Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2003-04-30
2004-12-07
Tran, Hoan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S055000, C399S284000, C399S285000
Reexamination Certificate
active
06829446
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a development device used for an electrophotography type image forming device, such as a photocopier, a printer, and a facsimile device; and a charging method used in the development device; and an image forming device having the development device.
BACKGROUND OF THE INVENTION
An electrophotography type image forming device (electrophotography device), such as a photocopier, a printer, or a facsimile device generally includes a LSU (Laser beam Scanner Unit), a photoconductive drum, and a development device. Here, the LSU irradiates a rotating photoconductive drum with a laser-beam so as to form an electrostatic latent image on a surface of the photoconductive drum. Then, the development device further supplies toner to the photoconductive drum so as to develop (visualize) the electrostatic latent image.
Further, the development device includes a development roller provided to be adjacent and opposite to the photoconductive drum. The development device uses, for example, a feed roller (toner feeding roller) for supplying toner on a surface of the development roller, and rotates the development roller, so as to sequentially supply the toner to all of the electrostatic latent images on the photoconductive drum.
Incidentally, in such a development device, the electrostatic latent image on the photoconductive drum absorbs the toner due to electrostatic force so as to carry out development. Therefore, it is required to charge the toner by some methods.
For example, in case of a development device using nonmagnetic toner of one-component system for development of an electrostatic latent image, the toner is sequentially supplied to the surface of a development roller by a feed roller in the circumferential direction, while the toner is held and carried by rotation of the development roller. Also, the thickness of the toner is controlled by a thickness control blade, which is provided downstream of the feed roller in the rotation direction of the development roller, while the toner is charged due to friction with the thickness control blade (friction charging).
The toner is held in this state until carried to an opposite portion to a photoconductor. The portion is provided further downstream in the rotation direction of the development roller. Then, the toner is supplied to an electrostatic latent image on the surface of the photoconductor due to electrostatic force. As a result, the electrostatic latent image is developed (visualized) as a toner image.
Note that, the developer used in the development device may be a one-component type magnetic toner containing magnetic powder, or a two-component type developer in which the toner is mixed with a carrier.
In this manner, the toner is charged by friction with the blade while its thickness is controlled by the blade applied to the development roller with a great pressure (F).
Considering this arrangement in terms of the energy budget, driving energy (Ek) supplied to the development roller is converted to toner thickness control energy (Es) and toner charging energy (Et). Also, the driving energy is partly consumed as heat loss energy (E
1
).
Namely, the following equation (1) is satisfied as the basic equation of the energy budget in such a friction charging method.
Ek=Es+Et+E
1
(1)
The heat loss energy (E
1
) generated by such a friction charging brings about such as destruction of toner, fusion of softened toner into the surface of the blade. This further causes degradation of friction charging property between the toner and the surface of the blade.
Further, in recent years, as one of energy saving technologies, melioration of toner has been in progress. For example, the softening point of toner is decreased for reduction of fixing energy, also the number of pigments of toner is increased for an improvement of coloring property.
However, as described, the foregoing friction charging method performing control of the thickness of the toner and the charging of the toner at the same time is carried out with a great thermal load, and therefore the foregoing improved toner cannot be used for the method. In this regard, a charging method with a small thermal load has been required in order to cope with the improved toner.
Further, the relation between the heat loss energy (E
1
) and the applied pressure (F) satisfies the following equation (2) where C
1
is a proportional constant.
heat loss energy (
E
1
)=
C
1×pressure (
F
) (2)
According to this equation (2), it is effective to decrease the applied pressure for reducing the thermal load with respect to the toner.
Further, the driving energy (Ek) of the development roller satisfies the following equation (3) where C
2
is a proportional constant.
driving energy (
Ek
)=
C
2
×pressure (
F
) (3)
According to the foregoing equations (1) through (3), the applied pressure (F) satisfies the following equations (4).
C
2
×
F=Es+Et+C
1
×
F
(
C
2
−
C
1)×
F=Es+Et
(4)
The equations revealed that, in order to realize pressure reduction, it is effective to use the method in which the toner charging energy (Et) does not rely on the applied pressure (F).
Then, the blade of friction charging method is here set to separately performs the toner thickness control function and the toner charging function. More specifically, the applied pressure (F) is mainly used as the toner thickness control energy (Es), while the toner charging energy (Et) relies on light energy instead of the pressure (F).
In such a case, the thermal load can be reduced and therefore, it is possible to prevent destruction of the toner, i.e., degradation of the toner, or fusion of the toner into the blade. Thus, reliability of the development operation can be increased. Further, this charging method may also be used with the improved toner which is for realizing reduction of fixing energy or improvement of coloring ability.
Further, as one example of the charging method using light energy, Japanese Laid-Open Patent Application Tokukaihei 07-281473/1995 (published on Oct. 27, 1995) discloses a toner charging method which controls the toner charging quantity by irradiating the toner with light in a developer tank after including a photochromic compound in the toner.
However, in such a charging method using light energy, assuming that all of the members in the development device are turned on, the toner is not thoroughly charged at the time that the light irradiation has just been started, i.e., the toner carriage has just been started.
In this case, the toner, which is still in an uncharged state, is carried to a latent image holding body by a carriage section. This causes adherence of the uncharged toner to the electrostatic latent image or scatter of the toner inside of the device. As a result, some blank spots appear on the image, or the image becomes unfocused, thus decreasing printing quality.
Further, in the configuration of the Japanese Laid-Open Patent Application Tokukaihei 07-281473/1995, which uses light energy, the irradiation of the toner is carried out in the developer tank, thus failing to ensure stability of the toner charging.
Further, even when the toner on the toner carriage section (developer carriage section) is irradiated outside of the developer tank, i.e., when electrons are applied to the toner by using photoelectric effect of a photoelectron emitting section, the toner may not be sufficiently charged at the time that the toner carriage has just been started, and therefore the uncharged toner adheres to the surface of the photoelectron emitting section, thereby decreasing toner charging property of the surface of the photoelectron emitting section.
SUMMARY OF THE INVENTION
The present invention is made in view of the foregoing conventional problems, and an object is to provide a development device with a small thermal load with respect to the developer, and capable of stably charging the developer even immediately after
Gotoh Toshimitsu
Kamimura Taisuke
Toizumi Kiyoshi
Conlin, Esq. David G.
Edwards & Angell LLP
Penny, Jr. John J.
Sharp Kabushiki Kaisha
Tran Hoan
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