The image-density-decrease phenomenon, which occurs at the initial printing with a brand new developing cartridge and at a printing done after several days of rest, during which printing is not done, was studied in the mono-component developing process. The toner charge, q/m, and toner supply, m/a, were measured by a suction type Faraday cage. The mechanism of the image-density-decrease phenomenon is discussed based on q/m, m/a and fluidity of toner. The image-density-decrease phenomenon was found to occur with decrease in m/a, and not with increase in q/m. The cause of the decrease in m/a is the shortage of the toner supply to the supply roller. Finally, modifications of the developing unit and the toner additives to eliminate the image-density-decrease phenomenon are proposed.

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In this paper, we propose an algorithm that adaptively arranges or grows clusters according to tone slope of the cluster-dot halftoning by bubble packing. This technique locates small cluster regions to increase effective resolution on the portion of rapid tone change, and locates large cluster regions to increase effective tone scale on the portion of mild tone change to achieve a good balance between effective resolution and effective tone scale. Since the clusters are arranged irregularly, our technique has an effect of suppressing interference with regular patterns, such as moiré, and produces a good tone reproduction without occurring artifacts.

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In normal operation during roller rotation in the mono-component development system, a current flows through each system part (i.e. development roller, blade, and supply roller). The possible mechanism of generation of these currents is discussed, focusing on the surface potential at the development roller surface. The surface charge of the development roller, which is determined by both the toner charge and the charge trapped on the development roller surface are released by contacting with the supply roller. It was clear that this release of charge is observed as a current together with the current generated from toner charging and/or the toner transport. It was found that the surface characteristics of the development roller considerably affected the value of the toner charging and the charge retention of the surface as well as the magnitude and the direction of the current. From these results, a possible mechanism for this current generation is proposed.

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Emulsion aggregation toner (nick-named as EA Toner) has been developed for digital color copiers&printers.
Emulsion aggregation toner has been made by using the following process steps: pigment/wax dispersion preparation, emulsion polymerization, mixing, aggregation, and coalescence. The emulsion aggregation process with stepwise aggregation in particle formation provides a capsule structure and it also exhibits narrow particle size distribution. Shape-optimized toner particles are obtained by the coalescence condition.EA Toner process requires less energy than conventional toner manufacturing process because no pulverization and no classification are in principle required even in the smaller size region.
The encapsulated toner enables the same level of charge for each color as well as stable print quality under various conditions and realized high level compatibility between oil-less fusing, high resolution print quality and wider applicability for different kinds of paper by internal wax incorporation and shape optimization.

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[in Japanese]

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