The surfaces of the electrophotographic layer which composed of zinc oxide and resin were charged up by using negative corona discharge and the characteristics of electrification were observed. The preparation of the specimens and the condition of measurement were the same as the recently published paper¹⁾. The ratios of resin to zinc oxide were 35, 50, 68.8 and 100 vol. %. Two Kinds of specimens were used; one was prepared by coating the emulsion on paper (P) and other on aluminum foil (M). In the other hand, the specimen which contained Rose Bengal dye (0.05 g/100g ZnO, 50 vol. % of ZnO to Resin) as a sensitizer was also prepared. The blockdiagram of the equipment is shown in Fig. 1. The corona stainless steel wire was of 0.2 mm in diameter. In Fig. 2 the building up of the surface potential V was shown in function of the discharge current I. In this case, the current was conventionally observed in order to check the condition of discharge. The saturation time T (in Fig. 2) vs. the current I was plotted in Fig. 3. From this result, the next relation between T and I was found,
T=A exp (-BI)
where, A is the constant which mainly concerned with the “external condition” such as the discharge gap, the atmosphere and so on, and B is the constant concerned with the “inner condition” depending on the thickness of the layer, the composition of a specimen and so on. The experimental result for some specimens (M) shown in Fig. 4 appeared to be not so different in their nature from those in Fig. 2 and Fig. 3, though a little discrepancy between both cases at the lower current were observed. Fig. 5 shows the dependency of the saturated surface potential Vs upon the resin content of the layer. This increased linearly with the ratio R of resin to zinc oxide, as follows
Vs=a R+b
where “a” and “b” are the constant concerning with properties of the specimen.

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Written in this paper the characteristics of xeroradiography for aluminium. Image of aluminium penetrameter whose step is respectively 1, 4, 8, 12 and 16 mm in thickness, is made on xeroplate. The surface potential of plate is measured by means of quadrant electrometer. Considerations to eliminate the ionization effect by X-ray were taken. Deviation of potential due to the difference of thickness shows the contrast of image. The deviation is small for lower voltage less than 70 KVP, and also for higher voltage greater than 150 KVP.
Relations between potential of plate and voltage of the tube, and also potential drop per röntgen per minute and tube voltage are shown.

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When a d-c field is applied to a phosphor layer, during or after the exciting irradiation, polarization occurs because of trapping of free carriers. The phenomenon is Known as persistent internal polarization. The investigation were sucessfully made to an application to electrophotography. In this paper, a process untill a latent image is made is reported with several discussions.

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The author discusses generally what the definition of photography and the contents of photographic Sensitometry are, and gives the general principle on the Sensitometry. This general principle is applied to the Electrophotographic Sensitometry.

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In this paper, test results were described concerning about the relationship between the toner producing conditions and the resolution of electrophotographic powder image as well as the toner particle size.
The process of toner producing is as follows: 1. drying the emulsion of raw material by spray method. 2. natural deposition. 3. collecting in a electrostatic precipitator.
The toner size was controlled mainly by varying the density and the spraying rate of the emulsion. The powder image was examined on electrophotographic paper printed in contact to resolution test charts. The resultant image has a maximum resolution of 120 lines/mm for 70 % resolution and 100 liines/mm for 90 % resolution.

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Three processes are known as the photoengraving process using the electrophotographic materials, ZnO-resin dispersed system. They are (I) Interim, (II) Direct. and, (III) Transfer processes. We have studied the optimum conditions of these processes when used in practical purpose. and compared these availability to the bi-chromate system, now used. Obtained optimum conditions are summarized as follows.
(I) Interim process.
i) The rose bengal sensitized ZnO layer thickness is 10-30 μ.
ii) PVA-bichromate layer thickness is 1-2 μ.
iii) Exposure value of ZnO top layer is 165 lux. sec. under thetungstem lamp of 10-150 lux.
iv) The second exposure time to PVA under layer is 18-30 sec in mean value under 80,000 lux arc lamp intensity.
v) The resolution power of obtained etching plate is 20 line/mm.
vi) The processing time is 16.5 min including the Dow etching time, and this process ls N→P system.
(II) Direct process
(i) The rose bengal sensitized ZnO layer thickness is 10 μ.
(II) Exposure value of ZnO layer coated on Mg plate is 130 lux・sec under the tungsten lamp of 10-150 lux.
(III) Exposure time in process cameras is f=18 20 sec, f=32 50 sec in mean value.
iv) Toner quantity necessary for etching is 7.0g/m² over.
v) The resolution power of obtained etching plate is 30 line/mm using Orifax Toner and Orifax Washoff Solution.
vi) The processing time is 13 min including the Dow etching time, and this process is P→P system.
vii) Etching coefficient is 28-128 in the Dow process and 50-700 in the powdered process.
(III) Transfer process
Afer examining of several toner-transfer processes, we concluded that Transfer process is not adapted to the practical use, because of its failures in toner-transfer ratio, transfer image qualities, such as resolution power, pinhole in image, and toner coagulation after fixing.
We confirm that Direct and Interim processes are more profitable than the PVA-bichnomate system in the following reasons. The process is simple and the processing time is short and then process film is not necessary, so that the engraving cost can be reduced.

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