JP7438442B1 - Boron nitride aggregated particles, sheet member, and method for producing boron nitride aggregated particles - Google Patents

Abstract

The present invention provides boron nitride agglomerated particles that have excellent strength and can be highly filled as a filler in a sheet member. [Solution] The boron nitride agglomerated particles of the present invention are boron nitride agglomerated particles in which primary particles of hexagonal boron nitride are agglomerated, and the crystallite diameter of the 002 plane of the primary particles is 160 Å or more and less than 200 Å, and is versatile. In the load displacement measurement using a testing machine that applies a load of up to 10,000 N, the load value of cohesive failure obtained by position correction based on the load variation measurement results of scale-like non-agglomerated boron nitride particles is the same as that of the standard sample. This is more than 2.5 times the load value in the test. [Selection diagram] None

Description

The present invention relates to boron nitride aggregate particles, a sheet member, and a method for producing boron nitride aggregate particles.

In recent years, with the increasing frequency of communication in semiconductor devices and the like, there has been an increasing need for low dielectric properties for insulating members. Since hexagonal boron nitride (hereinafter also referred to as h-BN) has excellent thermal conductivity, electrical properties, chemical stability, etc., its use as a filler for heat dissipation members is being considered. However, the crystal structure of h-BN is a layered hexagonal structure, and although the in-plane thermal conductivity is high, the interlayer thermal conductivity is low. General h-BN particles have a scaly particle shape due to this crystal structure, so although their thermal conductivity in the in-plane direction is high, their thermal conductivity in the thickness direction is extremely low. When particles are used as a filler, there is a problem in that orientation occurs during the resin molding process of a sheet member, which is a heat dissipating member, and the thermal conductivity in the thickness direction decreases.

To solve the above problem, boron nitride agglomerated particles, which are made by agglomerating scale-like h-BN particles into a spherical shape, have a crystallite diameter (002 plane) of 450 Å or more, a volume-based average particle diameter of 2 to 20 μm, and a ratio of Those with a surface area of 10 m ² /g or more have been proposed (see, for example, Patent Documents 1 and 2).
Further, crystallites having a crystallite diameter (002 plane) of 320 Å or more, a volume-based average particle diameter of 25 μm or more, and a specific surface area of 8 m ² /g or less have been proposed (see, for example, Patent Documents 3 to 7).

Furthermore, boron nitride powder containing non-spherical aggregates of scale-like h-BN particles has a crystallite size of 300 Å or more and 500 Å or less, a 50% volume cumulative particle size of 20 μm or more and 50 μm or less, and a specific surface area of less than 10 m ² /g. (For example, see Patent Document 7), Crystallite diameter is 260 Å or more and 1000 Å or less, Specific surface area is less than 5 m ² /g (For example, see Patent Document 8), Crystallite diameter is 250 Å or more and 375 Å or less, 50% volume cumulative particle size is 30 μm or more and 200 μm or less, and the specific surface area is 0.1 m ² /g or more and less than 5 m ² /g (for example, see Patent Document 7).

Patent No. 5679083 Patent No. 5915509 Patent No. 6447202 Patent No. 6493226 Patent No. 6773153 Patent No. 6794613 Patent No. 7207384 Patent No. 6678999 Patent No. 6822836 Patent No. 7096921

Patent Documents 1 to 7 state that boron nitride agglomerated particles with a crystallite diameter of 320 Å or more are preferable from the viewpoint of thermal conductivity, but as the crystallite diameter increases, the primary particle diameter also increases, making it difficult to use them as sheet members. Kneadability with resin deteriorates. In addition, since the number of contact points between the primary particles decreases, the strength decreases, the fluidity of the resin composition when preparing a sheet member decreases, and it becomes difficult to fill the resin composition with high filler.
Furthermore, since the boron nitride aggregate particles of Patent Documents 8 to 10 are non-spherical, the fluidity of the resin composition when preparing a sheet member may be reduced.

An object of the present invention is to provide boron nitride agglomerated particles that have excellent strength and can be highly filled as a filler in a sheet member.

In order to solve the above-mentioned problems and achieve the objects, boron nitride aggregate particles according to the present invention are boron nitride aggregate particles in which primary particles of hexagonal boron nitride are aggregated, and the crystals of the 002 plane of the primary particles are aggregated. The particles have a particle diameter of 160 Å or more and less than 200 Å, and are obtained by using a universal testing machine to perform load displacement measurements of up to 10,000 N, and correcting the position based on the results of load variation measurements of scale-like non-agglomerated boron nitride particles. The load value for cohesive failure is 2.5 times or more the load value of the standard sample in the same test.

Moreover, the sheet member according to the present invention includes the above-mentioned boron nitride aggregated particles and a resin.

