Hexagonal boron nitride particle-dispersed resin composite and production method for hexagonal boron nitride particle-dispersed resin composite

Abstract

The present invention develops a technology capable of easily obtaining a BN particle resin composite which exhibits high heat-conducting properties, from which, by cutting out pieces thereof, a large number of thin heat-transfer sheets having high heat conductivity and high electrical insulation properties can be produced, which can significantly improve productivity of thin heat-transfer sheets, and which is, even in the inside thereof, sufficiently impregnated with a resin despite of having a large-sized block shape that is large and thick.　The present invention pertains to a hexagonal boron nitride particle-dispersed resin composite that has a block shape in order to directly obtain a plurality of thin heat transfer sheets by cutting out sheet-like pieces thereof. The hexagonal boron nitride particle-dispersed resin composite is obtained using a porous BN molded body formed by including at least hexagonal boron nitride particles, continuous pores which are traces resulting from removal of a pore-forming agent, and a cured body composed of a binder which is at least one of an inorganic binder or an organic binder, and solidifying a resin in a state of impregnating said pores. In the composite, the cured body composed of the binder is interposed between the particles. The present invention also pertains to a production method for said composite.

Description

Hexagonal boron nitride particle-dispersed resin composite and method for producing the hexagonal boron nitride particle-dispersed resin composite

[0001] The present invention relates to a hexagonal boron nitride particle-dispersed resin composite and a method for producing the hexagonal boron nitride particle-dispersed resin composite. More specifically, the present invention relates to a technology for easily providing a resin composite that exhibits stable high thermal conductivity and high insulating properties, in which highly functional hexagonal boron nitride (h-BN) particles (hereinafter referred to as BN particles) are well dispersed in a resin. In particular, the present invention relates to a useful technology that enables the production of large, block-shaped BN particle-dispersed resin composites that exhibit stable high thermal conductivity and high insulating properties, and enables thin, highly thermally conductive, highly insulating heat transfer sheets to be directly cut from the blocks, thereby significantly increasing the productivity of thin heat transfer sheets. This technology also enables the direct production of multiple thin heat transfer sheets from large, block-shaped BN particle-dispersed resin composites.

[0002] Traditionally, ceramics have been preferred for use as highly thermally conductive plates in electronic control units, such as heat spreaders and heat transfer sheets that diffuse and transfer heat generated by semiconductors (ICs) to heat sinks, due to their excellent electrical insulation and thermal conductivity. However, ceramics are rigid, have hard surfaces, and exhibit poor adhesion to contact surfaces. Therefore, improvements in the thermal conductivity of the entire heat dissipation structure are required, and the following proposals have been made. For example, Patent Document 1 proposes a ceramic-resin composite in which a heat transfer member is formed by impregnating a ceramic sintered body, in which ceramic primary particles having a specific particle size and aspect ratio form a three-dimensional integral structure, with a resin composition. Patent Document 1 also discloses a heat dissipation structure for an electric circuit device using this composite. The ceramics used include boron nitride, aluminum nitride, and silicon nitride. The heat transfer member provided in Patent Document 1 is intended to be a thin, flat plate with a thickness of 0.05 mm to 1.0 mm, or a thin sheet with a thickness of 0.1 to 0.35 mm, particularly when low thermal resistance is desired.

[0003] Patent Document 2 discloses that hexagonal boron nitride (HBON) has attracted attention for its excellent properties as an electrical insulating material, such as high thermal conductivity and high insulation, and that its crystalline structure and scale shape result in a large anisotropy in thermal conductivity. It also discloses that impregnating the voids inside a boron nitride sintered body with resin and cutting it into a plate to produce a heat dissipation component makes it possible to control the orientation in any direction, making it easy to produce a heat dissipation component with excellent thermal conductivity and any thickness. Furthermore, a resin-impregnated boron nitride sintered body has been proposed, which is made of a boron nitride sintered body with a porosity of 10 to 70% in which boron nitride particles are bonded three-dimensionally, and a resin, and has through holes, the through holes of which are filled with an adhesive resin. In Cited Document 2, it is stated that a cubic resin-impregnated boron nitride sintered body having a side length of approximately 50 mm is obtained, and that the thickness of the plate-shaped resin-impregnated boron nitride sintered body is preferably 0.15 to 1.50 mm.

[0004] Patent Document 3 proposes, as a composite according to one embodiment, a thin and lightweight composite comprising a boron nitride sintered body obtained by sintering a mesh-like boron nitride sheet having an opening size of about 200 to 1000 μm, and a resin that fills the pores of the boron nitride sintered body.

[0005] Patent No. 7282950 Patent No. 6262522 Patent No. 7322323

[0006] However, in all of the above-mentioned conventional techniques, a ceramic-resin composite is formed by impregnating resin into voids formed inside a ceramic such as a boron nitride sintered body due to the structure specific to the material. That is, as described below, in all of the conventional techniques, a thin or small ceramic-resin composite is formed by impregnating resin into minute voids in a thin or small (thin) ceramic sintered body such as BN. According to the inventors' investigations, this point has led to the following problems.

[0007] Specifically, all of the above-mentioned conventional technologies involve ceramic-resin composites formed by impregnating a ceramic sintered body sintered at a high temperature of 1500°C or higher with a resin composition, and have the following technical problems. First, the technology of Patent Document 1 relates to a "resin composite of a boron nitride sintered body, in which a boron nitride sintered body obtained by three-dimensionally sintering boron nitride powder is impregnated with a thermosetting resin composition." However, the boron nitride sintered body for resin impregnation is prepared using a complicated procedure, utilizing high temperatures and high pressures, which is far from being a simple method, and has the problem of poor productivity. Specifically, a mixed powder containing boron nitride is filled into a mold and press-molded into a molded body, which is then further pressurized at 75 MPa using a CIP (cold isostatic pressing) device and sintered in a batch-type high-frequency furnace at 2000°C for 10 hours with a nitrogen flow rate of 10 L / min.

[0008] Furthermore, in the technology of Patent Document 1, as described in the examples, a 0.32 mm thick sheet is cut from the boron nitride sintered body obtained as described above, and the cut thin sintered body sheet is impregnated with a thermosetting resin composition such as an epoxy resin as described below. After impregnation, the resin is thermally cured to form a composite. Specifically, using a vacuum heating impregnation apparatus, the sintered body is degassed for 10 minutes at a temperature of 145°C and a pressure of 15 Pa in a vacuum, and then subsequently immersed in the thermosetting resin composition in the same apparatus under the same heating and vacuum conditions. The thin boron nitride sintered body impregnated with the thermosetting resin composition is then placed in a pressure heating impregnation apparatus and held at a temperature of 145°C and a pressure of 3.5 MPa for 120 minutes. It is then heated at atmospheric pressure at 160°C for 120 minutes to obtain a sheet-shaped ceramic resin composite in which the thermosetting resin composition is semi-cured. As with the technology described in Patent Document 1, producing a thin sheet of boron nitride sintered body and then impregnating the sintered body with resin to produce each piece individually requires an extremely large number of steps and is complicated, resulting in a significant practical problem of significantly poor productivity.

