Boron nitride agglomerated powder, heat dissipation sheet, and semiconductor device

Abstract

To provide a method for producing a boron nitride aggregated powder capable of improving the thermal conductivity of a heat dissipation sheet and simultaneously improving the withstand voltage characteristics, to provide a method for producing a heat dissipation sheet containing the boron nitride aggregated powder, and to provide a method for producing a semiconductor device using the heat dissipation sheet.SOLUTION: The method includes a pulverizing step of pulverizing raw boron nitride, a granulating step of granulating the raw boron nitride powder obtained by the pulverizing step, and a heat-treating step of heat-treating the boron nitride granulated powder obtained by the granulating step in a crucible, wherein after the heat-treating step, a heat-treated powder in an inside portion separated from an inside wall surface of the crucible is fractionated to obtain the boron nitride agglomerated powder having a tap concentration of 0. 6g / ml or more and less than 0. 8g / ml and an interparticle void volume of 0. 5ml / g or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a boron nitride agglomerated powder suitable for use in a heat dissipation sheet for a semiconductor device, a heat dissipation sheet containing the boron nitride agglomerated powder, and a semiconductor device using the heat dissipation sheet. [Background technology]

[0002] Boron nitride (BN) is an insulating ceramic and is known to have various crystal forms, such as c-BN with a diamond structure, h-BN with a graphite structure, and α-BN and β-BN with turbostratic structures. Among these, h-BN has the same layered structure as graphite, is relatively easy to synthesize, and has excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance, making it widely used in the electrical and electronic materials field.

[0003] In recent years, heat generation due to the increasing density of integrated circuits has become a major problem, particularly in the electrical and electronics fields, and how to dissipate heat has become an urgent issue. h-BN, which has high thermal conductivity despite being an insulator, has attracted attention as a thermally conductive filler for such heat dissipation components.

[0004] However, h-BN has a plate-like particle shape and exhibits high thermal conductivity (typically about 400 W / m·K) in the plate plane direction (in the ab plane or (002) plane), but only low thermal conductivity (typically about 2–3 W / m·K) in the plate thickness direction (the C axis direction). Therefore, when h-BN is blended with a resin to form a BN particle-containing resin composition and, for example, molded into a plate-like sheet-shaped product, the plate-shaped h-BN particles will be oriented in the plate plane direction of the sheet-shaped product, which is the flow direction of the BN particle-containing resin composition during molding. The resulting sheet-shaped product exhibits excellent thermal conductivity in the plate plane direction but only low thermal conductivity in the thickness direction.

[0005] To improve the anisotropy of the thermal conductivity of h-BN particles, agglomerated particles of h-BN with shapes other than scaly plates have been investigated, which have less orientation when filled into resin.

[0006] Patent Document 1 describes BN agglomerated particles with a purity of 93% and a porosity (void ratio) of 50% by volume or less. Patent Document 1 does not describe the tap density, and when used in a heat dissipation sheet for a semiconductor device, the thermal conductivity and withstand voltage were still insufficient.

[0007] Patent Document 2 describes BN agglomerated particles with a porosity of 50 to 70% by volume and a crushing strength of 1.0 to 4.0 MPa. Patent Document 2 does not describe tap density, and the thermal conductivity and withstand voltage when used in a heat dissipation sheet for a semiconductor device are still insufficient.

[0008] In Patent Document 3, the aggregate particle diameter (D 50 Patent Document 3 describes BN agglomerated particles having a diameter of 2 to 200 μm and a tap density of 0.5 to 1.0 g / ml. Patent Document 3 does not describe the interparticle volume, which is affected by the orientation of the primary particles that make up the agglomerated particles or the shape of the agglomerated particles, and the thermal conductivity and the withstand voltage, as determined by a relative evaluation, when used in a heat dissipation sheet for a semiconductor device are also insufficient. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2012 / 070289 [Patent Document 2] Japanese Patent Application Publication No. 2017-82091 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-98882 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a boron nitride agglomerated powder that can improve the thermal conductivity of a heat dissipation sheet while also providing good voltage resistance characteristics, a heat dissipation sheet containing this boron nitride agglomerated powder, and a semiconductor device that uses this heat dissipation sheet. [Means for solving the problem]

[0011] The present inventors have discovered that boron nitride agglomerated powder having a tap density and interparticle volume within specific ranges can achieve high thermal conductivity and voltage resistance characteristics when used in a heat dissipation sheet.

[0012] That is, the present invention is summarized as follows.

[0013] [1] A boron nitride agglomerated powder having a tap density of 0.6 g / ml or more but less than 0.8 g / ml and an interparticle void volume of 0.5 ml / g or more.

[0014] [2] The boron nitride agglomerated powder according to [1], wherein the interparticle volume is 0.9 g / ml or less.

[0015] [3] The agglomerated boron nitride powder according to [1] or [2], wherein the average particle size of the agglomerated boron nitride powder is 20 μm or more and 200 μm or less.

[0016] [4] The agglomerated boron nitride powder according to any one of [1] to [3], wherein the BN agglomerated particles contained in the agglomerated boron nitride powder have an intraparticle porosity of 40% or more and 60% or less.

[0017] [5] The agglomerated powder of boron nitride according to any one of [1] to [4], wherein the agglomerated powder of boron nitride has a house-of-cards structure.

[0018] [6] A heat dissipation sheet containing the boron nitride agglomerated powder according to any one of [1] to [5].

[0019] [7] A semiconductor device using the heat dissipation sheet described in [6]. [Effects of the Invention]

[0020] The boron nitride agglomerated powder of the present invention can provide a heat dissipation sheet that is excellent in both thermal conductivity and voltage resistance characteristics. By using a heat dissipation sheet containing the boron nitride agglomerated powder of the present invention, a high-quality, highly reliable power semiconductor module can be realized that has good heat dissipation performance and is excellent in thermal conductivity. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be implemented in various modified forms within the scope of the gist thereof.

[0022] [Boron nitride agglomerated powder] The boron nitride agglomerated powder of the present invention (hereinafter sometimes simply referred to as "the BN agglomerated powder of the present invention") is characterized by a tap density of 0.6 g / ml or more and less than 0.8 g / ml, and an interparticle volume of 0.5 ml / g or more. In the present invention, the boron nitride agglomerated powder refers to a powder that is an aggregation of boron nitride agglomerated particles (hereinafter, sometimes simply referred to as "BN agglomerated particles").

[0023] [mechanism] Although the details of the mechanism by which a heat-dissipating sheet excellent in thermal conductivity and voltage resistance characteristics can be obtained from the BN agglomerated powder of the present invention are not clear, it is presumed as follows.

[0024] When the tap density is less than 0.6 g / ml, the void ratio (volume between particles) between particles in the BN agglomerated powder tends to be large. If the void ratio between particles becomes too large, the probability of areas not being filled with resin increases. When a resin sheet containing BN agglomerated powder is produced and voltage is applied, current leaks in these unfilled areas, deteriorating the voltage resistance. When the tap density is 0.8 g / ml or higher, the void ratio between particles in the BN agglomerated powder becomes small, but if the void ratio between particles becomes too small, it becomes difficult for the resin to fill in. This makes it easy for fine voids to remain within the BN agglomerated powder, and when a resin sheet containing the BN agglomerated powder is made and voltage is applied, current leaks in these unfilled regions, deteriorating the voltage resistance. In the present invention, tap density is related to the growth and growth pattern of the BN primary particles that make up the BN agglomerate particles, and is a concept that also includes the amount of closed pores within the BN agglomerate particles, which cannot be expressed by porosity.

[0025] When a resin sheet containing BN agglomerated powder is produced using BN agglomerated powder with a particle void volume of less than 0.5 ml / g, the resin component becomes too large relative to the particle void volume, making it difficult to remove the voids remaining in the resin. As a result, when a voltage is applied to the resulting resin sheet, current leaks through the voids, resulting in a deterioration in voltage resistance.

[0026] The present invention was achieved by considering tap density as a comprehensive index of physical properties such as porosity, particle size distribution, particle shape, particle strength, primary particle size, and amount of closed pores of BN agglomerated particles, and finding that BN agglomerated powders having a tap density within the very narrow range of 0.6 g / ml or more and less than 0.8 g / ml, and further having an interparticle volume of 0.5 ml / g or more, have excellent thermal conductivity and voltage resistance characteristics when made into heat dissipation sheets.

[0027] The tap density in the present invention is the density of a powder tapped and filled into a measuring container, measured by the method described in the Examples section below. This tap density appears to be related to the porosity of the agglomerated particles described in Patent Documents 1 and 2. However, the tap density varies depending not only on the porosity of the agglomerated particles but also on the particle size distribution, particle shape, particle strength, primary particle size, and the amount of closed pores.

[0028] In the present invention, the interparticle void volume represents, in mercury intrusion measurement, the integrated volume at a division diameter of 2 μm or more of the particle pore diameter, that is, the amount of the gaps formed between particles when the particles are filled. The interparticle void volume is measured by the method shown in the Examples section described later.

[0029] The method for collecting the measurement powder from the BN agglomerated powder is not particularly limited, but it is preferable to collect it after uniformly mixing the powder.

[0030] [BN agglomerated powder] The BN agglomerated powder of the present invention is an aggregate of BN agglomerated particles formed by aggregating BN primary particles, preferably h-BN primary particles. Within a range not impairing the effects of the present invention, the BN agglomerated particles may contain components other than BN primary particles. Examples of components other than h-BN primary particles include components derived from binders, surfactants, and solvents that may be added to the slurry, as described in the [Method for Producing BN Agglomerated Powder] described later.

[0031] <Shape of BN Agglomerated Particles in BN Agglomerated Powder> The shape of the BN agglomerated particles in the BN agglomerated powder of the present invention is not particularly limited. For example, it may be any shape of agglomerated particles that can be produced by aggregating BN primary particles, such as spherical, ellipsoidal, cylindrical, hexagonal columnar, etc.

[0032] Particularly, it is preferable that the BN agglomerated particles have a card house structure in order to obtain high thermal conductivity. The card house structure is described, for example, in Ceramics 43 No.2 (published by the Ceramic Society of Japan in 2008), and is a structure in which plate-like particles are stacked complexly without orientation. More specifically, the BN agglomerated particles having a card house structure are an aggregate of BN primary particles, and are BN agglomerated particles having a structure in which the planar part and the end face part of the BN primary particles are in contact, and are preferably spherical. Also, it is preferable that the card house structure is the same structure inside the particles. The aggregation form and internal structure of these BN agglomerated particles can be confirmed by a scanning electron microscope (SEM).

