JP7175413B1 - Hexagonal boron nitride powder and method for producing the same - Google Patents

Abstract

A hexagonal boron nitride powder having few coarse particles is provided. A hexagonal boron nitride powder characterized by having a proportion of particles of 2.0 to 5.0 μm in wet particle size distribution measurement of 50% by volume or more and a particle size measured by grind gauge of 29 μm or less. Such a hexagonal boron nitride powder has few coarse particles and can be suitably used as a filler for a sealing material to be filled in narrow gaps, and can impart high thermal conductivity to the sealing material. is. [Selection figure] None

Description

The present invention relates to hexagonal boron nitride powder. More specifically, it relates to a hexagonal boron nitride powder that has very few coarse particles and exhibits good filling properties when filled into narrow gaps.

In recent years, due to the demand for miniaturization and high performance of electronic components, the integration of semiconductor devices has progressed. There is a demand for improved heat dissipation performance of materials. 2. Description of the Related Art Various heat dissipation materials are used for paths through which heat generated by a semiconductor element is released to a heat sink, a housing, or the like. High thermal conductivity fillers such as alumina, aluminum nitride, and hexagonal boron nitride are used in resin composite materials such as sealing materials, adhesives, greases, and resin sheets in semiconductor devices. In recent years, studies have been conducted to reduce the size of these heat dissipating members in order to further reduce their weight. It is an attractive filler that can contribute to weight reduction.

A sealing material is a material that fills gaps between semiconductor devices to improve heat dissipation. In recent years, along with the miniaturization and high integration of semiconductor devices, the gap to be filled with a sealing material is becoming narrower, and a sealing material suitable for a narrow gap of 30 μm or less has been demanded. When filling such a narrow gap with a sealing material, if the filler contains coarse particles, clogging may occur, and problems such as uneven filling, voids, and molding defects may occur. The need for coarse grain cutting is increasing from high thermal conductivity fillers. In addition, in the sealing material that fills the narrowed gap, the existence of a highly thermally conductive filler having a particle size corresponding to the size of the gap is important for improving thermal conductivity. Therefore, in order to increase the thermal conductivity of the sealing material filled in the narrow gap, it is necessary to control the particle size of the highly thermally conductive filler to an appropriate particle size according to the thickness of the gap.

Conventionally, Patent Document 1 reports a technique of using hexagonal boron nitride powder having a small particle size in order to realize a resin composition filled with a high thermal conductive filler. Patent Document 2 reports a boron nitride powder containing 0.1 to 5.0% by volume of particles of 36 μm or more in wet laser diffraction particle size distribution. However, coarse particles are not sufficiently removed from these hexagonal boron nitride powders, and the above problems cannot be fully resolved.

WO2015/122378 WO2019/172440

Accordingly, an object of the present invention is to provide a hexagonal boron nitride powder that is particularly suitable as a filler for a sealing material to fill gaps of about 30 μm or less by removing coarse particles from the hexagonal boron nitride powder. .

The inventors of the present invention have made intensive studies to solve the above problems. However, if the conventional hexagonal boron nitride powder is simply classified with a dry sieve to remove coarse particles, even if the amount of coarse particles can be controlled, the amount of fine powder increases, resulting in the sealing. The existence ratio of particles with a particle size of about 2.0 to 5.0 μm, which is a particle size suitable for increasing the thermal conductivity of the material, has decreased.

Therefore, as a result of further investigation, the melamine method using a mixed powder containing a boron oxide and a nitrogen-containing organic compound was used, and the raw material hexagonal nitriding having a large proportion of particles with a particle size of about 2.0 to 4.0 μm was obtained. After obtaining the boron powder, it is confirmed that all the above problems can be solved by the hexagonal boron nitride powder obtained by adopting a specific production method, which performs a specific wet classification treatment, and to complete the present invention. Arrived.

That is, the present invention is as described below.

[1]
A hexagonal boron nitride powder characterized by having a proportion of particles of 2.0 to 5.0 μm in wet particle size distribution measurement of 50% by volume or more and a particle size measured by grind gauge of 29 μm or less.

[2]
Further, a hexagonal boron nitride powder having a specific surface area of 6.0 to 12.0 m ² /g.

[3]
Further, a hexagonal boron nitride powder having a particle size (μm) measured by grind gauge/D100 (μm) measured by wet particle size distribution of 1.0 to 2.3.

[4]
It is a filler for a sealing material to be filled in a gap of X (μm) (where X is in the range of 10 to 30 μm), and the upper limit of the grain size measured by the grind gauge is X-1 (μm). The hexagonal boron nitride powder characterized by:

[5]
A sealing material for filling gaps of X (μm), comprising a resin composition containing the hexagonal boron nitride powder and a resin.

[6]
A hexagonal boron nitride slurry in which raw hexagonal boron nitride powder having a wet particle size distribution measurement D50 of 2.0 to 4.0 μm is dispersed in a solvent at a content ratio of 14% by mass or less is passed through a filter with an opening of 5 to 15 μm. A method for producing hexagonal boron nitride powder, comprising the step of treating.

[7]
A method for producing hexagonal boron nitride powder, wherein the step of passing through the filter includes a step of charging the hexagonal boron nitride slurry into a cylindrical filter in which a screw is rotated.

Since the hexagonal boron nitride powder of the present invention contains few coarse particles, it can be suitably used as a sealing material for filling narrow gaps.

The hexagonal boron nitride powder of the present invention has a proportion of particles of 2.0 to 5.0 μm in wet particle size distribution measurement of 50% by volume or more.

In the wet particle size distribution measurement of hexagonal boron nitride powder in the present invention, a measurement sample was prepared by adding 20 g of ethanol as a dispersion medium to a 50 mL screw tube bottle and dispersing 1 g of hexagonal boron nitride powder in ethanol. Ultrasonic treatment is not performed on the measurement sample. The particle size distribution of this was measured using a laser diffraction scattering type particle size distribution meter. The measuring device is not limited to this, but for example, a particle size distribution measuring device MT3000 manufactured by Nikkiso Co., Ltd. can be used as described in the examples below. From the volume frequency distribution of the particle diameter thus obtained, the volume ratio of particles of 2.0 to 5.0 μm is determined. In the volume frequency distribution of the particle size, D50 is the value of the particle size at which the cumulative value of the volume frequency is 50%, D95 is the value of the particle size at which the cumulative value of the volume frequency is 95%, and D95 is the value of the particle size at which the cumulative value of the volume frequency is 100%. Let the value of the diameter be D100.

In the sealing material with which the gap of 5 to 30 μm is filled, the thermal conductivity can be enhanced by particles having a particle size of about 2 to 5 μm. Therefore, in the hexagonal boron nitride powder of the present invention, the ratio of particles of 2.0 to 5.0 μm in wet particle size distribution measurement is 50% by volume or more, preferably 60% by volume or more.

