A Novel Dispersing Agent for Carbon Nanotubes

Since the discovery of carbon nanotubes (CNTs), researches of field emission display (FED) have been mainly focused on it, because of their high-aspect configuration, low work function, high mechanical stability and high conductivity. For CNTs to become a viable engineering material for FED applications, efficient assembly and integration processes for large size are required that are currently lacking. Several techniques have been developed to assemble/integrate preformed nanostructures into functional hierarchical structures. Screen-printing is currently used to fabricate CNT cathodes for FED with large screen size [1-3]. The primary advantage of the process is that the cathode can, in principle, be manufactured with a price that can be afforded. For the fabrication of cathode by the printing method, the CNT paste critically determines the cathode characteristics and hence the quality of the FED. Since the CNT has a cohesive characteristic in its nature, the CNT is not dispersed uniformly in the paste. Therefore the CNT is not equally distributed in the cathode layer which is fabricated by printing the paste. Moreover the printed layer becomes a rugged surface by the aggregation of the CNT. The rugged surface leads to the local field strengthening even when the uniform external electric field is applied on the cathode surface. By the non uniformity of the electric field and the CNT distribution on the cathode surface, the emission uniformity from the cathode is severely degraded and the picture quality of FED with the cathode is deteriorated. To overcome the difficulties, we developed a new dispersing agent and a process for preparing finely dispersed CNT paste. By using this paste, we obtained the flat CNT with the surface roughness (Ra) of less than 0.20um and the excellent emission property was obtained. The details of the results will be described in the followings.