Patent Publication Number: US-7914879-B2

Title: Thick fusing belt for a color electrophotographic printer

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to electrophotographic imaging device and, more particularly, to a thick fusing belt of a fuser of electrophotographic imaging devices. 
     2. Description of the Related Art 
     In the electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image, and thereafter the toner image is transferred to the media intended to receive the final permanent image. The toner is fixed to the media by the application of heat and pressure in a fuser. A fuser may include a heated roll and a backup roll forming a fusing nip through which media passes, known as a hot roll fuser. A fuser may also include a fuser belt and an opposing backup member, such as a backup roll, known as a belt fuser. 
     A hot roll fuser is a high force and pressure fuser that can deliver high print quality, however a hot roll fuser is not an instant on fuser due to the huge thermal mass of thick metal core and thick silicone rubber layer coated on the metal core. While a belt fuser with a ceramic heater or induction heater can be instant on, it is usually only used for low speed color laser printers as its fusing quality is not as good as that of a hot roll fuser. 
     In order to achieve a very short warm-up time, an instant on fuser, like a belt fuser with a ceramic or induction heater, uses an endless fusing belt that can be heated very fast due to its small thermal mass. Since the fusing belt is very thin and flexible, force cannot be directly applied to both ends of the belt to form a required fuser nip. To form a fuser nip, a stationary pressure member, a heater and a heater housing with a steel bracket for a ceramic belt fuser is put inside the belt tube. Forces are applied to both ends of the steel bracket and the pressure member forces the fusing belt to firmly contact against a backup roll to form a fuser nip. The pressure member is fixed and not turning. Since the pressure member is not turning with the belt, friction forces between the contact surfaces of the belt and the pressure member is very high and can wear the belt and reduce belt lifetime. Even with lubrication between the contact surface of the belt and the stationary pressure member, belt stall still occurs as the lubrication dries out. In order to reduce the friction force, the force used for forming a fusing nip has to be much lower than the force applied to a hot roll fuser. The lower force results in lower nip pressure and the lower nip pressure can cause many print quality problems, such as poor fuse grade, mottling, poor uniformity across a page, and transparency defects. 
     Based on the experience of a hot roll fuser and a belt fuser with a ceramic heater or induction heater, the depth of the fuser nip indentation must be kept small enough to allow the toner to release while the fuser nip size must be large enough for high speed fusing. Generally, in order to achieve a larger fuser nip size with a smaller fuser nip indentation, the size of the fuser must be increased, which necessarily increases the fuser warm up time significantly. 
     Thus, there is still a need for a fuser with fast warm up time, high force and pressure in order to deliver high print quality. Additionally, the fuser must have a flat or slightly dented fuser nip with a large enough fuser nip to achieve high speed fusing without increasing the fuser size. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need by providing a fuser that combines the advantages of a belt fuser and a hot roll fuser and overcomes the disadvantages of low pressure or slow warm up times. The fuser provides higher fusing quality than that of a belt fuser with a ceramic heater due to a wider fusing nip, higher force/higher nip pressure, and a lower friction force. The fuser also provides a fusing nip large enough to achieve high speed fusing while minimizing the fuser nip indentation in order to allow the toner to release adequately to achieve higher fusing quality. 
     Accordingly, in an aspect of the present invention, a quartz-tube fuser having an endless fusing thick belt for an electrographic imaging device having a flexible tubular configuration of predetermined diameter is disclosed. The endless fusing thick belt includes an outside surface toner release layer made of a coating and a sleeve; a silicone rubber layer positioned inside said outside surface toner release layer; a steel layer positioned inside the silicone rubber layer; and a silicone base layer positioned inside and affixed to the internal surface of the steel layer using an adhesive. 
     In another aspect of the present invention, a quartz-tube fuser having an endless fusing thick belt for an electrographic imaging device having a flexible tubular configuration of predetermined diameter is disclosed. The endless fusing thick belt includes an outside surface toner release layer comprised of a coating or a sleeve; a silicone rubber layer positioned inside the outside surface toner release layer; a polyimide layer positioned inside the silicone rubber layer; and a silicone base layer positioned inside and affixed to the internal surface of the polyimide layer using an adhesive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a side view of the quartz-tube belt fuser with a flat fuser nip of the present invention. 
         FIG. 2  is an exploded view of the quartz-tube support assembly of the present invention. 
         FIG. 3  is an expanded view of the thick fusing belt of the quartz-tube belt fuser in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numerals refer to like elements throughout the views. 
