Metal oxide-attached hexagonal boron nitride particles, powder containing particles, resin composition containing particles, resin sheet, metal wiring board, and method for producing particles

Abstract

Provided are metal oxide-attached hexagonal boron nitride particles which, when used as a filler, can suppress an increase in the viscosity of a resin composition and can increase the thermal conductivity of the resin composition, and when used in a metal wiring board, can improve the peel strength from a metal layer.　The metal oxide-attached hexagonal boron nitride particles are hexagonal boron nitride particles in which a metal oxide is attached to the surface of the particles, wherein the area coverage of the metal oxide on the basal plane of the hexagonal boron nitride particles is 10% or less, and the area coverage of the metal oxide on the prismatic plane of the hexagonal boron nitride particles is 30% or more.

Description

Metal oxide-coated hexagonal boron nitride particles, powder containing the particles, resin composition containing the particles, resin sheet, metal wiring substrate, and method for producing the particles

[0001] The present invention relates to metal oxide-deposited hexagonal boron nitride particles, a powder containing the particles, a resin composition containing the particles, a resin sheet, a metal wiring substrate, and a method for producing the particles.

[0002] In recent years, electronic devices have rapidly become more powerful and smaller. This has led to increased power density in semiconductor devices, making it difficult to control the heat they generate. Therefore, thermally conductive materials are being used in mounting and peripheral components. Highly thermally conductive compounds such as hexagonal boron nitride have traditionally been used as resin additives (fillers). Generally, the higher the content of thermally conductive fillers, the higher the thermal conductivity of the resulting resin composition. However, due to the plate-like shape of hexagonal boron nitride, its fillability into resins is poor. Therefore, improving this fillability is required to improve the thermal conductivity of the resulting resin composition and to improve the moldability of the resulting resin composition.

[0003] Furthermore, when using a resin composition as a metal wiring substrate, it is necessary to improve the peel strength between the metal layer and the substrate made of the resin composition. However, since hexagonal boron nitride has few functional groups present on the particle surface, it has been difficult to improve the peel strength of the metal layer.

[0004] Patent Document 1 describes a method of mixing silica or the like with boron nitride to provide a thermally conductive material with reduced viscosity.

[0005] Special Publication No. 2022-546342

[0006] However, in the method of Patent Document 1, as described in paragraph 0016, silica is uniformly dispersed on the surface of the platelet-shaped boron nitride, and in this case, the thermal conductivity of the resulting resin composition is insufficient.

[0007] In view of the above circumstances, an object of the present invention is to provide metal oxide-adhered hexagonal boron nitride particles, which, when used as a filler, can suppress an increase in the viscosity of a resin composition, can increase the thermal conductivity of the resin composition, and, when made into a metal wiring substrate, can improve the peel strength from the metal layer; powder containing the particles; resin composition, resin sheet, metal wiring substrate, and a method for producing the particles.

[0008] As a result of extensive research, the present inventors have completed the following invention: [1] Metal-oxide-attached hexagonal boron nitride particles having a metal oxide attached to the particle surface, wherein the area coverage of the metal oxide on the flat surfaces of the hexagonal boron nitride particles is 10% or less, and the area coverage of the metal oxide on the end faces of the hexagonal boron nitride particles is 30% or more.

[0009] [2] The metal oxide-coated hexagonal boron nitride particles according to [1], wherein the hexagonal boron nitride particles have an aspect ratio of 12 or less and a particle size of 5 μm or more and 12 μm or less. [3] The metal oxide-coated hexagonal boron nitride particles according to [1] or [2], wherein the metal oxide has a primary particle size of 100 nm or more and 700 nm or less.

[0010] [4] A powder comprising the metal oxide-deposited hexagonal boron nitride particles according to any one of [1] to [3]. [5] A resin composition comprising a base resin and the metal oxide-deposited hexagonal boron nitride particles according to any one of [1] to [3].

[0011] [6] A resin sheet obtained by molding the resin composition of [5]. [7] A metal wiring substrate having metal wiring on the surface of the resin sheet of [6].

[0012] [8] A method for producing a powder containing metal oxide-adhered hexagonal boron nitride particles, comprising a step of dry-mixing a powder containing hexagonal boron nitride particles having an average aspect ratio of 12 or less and an average particle size of 5 μm or more and 12 μm or less with a powder containing metal oxide particles having an average primary particle size of 100 nm or more and 700 nm or less.

[0013] When the metal oxide-attached hexagonal boron nitride particles of the present invention are used as a filler, they can suppress an increase in the viscosity of a resin composition, and can increase the thermal conductivity of the resin composition.Furthermore, when they are used as a metal wiring substrate, they can improve the peel strength from the metal layer.

[0014] Fig. 1 is a conceptual diagram of a hexagonal boron nitride particle. Fig. 2 is an SEM image showing the state of a metal oxide attached to a hexagonal boron nitride particle in the metal oxide-attached hexagonal boron nitride particle of the present invention.

