JP7611846B2 - Boron nitride particles and resin composition - Google Patents

Description

The present invention relates to boron nitride particles and a resin composition.

In electronic components such as transistors, thyristors, and CPUs, efficient dissipation of heat generated during use is an important issue. For this reason, heat dissipation components with high thermal conductivity are used together with such electronic components. Meanwhile, boron nitride particles have high thermal conductivity and high insulating properties, and are therefore widely used as a filler in heat dissipation components.

For example, Patent Document 1 discloses a boron nitride agglomerated particle composition that exhibits high thermal conductivity and is extremely useful for heat dissipation sheets required for power semiconductor devices and the like, the boron nitride agglomerated particle composition being a composition of boron nitride agglomerated particles having an average particle diameter (D ₅₀ ) of 1 μm to 200 μm and satisfying certain conditions.

JP 2017-036190 A

In recent years, devices equipped with electronic components have become faster and larger in capacity than ever before, so heat dissipation materials are also required to have properties that contribute to this. Specifically, heat dissipation materials with low dielectric constant and low dielectric loss tangent are desirable.

Therefore, the present invention aims to provide boron nitride particles that can realize heat dissipation components with low dielectric constant and low dielectric tangent.

One aspect of the present invention is boron nitride particles having a BET diameter of 160 nm or more and 300 nm or less and a total oxygen content of 0.4 mass % or more and 0.8 mass % or less.

The average circularity of the boron nitride particles may be 0.8 or more. The average particle size of the boron nitride particles may be 1 μm or less.

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

According to the present invention, it is possible to provide boron nitride particles that can realize heat dissipation components with low dielectric constant and low dielectric tangent.

One embodiment of the present invention is boron nitride particles having a specific BET diameter and total oxygen content.

The BET diameter of the boron nitride particles is 160 nm or more, preferably 170 nm or more, 180 nm or more, or 190 nm or more, from the viewpoint of reducing the dielectric constant and dielectric tangent of a heat dissipation member containing the boron nitride particles (hereinafter also simply referred to as a "heat dissipation member"). The BET diameter of the boron nitride particles is 300 nm or less, preferably 290 nm or less, 280 nm or less, 270 nm or less, or 260 nm or less, from the viewpoint of reducing the dielectric constant and dielectric tangent of the heat dissipation member.

The BET diameter of the boron nitride particles is a value calculated by the following formula.
BET diameter = diameter when 1 g of boron nitride is assumed to form one spherical particle / (BET specific surface area / surface area when 1 g of boron nitride is assumed to form one spherical particle)
Where:
Diameter of one spherical particle of 1 g of boron nitride = (6/(density of boron nitride particle x π)) ^1/3
(However, the density of boron nitride particles is 2.26 g/ ^cm3 .)
・Surface area when 1 g of boron nitride is assumed to form one spherical particle = π x (diameter when 1 g of boron nitride is assumed to form one spherical particle) ²
BET specific surface area: This is the BET specific surface area of boron nitride particles measured by a BET single-point method using nitrogen gas in accordance with JIS Z 8830 :2013.

The total oxygen content of the boron nitride particles is 0.4% by mass or more, preferably 0.45% by mass or more, 0.5% by mass or more, 0.55% by mass or more, or 0.6% by mass or more, from the viewpoint of lowering the dielectric constant and dielectric tangent of the heat dissipation member. The total oxygen content of the boron nitride particles is 0.8% by mass or less, preferably 0.75% by mass or less or 0.7% by mass or less, from the viewpoint of lowering the dielectric constant and dielectric tangent of the heat dissipation member. The total oxygen content of the boron nitride particles is the mass ratio of oxygen in the boron nitride particles, and is a value measured using an oxygen/nitrogen analyzer (for example, manufactured by Horiba, Ltd., product name: EMGA-620W/C).

The boron nitride particles preferably have a spherical or nearly spherical shape in order to improve the filling of the boron nitride particles when producing a 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, or 0.88 or more.

