Toner image

Transfer. The toner image is then transferred to the snbstrate... 

Step 4 Transfer. Paper is passed between the drum and the transfer corona, which has a polarity that is the opposite of the charge on the toner. The toner image is transferred by a combination of pressure and electrostatic attraction from the drum to the paper. On many color and high-speed machines, it is common to replace the transfer corona with one or more charged bias transfer rollers (BTRs), which apply greater pressure and a higher quality image. 

Step 5 Separation or detack. Electric charges on the paper are partially neutralized by AC from a second corona, usually constructed in tandem with the transfer corona and immediately after it. As a result, the paper, complete with most (but not all) of the toner image, is separated from the drum or belt surface. 

Step 6 Fixing or fusing. The toner image is permanently fixed to the paper using either a heat-and-pressure mechanism (hot-roll fuser) or a radiant fusing technology (oven fuser) to melt and bond the toner particles into the medium (usually paper) being printed on. 

A transfer material has been developed for transferring monochrome and full-color images produced by a xerographic process or a dry toner printing onto a substrate. The process requires the use of a film from TPX as the transfer material. This material is used to transfer the xerographic or dry toner image onto the substrate with the application of heat and pressure (27). 

In the final step, the fusing step, the toner image is made permanent. The registration rollers push the paper toward the fuser rollers. Once the fuser grabs the paper, the registration rollers push for only a short time more. The fuser is now in control of moving the paper. 

Figure 12. Corona-assisted electrostatic toner image transfer from photoconductor to paper overall configuration (left), and detailed cross section through contact zone (right). (Reproduced, with permission, from Ref. 75. Copyright Butterworth Co.)...

At the end of the process, the loose toner image is melted to fix it to the paper. We shall illustrate the interfaces involved for hot roll fusing, a process of choice for modern high volume duplicators. Radiant heaters, flash lamps, and cold pressure roll systems have all been incorporated in low volume copiers, whose intermittent mode favors instant start-up and low standby power. In continuous use, on the other hand, hot roll fusers have an approximately threefold advantage over their competitors in terms of power economy (.98) The toner comes into contact with more toner, with paper, and with the fusing roll. The first important interaction is one which must be avoided, and which therefore sets a temperature threshold for the materials and process it is a premature sintering ("blocking") of... 

Figure 2. Schematic of original bar pattern, toner image of bar pattern, and scanning slit aperture used to measure edge transition.

The statistical fluctuation or noise level of a toner image is also by these postulates dependent on the particle size distribution. The function which relates the statistical fluctuations to spatial frequency is the Wiener spectrum, which is the Fourier transform of the optical density autocorrelation function. In terms of toner images, it is a measure of the dimensional extent over which the presence or absence of a particular toner particle will contribute to density. The density fluctuations can be measured as a function of position, normally with a slit aperture. This is schematically represented in Figure 6 where the left-hand sketch is related to large particles and the right-hand one to small particles. The density data can be used to calculate noise power or Wiener spectrum (8). Formally, the Wiener spectrum is ... 

Tomita, J. Sakai, Y. Ohashi, M. lida, T. Kuramoto, S. Apparatus for decoloring electrostatographic toner images from receptor paper for reuse of paper. Jpn. Kokai Tokkyo Koho JP 04356087, 1992 Chem. Abstr. 1993,119, 170448. 

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