JP7019955B2 - Boron Nitride Particle Containing Sheet - Google Patents

Description

The heat dissipation sheet of the present invention relates to a boron nitride particle-containing sheet containing secondary boron nitride particles and having excellent thermal conductivity, withstand voltage, adhesive strength and bending resistance. Further, the present invention relates to an insulated heat dissipation sheet preferably used for electric / electronic parts, particularly for power semiconductor devices.

As electrical equipment becomes smaller and has higher performance, the mounting density of electronic components is increasing. With higher densities, the need to dissipate heat generated from electronic components is increasing, which has become an important issue. As a method of dissipating heat, a method of adhering a heat conductor such as aluminum having high heat dissipation and a thermal conductivity of 10 W / m · K or more to a heat generating source is widely adopted. Further, in order to bond the heat conductor to the heat generating source, an insulating adhesive material having an insulating property is used. The insulating adhesive material is strongly required to have high thermal conductivity.

As an example of the insulating adhesive material, Patent Document 1 describes an insulating adhesive sheet in which a glass cloth is impregnated with an adhesive composition containing an epoxy resin, a curing agent for an epoxy resin, a curing accelerator, an elastomer and an inorganic filler. Is disclosed.

On the other hand, hexagonal boron nitride (h-boron nitride) is widely used in the field of electrical and electronic materials as an inorganic filler for improving the thermal conductivity of an insulating adhesive. This is because h-boron nitride has the same layered structure as graphite, is relatively easy to synthesize, and is excellent in thermal conductivity, solid lubricity, chemical stability, heat resistance, insulation, and the like. This is because it is equipped with.

However, h-boron nitride has a plate-like particle shape, and although it exhibits high thermal conductivity in the plate surface direction (in the ab plane or (002) plane) (usually, the thermal conductivity is about 400 W / mK). ), Only low thermal conductivity (usually about 2 to 3 W / mK as thermal conductivity) is shown in the plate thickness direction (c-axis direction). Therefore, when this is blended with a resin to form a boron nitride particle-containing resin composition, for example, when a plate-shaped molded product (hereinafter, may be referred to as a sheet) is molded, the plate-shaped h-boron nitride is molded. Occasionally, it is oriented in the plate surface direction of the molded product, which is the flow direction of the boron nitride particle-containing resin composition. Although the obtained sheet has excellent thermal conductivity in the plate surface direction, it has a problem that it exhibits only low thermal conductivity in the thickness direction.

Therefore, in order to improve the anisotropy of the thermal conductivity of h-boron nitride, even when the sheet is molded, h-boron nitride has less orientation as described above and has a shape other than scaly. Secondary particles that have aggregated have been studied (Patent Documents 2, 3, 4 and 5). In particular, it is known that the h-boron nitride secondary particles having a cardhouse structure described in Patent Document 5 improve the disintegration resistance of the secondary particles and are also excellent in terms of thermal conductivity. Further, in Patent Document 6, high thermal conductivity and high withstand voltage are obtained by using boron nitride secondary particles in which the boron nitride secondary particles having a card house structure contain a resin (the resin exists inside the boron nitride secondary particles). It has been proposed to achieve both. However, the resin contained therein has not been examined in detail.

Japanese Unexamined Patent Publication No. 2006-342238 Japanese Unexamined Patent Publication No. 2006-257392 Japanese Patent Publication No. 2008-510878 Japanese Unexamined Patent Publication No. 9-202663 Japanese Unexamined Patent Publication No. 2016-135732 JP-A-2015-193752

Boron nitride has a drawback that the adhesion to the resin is low because the surface functional group is very small. Therefore, the conventional high thermal conductivity heat-dissipating sheet produced by using the boron nitride secondary particles as described in Patent Documents 2 to 5 exhibits high thermal conductivity, but the adhesive performance is not sufficient.
On the other hand, although Patent Document 6 shows boron nitride particles in which secondary boron nitride particles having a card house structure contain a resin, detailed studies have not been made on the contained resin. Further, according to the study of the present inventor, it has been found that since the boron nitride secondary particles have voids inside, it is difficult to completely fill the voids inside even if the resin is encapsulated.
An object of the present invention is to provide a heat-dissipating boron nitride secondary particle-containing sheet having excellent thermal conductivity, withstand voltage, adhesive strength and bending resistance by encapsulating a specific resin in the boron nitride secondary particles. do.

As a result of diligent studies, the present inventors have adjusted the epoxy equivalent of the resin contained in the boron nitride secondary particles and the epoxy equivalent of the resin existing outside the boron nitride secondary particles to adjust the epoxy equivalent of the resin inside the boron nitride secondary particles. We have found that the number of voids can be reduced. Furthermore, we have reached the point where we can obtain a boron nitride particle-containing sheet that has excellent thermal conductivity and withstand voltage, improves the adhesiveness between the boron nitride secondary particles and the resin, and is flexible and resistant to cracking. ..
That is, the gist of the present invention is as follows.

[1] A boron nitride particle-containing sheet containing a boron nitride secondary particle containing a resin B and a resin A.
Resin A and resin B each contain an epoxy resin, and the resin A and the resin B each contain an epoxy resin.
The epoxy equivalent of the epoxy resin A contained in the resin A is larger than the epoxy equivalent of the epoxy resin B contained in the resin B.
A boron nitride particle-containing sheet having an epoxy equivalent of epoxy resin B of less than 270.
[2] The boron nitride particle-containing sheet according to [1], wherein the epoxy equivalent of the epoxy resin A is 270 or more.
[3] The boron nitride particle-containing sheet according to [1] or [2], wherein the boron nitride secondary particles contain boron nitride secondary particles having a card house structure.

The present invention can provide a heat-dissipating boron nitride secondary particle-containing sheet having excellent thermal conductivity, withstand voltage, adhesive strength and bending resistance.

It is a scanning electron microscope (hereinafter referred to as "SEM") photograph of the boron nitride secondary particle of this invention with a magnification of 200,000 times. It is an SEM photograph with a magnification of 1 million times of the boron nitride secondary particle of this invention. It is a schematic diagram of a card house structure.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

The boron nitride secondary particle-containing sheet of the present invention is excellent in thermal conductivity, withstand voltage, adhesive strength and bending resistance by containing specific boron nitride secondary particles and a resin. The reason for the effect of the present invention is presumed as follows.
The sheet of the present invention can achieve high thermal conductivity by containing boron nitride secondary particles. Further, when the resin (resin B) contained in the boron nitride secondary particles contains an epoxy resin and the epoxy equivalent of the epoxy resin is less than 270, the resin B is highly crosslinked. Therefore, when a high voltage is applied, a short circuit due to deterioration of the resin is prevented, and the withstand voltage is excellent.
Further, the resin A contained in the boron nitride secondary particle-containing sheet contains the epoxy resin A, and the epoxy equivalent of the epoxy resin A is larger than the epoxy resin B, so that the resin A has a particularly flexible structure. Therefore, the bending resistance of the boron nitride secondary particle-containing sheet is improved, and further, the thermal conductivity tends to be improved by suppressing the interfacial peeling between the boron nitride secondary particles and the resin A.

<Resin A>
The boron nitride particle-containing sheet of the present invention contains the resin A, and the resin A is a resin constituting the sheet. The resin A contains an epoxy resin (hereinafter, may be referred to as “epoxy resin A”), and may contain other than the epoxy resin A.
The epoxy equivalent of the epoxy resin A (hereinafter, may be referred to as “WPE _A ”) is larger than the epoxy equivalent of the epoxy resin B contained in the epoxy resin B described later (hereinafter, may be referred to as “WPE _B ”). .. When WPE _A is larger than WPE _B , the distance between the cross-linking points of the epoxy resin A constituting the sheet becomes long, and the structure becomes more flexible than that of the epoxy resin B. Therefore, it is possible to obtain a sheet that is more supple and has excellent bending resistance that is hard to break.
The epoxy equivalent is a value obtained by dividing the molecular weight of the epoxy resin by the number of epoxy groups.

WPE _A is preferably 270 or more, more preferably 500 or more, still more preferably 1000 or more. Further, it is preferably 10000 or less, more preferably 7000 or less, and further preferably 5000 or less. When WPE _A is at least the above lower limit value, the distance between the cross-linking points of the epoxy resin A becomes long, so that it tends to be possible to obtain a sheet having a flexible structure, which is supple and has excellent bending resistance. Further, when the value is not more than the above upper limit value, the insulation property at a high voltage tends to be ensured.

The epoxy resin A may be only an epoxy resin having one kind of structural unit, but a plurality of epoxy resins having different structural units may be combined. Even when combined, it is important that the total epoxy equivalents (WPE _A ) of the epoxy resins A obtained in combination are larger than WPE _B.