Further, a method for producing boron nitride aggregate particles according to the present invention is a method for producing boron nitride aggregate particles described above, in which boron nitride particles, water, a dispersant, and an organic binder are mixed to form a slurry. a granulation process of granulating the prepared slurry; a degreasing process of degreasing the granulated particles in a non-oxidizing gas atmosphere; The ratio of the carbon-containing substance derived from the dispersant and the organic binder in the slurry is 5% by mass or more and 10% by mass, including a firing step in which the fired particles are fired in an atmosphere, and a classification step in which the fired particles are crushed and classified. % or less, and the firing step includes a first firing step in which the temperature is raised to a temperature of 1600°C to 1660°C at a rate of 300°C/hour to 600°C/hour and fired for 5 to 20 minutes, and a and a second firing step in which the temperature is raised to a temperature of 1800° C. to 2200° C. at a rate of 70° C./hour to 120° C./hour and fired for 10 hours to 20 hours.

According to the present invention, it is possible to provide boron nitride agglomerated particles that have excellent strength and can be highly filled as a filler in a sheet member.

FIG. 1 is a diagram showing the relationship between the crystallite diameter of the 002 plane and the strength of the boron nitride agglomerated particles according to the present embodiment. FIG. 2 is an electron micrograph ((A) 500x, (B) 1000x, (C) 2000x, (D) 5000x) of the boron nitride agglomerated particles (Example 1) according to the present embodiment. .

Hereinafter, a method for manufacturing boron nitride aggregated particles, a sheet member, and boron nitride aggregated particles according to the present embodiment will be described.

<Boron nitride aggregate particles>
The boron nitride agglomerated particles according to the present invention are boron nitride agglomerated particles in which primary particles of hexagonal boron nitride are agglomerated, and the crystallite diameter of the 002 plane of the primary particles is 160 Å or more and less than 200 Å. However, in load displacement measurements that apply loads of up to 10,000 N, the load value of cohesive failure obtained by position correction based on the results of load variation measurements of scale-shaped non-agglomerated boron nitride particles is the same as the load of the standard sample in the same test. The boron nitride agglomerated particles are more than 2.5 times the value. The boron nitride agglomerated particles of the present invention will be explained below.

The boron nitride agglomerated particles according to the present invention are boron nitride agglomerated particles in which primary particles of hexagonal boron nitride are aggregated into a spherical shape, and the crystallite diameter of the 002 plane of the primary particles is 160 Å or more and less than 200 Å. FIG. 1 is a diagram showing the relationship between the crystallite diameter of the 002 plane and the strength of the boron nitride agglomerated particles according to the present embodiment. Boron nitride aggregate particles were obtained by changing manufacturing conditions such as sintering temperature and holding time, and it was confirmed that the strength of boron nitride aggregate particles was highest when the crystallite diameter of the 002 plane was around 200 Å. Ta. Since the boron nitride agglomerated particles according to the present invention have a crystallite diameter of 002 plane of 160 Å or more and less than 200 Å, they have high strength and are excellent in kneading into resin when used as a filler for a sheet member. The crystallite diameter of the boron nitride agglomerated particles was measured by the following method using XRD diffraction of the boron nitride agglomerated particle powder.

The crystallite diameter was determined by measuring the diffraction line using Rigaku Co., Ltd.'s "Ultima IV" and using the Scherrer equation below from the half-width of the peak at 2θ=26.6° (002 plane).
D = Kλ/βcosθ
D: Crystallite diameter (Å)
K: Scherrer constant (set to 0.9)
λ: X-ray wavelength (Å)
β: Half width of diffraction line (rad)
θ: Bragg angle (rad)
Note that the value of β was corrected using the following formula.
β=(β ₀ ² - βi ² ) ^0.5
β ₀ : Half width obtained from the measurement peak of boron nitride agglomerated particles (actual value)
βi: Device-derived half-width obtained from measurement of standard sample Si

The boron nitride agglomerated particles according to the present invention are obtained by using a universal testing machine to perform load displacement measurements of applying loads of up to 10,000 N, and correcting the position based on the results of load variation measurements of scale-like non-agglomerated boron nitride particles. The boron nitride agglomerated particles have a load value of cohesive failure that is 2.5 times or more the load value of the standard sample in the same test. Since the boron nitride agglomerated particles according to the present invention have a breaking strength of 2.5 times or more by the above method, they do not break and maintain high thermal conductivity even when highly filled as a filler in a sheet member. can do.