[0009] Furthermore, as described in Patent Document 2, by producing a block-shaped ceramic-resin composite and then cutting out a thin heat transfer sheet, productivity is expected to be improved compared to Patent Document 1, which involves impregnating thin sheets cut from a boron nitride sintered body with resin to produce individual pieces. However, even in the technology described in Patent Document 2, the boron nitride sintered body before resin impregnation is preferably sintered at 1600°C or higher for at least one hour. Without sintering, the pore size becomes small, making resin impregnation difficult. The upper sintering temperature is considered to be approximately 2200°C, and the boron nitride sintered body is obtained by sintering a press-molded block in a batch-type high-frequency furnace at a nitrogen flow rate of 10 L / min. Thus, like Patent Document 1, the technology described in Patent Document 2 also involves a complicated procedure using high temperatures and high pressures, which results in poor productivity.

[0010] Furthermore, the technology described in Patent Document 3 cited above involves sintering a mesh-shaped coated body at 1600°C or higher or 1700°C or higher and 2200°C or lower or 2100°C or lower to obtain a boron nitride sintered body, which has the same technical problems as Patent Documents 1 and 2. The technology of Patent Document 3, which has the above-mentioned configuration, claims that the composite in which the pores of the boron nitride sintered body are filled with resin is thin, allowing the resin to be sufficiently filled into the pores, and the technology of Patent Document 3 also involves impregnating the sintered body with resin to manufacture each piece individually. Therefore, like Patent Document 1, the technology of Patent Document 3 also has major practical problems, such as requiring an extremely large number of steps and being cumbersome, resulting in significantly poor productivity.

[0011] Furthermore, according to the inventors' investigations, the following problem arises when a thin heat transfer sheet is cut out from a block-shaped ceramic-resin composite obtained by impregnating a sintered body with resin, as described in Patent Document 2. Specifically, when the ceramic-resin composite from which the sheet is cut is made larger in size in order to improve the productivity of thin heat transfer sheets, the conventional technology of impregnating the voids (pores) arising from the structure of the boron nitride sintered body with resin poses a technical problem in that it is difficult to sufficiently impregnate the interior of the block-shaped boron nitride sintered body with resin, even when sintered at high temperatures, and therefore it is not possible to make the sheet very large. This tendency becomes particularly pronounced when the thickness of the block-shaped boron nitride sintered body is increased.

[0012] According to the inventors' research, if the voids (pores) of a boron nitride sintered body are not impregnated with the matrix resin and remain hollow, the thermal conductivity of the resulting resin composite is significantly reduced. This is thought to be due to the fact that the air or vacuum state within the cavities is a highly insulating layer. The thermal conductivity of a resin composite varies significantly depending on whether or not the voids (pores) of the boron nitride sintered body are impregnated with resin. The hexagonal boron nitride (BN) particles considered for use in this invention are flaky. Therefore, when press-molded or sedimented to obtain a block-shaped compact, the short (thickness) sides of the flaky particles are stacked in the pressing direction or sedimentation direction, while the long sides of the flaky particles are oriented perpendicular to the pressing direction or sedimentation direction. Therefore, for example, if the pressing direction during press-molding to produce a block-shaped compact is aligned with the thickness direction of the resin composite from which the thin sheet is cut, the thermal conductivity of the cut thin sheet along the long side will be extremely high. However, as mentioned above, the conventional technology has a major problem in that when the thickness of a block-shaped boron nitride sintered body is increased, it becomes difficult to sufficiently impregnate the interior of the sintered body with resin.

[0013] Presumably due to the reasons mentioned above, conventional techniques involve either cutting thin heat transfer sheets from a block of boron nitride sintered body and then impregnating the cut sheets with resin, or cutting sheets from a composite of boron nitride sintered body and resin, cutting thin heat transfer sheets from a small block of the composite. When cutting thin heat transfer sheets from a small ceramic resin composite, the number of heat transfer sheets that can be cut from one ceramic resin composite is small, and this presents a practical problem in that it is difficult to say that this is an effective method for improving the productivity of thin heat transfer sheets.

[0014] Therefore, the object of the present invention is to develop a new technology that can easily obtain a BN particle-resin composite that can be cut into plate-like shapes to produce a large number of thin sheets, and each of the cut thin sheets becomes a heat transfer sheet with excellent performance, such as high thermal conductivity and high insulation, thereby significantly increasing the productivity of thin heat transfer sheets. In this specification, the term "thickness" is used to mean the length of the shortest side of a large block-shaped molded body or composite, and the longest side is referred to as the "maximum length."

[0015] The above-mentioned object is achieved by the present invention, which provides the following hexagonal boron nitride (BN) particle-dispersed resin composite: [1] A block-shaped hexagonal boron nitride particle-dispersed resin composite to be used for cutting into plates directly to obtain a plurality of thin heat transfer sheets, characterized in that the hexagonal boron nitride particle-dispersed resin composite is formed by solidifying a porous BN molded body containing at least hexagonal boron nitride (h-BN) particles, continuous pores remaining after a pore-forming agent has been removed, and a cured body of at least an inorganic or organic binder, with the resin impregnated into the pores, and the cured body of the binder being interposed between the particles.

[0016] Preferred embodiments of the BN particle-dispersed resin composite of the present invention include the following: [2] A volume of 200 cm ３ The BN particle-dispersed resin composite according to the above item [1], which has a large and thick shape, and in which the ratio m of maximum length to thickness, where m is the ratio of the longest side to the shortest side, is 1≦m≦3. [3] The BN particle-dispersed resin composite according to the above item [1] or [2], wherein the porous BN compact has a porosity of 20% or more and 50% or less. [4] The BN particle-dispersed resin composite according to any one of the above items [1] to [3], wherein the composite obtained by solidifying the porous BN compact in a state in which the pores of the porous BN compact are impregnated with resin has a thermal conductivity of 20 W / m K or more due to the orientation direction of the hexagonal boron nitride (h-BN) particles.

