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Thermal conductive sheet, insulating sheet, and heat dissipating member

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Thermal conductive sheet, insulating sheet, and heat dissipating member


A thermal conductive sheet contains a resin and a plate-like or flake-like filler. The average orientation angle of the filler is 29 degrees or more and the maximum orientation angle thereof is 65 degrees or more with respect to the plane direction of the thermal conductive sheet.

Browse recent Nitto Denko Corporation patents - Osaka, JP
Inventor: Keisuke HIRANO
USPTO Applicaton #: #20120285674 - Class: 165185 (USPTO) - 11/15/12 - Class 165 
Heat Exchange > Heat Transmitter

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The Patent Description & Claims data below is from USPTO Patent Application 20120285674, Thermal conductive sheet, insulating sheet, and heat dissipating member.

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CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2011-108583 filed on May 13, 2011, the contents of which are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal conductive sheet, an insulating sheet, and a heat dissipating member, to be specific, to a thermal conductive sheet for use in power electronics technology and the like, an insulating sheet and a heat dissipating member obtained by using the thermal conductive sheet.

2. Description of Related Art

In recent years, power electronics technology which uses semiconductor elements to convert and control electric power is applied in hybrid devices, high-brightness LED devices, and electromagnetic induction heating devices. In power electronics technology, a high current is converted to, for example, heat, and therefore materials that are disposed near the semiconductor element are required to have excellent heat dissipation characteristics (excellent heat conductivity) and insulating characteristics.

A thermal conductive sheet obtained by dispersing, for example, an inorganic filler having thermal conductivity and insulating characteristics, a flake-like boron nitride, and the like in a resin has been known.

The flake-like boron nitride has a high thermal conductivity in the longitudinal direction and a low thermal conductivity in the short-side direction. Therefore, for example, when the longitudinal direction of the boron nitride is allowed to be along the thickness direction of the thermal conductive sheet, the thermal conductivity in the thickness direction can be improved. Also, when the longitudinal direction of the boron nitride is allowed to be along the plane direction of the thermal conductive sheet, the thermal conductivity in the plane direction can be improved.

However, there is a disadvantage that, when the thermal conductive sheet is produced by press molding or roll forming, the boron nitride tends to be along the plane direction of the thermal conductive sheet, so that the obtained thermal conductive sheet has a poor thermal conductivity in the thickness direction, while having an excellent thermal conductivity in the plane direction.

On the other hand, there are cases where the thermal conductive sheet is required to have an excellent thermal conductivity not only in the plane direction but also in the thickness direction depending on its use.

Therefore, for example, a thermal conductive sheet, which is obtained by dispersing secondary aggregated particles having a porosity of 50% or less and an average pore size of 0.05 to 3 μm obtained by aggregating primary particles of the boron nitride in a thermosetting resin, has been proposed (ref: for example, Japanese Unexamined Patent Publication No. 2010-157563).

In the thermal conductive sheet, the boron nitride is contained as the secondary aggregated particles, that is, contained without being oriented in the thickness direction or the plane direction of the thermal conductive sheet, so that the thermal conductivity in the thickness direction and the plane direction can be ensured.

SUMMARY

OF THE INVENTION

However, there is a disadvantage that to obtain the thermal conductive sheet described in Japanese Unexamined Patent Publication No. 2010-157563, production of the secondary aggregated particles of the boron nitride is required, so that a complicated process such that the boron nitride is temporarily calcined at high temperature and pulverized to be in a slurry state and then is calcined is required.

It is an object of the present invention to provide a thermal conductive sheet capable of being obtained with an easy operation and having an excellent thermal conductivity in the thickness and plane directions, and an insulating sheet and a heat dissipating member obtained by using the thermal conductive sheet.

A thermal conductive sheet of the present invention contains a resin and a plate-like or flake-like filler, wherein the average orientation angle of the filler is 29 degrees or more and the maximum orientation angle thereof is 65 degrees or more with respect to the plane direction of the thermal conductive sheet.

In the thermal conductive sheet of the present invention, it is preferable that the resin contains a first resin and a second resin, and a difference between the softening temperature of the first resin and that of the second resin is 20° C. or more.

In the thermal conductive sheet of the present invention, it is preferable that a difference between the softening temperature of the first resin and that of the second resin is 40° C. or more, and the second resin has an average particle size of 10 to 500 μm and has its shape retained at a temperature between the softening temperature of the first resin and that of the second resin.

In the thermal conductive sheet of the present invention, it is preferable that the filler content is 50 to 95 parts by mass with respect to 100 parts by mass of the total amount of the thermal conductive sheet.

An insulating sheet of the present invention is obtained by using a thermal conductive sheet, wherein the thermal conductive sheet contains a resin and a plate-like or flake-like filler, and the average orientation angle of the filler is 29 degrees or more and the maximum orientation angle thereof is 65 degrees or more with respect to the plane direction of the thermal conductive sheet.

A heat dissipating member of the present invention is obtained by using a thermal conductive sheet, wherein the thermal conductive sheet contains a resin and a plate-like or flake-like filler, and the average orientation angle of the filler is 29 degrees or more and the maximum orientation angle thereof is 65 degrees or more with respect to the plane direction of the thermal conductive sheet.

