Carbon-coated vanadium dioxide particles

Abstract

A carbon-coated vanadium dioxide particle includes a vanadium dioxide particle; and a coating layer containing amorphous carbon on a surface of the vanadium dioxide particle, the amorphous carbon being derived from carbon contained in an oxazine resin, and having a peak intensity ratio of a G band to a band of 1.5 or greater as determined from a Raman spectrum. The coating layer has an average thickness of 50 nm or less. The coating layer has a coefficient of variation (CV value) of thickness of 7% or less.

Claims

1. A carbon-coated vanadium dioxide particle, comprising: a vanadium dioxide particle; and a coating layer containing amorphous carbon on a surface of the vanadium dioxide particle, wherein the amorphous carbon is derived from carbon contained in an oxazine resin, and has a peak intensity ratio of a G band to a D band of 1.5 or greater as determined from a Raman spectrum, the coating layer has an average thickness of 50 nm or less, the coating layer has a coefficient of variation (CV value) of thickness of 7% or less, and at least one of a mass spectrum derived from a benzene ring and a mass spectrum derived from a naphthalene ring is detected when the coating layer is analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the average particle size of the carbon-coated vanadium dioxide particle is 45 to 130 nm.

2. The carbon-coated vanadium dioxide particle according to claim 1, wherein no peak is detected at a position where 2 is 26.4 when the coating layer is analyzed by an X-ray diffraction method.

3. The carbon-coated vanadium dioxide particle according to claim 1, wherein the oxazine resin is a naphthoxazine resin.

4. The carbon-coated vanadium dioxide particle according to claim 1, wherein the vanadium dioxide particle has a structure represented by Formula (1):
V.sub.1-xM.sub.xO.sub.2(1), wherein M is at least one element selected from the group consisting of tungsten, molybdenum, tantalum, niobium, chromium, iron, gallium, aluminum, fluorine, and phosphorus, and x is a value of 0 to 0.05.

5. A resin composition, comprising: the carbon-coated vanadium dioxide particle according to claim 1; and a thermosetting resin.

6. A coating film comprising the resin composition according to claim 5.

7. A film, comprising: the carbon-coated vanadium dioxide particle according to claim 1; and a thermoplastic resin.

8. A bondable film, comprising the film according to claim 7 and an adhesive layer.

9. An interlayer film for laminated glass, the interlayer film comprising the film according to claim 7.

10. A laminated glass, comprising: two transparent plates; and the interlayer film for laminated glass according to claim 9 interposed between the transparent plates.

11. The carbon-coated vanadium dioxide particle according to claim 2, wherein the oxazine resin is a naphthoxazine resin.

12. The carbon-coated vanadium dioxide particle according to claim 2, wherein the vanadium dioxide particle has a structure represented by Formula (1):
V.sub.1-xM.sub.xO.sub.2(1), wherein M is at least one element selected from the group consisting of tungsten, molybdenum, tantalum, niobium, chromium, iron, gallium, aluminum, fluorine, and phosphorus, and x is a value of 0 to 0.05.

13. A resin composition, comprising: the carbon-coated vanadium dioxide particle according to claim 2; and a thermosetting resin.

14. The carbon-coated vanadium dioxide particle according to claim 3, wherein the vanadium dioxide particle has a structure represented by Formula (1):
V.sub.1-xM.sub.xO.sub.2(1), wherein M is at least one element selected from the group consisting of tungsten, molybdenum, tantalum, niobium, chromium, iron, gallium, aluminum, fluorine, and phosphorus, and x is a value of 0 to 0.05.

15. A resin composition, comprising: the carbon-coated vanadium dioxide particle according to claim 3; and a thermosetting resin.

16. A resin composition, comprising: the carbon-coated vanadium dioxide particle according to claim 4; and a thermosetting resin.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a transmission electron micrograph of a surface-coated particle according to one or more embodiments of the present invention.

(2) FIG. 2 is an electron micrograph of vanadium dioxide particles obtained in Example 3 before firing according to one or More embodiments of the present invention.

