The image density and fog density of ZnO electrofax paper are related with the surface potential given by the corona charging, that is, the image density is effected only by the initial surface potential just after the charging, but the fog density is not only to be effected by the surface potential discharged in illuminating, but also the initial surface potential just after the charging.
Therefore in order to clarify these relations, the experiments were carried out, varied initial surface potential and discharged surface potential, being fixed developer, developing process, (magnetic brush method) electrofax paper.
Data of this experiment were shown in Fig. 1~7
An empirical formula was given by the experimentation, that is,
(1)
(2)
(3)
where,
D₁: Non-illuminated density
D₂: Illuminated density (Fog density)
⊿V: Difference between the initial surface potential and the illuminated surface potential.
V₀: Illuminated surface potential.
k₁, k₂, k₃: Constant parameter decided by the experimental data.
The fog density has the term which is not related with surface potential, and related with the root of surface potential, and the difference between the initial surface potential and discharged surface potential.

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This paper describes also a study on the image quality for the electrophotographic system of ZnO. To obtain a good image quality on ZnO photoconductor layer. It is necessary to consider three factors, the charging process, the exposure and the developing process. The charge-build-up and the decay process were measured, by varying the moisture content of the base paper. We found that the charge-build-up, the decay and the light sensivity were affected by the moisture content in the base paper. In particular, the initial charge decay changed markedly by paper humidity.

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In ZnO-resin type electrophotography, we consider that the dielectric property of ZnO-resin film is one of the most important factors, especially in reference to the corona discharge and surface potential decay.
The impedance changes of ZnO-resin layer by light irradiation were studied. In the present work, the capacitance changes of ZnO-resin layer was described.
The frequency dependency (Fig. 5, Fig. 6) , light intensity dependency of capacitance (Fig. 7), time build-up and time decay of capacitance changes (Fig. 8, Fig. 9) were observed. From these experiments, the authors found photodielectric effect on ZnO-resin layer.

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A method has been developed, which is available to the printing system and the transferring system in electrostatic printing or electrophotography. Using the method, which is based on a fact that an electrostatic field gives a considerable effect on the static electrification, replica of a latent electrostatic charge pattern may be directly obtained. Procedures are very simple. A thin insulating film without any charges is placed on an insulating film with an electrostatic charge pattern. Thereafter, the surface of the former is rubbed by a soft material. After both films are separated into each film, a transferred charge pattern of the reversed sign is observed on the former, and the previous one still remains on the latter. Results of experiment and application are described in the present paper.

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Light decay characteristics of negative charge on the film of polyvinylcarbazole and polystyrene with several heterocyclic photoconductive compounds have been studied. The heterocyclic compounds used are I-VI_e (see the formulae).
The experimental arrangement and the preparation of photoconductive films are shown in Fig. 1. Decay curves like those in Fig. 2 (a) did not give any linear relation when the logarithm of the surface potential (V) was plotted versus time (t) (Fig. 2 (b)); Iog V versus t^1/2 plot however, gave a linear relation (Fig. 3). The value a in the equation V=V_0e^-αt1/2 was therefore used as the decay constant. The value α was found to be proportional to the light intensity I (Fig. 5) .
The increase of decay constant when illuminated with light I_A (Fig. 4) was given by is α_A (α with filter D 25) minus α_d (dark decay constant). The decay constant α_A⁰ inherent to the light of this wave-length region was therefore α_A⁰=(α_A-α_d)/I_A. The increase of decay constant when illuminated with light I_B (Fig. 4) was given as α_B= (α_III-α_d) - (α_IV-α_d), where α_III and α_IV were α values when filters VY 39 and VY 50 were used, respectively (Fig. 4) The decay constant α_B⁰ inherent to the light of this wave-length region was therefore α_B⁰=(α_B-α_d)/I_B. Values of α_A⁰ and α_B⁰ are listed in Table 1 and 2. As we are interrested only in the relative values of α_A⁰ and α_B⁰ in calculation, the value of I_A is assumed as I, the value of I_B being then 3.
As is evident from Table 1, polystyrene itself was not sensitive to light, When total light was used, pyrazoline derivatives and tetrahydroimidazole derivatives in polystyrene showed higher α values than others.
α_A⁰/α_B⁰ values are higher in compounds II, IV and III, being 22, 8 and 4 respectively. As is shown in Figs. 6 and 7, the light absorption by these compounds is small in the wave-length region of I_B, values of α_B⁰ being consequently small, increasing the values of α_A⁰/α_B⁰.
As is shown in Fig. 8, decay constant α decreased with increasing film thickness.
α_A⁰/α_B⁰ was 7.7 for polyvinylcarbazole, decreasing down to 2. 3 with increasing amount of pyrazoline VI_b. As is shown in Fig. 10, the light absorption of the film increased in the longer wave-length region when pyrazoline was added to polyvinylcarbazole, increasing α_B⁰ and decreasing α_A⁰/α_B⁰.
When pyrazoline was added in various amount to polyvinylcarbazole and illuminated with the total light, α values increased first a little then decreased to a minimum and again increased up to a fairly high value (Fig. 9). (View PDF for the rest of the abstract.)

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