[0015] Next, the present invention will be described based on embodiments. However, the present invention is not limited to the embodiments described below. In the present invention, when it is stated that "X or more" (X is any number), it also means "preferably larger than X" unless otherwise specified, and when it is stated that "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

[0016] <Metal Oxide-Coated Hexagonal Boron Nitride Particles> The metal oxide-coated hexagonal boron nitride particles of the present invention comprise hexagonal boron nitride particles and a metal oxide that is coated on the surfaces of the hexagonal boron nitride particles.

[0017] (Hexagonal boron nitride particles) Boron nitride is available in two phases: hexagonal boron nitride (h-BN), which is stable at atmospheric pressure, and cubic boron nitride (c-BN), which is stable at high pressure. The hexagonal boron nitride (h-BN) is used in the present invention.

[0018] The particle shape of the hexagonal boron nitride particles is flat, as shown in the conceptual diagram of Figure 1, and has a flat surface P1 and an end surface P2. The hexagonal boron nitride particles may also be secondary particles formed by aggregation of primary particles, and the shape of the secondary particles is not particularly limited. Furthermore, the hexagonal boron nitride particles have thermal conductivity, but are characterized by higher thermal conductivity in the planar direction DR1 than in the thickness direction DR2 of the tabular particles.

[0019] Aspect Ratio of Hexagonal Boron Nitride Particles The hexagonal boron nitride particles of the present invention are thick-walled, and the aspect ratio of the primary particles is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. The lower limit of the aspect ratio is preferably 1 or more, more preferably 2 or more. If the aspect ratio exceeds 12, adhesion of metal oxide particles to the end faces of the hexagonal boron nitride particles is limited. Furthermore, by setting the aspect ratio to 12 or less, it becomes easier to orient the planar direction DR1 of the hexagonal boron nitride particles in the thickness direction of the sheet, and it becomes easier to improve the thermal conductivity in the thickness direction of the sheet.

[0020] The aspect ratio was measured by analyzing an SEM image of the metal oxide-adhered hexagonal boron nitride particles using an image analyzer (A-Image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.), measuring the length of the major axis and the length in the thickness direction, and calculating the ratio of the length of the major axis to the length in the thickness direction as the aspect ratio.

[0021] Particle size of hexagonal boron nitride particles The particle size of the primary particles of the hexagonal boron nitride particles is preferably 5 μm to 12 μm, more preferably 6 μm to 10 μm, and even more preferably 6.5 μm to 8 μm. The particle size of the hexagonal boron nitride particles is the length of the major axis determined by analyzing an SEM image of the metal oxide-coated hexagonal boron nitride particles using an image analyzer (A-Image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.).

[0022] (Metal Oxide) The metal oxide constituting the metal oxide-adhered hexagonal boron nitride particles preferably includes zirconium oxide, titanium oxide, zinc oxide, tin oxide, iron oxide, tungsten oxide, nickel oxide, copper oxide, magnesium oxide, manganese oxide, cerium oxide, aluminum oxide, silicon dioxide, and any mixture thereof. Among these, silicon dioxide is preferably used as the metal oxide because it can be used for low dielectric purposes, has high chemical stability, and is widely used as a resin filler.

[0023] The metal oxide may be a colloidal metal oxide formed via a colloid such as colloidal silica, a wet-process metal oxide formed using a wet process such as a sol-gel method, or a fumed metal oxide such as fumed silica obtained by burning a raw material, but a wet-process metal oxide is preferred from the viewpoint of uniform control of particle size.

[0024] Primary Particle Diameter of Metal Oxide The primary particle diameter of the metal oxide is preferably 100 nm or more and 700 nm or less. The primary particle diameter of the metal oxide was determined by analyzing multiple metal oxide particles attached to hexagonal boron nitride particles from SEM images of the metal oxide-attached hexagonal boron nitride particles using an image analyzer (A-zo-kun, manufactured by Asahi Kasei Engineering Co., Ltd.), randomly selecting 100 different single particles, measuring the major axis length, and calculating the arithmetic mean value. Note that if there were fewer than 100 single particles whose major axis lengths could be measured, the arithmetic mean value of the major axis lengths of all single particles whose major axis lengths could be measured was used as the primary particle diameter of the metal oxide. If the primary particle diameter of the metal oxide is less than 100 nm, the metal oxide will likely adhere not only to the end faces of the hexagonal boron nitride particles but also to the flat surfaces, potentially resulting in a decrease in thermal conductivity. Furthermore, if the primary particle diameter of the metal oxide is greater than 700 nm, adhesion of the metal oxide to the end faces of the hexagonal boron nitride particles will be limited.

[0025] (Area Deposition Ratio of Metal Oxide on Plane of Hexagonal Boron Nitride Particle) Fig. 2 shows an SEM image showing the state of metal oxide particles adhering to a hexagonal boron nitride particle. The area deposition ratio of metal oxide R2 on plane P1 of hexagonal boron nitride particle R1 is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, still more preferably 7% or less, and particularly preferably 6% or less.