[0017] As another embodiment, the present invention provides the following method for producing a BN particle-dispersed resin composite. [5] A method for producing a block-shaped hexagonal boron nitride particle-dispersed resin composite used to directly obtain a plurality of thin plate-shaped heat transfer sheets by cutting them into plate shapes, the method comprising: a shaping step for producing a primary BN compact from a mixture containing at least hexagonal boron nitride (h-BN) particles, a pore-forming agent, and at least one binder selected from the group consisting of an inorganic binder and an organic binder; a binder hardening step for hardening the binder in the primary BN compact so that a hardened body of the binder is interposed between the particles as an adhesive layer to form a secondary BN compact having increased strength; a porosity-forming step for removing the pore-forming agent contained in the shaping step for producing the primary BN compact to form a porous BN compact having continuous pores; and a composite step for impregnating the porous BN compact obtained by the hardening and porosity-forming steps with a resin to perform composite formation.

[0018] Preferred embodiments of the method for producing a BN particle-dispersed resin composite of the present invention include the following: [6] The method for producing a BN particle-dispersed resin composite according to the above item [5], wherein in the shaping step, a primary BN compact is formed from the mixture by press molding or a precipitation method. [7] The method for producing a BN particle-dispersed resin composite according to the above item [5] or [6], wherein the curing and porosification form a porous BN compact having a porosity of 20% to 50%. [8] The method for producing a BN particle-dispersed resin composite according to any one of the above items [5] to [7], wherein the pore-forming agent is a solid having a particle size of 5 to 200 μm, and the binder curing step for forming the secondary BN compact and the porosity-forming step for removing the pore-forming agent are carried out simultaneously by heating. [9] The method for producing a BN particle-dispersed resin composite according to any one of [5] to [8] above, wherein in the composite forming step, when the porous BN compact is impregnated with resin, the resin is impregnated using either a vacuum suction impregnation method, a pressure impregnation method, or a combination of the vacuum suction impregnation method and the pressure impregnation method.

[0019] According to the present invention, it is possible to easily provide a BN particle-dispersed resin composite that is free of defects such as non-impregnation or uneven impregnation of the resin within the composite, has high uniformity, high thermal conductivity, and high insulation, and is sufficiently impregnated with resin to the interior, even though it is in a large, thick block shape. Furthermore, a large number of thin heat transfer sheets can be cut out from this large, block-shaped BN particle-dispersed resin composite, and each cut-out heat transfer sheet has uniform and stable high thermal conductivity and high insulation properties. According to the present invention, the productivity of thin heat transfer sheets with such excellent properties can be significantly improved. Furthermore, according to the present invention, it is possible to manufacture large heat dissipation components, such as heat sinks integrated with heat spreaders, by cutting a large, thick, block-shaped BN particle-dispersed resin composite that has high thermal conductivity and high insulation properties, and therefore its practical value is extremely high. According to the present invention, a large, block-shaped, high-thermal-conductivity BN particle-dispersed resin composite can be obtained, which has a thermal conductivity of 20 W / m·K or higher due to the orientation direction of the hexagonal boron nitride (h-BN) particles that make up the composite. Furthermore, even when the composite is large, the thermal conductivity of the composite exhibits little variation. As a result, according to the present invention, by cutting this large, block-shaped BN particle-dispersed resin composite into thin plates, it is possible to consistently obtain multiple thin heat transfer sheets that exhibit nearly uniform high thermal conductivities with little variation. In the present invention, the thermal conductivity of the composite was measured using a xenon flash analyzer by the xenon flash method in accordance with JIS R1611.

[0020] The present invention will now be described in detail with reference to preferred embodiments. The hexagonal boron nitride (BN) particle-dispersed resin composite of the present invention is characterized in that it is formed by impregnating a resin into the continuous pores of a porous BN molded body formed from at least BN particles, continuous pores remaining after the pore-forming agent has been removed, and a cured body made from either an inorganic or organic binder, and then solidifying the resin to form a composite, and the cured body made from the binder is interposed between the BN particles. The BN particle-dispersed resin composite of the present invention described above can be easily produced by the following method for producing a BN particle-dispersed resin composite of the present invention. The method for producing a BN particle-dispersed resin composite of the present invention is a method for producing a block-shaped hexagonal boron nitride particle-dispersed resin composite that is used to cut into plate-shaped pieces to directly obtain a plurality of thin plate-shaped heat transfer sheets, and is characterized by having: a shaping step for producing a primary BN compact from a mixture containing at least hexagonal boron nitride (BN) particles, a pore-forming agent, and either an inorganic binder or an organic binder; a binder hardening step for hardening the binder in the primary BN compact so that a hardened body made of the binder is interposed between the particles as an adhesive layer to form a secondary BN compact with increased strength; a porosification step for removing the pore-forming agent contained in the shaping step for producing the primary BN compact to form a porous BN compact having continuous pores; and a composite process for impregnating the porous BN compact obtained by the hardening and porosification with a resin to perform composite formation.

[0021] According to the above-described manufacturing method of the present invention, for example, ３As described above, it is possible to easily produce a BN particle-dispersed resin composite having a large, thick block shape that stably exhibits high thermal conductivity and high insulating properties, with the ratio m of the maximum length / thickness being in the range of 1≦m≦3, where m is the maximum length of the longest side and m is the thickness of the shortest side. According to the investigations of the present inventors, a BN particle-resin composite having a large, block shape yet sufficiently impregnated with resin to the inside and exhibiting high thermal conductivity, which can be cut into plate shapes to produce a large number of thin plate-shaped heat transfer sheets, can be produced with a volume of 800 cm. ３ More preferably, 1000 cm ３ Specifically, it is preferable to form a composite body having a large and thick shape with the following dimensions, for example.

[0022] For example, a cube with a maximum length / thickness ratio m of 1 is a cube with a side length of 93 mm to 150 mm (volume 804 cm ３ ~3375cm ３ ) shape of the BN particle-dispersed resin composite. Various shapes are conceivable for the rectangular block-shaped composite, and as an example, the BN particle-dispersed resin composite that satisfies the above-mentioned requirements can be shaped as shown below. For example, if the thickness is 50 mm and the maximum length / thickness ratio m is 3, the maximum length is 150 mm, and the volume of the composite is about 800 cm ３ To do this, 15cm x 10.7cm x 5cm = 802.5cm ３ Furthermore, if the maximum length / thickness ratio m is 2.5 and the thickness is 7 cm, the dimensions are 17.5 cm x 8.2 cm x 7 cm = 1004.5 cm ３ If the ratio m is 3 and the thickness is 8 cm, the result is 24 cm x 8.3 cm x 8 cm = 1594 cm ３ The volume is about 1600 cm ３The inventors' studies have shown that by forming the BN particle-dispersed resin composite into a thick, block-shaped cube or rectangular parallelepiped as described above, it is possible to cut it into plate-shaped pieces to produce a larger number of thin plate-shaped sheets. According to the present invention, it is possible to obtain block-shaped composites with excellent properties in other shapes, not just the cubes and rectangular parallelepipeds described above, depending on the intended use. Furthermore, by cutting out the BN particle-dispersed resin composite into the large block-shaped pieces described above, it is possible to stably and efficiently prepare a large number of thin plate-shaped heat transfer sheets, which are the ultimate goal of the present invention, as excellent functional products that all exhibit high thermal conductivity and high insulation.

