Hexagonal boron nitride powder for cosmetics, and cosmetics

Abstract

One aspect of this application is to provide a hexagonal boron nitride powder for cosmetic use, which contains primary particles of hexagonal boron nitride, wherein the aspect ratio of the primary particles is less than 25 and the oil absorption is 50-90 mL / 100 g.

Description

Technical Field

[0001] This application relates to hexagonal boron nitride powder for cosmetic use and cosmetic products. Background Technology

[0002] Hexagonal boron nitride possesses lubricating properties, high thermal conductivity, and insulating properties, making it suitable for various applications such as solid lubricants, mold release agents, fillers for resins and rubbers, raw materials for cosmetics, and heat-resistant insulating sintered bodies. Hexagonal boron nitride powder enhances the smoothness, spreadability, and concealing properties of cosmetics, as well as imparting gloss.

[0003] As a extender pigment that can perform the same function as hexagonal boron nitride powder, talc powder and mica powder can be used. However, talc powder and the like use natural minerals, resulting in significant inhomogeneity in particle size and thickness, requiring further adjustments to ensure consistent quality in cosmetics. Hexagonal boron nitride powder allows for adjustments in particle size and thickness, and its smoothness is superior to that of talc powder and mica powder. Therefore, hexagonal boron nitride powder is frequently used in cosmetics requiring excellent smoothness. Patent Document 1 proposes a hexagonal boron nitride powder with a shear stress to applied pressure ratio within a specified range to improve smoothness.

[0004] Cosmetics require a wide variety of properties, and the requirements for hexagonal boron nitride powder used as a raw material are even higher. For example, in cosmetics where hexagonal boron nitride powder is used to form films with excellent film-forming properties and enhances cooling sensation and transparency (natural makeup look), Patent Document 2 proposes a hexagonal boron nitride powder that increases oil absorption by reducing hydrophilic functional groups on the surface.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-043792

[0008] Patent Document 2: Japanese Patent Application Publication No. 2014-094878 Summary of the Invention

[0009] Furthermore, to improve the spreadability of cosmetics, a key aspect of their usability, some have considered reducing the particle size of hexagonal boron nitride (BON) primary particles, which are used as a body pigment. However, reducing the particle size can cause cosmetics containing BON powder to appear whiter due to light scattering, potentially compromising the smoothness of the makeup layer. Additionally, while a thin layer is preferred for enhancing transparency, excessively large aspect ratios of the BON primary particles can increase oil absorption, making it difficult to mix with other ingredients during cosmetic preparation. This necessitates additional surface treatments and ingredient adjustments, potentially compromising the original feel of BON or complicating the cosmetic manufacturing process. From the perspective of achieving a good balance between spreadability, transparency, and smoothness when used in cosmetics, there is still room for improvement.

[0010] The purpose of this application is to provide a hexagonal boron nitride powder for cosmetics, which has excellent spreadability when used in cosmetics, and excellent transparency and smoothness of the cosmetic layer.

[0011] One aspect of this application is to provide a hexagonal boron nitride powder for cosmetic use, which contains primary particles of hexagonal boron nitride, wherein the aspect ratio of the primary particles is less than 25 and the oil absorption is 50-90 mL / 100 g.

[0012] The hexagonal boron nitride powder used in cosmetics has a primary particle aspect ratio within a specified range and a specific oil absorption capacity, making it suitable as a raw material for cosmetics. When used in cosmetics, this hexagonal boron nitride powder exhibits excellent spreadability and can form a cosmetic layer that provides excellent transparency and smoothness.

[0013] The BET specific surface area of ​​the above-mentioned hexagonal boron nitride powder can be 1.5–5.0 m². 2 / g.

[0014] The tap density of the above-mentioned hexagonal boron nitride powder can be 0.35 g / cm³. 3 the following.

[0015] The total oxygen content of the above-mentioned hexagonal boron nitride powder can be 0.01 to 0.20% by mass.

[0016] One aspect of this application is to provide a cosmetic product comprising hexagonal boron nitride powder used in cosmetics.

[0017] Because the above-mentioned cosmetic contains the aforementioned hexagonal boron nitride powder, it has excellent spreadability, and the cosmetic layer formed by using the cosmetic has excellent transparency and smoothness.

[0018] According to this application, a hexagonal boron nitride powder for cosmetic use can be provided, which has excellent spreadability when used in cosmetics, and excellent transparency and smoothness of the cosmetic layer. Detailed Implementation

[0019] The embodiments of the present invention will now be described. However, these embodiments are merely examples to illustrate the present invention and are not intended to limit the present invention to the following content.

[0020] Unless otherwise specified, the materials illustrated in this specification may be used alone or in combination of two or more. When a composition contains multiple substances equivalent to each component, the content of each component in the composition, unless otherwise specified, refers to the total amount of the multiple substances present in the composition.

