JP6704271B2 - Hexagonal boron nitride primary particle aggregate, resin composition and use thereof - Google Patents

Description

The present invention relates to a primary particle aggregate of hexagonal boron nitride contained in a resin composition of an intermediate member that transfers heat of an exothermic electronic component such as a power device (also referred to as a power semiconductor element) to a heat dissipation member. The present invention also relates to a resin composition containing the hexagonal boron nitride primary particle aggregate. The present invention also relates to uses of the resin composition according to the present invention.

In heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to efficiently dissipate heat generated during use has become an important issue. Conventionally, as a measure for improving heat dissipation efficiency in this field, for example, the insulating layer of a printed wiring board on which a heat-generating electronic component is mounted has high thermal conductivity, and a heat-generating electronic component or a printed wiring on which the heat-generating electronic component is mounted. It has been common practice to attach the plate to a heat dissipation member such as a heat sink via an electrically insulating thermal interface material. As a main material for an electrical insulating layer of a printed wiring board, a thermal interface material and the like (these are collectively referred to as an electrical insulating member), for example, a resin composition obtained by filling a silicone resin or an epoxy resin with a ceramic powder having a high thermal conductivity. Is preferably used.

In recent years, as electronic devices have become lighter, thinner, shorter, and smaller, the mounting density of heat-generating electronic components has also increased, while the heat generation density inside electronic devices has also increased year by year. Ceramic powders with higher thermal conductivity than ever before Is being sought after. In addition, the demand for reliability of equipment, especially the demand for electrical reliability is increasing, and at the same time, ceramic powder having high electric insulation is also required.

Based on the above background, hexagonal boron nitride, which is basically excellent as an electrically insulating material having high thermal conductivity, is drawing attention. However, the primary particles of hexagonal boron nitride have a thermal conductivity of 400 W/(m·K) in the in-plane direction (also referred to as a-axis direction) and a thickness direction (also referred to as c-axis direction) due to their crystal structure. The thermal conductivity of 2) is 2 W/(m·K), and the anisotropy of thermal conductivity is extremely large (Non-Patent Document 1). When such a hexagonal boron nitride primary particle is directly filled in the resin, the primary particles are aligned in the same direction, and therefore, for example, in the production of the thermal interface material, the in-plane direction of the hexagonal boron nitride primary particle (that is, , The direction having high thermal conductivity) and the thickness direction of the thermal interface material (that is, the direction in which heat is to be transferred) are vertical, and the high thermal conductivity of the hexagonal boron nitride particles cannot be fully utilized.

In order to solve the problem caused by such anisotropy of thermal conductivity, the hexagonal boron nitride primary particles in the form of flakes are intended to have more isotropic thermal conductivity. Primary particle aggregates have been developed.

For example, Patent Documents 1 and 2 propose the use of hexagonal boron nitride agglomerates in which hexagonal boron nitride primary particles are aggregated so as not to be oriented in the same direction, and anisotropy of thermal conductivity is suppressed. It has been shown that Patent Document 3 proposes the use of hexagonal boron nitride-coated particles having a high average sphericity, in which borate particles are coated with hexagonal boron nitride primary particles.

JP, 9-202663, A JP, 2011-98882, A JP, 2001-122615, A

R. F. Hill, P.M. H. Supanic, J.M. Am. Ceram. Soc. , 85, 851 (2002)

The shapes of the hexagonal boron nitride aggregates proposed in Patent Documents 1 and 2 are pine cone-shaped (for example, Patent Document 1: Paragraph [0020] see FIG. 6) or lump-shaped (for example, Patent Document 2: Paragraph [ 3 to 5), and because the average sphericity is small, there is a limit to the filling of the resin, and a sufficient improvement in the thermal conductivity cannot always be achieved. Further, the coated particles proposed in Patent Document 3 have a certain effect in suppressing the anisotropy of thermal conductivity and improving the filling property into the resin. However, since the content of borate particles having a low thermal conductivity is high (see, for example, paragraphs [0020] and [0028] of Patent Document 3, the high thermal conductivity of hexagonal boron nitride cannot be fully utilized. There were challenges.

Furthermore, in the conventional hexagonal boron nitride primary particle agglomerates, there are many voids into which the resin does not easily penetrate, and therefore the resin that is responsible for electrical insulation is not sufficiently filled. There was a problem of lack of sex. That is, an aggregate of hexagonal boron nitride primary particles having both high thermal conductivity and electrical insulation has not been developed so far.

In view of the above-mentioned conventional techniques, it is an object of the present invention to provide a hexagonal boron nitride primary particle aggregate that contributes to both high thermal conductivity and high electrical insulation of a resin composition. Further, the present invention can be applied to an electrical insulating layer of a printed wiring board on which heat-generating electronic components such as power devices are mounted, and a thermal interface material that transfers heat to a heat radiating member. Another object is to provide a resin composition containing the aggregate. Another object of the present invention is to provide an electric insulating member using the resin composition.

