Plasma treatment method, method for producing plasma-treated hexagonal boron nitride powder, and plasma treatment device

Abstract

Provided is a hexagonal boron nitride powder that can obtain higher thermal conductivity when added to a resin as a filler. A plasma treatment method, wherein the hexagonal boron nitride powder is subjected to plasma treatment under reduced pressure, the hexagonal boron nitride powder is contained in a treatment container, a plasma generating gas is supplied into the treatment container and the pressure in the treatment container is maintained at a pressure lower than atmospheric pressure, the treatment container is rotated with the central axis of the treatment container as the rotation axis, and a high frequency is applied to an electrode disposed outside the treatment container, thereby subjecting the hexagonal boron nitride powder in the treatment container to plasma treatment, wherein the rotation axis of the treatment container is tilted relative to the horizontal, and during the plasma treatment, one or both of the treatment container and the electrode are cooled.

Description

Technical Field

[0001] The present invention relates to a plasma treatment method for plasma-treating hexagonal boron nitride powder under reduced pressure, a method for producing plasma-treated hexagonal boron nitride powder, and a plasma treatment device for plasma-treating hexagonal boron nitride powder under reduced pressure. Background Art

[0002] In recent years, as the energy density of electronic devices has increased due to the miniaturization of electronic devices, the amount of heat generated per unit volume has been increasing. Therefore, there is a strong demand for insulating materials that constitute electronic devices to have high heat dissipation properties.

[0003] As the above-mentioned insulating material, resins such as epoxy resins are widely used in view of the high insulation voltage and the ease of molding. However, the thermal conductivity of resins is low, so the desired heat dissipation cannot be obtained by resin alone. Therefore, in order to increase the thermal conductivity, inorganic fillers with high thermal conductivity and electrical insulation are usually added to the resin.

[0004] As the inorganic filler, powders of various materials such as hexagonal boron nitride and aluminum nitride are used. Among them, hexagonal boron nitride is excellent in thermal stability, chemical stability, electrical insulation and other properties, and is therefore widely used as a thermally conductive filler added to insulating materials.

[0005] However, since the particles of hexagonal boron nitride have a scaly shape derived from its crystal structure, when the particles of hexagonal boron nitride powder are directly added to the resin, the scaly particles are oriented parallel to each other. Moreover, as a result, although high thermal conductivity is obtained in the direction horizontal to the surface of the scaly particles, sufficient thermal conductivity cannot be obtained in the vertical direction. For example, when hexagonal boron nitride powder is used as a filler for a thermally conductive sheet, the surface of the scaly particles is oriented in parallel to the surface of the sheet, so the thermal conductivity in the thickness direction of the thermally conductive sheet cannot be fully improved.

[0006] Therefore, in order to reduce the anisotropy of thermal conductivity, it is proposed to use agglomerated particles (secondary particles) obtained by agglomerating flaky hexagonal boron nitride particles as primary particles as fillers (for example, Patent Document 1). Agglomerated particles include primary particles in various directions, so the anisotropy of thermal conductivity is low, and high thermal conductivity can be obtained in any direction.

[0007] On the other hand, as a method for improving the properties of an inorganic filler, a method of subjecting an inorganic filler to plasma treatment is also known. For example, Patent Document 2 proposes a technique for introducing amino groups into the surface of a boron nitride powder by subjecting the boron nitride powder to plasma treatment.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-116401

[0009] Patent Document 2: Japanese Patent Application Publication No. 2015-137335

[0010] The above-mentioned technique can improve the performance of hexagonal boron nitride powder as a filler. However, in recent years, as electronic devices are further miniaturized, the heat generated per unit volume is further increased, and higher heat dissipation properties are required for insulating materials constituting electronic devices. Summary of the invention

[0011] The present invention has been made in view of the above circumstances, and its object is to provide a hexagonal boron nitride powder that can obtain higher thermal conductivity when added to a resin as a filler. In addition, the present invention provides a plasma treatment method, a method for producing plasma-treated hexagonal boron nitride powder, and a plasma treatment device that can achieve the above object.

