Metal particle for cosmetics

Abstract

Provided is a metal particle for cosmetics that causes less skin damage. This metal particle for cosmetics is a metal particle having a flat shape, and has a volume-based particle diameter D50 of 1-200 μm (inclusive) and a perimeter-to-convex-hull ratio of 0.8-1 (inclusive).

Description

Metal particles for cosmetics

[0001] Generally, the present invention relates to metal particles, and specifically to metal particles for cosmetics.

[0002] Among cosmetic raw materials, there is a metallic effect pigment containing metal particles as one of the materials that bring luster. For example, Japanese Patent Application Laid-Open No. 2010-513619 (Patent Document 1) discloses a cosmetic raw material containing a thin aluminum pigment.

[0003] Japanese Patent Application Laid-Open No. 2010-513619

[0004] However, among such thin and flat metal particles, particularly those with a small particle size may pierce the skin and cause irritation when used as a cosmetic raw material and applied to the skin. In addition, the metal particles that have pierced the skin may remain on the skin after washing off the cosmetics in some cases.

[0005] Therefore, an object of the present invention is to provide metal particles for cosmetics that can suppress skin damage.

[0006] The metal particles for cosmetics of the present invention are flat-shaped metal particles, with a volume-based particle diameter D50 of 1 μm or more and 200 μm or less, and a perimeter length envelope degree of 0.8 or more and 1 or less.

[0007] By doing so, it is possible to provide metal particles for cosmetics that can suppress skin damage.

[0008] It is a diagram schematically showing the shape of a powder funnel used for powder fluidity measurement, and is a (A) top view and a (B) front view. (A) Before the friction test, (B) After the friction test of Example 1, and (C) A microscopic photograph of the surface of artificial skin after the friction test of Comparative Example 2.

[0009] Hereinafter, the metal particles for cosmetics of the present invention will be described in detail with specific examples. Note that the present invention is not limited to the embodiments shown below, and various modifications are possible within the scope not departing from the technical idea of the present invention.

[0010] The metal particles for cosmetics of the present invention are flattened metal particles with a volume-based particle diameter D50 of 1 μm or more and 200 μm or less, and a peripheral length envelope degree of the metal particles of 0.8 or more and 1 or less. Preferably, at least a portion of the surface of the metal particles for cosmetics is coated with an inorganic oxide and / or an organic compound. Each of the components will be described in detail below.

[0011] <Metal Particles for Cosmetics> In this invention, metal particles for cosmetics refer to metal particles that can be used as raw materials for cosmetics. The cosmetics containing the metal particles for cosmetics of this invention are not limited, but for example, the metal particles for cosmetics of this invention can be mixed with other inorganic particles or other cosmetic raw materials to produce a powder-type cosmetic containing the metal particles for cosmetics of this invention. Alternatively, they can be dispersed in a hydrocarbon-based cosmetic raw material such as paraffin to produce a paste-type cosmetic containing the metal particles for cosmetics of this invention.

[0012] <Metal Particles> The metal particles for cosmetics according to the present invention may be uncoated metal particles, or at least a portion of the surface of the uncoated metal particles may be coated with an inorganic oxide and / or organic compound described later. Any metal usable in cosmetics, such as aluminum or copper, can be used as the metal, but copper is preferred. For example, if the metal particles are copper, the uncoated copper particles only need to contain copper, preferably the main component is copper, more preferably 98 wt% or more of the composition of the uncoated copper particles is copper, and even more preferably 99 wt% or more of the composition is copper. The copper content may be less than 99 wt% of the composition, as long as it does not have adverse effects on the human body when used as a cosmetic. The method for producing uncoated copper particles is not particularly limited, but those produced by atomization are preferred.

