Tone reproduction in laser thermal transfer printing using dye sublimation type medium at high resolution was investigated. With this printing method, a laser is used as the heat source instead of a thermal head. As the laser beam can be focused to 2.8 microns in diameter, a high resolution image can be obtained by laser dye transfer printing.
In this paper, an experimental printing system that enables production of precise images by pulse width modulation was developed, and we evaluated the characteristics of continuous tone reproduction under various printing conditions such as pulse width, laser power and pulse cycle. Printing energy to obtain an image having an optical density of 1.0 is about 0.9 J/cm², and it is shown that there is little reciprocity law failure in this printing. The possibility of continuous tone printing at a high resolution was indicated, and we have obtained printed continuous tone image samples having a resolution over 3000 dpi.

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We have been studying the characteristics of laser dye transfer printing which enables the production of continuous tone images of high resolution. In this paper, in order to clarify the influence of the laser intensity profile, optical density and tone reproduction under printing conditions using a defocused laser beam were investigated.
As a result, experimental results of the relationship between optical density and the defocus level show good agreement with simulation results from a simplified model which introduced the idea of effective energy. It is shown that in proportion to increase of the optical spot diameter, density gradation is more dominant than area gradation, and it is possible to produce continuous tone images using a defocused laser beam. By printing standard images, we have confirmed the difference in tone reproduction which depends on the defocus level.

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In order to adhere nonmagnetic monocomponent toners to a roller and carry them to the developing region, we disclosed a new type of roller which is called Micro Field (MF)-Roller. The surface of the roller is made of many small part of two different materials, the one portion is conductive and the other is dielectric. At the surface of dielectric member there are triboelectric charges which bear fringe electric field between conductive base and dielectric member. That many small fringe electric field (Micro Field) attract a little charged toners from the neighborhood of the surface and contact them to the roller, so the toners can be charged up. And the layer of charged toners can have high intensitity of adhering force to the roller. We also disclosed a new development system with Micro Field-Roller, which can minimize the developing speed ratio of photoconductor and the roller.

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