MODIFIED BORON NITRIDE POWDER

Abstract

A boron nitride powder having a voltage density of not less than +1 V/g as measured by a triboelectric charging test.

Claims

1. A modified boron nitride powder having a voltage density of not less than +1 V/g as measured by a triboelectric charging test.

2. The modified boron nitride powder according to claim 1, having a voltage density of not less than +10 V/g as measured by a triboelectric charging test.

3. The modified boron nitride powder according to claim 1, having an avalanche energy of not more than 40 mJ/kg.

4. The modified boron nitride powder according to claim 1, containing primary particles with an average long diameter in a range of 2 to 20 μm, an average thickness in a range of 0.2 to 2.0 μm, and an average aspect ratio in a range of 5 to 20.

5. The modified boron nitride powder according to claim 1, for use as a compounding agent for cosmetics.

6. A method for modifying a boron nitride powder, comprising: heat treating a negatively triboelectrically charged boron nitride powder under a flow of an inert gas at a temperature of 1300° C. to 2200° C. until it has a voltage density of not less than +1 V/g as measured by a triboelectric charging test.

7. The method according to claim 6, wherein the heat treatment is performed until the negatively triboelectrically charged boron nitride powder has a voltage density of not less than +10 V/g as measured by the triboelectric charging test.

8. The method according to claim 6, wherein the heat treatment is performed while the negatively triboelectrically charged boron nitride powder is fluidized under the flow of the inert gas.

Description

EXAMPLES

[0077] Hereinafter, the present invention will be described in more detail by way of Examples; however, the present invention is not limited to these Examples.

[0078] In Examples and Comparative Examples below, various tests and measurements were performed in the following manner.

(1) Average Long Diameter, Average Thickness, Aspect Ratio

[0079] 10 parts by mass of a boron nitride powder was dispersed in 100 parts by mass of an epoxy resin (EA E-30CL manufactured by Henkel Japan Ltd.) The resultant resin composition was defoamed under reduced pressure, and poured into a 10×10 mm mold with a thickness of 1 mm, followed by curing at a temperature of 70° C.

[0080] Then, the cured resin composition was removed from the mold, and subjected to polish both surfaces so that the both surfaces were parallel to each other. Thereafter, one of the surfaces perpendicular to the direction of the thickness of the resin composition was subjected to cross section milling at its center, and an image of the milled surface was taken with a SEM at a magnification of 2500.

[0081] From among the obtained images, 100 boron nitride particles were randomly chosen, and the long side (=long diameter) and the short side (=thickness) of the particles were measured in consideration of the magnification, and their average values, i.e., the average long diameter (μm) and the average thickness (μm), were calculated. Further, the aspect ratio (average long diameter/average thickness) was calculated based on these average values.

(2) Median Diameter (D1: μm)

[0082] 0.3 g of a boron nitride powder was put in 50 cc of ethanol to prepare a boron nitride suspension. For this boron nitride suspension, the particle size distribution was measured by a laser diffraction scattering type particle size distribution measurement device (LA-950V2 manufactured by HORIBA, Ltd.) The obtained volume-based average particle diameter (D.sub.50) was defined as the median diameter (D1).

(3) Median Diameter (D2: μm)

[0083] 0.3 g of a boron nitride powder, together with 50 cc of ethanol, was put into a screw tube bottle with a capacity of 100 cc and a diameter of 4 cm to prepare a boron nitride suspension. A probe with a diameter of 0.2 cm was submerged in the water to a depth of 1 cm, and emitted ultrasonic waves at 100 W output power at room temperature for 20 minutes. For this boron nitride suspension, the particle size distribution was measured in the same manner as for the median diameter (D1). The obtained volume-based average particle diameter (D.sub.50) was defined as the median diameter (D2).

(4) Whiteness, Redness, Yellowness in Lab Color System

[0084] Whiteness (L value), redness (a value), and yellowness (b value) were measured by using ZE 6000 manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.

[0085] The measurement was performed by filling a quartz glass cell having a diameter of 30 mm and a height of 13 mm with a boron nitride powder.