[0013] The metal particles for cosmetics of the present invention are particles with a volume-based particle size D50 of 1 μm or more and 200 μm or less. The volume-based particle size D50 of the copper particles for cosmetics of the present invention is preferably 5 μm or more, more preferably 10 μm or more. Furthermore, the volume-based particle size D50 of the copper particles for cosmetics of the present invention is preferably 200 μm or less, more preferably 50 μm or less. If the volume-based particle size D50 of the metal particles is less than 1 μm, the difference from a spherical shape becomes small, and the specific surface area becomes large, resulting in poor luster. On the other hand, if the volume-based particle size D50 of the metal particles exceeds 200 μm, the particle appearance becomes strong, and when used in cosmetics, the particles may stand out unnaturally, potentially making them unsuitable for cosmetic use. It is more preferable that the volume-based particle size D50 of the metal particles is 10 μm or more and 50 μm or less. The method for calculating the volume-based particle size D50 of the metal particles is not particularly limited and can be determined by a known particle size distribution measuring device.

[0014] The metal particles for cosmetics of the present invention have a flattened shape. Specifically, the ratio of the maximum diameter to the thickness of the metal particles in a planar field of view (maximum diameter in a planar field of view / thickness) is preferably 1.4 or more, and more preferably 8.0 or more. The ratio of the maximum diameter to the thickness of the metal particles in a planar field of view (maximum diameter in a planar field of view / thickness) is also preferably 50 or less, and more preferably 20 or less. This flattened shape makes it possible to obtain a metal pigment for cosmetics that can achieve brightness while maintaining low risk of damaging the skin.

[0015] <Ratio of Maximum Diameter to Thickness in Planar Field of View of Metal Particles (Maximum Diameter / Thickness)> The maximum diameter of flattened metal particles can be determined from the particle's volume (equivalent to a sphere) using a particle size distribution analyzer. The thickness of flattened metal particles can be determined by cutting the flattened particles using ion milling or the like while they are forced oriented, and then measuring the distance from edge to edge in the thickness direction of the particles in the image captured by an optical microscope, laser microscope, SEM, etc. Ten or more particles are randomly selected from the cross-sectional image, and the average value of the thickness of each particle is taken as the particle thickness (μm). The maximum diameter of the metal particle in the planar field of view is divided by the thickness to obtain the ratio of the maximum diameter to thickness in the planar field of view (maximum diameter / thickness).

[0016] <Circumference Envelopment Degree of Metal Particles> The circumference envelope of the metal particles of the present invention is 0.8 or more and 1 or less. The circumference envelope degree is a value that represents the ratio of the envelope circumference of the particle to the measured circumference, and the closer it is to 1, the smoother the shape of the particle is. If the circumference envelope degree is less than 0.8, the shape of the particles in a planar view becomes more complex, which can cause friction between particles and on the skin. Methods for imparting this range of circumference envelope degree to metal particles include making the surface shape of the raw material metal powder smooth, and controlling the type of auxiliary agent used when molding into a flat shape, the temperature during molding, and the time taken for molding. The circumference envelope degree is preferably 0.8 or more, and more preferably 0.9 or more. The circumference envelope degree is also preferably 1 or less.

[0017] The envelope length can be determined, for example, by image analysis of an optical microscope image or SEM image of a particle in a planar field of view using image analysis software WinROOF. In this specification, the envelope length can be determined by using image analysis software WinROOF (WinROOF2023, manufactured by Mitani Corporation) to determine the envelope circumference and the measured circumference using an image of a single particle taken with an SEM or optical microscope, and then calculating the value from these values. The measurement procedure and conditions are as follows: (Procedure 1) Take an image of a flattened particle with an SEM or optical microscope. (Procedure 2) Read the image data from Procedure 1 from WinROOF (WinROOF2023, manufactured by Mitani Corporation) according to the WinROOF (WinROOF2023, manufactured by Mitani Corporation) instruction manual. (Procedure 3) Convert the image to black and white using image processing. (Step 4) Proceed to image analysis and manipulation according to the WinROOF (WinROOF2023 manufactured by Mitani Corporation) instruction manual. Similarly, after binarization, hole filling, and noise processing, perform shape feature measurement. (Step 5) Extract the "peripheral length envelope" from the measured values. (Step 6) Measure 10 particles and average the obtained "peripheral length envelope".

