JP7571122B2 - Boron nitride particles, and resin composition and container containing the boron nitride particles - Google Patents

Description

The present disclosure relates to boron nitride particles, as well as a resin composition and a container containing the boron nitride particles.

In electronic components such as power devices, transistors, thyristors, and CPUs, heat dissipation members are used to efficiently dissipate heat generated during use. Heat dissipation members contain, for example, ceramic particles with high thermal conductivity. As ceramic particles, boron nitride particles have attracted attention for their properties such as high thermal conductivity, high insulation, and low dielectric constant.

There are various known methods for producing boron nitride particles. One such method involves reacting ammonia with boric acid alkoxide in an ammonia/boric acid alkoxide molar ratio of 1 to 10 in an inert gas stream at 750°C or higher for 30 seconds or less, followed by heat treatment at 1,000 to 1,600°C for 1 hour or more in an atmosphere of ammonia gas or a mixed gas of ammonia gas and an inert gas, and then calcining the mixture at 1,800 to 2,200°C for 0.5 hours or more in an inert gas atmosphere (see, for example, Patent Document 1).

International Publication No. 2015/122379

In the above-mentioned manufacturing method, heating must be carried out in at least three stages while changing the conditions, but in order to manufacture boron nitride particles more efficiently, it is desirable to simplify the process. On the other hand, simplification of the process must not impair the properties required for boron nitride particles, such as thermal conductivity.

Therefore, one aspect of the present invention aims to provide boron nitride particles that can be produced more easily than conventional particles while having the same thermal conductivity as conventional particles.

Conventionally, it was thought that in order to obtain high thermal conductivity, it was necessary to crystallize boron nitride as much as possible throughout the entire particle, but after extensive research, the inventors of the present invention surprisingly found that, as long as the peripheral parts of the particle are sufficiently crystallized, there is no adverse effect on the thermal conductivity of the boron nitride particle even if the boron nitride in the center of the particle is insufficiently crystallized. In other words, it was discovered that a thermal conductivity equivalent to that of conventional methods can be obtained even if the process of crystallizing boron nitride is simplified.

One aspect of the present invention is a boron nitride particle having a central portion containing low-crystalline boron nitride and a peripheral portion surrounding the central portion and containing highly crystalline boron nitride.

The average circularity of the boron nitride particles may be 0.8 or more.

Another aspect of the present invention is a resin composition containing a resin and the above-mentioned boron nitride particles.

Another aspect of the present invention is a container comprising the above-mentioned boron nitride particles and a container for containing the boron nitride particles.

According to one aspect of the present invention, it is possible to provide boron nitride particles that can be produced more easily than conventional particles while having the same thermal conductivity as conventional particles.

1 is a TEM image of an entire boron nitride particle of an example. 2 is a TEM image of the peripheral region S of the boron nitride particle in FIG. 1. 3 is a diagram and graph showing the results of FFT analysis of region S1 of the boron nitride particle in FIG. 2. 2 is a diagram showing the results of FFT analysis of regions S2 to S5 of the peripheral portion S of the boron nitride particle in FIG. 1. 2 is a graph showing the results of FFT analysis of regions S2 to S5 of the peripheral portion S of the boron nitride particle in FIG. 1. 2 is a diagram showing the results of FFT analysis of regions C1 to C4 of the center C of the boron nitride particle in FIG. 1. 2 is a graph showing the results of FFT analysis of regions C1 to C4 of the center C of the boron nitride particle in FIG. 1.

The following describes in detail an embodiment of the present invention.

One embodiment of the present invention is a boron nitride particle comprising a central portion comprising low-crystalline boron nitride and a peripheral portion surrounding the central portion comprising highly crystalline boron nitride.

