BLACK PARTICLES AND PROCESS FOR PRODUCING BLACK PARTICLES

Abstract

The present invention provides black particles having high electrical insulation properties, high blackness in a visible light region, and excellent dispersibility, and a method for producing the black particles. The present invention relates to black particles containing amorphous carbon, the amorphous carbon being derived from carbon contained in an oxazine resin, the black particles having a specific gravity of 1.8 g/cm.sup.3 or less, a zeta potential of ?70 to +80 mV, an average total light reflectance measured at a wavelength of 400 to 800 nm of 5% or less, and a peak intensity ratio between G band and D band as determined from a Raman spectrum of 1.2 or more.

Claims

1. Black particles comprising amorphous carbon, the amorphous carbon being derived from carbon contained in an oxazine resin, the black particles having a specific gravity of 1.8 g/cm.sup.3 or less, a zeta potential of ?70 to +80 mV, an average total light reflectance measured at a wavelength of 400 to 800 nm of 5% or less, and a peak intensity ratio between G band and D band as determined from a Raman spectrum of 1.2 or more.

2. The black particles according to claim 1, wherein the black particles have an average particle size of 0.005 to 50 ?m, an average sphericity of 90% or more, and a coefficient of variation (CV value) of 20% or less.

3. The black particles according to claim 1, wherein the black particles have a volume resistivity of 1.0??.Math.cm or more.

4. The black particles according to claim 1, wherein the average total light reflectance measured at a wavelength of 400 to 800 nm is 4.5% or less.

5. The black particles according to claim 1, wherein at least one of a mass spectrum derived from a benzene ring and a mass spectrum derived from a naphthalene ring is detected in analysis of a coating layer by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

6. The black particles according to claim 1, wherein no peak is detected at a position where 2? is 26.4? in analysis of a coating layer by an X-ray diffraction method.

7. A method for producing the black particles according to claim 1, comprising the step of reacting a mixed solution containing triazine, dihydroxynaphthalene, and a solvent.

8. A method for producing the black particles according to claim 1, comprising the step of reacting a mixed solution containing formaldehyde, an aliphatic amine, dihydroxynaphthalene, and a solvent.

9. The method for producing the black particles according to claim 7, wherein the solvent consists of a single component and has a solubility parameter (SP value) of 9.0 or more and a boiling point of 150? C. or lower.

10. The method for producing the black particles according to claim 7, wherein the solvent is a mixed solvent comprising two or more solvents, the mixed solvent contains a solvent having a boiling point of 150? C. or higher, and the amount of the solvent having a boiling point of 150? C. or higher is 60 vol % or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0093] FIG. 1 is a FE-SEM image of particles obtained in Example 1.

[0094] FIG. 2 is a FE-SEM image of particles obtained in Example 2.

[0095] FIG. 3 is a FE-SEM image of particles obtained in Comparative Example 1.

[0096] FIG. 4 is a FE-SEM image of particles obtained in Comparative Example 2.

DESCRIPTION OF EMBODIMENTS

[0097] Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

Example 1

[0098] An amount of 1.20 g of 1,5-dihydroxynaphthalene (1,5-DHN, Tokyo Chemical Industry Co., Ltd.) and 0.98 g of 1,3,5-triazine (Tokyo Chemical Industry Co., Ltd.) were sequentially dissolved in 50 ml of ethanol to prepare a mixed ethanol solution.

[0099] The obtained mixed solution was then stirred (rotation frequency: 300 rpm) under heating at 80? C. for one hour. The solution was filtered through a glass filter, and the obtained particles were washed with ethanol three times and vacuum-dried at 50? C. for three hours, followed by heating at 110? C. for two hours. Thus, black carbon particles were obtained.

[0100] The mixed solution after heating at 80? C. for one hour was subjected to nuclear magnetic resonance spectroscopy (NMR spectroscopy). A peak (3.95 ppm) corresponding to the methylene group of benzene ring-CH.sub.2N and a peak (4.92 ppm) corresponding to the methylene group of OCH.sub.2N of a naphthoxazine ring were detected at almost the same intensity. This confirmed that a resin component containing a naphthoxazine ring was generated.

[0101] The nuclear magnetic resonance spectroscopy was performed with .sup.1H-NMR (600 MHz) available from Varian Inova using deuterated dimethyl sulfoxide. The number of spectral accumulations was 256, and the relaxation time was 10 seconds.

[0102] The obtained carbon particles were analyzed by Raman spectroscopy using Almega XR (Thermo Fisher Scientific K.K.). Peaks were observed at both G band and D band, indicating that the naphthoxazine resin was converted into amorphous carbon.