The hexagonal boron nitride powder of the present invention preferably has a D50 of 2.0 to 4.0 μm, a D95 of 4.5 to 7.0 μm, and a D100 of 15 μm or less. If D50 is less than 2.0 μm and D95 is less than 5.0 μm, the viscosity of the sealing material tends to be high and the operability at the time of filling the gap tends to deteriorate. In addition, it becomes difficult to obtain a high thermal conductivity in the sealing material that fills the gap of about 5 μm to 20 μm. If D50 is greater than 4.0 μm, D95 is greater than 7.0 μm, and D100 is greater than 15 μm, the operability of filling the sealing material tends to be reduced due to the resistance of the particles. D50 is more preferably 2.1-3.8 μm and D95 is more preferably 4.8-6.7 μm.

In conventional wet particle size distribution measurement, only particles contained in a certain amount or more are counted, so even particles that actually exist do not appear on the particle size distribution. sometimes loosens slowly. Therefore, the actual hexagonal boron nitride powder often contains particles larger than D100 measured by wet particle size distribution, and wet particle size distribution measurement sufficiently evaluates the presence of coarse particles and aggregated particles. However, it has been difficult to obtain hexagonal boron nitride powders that are particularly suitable for narrow gaps. On the other hand, when measured with a grind gauge, a very small amount of coarse particles causes spots, so when the hexagonal boron nitride powder is actually used as a filler for a sealing material that fills a narrow gap, it may cause problems. Coarse particles can be detected with high accuracy. Therefore, it is important to control the grind gauge measurement particle size in order to control the amount of coarse particles and agglomerated particles that do not appear in the particle size distribution measurement.

In the present invention, the preferred grain size measured by grind gauge is 29 μm or less. If the grain size measured by the grind gauge is 29 μm or less, clogging occurs when filling the gap with a sealing material that is assumed to be filled into a gap of about 30 μm, and uneven filling, voids, and molding defects occur. problem can be prevented to a high degree.

In addition, by adjusting the upper limit of the grind gauge measurement particle size of the hexagonal boron nitride powder, it can be used for sealing materials for gaps narrower than 30 μm. A hexagonal boron nitride powder can be disclosed. Specifically, when the target gap size is X (μm), it is preferable to adjust the upper limit of the grind gauge measurement particle size to X−1 (μm), for example, a sealing material to be filled in a gap of 25 μm When used as a sealing material to fill a gap of 20 μm, the upper limit of the grain size measured by grind gauge should be controlled to 19 μm. Therefore, the ratio of particles of 2.0 to 5.0 μm in wet particle size distribution measurement is 50% by volume or more, and the upper limit of the particle size measured by grind gauge is X−1 (μm). A hexagonal boron nitride powder (where the pore size X is in the range of 5-30 μm), which is a filler for , can also be disclosed as the present invention.

The lower limit of the grain size measured by the grind gauge is not particularly limited, but the grain size measured by the grind gauge is 4 μm or more because it becomes easy to obtain a resin sheet with high thermal conductivity in the sealing material filled in the gap of about 5 to 30 μm. is preferred.

Further, the hexagonal boron nitride powder of the present invention preferably has a grind gauge measurement particle size (μm)/wet particle size distribution measurement D100 (μm) in the range of 1.0 to 2.3. It is difficult to produce a powder where the grind gauge measurement particle size (μm)/wet particle size distribution measurement D100 (μm) is less than 1.0, and the grind gauge measurement particle size (μm)/wet particle size distribution measurement D100 (μm) is difficult to produce. When is more than 2.3, it means that the proportion of particles with a large particle size that effectively expresses thermal conductivity in the sheet is small, and the resin composition filled in the gap of 5 to 30 μm has a high thermal conductivity. difficult to obtain. Grind gauge measurement particle size (μm)/wet particle size distribution measurement D100 (μm) is preferably in the range of 1.0 to 2.1.

The grain size measured by grind gauge is measured according to JISK5600-2-5. Specifically, when a resin paste obtained by mixing 1 part by mass of hexagonal boron nitride powder and 10 parts by mass of a silicone resin having a kinematic viscosity of 1000 cSt at 25° C. is used with a grind gauge, spots appear. It was measured by observing the

The hexagonal boron nitride powder of the present invention preferably has a BET specific surface area in the range of 6.0 to 12.0 m ² /g as measured by the one-point nitrogen adsorption method. When the specific surface area is less than 6.0 m ² /g, the particle size of the hexagonal boron nitride single particles is large, and particularly when the single particles are aggregated or when the single particles are elliptical or elongated particles, coarse particles are formed. easier to exist. When the specific surface area exceeds 12.0 m ² /g, the primary particle size is small, so aggregated particles are formed, and coarse particles are likely to occur. The specific surface area is more preferably 6.5 to 11.0 m ² /g, still more preferably 7.0 to 10.0 m ² /g.

The average aspect ratio (length/thickness) of the primary particles of the hexagonal boron nitride particles of the present invention is preferably 3-20, particularly preferably 3-15. If it is less than 3, it is difficult to manufacture, and if it exceeds 20, in the case of a powder with a low specific surface area, there is a possibility that it will become a flaky plate-like particle with a large major axis, which is not preferable.

Moreover, the hexagonal boron nitride powder of the present invention preferably contains aggregated particles in which single particles are aggregated. In general, primary particles of hexagonal boron nitride are flat and have anisotropic thermal conductivity with high thermal conductivity in the width direction and low thermal conductivity in the thickness direction. Therefore, when blended in a resin, it exhibits anisotropic thermal conductivity, with high thermal conductivity in the width direction of the particles and low thermal conductivity in the thickness direction of the particles. Such anisotropy of thermal conductivity is particularly conspicuous in a resin sheet having a small thickness or a sealing material filled in a small gap, and the thermal conductivity tends to decrease. However, when the primary particles are agglomerated, the single particles are oriented in random directions in the agglomerate, so the anisotropy of thermal conductivity as described above is suppressed, and the direction of low thermal conductivity is generated. can be effectively prevented.

In the present invention, the presence of agglomerated particles in the hexagonal boron nitride powder is confirmed from the ratio (D50S/D50) of D50S calculated from wet particle size distribution measurement with ultrasonic treatment and D50 in the wet particle size distribution measurement. can be done. That is, since agglomerated particles are crushed by ultrasonic waves, the value of D50S/D50 becomes small if a large amount of agglomerated particles is contained. For example, the value of D50S/D50 is preferably 0.40 to 0.85, particularly 0.50 to 0.80.

