Abstract:
Multiple layer fuser belts having a woven fabric layer and a high conformability, low surface energy elastic layer. The fabric layer is formed from high modulus, high temperature fibers that are woven together at acute angles to the circumference of the belt fibers. The fabric layer forms a substrate with preferential stretching along the circumference of the fuser belt. The elastic layer is bonded to the fabric layer and is made from a highly conformable, low durometer material having a low surface tension. When the fuser belt is partially wrapped around a driven roller so as to form a nip with a pressure roller the fuser belt stretches in the direction of belt motion. As the fuser belt passes through the nip the fuser belt contracts, releasing surface tension and thus reduces sticking between the fuser belt and fused toner.

Description:
FIELD OF THE INVENTION 
     This invention relates to fuser belts. More particularly it relates to user belts having strain release provided by a fabric layer woven to provide a directionally preferred stretch. 
     BACKGROUND OF THE INVENTION 
     Electrophotographic marking is a well known and commonly used method of copying or printing original documents. Electrophotographic marking is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges, creating an electrostatic latent image of the desired document on the photoreceptor&#39;s surface. Toner particles are then deposited onto the latent image to form a toner image. That toner image is then transferred from the photoreceptor onto a receiving substrate such as a sheet of paper. The transferred toner image is then fused to the receiving substrate. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image. 
     Of the various electrophotographic printing processes mentioned above, this invention relates most generally to fusing the toner with the receiving substrate. While fusing has been performed in several ways, the most common method is to pass a toner-bearing substrate through a heated pressure nip. The combination of heat and pressure fuses the toner with the substrate. The heated pressure nip is often formed using a heated fuser roller, a pressure roller, and a conformable fuser belt that overlaps the fuser roller and that is disposed between the fuser roller and the pressure roller. When the toner-bearing receiving substrate passes between the fuser belt and the pressure roller, with the toner contacting the fuser belt, the toner is fused with the receiving substrate. 
     While heated pressure nips are successful, they have problems. One common problem is that the fused toner and the receiving substrate tend to stick to the fuser belt. A prior art approach to addressing the sticking problem is to use a small diameter fuser roller and/or a sharp fuser belt turn. The resulting sharp turn tends to separate the fused toner-substrate from the fusing system. Another approach is to coat the surface of the fuser belt with a release agent, thereby reducing the fuser belt&#39;s surface tension and reducing sticking. Yet another method of addressing the sticking problem is to use an elastic belt. Unfortunately, these methods are insufficient in some applications. Therefore, a new way of addressing the sticking problem would be beneficial. 
     SUMMARY OF THE INVENTION 
     The principles of the present invention provide for fuser belts with improved release characteristics. A fuser belt according to the principles of the present invention has at least two layers, a substrate layer comprised of a woven fabric that provides preferential stretching along the circumference of the fuser belt and of an elastic layer. This woven fabric can be comprised of high temperature resistant material that can be made electrically, thermally and magnetically conductive. A beneficial material goes by the trade name Nomex. The substrate layer is beneficially comprised of high modulus, high temperature fibers that are woven together at acute angles to the circumference of the belt. The elastic layer is beneficially comprised of a highly conformable, low durometer material having a low surface tension, for example, a silicone. The elastic layer material should survive the high fusing temperature. Suitable elastic layer materials include silicone, fluoropolymer, or silicone-flouropolymer hybrids. 
