Patent Publication Number: US-6668152-B1

Title: Textured fuser roller and method for texturing toner

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to fusing toner to print media. More particularly, the disclosure relates to a fuser roller having a textured surface and a method for texturing toner to mask toner gloss differential. 
     BACKGROUND 
     Electrophotographic imaging devices such as printers and photocopiers typically are provided with fusing systems that thermally fuse a toner image onto a print media, such as sheets of paper. Such fusing systems normally comprise a heated fuser roller and a pressure roller that presses against the fuser roller to form a nip in which the fusing occurs. The fuser and pressure rollers typically comprise hollow metal tubes that are surrounded with outer lavers of material. 
     High-end electrophotographic imaging devices normally include fusing systems in which one or more of the rollers are surrounded with an outer layer composed of a heat resistant, highly compliant material. such as silicon rubber. In that such fusing systems are relatively expensive, lower-end electrophotographic imaging devices typically include fusing systems that use less expensive materials. For example, such devices may comprise fusing systems in which one or both of the rollers are surrounded with a relatively inelastic polymeric material, such as a polyester material (e.g., mylar). 
     Although such materials are resistant to heat, they are less effective in terms of facilitating fusing of toner to print media. As is known in the art, most print media are non-uniform across their outer surfaces. For example, sheets of paper normally include depressions and high points that result from the fibers contained within the paper and the process used to form the sheets. When such print media pass through the nip of a fusing system, the toner particles within the depressions receive less pressure and, therefore, may not fully fuse to the media. Incomplete fusing results in relatively glossy and non-glossy (i.e., matte) portions of toner on the print media. In other words, a gloss differential is formed across the toner printed on the media. 
     Substantial gloss differential is undesirable from an aesthetics perspective. In particular, when light reflects off of the toner and into the eyes of the observer, the non-uniformity of the toner can be obvious and detract from the print or photo copy job. This is particularly the case where an image has been printed or copied in that more toner covers the media. 
     Although gloss differential can be reduced by using more compliant materials for the roller outer layers, as noted above the materials may be too expensive for inclusion in lower-end devices. More even fusing could, at least theoretically speaking, be obtained if greater pressure were used to squeeze the print media as the media pass through the nip. Practically speaking, however, there are limitations as to how firmly the rollers can be pressed together without causing undue flexion of the rollers, which ultimately could result in even less uniform pressure being applied to the media. 
     From the foregoing, it can be appreciated that it would be desirable to have a fusing system with which gloss differential can be masked so as to improve the aesthetics of print or photocopy jobs output from imaging devices having relatively noncompliant fusing system rollers. 
     SUMMARY 
     Accordingly, one embodiment of the invention is directed to a fuser roller having a textured outer surface. The textured outer surface can be used to produce a textured appearance on toner as it is fused to print media. Another embodiment of the invention is directed to a method that includes texturing the toner as it is fused to the print media. Texturing the toner helps mask gloss differential. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following drawings are provided to support the present disclosure. The components in the drawings are not necessarily to scale. 
     FIG. 1 is a schematic side view of an electrophotographic imaging device incorporating a fusing system that helps mask glass differential. 
     FIG. 2 is a detailed view of the fusing system shown in FIG.  1 . 
     FIG. 3 is partial perspective view of a fuser roller of the fusing system shown in FIG.  2 . 
     FIG. 4 is a partial, cross-sectional end view of the fuser roller shown in FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     Referring now in more detail to the drawings, in which like numerals indicate corresponding parts throughout the several views, FIG. 1 illustrates a schematic side view of an electrophotographic imaging device  100  that incorporates a fusing system  102 . By way of example, the device  100  comprises a laser printer. It is to be understood, however, that the device  100  can, alternatively, comprise any other imaging device that uses a fusing system including, for instance, a photocopier, a facsimile machine or a multifunction peripheral (MFP) device. 
     As indicated in FIG. 1, the device  100  includes a charge roller  104  that is used to charge the surface of a photoconductor drum  106  to a predetermined level. A laser diode (not shown) is provided within a laser scanner  108  that emits a laser beam  110  that is modulated as it is swept across the surface of the photoconductor drum  106  to selectively discharge the surface of the photoconductor drum. In the orientation shown in FIG. 1, the photoconductor drum  106  rotates in the counterclockwise direction. A developing roller  112  is used to develop a latent electrostatic image residing on the surface of photoconductor drum  106  after the surface of the photoconductor drum has been selectively discharged. Toner  114  is stored in a toner reservoir  116  of an electrophotographic print cartridge  118 . The developing roller  112  includes an internal magnet (not shown) that magnetically attracts the toner  114  from the print cartridge  118  to the surface of the developing roller. As the developing roller  112  rotates (clockwise in FIG.  1 ), the toner  114  is attracted to the surface of the developing roller  112  and is then transferred across the gap between the surface of the photoconductor drum  106  and the surface of the developing roller to develop the latent electrostatic image. 