The breaking strength of the boron nitride agglomerated particles was measured as follows. 100 mg of boron nitride agglomerated particles are placed in a mold with an inner diameter of 7.2 mm, and after being well leveled, the powder is compressed using a metal push rod with a diameter of 7.2 mm. To compress the powder, a universal testing machine "VE20D" manufactured by Toyo Seiki Co., Ltd. is used to measure load displacement up to 10,000N. SP-2 (manufactured by Denka Co., Ltd., BN content 97%, D50: 4 μm, specific surface area: 34 m ² /g), which is scaly boron nitride, was previously measured, and the measurement data of the prepared boron nitride particles and SP-2 measurement data are superimposed at the point of a load of 10,000 N (offsetting the displacement of the boron nitride agglomerated particle data). At the point of displacement 0, the load on SP-2 of scale-like non-agglomerated particles becomes 0N (it can be assumed that the agglomeration is broken at the point of displacement 0), but for boron nitride agglomerated particles, a certain amount of load is applied due to the destruction of agglomeration. A load is generated. The load of each boron nitride agglomerated particle prepared was divided by the load of PTX60, a boron nitride agglomerated particle manufactured by Momentive (PTX60 was used as a standard sample, and the particle strength value of PTX60 was set as 1), and the value was determined as the fracture strength of the particle. did.

The boron nitride agglomerated particles according to the present invention preferably have a median diameter of 50 μm or more and 100 μm or less. By setting the median diameter to 50 μm or more, the thermal conductivity when blended into a sheet member can be improved. Further, by setting the thickness to 100 μm or less, it is possible to prevent the filler from coming out when it is blended as a filler into a thin sheet member.

The boron nitride agglomerated particles according to the present invention preferably have a BET specific surface area of 30 m ² /g or more and 50 m ² /g or less. Generally, when boron nitride is used as a filler, the smaller the specific surface area, the better the kneading properties with the resin and the filling rate can be improved. However, the boron nitride aggregate particles of the present invention are primary particles of hexagonal boron nitride. BET specific surface area By setting the surface area to 30 m ² /g or more, the number of points of contact between primary particles increases, and the strength of the aggregated particles can be improved. Furthermore, when blended into a sheet member, the contact area between the boron nitride aggregate particles and the resin increases, making it possible to suppress desorption of the filler and the resin. Further, by setting the BET specific surface area to 50 m ² /g or less, kneading into the resin becomes easy.

<Method for producing boron nitride agglomerated particles>
The method for producing boron nitride aggregate particles according to the present invention includes a slurry preparation step of mixing boron nitride particles, water, a dispersant, and an organic binder to prepare a slurry, and granulating using the prepared slurry. A granulation step, a degreasing step of defatting the granulated particles, a firing step of firing the defatted granulated particles in a non-oxidizing gas atmosphere, and a classification step of crushing and classifying the fired particles. include. First, the materials used in the method for producing boron nitride aggregate particles will be explained.

The boron nitride particles used in the method for producing boron nitride aggregate particles according to the present invention are not particularly limited, but from the viewpoint of obtaining boron nitride aggregate particles with excellent strength, boron nitride particles have an oxygen content of 10% by mass or less. can be used in the process. The oxygen content of the boron nitride agglomerated particles is more preferably 5% by mass or less.

The water used in the method for producing boron nitride aggregate particles according to the present invention is preferably pure water. The water may contain an organic solvent as long as it does not affect the production of boron nitride aggregate particles. From the viewpoint of suppressing crystal growth of boron nitride agglomerated particles, it is preferable that it contains an organic solvent.

The dispersant used in the method for producing boron nitride agglomerated particles according to the present invention may be any dispersant as long as it enhances the dispersibility of boron nitride particles in the slurry and uniformly disperses the boron nitride particles. Examples of dispersants that can be used include polycarboxylic acid dispersants, acrylic dispersants, and urethane dispersants. Preferred are polycarboxylic acid dispersants, such as alkylolamine salts of carboxylic acid polymers and polycarboxylic acid copolymers. As the alkylolamine salt of a carboxylic acid polymer, for example, DISPERBYK-2010 manufactured by BYK-Chemie can be used. As the polycarboxylic acid copolymer, for example, Selander Dispersant S manufactured by HiChem Co., Ltd. can be used.

The organic binder used in the method for producing aggregated boron nitride particles according to the present invention may be any organic binder as long as it can firmly bind the hexagonal boron nitride particles and stabilize the shape of the granulated particles. As the organic binder, polyvinyl alcohol, methylcellulose, polyvinylidene fluoride, polyvinyl butyral, polyethylene glycol, glycerol, etc. can be used. Polyvinyl alcohol can be suitably used, and for example, Cerna WF-804 manufactured by Chukyo Yushi Co., Ltd. can be used.

In the method for producing boron nitride aggregate particles according to the present invention, the total proportion of the carbon-containing substance, that is, the dispersant and the organic binder in the slurry is 5% by mass or more and 10% by mass or less. Crystal growth of boron nitride is promoted by the presence of oxides such as boron oxide in the slurry, but the dispersant and carbon contained in the organic binder in the slurry reduce the oxides and suppress crystal growth. can. By setting the total proportion of the dispersant and organic binder in the slurry to 5% by mass or more and 10% by mass or less, it becomes easy to control the crystallite diameter of the boron nitride aggregate particles to 160 Å or more and 200 Å or less. In addition, in order to adjust the carbon content in the slurry, in addition to the dispersant and the organic binder, carbon-containing components such as hydrocarbons such as carbon and paraffin may be added.