(5) Light Bulk Density, Tapped Bulk Density

[0086] Light bulk density (g/cm.sup.3) and tapped bulk density (g/cm.sup.3) were measured by using Tap Denser KYT-5000 manufactured by SEISHIN ENTERPRISE Co., Ltd.

[0087] The measurement was performed under the following conditions: a sample cell of 100 ml, a tap speed of 120 times/min, a tap height of 5 cm, and a tapping frequency of 500 times.

(6) Amount of Eluted Boron

[0088] Eluted boron was extracted in a manner in accordance with the Japanese Standards of Quasi-drug Ingredients 2006, and the amount (ppm) of boron was measured by using an ICP optical emission spectrometer.

[0089] More specifically, 2.5 g of a boron nitride powder was put in a Teflon (registered trademark) beaker, to which 10 mL of ethanol was added and stirred well. Further, 40 mL of water was added and stirred well, followed by heating at 50° C. for 1 hour with a Teflon (registered trademark) watch glass placed over the beaker.

[0090] The resultant on the watch glass was cooled, followed by filtration. A residue was washed with a small amount of water, and the wash liquid and the filtrate were mixed together. The mixed liquid was further filtered through a membrane filter (0.22 μm). The entire filtrate was put in a Teflon (registered trademark) beaker, to which 1 mL of sulfuric acid was added, followed by boiling on a hot plate for 10 minutes.

[0091] The resultant liquid was cooled and then put in a polyethylene measuring flask. The Teflon (registered trademark) beaker was washed with a small amount of water, which was then added to the polyethylene measuring flask, and water was added thereto to make exactly 50 mL. The thus-obtained sample solution was subjected to measurement of the amount of boron contained therein by using an ICP optical emission spectrometer.

(7) Voltage Density (V/g)

[0092] A triboelectric charging test was performed by using, as a rotating drum type powder flowability measurement device, REVOLUTION manufactured by Mercury Scientific Inc., thereby measuring voltage density (V/g).

[0093] More specifically, 100 cc of a boron nitride powder was put in a standard rotating drum and destaticized by an ionizer. Then, the charge amount (V) of the boron nitride powder was measured while the rotating drum was rotating at a rotation frequency of 10 rpm for 300 seconds.

[0094] The charge amount (V) varies extremely unstably immediately after the rotating drum starts rotating. In light of this, the average of stable charge amounts (V) while the rotating drum was rotating for 200 to 300 seconds was calculated. This average value was divided by the weight (g) of the boron nitride powder put in the rotating drum to obtain voltage density (V/g).

[0095] The standard rotating drum has the shape of a cylinder with an inner surface made of alumite treated aluminum, includes windows made of boron silicate glass on both surfaces of the cylinder, and has a capacity of 332 cc.

(8) Avalanche Energy

[0096] A flowability test was performed by using the powder flowability measurement device as used for measuring the charge density, thereby measuring avalanche energy (mJ/kg).

[0097] More specifically, 100 cc of a boron nitride powder was put in the standard rotating drum and destaticized by an ionizer. Then, the avalanche energy (change in potential energy before and after an avalanche) (mJ/kg) of the boron nitride powder generated when the rotating drum was rotated at a rotation frequency of 0.3 rpm was measured. Here, the average of the measured values for 150 avalanches was defined as the avalanche energy (mJ/kg).

(9) Height of Powder Layer in Fluidization Test

[0098] A fluidization test was performed by using the powder flowability measurement device, thereby measuring the height (cm) of the powder layer.

[0099] More specifically, 100 cc of a boron nitride powder was put in the standard rotating drum and destaticized by an ionizer. Then, the height (cm) (of a lower portion) of the powder layer was measured when the rotating drum was rotated at predetermined rotation frequencies (20, 50 rpm).

[0100] The height (cm) of the powder layer, which is an indicator of the fluidizability of the powder, tends to be larger when the powder is more easily fluidized.

[0101] The results of Examples are summarized in Tables, in which “*” indicates that the height of the powder was not measured correctly because the voltage density was so high that the powder was charged and adhered to the wall surface of the drum.