(3) FIG. 3 is an electron micrograph of vanadium dioxide particles obtained in Example 3 after firing according to one or more embodiments of the present invention.

(4) FIG. 4 is an electron micrograph of vanadium dioxide particles obtained in Comparative Example 1 after firing according to one or more embodiments of the present invention.

(5) FIG. 5 is an example of results of analysis by TOF-SIMS according to one or more embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) One or more embodiments of the present invention will be described below with reference to examples. The present invention is not limited to these examples.

Example 1

(7) (Preparation of Vanadium Dioxide Particles)

(8) To 50 mL of an aqueous dispersion containing 1.299 g of ammonium metavanadate (NH.sub.4VO.sub.3) was slowly added dropwise of a 10% aqueous hydrazine solution, and the mixture was reacted at room temperature for one hour. Thereafter, the reaction mixture was transferred into a stainless steel-made pressure-resistant vessel equipped with a fluororesin inner tube, and then reacted at 270 C. for 48 hours. After the reaction, the particles were separated from the solution by centrifugation and washed three times. The particles were then recovered by drying at 50 C. The particle size (volume average particle size) of the obtained vanadium dioxide particles was measured using a particle size distribution analyzer (Microtrac UAM-1, available from Nikkiso Co., Ltd.).

(9) (Formation of Coating Layer)

(10) In sequence, 0.1 g of 1,5-dihydroxynaphthalene (available from Tokyo Chemical Industry Co. Ltd.), 0.05 g of 40% methylamine (available from Wako Pure Chemical industries, Ltd.), and 0.1 g of a 37% aqueous formaldehyde solution (available from Wako Pure Chemical Industries, Ltd.) were dissolved into ethanol. Thus, 20 g of a mixed solution in ethanol was prepared. Subsequently, 0.2 g of the vanadium dioxide particles were added to the obtained mixed solution, and the resulting mixture was treated in an ultrasonic tank for four hours. The solution was filtrated, followed by washing of the particles three times with ethanol, and further followed by vacuum-drying of the particles at 50 C. for three hours. The drier particles were then heated at 150 C. for two hours, whereby carbon-coated vanadium dioxide particles were obtained.

(11) The surface of the vanadium dioxide particles before the heating at 150 C. for two hours 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 deposited on the surface of the particles. 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.

(12) The obtained carbon-coated vanadium dioxide particles were analyzed by Raman spectroscopy using Almega XR (available from Thermo Fisher Scientific K.K.). Peaks were observed at both the G band and the D band, indicating that the naphthoxazine ream was converted into amorphous carbon. The peak intensity ratio of the G band to the D band was 1.72. The laser light was at 530 nm.

Example 2

(13) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 1, except that vanadium dioxide particles were prepared by the method described below. The heating at 150 C. for two hours in (Formation of coating layer) of Example 1 was changed to heating at 200 C. for two hours.

(14) (Preparation of Vanadium Dioxide Particles)

(15) To 50 mL of an aqueous dispersion containing 1.299 g of ammonium metavanadate (NH.sub.4VO.sub.3) and 0.0329 g of ammonium tungstate hydrate ((NH.sub.4).sub.10W.sub.12O.sub.41.5H.sub.2O) was slowly added dropwise 4.5 mL of a 10% aqueous hydrazine solution. The mixture was reacted at room temperature for one hour. Thereafter, the reaction mixture was transferred into a stainless steel-made pressure-resistant vessel equipped with a fluororesin inner tube, and reacted at 270 C. for 48 hours. After the reaction, the particles were separated from the solution by centrifugation and washed three times. Then, vanadium dioxide particles were recovered by drying at 50 C. X-ray fluorescence analysis of the composition of the particles showed that the vanadium dioxide particles contained about 1 mol % of tungsten.

Example 3

(16) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 1, except that the vanadium dioxide particles obtained in Example 2 were used and that the coating layer was formed by the method described below.