The average circularity of the boron nitride particles is measured by the following procedure.
An image of a 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 average particle diameter of the boron nitride particles may be preferably 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more, from the viewpoint of suppressing an increase in viscosity when the boron nitride particles are mixed with a resin. The average particle diameter of the boron nitride particles may be 1 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less, from the viewpoint of improving the dielectric breakdown characteristics of the 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 AMPLITUDE (amplitude) 80% using an ultrasonic homogenizer (e.g., manufactured by Nippon Seiki Seisakusho, trade name: US-300E) 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., manufactured by Beckman Coulter, trade name: LS-13 320). 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 boron nitride particles described above are obtained by a manufacturing method comprising a first step of reacting a boric acid ester with ammonia at 750-1400°C to obtain a first precursor, a second step of heating the first precursor at 1000-1600°C to obtain a second precursor, a third step of heating the second precursor at 1000-1600°C to obtain a third precursor, and a fourth step of heating the third precursor at 1800-2200°C to obtain a fourth precursor.

In addition, in this manufacturing method, after the second step is completed and before the third step is started, the environmental temperature in which the second precursor is placed is temporarily lowered to room temperature (10 to 30°C). In this way, after heating at 1000 to 1600°C, the temperature is returned to room temperature, and then heated again at 1000 to 1600°C, thereby obtaining boron nitride particles having the above-mentioned characteristics. On the other hand, as a conventional manufacturing method, for example, a manufacturing method including the above-mentioned first step, second step, and fourth step is known, but in the manufacturing method of this embodiment, as described above, the third step is performed in addition to the second step, and the environmental temperature is temporarily lowered to room temperature between the second step and the third step, thereby obtaining boron nitride particles having characteristics not found in the conventional method.

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 generate a first precursor (white powder). Some of the generated first precursor adheres to the inside of the reaction tube, but most of the first precursor is sent to a recovery container attached to the end of the reaction tube by an inert gas or unreacted ammonia gas and collected. The time (reaction time) for reacting the boric acid ester and ammonia is preferably within 30 seconds. The reaction time is the time during which the boric acid ester and ammonia remain in the part of the reaction tube heated to 750 to 1400 ° C (heated part), and can be adjusted by the gas flow rate when the boric acid 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 first 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, and as a result, the BET diameter of the finally obtained boron nitride particles tends to be smaller, and the total oxygen content tends to be smaller.

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 results in the second precursor.

After the second step is completed, the power to the resistance heating furnace is turned off, the introduction of nitrogen gas and ammonia gas is stopped, and the temperature inside the reaction tube is lowered to room temperature (10 to 30°C), and the second precursor is allowed to stand. The standing time may be, for example, 0.5 hours or more and may be 96 hours or less.

In the third step, nitrogen gas and ammonia gas are introduced into the reaction tube again, and the reaction tube is heated again to 1000-1600°C. Examples of the flow rates of nitrogen gas and ammonia gas, and the heating time may be similar to those described in the second step. The conditions of the second step and the third step may be the same as each other, or may be different from each other. This results in a third precursor.

In the fourth step, the third precursor obtained in the third step is placed in a boron nitride crucible and heated to 1800 to 2200°C in an induction heating furnace under a nitrogen atmosphere. The heating time may be, for example, 0.5 hours or more and 10 hours or less. This results in boron nitride particles having the above-mentioned characteristics.

The boron nitride particles described above are suitable for use in, for example, heat dissipation components. By using the above-mentioned boron nitride particles, a heat dissipation component with a low dielectric constant and low dielectric tangent can be obtained. When used in a heat dissipation component, the boron nitride particles are used as 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.

The content of the above-mentioned 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, polyolefin (polyethylene, etc.), 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 resin composition may further contain boron nitride particles other than the above-mentioned boron nitride particles (e.g., known boron nitride particles such as agglomerated boron nitride particles formed by agglomeration of scale-like primary particles).

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.