[0021] One embodiment of the hexagonal boron nitride powder for cosmetic use includes primary particles of hexagonal boron nitride, wherein the aspect ratio of the primary particles is 25 or less and the oil absorption is 50 to 90 mL / 100 g.

[0022] To improve smoothness, spreadability, and concealment, the primary particles of hexagonal boron nitride are preferably flaky. The upper limit of the aspect ratio of the primary particles of hexagonal boron nitride can be, for example, 22 or less, 20 or less, 19 or less, or 18 or less. By keeping the upper limit of the aspect ratio within the above range, the primary particles have an appropriate thickness, which can suppress breakage of the primary particles and thus suppress the increase in dissolved boron. Furthermore, it can prevent light reflection and provide appropriate transparency. The lower limit of the aspect ratio of the primary particles can be, for example, 5 or more, 7 or more, 10 or more, 12 or more, or 15 or more. By keeping the lower limit of the aspect ratio within the above range, the spreadability of the resulting cosmetic can be further improved when used as a body pigment in cosmetics. Furthermore, by keeping the lower limit of the aspect ratio within the above range, when using hexagonal boron nitride powder as a body pigment in cosmetics, the resulting cosmetic exhibits excellent concealment (coverage). The aspect ratio of the primary particles of hexagonal boron nitride can be adjusted within the above range, for example, it can be 5-22, 10-22 or 15-22.

[0023] The aspect ratio of a primary particle is expressed as the ratio of its longest (longest diameter) to its shortest (shortest diameter) ((longest diameter) / (shortest diameter)). In the case of hexagonal boron nitride, since the primary particles are scaly, the thickness of the scaly particles becomes the shortest (shortest diameter) of the particle. That is, the "aspect ratio of a primary particle" in this specification refers to the value obtained by actually measuring the particle's long diameter from an electron microscope image of a primary particle of hexagonal boron nitride and actually measuring the particle's thickness from a cross-sectional photograph image, and calculating the aforementioned ratio from the actual measurement results. In other words, the aspect ratio of a primary particle of hexagonal boron nitride is expressed as (longest diameter) / (thickness) of the primary particle of hexagonal boron nitride.

[0024] When determining the aspect ratio of flaky particles such as hexagonal boron nitride, errors can easily occur, for example, by directly analyzing particle images captured by an electron microscope (e.g., if the primary particles are tilted, errors will occur on the short side (particle thickness, equivalent to the short diameter of the particle), making accurate measurement difficult. Therefore, the aspect ratio of hexagonal boron nitride in this specification is calculated using the major and minor diameters of the primary particles of hexagonal boron nitride obtained by measurement according to the following method. First, for the major diameter of the primary particles of hexagonal boron nitride, hexagonal boron nitride powder is photographed using a scanning electron microscope, and the resulting particle image is loaded into image analysis software to determine the major side of the primary particles from the obtained image. Next, the minor diameter of the primary particles of hexagonal boron nitride is measured. First, using a compression molding machine, 3g of boron nitride powder was molded into a disc shape (diameter: 30mmφ) at a pressure of 5MPa. After embedding the molded body in resin, the cross-section was ground in a direction parallel to the applied pressure, thereby preparing a sample with the cross-section of the boron nitride particles exposed. Because the compression molding orients the primary boron nitride particles in one direction, the measurement error of the short side caused by the tilting of the primary particles can be suppressed. The cross-section was photographed with a scanning electron microscope, and the resulting particle image was loaded into image analysis software to determine the short side from the obtained image. In addition, the measurement of either the major or minor diameter of the particles was performed on 100 randomly selected primary particles, and their arithmetic mean was used.

[0025] The upper limit of oil absorption of hexagonal boron nitride powder can be, for example, 88 mL / 100g or less, 86 mL / 100g or less, 85 mL / 100g or less, or 80 mL / 100g or less. When hexagonal boron nitride powder with an upper limit of oil absorption within the above range is used as a body pigment for cosmetics, its dispersibility with oils can be maintained. Therefore, during formulation, surface treatment for mixing with oils is not required, and formulation can be easily carried out while maintaining the original tactile properties of hexagonal boron nitride. The lower limit of oil absorption of hexagonal boron nitride powder can be, for example, 55 mL / 100g or more, 60 mL / 100g or more, 65 mL / 100g or more, 70 mL / 100g or more, or 75 mL / 100g or more. By keeping the lower limit of oil absorption within the above range, affinity with sebum can be suppressed, preventing sebum from causing cosmetic deterioration. The oil absorption of hexagonal boron nitride powder can be controlled, for example, by adjusting the BET specific surface area of ​​the primary particles, or by adjusting conditions such as the heating temperature during the manufacture of the hexagonal boron nitride powder. The oil absorption of hexagonal boron nitride powder can be adjusted within the above-mentioned range, for example, it can be 50–88 mL / 100g, 60–88 mL / 100g, or 70–86 mL / 100g.

