This paper describes a new electrophotographic color process using a technology of superposing toner images on a photoconductor. The main technologies of this are an electrostatic latent image forming process and a non-contact development process
For the purpose of attaining high quality color prints, we have investigated and concluded the mechanisms and the process conditions as follows: (1) Charging phenomena of toner and photoconductor by a scorotron and discharging phenomena caused by exposure from above the toner layer and the photoconductor are studied. Then successive image forming above the toner layer and photoconductor should be controlled by means of the exposure power. (2) We developed the non-contact 2-component development method that prevents destruction of formerly developed toner images. Then the optimum condition of the non-contact development that doesn't generate defects like background stain, carrier deposition and color contamination is found. (3) A smaller toner and the order of developments are important to reduce the influence of superposing, and to improve the print quality.

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Aerodynamic size (d_a) and electrostatic charge (q) distributions of black and color toners are influenced particularly by agitation time, toner-to-carrier mass ratio and relative humidity. An electrical single particle aerodynamic relaxation time (E-SPART) analyzer was used to measure the d_a and q/m distributions providing non-contact, real-time, single-particle measurements.
Experimental data show most toners acquire bipolar charge distribution, but reverse polarity charging is more significant in color toners.

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The most important problem in the cleanerless printer using simultaneous development and cleaning is to find a condition in which the influence of the residual toner on the subsequent image can be eliminated. The authors calculated the relations between the major parameters and the memory appearance to obtain the way to optimize these parameters. The results are; (1) There is an optimum range for the development toner charge value. Negative memories tend to appear when the absolute value of the development toner is small, and positive memories when large. (2) The residual toner charge should be as small as possible. (3) The contact-type monocomponent non-magnetic development is suitable for the cleanerless process.

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Pressure wave propagation method, which is generally used to measure charge distribution directily in solid insulating materials, was applied to the measurement of the charge distribution in organic photoconductor (OPC). Validity of this technique for studying the electric properties of OPC was demonstrated by following experiments:
(1) The motions of charges in aggregate OPC and layered OPC under the conditions of dc voltage application and light exposure.
(2) Generation and separation of carriers in OPC under dc voltage application and transport of carriers with light exposure in layered OPC.
Consequently, using pressure wave propagation method, the charge distributions in OPC under the conditions of dc voltage application and light exposure were directly and clearly observed. Thus, this technique is reliable and useful for styudying the electric properties of OPC.

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Photocurrents in a layered photoreceptor consisting of amorphous silicon carbide as a carrier generation layer (CGL) and a 2, 4, 7 trinitro-9-fluorenone (TNF) doped polymer as a carrier transport layer (CTL) have been studied. The field dependence of the photocurrents obtained from photo-induced discharge curves were studied in order to obtain better understanding of the factors governing the limitation of photocurrents. The photocurrents depended on the thickness of the CTL and on the TNF content ratio relative to polymer. The photocurrents can be satisfactorily explained by carrier range limitation in the CTL From the comparison between calculated and experimental photocurrents for the photoreceptor, we estimated the values of the carrier range and the carrier lifetime in CTL. We found that the efficiency of generation of photocarrier in the CGL was high and that no interfacial barrier to retard carrier injection from CGL to CTL was observed.

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The possibility of a molecular orbital method (MOM) in developing charge control agents has been investigated. MOM showed that the relation between the ionization potential and the triboelectric charging quantity of model toner containing guanidine derivatives was linear. The positive-charging ability of guanidine derivatives was affected by the electron density on the SP² type nitrogen atom. In the case of polymers containing organic substances, MOM indicated that the state located around the middle energy level between HOMO and LUMO of organic substances acted as the triboelectric charging state. These results suggested that the MOM is very useful for the development of charge control agents because MOM can estimate their triboelectric charging quantity and give the direction for their molecular design.

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