It is assumed in the electric field theory of toner charging that toner particles triboelectrically charge until a material-dependent electric field is created at the surface of each toner particle. This is also called the high-density limit of the surface state theory. There are now two independent published experimental tests that are consistent with this theory. These experimental tests are reviewed and analyzed. In addition, several topics related to this theory are discussed, including (1) progress towards a microscopic theory of toner charging, (2) limitations on one of the theories of toner adhesion, and (3) a proposed new theory of the source of wrong sign toner.

In laser dye thermal transfer printing, high resolution and continuous tone images can be easily obtained, since a laser light focuses on a small spot, and its heat energy can be controlled by pulse width modulation. On the other hand, the physical phenomena occurring in an ink donor sheet during or just after the laser heating have not been clarified yet. In this article, the surface of the ink layer consisting of sublimation color dye is heated by microsecond laser pulse irradiation and is observed using time resolved optical microscopy. The ink layer is deformed during and after laser pulse irradiation. A small hole is formed as a result of melt and ablation of the ink layer upon laser heating. The diameter of the hole increases rapidly after passing through an induction period, but then the rate of increase slows down. A successful explanation is made of such thermal responses of the ink layer on the time scale of microseconds by assuming Gaussian spatial distribution of laser light intensity and the diffusion of the heat energy by thermal conduction.

Very little attention has been paid in the literature to the impact of the drop size on the dynamics of spreading and on the final dot quality with different paper grades. In this study, the development of the image properties was observed on a time scale of a few milliseconds and upwards, by using a special high speed imaging environment and continuous ink jet (CIJ) printers, with different nozzle sizes but similar water based ink compositions. The results clearly show that there is a strong paper dependent affiliation between the size of the ink jet drop and the high-speed dynamic phenomenon of dot spreading and drying. With coated paper grades, the interrelation between the drop size and the magnitude of the surface structure was found important, compared with the final shape of the dot. With uncoated papers, the growth of the dot is dependent on the size of the drop. The final intensity of the print was found to be the outcome of the characteristics of the ink and the absorption properties of the paper.

In this article, we discuss the relationship between a high-speed continuous ink jet system and the printing substrate. Nonabsorbent materials, with different surface topographies were used to evaluate the importance of the droplet impact and spreading without capillary penetration. Commercial papers were also used to evaluate the potential of the existing grades, and to find their essential performance parameters. A laboratory scale testing environment was used for the high-speed imaging of ink jet drops. The impact, spreading, absorption, and drying of the ink droplets on the samples can be observed and analyzed in this testing environment on the time scale of microseconds up to several minutes. The image technical performance of the samples was measured with an image analysis system which was specially designed for the analysis of print quality with non-impact printing techniques.

A method to quantify gamut based on equiluminance planes is applied to characterize ink jet media and ink sets. Due to a mixture of spectral interpolation and interpolation in L*,a*,b* the base set of experimental data can be much smaller if only L*,a*,b* interpolation is used. The robustness of the interpolation to the reduction of data points in hue direction is demonstrated. The method is applied to the characterization of different ink jet ink sets on photo glossy media. The effect of media gloss, paper color, printing pattern and colorants is shown. The influence of the spectral measurement geometry on gamut has to be taken into account when colors are compared on samples with different surface finish. Printed colors may change over time due to the diffusion of dyes inside the layer. A test pattern was developed to quantify dye diffusion of ink jet prints under varying environmental conditions.

A wide range of iron oxides is used for the production of toners for copiers and laser printers. However, the properties of the toner have to be tailored to the needs of each particular printing system. The precipitation process allows control of particle size, shape and particle size distribution of magnetic iron oxides. The influence of these parameters on magnetic and other data of the magnetite and the toner is discussed.

In a working xerographic developer, a portion of the charged toner particles is removed each time a xerographic image is developed. To balance this loss, an equivalent amount of toner is dispensed into the xerographic developer from a reservoir of uncharged toner. Because uncharged or poorly charged toner particles tend to develop in the non-image “background” areas of a latent xerographic image, the uncharged/dispensed toner particles must be rapidly brought to a charged state in order to avoid “background” development. Normally, the “added” toner and the “incumbent” toner (i.e., the charged toner particles already present in the developer) merge to a common level of charge. Clearly, the rate at which this merging process occurs (the so-called “admix rate”) is an important functional property of any xerographic developer design, and a rapid rate is especially desirable. In principle, the charge admix performance of any toner can be optimized via judicious adjustments to the chemical composition of the toner particles and/or that of the xerographic carrier particles. However, even for an apparently optimized xerographic toner/developer design, charge admix deficiencies may still be created as a result of extrinsic factors. For example, for certain developer designs, the admix rate can change from “rapid” to “almost-zero” as the degree of developer mixing is changed from “gentle” to “intense”; paradoxically, this latter admix failure mode actually occurs as a result of an ultra-rapid admixing process. In such a case, the added toner acquires a level of charge higher than that of the incumbent toner, and this increased charge is mirrored by an equivalent decrease in charge for the incumbent toner. In an extreme failure condition, the populations of “added” and “incumbent” toner particles scarcely show any tendency to merge to a common intermediate level of charge and the “added” toner particles remain at a high charge level. In the present report, experimental data taken on a simple black xerographic developer at various levels of developer mixing intensity (e.g., as created via changes in mixing times and modes of developer mixing), demonstrate a progression from an excellent admixing performance to a non-functional level for a single developer design.

The charge acceptance of single layer organic photoreceptors consisting of a-type Cu phthalocyanine pigments and hydrazone charge transport materials dispersed in thermosetting acrylic polymer is found to decrease when the surface is exposed to ambient NO₂ gas. The electronic surface properties of the photoreceptors are investigated by treating the surface with HNO₃ aqueous solutions and by measuring the applied voltage current characteristics. Internal photoemission experiments determine the energy level relationship between metal electrodes and the photoreceptors. The hole injection from the treated surface can be attributed to the formation of acceptor-like states at the surface. The improvement of charge acceptance based on this conclusion is presented.

Electrophoretic mobilities of copper phthalocyanine (CuPc) pigment particles dispersed in Isopar G™ are reported. The mobilities were measured as a function of particle charging agent (PCA) concentration using phase analysis light scattering (PALS). The role of particle stabilizing agents (PSAs) at the particle surface was also investigated. An equilibrium site binding model can describe the experimental data adequately. Conductivity measurements and adsorption isotherms facilitate an overall description of particle charging in these systems. The electric field dependence of the electrophoretic mobility of the pigment particles was also investigated up to field strengths of 10⁴ V cm⁻¹ and showed a marked dependence on the strength of the applied field. A modified version of the model proposed by Jin and co-workers in Ref. 18. is used to model the field dependence.