(10) Basic Flowability Energy in Dynamic Flowability Test

[0102] A dynamic flowability test was performed by using FT-4 Powder Rheometer manufactured by Malvern Instruments Ltd., thereby measuring basic flowability energy (mJ).

[0103] More specifically, a 160 mL split container with a height of 89 mm on which a cylinder with a height of 51 mm was placed was filled with a boron nitride powder to a height of more than 89 mm, which was then conditioned (a blade was operated at a tip speed of 60 mm/sec and an approach angle of 5°) for four times. Thereafter, the cylinder placed on the split container was slid to level off the boron nitride powder.

[0104] Then, torque (mJ) acting on the blade was measured while it was moving at a tip speed of 100 mm/sec and an approach angle of −5° from a height of 100 mm to 10 mm from the bottom surface of the container. The torque value was defined as the basic flowability energy (mJ). The basic flowability energy (mJ), which is an indicator of the flowability of the powder, tends to be smaller when the powder was more flowable.

Example 1

[0105] A mixture was prepared in accordance with the following formulation by using a ball mill: [0106] 70 g of boron oxide, [0107] 30 g of carbon black, and [0108] 10 g of calcium carbonate.

[0109] This mixture was placed in a graphite Tammann furnace and heated to a temperature of 1500° C. at 15° C./min in a nitrogen gas atmosphere. The mixture was kept at 1500° C. for 6 hours, followed by a reduction nitridation treatment. Then, the resultant mixture was heated to a temperature of 1800° C. at 15° C./min and kept at 1800° C. for 2 hours, followed by a crystallization treatment, thereby obtaining a crude hexagonal boron nitride powder.

[0110] Then, the thus-obtained crude hexagonal boron nitride powder was introduced into a polyethylene container, to which an aqueous hydrochloric acid solution (HCl of 10 mass %) was added in an amount 10 times as much as that of the crude hexagonal boron nitride, and stirred at a rotation frequency of 300 rpm for 15 hours.

[0111] After the acid washing as above, the acid was filtered. Then, the resultant powder was washed again with 300 times as much pure water as the introduced crude hexagonal boron nitride powder, the pure water having a specific resistance of 1 MΩ.Math.cm at 25° C. Then, the powder was dehydrated by suction filtration until the filtered powder had a moisture content of not more than 50 mass %.

[0112] The powder obtained after being washed with the pure water was dried under a reduced pressure of 1 kPaA at 200° C. for 15 hours, resulting in a white boron nitride powder. This boron nitride powder was lumpy.

[0113] A carbon container (inner diameter: 400 mm; inner height: 50 mm) with a surface coated with boron nitride was filled with the thus-obtained boron nitride powder. The boron nitride powder was filled at a density of 0.20 g/cm.sup.3 to a height of 45 mm. These containers were stacked in ten stages and placed in a graphite Tammann furnace with an inner capacity of 1,000 L, into which a nitrogen gas was fed in an amount of 40 L (volume at 25° C.)/min. Then, the boron nitride powder was heated to a temperature of 1500° C. at 15° C./min and kept at 1500° C. for 4 hours, whereby the boron nitride powder was modified. The modified boron nitride powder obtained after being cooled was less lumpy.

[0114] Each of the carbon containers includes a nitrogen flow channel between the respective stages of the containers to allow nitrogen to flow above the powder layer.

[0115] The thus-obtained modified boron nitride powder was subjected to the above-described measurements (1) to (10). Table 1 shows the conditions of producing and modifying the boron nitride powder, and Table 3 shows the results of the measurements.

[0116] In Table 1, “Maximum temperature” in the section on “Reduction nitridation” refers to the maximum temperature during the entire reduction nitridation process including the crystallization process after the reduction nitridation reaction. The same applies to Tables 2 and 5 below. In Tables 1 and 2, “x” in the section on “Fluidization” represents that the inert gas was fed in a state where the powder to be modified was not fluidized but left to stand. Further, “o” in Table 2 represents that the modification treatment was performed in a fluidized bed.