(17) (Formation of Coating Layer)

(18) In sequence, 0.07 g of 1,5-dihydroxynaphthalene (available from Tokyo Chemical Industry Co., Ltd.), 0.03 g of 40% methylamine (available from Wako Pure Chemical industries, Ltd.), and 0.07 g of a 37% aqueous formaldehyde solution (available from Wake Pure Chemical Industries, Ltd.) were dissolved into ethanol. Thus, 20 g of a mixed solution in ethanol was prepared. Subsequently, 0.2 g of tungsten-doped vanadium dioxide particles were added to the obtained mixed solution, and the resulting mixture was treated in an ultrasonic tank for six hours. The solution was filtrated, followed by washing of the particles three times with ethanol, and further followed by vacuum-drying of the particles at 50 C. for three hours. The dried particles were then heated at 150 C. for two hours, whereby carbon-coated vanadium dioxide particles were obtained.

(19) FIG. 1 is a transmission electron micrograph of a surface-coated particle. A dense coating layer with a thickness of about 4 nm was observed on the surface. This coating layer was confirmed to be carbon by elemental analysis using an energy dispersive X-ray detector attached to the transmission electron microscope.

Example 4

(20) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 1, except that the vanadium dioxide particles obtained in Example 2 were used, and that the coating layer was formed by the method described below.

(21) (Formation of Coating Layer)

(22) In sequence, 0.5 g of 1,5-dihydroxynaphthalene (available from Tokyo Chemical Industry Co., Ltd.), 0.5 g of 40% methylamine (available from Wako Pure Chemical industries, Ltd.), and 0.25 g of a 37% aqueous formaldehyde solution (available from Wako Pure Chemical Industries, Ltd.) were dissolved into ethanol. Thus, 20 g of a mixed solution in ethanol was obtained. Subsequently, 0.2 g of tungsten-doped vanadium dioxide particles were added to the obtained mixed solution, and the resulting mixture was treated in an ultrasonic tank for three hours. The solution was filtrated, followed by washing of the particles three times with ethanol, and further followed by vacuum-drying of the particles at 50 C. for three hours. The dried particles were then heated at 300 C. for two hours, whereby carbon-coated vanadium dioxide particles were obtained.

Example 5

(23) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 1, except that the vanadium dioxide particles were prepared by the method described below.

(24) (Preparation of Vanadium Dioxide Particles)

(25) To 50 mL of an aqueous dispersion containing 1,209 g of ammonium metavanadate (NH.sub.4VO.sub.3) and 0.02 g of ammonium molybdate hydrate ((NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O) was slowly added dropwise 4.5 mL of a 10% aqueous hydrazine solution. The mixture was reacted at room temperature for one hour. Thereafter, the reaction mixture was transferred into a stainless steel-made pressure-resistant vessel equipped with a fluororesin inner tube, and reacted at 270 C. for 48 hours. After the reaction, the particles were separated from the solution by centrifugation and washed three times. Then, vanadium dioxide particles were recovered by drying at 50 C. X-ray fluorescence analysis of the composition of the particles showed that the vanadium dioxide particles contained about 1 mol % of molybdenum.

Comparative Example 1

(26) The vanadium dioxide particles prepared in Example 2 were used without (Formation of coating layer).

Comparative Example 2

(27) A TiO.sub.2 coating layer was formed by the method described below using the vanadium dioxide particles obtained in Example 2.

(28) (Formation of Coating Layer)

(29) Into a dispersion of 1.0 g of the vanadium dioxide particles at Example 2 in 100 mL of dehydrated ethanol was dissolved 3.0 g of titanium isopropoxide (available from Kanto Chemical Co., Inc.). Subsequently, 50 mL of a solution containing 2.5 g of water (with a pH adjusted to 9.0 with ammonia water) in ethanol was added dropwise to the dispersion at 0.5 mL/min. After the completion of the dropwise addition, the dispersion was reacted with stirring for another one hour. This was followed by filtration, and further followed by washing and drying steps. Thus, coated vanadium dioxide particles were obtained.