[0023] The present invention employs the above-described configuration of the present invention to solve the problems of the prior art described above. Specifically, the inventors discovered that even with the prior art technique of using a boron nitride sintered body in which small pore sizes are enlarged by sintering at high temperatures ranging from 1600°C to 2000°C or higher, as described above, and thereby improved resin impregnation, it is difficult to sufficiently impregnate the internal voids (pores) with resin when the block-shaped sintered body is large. They conducted extensive research to improve this point. They recognized that obtaining a boron nitride sintered body with enlarged pore sizes requires complicated and strict processing conditions, and that this point also needed to be improved.

[0024] The inventors first discovered that to obtain a large, thick, block-shaped BN particle-dispersed resin composite, it is necessary to mold a large porous BN compact that can be stably and effectively impregnated with resin. However, according to the inventors' investigations, as the porous BN compact becomes larger and thicker, it becomes heavier, which can lead to breakage due to its own weight during transportation or when placed in a mold for resin impregnation, or deformation or breakage of the porous BN compact due to the impregnation pressure during resin impregnation. One feature of the manufacturing method of the present invention, as a means for solving the above-mentioned problems, is the use of at least one inorganic or organic binder as the molding material in the molding process for forming the primary BN compact, and the inclusion of a binder curing process for curing the binder added to the primary BN compact to form a secondary BN compact with increased strength. According to the method for producing a BN particle-dispersed resin composite of the present invention having the above-mentioned configuration, by curing the binder used as the raw material for the primary BN molded body, it is possible to easily obtain a secondary BN molded body that has increased strength and in which a cured body made of the binder is interposed as an adhesive layer between the particles, which is useful as an intermediate before being impregnated with resin.

[0025] When using a BN sintered body prepared by the aforementioned conventional technology, in which the small pore size is enlarged by sintering the BN compact at high temperatures ranging from 1600°C to 2000°C or higher, it is difficult to sufficiently and stably impregnate the BN sintered body with resin all the way to the center of the body, resulting in defects such as non-impregnation or uneven impregnation of the resin. The manufacturing method of the present invention is characterized by the aforementioned configuration for increasing the strength of the BN compact, and by using a completely different method from the conventional technology to solve this problem, namely, the formation of a porous BN compact, which is an intermediate body that can be stably impregnated with resin in a good condition by effectively using a pore-forming agent. Specifically, the manufacturing method of the present invention is characterized by including a pore-forming step in which a mixture used in the molding step for molding (forming) a primary BN compact is added with a pore-forming agent that can be evaporated or vaporized by heating or that can be dissolved in a solvent and removed by elution, and after molding the primary BN compact, the pore-forming agent is evaporated or vaporized by heating or the pore-forming agent is dissolved or eluted in a solvent and removed to form a porous BN compact. When the method of evaporating or vaporizing by heating is used as a means for removing the pore-forming agent, it may be possible to simultaneously carry out the binder hardening step described above, which hardens the binder used in the raw material for the primary BN compact to form a secondary BN compact with increased strength. This configuration can further shorten the manufacturing process.

[0026] In the porosification process for forming the porous BN compact, which characterizes the manufacturing method of the present invention, the pore-forming agent in the BN compact is removed by thermal evaporation or by dissolving in a solvent and eluting. Pores are then formed after the removal of the pore-forming agent, and these pores become continuous. Therefore, when the porous BN compact obtained by the manufacturing method of the present invention is used in resin impregnation, these continuous pores provide an excellent path for resin impregnation all the way to the center of the large block-shaped porous BN compact. As a result, the BN particle-dispersed resin composite obtained by the manufacturing method of the present invention overcomes the technical problem of incomplete or uneven resin impregnation observed within composites in the prior art. That is, the present invention overcomes the problem of significantly reduced thermal conductivity of the resulting resin composite, which was caused by the voids (pores) in the boron nitride sintered compact not being sufficiently impregnated with the matrix resin and remaining hollow.

[0027] Furthermore, the continuous pores formed in the porosity-imparting step, which is a feature of the manufacturing method of the present invention and which are traces of the pore-forming agent removed, facilitate resin impregnation into the porous BN compact, lowering the resin impregnation pressure (resistance) and reducing the stress that can deform or damage the porous BN compact. This solves the problem of deformation and damage that sometimes occurs in BN particle-dispersed resin composites after the porous BN compact is impregnated with resin. Furthermore, in the manufacturing method of a BN particle-dispersed resin composite of the present invention, each step can be carried out as described below, making it possible to more efficiently manufacture an excellent BN particle-dispersed resin composite. Specifically, the order of the binder hardening process, which hardens the inorganic or organic binder in the primary BN compact formed in the forming process for forming the primary BN compact to form a high-strength secondary BN compact, and the porosification process, which obtains a porous BN compact having continuous pores left behind after the pore-forming agent in the primary BN compact has been removed outside the BN compact, can be reversed, or the two processes can be performed simultaneously.

[0028] The aforementioned prior art, Patent Document 2, describes a process for forming through holes in a boron nitride sintered body or a resin-impregnated boron nitride sintered body. However, this through-hole formation process is not intended to improve resin impregnation, as is evident from the description that "through holes are provided and filled with an adhesive resin to ensure adhesion and efficiently dissipate heat generated by a heater to a heat sink or the like," and further, "a solid drill (manufactured by Ryoko Seiki Co., Ltd.) or the like" and "through holes with a diameter of 0.03 mm to 2.0 mm." Furthermore, according to the inventors' investigations, since the holes formed by drilling are linear and large in diameter, when the material is cut into thin plates to form thin heat transfer sheets, the difference in the VF% (volume ratio) between the high thermal conductivity BN particles and the low thermal conductivity resin between the areas near the through holes and those away from the through holes results in significant differences in thermal conductivity, resulting in non-uniformity and significantly reduced performance as a heat transfer sheet. In contrast, when a solid pore-forming agent having a particle size of, for example, 5 to 200 μm is used in the manufacturing method of the present invention, whether the pore-forming agent is inorganic or organic, the pores formed in the porous BN compact are smaller in diameter and form continuous pores with a non-linear shape compared to the 2 mm or less through-holes disclosed in Patent Document 2. According to the studies of the present inventors, due to the above-mentioned pore characteristics, the BN particle-dispersed resin composite of the present invention has very high uniformity in thermal conduction, even when cut into small thin plates to form heat transfer sheets, and is able to stably exhibit the properties of a heat transfer sheet.

