Abstract:
Examination of the side edges of available polyimide show that they are cut or formed on the angle that forms tapered extensions. 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 from which cracks can originate.

Description:
TECHNICAL FIELD  
       [0001]     This invention related to imaging with electrophotographic toner using a transfer belt of polyimide, which is particularly useful for three-color imaging.  
       BACKGROUND OF THE INVENTION  
       [0002]     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.  
         [0003]     In view of the otherwise desirable factors in using polyimide belts as toner transfer belts, a solution to the early-failure problem is needed.  
       DISCLOSURE OF THE INVENTION  
       [0004]     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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The details of this invention will be described in connection with the accompanying drawings, in which  
         [0006]      FIG. 1  illustrates the electrophotographic printer (often termed a laser printer) in which the belt would be in accordance with this invention;  
         [0007]      FIG. 2  is a cross section side view of a state of the art belt of polyimide as would be used unless modified in accordance with this invention; and  
         [0008]      FIG. 3  is a cross section side view of a polyimide belt in accordance with this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     A description of the illustrative imaging device is found in commonly-owned U.S. Pat. No. 6,549,225 B2, and  FIG. 1  is identical to  FIG. 1  of that patent. In  FIG. 1  there is shown a multicolor laser printer  10  in which the method of the present invention may be used. Printer  10  includes laser printheads  12 ,  14 ,  16 ,  18 , a black toner cartridge  20 , a magenta toner cartridge  22 , a cyan toner cartridge  24 , a yellow toner cartridge  26 , photoconductive drums  28 ,  30 ,  32 ,  34 , and intermediate transfer member belt  36  and a controller  37 . The controller is a combination of Application Specific Integrated Circuits (ASIC&#39;s), microprocessors, and firmware suited to the tasks described.  
         [0010]     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  FIG. 1 , across a respective on of photoconductive drums  28 ,  30 ,  32  and  34 . Each of photoconductive drums  28 ,  30 ,  32  and  34  is negatively charged to approximately −1000 volts and is subsequently discharged to a level of approximately −300 volts in the areas of its peripheral surface that are impinged by a respective one of laser beams  38 ,  40 ,  42  and  44 . During each scan of a laser beam across a photoconductive drum, each of photoconductive drums  28 ,  30 ,  32  and  34  is continuously rotated, clockwise in the embodiment shown, in a process direction indicated by direction arrow  54 . The scanning of laser beams  38 ,  40 ,  42  and  44  across the peripheral surfaces of the photoconductive drums is cyclically repeated, thereby discharging the areas of the peripheral surface on which the laser beams impinge.  
         [0011]     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 .  
         [0012]     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 .  
         [0013]     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.  
         [0014]     A second aspect in accordance with this invention is that the side edges not have tapered extensions.  FIG. 2  illustrates a polyimide belt  60  currently available commercially. It has opposed lateral surfaces  62  and  64  terminated in a side edge  66 . That side edge has a tapered extension  68 . To prevent early cracking of the belt  60  resulting from damaged thin areas, such tapered extensions are avoided.  
         [0015]      FIG. 3  illustrates a belt  70  in accordance with this invention. Belt  70  is made of all polyimide or is made essentially of polyimide. Belt  70  has a lateral surface  72  that is the image-receiving side and a lateral bottom surface  74 . Although generally not required, bottom surface  74  may be formed of materials for support purposes, which are different from polyimide.  
         [0016]     Surfaces  72  and  74  are sufficiently wide to receive the toner image. Belt  70  also has side edges  76   a  and  76   b  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.  
         [0017]     Available polyimide belts in accordance with  FIG. 2  survive a flex test to about 49 to 66 thousand cycles. State of the art belts not of polyimide survive the same test to 1,000,000 cycles. Belts in accordance with this invention, as illustrated in  FIG. 3  also survive the same test to about 1,000,000 cycles.  
         [0018]     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.  
         [0019]     Variations for the foregoing may be developed to avoid tapered extensions from the polyimide.