[0026] The "oil absorption" in this specification is a value determined according to the method described in JIS K 5101-13-1:2004 "Test Methods for Pigments - Part 13: Oil Absorption - Section 1: Purified Linseed Oil Method". When oil is added to the sample, the oil absorption corresponds to the amount of oil required to form a paste. For example, in the case of a highly oleophilic sample, a smaller amount of oil is needed to form a paste, resulting in less oil absorption. Conversely, in the case of a highly hydrophilic sample (for samples with low affinity for oil), more oil must be added to form a paste, thus increasing the oil absorption.

[0027] The lower limit of the BET specific surface area of ​​the aforementioned hexagonal boron nitride powder can be, for example, 1.5 m². 2 / g or more, 1.8m 2 / g or more, 1.9m 2 / g or more, 2.0m 2 / g or more, 2.3m 2 / g or more or 2.5m 2 / g or more. By keeping the lower limit of the BET specific surface area within the above range, excessive gloss in the cosmetic layer can be suppressed when using hexagonal boron nitride powder as a raw material. The upper limit of the BET specific surface area of ​​the hexagonal boron nitride powder can, for example, be 5.0m². 2 / g or less, 4.0m 2 / g or less or 3.0m 2 / g or less. By keeping the upper limit of the BET specific surface area within the above range, the amount of boron dissolved from the hexagonal boron nitride powder can be reduced, and a smoother feel can be imparted to the cosmetic layer through appropriate gloss. The BET specific surface area can be adjusted within the above range, for example, it can be 1.5 to 5.0 μm. 2 / g. The BET specific surface area of ​​hexagonal boron nitride can be controlled, for example, by adjusting conditions such as the heating temperature during the manufacture of hexagonal boron nitride powder.

[0028] The “BET specific surface area” in this specification is the value determined by the method described in JIS Z 8830:2013 “Method for determination of specific surface area of ​​powder (solid) by gas adsorption”, using nitrogen and the BET one-point method.

[0029] The upper limit of the tap density of the aforementioned hexagonal boron nitride powder can be, for example, 0.35 g / cm³. 3 Below, 0.30g / cm 3 Below, 0.25g / cm 3 Below or 0.23g / cm 3 Below. If the upper limit of the tap density is within the above range, because of the low density, there is less resistance during coating, allowing for a thin layer of hexagonal boron nitride to be applied to the skin with less force and spread out, thus giving the cosmetic layer a better transparency. The lower limit of the tap density of the above-mentioned hexagonal boron nitride powder is typically 0.02 g / cm³. 3 Above or 0.05 g / cm 3 The above, for example, could be 0.08 g / cm³. 3 Above, 0.10g / cm 3 Above, 0.10g / cm 3 Above, 0.15g / cm 3 Above or 0.20g / cm 3 The above describes the process. By keeping the lower limit of the tap density within the above range, it is easy to operate during manufacturing and can be easily mixed with oils for formulation. The tap density of hexagonal boron nitride powder can be adjusted within the above range, for example, it can be 0.02 to 0.35 g / cm³. 3 0.05~0.35g / cm 3 Or 0.20~0.35g / cm 3 .

[0030] The tap density in this specification refers to the value obtained according to JIS R 1628:1997 "Method for determination of bulk density of precision ceramic powders". Commercially available equipment can be used for the determination. Specifically, the determination is performed under the conditions described in the examples.

[0031] The upper limit of the total oxygen content of the aforementioned hexagonal boron nitride powder can be, for example, 0.20% by mass or less, 0.15% by mass or less, 0.12% by mass or less, or 0.10% by mass or less. By keeping the upper limit of the total oxygen content within the above range, the adhesion and aggregation of hexagonal boron nitride particles can be reduced, and the ductility can be further improved. The lower limit of the total oxygen content of the aforementioned hexagonal boron nitride powder can be, for example, 0.01% by mass or more, 0.02% by mass or more, 0.03% by mass or more, 0.04% by mass or more, or 0.05% by mass or more. By keeping the lower limit of the total oxygen content within the above range, the dispersibility in polar solvents can be further improved. Therefore, when using hexagonal boron nitride powder as an extender pigment to prepare cosmetics, it is easy to mix with other pigments, and cosmetics can be manufactured smoothly. The total oxygen content can be adjusted within the above range, for example, it can be 0.01 to 0.20% by mass or 0.01 to 0.10% by mass. The total oxygen content can be controlled, for example, by adjusting the heating temperature during the manufacturing of hexagonal boron nitride powder.