The present inventors have made extensive studies to solve the above problems, and the average particle diameter of the aggregate, the oil absorption amount, the ratio of the oil absorption amount and the specific surface area, the content of the metal element derived from the sintering aid, and the average. It has been found that a hexagonal boron nitride primary particle aggregate in which sphericity is properly combined is effective for the above problems.

The present invention is, in one aspect, a primary particle aggregate of hexagonal boron nitride, containing 500 mass ppm or more and 5000 mass ppm or less of a metal element derived from a sintering additive, having an oil absorption of 200 ml/100 g or more, and a specific surface area. Is 1 m ² /g or more and 6 m ² /g or less, the ratio of the oil absorption amount and the specific surface area (oil absorption amount/specific surface area) is 0.7 ml/m ² or more, and the average particle diameter of the aggregate is 10 μm or more and 200 μm or less. A hexagonal boron nitride primary particle aggregate having an average sphericity of 0.40 or more and 0.80 or less.

In one embodiment of the primary particle aggregate of hexagonal boron nitride according to the present invention, the metal element derived from the sintering aid is calcium.

The present invention, in another aspect, is a resin composition comprising the hexagonal boron nitride primary particle aggregate according to the present invention.

The present invention, in yet another aspect, is an electrical insulating member including the resin composition according to the present invention.

In still another aspect of the present invention, a step of firing a mixture containing a compound containing boron and a compound containing nitrogen to obtain a boron nitride precursor, an aqueous slurry containing the boron nitride precursor and a sintering aid. And a step of obtaining a water slurry in which a mass ratio of the metal derived from the sintering aid to the boron nitride precursor is 0.2% to 1.9%, and the atomization speed of the water slurry is 2000 to Spray drying at 18000 rpm to obtain a dried body, firing the dried body at a temperature of 1750° C. to 2200° C. to obtain a primary particle aggregate of hexagonal boron nitride, and a primary particle aggregation of the hexagonal boron nitride. A method for producing a primary particle agglomerate of hexagonal boron nitride, which comprises performing a roughening treatment by applying a shearing force to the assembly at a shear rate of 6000 to 20000 (1/sec).

By blending the hexagonal boron nitride primary particle aggregate according to the present invention with the resin composition, it becomes possible to obtain a resin composition having both high thermal conductivity and high electric insulation. Therefore, the resin composition containing the hexagonal boron nitride primary particle aggregate is suitable as a material for the electrical insulating member.

3 is a SEM photograph of a hexagonal boron nitride primary particle aggregate a before the roughening treatment, which is manufactured in an example. 6 is a SEM photograph of the hexagonal boron nitride primary particle aggregate A3 after the roughening treatment produced in the example.

The hexagonal boron nitride primary particle aggregates according to the first embodiment of the present invention include a step of firing a mixture containing a compound containing boron and a compound containing nitrogen to obtain a boron nitride precursor. A step of obtaining an aqueous slurry containing a precursor and a sintering aid, a step of spray-drying the aqueous slurry to obtain a dried body, a step of obtaining a hexagonal boron nitride primary particle aggregate by firing the dried body, It can be produced by performing a roughening treatment on the primary particle aggregates of hexagonal boron nitride under appropriate conditions. In one embodiment, the hexagonal boron nitride primary particle aggregate according to the present invention has an oil absorption of 200 ml/100 g or more, a ratio of the oil absorption to the specific surface area of 0.7 ml/m ² or more, and an average particle diameter of 10 μm. It is 200 μm or less.

The hexagonal boron nitride primary particle agglomerates of the present invention are hexagonal boron nitride primary particle agglomerates obtained in the prior art, and their average particle size, oil absorption, and the ratio of the specific surface area and the oil absorption are within a specific range. By further subjecting the resin composition to a roughening treatment so as to fall within the range, it is possible to obtain a boron nitride powder capable of simultaneously imparting high insulation and high thermal conductivity to a resin composition, which could not be achieved by conventional techniques.
The bonding between the primary particles by firing is evaluated by observing, using a scanning electron microscope, that a continuous structure is formed in the bonding portion between the primary particles of the hexagonal boron nitride primary particle aggregate cross section. can do. The state of the surface of the hexagonal boron nitride primary particle aggregate, that is, the degree of progress of roughening, can be determined by observing the aggregate using a scanning electron microscope.

<Method for producing hexagonal boron nitride primary particle aggregate>
An example of a method for producing a hexagonal boron nitride primary particle aggregate before roughening treatment (hereinafter, also referred to as an unroughened aggregate) according to the present invention will be described in detail. A mixture of a powder of a compound containing boron and a powder of a compound containing nitrogen (starting material) is fired to obtain a boron nitride precursor. As the compound containing boron, boric acid, boron oxide, borax, etc. are preferable, and boric acid can be particularly preferably used. As the nitrogen-containing compound, cyandiamide, melamine, urea and the like are preferable, and melamine can be particularly preferably selected. It is advantageous for the production of the aggregate that the boron nitride precursor is used in combination of two or more having different crystallinity.

