This invention related to imaging with electrophotographic toner using a transfer belt of polyimide, which is particularly useful for three-color imaging.
Polyimide as the intermediate transfer layer material is known to provide excellent results in terms of image quality. Other materials commonly used as.transfer belts, such as polyurethanes, have long physical endurance. In contrast commercially available polyimide belts crack and become useless much earlier.
In view of the otherwise desirable factors in using polyimide belts as toner transfer belts, a solution to the early-failure problem is needed.
Examination of the side edges of available polyimide belts shows that they are cut or formed on the angle, which forms tapered extensions. Since polyimide is very notch-sensitive, damage to the edge of the belt is more likely to occur at the weakest, thinnest regions. This invention minimizes such tapered extensions. In the embodiment the side edges are made to be generally perpendicular to the top and bottom surfaces. The perpendicular sides eliminate thin extensions which can be damaged in handling. Flex tests have shown polyimide belts with such sides to have the same physical life as other, conventional belts.
The details of this invention will be described in connection with the accompanying drawings, in which
A description of the illustrative imaging device is found in commonly-owned U.S. Pat. No. 6,549,225 B2, and
Each of laser printheads 12, 14, 16, and 18 projects a respective laser beam 38, 40, 42, 44 off of a respective one of polygon mirrors 46, 48, 50 and 52. As each of polygon mirrors 46, 48, 50 and 52 rotates, it scans a respective one of reflected laser beams 38, 40, 42, and 44 in a scan direction, perpendicular to the plane of
The toner in each of toner cartridge 20, 22, 24 and 26 is negatively charge and is transported upon the surface of a developer roll biased to approximately −600 volts. Thus, when the toner from cartridge 20, 22, 24 and 26 is brought into contact with a respective one of photoconductive drums 28, 30, 32 and 34, the toner is attracted to and adheres to the portions of the peripheral surfaces of the drums that have been discharged to −300 volts by the laser beams. As belts 36 rotates in the direction indicated by arrow 56, the toner from each of drums 28, 30, 32 and 34 is transferred to the outside surface of belt 36. As a print medium, such as paper, travels along path 58, the toner is transferred to the surface of print medium in nip 62.
It is belts corresponding to belt 36 that are structured in accordance with this invention. One structural aspect in accordance with this invention is that the material of the belt be polyimide or essentially polyimide. The reason for that aspect is that polyimide exhibits outstanding characteristics in receiving and transferring image that are of excellent fidelity to the images received from the photoconductors, such as drums 28, 30, 32 and 34.
By essentially polyimide or essentially of polyimide, it is meant that the polyimide can be diluted somewhat with other materials so long as it retains the outstanding characteristics of the entirely-polyimide belt in receiving and transferring images. Also, of course, a backing layer for support would not interfere with the characteristics of a belt, which is polyimide or essentially polyimide on the image-receiving side of the belt.
A second aspect in accordance with this invention is that the side edges not have tapered extensions.
Surfaces 72 and 74 are sufficiently wide to receive the toner image. Belt 70 also has side edges 76a and 76b on opposed sides that constitute the thin dimension of the belt 70. In accordance with this invention side edges are substantially perpendicular to the lateral surfaces 72 and 74. This configuration is readily obtained by cutting commercial belts at the perpendicular angle with a blade having a flat face facing the belt.
Available polyimide belts in accordance with
The occasional tapered extension in a belt would necessarily not expose the belt to failure to the same extent as the belt having extensive tapered regions. Accordingly, belts that are substantially in accordance with the avoidance of tapered extensions are consistent with this invention.
Variations for the foregoing may be developed to avoid tapered extensions from the polyimide.