     Print media  120 , for instance sheets of paper, are loaded from an input tray  122  by a pickup roller  124  into a conveyance path of the device  100 . Each print medium  120  is individually drawn through the device  100  along the conveyance path by drive rollers  126  such that the leading edge of each print medium is synchronized with the rotation of the region on the surface of the photoconductor drum  106  that comprises the latent electrostatic image. As the photoconductor drum  106  rotates, the toner adhered to the discharged areas of the drum contacts the print medium  120 , which has been charged by a transfer roller  128 , such that the medium attracts the toner particles away from the surface of the photoconductor drum and onto the surface of the medium. Typically, the transfer of toner particles from the surface of the photoconductor drum  106  to the surface of the print medium  120  is not completely efficient. Therefore, some toner particles remain on the surface of the photoconductor drum. As the photoconductor drum  106  continues to rotate, the toner particles that remain adhered to the drum surface are removed by a cleaning blade  130  and are deposited in a toner waste hopper  132 . 
     As the print medium  120  moves along the conveyance path past the photoconductor drum  106 , a conveyer  134  delivers the print medium to the fusing system  102 . The print medium  120  passes between a fuser roller  136  and a pressure roller  138  of the fusing system  102  that are described in greater detail below. As the pressure roller  138  rotates, the fuser roller  136  is rotated and the print medium  120  is pulled between the rollers. Heat and pressure applied to the print medium  120  as it passes between the rollers  136  and  138  fuses the toner to the surface of the print medium. Finally, output rollers  140  convey the print medium  120  from fusing system  102  and deliver it to an output tray  142 . 
     As identified in FIG. 1, the device  100  also includes a formatter  144  and a controller  146 . The formatter  144  receives print data, such as a display list, vector graphics, or raster print data, from a print driver operating in conjunction with an application program of a separate host computing device  148 . The formatter  144  converts the print data into a stream of binary print data and sends the data to the controller  146 . In addition, the formatter  144  and the controller  146  exchange data necessary for controlling the electrophotographic imaging process. In particular, the controller  146  supplies the stream of binary print data to the laser scanner  108 . The binary print data stream sent to the laser diode within the laser scanner  108  modulate the laser diode to create the latent electrostatic image on the photoconductor drum  106 . 
     In addition to providing the binary print data stream to the laser scanner  108 , the controller  146  controls a high voltage power supply (not shown) that supplies voltages and currents to the components used in the device  100  including the charge roller  104 , the developing roller  112 , and the transfer roller  128 . The controller  146  further controls a drive motor (not shown) that drives the printer gear train (not shown) as well as the various clutches and feed rollers (not shown) necessary to move print media  120  through the conveyance path of the device  100 . 
     A power control circuit  150  controls the application of power to the fusing system  102 . While the device  100  is waiting to begin processing a print or photo copy job, the temperature of the fusing system  102  is kept at a standby temperature corresponding to a standby mode. In the standby mode, power is supplied at a reduced level to the fusing system  102  by the power control circuit  150  to reduce power consumption, lower the temperature, and reduce the system degradation. 
     When processing of a fusing job begins, the controller  146 , sufficiently ahead of the arrival of a print medium  120  at the fusing system  102 , increases the power supplied by the power control circuit  150  to the fusing system to bring its temperature up to the fusing temperature. After completion of the fusing job, the controller  146  sets the power control circuit  150  to reduce the power supplied to the fusing system to a level corresponding to the standby mode. The cycling of the power supplied to the fusing system  102  is ongoing during operation of the device  100  as fusing jobs are received and processed and while the device is idle. 
     FIG. 2 illustrates a detailed end view of the fusing system  102  shown in FIG.  1 . As indicated in FIG. 2, the fusing system  102  comprises the fuser roller  136  and the pressure roller  138  that together form a nip  200  therebetween. In addition, the fusing system  102  can include a temperature sensor  202  that is associated with, for example, the fuser roller  136 . 