[0026] (Area Deposition Ratio of Metal Oxide on End Faces of Hexagonal Boron Nitride Particles) The area deposition ratio of metal oxide R2 on end faces P2 of hexagonal boron nitride particles R1 is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. The area deposition ratio of metal oxide on the flat surfaces or end faces of hexagonal boron nitride particles is determined by analyzing SEM observation images of the metal oxide-deposited hexagonal boron nitride particles using an image analyzer (A-Image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.), and calculating the ratio of the area of ​​the portions of the flat surfaces or end faces of the hexagonal boron nitride particles where the metal oxide is adhered to the area of ​​the portions of the flat surfaces or end faces of the hexagonal boron nitride particles that can be confirmed on the SEM image (including the portions where the metal oxide is adhered).

[0027] <Powder> The metal oxide-attached hexagonal boron nitride particles described above can be mixed with other particles, such as hexagonal boron nitride particles without metal oxide attached, aluminum nitride particles, or aluminum oxide particles, or can be used alone to form a powder, which can be used as a filler in applications requiring improved electrical insulation and thermal conductivity.

[0028] The content of the metal oxide-deposited hexagonal boron nitride particles in the powder is preferably 50 area % or more, more preferably 60 area % or more, and even more preferably 70 area % or more, in order to exert the effect thereof. The content is determined by the area ratio of the metal oxide-deposited hexagonal boron nitride particles of the present invention from an SEM image of the powder.

[0029] The average particle size of the hexagonal boron nitride particles constituting the metal oxide-deposited hexagonal boron nitride particles of the present invention contained in the powder is preferably 5 μm or more and 12 μm or less, more preferably 6 μm or more and 10 μm or less, and even more preferably 6.5 μm or more and 8 μm or less. The average particle size of the hexagonal boron nitride particles was determined by randomly selecting 100 different metal oxide-deposited hexagonal boron nitride particles from an SEM image of the powder, measuring the length of the major axis of the hexagonal boron nitride particles using the method described above, and calculating the arithmetic mean value.

[0030] The average aspect ratio of the hexagonal boron nitride particles constituting the metal oxide-deposited hexagonal boron nitride particles of the present invention contained in the powder is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. The lower limit of the aspect ratio is preferably 1 or more, more preferably 2 or more. The average aspect ratio of the hexagonal boron nitride particles was determined as the arithmetic average value by randomly selecting 100 different metal oxide-deposited hexagonal boron nitride particles from an SEM image of the powder and measuring the aspect ratios of the hexagonal boron nitride particles using the method described above.

[0031] In the metal oxide-coated hexagonal boron nitride particles of the present invention contained in the powder, the average area coverage of the metal oxide on the hexagonal boron nitride particle planes is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, and particularly preferably 6% or less. The average area coverage of the metal oxide on the hexagonal boron nitride particle planes is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more.

[0032] The average areal deposition rate of metal oxide on the flat surfaces of the hexagonal boron nitride particles of the present invention contained in the powder and the average areal deposition rate of metal oxide on the end faces were determined by randomly selecting 100 different metal oxide-deposited hexagonal boron nitride particles from an SEM image of the powder, measuring the areal deposition rate of each particle using the method described above, and calculating the arithmetic mean value.

[0033] The average particle size of the metal oxide constituting the metal oxide-adhered hexagonal boron nitride particles of the present invention contained in the powder is preferably 100 nm or more and 700 nm or less, more preferably 200 nm or more and 600 nm or less, and even more preferably 350 nm or more and 500 nm or less. The average particle size of the metal oxide particles was determined as the arithmetic mean value by randomly selecting 100 different metal oxide-adhered hexagonal boron nitride particles from an SEM image of the powder and measuring the primary particle sizes of the multiple metal oxide particles adhered to the hexagonal boron nitride particles using the method described above.

[0034] <Resin Composition> The above-described metal oxide-adhered hexagonal boron nitride particles can be mixed with a base resin to form a resin composition. Examples of base resins include thermoplastic resins such as polyolefins, vinyl chloride resins, methyl methacrylate resins, nylon resins, and fluororesins; thermosetting resins such as epoxy resins, phenolic resins, urea resins, melamine resins, unsaturated polyester resins, and silicone resins; and synthetic rubbers. The resin composition may be in the form of a dispersion of the metal oxide-adhered hexagonal boron nitride particles in the resin, or a mixture of a particulate or powdery base resin and the metal oxide-adhered hexagonal boron nitride particles. The amount of powder containing the metal oxide-adhered hexagonal boron nitride particles in the resin composition is not particularly limited, but is preferably 80 parts by volume or more, and more preferably 100 parts by volume or more, per 100 parts by volume of the base resin, since this facilitates achieving high thermal conductivity. The upper limit of the amount is not particularly limited, but is, for example, 1,000 parts by volume or less.

[0035] <Resin Sheet> The resin composition described above can be formed into a resin sheet by a known method and can be used, for example, as a heat dissipation sheet or an insulating sheet. For example, it can be used as a heat dissipation sheet used between an electronic device that generates heat, such as a power transistor, and a heat sink. The thickness of the heat dissipation sheet can be, for example, 0.02 mm or more and 10 mm or less.

