The color gamut in bi-level digital printers depends on the allocation of the CMY primary ink dots placed in dithering matrices. The typical color mixture model is based on Neugebauer theory, where CMY dots are placed at random, but recent digital printers don't obey that theory. The simplest method used in digital printers is “coaxial” allocation, where the CMY ink dots are placed in the same positions in each color dither matrix. The coaxial model produces sharp edges, but may generate too many secondary colors with unsaturated chromaticities. A mixture of C and M inks may produce a more brilliant bluish color when the C and M dots are placed side-by-side to avoid overlapping. In this paper, “min-med”, “min-max” and “min” models with side-by-side dot allocation are discussed. These are designed to suppress the occurrence of secondary colors. The corresponding color gamuts are analyzed and compared.

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Study on dispersion of CGM(Carrier Generation Material), surface voltage lowering after charging and smoky noise using α-form Oxotitanium Phthalocyanine(α-TiOPc) as CGM were carried out. Uneven thickness of CGL(Carrier Generation Layer) was improved by addition of polydimethylsiloxane humed silica without degradation of electrophotographic properties.
Surface voltage lowering after charging in High temperature/High humidity(H/H)environment was improved by using thermoset resin (PVB(polyvinylbutyral resin)/melamine resin) as binder. Surface voltage lowering in H/H environment was also improved by using CGM which is treated by dry milling and chloroform reflux, instead of CGM which is treated by acidpasting and acetonitrile reflux.
Smoky noise on printings in H/H environment was also improved by using thermoset resin as binder. It was also improved by using CGM which is treated by dry milling and chloroform reflux, instead of CGM which is treated by acidpasting and acetonitrile reflux.

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Charging characteristic of photoreceptor is changed by pre-exposure. An extraction method of the charging characteristic change is proposed. The method is applied to an organic photoreceptor and a peak, which is thought to be due to traps, is found in the change of absorption current. The method is expected to be useful to examine photoreceptors.

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