WO2025253676A1 - Hexagonal boron nitride particle-dispersed resin composite and production method for hexagonal boron nitride particle-dispersed resin composite - Google Patents

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

The present invention relates to a hexagonal boron nitride particle-dispersed resin composite and a method for producing the same. Specifically, the present invention relates to a technology for easily providing a resin composite in which highly functional hexagonal boron nitride (h-BN) particles (hereinafter referred to as BN particles) are well dispersed in a resin, thereby exhibiting stable high thermal conductivity and high electrical insulation. 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 electrical insulation. By directly cutting thin, highly thermally conductive, highly insulating heat transfer sheets from the blocks, the productivity of thin heat transfer sheets can be significantly improved.

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

Patent Document 2 also discloses that hexagonal boron nitride, which has excellent properties as an electrical insulating material, such as high thermal conductivity and high insulation, is attracting attention, and that its crystalline structure and scale shape result in large anisotropy in thermal conductivity. It also discloses that by impregnating the voids inside a boron nitride sintered body with resin and cutting it into plates to produce heat dissipation components, it is possible to control the orientation in any direction, making it easy to create heat dissipation components with excellent thermal conductivity and any thickness. It also proposes a resin-impregnated boron nitride sintered body consisting of a boron nitride sintered body with a porosity of 10-70% in which boron nitride particles are bonded three-dimensionally, and resin, with through holes, the through holes filled with adhesive resin. Cited Document 2 states that a cubic resin-impregnated boron nitride sintered body with a side length of approximately 50 mm was obtained, and that the thickness of the plate-shaped resin-impregnated boron nitride sintered body was preferably 0.15 to 1.50 mm.

Patent Document 3 proposes a thin, lightweight composite in one embodiment, which includes a boron nitride sintered body made by sintering a mesh-like boron nitride sheet with openings of approximately 200 to 1000 μm, and a resin that fills the pores in the boron nitride sintered body.

Patent No. 7282950 Patent No. 6262522 Patent No. 7322323

However, in all of the above-mentioned conventional technologies, a ceramic-resin composite is formed by impregnating resin into voids formed inside ceramics such as boron nitride sintered bodies due to the structure specific to the material. In other words, as shown below, all of the conventional technologies form a ceramic-resin composite in the shape of a thin plate or a small (thin) ceramic sintered body such as BN by impregnating resin into the minute voids inside the ceramic sintered body. According to the inventors' investigations, this has led to the following problems.

Specifically, all of the above-mentioned conventional technologies involve ceramic-resin composites made by impregnating a resin composition into a ceramic sintered body sintered at a high temperature of 1500°C or higher, and have the following technical issues. First, the technology of Patent Document 1 relates to a "resin composite of boron nitride sintered body, in which a thermosetting resin composition is impregnated into a boron nitride sintered body obtained by three-dimensionally sintering boron nitride powder." However, the boron nitride sintered body for resin impregnation is prepared using a complicated procedure that utilizes high temperatures and pressures, making it difficult to say it is a simple method, and has the issue of poor productivity. Specifically, a mixed powder containing boron nitride is filled into a mold and pressed into a compact, 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.

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. The cut thin sintered body sheet is then impregnated with a thermosetting resin composition such as epoxy resin as described below, and the resin is thermally cured after impregnation to form a composite. Specifically, using a vacuum heating impregnation device, the body is degassed for 10 minutes in a vacuum at 145°C and 15 Pa, and then immersed in the thermosetting resin composition in the same device under the same heating and vacuum conditions. The thin boron nitride sintered body impregnated with the thermosetting resin composition is then placed in a pressurized heating impregnation device and held at 145°C and 3.5 MPa for 120 minutes. It is then heated at atmospheric pressure at 160°C for 120 minutes to obtain a sheet-like ceramic resin composite in which the thermosetting resin composition is semi-cured. As with the technology described in Patent Document 1 above, producing individual pieces by obtaining a thin sheet of boron nitride sintered body and impregnating the sintered body with resin requires an extremely large number of steps and is cumbersome, posing a major practical problem in that it significantly reduces productivity.