[0029] Furthermore, the aforementioned prior art, Patent Document 3, describes "a boron nitride sintered body and a resin filling the pores of the boron nitride sintered body." However, these are micropores (the average pore diameter is said to be less than 4.0 μm) that naturally form in the gaps between stacked boron nitride particles when a boron nitride compact is formed using a powder press or doctor blade method, and are much smaller than the pores formed as vestiges after the pore-forming agent, which characterizes the present invention. For this reason, even if a large, thick, block-shaped porous BN compact is produced using the technology described in Patent Document 3, the micropores that naturally form in the gaps between stacked boron nitride particles do not allow the resin to be sufficiently impregnated into the center of the compact without defects.

[0030] In any event, the prior art disclosed in the aforementioned Patent Documents 1 to 3 does not disclose any technical concept of utilizing the continuous pores formed as a trace of the pore-forming agent removed, which characterizes the present invention. Due to the differences in basic structure described above, the hexagonal boron nitride particle-dispersed resin composite of the present invention and composites formed by prior art techniques exhibit the following significant differences when observed under a microscope. As explained above, the prior art techniques all use a ceramic sintered body such as BN as the material to be impregnated with resin. Since the raw material particles are heated to a high temperature below the melting point (at least 1500°C) during sintering, the raw material particles react directly with each other to bond (fuse). In contrast, the hexagonal boron nitride particle-dispersed resin composite of the present invention is formed by curing at least one of an inorganic binder and an organic binder at a low temperature to bond the raw material particles together. Therefore, a cured body made of the binder is present between the particles, and the cured body acts as an adhesive layer (binder layer) between the raw material particles. Thus, the hexagonal boron nitride particle-dispersed resin composite of the present invention differs from the composites of the prior art not only in the completely different morphology of the pores impregnated with the resin as described above, but also in the presence of an adhesive layer (binder layer) between the raw material particles, and the resin-impregnated composites of both types have different morphological characteristics.

[0031] The BN particle-dispersed resin composite of the present invention is characterized in that the porous BN compact to be impregnated with resin has a structure that includes not only voids due to the three-dimensional structure of boron nitride used in prior art resin impregnation and fine pores naturally formed in the gaps between boron nitride particles during molding, but also continuous pores intentionally (forcefully) formed by a pore-forming agent used during the molding of the primary BN compact. By using a porous BN compact with the above-described structure, the BN particle-dispersed resin composite of the present invention achieves significantly improved fillability during the resin impregnation composite formation process, resulting in a composite with good resin impregnation deep into the interior, even when formed into a large, thick block-shaped composite. As a result, the problems of under-impregnation and uneven impregnation of resin in BN particle-dispersed resin composites of prior art are resolved. Therefore, when the large, thick block-shaped BN particle-dispersed resin composite of the present invention is cut into thin heat transfer sheets, it is possible to produce a large number of thin heat transfer sheets of excellent quality that exhibit uniform and stable high thermal conductivity and high insulation. Specifically, for example, by cutting out the large, thick block-shaped BN particle-dispersed resin composite of the present invention, it is possible to provide thousands of uniform and stable high thermal conductivity and high insulation heat transfer sheets.

[0032] The hexagonal boron nitride (h-BN) particles constituting the BN particle-dispersed resin composite of the present invention can be the boron nitride particles used in the prior art mentioned above. Hexagonal boron nitride is a compound composed of boron (B) and nitrogen (N). Its flaky crystalline structure resembles graphite, and it is also known as "white graphite." Due to its many unique features, including resistance to metal wettability, high thermal conductivity, low thermal expansion coefficient, and electrical insulation, it is primarily used in probe cards for semiconductors and electronic components. BN particles with appropriate particle sizes are readily available commercially. While the BN particles constituting the present invention vary depending on the application, it is preferable to use high-purity boron nitride powder with an average particle size of approximately 5 μm to 30 μm. The average particle size is the particle size at 50% of the cumulative value of the cumulative particle size distribution measured by laser diffraction light scattering.

[0033] In the manufacturing method of a BN particle-dispersed resin composite of the present invention, at least one of the inorganic or organic binders used in the raw material mixture in the molding process for forming a primary BN compact can be contained in the following: Examples of inorganic binders include colloidal silica, ethyl silicate, and sodium silicate (water glass). Examples of organic binders include thermosetting resins such as phenolic resin, epoxy resin, urea resin, silicone resin, and polyimide resin. These inorganic or organic binders are used to form a secondary BN compact with increased strength by curing the inorganic or organic binder in the primary BN compact to form a cured body in the binder curing process. As mentioned above, this cured body serves as an adhesive layer (binder layer) between the BN particles.

[0034] The pore-forming agent used in the method for producing a BN particle-dispersed resin composite of the present invention is contained in a mixture of raw materials in the molding process for forming a primary BN compact, and is used in the porosity-forming process to remove the pore-forming agent from the primary BN compact by various methods to form a porous BN compact with continuous pores that allows for good resin impregnation. Pore-forming agents that can be used include those listed below. For example, "compounds that can be removed from the BN compact by evaporation or vaporization," such as crystalline terpenoid compounds such as granular melamine cyanurate and granular camphor; "organic compounds that can be dissolved in a solvent and eluted and removed from the BN compact," such as polyvinyl alcohol, polyethylene oxide, and water; and compounds such as table salt (NaCl), potassium chloride (KCl), and potassium nitrate (KNO). ３ ) and sodium nitrate (NaNO ３ ) and "water-soluble inorganic compounds" such as ice and dry ice, which are "water or CO at room temperature" ２ A compound that can be turned into a gas and dissolved and removed from the BN compact can be used.

[0035] In the method for producing a BN particle-dispersed resin composite of the present invention, the mixture used as the raw material in the molding step for forming the primary BN compact can contain, as needed, the following additives in addition to the BN particles, pore-forming agent, and at least one of the inorganic and organic binders described above: For example, auxiliary agents such as surfactants, antifoaming agents, and viscosity modifiers that improve wettability, as well as solvents, can also be added as appropriate.