[0032] The term "total oxygen content" in this specification refers to the total oxygen content of hexagonal boron nitride powder. The total oxygen content can be determined using the following steps: The oxygen and nitrogen content of the hexagonal boron nitride powder is analyzed using an oxygen-nitrogen analyzer. In a helium atmosphere, the sample is heated from 20°C to approximately 2500°C, i.e., above the decomposition temperature of boron nitride. Oxygen is detected as it is released with increasing temperature. At the beginning of the heating process, oxygen bonded to the surface of the hexagonal boron nitride powder is released. The surface oxygen content is determined by quantifying the released oxygen. Subsequently, if the temperature reaches approximately 1400°C, the hexagonal boron nitride begins to decompose. The onset of decomposition can be determined by the detection of nitrogen. If the hexagonal boron nitride begins to decompose, oxygen is released from within the hexagonal boron nitride particles. The internal oxygen content is determined by quantifying the oxygen released during this stage. The sum of the surface oxygen content and the internal oxygen content obtained in this way is the total oxygen content.

[0033] In hexagonal boron nitride powder, the lower limit of the average particle size can be, for example, 4 μm or more, 5 μm or more, 7 μm or more, or 8 μm or more. By keeping the lower limit of the average particle size within the above range, when using hexagonal boron nitride powder as a body pigment in cosmetics, the resulting cosmetics can have improved spreadability. The upper limit of the average particle size can be, for example, 19 μm or less, 18 μm or less, 17 μm or less, or 16 μm or less. By keeping the upper limit of the average particle size within the above range, excessive gloss can be suppressed. The average particle size can be adjusted within the above range, for example, from 4 to 19 μm. The average particle size can be controlled, for example, by adjusting conditions such as the heating temperature during the manufacture of hexagonal boron nitride powder.

[0034] The average particle size in this specification refers to the 50% cumulative diameter (median diameter) of the cumulative particle size distribution on a volume basis. The "50% cumulative diameter of the cumulative particle size distribution on a volume basis" in this specification refers to the particle size (D50) at which the cumulative value in the cumulative particle size distribution on a volume basis is 50% when the particle size distribution is determined by laser diffraction scattering for hexagonal boron nitride powder. Laser diffraction scattering is performed according to the method described in JIS Z 8825:2013 "Particle Size Analysis by Laser Diffraction and Scattering". The determination can be performed using a laser diffraction scattering particle size distribution measuring device, such as the "LS-13 320" (product name) manufactured by Beckman Coulter, Inc.

[0035] In hexagonal boron nitride powder, the amount of dissolved boron is sufficiently reduced. For example, the amount of dissolved boron in hexagonal boron nitride powder can be less than 20 ppm by mass, less than 15 ppm by mass, less than 10 ppm by mass, less than 8 ppm by mass, or less than 6 ppm by mass. By reducing the amount of dissolved boron in hexagonal boron nitride powder, skin irritation can be reduced, making it more useful as a body pigment for use in cosmetics.

[0036] The “boron leaching amount” in this instruction manual refers to the value measured according to the specifications of quasi-drug raw materials 2006.

[0037] The aforementioned hexagonal boron nitride powder for cosmetic use can be suitably used as a pigment, or it can be considered a raw material for cosmetics. Therefore, the aforementioned hexagonal boron nitride powder can be called a pigment for cosmetics. Furthermore, this application can provide cosmetics containing the aforementioned hexagonal boron nitride powder.

[0038] Examples of cosmetic products include: foundation (powder foundation, liquid foundation, cream foundation), loose powder, point makeup, eyeshadow, eyeliner, nail polish, lipstick, blush, and mascara. Among these, hexagonal boron nitride powder is particularly suitable for foundation and eyeshadow. The content of hexagonal boron nitride powder in cosmetics is, for example, 0.1% to 70% by mass. Cosmetics can be manufactured using known methods. For example, a method for manufacturing cosmetics includes a step of combining and mixing hexagonal boron nitride powder with other raw materials.

[0039] The aforementioned hexagonal boron nitride powder for cosmetics can be manufactured, for example, by the following method. An example of a method for manufacturing hexagonal boron nitride powder for cosmetics includes the following steps: calcining a raw material composition containing a boron-containing compound including boric acid and a nitrogen-containing compound including melamine at 600–1300°C in an environment containing at least one of an inactive gas and ammonia, to obtain a pre-calcined material containing at least one of low-crystallinity boron nitride and amorphous boron nitride (hereinafter also referred to as the pre-calcination step); calcining a mixed powder containing the pre-calcined material and an additive at a temperature of 1500–1750°C in an environment containing at least one of an inactive gas and ammonia to obtain a calcined material (hereinafter also referred to as the calcination step); pulverizing, washing, and drying the calcined material to obtain a dry powder (hereinafter also referred to as the purification step); and heat-treating the dry powder at a temperature of 1900°C or higher in an environment containing at least one of an inactive gas and ammonia (annealing step).