The epoxy resin A is not particularly limited, and examples thereof include a resin obtained by reacting epihalohydrin with a divalent phenol compound, and a resin obtained by reacting a divalent epoxy compound with a divalent phenol compound.

Specific examples of the structural unit contained in the epoxy resin A include an epoxy monomer having a bisphenol skeleton, an epoxy monomer having a dicyclopentadiene skeleton, an epoxy monomer having a naphthalene skeleton, an epoxy monomer having an adamanten skeleton, and an epoxy monomer having a fluorene skeleton. Examples thereof include an epoxy monomer having a biphenyl skeleton, an epoxy monomer having a bi (glycidyloxyphenyl) methane skeleton, an epoxy monomer having a xanthene skeleton, an epoxy monomer having an anthracene skeleton, and an epoxy monomer having a pyrene skeleton. Only one of these may be used, or two or more thereof may be used in combination.

Examples of the epoxy monomer having a bisphenol skeleton include an epoxy monomer having a bisphenol A type, a bisphenol F type or a bisphenol S type bisphenol skeleton.

Examples of the epoxy monomer having a naphthalene skeleton include 1-glycidylnaphthalene, 2-glycidylnaphthalene, 1,2-diglycidylnaphthalene, 1,5-diglycidylnaphthalene, 1,6-diglycidylnaphthalene, and 1,7-diglycidyl. Examples thereof include naphthalene, 2,7-diglycidylnaphthalene, triglycidylnaphthalene, 1,2,5,6-tetraglycidylnaphthalene and the like.

Examples of the epoxy monomer having an adamanten skeleton include 1,3-bis (4-glycidyloxyphenyl) adamanten and 2,2-bis (4-glycidyloxyphenyl) adamanten.

Examples of the epoxy monomer having a fluorene skeleton include 9,9-bis (4-glycidyloxyphenyl) fluorene, 9,9-bis (4-glycidyloxy-3-methylphenyl) fluorene, and 9,9-bis (4-). Glycidyloxy-3-chlorophenyl) fluorene, 9,9-bis (4-glycidyloxy-3-bromophenyl) fluorene, 9,9-bis (4-glycidyloxy-3-fluorophenyl) fluorene, 9,9-bis (4-Glysidyloxy-3-methoxyphenyl) Fluorene, 9,9-bis (4-Glysidyloxy-3,5-dimethylphenyl) Fluorene, 9,9-bis (4-Glysidyloxy-3,5-dichlorophenyl) Fluorene, 9,9-bis (4-glycidyloxy-3,5-dibromophenyl) fluorene and the like can be mentioned.

Examples of the epoxy monomer having a biphenyl skeleton include 4,4'-diglycidyl biphenyl, 4,4'-diglycidyl-3,3', 5,5'-tetramethylbiphenyl and the like.

Examples of the epoxy monomer having a bi (glycidyloxyphenyl) methane skeleton include 1,1'-bi (2,7-glycidyloxynaphthyl) methane and 1,8'-by (2,7-glycidyloxynaphthyl) methane. 1,1'-by (3,7-glycidyloxynaphthyl) methane, 1,8'-by (3,7-glycidyloxynaphthyl) methane, 1,1'-by (3,5-glycidyloxynaphthyl) methane , 1,8'-by (3,5-glycidyloxynaphthyl) methane, 1,2'-by (2,7-glycidyloxynaphthyl) methane, 1,2'-by (3,7-glycidyloxynaphthyl) Examples thereof include methane, 1,2'-by (3,5-glycidyloxynaphthyl) methane and the like.

Examples of the epoxy monomer having a xanthene skeleton include 1,3,4,5,6,8-hexamethyl-2,7-bis-oxylanylmethoxy-9-phenyl-9H-xanthene.

Further, an epoxy resin having a tertiary amine structure can also be used. Specifically, N, N-dimethylaminoethyl glycidyl ether, N, N-dimethylaminotrimethyl glycidyl ether, N, N-dimethylaminophenyl glycidyl ether, N, N-diglycidyl-4-glycidyloxyaniline, 1,3 , 5-Triglycidyl isocyanurate and the like.

Examples of the polyfunctional aliphatic epoxy resin include 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, trimethylolpropane triglycidyl ether, and trimethylolpropanepolymethyl ether. , Diethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, sorbitol polyglycidyl ether and the like.
Among the above, a polyfunctional aliphatic epoxy resin is preferable, and trimethylolpropane polyglycidyl ether is particularly preferable because it has a small epoxy equivalent of 140.

The resin A may contain a component other than the epoxy resin A, and examples thereof include a curable resin other than the epoxy, a thermoplastic resin, and rubber.
The curable resin may be any polymerizable such as thermosetting, photocurable, and electron beam curable, but the thermosetting resin and / or the thermosetting resin and / or the curable resin in terms of heat resistance, water absorption, dimensional stability, and the like. Thermoplastic resin is preferred.

Examples of the thermosetting resin include acrylic monomers having a double bond.
Examples of the thermoplastic resin include polyolefin resins such as polyethylene resin, polypropylene resin and ethylene-vinyl acetate copolymer resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyester resin such as liquid crystal polyester resin, polyvinyl chloride resin and acrylic. Examples thereof include resins, polycarbonate resins, polyphenylene sulfide resins, polyphenylene ether resins, polyamide resins, polyamideimide resins, polyimide resins, polyetheramideimide resins, polyetheramide resins, and polyetherimide resins. Further, copolymers such as block copolymers and graft copolymers thereof are also included. These may be used alone or in admixture of two or more.

Examples of the rubber include natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, butadiene-acrylonitrile copolymer rubber, and the like. Examples thereof include isobutylene-isoprene copolymer rubber, chloroprene rubber, silicon rubber, fluorine rubber, chloro-sulfonated polyethylene, polyurethane rubber and the like. One of these may be used alone, or two or more thereof may be mixed and used.

The content of the epoxy resin A in the resin A is not particularly limited, but is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more. Further, it is preferably 95% by mass or less, and more preferably 80% by mass or less. Within this range, the film forming property of the sheet composition described later is improved, and further, the withstand voltage, adhesive force and bending resistance of the boron nitride secondary particle-containing sheet tend to be improved.

<Boron Nitride Secondary Particles>
The boron nitride secondary particles according to the present invention are characterized by containing resin B (hereinafter, may be referred to as “resin-encapsulated boron nitride secondary particles”). Boron nitride secondary particles formed by aggregating boron nitride primary particles have voids formed when the primary particles are aggregated inside the boron nitride secondary particles. The resin-encapsulating boron nitride secondary particles of the present invention are characterized in that the voids are filled with a special resin.
The resin B has a composition different from that of the resin A contained in the above-mentioned boron nitride particle-containing sheet, and the epoxy equivalent of the epoxy resin contained therein is different. The epoxy resin A may contain the same epoxy resin as the epoxy resin B, but the epoxy equivalent of the epoxy resin B needs to be smaller than the epoxy equivalent of the epoxy resin A.

[Resin B]
In the resin-encapsulating boron nitride secondary particles of the present invention, the resin B is encapsulated in the secondary particles. Encapsulation in the secondary particles means that the resin is present in the voids of the aggregated primary particles in the boron nitride secondary particles.
The resin B contains an epoxy resin B, and the epoxy equivalent (WPE _B ) of the epoxy resin B is less than 270. When a plurality of types of epoxy resins are contained, the total number obtained by multiplying the epoxy equivalents of each epoxy resin by the mass fraction may be less than 270. That is, in the case of 70 parts of epoxy resin having an epoxy equivalent of 300 and 30 parts of epoxy resin having an epoxy equivalent of 100, it can be calculated as 300 × 0.7 + 100 × 0.3 = 240.
When WPE _B is less than 270, the crosslink density of the epoxy resin B becomes high, and the resin B when cured has an appropriate hardness. Since the resin structure has an appropriate hardness, even when a high potential of alternating current is applied, the destruction due to the suppression of vibration due to the polarization inside the resin tends to be reduced, and the insulating property tends to be improved.

WPE _B is more preferably less than 250, still more preferably less than 200. Further, on the surface of the boron nitride secondary particles, the boron nitride primary particles are oriented in various directions, and the surface is uneven. The resin B oozes out of the boron nitride secondary particles from the inside, that is, toward the sheet side so as to fill the unevenness, and an epoxy equivalent is provided at the interface between the resin-encapsulated boron nitride secondary particles and the resin A outside the resin. There will be a small epoxy resin B layer. Therefore, the highly crosslinked epoxy resin is also present at the interface between the boron nitride secondary particles, which is the weakest electrically, and the resin A, and thus has a characteristic of high withstand voltage.