[0033] <Physical Properties of BN Agglomerated Powder> (tap density) The BN agglomerated powder of the present invention is characterized by having a tap density of 0.6 g / ml or more and less than 0.8 g / ml. If the tap density is outside the range of 0.6 g / ml or more and less than 0.8 g / ml, the object of the present invention of improving the thermal conductivity and voltage resistance characteristics cannot be achieved.

[0034] The tap density of the BN agglomerated powder of the present invention is 0.6 g / ml or more, preferably 0.61 g / ml or more, more preferably 0.63 g / ml or more, and even more preferably 0.65 g / ml or more. It is also less than 0.8 g / ml, preferably 0.79 g / ml or less, and more preferably 0.78 g / ml. It is also 0.6 g / ml or more and less than 0.8 g / ml, preferably 0.61 g / ml to 0.79 g / ml, and more preferably 0.63 to 0.78 g / ml. Having a tap density within the above ranges tends to further improve thermal conductivity and voltage resistance characteristics.

[0035] (particle interstitial volume) The BN agglomerated powder of the present invention is characterized by having an interparticle volume of 0.5 ml / g or more. By ensuring that the interparticle volume is equal to or greater than the lower limit, improvements in thermal conductivity and voltage resistance characteristics can be obtained.

[0036] The interparticle volume of the BN agglomerated powder of the present invention is 0.5 ml / g or more, preferably 0.55 ml / g or more, more preferably 0.58 ml / g or more, and even more preferably 0.6 ml / g or more. It is also preferably 0.9 ml / g or less, more preferably 0.8 ml / g or less. Having an interparticle volume within the above range ensures an appropriate amount of resin between the BN agglomerated particles when formed into a sheet, suppresses voids in the sheet, and tends to further improve thermal conductivity and voltage resistance.

[0037] (Volume average particle diameter (D 50 )) The volume average particle diameter (D 50) is not particularly limited, but is preferably 20 μm or more, more preferably 25 μm or more, even more preferably 26 μm or more, particularly preferably 30 μm or more, and most preferably 40 μm or more. On the other hand, D of the BN agglomerated powder 50 is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less. 50 When D is equal to or greater than the lower limit, the contact resistance between the BN agglomerated particles is suppressed when the heat dissipation sheet is formed, and the thermal conductivity of the BN agglomerated powder itself tends to be increased. 50 When the surface roughness is equal to or less than the upper limit, the surface smoothness of the heat dissipation sheet is improved and the gaps between the BN agglomerated particles are appropriate, which tends to improve the thermal conductivity.

[0038] Here, the volume average particle diameter (D 50 ) means the particle diameter when the cumulative volume is exactly 50% when the cumulative volume of the powder used for measurement is set to 100% and a cumulative curve is drawn. 50 As a wet measurement method, a sample in which BN agglomerated powder is dispersed in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer is measured using a laser diffraction / scattering particle size distribution analyzer, etc. As a dry measurement method, a measurement method using "Morphologi" manufactured by Malvern is exemplified.

[0039] (intraparticle porosity) The intra-particle porosity of the BN agglomerated particles contained in the BN agglomerated powder of the present invention is not particularly limited, but is preferably 40% or more, more preferably 45% or more. Also, it is preferably 60% or less, more preferably 55% or less. When the intra-particle porosity is within the above range, a heat dissipation sheet with excellent voltage resistance tends to be stably produced.

[0040] The intraparticle porosity of BN agglomerated particles is determined by measuring the powder density, total pore volume, and interparticle volume with a mercury porosimeter, subtracting the interparticle volume from the total pore volume to determine the intraparticle pore volume, and the ratio of the intraparticle pore volume to the powder volume (1 / powder density) is taken as the intraparticle porosity.

[0041] (average circularity) The average circularity of the BN agglomerated powder of the present invention is not particularly limited, but is preferably 0.8 or more, and more preferably 0.85 or more. The upper limit of the average circularity is not particularly limited, and may be 1. When the average circularity is in the above range, the interparticle volume falls within an appropriate range, and the effects of the present invention tend to be easily achieved.

[0042] The average circularity of the BN agglomerated powder is determined by dispersing the BN agglomerated powder using a pressure pulse sample dispersion unit, such as a Mohorogi G3S manufactured by Malvern, and analyzing the image.

[0043] (Compression fracture strength) The compressive fracture strength of the BN agglomerated powder of the present invention is not particularly limited, but is preferably 20 MPa or less, more preferably 15 MPa or less, even more preferably 10 MPa or less, and particularly preferably 9 MPa or less. Furthermore, the compressive fracture strength is preferably 1 MPa or more, more preferably 2 MPa or more, and even more preferably 3 MPa or more. With a compressive fracture strength within the above range, the BN agglomerated powder can be appropriately deformed, and when a heat dissipation sheet is produced, the thermal conductivity of the heat dissipation sheet tends to be improved.

[0044] The compressive fracture strength of BN agglomerated powder is measured at room temperature (20-30°C) using a Shimadzu Micro Compression Tester MCT-510 manufactured by Shimadzu Corporation, with a test force of 98 mN, a loading rate of 4.84 mN / sec, and a flat φ100 μm upper pressure indenter. For the measurement, a single BN agglomerated particle with a particle diameter of approximately 50 μm is selected and tested, and this is repeated five times to determine the compressive fracture strength as the average of the five measurements. The compressive fracture strength is calculated using the following formula: Cs=2.48 / πd 2 Cs: Compressive fracture strength (MPa) P: Breaking test force (N) d: Particle diameter (mm)

[0045] (elastic modulus) The elastic modulus of the BN agglomerated powder of the present invention is not particularly limited, but is preferably 40 MPa or more, more preferably 45 MPa or more, and even more preferably 50 MPa or more. The elastic modulus is preferably 100 MPa or less, and more preferably 90 MPa or more. With the elastic modulus in the above range, the BN agglomerated particles can be appropriately deformed, and when a heat-dissipating sheet is produced, the thermal conductivity of the heat-dissipating sheet tends to be improved.

[0046] The elastic modulus of BN agglomerated powder is calculated from the following formula using the test force (N), compression displacement (mm), and particle diameter (mm) obtained from a compression test of BN agglomerated particles (compression test using a Shimadzu micro-compression tester, measured at room temperature (20-30°C)), with reference to Physical Properties Research, Tanaka Yoshimi, 85(4), 499-518, 2006. E=3×(1-ν 2 )×P / 4×(d / 2) 1 / 2 ×Y 3 / 2 ν: Poisson's ratio (Poisson's ratio was set to 0.13) P: Test force (N) d: Particle diameter (mm) Y: Compression displacement (mm)

[0047] [Method of manufacturing BN agglomerated powder] Although there are no limitations on the method for producing the BN agglomerated powder of the present invention, it is particularly preferred to pulverize the raw material boron nitride (hereinafter, together with the pulverized product thereof, may be referred to as "raw BN powder") in a pulverization step, then granulate by agglomeration in a granulation step, and then further pass through a heating step in which heat treatment is performed. More specifically, it is preferred to disperse the raw material BN powder in a medium to form a raw material BN powder slurry (hereinafter, may be referred to as "BN slurry"), then perform a pulverization treatment, and then granulate the obtained slurry into spherical particles, and perform a heat treatment to crystallize the granulated BN powder.

[0048] <Raw material BN powder> Any of the following can be used as the raw BN powder without limitation: commercially available h-BN, commercially available α- and β-BN, BN produced by the reduction-nitridation method of a boron compound and ammonia, BN synthesized from a boron compound and a nitrogen-containing compound such as melamine, etc. h-BN is particularly preferred as the raw BN powder because it more effectively exhibits the effects of the present invention.

[0049] The preferred form of the raw BN powder is powdered BN particles with a wide peak half-width obtained by powder X-ray diffraction measurement and low crystallinity. While plate-shaped h-BN can be used as the raw material, non-plate-shaped nanoparticles are also suitable. As a measure of crystallinity, the peak half-width of the (002) plane obtained by powder X-ray diffraction measurement is typically 0.4° or more, preferably 0.45° or more, and more preferably 0.5° or more, in terms of 2θ angle. Furthermore, the peak half-width of this (002) plane is typically 2.0° or less, preferably 1.5° or less, and more preferably 1° or less. When the peak half-width of the (002) plane is below the upper limit, crystallite growth tends to be facilitated, and productivity tends to be sufficiently improved. When the peak half-width of the (002) plane is above the lower limit, crystallinity falls within an appropriate range, crystal growth is facilitated, and dispersion stability during slurry preparation tends to be improved.

[0050] The method for producing the raw material BN powder is not particularly limited, but examples thereof include the method described in Microstructural development with crystallization of hexagonal boron nitride (TSUYOSHI et al., JOURNAL OF MATERIALS SCIENCE LETTERS 16 (1997) 795-798).

[0051] From the viewpoint of BN crystal growth, it is preferable that a certain amount of oxygen atoms are present in the raw BN powder. In the present invention, the total oxygen concentration in the raw BN powder is preferably 1 wt% or more, more preferably 2 wt% or more, even more preferably 3 wt% or more, particularly preferably 4 wt% or more, and preferably 10 wt% or less, more preferably 9 wt% or less. When the total oxygen concentration is below the upper limit, residual oxygen after heat treatment is suppressed, and the effect of improving thermal conductivity tends to be enhanced. When the total oxygen concentration is above the lower limit, crystal growth tends to be achieved without excessive crystallinity.

[0052] Methods for adjusting the total oxygen concentration of the raw BN powder to fall within the above range include, for example, synthesizing BN at a low temperature of 1500°C or less, or heat-treating the raw BN powder in an oxidizing atmosphere at a low temperature of 500 to 900°C.

[0053] The total oxygen concentration of the raw material BN powder can be measured by the inert gas fusion-infrared absorption method using an oxygen / nitrogen analyzer manufactured by Horiba, Ltd.

[0054] The total pore volume of the raw BN powder is preferably 1.5 cm 3 / g or less. The total pore volume is 1.5 cm 3 When the total pore volume is 0.3 cm3 / g or less, the raw BN powder is dense, and granulation with high sphericity is possible. Although there is no particular lower limit for the total pore volume, it is preferably 0.3 cm3 / g or less. 3 / g or more, more preferably 0.5 cm 3 / g or more.

[0055] The specific surface area of ​​the raw BN powder is preferably 50m 2 / g or more, more preferably 60m 2 / g or more, more preferably 70m 2 / g or more, preferably 1000m 2 / g or less, more preferably 500m 2 / g or less, more preferably 300m 2 / g or less. The specific surface area of ​​the raw BN powder is 50m 2 / g or more, the dispersed particle size in the BN slurry used for spheroidization by granulation can be made small, which is preferable. 2 / g or less is preferable because it is possible to suppress an increase in the viscosity of the slurry.