In the wet particle size distribution measurement using ultrasonic treatment, in the preparation of the measurement sample, 20 g of ethanol was added to a 50 mL screw tube bottle as a dispersion medium, and 1 g of hexagonal boron nitride powder was dispersed in ethanol. Except for performing ultrasonic treatment for a minute, the same method as in the case of not performing ultrasonic treatment can be used.

Since the hexagonal boron nitride powder of the present invention preferably has high purity, it is preferable that the amount of impurity boron oxide is 400 ppm or less. More preferably, it is 250 ppm or less. For the same reason, it is preferable that the carbon content is 0.001 to 0.050% by mass and the oxygen content is 0.01 to 0.95% by mass.

The method for producing the hexagonal boron nitride powder of the present invention is not particularly limited. can be obtained by The raw material hexagonal boron nitride powder has a wet particle size distribution measurement D50 of 2.0 to 4.0 μm. If the D50 is less than 2.0 μm, the ratio of small-diameter particles increases, and the grind gauge measurement particle size tends to increase due to aggregation, which is not preferable, and if it exceeds 4.0 μm, coarse particles are mixed. easier to do. The raw material hexagonal boron nitride powder preferably has a particle size distribution measurement D50 of 2.0 to 3.5 μm, more preferably 2.0 to 3.0 μm. In addition, as described later, aggregated particles may be generated after wet classification to generate coarse particles, so the specific surface area of the raw material boron nitride powder is preferably 12.0 m ² /g or less, and 11.0 m ² /g or less, more preferably 10.0 m ² /g or less. When the specific surface area is 12.0 m ² /g or less, the primary particles are small and agglomeration is less likely to occur after wet classification.

(Method for producing raw material hexagonal boron nitride powder)
In the present invention, the method for producing the raw material hexagonal boron nitride powder is not particularly limited. A so-called melamine method, which includes a heating step for heating, can be mentioned. The melamine method is a preferable method for obtaining the starting hexagonal boron nitride powder of the present invention, since it is easy to obtain a small particle size boron nitride powder.

In the method for producing the raw material hexagonal boron nitride powder, the boron oxide contained in the mixed powder includes diboron trioxide (boron oxide), diboron dioxide, tetraboron trioxide, tetraboron pentoxide, borax, or anhydrous Borax and the like can be exemplified, and among them, it is preferable to use diboron trioxide. The use of diboron trioxide as the boron oxide is industrially beneficial because it uses inexpensive raw materials. In addition, as a boron oxide, you may use together 2 or more types.

Examples of the nitrogen-containing organic compound contained in the mixed powder include melamine, ammeline, ammelide, melam, melon, dicyandiamide, and urea, among which melamine is preferred. The use of melamine as the nitrogen-containing organic compound is industrially advantageous because it uses inexpensive raw materials. Two or more kinds of nitrogen-containing organic compounds may be used in combination.

The mass ratio (B/N) of boron atoms to nitrogen atoms in the mixed powder is preferably 0.30 or more and 1.00 or less, and more preferably 0.35 or more and 0.95 or less. When B/N is 0.30 or more, the source of B can be secured and a sufficient yield can be secured. In addition, when B/N is 1.00 or less, a sufficient N source for nitridation can be secured. The nitrogen atoms in the mixed powder heated in the heating step are derived from the nitrogen-containing organic compound, and the boron atoms in the mixed powder heated in the overheating step are derived from boron oxide.

The mixed powder may contain alkali metal and alkaline earth metal carbonates, oxides, and composite oxides as a fluxing agent, in addition to boron oxides and nitrogen-containing organic compounds. Carbonates, oxides, and composite oxides of the above alkali metals and alkaline earth metals include lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, lithium oxide, sodium oxide, potassium oxide, and magnesium oxide. , calcium oxide, strontium oxide, borax, anhydrous borax. Two or more kinds of carbonates, oxides, and composite oxides of alkali metals and alkaline earth metals may be used in combination.

Further, the ratio of the fluxing agent in the mixed powder (the total mass of the nitrogen-containing organic compound and the boron oxide converted to B-based boron oxide)/(mass of the fluxing agent) is 1.0 or more and 2.5 or less. It is preferably 1.1 or more and 2.2 or less. If the ratio (total mass of nitrogen-containing organic compound and boron oxide converted to B-based boron oxide)/(fluxing agent mass) ratio is less than 1.0, the amount of fluxing agent is unfavorably small. If it exceeds 2.5, the baked nitrided product becomes hard, which is not preferable.

In the method for producing the raw material hexagonal boron nitride powder, the mixed powder is preferably heated at a maximum temperature of 1000° C. or higher and 1500° C. or lower in the heating step. By heating the mixed powder at a temperature of 1000° C. or higher, it is possible to prevent the particle size of the hexagonal boron nitride primary particles from becoming excessively small. The maximum temperature is more preferably 1100° C. or higher, even more preferably 1150° C. or higher. In addition, by heating the mixed powder at a temperature of 1500° C. or less, volatilization of the fluxing agent can be prevented and an increase in the particle size of the hexagonal boron nitride primary particles can be suppressed. More preferably, the maximum temperature is 1450° C. or less.

In the heating step, the mixed powder is preferably heated under an inert gas atmosphere under normal pressure or under reduced pressure. By heating in the above environment, damage to the heating furnace body can be suppressed. In this specification, the term "under an inert gas atmosphere" means a state in which an inert gas is introduced into a container for heating the mixed powder, and the gas inside the container is replaced with the inert gas. The amount of inert gas inflow is not particularly limited. or more. Also, the inert gas may be, for example, nitrogen gas, carbon dioxide gas, argon gas, or the like.

(Crushing process)
In the method for producing the hexagonal boron nitride powder of the present invention, since the hexagonal boron nitride nitrided product obtained by the above method is agglomerated, a crushing step may be provided for the purpose of adjusting the particle size. This crushing step is a step of crushing a hexagonal boron nitride nitride product constituted by agglomeration of hexagonal boron nitride primary particles contained in the hexagonal boron nitride nitride product. The crushing method is not particularly limited, and crushing by a roll crusher, a jet mill, a bead mill, a planetary mill, a stone mill, or the like may be used. Moreover, these crushing methods may be combined, and may be carried out more than once. In addition, metal impurities may be mixed from an apparatus or the like in the crushing process, but it is possible to remove them to a high degree by the acid washing process and the water washing process described later.

(Acid cleaning)
In the production method, the nitride obtained by the above-described melamine method contains impurities such as oxides of boron oxide in addition to the hexagonal boron nitride powder, so it is preferable to wash the nitride with an acid. The method of acid washing is not particularly limited, and known methods are employed without limitation. For example, a method of pulverizing the nitride obtained after the nitriding treatment, putting it into a container, adding dilute hydrochloric acid (5 to 20% by mass HCl) of 5 to 10 times the amount of the nitride, and keeping it in contact for 4 to 8 hours. is mentioned. In addition to hydrochloric acid, nitric acid, sulfuric acid, acetic acid, etc. may be used as the acid used for the acid cleaning.