[0012] First, the findings obtained as a result of the inventors' research to solve the above-mentioned problems are described. In the following description, the "thermal conductivity" of the hexagonal boron nitride powder refers to the thermal conductivity of the resin material to which the hexagonal boron nitride powder is added as a filler.

[0013] Usually, as the plasma treatment for the purpose of surface modification, atmospheric pressure plasma treatment is used. In the atmospheric pressure plasma treatment, it is possible to process under atmospheric pressure, so there is the advantage that the processing of the processed object is easy and a decompression device is not required. In fact, in the embodiment of patent document 2, atmospheric pressure plasma treatment is also used.

[0014] However, the inventors' research results show that sufficient thermal conductivity cannot be obtained when atmospheric pressure plasma treatment is applied to hexagonal boron nitride powder having an aggregate structure. This is believed to be because the atmospheric pressure plasma treatment destroys the aggregate structure and increases the anisotropy of thermal conductivity.

[0015] On the other hand, it is known that the thermal conductivity of the hexagonal boron nitride powder having an aggregate structure can be further improved by the reduced pressure plasma treatment.

[0016] Reduced pressure plasma is a type of low-temperature plasma. In reduced pressure plasma, only the electrons generated by ionization have high energy (several eV to tens of eV), while the atoms and molecules of the gas and the ions generated by ionization have only low energy (less than 0.1 eV) at room temperature. By utilizing the high energy of the electrons, plasma processing can be performed at low temperatures.

[0017] However, most conventional reduced pressure plasma treatment devices process substrate-shaped or sheet-shaped objects to be treated, and therefore cannot efficiently process powders. For example, when powder is spread on a flat workbench and plasma is irradiated from above, only the surface of the spread powder is treated, and the powder inside is not treated. Therefore, a method for efficiently and uniformly performing reduced pressure plasma treatment on hexagonal boron nitride powder is sought.

[0018] In addition, plasma treatment for the purpose of improving wettability is usually carried out for a treatment time of tens of seconds to several minutes, but it is also clear that a long treatment time of tens of minutes is required to improve the thermal conductivity of hexagonal boron nitride powder by reduced pressure plasma treatment. However, if a long-term reduced pressure plasma treatment is carried out, the temperature of the processing container and the electrode will rise, so there is a concern that the plasma treatment device will be damaged. In addition, due to long-term exposure to plasma at high temperature, there is also a concern that the boron nitride powder, which is the object to be treated, will deteriorate. In order to suppress the temperature rise, it is also considered to perform plasma treatment intermittently, but in this case, the time required for the treatment increases and the treatment efficiency decreases.

[0019] As a result of the research, it was found that the above-mentioned problem can be solved by using a processing container that rotates in an inclined state to cool one or both of the processing container and the electrode while performing reduced pressure plasma treatment, thereby efficiently obtaining hexagonal boron nitride powder with excellent thermal conductivity.

[0020] The present invention has been accomplished based on the above findings, and its main structure is as follows.

[0021] 1. A plasma treatment method, wherein hexagonal boron nitride powder is subjected to plasma treatment under reduced pressure, wherein:

[0022] The hexagonal boron nitride powder is placed in a processing container.

[0023] supplying a plasma generating gas into the processing container and maintaining the pressure in the processing container at a pressure lower than atmospheric pressure,

[0024] The processing container is rotated with the central axis of the processing container as the rotation axis, and a high frequency is applied to an electrode disposed outside the processing container, thereby performing plasma treatment on the hexagonal boron nitride powder in the processing container.

[0025] At this time, the rotation axis of the processing container is inclined relative to the horizontal.

[0026] During the plasma processing, one or both of the processing container and the electrode are cooled.

[0027] 2. A method for producing plasma treated hexagonal boron nitride powder, wherein:

[0028] The raw material hexagonal boron nitride powder is placed in a processing container.

