Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-08-25
2001-04-10
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C399S252000
Reexamination Certificate
active
06214510
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an external addition toner, an apparatus for forming an image, and a process for forming an image.
BACKGROUND OF THE INVENTION
In the electrophotographic process, an electrostatic latent image formed on a photoreceptor is developed with a developer containing a toner, and a toner image obtained is transferred to a recording medium such as paper, followed by fixing with a heat roll, so as to obtain an image on the recording medium. A full color image can be obtained by overlapping toner images of four colors, i.e., cyan, yellow, magenta and black, utilizing the electrophotographic process.
In recent years, an image forming apparatus of an intermediate transfer type has been subjected to practical use, in which toner images of cyan, yellow, magenta and black formed on a photoreceptor are primarily transferred on an intermediate transfer material, and a multi-color image formed on the intermediate transfer material is secondarily transferred to a recording media, and thus speeding up of a color duplicator using the electrophotographic process is realized. In the image forming apparatus of an intermediate transfer type, however, because the number of times of transfer is large, and the multi-color toner image is transferred to a recording medium at a time, it is liable to cause a problem of image defects, such as transfer unevenness and drop-off. Furthermore, it is liable to cause another problem of lack of general purpose property in that even though a good image can be formed on a recording medium having a smooth surface, such as coated paper, image defects occur when an image is formed on a recording medium having a rough surface, such as recycled paper.
JP-A-5-34979, JP-A-5-88409, JP-A-5-197193 and JP-A-5-341573 disclose that the transfer property of the toner is improved by providing fine holes or protrusions on the surface of toner particles having a substantially spherical shape.
In the toner using the toner particles having fine holes and protrusions on the surface thereof, however, there is a problem in that the effect of an external additive coated on the toner particles cannot be sufficiently exhibited.
The external additive fundamentally exhibits such a function in that it intervenes between an image holding member and the toner particles to prevent the toner particles from adhering on the image holding member, whereby the transfer property of the toner is improved. However, in the case where unevenness is present on the surface of the toner particles, when the toner is stirred and subjected to mechanical stress in a developing device, the external additive fails at the protruded surface of the toner particles, whereas the external additive is accumulated at the reentrant surface. Thus, the toner particles are in contact with the image holding member without the external additive intervening at the protruded surface, so as to prevent the external additive from exhibiting the function thereof, whereby image defects, such as transfer unevenness and drop off, occur.
With the progress of decrease in particles size of the toner for realizing a high quality image, it is becoming difficult to completely transfer the toner particles without remaining on the image holding member. The conventional apparatus for forming an image is designed without sufficiently considering the difference in transfer property depending on the size of the toner particles.
SUMMARY OF THE INVENTION
Therefore, the invention has been made to provide an external addition toner excellent in transfer property. The invention has also been made to provide an apparatus for forming an image and a process for forming an image excellent in general purpose property that can provide an image of high quality without forming image defects, such as transfer unevenness and drop off, due to transfer failure of the toner, irrespective to the type of the recording medium.
The invention relates to an external addition toner containing toner particles having a shape coefficient of 134 or less coated with an external additive, the external additive containing fine particles having a volume average particle diameter (d) of from 0.05 to 0.5 &mgr;m, a coating ratio x of the external additive to a surface area of the toner particles being in a range of from 15 to 100%, and the coating ratio x (%), a volume average particle diameter of the toner particles D (&mgr;m) and a volume average particle diameter of the external additive having the maximum average particle diameter d (&mgr;m) satisfying the following equation (1):
100
≤
(
D
+
2
d
)
2
π
(
D
2
)
2
+
n
π
(
d
2
)
2
·
π
4
·
100
≤
165
(
1
)
wherein
n
=
π
D
x
100
d
The invention also relates to an external addition toner containing toner particles having a surface property index of 5.1 or less coated with an external additive, the external additive containing fine particles having a volume average particle diameter (d) of from 0.05 to 0.5 &mgr;m, a coating ratio x of the external additive to a surface area of the toner particles being in a range of from 15 to 100%, and the coating ratio x (%), a volume average particle diameter of the toner particles D (&mgr;m) and a volume average particle diameter of the external additive d (&mgr;m) satisfying the following equation (2):
1.005
≤
4
π
(
D
2
)
2
+
n
·
4
π
(
d
2
)
2
4
·
π
(
D
2
)
2
≤
1.524
(
2
)
wherein
n
=
π
·
D
·
x
100
d
In a preferred embodiment of the invention, the external addition toner contains toner particles having a shape coefficient of 134 or less and a surface property index of 5.1 or less coated with an external additive having a volume average particle diameter (d) of from 0.05 to 0.5 &mgr;m, a coating ratio x of the external additive to a surface area of the toner particles being in a range of from 15 to 100%, and the coating ratio x (%), a volume average particle diameter of the toner particles D (&mgr;m) and a volume average particle diameter of the external additive d (&mgr;m) satisfying the equations (1) and (2).
The invention also relates to an apparatus for forming an image containing a developing device charged with a developer containing a toner that is charged to a charge amount q (&mgr;C/g) corresponding to a volume average particle diameter D (&mgr;m) of the toner particles satisfying the following equation (3), an image holding member retaining a developed image formed by the developer containing a toner charged to a charge amount q (&mgr;C/g), and a transfer device transferring the developed image on the image holding member to a transfer medium:
q≧
929.5/
D
2
(3)
While a one-component developer containing the external addition toner of the invention may be used as the developer for the apparatus for forming an image, it is preferred to use a two-component developer containing the external addition toner of the invention and a carrier. The apparatus for forming an image can be used for forming a multi-color image, in which a multi-color developed image formed by accumulating plural toner images of plural colors on the image holding member.
The apparatus for forming an image of the invention may contain a photoreceptor forming an electrostatic latent image corresponding to image information, a developing device for developing the electrostatic latent image with a developer containing a toner that is charged to a charge amount q (&mgr;C/g) corresponding to a volume average particle diameter D (&mgr;m) of the toner particles satisfying the following equation (3), an intermediate transfer material, in which a developed image formed by the developer containing a toner charged to a charge amount q (&mgr;C/g) is transferred thereon, and the transferred image is temporarily retained, and a transfer device transferring the image on the intermediate transfer material to a recording medium by pressing the intermediate transfer material with a tran
Ishikawa Takatoshi
Koide Hiroyuki
Kojima Noriaki
Masuko Kazuhisa
Fuji 'Xerox Co., Ltd.
Martin Roland
Oliff & Berridg,e PLC
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