[0056] The total pore volume of the raw material BN powder can be measured by nitrogen adsorption and mercury intrusion methods. The specific surface area of ​​the raw BN powder can be measured by the BET one-point method (adsorption gas: nitrogen). The nitrogen adsorption method is performed in accordance with JIS Z8830, and the measurement temperature is -196°C (liquid nitrogen temperature). The mercury intrusion method is performed in accordance with JIS R1655, and the surface tension of BN is 485 dyn / cm. 2 The contact angle is 140° and the measurement temperature is 23 to 26°C.

[0057] <medium> The medium used to prepare the BN slurry is not particularly limited, and water and / or various organic solvents can be used. From the viewpoints of ease of spray drying and simplification of the equipment, it is preferable to use water as the medium, and pure water is more preferable.

[0058] The medium used to prepare the BN slurry is preferably added in an amount that gives a BN slurry viscosity of 200 to 5000 mPa·s. The viscosity of the BN slurry refers to the viscosity when the slurry temperature is 10°C or higher and 60°C or lower, and is preferably 15°C or higher and 50°C or lower, more preferably 15°C or higher and 40°C or lower, and even more preferably 15°C or higher and 35°C or lower. Specifically, the amount of medium used in preparing the BN slurry is preferably 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more, relative to the BN slurry, and is preferably 70% by weight or less, more preferably 65% ​​by weight or less, and even more preferably 60% by weight or less. When the amount of medium used is below the above upper limit, the slurry viscosity does not become too low, so sedimentation and the like are suppressed, and the BN slurry tends to be uniform. Therefore, the tap density of the obtained BN agglomerated particles tends to be within the desired range. When the amount of medium used is above the above lower limit, the slurry viscosity does not become excessively high, and granulation tends to be easier.

[0059] <Surfactant> Various surfactants may be added to the BN slurry to adjust the viscosity of the slurry and to improve the dispersion stability (suppression of aggregation) of the raw BN powder in the slurry.

[0060] The surfactant may be an anionic surfactant, a cationic surfactant, a nonionic surfactant, etc. These may be used alone or in combination of two or more.

[0061] Generally, surfactants can change the viscosity of a slurry. Therefore, when adding a surfactant to a BN slurry, the amount is adjusted so that the viscosity of the BN slurry is 200 to 5000 mPa·s. Note that the viscosity of the BN slurry refers to the viscosity within the temperature range described above for the medium used to prepare the BN slurry. For example, when preparing a slurry with a solid content of 50 wt% using BN raw material with a (002) plane peak half-width 2θ of 0.67° as determined by powder X-ray diffraction measurement and a total oxygen concentration of 7.5 wt%, an anionic surfactant is typically added as an active ingredient in an amount of preferably 0.01 wt% or more, more preferably 0.05 wt% or more, even more preferably 0.1 wt% or more, and preferably 10 wt% or less, more preferably 7 wt% or less, even more preferably 5 wt% or less, and particularly preferably 3 wt% or less, based on the total amount of the slurry. By keeping the amount added below the upper limit, a decrease in the slurry viscosity is suppressed and carbon components derived from the surfactant tend to be less likely to remain in the resulting BN agglomerated particles. By keeping the amount added above the lower limit, an excessive increase in the slurry viscosity is suppressed, tending to facilitate granulation.

[0062] <Binder> The BN slurry may contain a binder to effectively granulate the raw BN powder into particles. The binder acts to firmly bind the BN primary particles together and stabilize the granulated particles.

[0063] The binder used in the BN slurry may be any binder capable of enhancing the adhesiveness between BN particles. In the present invention, since the granulated particles are heat-treated after granulation, a binder having heat resistance to the high temperature conditions in this heat-treatment step is preferred.

[0064] As such a binder, metal oxides such as aluminum oxide, magnesium oxide, yttrium oxide, calcium oxide, silicon oxide, boron oxide, cerium oxide, zirconium oxide, titanium oxide, etc. are preferably used. Among these, aluminum oxide and yttrium oxide are preferred from the viewpoints of thermal conductivity and heat resistance as oxides, and the bonding strength for bonding BN particles together. The binder may be a liquid binder such as alumina sol, or may be one that reacts during heat treatment and is converted into other inorganic components. These binders may be used individually or in combination of two or more.

[0065] The binder may or may not be included, and may be 0% by weight with respect to the raw material BN powder in the BN slurry. When the binder is included, the amount used (in the case of a liquid binder, the amount used as the solid content) is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, still more preferably 1.0% by weight or more, preferably 30% by weight or less, more preferably 20% by weight or less, and still more preferably 15% by weight or less with respect to the raw material BN powder in the BN slurry. When the amount of the binder used is below the above upper limit, crystal growth can be obtained, and when used as a filler for improving thermal conductivity, a tendency to obtain an effect of improving thermal conductivity is observed.

[0066] <BN Slurry Preparation Method> The method for preparing the BN slurry is not particularly limited as long as the raw material BN powder, the medium, and further, if necessary, the binder and the surfactant are uniformly dispersed and adjusted to a desired viscosity range. When using the raw material BN powder, the medium, and further, if necessary, the binder and the surfactant, the BN slurry is preferably prepared as follows.

[0067] Weigh a predetermined amount of the raw material BN powder into a resin bottle, and then add a predetermined amount of the binder. Further, after adding a predetermined amount of the surfactant, add zirconia ceramic balls and stir for about 0.5 to 5 hours on a pot mill turntable until the desired viscosity is reached.

[0068] The order of addition is not particularly limited. However, when slurrying a large amount of raw material BN powder, aggregates such as lumps are likely to form. Therefore, after preparing an aqueous solution by adding the surfactant and the binder to water, add a predetermined amount of the raw material BN powder little by little, add zirconia ceramic balls thereto, and disperse and slurry on a pot mill turntable.

[0069] For dispersion, in addition to a pot mill, a dispersing device such as a bead mill or a planetary mixer may be used.

[0070] When forming the slurry, the temperature of the slurry is preferably 10° C. or higher and 60° C. or lower. When the slurry temperature is equal to or higher than the lower limit, an increase in the viscosity of the slurry tends to be suppressed, and when the slurry temperature is equal to or lower than the upper limit, decomposition of the raw material BN powder into ammonia in the slurry tends to be suppressed.

[0071] The temperature of the slurry is more preferably 15°C or higher and 50°C or lower, even more preferably 15°C or higher and 40°C or lower, and particularly preferably 15°C or higher and 35°C or lower.

[0072] <Granulation> To obtain granulated powder from the BN slurry, a general granulation method such as spray drying, tumbling, fluidized bed, stirring, etc. can be used, of which spray drying is preferred.

[0073] In the spray drying method, it is possible to produce granulated powder of a desired size by adjusting the concentration of the raw material slurry, the amount of liquid fed into the device per unit time, and the compressed air pressure and amount of compressed air used to spray the fed slurry. The spray drying method also makes it possible to obtain spherical granulated powder.

[0074] There are no restrictions on the spray drying equipment that can be used, but to produce larger spherical granulated powder, a rotary disk type is optimal. Examples of such equipment include the F Series spray dryer manufactured by Okawara Kakoki Co., Ltd., the MDL-050M spray dryer manufactured by Fujisaki Electric Co., Ltd., and the PRIS spray dryer P260.

[0075] The average particle size of the granulated powder obtained by granulation is the volume-based average particle size D of the BN agglomerated powder of the present invention. 50 When the range is 20 μm or more and 200 μm or less, the volume-based average particle diameter D 50 It is preferably 10 μm or more, more preferably 15 μm or more, and preferably 150 μm or less, more preferably 100 μm or less. Average particle size D of granulated powder by volume50 can be measured using, for example, a wet method such as "LA920" manufactured by Horiba Ltd., or a dry method such as "Morphorogi" manufactured by Malvern.

[0076] <Heat treatment> The above-mentioned BN granulated powder can be further heat-treated in a non-oxidizing gas atmosphere to produce BN agglomerated powder.

[0077] The non-oxidizing gas atmosphere includes nitrogen gas, helium gas, argon gas, ammonia gas, hydrogen gas, methane gas, propane gas, carbon monoxide gas, etc. The crystallization speed of the BN agglomerated particles varies depending on the type of atmospheric gas used. In order to perform crystallization in a short time, nitrogen gas or a mixed gas containing nitrogen gas and other gases is particularly suitable.

[0078] The heat treatment temperature is preferably 1600°C or higher, more preferably 1800°C or higher, and preferably 2300°C or lower, more preferably 2200°C or lower. When the heat treatment temperature is above the lower limit, sufficient growth of the average crystallites of the BN primary particles is obtained, and the thermal conductivity of the BN agglomerated powder tends to increase. When the heat treatment temperature is below the upper limit, decomposition of the BN agglomerated powder tends to be suppressed.

[0079] The heat treatment time is preferably 5 hours or more and 20 hours or less, more preferably 5 hours or more and 15 hours or less. When the heat treatment time is equal to or more than the lower limit, sufficient crystal growth can be obtained. When the heat treatment time is equal to or less than the upper limit, decomposition of BN tends to be suppressed.

[0080] Since the heat treatment is carried out in a non-oxidizing gas atmosphere, it is preferable that the inside of the calcination furnace is evacuated using a vacuum pump, and then the temperature is raised to the desired temperature while introducing a non-oxidizing gas. If the atmosphere inside the calcination furnace can be sufficiently replaced with a non-oxidizing gas, the temperature may be raised by heating while introducing a non-oxidizing gas under normal pressure. Examples of calcination furnaces include batch furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces, and continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces, and these are used depending on the purpose.

[0081] Typically, the granulated powder to be heat-treated is placed in a circular graphite crucible with a lid and heated and sintered to reduce non-uniformity in the composition during sintering. In addition to reducing non-uniformity in the composition, graphite dividers may be inserted to prevent sintering of BN agglomerates during sintering. The number of divisions by the dividers is not particularly limited as long as sintering is suppressed, but is typically between 2 and 16. When the number of divisions is above the upper limit, sintering is suppressed and the crystals of the h-BN primary particles tend to grow sufficiently. When the number of divisions is above the lower limit, the progress of sintering tends to be suppressed.

[0082] <Classification> The BN agglomerated powder after the heat treatment is preferably classified to narrow the particle size distribution and suppress an increase in viscosity when blended into a BN agglomerated powder-containing resin composition. This classification is usually performed after the heat treatment of the granulated powder, but it may also be performed on the granulated powder before the heat treatment and then subjected to the heat treatment.

[0083] The classification may be either wet or dry, but dry classification is preferred from the viewpoint of suppressing the decomposition of BN, especially when the binder is water-soluble.

[0084] Dry classification includes sieving and air classification, which classifies particles based on the difference between centrifugal force and fluid drag. Dry classification can also be performed using a classifier such as a swirling air classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier. These classifiers can be used appropriately depending on the particle size of the particles to be classified, such as using a swirling air classifier to classify small particles in the submicron to single micron range, and using a semi-free vortex centrifugal classifier to classify larger particles.