In the method for producing boron nitride agglomerated particles according to the present invention, the slurry contains boron nitride particles, water, a dispersant, and an organic binder. It is preferable that the composition contains 30% by mass or more and 60% by mass or less, a dispersant in a proportion of 5% by mass or more and 10% by mass or less, and an organic binder in a proportion of 1% by mass or more and 4% by mass or less. By setting the ratio of each component in the slurry within the above range, boron nitride aggregate particles with excellent strength can be produced. Further, the solid content concentration in the slurry is preferably 35% by mass or more and 50% by mass or less, and the proportion of the carbon-containing substance derived from the dispersant and the organic binder with respect to the total solid content is 10% by mass or more and 20% by mass. It is preferable that it is below.

Next, each step of the method for producing boron nitride agglomerated particles will be explained.
In the slurry preparation step, boron nitride particles as materials, water, a dispersant, and an organic binder are weighed and mixed. Mixing can be performed using a general mixer such as a ball mill, bead mill, planetary mixer, Henschel mixer, ribbon blender, etc., but it is preferable to use a ball mill. From the viewpoint of uniformly dispersing the boron nitride particles, it is preferable to mix the liquid material and then add the solid material in several portions and repeat the stirring.

The granulation process can be performed by a granulation method such as a spray drying method, a rolling method, a fluidized bed method, or a stirring method. It is preferable to carry out granulation by a spray drying method. In order to obtain boron nitride agglomerated particles with a large median diameter, a device equipped with a rotating disk is preferred. Slurry particles formed into droplets using a spray dryer or the like are dried at 150°C to 200°C.

In the degreasing step, organic components such as a dispersant and an organic binder component are removed from the granulated particles. The degreasing process is performed under a nitrogen gas atmosphere. By performing the degreasing step in a nitrogen gas atmosphere, desorption of carbon from the granulated particles can be reduced, and crystal growth of the boron nitride agglomerated particles can be suppressed. The degreasing treatment can be carried out by raising the temperature to 400 °C to 600 °C at a rate of 10 °C/hour to 40 °C/hour, and then heating for 3 to 6 hours, but it is preferable to perform the degreasing treatment in two stages by changing the temperature. . When performing the degreasing treatment in two stages, the first degreasing step is to raise the temperature to 400° C. at a rate of 8° C./hour to 15° C./hour and heating for 1.5 to 2.5 hours, and the second degreasing step is as follows: The temperature may be raised to 600°C at a rate of 20°C/hour to 40°C/hour and heated for 2.5 hours to 3.5 hours. After heat treatment, cool to room temperature. Natural cooling is preferable for cooling.

In the firing step, the degreased granulated particles are heated in a non-oxidizing gas atmosphere at a temperature of 1800° C. or more and 2200° C. or less for about 10 to 20 hours. Examples of the non-oxidizing gas include nitrogen gas, helium gas, and argon gas. The firing process is preferably performed in two stages at different temperatures. When performing the firing process in two stages, the first firing step is to raise the temperature to 1,600°C to 1,660°C at a rate of 300°C/hour to 600°C/hour and heat for 5 to 20 minutes, and the second firing step is to The temperature may be raised from 70°C to 2200°C at a rate of 70°C/hour to 120°C/hour and heated for 10 hours to 20 hours.

The firing step can also be performed by placing the defatted granulated particles in a container. When granulated particles are placed in a container and fired, the smaller the amount of granulated particles relative to the capacity of the container, the more suppressed crystal growth can be. The height of the granulated particles placed inside the container relative to the height inside the container is preferably 5% or more and 20% or less. More preferably, it is 10% or more and 15% or less. As the container material, carbon, aluminum nitride, silicon carbide, boron nitride, etc. can be used as appropriate.

After heat treatment, cool to room temperature. Preferably, the cooling is performed in two stages. In the case of cooling in two stages, the first cooling step may be to lower the temperature from 1200° C. to 1400° C. at a rate of 250° C./hour to 350° C./hour, and the second cooling step may be natural cooling to room temperature.

In the classification step, the fired boron nitride aggregate particles are crushed and classified. The crushing can be performed using a mortar or the like, or a jaw crusher, a roll crusher, or the like. After crushing, the boron nitride aggregate particles are classified using a vibrating sieve or the like. Alternatively, crushing and classification may be performed using a mass colloider. Preferably, after crushing with a jaw crusher, the particle size distribution of the boron nitride agglomerated particles is adjusted with a mass colloider, and classified with a vibrating sieve.