     The principles of the present invention further provide for printing machines with fusers belts that have improved release characteristics. A printing machine according to the principles of the present invention includes a photoreceptor having a photoconductive surface, a charging station for charging that photoconductive surface to a predetermined potential, at least one exposure station for exposing the photoconductive surface to produce an electrostatic latent image on the photoconductive surface, at least one developing station for depositing a toner layer on the latent image, and a fuser that fuses the toner layer onto a receiving substrate. The fuser includes a fuser belt that is comprised of at least two layers, a substrate layer comprised of a woven fabric that provides preferential stretching along the circumference of the fuser belt and of an elastic contact layer. The substrate layer is beneficially comprised of high modulus, high temperature fibers that are woven together at acute angles to the circumference of the belt. The elastic contact layer is beneficially comprised of a highly conformable, low durometer material having a low surface tension, for example, a silicone. The elastic layer material should survive the high fusing temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: 
     FIG. 1 schematically illustrates an electrophotographic printing machine that incorporates the principles of the present invention; 
     FIG. 2 illustrates the fuser used in the printing machine of FIG. 1; 
     FIG. 3 illustrates a cutaway view of a fuser belt used in the fuser of FIG. 2; 
     FIG. 4 illustrates a top-down view of the fuser belt substrate; 
     FIG. 5 illustrates a cutaway view of an alternative fuser belt having three layers; and 
     FIG. 6 illustrates a simplified schematic diagram of a printer having a transfix belt. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an electrophotographic printing machine  8  that reproduces an original document. Although the principles of the present invention are well suited for use in such reproduction machines, they are also well suited for use in other marking devices. Therefore it should be understood that the present invention is not limited to the particular embodiment illustrated in FIG. 1 or to the particular application shown therein. 
     The electrophotographic printer  8  is a color electrophotographic, multipass, Recharge-Expose-and-Develop (REaD), Image-on-Image (IOI) printer. That machine includes an Active Matrix (AMAT) photoreceptor belt  10  that travels in the direction  12 . Belt travel is brought about by mounting the photoreceptor belt about a driven roller  14  and about tension rollers  16  and  18 , and then driving the driven roller  14  with a motor  20 . 
     As the photoreceptor belt travels each part of it passes through each of the subsequently described process stations. For convenience, a single section of the photoreceptor belt, referred to as the image area, is identified. The image area is that part of the photoreceptor belt which is to receive the various actions and toner layers that produce the final composite color image. While the photoreceptor belt may have numerous image areas, since each image area is processed in the same way a description of the processing of one image area suffices to explain the operation of the printing machine  8 . 
     The imaging process begins with the image area passing a “precharge” erase lamp  21  that illuminates the image area so as to cause any residual charge which might exist on the image area to be discharged. Such erase lamps are common in high quality systems and their use for initial erasure is well known. 
     As the photoreceptor belt continues its travel the image area passes a charging station comprised of a DC corotron  22 . The DC corotron charges the image area in preparation for exposure to create a latent image for black toner. For example, the DC corotron might charge the image area to a substantially uniform potential of about −500 volts. It should be understood that the actual charge placed on the photoreceptor will depend upon many variables, such as the black toner mass that is to be developed and the settings of the black development station (see below). 
     After passing the charging station the image area advances to an exposure station  24 A. At the exposure station the charged image area is exposed to a modulated laser beam  26 A from a raster output scanner  27 A that raster scans the image area such that an electrostatic latent representation of a black image is produced. 
     After passing the exposure station  24 A the exposed image area with the black latent image passes a black development station  32  that advances black toner  34  onto the image area so as to develop a black toner image. Biasing is such as to effect discharged area development (DAD) of the lower (less negative) of the two voltage levels on the image area. The charged black toner  34  adheres to the exposed areas of the image area, thereby causing the voltage of the illuminated parts of the image area to be about −200 volts. The non-illuminated parts of the image area remain at about −500 volts. 
     After passing the black development station  32  the image area advances to a recharging station  36  comprised of a DC corotron  38  and an AC scorotron  40 . The recharging station  36  recharges the image area and its black toner layer using a technique known as split recharging. Briefly, the DC corotron  38  overcharges the image area to a voltage level greater than that desired when the image area is recharged, while the AC scorotron  40  reduces that voltage level to that which is desired. Split recharging serves to substantially eliminate voltage differences between toned areas and untoned areas and to reduce the level of residual charge remaining on the previously toned areas. 
     The recharged image area with its black toner layer then advances to an exposure station  24 B. There, a laser beam  26 B from a raster output scanner  27 B exposes the image area to produce an electrostatic latent representation of a yellow image. The now re-exposed image area then advances to a yellow development station  46  that deposits yellow toner  48  onto the image area. After passing the yellow development station the image area advances to a recharging station  50  where a DC scorotron  52  and an AC scorotron  54  split recharge the image area. 