After the acid cleaning, pure water may be used for cleaning the remaining acid. As the cleaning method, after filtering the acid used for the acid cleaning, the acid-cleaned boron nitride is dispersed in the same amount of pure water as the acid used, and filtered again.

(dry)
It is preferable to dry the water-containing mass after the acid washing and, if necessary, water washing, in the air at 50 to 250° C. or under reduced pressure. Although the drying time is not specified, it is preferable to dry until the moisture content approaches 0%.

(Dry classification)
The raw material hexagonal boron nitride powder after drying can be subjected to removal of coarse particles by dry sieving or the like or fine powder removal by air classification or the like, if necessary, after pulverization and before wet classification described later. A dry sieving step is particularly preferred. When the raw material hexagonal boron nitride powder has a wide particle size distribution and many coarse particles, clogging often occurs during the wet classification described later, making it difficult to perform the wet classification treatment. This can be easily prevented by removing coarse particles to some extent by dry sieving. The dry sieve is preferably a sieve with an opening of 38 to 90 μm. Here, the reason why the lower limit of the mesh size is set to 38 μm is that in dry sieving, processing with a mesh size of less than 38 μm causes clogging and the like, making it difficult to perform continuous sieving processing.

By the production method described above, a raw material hexagonal boron nitride powder having a wet particle size distribution measurement D50 of 2.0 to 4.0 μm can be easily obtained. In the above production method, the average aspect ratio (major axis / thickness) of the primary particles is 3 to 20, the content of flake particles is small, and the raw material hexagonal boron nitride powder suitable for performing the wet classification treatment described later. can be easily obtained.

(Wet classification operation)
The hexagonal boron nitride powder of the present invention can be obtained by wet-classifying the raw material hexagonal boron nitride powder as described above to remove coarse particles having a specific particle size or larger. By performing wet classification, coarse particles can be efficiently removed to obtain the hexagonal boron nitride powder of the present application. In the wet classification, a hexagonal boron nitride slurry obtained by dispersing the raw material hexagonal boron nitride powder in a solvent is processed by passing it through a filter (hereinafter sometimes referred to as "filter classification"). Although there is fluid classification for separating coarse particles and fine particles, filter classification is preferable because of its high classification accuracy and high production capacity.

(Dispersion medium for wet classification)
The wet classification is performed by treating a hexagonal boron nitride slurry obtained by dispersing raw material hexagonal boron nitride powder in a solvent. The solvent for the hexagonal boron nitride slurry can be used without any particular limitation as long as it can disperse the raw material hexagonal boron nitride powder. and ketones such as acetone and methyl ethyl ketone. These solvents may be used alone or in combination of two or more.

(Amount of dispersion medium)
The content of the starting hexagonal boron nitride powder in the hexagonal boron nitride slurry is preferably 14% by mass or less. If the slurry viscosity exceeds 14% by mass, clogging occurs, making it difficult for the slurry to pass through the screen, making it impossible to obtain the hexagonal boron nitride powder of the present invention. The content of the raw material hexagonal boron nitride is more preferably 12% by mass or less, and even more preferably 5% by mass or less. Moreover, from the viewpoint of productivity, the content of the raw material hexagonal boron nitride is preferably 1% by mass or more.

(Distribution method)
The step of dispersing the raw material hexagonal boron nitride in the solvent is not particularly limited, and a predetermined amount of the raw material hexagonal boron nitride powder and the solvent may be measured and mixed to prepare a slurry. Most of the particles of the starting hexagonal boron nitride powder before being dispersed in the solvent are loosely aggregated in many cases. Therefore, in order to sufficiently disperse and suppress clogging, collision dispersers such as dispersers, homogenizers, ultrasonic dispersers, nanomizers, planetary mixers, ejectors, water jet mills, high-pressure dispersers, wet ball mills, wet The slurry is preferably treated with a vibrating ball mill, wet bead mill, or the like, and particularly preferably with a disperser, homogenizer, ultrasonic disperser, or the like.

(Slurry viscosity)
The starting material hexagonal boron nitride slurry preferably has a viscosity of 1.0 to 60 mPa·S at 25°C. By setting the viscosity within the above range, the wet filter classification described later can be efficiently performed.

(wet filter classification)
Filter classification uses a filter with an opening of 5 to 15 μm. This makes it possible to efficiently produce the hexagonal boron nitride powder of the present invention having a grind gauge measurement particle size of 29 μm or less.

A plurality of filters with openings may be used in a stepwise combination. For example, a filter with an opening of more than 15 μm may be passed before a filter with an opening of 5 to 15 μm.

The material, structure, shape, etc. of the filter are not particularly limited, but since the classification point, classification accuracy, degree of clogging, etc. differ depending on these properties of the filter, the physical properties of the raw hexagonal boron nitride powder and the intended grind gauge measurement It may be appropriately selected according to the particle size.

As a filter, a membrane filter, a resin filter, a metal filter, a filter paper, or the like can be used, but a resin filter or a stainless steel filter is preferable because high-purity hexagonal boron nitride powder can be easily obtained. In addition, in the method for producing the raw material hexagonal boron nitride, if water washing is not performed after acid washing, the slurry becomes acidic, so it is necessary to use a resin filter.

In addition, by immersing the filter in the solvent used for the hexagonal boron nitride slurry before use, the compatibility with the hexagonal boron nitride slurry is improved, and filtration can be performed efficiently.

The method of passing the slurry through the filter is not particularly limited, and known methods such as gravity, suction, pressurization, and pressure feeding can be used. A preferred method is a method of introducing a boron slurry. This method is preferable because the centrifugal force of the screw hardly causes clogging, and efficient wet classification is easily performed.

(Solvent removal/drying)
In order to obtain the hexagonal boron nitride powder of the present invention, it is necessary to remove the solvent from the slurry after wet classification. A method for removing the solvent is not particularly limited, and for example, it can be carried out by heating a slurry containing hexagonal boron nitride powder with a heating device. The heating device can be used without any particular limitation as long as it is possible to evaporate and remove the solvent from the slurry. A granulator, a vacuum emulsifier, and other agitation-type vacuum drying devices can be suitably used. Drying may be performed in multiple stages, and before heating with a heating device, for example, a rotary evaporator, a thin film dryer, a spray dryer, a drum dryer, a disk dryer, a fluidized bed dryer, etc. are used to remove the solvent. A part may be removed. Moreover, before drying by heating with a heating device, filtration may be performed to remove part of the solvent. The device for filtration can be suitably used as long as it separates the slurry into solid components and liquid components. Examples include a filter press machine and a filter drying apparatus capable of performing filtration and drying in one unit. The material of the filter medium to be used, the retained particle size, the conditions for separation, etc. may be appropriately selected according to the method to be used and the collection rate.