[0036] The surface of hexagonal boron nitride particles has relatively few functional groups, whereas metal oxide particles have relatively many functional groups. The metal oxide-attached hexagonal boron nitride particles of the present invention have an increased number of functional groups on their surfaces due to the attachment of the metal oxide, which improves the affinity with the base resin and reduces the viscosity of the resin composition. This improves the moldability of the resin composition and allows for a higher filling ratio to increase the thermal conductivity of the resin sheet.

[0037] Furthermore, when silica is uniformly adhered to the surface of the platelet-shaped boron nitride, as in the technology of Patent Document 1, the thermal conductivity of silica itself is lower than that of boron nitride, so the silica adhered to the surface of the platelet-shaped boron nitride becomes thermally resistive, and the thermal conductivity of the platelet-shaped boron nitride after silica adhesion tends to be low. In contrast, in the metal oxide-adhered hexagonal boron nitride particles of the present invention, the metal oxide does not adhere to the entire surface of the metal oxide-adhered hexagonal boron nitride particles, but rather the metal oxide adheres selectively to the end faces of the hexagonal boron nitride particles. Therefore, the thermal conductivity is improved compared to the technology of Patent Document 1. Furthermore, the filling viscosity of the metal oxide-adhered hexagonal boron nitride particles in the resin composition can be reduced, improving the moldability of the resin sheet and increasing the filling rate, thereby further improving the thermal conductivity.

[0038] Furthermore, since the resin sheet is preferably provided with hexagonal boron nitride particles having a predetermined aspect ratio, it is possible to orient the planar direction of the hexagonal boron nitride particles close to the thickness direction of the resin sheet, which also makes it possible to increase the thermal conductivity of the resin sheet in the thickness direction. Furthermore, hexagonal boron nitride has a low dielectric constant, low specific gravity, and high water resistance, making it suitable for use in applications requiring such properties.

[0039] <Metal Wiring Substrate> The resin sheet described above can be suitably used as a metal wiring substrate having metal wiring on its surface, taking advantage of its heat dissipation and insulating properties. A metal wiring substrate can be produced by forming a metal layer on the surface of a resin sheet by a predetermined method and then forming a wiring pattern on the metal layer by a method such as photolithography. The metal layer is not particularly limited, but copper, for example, can be used. The resin sheet of the present invention has a morphology in which a metal oxide having a surface functional group is attached to the end faces of the contained metal oxide-adhered hexagonal boron nitride particles, thereby improving the peel strength of the resin sheet surface from the metal layer. Furthermore, as described above, the content of metal oxide-adhered hexagonal boron nitride particles in the resin sheet can be set high, thereby further improving the peel strength.

[0040] <Method for producing metal oxide-coated hexagonal boron nitride particles> The method for producing metal oxide-coated hexagonal boron nitride particles of the present invention comprises a step of dry-mixing a powder containing hexagonal boron nitride particles (before metal oxide is coated) having an aspect ratio of 12 or less and a particle diameter of 5 μm or more and 12 μm or less, with a powder containing metal oxide particles (before coating) having a primary particle diameter of 100 nm or more and 700 nm or less.

[0041] The method of dry mixing is not particularly limited, and for example, the powder containing hexagonal boron nitride particles (before metal oxide adhesion) and the powder containing metal oxide particles (before adhesion) can be placed in a predetermined bag, and the bag can be shaken by hand, preferably for 10 seconds to 10 minutes.

[0042] (Hexagonal boron nitride particles (before metal oxide is attached)) The powder containing hexagonal boron nitride particles (before metal oxide is attached) as the raw material is not particularly limited, and any known material can be used without any restrictions. For example, hexagonal boron nitride powder produced according to a known production method may be used. An example of a known production method is a method in which a mixture of a boron compound, a carbon source, and, if necessary, a crystallization catalyst is heated in a nitrogen atmosphere to reduce and nitride the boron compound. Alternatively, a commonly available hexagonal boron nitride powder may be used.

[0043] Aspect ratio of hexagonal boron nitride particles (before metal oxide is attached) The aspect ratio of the hexagonal boron nitride particles (before metal oxide is attached) is more preferably 10 or less, and even more preferably 8 or less. The lower limit of the aspect ratio is preferably 1 or more, and more preferably 2 or more. Hexagonal boron nitride particles have OH and NH groups on their end faces rather than on their flat faces. ２ The hexagonal boron nitride particles (before metal oxide adhesion) have the above-mentioned preferred aspect ratio, and are thick, tabular particles with a high proportion of end faces where many functional groups are present, facilitating adhesion of metal oxide to the end faces. This makes it easy to achieve an area adhesion rate of metal oxide to the end faces of 30% or more.

[0044] The powder containing the raw material hexagonal boron nitride particles (before the metal oxide is attached) preferably has an average aspect ratio of 12 or less, more preferably 10 or less, and even more preferably 8 or less. The lower limit of the average aspect ratio is preferably 1 or more, more preferably 2 or more. By setting the average aspect ratio within the above range, the number of hexagonal boron nitride particles (before the metal oxide is attached) having an aspect ratio within the above range can be increased, and the metal oxide-attached hexagonal boron nitride particles of the present invention can be efficiently produced.