[0029] supplying a plasma generating gas into the processing container and maintaining the pressure in the processing container at a pressure lower than atmospheric pressure,

[0030] The processing container is rotated with the central axis of the processing container as the rotation axis, and a high frequency is applied to an electrode disposed outside the processing container, thereby plasma-treating the hexagonal boron nitride powder in the processing container to obtain plasma-treated hexagonal boron nitride powder.

[0031] At this time, the rotation axis of the processing container is inclined relative to the horizontal.

[0032] During the plasma processing, one or both of the processing container and the electrode are cooled.

[0033] 3. A plasma treatment apparatus for performing plasma treatment on hexagonal boron nitride powder under reduced pressure, comprising:

[0034] A processing container for containing the hexagonal boron nitride powder;

[0035] A gas supply unit for supplying a plasma generating gas into the processing container;

[0036] A decompression unit for maintaining the pressure in the processing container at a pressure lower than atmospheric pressure;

[0037] A rotating mechanism for rotating the processing container with the central axis of the processing container as the rotation axis in a state where the rotation axis is inclined relative to the horizontal;

[0038] An electrode, disposed outside the processing container;

[0039] A high-frequency power source applies a high frequency to the electrodes; and

[0040] The cooling unit cools one or both of the processing container and the electrode.

[0041] According to the present invention, a hexagonal boron nitride powder can be obtained that can obtain higher thermal conductivity when added to a resin as a filler. Therefore, the hexagonal boron nitride powder obtained by the method of the present invention can be extremely suitable for use as a thermal conductive filler added to a resin material. In addition, according to the present invention, a hexagonal boron nitride powder having the above-mentioned characteristics can be efficiently manufactured. The resin material containing the hexagonal boron nitride powder obtained by the present invention can be extremely suitable for use as an insulating material for electronic equipment that requires heat dissipation, such as a heat dissipation insulating sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram showing the structure of a plasma processing apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION

[0043] Next, a method for implementing the present invention will be specifically described. In addition, the following description shows a preferred embodiment of the present invention, and the present invention is not limited to the following description at all.

[0044] In a plasma treatment method according to an embodiment of the present invention, a hexagonal boron nitride powder as a treatment object is contained in a treatment container, and plasma treatment is performed under reduced pressure. In addition, in a method for producing a plasma-treated hexagonal boron nitride powder according to another embodiment of the present invention, a hexagonal boron nitride powder as a raw material is contained in a treatment container, and plasma treatment is performed under reduced pressure, thereby obtaining a plasma-treated hexagonal boron nitride powder. In addition, a plasma treatment apparatus according to an embodiment of the present invention includes a treatment container for containing the hexagonal boron nitride powder.

[0045] [Boron nitride powder]

[0046] The boron nitride powder as the object to be processed (raw material) is not particularly limited, and any hexagonal boron nitride powder can be used. In the following description, the hexagonal boron nitride powder may be simply referred to as boron nitride powder.

[0047] The shape of the boron nitride particles constituting the hexagonal boron nitride powder is not particularly limited, but is preferably scaly.

[0048] As the hexagonal boron nitride powder, it is preferable to use a hexagonal boron nitride powder having an aggregate structure. In other words, it is preferable that the hexagonal boron nitride powder has an aggregate structure in which hexagonal boron nitride particles as primary particles are aggregated to form secondary particles.

[0049] As described above, the hexagonal boron nitride powder having an aggregate structure reduces the anisotropy of thermal conductivity, so the thermal conductivity when added to the resin material as a filler is better. In addition, compared with the boron nitride powder without an aggregate structure, the boron nitride powder having an aggregate structure has a smaller specific surface area. Therefore, by using the boron nitride powder having an aggregate structure, the contact area between the boron nitride powder and the resin when mixed with the resin is reduced, and the viscosity of the resin composition can be reduced. Therefore, when the boron nitride powder has an aggregate structure, the manufacture of the resin material becomes easier.

[0050] Furthermore, in the present invention, since the reduced pressure plasma treatment is adopted, the aggregate structure of the hexagonal boron nitride powder is not destroyed, and a high thermal conductivity can be achieved.