[0085] <Mechanism for obtaining the BN agglomerated powder of the present invention> There are no particular limitations on the method for producing the BN agglomerated powder of the present invention having a tap density of 0.6 g / ml or more and less than 0.8 g / ml and an interparticle volume of 0.5 ml / g or more, but the following methods can be mentioned.

[0086] A method for obtaining the BN agglomerated powder of the present invention includes, after heat treatment, separating and collecting the heat-treated powder from the inner portion separated from the inner wall surface of the crucible, rather than from the inner wall surface side of the crucible.

[0087] The vicinity of the inner wall surface of the crucible tends to be significantly affected by the crucible material and the furnace material, and therefore the tap density tends to exceed the range specified in the present invention, resulting in large BN agglomerated particles. On the other hand, the inside of the crucible (the region away from the inner wall of the crucible) tends to be less affected by the crucible material and the heating furnace material, and therefore, BN agglomerates with a tap density within the range specified in the present invention tend to be obtained from the vicinity of the center of the crucible.

[0088] The tap density and interparticle volume of the BN agglomerated powder vary depending on the growth of the BN primary particles and the shape of the BN agglomerated particles, but the growth of the BN primary particles and the shape of the BN agglomerated particles vary depending on the oxygen concentration contained in the BN raw material. Therefore, by performing a heat treatment while controlling the oxygen concentration, the tap density and interparticle volume can be adjusted to fall within the specified ranges of the present invention. Specific examples include heating in the presence of carbon as a reducing agent and adjusting the oxygen concentration under reduced pressure. Further, other methods for controlling the oxygen concentration include a method in which multiple heat treatment steps are performed, in which the material is held in the crystal growth temperature range of the BN primary particles for a long period of time, and then heat treated at a temperature higher than the crystal growth temperature range.

[0089] The above methods may be used alone or in combination.

[0090] [BN agglomerated powder-containing resin composition] To produce the heat dissipation sheet of the present invention containing the BN agglomerated powder of the present invention, a resin composition containing at least the BN agglomerated powder of the present invention as an inorganic filler and a resin (hereinafter sometimes referred to as the "BN agglomerated powder-containing composition of the present invention" or the "composition of the present invention") is usually prepared, and the prepared composition of the present invention is molded into a sheet to produce the heat dissipation sheet of the present invention. The BN agglomerated powder-containing composition of the present invention will be described below.

[0091] The resin composition containing the BN agglomerated powder of the present invention is generally composed of a resin component, preferably a thermosetting resin component, an inorganic filler containing the BN agglomerated powder of the present invention, a curing agent, a curing catalyst, other components used as needed, a solvent for preparing a coating slurry, etc. When forming a composite molded article as described below, the composition of the present invention preferably further contains a compound having a heterocyclic structure containing a nitrogen atom, from the viewpoint of improving adhesion to metals.

[0092] [Ingredients other than inorganic fillers] <Thermosetting resin component> The thermosetting resin contained in the composition of the present invention is not particularly limited as long as it cures in the presence of a curing agent or curing catalyst. Specific examples of thermosetting resins include epoxy resins, phenolic resins, polycarbonate resins, unsaturated polyester resins, urethane resins, melamine resins, and urea resins. Among these, epoxy resins are preferred from the viewpoints of viscosity, heat resistance, moisture absorption, and ease of handling. Examples of epoxy resins include epoxy group-containing silicon compounds, aliphatic epoxy resins, bisphenol A or F epoxy resins, novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, multifunctional epoxy resins, and polymeric epoxy resins.

[0093] (epoxy resin) Epoxy resin is a general term for compounds that have one or more oxirane rings (epoxy groups) in the molecule. The oxirane ring (epoxy group) contained in the epoxy resin may be either an alicyclic epoxy group or a glycidyl group, but from the viewpoint of reaction rate or heat resistance, a glycidyl group is more preferable.

[0094] The epoxy resin used in the present invention may be an aromatic oxirane ring (epoxy group)-containing compound. Specific examples thereof include bisphenol-type epoxy resins obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy resins; epoxy resins obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; and novolac-type epoxy resins obtained by glycidylating novolacs such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac.

[0095] The following describes epoxy resins suitable for use in the present invention (hereinafter, sometimes referred to as "specific epoxy resins") and polyfunctional epoxy resins that are preferably used in combination with these specific epoxy resins.

[0096] Hereinafter, the term "organic group" includes any group containing carbon atoms, such as alkyl groups, alkenyl groups, and aryl groups, which may be substituted with halogen atoms, groups containing heteroatoms, or other hydrocarbon groups.

[0097] (Specific epoxy resin) The specific epoxy resin includes an epoxy resin having at least one structure selected from the structure represented by the following structural formula (1) (hereinafter, sometimes referred to as "Structure (1)") and the structure represented by the following structural formula (2) (hereinafter, sometimes referred to as "Structure (2)").

[0098] [ka]

[0099] In formula (1), R 1 and R 2 Each of R represents an organic group, and at least one of them is an organic group having a molecular weight of 16 or more. 3 represents a divalent cyclic organic group.

[0100] Furthermore, the specific epoxy resin may be an epoxy resin having a structure represented by the following structural formula (3) (hereinafter, sometimes referred to as "structure (3)").

[0101] [ka]

[0102] In formula (3), R 4 , R 5 , R 6 , R 7 represents an organic group with a molecular weight of 15 or more.

[0103] In the above formula (1), R 1 and R 2 At least one of R represents an organic group having a molecular weight of 16 or more, preferably a molecular weight of 16 to 1000. Examples of organic groups having a molecular weight of 16 or more include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl groups. 1 and R 2 may both be organic groups with a molecular weight of 16 or more, or one may be an organic group with a molecular weight of 16 or more and the other may be an organic group with a molecular weight of 15 or less or a hydrogen atom. 1 and R 2 One of the groups is an organic group having a molecular weight of 16 or more, and the other is an organic group having a molecular weight of 15 or less. 1 and R 2It is preferable that one of the groups is a methyl group and the other is a phenyl group, since this makes it easier to control the handling properties such as the viscosity of the resin, and from the viewpoint of the strength of the cured product.

[0104] In equation (2), R 3 is a divalent cyclic organic group, and may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. These may also independently have a substituent such as a hydrocarbon group or a halogen atom. The divalent bonding moiety may be a divalent group on a single carbon atom, or may be a divalent group on different carbon atoms. Preferred examples include divalent aromatic groups having 6 to 100 carbon atoms, and groups derived from cycloalkanes having 2 to 100 carbon atoms, such as cyclopropane and cyclohexane. R 3 In particular, a 3,3,5-trimethyl-1,1-cyclohexylene group represented by the following structural formula (4) is preferred from the viewpoint of controlling the handleability of the resin such as viscosity and the strength of the cured product.

[0105] [ka]

[0106] In equation (3), R 4 , R 5 , R 6 , R 7 are each an organic group having a molecular weight of 15 or more, and are preferably alkyl groups having a molecular weight of 15 to 1000. 4 , R 5 , R 6 , R 7 It is preferable that all of the groups be methyl groups from the viewpoint of controlling the handling properties such as the viscosity of the resin and the strength of the cured product.

[0107] The specific epoxy resin is preferably an epoxy resin containing either one of Structure (1) and Structure (2) and Structure (3), from the viewpoint of achieving both reduced moisture absorption and strength retention in the resulting cured heat dissipation sheet.

[0108] Compared to typical epoxy resins with bisphenol A or bisphenol F skeletons, these specific epoxy resins contain a large amount of hydrophobic hydrocarbon and aromatic structures, and therefore by blending the specific epoxy resins, it is possible to reduce the moisture absorption of the resulting cured heat dissipation sheet.

[0109] From the viewpoint of reducing moisture absorption, the specific epoxy resin preferably contains a large amount of structures (1), (2), and (3), which are hydrophobic structures. Specifically, the specific epoxy resin preferably has a weight-average molecular weight of 10,000 or more, more preferably has a weight-average molecular weight of 20,000 or more, and even more preferably has a weight-average molecular weight of 30,000 or more, for example, 30,000 to 40,000.

[0110] The specific epoxy resin is preferably more hydrophobic, and specifically, the epoxy equivalent of the specific epoxy component is preferably larger, more preferably 5,000 g / equivalent or more, and more preferably 7,000 g / equivalent or more, for example, 8,000 to 15,000 g / equivalent.

[0111] Here, the weight average molecular weight of the epoxy resin is a value calculated as polystyrene measured by gel permeation chromatography. The epoxy equivalent is defined as "the weight of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.

[0112] Such specific epoxy resins may be used alone or in combination of two or more.

[0113] (multifunctional epoxy resin) A multifunctional epoxy resin is an epoxy resin that has three or more oxirane rings (epoxy groups) per molecule.

[0114] From the viewpoint of increasing the storage modulus of the cured product after thermal curing, particularly the storage modulus at high temperatures, which is important in cases where a large amount of heat is generated, such as in power semiconductors, epoxy resins having two or more oxirane rings (epoxy groups) in the molecule are preferred, epoxy resins having three or more oxirane rings (epoxy groups) in the molecule are more preferred, and epoxy resins having four or more glycidyl groups in the molecule are even more preferred.

[0115] The presence of multiple oxirane rings (epoxy groups), especially glycidyl groups, in the molecule improves the crosslink density of the cured product, resulting in a stronger cured heat-dissipating sheet. As a result, when internal stress is generated in the heat-dissipating sheet during a moisture absorption reflow test, the heat-dissipating sheet retains its shape without deforming or breaking, thereby preventing the formation of voids or other gaps within the heat-dissipating sheet.

[0116] From the viewpoint of increasing the storage modulus of the heat-dissipating sheet after thermal curing, the molecular weight of the polyfunctional epoxy resin is preferably 1,000 or less, and particularly preferably 100 to 800.

[0117] The addition of a multifunctional epoxy resin makes it possible to introduce a high density of highly polar oxirane rings (epoxy groups), which increases the effects of physical interactions such as van der Waals forces and hydrogen bonds, improving adhesion between the metal in the composite molded body described below and the heat-dissipating sheet of the present invention, which is the cured resin. The addition of a multifunctional epoxy resin also increases the storage modulus of the heat-dissipating sheet after thermal curing, which allows the cured thermosetting resin composition to penetrate into the irregularities of the metal to be adhered, thereby exerting a strong anchoring effect and improving adhesion between the metal and the heat-dissipating sheet.