Then, the boron nitride precursor, such as an alkali metal, an alkaline earth metal compound, a powder of a sintering aid that promotes the conversion of the starting material into hexagonal boron nitride during firing, and the object of the present invention is not deviated. Within the range, a water slurry is prepared by heating and stirring in water together with a simple substance or a compound other than the starting material and the sintering aid, which is added as necessary. Examples of the alkali metal and alkaline earth metal compounds that can be used as a sintering aid include potassium carbonate, magnesium carbonate, calcium carbonate, and sodium carbonate. Calcium carbonate is used because it is easy to form agglomerated particles with a small addition amount. Is preferred. Examples of simple substances or compounds other than the starting materials and sintering aids include reducing substances such as carbon and boron-containing compounds such as boron carbide.

In the water slurry, the metal derived from the sintering aid is contained in a mass ratio of 0.2 to 1.9%, preferably 1.0 to 1.6% with respect to the boron nitride precursor. Therefore, it is desirable to adjust the addition amount of the sintering aid. If the amount of metal derived from the sintering aid is too large or too small, the characteristics of thermal conductivity and dielectric breakdown voltage tend to deteriorate.

The obtained water slurry is spray-dried to obtain a dried body. At this time, since the number of revolutions of the atomizer affects the particle size of the aggregate finally obtained, spray drying is preferably performed at 2000 to 18000 rpm, more preferably 5000 to 10000 rpm.

It should be noted that the starting materials for producing hexagonal boron nitride and various compounds used as sintering aids do not have to be limited to one kind, and a plurality of kinds of compounds can be used at the same time. The molar ratio of the boron atom and the nitrogen atom contained in the starting material does not necessarily have to be fixed to 5:5, and the molar ratio of the boron atom and the nitrogen atom is 2:5 depending on the reactivity and the yield. It can be appropriately changed within the range of 8 to 8:2, preferably within the range of 3:7 to 7:3.

By firing the dried body at a temperature of 1750° C. or higher, a primary particle aggregate of hexagonal boron nitride can be obtained. A method of applying an inert atmosphere of nitrogen, helium, argon, ammonia or the like as an atmosphere during firing is preferably applied. The maximum temperature for firing the dried product is preferably set to a temperature in the range of 1750°C or higher and 2200°C or lower. If the maximum firing temperature is less than 1750° C., conversion to hexagonal boron nitride is difficult to proceed. When the maximum firing temperature exceeds 2200° C., the crystal growth of hexagonal boron nitride proceeds too much, so that the specific surface area tends to be small, and crushing may be difficult. The calcination temperature may be kept constant or may be changed continuously or discontinuously, and the calcination time and the heating/cooling rate are not particularly limited. Further, the apparatus for firing the dried body is not particularly limited, but a container made of hexagonal boron nitride, for example, can be used as a container for housing the dried body, and as a heating device, for example, an electric heater is used. A conventional firing furnace can be used.
Further, it is possible to further add operations of heating, cooling, humidifying, drying, and washing within a range not departing from the object of the present invention, from the preparation of the starting material to the end of the firing.

<Method of roughening treatment>
The principle and method of the roughening treatment performed to obtain the hexagonal boron nitride primary particle aggregate of the present invention is not particularly limited, but a treatment method for roughening the surface of the aggregate to increase pores or gaps is used. It can be preferably adopted. The apparatus used for the roughening treatment is not particularly limited, but in consideration of industrial efficiency and operability, shearing force, compressive force, impact force, and frictional force are applied to the object to be ground so that the surfaces of the aggregates are separated from each other. An apparatus capable of rubbing for roughening treatment, generally, an apparatus called a shear type crusher or a shear type crusher (hereinafter, collectively referred to as shear type crusher) can be preferably used.
By the roughening treatment, the oil absorption of the hexagonal boron nitride primary particle aggregates can be increased by 10% or more, preferably 15% or more, and more preferably 20% with respect to the oil absorption before the roughening treatment. % Or more, for example, 10 to 30%. When the roughening treatment is not performed, the oil content is less likely to get inside because the surface pores are few. Therefore, it is difficult to achieve an oil absorption of 200 ml/100 g or more.
Since the roughening treatment is not a treatment intended for pulverization, it is preferably carried out under the condition that the average particle diameter of the hexagonal boron nitride primary particle aggregates hardly changes. For example, before and after the roughening treatment, the change in average particle diameter can be ±10 μm or less, typically ±5 μm or less, and more typically ±2.5 μm or less. And even more typically ±1 μm or less. The change in specific surface area before and after the roughening treatment can be ±10 m ² /g or less, typically ±5 m ² /g or less, and more typically ±2.5 m It can be ² /g or less, and more typically ±1 m ² /g or less. The mechanical structure of the shearing type crusher has, for example, a structure in which two types of blades that give a shearing force to the object to be crushed are arranged in the crushing space so as to have a gap of a predetermined length. There is. One of the two types of blades may be a fixed blade and the other may be a rotary blade, or may be two types of blades that rotate in mutually opposite directions. The number of the two types of blades is not particularly limited, but the shear rate generated between the two types of blades is preferably in the range of 6000 to 20000 (1/sec), and 8000 to 15000 (1/second). It is more preferable that it is in the range of (sec). When the shear rate is less than 6000 (1/sec), the effect and ability to roughen the pulverized product are small, and the crushed product may not be sufficiently roughened, or the treatment may take time. Further, when the treatment is performed under the condition that the shear rate exceeds 20000 (1/sec), the sphericity becomes too small, and the effect of finely divided particles close to the shape of primary particles cannot be ignored, so that the present invention There is a tendency that the desired thermal conductivity cannot be exhibited.
Further, it is preferable to provide a screen in the crushing space so that only particles crushed to a predetermined particle size or less are discharged to the outside of the crushing space.

