Abstract:
An improved apparatus for cooling or heating, or both, a fuser belt in a process for producing electrophotographic toner images on a substrate. The images are produced by passing a substrate bearing an image through a fusing zone to fuse fusible toner particles comprising the image to produce a substrate bearing a fused toner image, passing the substrate bearing the fused toner image through a cooling zone to produce a cooled substrate, which is thereafter passed to a release zone where it is released to produce the substrate bearing the toner image.

Description:
FIELD OF THE INVENTION 
   This invention relates to improved apparatus for cooling a fuser belt in a process for producing electrophotographic toner images on a substrate. The images are produced by passing a substrate bearing an image through a fusing zone to fuse fusible toner particles comprising an image to produce a substrate bearing a fused toner image and passing the substrate bearing the fused toner image through a cooling zone to produce a cooled substrate, which is thereafter passed to a release zone where it is released to produce the substrate bearing the toner image. 
   The present invention is directed to an improved cooler for use between the fusing zone and the release zone to cool the fuser belt. 
   The present invention also relates to a system wherein a high efficiency cooling apparatus is used in combination with a high efficiency heating system to cool the fuser belt moving from the fuser roller toward the release roller and heat the fuser belt moving from the release roller toward the fuser roller. 
   BACKGROUND OF THE INVENTION 
   Various methods are known for fusing toner particle images on substrates. In conventional fusing systems, one or both of a fuser roller and a pressure roller may be heated and are somewhat compliant to create a wide nip to allow sufficient heating area. Such conventional fusing systems typically provide gloss levels less than about 20 at a 20° measurement. Furthermore, the wide nip prevents obtaining sufficiently high pressure to remove the image relief in these materials. 
   Finishing color images containing fusible toner particles has been attempted in typical fusing systems. In these fusing systems, as noted above, typically the gloss is relatively low. As a result, systems for fusing colored images using methods and apparatus that result in fusing the black images to the substrate do not provide the desired gloss. Alternate methods have been used to produce enhanced gloss images by fusing the toner particle images and thereafter passing the substrate bearing the fused toner image to a cooling zone and then passing the cooled substrate bearing the fused toner image to a release zone where the cooled substrate bearing an enhanced gloss image is released. 
   Typically the cooling has been achieved by the use of a cooling device which has an air inlet with a plurality of downwardly directed small air inlets which are positioned above the fuser belt between the fuser roller and a release roller so that as the belt passes beneath the cooler with the substrates stuck to the bottom of the belt, the cooling air is blown downwardly onto the upper surface of the fuser belt to cool the belt. Coolers of this type have been widely used but are not efficient since the air blown downwardly toward the belt at most can travel one-half the width of the cooling device to the edge of the belt. As a result the cooling efficiency of the air is relatively low. Since it is desirable that a significant amount of cooling be achieved, improved methods and apparatus for achieving such cooling have been sought. 
   SUMMARY OF THE INVENTION 
   The present invention provides a high efficiency cooling device for a belt fuser, the device comprising: a coolant chamber wherein a coolant is passed in heat exchange with a fuser belt; a coolant inlet into a first end of the coolant chamber; and, a coolant outlet from a second end of the coolant chamber, the second end of the coolant chamber being upstream from the first end of the coolant chamber relative to movement of the fuser belt. 
   The present invention further provides a high efficiency cooling and heating system for use with a belt fuser, the belt fuser including a fusing section having a fuser roller and a pressure roller and a fuser belt around the fuser roller and a release roller, the system comprising: a coolant chamber between the fuser roller and the release roller and downstream from the fuser roller relative to movement of the fuser belt wherein a coolant is passed in heat exchange with the fuser belt; a coolant inlet into a first end of the coolant chamber; a coolant outlet from a second end of the coolant chamber, the second end of the coolant chamber being upstream from the first end of the coolant chamber relative to movement of the fuser belt; a heat exchange chamber between the release roller and the fuser roller and downstream from the release roller relative to movement of the fuser belt wherein a heat exchange fluid is passed in heat exchange with the fuser belt; a heated fluid inlet into a first end of the heat exchange chamber; a fluid outlet from a second end of the heat exchange chamber, the second end of the heat exchange chamber being up-stream from the first end of the heat exchanger relative to movement of the fuser belt; and, a line in fluid communication with the coolant outlet and the heated fluid inlet. 