[0045] Particle diameter of hexagonal boron nitride particles (before metal oxide is attached) The particle diameter of the hexagonal boron nitride particles (before metal oxide is attached) is preferably 5 μm or more and 12 μm or less, more preferably 6 μm or more and 10 μm or less, and even more preferably 6.5 μm or more and 8 μm or less.

[0046] The powder containing the raw material hexagonal boron nitride particles (before the metal oxide is attached) preferably has an average particle size of 5 μm to 12 μm, more preferably 6 μm to 10 μm, and even more preferably 6.5 μm to 8 μm. By setting the average particle size within this range, the number of hexagonal boron nitride particles (before the metal oxide is attached) having a particle size within this range can be increased, and the metal oxide-attached hexagonal boron nitride particles of the present invention can be efficiently produced.

[0047] Specific surface area of ​​powder containing hexagonal boron nitride particles (before metal oxide adhesion) The powder containing the raw material hexagonal boron nitride particles (before metal oxide adhesion) has a specific surface area of ​​0.5 m ２ / g or more 3.0m ２ / g or less, and ２ / g or more 2.0m ２ The specific surface area can be measured by a BET single-point method using nitrogen as the adsorbed species, using a Macsorb HM model-1201 manufactured by Mountech Co., Ltd.

[0048] Regarding the surface functional groups of hexagonal boron nitride particles (before metal oxide is attached) The hexagonal boron nitride particles (before metal oxide is attached) used in the present invention have OH groups or NH groups as surface functional groups.２ It is preferable that the hexagonal boron nitride particles have a functional group, a group having a hydroxyl group, or both. Generally, the functional groups of hexagonal boron nitride particles are not present on the particle planes but on the particle edge faces. The presence of such functional groups facilitates selective attachment of metal oxide to the edge faces of the hexagonal boron nitride particles through interaction between the hexagonal boron nitride particles (before attachment of the metal oxide) and the metal oxide.

[0049] Specifically, when measuring the infrared absorption spectrum of a powder containing raw material hexagonal boron nitride particles (before metal oxide adhesion), －１ ~3500cm －１ NH in the range ２ Symmetrical shrinkage vibration peak of the group, 3530 cm －１ ~3590cm －１ NH in the range ２ Group asymmetric shrinkage vibration peak, 3600 cm －１ ~3750cm －１ It is preferable that any of the peaks of OH groups in the range of

[0050] In the infrared absorption spectrum, －１ ~3800cm －１ The highest absorption peak in the range is 3530 cm －１ ~3590cm －１ In particular, the range of 3568 cm －１ The fact that the particle has the highest absorption peak is due to the presence of NH ２ This indicates that groups are present at a high density. Such powders can be produced, for example, by the method disclosed in WO 2018 / 101241.

[0051] (Metal Oxide Particles (Before Adhesion)) The powder containing metal oxide particles (before adhesion) having a primary particle diameter of 100 nm or more and 700 nm or less is not particularly limited, and any known powder can be used without limitation. For example, a metal oxide powder produced based on a known production method may be used, or a commercially available powder may be used.

[0052] Primary particle diameter of metal oxide particles (before attachment) The metal oxide particles (before attachment) contained in the powder containing metal oxide particles (before attachment) preferably have a primary particle diameter of 100 nm or more and 700 nm or less. The powder containing metal oxide particles (before attachment) preferably has an average primary particle diameter of 100 nm or more and 700 nm or less, more preferably 200 nm or more and 600 nm or less, and even more preferably 350 nm or more and 500 nm or less. By setting the average primary particle diameter within the above range, the number of metal oxide particles (before metal oxide attachment) having a primary particle diameter within the above range can be increased, and the metal oxide-attached hexagonal boron nitride particles of the present invention can be efficiently produced.

[0053] Specific surface area of ​​powder containing metal oxide particles (before attachment) The powder containing metal oxide particles (before attachment) has a specific surface area of ​​4.0 m ２ / g or more 50m ２ / g or less, and ２ / g or more 30m ２ / g or less is more preferable. The ratio of the powder containing hexagonal boron nitride particles (before metal oxide adhesion) to the powder containing metal oxide particles (before adhesion) during mixing is not particularly limited, but for example, the powder containing metal oxide particles (before adhesion) can be 0.4 parts by mass or more and 15 parts by mass or less, preferably 0.6 parts by mass or more and 13 parts by mass or less, and more preferably 4 parts by mass or more and 12 parts by mass or less, per 100 parts by mass of the powder containing hexagonal boron nitride particles (before metal oxide adhesion). If the ratio is less than the lower limit, it is difficult to adhere a sufficient amount of metal oxide, and if the ratio is greater than the upper limit, the proportion of adsorption to flat surfaces will be high and production efficiency will be reduced.

