Bioplastics for Electronic Equipment

Tackling the development of biomass-based plastics -(Bioplastics) for electronic equipment-

High-thermal conductivity polylactic acid composite materials

Following the addition of shape memory, as described above, we further increased the added value of polylactic acid by developing a polylactic acid composite of high thermal conductivity that can contribute to better heat dissipationa major issue in the design of today's electronic equipment. As electronic devices become ever smaller and thinner, the rise in temperature inside their housing, due to internal heat generation, is becoming a serious challenge, but it is difficult to deal with this using conventional parts for promoting heat dissipation, such as fans and sheets. In addition, when stainless steel or other metallic material is used for a device housing, heat conductivity is high only in the direction of the thickness, resulting in localized points of high temperature around the outside of the device, and to discomfort during use. Furthermore, since metals have a higher specific gravity than plastic, it is more difficult to reduce their weight and more demanding to form them into complicated shapes.

A conventional method of increasing the thermal conductivity of plastic is to include, in a petroleum-based plastic, a high proportion (≥ 50%) of a high-conductivity material such as powdered metal or carbon, or fiber. In practice, however, this method presents problems such as reduced formability and strength, and an increase in specific gravity. Also, since this plastic is made from petroleum-based raw materials, it is not very environment-friendly.

In addressing this problem, we succeeded in producing polylactic acid of higher thermal conductivity using a significantly lower amount of added carbon fiber (≥ 10%), using polylactic acid (a type of bioplastic) as a base resin, and an original plant-based binding agent to achieve reticulate (mesh-shaped) bonding (cross-linking) of carbon fibers in resin. (See Fig. 9.) This material has a low specific specific gravity (≤ 1.3)close to that of polylactic acidand combines a thermal diffusivity that is better than that of stainless steel, while keeping the typical light weight of plastics. (See Fig. 10.) Furthermore, we achieved anisotropic heat transfer in the planar directiona feature that cannot be achieved with metalsby means of orienting the carbon fibers during the formation process. (See Fig. 11.) When this material is used for the housing of today's increasingly small and thin electronic equipments, these features will enable good heat dissipation from the housing without allowing localized points of high temperature. They will also prove useful in various other fields of application.

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