The resin B is not particularly limited as long as it has the epoxy resin B. For example, it may have a phenol resin or the like. The phenol resin is also not particularly limited, but the number of hydroxyl groups of the phenol is preferably 20 or more, more preferably 40 or more, still more preferably 50 or more, with respect to the number of epoxy groups of the epoxy resin B. Further, 100 or less is preferable, 80 or less is more preferable, and 70 or less is further preferable.

Specific examples of the above-mentioned phenolic resin include phenol novolac, o-cresol novolak, p-cresol novolak, t-butylphenol novolak, dicyclopentadiencresol, polyparavinylphenol, bisphenol A type novolak, xylylene-modified novolak, and decalin-modified novolak. Examples thereof include poly (di-o-hydroxyphenyl) methane, poly (di-m-hydroxyphenyl) methane, poly (di-p-hydroxyphenyl) methane and the like. Among them, at least one selected from a phenol resin having a melamine skeleton, a phenol resin having a triazine skeleton, and a phenol resin having an allyl group is preferable.

Commercially available products of the above phenol resin include MEH-8005, MEH-8000H and NEH-8015 (all of which are manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751 and the like. Examples thereof include LA-1356 and LA-3018-50P (all manufactured by Dainippon Ink Co., Ltd.), and PS6313 and PS6492 (manufactured by Gun Ei Chemical Industry Co., Ltd.).

The structure of the boron nitride secondary particles used in the present invention is not particularly limited, and may be a structure in which scaly primary particles are solidified into a dumpling shape, and the secondary particles thus solidified are heated. Sintered boron nitride secondary particles may be used. Further, it may have a card house structure in which scaly boron nitride primary particles are intricately laminated without being oriented. The aggregated morphology of the boron nitride secondary particles can be confirmed by a scanning electron microscope (SEM).

The cardhouse structure is a uni-like morphology in which crystals of boron nitride primary particles radiate from the center side to the surface side of the boron nitride secondary particles on the surface of the boron nitride secondary particles, or a boron nitride primary. It is preferable that the particles are small plates and have a uni-like spherical shape in which they are sintered and aggregated. In such a cardhouse structure, since the scaly primary particles are randomly oriented, the crystal plane having high thermal conductivity is oriented in any direction, and it is possible to develop isotropically high thermal conductivity. Since the structure is such that the flat surface portion and the end face portion of the primary particles are in contact with each other, the thermal resistance between the particles is small, and the thermal conductivity tends to be very high.
The boron nitride secondary particles may contain components other than the above-mentioned boron nitride primary particles as long as the effects of the present invention are not impaired. Examples of the component other than the boron nitride primary particles include a binder, a surfactant, a component derived from a solvent, and the like.

(shape)
The resin-encapsulated boron nitride secondary particles are preferably spherical. Here, "spherical" means that the aspect ratio (ratio of major axis to minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.5 or less. The aspect ratio of the boron nitride secondary particles of the present invention is determined by arbitrarily selecting 200 or more particles from the image taken by SEM, calculating the ratio of the major axis and the minor axis of each, and calculating the average value. do.

(Average particle size (D ₅₀ ))
The average particle size (D ₅₀ ) of the resin-encapsulated boron nitride secondary particles is usually 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, still more preferably 25 μm or more, still more preferably 30 μm or more, and more. It is more preferably 40 μm or more, further preferably 45 μm or more, and particularly preferably 50 μm or more. Further, it is usually 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less. When it is not more than the above upper limit value, the smoothness of the surface is improved when the molded product is formed, and further, the resin-encapsulated boron nitride secondary particles have an appropriate gap, so that the thermal conductivity tends to be improved. Further, when the value is equal to or higher than the above lower limit, the contact resistance between the resin-encapsulated boron nitride secondary particles does not become too large when the molded body is formed, and the thermal conductivity of the boron nitride secondary particles themselves tends to increase. ..

Note that D ₅₀ means the particle size when the cumulative volume is exactly 50% when the cumulative volume is drawn with the volume of the powder used for measurement as 100%, and the measurement method is as a wet measurement method. Can be measured by using a laser diffraction / scattering type particle size distribution measuring device or the like for a sample in which secondary boron nitride particles are dispersed in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer. As a dry measurement method, "Morphorugi" manufactured by Malvern can be used for measurement.

(destruction strength)
The fracture strength of the resin-encapsulated boron nitride secondary particles is usually 2.5 MPa or more, preferably 3.0 MPa or more, more preferably 3.5 MPa or more, still more preferably 4.0 MPa or more, and usually 20 MPa or less, preferably 15 MPa. Below, it is more preferably 10 MPa or less. When it is not more than the above upper limit, the strength of the resin-encapsulated boron nitride secondary particles does not become excessive, the surface smoothness is improved when the molded product is formed, and the thermal conductivity tends to be improved. When it is at least the above lower limit value, particle deformation due to pressure at the time of producing a sheet is suppressed, and thermal conductivity tends to be improved.

The fracture strength can be calculated by a compression test of one particle according to JIS R 1639-5 and the following formula. Usually, particles are measured at 5 points or more, and the average value is adopted.
Equation: Cs = 2.48P / πd ²
Cs: Breaking strength (MPa)
P: Destruction test force (N)
d: Particle diameter (mm)

(Total pore volume)
The total pore volume of the resin-encapsulated boron nitride secondary particles is not particularly limited, but is preferably 2.2 cm ³ / g or less. Further, it is preferably 0.01 cm ³ / g or more, more preferably 0.02 cm ³ / g or more, preferably 2 cm ³ / g or less, and more preferably 1.5 cm ³ / g or less.
The total pore volume can be measured by the nitrogen adsorption method and the mercury intrusion method. When the value is not more than the above upper limit, the boron nitride secondary particles in the sheet are dense, so that it is possible to reduce the boundary surface that hinders heat conduction, and boron nitride having higher heat conductivity. It tends to be secondary particles. Further, when the value is equal to or higher than the above lower limit, the resin may not be excessively taken into the pores, and an increase in apparent viscosity may be suppressed, so that the molding process of the sheet composition or the coatability of the coating liquid tends to be improved. It is in.

(Specific surface area)
The specific surface area of the resin-encapsulated boron nitride secondary particles is preferably 1 m ² / g or more, more preferably 3 m ² / g or more, and further preferably 5 m ² / g or more. Further, it is preferably 50 m ² / g or less, more preferably 40 m ² / g or less, still more preferably 8 m ² / g or less, and particularly preferably 7.25 m ² / g or less. When the specific surface area of the resin-encapsulated boron nitride secondary particles is within this range, the contact resistance between the resin-encapsulated boron nitride secondary particles tends to be reduced when the particles are combined with the resin. It is preferable because it can suppress an increase in the viscosity of the particles. The specific surface area can be measured by the BET 1-point method (adsorbed gas: nitrogen).

(Bulk density)
The bulk density of the resin-encapsulated boron nitride secondary particles is usually preferably 0.3 g / cm ³ or more, more preferably 0.35 g / cm ³ or more, and further preferably 0.4 g / cm ³ or more. When the bulk density is at least the above lower limit value, the apparent volume does not become too large, and the volume of the resin-encapsulated boron nitride secondary particles can be suppressed with respect to the resin component in the sheet. Therefore, there is a tendency that an increase in viscosity of the sheet composition when a sheet composition or the like containing resin-encapsulated boron nitride secondary particles is produced can be suppressed.
The upper limit of the bulk density of the resin-encapsulated boron nitride secondary particles is not particularly limited, but is usually 0.95 g / cm ³ or less, preferably 0.9 g / cm ³ or less, and more preferably 0.85 g / cm ³ or less. be. When the bulk density is not more than the above upper limit value, the dispersion of the resin-encapsulating boron nitride secondary particles becomes uniform in the resin composition containing the resin-encapsulating boron nitride secondary particles, and the sedimentation tends to be suppressed.
The bulk density of the resin-encapsulated boron nitride secondary particles can be determined by using a usual device or method for measuring the bulk density of the powder.

[Manufacturing method of resin-encapsulated boron nitride secondary particles]
The method for producing the resin-encapsulating boron nitride secondary particles of the present invention is not particularly limited, and the method for producing the resin-encapsulating boron nitride secondary particles before encapsulation of the resin B is not particularly limited.
(Manufacturing method of boron nitride secondary particles)
As a method for producing the boron nitride secondary particles before encapsulating the resin B, a known method can be used, and examples thereof include the methods shown in Patent Documents 2 to 6 above. As a specific example, the following method is given.
The boron nitride secondary particles are preferably granulated by granulating the particles using a slurry containing a raw material boron nitride powder having a viscosity of 200 to 5000 mPa (hereinafter, may be referred to as “boron nitride slurry”). By heat-treating the particles, the crystallites of the boron nitride primary particles can be grown and produced while maintaining the size of the granulated particles. The viscosity of the boron nitride slurry is preferably 300 mPa · s or more, more preferably 500 mPa · s or more, further preferably 700 mPa · s or more, particularly preferably 1000 mPa · s or more, preferably 4000 mPa · s or less, more preferably 4000 mPa · s or less. It is 3000 mPa · s or less.