[0051] (Main diameter of primary particle)

[0052] The major diameter of the particles (primary particles) constituting the boron nitride powder is preferably 1 μm or more. If the above-mentioned major diameter is 1 μm or more, it is easy to form the above-mentioned agglomerate structure. On the other hand, the major diameter of the preferred primary particles is 10 μm or less. If the above-mentioned major diameter is 10 μm or less, the manufacture does not require long-term high-temperature heating, so it can be easily manufactured.

[0053] In addition, the major diameter of primary particles can be measured using a scanning electron microscope (SEM). Specifically, secondary electron images are taken at an accelerating voltage of 1kV, and the size of the flaky boron nitride particles with the largest area in an agglomerate is set to major diameter. Wherein, the above-mentioned major diameter is the length in the SEM image. In addition, the major diameter of primary particles does not change due to plasma treatment. Therefore, the major diameter of the primary particles of the boron nitride powder as the processed object (raw material) is equal to the major diameter of the primary particles of the plasma-treated hexagonal boron nitride powder finally obtained.

[0054] (Median diameter of secondary particles)

[0055] In the case where the boron nitride powder has an agglomerate structure, the median particle size of the secondary particles is preferably set to be 20 μm or more. If the median particle size of the secondary particles is 20 μm or more, the specific surface area is small, and the viscosity increase when mixed with the resin can be suppressed, so the resin material is easy to form. On the other hand, the median particle size of the secondary particles is preferably 150 μm or less. If the median particle size of the secondary particles is 150 μm or less, the manufacturing does not require long-term high-temperature heating, and it is easy to manufacture.

[0056] In addition, in the present invention, the median particle size of the secondary particles refers to the median particle size D50 in the volume-based particle size distribution (cumulative distribution) measured by a laser diffraction particle size distribution measuring device. More specifically, the median particle size of the above-mentioned secondary particles can be obtained based on the volume-based particle size distribution measured at a discharge pressure of 0.01MPa using a laser diffraction particle size distribution measuring device (Malvern Panalytical: MASTERSIZER 3000). In addition, as described above, reduced pressure plasma treatment is used in the present invention, so the agglomerate structure of the boron nitride powder is not destroyed. Therefore, the median particle size of the secondary particles does not change due to plasma treatment. Therefore, the median particle size of the secondary particles of the boron nitride powder as the processed object (raw material) is equal to the median particle size of the secondary particles of the plasma-treated hexagonal boron nitride powder finally obtained.

[0057] [Processing container]

[0058] As the processing container, any container can be used as long as the hexagonal boron nitride powder to be processed can be contained, and the reduced pressure plasma treatment can be performed. Generally, a processing container made of glass is preferably used.

[0059] The shape of the processing container is not particularly limited, but it is preferably used with a substantially cylindrical main body because it is rotated as described below. More preferably, the processing container has a substantially cylindrical main body, a bottom provided at one end of the main body, and an opening provided at the other end of the main body. In addition, in order to smoothly stir the boron nitride powder inside during rotation, the processing container is preferably spherical-bottomed, in other words, the bottom is composed of a curved surface.

[0060] Preferably, the processing container has one or more convex portions on the inner surface for promoting stirring. By providing the convex portions on the inner surface of the processing container, the hexagonal boron nitride powder can be stirred more effectively when the processing container is rotated. Preferably, the convex portions are provided on one or both of the side and bottom surfaces of the processing container. The number of the convex portions is not particularly limited, but from the viewpoint of improving the stirring effect, it is preferably two or more, and more preferably three or more. On the other hand, if the number of convex portions is too large, in addition to the saturation of the effect, the structure of the processing container also becomes complicated and the manufacturing becomes difficult. Therefore, the number of convex portions is preferably less than 10, and more preferably less than 5. In the case where the processing container has a plurality of convex portions, the plurality of convex portions are preferably arranged to be symmetrical with the rotation axis of the processing container as the center point.