Furthermore, as described in Patent Document 2, if a block-shaped ceramic-resin composite is produced and then thin heat-transfer sheets are cut out, this is expected to improve productivity compared to Patent Document 1, which involves impregnating thin sheets cut from boron nitride sintered compact with resin and producing each piece individually. However, even with the technology described in Patent Document 2, the boron nitride sintered compact before resin impregnation "is preferably produced by sintering at 1600°C or higher for at least one hour. Without sintering, the pore size will be small, making resin impregnation difficult." The upper sintering temperature is considered to be around 2200°C, and the boron nitride sintered compact 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 requires complicated procedures using high temperatures and pressures, which results in poor productivity.

Furthermore, the technology described in Patent Document 3 cited above involves sintering a mesh-like 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, and this presents the same technical issues as Patent Documents 1 and 2 mentioned above. With the technology of Patent Document 3 configured as above, the composite in which resin is filled into the pores of the boron nitride sintered body is thin, so it is possible to sufficiently fill the resin in the pores, and the technology of Patent Document 3 is also a technology in which the sintered body is impregnated with resin to manufacture each piece individually. Therefore, like Patent Document 1, the technology of Patent Document 3 also presents major practical issues in that it is extremely labor-intensive and cumbersome, and significantly reduces productivity.

Furthermore, according to the inventors' research, the following problem arises when using the configuration described in Patent Document 2, in which thin heat transfer sheets are cut out from a block-shaped ceramic-resin composite obtained by impregnating a sintered body with resin. Specifically, when the ceramic-resin composite from which the sheet is cut is made larger in order to improve the productivity of thin heat transfer sheets, the conventional technology of impregnating resin into the voids (pores) inherent in the structure of the boron nitride sintered body poses the technical problem that it is difficult to sufficiently impregnate the resin deep into the block-shaped boron nitride sintered body, even when sintered at high temperatures, making it impossible to make the sheet very large. This tendency becomes particularly pronounced when the thickness of the block-shaped boron nitride sintered body is increased.

According to the inventors' research, if the voids (pores) in 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 cavity acts as a highly insulating layer. The thermal conductivity of a resin composite varies significantly depending on whether or not the voids (pores) in 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 body, 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 or sedimentation direction. Therefore, for example, if the pressing direction during press-molding to produce a block-shaped body 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, 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.

Probably due to the reasons mentioned above, conventional techniques involve cutting thin sheets from a block of boron nitride sintered compact and then impregnating the cut sheets with resin, or cutting sheets from a composite of boron nitride sintered compact 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 limited, posing a practical problem in that it is hardly an effective method for improving the productivity of thin heat transfer sheets.

The object of the present invention is therefore to develop a new technology that can easily produce a BN particle-resin composite that exhibits high thermal conductivity and is fully impregnated with resin to the interior despite being in the shape of a large, thick block, and that can be cut into plates to produce a greater number of thin sheets, and each of the cut thin sheets will become a heat transfer sheet with excellent performance, including 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."

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

Preferred embodiments of the BN particle-dispersed resin composite of the present invention are as follows.
[2] The BN particle-dispersed resin composite according to [1] above, which has a volume of 200 ^cm3 or more and a large, thick shape in which the ratio m of maximum length to thickness, m being 1≦m≦3, is satisfied when the longest side is the maximum length and the length of the shortest side is the thickness.
[3] The BN particle-dispersed resin composite according to the above [1] or [2], wherein the porosity of the porous BN molded body is 20% or more and 50% or less.
[4] The BN particle-dispersed resin composite according to any one of [1] to [3] above, wherein the composite obtained by solidifying the porous BN compact in a state in which the pores 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.

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 heat transfer sheets by cutting into plate shapes, comprising:
a shaping step for shaping 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 an inorganic binder and an organic binder;
a binder hardening step for hardening the binder in the primary BN compact so that a hardened binder intervenes between the particles as an adhesive layer to form a secondary BN compact having increased strength;
a porosifying step for forming a porous BN compact having continuous pores by removing the pore-forming agent contained in the shaping step for shaping the primary BN compact;
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.

