Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-02-02
2002-10-22
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Transfer
C156S137000, C264S408000, C399S302000, C425S140000
Reexamination Certificate
active
06470165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing a transfer member such as an intermediate transfer belt or a transfer belt, used in electrophotographic apparatus in which a toner image formed on a first image-bearing member is electrostatically transferred to a second image-bearing member to obtain an image, and also relates to a transfer member produced by such a production process, and an image-forming apparatus having the transfer member.
2. Related Background Art
Conventionally proposed are full-color image-forming apparatus having a plurality of recording apparatus in which the surface of at least one photosensitive member is exposed to laser beams light-modulated in accordance with recording information to form electrostatic latent images, which are then developed with toners to form toner images, and the toner images formed by development are transferred to a transfer sheet, where the toner images, having different colors, are superimposingly transferred while the transfer sheet is sequentially transported to the respective recording apparatus by means of a transfer member to form full-color toner images, or the different color toner images are superimposingly transferred onto an intermediate transfer member and the resultant full-color toner images are one time transferred to the transfer sheet.
Full-color image-forming apparatuses making use of a transfer belt as the transfer member are so designed that different color toner images are formed on a plurality of photosensitive members and the toner images formed on the respective photosensitive members are transferred, under registration, to one sheet of transfer material being transported in sequential contact with the photosensitive members, to obtain a full-color image.
The full-color image-forming apparatus making use of a transfer belt have an advantage that, a full-color image is formed through one process because the different color toner images are superimposingly transferred while the transfer material is sequentially transported to the respective recording apparatus, so that the images can be formed in a short time.
Meanwhile, compared with image-forming apparatus in which toner images are transferred from a first image bearing member to a second image bearing member transfer material fastened or attracted onto a transfer drum (e.g., Japanese Patent Application Laid-open No. 63-301960), the full-color image-forming apparatus (electrophotographic apparatus) making use of an intermediate transfer member have an advantage that a variety of second image bearing member transfer materials can be selected without regard to their width and length, including thin paper (40 g/m
2
paper) and up to thick paper (200 g/m
2
paper) such as envelopes, post cards and labels. This is because any processing or control (e.g., the transfer material is held with a gripper, attracted, and made to have a curvature) is not required for the second image bearing member transfer material.
Because of such advantages, full-color copying machines and full-color printers making use of transfer members such as transfer belts or intermediate transfer belts have already begun to be available in the market.
The full-color copying machines and printers making use of such transfer members have various advantages as stated above. On the other hand, they also have some subjects for improvement.
One of them is production cost. These transfer members are required to have various properties such as electrical characteristics, dimensional stability, surface properties and mechanical properties, which must each be controlled strictly. Moreover, any portion which causes a great change in properties even in part makes them unusable. In particular, transfer belts are required to have a surface area larger than image-forming regions and are necessarily large in size. Also, in the case of the apparatus having construction where a plurality of photosensitive members are used, the transfer belt or intermediate transfer member is made to have a large peripheral length because a space for disposing the photosensitive members must be ensured, making it necessary to use a much larger belt member. Accordingly, resistance uniformity, dimensional precision of peripheral length, thickness and so forth and mechanical strength which are required in transfer members are demanded to be on much higher levels. Because of these points, the production of belt members involves a high cost.
Also, with regard to durability, some are not necessarily satisfactory. As a result, this may raise the main-body price and running cost of copying machines and printers and also it may take more labor and time for their maintenance.
Meanwhile, in order to form good full-color images, especially in the case of intermediate transfer belts, some other problems must also be solved which may occur because a plurality of different colors are superimposed on the transfer member.
One of them is a misregistration which may occur between individual colors. In fine lines and character images, even a slight color misregistration tends to be conspicuous to provide a possibility of damaging image quality. When the intermediate transfer belt is used, it must be put over a plurality of shafts, where the tension applied to every part of the intermediate transfer belt is not necessarily uniform when driven and rotated. Hence, the intermediate transfer belt tends to undergo local elongation and, concurrently therewith, may cause a delicately uneven rotation. As the result, a delicate color misregistration may appear when colors are superimposed, as so presumed.
Another problem is occurrence of spots around images. In full-color image formation, superimposing different color toners enlarges the quantity of toner per unit area than in the case of monochromatic images. Especially in characters and fine lines, toners are present in a large quantity on narrow lines. Moreover, individual color toners have electric charges with the same polarity, and hence they are electrostatically repulsive to each other. Thus, it can be said that the toners are on the intermediate transfer belt in an unstable state.
Meanwhile, because of a difference in arcs drawn by the outer surface of the intermediate transfer belt and its inner back surface with belt thickness between them, the difference being produced when the belt passes each shaft about which it is put, the intermediate transfer belt elongates in the peripheral direction at its surface and in the vicinity thereof. Hence, the toner images standing unstable and weak to external disturbance as stated above are disordered because of such surface elongation of the intermediate transfer belt when it passes the shafts, so that the spots around line images come to occur, as so presumed.
Still another problem is transfer performance of halftone toner images. Faulty images tend to occur when the intermediate transfer belt has any uneven electrical resistance or uneven wall thickness.
In addition to these, the intermediate transfer belt, which always undergo tension and repeated bending and stretching stress, is required to have a material stiffness high enough not to cause breakage or cracking of the intermediate transfer belt even in its long-term service.
However, in order to satisfy all of these low cost, high durability and high image quality, technical difficulties are involved. Accordingly, studies are being made on transfer members including intermediate transfer belts, having much superior performances.
In the case of transfer belts, though not the case that images are directly transferred onto the belt, they are also required to have properties comparable to those of intermediate transfer belts in respect of cost reduction, electrical characteristics, surface properties, durability and so forth.
At present, various processes for producing belts and tubes used for transfer members are already known in the art. For example, Japanese Patent Application Laid-open No. 3-89357 and No. 5-345368 disclose a process for produc
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