<Average sphericity>
The degree of roughening treatment can be evaluated by the average sphericity. Whereas the sphericity of a true sphere is 1, the sphericity is generally reduced by the roughening treatment. In a preferred embodiment of the hexagonal boron nitride primary particle aggregate of the present invention, the average sphericity is 0.40 to 0.80. The fact that the average sphericity is within the above range indirectly indicates that a suitable roughening treatment is performed. If the average sphericity is less than 0.40, it becomes difficult to exhibit high thermal conductivity, and if the average sphericity exceeds 0.80, it becomes difficult to secure a sufficient oil absorption amount. The average sphericity is more preferably 0.45 to 0.60, and even more preferably 0.45 to 0.50.

In the present invention, the average sphericity of the hexagonal boron nitride primary particle aggregate is measured as follows. The primary particle aggregate fixed to the conductive double-sided tape on the sample stage was photographed with a scanning electron microscope, for example, "JSM-6010LA" (manufactured by JEOL Ltd.), and the obtained aggregate image was analyzed with image analysis software. For example, it is incorporated in “Mac-View” (manufactured by Mountech Co., Ltd.). Next, the projected area (A) and the perimeter (PM) of the primary particle aggregate are measured from the obtained photograph. When the area of a perfect circle corresponding to the perimeter (PM) is (B), the roundness of the primary particle aggregate can be expressed as A/B. Therefore, assuming a perfect circle having the same perimeter as the perimeter (PM) of the primary particle aggregate, PM=2πr and B=πr ² , so B=π×(PM/2π) ² The sphericity of the particles can be calculated as sphericity=A/B=A×4π/(PM) ² . The sphericity of 100 of any primary particle agglomerates thus obtained is determined and the average value is taken as the average sphericity.

<Average particle size>
In a preferred embodiment of the hexagonal boron nitride primary particle aggregate of the present invention, the average particle diameter of the aggregate is 10 μm or more and 200 μm or less. Generally, when the average particle size becomes smaller, the thermal conductivity tends to decrease due to the increase in the contact thermal resistance with the increase in the total number of the aggregates and the resin interface. However, the larger the average particle size of the hexagonal boron nitride primary particle aggregates, the mechanical strength of the aggregates tends to decrease, and a part of the structure of the aggregates due to the shear stress received during kneading into the resin. The scale-shaped hexagonal boron nitride, which has been destroyed and returned to the primary particles, is oriented in the same direction, so that high thermal conductivity may not be exhibited. Therefore, the average particle size of the hexagonal boron nitride primary particle aggregate is 200 μm or less. A preferable average particle diameter is in the range of 20 μm or more and 120 μm or less. A more preferable average particle diameter is in the range of 40 μm or more and 70 μm or less. The average particle size referred to in the present invention is a particle size having a cumulative value of 50% of the cumulative particle size distribution based on volume in the particle size distribution measurement by the laser diffraction light scattering method. In measuring the particle size distribution, water can be used as a solvent for dispersing the aggregate and hexametaphosphoric acid can be used as a dispersant. At this time, 1.33 can be used for the refractive index of water, and 1.80 can be used for the refractive index of the boron nitride powder. Further, the measurement time per measurement is not particularly limited, but is usually 5 seconds or more and 120 seconds or less, and it is generally and preferably set to about 15 seconds or more and 60 seconds or less.