[0061] The shape of the convex portion is not particularly limited and can be any shape. For example, the convex portion can also be a ridge-shaped protrusion. In addition, the method for forming the convex portion is not particularly limited and can be formed by any method. For example, in the case where the processing container is made of glass, the convex portion can be formed by heating a part of the processing container to soften it and pressing the softened part from the outside to the inside.

[0062] [Gas supply / decompression]

[0063] In the present invention, a plasma generating gas is supplied into the processing container, and the pressure in the processing container is maintained at a pressure lower than the atmospheric pressure.

[0064] The plasma generating gas is not particularly limited, and any gas can be used. For example, a gas consisting of one or more selected from the group consisting of CO2, CO, O2, N2, H2O, Ar, He, and Ne can be used. In addition, the gas used can be changed in the middle of the plasma treatment, and the plasma treatment can be performed in multiple stages under different environments.

[0065] In addition, a plasma processing apparatus according to an embodiment of the present invention includes a gas supply unit for supplying a plasma generating gas into the processing container. As the gas supply unit, any device can be used as long as it can supply the required gas. The gas supply unit can include, for example, one or more gas cylinders. In addition, the gas supply unit preferably includes a flow rate adjustment unit such as a mass flow controller.

[0066] The pressure in the processing container is not particularly limited and can be any pressure as long as it allows reduced pressure plasma processing, but is usually preferably 1 to 100 Pa. If the pressure of the environment during plasma processing is 1 Pa or more and 100 Pa or less, the effect of plasma processing can be further improved.

[0067] In addition, a plasma processing apparatus according to an embodiment of the present invention includes a decompression unit for maintaining the pressure in the processing container at a pressure lower than the atmospheric pressure. As the decompression unit, any device can be used as long as the required pressure can be maintained. For example, a vacuum pump can be used as the decompression unit. In addition, the plasma processing apparatus of the present invention preferably includes a pressure gauge, which measures the pressure in the processing container or in a space connected to the processing container.

[0068] [Rotate]

[0069] In the present invention, the plasma treatment is performed while the processing container is rotated with the central axis of the processing container as the rotation axis. Moreover, at this time, the rotation axis of the processing container is in a state of being inclined relative to the horizontal. In addition, a plasma treatment apparatus according to an embodiment of the present invention includes a rotating mechanism, which rotates the processing container with the central axis of the processing container as the rotation axis while the rotation axis is inclined relative to the horizontal.

[0070] In this way, by rotating the processing container in an inclined state, the boron nitride powder inside the processing container is effectively stirred, and even when the amount of boron nitride powder is large, plasma processing can be uniformly performed in a short time. In addition, "the state in which the rotation axis is inclined relative to the horizontal" is defined as a state in which the smaller angle of the angle formed by the above-mentioned rotation axis and the horizontal plane exceeds 0° and is less than 90°. Hereinafter, the smaller angle of the angle formed by the above-mentioned rotation axis and the horizontal plane is sometimes referred to as "the inclination angle of the rotation axis" or simply "the inclination angle".

[0071] From the viewpoint of improving the stirring efficiency of the hexagonal boron nitride powder in the processing container, the inclination angle of the rotation axis is preferably 5° or more, more preferably 20° or more, and preferably 85° or less, more preferably 75° or less.

[0072] The rotation speed of the processing container is not particularly limited and can be any speed. Generally, the rotation speed can be adjusted so as to appropriately stir the hexagonal boron nitride powder. The rotation speed is, for example, preferably 1 to 50 rpm, and more preferably 5 to 30 rpm.

[0073] [Application of high frequency]

[0074] In the present invention, high frequency is applied to an electrode disposed outside the processing container while the processing container is rotated, thereby plasma-treating the hexagonal boron nitride powder in the processing container. Thus, plasma-treated hexagonal boron nitride powder can be obtained. In addition, a plasma processing apparatus according to an embodiment of the present invention includes: an electrode disposed outside the processing container; and a high frequency power supply for applying high frequency to the electrode.