<Sheet member>
The sheet member according to the present invention contains the above-described boron nitride agglomerated particles and resin. The resin used for the sheet member is not particularly limited, and may include various rubbers, thermoplastic elastomers, etc. in addition to thermoplastic resins and thermosetting resins. As the resin, a thermosetting resin can be suitably used from the viewpoint of heat resistance, dimensional stability, etc. Examples of the thermosetting resin include epoxy resin, silicone resin, phenol resin, urea resin, unsaturated polyester resin, polyimide resin, urethane resin, and melamine resin.

In general, boron nitride has hydroxyl groups covalently bonded to its surface, so it is well kneaded into polar resins such as epoxy resins, but it is difficult to knead into less polar silicone resins, so silicone resins etc. When a high concentration of boron nitride is blended into a low polar resin, the viscosity of the resin composition increases, and during kneading, boron nitride agglomerated particles with low strength are destroyed, resulting in a low thermal conductivity. was. Since the boron nitride agglomerated particles according to the present invention have excellent strength, they can maintain thermal conductivity without being destroyed even during high-load kneading when producing sheet members using low polarity resins such as silicone resins, making them suitable for use. It can be used for.

As the silicone resin, an addition reaction type silicone resin having an alkenyl group as a functional group and crosslinked with a crosslinking agent can be suitably used. Two or more types of silicone resins may be used in combination in consideration of ease of handling and the like. For example, a silicone resin that is gel-like after curing and a silicone resin that is rubber-like after curing can be used together. An example of a silicone resin that becomes gel-like after curing is "TSE3062" manufactured by Momentive, and an example of a silicone resin that becomes rubber-like after curing is "TSE3033" manufactured by Momentive.

The sheet member according to the present invention may contain, in addition to the boron nitride aggregated particles and the resin, an inorganic filler whose median diameter is 1/200 to 1/2 of the boron nitride aggregated particles. Examples of the inorganic filler include boron nitride, alumina, silica, aluminum nitride, silicon nitride, and magnesium oxide. Two or more kinds of inorganic fillers, or a plurality of the same kinds having different median diameters may be used in combination. By using the boron nitride agglomerated particles according to the present invention together with inorganic fillers having different median diameters, it becomes possible to fill the filler with a high degree of filling, and high thermal conductivity can be obtained.

The sheet member according to the present invention contains boron nitride aggregate particles in a proportion of 20% by mass to 60% by mass, resin in a proportion of 20% by mass to 60% by mass, and inorganic filler in a proportion of 20% by mass to 60% by mass. preferable. By setting the above content ratio, a sheet member having excellent thermal conductivity and moldability can be obtained.

A conventionally known method can be used to prepare the sheet member. The sheet member is first made by mixing materials to form a resin composition, and then molding the resin composition into a shape such as a sheet. When a thermosetting resin is used as the resin, it may be cured by heating after molding. The resin composition is prepared by adding filler such as boron nitride agglomerated particles to a liquid resin material or a resin material melted by heating, and then kneading the mixture using a rotation-revolution stirrer, a planetary mixer, a kneader, a single-screw or twin-screw kneader, etc. It can be adjusted using a device. From the viewpoint of uniformly dispersing the boron nitride agglomerated particles, it is preferable to add the filler to the liquid resin in several portions and repeat stirring. After the resin composition is prepared, it can be molded into a sheet member by injection molding, extrusion molding, injection compression molding, compression molding, or the like.

The thickness of the sheet member is 50 μm or more and 10 mm or less, more preferably 100 μm or more and 2 mm or less, even more preferably 100 μm or more and 1 mm or less, particularly preferably 100 μm or more and 500 μm or less. From the viewpoint of reducing the thickness and thermal conductivity of electronic components using the sheet member, the thickness of the sheet member is preferably 100 μm or more and 200 μm or less.

The boron nitride agglomerated particles according to the present invention can be suitably used as a filler for a sheet member for the purpose of dissipating heat from heat generating members such as microprocessors and power transistors. Since the boron nitride agglomerated particles according to the present invention have excellent strength, they can be highly filled even in low polar resins such as silicone resins that are difficult to be compatible with boron nitride, and exhibit a high heat transfer effect.

Examples are shown below to explain the present invention in more detail, but the present invention is not limited to these Examples.

<Evaluation method>
- Median diameter Dry particle size distribution measurement of the prepared boron nitride aggregate particles was performed using "MASTERSIZER 3000" manufactured by Malvern Panalytical, and the median diameter was calculated.
- BET specific surface area Measurement was performed by nitrogen gas adsorption using "TriStar II 3020" manufactured by Micrometrics.
- SEM observation A tabletop electron microscope "JCM-6000" manufactured by JEOL Ltd. was used.