[0103] The peak intensity ratio between G band and D band was 1.8. The laser light had a wavelength of 530 nm.

Example 2

[0104] Black carbon particles were obtained in the same manner as in Example 1, except that 35 ml of ethanol and 15 ml of N,N-dimethylformamide (DMF) were used instead of 50 ml of ethanol in Example 1 and the stirring under heating was performed at 80? C. for six hours. The heating temperature after drying was 200? C.

Example 3

[0105] Black carbon particles were obtained in the same manner as in Example 1, except that 20 ml of ethanol and 30 ml of N,N-dimethylformamide (DMF) were used instead of 50 ml of ethanol in Example 1 and the stirring under heating was performed at 80? C. for six hours. The heating temperature after drying was 350? C.

Example 4

[0106] An amount of 0.012 g of 1,5-dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd.), 0.006 g of 40% methylamine (Wako Pure Chemical Industries, Ltd.), and 0.012 g of a 37% formaldehyde aqueous solution (Wako Pure Chemical Industries, Ltd.) were sequentially dissolved in 50 ml of ethanol to prepare a mixed ethanol solution.

[0107] The obtained mixed solution was treated in an ultrasonic bath at 50? C. for two hours (ultrasonic frequency: Hz). The solution was then filtered through a glass filter, and the obtained particles were washed with ethanol three times. The recovered particles were vacuum-dried at 50? C. for three hours and then subjected to heat treatment at 110? C. for two hours. Thus, black carbon particles were obtained.

Comparative Example 1

[0108] Carbon particles were obtained in the same manner as in Example 1, except that 50 ml of DMF was used instead of 50 ml of ethanol in Example 1 and the stirring under heating was performed at 80? C. for six hours. The heating temperature after drying was 110? C.

Comparative Example 2

[0109] Carbon particles were obtained in the same manner as in Example 1, except that 15 ml of ethanol and 35 ml of DMF were used instead of 50 ml of ethanol in Example 1 and the stirring under heating was performed at 80? C. for six hours. The heating temperature after drying was 150? C.

Comparative Example 3

[0110] To 100 g of pure water was added 12.3 g of a formaldehyde solution (37% by weight). Then, to the mixture was added 9 g of resorcinol (m-dihydroxybenzene) under stirring. To the solution was further added 0.45 g of sodium carbonate, and the mixture was allowed to react at 50? C. for five hours. The obtained product was subjected to filtering and washing, and then dried in vacuum in a vacuum dryer at 110? C., thereby obtaining carbon particles.

Comparative Example 4

[0111] Acetylene black particles (Li-400 available from DENKA) having an average particle size of about 48 nm were used.

[0112] (Evaluation Method)

[0113] (1) Average Particle Size, CV Value, Average Sphericity

[0114] FE-SEM images of the particles obtained in the examples and comparative examples were analyzed using image analysis software (WINROOF available from Mitani Corporation), thereby determining the average particle size of each.

[0115] The standard deviation was calculated, and the coefficient of variation (CV value) of the particle size was calculated based on the obtained value.

[0116] The sphericity was determined based on the ratio between the smallest diameter and the largest diameter of the particle, and the average sphericity was calculated.

[0117] FIGS. 1 to 4 show FE-SEM images of Examples 1 and 2 and Comparative Examples 1 and 2. As shown in FIGS. 3 and 4, spherical particles were not obtained in Comparative Examples 1 and 2. Accordingly, Evaluations (1) to (5) and (8) were not performed.

[0118] (2) Specific Gravity

[0119] The specific gravity of the particles obtained in each of the examples and comparative examples was measured using a dry automatic pycnometer (Accupyc 11134 available from Shimadzu Corporation) (sample amount: 0.2 g).

[0120] (3) Volume Resistivity

[0121] The volume resistivity of the particles obtained in each of the examples and comparative examples was determined by measuring the volume resistance value of the particles at a load of 15 N using a powder resistivity measurement system (Mitsubishi Chemical Analytech Co., Ltd.).

[0122] (4) Total Light Reflectance

[0123] The reflection spectrum in the whole visible light region from 400 to 800 nm of the particles obtained in each of the examples and comparative examples was measured using a spectrophotometer equipped with an integrating sphere (U-4100 type available from Hitachi, Ltd.), and the average of the reflectance of each was determined.