A preferred embodiment of the method for producing a BN particle-dispersed resin composite of the present invention is as follows.
[6] The method for producing a BN particle-dispersed resin composite according to the above [5], wherein in the molding step, a primary BN molded body 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 [5] or [6], wherein the curing and the porosity-imparting process result in a porous BN molded body having a porosity of 20% or more and 50% or less.
[8] The method for producing a BN particle-dispersed resin composite according to any one of [5] to [7] above, 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-providing 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.

The present invention makes it possible to easily provide a large, thick, block-shaped BN particle-dispersed resin composite that is fully impregnated with resin, has high thermal conductivity and high insulation, and is free of defects such as non-impregnation or uneven impregnation of the resin within the composite. Furthermore, a large number of thin heat transfer sheets can be cut from this large, thick, block-shaped BN particle-dispersed resin composite, and each cut heat transfer sheet has uniform and stable high thermal conductivity and high insulation properties. The present invention significantly improves the productivity of thin heat transfer sheets with such excellent properties. Furthermore, the present invention makes it 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 with high thermal conductivity and high insulation properties, thereby providing extremely high practical value. According to the present invention, it is possible to obtain a large, block-shaped, highly thermally conductive BN particle-dispersed resin composite that 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, and that exhibits little variation in the thermal conductivity of the composite even when it is large. As a result, according to the present invention, by cutting this large, block-shaped BN particle-dispersed resin composite into thin sheets, it is possible to consistently obtain multiple thin heat transfer sheets that exhibit similar high thermal conductivities with little variation. In this invention, the thermal conductivity of the composite was measured using a xenon flash analyzer according to JIS R1611 using the xenon flash method.

Next, the present invention will 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 solidifying a composite in a state in which a resin is impregnated into the continuous pores of a porous BN molded body formed at least containing BN particles, continuous pores remaining after the pore-forming agent has been removed, and a hardened body made of either an inorganic or organic binder, and in that the hardened body made of 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 can be cut into plates to directly obtain a plurality of thin heat transfer sheets. The method comprises: 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 or organic binder; a binder curing step for curing the binder in the primary BN compact to form a secondary BN compact with increased strength, such that the cured binder forms an adhesive layer between the particles; 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 with continuous pores; and a composite process for impregnating the porous BN compact obtained by the curing and porosification steps with a resin to form the composite.

According to the manufacturing method of the present invention described above, it is possible to easily produce a BN particle-dispersed resin composite that stably exhibits high thermal conductivity and high insulating properties, for example, a ^large , thick block shape having a volume of 200 cm or more, and a maximum length/thickness ratio m within the range of 1≦m≦3, where m is the maximum length of the longest side and the thickness of the shortest side. According to the inventors' investigations, the BN particle-resin composite that exhibits high thermal conductivity despite being in a large block shape and sufficiently impregnated with resin to the interior, which can be cut into plates to produce a large number of thin heat transfer sheets, can be configured to have a volume of 800 cm ^or more, more preferably 1000 cm or ^more . Specifically, it is preferable to produce a large, thick composite having the following dimensions, for example:

For example, a cubic shape in which the maximum length/thickness ratio m is 1 includes a BN particle-dispersed resin composite in the shape of a cube with one side measuring 93 mm to 150 mm (volume 804 ^cm to 3375 ^cm ). Various shapes are conceivable for rectangular block-shaped composites, and an example of a BN particle-dispersed resin composite that satisfies the above-mentioned requirements is the shape 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 in order to make the volume of the composite approximately 800 ^cm , the composite would be a rectangular parallelepiped measuring 15 cm x 10.7 cm x ⁵ cm = 802.5 cm. Furthermore, if the maximum length/thickness ratio m is 2.5 and the thickness is 7 cm, the resulting composite will be a rectangular parallelepiped with a volume of 17.5 cm × 8.2 cm × 7 cm = 1004.5 ^cm³ . If the ratio m is 3 and the thickness is 8 cm, the resulting rectangular parallelepiped will have a volume of 24 cm × 8.3 cm × 8 cm = 1594 ^cm³ , or approximately 1600 ^cm³ . According to the inventors' studies, by producing a thick, block-shaped cubic or rectangular BN particle-dispersed resin composite as described above, it becomes possible to cut the composite into plates and produce a larger number of thin plate-shaped sheets. According to the present invention, composites with excellent properties in block shapes other than the cubic or rectangular shapes described above can be obtained depending on the intended use. Furthermore, by cutting the BN particle-dispersed resin composite into the large block-shaped BN particle-dispersed resin composite described above, it becomes possible to stably and efficiently produce 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.