[0018] The metal particles for cosmetics of the present invention preferably have at least a portion of their surface coated with an inorganic oxide and / or an organic compound. This improves the moisture resistance and heat resistance of the particles. When at least a portion of the surface of the metal particles is coated with an inorganic oxide and / or an organic compound, the metal particles for cosmetics of the present invention, with at least a portion of their surface coated, have a volume-based particle diameter D50 of 1 μm or more and 200 μm or less, and a peripheral length envelope degree of 0.8 or more and 1 or less.

[0019] <Inorganic Oxides> In the metal particles for cosmetics of the present invention, an inorganic oxide is coated on at least a portion of the surface of the metal particles, thereby preventing the outflow of metal ions and inhibiting the oxidation of the metal. The type of inorganic oxide is not particularly limited, but for example, SiO ２ , Cr ２ O ３ Al ２ O ３ These are some examples. In particular, SiO ２In terms of stability and safety, inorganic silicon compounds are preferred, and organosilicon compounds can be used as well as inorganic silicon compounds. When both inorganic silicon compounds and organosilicon compounds are used, both may be used in a single process, or each compound may be used in separate processes. Examples of organosilicon compounds include methyltriethoxysilane, methyltrimethoxysilane, tetraethoxysilane, tetramethoxysilane, tetraisopropoxysilane, and their condensates, γ-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, etc. The amount of inorganic compound coated on the surface of the metal particles is not particularly limited, but it is preferably 0.5 wt% or more of the total metal particles, and more preferably 2.0 wt% or more. If it is less than 0.5%, there is a risk of insufficient coating. Furthermore, the amount of inorganic compound coated on the surface of the metal particles is preferably 50 wt% or less of the total metal particles, and more preferably 5.0 wt% or less. Concentration exceeding 50 wt% may impair the luster of the metal.

[0020] <Organic Compounds> In the metal particles for cosmetics of the present invention, the coating of at least a portion of the surface of the metal particles with organic compounds provides an effect of suppressing the outflow of metal ions and inhibiting metal oxidation. The type of organic compound is not particularly limited, but examples include carboxylic acids such as fatty acids, imidazole compounds, thiazole compounds, and high molecular weight organic compounds, but imidazole organic compounds are preferred in terms of inhibiting oxidation. The amount of organic compound coating the surface of the metal particles is not particularly limited, but is designed based on the specific surface area of ​​the metal particles, and excess organic compounds are washed away and removed after film formation. If excess organic compounds remain, it may affect the quality of the cosmetic. This does not apply if it does not affect the quality or becomes part of the raw materials for the cosmetic. The amount of organic compound coating the surface of the metal particles is not particularly limited, but is preferably 0.01 wt% or more of the total metal particles, and more preferably 0.1 wt% or more. If it is less than 0.01%, it may result in insufficient coating. Furthermore, the amount of organic compound coating the surface of the metal particles is preferably 50 wt% or less of the total metal particles, and more preferably 5 wt% or less. Concentration exceeding 50 wt% may impair the luster of the metal.

[0021] The present invention can be summarized as follows:

[0022] (1) Flat metal particles having a volume-based particle diameter D50 of 1 μm or more and 200 μm or less, and a peripheral envelope degree of 0.8 or more and 1 or less, for use in cosmetics.

[0023] (2) The metal particle for cosmetics according to claim 1, wherein the metal is copper.

[0024] (3) Cosmetic metal particles as described in (1) or (2) above, wherein the powder flowability is 5 g or more and 10 g or less.

[0025] (4) Cosmetic metal particles according to any one of (1) to (3) above, wherein at least a portion of the surface is coated with an inorganic oxide and / or an organic compound.

[0026] (5) Cosmetics containing the metal particles for cosmetics described in any one of (1) to (4) above.

[0027] Example 1 Example 1 involved following steps 1 to 3 in order.

[0028] Step 1: 200 g of copper particles (SFR-Cu D50, manufactured by Nippon Atomize Co., Ltd., 10 μm) were used as the raw material for molding the particles. 0.5 g of fatty acid was added to 200 g of organic solvent as a grinding lubricant, and the mixture was ground and molded using a ball mill at 50 rpm for 7 hours. The mixture was then filtered by suction using a Buchner funnel and washed to prepare a paste-like, flattened copper particle sample.