[0075] The conditions for applying high frequency are not particularly limited and may be adjusted according to the type of gas used, pressure, size of the processing container, etc. For example, the voltage is preferably 1.0 to 5.0 kV, and the RF output is preferably 50 to 10,000 W.

[0076] The time required for plasma treatment depends on the amount of hexagonal boron nitride powder of the treatment object and the stirring conditions, so it is not particularly limited, and it can be adjusted to obtain the desired characteristics. However, as mentioned above, it takes a relatively long time to improve the thermal conductivity of hexagonal boron nitride powder. Therefore, typically, the plasma treatment time is preferably more than 10 minutes, and more preferably more than 20 minutes. On the other hand, if the treatment time is too long, in addition to the saturation effect, the productivity is also reduced. Therefore, the plasma treatment time is preferably less than 100 minutes, and more preferably less than 60 minutes.

[0077] [cool down]

[0078] Furthermore, in the present invention, it is important to cool one or both of the processing container and the electrode during the plasma treatment. In addition, a plasma treatment apparatus according to one embodiment of the present invention includes a cooling unit that cools one or both of the processing container and the electrode. By cooling at least one of the processing container and the electrode, it is possible to prevent the temperature of the apparatus from rising, and plasma treatment can be performed continuously even for a long time. Moreover, as a result, plasma treatment can be performed efficiently.

[0079] The cooling is not particularly limited and can be performed using any device. For example, the cooling can be performed by one or both of air cooling and heat exchange with a refrigerant. In the case of air cooling, for example, an air supply device can be used as the cooling unit. In addition, in the case of cooling by heat exchange, for example, a heat exchanger configured to contact one or both of the processing container and the electrode and a cooling water circulation device that circulates cooling water in the heat exchanger can be used as the cooling unit. As the heat exchanger, for example, a pipe for cooling water to flow that is configured to contact one or both of the processing container and the electrode can be used.

[0080] Furthermore, in order to promote heat dissipation, the electrode preferably includes a heat sink.

[0081] Next, an example of the structure of a plasma processing apparatus according to an embodiment of the present invention will be described in more detail with reference to the drawings.

[0082] Figure 11 is a schematic diagram showing the structure of a plasma processing apparatus 1 according to an embodiment of the present invention. The plasma processing apparatus 1 includes a processing container 10 for accommodating hexagonal boron nitride powder P. The processing container 10 is a spherical bottom glass container, including a substantially cylindrical main body 11, a bottom 12 connected to one end of the main body 11 and consisting of a curved surface convex to the outside, and an opening 13 provided at the other end of the main body 11. A flange 14 protruding to the outside of the processing container 10 is formed in the opening 13. The flange 14 is fixed to a support member 43 described later by a clamp not shown.

[0083] The plasma processing apparatus 1 includes a gas supply unit 20 for supplying a plasma generating gas into the processing container 10. The gas supply unit 20 includes a gas cylinder 21, a pipe 22, and a flow rate regulating valve 23 provided in the middle of the pipe 22. Figure 1 Only one gas cylinder 21 is shown in the figure, but when an atmosphere gas composed of a plurality of gases is used, a plurality of gas cylinders and corresponding pipes and flow regulating valves may be used.

[0084] The plasma processing apparatus 1 also includes a decompression unit 30 for maintaining the pressure in the processing container 10 at a pressure lower than the atmospheric pressure. The decompression unit 30 includes a vacuum pump 31 , a pipe 32 , and a valve 33 provided on the pipe 32 .

[0085] The plasma processing apparatus 1 includes a rotating mechanism 40 for rotating the processing container 10. The rotating mechanism 40 includes: a driving motor 41; a first pulley 42 connected to the rotating shaft of the motor 41; a supporting member 43 supporting the processing container 10; a second pulley 44 coupled to the supporting member 43, and a belt 45 spanned between the first pulley 42 and the second pulley 44. The rotation of the motor 41 is transmitted to the supporting member 43 through the belt 45, and the processing container 10 fixed to the supporting member 43 rotates with the central axis of the processing container 10 as the rotating axis as shown by the arrow R. Figure 1 The above rotation axis is represented by line A. Figure 1 As shown, the rotation axis of the processing container 10 is inclined at an inclination angle θ relative to the horizontal indicated by the line H.

