The force needed to detach five sets of different size toner particles, having number averaged diameters between 3.6 and 8.5 μm, from a composite aggregate photoconductor was measured using an ultracentrifuge. In addition to size variations, each toner size had four different levels of silica concentration, adjusted so that the surface area concentration at each level was kept constant for the five toner sizes. Due to the changing silica concentration and particle size, toner charge also varied. It was found that the dependence of detachment force on toner charge was small, with the correlation actually being slightly negative. However, the detachment force increased monotonically with increasing toner diameter and decreased monotonically with increasing silica concentration. Moreover, upon normalizing the detachment force to the toner diameter and the silica concentration to the surface area concentration of silica, it was found that the detachment force clustered into groups in which the force needed to separate the toner from the photoconductor depended only on the silica concentration. These results suggest that van der Waals interaction, rather than electrostatic forces, are the dominant mechanism controlling toner adhesion in this instance.

An investigation of toner adhesion using a novel apparatus based on vibratory detachment of toners is presented. The toner size and toner charge dependences of the electrostatic and the non-electrostatic (or van der Waals) components of adhesive force are determined. The empirical relationship is consistent with the expression derived by Rimai et al. from the theory of Johnson et al. (the JKR theory). Based on this relationship, the requirements on electrophotographic process parameters for the use of small size toners are discussed quantitatively.

Corona discharge is applied to various fields. In these application fields, changes in the corona discharge characteristics due to atmospheric conditions is often a problem. The effects of airflow and isopar™ G (which is a mixture of several kinds of iso-paraffin: nonane, decane, etc.) vapor on corona discharge are investigated. The voltage required in order to maintain the corona current constant was found to decrease when airflow is applied to the corona discharge area, and the voltage was found to increase when the airflow contains isopar™ vapor. In addition, we found that the accumulation of polymer containing C and O occurs on corona wire when the wire is negatively charged and the airflow contains isopar™ vapor. The initial mechanism of the accumulation is proposed to be due to isopar™ ionization by electron collision to form positive ions, after which, the isopar™ attracted to the wire surface is polymerized at the surface.

4,4′,7,7′-tetrachlorothioindigo (TCTI) is an industrially important red pigment which also is used as a photoconductor for electrophotographic photoreceptors. Although TCTI is quite similar in molecular and crystal structures to 4,4′,5,5′,7,7′-hexachlorothioindigo (HCTI), the electrophotographic gain of TCTI has been reported to be about four times higher than that of HCTI. The high photosensitivity was interpreted in terms of the formation of weakly bound intermolecular charge transfer (CT) excitons and their subsequent electron hole pair dissociation; whereas tightly bound Frenkel excitons prevail in HCTI. In order to directly prove the formation of CT excitons in TCTI, an attempt has been made in the present investigation to observe the CT transition by means of polarized light using single crystals. No CT transition was, however, observed either in TCTI or HCTI, and both electronic structures are quite similar. Furthermore, the photoconductivity of TCTI and HCTI is found to be equally high, but depends significantly on the electrode material. This indicates that the exciton is extrinsically dissociated at the Schottky barrier between TCTI (or HCTI) and the electrode. These results lead us to conclude that the difference in electrophotographic gain between TCTI and HCTI-based photoreceptors might presumably be attributed to the carrier formation or injection efficiency at the interface between the charge generation layer and charge transport layer.

Y-Titanylphthalocyanine (Y-TiOPc) is widely used as the photoconductor for laser printers. However, little is known about its crystal structure. An attempt has therefore been made to grow single crystals from water containing solution on the assumption that the Y-phase includes water. An autoclave was utilized for the crystal growth so as to suppress the solvent evaporation and thus to increase the solubility of TiOPc. The single crystals have successfully been obtained, but these are found to be phase I according to the structure analysis. However, our single crystal exhibits an intense, Y-phase-like reflection around 790 nm as revealed from polarized reflection measurements on single crystals. The present fact evidently indicates that the Y-like layer of TiOPc is formed on the surface (thickness at least 2500 Å) and that the core of the single crystal is phase I. The present interpretation is also borne out by X-ray diffraction analysis on powders as well as XPS measurements monitoring O1s and Ti2p signals.

The use of low cost coated ink jet papers as a replacement for silica coatings has become more common lately. These novel paper grades consist of components typical for conventional printing papers, but have generally been modified to improve ink jet printability. However, knowledge of the fastness properties obtained with such papers is, to date, quite limited. The objective of this study was to clarify the effects of a coating polymer system on the light fastness of ink jet prints on kaolin coated papers. This was studied with FTIR and Raman spectroscopic methods using experimental dye based inks and papers with a known composition. The data on light fastness were consistent with the hypotheses of the study. The light fastness of ink jet prints was affected by both the physical and the chemical properties of the coating. The light fastness of the prints was improved when the porosity of the coating decreased as a result of increased binder content. This behavior could be observed for all coatings independent of the polymer types. The chemical stabilization of the colorants in consequence of hydrogen bonding to coating polymers was found to improve light fastness in PVA coatings.

The use of coated ink jet papers consisting of components typical for conventional printing papers would be advantageous in small scale applications for economical reasons. This study attempted to gain an understanding of the mechanisms affecting the water fastness of ink jet prints on conventionally coated papers. The effect of the polymer system of the coating was of particular interest. This was studied with FTIR and Raman spectroscopy using dye based model inks and kaolin coated pilot papers with known compositions. The data on water fastness were consistent with the hypotheses of the study. The results indicated that the water fastness of the studied ink jet prints was improved when the impermeability of the coating or its ability to fix the colorants with ionic bonds increased. With hydrophilic coatings, the structural properties of the coatings were of minor importance due to the dissolution of the binder. Rather, the ability of the coating to fix the colorants with ionic bonds proved to be critical. With hydrophobic coatings the structural properties of the coatings had more relevance. In this case, water fastness was improved with decreases in the porosity and wettability of the coating.

Contact angle is important in the study of many industrial processes, involving wetting, such as ink jet printing, lithoplating, coating adhesion, and floatation. Numerous methodologies have been developed for the measurement of contact angles. But there still exist many problems; in particular, there is no good method available for measuring contact angles of irregular liquid drop shape. To overcome these difficulties, we developed a method, Contact Angle Measurement of Arbitrary Drop Shape (CAMADS), based on image analysis, with edge detection in sub-pixel resolution. Comparing with other methods, CAMADS has a good combination of features: simple, reliable, flexible, and reasonably precise, in measuring contact angles; it can be applied to situations of asymmetric drop shape. CAMADS was demonstrated by studying the in vitro wettability of hydrogel contact lenses, and superior, excellent results were obtained in comparison with other existing methods.

The perceived magnitude of a stimulus detected by the human visual system is, according to Fechner's Law, proportional to the logarithm of its physical intensity. This suggests that the perceived mottle in a printed image depends not only on the reflectance variation of the image, but also on its mean reflectance level. One possible approach is therefore to use the reflectance variation divided by the mean reflectance level, dR/R, as an estimate of the perceived mottle in an image. However, practical use of this method indicates that perceived mottle may be overestimated in dark and underestimated in light images. The present study therefore attempts to establish a better relationship between perceived mottle and mean reflectance level. A set of halftone patches was constructed by digital simulation, and then visually evaluated. Results suggest that the measured variation should be divided by a power function, with an exponent less than 1, of the mean reflectance to obtain the best correlation between visual and instrumental evaluation. The highest correlation was attained using the inverse square root, i.e., an exponent equal to 0.5.