<Oil absorption>
The oil absorption amount is a specific resin penetration amount in the hexagonal boron nitride primary particle aggregate of the present invention, that is, an index showing the insulating property. The inventors of the present invention have made earnest studies and found that it is possible to improve the oil absorption amount by further roughening the hexagonal boron nitride immediately after firing. The higher the oil absorption value, the higher the resin penetration amount. In a preferred embodiment, the oil absorption amount per 100 g of the hexagonal boron nitride primary particle aggregate of the present invention is 200 ml or more (hereinafter referred to as 200 ml/100 g). If the oil absorption is less than 200 ml/100 g, the resin infiltration amount is insufficient and voids remain, so that electrical high insulation cannot be obtained. A preferable oil absorption amount is 220 ml/100 g or more. From the viewpoint of the amount of resin infiltration, it is preferable that the oil absorption is high, but if the oil absorption is too high, the aggregate density of the aggregate is low, the mechanical strength is low, and the insulation performance is not always excellent. Therefore, it is generally desirable to be 500 ml/100 g or less, more desirably 400 ml/100 g or less, and even more desirably 300 ml/100 g or less.
In the present invention, the oil absorption is measured based on the procedure shown in JIS K5101-13-1:2004 (“Pigment test method”-Part 13: Oil absorption-Section 1: Purified linseed oil method).

<Specific surface area>
The specific surface area of the hexagonal boron nitride primary particle agglomerate of the present invention is a value calculated by using a BET one-point method as a method of calculating the specific surface area using a commercially available measuring device utilizing a gas adsorption phenomenon. ..

<Ratio between oil absorption and specific surface area>
In a preferred embodiment, the ratio of the oil absorption amount and the specific surface area of the hexagonal boron nitride primary particle aggregate of the present invention, that is, the value of (oil absorption amount/specific surface area) is 0.70 ml/m ² or more. A more preferable ratio is 0.75 ml/m ² or more, and an even more preferable ratio is 0.80 ml/m ² or more. If this ratio is less than 0.70 ml/m ² , the amount of resin infiltrating into the inside of the primary particle agglomerate tends to decrease, and the required high electrical insulation cannot be satisfied. The upper limit of this ratio is not particularly set, but is typically 2.0 ml/m ² or less, and more typically 1.8 ml/m ² or less.

<Content of metal element derived from sintering aid>
In order for the hexagonal boron nitride primary particle aggregate of the present invention to be an aggregate having the characteristics of the present invention, the hexagonal boron nitride primary particle aggregate that is the first embodiment of the present invention finally obtained. The content of the metal element derived from the sintering aid contained in is preferably 500 to 5000 mass ppm. A more preferable range of the content of the metal element is 1000 to 3000 mass ppm. In the present invention, the metal element derived from the sintering aid is preferably calcium. When the content of the metal element is less than 500 mass ppm, the bonding strength due to firing of the primary particles becomes insufficient, the shear stress of kneading when filling the resin and the compressive stress at the surface contact of the boron nitride particles ( In particular, it is not possible to obtain an aggregate strength that can withstand heat-press molding. Further, when the content of the metal element is more than 5000 mass ppm, the elastic modulus of the boron nitride particles becomes high, so that the surface contact between the hexagonal boron nitride primary particles becomes insufficient, and the second embodiment of the present invention is performed. The thermal conductivity of the resin composition in the form is lowered, and the electrical insulating member according to the third embodiment of the present invention cannot be obtained.
The content of the metal element derived from the sintering aid contained in the hexagonal boron nitride primary particle aggregate of the present invention can be measured using, for example, a scanning fluorescent X-ray analyzer.

<Resin composition containing hexagonal boron nitride primary particle aggregates>
Next, a resin composition containing a hexagonal boron nitride primary particle aggregate, which is a second embodiment of the present invention, will be described. The proportion of the primary particle aggregates contained in the resin composition is preferably 20% by volume or more and 80% by volume or less. At this time, various ceramic mix powders having an average particle size smaller than that of the hexagonal boron nitride primary particle aggregate of the present invention (hereinafter referred to as various ceramic powders), for example, aluminum nitride, hexagonal boron nitride, boron nitride, silicon nitride One or more powders of aluminum oxide, zinc oxide, magnesium oxide, magnesium hydroxide, silicon dioxide, and silicon carbide may be appropriately added within a range that does not impair the object of the present invention. The appropriate average particle size of various ceramic powders varies depending on the average particle size of the aggregate of the boron nitride powder of the present invention, but is 40% or less with respect to the average particle size of the aggregate of the boron nitride powder of the present invention. It is preferably 20% or less, more preferably 20% or less. For example, when the average particle diameter of the aggregate of the boron nitride powder of the present invention is 50 μm, it is preferably 20 μm or less, more preferably 10 μm or less. Since the packing structure of the particles can be made denser, the packing property is improved, and as a result, the thermal conductivity of the resin composition can be significantly improved. The average particle size of various ceramic powders is measured by the same procedure as that for the hexagonal boron nitride primary particle aggregate of the present invention.