In this specification, "high crystallinity" means a state in which a bright spot (peak) due to periodicity derived from the h-BN (0002) plane is present in the range of 1 to 4 nm ^-1 in the reciprocal lattice space in an FFT image of boron nitride particles obtained by the following method, and "low crystallinity" means a state in which the bright spot (peak) is not present. The presence of a bright spot (peak) means that there is a point in the range of 1 to 4 nm ^-1 in the reciprocal lattice space where the intensity S after subtracting the background by the B-spline method is 15 times or more the noise intensity N. Here, the noise intensity N is defined as the standard deviation value in the range of more than 4 nm ^-1 to 6 nm ^-1 in the reciprocal lattice space after background processing by the B-spline method. In addition, the bright spot (peak) also includes those having fluctuations in the wave number direction or the circumferential direction. In the surrounding area containing highly crystalline boron nitride, there may be a point within the range of 1 to 4 nm ⁻¹ in the reciprocal lattice space where the intensity S is preferably 20 times or more, more preferably 23 times or more, and even more preferably 25 times or more, the noise intensity N.

(Method of acquiring FFT image)
First, a TEM image of boron nitride particles at 400,000 times magnification is obtained using a transmission electron microscope (for example, "JEM-2100" manufactured by JEOL Ltd.) under the following conditions.
Objective lens aperture: φ120 μm
Focusing lens aperture: φ150 μm
Recording medium: AMETEK's "Orisus SC1000A1"
Binning: 2
Exposure time: 0.5 seconds. For TEM observation and FFT analysis described later, image analysis software (for example, "GMS3" manufactured by AMETEC Corporation) is used.
Next, an FFT analysis is performed on an 8.556 nm square region in the obtained TEM image to obtain an FFT image of 256×256 pixels.

The diameter of the center of the boron nitride particle may be, for example, 0.1d or more, 0.15d or more, or 0.2d or more, and 0.6d or less, 0.5 or less, 0.4d or less, 0.35d or less, or 0.3d or less, where d is the particle diameter of the boron nitride particle. The diameter of the center of the boron nitride particle may be, for example, 1 nm or more, 5 nm or more, 10 nm or more, 20 nm or more, or 30 nm or more, and 400 nm or less, 300 nm or less, 200 nm or less, or 100 nm or less. The diameter of the center of the boron nitride particle means the diameter of the "highly crystalline" portion defined as above, that is, the portion in the range of 1 to 4 nm ^-1 on the reciprocal lattice space where there is a bright spot (peak) due to the periodicity derived from the h-BN (0002) plane.

The thickness of the peripheral part in the boron nitride particle may be, for example, 0.3d or more, 0.33d or more, or 0.35d or more, and 0.45d or less, 0.43d or less, or 0.4d or less, when the particle diameter of the boron nitride particle is d. The diameter of the center part in the boron nitride particle may be, for example, 5 nm or more, 10 nm or more, 20 nm or more, 40 nm or more, or 60 nm or more, and 450 nm or less, 300 nm or less, 200 nm or less, or 100 nm or less. The thickness of the peripheral part in the boron nitride particle means the thickness of the "low crystallinity" part defined as above, that is, the part in the range of 1 to 4 nm ^-1 on the reciprocal lattice space where there is no bright spot (peak) due to the periodicity derived from the h-BN (0002) plane.

The average particle diameter of the boron nitride particles is preferably 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, or 0.15 μm or more, from the viewpoint of suppressing an increase in viscosity when the boron nitride particles are mixed with a resin, and may be 1 μm or less, 0.8 μm or less, 0.6 μm or less, or 0.4 μm or less, from the viewpoint of improving the dielectric breakdown characteristics of a heat dissipation member containing the boron nitride particles (hereinafter also simply referred to as a "heat dissipation member").