Comparative Example 3

(30) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 1, except that the vanadium dioxide particles obtained in Example 2 were used, and that the coating layer was formed by the method described below.

(31) (Formation of Coating Layer)

(32) To a solution of 1.5 g of glucose in 70 mL of water were added 0.5 g of the vanadium dioxide particles obtained in Example 2. The particles were dispersed by stirring. The dispersion was then transferred into a stainless-steel made pressure-resistant vessel equipped with a fluororesin inner tube, and heat-treated at 180 C. for eight hours. After the reaction, the dispersion was cooled to room temperature, followed by centrifugation, and further followed by washing. Thus, carbon-coated vanadium dioxide particles were obtained.

Comparative Example 4

(33) Carbon-coated vanadium dioxide particles were obtained in the same manner as in Example 2, except that the heat treatment after the coating treatment was performed at 135 C. for four hours.

(34) (Evaluation)

(35) (1) Measurement of Thickness (Average Thickness and CV Value) of Coating Layer

(36) The average thickness and the CV value of the coating layer were evaluated using a transmission electron microscope (FE-TEM). Specifically, the cross-sections of the coating layers of randomly selected 20 particles were photographed with the FE-TEM. In the obtained cross-sectional photographs, the thickness of the coating layer was randomly measured at different 10 sites for each particle, and the average thickness and the standard deviation were calculated. The coefficient of variation of the thickness was calculated from the obtained values. Here, since the atomic weight of the coating carbon on the surface and that of the vanadium inside are greatly different, the thickness of the coating layer (carbon layer) can be estimated from the contrast in the TEM image.

(37) (2) Average Particle Size

(38) The average particle size of the particles obtained in the examples and the comparative examples was measured by analyzing FE-SEM images of the particles using image analyzing software (WINROOF, available from Mitani Corporation). The average particle size after firing at 800 C. for two hours was also measured. As for the vanadium dioxide particles obtained in Example 3, electron micrographs of the particles before firing (FIG. 2) and after firing (FIG. 3) were taken. Comparison of these micrographs showed almost no change in the size of the vanadium dioxide particles before and after the firing. In the case where no coating layer was formed (Comparative Example 1), the particles became coarser after firing (FIG. 4). This indicates that the formation of the coating layer prevents interparticle sintering at high temperatures.

(39) (3) TOF-SIMS Analysis

(40) For the coating layer of 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.

(41) Primary ion 209Bi+1

(42) Ion voltage 25 kV

(43) Ion current: 1 pA

(44) Mass range 1 to 300 mass

(45) Analysis area: 500500 m

(46) Charge-up prevention: electron irradiation neutralization

(47) Random raster scan

(48) (4) X-Ray Diffraction

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

(50) X-ray wavelength: CuK 1.54 A

(51) Analysis range: 2=10 to 70

(52) Scanning rate: 4/min

(53) Step: 0.02

(54) For the obtained diffraction data, whether a peak was detected at a position of 2=26.4 was checked. The crystallite size was also determined by calculating the half value width from the obtained diffraction data and applying the value to the Scherrer equation. Specifically, the average crystallite size calculated from the half value width at 2=27.86 was used. The average crystallite size after firing at 800 C. for two hours was also determined. A series of analyses was performed using analysis software (PDXL2).

(55) (5) Phase Transition Energy (Thermochromic Properties)

(56) The heat absorption H (mJ/mg) of the obtained particles at the time of phase transition was measured using a differential scanning calorimeter DSC (DSC6220, available from SII NanoTechnology Inc.) at a temperature range of 0 C. to 100 C. and a temperature-increasing rate of 5 C./min under nitrogen atmosphere.

(57) (6) Oxidation Resistance

(58) The vanadium dioxide particles obtained in the examples and comparative examples were subjected to heat treatment in the air atmosphere at 300 C. for two hours. The oxidation resistance was evaluated based on the retention (%) of the phase transition energy of the particles after the heat treatment.