<Resin>
The type of resin that can be used in the resin composition containing the hexagonal boron nitride primary particle aggregates, which is the second embodiment of the present invention, is not particularly limited, and examples thereof include epoxy resin, silicone resin, and silicone rubber. , Acrylic resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyimide such as polyetherimide, polyester such as polybutylene terephthalate and polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic Group polyester, polysulfone, liquid crystal polymer, polyether sulfone, polycarbonate, maleimide modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber/styrene) resin, AES (acrylonitrile/ethylene/propylene/diene rubber-styrene) resin, polyglycolic acid resin Preferable examples include polyphthalamide, polyacetal, nylon resin and the like. For these resins, especially thermosetting resins, a curing agent, an inorganic filler, a silane coupling agent, and further improvement of wettability and leveling property and acceleration of viscosity reduction are promoted to reduce the occurrence of defects during heat and pressure molding. Additives can be included. Examples of this additive include a defoaming agent, a surface conditioner, and a wetting and dispersing agent. Further, the epoxy resin is suitable as an insulating layer of a printed wiring board because it has excellent heat resistance and adhesive strength to a copper foil circuit. Furthermore, silicone resin and silicone rubber are suitable as a thermal interface material because they have excellent heat resistance, flexibility, and adhesion to a heat sink and the like.

When the hexagonal boron nitride primary particle agglomerates of the present invention are mixed with a resin to form a resin composition, an organic solvent may be added as necessary in order to facilitate mixing of the two. Examples of the organic solvent include alcohols such as ethanol and isopropanol, 2-methoxyethanol, 1-methoxyethanol, 2-ethoxyethanol, 1-ethoxy-2-propanol, 2-butoxyethanol, 2-(2-methoxyethoxy). ) Ethanol, ether alcohols such as 2-(2-ethoxyethoxy)ethanol and 2-(2-butoxyethoxy)ethanol, glycol ethers such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether, acetone, methyl ethyl ketone, methyl isobutyl ketone And ketones such as diisobutyl ketone ketone, and hydrocarbons such as toluene and xylene. These diluents may be used alone or in combination of two or more.

The electrical insulating member according to the third embodiment of the present invention is obtained by molding and processing the resin composition containing the hexagonal boron nitride primary particle aggregates according to the second embodiment, and further, if necessary, with another material or the like. It is an electrical insulating member made by combining them.

Hereinafter, the present invention will be described more specifically with reference to Reference Examples, Examples, and Comparative Examples.
<Reference Example 1: Preparation of unroughened aggregate a>
Boric acid (52 kg) and melamine (50 kg) were mixed, and the precursor (a) was fired in a batch type high-frequency furnace in a nitrogen atmosphere as a primary calcination at 1000° C. for 4 hours and then as a secondary calcination at 1600° C. for 4 hours. , A mixture of 52 kg of boric acid and 50 kg of melamine, which was fired in a batch type high-frequency furnace in a nitrogen atmosphere at 1000° C. for 4 hours as primary firing, and then at 2000° C. for 4 hours as secondary firing (B) Got
15.72 kg of the powder of the precursor (a), 5.24 kg of the powder of the precursor (b), 0.54 kg of calcium carbonate (PC-700 manufactured by Shiraishi Industry Co., Ltd.) as a sintering aid, and 78. After additionally adding 5 kg and mixing using a Henschel mixer, it was pulverized with a ball mill for 5 hours to obtain a water slurry. Furthermore, to 100 parts by mass of the water slurry, 0.5 parts by mass of a polyvinyl alcohol resin (Gosenol manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) for gluing boron nitride particles was added, and after heating and stirring at 50° C. until dissolution. , Through a rotary atomizer operated at a rotation speed of 7,000 rpm into a spray dryer at a temperature of 230°C. The recovered dried product of the water slurry was further subjected to a third calcination in a batch type high-frequency furnace in a nitrogen atmosphere at 1850° C. for 4 hours, and then roughly crushed to obtain an unroughened aggregate a. .. The conditions at this time are summarized in Table 1.

<Reference Examples 2 to 14: Preparation of unroughened aggregates b to n>
Further, the same precursors (a) and (b) as in Reference Example 1 were used, and the mixing conditions thereof, calcium carbonate and water mixing conditions, ball milling time, spray drying conditions, and tertiary firing conditions were adjusted. The unroughened aggregates b to n were produced in the same procedure as the unroughened aggregate a. These conditions and the like are shown in Table 1 together with Reference Example 1.

<Examples 1 to 10 and Comparative Examples 1 to 10: Preparation of roughened aggregate>
The unroughened aggregate a was roughened using a shear type crusher having a fixed blade and a rotary blade (rotary cutter mini RC-1S manufactured by Glow Engineering Co., Ltd.). At this time, the number of rotations of the rotary cutter rotary blade was set to a value shown in Table 2, the aggregate was supplied at a rate of 1 kg/min, and a coarse screen was used with a 0.3 mm diameter screen installed at the exit of the crusher. After removing the particles, the hexagonal boron nitride primary particle aggregates (hereinafter referred to as roughening-treated aggregates A3) were collected. The shear rate calculated for each rotation speed of the rotary cutter is also shown in Table 2. The surface state of the finally obtained hexagonal boron nitride primary particle aggregate was observed with a scanning electron microscope (JSM-6010LA, manufactured by JEOL Ltd.) to confirm the state of roughening treatment. Electron microscope images before roughening treatment (that is, unroughened aggregate a) and after roughening treatment (that is, roughened aggregate A3) are illustrated in FIGS. 1 and 2. From the image shown in FIG. 2, it was confirmed that the roughening-treated aggregate A3 had pores of about 5 to 10 μm formed on the surface thereof while maintaining the state in which the primary particles were aggregated.
Regarding the unroughened aggregate a, the roughening conditions were changed as shown in Table 2 and Table 3 to prepare roughened aggregates A1 to A7. Further, the unroughened aggregates b to n (excluding the unroughened aggregate h) are also subjected to the roughening treatment according to the conditions shown in Tables 2 and 3, and the roughened aggregates B to I got N.

