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World's First Facsimile with a Cleanerless Process

Toshiba developed the ultimate electrophotographic technology used for copiers, facsimiles, etc., allowing more compact, maintenance-free laser printers to be realized that produced higher image quality.

World's First Facsimile with a Cleanerless Process

Conventional electrophotography used a developer consisting of two particle components: toner particles and magnetic carrier particles. These were subjected to a process called triboelectrification in which the toner particles were electrified with a specified polarity. The particles were then conveyed to a photoreceptor drum by a magnetic roller. An electrostatic latent image was formed on the photoreceptor drum by image exposure. This image was visualized by the development process and transferred to paper. The toner particles remaining on the photoreceptor drum that had not been transferred to paper were removed by a cleaning blade and collected in a waste toner box. This gave rise to the need for periodical maintenance, which was an issue for this type of system. Moreover, the surfaces of the carrier particles were degraded by a coating of fine powder, etc. that was generated when they were churned together with the toner particles, so it was also necessary to periodically replace the carrier. On top of that, the carrier was held in place on the magnetic roller by magnetic force, and removing the carrier and toner particles from the roller was difficult work. We therefore focused our efforts on creating a developer consisting of a single component, with the aim of giving birth to a new technology that would eliminate these tasks and realize a maintenance-free system. Initially, we attempted to make a single-component magnetic toner that incorporated the carrier's function of conveyance by magnetic force into the function of the toner particles. However, due to the fact that the magnetic roller was necessary to carry the magnetic toner, miniaturization was difficult. We also judged that colorization would be problematic, and therefore abandoned that approach. Subsequently, we began to feel confident that a singlecomponent nonmagnetic toner was the best approach, and started development. Three difficult obstacles had to be overcome in order to realize such a system. The first was how to subject the toner particles to triboelectrification without the use of a carrier. The second was how to convey the nonmagnetic toner particles to the photoreceptor drum without magnetic force. And the third was how to reliably deposit the toner particles onto the charge distribution of the latent image in order to obtain high-quality images.

The first issue was solved by a design in which the toner particles were fed between the developing roller and an elastic blade. By optimizing the relations among the surface friction coefficients of the developing roller, the elastic blade and the toner, a thin monolayer of the toner on the rotating roller passed through under the blade. At the same time, a predetermined charge was given to the toner particles by triboelectric charging between the toner particles and the roller. Once a thin layer of charged toner particle was formed, it adhered to the roller by electrostatic force between the toner charge and the opposite charge which was induced on the conductive roller surface. As a result, toner particles were carried toward the photoreceptor drum without magnetic force, and the second issue was solved. As regards the third issue, we initially selected a noncontact developing method in which the toner was conveyed between the developing roller and the photoreceptor drum in a contact-free manner, and proceeded toward commercialization. Unfortunately, however, we had to abandon this method due to a problem with stability as well as an issue related to another company's patent, so we ultimately selected a contact type developing method. The development of an elastic developing roller using conductive rubber with specified triboelectrification and electrical resistivity properties was the key to success here.

We also found that the electric field enhancement effect produced by this newly developed contact type singlecomponent nonmagnetic developing method not only achieved developing with high image quality, but also a function of cleaning by the electric field used for developing. In 1995, after more than 10 years since the start of development work, we were able to commercialize a multifunctional laser facsimile.

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