[0036] In the method for producing a BN particle-dispersed resin composite of the present invention, the molding process for producing a primary BN compact can be performed using, for example, press molding, precipitation, extrusion molding, freeze molding, and pressure molding. As described below, when a primary BN compact is produced using press molding, a large block-shaped BN particle-dispersed resin composite with a fixed BN particle orientation is obtained. Therefore, by selecting the cutting direction as described below, it is possible to produce a thin heat transfer sheet with an adjusted heat transfer direction. As described above, because BN particles are flaky, when press-molded, the short (thickness) sides of the flaky particles are stacked in the pressing direction, and the long (length) sides of the flaky particles are oriented in the direction perpendicular to the pressing direction. Therefore, for example, if the direction perpendicular to the pressing direction is the thickness (short) direction of the BN particle-dispersed resin composite, which is the cutout material for the thin sheet, the thermal conductivity of the cut thin sheet in the longitudinal direction is significantly increased. On the other hand, if the pressing direction is the thickness direction of the BN particle-dispersed resin composite, which is the cut-out thin plate material, the thermal conductivity in the thickness (short side) direction of the cut-out thin plate-like sheet becomes very high. By selecting the cutting direction as described above, it is possible to adjust and change the direction of thermal conductivity of the cut-out thin plate-like sheet. In addition to the above, if the technology of the present invention can be used to form a large block-shaped BN particle-dispersed resin composite, it will be possible to manufacture a large heat dissipation component in which the heat removal (heat transfer) direction can be freely changed by changing the cutting direction.

[0037] In the method for producing a BN particle-dispersed resin composite of the present invention, the strength of the porous BN molded body is increased in the binder curing step, and the pore-forming agent is removed in the porosity-imparting step to form continuous pores. The method for impregnating the porous BN molded body with a resin is not particularly limited. For example, vacuum suction impregnation, pressure impregnation, and vacuum suction and pressure impregnation, which involve vacuum suction followed by pressure impregnation, can be used.

[0038] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" are by mass unless otherwise specified.

[0039] [Example 1] (Preparation of porous BN compact) A mixed powder was prepared by adding 90 parts of BN particles with an average particle size of 30 μm, 10 parts of BN particles with an average particle size of 5 μm, 10 parts of ethyl silicate as an inorganic binder, and 10 parts of melamine cyanurate particles with an average particle size of 100 μm as a pore-forming agent. The resulting mixed powder was filled into a mold for preparing a primary BN compact and press-molded at a pressure of 10 MPa to form a cubic primary BN compact with one side measuring 100 mm. The shaped primary BN compact was heated to 500°C to harden the inorganic binder ethyl silicate, forming a secondary BN compact with greater strength than the primary BN compact, and at the same time, the melamine cyanurate particles contained in the primary BN compact were evaporated and vaporized outside the secondary BN compact, forming continuous pores where the pore-forming agent had been removed. This resulted in the production of a porous BN compact with a porosity of 30%.

[0040] (Preparation of BN particle-dispersed resin composite) The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and the porous BN compact was impregnated with epoxy resin (two-component curing type) under a reduced pressure of -90 kPa. After 48 hours at room temperature, a large cubic BN particle-dispersed resin composite with a side length of 100 mm was produced. The thermal conductivity of the composite obtained in this example was measured using a xenon flash analyzer (product name: LFA467, manufactured by NETZSCH). First, the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the pressing direction was confirmed. Therefore, a test piece (φ10 mm, thickness 2 mm) for measuring thermal conductivity was cut out so that the thickness was in the direction of the longitudinal plane orientation of the BN particles. Test pieces were cut out from the center of the press surface of a large, 100 mm cube-shaped BN particle-dispersed resin composite, measuring five points along the press direction: the top surface, the center surface, the bottom surface, and each intermediate portion. Measurements were performed on five test pieces. The results showed that the thermal conductivity was high, ranging from 25 W / m K to 30 W / m K, with little variation, averaging 27.4 W / m K ±9.5%. This demonstrates that the large BN particle-dispersed resin composite of this example exhibits stable, high thermal conductivity.

[0041] (Production of thin heat transfer sheets) The large 100 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 5 mm square plates with a thickness of 1 mm in the direction perpendicular to the press molding direction, and more than 6,000 thin heat transfer sheets were prepared. It was confirmed that none of the obtained thin heat transfer sheets had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0042] Example 2 (Preparation of Porous BN Compact) A mixed powder was prepared by adding 100 parts of BN particles with an average particle size of 30 μm to 5 parts of a liquid resol-type phenolic resin as an organic binder and 20 parts of granular camphor (a crystalline terpenoid compound) with an average particle size of 50 μm as a pore-forming agent. The resulting mixed powder was filled into a mold for preparing a primary BN compact and press-molded at a pressure of 7 MPa to form a cubic primary BN compact with a side length of 100 mm. The shaped primary BN compact was heated to 180°C to harden the phenolic resin, forming a secondary BN compact with higher strength than the primary BN compact. The primary BN compact was then heated to 250°C under a reduced pressure of -70 kPa, causing the granular camphor (a crystalline terpenoid compound) serving as a pore-forming agent in the primary BN compact to evaporate and vaporize outside the primary BN compact, forming pores, and producing a porous BN compact with a porosity of 20%.

[0043] (Preparation of BN particle-dispersed resin composite) The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and the porous BN compact was impregnated with a silicone resin by vacuum suction under a reduced pressure of -90 kPa. The silicone resin was then continuously impregnated under pressure at 5 MPa, and the resulting composite was allowed to stand at room temperature for 72 hours to produce a large cubic BN particle-dispersed resin composite with a side length of 100 mm. The thermal conductivity of the resulting composite of this example was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. As a result, the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the pressing direction was confirmed. Then, in the same manner as in Example 1, five test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were obtained by cutting out the large cubic BN particle-dispersed resin composite with a side length of 100 mm from five locations so that the thickness was in the direction of the longitudinal plane orientation of the BN particles. The thermal conductivity of the obtained test pieces was high, ranging from 30 W / m K to 35 W / m K, and the variation was small, with an average value of 33.0 W / m K ±9.1%. This confirmed that the large BN particle-dispersed resin composite of this example obtained above exhibited stable high thermal conductivity.