The atmosphere for heating with a heating device is not particularly limited, but a vacuum, an inert gas atmosphere, or a dry air atmosphere is preferable. Among them, a vacuum or an inert gas atmosphere, which is less affected by environmental moisture, is more preferable, and a vacuum is particularly preferable.

It is preferable to remove the solvent from the slurry until the mass change rate before and after the obtained hexagonal boron nitride powder is allowed to stand in the air at 120° C. for 3 minutes is less than 0.9%.

<Resin composition>
A resin composition can be obtained by blending the hexagonal boron nitride powder of the present invention with a resin.

The resin constituting the resin composition is not particularly limited, and may be, for example, a silicone-based resin or an epoxy-based resin. Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol S type epoxy resin, bisphenol F type epoxy resin, bisphenol A type hydrogenated epoxy resin, polypropylene glycol type epoxy resin, polytetramethylene glycol type epoxy resin, naphthalene type Epoxy resin, phenylmethane type epoxy resin, tetrakisphenolmethane type epoxy resin, biphenyl type epoxy resin, phenol novolak type epoxy resin, tetrafunctional naphthalene type epoxy resin, cresol novolac type epoxy resin, dicyclopentadiene type epoxy resin, trisphenol epoxy resin, naphthol novolak epoxy resin, naphthylene ether type epoxy resin, aromatic glycidylamine type epoxy resin, hydroquinone type epoxy resin, stilbene type epoxy resin, triphenolmethane type epoxy resin, aralkyl type epoxy resin, polypropylene glycol type epoxy resin, Examples include polysulfide-structured epoxy resins, epoxy resins having a triazine core in the skeleton, and bisphenol A alkylene oxide adduct type epoxy resins. One of these epoxy resins may be used alone, or two or more may be used in combination. In addition, amine-based resins, acid anhydride-based resins, phenol-based resins, imidazoles, active ester-based curing agents, cyanate ester-based curing agents, naphthol-based curing agents, benzoxazine-based curing agents, etc. may be used as curing agents. . These curing agents may also be used singly or in combination of two or more. The blending amount of these curing agents to the epoxy resin is 0.5 to 1.5 equivalent ratio, preferably 0.7 to 1.3 equivalent ratio to the epoxy resin. In this specification, these curing agents are also included in resins.

As the silicone resin, any known curable silicone resin, which is a mixture of an addition reaction type silicone resin and a silicone cross-linking agent, can be used without limitation. Addition reaction type silicone resins include, for example, polyorganosiloxanes such as polydimethylsiloxane having alkenyl groups such as vinyl groups and hexenyl groups as functional groups in the molecule. Examples of silicone cross-linking agents include dimethylhydrogensiloxy group-blocked dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxy group-blocked dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxane group-blocked poly( and polyorganosiloxanes having silicon-bonded hydrogen atoms such as poly(hydrodienesilsesquioxane) and poly(hydrodienesilsesquioxane). As the curing catalyst, known platinum-based catalysts and the like used for curing silicone resins can be used without limitation. Examples thereof include particulate platinum, particulate platinum supported on carbon powder, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, palladium, and rhodium catalysts.

As resins, liquid crystal polymers, polyesters, polyamides, polyimides, polyphthalamides, polyphenylene sulfides, polycarbonates, polyaryletherketones, polyphenylene oxides, fluorine resins, cyanate ester compounds, maleimide compounds, etc. can also be used. is.

Liquid crystal polymers include thermotropic liquid crystal polymers that exhibit liquid crystallinity in a molten state and rheotropic liquid crystal polymers that exhibit liquid crystallinity in a solution state, and either liquid crystal polymer may be used.

Thermotropic liquid crystal polymers include, for example, a polymer synthesized from parahydroxybenzoic acid (PHB), terephthalic acid, and 4,4'-biphenol, a polymer synthesized from PHB and 2,6-hydroxynaphthoic acid, and PHB. , terephthalic acid, and polymers synthesized from ethylene glycol.

Examples of the fluororesin include tetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (PFEP), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin (PFA), and the like. be done.

Examples of the cyanate ester compounds include phenol novolak-type cyanate ester compounds, naphthol aralkyl-type cyanate ester compounds, biphenyl aralkyl-type cyanate ester compounds, naphthylene ether-type cyanate ester compounds, xylene resin-type cyanate ester compounds, Adamantane skeleton-type cyanate ester compounds are preferred, and examples include phenol novolac-type cyanate ester compounds, biphenylaralkyl-type cyanate ester compounds, and naphthol aralkyl-type cyanate ester compounds.

Examples of maleimide compounds include N-phenylmaleimide, N-hydroxyphenylmaleimide, bis(4-maleimidophenyl)methane, 2,2-bis{4-(4-maleimidophenoxy)-phenyl}propane, bis(3, 5-dimethyl-4-maleimidophenyl)methane, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, bis(3,5-diethyl-4-maleimidophenyl)methane, represented by the following formula (1) and maleimide compounds represented by the following formula (2).

In the above formula (1), each R ₅ independently represents a hydrogen atom or a methyl group, preferably a hydrogen atom. In addition, n1 represents an integer of ₁ or more, preferably an integer of 10 or less, more preferably an integer of 7 or less.

In the above formula (2), multiple Rs are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms (e.g., methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group , isobutyl group, t-butyl group, n-pentyl group, etc.), or a phenyl group, and from the viewpoint of further improving flame resistance and peel strength, it is selected from the group consisting of a hydrogen atom, a methyl group, and a phenyl group. is preferably a group, more preferably one of a hydrogen atom and a methyl group, and even more preferably a hydrogen atom. n is an integer from 1 to 20;

The compounding ratio of the resin and the hexagonal boron nitride powder may be appropriately determined according to the application. It can be blended in an amount of 40 to 80% by volume, more preferably 50 to 70% by volume.

The resin composition may contain components other than the hexagonal boron nitride and the resin. The resin composition includes, for example, inorganic fillers such as aluminum oxide, magnesium oxide, silica, and aluminum nitride, curing accelerators, anti-tarnishing agents, surfactants, dispersants, coupling agents, coloring agents, plasticizers, and viscosity adjusting agents. Agents, antibacterial agents, etc. may be included as appropriate within a range that does not affect the effects of the present invention.

