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Kokuten High-Visibility Black Xerographic Background

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On black-and-white xerographic prints, normal-sized, black toner particles in non-image areas (xerographic background) are visible only if present at a high concentration, or if viewed through a magnifying loupe, since fused individual toner particles cannot be resolved by the unaided human eye. As a result, a zero level for visual evaluations may in fact represent a background level of about 200 normal-sized toner particles per cm2. By contrast, isolated, oversized fused black kokuten background particles (e.g., in the 50 - 80 μm diameter range) are quite visible in non-image areas even at a level of about 2 particles per cm2. Another important difference between normal and kokuten background particles is their response to xerographic development fields in background areas — normal particles can be markedly suppressed by a reversedevelopment electrical bias applied to a xerographic development roll, but kokuten production is unaffected by bias level. As a result, kokuten background particles represent a copy quality shortfall that cannot be cured by conventional xerographic strategies (e.g., development bias control or background exposure level), so that the minimization of such particles must be centered on improved toner properties.

Since kokuten particles occur on developed images at a low (but highly visible) concentration, qualitative copy quality evaluations for such particles are most conveniently obtained by a ranking system based on a direct visual comparison between test xerographic prints and standard prints. For quantitative evaluations based on a direct counting of visible particles, xerographic enlargements of test prints enhance the visibility of kokuten particles, and thereby facilitate particle assays over large background areas.

A range of intrinsic and extrinsic factors in the toner production and xerographic imaging processes can affect the generation of kokuten background. For example, blending trials on a single test toner indicate that the level of kokuten background can be altered by changes in blender type and blender settings. Likewise, a comparison of unfused and fused xerographic test prints illustrates the background enhancement effects of fuser roll and paper texture, while tests based on an uncharged photoreceptor reveal that a non-xerographic process, namely mechanical agitation, can eject kokuten particles from a development housing, and thereby be a significant source of random “noise” in background print tests

Document Type: Research Article

Publication date: January 1, 2004

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  • For more than 25 years, NIP has been the leading forum for discussion of advances and new directions in non-impact and digital printing technologies. A comprehensive, industry-wide conference, this meeting includes all aspects of the hardware, materials, software, images, and applications associated with digital printing systems, including drop-on-demand ink jet, wide format ink jet, desktop and continuous ink jet, toner-based electrophotographic printers, production digital printing systems, and thermal printing systems, as well as the engineering capability, optimization, and science involved in these fields.

    Since 2005, NIP has been held in conjunction with the Digital Fabrication Conference.

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