Photoreceptor material

Where visible absorption peaks have been found in natural photoreceptor material, no NMR or X-ray crystallographic data has been put forward to demonstrate the presence of a retinene in the material (See Chapter 7). It is proposed here that any such tests will demonstrate the presence of a Rhodonine instead. Rhodonine contains two polar groups separated by a conjugated carbon chain. It is further proposed that opsin is only present as a completely passive substrate. Its association with the liquid crystalline Rhodonine is via a weak hydrogen bond that does not change the electronic configuration of the Rhodonines. 

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Liquid toners are suspensions of toner particles in a fluid carrier. The carrier is typically a hydrocarbon. Dielectric, chemical, and mechanical properties of the Hquid must be compatible with the photoreceptor, the suspended toner particles, and the materials of the development equipment. Liquid toners are capable of producing higher resolution than dry toners because of the smaller (3—5 -lm) particle size achievable. Development of the latent image occurs as it passes through a bath of toner and the charged particles are attracted to the oppositely charged surface. 

The abihty to accept and hold the electrostatic charge in the darkness. The photoconductive layer should support a surface charge density of approximately 0.5-2 x 10 C/cm. The charge also has to be uniformly distributed along the surface, otherwise nonuniformities can print out as spot defects. The appHed surface potential should be retained on the photoreceptor until the time when the latent electrostatic image is developed and transferred to paper or, if needed, to an intermediate belt or dmm. In other words, the "dark decay" or conductivity in the dark must be very low. The photoconductor materials must be insulators in the dark. 

Triboelectricity. For development to occur, the toner particles must be reproducibly charged to the correct level and polarity for the specific photoreceptor. The phenomena of triboelectricity, which involves the transfer of charge from one soHd to another, are exceedingly complex, involving the surfaces of soHds and interaction of the surfaces with each other and with the ambient (52). Consequentiy, the specific experimental observations are highly sensitive to the nature and purity of the materials, the physical and chemical state of both surfaces, and the precise details of the experiments performed. 

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