[0118] On the other hand, the introduction of a multifunctional epoxy resin tends to increase the moisture absorption of the thermosetting resin composition, but by improving the reactivity of the oxirane ring (epoxy group), the amount of hydroxyl groups during the reaction can be reduced, thereby suppressing the increase in moisture absorption. Furthermore, by combining the above-mentioned specific epoxy resin with a multifunctional epoxy resin to produce a thermosetting resin composition, it is possible to achieve both high elasticity and low moisture absorption in the resulting heat dissipation sheet.

[0119] Specifically, the polyfunctional epoxy resin is preferably an epoxy resin having three or more epoxy groups, and for example, EX321L, DLC301, DLC402, etc. manufactured by Nagase ChemteX Corporation can be used. These polyfunctional epoxy resins may be used alone or in combination of two or more.

[0120] (Content) The composition of the present invention preferably contains a thermosetting resin component in an amount of 5% by weight or more, particularly 50% by weight or more, and 99% by weight or less, particularly 98% by weight or less, based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. When the content of the thermosetting resin component is above the above-mentioned lower limit, moldability is improved. When the content of the curable resin component is below the above-mentioned upper limit, the content of other components can be ensured, and thermal conductivity can be improved.

[0121] The composition of the present invention preferably contains 20 to 100% by weight, particularly 45 to 100% by weight, of an epoxy resin in the thermosetting resin component.

[0122] The composition of the present invention preferably contains the specific epoxy resin, which is the aforementioned preferred epoxy resin, in an amount of 50% by weight or less, particularly 40% by weight or less, and 5% by weight or more, particularly 10% by weight or more, based on the total epoxy resin content. When the content of the specific epoxy resin is above the above-mentioned lower limit, the aforementioned effects of containing the specific epoxy resin can be effectively obtained. If the content of the specific epoxy resin is too high, the crosslink density decreases and the cured product becomes brittle. By keeping the content of the specific epoxy resin below the above-mentioned upper limit, it is possible to suppress the moisture absorption of the cured product and improve the strength performance of the cured product, thereby achieving both of these performances.

[0123] The composition of the present invention preferably contains 5 wt% or more, particularly 10 wt% or more, and 50 wt% or less, particularly 40 wt% or less, of the polyfunctional epoxy resin, which is the aforementioned preferred epoxy resin, based on the total epoxy resin content. When the content of the polyfunctional epoxy resin is equal to or greater than the above-mentioned lower limit, the aforementioned effects of containing the polyfunctional epoxy resin can be effectively obtained. When the content of the polyfunctional epoxy resin is equal to or less than the above-mentioned upper limit, the moisture absorption of the cured product can be suppressed and the strength performance of the cured product can be improved, thereby achieving both of these performances.

[0124] The composition of the present invention preferably contains both a specific epoxy resin and a polyfunctional epoxy resin as epoxy resins, in order to obtain a cured product with high elasticity and low moisture absorption. In this case, the content ratio of the specific epoxy resin to the polyfunctional epoxy resin is preferably specific epoxy resin:polyfunctional epoxy resin = 10-90:90-10, particularly 20-80:80-20 (weight ratio).

[0125] The epoxy resin other than the specific epoxy resin and the polyfunctional epoxy resin contained in the composition of the present invention is not particularly limited, but is preferably one or more selected from the group consisting of various bisphenol-type epoxy resins obtained by glycidylating bisphenols, such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; various biphenyl-type epoxy resins obtained by glycidylating biphenyls; epoxy resins obtained by glycidylating aromatic compounds having two hydroxyl groups, such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy resins obtained by glycidylating trisphenols, such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy resins obtained by glycidylating tetrakisphenols, such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy resins obtained by glycidylating novolacs, such as phenol novolac, cresol novolac, bisphenol A novolac, and brominated bisphenol A novolac; and silicone-containing epoxy resins.

[0126] <Compounds having a heterocyclic structure containing a nitrogen atom> A compound having a heterocyclic structure containing a nitrogen atom (hereinafter, may be referred to as a "nitrogen-containing heterocyclic compound") exhibits the effect of improving the adhesion between a cured product of the composition of the present invention and metal. When the composition of the present invention is composited with a metal, the nitrogen-containing heterocyclic compound is located at the interface between the two, thereby improving the adhesion between the composition of the present invention and the metal. From this perspective, a low molecular weight is preferable so that the nitrogen-containing heterocyclic compound can easily reside at the interface between the composition of the present invention and the metal. The molecular weight of the nitrogen-containing heterocyclic compound is preferably 1,000 or less, more preferably 500 or less.

[0127] Examples of the heterocyclic structure of the nitrogen-containing heterocyclic compound include structures derived from imidazole, triazine, triazole, pyrimidine, pyrazine, pyridine, and azole. From the viewpoint of improving the insulating properties of the thermosetting resin composition and adhesion to metals, imidazole-based compounds and triazine-based compounds are preferred.

[0128] Preferable imidazole compounds and triazine compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, 2,4-diamino-6-methacryloyloxyethyl-s-triazine isocyanuric acid adduct, and the like.

[0129] Among these, those having a structure derived from imidazole or triazine are particularly preferred, since their high resin compatibility and high reaction activation temperature make it possible to easily adjust the curing rate and post-curing physical properties, thereby improving the storage stability of the composition of the present invention and further improving the adhesive strength after heat molding. As the heterocyclic structure of the nitrogen-containing heterocyclic compound, a structure derived from 1,3,5-triazine is particularly preferred. The nitrogen-containing heterocyclic compound may have a plurality of the structural moieties exemplified above.

[0130] The nitrogen-containing heterocyclic compound may contain a curing catalyst, which will be described later, depending on the structure. Therefore, the composition of the present invention may contain a nitrogen-containing heterocyclic compound as a curing catalyst.

[0131] The nitrogen-containing heterocyclic compound may be used alone or in combination of two or more kinds. The nitrogen-containing heterocyclic compound may simultaneously have a plurality of heterocyclic structures in one molecule.

[0132] The nitrogen-containing heterocyclic compound is preferably contained in an amount of 0.001 wt% or more, particularly 0.1 wt% or more, and 10 wt% or less, particularly 5 wt% or less, based on 100 wt% of the composition of the present invention excluding the solvent and inorganic filler. When a curing catalyst, as described below, is contained in the nitrogen-containing heterocyclic compound due to its molecular structure, the total amount, including the content thereof, is preferably within the above range. When the content of the nitrogen-containing heterocyclic compound is above the above lower limit, the above-mentioned effects of containing this compound can be fully obtained. When the content of the nitrogen-containing heterocyclic compound is below the above upper limit, the reaction proceeds effectively, improving crosslink density, increasing strength, and further improving storage stability.

[0133] <Curing agent> The curing agent is not particularly limited, but preferred curing agents are phenolic resins, acid anhydrides having an aromatic or alicyclic skeleton, or hydrides of such acid anhydrides or modified products of such acid anhydrides. By using these preferred curing agents, a cured resin having an excellent balance of heat resistance, moisture resistance, and electrical properties can be obtained. Only one type of curing agent may be used, or two or more types may be used in combination.

[0134] The phenolic resin is not particularly limited. Specific examples of the phenolic resin include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane. Among these, novolac-type phenolic resins with a rigid main chain skeleton and phenolic resins with a triazine skeleton are preferred for further improving the flexibility and flame retardancy of the thermosetting resin composition and the mechanical properties and heat resistance of the cured resin. Phenolic resins with allyl groups are preferred for improving the flexibility of the uncured thermosetting resin composition and the toughness of the cured resin.

[0135] Commercially available phenolic resins include MEH-8005, MEH-8000H, and NEH-8015 (all manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751, LA-1356, and LA-3018-50P (all manufactured by Dainippon Ink Co., Ltd.), and PSM6200, PS6313, and PS6492 (manufactured by Gun-ei Chemical Industry Co., Ltd.).

[0136] The acid anhydride having an aromatic skeleton, the water-added product of the acid anhydride, or the modified product of the acid anhydride is not particularly limited. Specific examples include SMA Resin EF30 and SMA Resin EF60 (both manufactured by Sartomer Japan), ODPA-M and PEPA (both manufactured by Manac), Ricadit MTA-10, Ricadit TMTA, Ricadit TMEG-200, Ricadit TMEG-500, Ricadit TMEG-S, Ricadit TH, Ricadit MH-700, Ricadit MT-500, Ricadit DSDA, and Ricadit TDA-100 (all manufactured by New Japan Chemical Co., Ltd.), EPICLON B4400, and EPICLON B570 (all manufactured by Dainippon Ink and Chemicals Co., Ltd.).

[0137] The acid anhydride having an alicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride is preferably an acid anhydride having a polyalicyclic skeleton, the hydration product of the acid anhydride, or the modified product of the acid anhydride, or an acid anhydride having an alicyclic skeleton obtained by the addition reaction of a terpene compound with maleic anhydride, the hydration product of the acid anhydride, or the modified product of the acid anhydride.Specific examples include Ricadit HNA and Ricadit HNA-100 (both manufactured by New Japan Chemical Co., Ltd.), and Epicure YH306 and Epicure YH309 (both manufactured by Mitsubishi Chemical Corporation).

[0138] The curing agent is preferably contained in an amount of 0 to 70% by weight, particularly 0 to 55% by weight, based on 100% by weight of the composition of the present invention excluding the solvent and inorganic filler. When the content of the curing agent is equal to or greater than the lower limit, sufficient curing performance can be obtained. When the content of the curing agent is equal to or less than the upper limit, the reaction proceeds effectively, improving the crosslink density, increasing strength, and further improving film formability.

[0139] <Curing catalyst> The composition of the present invention preferably contains a curing catalyst together with the above curing agent in order to adjust the curing rate and the physical properties of the cured product.

[0140] The curing catalyst is not particularly limited, but is appropriately selected depending on the type of thermosetting resin component and curing agent used. Specific examples of the curing catalyst include linear or cyclic tertiary amines, organophosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, etc. Organometallic compounds, quaternary ammonium salts, metal halides, etc. can also be used as the curing catalyst. Examples of the organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complex. These may be used alone or in combination of two or more.

[0141] The curing catalyst is preferably contained in an amount of 0.1 to 10 wt %, particularly 0.1 to 5 wt %, based on 100 wt % of the composition of the present invention, excluding the solvent and inorganic filler. When the content of the curing catalyst is equal to or greater than the lower limit, the progress of the curing reaction can be sufficiently promoted, resulting in good curing. When the content of the curing catalyst is equal to or less than the upper limit, the curing rate is not too fast, and therefore the storage stability of the composition of the present invention can be improved.

