12 Charge Transport Experiments in Monocomponent Toners W. IMAINO, K. LOEFFLER, and R. BALANSON
Downloaded by TUFTS UNIV on June 14, 2017 | http://pubs.acs.org Publication Date: October 13, 1982 | doi: 10.1021/bk-1982-0200.ch012
IBM Research Laboratory, San Jose, CA 95193
Charge transport through insulating, agitated monocomponent toners, first observed by Nelson, has been investigated in greater detail. Employing a standard monocomponent developer, the dc and transient currents through the agitated toners have been measured. It is apparent that current flows due to some kinetic mechanism; specifically, the experiments indicate that charge is injected onto the toner surface and current results due to the toner translational motion.
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In the monocomponent development process for copying onto plain paper , a magnetic and highly insulating toner is employed to render visible the latent electrostatic image on the photoconductor. As shown by Nelson , the toner brush is inductively charged and subsequently attracted and deposited onto the high charge areas of the photoconductor. He notes that the inductive charging is made possible, in these usually highly insulating materials, by a kinetically enhanced conductivity, i.e., the conductivity of the toner powder increases dramatically with greater agitation. This kinetically enhanced conductivity is the subject of the present investigation. The topic of electrical or thermal conduction through particulate media has been the subject of numerous theoretical and experimental investigations, encompassing a wide variety of applications. For example, the electrical conductivity of two phase dispersions with results of experiments on fluidized beds of spheres has been studied by Connelly and Turner. Charge transport of individual particles in electrostatic precipitators has been studied by McDonald et al. while Vincett investigated the high field electrophoresis of insulating particles in insulating liquids. These authors as well as others in related studies, demonstrate that electrical conduction in a system of insulating particles may take place as a result of mass transport (electrophoresis, electrostatic precipitators) or by interparticle contact (fluidized beds). For charge transport through a magnetically agitated, 3
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0097-6156/82/0200-0249$06.00/0 © 1982 American Chemical Society Hair and Croucher; Colloids and Surfaces in Reprographic Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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REPROGRAPHIC TECHNOLOGY
Downloaded by TUFTS UNIV on June 14, 2017 | http://pubs.acs.org Publication Date: October 13, 1982 | doi: 10.1021/bk-1982-0200.ch012
insulating powder one can envision current flow due to charge injection across interfaces and charge migration by both interparticle contact and mass transport. In Section II a description of the monocomponent developer is provided, in Section III the static (bulk) resistivity of the toners is discussed, the results of the kinetic conductivity experiments are displayed in Section IV, and we close with a few concluding remarks. Monocomponent Development Figure 1 displays a highly schematized illustration of a monocomponent developer station; the multi-poled cylindrical magnet sheathed in a non-magnetic (stainless steel) shell serve as a convenient reservoir of toner, forming a so-called magnetic brush, which can be rotated and swept across the latent charge image rendering it visible, due to the deposition of toner in the high charge areas. For adequate toner deposition, the magnets and shell must be rotated rapidly, so as to increase the kinetically enhanced conductivity which permits the induced charging. Figure 2 shows a more detailed schematic view of the nip region indicating the charging of the toner brush which may be represented by a simplified equivalent circuit shown in Fig. 3. Here, C is the capacitance of the layered photoconductor, C is the capacitance between the photoconductor and toner, and R is the effective resistance of the agitated toner. In a straightfoward procedure, one finds p c
p t
t
iR
V / C p c + VCpt + t -
0
and
where q and q are the charges on C and Cp , respectively, and q is the initial charge on the photoconductor. Combining these two equations, the charge accumulated on the toner brush must satisfy the following relation: t
p c
dq
t
Q
« + _2L + _22_ = o
dt
c
{
c,,.
where
C
|
=
(2)
The solution to Eq. (2) is q
Z £ ^ . (,-e-
