The zinc oxide-resin photoconductive layers are prepared as follows; zinc oxide powder with crystal size of about 0. 1 to 0. 7 microns is dispersed in toluene solution of Silicone, Alkyd and Polyolefin resins and this mixture is then poured onto aluminum base plates and dried immediately.
The thickness of these layers are between 15 and 25 microns.
The surface voltage of the layer under dark adaptation (contact potential difference between sample and electrode) and the surface photovoltage under the illumination of white light (variation of contact potential difference) are measured by the Kelvin method.
The large fast and slow photovoltages are observed under the illumination of white light. The rise up time constant of fast photovoltage is about 0. 5 second and that of slow photovoltage is a few minutes or longer. The contact potential difference and the surface photovoltage are changed with zinc oxidP content of the layer. The dark decay curve of surface phototovoltage is approximately shown in the form of V_ph=^V_ophexp(−t/τ) where ^V_oph is the inital surface photovoltage after the illumination, τ_D is recovery time of surface photovoltage which depends on zinc oxide content. The observed value of r:n is about 20 minutes in the case of zinc oxide-silicone resin layer and longer than an hour in the case of other layers. The observed value of τ_D is associated with fatigue by pre-illumination on electrophotographic properties. The thickness and light intensity dependence of the surface photovoltage are measured.

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The electrophotographic properties of zinc oxide-resin dispersion layers by corona charging are investigated, especially concerned with zinc oxide content dependence of saturation surface potential, dark decay ratio, over charge ratio and quantity of fatigue by pre-illumination.
The saturated surface potential for zinc oxide-resin layers vary considerably depending on type of zinc oxide, type of resin binder, and especially on content of zinc oxide. In positive corona discharging, the aceptance of positive surface potential depend on type of resin binder and content of zinc oxide.
The dark decay ratio for zinc oxide-polyolefin resin layers intensely depend on content of zinc oxide, it abruptly decreases with increasing content of zinc oxide at 60%.
The phenomenon of over charge which the surface potential is decreasing slowly from maximum value of surface potential during corona discharging, is observed for all zinc oxideresin layers at a specified content of zinc oxide. The same minimum over charge ratio is observed at 99% of zinc oxide content for zinc oxide-silicone resin layers and at 95% of zinc oxide content for zinc oxide-polyolefin resin layers.

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Dihydroxynaphthofluoran (disodium salt), one of xanthene dyes, has been observed to sensitize sensitize the zinc oxide-resin electrophotographic layer in the red portion of the spectrum.
Activation spectra show that the response (λ_max. of sensitivity) is under the influence of the nature of a binder resin.
When the dye (DHNF·Na₂) is applied to ZnO-Silicone Resin or ZnO-Polyvinyl acetate system, λ_max. of the response is around 610 mμ or 640 mμ, respectively. These values agree with λ_max. of absorption spectra of solid solutions of the dye in Silicone Resin or Polyvinyl acetate. When, on the other hand, the dye is adsorbed to zinc oxide fine crystals, λ_max. of the absorption spectrum is observed at 600 mμ.
These experimental results show that the "solvent effects" caused by a binder resin is more significant than those by an adsorbent (zinc oxide) at least in the zinc oxide-resin-DHNF·Na₂ systems.
A chromophore of the dye is supposed to be the carbonyl group attached to the naphthalene ring, while the adsorption site of the dye is considered to be the carboxyl group of the benzene ring. Since the chromophore is located far from the adsoption site, namely the surface of a zinc oxide crystal, and surrounded by the binder resin, it is supposed that the “solvent effects” by the binder resin are significant enough to shift the absorption maximum of the dye to longer wave lengths.

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In electrostatic electrography, electrostatic charges are produced directly on dielectric surfaces in a variety of patterns or configurations with the use of electrode. After electrostatic images are made visible by brushing with an magnetic brush, there appears ghost images around the image area.
In this paper, the static field of latent images were solved in the form of equation (10) and illustrated in the figure 5. Following the equation obtained in this paper, the distribution of static field around the image area was fixed by surface charge density and the width of latent images. By applying the optional bias-voltage between magnetic brush and base electrode, ghost images could be conveniently vanished. According to the solution of static fields, it was well explained of ghost images in electrostatic recording.

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