[0054] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. <Infrared absorption spectrum of hexagonal boron nitride powder> Diffuse reflectance infrared spectroscopy was performed on the hexagonal boron nitride powders obtained in the following examples and comparative examples using an FTS-3000 manufactured by Agilent Technologies. As a pretreatment for the samples, they were dried at 200°C under reduced pressure for 2 hours. The samples were packed into a measuring cup and measured. The resolution was 4 cm －１ The number of accumulations was 64.

[0055] <Specific surface area (m) of hexagonal boron nitride powder and metal oxide ２ / g) The specific surface area of ​​the hexagonal boron nitride powders obtained in the following examples and comparative examples, and the metal oxides used, was measured using a Macsorb HM model-1201 manufactured by Mountech Co., Ltd.

[0056] Examples 1 to 10 and Comparative Examples 1 to 5: 195 g of boron oxide, 82 g of carbon black with a sulfur concentration of 3500 ppm, and 55 g of calcium carbonate were mixed using a ball mill. 100 g of the mixture was nitrided in a graphite Tammann furnace by holding the mixture at 1500°C for 4 hours and then at 1850°C for 5 hours under a nitrogen gas atmosphere, thereby obtaining by-product-containing boron nitride.

[0057] The obtained by-product-containing boron nitride was then crushed and placed in a container, and hydrochloric acid (7 wt % HCl) was added in an amount five times the amount of the by-product-containing boron nitride, followed by stirring at 700 rpm for 24 hours. After the acid washing, the acid was filtered, and the resulting product was dispersed in pure water in an amount equal to the amount of acid used, and filtered again. This procedure was repeated five times, and then vacuum dried at 200°C for six hours. The powder obtained after drying was passed through a sieve with 90 μm openings to obtain "BN-A," a white hexagonal boron nitride powder. The obtained white powder was identified as hexagonal boron nitride by X-ray diffraction measurement.

[0058] The diffuse reflectance infrared absorption spectrum and specific surface area of ​​the obtained hexagonal boron nitride powder were measured by the methods described above. The specific surface area of ​​BN-A was 1.4 m ２ / g. BN-A was 3568 cm －１ NH ２The highest absorption peak was observed in the asymmetric shrinkage vibration of the hydroxyl group. BN-A (before mixing with the metal oxide) was analyzed from multiple SEM images using an image analyzer (A-Image-kun: manufactured by Asahi Kasei Engineering Co., Ltd.), and it was confirmed that it contained hexagonal boron nitride particles (before metal oxide adhesion) with a particle diameter of 6.5 μm to 8 μm and an aspect ratio of 2 to 8. In addition, 100 different single particles were randomly selected, and the length of the major axis and the length in the thickness direction were measured. The aspect ratio was calculated as the length of the major axis / length in the thickness direction, and the average particle diameter D1 was 6.8 μm and the average aspect ratio was 5.7.

[0059] A powder containing hexagonal boron nitride particles with a metal oxide attached was obtained by dry mixing BN-A with silicon dioxide (manufactured by Tokuyama Corporation) shown below as a metal oxide in the ratio shown in Table 1. For the dry mixing method, hexagonal boron nitride powder BN-A and the metal oxide were placed in a Unipack (L-8) manufactured by Seisan Nippon Co., Ltd. so that the total amount was 100 g, and the mixture was mixed by hand for 1 minute.

[0060] 1: Sunsil SS-01 specific surface area 24m ２ / g Primary particle diameter 100 nm 2: Sunsil SS-03 Specific surface area 11 m ２ / g Primary particle diameter 300 nm 3: Sunsil SS-04 Specific surface area 7 m ２ / g Primary particle diameter 400 nm 4: Sunsil SS-07 Specific surface area 4 m ２ / g Primary particle diameter 700 nm 5: Sunsil SS-10 Specific surface area 3 m ２ / g Primary particle diameter 1000 nm 6: Reolosil QS-20 Specific surface area 220 m ２ / g primary particle diameter 12nm

[0061] The powder containing the metal oxide-adhered hexagonal boron nitride particles obtained in Example 1 was analyzed using an image analyzer (A-Image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.) based on SEM observation images. It was confirmed that the metal oxide-adhered hexagonal boron nitride particles had a particle diameter of 6.5 μm to 8 μm and an aspect ratio of 2 to 8, with a metal oxide having a primary particle diameter of 100 nm to 700 nm attached to the surface, and that the area coverage of the metal oxide attached to the end faces was 30% or more and the area coverage of the metal oxide attached to the flat surfaces was 6% or less. Furthermore, the content of the metal oxide-adhered hexagonal boron nitride particles in the powder was 50 area% or more. Furthermore, 100 different metal oxide-adhered hexagonal boron nitride particles were randomly selected, and the average particle diameter D2 of the metal oxide-adhered hexagonal boron nitride particles, the average particle diameter D3 of the metal oxide, the average area coverage of the metal oxide attached to the end faces, and the average area coverage of the metal oxide attached to the flat surfaces were calculated. The hexagonal boron nitride and the metal oxide were distinguished using SEM-EDX (energy dispersive X-ray spectrometer Genesis 2000: EDAX). The results are shown in Table 1.