[0044] (Production of thin heat transfer sheets) The large, 100 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 10 mm square plates with a thickness of 2 mm in the press molding direction, and more than 2,000 thin heat transfer sheets were prepared. None of the thin heat transfer sheets obtained had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0045] Example 3 (Preparation of Porous BN Compact) A mixed powder was prepared by adding 100 parts of BN particles with an average particle size of 30 μm, 5 parts of powdered phenolic resin and 5 parts of liquid resol-type phenolic resin as organic binders, and 25 parts of table salt (coarse salt) with an average particle size of 100 μm as a pore-forming agent. The resulting mixed powder was filled into a mold for preparing a primary BN compact and press-molded at a pressure of 30 MPa to form a cubic primary BN compact with a side length of 150 mm. The formed primary BN compact was heated to 180°C to harden the phenolic resin, forming a secondary BN compact with higher strength than the primary BN compact. This high-strength secondary BN compact was immersed in running water at room temperature for 24 hours, and the table salt (coarse salt) used as the pore-forming agent was dissolved and eluted out of the secondary BN compact, forming pores. Then, a porous BN compact with a porosity of 40% was produced.

[0046] (Preparation of BN Particle-Dispersed Resin Composite) After drying the porous BN compact obtained above, it was placed in a vacuum impregnation apparatus. The porous BN compact was impregnated with a silicone resin under a reduced pressure of -90 kPa, and then left at room temperature for 72 hours to produce a large cubic BN particle-dispersed resin composite with a side length of 150 mm. The thermal conductivity of the obtained composite of this example was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. As a result, the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the pressing direction was confirmed. For this reason, test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were cut out so that the thickness was the direction of the longitudinal plane orientation of the BN particles. Furthermore, the test pieces were cut out at five locations in the pressing direction, from the center of the pressing surface of the large cubic BN particle-dispersed resin composite with a side length of 150 mm: the top surface, the central surface, the bottom surface, and each intermediate portion. The thermal conductivity of the five test pieces was measured, and the results showed that the thermal conductivity was high, ranging from 20 W / m K to 25 W / m K, with little variation, averaging 22.8 W / m K ±12.3%. This demonstrates that the large BN particle-dispersed resin composite obtained above exhibits stable high thermal conductivity.

[0047] (Production of thin heat transfer sheets) The large, 150 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 10 mm thick plates in a direction perpendicular to the press-molding direction, and more than 8,000 thin heat transfer sheets were prepared. None of the thin heat transfer sheets obtained had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0048] Example 4 (Preparation of Porous BN Compact) A mixed powder was prepared by adding 80 parts of BN particles with an average particle size of 30 μm, 20 parts of BN particles with an average particle size of 5 μm, 5 parts of powdered phenolic resin and 5 parts of liquid resol-type phenolic resin as organic binders, and 20 parts of potassium nitrate with an average particle size of 50 μm as a pore-forming agent. The prepared mixed powder was filled into a primary BN compact mold and press-molded at a pressure of 30 MPa to form a cubic primary BN compact with a side length of 150 mm. The shaped primary BN compact was heated to 180°C to harden the phenolic resin, forming a secondary BN compact with higher strength than the primary BN compact. This high-strength secondary BN compact was immersed in a water bath at 60°C for 12 hours, and the pore-forming agent potassium nitrate was dissolved and removed from the secondary BN compact, forming pores, resulting in a porous BN compact with a porosity of 35%.

[0049] (Preparation of BN Particle-Dispersed Resin Composite) The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and the porous BN compact was impregnated with epoxy resin (one-component curing type) under a reduced pressure of -85 kPa. The porous BN compact was then left at 50°C for 24 hours to produce a large cubic BN particle-dispersed resin composite with a side length of 150 mm. The thermal conductivity of the resulting composite of this example was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. The results confirmed the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the pressing direction. For this purpose, test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were cut out so that the thickness coincided with the direction of the longitudinal plane orientation of the BN particles. Each test piece was cut out at five locations, similar to Example 3, from the center of the pressed surface of the cubic BN particle-dispersed resin composite with a side length of 150 mm, to obtain five test pieces. The thermal conductivity of the five cut-out test pieces was measured, and the results showed that the thermal conductivity was high, ranging from 23 W / m K to 26 W / m K, with little variation, averaging 24.4 W / m K ±6.6%. This demonstrates that the large BN particle-dispersed resin composite of this example obtained above exhibits stable high thermal conductivity.

[0050] (Production of thin heat transfer sheets) The large, 150 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 70 mm square plates with a thickness of 2 mm in the press molding direction, enabling the preparation of more than 200 thin heat transfer sheets. None of the thin heat transfer sheets obtained had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0051] Example 5 (Preparation of Porous BN Compact) A slurry was prepared by adding 80 parts of BN particles 1 having an average particle size of 30 μm, 20 parts of BN particles 2 having an average particle size of 5 μm, 5 parts of ethyl silicate as an inorganic binder, and 200 parts of water as a pore-forming agent and solvent. The prepared slurry was filled into a mold for preparing a primary BN compact and left to settle for one day and night to allow the BN particles to settle. After removing the clean water, the mixture was placed in a freezer at −20°C for one day and night to freeze and solidify, forming a cubic primary BN compact with a side length of 100 mm. The formed primary BN compact was placed in a drying furnace at 500°C and heated to harden the ethyl silicate, while simultaneously evaporating the frozen water, to produce a porous BN compact with a porosity of 40%.

[0052] (Preparation of BN Particle-Dispersed Resin Composite) The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and an epoxy resin (two-component curing type) was impregnated into the porous BN compact under a reduced pressure of -85 kPa. The porous BN compact was then left at room temperature for 24 hours to produce a large, cubic BN particle-dispersed resin composite with a side length of 100 mm. The thermal conductivity of the resulting composite of this example was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. As a result, the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the sedimentation direction was confirmed. Then, in the same manner as in Example 1, five test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were obtained by cutting out the large, cubic BN particle-dispersed resin composite with a side length of 100 mm from five locations so that the thickness was in the direction of the longitudinal plane orientation of the BN particles. The thermal conductivity of the obtained test pieces was high, ranging from 22 W / m K to 25 W / m K, and the variation was small, with an average value of 23.6 W / m K ±6.8%. This confirmed that the large BN particle-dispersed resin composite of this example obtained above exhibited stable high thermal conductivity.

[0053] (Production of thin heat transfer sheets) The large, 100 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 2 mm thick plates in a direction perpendicular to the sedimentation direction, and more than 2,000 thin heat transfer sheets were prepared. None of the thin heat transfer sheets obtained had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0054] Example 6 (Preparation of Porous BN Compact) A raw material was prepared by mixing 100 parts of BN particles with an average particle size of 30 μm, 5 parts of powdered phenolic resin and 5 parts of liquid resol-type phenolic resin as organic binders, and 15 parts of ice with an average particle size of 100 μm as a pore-forming agent. The resulting raw material was filled into a mold for preparing a primary BN compact cooled to -20°C and press-molded at a pressure of 3 MPa to form a cubic primary BN compact with a side length of 100 mm. Immediately after molding, the primary BN compact was placed in a drying furnace at 200°C and heated to harden the liquid resol-type phenolic resin while simultaneously evaporating the ice, producing a porous BN compact with a porosity of 30%.