[0086] In addition, Figure 1 In the embodiment, the rotation of the motor is transmitted by a pulley and a belt, but the method of transmitting the rotation is not limited to this. For example, the rotation may be transmitted by using a chain and a sprocket, or by using a plurality of gears. In addition, a direct drive method may be used in which the processing container is directly rotated by the rotation of the motor.

[0087] An electrode 50 is provided outside the processing container 10, and the electrode 50 is electrically connected to a high-frequency power supply 60 for applying a high frequency to the electrode 50. Figure 1As shown, the electrode 50 is preferably in a substantially cylindrical shape surrounding the outer circumference of the processing container 10 .

[0088] The plasma processing apparatus 1 further includes a cooling unit 70. In this embodiment, the cooling unit 70 is a cooling fan, which has a function of cooling the processing container 10 and the electrode 50 by sending air in the direction indicated by the arrow F. In addition, in this embodiment, the cooling fan is used for air cooling, but other cooling methods such as water cooling can also be used as described above. In addition, it is also preferable to use air cooling and water cooling together.

[0089] Example

[0090] A plasma-treated hexagonal boron nitride powder was obtained by subjecting a raw material hexagonal boron nitride powder (hereinafter referred to as "raw material boron nitride powder") to a plasma treatment under the conditions described below.

[0091] (Raw material Boron nitride powder)

[0092] HP40MF100 (Mizushima Iron & Steel Co., Ltd.) was used as the raw material boron nitride powder. HP40MF100 is a boron nitride powder having an aggregate structure of secondary particles formed by agglomeration of scaly primary particles composed of hexagonal boron nitride, the major diameter of the primary particles is 10 μm, and the median particle size of the secondary particles is 40 μm.

[0093] (Plasma Treatment Conditions)

[0094] Under the conditions shown in Table 1, using Figure 1 The raw material boron nitride powder was subjected to reduced pressure plasma treatment using a plasma treatment device having the structure shown in FIG. 1 . Specifically, 20 g of the raw material boron nitride powder was placed in a glass processing container and sealed, and the pressure in the processing container was reduced to less than 1 Pa. Next, a gas having the composition described in Table 1 was introduced into the processing container at a flow rate of 10 mL / min, and the pressure in the processing container was adjusted to the value described in Table 1. Then, a high frequency was applied under the conditions shown in Table 1 while a blower fan as a cooling unit was used to blow air toward the processing container and the electrode, and reduced pressure plasma treatment was performed. At this time, the rotation speed and the inclination angle of the processing container are as shown in Table 1.

[0095] However, for comparison, no plasma treatment was performed in Comparative Example No. 16. Also, for comparison, no cooling was performed in Comparative Example No. 17, and only the plasma treatment was performed for 1 minute.

[0096] (Thermal conductivity)

[0097] The thermal conductivity of the obtained plasma-treated hexagonal boron nitride powder was evaluated in the following procedure.

[0098] Bisphenol F type epoxy resin (Mitsubishi Chemical Co., Ltd., "jER807"), the above-mentioned boron nitride powder, methyl cellosolve as a solvent, and a modified alicyclic amine curing agent (Mitsubishi Chemical Co., Ltd., "jER Curing 113") were added and mixed in the ratio shown in Table 2. The filling rate of the boron nitride powder in the resin material of each example was 70% by volume. In addition, the filling rate of boron nitride here refers to the ratio of the boron nitride powder to the total solid content of the resin material, and the volume is calculated based on the mass of the mixed epoxy resin, curing agent and boron nitride, and the ratio of boron nitride in the total volume is calculated by the following formula.

[0099] Filling rate (volume %) = (volume of BN) / (volume of BN + volume of epoxy resin + volume of curing agent)

[0100] In the above calculations, the following density values ​​were used.

