Many studies about offset printing plate surface energetics have dealt with determinations of the difference between image and non-image areas through contact angle measurements. On another hand, contact angle hysteresis studies have highlighted the influence of surface state and/or heterogeneity. The novel approach of Shanahan and Di Meglio expresses hysteresis as a function of surface defects parameters. In the case of offset printing plates we have considered screen dots as defects, and we have evaluated the corresponding hysteresis energy by the use of some liquids such as pure water, glycerol and a series of fountain solutions. The experimental results turned out to validate this approach and to show the way this energy is linked to the screen geometry and the relative dot area. In parallel with this new approach, we have also shown that the classical Cassie and Baxter model of averaging effects may be applied to liquids on screened areas.

In order to improve the quality of text and graphic printers, companies have increased the resolution of the imaging subsystem and decreased the diameter of toner particles in electrophotographic powder marking technologies. We have been developing a new electrographic printing technology in which the latent image is formed by contacting a write head with many metal fingers to square metal pads on 50 μm centers (500 dpi) fabricated on an insulating cylinder. This system has demonstrated the ability to print for the first time, to our knowledge, in any powder marking system, both black and white single pixels at 500 dpi, using normal 9 μm diameter toner. A theoretical explanation for this result is given.

Carbon black is the most widely used pigment for black electrophotographic toners. In this article the effects of carbon black on tribocharaging of two-component developers reported in the published literature are reviewed and compared to experemental work done recently. Carbon black is found to have the following effects on the triboelectric properties of model toners made from carbon black in a polymer binder: (1) In toners compared at the same carbon black loading, toners containing carbon blacks with greater work function (or surface acidity) charge more negatively. (2) Increasing the carbon black content causes the absolute value of the charge-to-mass of model toners to decrease when the toner is charged either positively or negatively using poly(methylmethacrylate) coated carrier or poly(vinylidine fluoride) coated carrier. (3) Q/m when the toner is charged negatively is a linear function of Q/m when the same toner is charged positively. (4) Increasing the carbon black content causes the absolute value of the slope and the intercept of linear plots of mass-to-charge as a function of the mass ratio of toner to carrier to increase. A steady-state version of the surface state model of tribocharging is developed and compared to experimentally observed tribocharging behavior. In this model, the rate of charging of the toner and the rate of discharging of the toner due to increased conductivity related to the carbon content of the toner are assumed to be equal at steady state. The model predicts all four of the observed behaviors.

We examined the porous nature of the silica coating color for papers using N₂ adsorption isotherms. Silica was used as the coating color pigment. It was suspended in a 10 wt% aqueous solution of polyvinylalcohol. The silica contents were 10 and 20 wt%. Air-dried pieces of the coated layer were used for the adsorption experiments. The porosity of the coating colors was determined by the BET plot, the SPE method, and the DR plot. These results indicate that pristine silica does not have very small intrinsic intraparticle pores, but the interparticle pores determine the external surface area, which indicates that the entrance of the pores should be covered with the binder polymer and the micropores behave as latent pores.

Electrostatic transfer process of four layers structure (photoreceptor, toner, paper, and transfer belt) which is specified by four R–C parallel circuits combined in series and expressed by a set of 3 differential equations, is investigated with coefficients of time constant and dielectric thickness instead of R and C. The analytic closed form solutions are obtained with a method of eigenvalue and eigenvectors. Initial conditions of solutions are determined by static voltage difference of each layer, which are given by electrostatic Poisson's equations, and then space dependence and time one of solutions are unified by this analysis. Time evolution of each voltage, transfer efficiency, and Paschen's discharge are discussed. It is shown that Paschen's discharge occurs in non-image white area, dominantly.

The belt transfer system is one of the image transfer processes used in electrophotography. In this process, paper clings to the electro-resistive belt, and is stably fed through the processor. However, electrical discharge may occur between the paper and the belt when the paper is separated from the belt under particular conditions. This discharge is named “separating discharge”. Because this discharge causes image degradation, it is important to make clear the separating discharge phenomenon. A model experiment and numerical simulation of separating discharge are carried out for the study of such phenomena. When the sheet is charged at low electrification level, local strong discharge occurs intermittently. On the other hand, the separating discharge becomes continuous and weak when the sheet is charged at high electrification level. Toner movement due to the discharge is also numerically simulated using discrete element method, and the result shows that the image degradation occurs at low electrification level of the sheet, whereas it does not occur at high electrification.

Statics of a pin electrode in a pin-to-plate system has been investigated to utilize the system for the new low ozone charger and to clarify the fundamental mechanism of bead carry-out in the two-component magnetic brush development subsystem of electro-photography. The electrostatic force in the system was measured and numerically calculated with a static unipolar model. Calculated voltage-current characteristics qualitatively agreed with those measured. Electrostatic force was also measured and calculated. Although extremely small electrostatic pull force was induced if discharge did not take place, the force became repulsive and relatively large when the corona discharge took place. Force in negative corona was almost the same as in positive corona. Calculated force without discharge agreed with the measured but the calculation did not simulate repulsive characteristics at corona discharging. Convection of air must be included in the model.

The Poole–Frenkel effect was studied in xerographic carriers comprised of a soft-magnetic strontium ferrite core coated with 0 – 1.5 wt.% of polymethylmethacrylate (PMMA), either undoped, or doped with 6 wt.% of carbon black. DC current-voltage characteristics were measured in carriers formed into uniform compacts at two different levels of compacting force. Two types of Poole– Frenkel behavior were observed: the intrinsic Poole–Frenkel conduction of the carrier core, and the percolation effect, which arises at low compaction pressures due to insufficient interparticle contact. The percolation effect is believed to be the major cause of the non-Ohmic low voltage behavior of xerographic carriers in a magnetic brush. The percolation effect disappears at compaction pressures higher than typical compaction pressures in a magnetic brush, when the force at interparticle contacts becomes sufficient for the Ohmic conduction. Theoretical I-V curves were calculated on the basis of the non-linear equivalent circuit representing the conduction mechanisms in carriers, and showed a good agreement with the experimental data.