[0142] <Other ingredients> The composition of the present invention may contain other components in addition to the inorganic filler as long as the effects of the present invention are not impaired. Examples of other components include a surface treatment agent such as a silane coupling agent that improves the interfacial adhesive strength between the inorganic filler and the resin component when producing a cured resin product using the composition of the present invention, an insulating carbon component such as a reducing agent, a viscosity modifier, a dispersant, a thixotropy-imparting agent, a flame retardant, a colorant, an organic filler, an organic solvent, and a thermoplastic resin.

[0143] Among these, the composition of the present invention contains a dispersant, which makes it possible to form a uniform cured resin product, and may improve the thermal conductivity and dielectric breakdown characteristics of the obtained cured resin product. Furthermore, the composition of the present invention contains an organic filler and a thermoplastic resin, which may impart appropriate elongation to the composition, relieve generated stress, and suppress the occurrence of cracks in a temperature cycle test.

[0144] The dispersant preferably has a functional group containing a hydrogen atom capable of hydrogen bonding. By having the dispersant have a functional group containing a hydrogen atom capable of hydrogen bonding, the thermal conductivity and dielectric breakdown characteristics of the resulting cured heat dissipation sheet can be further improved. Examples of the functional group containing a hydrogen atom capable of hydrogen bonding include a carboxyl group (pKa=4), a phosphate group (pKa=7), and a phenol group (pKa=10).

[0145] The pKa of the functional group containing a hydrogen atom capable of hydrogen bonding is preferably in the range of 2 to 10, more preferably in the range of 3 to 9. A pKa of 2 or more ensures that the acidity of the dispersant falls within an appropriate range, which may facilitate the suppression of the reaction of the epoxy resin in the thermosetting resin component. Therefore, when an uncured molded product is stored, the storage stability tends to be improved. A pKa of 10 or less tends to adequately function as a dispersant, and the thermal conductivity and dielectric breakdown characteristics of the resulting cured heat dissipation sheet tend to be sufficiently improved.

[0146] The functional group containing a hydrogen atom capable of forming a hydrogen bond is preferably a carboxyl group or a phosphate group, which can further improve the thermal conductivity and dielectric breakdown characteristics of the heat dissipation sheet.

[0147] Specific examples of dispersants include polyester-based carboxylic acids, polyether-based carboxylic acids, polyacrylic-based carboxylic acids, aliphatic carboxylic acids, polysiloxane-based carboxylic acids, polyester-based phosphoric acids, polyether-based phosphoric acids, polyacrylic-based phosphoric acids, aliphatic phosphoric acids, polysiloxane-based phosphoric acids, polyester-based phenols, polyether-based phenols, polyacrylic-based phenols, polysiloxane-based phenols, etc. Only one type of dispersant may be used, or two or more types may be used in combination.

[0148] Any commonly known thermoplastic resin can be used as the thermoplastic resin, including, for example, vinyl polymers such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, (meth)acrylic resin, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer, polyesters such as polylactic acid resin, polyethylene terephthalate, and polybutylene terephthalate, polyamides such as nylon and polyamidoamine, polyvinyl acetal resins such as polyvinyl acetoacetal, polyvinyl benzal, and polyvinyl butyral resin, ionomer resin, polyphenylene ether, polyphenylene sulfide, polycarbonate, polyether ether ketone, polyacetal, ABS resin, LCP (liquid crystal polymer), fluororesin, urethane resin, silicone resin, various elastomers, and modified products of these resins.

[0149] These thermoplastic resins may be uniform in the resin phase of the heat-dissipating sheet, or may be phase-separated and have a recognizable shape. If the thermoplastic resin undergoes phase separation, it may be particulate or fibrous in shape in the heat-dissipating sheet. If the shape of the thermoplastic resin is recognizable in the heat-dissipating sheet, the thermoplastic resin may be recognized as an organic filler. However, in the present invention, organic fillers refer to natural products such as wood flour, cellulose which may be modified, starch, various organic pigments, etc., and thermoplastic resins are not included in the organic fillers.

[0150] The inclusion of a thermoplastic resin or an organic filler may impart appropriate elongation to the composition, alleviate the stress that occurs, and suppress the occurrence of cracks during a temperature cycle test.

[0151] When the thermoplastic resin or organic filler is insoluble in the thermosetting resin, the viscosity of the composition of the present invention is prevented from increasing, and the smoothness of the sheet surface can be improved, for example, when the composition is molded into a sheet as described below. In this case, by simultaneously mixing a thermoplastic resin and an organic filler that are insoluble in the thermosetting resin with a large amount of inorganic filler, the thermoplastic component phase that improves elongation can be efficiently dispersed in the cured product, making it easy to relieve stress. Therefore, the occurrence of cracks in the cured product can be suppressed without reducing the elastic modulus of the cured product. For these reasons, polyamide resins such as nylon, cellulose resins, etc. are preferred as the thermoplastic resin, and polyamide resins such as nylon are particularly preferred.

[0152] When the thermoplastic resin observed in the heat dissipation sheet as a cured product is in the form of particles, the upper limit of the average particle size is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By keeping the average particle size below the upper limit, it is possible to produce sheet-shaped cured products of various thicknesses without risking a decrease in thermal conductivity. The average particle size of the particulate thermoplastic resin is determined by observing the cross section of the cured product and averaging the longest diameters of any 20 particles.

[0153] The composition of the present invention may contain an organic solvent, for example, to improve the coatability when the composition is subjected to a coating step to form a sheet-like cured product.

[0154] Examples of organic solvents that may be contained in the composition of the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.

[0155] When the composition of the present invention contains an organic solvent, the content thereof is appropriately determined depending on the handleability during the production of the heat-dissipating sheet, etc. Usually, the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the composition of the present invention is 10% by weight or more, particularly 40% by weight or more, and 90% by weight or less, particularly 80% by weight or less.

[0156] [Inorganic filler] The composition of the present invention contains at least the BN agglomerated powder of the present invention as an inorganic filler.

[0157] The composition of the present invention may contain an inorganic filler other than the BN agglomerated powder of the present invention. In this case, a spherical filler is preferred as the inorganic filler other than the BN agglomerated powder of the present invention.

[0158] The spherical filler used together with the BN agglomerated powder of the present invention preferably has a thermal conductivity of 10 W / m·K or more, more preferably 15 W / m·K or more, and even more preferably 20 W / m·K or more. The spherical filler used together with the BN agglomerated powder of the present invention preferably has a modified Mohs hardness of 3.1 or more, more preferably 5 or more. In particular, the spherical filler used together with the BN agglomerated powder of the present invention preferably has a thermal conductivity of 20 to 30 W / m·K and a modified Mohs hardness of 5 to 10. By using such a spherical filler in combination with the BN agglomerated powder of the present invention, the adhesive strength to metal and heat dissipation properties of the resulting heat dissipation sheet can be improved.

[0159] Here, "spherical" means anything that is generally recognized as spherical; for example, an average circularity of 0.4 or more may be considered spherical, or an average circularity of 0.6 or more may be considered spherical. The upper limit of the average circularity is usually 1. The circularity can be measured by image processing the projected image. The circularity can be measured, for example, using an FPIA series from Sysmex Corporation.

[0160] The spherical filler is preferably at least one selected from the group consisting of alumina, synthetic magnesite, crystalline silica, aluminum nitride, silicon nitride, silicon carbide, zinc oxide, and magnesium oxide. Use of these preferred spherical fillers can further improve the heat dissipation properties of the resulting heat dissipation sheet.

[0161] The average particle size of the spherical filler is preferably in the range of 0.5 μm or more and 40 μm or less. An average particle size of 0.5 μm or more allows the resin and filler to flow easily during heat molding, which is thought to increase the interfacial adhesive strength of the heat dissipation sheet. An average particle size of 40 μm or less makes it easier to maintain the dielectric breakdown characteristics of the heat dissipation sheet.

[0162] Other inorganic fillers that can be used include electrically insulating fillers, such as at least one type of particles selected from the group consisting of carbon, metal carbides, metal oxides, and metal nitrides. Examples of carbon include diamond. Examples of metal carbides include silicon carbide, titanium carbide, and tungsten carbide. Examples of metal oxides include magnesium oxide, aluminum oxide, silicon oxide, calcium oxide, zinc oxide, yttrium oxide, zirconium oxide, cerium oxide, ytterbium oxide, and sialon (ceramics composed of silicon, aluminum, oxygen, and nitrogen). Examples of metal nitrides include boron nitride, aluminum nitride, and silicon nitride, other than the BN agglomerated particles of the present invention.

[0163] There is no limitation on the shape of the other inorganic fillers, and they may be in the form of particles, whiskers, fibers, plates, or aggregates thereof.

[0164] These inorganic fillers may be surface-treated with a surface treatment agent, and known surface treatment agents can be used as the surface treatment agent.

[0165] These inorganic fillers may be used singly or as a mixture of two or more kinds in any combination and ratio.

[0166] The content of the inorganic filler in the composition of the present invention is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more, based on 100% by weight of the composition of the present invention excluding the solvent, and the content of the inorganic filler is preferably 99% by weight or less, more preferably 90% by weight or less, and even more preferably 80% by weight or less. When the content of the inorganic filler is equal to or greater than the lower limit, the effect of improving thermal conductivity and the effect of controlling the linear expansion coefficient due to the inclusion of the inorganic filler can be sufficiently obtained. When the content of the inorganic filler is equal to or less than the upper limit, the formability of the cured product and the interfacial adhesion of the composite molded product described below tend to be obtained.

[0167] When the BN agglomerated powder of the present invention and a spherical filler such as alumina are used in combination as the inorganic filler, the content ratio of the BN agglomerated powder of the present invention to the spherical filler in the composition of the present invention is not particularly limited, but is preferably 90:10 to 10:90 by weight, and more preferably 80:20 to 20:80.

[0168] In order to effectively obtain the effects of using the BN agglomerated powder of the present invention, it is preferable that 30% by weight or more, particularly 40% by weight or more of the inorganic filler used is the BN agglomerated powder of the present invention. In the present invention, it is preferable to use only the BN agglomerated powder of the present invention, or only the BN agglomerated powder of the present invention and the above-mentioned spherical filler, as the inorganic filler.

[0169] <Method of producing the composition of the present invention> The composition of the present invention can be obtained by uniformly mixing an inorganic filler containing the BN agglomerated powder of the present invention, a resin component such as a thermosetting resin, and other components added as needed by stirring or kneading. A general kneading device such as a mixer, kneader, or single- or twin-screw kneader can be used for mixing. Heating may be applied during mixing, if necessary.

[0170] The order of mixing the various components may also be arbitrary as long as there are no particular problems, such as the occurrence of reactions or precipitates. For example, a method may be used in which a thermosetting resin component is mixed and dissolved in an organic solvent (e.g., methyl ethyl ketone) to prepare a resin liquid, and then a sufficiently mixed inorganic filler and other components are added to the obtained resin liquid and mixed, and then an organic solvent is further added to adjust the viscosity, and mixed, and then additives such as a curing agent, a curing accelerator, or a dispersant are further added and mixed.