Applications of the resin composition of the present invention include, for example, adhesive films, sheet-like laminate materials (resin sheets) such as prepreg, circuit boards (laminated board applications, multilayer printed wiring board applications), solder resists, underfill materials, heat Adhesives, die bonding materials, semiconductor encapsulants, filling resins, component embedding resins, thermal interface materials (sheets, gels, greases, etc.), substrates for power modules, heat radiation members for electronic components, and the like.

In particular, it can be suitably used as a sealing material that fills a gap of 5 to 30 μm. As described above, the hexagonal boron nitride powder of the present invention does not contain coarse particles, so it is suitable for sealing materials that fill narrow gaps, and has high thermal conductivity in sealing materials that fill gaps of 5 to 30 μm. It has a particle size distribution that realizes Therefore, the resin composition containing the hexagonal boron nitride powder of the present invention is particularly suitable as a sealing material for filling gaps of 5 to 30 μm. The upper limit of the grind gauge measurement particle size of the hexagonal boron nitride powder is preferably adjusted according to the gap X (μm) to be filled. The upper limit of the grain size of the hexagonal boron nitride powder measured by a grind gauge is preferably (X−1) μm.

The resin composition of the present invention is particularly suitable as a sealing material for filling narrow gaps of 5 to 30 μm, but it can also be used as a sealing material for filling gaps of more than 30 μm. Examples of sealing materials include underfill materials and grease-like thermal interface materials.

When the resin composition of the present invention is used as an underfill material, the resin is preferably an epoxy resin from the viewpoint of heat resistance, constitution, mechanical strength, etc., and an epoxy resin that is liquid at room temperature is used. is particularly preferred.

When the resin composition of the present invention is used as a grease-like thermal interface material, it is preferable to use a silicone resin as the resin. As the silicone resin, it is possible to use a polyorganosiloxane represented by the following formula (3) as an addition reaction type silicone resin, and a polyorganosiloxane having at least silicon-bonded hydrogen atoms in one molecule as a silicone cross-linking agent. preferable.

In the formula, R ¹ is independently an unsubstituted or substituted monovalent hydrocarbon group, preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms. R ³ is independently an alkyl group having 1 to 4 carbon atoms, an alkoxyalkyl group, an alkenyl group or an acyl group. p is an integer of 5-100, preferably 10-50. a is an integer from 1 to 3;

The resin composition of the present invention can also be suitably used for resin sheets, particularly resin sheets having a thickness of 5 to 30 μm. As described above, the resin composition containing the hexagonal boron nitride powder of the present invention exhibits high thermal conductivity even in a resin sheet with a thickness of 5 to 30 μm, as when it is filled in a gap of 5 to 30 μm. can be done. In addition, since coarse particles do not exist, a decrease in dielectric strength due to penetration of coarse particles into the sheet is suppressed, and high dielectric strength can be obtained. The upper limit of the grind gauge measurement particle size of the hexagonal boron nitride powder is preferably adjusted according to the film thickness X (μm). Specifically, in the case of a resin sheet with a film thickness X (μm), The grain size of the hexagonal boron nitride powder measured by a grind gauge is preferably X-1 (μm) or less. Although the use of the resin sheet is not particularly limited, it can be used, for example, as a circuit board (particularly as a copper-clad laminate obtained by laminating a resin composition and a copper foil) or as an insulating layer of a multilayer printed wiring board. In these applications, it is possible to reduce thermal resistance and miniaturize various devices by using a thin resin sheet.

Suitable resins for use in copper clad laminates include epoxy resins, polyimide resins, liquid crystal polymers, fluorine resins, cyanate ester compounds, maleimide compounds, and the like. Among these, in the use of copper-clad laminates mounted in electronic communication equipment such as satellite broadcasting receivers and mobile phones, fluorine Resins are mentioned as particularly suitable resins. In addition, when the circuit board is manufactured using lead-free solder, the reflow temperature of lead flow solder is about 260° C., so it is preferable to use a liquid crystal polymer with high heat resistance. Thermotropic liquid crystal polymers are particularly preferred due to their superior toughness and flame retardancy.

Moreover, in the use of copper-clad laminates, it is also preferable to use an epoxy resin and/or a maleimide compound and a cyanate ester compound. By setting it as such a resin composition, it becomes easy to set it as the resin composition excellent in peel strength and moisture absorption heat resistance. In this case, as the epoxy resin, biphenyl aralkyl type epoxy resin, naphthylene ether type epoxy resin, polyfunctional phenol type epoxy resin, and naphthalene type epoxy resin are preferable from the viewpoint of flame retardancy and heat resistance. , 2′-bis{4-(4-maleimidophenoxy)-phenyl}propane, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane and a maleimide compound represented by the above formula (B-1), and the maleimide compound represented by the above formula (B-2) is preferable from the viewpoint of the thermal expansion coefficient and the glass transition temperature. , and naphthol aralkyl-type cyanate ester compounds are preferred from the viewpoint of glass transition temperature and plating adhesion.

When used as an insulating layer of a multilayer printed wiring board, it is preferable to use an epoxy resin as the resin because of its excellent heat resistance and adhesiveness to copper foil circuits. As the epoxy resin, a combination of an epoxy resin that is liquid at a temperature of 20° C. and an epoxy resin that is solid at a temperature of 20° C. is used to obtain a resin composition having excellent flexibility and prevent breakage of the insulating layer. It is preferable because it improves the strength. Preferred examples of epoxy resins that are liquid at a temperature of 20° C. include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and naphthalene-type epoxy resins. Preferred solid epoxy resins at a temperature of 20° C. include tetrafunctional naphthalene type epoxy resins, biphenyl type epoxy resins, and naphthylene ether type epoxy resins. The mixing ratio of the epoxy resin that is liquid at 20°C and the epoxy resin that is solid at 20°C is preferably in the range of 1:0.1 to 1:4, more preferably 1:0.8 to 1:2. .5 is more preferred.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. Various physical property measuring methods in the present invention are as follows.

[Wet particle size distribution measurement]
Measured using a particle size distribution analyzer MT3000 manufactured by Nikkiso Co., Ltd. In addition, the measurement sample was prepared by the method shown below. First, 20 g of ethanol was added as a dispersion medium to a 50 mL screw tube bottle, and 1 g of hexagonal boron nitride powder was dispersed in the ethanol. The particle size distribution of this was measured using a laser diffraction scattering type particle size distribution analyzer. At this time, in order not to break the aggregated particles, the measurement was carried out without ultrasonic treatment or the like. From the obtained volume frequency distribution of particle diameters, the existence ratio of particles having a diameter of about 2.0 to 5.0 μm was determined. In addition, the value of the particle size at which the cumulative value of the volume frequency is 50% was determined as D50, the value of the particle size at which the cumulative value of the volume frequency was 95% was determined as D95, and the value of the particle size at which the cumulative value was 100% was determined as D100.