[0040] The above calcination process can be repeated multiple times (hereinafter referred to as the first calcination process, the second calcination process, etc., respectively). When the calcination process is repeated multiple times, the calcined material obtained in each calcination process can be pulverized. By pulverizing the calcined material, melamine and other components in the raw material composition of subsequent calcination processes can be fully consumed. Furthermore, the pulverization process may also include washing and drying the pulverized powder to form a dry powder.

[0041] Boron-containing compounds are compounds that contain boron atoms as constituent elements. Besides boric acid, boron-containing compounds may further include, for example, boron oxide and borax. Nitrogen-containing compounds are compounds that have nitrogen atoms as constituent elements and can be organic compounds. Besides melamine, nitrogen-containing compounds may further include, for example, dicyandiamine and urea. The raw material composition may also include components other than the above-mentioned compounds. For example, carbonates such as lithium carbonate and sodium carbonate may be included as pre-calcining aids. Additionally, reducing substances such as carbon may be included.

[0042] In the above-mentioned raw material composition, the proportion of boron-containing compounds and nitrogen-containing compounds can be adjusted according to the molar ratio of boron atoms to nitrogen atoms. For example, they can be combined in a manner where boron atoms:nitrogen atoms = 2:8 to 8:2, or in a manner where they are 2.5:7.5 to 7.5:2.5.

[0043] In the pre-calcination process, for example, an electric furnace is used to pre-calcine the above-mentioned raw material composition to obtain a pre-calcined product. The pre-calcination process is carried out in an environment containing at least one of an inert gas and ammonia. Examples of inert gases include nitrogen and rare gases. Examples of rare gases include helium and argon. The pre-calcination process can be carried out in a mixed gas environment consisting of an inert gas and ammonia. The pre-calcination temperature can be, for example, 600–1300°C, 800–1200°C, or 900–1100°C. The pre-calcination time can be, for example, 0.5–5.0 hours or 1.0–4.0 hours.

[0044] The pre-calcined product obtained from the pre-calcination comprises at least one selected from low-crystallinity boron nitride and amorphous boron nitride, and may further comprise hexagonal boron nitride. The pre-calcination process may also be carried out at a lower temperature than the calcination process described later. By lowering the pre-calcination temperature, grain growth can be suppressed, thereby reducing the average particle size of the final hexagonal boron nitride powder. Furthermore, by lowering the pre-calcination temperature, grain growth can be suppressed, thereby increasing the BET specific surface area of ​​the hexagonal boron nitride powder.

[0045] Next, in the calcination process, additives are mixed into the pre-calcined product obtained above to prepare a mixed powder, which is then calcined. During the calcination process, the raw material components are fully consumed in the presence of the additives, and boron nitride is generated and crystallized. This improves the crystallinity of the boron nitride contained in the calcined product, forming hexagonal boron nitride. Boric acid may also be further incorporated into the mixed powder.

[0046] Examples of additives include borates such as sodium borate, and carbonates such as sodium carbonate, calcium carbonate, and lithium carbonate. Sodium carbonate is preferred as an additive. The amount of additive is 2 parts by mass or more and less than 20 parts by mass relative to 100 parts by mass of the pre-calcined product containing boron nitride; for example, it can be 3 to 10 parts by mass or 3 to 7 parts by mass.

[0047] In the calcination process, the mixed powders are calcined, for example, using an electric furnace, to obtain a calcined product. The calcination process is carried out in an environment containing at least one of an inert gas and ammonia. Examples of inert gases include nitrogen and rare gases. Examples of rare gases include helium and argon. The calcination process can be carried out in a mixed gas environment containing an inert gas and ammonia.

[0048] The calcination temperature is 1500–1750℃. This calcination temperature can be, for example, 1550–1850℃ or 1600–1750℃. The calcination time can be, for example, 0.5–5 hours or 1–4 hours.

[0049] In addition, the calcination time, heating time, and calcination time mentioned in this specification refer to the time (holding time) after the temperature of the surrounding environment of the object reaches the specified temperature.

[0050] By setting a higher calcination temperature, the consumption of raw material components, the consumption of amorphous carbon and graphite generated from the reaction of raw material components, and the formation and crystallization of hexagonal boron nitride can be fully achieved. Reducing carbon-containing raw materials such as melamine in the raw material components can further improve the quality of the obtained hexagonal boron nitride powder. Extending the calcination time also tends to have the same effect. On the other hand, if the calcination temperature becomes too high, the crystallization of hexagonal boron nitride tends to over-grow, making micronization difficult. The same tendency exists when the calcination time becomes too long.

