Provided is a thermosetting resin composition including an epoxy resin and thermally conductive particles. A thermal conductivity λ.sub.200 at 200° C. of a cured product obtained by heating the thermosetting resin composition at 200° C. for 90 minutes is 12 W/(m.Math.K) or higher. In addition, a volume resistivity R.sub.200 of the cured product at 200° C. is preferably 1.0×10.sup.10 Ω.Math.m or more. In addition, a resin sheet using this thermosetting resin composition is provided. Furthermore, a metal base substrate using this thermosetting resin composition is provided.

A resin composition including: a thermosetting resin component including a mesogen; and a phosphorus atom-containing thermoplastic polymer type frame retardant, wherein the thermoplastic polymer type frame retardant is a phosphorous atom-containing formed by polymerizing or copolymerizing one of monomers represented by general formulae (1) and (2) below, ##STR00001## wherein, in the general formulae (1) and (2), each of R1 and R2 is any one of an alkyl group, an alkoxy group, an aryl group and an aryloxy group, R1 and R2 being different or identical, and R3 is a methyl group or a hydrogen atom.

A thermally conductive sheet has a thermally conductive resin composition layer, wherein the thermally conductive resin composition layer is made of a thermally conductive resin composition (1) including an inorganic filler and a binder resin (3). The inorganic filler includes a boron nitride particle (2), the content of the inorganic filler in the thermally conductive resin composition layer is 65% by volume or more, and the boron nitride particle (2) has an average aspect ratio of 7 or less, which is calculated from a major axis and a minor axis of a primary particle measured by a specific method. The thermally conductive resin composition layer has a thickness of 200 μm or less.

Provided is a production method which makes it possible to improve a filling property, with respect to a resin, of a hexagonal boron nitride powder which contains hexagonal boron nitride particles each having a low aspect ratio, while maintaining low thermal conduction anisotropy of the hexagonal boron nitride powder. A method of producing a hexagonal boron nitride powder includes disintegrating, by a means which substantially does not involve pulverization of primary particles, a hexagonal boron nitride raw material powder which contains (i) hexagonal boron nitride particles each having an aspect ratio of 1.5 to 5.0 and (ii) an aggregate that contains hexagonal boron nitride particles each having an aspect ratio of more than 5.0.

A thermally conductive silicone composition contains a silicone polymer and a thermally conductive inorganic filler. The ratio X of the BET specific surface area (m.sup.2/g) to the average particle size (μm) of the thermally conductive inorganic filler is 0.1 or more. The thermally conductive inorganic filler is surface treated with a first surface treatment agent and further surface treated with a second surface treatment agent. The first surface treatment agent contains an organic silane compound represented by R.sup.11SiR.sup.12.sub.x(OR.sup.13).sub.3-x (where R.sup.11 is, e.g., a monovalent aliphatic hydrocarbon group having 1 to 4 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 30 carbon atoms, R.sup.12 is, e.g., a methyl group, and R.sup.13 is, e.g., a hydrocarbon group having 1 to 4 carbon atoms). The second surface treatment agent contains a silicone polymer that has a kinematic viscosity of 1000 mm.sup.2/s or less and does not have a hydrolyzable group. Thus, the present invention provides a thermally conductive silicone composition that has improved viscoelasticity and heat resistance, and a method for producing the thermally conductive silicone composition.

Boron nitride nanotube (BNNT) dispersions and methods of fabricating the same are provided. Tip sonication-assisted hydrolysis can be utilized, with a dispersant/surfactant (e.g., polyvinyl alcohol (PVA)). The fabrication process can be used to obtain large scale BNNT dispersions with long term stability (e.g., stability for at least 3 months, at least 4 months, at least 5 months, at least 6 months, or about 6 months).

Provided is a heat dissipation sheet capable of effectively enhancing adhesiveness and long-term insulation reliability. The heat dissipation sheet according to the present invention contains first inorganic particles having an aspect ratio of 2 or less, second inorganic particles having an aspect ratio of more than 2, and a binder resin. In this heat dissipation sheet, a content of the second inorganic particles is larger than a content of the first inorganic particles in 100% by volume of a region having a thickness of 15% on a first surface side in a thickness direction, and the content of the first inorganic particles in 100% by volume of the region having a thickness of 15% is larger than the content of the first inorganic particles in 100% by volume of a central region having a thickness of 70%.

An object of the present invention is to provide a composition for forming a thermally conductive material, from which a thermally conductive material having excellent thermally conductive properties can be obtained. In addition, another object of the present invention is to provide a thermally conductive material formed of the composition for forming a thermally conductive material, a thermally conductive sheet, and a device with a thermally conductive layer.

A composition for forming a thermally conductive material of the present invention includes an epoxy compound, an inorganic substance, and a compound X containing one or more functional groups selected from the group consisting of an alkenyl group, an acrylate group, a methacrylate group, a silyl group, an acid anhydride group, a cyanate ester group, an amino group, a thiol group, and a carboxylic acid group, or having a polyamic acid structure, in which a content of the inorganic substance is 10% by mass or more with respect to a total solid content of the composition, and a content of the compound X is 10% by mass or more with respect to the total solid content of the composition.

A thermoplastic resin (A) including, in its main chain structure, a unit (i) having a biphenyl group, a unit (ii) having a substituent biphenyl group, a unit (iii) having a specific number of atoms in its main chain, and a unit (iv) having a specific number of atoms in its main chain provides a thermoplastic resin which has a low liquid crystal phase transition temperature and a low isotropic phase transition temperature, is highly thermally conductive, and can be processed by molding at a low melting temperature.

The thermosetting resin composition of the present invention includes an epoxy resin (A), a curing agent (B), and thermally conductive particles (C), in which the epoxy resin (A) includes a mesogen skeleton and has a softening point of 60° C. or lower, and a thermal conductivity λ.sub.200 of a cured product of the thermosetting resin composition at 200° C. is 12.0 W/(m.Math.K) or higher.