron nitride after the heating of the above 2 nd is changed into a massive block by the heating at a high temperature. Thus, the above-described block is pulverized. The method for the above-mentioned pulverization is not particularly limited, and may be carried out according to a conventional method.

(6) Washing with water and drying

After the above-mentioned pulverization, the hexagonal boron nitride is washed with water, sieved, and then dried.

Examples

The effects of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(example 1)

Hexagonal boron nitride powder was produced by the following procedure, and the characteristics thereof were evaluated.

First, boric acid as a raw material: 100 parts by mass of melamine: 80 parts by mass and boron carbide: 5 parts by mass, and additives shown in Table 1: 5 parts by mass.

Next, the mixed raw materials and additives were heated to the heating temperature shown in table 1 in a nitrogen atmosphere, and held at the heating temperature for 3 hours to produce boron nitride having a turbostratic structure (1 st heating). After heating in the above item 1, the mixture was cooled to room temperature.

Next, the obtained boron nitride having a turbostratic structure was heated to a heating temperature shown in table 1 in a nitrogen atmosphere, and held at the heating temperature for 5 hours (heating No. 2). And then, cooling to room temperature to obtain the hexagonal boron nitride. The average temperature increase rate of the 2 nd heating is shown in table 1. The obtained hexagonal boron nitride is pulverized, and is subjected to water washing, wet screening, dehydration and drying according to a conventional method. In the wet sieving, a sieve having a mesh opening of 200 μm was used to remove particles that did not pass through the sieve.

(evaluation method)

The obtained hexagonal boron nitride powder was measured for the fold grain ratio, the average grain diameter, the apparent thickness, the proportion of coarse grains, and the full width at half maximum of the reflectance peak, respectively, by the methods described below. Further, a sensory test was carried out by the following method to evaluate the glitter, the rough feeling, and the skin adhesion of the hexagonal boron nitride powder, and the glitter when the hexagonal boron nitride powder was used in combination with a glitter pigment. The evaluation results are summarized in Table 1.

[ bending particle ratio ]

The hexagonal boron nitride powder was observed using an electron microscope, and the number of particles having a bent structure among the randomly selected 50 primary particles was counted. In the case where bending occurs in the primary particles of hexagonal boron nitride, the hexagonal boron nitride powder "with bending" is observed to have a bending angle of 110 ° to 160 ° with respect to the crystal (1,0,0) plane of the primary particles with virtually no exception using an electron microscope. Therefore, in a microscopic field of view, both the particles in which bending was observed from the side surface of the particles and the particles in which the bending line was observed from the top surface of the particles can be regarded as particles having a structure bent at an angle of 110 ° to 160 °. Therefore, the folded particle ratio can be determined as (the number of particles having a folded structure/the number of primary particles to be subjected) × 100 (%). The above observation was performed under conditions of 2000 magnifications and 10 or more visual fields, and a total of 50 particles were observed.

[ average particle diameter ]

Hexagonal boron nitride powder was dispersed in water, and the particle size distribution of the hexagonal boron nitride powder was measured using a laser diffraction particle size distribution measuring apparatus (spectroris co., ltd., Mastersizer 3000). The analysis conditions were as follows: measurement target: aspherical, refractive index: 1.74, absorptivity: 0. density: 1g/cm³And a dispersion medium: ethanol (refractive index 1.33). The 50% cumulative particle diameter (median diameter, D50) of the obtained particle size distribution was defined as the average particle diameter.

[ apparent thickness ]

The hexagonal boron nitride powder was observed with an electron microscope, and the apparent thickness of the primary particles was measured. Observation was performed in magnification: 10000 times and 5 visual fields were performed, and the average value of the thicknesses of the primary particles observed was defined as the apparent thickness.

[ proportion of coarse particles ]

The "proportion of coarse particles" defined as the proportion of particles having a particle diameter of 200 μm or more was measured by the following procedure. First, the total weight of hexagonal boron nitride powder was measured. Next, the hexagonal boron nitride powder was dispersed in ethanol and subjected to ultrasonic treatment for 10 minutes to obtain a dispersion. Subsequently, the dispersion was suction-filtered through a 200 μm mesh screen, and then the mesh screen was dried at 120 ℃ for 10 minutes and cooled in a dryer. The ratio of the coarse particles was determined from the weight on the mesh after the cooling and the total weight of the hexagonal boron nitride powder measured first. That is, the ratio of coarse particles (weight on screen/total weight) × 100 (%).

[ full Width at half maximum of reflectance peaks ]

Boron nitride powder was applied to artificial leather, and the reflected light intensity of-90 ° to 90 ° with respect to incident light of-45 ° was measured using a variable angle photometer (MURAKAMI COLOR reset label co., LTD, GP-200 (horizontal rotation)). The full width at half maximum of the peak when the angle of the reflected light is plotted on the X axis and the intensity of the reflected light is plotted on the Y axis is taken as the full width at half maximum of the peak of the reflected light.