[0062] For Examples 2 to 10 and Comparative Examples 1 to 5, metal oxide composite particles (metal oxide-deposited hexagonal boron nitride particles) were obtained and measured in the same manner as in Example 1, except that silicon dioxide was dry-mixed in the proportions shown in Table 1. The content of metal oxide-deposited hexagonal boron nitride particles in the powder was 50 area % or more in all Examples.

[0063] Furthermore, in Example 2, it was confirmed that metal oxide-attached hexagonal boron nitride particles existed, in which metal oxide having a primary particle diameter of 100 nm or more and 700 nm or less was attached to the surface of hexagonal boron nitride particles having a particle diameter of 6.5 μm or more and 8 μm or less and an aspect ratio of 2 or more and 8 or less, and in which the area deposition rate of metal oxide attached to the end faces was 40% or more and the area deposition rate of metal oxide attached to the flat surfaces was 6% or less.

[0064] In Examples 3 and 9, it was confirmed that metal oxide-attached hexagonal boron nitride particles existed, in which metal oxide having a primary particle diameter of 100 nm or more and 700 nm or less was attached to the surface of hexagonal boron nitride particles having a particle diameter of 6.5 μm or more and 8 μm or less and an aspect ratio of 2 or more and 8 or less, and in which the area deposition rate of metal oxide attached to the end faces was 50% or more and the area deposition rate of metal oxide attached to the flat surfaces was 6% or less.

[0065] In Examples 4, 5, and 10, it was confirmed that metal oxide-attached hexagonal boron nitride particles were present, with a particle diameter of 6.5 μm or more and 8 μm or less and an aspect ratio of 2 or more and 8 or less, and a metal oxide with a primary particle diameter of 100 nm or more and 700 nm or less attached to the surface, and with an area deposition rate of metal oxide attached to the end faces of 60% or more and an area deposition rate of metal oxide attached to the flat surfaces of 6% or less.

[0066] In Examples 6 and 7, it was confirmed that metal oxide-attached hexagonal boron nitride particles existed, in which metal oxide having a primary particle diameter of 100 nm or more and 700 nm or less was attached to the surface of hexagonal boron nitride particles having a particle diameter of 6.5 μm or more and 8 μm or less and an aspect ratio of 2 or more and 8 or less, and in which the area deposition rate of metal oxide attached to the end faces was 70% or more and the area deposition rate of metal oxide attached to the flat surfaces was 6% or less.

[0067] In Example 8, it was confirmed that metal oxide-attached hexagonal boron nitride particles existed, in which metal oxide having a primary particle diameter of 100 nm or more and 700 nm or less was attached to the surface of hexagonal boron nitride particles having a particle diameter of 6.5 μm or more and 8 μm or less and an aspect ratio of 2 or more and 8 or less, and in which the area deposition rate of metal oxide attached to the end faces was 60% or more and the area deposition rate of metal oxide attached to the flat surfaces was 9% or less.

[0068] Comparative Examples 6 to 10 A hexagonal boron nitride powder, "BN-B," was obtained in the same manner as in Example 1, except that the sulfur concentration of the raw carbon black was 100 ppm and calcium carbonate was 20 g. The resulting white powder, BN-B, was identified as hexagonal boron nitride by X-ray diffraction measurement. The diffuse reflectance infrared absorption spectrum, specific surface area, average particle diameter D1, and average aspect ratio of the resulting hexagonal boron nitride powder were measured using the methods described above. The specific surface area of ​​BN-B was 2.0 m ２ The hexagonal boron nitride powder BN-B had a diffuse reflectance infrared spectrum (3100-3800 cm －１ ) no clear peak was observed.

[0069] Four types of silicon dioxide, as mentioned above, manufactured by Tokuyama Corporation, were prepared as metal oxides and mixed with BN-B in the proportions shown in Table 1 in the same manner as in Example 1 to prepare composite particles of hexagonal boron nitride powder (BN-B) and metal oxide. The composite particles were observed under an SEM in the same manner as in Example 1, and the average particle diameter D2 of the metal oxide-adhered hexagonal boron nitride particles, the average particle diameter D3 of the metal oxide, the average area deposition rate of the metal oxide adhered to the end faces, and the average area deposition rate of the metal oxide adhered to the flat surfaces were calculated. The respective results are shown in Table 1.

[0070] Comparative Example 11 The BN-A obtained in Example 1 was heated in a graphite Tammann furnace under a nitrogen gas atmosphere at 1000°C for 5 hours to produce "BN-C," a hexagonal boron nitride powder. The resulting white powder, "BN-C," was identified as hexagonal boron nitride by X-ray diffraction measurement. The diffuse reflectance infrared absorption spectrum, specific surface area, average particle diameter D1, and average aspect ratio of the resulting hexagonal boron nitride powder (BN-C) were measured using the methods described above. The specific surface area of ​​BN-C was 1.5 m ２ / g, average particle diameter D1 = 7.8 μm, and average aspect ratio was 6.3. BN-C was measured by the diffuse reflectance infrared spectroscopy (3100-3800 cm －１ ) no clear peak was observed.

