This paper describes the tone improving process of electrostatic latent image characteristics which is one of the important factors required for obtaining high fidelity color reproduction in the Canon NP-Color copier.
The tone improving process can be realized only in the Canon NP system using a photoreceptor composed of an insulating layer, a photoconductive layer and a conductive layer.
This process is characterized by the grid wires of the secondary corona charger which are classified into three sections, that is, positive, negative and neutral polarity.
Controlling the bias levels applied to the each section of the grid during the secondary discharging simultaneous with image exposure makes it possible to selectively reduce the surface potential in halftone areas, and to extend the linearity of the latent image characteristics, so that image with good tone and color reproduction can be produced.
The computer simulation was made by applying a CR equivalent circuit model to the tone improving process. As a result, it has been found that the values obtained from computer simulation agree well with those measured by using NP-Color copier. Therefore, the tone improving process can be explained by the CR equivalent circuit model.

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A new type of color imaging process has been developed. In this process filter beads containing color-former and a panchromatic photoconductor are employed.
In this report, the principle of this process, the structure of the filter beads, the photoconductor and the image receiving paper are described.
The main technical feature of this novel process resides in filter beads. Beads are the mixture of three kinds of colored particle. The core of each particle is made of a transparent melamine-formaldehyde resin sphere, which is colored red, green and blue, respectively. The core is covered with two layers, the inner layer is made of color-former and the outer one cuprous iodide. The colored core only plays a role of color separation filter, and the final image is obtained by the reaction of the color-former. Since the CuI layer makes the beads conductive, only a mono-layer of the beads covers the charged photoconductor.
The process of image reproduction is as follows:
1) The filter beads are brought into contact with the charged photoconductor to forma color filter layer on the photoconductor.
2) The photoconductor covered with the filter beads is exposed to an image to give rise to an imagewise charge pattern thereon.
3) The originally existing electrostatic attraction between the beads and the photoconductor disappears at the exposed area, and these beads are easily removed from the photoconductor surface.
4) The remaining beads are transferred to the image receiving paper after blanket exposure, and then heated whereby the color-former in the beads sublimes onto the paper to form a dye image.
The resolving power of the copy using 20∼40-μm-diameter beads was 4 lines/mm.
The black density was about 1. 2 and the background is 0.13.
In contrast to the conventional Carlson process, which needs three cycles of imaging.

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A new Two-Color Electrophotography with multilayer photoreceptor describing its principle and application has been studied.
The multilayer photoreceptor consists of two photoconductive layers, of which spectral property is different each other.
In the two color electrophotography, the electrostatic latent images corresponding to red and black area of an original are formed on the photoreceptor in opposite polarity by two charging steps and one exposing step.
Four types of practical processes, α-I, α-II, β and γ, have been proposed depending on the structure of multilayer photoreceptor and charging process.
The formation of latent images in the β-type utilising a simple capacitor model has been investigated.
According to the results, it was found important factors are capacitance ratio and the balance in photosensitivity between these two potoconductive layers in the multilayer photoreceptor.

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An almost ideal tone reproduction realized by the combination of a photographic negative film and positive printing material was processed by a “photographic image simulation system”¹⁾ to simulate the tone reproduction characteristics of typical electrophotographic photoreceptors whereby assumptions were made that the resultant characteristics can be represented by those of surface potential decay and that no substantial noises are introduced throughout imaging procedures.
The photoconductors of the simulated photoreceptors were ZnO/binder, amorphous Se and organic of transparent, solid solution type.

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A simple processor for measuring the static surface potential photodecay in photoreceptors was manufactured utilizing a commercially available X-Y recorder. The movement of a sample placed on a mobile pen stage of an X-Y recorder is controlled by an appropriate functionalized voltage to an X-axis input for the successive processes of corona charging, dark- and photo-decay measurements. A commercially available electrostatic voltmeter is used for measuring the surface potential. A simple electrical circuit of the time-sequence control is presented.

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Thermal recording process has been favorably applied to facsimile and non-impact printers of computer output, because of its advantages such as simplicity, cleanness and maintenance-free. However, for unstability of the formed image and possibility of additional printing, this process is unsuitable for print certificates and official documents. The thermal dye and/or ink-transfer printers possess same merits as thermal printers and are able to form the stable image.
We have developed the thermal ink-transfer printer for season ticket, and have tried to compat this printer. As one of improvement of this printer, uses of photofixable type thermal paper in place of ink-transfer tape have been investigated.
Several diazo type thermal papers were prepared using several kinds of diazonium salt and guanidine derivatives which are fusible base, and their print characteristics were examined.
Some of the thermal papers prepared are as sensitive as the commercial thermal paper, and is not inferior to the photo sensitive diazo type paper in the stability. It is able to estimate that photo-decomposition rate of diazonium salt in the layer coated on paper as well as in solution.

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