Higher Resolution for Color Laser Printers and Copiers: Why and How

Abstract

This paper proposes that to achieve the high quality color print goal requires increasing the resolution of current Electrophotographic (EP) printers from 600 dots per inch (dpi) to true 1200 dpi as a minimum and preferably higher. The central point of the argument is that in order to take advantage of the stability of digital printing and reduce the sensitivity to noise arising from photoreceptor non-uniformity and developer noise, the edges of the photodischarged halftone pixels must be sharpened. Since the light spots are diffraction limited, sharper pixel voltage edges can only be achieved by using higher resolution spots. Increasing resolution has consequences on the entire EP system, but only two substems are considered here: the laser scanning imaging system and the photoreceptor. Two laser technologies are discussed for higher resolution imaging systems, VCELs and blue (violet) lasers. A key OPC limitation to higher resolution is coulomb blooming caused by thick CTLs of current photoreceptors. To take full advantage of higher resolution requires photoreceptors with top surface generation. The key technology to enable this is single layer photoreceptor design.