[0171] [Heat dissipation sheet] A method for producing the heat-dissipating sheet of the present invention as a sheet-shaped cured product using the composition of the present invention will be described below. The sheet-shaped cured product can be produced by a commonly used method, for example, by forming the composition of the present invention into a sheet and curing it.

[0172] The composition of the present invention can be formed into a sheet by any commonly used method. For example, when the composition of the present invention has plasticity and flowability, the composition can be molded into a desired shape by, for example, curing the composition while it is contained in a mold, and in this case, injection molding, injection compression molding, extrusion molding, compression molding, or vacuum compression molding can be used.

[0173] The solvent in the composition of the present invention can be removed by a known heating method such as a hot plate, a hot air oven, an IR heating oven, a vacuum dryer, or a high-frequency heater. Alternatively, a sheet-like cured product can be obtained by cutting the cured composition of the present invention into a desired shape.

[0174] A sheet-like cured product can also be obtained by forming a slurry of the composition of the present invention (hereinafter referred to as "sheet slurry") into a sheet by a doctor blade method, a solvent casting method, an extrusion film formation method, or the like.

[0175] An example of a method for producing a sheet-like cured product using this sheet slurry will be described below.

[0176] <Coating process> First, a coating film is formed on the surface of the substrate using a sheet slurry. That is, a coating film is formed on a substrate using the sheet slurry by a dip method, a spin coating method, a spray coating method, a blade method, or any other method. A coating device such as a spin coater, a slit coater, a die coater, or a blade coater can be used to apply the sheet slurry. These devices enable the formation of a uniform coating film of a predetermined thickness on the substrate.

[0177] As the substrate, copper foil or PET film, which will be described later, is generally used, but there is no limitation thereto.

[0178] <Drying process> The coating film formed by applying the sheet slurry is dried generally at a temperature of 10 to 150°C, preferably 25 to 120°C, and more preferably 30 to 110°C to remove the solvent and low molecular weight components. When the drying temperature is equal to or lower than the upper limit, the curing of the thermosetting resin in the slurry is suppressed, and the resin flows in the subsequent pressing process, which tends to make it easier to remove voids.When the drying temperature is equal to or higher than the lower limit, the solvent can be effectively removed.

[0179] The drying time is usually 5 minutes to 10 days, preferably 10 minutes to 3 days, more preferably 20 minutes to 1 day, and particularly preferably 30 minutes to 4 hours. When the drying time is equal to or greater than the lower limit, the solvent can be sufficiently removed, and the residual solvent tends to be prevented from forming voids in the sheet-shaped cured product. When the drying time is equal to or less than the upper limit, productivity tends to be improved and production costs tend to be reduced.

[0180] <Pressure process> After the drying process, it is desirable to carry out a pressurizing process for the purposes of bonding inorganic fillers together to form heat paths, eliminating voids and gaps within the sheet, and improving adhesion to the substrate. The pressurizing process involves applying a pressure of 10 kgf / cm to the dried film on the substrate.2 It is desirable to apply a load of 20 kgf / cm or more. 2 More than 50kgf / cm 2 More than 2000kgf / cm 2 Less than 1000 kgf / cm 2 , and more preferably 800 kgf / cm 2 By setting the load during pressure to the above upper limit or less, the secondary particles of the inorganic filler are not destroyed, and a sheet having high thermal conductivity without voids in the sheet can be obtained. By setting the load during pressure to the above lower limit or more, contact between the inorganic fillers is improved, making it easier to form heat conduction paths, and a sheet having high thermal conductivity can be obtained.

[0181] In the pressurizing step, it is desirable to heat the dried film on the substrate to 25°C or higher. This heating temperature is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 180°C or lower. By carrying out the pressurizing step within this temperature range, the melt viscosity of the resin in the coating film can be reduced, and voids and gaps in the sheet can be eliminated. A heating temperature below the above upper limit is preferable because it eliminates the risk of decomposition of organic components and the risk of residual solvents vaporizing and forming voids.

[0182] The time for the pressurizing step is usually 30 seconds or more, preferably 1 minute or more, more preferably 3 minutes or more, even more preferably 5 minutes or more, and preferably 4 hours or less, more preferably 2 hours or less, even more preferably 1 hour or less, and particularly preferably 45 minutes or less. By keeping the pressurizing time at or below the upper limit, the production time for the sheet-shaped cured product can be reduced, which tends to reduce production costs. On the other hand, by keeping the pressurizing time at or above the lower limit, voids and gaps in the sheet-shaped cured product can be sufficiently removed, which tends to improve heat transfer performance and voltage resistance.

[0183] <Curing process> The curing step for completely completing the curing reaction may be carried out under pressure or without pressure, but when pressure is applied, it is desirable to carry out the step under the same conditions as the above-mentioned pressurizing step for the same reasons as above. The pressurizing step and the curing step may be carried out simultaneously. In particular, in the sheet forming process which involves a pressing step and a curing step, it is preferable to apply a load within the above range to carry out pressing and curing.

[0184] The thickness of the heat-dissipating sheet of the present invention, which is the sheet-like cured product thus formed, is not particularly limited, but is preferably 50 μm or more, more preferably 100 μm or more, and preferably 400 μm or less, more preferably 300 μm or less. When the thickness of the heat-dissipating sheet is above the above-mentioned lower limit, voltage resistance characteristics are obtained and the breakdown voltage tends to be improved. When the thickness of the heat-dissipating sheet is below the above-mentioned upper limit, the device can be made smaller and thinner, and the thermal resistance of the resulting heat-dissipating sheet tends to be reduced.

[0185] [Composite molded body] The heat dissipation sheet of the present invention can be used as a composite molded product in which the heat dissipation sheet of the present invention and a metal part are laminated together. In this case, the metal part may be provided on only one side of the heat dissipation sheet of the present invention, or on two or more sides. For example, the heat dissipation sheet of the present invention may have a metal part on only one side, or may have a metal part on both sides. The metal part may also be patterned.

[0186] Such a composite molded article can be produced by using a metal part as the substrate and forming a sheet-like article made of the composition of the present invention on the substrate according to the method described above.

[0187] The composite molded body can also be produced by peeling a sheet formed on a substrate separate from the metal part from the substrate, and then heat-pressing the sheet onto a metal member that will become the metal part. In this case, a sheet-like material made from the composition of the present invention is formed in the same manner as described above, except that it is applied to a substrate such as PET which may be treated with a release agent, and then the sheet-like material is peeled off from the substrate and placed on another metal plate or sandwiched between two metal plates and pressed together.

[0188] The metal plate may be a metal plate having a thickness of about 10 to 10,000 μm and made of copper, aluminum, nickel-plated metal, or the like. The surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent or the like. From the viewpoint of adhesion between the resin composition and the metal plate, it is more preferable that the metal plate be subjected to such treatment.

[0189] [Semiconductor Devices] The semiconductor device of the present invention is mounted with the heat dissipation sheet of the present invention as a heat dissipation substrate, and its high thermal conductivity provides a heat dissipation effect and voltage resistance characteristics, enabling high reliability and high output and high density. In the semiconductor device, conventionally known materials can be used as appropriate for the aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, and other components other than the heat dissipation sheet of the present invention. [Example]

[0190] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. The various conditions and values ​​of evaluation results in the following examples indicate the preferred ranges of the present invention, as well as the preferred ranges in the embodiments of the present invention. The preferred ranges of the present invention can be determined by taking into consideration the preferred ranges in the above-mentioned embodiments and the values ​​in the following examples or the ranges indicated by combining the values ​​of the examples.

[0191] [Measurement conditions] Various characteristics and physical properties in the following examples and comparative examples were measured by the methods described below.

[0192] <Volume average particle diameter (D of BN agglomerated powder 50 )> Using "Morphologi" manufactured by Malvern, D of BN agglomerated powder 50 (μm) was measured.

[0193] <Tap density of BN agglomerated powder> The sample after heat firing was subjected to air classification to prepare a powder sample with a volume average particle diameter of less than 100 μm. This sample was placed in a 10 ml graduated cylinder, and tapping was manually performed until the sample volume became constant. The tap density was calculated by dividing the weight of the sample by the volume after tapping. The above method was performed according to the method specified in JIS R1628 except for using a 10 ml graduated cylinder.

[0194] <Interparticle void volume of BN agglomerated powder, intraparticle porosity of BN agglomerated particles> It was determined from mercury intrusion measurement using a mercury porosimeter. Using AutoPore IV manufactured by Micromeritics, the sample was degassed under reduced pressure (50 μmHg or less) for 10 minutes, and then the powder density and total pore volume were determined. Also, the mercury intrusion / withdrawal curve was measured. Assuming the pores are cylinders, the pore volume in the region where the pore diameter is 2.0 μm or more (segmentation diameter) was calculated as the interparticle void volume. The intraparticle pore volume was obtained by subtracting the interparticle void volume from the total pore volume, and the ratio of the intraparticle pore volume to the volume of the powder (1 / powder density) was defined as the intraparticle porosity. Note that the mercury intrusion measurement was carried out according to the method compliant with JIS R1655, and the surface tension of BN was 485 dyn / cm 2 , the contact angle was 140°, and the measurement temperature was 23 - 26°C.

[0195] <Compressive fracture strength of BN agglomerated powder> Using the Shimadzu Micro Compression Tester MCT-510 manufactured by Shimadzu Corporation, at room temperature (20 - 30°C), a test force of 98 mN, a loading rate of 4.84 mN / sec, and a flat φ100 μm was used for the upper pressing plunger. One BN agglomerated particle with a particle diameter of around 50 μm was selected for the test, and this was carried out 5 times. The compressive fracture strength was determined as the average value of the 5 times. The fracture strength was calculated using the following formula. Cs = 2.48 / πd 2 Cs: Compressive failure strength (MPa) P: Failure test force (N) d: Particle diameter (mm)

[0196] <Thermal conductivity in the thickness direction of the sheet-shaped molded body> The thermal conductivity of the heat dissipation sheet was measured by the steady-state method (in accordance with ASTM D5470) from the slope represented by the thermal resistance value with respect to the sheet thickness by measuring the thermal resistance values of four sheets with different thicknesses under the following apparatus and conditions. (1) Thickness: Thickness (μm) when the press pressure was 3400 kPa using T3Ster-DynTIM manufactured by Mentor Graphics (2) Measurement area: Area (cm 2 ) of the part that transfers heat when using T3Ster-DynTIM manufactured by Mentor Graphics (3) Thermal resistance value: Thermal resistance value (K / W) when pressed at a press pressure of 3400 kPa using T3Ster-DynTIM manufactured by Mentor Graphics (4) Thermal conductivity: The thermal resistance values of four sheets with different thicknesses were measured, and the thermal conductivity (W / m·K) was calculated from the following formula. Formula: Thermal conductivity (W / m·K) = 1 / ((slope (thermal resistance value / thickness): K / (W·μm)) × (area: cm 2 )) × 10 -2

[0197] <Voltage resistance characteristics of the sheet-shaped molded body> For a sheet-shaped molded body with a thickness of 150 μm, the voltage was increased by 500 V every minute in insulating oil, and the voltage at which the sample was destroyed was determined.

