Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
2002-01-14
2003-11-11
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S176000
Reexamination Certificate
active
06647229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer or the like which has a charging member for charging an image bearing body such as an electrophotographic sensitive body, an electrostatic recording dielectric or the like to predetermined polarity and potential.
More particularly, the present invention relates to an image forming apparatus which adopts, as a charging means for the image bearing body, a contact charging means using charging accelerating particles.
2. Related Art
Conventionally, in an image forming apparatus such as a copying machine, a printer or the like, a latent image formed on an image bearing body such as an electrophotographic sensitive body, an electrostatic recording dielectric or the like is visualized by using a dry developing agent (developer) being granular materials. In recent years, to cope with downsizing, simplification, energy saving and environmental measures of the apparatus, it pays attention to an image forming apparatus which disuses a cleaning container and a waste toner container and can achieve ozoneless operation that generation of ozone due to electrical discharge is decreased and a cleanerless operation.
1. Ozoneless Charging Means
As a means for performing an ozoneless charging process to the image bearing body, a contact charging means using charging accelerating particles is disclosed in Japanese Patent Application Laid-Open Nos. 10-307454 to 10-307459, U.S. Pat. Nos. 6,134,407, 6,081,681 and 6,128,456, and the like.
In this contact charging means, the charging accelerating particles are interposed in a charging nip (charging area, charging part) which is the contact portion of at least both the image bearing body (hereinafter called a photosensitive drum) functioning as the body to be charged and a contact charging member (hereinafter called a charging roller) being generally a conductive/elastic roller caused to be in contact with the photosensitive drum, whereby a direct injection charging mechanism is more predominant than a discharge charging mechanism.
The charging accelerating particles are the conductive particles which aim to assist the charging. For example, various conductive particles, each having the particle diameter 0.1 mm to 5 mm and the volume resistance 1×10
12
&OHgr;·cm or less, more desirably 1×10
10
&OHgr;·cm or less, such as metal oxide particles (e.g., conductive zinc oxide), other conductive inorganic particles, compounds with organic materials, and the like can be used.
Since the charging accelerating particles exist, the charging roller can be in contact with the photosensitive drum in the charging nip with a speed difference and also be in contact with the photosensitive drum closely through the charging accelerating particles. That is, the charging accelerating particles existing in the charging nip compactly scrape the surface of the photosensitive drum, whereby a charge is directly injected into the photosensitive drum, then, in the charging of the photosensitive drum by the charging roller, the direct injection charging mechanism can be made predominant by the existence of the charging accelerating particles.
Therefore, it is possible to achieve with simple structure low-apply-voltage and ozoneless direct injection charging that high charging efficiency which could not be obtained in conventional roller charging and the like can be obtained, and the surface of the photosensitive drum provided with a charge injection layer can be charged, without using any discharge, to a potential approximately equal to a charging bias voltage applied to the charging roller. Such the direct injection charging is effective for the charging means which performs the direct injection charging process uniformly and ozonelessly to the image bearing body such as the electrophotographic sensitive body, the electrostatic recording dielectric or the like so that the image bearing body has predetermined polarity and potential, in an electrophotographic image forming apparatus and an electrostatic recording image forming apparatus.
The charging roller has a foamed body so that the charging accelerating particles may effectively exist in the charging nip. That is, the charging accelerating particles are maintained within the foams on the surface of the charging roller, whereby an opportunity that the charging roller comes into contact with the photosensitive drum is increased.
Such a charging system not using the discharge can prevent discharge products from being created, whereby abrasion of the photosensitive drum due to the discharge products can be prevented, and a lifetime of the photosensitive drum can be thus prolonged. Besides, as compared with a general charging system using AC voltage, the above charging system is effective for energy saving and cost reduction because the photosensitive drum can be charged by low DC voltage.
2. Cleanerless
The image forming apparatus of cleanerless system has the structure that the cleaning container and the waste toner container for eliminating from the surface of the photosensitive drum a developing agent (hereinafter called toner) slightly remaining on this surface after a developing-agent image was transferred from the photosensitive drum to a recording medium are disused, the transfer residual toner on the photosensitive drum is eliminated therefrom by “developing simultaneous cleaning” with a developing means, and the eliminated toner is then retrieved to the developing means and reused.
The developing simultaneous cleaning is the method that the toner slightly remaining on the photosensitive drum after the image was transferred is retrieved by a fog elimination bias (fog elimination potential difference Vback being the potential difference between the DC voltage applied to the developing means and the surface potential on the photosensitive drum) when developing is performed in next and following steps.
According to such a method, since the transfer residual toner is collected (retrieved) by the developing means and used for the developing in the next and following steps, the waste toner can be suppressed, and thus trouble for maintenance can be decreased. Besides, since the cleanerless system is adopted, an advantage in respect of space is great, whereby the image forming apparatus can be greatly downsized.
If the charging means of the photosensitive drum is the contact charging means, it is possible to cause the contact charging member being in contact with the photosensitive drum to once retrieve the transfer residual toner for charging polarity adjusting and then emit the retrieved toner again to the photosensitive drum so that the emitted toner is retrieved by the developing means.
Further, if the charging means of the photosensitive drum performs the direct injection charging process using the charging accelerating particles, it is possible to uniformly charge the photosensitive drum in the image forming apparatus of cleanerless type.
Concretely, the charging accelerating particles are mixed with the developing agent of the developing means. Then, at the developing portion, the charging accelerating particles are supplied from the developing means to the surface of the photosensitive drum together with the toner, and at the transferring portion, only the toner is mainly transferred to the recording medium, and the charging accelerating particles are supplied to the charging nip being the contact portion between the charging roller and the photosensitive drum. Thus, it is possible to uniformly charge the photosensitive drum by the injection charging in the image forming apparatus of cleanerless type.
As above, the structure to supply the charging accelerating particles from the developing means to the charging nip being the contact portion between the charging roller and the photosensitive drum is disclosed in Japanese Patent Application Laid-Open No. 10-307455 and the like.
Incidentally, if the image forming operation is performed by using the image forming ap
Haraguchi Manami
Sakaizawa Katsuhiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ngo Hoang
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