[0029] Step 2: 100 g of the flattened copper particles obtained in Step 1 with organic compound coating was taken, washed with isopropyl alcohol, and then suspended in 50 mL of an antioxidant (benzone HC-1 manufactured by Yamato Kasei Co., Ltd.) diluted 100 times with deionized water. The suspended material was then filtered, the resulting filtrate was washed with isopropyl alcohol, and the material was dried in a dryer (dryer: PHH-201 manufactured by ESPEC) at 105°C for 2 hours. The isopropyl alcohol was then removed by distillation to obtain powdered flattened copper particles.

[0030] Step 3: 50 g of the flattened copper particles obtained in Step 2 with inorganic compound coating was taken, dispersed in 100 g of isopropyl alcohol, and alkylsilane was added dropwise. The mixture was then stirred for 2 hours. After that, it was filtered using a Buchner funnel and washed with isopropyl alcohol to obtain copper flakes as a paste. This was heated and dried to remove the isopropyl alcohol by distillation, and powdered flattened copper particles coated with alkylsilane were obtained.

[0031] The brightness, volume-based particle diameter D50, ratio of maximum diameter to thickness in a planar field of view (maximum diameter / thickness), perimeter envelope, powder flowability, and susceptibility to damaging artificial skin (artificial skin injury degree) of the obtained flattened copper particles were measured. The same measurement method was used in the following examples and comparative examples.

[0032] <Brightness> The brightness of the copper particles for cosmetics was measured using a multi-angle colorimeter (BYK mac i, manufactured by Tetsutani Corporation), and the L* value at 15 degrees was defined as the brightness. For the measurement sample, 1 g of the sample was mixed with 9 g of paint resin (acrylic lacquer), stirred for 120 seconds in a stirrer (Mazelstar, manufactured by Kurabo Corporation), and then coated to a thickness of 9 mils using a 9 mil doctor blade type applicator. The brightness of the copper particles for cosmetics in Example 1 was 108.50.

[0033] <Volume-based particle size D50> The volume-based particle size D50 was measured using a particle size distribution analyzer (SYNC particle size distribution and particle shape analyzer manufactured by Microtrac-Bell). The measured volume-based particle size D50 was 19.12 μm.

[0034] <Ratio of maximum diameter to thickness in a planar field of view of a particle (maximum diameter / thickness)> The particle size distribution of flattened copper particles was measured using a particle size distribution analyzer (SYNC particle size distribution and particle shape analyzer manufactured by Microtrac-Bell). Particle information was obtained from the obtained data using the analysis function of the same particle size distribution analyzer. The diameter of the particle was determined from the "volume (equivalent to a sphere)" value of the particle information, and this value was taken as the maximum diameter in a planar field of view. Specifically, the maximum diameter was determined by the following procedure: (Procedure A1) Flattened particles were measured with a particle size distribution analyzer. (Procedure A2) Measurement data was selected on the analysis screen and the "Image Analysis" button was pressed. (Procedure A3) The data tab was selected and the analysis data for all particles was displayed. (Procedure A4) The data was exported to an Excel sheet. (Procedure A5) All data in the "volume (equivalent to a sphere)" column was selected from the data list in Excel and the average value was calculated. (Procedure A6) The average diameter of the sphere was calculated from the average volume of the sphere. (Procedure A7) The obtained value was taken as the maximum diameter (μm) of the flattened copper particle in the planar field of view.

