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6. Step 4 Developing
Figure 2-8
As shown in Figure 2-8, the developing
unit consists of a developing
cylinder
(a
stationary magnet surrounded by a rotating
sleeve)
and a blade
made
of magnetic
material. Black toner'is a single component
type consisting of a fine powder of mixed
magnetite and resin binder. The toner has
insulating
properties
and is charged to a
positive potential by friction with the rotat-
ing cylinder.
Color developer
is a two-component
type consisting of iron powder (carrier) and
toner mixed together
in a fixed ratio. The
main component
of the toner is resin. The
toner is charged to a positive potential and
the iron powder to a negative potential by
friction with the rotating cylinder.
Figure 2-9
Figure 2-11
A concentrated
magnetic field develops
between the magnet and the edge of the
blade.
This
field
attracts
the
charged
developer.
In this step, a negative corona is applied
to the back of the copy paper, attracting the
toner from the surface of the drum to the
copy paper.
The developer is held virtually immobile
by the magnetic
field, forming
a curtain
along the edge of the blade. As the cylinder
rotates, this curtain skims the toner parti-
cles on its surface to a thin uniform layer.
An AC bias plus a negative DC bias are
applied simultaneously
to the developing
cylinder so that the waveform of the devel-
oping bias has a larger negative excursion
than positive.
Figure 2-10
During copying toner is attracted to the
drum by the charges on the drum surface
and by repulsion due to the developing bias
(during the positive excursion), transform-
ing the latent electrostatic
image
into a
visible image.
Excess toner particles
are
attracted back to the cylinder from the drum
due to the charges on the drum surface and
the developing
bias (during the negative
excursion).
The DC bias affects copy density and
fogging:
As the
DC bias becomes
less
negative (approaches
OV), the density and
degree of fogging both increase.
7. Step 5 Transfer
'..
.,
J ;:;j
'....
. . .::
-*
v
COPY
L-Per
,_I..
_
T-
Transfer
corona
unit
COPYAlGHT
0
1900 CAMIN
INC.
CANON HP-1015/1215S
AN.0
OCT.
1980 PRINTEO
IN JAPAN llMPAlMf
AU JAPON]
2-3
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