     The fuser roller  136  typically is formed as a hollow tube  204 . By way of example, the tube  204  is composed of a metal such as aluminum or steel and has a diameter of approximately 45 millimeters (mm). By further way of example, the tube  204  has a thickness of approximately 2.5 mm. The fuser roller  136  includes an outer layer  206  that has a thickness of, for instance, approximately 4 mm. As is described in greater detail below, an outer surface  210  of the outer layer  206  is provided with a textured pattern that transfers a similar (mirror image) pattern to toner fused to the print media as the media pass through the fusing system  102 . As explained, the provision of such a pattern helps mask toner gloss differential that may be present across the media. Although the textured pattern may be provided with any surface material, it is expected that the greatest benefit is achieved by providing the textured pattern on an outer layer  206  made of relatively inelastic polymeric material such as is used with lower end printing devices. To prevent toner from adhering to the outer layer  206 , a coating (not visible in FIG. 2) of nonstick material, such as polytetrafluoroethylene (PTFE), can be applied to the outer surface  210  of the outer layer. This nonstick coating can, for instance, have a thickness of approximately 1.5 to 2 mils. In that it is so thin, the coating does not occlude the texture of the outer layer  206 . 
     Provided within the fuser roller  136  is an internal heating element  208  that, by way of example, comprises a halogen lamp or a nichrome heating element. It is to be noted that, although an internal heating element  208  is shown and described, the fuser roller  136  could, alternatively, be provided with an external heat source, or without any heat source at all, if desired. 
     The pressure roller  138  can comprise, for instance, a hollow metal tube  212  that is provided with an outer layer  214  of polymeric material. As with the fuser roller  136 , the pressure roller  138  may be provided with a coating (not visible in FIG. 2) of nonstick material, such as PTFE. Optionally provided within the pressure roller  138  is an internal heating element  216  that, by way of example, comprises a halogen lamp or a nichrome heating element. Alternatively, the pressure roller  138  can be configured without its own heat source. Provision of a heat source may, however, prevent the accumulation of toner on the pressure roller  138 . 
     The temperature sensor  202  typically comprises a thermistor that is placed in close proximity to or in contact with the fuser roller  136  at a position adjacent the entry of the nip  200 . Although this placement is preferred, it will be appreciated that other placement is also feasible. In an alternative arrangement, the sensor  202  can comprise a non-contact thermopile (not shown). Although non-contact thermopiles are preferable from the standpoint of reliability, they are more expensive and therefore increase the cost of the device  100 . 
     The fuser roller  136  is illustrated in greater detail in FIGS. 3 and 4. As indicated in FIG. 3, the outer surface  210  of the outer layer  206  of the fuser roller  136  comprises a textured pattern  300  (although only a portion of the pattern is indicated in FIG. 3, the entire outer surface  210  is preferably textured) that comprises a plurality of repeated elements  302 . The nature of the elements  302  can be varied depending upon the desired result. Preferably, however, the elements  302  are small, for instance approximately 0.01-10 square millimeters in area, such that a high frequency pattern results. As will be appreciated by persons having ordinary skill in the art patterns with smaller areas may mask the gloss differential better by producing a matte appearance. By way of example, as shown in FIG. 3, the textured pattern  300  can comprise repeating geometric shapes such as honeycombs. Other geometric shapes can be used including rectangles, triangles, diamonds, circles, etc. 
     In an alternative embodiment, the textured pattern  300  comprise an asymmetric, non-geometric pattern such as a paisley pattern. Asymmetric patterns may be preferable in that their seemingly non-repetitive nature may be better for masking gloss differential. Another example of an asymmetric pattern is a pattern of simulated brush strokes. Such a pattern may be particularly preferable for printing images such as photographs, drawings, or paintings. 
     As indicated in FIG. 4, the textured pattern  300  can be created by forming a plurality of protrusions  400  on the outer surface  210  of the outer layer  206  of the fusing roller  136 . Alternatively, however, the pattern  300  can be created by forming a plurality of impressions on the outer surface  210 . In either case, however, the pattern  300  can be created through a commonly known molding process (e.g., injection molding). 
     In operation, the fuser and pressure rollers  136  and  138  are heated by the provided heating elements (e.g., internal heating elements  208  and  216 ). Once the fusing system  102  is heated to operating temperature, print media (e.g., paper) can be passed through the nip  200  such that the toner side faces the fuser roller  136  and, therefore, the textured pattern  300 . As the media pass through the nip  200 , the toner is fused to the media. Due to the provision of the textured pattern  300 , a mirror image of the pattern is imprinted or embossed into the fused toner so as to provide a visible pattern to the toner. As noted above, where the roller are relatively non-compliant toner gloss differential may result. However, the pattern transferred to the toner masks such gloss differential and, therefore, provides a more aesthetically pleasing result. In particular, when the printed media (e.g., printed page) are viewed such that light is reflected into the eyes of the observer, the observer&#39;s eyes will register the transferred pattern more readily than the gloss differential. 
     While particular embodiments of the fusing system and its operation have been disclosed in detail in the foregoing description and drawings for purposes of example, it will be understood by those skilled in the art that variations and modifications thereof can be made without departing from the scope of the invention as set forth in the following claims.