The viscosity of the boron nitride slurry greatly affects the average particle diameter D ₅₀ of the generated boron nitride secondary particles based on the volume and the average crystallite diameter of the boron nitride primary particles constituting the boron nitride secondary particles. By setting the value to 200 mPa · s or more, the average crystallite diameter of the boron nitride primary particles and the average particle diameter D ₅₀ based on the volume of the boron nitride secondary particles can be increased.
On the other hand, by setting the viscosity of the boron nitride slurry to 5000 mPa · s or less, granulation can be facilitated.
The viscosity of the boron nitride slurry in the present invention is the viscosity measured at a blade rotation speed of 100 rpm using a rotational viscometer "VISCO BASIC Plus R" manufactured by FUNGILAB.

By adjusting the viscosity of the boron nitride slurry, a resin-encapsulated boron nitride secondary particle-containing resin composition using resin-encapsulated boron nitride secondary particles (may be referred to as a “sheet composition” in the present invention). In the case of production, the thermal conductivity of the obtained sheet tends to be improved as compared with other boron nitride particles even with the same filling amount. This is because the crystal grain boundaries in the boron nitride primary particles decrease due to the increase in the average crystal particle size of the boron nitride primary particles constituting the boron nitride secondary particles, and the boron nitride primary particles constituting the boron nitride secondary particles. It is presumed that this is because the specific surface of the particle is oriented. Preferably, it is considered that the reduction of the contact resistance between the boron nitride secondary particles is also affected by the large volume-based average particle diameter D ₅₀ of the boron nitride secondary particles.
The peak intensity ratio and crystallite diameter can also be controlled by the firing temperature when the granulated particles produced from the boron nitride slurry are heat-treated and the oxygen concentration present in the raw material boron nitride powder. Specifically, as described later, the peak intensity ratio can be set to 3 or more by setting the firing temperature range when heat-treating the granulated particles produced from the boron nitride slurry to 1800 ° C. or higher and 2300 ° C. or lower. By using a raw material having an oxygen concentration of 1.0% by mass or more present in the raw material boron nitride powder, the crystallite diameter can be controlled within a desired range. That is, the peak intensity ratio and the average crystallite diameter can be controlled at the same time by using the raw material boron nitride powder having an appropriate firing temperature range and an appropriate oxygen concentration.

As a result, the contact resistance between the boron nitride secondary particles when the resin-encapsulated boron nitride secondary particles are used as the sheet composition is reduced, and the crystal grain boundaries in the boron nitride primary particles constituting the boron nitride secondary particles are reduced. Boron nitride secondary particles having high thermal conductivity can be produced in which specific crystal planes of the boron nitride primary particles constituting the boron nitride secondary particles are oriented.

(Method of including resin B)
The method of encapsulating the resin B in the boron nitride secondary particles is also not particularly limited. For example, a method of mixing a phenol resin having a hydroxyl group amount of 50 with respect to an epoxy group amount of 100 of the epoxy resin B and an imidazole-based curing accelerator and mixing them with boron nitride secondary particles to perform vacuuming can be mentioned. As a result, the resin is impregnated inside the boron nitride secondary particles, and the particles are contained therein. After that, a phenol and an imidazole-based curing accelerator having a hydroxyl group corresponding to 50% of the epoxy group amount of the resin A and the epoxy resin A, for example, the constituent components of the sheet such as the resin A existing outside the boron nitride secondary particles. Etc. can be mixed. When the viscosity of the resin A is high, a solvent may be appropriately used.

[Primary particles constituting resin-encapsulating boron nitride secondary particles]
(Major axis of boron nitride primary particles)
The major axis of the boron nitride primary particles constituting the resin-encapsulated boron nitride secondary particles is usually 0.5 μm or more, preferably 0.6 μm or more, more preferably 0.8 μm or more, still more preferably 1.0 μm or more, and particularly preferably 1.0 μm or more. It is 1.1 μm or more. Further, it is usually 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. Since it has a high thermal conductivity in the long axis direction, when the primary particles are at least the above lower limit value, the entire secondary particles tend to have a high thermal conductivity. Further, when the value is not more than the above upper limit value, the number of bonding points between the primary particles increases, and it tends to be difficult to crush the primary particles at high pressure.
The major axis is the boron nitride primary particles that can be observed on the image of the boron nitride primary particles that make up one boron nitride secondary particle by enlarging one boron nitride secondary particle obtained by SEM measurement. It is a value obtained by averaging the maximum lengths of primary particles.

(Crystal structure of boron nitride primary particles)
The crystal structure of the boron nitride primary particles is not particularly limited, but those containing hexagonal h-boron nitride as a main component are preferable in terms of ease of synthesis and thermal conductivity. When the binder contains an inorganic component other than boron nitride, they crystallize in the process of heat treatment, but it is sufficient that boron nitride is contained as the main component. The crystal structure of the boron nitride primary particles can be confirmed by powder X-ray diffraction measurement.

(Average crystallite diameter of boron nitride primary particles)
The average crystallite diameter of the boron nitride primary particles obtained from the (002) plane peak of the boron nitride primary particles obtained by powder X-ray diffraction measurement of the resin-encapsulated boron nitride secondary particles of the present invention is not particularly limited. A large average crystallite diameter is preferable from the viewpoint of thermal conductivity. For example, it is usually 300 Å or more, preferably 320 Å or more, more preferably 375 Å or more, still more preferably 380 Å or more, still more preferably 390 Å or more, particularly preferably 400 Å or more, usually 5000 Å or less, preferably 2000 Å or less, and further. It is preferably 1000 Å or less. When the average crystallite diameter is not more than the above upper limit value, the excessive growth of the boron nitride primary particles is suppressed, the gaps in the resin-encapsulated boron nitride secondary particles do not become too wide, and the moldability when forming a molded product is achieved. Tends to improve. In addition, the thermal conductivity tends to be improved by not making the gap too wide. On the other hand, when the average crystallite diameter is equal to or larger than the above lower limit, the increase of grain boundaries in the boron nitride primary particles is suppressed, the occurrence of phonon scattering at the crystal grain boundaries is prevented, and the heat conduction tends to be improved. be.

The powder X-ray diffraction measurement is performed by filling a glass sample plate having a depth of 0.2 mm with resin-encapsulating boron nitride secondary particles so that the surface becomes smooth.
The average crystallite diameter is the crystallite diameter obtained from the (002) plane peak of the boron nitride primary particles obtained by powder X-ray diffraction measurement by the Scherrer equation as described in Examples described later. ..

(Peak intensity ratio of boron nitride primary particles)
In the boron nitride primary particles according to the present invention, the peak intensity ratio ((100) / (004)) of the (100) plane and the (004) plane is preferably 3 or more. The peak intensity ratio is determined by filling a glass sample plate with a depth of 0.2 mm with resin-encapsulated boron nitride secondary particles of powder before molding into a molded body such as a sheet so that the surface becomes smooth, and powder X-ray. It is obtained by diffraction measurement. Further, the peak intensity ratio of the (100) plane and the (004) plane of the resin-encapsulated boron nitride secondary particles is preferably 3 or more, more preferably 3.2 or more, still more preferably 3. It is 0.4 or more, particularly preferably 3.5 or more. Further, it is preferably 10 or less, more preferably 8 or less, and further preferably 7 or less.
Since the peak intensity of the boron nitride primary particles and the resin-encapsulated boron nitride secondary particles is not more than the above upper limit value, the resin-encapsulated boron nitride secondary particles tend to be less likely to collapse when the sheet is formed, and above the above lower limit value. As a result, the thermal conductivity in the thickness direction of the heat dissipation sheet tends to be improved.
The peak intensity ratio can be calculated from the intensity ratio of the corresponding peak intensity measured by the powder X-ray diffraction measurement.