[0198] [Production and evaluation of BN agglomerated powder from BN slurry] The BN agglomerated particles used in the following examples and comparative examples were produced and evaluated by the following method.

[0199] <Preparation of BN slurry> (Raw materials) Raw material h-BN powder (half-value width of the (002) plane peak obtained by powder X-ray diffraction measurement is 2θ = 0.67°, total oxygen concentration = 7.5 wt%, specific surface area 116 m 2 / g, total pore volume 0.754 cm 3 / g): 10000 g Binder (Takiseram M160L manufactured by Takagi Chemical Co., Ltd., solid content concentration 21 wt%): 11496 g Surfactant (surfactant "Ammonium Lauryl Sulfate" manufactured by Kao Corporation, solid content concentration 14 wt%): 250 g

[0200] (Preparation of slurry) Weighed a predetermined amount of the raw material h-BN powder into a resin bottle, then added a predetermined amount of the binder. Further, after adding a predetermined amount of the surfactant, ceramic balls made of zirconia were added, and the mixture was stirred on a pot mill turntable for 1 hour to prepare a slurry.

[0201] (Granulation) Granulation from the BN slurry was carried out using a spray dryer P260 manufactured by Pulice Co., Ltd. at a disk rotation speed of 15000 - 20000 rpm and a drying temperature of 85°C.

[0202] (Production of BN agglomerated particles) Put the above BN granulated powder into a graphite crucible with a lid, heated it to 2000°C at a rate of 63°C / h while introducing nitrogen gas. After reaching 2000°C, maintain the temperature as it is and hold for 5 hours while introducing nitrogen gas. Then, cool it to room temperature to obtain a heat-treated sample. The heated sample in the graphite crucible was divided and taken separately from the inner wall surface side of the graphite crucible (upper layer, side peripheral layer, lower layer) as follows: the outer part 1 cm away was sample (A), the inner layer part 1 cm within the sample (A) part was sample (B), and the inner layer part 1 cm further from the sample (B) part was sample (C). Sample (C) is the part 2 cm inside from the inner wall surface side of the graphite crucible (upper layer, side peripheral layer, lower layer).

[0203] (Classification) The heat-treated BN agglomerated powder that had been divided and separately taken was subjected to air classification. The air classification was performed using AC-15 manufactured by Nisshin Engineering Co., Ltd., and each divided sample (A), (B), and (C) was classified into particles smaller than 100 μm and particles 100 μm or larger.

[0204] <Evaluation> After classification, for the particles smaller than 100 μm, the tap density, interparticle void volume, intra-particle porosity, and compressive fracture strength were measured according to the above method. Also, the average particle diameter was measured. Each divided sample (A), (B), and (C) was designated as sample No. (A)-1 to (A)-2, (B)-1, and (C)-1 to (C)-5, respectively, and the measurement results are shown in Table 1.

[0205]

Table 1

[0206] Note that it was confirmed by SEM observation that the BN agglomerated powders of sample No. (A)-1 to (A)-2, (B)-1, and (C)-1 to (C)-5 all had a card house structure.

[0207] [Preparation and Evaluation of Sheet-like Molded Bodies] In the following examples and comparative examples, the BN agglomerated powders of (A)-1 to (A)-2, (B)-1, and (C)-1 to (C)-5 obtained above were used as inorganic fillers respectively, and BN agglomerated powder-containing resin compositions were prepared by the following method, and sheet-like molded bodies were manufactured.

[0208] [Preparation of BN Agglomerated Powder-Containing Resin Composition] The raw materials used were as follows.

[0209] [Thermosetting Resin Component] Resin Component 1: Manufactured in accordance with the method for manufacturing an epoxy resin disclosed in the examples of JP-A-2006-176658, structure (2) (R 3 = structure (4)) and structure (3) (R 4 , R 5 , R 6,R 7 (=methyl group) specific epoxy resin Weight average molecular weight in polystyrene equivalent: 30,000 Epoxy equivalent: 9,000g / equivalent Resin component 2: Mitsubishi Chemical Bisphenol F solid epoxy resin Weight average molecular weight in polystyrene equivalent: 60,000 Resin component 3: Mitsubishi Chemical Corporation bisphenol A liquid epoxy resin Resin component 4: Nagase ChemteX Corporation, multifunctional epoxy resin containing a structure having four or more glycidyl groups per molecule Resin component 5: Mitsubishi Chemical hydrogenated bisphenol A liquid epoxy resin Resin component 6: p-aminophenol liquid epoxy resin manufactured by Mitsubishi Chemical Corporation

[0210] <Curing agent component> Hardener 1: Meiwa Kasei "MEH-8000H" Phenolic resin curing agent

[0211] <Curing catalyst component> Curing catalyst 1: Shikoku Chemicals "2E4MZ-A" 2,4-Diamino-6-[2'-ethyl-4'-methylimidazolyl-(17')]-ethyl-s-triazine (Compounds having a triazine ring as a nitrogen-containing heterocyclic structure) Molecular weight: 247 Curing catalyst 2: Shikoku Chemicals "C11Z-CN" 1-Cyanoethyl-2-undecylimidazole Molecular weight: 275

[0212] <Inorganic filler component> Inorganic filler 1: BN agglomerated powder (C)-1 to (C)-5 Inorganic filler 2: BN agglomerated powder (B)-1 Inorganic filler 3: BN agglomerated powder (A)-1 to (A)-2 Inorganic filler 4: Spherical alumina particles manufactured by Admatechs New Mohs hardness: 9 Volume average particle size: 6.5 μm Thermal conductivity: 20-30 W / m K

[0213] Example 1 Using a planetary stirring device, a mixture was prepared to have the following composition: Resin Component 1: 7.02 wt%, Resin Component 3: 7.02 wt%, Resin Component 4: 6.67 wt%, Curing Agent 1: 7.37 wt%, Curing Catalyst 1: 0.42 wt%, Inorganic Filler 1: 51.14 wt%, Inorganic Filler 4: 20.35 wt%. Furthermore, when preparing the mixture, 18.6 wt% each of methyl ethyl ketone and cyclohexanone was used so that the mixture would have a solids concentration of 62.8 wt% of the coating slurry. The obtained coating slurry (slurry for sheets) was applied to a PET substrate by the doctor blade method, and after heating and drying at 60°C for 120 minutes, it was dried at 42°C and 1500 kgf / cm 2 The mixture was pressed at 100° C. for 10 minutes to obtain a sheet-like molded product having a thickness of 150 μm. The total content of methyl ethyl ketone and cyclohexanone in the sheet-like molded product was 1% by weight or less.

[0214] The thermal conductivity and withstand voltage characteristics of the obtained sheet-like molded body were measured, and the results are shown in Table 2.

[0215] <Examples 2 to 6, Comparative Examples 1 and 2> Sheet-shaped molded articles were produced using the compositions shown in Table 2 according to the method of Example 1, and the evaluations were carried out. The results are shown in Table 2.

[0216] [Table 2]

[0217] From Table 2, it can be seen that by using the BN agglomerated powder of the present invention having a tap density and interparticle volume within specific ranges, a heat dissipation sheet with excellent thermal conductivity and voltage resistance characteristics can be realized.

[0218] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2019-034518, filed on February 27, 2019, the entire contents of which are incorporated by reference.

Claims

1. 1. A method for producing a boron nitride agglomerated powder having a tap density of 0.6 g / ml or more but less than 0.8 g / ml and an interparticle void volume of 0.5 ml / g or more as determined by the following method, comprising: The method includes a pulverization step of pulverizing raw material boron nitride, a granulation step of granulating the raw material boron nitride powder obtained by the pulverization, and a heating step of placing the granulated boron nitride powder obtained by the granulation in a crucible and heat-treating the same, After the heat treatment, the heat-treated powder is separated from the inner wall surface of the crucible and collected. <Method for measuring interparticle volume> It is determined by mercury intrusion measurement using a mercury porosimeter. Using a mercury porosimeter, the sample is subjected to a reduced pressure treatment (50 μmHg or less) for 10 minutes, and then the powder density and total pore volume are determined, and a mercury intrusion / extrusion curve is measured. Assuming that the pores are cylindrical, the pore volume in the region with a pore diameter of 2.0 μm or more (division diameter) is calculated as the interparticle volume. The mercury intrusion measurement was carried out in accordance with JIS R1655, and the surface tension of BN was 485 dyn / cm ２ The contact angle is 140° and the measurement temperature is 23 to 26°C.

2. 2. The method for producing a boron nitride agglomerated powder according to claim 1, wherein the heating step comprises heat treatment in a non-oxidizing gas atmosphere at a temperature of 1600°C or higher and 2300°C or lower for 5 hours or longer and 20 hours or shorter.

3. 3. The method for producing a boron nitride agglomerated powder according to claim 1, wherein the interparticle void volume of the boron nitride agglomerated powder is 0.9 ml / g or less.

4. 4. The method for producing a boron nitride agglomerated powder according to claim 1, wherein the intraparticle porosity of BN agglomerated particles contained in the boron nitride agglomerated powder is 40% or more and 60% or less, as determined by the following method. <Method for measuring intraparticle void ratio of BN agglomerated particles> The intra-particle pore volume is determined by subtracting the inter-particle pore volume from the total pore volume determined in the measurement of the inter-particle pore volume using the mercury porosimeter, and the ratio of the intra-particle pore volume to the powder volume (1 / powder density) is defined as the intra-particle porosity.

5. 5. The method for producing a boron nitride agglomerated powder according to claim 1, wherein the boron nitride agglomerated powder has an average particle size of 20 μm or more and 200 μm or less.

6. 6. The method for producing a boron nitride agglomerated powder according to claim 1, wherein the boron nitride agglomerated powder has a house-of-card structure.

7. A method for producing a heat dissipation sheet, comprising producing a boron nitride agglomerated powder by the method for producing a boron nitride agglomerated powder according to any one of claims 1 to 6, and using the produced boron nitride agglomerated powder to produce a heat dissipation sheet.

8. A method for manufacturing a semiconductor device, comprising manufacturing a heat dissipation sheet by the method for manufacturing a heat dissipation sheet according to claim 7, and manufacturing a semiconductor device using the manufactured heat dissipation sheet.

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