The present invention employs the above-described configuration to solve the problems associated with the prior art. Specifically, the inventors discovered that even with the prior art technology of using boron nitride sintered bodies 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 fully impregnate the internal voids (pores) with resin when the block-shaped sintered body is large, and they conducted extensive research to improve this issue. Obtaining the boron nitride sintered body with enlarged pore sizes described above requires complicated and strict processing conditions, and they recognized that this issue also needed to be improved.

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 molded body that can be stably and effectively impregnated with resin all the way to the interior. However, according to the inventors' research, as the porous BN molded body becomes larger and thicker, it also becomes heavier. This 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 molded body due to the impregnation pressure during resin impregnation. One of the features of the manufacturing method of the present invention, as a means for solving the above-mentioned problem, is that it uses at least one inorganic or organic binder as the molding material in the molding process for molding the primary BN molded body, and further includes a binder curing process in which the binder added to the primary BN molded body is cured to form a secondary BN molded body with increased strength. According to the method for producing a BN particle-dispersed resin composite of the present invention having the above-described configuration, by curing the binder used as a raw material for the primary BN compact, it is possible to easily obtain a secondary BN compact that is useful as an intermediate before resin impregnation, with the cured binder interposed between the particles as an adhesive layer and has increased strength.

When impregnating with resin, if a BN sintered body, which is prepared using the aforementioned conventional technology and has small pores enlarged by sintering the BN compact at high temperatures ranging from 1600°C to 2000°C or higher, is used, it is difficult to impregnate the BN sintered body with resin sufficiently and stably all the way to the center of the interior, 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 structure for increasing the strength of the BN compact, and by the fact that, in order to solve this problem, a completely different method from conventional technology is used, which effectively utilizes a pore-forming agent to form a porous BN compact, an intermediate body that can be impregnated with resin in a good and stable state. Specifically, the manufacturing method of the present invention is characterized by including a porosity-increasing step in which a pore-forming agent that can be evaporated or vaporized by heating or that can be dissolved in a solvent and removed by elution is added to the mixture used in the shaping step for shaping (molding) the primary BN compact. After molding the primary BN compact, the pore-forming agent is evaporated or vaporized by heating or removed by dissolving or eluting in a solvent, thereby forming a porous BN compact. When using the method of evaporation or vaporization by heating as a means for removing the pore-forming agent, it is sometimes 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.

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 evaporating or vaporizing it with heat or by dissolving it in a solvent and eluting it. Pores are then formed in the remains left behind after the pore-forming agent is removed, and these pores become continuous. Therefore, when the porous BN compact obtained by the manufacturing method of the present invention is used during 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 solves the technical problem of incomplete or uneven resin impregnation observed within composites in prior art. In other words, the present invention solves the problem of significantly reduced thermal conductivity of the resulting resin composite, which arose in prior art when the voids (pores) in the boron nitride sintered compact were not sufficiently impregnated with the matrix resin and remained hollow.

Furthermore, the continuous pores formed during the porosity-making process, which is a feature of the manufacturing method of the present invention and are traces of the pore-forming agent removed, make it easier for the resin to impregnate the porous BN molded body, lowering the resin impregnation pressure (resistance) and reducing the stress that can deform or damage the porous BN molded body. This solves the problem of deformation and damage that can occur in BN particle-dispersed resin composites after the porous BN molded body 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 excellent BN particle-dispersed resin composites. 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 to form a high-strength secondary BN compact, and the porosity forming process, which obtains a porous BN compact with 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.