(Peak area intensity ratio of boron nitride primary particles)
The peak area intensity ratio ((100) / (004)) (hereinafter, may be referred to as peak area intensity ratio 1) of the (100) plane and the (004) plane of the boron nitride primary particles according to the present invention is 0. It is preferably 25 or more. For the peak area intensity ratio 1, a pellet-shaped sample obtained by molding resin-encapsulated boron nitride secondary particles with a powder tablet molding machine having a diameter of 10 mm at a molding pressure of 0.85 ton / cm ² is measured by powder X-ray diffraction. Obtained by
The peak area intensity ratio 1 is more preferably 0.3 or more, still more preferably 0.5 or more, still more preferably 0.7 or more, still more preferably 0.81 or more, particularly preferably 0.85 or more, and particularly preferably. Is 0.91 or more. The upper limit is not particularly limited, but is preferably 10.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, still more preferably 2.0 or less, and particularly preferably 1. It is 6.6 or less.

As another expression of the peak area strength ratio, resin-encapsulated boron nitride secondary particles are obtained by molding with a powder tablet molding machine of 10 mmφ at a molding pressure of 0.85 ton / cm ² or more and 2.54 ton / cm ² or less. The peak area intensity ratio (100) / (004) of the (100) plane and the (004) plane of the boron nitride primary particles constituting the resin-encapsulated boron nitride secondary particles in the pellet-shaped sample (hereinafter) can be mentioned. , The peak area intensity ratio may be expressed as 2.). The peak area intensity ratio 2 is preferably 0.25 or more, more preferably 0.30 or more, still more preferably 0.35 or more, still more preferably 0.40 or more. Further, it is preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.2 or less. When the peak area intensity ratio 2 is smaller than the above upper limit value, the contact resistance between the boron nitride secondary particles tends not to be too large when the molded product is formed. Further, when the peak area strength ratio 2 is larger than the above lower limit value, the disintegration of the resin-encapsulated boron nitride secondary particles during sheet molding is suppressed, and the thermal conductivity in the thickness direction tends to be improved.

Usually, the optimum press pressure condition for a heat radiating sheet or the like differs depending on the type of the heat radiating sheet. The boron nitride secondary particles dispersed in the resin matrix are exposed to pressure conditions depending on the application, but the boron nitride particles usually tend to have the ab plane oriented in a direction orthogonal to the pressure direction. Even when boron nitride secondary particles are used, particle deformation occurs with respect to the forming pressure, and as a result, the ab surface tends to be oriented in the direction orthogonal to the pressure direction.
For example, a high heat dissipation substrate made of resin has 0.85 ton / cm ² or more and 2.54 ton / cm ² or less in order to reduce voids inside the resin substrate and to completely contact the dispersed boron nitride secondary particles. It is considered that the molding is performed at a relatively high pressure. Therefore, boron nitride secondary particles with a small change in orientation of the boron nitride primary particles are required for improving thermal conductivity even in the pressure range used for the peak surface intensity ratio 2.

In the resin-encapsulated boron nitride secondary particles of the present invention, preferably, the boron nitride primary particles constituting the resin-encapsulated boron nitride secondary particles have a cardhouse structure. This is because the boron nitride primary particles have a mutually reinforcing structure due to contact between the primary particle plane portion and the end face portion, so that it is possible to suppress the deformation of the resin-encapsulated boron nitride secondary particles in a wide molding pressure range. be. The optimum pressure range varies depending on the application, but in order to achieve high thermal conductivity in the thickness direction of the compact, the primary particle orientation is at least constant or higher in the range of 0.85 ton / cm ² or more and 2.54 ton / cm ² . It is preferable to achieve a state in which.

The primary particle orientation above a certain level is expressed by, for example, the peak area intensity ratio (100) / (004) of the (100) plane and the (004) plane of the primary particle, which is the (004) plane, that is, It expresses how small the ratio of the ab planes oriented in the direction orthogonal to the pressure direction is. Therefore, the larger the above-mentioned peak area intensity ratio, the less the deformation of the boron nitride secondary particles due to the forming pressure. In order to achieve high thermal conductivity, it is necessary that the peak area intensity ratio is at least 0.25 or more. The lower and upper limits of the peak area intensity ratio are as described above.
The peak area intensity ratio in the range of 0.85 ton / cm ² or more and 2.54 ton / cm ² does not have any problem as long as even one point in the above pressure range satisfies a predetermined value, and it is necessary to achieve it in the entire pressure range of the present invention. do not have. Further, it is preferable that a predetermined value is satisfied at three points of 0.85 ton / cm ² , 1.69 ton / cm ² , and 2.54 ton / cm ² .

The peak area strength ratio is determined by filling a tablet molding machine (10 mmφ) with about 0.2 g of powder and using a manual hydraulic pump (P-1B-041 manufactured by RIKEN Seiki Co., Ltd.) at various press pressures. The tableted sample is subjected to measurement (eg, 0.85 ton / cm ² , 1.69 ton / cm ² , 2.54 ton / cm ² , etc.). The measurement can be performed using an X'PertPro MPD powder X-ray diffractometer manufactured by PANalytical in the Netherlands, and the intensity ratio of the corresponding peak area can be calculated.

<Boron Nitride Particle Containing Sheet>
[Resin-encapsulated boron nitride secondary particle-containing resin composition]
When producing the boron nitride particle-containing sheet of the present invention, the resin-encapsulated boron nitride secondary particle-containing resin composition containing the resin-encapsulated boron nitride secondary particles and the resin A (hereinafter referred to as “sheet composition” may be referred to. By using the above), it becomes possible to manufacture a boron nitride particle-containing sheet having both higher thermal conductivity and withstand voltage.
The content ratio of the resin-encapsulated boron nitride secondary particles in the sheet composition is usually 5% by mass or more, preferably 30% by mass or more, more preferably, with the total of the resin-encapsulating boron nitride secondary particles and the resin A as 100% by mass. Is 50% by mass or more, usually 95% by mass or less, preferably 90% by mass or less. When it is smaller than the above upper limit, the viscosity of the sheet composition is suppressed and the molding processability tends to be obtained. Further, the resin-encapsulated boron nitride secondary particles are densely packed, and the thermal conductivity of the boron nitride particle-containing sheet tends to be improved. Further, when the value is equal to or higher than the above lower limit, the molding processability and the thermal conductivity are improved. Both tend to improve.

(Hardener)
The sheet composition and the boron nitride particle-containing sheet according to the present invention may contain a curing agent, and the contained curing agent is not particularly limited. The curing agent is preferably a phenolic resin, an acid anhydride having an aromatic skeleton or an alicyclic skeleton, a water additive of the acid anhydride, a modified product of the acid anhydride, or the like. By using this preferable curing agent, it is possible to obtain a cured product of a resin-encapsulated boron nitride secondary particle-containing sheet having an excellent balance of heat resistance, moisture resistance and electrical characteristics. As the curing agent, only one kind may be used, or two or more kinds may be used in combination.

The phenol resin is not particularly limited. Specific examples of the above-mentioned phenolic resin include phenol novolac, o-cresol novolak, p-cresol novolak, t-butylphenol novolak, dicyclopentadiencresol, polyparavinylphenol, bisphenol A type novolak, xylylene-modified novolak, and decalin-modified novolak. Examples thereof include poly (di-o-hydroxyphenyl) methane, poly (di-m-hydroxyphenyl) methane, poly (di-p-hydroxyphenyl) methane and the like. Among them, since the flexibility and flame retardancy of the boron nitride secondary particle-containing sheet can be further enhanced, it is selected from a phenol resin having a melamine skeleton, a phenol resin having a triazine skeleton, and a phenol resin having an allyl group. At least one is preferable.

Commercially available products of the above phenol resin include MEH-8005, MEH-8000H and NEH-8015 (all of which are manufactured by Meiwa Kasei Co., Ltd.), YLH903 (manufactured by Mitsubishi Chemical Corporation), LA-7052, LA-7054, LA-7751 and the like. Examples thereof include LA-1356 and LA-3018-50P (all manufactured by Dainippon Ink Co., Ltd.), PS6313 and PS6492 (manufactured by Gun Ei Chemical Industry Co., Ltd.).

The acid anhydride having an aromatic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride is not particularly limited. Examples of the acid anhydride having an aromatic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride include styrene / maleic anhydride copolymer, benzophenone tetracarboxylic acid anhydride, and pyromellitic acid anhydride. Trimellitic anhydride, 4,4'-oxydiphthalic anhydride, phenylethynylphthalic anhydride, glycerol bis (anhydrotrimericate) monoacetate, ethylene glycol bis (anhydrotrimericate), methyltetrahydrohydroanhydride Examples thereof include an acid, methylhexahydroanhydride phthalic acid, and trialkyltetrahydroanhydride phthalic acid. Of these, methylnadic acid anhydride or trialkyltetrahydrophthalic anhydride is preferable. The use of methylnadic acid anhydride or trialkyltetrahydrophthalic anhydride can enhance the water resistance of the cured product of the boron nitride secondary particle-containing sheet.