[0117] Further, the modified boron nitride powder was examined visually as to how lumpy the powder was. Table 3 also shows the results of evaluation by means of the following criteria. The same applies to Table 6. [0118] o: Fluffy with few lumps [0119] Δ: Fluffy with a slight amount of lumps [0120] x: Heavy in texture with a large amount of lumps

Examples 2-7, 11, Comparative Examples 1-6

[0121] Modified boron nitride powders were prepared in the same manner as in Example 1, except that the following conditions were altered: the proportion of calcium carbonate, the maximum temperature and maximum temperature holding time during the crystallization after the reduction and nitridation, the filling density of the powder in the modification treatment (heat treatment), the type and flow amount of the inert gas, the treatment temperature, and the temperature holding time.

[0122] Tables 1 and 2 show the conditions of producing and modifying the boron nitride powders in the Examples, and Tables 3 and 4 show the results of the measurements. Table 5 shows the conditions of producing and modifying the boron nitride powders in the Comparative Examples, and Table 6 shows the results of the measurements.

Example 8

[0123] A crude hexagonal boron nitride powder was obtained in the same manner as in Example 1.

[0124] Then, the obtained crude hexagonal boron nitride powder was introduced into a polyethylene container, to which an aqueous hydrochloric acid solution (HCl of 10 weight %) was added in an amount 10 times as much as that of the crude hexagonal boron nitride, and stirred at a rotation frequency of 300 rpm for 15 hours. After the acid washing as above, the acid was filtered. Then, the resultant powder was washed again with 300 times as much pure water as the introduced crude hexagonal boron nitride powder, the pure water having a specific resistance of 1 MΩ.Math.cm at 25° C. Then, the powder was dehydrated by suction filtration until the filtered powder had a moisture content of not more than 50 weight %.

[0125] The powder obtained after being washed with the pure water was dried under a reduced pressure of 1 kPaA at 200° C. for 15 hours, resulting in a white boron nitride powder. This boron nitride powder was lumpy.

[0126] In order to understand the gas flow velocity required to fluidize the boron nitride powder, a ventilation test was performed by using a powder flowability measurement device, REVOLUTION manufactured by Mercury Scientific Inc. The ventilation test was performed in the same manner as the dynamic flowability test described in section (10) above, except that air was supplied from the bottom of the 160 mL split container. Torque (mJ) acting on the blade was measured as the air flow velocity was gradually increased. A small torque change represents the fluidization start flow velocity (mm/sec), which was 3.0 mm/sec for this boron nitride powder.

[0127] Next, a carbon container (inner diameter: 150 mm; inner height: 600 mm) with a surface coated with boron nitride was filled with 600 g (about 5 L) of the boron nitride powder. At the bottom of the container, there is a gas supply port, through which a gas is supplied into the container via a porous plate and then discharged from the top of the container.

[0128] The container filled with the boron nitride powder was placed in a graphite Tammann furnace. While a nitrogen gas was fed into the container in an amount of 0.6 L (volume at 25° C.)/min, the boron nitride powder was heated to a temperature of 1300° C. at 15° C./min and kept at 1300° C. for 4 hours (the nitrogen flow velocity at 1300° C. was 3.0 mm/sec), whereby the boron nitride powder was modified. The modified boron nitride powder obtained after being cooled was fluffy with no lumps.

[0129] Table 2 shows the conditions of producing and modifying the boron nitride powder, and Table 4 shows the results of the measurements.

Examples 9, 10

[0130] Modified boron nitride powders were obtained in the same manner as in Example 8, except that the type and flow amount of the inert gas, and the treatment temperature were altered as shown in Table 2. Table 4 shows the results of the measurements of the modified boron nitride powders.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Raw material Boron oxide (g) 70 70 70 70 70 70 Carbon black (g) 30 30 30 30 30 30 Calcium carbonate (g) 10 10 10 10 10 10 Reduction Maximum temperature 1800 1800 1800 1800 1800 1800 nitridation (° C.) Maximum temperature 2 2 2 2 2 2 holding time (hr) Heat Filling density (g/cm.sup.3) 0.20 0.20 0.20 0.20 0.20 0.20 treatment Type of inert gas Nitrogen Nitrogen Nitrogen Nitrogen Argon Argon Gas flow amount 40 40 10 40 40 40 (L/min) Fluidization x x x x x x Treatment 1500 1800 1300 2000 1400 1800 temperature (° C.) Temperature holding 4 4 1 10 4 4 time (hr)