The aforementioned prior art document, 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 formed and filled with an adhesive resin to ensure adhesion and efficiently dissipate heat generated by the heater to a heat sink or the like," and further that "a solid drill (manufactured by Ryoko Seiki Co., Ltd.) or the like is used" and "through-hole diameters are 0.03 mm to 2.0 mm." Furthermore, according to the inventors' investigations, since the holes formed by drilling are linear and have large diameters, when the material is cut into thin plates to form thin heat transfer sheets, the VF% (volume ratio) between the high thermal conductivity BN particles and the low thermal conductivity resin differs between the areas near the through-holes and those away from the through-holes, resulting in significant differences in thermal conductivity and resulting in non-uniformity and significantly reduced performance as a heat transfer sheet. In contrast, when a solid pore-forming agent with a particle size of 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 than the 2 mm or less through-holes disclosed in Patent Document 2, and continuous pores with a non-linear shape are formed. According to the inventors' studies, due to the above-mentioned pore characteristics, the BN particle-dispersed resin composite of the present invention has very high uniformity in thermal conductivity, 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.

Furthermore, the previously mentioned prior art, Patent Document 3, describes "a boron nitride sintered body and a resin filling the pores in the boron nitride sintered body." However, these are tiny pores (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 powder press or doctor blade methods, and are much smaller than the pores that form after the pore-forming agent that characterizes the present invention is removed. For this reason, even if a large, thick, block-shaped porous BN compact were to be produced using the technology described in Patent Document 3, the tiny pores that naturally form in the gaps between stacked boron nitride particles would not allow the resin to be fully impregnated all the way to the center of the compact without defects.

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 after the pore-forming agent is 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. During sintering, the raw material particles are heated to a temperature below the melting point (at least 1500°C), resulting in the raw material particles reacting directly with each other and bonding (fusing) together. In contrast, the hexagonal boron nitride particle-dispersed resin composite of the present invention is formed by bonding the raw material particles together by curing at least one of an inorganic binder or an organic binder at a low temperature, resulting in a cured body of the binder interposed between the particles, and this cured body exists 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 composites made using conventional technology 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, resulting in the resin-impregnated composites of the two types having different morphological characteristics.

The BN particle-dispersed resin composite of the present invention is characterized by the configuration of the porous BN compact into which the resin is impregnated. In addition to the voids resulting from the three-dimensional structure of boron nitride used in resin impregnation in conventional technologies and the fine pores that naturally form in the gaps between boron nitride particles when forming the boron nitride compact, the porous BN compact also has continuous pores intentionally (forcibly) formed by the pore-forming agent used in forming the primary BN compact. By using a porous BN compact with the above configuration, the BN particle-dispersed resin composite of the present invention achieves significantly improved filling during the resin impregnation composite formation process, resulting in a composite with excellent 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 conventional technologies are resolved. Therefore, when the large, thick block-shaped BN particle-dispersed resin composite of the present invention is cut into plates to form thin heat transfer sheets, it is possible to produce a large number of high-quality thin heat transfer sheets that exhibit uniform and stable high thermal conductivity and high insulation. Specifically, for example, by cutting out the large, 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.

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 properties, including resistance to metal wetting, 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 when measured using laser diffraction light scattering.

In the manufacturing method of a BN particle-dispersed resin composite of the present invention, the inorganic or organic binders used in the raw material mixture in the molding process for forming a primary BN compact can be at least one of the following: Examples of inorganic binders include colloidal silica, ethyl silicate, and sodium silicate (water glass). Examples of organic binders that can be used 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 hardened body in the binder curing process. As mentioned above, this hardened body serves as an adhesive layer (binder layer) between the BN particles.

The pore-forming agent used in the method for producing a BN particle-dispersed resin composite of the present invention is incorporated into a raw material mixture in the molding process for forming a primary BN compact. The pore-forming agent is then removed from the primary BN compact by various methods in the porosity-forming process to form a porous BN compact with continuous pores that allows for good resin impregnation. Examples of pore-forming agents that can be used include compounds that can be evaporated and removed from the BN compact, such as crystalline terpenoid compounds like granular melamine cyanurate and granular camphor; organic compounds that can be dissolved in a solvent and eluted from the BN compact, such as polyvinyl alcohol and polyethylene oxide, and water; water-soluble inorganic compounds like sodium chloride (NaCl), potassium chloride (KCl), potassium nitrate ( _KNO3 ), and sodium nitrate ( _NaNO3 ); and compounds that can be eluted and removed from the BN compact, such as ice and dry ice, that become water or _CO2 gas at room temperature.