・Crystallite size evaluation (powder XRD diffraction)
Diffraction lines were measured using "Ultima IV" manufactured by Rigaku Corporation, and the half width of the peak at 2θ=26.6° (002 plane) was determined using the following Scherrer equation.
D = Kλ/βcosθ
D: Crystallite diameter (Å)
K: Scherrer constant (set to 0.9)
λ: X-ray wavelength (Å)
β: Half width of diffraction line (rad)
θ: Bragg angle (rad)
Note that the value of β was corrected using the following formula.
β=(β ₀ ² - βi ² ) ^0.5
β ₀ : Half width obtained from the measurement peak of boron nitride agglomerated particles (actual value)
βi: Device-derived half-width obtained from measurement of standard sample Si

・Particle strength evaluation - JIS method -
Fracture strength was measured in accordance with JIS R1639-5 and JIS Z8844 using a micro compression testing machine "MCT510" manufactured by Shimadzu Corporation.
-Internal law-
100 mg of boron nitride agglomerated particles are placed in a mold with an inner diameter of 7.2 mm, and after being well leveled, the powder is compressed using a metal push rod with a diameter of 7.2 mm. To compress the powder, a universal testing machine "VE20D" manufactured by Toyo Seiki Co., Ltd. is used to measure load displacement up to 10,000N. SP-2 (manufactured by Denka Co., Ltd., BN content 97%, D50: 4 μm, specific surface area: 34 m ² /g), which is scaly boron nitride, was previously measured, and the measurement data of the prepared boron nitride particles and SP-2 measurement data are superimposed at the point of a load of 10,000 N (offsetting the displacement of the boron nitride agglomerated particle data). At the point of zero displacement, the load on SP-2 is 0N, but in the case of boron nitride agglomerated particles, a constant load is generated due to the destruction of the agglomeration. The particle strength was determined by dividing the load of each prepared boron nitride agglomerated particle by the load of PTX60, which is a commercially available boron nitride agglomerated particle (the value of PTX60 was taken as 1).

・Thermal conductivity of the sheet Aluminum blocks with the same area and holes for inserting thermocouples are pasted on the top and bottom surfaces of the sheet measurement sample, and an air-cooled heat sink is placed on the bottom surface of the sample sandwiched between the blocks. , a resistance heating type heater with the same area is placed on the top surface. A constant load is applied from above the resistance heating type heater to generate a constant amount of heat Q from the heater. After a certain period of time has passed, the temperature difference between the upper and lower thermocouples becomes a constant value △T, and from the amount of heat Q and the area S of the sample, the sum of the thermal resistance (Rc) of the aluminum block and the interface, and the thermal resistance (Rs) of the sample is Rt. (Rc+Rs) is calculated. By performing measurements with different sample thicknesses, it is possible to measure the thermal resistance that increases with thickness, and since this depends on the thermal conductivity of the material, the thermal conductivity λ of the sheet can be obtained from this. In this example, sheets with thicknesses of 0.6, 0.8, 1.0, 1.2, and 1.4 m were produced and their thermal conductivities were measured.
Rt=△T・S/Q
λ=d/Rs=d/(Rt-Rc)
Rt: Overall thermal resistance (K・m ² /W)
△T: Temperature difference (K)
Q: Heat amount (W)
S: Area (m ² )
λ: Thermal conductivity (W/m・K)
d: Sample thickness (m)
Rs: Thermal resistance of sample (K・m ² /W)
Rc: Thermal resistance of the aluminum block and sample interface (K・m ² /W)

- Kneadability into resin After a resin composition was prepared using a rotation-revolution stirrer, the kneadability of the boron nitride aggregate particles into the resin was visually evaluated.
〇: The resin composition is cohesive. △: Some parts of the resin composition are not cohesive. ×: The resin composition is scattered and not cohesive.

<Materials used>
Boron nitride powder... Nissin Refratec Co., Ltd. "ABN"
Dispersant: BYK-Chemie “DISPERBYK-2010”
Or Hichem's "Selander Dispersant S"
Binder: Chukyo Yushi Co., Ltd. “Serna WF-804”
Alumina filler...Nippon Steel Chemical & Materials Co., Ltd. "AX3-15" (median diameter: 4.5±0.6μm)
Carbon: Mitsubishi Chemical Corporation “Mitsubishi Carbon Black #30”
Matrix resin: Momentive silicone resin “TSE3033”
Momentive silicone resin “TSE3062”