TABLE-US-00002 TABLE 2 Example 7 Example 8 Example 9 Example 10 Example 11 Raw material Boron oxide (g) 70 70 70 70 70 Carbon black (g) 30 30 30 30 30 Calcium carbonate (g) 10 10 10 10 20 Reduction Maximum temperature 1800 1800 1800 1800 1900 nitridation (° C.) Maximum temperature 2 2 2 2 3 holding time (hr) Heat Filling density (g/cm.sup.3) 0.20 0.12 0.12 0.12 0.40 treatment Type of inert gas Argon Nitrogen Nitrogen Argon Nitrogen Gas flow amount 40 0.6 0.5 0.5 40 (L/min) Fluidization x ∘ ∘ ∘ x Treatment 20000 1300 1800 1800 1800 temperature (° C.) Temperature holding 10 1 1 1 4 time (hr)

TABLE-US-00003 TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Average long diameter (μm) 4.3 4.0 4.1 4.2 4.2 4.2 Average thickness (μm) 0.6 0.6 0.6 0.6 0.6 0.6 Aspect ratio 7.2 6.7 6.8 7.0 7.0 7.0 Median diameter D1 (μm) 26 26 25 27 26 25 Median diameter D2 (μm) 6.9 7.6 7.0 7.2 7.1 7.2 Light bulk density (g/cm.sup.3) 0.10 0.08 0.10 0.07 0.09 0.08 Tapped bulk density (g/cm.sup.3) 0.31 0.28 0.32 0.23 0.30 0.27 Amount of eluted boron (ppm) 19 18 20 15 20 18 Whiteness (L value) 99.6 99.1 99.0 99.3 99.2 96.7 Redness (a value) −0.2 −0.3 −0.2 −0.1 −0.1 −1.6 Yellowness (b value) 0.4 1.3 1.0 0.9 0.5 8.2 Voltage density (V/g) +32 +40 +11 456 +22 442 Avalanche energy (mJ/kg) 30 27 37 24 31 26 Height of Rotation 3.4 3.7 2.5 * 3.2 3.5 powder layer frequency 20 rpm (cm) Rotation 4.2 4.7 3.0 * 3.9 4.6 frequency 50 rpm Basic flowability energy (mJ) 81 77 88 76 80 79 Development of lumps ∘ ∘ ∘ ∘ ∘ ∘ (visual examination)

TABLE-US-00004 TABLE 4 Example 7 Example 8 Example 9 Example 10 Example 11 Average long diameter (μm) 4.3 4.0 4.1 4.1 9.2 Average thickness (μm) 0.6 0.6 0.6 0.6 1.1 Aspect ratio 7.2 6.7 6.8 6.8 8.3 Median diameter D1 (μm) 27 23 22 23 30 Median diameter D2 (μm) 7.2 6.6 6.7 6.7 10.4 Light bulk density (g/cm.sup.3) 0.07 0.08 0.07 0.07 0.17 Tapped bulk density (g/cm.sup.3) 0.25 0.22 0.23 0.22 0.55 Amount of eluted boron (ppm) 16 20 17 17 10 Whiteness (L value) 95.8 99.5 99.4 93.6 99.3 Redness (a value) −2.8 −0.2 −0.1 −1.5 −0.1 Yellowness (b value) 12.3 0.6 0.8 14.1 0.8 Voltage density (V/g) +53 +38 +59 +57 +43 Avalanche energy (mJ/kg) 25 23 21 22 24 Height of Rotation * 3.6 * * 3.8 powder layer frequency 20 rpm (cm) Rotation * 4.7 * * 4.6 frequency 50 rpm Basic flowability energy (mJ) 74 75 72 69 79 Development of lumps ∘ ∘ ∘ ∘ ∘ (visual examination)