     An exposure station  24 C then exposes the recharged image area. A modulated laser beam  26 C from a raster output scanner  27 C then exposes the image area to produce an electrostatic latent representation of a magenta image. After passing the magenta exposure station the now re-exposed image area advances to a magenta development station  56  that deposits magenta toner  58  onto the image area. After passing the magenta development station the image area advances another recharging station  60  where a DC corotron  62  and an AC scorotron  64  split recharge the image area. 
     The recharged image area with its toner layers then advances to an exposure station  24 D. There, a laser beam  26 D from a raster output scanner  27 D exposes the image area to produce an electrostatic latent representation of a cyan image. After passing the exposure station  24 D the re-exposed image area advances past a cyan development station  66  that deposits cyan toner  68  onto the image area. At this time four colors of toner are on the image area, resulting in a composite color image. However, the composite color toner image is comprised of individual toner particles that have charge potentials that vary widely. Directly transferring such a composite toner image onto a substrate would result in a degraded final image. Therefore it is beneficial to prepare the composite color toner image for transfer. 
     To prepare for transfer a pretransfer erase lamp  72  discharges the image area to produce a relatively low charge level on the image area. The image area then passes a pretransfer DC scorotron  80  that performs a pre-transfer charging function. The image area continues to advance in the direction  12  past the driven roller  14 . A substrate  82  is then placed over the image area using a sheet feeder (which is not shown). As the image area and substrate continue their travel they pass a transfer corotron  84  that applies positive ions onto the back of the substrate  82 . Those ions attract the negatively charged toner particles onto the substrate. As the substrate continues its travel is passes a detack corotron  86 . That corotron neutralizes some of the charge on the substrate to assist separation of the substrate from the photoreceptor  10 . As the lip of the substrate  82  moves around the tension roller  18  the lip separates from the photoreceptor. 
     The substrate is then directed into a fuser  90  where a heated fuser roller, a fuser belt, and a pressure roller create a nip through which the substrate  82  passes. The combination of pressure and heat at the nip causes the composite color toner image to fuse into the substrate. After fusing, a chute, not shown, guides the substrate to a catch tray, also not shown, for removal by an operator. As the principles of the present invention operation are closely related to the fuser  90 , that fuser and its fuser belt are described in more detail below. 
     After the substrate  82  separates from the photoreceptor belt  10  the image area continues its travel and passes a preclean erase lamp  98 . That lamp neutralizes most of the charge remaining on the photoreceptor belt. After passing the preclean erase lamp the residual toner and/or debris on the photoreceptor is removed at a cleaning station  99 . The image area then passes once again to the precharge erase lamp  21  and the start of another printing cycle. 
     In addition to the elements described above, the printer  8  also includes a system controller  101  (shown in four places in FIG. 1) that controls the overall operation of the printer and that applies video information to the exposure stations. 
     FIG. 2 illustrates the fuser  90  in more detail. The fuser includes a slightly stretchable, double layer fuser belt  112  that is supported along its circumference by a driven roller  114  and by an idler roller  116 . The driven roller  114  is rotated by a motor  118  such that the fuser belt travels in the direction  113 . As the fuser belt  112  passes around the driven roller  114  it forms a fusing nip  120  with a pressure roller  122 . The substrate  82  with its toner  126  advances in the direction  128  through the fusing nip such that toner contacts an outer surface  130  of the belt  112 . The fusing nip  120  beneficially comprises a single nip, in that, the section of the belt  112  that contacts the driven roller  114  is coextensive with the opposite side of the belt that contacts the pressure roller  122 . A single nip insures a single nip velocity through the entire nip. As shown in FIG. 2 the driven roller  114  is heated by an internal quartz lamp  144 . The driven roller is beneficially comprised of a highly thermal conductive material such as aluminum. Therefore, as the substrate  82  passes through the nip the toner is heated and pressed into the substrate, causing the toner to fuse with the substrate. 
     As previously mentioned the fuser belt  112  is a double layer belt. FIG. 3 illustrates a cut-away view of the fuser belt  112 . As shown, the fuser belt includes an elastic layer  140  and a fabric layer  142 . The elastic layer is preferably comprised of a silicone rubber, flouropolymer, or other material of the type that is conventionally utilized in fuser belts. As such, the elastic layer has a low surface tension such that the toner  126  (see FIG. 2) does not readily stick to the outer surface  130 . Furthermore, the conformability of the elastic layer is such that under tension the elastic layer  140  will deform (stretch) slightly. The thickness of the elastic layer  140  is in the order of 0.006 to 0.125 inch. 
