Printing System Models - Control of Color Imaging Systems: Analysis and Design - page 583

operating range of the applied voltage. Beyond this operating range, the TMA
saturates. As fields build up and decay in the transfer nip, there is a constraint on

the maximum field strength allowable across the air gap. If voltages rise above this

value, known as the Paschen voltage, air molecules will undergo ionization to reduce
the electric field below this constraint, which limits transfer [23]. There is also

enough latitude needed in the applied voltage to ensure smooth transfer over a
range of toner and paper states.

10.2.5 F USING M ODEL
In the fusing process, toner is fixed to the paper using heat and pressure permanently

adhering it to the paper. Prior to the fusing, toner is only loosely bonded to the paper

fibers due to electrostatic forces; it can easily be disturbed or rubbed off. Most high-
speed fusing is done using hot roll pressure fusers, in which parameters like time,
temperature, and pressure determine the quality of the prints. Other techniques include
pressure only

fixing and solvent fixing. Thermal fixing with pressure rolls has proven

to be very ef cient. The fusing assembly typically has two rollers: a heated upper

roller and a lower rubber pressure roller. The fuser roller heats the toner suf ciently to

cause it to melt, and the pressure roller presses the melted toner into the paper, causing
it to bond to the paper. There is usually a long warm-up time (5 - 10 min) associated

with the process of thermal fixing with pressure. Typical fusing temperatures are

controlled around 140 C. When the heat rods are switched on, the entire fuser roll

surface is heated through conduction. The nip between the fuser roll and the pressure
roll induces the fused print to self-strip from the fuser roll. To ensure that the toner is
released from the fuser roll surface reliably, a release agent (such as amino functional
oil) management system is incorporated into the design. There are many important
(printer-speci

8

c) practical considerations required for fuser design. Pressure and
temperature change the physical form of toner particles from solid to viscoelastic
then to rubber, and finally the toner coalesces to fluid spreads and penetrates into the

paper fibers. The complex interactions between the toner, the substrate, and the fusing

method give a glossy appearance to the bonded toner that has signi cant effect on

perceived color of the image [24].
To determine its fusing latitude for variety of media thickness and toner mater-
ials, a comprehensive (physics-based) parametric study is required. For the purpose
of controlling the overall image reproduction process, we require a simpli ed model

of gloss as a function of the TMA and the fusing temperature. Generally, fuser roll
pressures are held constant for a given media thickness. Hence, we present an
experimental gloss model at a constant roll pressure below. Since, for now, we are
interested only in the color quality of a solid area dot, effects of the fusing process on
line width, blurriness and edge quality, etc. are ignored. More complex time-domain
models for designing the fusing system are available in Refs. [25

27]. They can be
easily integrated with the process models for a variety of media thickness and
coatings.
Figure 10.24 shows the measured gloss, G, as a function of the TMA in mg

-

cm 2
and temperature. Data was created by fusing toner patches for cyan, magenta,
yellow, black, red (magenta with yellow), green (cyan with yellow), and blue

=