[0051] The calcined product obtained in the calcination process can be pulverized using a pulverizing device, for example. An impact pulverizer can also be used. Preferably, an impact pulverizer is used that allows the particle size of the pulverized material to be adjusted by passing it through a screen, such as an impact-type screen micro-pulverizer. The mesh size of the screen can be, for example, 0.1–1 mm or 1–3 mm.

[0052] In the pulverization process, the calcined material is pulverized to adjust the particle size. Adjusting the particle size improves the efficiency of the subsequent annealing process. The pulverized material obtained from pulverizing the calcined material contains impurities in addition to hexagonal boron nitride. Therefore, a purification process can be performed before the annealing process to reduce these impurities. Examples of impurities include residual raw materials and additives, as well as water-soluble boron compounds. In the purification process, such impurities can be reduced, for example, by washing. After washing, solid-liquid separation and drying are performed to obtain a dry powder. By performing the pulverization and purification processes before the annealing process, a powder or dry powder with a lower content of additives than the calcined material is prepared. Annealing this powder or dry powder can suppress grain growth and further reduce oxygen content.

[0053] Examples of cleaning solutions include aqueous solutions containing water and acidic substances, organic solvents, and mixtures of organic solvents and water. From the viewpoint of avoiding secondary contamination, water with a conductivity of 1 mS / m or less can be used. Examples of aqueous solutions containing acidic substances include inorganic acids such as hydrochloric acid and nitric acid. Examples of organic solvents include water-soluble organic solvents such as methanol, ethanol, propanol, isopropanol, and acetone. There are no particular limitations on the cleaning method; for example, the pulverized material can be immersed in the cleaning solution and stirred for cleaning, or the cleaning solution can be sprayed onto the pulverized material for cleaning.

[0054] After cleaning, the cleaning liquid can be separated into solid and liquid components using a decanter, vacuum filter, pressure filter, rotary filter, sedimentation separator, or a combination thereof. The separated solid components can also be dried using a general dryer to obtain a dry powder. Examples of dryers include rack dryers, fluidized bed dryers, spray dryers, rotary dryers, belt dryers, and combinations thereof. After drying, coarse particles can be removed, for example, by sieving.

[0055] In the annealing process, for example, an electric furnace is used to heat-treat the pulverized or dried powder of the calcined material. The annealing process is carried out in an environment containing at least one of an inert gas and ammonia. Examples of inert gases include nitrogen and rare gases. Rare gases may include, for example, helium and argon. The calcination process can be carried out in a mixed gas environment containing an inert gas and ammonia. The heating temperature in the annealing process is 1900°C or higher, but from the viewpoint of sufficiently reducing oxygen content, it can be 1950°C or higher, or even 2000°C or higher. By performing the annealing process, oxygen present on the particle surface as functional groups, etc., dissipates, thereby reducing the oxygen content.

[0056] From the perspective of suppressing particle growth, the heat treatment temperature in the annealing process can be below 2200°C or below 2100°C. The heating time in the annealing process, from the perspective of sufficiently reducing oxygen content and suppressing particle growth, can be, for example, 0.5 to 5.0 hours or 1.0 to 4.0 hours.

[0057] The above describes several embodiments, and common configurations can be described interchangeably. Furthermore, the present invention is not limited to the embodiments described above.

[0058] Example

[0059] The present invention will be described in more detail with reference to the embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0060] (Example 1)

[0061] [Manufacturing of Hexagonal Boron Nitride Powder]

[0062] <Pre-calcination process>

[0063] 100.0 g of boric acid powder (purity: ≥99.8% by mass, manufactured by Kanto Chemical Co., Ltd.) and 90.0 g of melamine powder (purity: ≥99.0% by mass, manufactured by Wako Pure Chemical Co., Ltd.) were mixed for 10 minutes using an alumina mortar to obtain a mixed raw material. The dried mixed raw material was placed in a container made of hexagonal boron nitride and placed in an electric furnace. Nitrogen gas was introduced into the electric furnace while the temperature was increased from room temperature to 1000°C at a rate of 10°C / min. Heating was stopped after maintaining the temperature at 1000°C for 2 hours, and the mixture was allowed to cool naturally. The electric furnace was turned on when the temperature dropped below 100°C. Thus, a pre-calcined product containing low-crystallinity boron nitride was obtained.

[0064] <Calcination Process>

[0065] Add 5.0g of sodium carbonate (purity: ≥99.5% by mass) as an additive to 100.0g of calcined material and mix for 10 minutes using an alumina mortar. Place the mixture in the aforementioned electric furnace. While introducing nitrogen gas into the furnace, raise the temperature from room temperature to 1600°C at a rate of 10°C / min. Maintain the calcination temperature at 1600°C for 4 hours, then stop heating and allow it to cool naturally. Turn on the furnace when the temperature drops below 100°C. Recover the calcined material and pulverize it in an alumina mortar for 3 minutes to obtain a coarse powder containing hexagonal boron nitride.