<Measurement of average sphericity>
The average sphericity of the roughened aggregates A1 to A7 and B to N (hereinafter, A1 and H to which substantially no roughening treatment was added are also combined with the roughened aggregate) is as follows. Measured. Each roughening-treated aggregate fixed to the conductive double-sided tape on the sample table was photographed with a scanning electron microscope "JSM-6010LA" (manufactured by JEOL Ltd.), and the obtained aggregate image was analyzed with image analysis software. The projected area (A) and the peripheral length (PM) of the aggregate were measured by the procedure described above from the photograph by taking in “Mac-View” (manufactured by Mountech Co., Ltd.) to calculate the sphericity of one aggregate. The magnification of the image at this time was 100 times, and the number of pixels for image analysis was 15.1 million pixels. By repeating this, the sphericity of 100 arbitrary aggregates was obtained and the average value was used as the average sphericity.

<Measurement of average particle size>
The average particle size of the roughening-treated aggregates A1 to A7 and B to N (hereinafter, A1 and H to which substantially no roughening treatment was added are also combined with the roughening-treated aggregate) It measured using the measuring machine (The Nikkiso Co., Ltd. make, MT3300EX). In measuring the particle size distribution, water was used as the solvent for dispersing the aggregates and hexametaphosphoric acid was used as the dispersant. At this time, 1.33 was used as the refractive index of water, and 1.80 was used as the refractive index of the boron nitride powder. The measured values of the average particle diameter are shown in Tables 2 and 3.

<Measurement of oil absorption>
The oil absorptions of the roughened aggregates A1 to A7 and B to N are measured according to JIS K5101-13-1:2004 ("Pigment test method"-Part 13: Oil absorption-Section 1: Purified linseed oil method. ) It measured based on the procedure shown by. The measured values of the amount of oil supplied are shown in Tables 2 and 3.

<Calculation of specific surface area and (oil absorption/specific surface area) value>
The values of the specific surface areas of the roughened aggregates A1 to A7 and B to N were measured by a BET one-point method using a specific surface area measuring device (Cantersorb, manufactured by Yuasa Ionics Inc.). The value of (oil absorption/specific surface area) of the roughened aggregates A1 to A7 and B to N was calculated by dividing the previously measured oil absorption by the value of the measured specific surface area. When measuring the specific surface area, 1 g of the sample was dried and degassed at 300° C. for 15 minutes and then used for the measurement. The values of specific surface area and (oil absorption/specific surface area) are shown in Tables 2 and 3.

<Measurement of content rate of metal element derived from sintering aid>
The content of the metal element derived from the sintering aid, which is contained in the roughened aggregates A1 to A7 and B to N, is determined by using a scanning fluorescent X-ray analyzer (ZSX PrimusII, manufactured by Rigaku Corporation). It was measured. A hexagonal boron nitride primary particle agglomerate was press-molded according to the device, a test object was placed in the device, an Rh tube was used as the X-ray tube, the X-ray tube power was 3.0 kW, and the measurement diameter was Φ. =30 mm was measured. The metal element is calcium. The measured values of calcium are shown in Tables 2 and 3.

<Filling resin>
In order to evaluate the practical properties of the obtained roughened aggregates A1 to A7 and B to N as an electric insulating member, 90% by volume of an epoxy resin (Epicoat 807, manufactured by Mitsubishi Chemical Corporation) and a curing agent ( Acmex H-84B, manufactured by Nippon Gohsei Co., Ltd., was mixed so as to be 10% by volume and 60% by volume of roughened aggregates to form a resin composition, and the thickness was 1.0 mm on a PET sheet. After being applied so as to be, the defoaming under reduced pressure of 500 Pa (abs) was performed for 10 minutes. After that, press heating and pressing were performed for 60 minutes under conditions of a temperature of 150° C. and a pressure of 160 kg/cm ² to obtain a sheet having a thickness of 0.5 mm. Using the sheet, evaluation as an electrically insulating member was performed on Examples 1 to 10 and Comparative Examples 1 to 10.

The thermal conductivity and the dielectric breakdown voltage of the obtained resin composition sheet containing the roughened aggregate and the epoxy resin were evaluated according to the following methods.