[0035] Thickness of Flattened Copper Particles The thickness of flattened copper particles was determined by cutting the flattened particles using ion milling or the like while they were forced to be oriented, and then measuring the distance from edge to edge in the thickness direction of the particles in the image captured by an optical microscope, laser microscope, SEM, etc. Specifically, the thickness was determined by the following procedure: (Procedure B1) Flattened particles were forced to be oriented in resin or the like and completely solidified. (Procedure B2) A sample piece prepared in (Procedure B1) was cut perpendicular to the orientation direction by ion milling or the like to prepare a sample for cross-sectional observation. (Procedure B3) The sample for cross-sectional observation was photographed with an optical microscope, laser microscope, or SEM. (Procedure B4) The distance from edge to edge in the thickness direction of the particles was measured using the "distance between two points" function of the analysis function of the obtained cross-sectional image. In addition to the analysis function attached to the microscope, image analysis software (e.g., WinROOF2023) can be used. In addition, by using the "distance between two points" analysis function, and by displaying a gauge when capturing a cross-sectional image, the same distance can be easily measured on the screen using a ruler as a guide. (Procedure B5) Ten or more particles were randomly selected from the cross-sectional image, and the operation in (Procedure B4) was performed for each particle. The average of these values ​​was taken as the particle thickness (μm).

[0036] The ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar field of view was calculated by dividing the maximum diameter in the planar field of view of the copper particles obtained in steps A1 to A7 by the thickness of the copper particles obtained in steps B1 to B5. The ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar field of view of the copper particles in Example 1 was 12.7.

[0037] <Peripheral Length Envelopment> The peripheral length envelope was measured using WinROOF (WinROOF2023, manufactured by Mitani Corporation). The measured peripheral length envelope was 0.80.

[0038] <Powder Flowability> Powder flowability was measured as follows. The outlet of the powder funnel (powder funnel (PP) manufactured by AS ONE Corporation) shown in Figure 1 was closed with a glass plate, 10 g of sample copper powder was placed on top of the powder funnel (powder funnel (PP) manufactured by AS ONE Corporation), and the outlet was opened all at once within 10 seconds. After 1 minute, the weight of the copper powder that flowed out was taken as the measured value. The measurement was repeated 10 times, and the average value of the measured values ​​from each time was taken as the powder flowability (g). For evaluation of powder flowability, 5 g or more was rated as A, and less than 5 g was rated as B. If the powder flowability value is 5 g or more, it means that at least all of the powder in the volume directly above the outlet of the funnel has flowed out, and the flowability can be evaluated as good. The powder flowability value of the flattened copper particles in Example 1 was 9.82, and the evaluation was A.

[0039] <Artificial Skin Injury Resistance> The susceptibility of the artificial skin to injury was measured as follows: 0.5 mL of copper particles were placed at a single point on the artificial skin (AS ONE training model (NaviTrain) single-layer skin suture model sheet). A spherical indenter (1 mm in diameter) of a friction tester (Tribogear, manufactured by Shinto Kagakusha) was placed so as to align with the center of the copper particles. Starting from this point, friction was applied over a distance of 10 cm in a straight line under conditions of a load of 50 g and a speed of 100 mm / min. Afterwards, the surface of the friction-treated artificial skin was washed without friction using hand soap (Biore U Foaming Hand Soap), and the copper powder was washed away with a stream of water. The surface roughness of the artificial skin was then measured at a position 50 mm away in a straight line from the starting point where the indenter of the friction tester was placed.

[0040] Surface roughness was measured non-contact using a laser microscope (Keyence VK-X3000 laser microscope). The measurement was performed under conditions of zoom 1.0 and objective lens 10x. The cutoff values ​​were S-filter 5 μm, L-filter 0.1 mm, F-operation not used, processed with a Gaussian filter, and the entire field of view at a measurement magnification of 10x was used as the evaluation area, with the parameter Vvv (mL / m³) according to ISO 25178. ２ ) and Vmp (mL / m³) ２)(The sum was obtained, and the value obtained by dividing this sum by the measured area was subtracted from the value of the surface roughness of the artificial skin surface in the initial state calculated in the same manner in advance. The test and measurement were performed 5 times, and the average was obtained. This average value was defined as the "degree of injury". For the evaluation of the degree of injury, a value of 0.2 or less was rated as A, and a value exceeding 0.2 was rated as B. If the degree of injury was 0.2 or less, the wound on the artificial skin could not be visually recognized, and if the degree of injury exceeded 0.2, the wound on the artificial skin could be visually recognized. The value of the degree of injury of the flat copper particles in Example 1 was 0.14, and the evaluation was A.)