[0066] <Purification Process>

[0067] To reduce impurities in the coarse powder, 30g of the powder was added to 500g of dilute nitric acid (nitric acid concentration: 5% by mass) and stirred at room temperature for 60 minutes. After stirring, solid-liquid separation was performed by vacuum filtration, and water (with a conductivity of 1 mS / m) was passed through for washing until the filtrate became neutral. After washing, the powder was dried at 120°C for 3 hours using a dryer to obtain a dry powder.

[0068] <Annealing process>

[0069] The dried powder was placed in the aforementioned electric furnace. Nitrogen gas was introduced into the furnace while the temperature was increased from room temperature to 2000°C at a rate of 10°C / min. Heating was stopped after maintaining the temperature at 2000°C for 4 hours, and the furnace was allowed to cool naturally. The furnace was then turned on once the temperature dropped below 100°C.

[0070] <Pyrolysis Process>

[0071] The recovered calcined material was pulverized in an alumina mortar for 3 minutes, and coarse powder was removed from the obtained dry powder using an ultrasonic vibrating screen (KFS-10000, manufactured by Xinghe Industrial Co., Ltd., with a mesh size of 250μm) to obtain the hexagonal boron nitride powder of Example 1.

[0072] [Determination of physical properties of hexagonal boron nitride powder]

[0073] For the hexagonal boron nitride powder prepared in Example 1, the aspect ratio, oil absorption, BET specific surface area, tap density, and total oxygen content of the primary particles were evaluated using the methods described below. The results are shown in Table 1.

[0074] Aspect Ratio

[0075] The aspect ratio of primary hexagonal boron nitride particles is determined by calculating the aspect ratio (length / short diameter) using the length and short diameter of the obtained primary hexagonal boron nitride particles. Regarding the length, instead of using a molded object, hexagonal boron nitride powder is placed on a carbon ribbon on an electron microscope stage, and excess powder is removed using an air gun or similar tool. The sample is then photographed using a scanning electron microscope (JEOL Ltd., product name: JSM-6010LA). The resulting particle image is loaded into image analysis software (Mountech Ltd., product name: Mac-View), and the longer side (equivalent to the particle's length) is calculated from the photograph. This length is then combined with the short diameter to calculate the aspect ratio (length / short diameter). Regarding the particle short diameter, 3g of hexagonal boron nitride powder was first molded into a disc shape (diameter: 30mmφ) under a pressure of 5MPa using a compression molding machine (Rigaku Co., Ltd., trade name: BRE-32). The resulting molded body was then embedded in resin (GATAN Co., Ltd., trade name: G2 Epoxy). Next, the cross-section was ground in a direction parallel to the applied pressure, thereby preparing a sample with the cross-section of the hexagonal boron nitride particles exposed. This cross-section was photographed using a scanning electron microscope (Nippon Electron Co., Ltd., trade name: JSM-6010LA). The resulting particle images were loaded into image analysis software (Mountech Co., Ltd., trade name: Mac-View), and the short side (particle thickness, equivalent to the particle short diameter) of the rectangular particles was determined from the obtained images. In addition, the determination of either the particle major diameter or the particle short diameter was performed on 100 randomly selected primary particles, and their arithmetic mean was used.

[0076] <Oil absorption>

[0077] The oil absorption of hexagonal boron nitride powder was determined according to the method described in JIS K 5101-13-1:2004 "Test methods for pigments - Part 13: Oil absorption - Section 1: Purified linseed oil method".

[0078] <BET surface area of ​​primary particles>

[0079] The BET specific surface area of ​​primary particles of hexagonal boron nitride was determined using the BET one-point method with nitrogen gas, according to the method described in JIS Z 8830:2013 "Method for determination of specific surface area of ​​powder (solid) by gas adsorption".

[0080] <Tap density>

[0081] Regarding tap density, according to JIS R 1628:1997 "Method for Determination of Bulk Density of Precision Ceramic Powders", the sample to be measured is filled into a 100cm³ container. 3 The special container was compacted under the conditions of 180 seconds of compaction time, 180 times of compaction, and 18 mm of compaction height. The volumetric density was then measured, and the obtained value was taken as the compacted density.

[0082] Total Oxygen

[0083] The total oxygen content of primary particles in hexagonal boron nitride was determined using an oxygen / nitrogen simultaneous analysis apparatus (manufactured by Horiba Manufacturing Co., Ltd., apparatus name: EMGA-920). Specifically, the hexagonal boron nitride powder was heated from 20°C to 2500°C in a helium atmosphere and the result was measured.

