Thermally conductive formed article and method of manufacturing the same

#The present invention relates to a thermally conductive formed article and a method of manufacturing the same.

#Conventionally, as a thermally conductive formed article, Japanese Laid-open Patent Publication No. 5-222620 discloses a formed article in which pitch-based short carbon fibers having a specific cross-sectional structure are dispersed in a matrix. Japanese Laid-open Patent Publication No. 9-283955 discloses a formed article in which short graphitized carbon fibers having a specific aspect ratio are dispersed in a matrix. Japanese Laid-open Patent Publication No. 4-173235, Japanese Laid-open Patent Publication No. 10-330502, Japanese Laid-open Patent Publication No. 11-46021, Japanese Laid-open Patent Publication No. 11-302545, Japanese Laid-open Patent Publication No. 2000-195998, Japanese Laid-open Patent Publication No. 2000-281802, Japanese Laid-open Patent Publication No. 2001-139833, and Japanese Laid-open Patent Publication No. 2001-353736 disclose formed articles in which short carbon fibers are oriented in a fixed direction in a polymer matrix. Japanese Laid-open Patent Publication No. 11-97593, and Japanese Laid-open Patent Publication No. 11-199949 disclose formed articles in which short carbon fibers are oriented in a fixed direction in a metal matrix.

#The above conventional thermally conductive formed articles are used, for instance, in electronic devices and apparatuses as heat-conducting members for conducting heat generated from electronic components out of the apparatus so as to prevent overheat of the electronic components. In electronic devices and apparatuses, with enhancement of performance thereof, the electronic components thereof generate an increasing amount of heat. Therefore, recently, thermally conductive formed articles used as heat-conducting members have a requirement of having high thermal conductivity. However, the conventional thermally conductive formed articles do not always have thermal conductivity high enough to meet the requirement.

#The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

#FIG. 1 shows a graph illustrating a correlation between a thermal resistance and a ratio I(002)/I(110) found in the thermally conductive sheet of Examples 1 to 5 and Comparative Examples 1 to 5;

#FIG. 2 is a diagram showing an X-ray diffraction pattern of Example 1 of the thermally conductive sheet;

#The present invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof.

#A thermally conductive sheet according to the present embodiment includes a polymer matrix, and short carbon fibers which are present in the polymer matrix in a state oriented in the direction of thickness of the thermally conductive sheet. A ratio I(002)/I(110) between the intensity I(110) of a diffraction peak ascribable to a (110) surface of carbon and the intensity I(002) of a diffraction peak ascribable to a (002) surface of carbon is 10 or less occurring when X-rays are irradiated onto the thermally conductive sheet along the direction of orientation of the short carbon fibers, that is, the direction of the thickness of the thermally conductive sheet. The ratio I(002)/I(110) is preferably 1 or less, and more preferably 0.2 or less. Normally, the lower limit value of the ratio I(002)/I(110) is equal to 0.01. In the case of carbon fibers, the (110) surface is orthogonal to the (002) surface corresponding to a base surface, i.e. C surface, and in parallel with the fiber axis. Therefore, the ratio I(002)/I(110) serves as an index indicating the degree of orientation of the short carbon fibers in the thermally conductive sheet.

#Although the thermally conductive sheet is not particularly limited in hardness, it has preferably a Shore A hardness of 70 or less, and more preferably a Shore A hardness of 40 or less. Particularly preferably, it has an Asker C hardness of 30 or less.