[0041] Example 2 Paste-like copper particles obtained by molding and washing copper particles in the same manner as in Steps 1 and 2 of Example 1 were washed with isopropyl alcohol and then dried in a dryer (dryer: PHH-201 manufactured by ESPEC) at 105 °C for 3 h to distill off isopropyl alcohol, thereby obtaining powdery flat copper particles. The brightness of the obtained flat copper particles was 109.56, the volume-based particle diameter D50 was 17.71 μm, the ratio of the maximum diameter to the thickness in the planar view (maximum diameter / thickness) was 12.3, the perimeter length envelope was 0.80, the fluidity value of the powder was 5.69, and the artificial skin injury degree was 0.01.)

[0042] Example 3 Flat copper particles were obtained in paste form in the same manner as in Step 1 of Example 1. In Step 3 of Example 1, instead of taking 50 g of the flat copper particles coated with the organic compound obtained in Step 2, 50 g of the uncoated paste-like copper particles that had not undergone Step 2 was taken as the particle content, and the surface was coated with an alkylsilane in the same manner as in Step 3 of Example 1. The brightness of the obtained flat copper particles was 106.09, the volume-based particle diameter D50 was 18.12 μm, the ratio of the maximum diameter to the thickness in the planar view (maximum diameter / thickness) was 12.7, the perimeter length envelope was 0.90, the fluidity value of the powder was 9.90, and the artificial skin injury degree was 0.07.)

[0043] Example 4: Except for using copper flakes E3 manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. as the raw material copper particles, powdery flattened copper particles coated with an alkylsilane on the surface were obtained in the same manner as in step 2 and subsequent steps of Example 1. The brightness of the obtained flattened copper particles was 116.53, the volume-based particle size D50 was 55.5 μm, the ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar view was 41.2, the perimeter length envelope was 0.80, the fluidity value of the powder was 6.80, and the artificial skin injury degree was 0.15.

[0044] Example 5: Except for using copper flakes 2L3 manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. as the raw material copper particles, powdery flattened copper particles coated with an alkylsilane on the surface were obtained in the same manner as in Example 4. The brightness of the obtained flattened copper particles was 89.23, the volume-based particle size D50 was 6.7 μm, the ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar view was 6.9, the perimeter length envelope was 0.8, the fluidity value of the powder was 5.50, and the artificial skin injury degree was 0.18.

[0045] Example 6: Using copper powder CB-0500 manufactured by Mitsui Chemicals, Inc. as the raw material copper particles, powdery flattened copper particles coated with an alkylsilane on the surface were obtained in the same manner as in Example 1. The brightness of the obtained flattened copper particles was 89.03, the volume-based particle size D50 was 9.1 μm, the ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar view was 9.1, the perimeter length envelope was 0.8, the fluidity value of the powder was 6.80, and the artificial skin injury degree was 0.18.

[0046] Comparative Example 1: Except for making the processing time of the grinding and molding in step 1 three times (21 hours), flattened copper particles with a coating were obtained in the same manner as in Example 1. The brightness of the obtained flattened copper particles was 104.68, the volume-based particle size D50 was 34.55 μm, the ratio of the maximum diameter to the thickness (maximum diameter / thickness) in the planar view was 54.7, the perimeter length envelope was 0.70, the fluidity value of the powder was 0.00, and the artificial skin injury degree was 0.45.

[0047] Comparative Example 2 Uncoated flat copper particles were obtained in the same manner as in Example 1, except that the raw material copper particles were changed (manufactured by Nippon Atomize Co., Ltd. (HXR-Cu, D50 2.5 μm)) and the grinding and molding processing time in Step 1 was tripled (21 hours). This copper particle sample was washed with isopropyl alcohol, and in Step 3 of Example 1, instead of taking 50 g of flat copper particles coated with the organic compound obtained in Step 2, 50 g of uncoated copper particles that had not gone through Step 2 were taken, and flat copper particles coated with alkylsilane on the surface were obtained in the same manner as in Step 3 of Example 1. The brightness of the obtained flat copper particles was 100.11, the volume-based particle diameter D50 was 19.44 μm, the ratio of maximum diameter to thickness in a planar field of view (maximum diameter / thickness) was 130.6, the perimeter envelopeness was 0.40, the powder fluidity value was 0.00, and the artificial skin injury degree was 3.35.