(Example 1)
A slurry was prepared by mixing 600 g of boron nitride powder as a raw material, 900 g of ion-exchanged water, 72 g of DISPERBYK-2010 as a dispersant, and 30 g of a binder, and using a ball mill. The ball mill had a pot made of nylon, an inner diameter of 250 mm, a pot volume of 17 L, and nylon balls with iron cores of Φ25 (1.5 kg) and Φ12 (1 kg) as balls, and mixing was carried out at a rotation speed of 50 rpm for 2 hours.
Boron nitride was granulated from the prepared slurry using a "TR160 turning spray dryer" manufactured by Priss Co., Ltd. Granulation was carried out at a spray dryer with an atomizer disk rotating at 18,000 rpm, a slurry feed rate of 3 kg/hour, and a drying time of 180°C.
The granulated boron nitride particles were degreased in three stages under a nitrogen gas atmosphere. First, the temperature was raised from room temperature to 400°C at a rate of 11.2°C/hour, held at 400°C for 2 hours, then the temperature was raised from 400°C to 600°C at a rate of 31.1°C/hour, and held at 600°C for 3 hours. After that, it was naturally cooled to room temperature. The atmosphere for the degreasing step was nitrogen gas.
After the degreasing process, the boron nitride particles were fired in four stages under nitrogen gas. First, the temperature was raised from room temperature to 1650°C at a rate of 511.6°C/hour, held at 1650°C for 10 minutes, then the temperature was raised from 1650°C to 1910°C at a rate of 90.2°C/hour, and held at 1910°C for 16 hours. After that, the temperature was lowered from 1910°C to 1300°C at a rate of 310.2°C/hour, and then naturally cooled to room temperature. Note that the firing was performed with the sample placed in a boron nitride container up to 14.0% of the height of the container.
The boron nitride particles after the heat treatment were crushed in an agate mortar and sieved with an opening of 500 μm. The boron nitride particles on the sieve were repeatedly crushed and classified until the entire amount passed through the sieve. The median diameter, BET specific surface area, and crystallite diameter of the obtained boron nitride agglomerated particles were measured by the method described above, and SEM observation was performed.

A sheet member was also molded from the obtained boron nitride aggregated particles, alumina filler, and silicone resin.
First, 1 g of silicone resin TSE3033 (A), 1 g of TSE3033 (B), 3 g of TSE3062 (A), and 3 g of TSE3062 (B) were mixed under vacuum using a revolution-revolution stirrer (SK-300TVS, Photo Chemical Co., Ltd.). The mixture was stirred by rotating at 182 rpm and rotating at 550 rpm for 60 seconds.
Thereafter, boron nitride aggregate particles and alumina filler were added to the silicone resin, and the mixture was stirred under atmospheric pressure for 60 seconds while revolving at 1420 rpm and rotating at 781 rpm to prepare a resin composition. Boron nitride agglomerated particles and alumina filler are added in multiple batches while checking the state of the composition, and the total addition amount is 7.19 g of boron nitride agglomerated particles and 7.83 g of alumina filler. Stirring was performed under the above conditions.

The prepared resin composition was sandwiched between release films in a stretching machine in which a metal movable stage and a metal rotating roll could be placed in an arbitrary gap, and the gap between the stage and the roll was set to 2.5 mm. After passing through the resin composition, the release film on one side of the resin composition was peeled off, and the resin composition was left standing in a vacuum desiccator with that side facing up, and degassed by evacuating with a rotary pump (relative to atmospheric pressure). Pressure: -0.1 Pa or less, maintained for 30 minutes or more).
The gap of the stretching machine was set to the desired sheet thickness (thickness: 0.6, 0.8, 1.0, 1.2, 1.4 mm), and after vacuuming, the resin composition was affixed with a release film again. was placed on a stage and passed between the roll and the stage to form a sheet member of the desired thickness.
The formed sheet member was heated and cured at 135° C. for 24 hours using a forced convection dryer.
The thermal conductivity of the obtained sheet member was calculated by the method described above.

(Example 2)
Boron nitride agglomerated particles were prepared in the same manner as in Example 1, except that 1.8 g of carbon was added to the slurry, and a sheet member was molded using the obtained boron nitride agglomerated particles.

(Comparative example 1)
A sheet member was molded in the same manner as in Example 1 using PTX60 manufactured by Momentive.

(Comparative example 2)
Example 1 except that the amount of binder used was 18 g, the degreasing process was performed under atmospheric flow, and the firing was performed with the sample placed in the boron nitride container to a height of 70.0% of the container height. Boron nitride aggregated particles were prepared in the same manner, and a sheet member was molded using the obtained boron nitride aggregated particles.

(Comparative example 3)
The amount of dispersant used was 90 g, the amount of binder used was 18 g, and the sample was placed in a boron nitride container to a height of 18.0% of the container height at 1855°C (heating rate and cooling rate were determined by Boron nitride agglomerated particles were prepared in the same manner as in Example 1, except that baking was performed for 8 hours (same as in Example 1), and a sheet member was formed using the obtained boron nitride agglomerated particles.