   The invention also provides a method for efficient operation of a belt fuser system, the system including a fusing section having a fuser roller and a pressure roller and a fuser belt around the fuser roller and a release roller, the method comprising: passing a coolant fluid in heat exchange with the fuser belt between the fuser roller and the release roller and downstream from the fuser roller relative to movement of the fuser belt to cool the fuser belt and produce a heated fluid; and, passing the heated fluid in heat exchange with the fuser belt between the release roller and the fuser roller and downstream from the release roller relative to the movement of the fuser belt. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a prior art belt fusing system; 
       FIG. 2  shows a prior art air-cooling system for use in the belt fusing system of  FIG. 1 ; 
       FIG. 3  shows an embodiment of the present high efficiency cooling device of the present invention; 
       FIG. 4  is a an end view of the apparatus shown in  FIG. 3 ; 
       FIGS. 5 ,  6 ,  7 ,  8  and  9  are schematic diagrams of alternate embodiments of the cooling device of the present invention; and 
       FIG. 10  is a schematic diagram of the system of the present invention showing the use of the improved heat exchange devices of the present invention in use to cool the fuser belt between the fuser roller and a release roller and heat the fuser belt between the release roller and the fuser roller. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the present invention, the same numbers will be used to refer to the same or similar components throughout to the extent consistent with an accurate disclosure. Further, not all components required for the actual fabrication of the devices have been shown since their description is not necessary to a full understanding of the invention. In the description of the heat exchange apparatus, the apparatus is described as a cooling system but it should be understood that the heat exchange apparatus may also be used for heating. 
   In  FIG. 1 , a typical prior art belt fusing system  10  is shown. The belt fusing system  10  includes a fusing roller  12 , which may include a roller coating  14  as known to those skilled in the art. A heater  16  is positioned in fusing roller  12  to heat fusing roller  12 . It is well known in the art that alternatively exterior rollers (not shown) could be used to heat fuser roller  12  and the like. A pressure roller  18  is positioned to engage fuser roller  12  and includes a coating  20 , also known to those skilled in the art. A belt  22  is positioned around fuser roller  12  and a release roller  24 . A sheet  26  bearing images  28  is passed by known means to the fusing nip between fuser roller  12  and pressure roller  18  where the sheet bearing the images is fused and emerges from the fusing nip adhering to the bottom of belt  22 . Belt  22  passes by a cooler  32 , which is typically an air cooler. The movement of the belt is in a direction shown by an arrow  30 . As the fuser belt passes to and around release roller  24 , the sheets adhering to the bottom of belt  22 , which are now cooled and are less tacky, are released from fuser belt  22  and collected at a downstream location (not shown), as known to those skilled in the art. 
   In  FIG. 2  a more detailed schematic showing of air cooler  32  from  FIG. 1  is shown. Air cooler  32  includes a chamber  34  into which air is passed through a cooling fluid inlet  36  as shown by an arrow  38 . A plurality of cooling fluid outlets  40  are positioned on the bottom of chamber  34  as shown to pass air downwardly toward the top surface of belt  22 . As discussed previously, such air cooling systems are relatively inefficient since the air can spill over the edges of the fuser belt relatively quickly after passing from chamber  34  and since in the best case scenario, the air passes no more than half the width of air cooler  32  over the surface of fuser belt  32 . 
   In  FIG. 3 , an improved cooling apparatus is shown. The improved cooling apparatus includes a first end  42  and a second end  44 . A cooling chamber  34  is formed by ends  42  and  44  and a top  46 . Air is passed into chamber  34  through a heat exchange fluid inlet  36  as shown by an arrow  38  and passed through chamber  34  as shown by an arrow  50  and recovered via a heat exchange fluid outlet  48  as shown by an arrow  52 . In this embodiment, the cooling fluid, which will be discussed as air but could be any other suitable heat exchange gas useful for either heating or cooling, is passed into the cooling chamber  34  in direct contact with the top of fuser belt  22 . The air is maintained in chamber  34  by felt or other suitable seals  54  positioned around the bottom of chamber  34  to prevent the escape of air around the bottom of chamber  34 . 
   In this embodiment a length  47  of chamber  34  can be much greater than the width of the air cooler described in  FIG. 2 . Accordingly the air or other heat exchange medium may be kept in contact with the top of the fuser belt for a greater time than by the prior art methods. Since it is desirable in many instances to cool the top of the fuser belt from about 150 to 160° C. to a temperature from about 70 to about 80° C., it is desirable in many instances to maintain the cooling gas in contact with the fuser belt for a longer period of time. Further, while seals  54  have been described to be of felt, they can be of any suitably resilient material which is stable at the temperatures discussed. Many such materials are known to those skilled in the art. 
   In  FIG. 4 , an end view of the device shown in  FIG. 3  is shown. Clearly the width  56  of the chamber  34  can be nearly as wide as the top of the fuser belt  22 . This permits the air to uniformly contact the top of fuser belt  22 . The air inlet is shown as an inlet slot of substantially the same width as chamber  34  with the air being injected as shown by an arrow  38 . It will be understood that air or other cooling gas can be injected through an inlet of any suitable configuration, which is effective to uniformly distribute the cooling air over the surface of fuser belt  22 . 
   In  FIG. 5 , an alternate embodiment is shown wherein chamber  34  includes a bottom  58 , which is in heat exchange contact with the top of fuser belt  22 . The term “heat exchange contact” may refer to actual contact or sufficiently close proximity between the bottom  58  of chamber  54  and the top of fuser belt  22  so that intimate heat exchange is accomplished. By both the embodiments shown in  FIGS. 3 and 5 , it will be noted that the cooling media is recovered and may be passed from the equipment or passed to use for other purposes. This obviates a major disadvantage of the previously used systems which result in a substantial air flow in the vicinity of the air cooler which may result in cooling surfaces which are desirably maintained at high temperatures, such as the surface of the fuser roller and the like. 