(59) (7) Durability

(60) The durability of the vanadium dioxide particles was evaluated by an accelerated weathering test of an interlayer film for laminated glass containing the particles. A film was formed by hot-pressing a resin composition containing the particles obtained in the corresponding example or the comparative example, vanadium dioxide particles, butyral resin, and a plasticizer (triethylene glycol di-2-ethylhexanoate). Each film was interposed between two glass plates using a vacuum laminator, whereby an interlayer film for laminated glass was prepared. The weight ratio of the butyral resin to the plasticizer in the film was 3:1, and the vanadium dioxide particle concentration in the film was 0.05%. The interlayer film for laminated glass was subjected to an accelerated weathering test for 500 hours using a weather meter (Super Xenon SX-75, available from Suga Test instruments Co., Ltd.) under the following conditions: radiation intensity: 180 W/m.sup.2 (300 to 400 nm); temperature (BPT): 63 C.; water sprinkling: 18 min/120 min. The durability was evaluated based on the retention of the thermochromic properties of the film after the test.

(61) TABLE-US-00001 TABLE 1 Vanadium Coating layer dioxide particles CV Average Average value particle thick- of Peak TOF-SIMS analysis size ness thickness intensity Benzene Naphtha- Structure (nm) Material (nm) (%) ratio ring lene ring Example 1 VO.sub.2 40 Amorphous 10 4.0 1.72 Present Present carbon Example 2 V.sub.0.99W.sub.0.01O.sub.2 35 Amorphous 10 4.0 2.00 Present Present carbon Example 3 V.sub.0.99W.sub.0.01O.sub.2 35 Amorphous 4 3.5 1.60 Present Present carbon Example 4 V.sub.0.99W.sub.0.01O.sub.2 35 Amorphous 50 6.5 2.30 Present Present carbon Example 5 V.sub.0.99Mo.sub.0.02O.sub.2 30 Amorphous 10 4.0 1.70 Absent Present carbon Comparative V.sub.0.99W.sub.0.01O.sub.2 35 Absent Absent Example 1 Comparative V.sub.0.99W.sub.0.01O.sub.2 35 TiO.sub.2 10 25 Absent Absent Example 2 Comparative V.sub.0.99W.sub.0.01O.sub.2 35 Amorphous 60 30 G and D Absent Absent Example 3 carbon bands not detected Comparative V.sub.0.99W.sub.0.01O.sub.2 35 Amorphous 15 8.5 1.3 Present Present Example 4 carbon Evaluation Oxidation resistance Durability of of interlayer particles film Coating Average Average (Phase (Thermo- layer particle size crystallite size Phase transition chromic X-ray (nm) () transition energy properties diffrac- Before After Before After energy retention retention tion firing firing firing firing (mJ/mg) (%)) (%)) Example 1 Absent 60 58 4.0 24 19.8 92 90 Example 2 Absent 55 56 3.2 20 12.4 95 98 Example 3 Absent 43 45 3.2 25 12.0 88 85 Example 4 Absent 135 130 5.5 30.0 12.1 93 92 Example 5 Absent 50 52 10.6 44.0 9.5 95.0 94 Comparative Absent 35 800 3.2 65.0 35.6 25.0 10 Example 1 Comparative Absent 55 500 3.2 60.0 26.7 85.0 80 Example 2 Comparative Absent 155 130 3.2 18.0 2.0 70.0 65 Example 3 Comparative Absent 52 48 3.2 22 12 75 60 Example 4

(62) The present disclosure provides a carbon-coated vanadium dioxide particle which may suppress interparticle sintering during high-temperature firing, may have high crystallinity and high oxidation resistance, and may maintain its thermochromic properties even after long-term storage or use. The carbon-coated vanadium dioxide particle obtained on the present disclosure may be used in, for example, a resin composition, a coating film, a film, an interlayer film for laminated glass, a laminated glass, and a film to be attached.

(63) Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the disclosure should be limited only by the attached claims.