NEC Corporation has developed a completely new kind of bioplastic composed of plant-based material and carbon fiber, which realizes heat conductivity higher than that of stainless steel. The innovative bioplastic is expected to make electronic products more environmentally sound, while solving conventional heat release issues.
The features of the new bioplastic are as follows:
*Creation of a cross-linked structure of carbon fiber through use of a unique binder in the polylactic acid (PLA)*1 resin achieves high heat diffusion (with carbon fiber of 10% and 30% the heat diffusion ability of the new bioplastic composite is comparable to and double that of stainless steel respectively). This enables good heat conductivity in the plane direction of the PLA resin board, which is a characteristic conventionally difficult to attain in metal boards.
*The composite is extremely environmentally friendly as it is mainly composed of biomass-based components including the binder (the biomass ratio exceeds 90%, excluding inorganic components such as the carbon fiber).
*The strength and moldability of the composite have been fundamentally verified for use in electronic products.
NEC's newly developed bioplastic composite in the housings of electronic products easily releases the heat generated from electronic parts with high temperatures through whole housing surfaces, while slowing up an increase in the temperature of the housings near parts.
Recently, small-sized electronic products such as mobile phones and personal computers have suffered heat-release issues due to an increase in the amount of heat being generated from electronic parts. However, conventional heat-release devices such as fans and sheets are difficult to incorporate as products become smaller and slimmer.
In electronic product housings, the use of heat-conductive metals is considered to be one alternative to plastic for improving heat release, however, heat conductivities in the thickness direction of metal boards are too high and can cause partial or rapid increase in the temperatures of housings near electronic parts that have high temperatures, causing unnecessary anxiety to the user.
Attempts have been made to increase heat release from whole parts of housings by using heat-conductive plastics. However, previous heat-conductive plastics have had the disadvantages of low moldability, as well as high densities and costs, as they contain large amounts (more than 50%) of heat-conductive fillers such as fibers or particles made from carbon and metals. Therefore, a new kind of heat-conductive material has been long sought after to solve these issues.
On the other hand, however, recent bioplastics made from renewable plant resources, including PLA, have been enjoying increasing attention as new environmentally friendly materials and are now starting to be used in electronic products. But, PLA has low heat conductivity like current petroleum-based plastics and many of its practical characteristics are also lower than those of petroleum-based plastics.
NEC has been focusing its research activities on how to solve these bioplastic issues and has succeeded in the development of a kenaf*2 fiber- reinforced PLA composite that realizes high heat resistance and strength. Moreover, the composite is already being used in a mobile phone commercialized by NEC. In addition, NEC has also discovered how to add flame retardancy - without using toxic flame retardants - and shape memory to PLA.
The new bioplastic that achieves high heat conductivity has been enabled by new technology for carbon-fiber cross-linking with a unique biomass-based binder, which were both realized at NEC's fundamental and environmental research laboratories.
NEC will continue to develop these technologies toward realization of mass production of the bioplastic composite by the end of the fiscal year ending March, 2009, after which it will start to use the composite in housings of electronic products and seek out new applications.