The average particle size of the boron nitride particles is measured by the following procedure.
Using distilled water as a dispersion medium for dispersing boron nitride particles and sodium hexametaphosphate as a dispersant, a 0.125% by mass aqueous solution of sodium hexametaphosphate is prepared. Boron nitride particles are added to this aqueous solution at a ratio of 0.1 g/80 mL, and ultrasonic dispersion is performed once for 1 minute and 30 seconds at an AMPLITUDE (amplitude) of 80% using an ultrasonic homogenizer (e.g., "US-300E" manufactured by Nippon Seiki Seisakusho) to prepare a dispersion of boron nitride particles. The dispersion is taken while stirring at 60 rpm, and the volume-based particle size distribution is measured using a laser diffraction scattering particle size distribution measuring device (e.g., "LS-13 320" manufactured by Beckman Coulter, Inc.). At this time, 1.33 is used as the refractive index of water, and 1.7 is used as the refractive index of boron nitride particles. From the measurement results, the average particle size is calculated as the particle size (median diameter, d50) at the cumulative value of 50% of the cumulative particle size distribution. The average particle size measured in this manner is considered to be the average particle size of boron nitride particles including not only primary particles of boron nitride particles but also particles (secondary particles) formed by agglomeration of the primary particles.

The boron nitride particles preferably have a spherical or nearly spherical shape in order to improve the filling property when preparing the heat dissipation member and to make the properties of the heat dissipation member (thermal conductivity, dielectric constant, etc.) isotropic. From the same viewpoint, the average circularity of the boron nitride particles may preferably be 0.8 or more, 0.82 or more, 0.84 or more, 0.86 or more, 0.88 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, or 0.94 or more.

The average circularity of the boron nitride particles is measured by the following procedure.
The image of the boron nitride particle taken with a scanning electron microscope (SEM) (magnification: 10,000 times, image resolution: 1280 x 1024 pixels) is analyzed using image analysis software (e.g., "MacView" manufactured by Mountec Co., Ltd.) to calculate the projected area (S) and perimeter (L) of the boron nitride particle. Using the projected area (S) and perimeter (L), the following formula is used:
Circularity = 4πS/ ^L2
The circularity is calculated according to the following formula: The average value of the circularities calculated for 100 randomly selected boron nitride particles is defined as the average circularity.

The boron nitride particles described above are obtained by deliberately stopping the crystal growth of boron nitride in an incomplete state. In the production of boron nitride particles, crystal growth progresses gradually from the periphery to the center of the particle, but by stopping the crystal growth of boron nitride in an incomplete state, the resulting boron nitride particles have boron nitride contained in the periphery that is highly crystalline, while the boron nitride contained in the center is less crystalline.

The manufacturing method of the above-mentioned boron nitride particles will be specifically described below. The above-mentioned boron nitride particles can be obtained by a manufacturing method including, for example, a first step of reacting a boric acid ester with ammonia at 750 to 1400°C to obtain a precursor of the boron nitride particles, and a second step of heating the precursor at 1000 to 1600°C to obtain the boron nitride particles.

In the first step, for example, a reaction tube (e.g., a quartz tube) installed in a resistance heating furnace is heated to 750 to 1500°C. On the other hand, an inert gas is passed through a liquid borate ester and then introduced into the reaction tube, thereby introducing the borate ester into the reaction tube. On the other hand, ammonia gas is directly introduced into the reaction tube. Examples of inert gases include rare gases such as helium, neon, and argon, and nitrogen gas. The borate ester may be, for example, an alkyl borate ester, preferably trimethyl borate.

The molar ratio of the amount of ammonia introduced to the amount of borate ester introduced (ammonia/borate ester) may be, for example, 1 or more and 10 or less.

The introduced boric acid ester and ammonia react in the heated reaction tube to produce a precursor of boron nitride particles. This precursor contains amorphous boron nitride and may be, for example, a white powder. Some of the generated precursor adheres to the inside of the reaction tube, but most of the precursor is transported by the inert gas and unreacted ammonia gas to a collection vessel attached to the end of the reaction tube and collected.

The time (reaction time) for reacting the borate ester with ammonia in the first step is preferably within 30 seconds. The reaction time is the time during which the borate ester and ammonia remain in the part of the reaction tube that is heated to 750 to 1400°C (heated part), and can be adjusted by the gas flow rate when the borate ester and ammonia are introduced and the length of the reaction tube installed in the resistance heating furnace (the length of the heated part of the reaction tube).