[ Brilliance of hexagonal boron nitride powder ]

The back of the hand of 10 test persons was coated with 10mg of hexagonal boron nitride powder to determine whether the light was present or absent. The presence or absence of the glitter was evaluated by whether the glitter was visually confirmed when the back of the hand was tilted. Excellent, good, insufficient Δ, and poor x as evaluation criteria based on the degree of brightness. The most evaluated results among the evaluation results of 10 testers were used as the evaluation of the hexagonal boron nitride powder in the test. However, when the number of persons evaluated by 2 or more persons was the same and the number was the largest, the lowest evaluation among the numbers was regarded as the evaluation of the hexagonal boron nitride powder in the test.

[ feeling of roughness ]

The back of the hand of 10 test subjects was coated with 10mg of hexagonal boron nitride powder, and whether or not the test subjects had a rough feel when they were applied with fingers was evaluated. The evaluation criteria were excellent when no rough feel was sensed at all, a pass level slightly inferior to excellent was good, and a rough feel was poor.

[ adhesion to skin ]

The back of the hand of 10 test subjects was coated with 10mg of hexagonal boron nitride powder, and the amount of the hexagonal boron nitride powder adhering to the back of the hand when the test subject was applied with one finger was visually evaluated. Excellent evaluation criteria, good evaluation criteria, insufficient Δ, and defective × were ∈. The most evaluated results among the evaluation results of 10 testers were used as the evaluation of the hexagonal boron nitride powder in the test. However, when the number of persons evaluated by 2 or more persons was the same and the number was the largest, the lowest evaluation among the numbers was regarded as the evaluation of the hexagonal boron nitride powder in the test.

[ Brightness when a bright pigment is used in combination ]

In order to evaluate the glitter when hexagonal boron nitride powder is used in combination with a glitter pigment, a sensory test of the glitter was performed under conditions similar to those of actual cosmetics. Specifically, a test composition was obtained by mixing 20 mass% of hexagonal boron nitride powder, 60 mass% of talc, and 20 mass% of a glitter pigment (glass flake) in a mortar. The back of the hand of 10 test subjects was coated with 10mg of the above-mentioned test composition to determine whether or not the light was shining. The presence or absence of the glitter was evaluated by visually confirming whether the glitter was observed when the back of the hand was tilted. As in the case of the test of the hexagonal boron nitride powder alone, the evaluation criteria were excellent as excellent, good as excellent, insufficient Δ, and poor as x based on the degree of the glitter. The most evaluated results among the evaluation results of 10 testers were used as the evaluation of the hexagonal boron nitride powder in the test. However, when the number of persons evaluated by 2 or more persons was the same and the number was the largest, the lowest evaluation among the numbers was regarded as the evaluation of the hexagonal boron nitride powder in the test. In addition, although the above example shows an example in which the addition ratio of the hexagonal boron nitride powder is 20 mass%, the same effects as those shown in table 1 were confirmed even in the case of the usual addition ratio of 3 to 30 mass%.

[ Table 1]

From the results shown in table 1, it is understood that hexagonal boron nitride powders satisfying the conditions of the present invention all have excellent brightness. On the other hand, hexagonal boron nitride powder which does not satisfy the conditions of the present invention has poor brightness.

Since no predetermined additive was used in the production of the powder of No.6, the bent particle ratio was low, and as a result, the brightness was poor. Since the temperature increase rate of the No.8 and No. 10 powders exceeds 20 ℃/min in the 2 nd heating, the growth rate of the primary particles was high, facet growth did not proceed sufficiently, and as a result, the bent particle ratio was low. The reason why the average particle size becomes smaller than 15 μm is that the temperature at the time of heating at 2 nd stage is high (2050 ℃), and therefore the volatilization rate of boron oxide involved in the growth of particles is higher than the growth rate of particles. The powder of No.13 was excessively pulverized until the average particle diameter became 4 μm, and therefore the bending ratio was 5%.

Further, in the hexagonal boron nitride powder of the invention example, the powder having an average particle diameter of 6 to 100 μm was more excellent in skin adhesion than the powder of No.14 having an average particle diameter of 130 μm. In the hexagonal boron nitride powder of the invention example, the powder having a grain ratio of coarse grains of 0.5 mass% or less had a suppressed feeling of coarsening as compared with the powder of No.15 having a grain ratio of coarse grains of 0.8 mass%.

In addition, an experiment was also conducted in which bright tablets were used as a glittering material instead of the glass flakes, and the tendency was similar to that in the case of using the glass flakes.

(example 2)

Hexagonal boron nitride powder was produced under the production conditions shown in table 2. The production conditions other than those shown in table 2 were the same as in example 1. Next, the hexagonal boron nitride powders obtained were evaluated in the same manner as in example 1. However, as the bent grain ratio, the number ratio (2 nd bent grain ratio) of grains having a structure bent at an angle of 110 ° to 130 ° with respect to the crystal (1,0,0) plane of the grains was measured. The 2 nd bend particle ratio is obtained by image analysis (3-dimensional analysis) according to a conventional method on an image obtained by observing hexagonal boron nitride powder with an electron microscope.

From the results shown in table 2, it is understood that the hexagonal boron nitride powder having a 2 nd bent particle ratio of 60% or more has more excellent brightness than the hexagonal boron nitride powder having a 2 nd bent particle ratio of less than 60%.

[ Table 2]