Electrophotography – Image formation – Development
Reexamination Certificate
2000-03-27
2001-09-11
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S092000, C399S237000, C399S359000
Reexamination Certificate
active
06289192
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-089339, filed Mar. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic type color image forming apparatus and, more particularly, to a color image forming apparatus using a liquid developer with a fine particle coloring material mixed into an insulating solvent.
Of the electrophotographic type image forming apparatus, a so-called wet type image forming apparatus using a liquid developer has advantages not realized by a dry type image forming apparatus and, in recent years, their merits have been reevaluated. The wet type image forming apparatus has major advantages over the dry type image forming apparatus in terms of (a) being capable of realizing a high image quality with the use of a very fine particle toner of the order of a submicron size, (b) capable of obtaining an adequate image density with less amount of toner and, in addition to being thus economical, also capable of realizing a texture just equal to that of a printing (for example, an offset printing), (c) capable of fixing the toner to a recording sheet at a relatively low temperature and thus achieving an energy saving, etc.
In the conventional wet type electrophotographic technique using a liquid toner as a developer, however, there arise essential problems and, for this reason, the dry type electrophotographic technique has been unrivaled in its market. As its one problem, it has to use a liquid developer containing a high resistant or insulating petroleum solvent as a carrier solvent so as to develop an electrostatic latent image. In an image forming process, this solvent is quickly consumed and it is, therefore, necessary to effect a frequent exchange of the solvent tanks, so that the maintenance becomes poor.
For this reason a squeegee roller is provided so as to, after a developing step, scrape any excessive solvent from a photosensitive drum surface. It is thus necessary to collect any not-requisite solvent, even if being small in its amount, from the drum surface for a recycling purpose. Since, at the same time, there arise an evolution of an odor resulting from the evaporation of the solvent as well as an allergy action of it on a human body, etc. It is, therefore, desirable to collect the solvent into the apparatus to a practically possible extent and prevent it from being evaporated to an outside.
In the image forming apparatus using a liquid developer, an indirect transfer method has usually been employed according to which, in order to retain a better image, an image on a photosensitive drum is once transferred to a transfer roller, such as a transfer drum, instead of effecting an image transfer in a way to set a recording sheet in direct contact with the photosensitive drum, and an image on the transfer roller is transferred to a recording sheet by contacting the image with the recording sheet under an application of a pressure to the recording sheet. In this case, the image on the photosensitive drum is placed under an electric field or a pressure such that the image can be readily moved onto the transfer drum.
In such a process, the solvent is evaporated on a heated transfer drum and, when the evaporated solvent (solvent vapor) is exhausted to an outside of the apparatus, the odor and allergy problems may occur as set out above. It is, therefore, necessary to prevent the diffusion of such solvent vapor produced on the transfer drum.
In the image forming apparatus using a liquid developer, it is required that, while maintaining the conditions of forming a good quality image, consideration be paid to ensuring an effective consumption of the developer and environmental health. It is, therefore, necessary to prevent any leakage of the solvent vapor from the apparatus and to collect the solvent vapor, through liquefaction, for a recycling purpose. The greatest task of the wet type image forming apparatus using the liquid developer is as to how the developer solvent should be recovered for recycling and how the leakage of the solvent to an outside be suppressed to a minimal extent.
Against these requests a method may be considered by which the solvent vapor is reduced by passing air in the apparatus, for example, through a filter. In this case, the solvent vapor collection method is by introducing a circulation air in the apparatus into a filter using an adsorbent such as an activated carbon and, after adsorbing the solvent vapor onto the adsorbent, returning it again into the apparatus or exhausting it to an outside, etc. Since, in this method, no entire consideration is paid to the recycling of the solvent vapor, much more solvent is consumed and, since the life of the filter is usually limited, it is determined depending upon an amount of adsorbing solvent. Therefore, the greater the amount of solvent vapor, the quicker the filter's performance begins to be lowered. This necessitates the frequent exchanges of filters. Further it may be considered that a scattered solvent vapor in the apparatus is deposited here and there and gives a serious damage to the apparatus.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an image forming apparatus which can suppress the diffusion of solvent in a liquid developer to a minimum extent, effectively collect the solvent and obtain a stable developing characteristic.
According to one aspect of the present invention, there is provided an image forming apparatus, comprising: a latent image carrier; an image exposure unit configured to form a latent image on the latent image carrier; a development unit configured to develop the latent image on the latent image carrier into a visible image by a liquid developer having a coloring material mixed in solvent; a transfer body configured to transfer the visible image from the latent image carrier onto a recording medium; and a first partition wall covering part of the latent image carrier or part of the transfer body, and having an inner surface facing the part of the latent image carrier or the part of the transfer body.
The apparatus may further comprise a solvent collection unit configured to collect part of the solvent liquefying on the inner surface of the first partition wall. In this case, the solvent collection unit may comprise a roller supported by the first partition wall and a blade which scrapes off part of the solvent from the roller. The solvent collection unit may comprise a roller on which part of the solvent liquefies and a blade which scrapes off the part of the solvent from the roller, and wherein the first partition wall covers the roller.
The apparatus may further comprise a cooling unit configured to cool the first partition wall. In this case, the cooling unit may comprise a fan. The apparatus may further comprise a solvent collection unit configured to collect part of the solvent liquefying on the inner surface of the first partition wall. In this case, the solvent collection unit may comprise a wiper which wipes off part of the solvent from the inner surface of the first partition wall. The solvent collection unit may comprise a belt running in a predetermined direction on which part of the solvent liquefies, and a blade which scrapes off the part of the solvent from the belt. The solvent collection unit may comprise a tank which mixes a coloring material into the solvent collected by the solvent collection unit to produce a liquid developer, and a circulating path which supplies the liquid developer produced in the tank to the development unit.
The first partition wall may cover the part of the transfer body and the transfer body has a heater.
The apparatus may further comprise: a cleaner configured to clean the image carrier by removing residual coloring material from the latent image carrier; and a second partition wall covering part of the cleaner and having an inner wall surface fac
Hiroki Masashi
Nukada Hideki
Takahara Kenichi
Chen Sophia S.
Kabushuki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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