[0124] (5) Dispersibility

[0125] The dispersibility of the particles obtained in each of the examples and comparative examples was evaluated using a centrifugal sedimentation and light transmissive type dispersion stability analyzer (LUMiSizer 612 available from L.U.M GmbH). Specifically, the particles were dispersed in a 5% aqueous solution of polyvinylalcohol (PVA) at a proportion of 5% by weight, and about 1 ml of the obtained composition was put in a glass cell for analysis. The supernatant was irradiated with light, and the integral value of the variation in the amount of the transmitted light per hour was obtained. The dispersibility was evaluated based on the following criteria.

[0126] Variation in the amount of light after one hour was 5% or less: ? (Good)

[0127] Variation in the amount of light after one hour was more than 5%: x (Poor)

[0128] (6) TOF-SIMS Analysis

[0129] For the obtained particles, whether a mass spectrum (around 77.12) derived from a benzene ring and a mass spectrum (around 127.27) derived from a naphthalene ring were present was determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS) with TOF-SIMS 5 (available from ION-TOF). The TOF-SIMS was performed under the conditions below. In order to minimize contamination due to the air or the storage casing, the sample prepared was stored in a clean casing for silicon wafer storage.

[0130] <Measurement Conditions>

[0131] Primary ion: 209Bi+1

[0132] Ion voltage: 25 kV

[0133] Ion current: 1 pA

[0134] Mass range: 1 to 300 mass

[0135] Analysis area: 500?500 ?m

[0136] Charge-up prevention: electron irradiation neutralization Random raster scan

[0137] (7) X-Ray Diffraction

[0138] Analysis was performed using an X-ray diffractometer (SmartLab Multipurpose available from Rigaku Corporation) under the following conditions.

[0139] <Analysis Conditions>

[0140] X-ray wavelength: CuK? 1.54 A, Analysis range: 2?=10? to 70?, Scanning rate: 4?/min, Step: 0.02?

[0141] For the obtained diffraction data, whether a peak was detected at a position of 20=26.4? was checked.

[0142] (8) Zeta Potential

[0143] The zeta potential of the particles was measured using a micro-electrophoresis zeta potential analyzer (MODEL 502 available from Nihon Rufuto Co., Ltd.). Specifically, a KCl aqueous solution (concentration: 0.01 M) was used as a support electrolyte, and the KCl solution containing a small amount of black particles dispersed therein was injected into a measurement cell. A voltage was applied thereto under observation using a microscope and adjusted until the particles stopped moving (became still). The potential at that time was taken as the zeta potential.

TABLE-US-00001 TABLE 1 Production step Carbon particles Heating TOF-SIMS Concentration Reaction Solvent temperature Peak measurement of 1.5-DHN temperature Reaction (vol %) after drying intensity Benzene Naphthalene (mol/L) (? C.) time (h) Ethanol DMF (? C.) Material ratio ring ring Example 1 0.15 80 1 100 0 110 Amorphous 1.8 Present Present carbon Example 2 0.15 80 6 70 30 200 Amorphous 1.5 Present Present carbon Example 3 0.15 80 6 40 60 350 Amorphous 1.3 Present Present carbon Example 4 0.0015 50 2 100 0 110 Amorphous 1.4 Present Present (Ultrasonic carbon wave) Comparative 0.15 80 6 0 100 110 Amorphous 1.1 Present Present Example 1 carbon Comparative 0.15 80 6 30 70 150 Amorphous 1.0 Present Present Example 2 carbon Comparative Produced by conventional method Amorphous 0.8 Present Absent Example 3 carbon Comparative Acetylene black particles Amorphous 0.85 Example 4 carbon Evaluation Carbon particles Average CV value Average Specific Volume Zeta Total light X-ray particle of particle sphericity gravity resistivity potential reflectance diffraction size (?m) size (%) (%) (g/cm.sup.3) (? .Math. cm) Dispersibility (mV) (%) Example 1 Not 2.1 5 98.0 1.53 >10.sup.7 ? 16 4.5 detected Example 2 Not 0.61 7 95.0 1.45 >10.sup.7 ? ?44 4.0 detected Example 3 Not 0.20 10 92.0 1.34 >10.sup.7 ? ?58 3.2 detected Example 4 Not 0.007 14 92.0 1.30 >10.sup.7 ? 78 2.5 detected Comparative Not No spherical Example 1 detected particles obtained Comparative Not No spherical Example 2 detected particles obtained Comparative Not 3.5 30 89 1.8 >10.sup.7 x ?9 10 Example 3 detected Comparative Not 0.048 25 85 1.9 .sup.0.2 x ?19.7 1.5 Example 4 detected

INDUSTRIAL APPLICABILITY

[0144] The present invention can provide black particles having high electrical insulation properties, high blackness in a visible light region, and excellent dispersibility, and a method for producing the black particles.