<Thermal conductivity>
The thermal conductivity (H (W/(m·K)) is the thermal diffusivity (A (m ² /sec)), density (B (kg/m ³ )) and specific heat capacity ( From C (J/(kg·K)), H=A×B×C was calculated. The thermal diffusivity was determined by a laser flash method after processing a sheet as a measurement sample into a width of 10 mm×10 mm×a thickness of 0.5 mm. A xenon flash analyzer (LFA447NanoFlash, manufactured by NETZSCH) was used as a measuring device. The density was obtained using the Archimedes method. The specific heat capacity was determined using a DSC measurement device (ThermoPlus Evo DSC8230, manufactured by Rigaku Corporation).

<Dielectric breakdown voltage>
The dielectric breakdown voltage was measured based on JIS C2110-1:2010 (solid electric insulating material-testing method for strength of dielectric breakdown-part 1: test by applying commercial frequency AC voltage). Five sheets each having a size of 100 mm×100 mm were processed as a measurement sample, and each sheet was measured at 5 points using an electrode having a diameter of 25 mm.

The thermal conductivity and the dielectric breakdown voltage of Examples 1 to 10 and Comparative Examples 1 to 10 are also shown in Tables 2 and 3.

From the results of Table 2, the electrical insulating member using the resin composition containing the hexagonal boron nitride primary particle aggregate of the present invention has a thermal conductivity of more than 8 (W/m·K) and 10 (kV). It can be seen that the electrical insulation properties that exceed are compatible. In addition, from the results of Table 3, the electrical insulating member using the resin composition containing the hexagonal boron nitride primary particle aggregate of the comparative example had a thermal conductivity of more than 8 (W/m·K) and 10 (kV). It can be seen that it is not possible to achieve both electrical insulation properties exceeding the range. The cause is as described below.
In Comparative Example 1 and Comparative Example 2, the roughening treatment was not performed, and the oil absorption amount was insufficient.
In Comparative Example 3, the crushing time by the ball mill at the time of producing the unroughened aggregate was too long, and the atomizer rotation speed at the time of spray drying was too fast, so that the aggregated particles became small. Therefore, the oil absorption is high, but the specific surface area is also large, and the ratio between the oil absorption and the specific surface area has not been optimized.
In Comparative Example 4, the atomizer rotation speed at the time of spray-drying when producing the unroughened aggregate was too slow, and therefore the aggregated particles became excessively large.
Comparative Example 5 lacked calcium derived from the sintering aid.
In Comparative Example 6, the calcium derived from the sintering aid was excessive.
In Comparative Example 7, the specific surface area was increased because the firing temperature during the third firing was too low, and the ratio between the oil absorption amount and the specific surface area was not optimized.
In Comparative Example 8, the specific surface area was reduced because the baking temperature during the third baking was too high, and the specific surface area was not optimized.
In Comparative Example 9, the sphericity was less than 0.4 because the shear rate during the roughening treatment was too fast.
In Comparative Example 10, the oil absorption amount was insufficient because the shear rate during the roughening treatment was too slow.

The hexagonal boron nitride primary particle aggregate of the present invention has both high thermal conductivity and electrical insulation, and an electrical insulating member using a resin composition containing the same is used as an insulating layer and a thermal interface material of a printed wiring board. It can be preferably used.

Claims (4)

It is a primary particle aggregate of hexagonal boron nitride, contains 500 mass ppm or more and 5000 mass ppm or less of calcium derived from a sintering additive, has an oil absorption of 200 ml/100 g or more, and a specific surface area of 1 m ² /g or more 6 m ² /G or less, the ratio of the oil absorption amount and the specific surface area (oil absorption amount/specific surface area) is 0.7 ml/m ² or more, the average particle diameter of the aggregate is 10 μm or more and 200 μm or less, and the average sphericity is 0.40. Hexagonal boron nitride primary particle aggregate of not less than 0.80. A resin composition comprising the primary particle aggregate of the hexagonal boron nitride according to claim 1 . An electrical insulating member comprising the resin composition according to claim 2 . By firing a mixture comprising a compound comprising a compound and nitrogen containing boron, a water slurry containing step of obtaining a boron nitride precursor, a nitride boron precursor, and a sintering aid containing calcium, the A step of obtaining a water slurry in which the mass ratio of the calcium derived from the sintering aid to the boron nitride precursor is 0.2% to 1.9%, and the water slurry is spray-dried at an atomizer rotation speed of 2000 to 18000 rpm. To obtain a dried body, a step of obtaining a primary particle aggregate of hexagonal boron nitride by firing the dried body at a temperature of 1750° C. to 2200° C., a shear rate of the primary particle aggregate of the hexagonal boron nitride. A method for producing a primary particle aggregate of hexagonal boron nitride, which comprises performing a roughening treatment by applying a shearing force at 6000 to 20000 (1/sec).