     Referring now to  FIG. 1 , there is illustrated a side view of the quartz-tube belt fuser of the present invention. A lamp heater  25  serves as a heating source and is positioned inside a quartz tube  23 , which has an elongated tubular body of predetermined diameter and a pair of opposite ends, with the tubular body being substantially transparent to allow the passage of radiant heat from the lamp heater  25 . An endless fusing belt  21  having a flexible tubular configuration of predetermined diameter is positioned about the lamp heater  25  and spaced outwardly from the lamp heater  25 . The quartz tube  23  is positioned around the lamp heater  25  and inside the fusing belt  21  and enables transmission of radiant heat from the lamp heater  25  to the fusing belt  21  to heat the fusing belt  21 . The quartz tube  23  is seated upon a quartz-tube support assembly (not shown). A pressure roll  27  is positioned in opposition to the length-wise segment of the fusing belt  21  and to the quartz tube  23  contained within the fusing belt  21 . Pressure is applied by the quartz tube  23  on the length-wise segment of the fusing belt  21  such that the fusing belt  21  and said pressure roll  27  form a fuser nip  29 . 
     The quartz tube  23  must have above 90% transparency to the IR lamp emission spectrum of the lamp heater  25 . The quartz tube  23  is used as a pressure member and can be stationary or rotational. The quartz tube  23  diameter must be smaller than the diameter of the fusing belt  21  in order to assure that the firm contact area between the fusing belt  21  and the quartz tube  23  only occurs at the fuser nip  29 . The diameters of the fusing belt  21  and the quartz tube  23  are selected in order to make the contact area of the fusing belt  21  and the quartz tube  23  as small as possible. The diameter of the quartz tube  23  can be determined first based on fuser nip size requirements or residence time requirement. Then based on the determined quartz tube size, the diameter of the fusing belt  21  can be selected by minimizing the fusing belt diameter to minimize the thermal mass of the belt and maximizing the fusing belt diameter to minimize the contact area of the fusing belt  21  and the quartz tube  23 . As a result, the thermal mass of the belt and the heat conducted to the quartz tube from the belt are minimized. Since the quartz tube  23  is transparent enough to allow 90% of the radiant heat generated by the lamp heater  25  to pass through the quartz tube  23  to heat the fusing belt  21  directly, the warm-up time of the belt from room temperature to its fusing temperature is minimized. 
     Referring now to  FIG. 2 , there is illustrated an exploded view of the quartz-tube support assembly of the present invention. A quartz tube support assembly  31  has a frame  33  and a pair of bearings  35 A and  35 B mounted on the frame  33  spaced apart from one another and supporting the quartz tube  23  at said opposite ends of the tubular body such that the tubular body of the quartz tube  23  is positioned around the lamp heater (not shown) and inside the fusing belt (not shown) and enables transmission of radiant heat generated by the lamp heater to fusing belt to heat the fusing belt. The quartz tube support assembly  32  is adapted to apply a force via the bearings  35 A and  35 B to the quartz tube  23  such that the quartz tube  23  applies pressure contact to the fusing belt along a length-wise segment of the fusing belt. Since the quartz tube  23  is seated on the ball bearings  35 A and  35 B at both ends, the friction torque is significantly lower than that of the prior art belt fusers shown in  FIGS. 1 and 2  that have stationary pressure members. Therefore, the quartz tube  23  can take a high load to generate enough nip pressure for printing quality without causing high torque and belt stall issues. 
     Referring now to  FIG. 3 , there is illustrated an expanded view of the endless fusing belt  21 . The endless fusing belt  21  has an outside surface toner release layer  3  which can be made from a coating and a sleeve and can vary in thickness from about 20 to about 50 microns. A silicone rubber layer  5  that provides better compliance and better fusing quality is positioned inside the toner release layer  3 . The silicone rubber layer  5  can be made out of high thermal conductive rubber and can vary in thickness from about 200 to about 500 microns. A rigid material layer  7  is positioned inside the silicone rubber layer  5 . The rigid material layer  7  can be made from steel of about 50 microns in thickness or polyimide of thickness from about 50 to about 250 microns. If the rigid material layer  7  is made from polyimide, both filled and unfilled. An unfilled polyimide with natural amber color is preferred which has very low infrared absorption, so that the infrared energy from the lamp heater can pass through the polyimide layer and directly heat the silicone rubber layer  5 . A silicone base layer  9  is positioned inside and affixed to the internal surface of the rigid material layer  7  layer using an adhesive or primer (not shown). The silicone base layer  9  must have a very low IR absorption so that less IR energy is absorbed by the silicone base layer  9  and more IR energy can pass through the silicone base layer  9  and directly heat the rigid material layer  7 , silicone rubber layer  5  and outside surface toner release layer  3  of the thick fusing belt. As a result, the silicone base layer  9  material is from translucent silicone foam, light color silicone foam, transparent silicone rubber, translucent silicone rubber, or other suitable low IR energy absorption material. The silicone base layer  9  is from about 1 mm to about 2.5 mm in thickness and from about 2 to about 40 shore A in hardness. 
     Since the belt is thick and flexible, it can easily form a slightly indented, flat, or reversed nip by adjusting the thickness, hardness, or both of the foam or rubber base layer. By this way, toner release problem of a quartz tube belt fuser can be easily fixed. Since the most IR energy emitted by a lamp can easily pass through quartz tube and the base foam or rubber layer to heat the outside layer directly, the surface temperature of the thick belt can be warmed up to fusing temperature within a very short time. 
     The foregoing description of several embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.