In the second step, the precursor obtained in the first step is placed in another reaction tube (e.g., an alumina tube) installed in a resistance heating furnace, and nitrogen gas and ammonia gas are separately introduced into the reaction tube. The gas introduced at this time may be only ammonia gas. The flow rates of the nitrogen gas and ammonia gas may be appropriately adjusted so that the reaction time is the desired value. For example, the higher the flow rate of ammonia gas, the shorter the reaction time.

The reaction tube is then heated to 1000-1600°C. The heating time may be, for example, 1 hour or more and 10 hours or less. This allows the crystallization of the boron nitride in the precursor to proceed, resulting in boron nitride particles. However, not all of the boron nitride in the precursor is crystallized, and low-crystalline boron nitride remains inside the boron nitride particles.

This manufacturing method does not include a step of heating the boron nitride particles obtained in the second step at 1800°C or higher after the second step (a step that has been conventionally performed to promote crystal growth of boron nitride). That is, in this manufacturing method, the desired boron nitride particles are obtained in an incompletely crystal-grown state after the heating in the second step. This manufacturing method does not necessarily include a step of heating the boron nitride particles obtained in the second step at 1700°C or higher, 1600°C or higher, 1500°C or higher, 1400°C or higher, 1300°C or higher, 1200°C or higher, 1100°C or higher, 1000°C or higher, 900°C or higher, 800°C or higher, 700°C or higher, 600°C or higher, 500°C or higher, 400°C or higher, 300°C or higher, 200°C or higher, 100°C or higher, 50°C or higher, 40°C or higher, or 30°C or higher after the second step.

The above-mentioned boron nitride particles are suitable for use in, for example, heat dissipation components. When the boron nitride particles are used in a heat dissipation component, they are used in the form of a resin composition mixed with, for example, a resin. That is, another embodiment of the present invention is a resin composition containing a resin and the above-mentioned boron nitride particles. This resin composition is suitable for use as a heat dissipation component.

The content of the above boron nitride particles is preferably 30% by volume or more, more preferably 40% by volume or more, and even more preferably 50% by volume or more, based on the total volume of the resin composition, from the viewpoint of improving the thermal conductivity of the resin composition and making it easier to obtain excellent heat dissipation performance, and is preferably 85% by volume or less, more preferably 80% by volume or less, and even more preferably 70% by volume or less, from the viewpoint of being able to suppress the occurrence of voids during molding and the deterioration of insulation and mechanical strength.

Examples of resins include epoxy resin, silicone resin, silicone rubber, acrylic resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin.

The resin content may be 15 vol.% or more, 20 vol.% or more, or 30 vol.% or more, and may be 70 vol.% or less, 60 vol.% or less, or 50 vol.% or less, based on the total volume of the resin composition.

The resin composition may further contain a curing agent that cures the resin. The curing agent is appropriately selected depending on the type of resin. For example, when the resin is an epoxy resin, examples of the curing agent include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The content of the curing agent may be, for example, 0.5 parts by mass or more or 1.0 parts by mass or more, and 15 parts by mass or less or 10 parts by mass or less, relative to 100 parts by mass of the resin.

The boron nitride particles may be distributed, for example, in a form contained in a container. That is, another embodiment of the present invention is a container comprising the above-mentioned boron nitride particles and a container for containing the boron nitride particles. The container may have any shape capable of containing the boron nitride particles, and may be, for example, a bag, box, bottle, can, etc.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
(Preparation of boron nitride particles)
First, in the first step, a reaction tube (quartz tube) installed in a resistance heating furnace was heated to 1150°C. Meanwhile, nitrogen gas was passed through trimethyl borate and then introduced into the reaction tube, thereby introducing trimethyl borate into the reaction tube. Meanwhile, ammonia gas was directly introduced into the reaction tube. The molar ratio of the amount of ammonia introduced to the amount of trimethyl borate introduced (ammonia/trimethyl borate) was set to 4.5. Thus, trimethyl borate and ammonia were reacted to obtain a precursor (white powder) of boron nitride particles. The reaction time was 10 seconds.

In the second step, the precursor obtained in the first step was placed in another reaction tube (alumina tube) installed in a resistance heating furnace, and nitrogen gas and ammonia gas were separately introduced into the reaction tube at flow rates of 10 L/min and 15 L/min. The reaction tube was then heated at 1500°C for 2.5 hours. This resulted in the production of boron nitride particles.