     FIG. 4 shows a schematic, top-down view of the fabric layer  142 . The fabric layer  142  is comprised of high modulus, high temperature fibers fibers  146  and  148  that are woven at acute angles with the direction  113  of motion of the fuser belt. The fibers, fiber density, and weave angle are selected such that the fabric layer is slightly stretchable in the direction  113 . A stretch of 1-10% in the direction  113  for a given fuser belt tension is usually adequate. Turning back to FIG. 3, the elastic layer  140  is bonded to the substrate layer  142  using a strong, heat-resistant glue. If the elastic layer is formed from a liquid elastomer, and if that liquid elastomer adequately soaks into the fabric matrix, glue may not be required. In any event embedding the elastomer that comprised the elastic layer into the fabric layer improves the adhesion of the composite belt. This enables the belt to be subjected to sharp directional changes without delaminating. In some applications the fabric layer can be made thermally, electrically or magnetically conductive to facilitate toner release or transfer. 
     The combination of the elastic layer and the fabric layer significantly changes the nip dynamics so as to improve toner release. In operation, as the fuser belt  112  advances around the idler roller  116  the fuser belt stretches slightly as the driven roller  114  pulls on the fuser belt. This stretch is a result of the stretchability of both the elastic layer  140  and the fabric layer  142 . The result is a strain energy on the outer surface  130  of the fuser belt. After the fuser belt passes through the nip  120  the strained fabric layer  142  relaxes because the pull on the fuser belt is reduced. This shrinks the fuser belt, which decreases the adherence between the fused toner and the outer surface  130 . 
     While FIG. 3 illustrates a two layer belt, the principles of the present invention can be used with belts having more layers. For example, FIG. 5 illustrates a cut-away view of a three layer fuser belt  158 . As shown, the fuser belt includes not only the elastic layer  140  and the rigid substrate layer  142 , but also a lower elastic layer  160 . Like the elastic layer  140 , the lower elastic layer  160  is preferably comprised of an elastic material that will maintain its strength and life with repeated cycling at high temperatures. However, since the lower elastic layer  160  makes contact with a driven roller the lower elastic layer  160  should present a relatively high friction surface. 
     While the foregoing illustrates the present invention with one type of fuser belt, the principles of the present invention can find use with other types of fusing belts, such as transfix belts. With transfix belts toner on a photoreceptor is first transferred onto the transfix belt, a substrate is placed over the transferred toner, and then the transfix belt fuses the toner with the substrate. Turn now to FIG. 6 for a simplified schematic diagram of a printer  200  that uses a transfix belt  202 . A photoreceptor  206  is held in position by a driven roller  208 , idler rollers  210  and  212 , and transfer roller  214 . The photoreceptor is rotated in the direction  213  by the driven roller. The transfix belt  202  is held adjacent the transfer roller by idle roller  216  and  218 , and a heated roller  220 . Opposite the heated roller is a pressure roller  222 . The transfix belt is driven by the motion of the photoreceptor in the direction  226 . The toner image on the photoreceptor is transferred to the transfix belt when the toner image contacts the transfix belt (electrostatic forces produced by power supplies that are not shown may be used for transfer). The transferred image is subsequently transferred to a substrate  230  that is feed into the nip between the heated roller  220  and the pressure roller  222 . As the substrate passes through the nip the toner is simultaneously transferred and fused to the substrate. 
     While not shown in the figures for clarity, it is common practice to apply a release fluid to the outer surface  130  of the fuser belt  112 . This release fluid is usually applied by a release management system. Release fluids further reduce sticking. 
     It is to be understood that while the figures and the above description illustrate the present invention, they are exemplary only. Others who are skilled in the applicable arts will recognize numerous modifications and adaptations of the illustrated embodiment that will remain within the principles of the present invention. For example, it is possible to arrange the fuser components such that the fuser belt is pre-heated by the driven roller before the fuser belt enters the fuser nip. In addition, the belt materials can be selected to improve the operational characteristics of the belt. For example, in some applications the belt materials might be optimized to improve toner release or to assist in driving the belt. Therefore, the present invention is to be limited only by the appended claims.