(Comparative example 4)
Boron nitride was prepared in the same manner as in Example 1, except that the amount of dispersant used was 90 g, and the sample was placed in the boron nitride container to a height of 18.0% of the container height, and firing was performed for 5 hours. Aggregated particles were prepared, and a sheet member was molded using the obtained boron nitride agglomerated particles.

(Comparative example 5)
The dispersant was changed to Selander S and 90g was added, and the degreasing process was performed under atmospheric flow, and the sample was placed in a boron nitride container to a height of 23.2% of the container height, and baked for 5 hours. Except for the above steps, boron nitride aggregated particles were prepared in the same manner as in Example 1, and the obtained boron nitride aggregated particles were used to mold a sheet member.

(Comparative example 6)
Nitriding was carried out in the same manner as in Example 1, except that the degreasing process was carried out under atmospheric flow, and the sample was placed in the boron nitride vessel to a height of 15.1% of the container height, and firing was carried out for 5 hours. Boron aggregated particles were prepared, and a sheet member was molded using the obtained boron nitride aggregated particles.

(Comparative Example 7)
90g of dispersant was blended, no binder was used, the degreasing process was performed under atmospheric flow, and the sample was placed in a boron nitride container to a height of 7.5% of the container height and fired for 5 hours. Except for the above steps, boron nitride aggregated particles were prepared in the same manner as in Example 1, and the obtained boron nitride aggregated particles were used to mold a sheet member.

As shown in Table 1, it was confirmed that the boron nitride agglomerated particles of Examples 1 and 2 with crystallite diameters of 160 Å or more and 200 Å or less had very high breaking strength and were excellent in kneading into resin.

Claims (13)

Boron nitride agglomerated particles in which primary particles of hexagonal boron nitride are agglomerated,
The crystallite diameter of the 002 plane of the primary particle is 160 Å or more and less than 200 Å,
In the load displacement measurement using a universal testing machine and applying a load of up to 10,000 N, the load value of cohesive failure obtained by position correction based on the load variation measurement results of scale-like non-agglomerated boron nitride particles is the same as that of the standard sample. Boron nitride agglomerated particles with a load value of 2.5 times or more in the same test. The median diameter is 50 μm or more and 100 μm or less,
The boron nitride agglomerated particles according to claim 1, having a BET specific surface area of 30 m ² /g or more and 50 m ² /g or less. A sheet member comprising the boron nitride agglomerated particles according to claim 1 or 2 and a resin. The sheet member according to claim 3, comprising an inorganic filler having a median diameter of 1/50 to 1/5 of the boron nitride agglomerated particles. Boron nitride aggregate particles, resin, and inorganic filler, boron nitride aggregate particles from 20% by mass to 60% by mass, resin from 20% by mass to 60% by mass, and inorganic filler from 20% by mass to 60% by mass. The sheet member according to claim 4, wherein the sheet member comprises a proportion. 5. The sheet member according to claim 4, wherein the inorganic filler is selected from boron nitride, alumina, silica, aluminum nitride, silicon nitride, and magnesium oxide. The sheet member according to claim 3, wherein the resin is a thermosetting resin. The sheet member according to claim 7, wherein the resin is a silicone resin. A method for producing boron nitride agglomerated particles according to claim 1 or 2, comprising:
a slurry preparation step of mixing boron nitride particles, water, a dispersant, and an organic binder to prepare a slurry;
A granulation step of granulating using the adjusted slurry;
a degreasing step of degreasing the granulated particles in a non-oxidizing gas atmosphere;
a firing step of firing the degreased granulated particles in a non-oxidizing gas atmosphere;
A classification step of crushing and classifying the fired particles,
The proportion of carbon-containing substances derived from the dispersant and the organic binder in the slurry is 5% by mass or more and 10% by mass or less,
The firing step includes:
A first firing step of raising the temperature at 300°C/hour to 600°C/hour to a temperature of 1600°C to 1660°C and firing for 5 to 20 minutes;
A method for producing boron nitride agglomerated particles, comprising: a second firing step in which the temperature is raised from the first firing temperature to a temperature of 1800° C. to 2200° C. at a rate of 70° C./hour to 120° C./hour and fired for 10 hours to 20 hours. The method for producing aggregated boron nitride particles according to claim 9, wherein the boron nitride particles used in the slurry preparation step have an oxygen content of 10% by mass or less. The method for producing boron nitride aggregate particles according to claim 9, wherein the degreasing step is performed under a nitrogen gas atmosphere. 10. The method for producing boron nitride aggregate particles according to claim 9, wherein the degreasing step is performed with the granulated particles placed in a container to a height of 5% or more and 20% or less of the container height. A claim in which the solid content concentration in the slurry is 35% by mass or more and 50% by mass or less, and the ratio of the carbon-containing substance derived from the dispersant and the organic binder to the total solid content is 10% by mass or more and 20% by mass or less. 9. The method for producing boron nitride agglomerated particles according to 9.

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