Examples of commercially available products of the acid anhydride having an aromatic skeleton, a water additive of the acid anhydride, or a modified product of the acid anhydride include SMA resin EF30, SMA resin EF40, SMA resin EF60, and SMA resin EF80 (any of the above). Also manufactured by Sartmer Japan), ODPA-M and PEPA (all manufactured by Manac), Rikagit MTA-10, Rikagit MTA-15, Rikagit TMTA, Rikagit TMEG-100, Rikagit TMEG-200, Rikagit TMEG-300, Rikagit TMEG-500, Rikagit TMEG-S, Rikagit TH, Rikagit HT-1A, Rikagit HH, Rikagit MH-700, Rikagit MT-500, Rikagit DSDA and Rikagit TDA-100 (all manufactured by Shin Nihon Rika Co., Ltd.), and EPICLON B4400, EPICLON B650, EPICLON B570 (all of which are manufactured by Dainippon Ink and Chemicals Co., Ltd.) and the like can be mentioned.

The acid anhydride having an alicyclic skeleton, a water additive of the acid anhydride or a modified product of the acid anhydride is an acid anhydride having a polylipocyclic skeleton, a water additive of the acid anhydride or the acid anhydride thereof. A modified acid anhydride, an acid anhydride having an alicyclic skeleton obtained by an addition reaction between a terpene compound and maleic anhydride, a water additive of the acid anhydride, or a modified product of the acid anhydride. Is preferable. In this case, the flexibility, moisture resistance or adhesiveness of the boron nitride secondary particle-containing sheet can be further enhanced. The acid anhydride having an alicyclic skeleton, the water additive of the acid anhydride, or the modified product of the acid anhydride includes methylnadic acid anhydride, an acid anhydride having a dicyclopentadiene skeleton, or the acid. Modified products of anhydrides and the like can also be mentioned.

As commercially available products of the acid anhydride having an alicyclic skeleton, a water additive of the acid anhydride, or a modified product of the acid anhydride, Rikagit HNA and Rikagit HNA-100 (all of which are manufactured by Shin Nihon Rika Co., Ltd.). , Epicure YH306, Epicure YH307, Epicure YH308H, Epicure YH309 (all of which are manufactured by Mitsubishi Chemical Co., Ltd.) and the like.

(Curing accelerator)
In order to adjust the curing rate, the physical properties of the cured product, and the like, the above-mentioned curing agent and the curing accelerator may be used in combination.

The curing accelerator is not particularly limited. Specific examples of the curing accelerator include tertiary amines, imidazoles, imidazolines, triazines, organic phosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes such as organic acid salts, and the like. Examples of the curing accelerator include organometallic compounds, quaternary ammonium salts, metal halides and the like. Examples of the organometallic compounds include zinc octylate, tin octylate, and an aluminum acetylacetone complex.

As the above-mentioned curing accelerator, a cyano group-containing imidazole-based curing accelerator, a high melting point imidazole-based curing accelerator, a high melting point dispersed latent curing accelerator, a microcapsule type latent curing accelerator, and an amine salt type latent curing agent. Accelerators, high temperature dissociation type and thermocationic polymerization type latent curing accelerators and the like can be used. As the curing accelerator, only one kind may be used, or two or more kinds may be used in combination.

The curing accelerator is preferably a cyano group-containing imidazole type. The cyano group-containing imidazole system has high resin compatibility, but is also characterized by a high reaction active region. As a result, the reaction system can be easily controlled, and the curing rate of the boron nitride secondary particle-containing sheet and the physical properties of the cured product of the boron nitride secondary particle-containing sheet can be adjusted more easily.

It is preferable that the curing agent is contained in the range of 5 to 50 parts by mass in 100 parts by mass of the resin A contained in the sheet composition and the boron nitride particle-containing sheet. The more preferable lower limit of the content of the curing agent in 100 parts by mass of the resin A is 10% by mass, and the more preferable upper limit is 40% by mass. When the amount of the curing agent is at least the above lower limit value, the boron nitride secondary particle-containing sheet tends to be sufficiently cured. When the amount of the curing agent is not more than the above upper limit, excess curing agent not involved in curing is not generated, and the cross-linking of the cured product tends to proceed sufficiently. Therefore, the heat resistance and adhesiveness of the cured product of the boron nitride secondary particle-containing sheet can be sufficiently obtained.
In particular, when a phenol resin is used as a curing agent, it is preferable to adjust the number of hydroxyl groups and the number of epoxy groups contained in the phenol. The number of hydroxyl groups of phenol is 20 or more, more preferably 40 or more, still more preferably 50 or more, 100 or less, more preferably 80 or less, still more preferably 70 or less, relative to the number of epoxy groups of 100.

(Other fillers)
The sheet composition and the boron nitride particle-containing sheet of the present invention may contain a filler in addition to the resin-containing boron nitride secondary particles. Fillers other than resin-containing boron nitride secondary particles include aluminum nitride, boron nitride primary particles, alumina, crystalline silica, synthetic magnesite, silicon carbide, zinc oxide and magnesium oxide, nylon beads, acrylic beads, and epoxy beads. Examples thereof include synthetic resin particles such as styrene beads and urethane beads. The shape of the filler may be spherical, scaly, or irregular such as a crushed product. As the filler other than the resin-containing boron nitride secondary particles, only one kind may be used, or two or more kinds may be used in combination.

The volume average particle size (D ₅₀ ) of the other filler is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more, further preferably 0.5 μm or more, and particularly preferably 1 μm or more. Further, 60 μm or less is preferable, 40 μm or less is more preferable, 20 μm or less is further preferable, and 10 μm or less is particularly preferable.
When the average particle size is at least the above lower limit, the viscosity of the sheet composition is suppressed, and the filler can be filled with a high density. Further, when the average particle diameter is not more than the above upper limit value, the dielectric breakdown characteristics of the cured product of the boron nitride particle-containing sheet tend to be improved.
The above-mentioned "average particle size" is an average particle size obtained from the particle size distribution measurement result of the volume average measured by the laser diffraction type particle size distribution measuring device.

The content volume% of the other filler in 100% by volume of the heat-dissipating boron nitride particle-containing sheet is not particularly limited, but is preferably 5% by volume or more, more preferably 10% by volume or more, still more preferably 15% by volume or more. Further, 65% by volume or less is preferable, 60% by volume or less is more preferable, and 50% by volume or less is further preferable. When it is at least the above lower limit value, sufficient thermal conductivity tends to be obtained, and when it is at least the above upper limit value, the amount of resin between the fillers becomes an appropriate amount and the sheet shape can be maintained. It is in.

(Organic solvent)
The sheet composition and the boron nitride particle-containing sheet of the present invention may contain an organic solvent. The amount of the organic solvent contained is preferably 5 parts by mass or less with respect to 100 parts by mass of the heat-dissipating boron nitride particle-containing sheet. It is more preferably 1% by mass or less, still more preferably 0.5% by mass or less. If the amount of the organic solvent exceeds 5 parts by mass, void formation may occur due to solvent volatilization during curing.
The boiling point of the organic solvent is preferably 200 ° C. or lower, more preferably 180 ° C. or lower.

Examples of the organic solvent include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether and the like.

(Dispersant)
The sheet composition and the boron nitride particle-containing sheet according to the present invention may contain a dispersant. By using the dispersant, the thermal conductivity and dielectric breakdown characteristics of the cured product of the boron nitride particle-containing sheet can be further enhanced.

The dispersant preferably has a functional group containing a hydrogen atom having a hydrogen bonding property. When the dispersant has a functional group containing hydrogen atoms having hydrogen bonding properties, the thermal conductivity and dielectric breakdown characteristics of the cured product of the insulating sheet can be further enhanced. Examples of the functional group containing a hydrogen atom having hydrogen bonding property include a carboxyl group (pKa = 4), a phosphate group (pKa = 7), a phenol group (pKa = 10) and the like.

The pKa of the functional group containing a hydrogen atom having hydrogen bonding property is preferably in the range of 2 to 10, and more preferably in the range of 3 to 9. When the pKa is 2 or more, the reaction of the epoxy component is suppressed, and when the uncured boron nitride particle-containing sheet is stored, the storage stability of the boron nitride particle-containing sheet tends to be obtained. When the pKa is 10 or less, the function as a dispersant is sufficiently fulfilled, and the thermal conductivity and dielectric breakdown characteristics of the cured product of the boron nitride particle-containing sheet tend to be sufficiently enhanced.

The functional group containing a hydrogen atom having hydrogen bonding property is preferably a carboxyl group or a phosphoric acid group. In this case, the thermal conductivity and dielectric breakdown characteristics of the cured product of the boron nitride particle-containing sheet can be further enhanced.

