Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2000-10-20
2002-01-15
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C430S120400
Reexamination Certificate
active
06339687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing method for developing an electrostatic latent image on an image support into a visible image, in an image-formation apparatus of an electronic photographing system.
2. Description of the Prior Art
(Prior Art 1)
A photosensitive unit as an image support on which an electrostatic latent image is formed can be expressed by a model consisting of a resistance component &Dgr;Rv and a capacity component &Dgr;Cp in a thickness direction respectively and a resistance component &Dgr;Rs in a surface direction as shown by an equivalent circuit in FIG.
2
. Therefore, if the resistance component &Dgr;Rs is sufficiently high, an electric charge accumulated in the capacity component &Dgr;Cp, that is, an electrostatic latent image, can be held during a period between finish of an exposure and finish of a development. However, when the resistance component &Dgr;Rs has become lower due to an adhesion of a stain or the like, the electric charge accumulated in the capacity component &Dgr;Cp is lost. As a result, it becomes impossible to obtain a desired resolution.
This state is shown in FIG.
3
.
FIG. 3
shows one example of a diffusion along a lapse of time of an electrostatic latent image that has been formed with an edge located at a position of x=0. It can be understood from
FIG. 3
that there occurs a leakage of an electric charge in the surface direction and the electrostatic latent image changes along with a lapse of time.
As a publication that introduces a prior art of investigation carried out into the resolution of a photosensitive unit from the viewpoint of a change in the electrostatic latent image due to a diffusion of an electric charge along with the lapse of time, there is “A study in the resolution characteristics of a photosensitive unit based on analysis of an electrostatic latent image”, Electronic Photograph Academy Magazine, Volume 30, No. 4, 1991, pp. 432-438. This publication reports on a result of a simulation carried out for the deterioration in the resolution of an electrostatic latent image along with a lapse of time based on an electrostatic capacity of a photosensitive unit and a resistance of a charged member. A potential change on a photosensitive unit is expressed by the following.
(&dgr;
V/&dgr;t
)=(1/(
Rs·Cp
))·(&dgr;
V
2
/&dgr;x
2
)−
V
/(
Rv·d·Cp
) (1)
A general solution of this expression is given as follows.
V=Vs
(
x, t
)·exp(−
t
/(
Rv·d·Cp
)) (2)
Further, an edge width W of a one-dimensional electrostatic latent image is given as follows.
W=
3.55(
t
/(
Cp·Rs
))
½
(3)
(Prior Art 2)
Various results of investigations have been announced that model a development area and express development characteristics by a numerical equation in an attempt to optimize the development characteristics that are determined based on a combination of a potential of a photosensitive unit, a thickness of a toner layer, a toner charge volume, a resistance of a developing roller, a development bias, etc. As a representative prior art of this trial, there is “A contact type component nonmagnetic development system (1)”, Electronic Photograph Academy Magazine, Volume 31, No. 4, 1992, pp. 531-541. According to this method, the electric field of the development area is obtained from a Poisson equation, and a development equation and a simulation result are reported. As a development equation in the case of using a semiconductive developing roller, the following expression is shown.
m
si
=(1/
A
)·(
m
c
+k·m
o
/A
)·(
qp/q
)·
R
1
)/(1+(1/(
A·k
)·
R
1
)) (4)
where
A=dp/∈p+dt/∈t
(5)
m
c
=(1/
A
)·(−(
V
o
−V
b
)/
q+
(
k·m
o
/2)·(
dt/∈t
)) (6)
The prior art 1 is based on a simulation that assumes that the development potential is at an intermediate point between the potential of an unexposed portion (VH in the case of an inversion development) and the potential of an exposed portion (VL in the case of an inversion development). The prior art 1 has no disclosure about a correlation with an optional latent image potential. Therefore, there is a problem in that it is not possible to understand a resolution at an optional latent image potential based on an actual using state, such as a development potential at which a highest resolution can be obtained leaving the characteristics of a photosensitive unit as it is, or a development potential that can guarantee the initial performance despite adhesion of stain.
According to the prior art 2, a development current that flows based on the charge qp generated by a frictional charging of a development nip portion is treated with too much emphasis. Further, there is a problem in that no consideration has been taken into the resistance at the photosensitive unit side.
SUMMARY OF THE INVENTION
In the light of the above problems, it is, therefore, an object of the present invention to provide a developing method capable of realizing a satisfactory image quality in high resolution, based on a setting of a development condition that takes into account the charge diffusion of a latent image due to a surface resistance of an image support.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a developing method for developing an electrostatic latent image formed on an image support, by an inversion development is characterized in setting the following relationship:
abs
(
V
1
)<
abs
(
Vth
)
where abs (X) represents an absolute value of X,
when
V
1
=(0.348
Wr
2
−1.161
Wr+
1.0163)
Vo,
and
Wr=
(1/3.63)·(
Rs·Cp/t
)
½
·W,
where
Cp (F/m
2
) represents an electrostatic capacity of an image support, Rs (&OHgr;) represents a surface resistance, t (sec) represents a moving time from an electrostatic latent image formation area to a development completion area, Vo (V) represents a potential of a non-image portion of an electrostatic latent image in an image area at the time of forming the electrostatic latent image, Vth (V) represents a surface voltage of the image support when a developing member starts a development at a saturated latent image potential in a solid image, W (m) represents a desired minimum image width, and V
1
(V) represents a marginal latent image potential in the minimum image width.
In accordance with the second aspect of the present invention, the developing method having the above first aspect is further characterized in setting the following relationship:
abs
(
V
1
′)<
abs
(
Vth
)
when
V
1
′=
V
1
·exp(−
t
/(
Rv·Cp
))
where
Rv (&OHgr;·m
2
) represents a resistance of the image support in a thickness direction.
In accordance with the third aspect of the present invention, the developing method having the above first aspect is further characterized in that, when a toner layer is formed on the surface of the developing member that is applied with a bias voltage Vb (V), and when this developing member is brought into a sliding contact with the image support by a development nip of a predetermined width, values of the following parameters are adjusted to satisfy the following relationship:
(−
V
1
+
n·Vt+Vb
)/&rgr;
d>
0
where
&rgr;d represents a charge density of the toner layer immediately after the image support passes through the development nip, Vt (V) represents a potential of the toner layer on the developing member, Rr (&OHgr;·m
2
) represents a resistance of the developing member, and n represents a ratio (vb/vp) of a rotational speed vb (m/sec) of the developing member to a rotational speed vp (m/sec) of the image support.
In accordance with the fourth aspect of the present invention, the developing method having the above third aspect is further characterized in that values of the following parameters are adjusted to satisfy the following relationship:
(−(
V
1
+
dV
)+
n·Vt&pl
Pendegrass Joan
Sharp Kabushiki Kaisha
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