TABLE-US-00005 TABLE 5 Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Raw material Boron oxide (g) 70 70 70 70 70 70 Carbon black (g) 30 30 30 30 30 30 Calcium carbonate (g) 10 10 10 10 10 20 Reduction Maximum temperature 1800 1800 1800 1800 1800 1900 nitridation (° C.) Maximum temperature 2 2 2 2 2 3 holding time (hr) Heat Filling density (g/cm.sup.3) Not 0.20 0.20 0.20 0.20 Not treatment Type of inert gas performed Nitrogen Nitrogen Vacuum Vacuum performed Gas flow amount 40 0 0 0 (L/min) Fluidization x x x x Treatment 1200 1500 1500 1800 temperature (° C.) Temperature holding 1 4 4 4 time (hr)

TABLE-US-00006 TABLE 6 Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Average long diameter (μm) 4.0 4.1 4.1 4.2 4.1 9.2 Average thickness (μm) 0.6 0.6 0.6 0.6 0.6 1.1 Aspect ratio 6.7 6.8 6.8 7.0 6.8 8.3 Median diameter D1 (μm) 23 24 25 27 25 29 Median diameter D2 (μm) 6.7 7.0 7.0 6.8 7.3 10.1 Light bulk density (g/cm.sup.3) 0.12 0.12 0.11 0.12 0.10 0.21 Tapped bulk density (g/cm.sup.3) 0.35 0.34 0.32 0.35 0.30 0.69 Amount of eluted boron (ppm) 8 20 20 19 18 5 Whiteness (L value) 98.8 98.7 98.2 98.9 96.4 98.5 Redness (a value) −0.3 −0.2 −0.4 −0.3 −1.1 −0.2 Yellowness (b value) 1.6 1.4 2.1 1.8 4.1 1.9 Voltage density (V/g) −34 −12 −6 −4 −1 −28 Avalanche energy (mJ/kg) 48 45 45 44 42 43 Height of Rotation 1.7 1.6 2.1 1.9 2.2 1.5 powder layer frequency 20 rpm (cm) Rotation 1.9 2.1 2.6 2.5 2.8 1.8 frequency 50 rpm Basic flowability energy (mJ) 203 195 161 174 140 218 Development of lumps x x Δ Δ Δ x (visual examination)

Cosmetics Test

[0131] A powder foundation was prepared by using the modified boron nitride powder obtained in each of the Examples and Comparative Examples in accordance with the following blending proportions (here, for the modified boron nitride powder in each of Examples 6, 7, 10, and Comparative Example 5, the proportions of a red oxide of iron, a yellow oxide of iron, and a black oxide of iron were properly adjusted to prepare a powder foundation whose color was identical to that of a powder foundation using the other white boron nitride.)

TABLE-US-00007 Hexagonal boron nitride powder 20.0 mass % Mica 15.0 mass % Synthetic phlogopite 12.0 mass % Ethylhexyl methoxycinnamate 8.0 mass % (Vinyl dimethicone/methicone silsesquioxane 8.0 mass % crosspolymer) (Diphenyl dimethicone/vinyl diphenyl 8.0 mass % dimethicone/silsesquioxane crosspolymer) Nylon 12 3.0 mass % Silica 3.0 mass % Talc 3.0 mass % Acrylates crosspolymer 3.0 mass % Perfluorooctyl triethoxysilane 3.0 mass % Zinc oxide 3.0 mass % Polymethyl methacrylate polymer 3.0 mass % Silicone treated red iron oxide 1.0 mass % (red oxide of iron) Silicone treated yellow iron oxide 0.6 mass % Silicone treated black iron oxide 0.4 mass % Silicone treated titanium oxide 6.0 mass %

[0132] The obtained powder foundation was taken onto a cosmetic sponge and applied to skin. The foundation using the modified boron nitride powder visually examined as “o” in Tables 3 and 4 was spread evenly in one application, while the foundation using the modified boron nitride powder visually examined as “Δ” or “x” in Table 6 was spread unevenly in one application and had to be applied two or three times until it was spread evenly.

[0133] Further, the powder foundation using the modified boron nitride powder whose color was close to human skin tone as in Examples 6, 7, 10, and Comparative Example 5 had a more natural finish than the powder foundation using the other modified boron nitride powder with higher whiteness.