(Observation of boron nitride particles and evaluation of crystallinity)
The boron nitride particles obtained under the following conditions were observed using a transmission electron microscope (TEM; "JEM-2100" manufactured by JEOL Ltd.).
Objective lens aperture: φ120 μm
Focusing lens aperture: φ150 μm
Recording medium: AMETEK's "Orisus SC1000A1"
Binning: 2
Exposure time: 0.5 seconds. Furthermore, "GMS3" manufactured by AMETEK was used as image analysis software for TEM observation and FFT analysis described later.

A TEM bright-field image (magnification: 100,000 times) of the entire boron nitride particle obtained is shown in Figure 1. Figure 2 shows a TEM dark-field image of the peripheral portion S of the boron nitride particle shown in Figure 1, observed at 400,000 times.

Next, FFT analysis was performed on the 8.556 nm square region S1 in Figure 2, and a 256 x 256 pixel FFT image was obtained. As shown in Figures 3(a) and 3(b), the obtained FFT pattern showed bright spots (peaks) due to periodicity derived from the h-BN (0002) plane in the range of 1 to 4 nm ^-1 in the reciprocal lattice space. In other words, it was confirmed that the region S1 in the peripheral portion S of the boron nitride particle is composed of highly crystalline boron nitride.

Furthermore, as shown in Figure 4, FFT analysis was also performed on other regions S2 to S5 in the peripheral region S of the boron nitride particle in the same manner as for region S1. As a result, as shown in Figures 4 and 5, bright spots (peaks) due to periodicity derived from the h-BN (0002) plane were confirmed in the range of 1 to 4 nm ^-1 in the reciprocal lattice space. In other words, it was confirmed that regions S2 to S5 in the peripheral region S of the boron nitride particle are also composed of highly crystalline boron nitride.

FIG. 6 shows a TEM dark-field image of the central portion C of the boron nitride particle shown in FIG. 1, observed at 400,000 times. As shown in FIG. 6, FFT analysis was also performed on regions C1 to C4 in the central portion C of the boron nitride particle in the same manner as for region S1. As a result, as shown in FIGS. 6 and 7, no bright spots (peaks) due to periodicity derived from the h-BN (0002) plane were confirmed in the range of 1 to 4 nm ⁻¹ in the reciprocal lattice space. In other words, it was confirmed that regions C1 to C4 in the central portion C of the boron nitride particle are composed of low-crystalline boron nitride.

The graphs shown in Figures 3(b), 5, and 7 show the intensities after subtracting the background by the B-spline method. From the graphs shown in Figures 3(b), 5, and 7, the maximum intensity (relative intensity) Smax in the range of 1 to 4 nm ^-1 in the reciprocal lattice space, the noise intensity (standard deviation in the range of more than 4 nm ^-1 to 6 nm ^-1 in the reciprocal lattice space), and the ratio thereof (Smax/N) were determined for each of the regions S1 to S5 and C1 to C4. The results are shown in Table 1.

As described above, it was found that the peripheral portion of the obtained boron nitride particles contains highly crystalline boron nitride (dominated by the area where the above-mentioned bright spots (peaks) can be confirmed), and the central portion contains less crystalline boron nitride (dominated by the area where the above-mentioned bright spots (peaks) cannot be confirmed). In addition, the diameter of the central portion was approximately 40 nm, and the thickness of the peripheral portion was approximately 50 nm.

(Measurement of average circularity)
First, a scanning electron microscope (SEM) was used to take an SEM image (magnification: 10,000 times, image resolution: 1280 x 1024 pixels) of the obtained boron nitride particles. The obtained SEM image was analyzed using image analysis software (e.g., "MacView" manufactured by Mountec Co., Ltd.) to calculate the projected area (S) and perimeter (L) of the boron nitride particles. Next, the projected area (S) and perimeter (L) were calculated using the following formula:
Circularity = 4πS/ ^L2
The circularity was calculated according to the formula: The average value of the circularities calculated for 100 randomly selected boron nitride particles was calculated as the average circularity. The average circularity of the obtained boron nitride particles was 0.94.