In the thermal conductive sheet, the insulating sheet, and the heat dissipating member of the present invention, the plate-like or flake-like filler is contained so that the average orientation angle thereof is 29 degrees or more and the maximum orientation angle thereof is 65 degrees or more. Therefore, the thermal conductivity in the thickness and plane directions of the thermal conductive sheet can be ensured.

Thus, the thermal conductive sheet, the insulating sheet, and the heat dissipating member of the present invention can be used for various applications as a thermal conductive sheet, an insulating sheet, and a heat dissipating member having an excellent thermal conductivity in the thickness and plane directions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of one embodiment of a thermal conductive sheet of the present invention.

FIG. 2 shows an X-ray CT image of the thermal conductive sheet of Example 1.

FIG. 3 shows a histogram of an orientation angle obtained by analyzing the X-ray CT image of the thermal conductive sheet of Example 1.

FIG. 4 shows an X-ray CT image of the thermal conductive sheet of Example 2.

FIG. 5 shows a histogram of an orientation angle obtained by analyzing the X-ray CT image of the thermal conductive sheet of Example 2.

FIG. 6 shows an X-ray CT image of the thermal conductive sheet of Example 4.

FIG. 7 shows a histogram of an orientation angle obtained by analyzing the X-ray CT image of the thermal conductive sheet of Example 4.

FIG. 8 shows an X-ray CT image of the thermal conductive sheet of Comparative Example 1.

FIG. 9 shows a histogram of an orientation angle obtained by analyzing the X-ray CT image of the thermal conductive sheet of Comparative Example 1.

DETAILED DESCRIPTION

OF THE INVENTION

A thermal conductive sheet of the present invention contains a resin and a filler.

The resin is a component that is capable of dispersing the filler, that is, a dispersion medium (matrix) in which the filler is dispersed, including, for example, a thermosetting resin and a thermoplastic resin.

Examples of the thermosetting resin include epoxy resin, thermosetting polyimide, phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, silicone resin, and thermosetting urethane resin.

Examples of the thermoplastic resin include polyolefin (for example, polyethylene, polypropylene, and ethylene-propylene copolymer), acrylic resin (for example, polymethyl methacrylate), polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide (nylon (trade mark)), polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether sulfone, poly ether ether ketone, polyallyl sulfone, thermoplastic polyimide, thermoplastic urethane resin, polyamino-bismaleimide, polyamide-imide, polyether-imide, bismaleimide-triazine resin, polymethylpentene, fluorine resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and acrylonitrile-styrene copolymer.

A preferable example of the thermosetting resin is epoxy resin.

The epoxy resin is in a state of liquid, semi-solid, or solid under normal temperature.

To be specific, examples of the epoxy resin include aromatic epoxy resins such as bisphenol epoxy resin (for example, bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, hydrogenated bisphenol A epoxy resin, dimer acid-modified bisphenol epoxy resin, and the like), novolak epoxy resin (for example, phenol novolak epoxy resin, cresol novolak epoxy resin, biphenyl epoxy resin, and the like), naphthalene epoxy resin, fluorene epoxy resin (for example, bisaryl fluorene epoxy resin and the like), and triphenylmethane epoxy resin (for example, trishydroxyphenylmethane epoxy resin and the like); nitrogen-containing-cyclic epoxy resins such as triepoxypropyl isocyanurate (triglycidyl isocyanurate) and hydantoin epoxy resin; aliphatic epoxy resin; alicyclic epoxy resin (for example, dicyclo ring-type epoxy resin and the like); glycidylether epoxy resin; and glycidylamine epoxy resin.

These epoxy resins can be used alone or in combination of two or more.

The epoxy resin has an epoxy equivalent of, for example, 100 to 1000 g/eqiv., or preferably 150 to 700 g/eqiv.

The epoxy resin has a melt viscosity at 80° C. of, for example, 10 to 20000 mPa·s, or preferably 50 to 10000 mPa·s.

The epoxy resin can also be prepared as an epoxy resin composition containing, for example, an epoxy resin, a curing agent, and a curing accelerator.

The curing agent is a latent curing agent (epoxy resin curing agent) that can cure the epoxy resin by heating, and examples thereof include an imidazole compound, an amine compound, an acid anhydride compound, an amide compound, a hydrazide compound, and an imidazoline compound. In addition to the above-described compounds, a phenol compound, a urea compound, and a polysulfide compound can also be used.

Examples of the imidazole compound include 2-phenyl imidazole, 2-methyl imidazole, 2-ethyl-4-methyl imidazole, and 2-phenyl-4-methyl-5-hydroxymethyl imidazole.

Examples of the amine compound include aliphatic polyamines such as ethylene diamine, propylene diamine, diethylene triamine, and triethylene tetramine; and aromatic polyamines such as metha phenylenediamine, diaminodiphenyl methane, and diaminodiphenyl sulfone.

Examples of the acid anhydride compound include phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, methyl nadic anhydride, pyromelletic anhydride, dodecenylsuccinic anhydride, dichloro succinic anhydride, benzophenone tetracarboxylic anhydride, and chlorendic anhydride.

Examples of the amide compound include dicyandiamide and polyamide.

An example of the hydrazide compound includes adipic acid dihydrazide.



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stats Patent Info
Application #
US 20120285674 A1
Publish Date
11/15/2012
Document #
13469988
File Date
05/11/2012
USPTO Class
165185
Other USPTO Classes
International Class
28F7/00
Drawings
9



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