   In  FIG. 6 , an alternate embodiment of the apparatus shown in  FIG. 5  is shown. In this embodiment, fins  60  are used on the bottom of chamber  34  to result in enhanced heat exchange. 
   In  FIG. 7 , an alternate embodiment is shown. In this embodiment, a cooling fluid is injected into chamber  34  via a cooling fluid inlet  62  and recovered by a coolant fluid outlet  64 . In this embodiment as further shown in  FIG. 8 , a plurality of dividers  66  are positioned to cause the cooling fluid to flow in a circuitous path through cooler  32 . In this embodiment, chamber  34  may or may not have a bottom. If no bottom is present, then a seal such as a felt seal as shown in  FIG. 3  may be used. In these instances, the cooling fluid, which is desirably a gas, is passed through the circuitous path to cool the top of the fuser belt by direct contact of the cooling gas with the top of the fuser belt. Alternatively a bottom may be provided in chamber  34  so that the cooling is through the bottom of chamber  34 . 
   In  FIG. 9 , an alternate embodiment is shown wherein a plurality of coils  68  is provided in chamber  34 . In this embodiment liquid can be used as well as gas as a coolant. In this embodiment there may or may not be a bottom on chamber  34 . The cooling achieved in chamber  34  may be achieved by simply passing a coolant through the coils or the coils may be formed as the part of bottom  58  of chamber  34  and the like. In any event, effective cooling is achieved. 
   In  FIG. 10 , an embodiment of a system for cooling the fuser belt between fuser roller  12  and release roller  24  is shown. This embodiment also includes a system for heating the fuser belt between release roller  24  and fuser roller  12 . All references to the positioning of elements upstream or downstream from other elements are based upon the motion of the fuser belt  22 . The movement of fuser belt  22  beneath air cooler  32  is downstream of fuser roller  12  and upstream of release roller  24 . Similarly the use of a heater between release roller  24  and release roller  12  positions the heater downstream from release roller  24  and upstream with respect to fuser roller  12 . 
   Any of the embodiments discussed above may be used as an air-cooling or a heating and cooling apparatus. As noted, in at least one embodiment, liquid may also be used as a coolant in the cooling system although the system will be discussed with reference to a gas coolant and a gas heating fluid. 
   The heated gas recovered from the cooler is passed via a transfer line  72  to a heater  70  where it heats fuser belt  22  between release roller  24  and fuser roller  12 . The heating fluid is introduced via an inlet into a first end  76  of heater  70  and discharged through an outlet  74  at second end  78  of heater  70 . First end  76  is downstream from second end  78 . Desirably, the fuser belt is reheated upstream from fuser roller  12  and at fuser roller  12  to reach a suitable temperature to fuse images  28  on substrate  26  at the nip between fuser roller  12  and pressure roller  18 . The discharged heat exchange fluid may be discarded by any suitable means or recycled as a coolant. 
   Desirably, the heating of fuser belt  22  by heater  70  is at least from about 20 to about 30° C. This is a substantial heat recovery and reduces the heat load on the heater for fuser roller  12  and results in better fusing of the substrates passed through the fusing nip. 
   The air cooler has been discussed above by reference to the use of air as a gas, although in some embodiments, as clearly disclosed, liquids could be used. Suitable liquids are water or any other desirable heat exchange fluid. Similarly, gases other than air could be used if desired. Preferably air and water are used since both are economical, readily available and readily disposed of after passing through the system. 
   Accordingly, the apparatus of the present invention is effective to carry out a method for cooling a fuser belt at a desired point and reheating the fuser belt at a second downstream point. The method comprises passing a coolant fluid in heat exchange with the fuser belt between the fuser roller and the release roller and downstream from the fuser roller relative to movement of the fuser belt to cool the fuser belt and produce a heated fluid and passing the heated fluid in heat exchange with the fuser belt between the release roller and the fuser roller and downstream from the release roller relative to the movement of the fuser belt. 
   In some instances the heat exchange fluid may be in direct contact with the fuser belt and in those instances it is desirable that a gas heat exchange fluid be used. In other instances the heat exchange fluid is not in contact with the fuser belt but is in contact with the chamber, which is in heat exchange contact with the fuser belt. 
   Further, additional configurations of belt fusers may be suitable for use in the present invention. In such systems, the same steps are accomplished in substantially the same sequence and the heating and cooling may be accomplished by the use of the heat exchange apparatus disclosed in the present invention. In many instances, only cooling may be used but in those instances the increased efficiency achieved by the cooling apparatus of the present invention is considered to be a significant improvement. 
   As also noted previously, the heat exchange apparatus disclosed may be used for cooling or heating and cooling. 
   While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.