(Measurement of average particle size)
Using distilled water as a dispersion medium for dispersing boron nitride particles and sodium hexametaphosphate as a dispersant, a 0.125% by mass aqueous solution of sodium hexametaphosphate was prepared. The boron nitride particles obtained at a ratio of 0.1 g/80 mL were added to this aqueous solution, and ultrasonic dispersion was performed once for 1 minute and 30 seconds at an AMPLITUDE (amplitude) of 80% using an ultrasonic homogenizer ("US-300E" manufactured by Nippon Seiki Seisakusho) to prepare a dispersion of boron nitride particles. The dispersion was taken while stirring at 60 rpm, and the volume-based particle size distribution was measured using a laser diffraction scattering particle size distribution measuring device ("LS-13 320" manufactured by Beckman Coulter, Inc.). At this time, 1.33 was used as the refractive index of water, and 1.7 was used as the refractive index of boron nitride particles. From the measurement results, the average particle size was calculated as the particle size (median size, d50) at 50% cumulative value of the cumulative particle size distribution. The average particle size of the obtained boron nitride particles was 510 nm.

[Comparative Example 1]
Comparative boron nitride particles were obtained in the same manner as in Example 1, except that after the second step of Example 1, the boron nitride particles were placed in a boron nitride crucible and heated in an induction heating furnace under a nitrogen atmosphere at 2000° C. for 5 hours. That is, in Comparative Example 1, comparative boron nitride particles were obtained by a conventional manufacturing method.

<Measurement of thermal conductivity>
The thermal conductivity of the boron nitride particles obtained in Example 1 and the comparative boron nitride particles obtained in Comparative Example 1 was measured by the following procedure.
A resin composition was obtained by mixing 40% by volume of boron nitride particles into a mixture of 100 parts by mass of a naphthalene type epoxy resin (DIC Corporation, "HP4032") and 10 parts by mass of an imidazole (Shikoku Kasei Corporation, "2E4MZ-CN") as a curing agent. This resin composition was applied to a PET sheet to a thickness of 1.0 mm, and then degassed under reduced pressure of 500 Pa for 10 minutes. Thereafter, a 0.5 mm sheet was produced by pressing for 60 minutes ^under conditions of a temperature of 150°C and a pressure of 160 kg/cm2.
A measurement sample having a size of 10 mm x 10 mm was cut out from the obtained sheet, and the thermal diffusivity A (m ² /sec) of the measurement sample was measured by a laser flash method using a xenon flash analyzer (NETZSCH, "LFA447NanoFlash"). The specific gravity B (kg/m ³ ) of the measurement sample was measured by the Archimedes method. The specific heat capacity C (J/(kg·K)) of the measurement sample was measured using a differential scanning calorimeter (Rigaku Corporation, "ThermoPlusEvoDSC8230"). Using these physical property values, the thermal conductivity H (W/(m·K)) was calculated from the formula H=A×B×C.

As a result, the boron nitride particles obtained in Example 1 showed a thermal conductivity of 1.13 W/(m·K), and the comparative boron nitride particles obtained in Comparative Example 1 showed a thermal conductivity of 1.12 W/(m·K). Thus, in Example 1, boron nitride particles having a thermal conductivity equivalent to that of Comparative Example 1 were obtained, despite the omission of the step of Comparative Example 1 (a step carried out in conventional manufacturing methods) of heating at 2000°C for 5 hours under a nitrogen atmosphere.

Claims (3)

a core portion including low crystalline boron nitride;
a peripheral portion disposed so as to surround the central portion and including highly crystalline boron nitride ;
The average circularity is 0.8 or more,
The average particle size is 0.15 μm or more,
Boron nitride particles are used to form heat dissipation components . A resin composition comprising a resin and the boron nitride particles according to claim 1 . A container comprising the boron nitride particles according to claim 1 and a container for containing the boron nitride particles.

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