[Ultrasonic treatment wet particle size distribution measurement]
Measured using a particle size distribution analyzer MT3000 manufactured by Nikkiso Co., Ltd. In addition, the measurement sample was prepared by the method shown below. First, 20 g of ethanol was added as a dispersion medium to a 50 mL screw tube bottle, and 1 g of hexagonal boron nitride powder was dispersed in the ethanol. The particle size distribution of this was measured using a laser diffraction scattering type particle size distribution analyzer. At this time, ultrasonic treatment was performed at 90 W for 20 minutes in order to break aggregated particles. From the obtained volume frequency distribution of particle diameters, the value of the particle diameter at which the cumulative value of the volume frequency is 50% was obtained as D50S.

[BET specific surface area]
BET specific surface area measurement of hexagonal boron nitride powder was obtained by BET method (nitrogen adsorption one-point method) using a specific surface area measuring device (manufactured by Shimadzu Corporation: Flowsorb 2-2300 type) [Oxygen/carbon analysis]
The oxygen concentration of the hexagonal boron nitride powder was measured using an oxygen/nitrogen analyzer EMGA-620 manufactured by Horiba. The carbon content of the hexagonal boron nitride powder was measured with a carbon analyzer (EMIA-110 manufactured by Horiba, Ltd.). All the hexagonal boron nitride powders of the examples of the present invention had an oxygen content within the range of 0.01-0.95% by weight and a carbon content within the range of 0.001-0.050% by weight.

[Amount of eluted boron]
In a 150 cc beaker, 50 g of an aqueous sulfuric acid solution with a concentration of 0.04 mol/L and 2 g of hexagonal boron nitride powder were added, shaken and stirred, and allowed to stand for 120 minutes. During this time, the temperature of the liquid was adjusted to 25°C. After that, the amount of boron measured by analyzing the boron in the resulting liquid with an ICP emission spectrometer (iCAP6500 manufactured by THERMO FISHER) was converted to B ₂ O ₃ , which was the mass of the hexagonal boron nitride powder. to determine the amount of eluted boron (ppm), which was taken as the concentration of boron oxide on the surface of the hexagonal boron nitride particles constituting the hexagonal boron nitride powder. All the hexagonal boron nitride powders of the examples of the present invention had an impurity amount of boron oxide of 400 ppm or less.

[Thermal conductivity]
The thermal conductivity (W/m·K) of the produced resin sheet was obtained by thermal diffusivity (m ² /sec) x density (kg/m ³ ) x specific heat (J/kg·K). Thermal diffusivity is measured by temperature wave thermal analysis (AI-Phase Mobile u, ISO22007-3), density is measured by Archimedes method (Mettler Toledo: XS204V), specific heat is measured by differential scanning calorimeter (DSC) method. (Rigaku: Thermo Plus Evo DSC8230).

[Grind gauge measurement particle size]
Evaluation was made using a grind gauge (grain gauge) having a width of 90 mm, a length of 240 mm and a maximum depth of 50 μm in accordance with JIS-K5600-2-5. 0.4 g of hexagonal boron nitride powder and 4 g of a silicone resin (Element 14 PDMS 1000-J manufactured by Momentive) having a kinematic viscosity of 1000 cSt at 25° C. are put into a 24 ml plastic ointment pot, and the ointment pot is rotated. - Treated for 2 minutes with a revolution mixer (manufactured by Thinky Co., Ltd.: ARE-310) at a revolution speed of 2000 rpm and a rotation speed of 800 rpm to obtain a paste for measurement. A grind gauge was placed with the measuring paste and the scraper was applied vertically and slid over the grooves to observe the point at which noticeable spots began to appear. Observations were made in increments of 2.5 μm, and the largest point containing 5 or more particles in a width of 3 mm across the groove was the grind gauge measurement particle size. The operation was performed with n=6, and the average value of 6 times was taken as the grain size measured by grind gauge.

[aspect ratio]
The aspect ratio of the hexagonal boron nitride primary particles was measured using an analytical scanning electron microscope (manufactured by Hitachi High-Technologies Corporation: S-3400N). Randomly select 100 different hexagonal boron nitride primary particles from a scanning electron microscope observation image at a magnification of 10000 times, measure the length and thickness of the major axis of the hexagonal boron nitride primary particles, and measure the aspect ratio (length of the major axis) length/thickness) was calculated, and the average value was taken as the aspect ratio. As a result, the aspect ratios of the starting hexagonal boron nitride and the hexagonal boron nitride were in the range of 3-15 in all the examples and comparative examples.

[Measurement of slurry viscosity]
The starting hexagonal boron nitride slurry was measured using a viscometer (ASJ-8ST: AS ONE Co., Ltd.) at a rotation speed of 3 rpm. In all examples, the viscosity of the starting hexagonal boron nitride slurry at 25° C. was within the range of 1 to 60 mPa·S.

Example 1
50 g of boron oxide, 40 g of melamine and 80 g of anhydrous borax were mixed using a mortar. This mixture was heated to 1200° C. in a nitrogen gas atmosphere using a graphite Tammann furnace, and heated at 1200° C. for 12 hours to obtain nitrided powder by the melamine method. Next, the obtained nitrided powder was pulverized with a stone mill grinder, put into a polyethylene container, and added with 100 g of hydrochloric acid (37% by weight HCl) and 300 g of pure water to 100 g of the nitrided powder to obtain an acidified powder. A slurry was prepared and stirred for 8 hours for acid washing. After washing with acid, the acid slurry is filtered using a Buchner funnel, and then washed by adjusting the water slurry using pure water of 10 times the amount (weight ratio) or more of the nitriding powder, and then nitriding by suction filtration. After dehydration was carried out until the moisture content of the powder became 40% by weight or less, it was vacuum-dried at 200° C. for 12 hours. The powder obtained after drying was passed through a sieve with an opening of 90 μm to obtain raw material hexagonal boron nitride powder.
10 L of 4% by mass raw material hexagonal boron nitride slurry (hexagonal boron nitride powder: pure water = 1 mass: 25 mass) was prepared, and a slurry screener manufactured by Accor Japan Co., Ltd. was used to rotate the screw inside at 50 Hz. , First, 5 L of pure water is passed through a nylon cylindrical filter with an opening of 10 μm rotated at a rotation angle of 40 °, and then the raw material hexagonal boron nitride slurry is added. Wet at a rate of 1 L / min. A classification process was performed. The filter-passed slurry was filtered to obtain a dehydrated cake, and the dehydrated cake was vacuum-dried at 200° C. to obtain the intended hexagonal boron nitride powder. In addition, the powder obtained by drying the powder remaining on the filter and the slurry that did not pass through the filter is less than 5% by mass with respect to the raw material hexagonal boron nitride powder, and 95% of the raw material hexagonal boron nitride powder. % by weight and above passed through a 10 μm filter. Tables 1 to 3 show the production conditions and the evaluation results of the obtained hexagonal boron nitride powder.