[0048] Comparative Example 3 Using the same raw materials as Comparative Example 2, flat copper particles without coating were obtained in the same manner as in Step 1 of Example 1, except that the grinding and molding process time in Step 1 of Example 1 was tripled (21 hours). After washing this copper particle sample with isopropyl alcohol and distilling off the isopropyl alcohol at room temperature, in Step 3 of Example 1, instead of taking 50 g of flat copper particles coated with the organic compound obtained in Step 2, 50 g of uncoated copper particles that had not gone through Step 2 were taken, and flat copper particles coated with alkylsilane on the surface were obtained in the same manner as in Step 3 of Example 1. The brightness of the obtained flat copper particles was 73.33, the volume-based particle diameter D50 was 18.36 μm, the ratio of maximum diameter to thickness in a planar field of view (maximum diameter / thickness) was 106.8, the perimeter envelopeness was 0.60, the powder fluidity value was 0.08, and the artificial skin injury degree was 4.32.

[0049] Comparative Example 4 Flattened copper particles coated with alkylsilane were obtained in the same manner as in Example 1, except that EFC-20 (D50 of 0.56 μm) manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd. was used as the raw material copper particles. The obtained flattened copper particles had a brightness of 51.25, a volume-based particle diameter D50 of 1.0 μm, a ratio of maximum diameter to thickness (maximum diameter / thickness) in a planar field of view of 1.1, a peripheral envelopment degree of 0.50, a powder fluidity value of 0.00, and an artificial skin injury degree of 0.77.

[0050] Comparative Example 5: Flattened copper particles in powder form coated with alkylsilane were obtained in the same manner as in Example 1, except that copper powder Cu-B manufactured by Nippon Atomize Processing Co., Ltd. was used as the raw material copper particles, and the grinding and molding time was 21 hours. The obtained flattened copper particles had a brightness of 122.34, a volume-based particle diameter D50 of 203.4 μm, a ratio of maximum diameter to thickness (maximum diameter / thickness) in a planar field of view of 253.4, a peripheral envelopment degree of 0.2, a powder fluidity value of 3.98, and an artificial skin injury degree of 3.24.

[0051] Table 1 shows the volume-based particle size D50, periphery envelope, fluidity, artificial skin injury severity, and evaluation for Examples 1-6 and Comparative Examples 1-5.

[0052]

[0053] Figure 2 also shows micrographs of the surface of the artificial skin (A) before the friction test, (B) after the friction test of Example 1, and (C) after the friction test of Comparative Example 2. The surface condition of the artificial skin was photographed using a Keyence VK-X3000 laser microscope.

[0054] As shown in Table 1, all of the copper particles for cosmetics in Examples 1-3 and Comparative Examples 1-3 obtained sufficient brightness to impart a metallic effect to cosmetics. On the other hand, fluidity and artificial skin damage (see also Figure 2) were well evaluated for Examples 1-3, but not so well for Comparative Examples 1-3.

[0055] As shown in the results above, the copper particles for cosmetics of the present invention were able to suppress skin damage.

[0056] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description and includes all variations within the meaning and scope equivalent to the claims.

Claims

1. Flat-shaped metal particles having a volume-based particle diameter D50 of 1 μm or more and 200 μm or less, and a peripheral envelope degree of 0.8 or more and 1 or less, for use in cosmetics.

2. The metal particle for cosmetics according to claim 1, wherein the metal is copper.

3. Cosmetic metal particles according to claim 1, wherein the powder fluidity is 5 g or more and 10 g or less.

4. Cosmetic metal particles according to claim 1, wherein at least a portion of the surface is coated with an inorganic oxide and / or an organic compound.

5. A cosmetic comprising the metal particles for cosmetic use described in any one of claims 1 to 4.

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