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 process for forming the primary BN molded body can contain, as needed, the BN particles, pore-forming agent, and at least one of an inorganic binder and an organic binder, as 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.

In the manufacturing method of a BN particle-dispersed resin composite of the present invention, methods for forming a primary BN molded body include, for example, press molding, precipitation, extrusion molding, freeze molding, and pressure molding. As described below, when a primary BN molded body is formed by press molding, a large block-shaped BN particle-dispersed resin composite with a uniform 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 adjustable heat transfer direction. As mentioned 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 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 plate, the thermal conductivity of the cut thin plate-shaped sheet in the longitudinal direction is extremely high. 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 extremely 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 this invention can be used to form a large block-shaped BN particle-dispersed resin composite, it will also be possible to manufacture large heat dissipation components in which the heat removal (heat transfer) direction can be freely adjusted by changing the cutting direction.

In the method for producing a BN particle-dispersed resin composite of the present invention, the strength is increased in the binder curing step, and the porous BN molded body formed in the porosity-forming step by removing the pore-forming agent to have continuous pores is impregnated with resin by a method that is not particularly limited. For example, methods that can be used include vacuum suction impregnation, pressure impregnation, and vacuum suction and pressure impregnation, which involves vacuum suction followed by pressure impregnation.

The present invention will be explained in detail below using examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" in the examples and comparative examples are by mass unless otherwise specified.

[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 a side length of 100 mm. The shaped primary BN compact was heated to 500°C to harden the inorganic binder ethyl silicate and form a secondary BN compact with higher strength than the primary BN compact. At the same time, the melamine cyanurate particles as a pore-forming agent 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. Then, a porous BN compact with a porosity of 30% was produced.

(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. The resulting composite was then left at room temperature for 48 hours to produce a large, 100 mm-side cubic BN particle-dispersed resin composite. The thermal conductivity of the resulting composite 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. For this purpose, test pieces (φ10 mm, thickness 2 mm) for thermal conductivity measurement were cut out so that the thickness of the test pieces was the direction of the longitudinal orientation of the BN particles. Furthermore, test pieces were cut out at five locations in the pressing direction from the center of the pressing surface of the large, 100 mm-side cubic BN particle-dispersed resin composite: the top, middle, and bottom surfaces, as well as intermediate portions of each surface. Five test pieces were measured. As a result, the thermal conductivity was high, ranging from 25 W/m K to 30 W/m K, and the variation was small, with an average value of 27.4 W/m K ±9.5%. This demonstrates that the large BN particle-dispersed resin composite obtained above exhibits stable high thermal conductivity.

(Production of thin heat transfer sheet)
The large, 100 mm cube-shaped BN particle-dispersed resin composite obtained above was cut into 1 mm thick, 5 mm square plates in a 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 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.

[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 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. The primary BN compact was further heated to 250°C under a reduced pressure of -70 kPa to evaporate and vaporize the granular camphor (a crystalline terpenoid compound) in the primary BN compact, forming pores, and a porous BN compact with a porosity of 20% was produced.

(Preparation of BN particle-dispersed resin composite)
The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and the silicone resin was vacuum-impregnated into the porous BN compact under a reduced pressure of -90 kPa. The silicone resin was then continuously pressure-impregnated at 5 MPa, and the resulting composite was left 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 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.

(Production of thin heat transfer sheet)
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, resulting in more than 2,000 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.

[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 to 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 to dissolve and remove the table salt (coarse salt) used as the pore-forming agent from the secondary BN compact, forming pores. A porous BN compact with a porosity of 40% was then produced.

(Preparation of BN particle-dispersed resin composite)
After drying the porous BN compact obtained above, it was placed in a vacuum impregnation apparatus. Silicone resin was impregnated into the porous BN compact under a reduced pressure of -90 kPa, and the resulting mixture was 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 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. For this purpose, thermal conductivity measurement test pieces (φ10 mm, thickness 2 mm) 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, starting 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.

(Production of thin heat transfer sheet)
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.

[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 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 a water bath at 60°C for 12 hours to dissolve and remove the pore-forming agent potassium nitrate from the secondary BN compact, forming pores, and producing a porous BN compact with a porosity of 35%.