[0071] Silicon dioxide (SS-04) manufactured by Tokuyama Corporation, as described above, was prepared as the metal oxide for BN-C, and dry-mixed in the proportions shown in Table 1 in the same manner as in Example 1 to form composite particles of hexagonal boron nitride powder and metal oxide. The composite particles were observed under an SEM in the same manner as in Example 1, and the average particle diameter D2 of the metal oxide-adhered hexagonal boron nitride particles, the average particle diameter D3 of the metal oxide, the average area deposition rate of the metal oxide adhered to the end faces, and the average area deposition rate of the metal oxide adhered to the flat surfaces were calculated. The respective results are shown in Table 1.

[0072]

[0073] Examples 11-20, Comparative Examples 12-22 The powders obtained in Examples 1-10 and Comparative Examples 1-11 were filled into epoxy resin to prepare resin compositions, and their thermal conductivity was evaluated. A mixture of 100 parts by weight of epoxy resin (JER806 manufactured by Mitsubishi Chemical Corporation) and 28 parts by weight of a curing agent (alicyclic polyamine curing agent, JER Cure 113 manufactured by Mitsubishi Chemical Corporation) was prepared. Next, 42% by volume of each base resin and 58% by volume of each powder were mixed in a planetary centrifugal mixer (MAZERUSTAR manufactured by Kurabo Industries, Ltd.) to obtain resin compositions.

[0074] <Evaluation of Thermal Conductivity> This was poured into a mold and cured using a heat press under conditions of a temperature of 200°C, a pressure of 5 MPa, and a holding time of 30 minutes to produce a sheet with a diameter of 40 mm and a thickness of 0.22 mm. The sheet was analyzed using a temperature wave thermal analyzer (iPhase Corporation) and the thermal conductivity was calculated, with the results shown in Table 2. The thermal conductivity of the sheets filled with the composite particles of boron nitride powder and metal oxide produced in Examples 1 to 10 was 10.0 W / m K or higher, demonstrating high thermal conductivity.

[0075] <Evaluation of Dielectric Strength> Furthermore, the sheets filled with the powders obtained in Examples 1 to 10 and Comparative Examples 1 to 11 were measured for dielectric strength using a voltage resistance tester (manufactured by Tama Densoku Co., Ltd.), and the results are shown in Table 2. The sheets filled with the composite particles of boron nitride powder and metal oxide prepared in Examples 1 to 10 had a high dielectric strength of 90 kV / mm or more.

[0076] <Evaluation of Peel Strength> Furthermore, the copper foil peel strength between the copper foil and each of the obtained sheets was determined based on JIS C6481. The copper foil peel strength was determined as a relative value, with the value obtained using hexagonal boron nitride powder (BN-A without any metal oxide mixed in) in Comparative Example 1 being set at 1. The copper foil peel strength of the sheets filled with the composite powder of boron nitride powder and metal oxide prepared in Examples 1 to 10 showed a high relative value of 1.1 or more.

[0077] <Viscosity Evaluation> Next, 80% by volume of each base epoxy resin and 20% by volume of the powder containing the composite particles of each Example and Comparative Example were mixed in a mortar under the same conditions for each test, and the viscosity was measured at a measurement temperature of 25°C using a Brookfield viscometer TBA-10 (manufactured by Toki Kogyo Co., Ltd.). The viscosity was determined relative to the value obtained using the hexagonal boron nitride powder (BN-A without any metal oxide mixed in) in Comparative Example 1, which was set to 1. The relative values ​​of the resin filling viscosity of the composite powders of boron nitride powder and metal oxide prepared in Examples 1 to 10 were low, being 0.8 or less.

[0078]

Claims

1. Hexagonal boron nitride particles having a metal oxide attached to the particle surface, wherein the area coverage of the metal oxide on the flat surfaces of the hexagonal boron nitride particles is 10% or less, and the area coverage of the metal oxide on the end faces of the hexagonal boron nitride particles is 30% or more.

2. The metal oxide-coated hexagonal boron nitride particles according to claim 1, wherein the hexagonal boron nitride particles have an aspect ratio of 12 or less and a particle diameter of 5 μm or more and 12 μm or less.

3. The metal oxide-coated hexagonal boron nitride particles according to claim 1 or 2, wherein the primary particle size of said metal oxide is 100 nm or more and 700 nm or less.

4. A powder comprising the metal oxide-coated hexagonal boron nitride particles according to claim 1 or 2.

5. A resin composition comprising a base resin and the metal oxide-attached hexagonal boron nitride particles according to claim 1 or 2.

6. A resin sheet formed from the resin composition of claim 5.

7. A metal wiring board comprising the resin sheet of claim 6 and metal wiring on the surface thereof.

8. A method for producing a powder containing metal oxide-adhered hexagonal boron nitride particles, comprising a step of dry-mixing a powder containing hexagonal boron nitride particles having an average aspect ratio of 12 or less and an average particle size of 5 μm or more and 12 μm or less with a powder containing metal oxide particles having an average primary particle size of 100 nm or more and 700 nm or less.

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