[Examples 1 to 3]
Boron nitride particles were prepared by the following procedure.
First, in the first step, a reaction tube (quartz tube) installed in a resistance heating furnace was heated to a temperature shown in Table 1. On the other hand, nitrogen gas was passed through trimethyl borate and then introduced into the reaction tube, thereby introducing trimethyl borate into the reaction tube. On the other hand, 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. As a result, trimethyl borate and ammonia were reacted to obtain a first precursor (white powder). The reaction time is as shown in Table 1.

In the second step, the first 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 the flow rates shown in Table 1. The reaction tube was then heated at the temperature and for the time shown in Table 1. This resulted in the production of a second precursor.

Next, the power to the resistance heating furnace was turned off, the introduction of nitrogen gas and ammonia gas was stopped, and the temperature inside the reaction tube was lowered to 25°C, and the second precursor was left to stand for 2 hours.

In the third step, nitrogen gas and ammonia gas were again introduced into the reaction tube at the flow rates shown in Table 1, and the reaction tube was again heated at the temperature and for the time shown in Table 1. This produced a third precursor.

In the fourth step, the third precursor obtained in the third step was placed in a boron nitride crucible and heated in an induction heating furnace under a nitrogen atmosphere at the temperature and for the time shown in Table 1. This resulted in the production of boron nitride particles.

[Comparative Example 1]
Boron nitride particles were obtained in the same manner as in Example 1, except that the third step was not performed.

The BET diameter, total oxygen content, average circularity, and average particle size of each of the obtained boron nitride particles were measured by the following methods. The results are shown in Table 1.

(BET diameter)
The BET diameter was calculated by the following formula.
BET diameter = diameter when 1 g of boron nitride is assumed to form one spherical particle / (BET specific surface area / surface area when 1 g of boron nitride is assumed to form one spherical particle)
Where:
Diameter of one spherical particle of 1 g of boron nitride = (6/(density of boron nitride particle x π)) ^1/3
(However, the density of boron nitride particles is 2.26 g/ ^cm3 .)
・Surface area when 1 g of boron nitride is assumed to form one spherical particle = π x (diameter when 1 g of boron nitride is assumed to form one spherical particle) ²
BET specific surface area: This is the BET specific surface area of boron nitride particles measured by a BET single-point method using nitrogen gas in accordance with JIS Z 8830 :2013.

(Total oxygen)
The total oxygen amount was measured using an oxygen/nitrogen analyzer (manufactured by Horiba, Ltd., product name: EMGA-620W/C).

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

(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. Boron nitride particles were added to this aqueous solution at a ratio of 0.1 g/80 mL, and ultrasonic dispersion was performed once for 1 minute and 30 seconds at AMPLITUDE (amplitude) 80% using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, product name: US-300E was used) to prepare a dispersion of boron nitride particles. This 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 (manufactured by Beckman Coulter, product name: LS-13 320). 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 the cumulative value of 50% of the cumulative particle size distribution.

The dielectric constant and dielectric loss tangent of each of the obtained boron nitride particles were measured by the following method. The results are shown in Table 1.
The boron nitride particles were mixed with polyethylene (manufactured by Japan Polyethylene Co., Ltd., product name "Novatec HY540") in an amount such that the boron nitride particles constituted 20 volume % and then formed into a sheet having a thickness of 0.2 mm. The mixing and sheet forming were carried out using a twin-screw extruder at a temperature of 180°C. The sheet obtained was measured using a cavity resonator method measuring device at a frequency of 36 GHz and a temperature of 25°C to determine the dielectric constant and dielectric tangent of the sheet.

Claims (3)

Boron nitride particles having a BET diameter of 160 nm or more and 300 nm or less, a total oxygen content of 0.4 mass % or more and 0.8 mass % or less, and an average circularity of 0.8 or more . 2. The boron nitride particles according to claim 1 , having an average particle size of 1 μm or less. A resin composition comprising a resin and the boron nitride particles according to claim 1 or 2 .