(Preparation of BN particle-dispersed resin composite)
The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and epoxy resin (one-component curing type) was impregnated into the porous BN compact under a reduced pressure of -85 kPa. The resulting composite 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 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 thermal conductivity measurement 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. Five test pieces were obtained. 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.

(Production of thin heat transfer sheet)
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, resulting in 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.

[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 slurry was placed in a freezer at −20°C for one day and night to freeze and solidify, thereby 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%.

(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 -85 kPa. The resulting composite 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 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 long planes of the BN particles in the direction perpendicular to the sedimentation direction. 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 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 long 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.

(Production of thin heat transfer sheet)
From the large, 100 mm cube-shaped BN particle-dispersed resin composite obtained above, 2 mm thick pieces were cut in the direction perpendicular to the sedimentation direction into 10 mm square plates, enabling the preparation of more than 2,000 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.

[Example 6]
(Preparation of Porous BN Compact)
A prepared raw material was obtained 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 prepared 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%.

(Preparation of BN particle-dispersed resin composite)
The porous BN compact obtained above was placed in a vacuum impregnation apparatus, and an epoxy resin (one-component curing type) was impregnated into the porous BN compact under a reduced pressure of -85 kPa. The resulting composite was then left at 50°C 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 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. 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 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.

(Production of thin heat transfer sheet)
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, enabling the preparation of 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.

[Comparative Example 1]
A BN compact of 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 of this Comparative Example 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 thermal conductivity measurement 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 showed 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.

[Comparative Example 2]
A BN molded body of Comparative Example 2 was produced by heating a mixed powder prepared in the same manner as in Example 2, except that no organic binder was added, to 180°C to cure the phenolic resin. The obtained BN molded body was impregnated with 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.

 

Claims (9)

A block-shaped hexagonal boron nitride particle-dispersed resin composite used to directly obtain a plurality of thin heat transfer sheets by cutting into plate shapes,
A hexagonal boron nitride particle-dispersed resin composite is characterized in that the composite is formed by solidifying a porous BN molding containing at least hexagonal boron nitride (h-BN) particles, continuous pores remaining after a pore-forming agent has been removed, and a hardened body made of at least one of an inorganic binder and an organic binder, with the pores impregnated with a resin, and the hardened body made of the binder being interposed between the particles. 2. The hexagonal boron nitride particle-dispersed resin composite according to claim ¹ , which has a large and thick shape with a volume of 200 cm3 or more and a maximum length/thickness ratio m of 1≦m≦3, where m is the ratio of the longest side to the shortest side. The hexagonal boron nitride particle-dispersed resin composite according to claim 1 or 2, wherein the porosity of the porous BN compact is 20% or more and 50% or less. A hexagonal boron nitride particle-dispersed resin composite according to any one of claims 1 to 3, wherein the composite formed by solidifying the porous BN compact with the resin 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. A method for producing a block-shaped hexagonal boron nitride particle-dispersed resin composite that is used to directly obtain a plurality of thin plate-shaped heat transfer sheets by cutting the resin composite into plate shapes, comprising:
a shaping step for shaping 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 an inorganic binder and an organic binder;
a binder hardening step for hardening the binder in the primary BN compact so that a hardened binder is interposed between the particles as an adhesive layer to form a secondary BN compact having increased strength;
a porosification step for removing the pore-forming agent contained in the shaping step for shaping the primary BN compact to form a porous BN compact having continuous pores, which is carried out in a reverse order to the binder hardening step or 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. The method for producing a hexagonal boron nitride particle-dispersed resin composite according to claim 5, wherein in the molding process, a primary BN compact is formed from the mixture by press molding or precipitation. The method for producing a hexagonal boron nitride particle-dispersed resin composite according to claim 5 or 6, wherein the curing and porosification process results in a porous BN compact having a porosity of 20% or more and 50% or less. 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 process for forming the secondary BN compact and the porosity-improving process for removing the pore-forming agent are carried out simultaneously by heating, thereby combining the two processes. 9. The method for producing a hexagonal boron nitride particle-dispersed resin composite according to claim 5, wherein, in the composite forming step, when the porous BN compact is impregnated with the 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.