Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-09-14
2003-06-10
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06577836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-forming apparatus and a fixing unit used in electrophotographic copying machines, printers, etc.
2. Description of the Related Art
Heretofore, an image-forming apparatus is widely used in electrophotographic copying machine and printers, in which an electrostatic latent image is formed on a photoreceptor, it is developed with a dry toner, and the resulting toner image is electrostatically transferred onto a recording medium and fixed thereon. In the image-forming apparatus, however, recording paper, a type of recording medium could not be kept in tight contact with the photoreceptor owing to its surface roughness, and often forms some uneven gaps between them, whereby the transfer field around the recording paper will be disordered and the toner grains thereon will produce Coulomb repulsion. One problem with it is that the image formed on the recording paper is thereby often disordered to cause image deletion or noise.
To solve the problem, some advanced types of image-forming apparatus have been proposed. In one type of the apparatus for image formation, plural toner images of different colors are electrostatically transferred onto an intermediate transfer member to form a multi-layer toner image thereon, then the multi-color multi-layer toner image is fed on the member, and the thus-fused multi-layer toner image is transferred and simultaneously fixed on a recording medium in a predetermined simultaneous transfer and fixing zone to thereby form a color image on the recording medium, and in another type, the toner image formed on an endless photoreceptor is fused thereon, and is then transferred and fixed on a recording medium.
In these types of image-forming apparatus, the toner image is non-electrostatically transferred onto the recording medium and will be therefore free from the problem of image quality deterioration noted above. In these, however, the part of the intermediate transfer member and that of the photoreceptor which are directly or indirectly kept in contact with a photoreceptor cleaner and a development unit must be cooled to a temperature not higher than melting temperature of the toner, in order that the toner in the photoreceptor cleaner and in the development unit is prevented from melting therein. To meet the requirement, another type of image-forming apparatus is disclosed, for example, in Japanese Patent Laid-Open Nos. 12988/1984 and 95568/1987, in which a forcedly or spontaneously cooling member is disposed in the traveling route of the intermediate transfer member and the photoreceptor along which the intermediate transfer medium with a toner image formed thereon passes through the simultaneous transfer and fixing zone to reach the photoreceptor cleaner and the development unit, or the traveling route of the two is prolonged to ensure a prolonged cooling time for the two.
However, in the image-forming apparatus of that type, the intermediate transfer medium and the photo or cooled to a temperature not higher than the melting temperature of the toner must be re-heated up to the temperature necessary for transfer and fixation in every image formation cycle, and this carries another problem as requiring large power.
To solve the problem Japanese Patent Publication No. 36341/1983 discloses a modified image-forming apparatus in which the heat capacity of the intermediate transfer member is limited to at most 3.1×10
13
cal/cm
2
·° C. to thereby reduce the heat energy necessary for heating the member in every image formation cycle. To reduce the heat capacity of the belt in the apparatus, in general, the belt is thinned. However, the belt could not be thinned so much so as not to reduce its strength. The belt not so much thinned to have a practicable thickness could not attain a significant result. A metallic belt may be employed to reduce its thickness without lowering its strength, but this is electroconductive and is therefore problematic in that it could not apply to an ordinary electrostatic transfer system widely used for forming a toner image on an intermediate transfer member. Another method may be employed that includes applying pressure to an intermediate transfer member for forming a toner image thereon. However, this is problematic in that, when high pressure is applied to the member, the apparatus shall be complicated and large-sized.
On the other hand, Japanese Patent Laid-Open No. 298777/1992 discloses an image-forming apparatus in which the belt running toward the image-forming zone and the belt running toward the simultaneous transfer and fixing zone are contacted with each other for heat exchange therebetween in the region between the image-forming site of a belt-like image bearing member and the simultaneous transfer and fixing zone, to thereby reduce the energy loss in that region of the apparatus.
In the image-forming apparatus of that type, however, the two belts are directly contacted with each other and therefore require an additional urging member to press the belts against each other. In this, the urging member is provided above the surface of the upper belt, and it will scratch the surface of the belt to worsen the quality of the images formed. In addition, since the belts are contacted with each other, they must be elastic and require a space in which they are warped before and after they are contacted with each other. This is problematic as the apparatus must be large-sized. Moreover, since the belts are insulators, they are electrostatically charged when contacted with each other. Therefore, their adhesion to each other will be good to enhance beat exchange between them, but the belts could not well run and will often cause image registration failure and other image defects. This is still another problem with the image-forming apparatus.
To solve these problems, a heat conductor may be disposed between a part of the belt running toward the image-forming zone and a part thereof running toward the simultaneous transfer and fixing zone for attaining heat exchange between the two parts of the belt. However, merely disposing such a heat conductor between the parts of the belt would average the temperatures of those parts, but could not attain sufficient heat energy exchange between them, and the heat exchange efficiency of this system will be low.
To solve this problem, Japanese Patent Laid-Open No. 213977/1998 discloses an image-forming apparatus in which a heat circulator is disposed between a part of the belt running toward the image-forming zone and a part thereof running toward the simultaneous transfer and fixing zone. The heat circulator is directly contacted with the two parts of the belt to attain heat exchange between them, and this prevents the tempts of the two parts of the belt from being averaged, and therefore realizes high heat exchange efficiency. Precisely, the heat circulator includes plural metal members aligned perpendicularly to the traveling direction of the belt both on the side of the belt that runs toward the image-forming zone and on the other side thereof that runs toward the simultaneous transfer and fixing zone, and heat pipes that connect these plural metal members. In his, the neighboring plural metal members are bonded to each other via a heat-insulating spacer therebetween.
However, the heat circulator carries some problems mentioned below. Specifically, in the heat circulator, the neighboring plural metal members are connected with each other via a heat-insulating spacer therebetween. Therefore, in order that the heat circulator has satisfactory mechanical strength, the side surface area of each metal member must be enough to connect the neighboring metal members to each other, and too small metal members could not satisfy the requirement. As a result, it is inevitable to enlarge the heat circulator, and cutting the cost for producing the heat circulator will be difficult. In addition, in order that the heat circulator attains efficient heat exchange between the two parts of the running belt whil
Matsuda Tsukasa
Yamada Tetsuo
Yamashita Takayuki
Brase Sandra
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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