Specific examples of the dispersant include polyester-based carboxylic acid, polyether-based carboxylic acid, polyacrylic carboxylic acid, aliphatic carboxylic acid, polysiloxane-based carboxylic acid, polyester-based phosphoric acid, and polyether-based dispersant. Examples thereof include phosphoric acid, polyacrylic phosphoric acid, aliphatic phosphoric acid, polysiloxane-based phosphoric acid, polyester-based phenol, polyether-based phenol, polyacrylic-based phenol, aliphatic phenol, polysiloxane-based phenol and the like. As the dispersant, only one kind may be used, or two or more kinds may be used in combination.

Further, the sheet composition of the present invention and the boron nitride particle-containing sheet may contain a thixotropic agent, a flame retardant, a colorant and the like, if necessary.

[Method for preparing sheet composition]
The method for preparing the sheet composition is not particularly limited, and a conventionally known method can be used. At that time, for the purpose of improving the uniformity of the sheet composition, defoaming, etc., a paint shaker, a bead mill, a planetary mixer, a stirring type disperser, a self-rotating stirring mixer, a three-roll, a kneader, a single shaft or two. It is preferable to mix and stir using a general kneading device such as a shaft kneader.

The mixing order of each compounding component is also arbitrary unless there is a particular problem. For example, a matrix resin is mixed and dissolved in an organic solvent to prepare a resin solution, and the obtained resin solution is mixed with a resin-encapsulated boron nitride secondary. A sufficiently mixed mixture of particles and the above other components is added and mixed, and then an organic solvent for viscosity adjustment is added and mixed, and then a resin curing agent, a curing accelerator, a dispersant or the like is further added. Examples thereof include a method of adding an agent and mixing.

[Manufacturing method of boron nitride particle-containing sheet]
Hereinafter, a method for producing the boron nitride particle-containing sheet of the present invention using the sheet composition will be specifically described.

(Applying process)
First, a coating film is formed on the surface of the base material with the sheet composition.
That is, the sheet composition is used to form a coating film by a dip method, a spin coating method, a spray coating method, a blade method, or any other method. By using a coating device such as a spin coater, a slit coater, a die coater, or a blade coater for coating the slurry, it is possible to uniformly form a coating film having a predetermined film thickness on the substrate, which is preferable. As the base material, a copper foil or PET film described later is generally used, but the substrate is not limited in any way.

(Drying process)
Next, the sheet composition applied to the substrate is dried. The drying temperature is usually 10 ° C. or higher, preferably 15 ° C. or higher, more preferably 20 ° C. or higher, still more preferably 25 ° C., usually 140 ° C. or lower, preferably 100 ° C. or lower, more preferably 90 ° C. or lower, still more preferable. Is 80 ° C. or lower, more preferably 70 ° C. or lower. When it is at least the above lower limit, the organic solvent in the coating film can be sufficiently removed, and the organic solvent is prevented from evaporating in the high temperature pressure treatment in the next sheeting step, and the evaporation trace of the residual solvent becomes a void. Tend to be able to. When it is not more than the above upper limit value, the curing of the matrix resin can be suppressed, and a good dry film tends to be obtained.

The drying time is usually 1 hour or longer, preferably 2 hours or longer, more preferably 3 hours or longer, still more preferably 4 hours or longer, and usually 168 hours or shorter, preferably 144 hours or shorter, more preferably 120 hours or shorter. , More preferably 96 hours or less. When it is at least the above lower limit, the organic solvent in the coating film can be sufficiently removed, and the organic solvent is prevented from evaporating in the high temperature pressure treatment in the next sheeting step, and the evaporation trace of the residual solvent becomes a void. Tend to be able to. When it is not more than the above upper limit, a coating film having good strength can be obtained, and further, sufficient fluidity can be obtained by plasticizing the matrix resin in the sheeting step, which is sufficient for voids existing in the boron nitride particle-containing sheet. It tends to be able to penetrate the resin.

The film thickness of the boron nitride particle-containing sheet before drying is usually 100 μm or more, preferably 150 μm or more, more preferably 200 μm or more, still more preferably 300 μm or more, and usually 800 μm or less, preferably 700 μm or less, more preferably 600 μm. Below, it is more preferably 500 μm or less. When the film thickness is not more than the above upper limit value, it becomes easy to control the evaporation rate of the organic solvent, and the void in the boron nitride particle-containing sheet tends to be reduced. Further, when the value is not more than the above lower limit, a sheet containing boron nitride particles having good strength tends to be obtained.

At this time, the heat treatment may be performed at a constant temperature, but the heat treatment may be performed under reduced pressure conditions in order to smoothly remove volatile components such as an organic solvent in the coating liquid. Further, heat treatment may be performed by gradually raising the temperature as long as the curing of the resin does not proceed. For example, a method of heating at 25 to 40 ° C., a method of first heating at 30 ° C., then a method of heating at 40 to 90 ° C., a method of heating at 50 ° C., and the like can be mentioned. The heating time can be, for example, about 30 to 60 minutes.

(Pressurization process)
After the drying step, a pressurizing step may be performed. It is desirable to pressurize the sheeting step for the purpose of joining fillers containing secondary particles of boron nitride contained in the resin to form a heat path, eliminating voids and voids in the sheet, and for making the sheet adhere to the substrate. ..
In the pressurizing step, a weight of usually 10 kgf / cm ² to 2000 kgf / cm ² , preferably 20 kgf / cm ² to 1000 kgf / cm ² , more preferably 50 kgf / cm ² to 800 kgf / cm ² is applied to the dry film on the substrate. It is desirable to carry out over. By setting the load during pressurization to the above upper limit or less, it tends to be possible to obtain a sheet having high thermal conductivity with no voids in the sheet without breaking the resin-containing boron nitride secondary particles. .. Further, by setting the weight to the above lower limit or more, the contact between the fillers containing the resin-encapsulated boron nitride secondary particles becomes good, and it becomes easy to form a heat conduction path, so that a sheet having high heat conductivity can be obtained. There is a tendency to do it.
In the pressurizing step, it is desirable to heat the composition film coated and dried on the copper substrate at usually 25 to 300 ° C, preferably 40 to 250 ° C, more preferably 50 to 200 ° C, and particularly preferably 60 to 180 ° C. .. By performing the sheet forming step in this temperature range, the melt viscosity of the resin in the coating film can be lowered, and voids and voids in the sheet can be eliminated.
The pressurizing step is usually 30 seconds to 4 hours, preferably 1 minute to 2 hours, more preferably 3 minutes to 1 hour, and particularly preferably 5 minutes to 45 minutes. By performing this within this range, the manufacturability is improved, and there is a tendency that voids and voids in the sheet can be sufficiently removed.

After drying, the film thickness of the boron nitride particle-containing sheet before pressing is usually 50 μm or more, preferably 80 μm or more, more preferably 100 μm or more, still more preferably 150 μm or more, and usually 600 μm or less, preferably 400 μm or less, more preferably. Is 300 μm or less, more preferably 200 μm or less.
Further, the film thickness of the boron nitride particle-containing sheet after pressing can be appropriately adjusted according to the intended use. It is usually 40 μm or more, preferably 70 μm or more, more preferably 100 μm or more, and usually 500 μm or less, preferably 300 μm or less, more preferably 200 μm or less. With the above film thickness, the withstand voltage tends to be improved and the thermal resistance tends to be suppressed.

The curing step for completely performing the curing reaction may be performed under pressure or without pressurization, but in the case of pressurization, the conditions are the same as those for the above-mentioned pressurization step for the same reason as above. It is desirable to do it in. The pressurizing step and the curing step may be performed at the same time.

The thermal conductivity (W / mK) of the boron nitride particle-containing sheet is not particularly limited, but is preferably 2 W / mK or more, more preferably 3 W / mK or more, still more preferably 5 W / mK or more, still more preferably 10 W / mK. It is mK or more, more preferably 13 W / mK, particularly preferably 15 W / mK or more, and particularly preferably 17 W / mK or more.
The withstand voltage performance is not particularly limited, but is preferably 3 kV / mm or more, more preferably 3.3 kV / mm or more, still more preferably 5 kV / mm or more, still more preferably 8 kV / mm or more, still more preferably. Is 10 kV / mm or more, more preferably 15 kV / mm or more, still more preferably 20 kV / mm or more, and particularly preferably 30 kV / mm or more.
The adhesive strength (N / cm) of the boron nitride particle-containing sheet is not particularly limited, but is usually 0.5 N / cm or more, preferably 1 N / cm or more, more preferably 2 N / cm, and particularly preferably 3 N / cm. It is cm or more, particularly preferably 5 N / cm or more.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. The values of various conditions and evaluation results in the following examples indicate the preferable range of the present invention as well as the preferable range in the embodiment of the present invention, and the preferable range of the present invention is the above-mentioned embodiment. It can be determined in consideration of the preferred range and the range indicated by the combination of the values of the following examples or the values of the examples.
The measurement conditions in the examples are described below.

