Size Distribution Effect of Fine Graphite Particles on the Textures of Colloidal Graphite Films

The electrical properties of colloidal graphite films composed of fine graphite particles with different sizes and size distributions have been examined in detail to elucidate the effect of the particle size or the size distribution of graphite particles on the textures of the coated films. Sheet resistivity or specific resistivity was measured by a DC four terminal method for various films heat-treated in the temperature range from 110°C to 400°C. From an empirical equation representing the thickness dependence of sheet resistivity in films, the uniformity of the films could be estimated. A rapid decrease in the sheet resistivity of the films heat-treated in range 200-300°C was directly associated with decreasing barrier resist ance on contact areas of graphite particles and polymer colloids. The specific resistivity of films after heating at 400°C was found to be correlated with the packing density of graphite particles in the films. Additionally, the packing density of graphite particles was strongly dependent on colloidal graphite samples examined. The remarkable difference in film tex ture between the examined samples was confirmed by microstructural observation with SEM. Flow properties of sample suspensions showed that the diffrence in film texture was probably caused by different orientation property of suspended graphite particles, which might depend on the size distribution of the suspended particles, under a given shear stress. These results suggest that particle size distribution is an important quality govering the texture uniformity and the packing of graphite particles in colloidal graphite films.