[0055] (Preparation of BN Particle-Dispersed Resin Composite) The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and the porous BN compact was impregnated with an epoxy resin (one-component curing type) under a reduced pressure of -85 kPa. The porous BN compact was then left at 50°C for 24 hours to prepare a large cubic BN particle-dispersed resin composite with a side length of 100 mm. The thermal conductivity of the resulting composite of this example was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. As a result, the orientation of the longitudinal planes of the BN particles in the direction perpendicular to the pressing direction was confirmed. Then, in the same manner as in Example 1, five test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were obtained by cutting out the large cubic BN particle-dispersed resin composite with a side length of 100 mm from five locations so that the thickness was in the direction of the longitudinal plane orientation of the BN particles. The thermal conductivity of the obtained test pieces was high, ranging from 25 W / m K to 30 W / m K, and the variation was small, with an average value of 27.6 W / m K ±9.4%. This demonstrates that the large BN particle-dispersed resin composite obtained above according to this example exhibits stable high thermal conductivity.

[0056] (Production of thin heat transfer sheets) The large, 100 mm cube-shaped BN particle-dispersed resin composite obtained above was cut in the press molding direction to a thickness of 1 mm and into 5 mm square plates, thereby preparing more than 6,000 thin heat transfer sheets. Furthermore, none of the thin heat transfer sheets obtained had any defects such as non-impregnation or uneven impregnation of the resin, and were of excellent quality, exhibiting uniform and stable high thermal conductivity and high insulation.

[0057] Comparative Example 1: A BN compact for Comparative Example 1 was produced using a mixed powder prepared in the same manner as in Example 1, except that no pore-forming agent was added. The mixture was heated to 500°C to cure the inorganic binder, ethyl silicate. The resulting BN compact was impregnated with epoxy resin (two-component curing type) in the same manner as in Example 1. The resin impregnation into the BN compact was poor, with many areas unimpregnated in the center, and cracks were observed in the BN compact. The thermal conductivity of the resulting composite was measured using a xenon flash analyzer (product name: LFA467) in the same manner as in Example 1. Then, as in Example 1, five test pieces (φ10 mm, thickness 2 mm) for measuring thermal conductivity were obtained by cutting out a large cubic BN particle-dispersed resin composite with a side length of 100 mm from five locations, with the thickness being in the direction of the longitudinal orientation of the BN particles. Measurements of the obtained test pieces revealed that, unlike the composites of the Examples, the thermal conductivity varied greatly, from 1 W / m K to 30 W / m K, and it was not possible to obtain a large BN particle-dispersed resin composite that exhibited stable high thermal conductivity. For this reason, a thin heat transfer sheet was not produced.

[0058] A BN molded body of Comparative Example 2 was produced by using a mixed powder prepared in the same manner as in Example 2, except that no organic binder was added, and heating to 180° C. to cure the phenolic resin. The obtained BN molded body was impregnated with a silicone resin in the same manner as in Example 2, but the BN molded body was damaged during the resin impregnation, and a BN particle-dispersed resin composite itself could not be obtained.

[0059]

[0060]

Claims

1. A block-shaped hexagonal boron nitride particle-dispersed resin composite that can be used to directly obtain a plurality of thin heat transfer sheets by cutting into plates, characterized in that the hexagonal boron nitride particle-dispersed resin composite is formed by solidifying a porous BN molding containing at least hexagonal boron nitride (h-BN) particles, continuous pores that remain after the pore-forming agent has been removed, and a hardened body of at least one of an inorganic binder and an organic binder, with the resin impregnated into the pores, and the hardened body of the binder being interposed between the particles.

2. Volume is 200 cm ３ The hexagonal boron nitride particle-dispersed resin composite according to claim 1, which has a large and thick shape, and in which the ratio m of maximum length / thickness is 1≦m≦3, where m is the maximum length of the longest side and m is the thickness of the shortest side.

3. A hexagonal boron nitride particle-dispersed resin composite according to claim 1 or 2, wherein the porosity of said porous BN compact is 20% or more and 50% or less.

4. A hexagonal boron nitride particle-dispersed resin composite according to any one of claims 1 to 3, wherein the composite, obtained by solidifying the porous BN compact while the resin is impregnated into the pores thereof, has a thermal conductivity of 20 W / m·K or more due to the orientation direction of the hexagonal boron nitride (h-BN) particles.

5. A method for producing a block-shaped hexagonal boron nitride particle-dispersed resin composite used to directly obtain a plurality of thin heat transfer sheets by cutting them into plate shapes, comprising: a shaping step for forming a primary BN compact from a mixture containing at least hexagonal boron nitride (h-BN) particles, a pore-forming agent, and at least one binder selected from the group consisting of an inorganic binder and an organic binder; a binder hardening step for hardening the binder in the primary BN compact to form a secondary BN compact having increased strength by interposing a hardened body of the binder between the particles as an adhesive layer; and a porosification step for removing the pore-forming agent contained in the shaping step for forming the primary BN compact to form a porous BN compact having continuous pores, which step is carried out in an order reversed to the binder hardening step or is carried out simultaneously with the binder hardening step to serve as two combined steps. A method for producing a hexagonal boron nitride particle-dispersed resin composite, comprising a composite process for impregnating the porous BN compact obtained by the curing and porosification with a resin to form a composite.

6. A method for producing a hexagonal boron nitride particle-dispersed resin composite according to claim 5, wherein in the molding step, a primary BN compact is formed from the mixture by press molding or precipitation.

7. A method for producing a hexagonal boron nitride particle-dispersed resin composite according to claim 5 or 6, wherein the curing and porosification result in a porous BN molded body having a porosity of 20% or more and 50% or less.

8. A method for producing a hexagonal boron nitride particle-dispersed resin composite according to any one of claims 5 to 7, wherein the pore-forming agent is a solid having a particle size of 5 to 200 μm, and the binder hardening step for forming the secondary BN compact and the porosity-imparting step for removing the pore-forming agent are carried out simultaneously by heating, thereby combining the two steps.

9. A method for producing a hexagonal boron nitride particle-dispersed resin composite according to any one of claims 5 to 8, wherein in the composite forming step, when the porous BN compact is impregnated with resin, the resin is impregnated using either a vacuum suction impregnation method, a pressure impregnation method, or a combination of the vacuum suction impregnation method and the pressure impregnation method.

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