[Thermal conductivity in the thickness direction of the molded product]
Using the thermal resistance measuring device "T3star" manufactured by Mentor Graphics Co., Ltd., the thermal resistance values of the sheet molded bodies containing boron nitride secondary particles with the same composition and the same conditions and different thicknesses were measured, and the thermal resistance values were determined. The thermal conductivity was obtained from the slope of the graph plotted against the thickness.

[Measurement of withstand voltage of molded product (sheet)]
Compliant with JIS C2110: 1994 Using AC Withstand Voltage Tester 7473 manufactured by Measurement Technology Laboratory Co., Ltd., a molded sheet is placed in Florinate FC-40 using a cylindrical electrode with a diameter of 25 mm at a load of 500 g from 0 V to 20 kV at 0.5 kV / s. The voltage was applied at the boosting speed, and the voltage exceeding the current threshold of 10 mA was measured to obtain the dielectric breakdown voltage. The number of data was measured at points from one sample and averaged.

[Evaluation of adhesive strength of cured sheet]
Using a tensile test device manufactured by A & Co., Ltd., the adhesive strength of a sample to which a copper foil was bonded using a heat-dissipating boron nitride secondary particle-containing sheet was evaluated by a 90 ° peel test. The tensile speed at the time of evaluation was evaluated at 50 mm / min.

[Example 1]
<Manufacturing of Boron Nitride Secondary Particles>
Boron nitride secondary particles having a card house structure were produced by the following method.
As a raw material, hexagonal boron nitride (hereinafter referred to as raw material h-BN powder) having a half width of the (002) plane peak obtained by powder X-ray diffraction measurement of 2θ = 0.67 ° and an oxygen concentration of 7.5% by mass is described. ) Was used.

(material)
Raw material h-BN powder: 10,000 g
Binder ("Taxerum M160L" manufactured by Taki Chemical Co., Ltd., solid content concentration 21% by mass): 11496 g
Surfactant (Kao Corporation surfactant "ammonium lauryl sulfate": solid content concentration 14% by mass): 250 g

(Preparation of slurry)
A predetermined amount of the raw material h-BN powder was weighed in a resin bottle, and then a predetermined amount of a binder was added. Further, after adding a predetermined amount of the surfactant, a zirconia-based ceramic ball was added, and the mixture was stirred on a pot mill rotary table for 1 hour. The viscosity of the slurry was 810 mPa · s.

(Granulation)
Granulation from the BN slurry was carried out using FOC-20 manufactured by Okawara Kakoki Co., Ltd. at a disk rotation speed of 20000 to 23000 rpm and a drying temperature of 80 ° C. to obtain spherical BN granulated particles.

(Preparation of Boron Nitride Secondary Particles)
After vacuuming the above BN granulated particles at room temperature, nitrogen gas is introduced to repressurize the particles, and the temperature is raised to 2000 ° C. at 83 ° C./hour while introducing nitrogen gas as it is. It was held for 5 hours while introducing gas. Then, it was cooled to room temperature to obtain spherical boron nitride secondary particles having a curd house structure.

(Classification)
Further, the boron nitride secondary particles after the heat treatment were lightly pulverized using a mortar and a pestle, and then classified using a sieve having an opening of 90 μm. After classification, the average crystallite diameter of the BN primary particles constituting the boron nitride secondary particles, the peak intensity ratio between the (100) plane and the (004) plane of the BN primary particles ((100) / (004)), and boron nitride. The D ₅₀ of the secondary particles was measured. The measurement results are shown in Table 1.

<Manufacturing of resin-encapsulated boron nitride secondary particles>
As the resin B, 1.92 g of epoxy resin 1 (bifunctional aliphatic epoxy resin, epoxy equivalent 205 g / eq) and 0.647 g of phenol resin 1 (hydroxyl equivalent 143 g / eq) were used. 0.135 g of imidazole-based curing accelerator 1 (MEK solution having a solid content concentration of 20% by mass) was mixed with resin B, and 2.5 g of boron nitride secondary particles having a curdhouse structure were added. The mixture was stirred at 400 rpm for 30 seconds and at 2000 rpm for 3 minutes. Further, 2.74 g of boron nitride secondary particles were added (5.24 g in total of the boron nitride secondary particles), and the mixture was similarly stirred with Awatori Rentaro.
Then, the mixture was exposed to vacuum at 30 ° C. for 15 minutes in a vacuum oven to enclose the resin B in the boron nitride secondary particles to obtain the resin-encapsulated boron nitride secondary particles 1. The epoxy equivalent of the epoxy resin B contained in the resin-encapsulating boron nitride secondary particles 1 was 205 g / eq.

<Manufacturing of Boron Nitride Particle-Containing Sheets>
As the resin A, 1.04 g of epoxy resin 1, 0.522 g of phenol resin 1, and bisphenol F-based phenoxy resin 1 (MEK solution having a solid content concentration of 45% by mass, epoxy equivalent 9).
840 g / eq) was prepared at 3.49 g, and epoxy resin 2 (trifunctional aromatic epoxy resin, epoxy equivalent 97 g / eq) was prepared at 0.207 g.
Alumina particles 1 (average particle size 7 μm, specific surface area 0.9 m ² / g manufactured by Admatex Co., Ltd.) 26.3 g, nylon particles 1 (5 μmΦ manufactured by Toray Co., Ltd.) 0.014 g, and imidazole-based curing accelerator 1 are added to the resin A. 0.146 g, methyl ethyl ketone (MEK) 5 as a solvent
.. 25 g was mixed and added to 7.83 g of resin-encapsulated boron nitride secondary particles 1. after that,
Stirring and mixing was carried out by Rentaro Awatori under the same conditions as above. The epoxy equivalent of the epoxy resin A was 5568 g / eq.
The above sheet composition was cast on a PET film using an applicator with a gap of 300 μm. After drying on a hot plate at 60 ° C. for 1 hour, the solvent was removed by further heating in a vacuum oven at 60 ° C. for 1 hour to obtain a boron nitride particle-containing sheet 1.
A PET film was placed on the boron nitride particle-containing sheet 1 and pressed at 100 kgf / cm ² and 70 ° C. for 10 minutes using a hand press machine. The thickness of the boron nitride particle-containing sheet 1 after pressing was 135 μm. When the withstand voltage was measured in Fluorinert using a cylindrical electrode, it was 3.31 kV / mm, which was a good value. Further, the boron nitride particle-containing sheet 1 after pressing was very flexible and did not crack even when wound around a Φ5 mm cylinder.

[Comparative Example 1]
Mix 5.79 g of bisphenol F-based phenoxy resin 1, 1.70 g of epoxy resin 1, 0.342 g of epoxy resin 2, 0.868 g of phenol resin 1, 0.28 g of imidazole-based curing accelerator 1, and 4 g of MEK. , Stirred well. Further, the resin-encapsulated boron nitride secondary particles 2 are 5.22 g, the alumina particles 1 are 26.51 g, and the nylon particles 1 are 0.014.
9 g was added, and stirring and mixing was carried out using Awatori Rentaro under the same conditions as in Example 1.
In Comparative Example 1, the epoxy resin A and the epoxy resin B have the same composition, and WPE _A and W have the same composition.
PE _B was 5599 g / eq. The boron nitride particle-containing sheet 2 was produced in the same manner as in Example 1. The thickness of the obtained boron nitride particle-containing sheet 2 was 148 μm, and the withstand voltage was 2.9 kV / mm.

Claims (2)

Boron nitride secondary particles containing resin B,
Resin A ,
as well as
Contains alumina
A sheet containing boron nitride particles,
Resin A and resin B contain an epoxy resin and a phenol resin , respectively.
The content of the epoxy resin A in the resin A is 5% by mass or more and 95% by mass or less.
The epoxy equivalent of the epoxy resin A contained in the resin A is larger than the epoxy equivalent of the epoxy resin B contained in the resin B.
The epoxy equivalent of the epoxy resin A is 1000 or more and 10000 or less.
The epoxy equivalent of the epoxy resin B is less than 270,
Alumina content is 5% by volume or more and 65% in 100% by volume of boron nitride particle-containing sheet.
Less than volume,
Boron nitride particle-containing sheet. The boron nitride particle-containing sheet according to claim 1, wherein the boron nitride secondary particles contain boron nitride secondary particles having a card house structure.

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