Expanded-graphite sheet

Abstract

This invention provides an expanded-graphite sheet whose thermal conductivity in their surfacewise directions is relatively uniform and higher than its thermal conductivity in perpendicular direction and which can be produced efficiently at relatively low cost. Because the expanded-graphite sheet is made of expanded graphite alone and has the thermal conductivities in parallel direction of 350 W/(m·K) or more, its thermal conductivities in parallel direction is much higher than its thermal conductivity in perpendicular direction; therefore, it is suitable for the conduction and diffusion of heat. Besides, the expanded-graphite sheet can be produced easily, in a short time, efficiently, at relatively low cost.

Description

[0001] This application is a continuation of International Application No. PCT / JP2005 / 012733, filed Jul. 11, 2005 which claims priority on Japanese Patent Application 2004-249137 filed Aug. 27, 2004.TECHNICAL FIELD [0002] This invention relates to a thermally anisotropic expanded-graphite sheet whose thermal conductivity in its surfacewise directions is higher than that in its thicknesswise directions. BACKGROUND OF THE INVENTION [0003] Thermally anisotropic sheets whose thermal conductivity in their surfacewise directions (hereinafter referred to as “thermal conductivity in parallel direction”) is higher than that in their thicknesswise directions (hereinafter referred to as “thermal conductivity in perpendicular direction”) have been used to conduct heat from heat sources to other places. The higher the thermal conductivity in parallel direction of a sheet is, the quicker the thermal conduction through it is; accordingly, sheets of high thermal conductivity in parallel direction h...

AI Technical Summary

Benefits of technology

[0013] The advantage offered by the first feature of the present invention is as follows. Because the thermal conductivity in parallel direction of the expanded-graphite sheet is 350 W / (m·K) or more, surfacewise thermal conduction through the sheet is quick; therefore, the expanded-graphite sheet is suitable for the conduction and diffusion of heat. Especially if the expanded-graphite sheet is made of expanded graphite alone, its thermal conductivity in parallel direction can be made much higher than its thermal conductivity in perpendicular direction; therefore, it is more suitable for the conduction and diffusion of heat. If the expanded-graphite sheet is made by compressing with a rolling mill or the like expanded graphite which is made by heating and forming graphite soaking up liquid such as sulfuric acid, no heat treatment in particular is required and, hence, the expanded-graphite sheet can be produced easily in a short time. If the expanded-graphite sheet is produced with a rolling mill, the expanded-graphite sheet can be produced continuously; therefore, the expanded-graphite sheet can be produced efficiently. If the expanded-graphite sheet is made of expanded graphite alone, the raw-material cost of the expanded-graphite sheet is relatively low and, hence, the expanded-graphite sheet can be produced at relatively low cost.

[0014] The advantage offered by the second feature of the present invention is as follows. Because the arithmetic mean surface roughness of the expanded-graphite sheet is less than 5 μm, its thermal conductivity is relatively uniform; accordingly, no heat spot is made on it while heat is conducted and diffused through it.

[0015] The advantage offered by the third feature of the present invention is as follows. Because the thermal conductivity of the expanded-graphite sheet is relatively uniform, no heat spot is made on it while heat is conducted and diffused through it.

[0016] The advantage offered by the fourth feature of the present invention is as follows. The expanded-graphite sheet is suitable not only for conducting heat from heat sources to other places but also for shielding objects from electromagnetic waves.

[0017] The advantage offered by the fifth feature of the present invention is as follows. Because the total impurity content of the expanded-graphite sheet is as low as 10 ppm or less, components and devices fitted with the expanded-graphite sheet are prevented from deteriorating due to impurities.

[0018] The advantage offered by the sixth feature of the present invention is as follows. Because the entanglement of graphite fibers of the expanded-graphite sheet is firm and, hence, the graphite fibers are firmly bonded together, the expanded-graphite sheet is strong and does not easily tear.

Problems solved by technology

However, such polymer films are costly.

Besides, heat-treating of such polymer films takes a long time; therefore, the production efficiency of the graphite sheet is low.

Accordingly, the graphite sheet is very costly and, hence, the application of the graphite sheet to apparatuses and equipment is limited.

Although the thermal conductivity in parallel direction of the graphite sheet of the above Japanese Unexamined Patent Publication No. 2001-79977 is very high, its thermal conductivity in parallel direction is not uniform if its thickness or density is not uniform.

When it is used to conduct heat from a heat source to other places, spots of low thermal conductivity becomes heat spots which affect nearby components or devices.

However, no method of preventing such heat spots from being made is disclosed in the Japanese Unexamined Patent Publication No. 2001-79977.

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