Abstract Time-resolved particle image velocimetry (PIV) has been performed inside the nozzle of a commercially available inkjet printhead to obtain the time-dependent velocity waveform. A printhead with a single transparent nozzle 80 μm in orifice diameter was used to eject single droplets at a speed of 5 m/s. An optical microscope was used with an ultra-high-speed camera to capture the motion of particles suspended in a transparent liquid at the center of the nozzle and above the fluid meniscus at a rate of half a million frames per second. Time-resolved velocity fields were obtained from a fluid layer approximately 200 μm thick within the nozzle for a complete jetting cycle. A Lagrangian finite-element numerical model with experimental measurements as inputs was used to predict the meniscus movement. The model predictions showed good agreement with the experimental results. This work provides the first experimental verification of physical models and numerical simulations of flows within a drop-on-demand nozzle.

Abstract Ceramic tile decorating techniques have evolved significantly in recent years. Digital inkjet printing technology has enabled digital systems to be used for the direct decoration of ceramic tiles, revolutionizing ceramic tile decoration and providing many advantages over traditional decoration techniques. It was the formulation of inks with soluble and vitrifiable stains that allowed inkjet printing technology to be introduced into ceramic tile decoration. The incorporation of milled inorganic pigments into the inks broadened the available color palette. However, the colloidal instability of these inks and the constraints of the printing heads themselves made it necessary to reduce pigment particle size, thus limiting color saturation and the color gamut. In order to increase color saturation and obtain a set of pigmented inks with colors more closely resembling CMYK colors, pigments with larger particle sizes need to be used. Indeed, other digital decorating techniques, such as xerography, allow larger particle sizes to be used, while also providing the advantages associated with digital decoration. However, the implementation of this technique for ceramic tile decoration requires the development of appropriate ceramic toners and adaptation of printing machines. This article reviews the technical evolution of ceramic tile printing and describes the development of a prototype, based on xerographic printing, that is able to print ceramic tiles directly and provides greater color intensity and a wider color gamut.

Abstract Hydrophobically modified fumed silica particles are widely used in toner formulations to enhance toner free flow and triboelectric charging. Despite the important role that dielectric powders have in electrophotography, the triboelectric charging of such powders is still poorly understood. In this article, the authors present experimental data on the charging properties of toners formulated with fumed silica additives that were modified with different levels of fluoroalkylsilanes. The results show that at high ambient relative humidity (RH) conditions, the triboelectric charge correlates with the fluorine content of the additive, whereas at low RH, the triboelectric charge is effectively constant with respect to fluorine content. The same result was obtained with two different types of toner particles. The authors attempt to rationalize these results in terms of surface conductivity at high RH conditions and charge saturation at low RH conditions. They also present a series of zeta potential measurements that show a correlation with tribocharge at high RH and interpret the results in terms of the ion-transfer model for triboelectric charging.

Abstract Particles of externally added charge control agent (EA-CCA) were prepared by means of a coacervation process and their effects on toner charge were investigated. The EA-CCA particles comprised silica core particles of 110 nm diameter and CCA molecules adhered to the core surface. Four kinds of negative charge control agent (CCA), namely a boron complex (N-1), a zinc complex (N-2), an iron complex (N-3), and a styrene‐acrylate copolymer with sulfonic acid (N-4), were prepared as EA-CCAs. The tribo-charge of the mixture of model toner and EA-CCA was measured using the blow-off method. The CCA concentration range was up to 1 μmol/g with respect to the model toner. In both the N-1 and N-3 experiments, the maximum tribo-charge values appeared around 0.01 μmol/g of CCA concentration. On the other hand, in both the N-2 and N-4 experiments, the tribo-charge was increased with increasing CCA concentration. The CCAs were classified into two types. One was the low concentration type, N-1 and N-3, and the other was the high concentration type, N-2 and N-4. The CCA efficiency on tribo-charge was different between the two types of CCA. Low concentration type CCAs were effective in the low concentration region. They had no effect in the high concentration region. High concentration type CCAs were effective in the high concentration region. They still had a small effect in the low concentration region.

Abstract External additive blending is one of the most important processes in toner manufacturing. It determines the electrostatic properties, powder properties, and physical properties of the toner, and therefore the xerographic performance of the toner. Additive-blending conditions, as well as additive compositions, have huge effects on several important toner properties such as the triboelectric charge level, charging rate, free flow, cohesiveness, and powder density. Understanding the additive-blending process and its effects on toner performance is of practical use in designing additive-blending processes and choosing optimal blending conditions. The effects of additive-blending conditions, such as blending intensity and blending temperature, have been studied, and their effects on toner properties and image quality have been tested. The temperature dependency of the blending process and hence the resulting properties and performances of the toner have not been studied extensively before, and this forms the purpose of this report. In most cases, the blending temperature during the additive-blending process is maintained at a fixed temperature, usually atmospheric temperature, or below, to remove the heat generated during high-speed blending. The blending temperature has an effect on additive adhesion, which indicates how effectively additives adhere to the toner surface after mechanical stress, which toner experiences in a cartridge during life.

Abstract Color image difference metrics have been proposed to find differences between an original image and a reproduction. One of these metrics is the hue angle algorithm proposed by Hong and Luo in 2002. This metric does not take into account the spatial properties of the human visual system, and it could therefore miscalculate the differences between the original and the reproduction. In this article we propose a new color image difference metric based on the hue angle algorithm that takes into account the spatial properties of the human visual system. The proposed metric, the Spatial Hue Angle Metric, has been subjected to extensive testing. The results show improvement in performance compared to the original metric proposed by Hong and Luo, and improvement over or similar performance to traditional metrics, such as the Structural Similarity Metric and Spatial-CIELAB.

Abstract A relative perceived visual contrast (RPVC) model is proposed for high dynamic range (HDR) photography. This approach assumes that an equivalence of perceived visual contrast can be implemented between HDR and low dynamic range (LDR) images. An RPVC function is derived in this study to perform the visual contrast mapping, which provides uncomplicated but effective transformation to compensate for the luminance change in the HDR environment. Other essential features such as the bilateral-type filter and computation in IPT color spacing found in prior HDR models are also incorporated. A specially designed lighting environment was configured to generate a real HDR scene not only for the purpose of model developing but also for psychophysical evaluation. Six other HDR models were compared by the paired comparison method in a real scene. Further comparisons were performed between iCAM06 and this RPVC model for computation efficiency. The results indicate that this RPVC model is effective and that it may bring a new thought to HDR research.