Kar P. Lok

Material and physicochemical properties of electrostatically-based liquid developers

Abstract During the last decade, liquid immersion development (LID) of a latent electrostatic image has become established as an important alternative to dry toning. In this development method, charged, colloidally stable pigment particles dispersed in a dielectric liquid undergo electrophoresis under the influence of an applied field. These particles thus neutralize a latent electrostatic image of opposite sign, which resides on either a photoreceptor drum or on dielectric paper and results in a hard copy of the latent image being obtained. This paper is concerned with the materials and physicochemical properties of LID developers and has been organized into three parts. In Part 1, the criteria pertaining to selection of the materials for such developers is reviewed. In Part 2, a discussion of the physicochemical properties of the materials is given, while in Part 3 we report some of the results of a systematic study that has been undertaken in order to understand the behavior and limitations of LID toners. The materials package considered in detail in this paper consisted of a dispersion of a laked carbon black in Isopar G that was colloidally stabilized by a soluble alkyl methacrylate based copolymer, Goodyear Pliolite OMS. The developer was electrostatically charged using a variety of heavy metal soaps. Experimental results concerning the colloidal stability, charge-to-mass ratio and evaluation of the final image properties of this developer are discussed. It is concluded that only by making a systematic investigation of the complex interactions that occur in such LID inks will a materials package with optimal shelf life and imaging properties be obtained.