[0084] [Evaluation of hexagonal boron nitride powder as a raw material for cosmetics]

[0085] The hexagonal boron nitride powder prepared in Example 1 was evaluated using the following methods for its spreadability when used in cosmetics, as well as the transparency and smoothness of the cosmetic layer formed by the cosmetic.

[0086] <Evaluation of Extensibility>

[0087] At one end of an artificial skin (longitudinal × transverse = 10mm × 50mm), 0.2g of hexagonal boron nitride powder was placed in a 10mm wide area. The hexagonal boron nitride powder was applied to the surface of the artificial skin, and then spread longitudinally using a spatula. Image analysis was performed using commercially available image analysis software (WinROOF) to determine the ratio of the hexagonal boron nitride powder coating area to the total area of ​​the artificial skin. A larger ratio indicates better spreadability. Based on the results, the spreadability was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0088] A: The above-mentioned coating area accounts for more than 95%.

[0089] B: The proportion of the above-mentioned coated area is 80% or more but less than 95%.

[0090] C: The proportion of the above-mentioned coated area is more than 70% and less than 80%.

[0091] D: The proportion of the above-mentioned coated area is more than 60% and less than 70%.

[0092] E: The proportion of the above-mentioned coated area is more than 40% and less than 60%.

[0093] F: The proportion of the above-mentioned coated area is less than 40%.

[0094] <Evaluation of the transparency and smoothness of the makeup layer>

[0095] Sensory evaluations were conducted on the transparency and smoothness of the makeup layer. The evaluations were performed by 10 randomly selected professional sensory examiners (panelists). The evaluation items were defined as the transparency and smoothness of the makeup layer. The transparency and smoothness of the makeup layer formed using the hexagonal boron nitride powder obtained in Example 2 (the baseline makeup layer) were each set to "3". A result superior to the baseline makeup layer was considered "4", even better than the baseline makeup layer was considered "5", inferior to the baseline makeup layer was considered "2", and even worse than the baseline makeup layer was considered "1", with an evaluation of 5 stages. The arithmetic mean of the evaluation results from the 10 professional sensory examiners was taken as the evaluation result of the evaluated makeup layer, determined according to the following criteria. The results are shown in Table 1. Furthermore, for "transparency," the difference from the baseline makeup layer was evaluated based on whether the finished makeup layer did not appear thick and felt integrated with the skin. For "smoothness," the difference from the baseline makeup layer was evaluated based on whether the finished makeup layer felt smooth.

[0096] A: The above evaluation result is 4.5 or higher.

[0097] B: The above evaluation result is 3.5 or higher and less than 4.5.

[0098] C: The above evaluation result is 2.5 or higher and less than 3.5.

[0099] D: The above evaluation result is above 1.5 and less than 2.5.

[0100] E: The above evaluation result is less than 1.5.

[0101] (Comparative Example 1)

[0102] The calcination temperature was set at 1800℃. Otherwise, hexagonal boron nitride powder was prepared in the same manner as in Example 1. Then, the hexagonal boron nitride powder was subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0103] (Example 2)

[0104] The calcination temperature for the annealing process was set to 1800°C. Otherwise, hexagonal boron nitride powder was prepared in the same manner as in Example 1. Then, the hexagonal boron nitride powder was subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0105] (Comparative Example 2)

[0106] Hexagonal boron nitride powder was prepared in the same manner as in Example 1, except that an annealing process was not performed. Then, the hexagonal boron nitride powder was subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0107] (Comparative Example 3)

[0108] The amount of sodium carbonate added in the calcination process was set to 20 g. Otherwise, hexagonal boron nitride powder was prepared in the same manner as in Example 1. Then, the hexagonal boron nitride powder was subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 1.

[0109] [Table 1]

[0110]

[0111] Industrial availability

[0112] According to this application, the purpose is to provide a hexagonal boron nitride powder for cosmetics, which has excellent spreadability when used in cosmetics, and excellent transparency and smoothness of the cosmetic layer.

Claims

1. A hexagonal boron nitride powder for cosmetic use, comprising primary particles of hexagonal boron nitride. The aspect ratio of the primary particle is 5 to 22. The total oxygen content is 0.02–0.08% by mass. The oil absorption rate is 78-85 mL / 100g. The specific surface area of ​​BET is 2.4–2.8 m². 2 / g, The tap density is 0.20 g / cm³. 3 above.

2. The hexagonal boron nitride powder for cosmetic use according to claim 1, wherein, The tap density is 0.35 g / cm³. 3 the following.

3. A cosmetic product comprising the hexagonal boron nitride powder for cosmetic use as described in claim 1 or 2.

Images