Examples 2-7
The procedure was carried out in the same manner as in Example 1, except that each condition was changed as shown in Table 1. Tables 1 to 3 show the production conditions and the evaluation results of the obtained hexagonal boron nitride powder.

Comparative Examples 1-4
The procedure was carried out in the same manner as in Example 1, except that each condition was changed as shown in Table 1. Tables 1 to 3 show the production conditions and the evaluation results of the obtained hexagonal boron nitride powder.

Comparative example 5
As shown in Table 1, commercially available BN powder was subjected to wet classification in the same manner as in Example 1. Tables 1 to 3 show the production conditions and the evaluation results of the obtained hexagonal boron nitride powder.

Comparative example 6
The procedure of Example 1 was repeated except that the slurry concentration was changed to 15% by mass. In Comparative Example 6, the slurry concentration was as high as 15% by mass or more, the slurry hardly passed through the screen, and the hexagonal boron nitride powder of the present invention could not be obtained.

As described below, the hexagonal boron nitride powders obtained in Examples 1 to 7 and Comparative Examples 1 to 5 were filled in an epoxy resin to prepare a resin composition, and thermal conductivity was evaluated. A varnish-like mixture of 100 parts by mass of a curable epoxy resin (JER828 manufactured by Mitsubishi Chemical Co., Ltd.), 5 parts by mass of a curing agent (imidazole-based curing agent, Curesol 2E4MZ manufactured by Shikoku Kasei Co., Ltd.), and 210 parts by mass of methyl ethyl ketone as a solvent. After preparing the mixture, the varnish-like mixture and the hexagonal boron nitride powder are mixed so that the resin becomes 35% by volume and the hexagonal boron nitride powder is 65% by volume. to obtain a resin composite mixture.

The resin composite mixture was coated on a PET film to a thickness of about 25 μm using an automatic coater PI-1210 manufactured by Tester Sangyo Co., Ltd., and then dried to remove the solvent. Then, the two sheets were bonded together and cured under reduced pressure under the conditions of temperature: 200° C., pressure: 5 MPa, holding time: 30 minutes, to prepare a resin sheet with a thickness of 30 μm. Moreover, regarding the resin composition containing the hexagonal boron nitride powder produced in Example 5, a resin sheet having a film thickness of 10 μm was produced in the same manner, and the thermal conductivity was measured. Table 4 shows the results of measuring the thermal conductivity of the resin sheet.

From the test results, the resin compositions containing hexagonal boron nitride powders of Examples 1 to 7 and Comparative Examples 1 to 3, in which the ratio of particles of 2.0 to 5.0 μm is 50% by volume or more, have a film thickness A high thermal conductivity was obtained with a resin sheet having a thickness of 10 to 30 μm. The above test results are obtained by measuring the thermal conductivity of the resin sheet, but the sealing material filled to the same thickness exists in a sheet-like shape, and the sheet and the sealing material form a thermal conduction path. Since the mechanism is common, a resin composition containing hexagonal boron nitride powder in which the ratio of particles of 2.0 to 5.0 μm is 50% by volume or more is used as a sealing material. Even in this case, it can be said that high thermal conductivity can be obtained as in the case of the resin sheet.

The hexagonal boron nitride powders obtained in Examples 1 to 7 and Comparative Examples 1 to 6 were filled in an epoxy resin to prepare a resin composition, which was evaluated for interstitial permeability. 0.85 g of hexagonal boron nitride powder and 3 g of liquid epoxy resin (YDF-8170C manufactured by Nippon Steel Chemical & Material Co., Ltd.) are put into a 24 ml plastic ointment pot, and this ointment pot is placed in a rotation/revolution mixer (Shinki Co., Ltd.). - company: ARE-310) at a revolution speed of 2000 rpm and a rotation speed of 800 rpm for 2 minutes to obtain a resin composition. Two glass slides (76 x 26 mm, thickness 1.0 mm) were adjusted with double-sided tape (Nitto Denko double-sided tape NO.5603 = 30 µm, NO.5601 = 10 µm) so that a gap with a width of 1 cm and a predetermined thickness was formed. After heating to 100° C. for 3 minutes on a hot plate (ASONE HHP-170D), 0.005 to 0.01 g of the above resin composition was added dropwise to conduct a gap permeability test. In the pore penetration test, the pore penetration distance was measured with a ruler 1 minute after the initiation of penetration. If it did not permeate, it was marked as x. Table 3 shows the results.

From the test results, it can be seen that in a resin composition comprising a resin and hexagonal boron nitride powder, when the grind gauge measured particle size of the hexagonal boron nitride powder is smaller than the pore size, the permeability is significantly increased. For this reason, by setting the grind gauge measurement particle size of the hexagonal boron nitride powder to be equal to or less than the size of the gap to be filled with the sealing material, clogging is less likely to occur when the gap is filled with the sealing material, and filling unevenness. It can be said that it is possible to prevent problems such as occurrence of voids, voids, and molding defects to a high degree.

Claims (7)

A hexagonal boron nitride powder characterized by having a proportion of particles of 2.0 to 5.0 μm in wet particle size distribution measurement of 50% by volume or more and a particle size measured by grind gauge of 29 μm or less. The hexagonal boron nitride powder according to claim 1, having a specific surface area of 6.0-12.0 m ² /g. 3. The hexagonal boron nitride powder according to claim 1, wherein the particle size (μm) measured by grind gauge/the D100 (μm) measured by wet particle size distribution is 1.0 to 2.3. It is a filler for a sealing material that is filled in a gap of X (μm) (where X is in the range of 10 to 30 μm), and the upper limit of the grain size measured by the grind gauge is X-1 (μm). The hexagonal boron nitride powder according to claim 1 or 2. A sealing material for filling gaps of X (μm), comprising a resin composition containing the hexagonal boron nitride powder according to claim 4 and a resin. A hexagonal boron nitride slurry in which raw material hexagonal boron nitride powder with a wet particle size distribution measurement D50 of 2.0 to 4.0 μm is dispersed in a solvent at a content ratio of 14% by mass or less is passed through a filter with an opening of 5 μm to 15 μm. A method for producing hexagonal boron nitride powder, comprising the step of treating. 7. The method for producing hexagonal boron nitride powder according to claim 6, wherein the step of passing through the filter includes a step of charging the raw material hexagonal boron nitride slurry into a cylindrical filter with a screw rotating inside.