[0101] Boron nitride powder: 2.26g / cm 3

[0102] Epoxy resin: 1.20g / cm 3

[0103] Curing agent: 0.945g / cm 3

[0104] Next, the mixture was mixed at room temperature for 2 minutes using a rotary mixer (THINKY: ARV-310), and then applied to the polyimide film using a manual coater with a film thickness of 200 μm. After drying, the mixture was heat-pressed (170°C, 80 kgf·cm 2 ), and a resin material was obtained.

[0105] The thermal diffusivity, density and specific heat of the obtained resin material were measured, and the thermal conductivity of the resin material in the thickness direction was calculated by multiplying the measured thermal diffusivity, density and specific heat. The obtained thermal conductivity is shown in Table 1. In addition, the values ​​of thermal diffusivity, density and specific heat were measured by the following methods.

[0106] Thermal diffusivity: Laser flash method thermal constant measuring device (Vacuum Riko Co., Ltd.: TC-3000)

[0107] Density: Archimedean method

[0108] Specific heat: Differential scanning calorimetry (DSC) method

[0109] [Table 1]

[0110] Table 1

[0111]

[0112] According to the results shown in Table 1, in the inventive examples satisfying the conditions of the present invention, hexagonal boron nitride powder with excellent thermal conductivity can be efficiently obtained. In addition, since cooling is performed in the inventive examples, the temperature rise is suppressed, and the plasma treatment can be stably performed for a long time. On the other hand, in the comparative examples that do not satisfy the conditions of the present invention, the thermal conductivity of the obtained hexagonal boron nitride powder is poor. In addition, if the time is short, such as in Comparative Example No. 17, the plasma treatment can be performed even without cooling, but the hexagonal boron nitride powder with excellent thermal conductivity cannot be obtained.

[0113] Description of Reference Numerals

[0114] 1… plasma treatment device; 10… treatment container; 11… main body; 12… bottom; 13… opening; 14… flange; 20… gas supply unit; 21… gas cylinder; 22… piping; 23… flow rate regulating valve; 30… pressure reducing unit; 31… vacuum pump; 32… piping; 33… valve; 40… rotating mechanism; 41… motor; 42… first pulley; 43… supporting member; 44… second pulley; 50… electrode; 60… high-frequency power supply; 70… cooling unit; A… rotating axis; H… horizontal; P… hexagonal boron nitride powder; R… rotating direction; θ… tilt angle.

Claims

1. A plasma treatment method, comprising: performing plasma treatment on hexagonal boron nitride powder having an agglomerated structure under reduced pressure, characterized in that: The boron nitride particles constituting the hexagonal boron nitride powder are in the form of scales. The hexagonal boron nitride powder is placed in a processing container. supplying a plasma generating gas into the processing container and maintaining the pressure in the processing container at a pressure lower than atmospheric pressure, The processing container is rotated with the central axis of the processing container as the rotation axis, and a high frequency is applied to an electrode disposed outside the processing container, thereby performing plasma treatment on the hexagonal boron nitride powder in the processing container. At this time, the rotation axis of the processing container is inclined relative to the horizontal. During the plasma processing, one or both of the processing container and the electrode are cooled.

2. A method for producing plasma treated hexagonal boron nitride powder, characterized in that: The hexagonal boron nitride powder having an aggregate structure as a raw material is placed in a processing container. The boron nitride particles constituting the hexagonal boron nitride powder are in the form of scales. supplying a plasma generating gas into the processing container and maintaining the pressure in the processing container at a pressure lower than atmospheric pressure, The processing container is rotated with the central axis of the processing container as the rotation axis, and a high frequency is applied to an electrode disposed outside the processing container, thereby plasma-treating the hexagonal boron nitride powder in the processing container to obtain plasma-treated hexagonal boron nitride powder. At this time, the rotation axis of the processing container is inclined relative to the horizontal. During the plasma processing, one or both of the processing container and the electrode are cooled.

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