Patent Publication Number: US-2010126021-A1

Title: Method for refurbishing pressure members

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to commonly assigned, copending U.S. application Ser. No. 11/746,083, filed May 9, 2007, and entitled “IN-LINE METHOD TO REFURBISH FUSER MEMBERS.” 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to electrostatographic devices and methods for refurbishing fuser and pressure members, and is particularly concerned with the refurbishment of a pressure roller or member which is coated with an outermost layer of fluoropolymer resin. 
     BACKGROUND OF THE INVENTION 
     The surface (or the topcoat) for both fuser and pressure members in oil-less fusing of toner material requires ultra low surface energy to release the substrate. An improved topcoat material for oil-less fusing is high-temperature tolerant thermoplastic, such as FEP, PFA, or PTFE described in US Published Applications 2007/0298252, 2007/0298251, 2007/0298217, and 2007/0296122 each of which were published on Dec. 27, 2007. 
     However, the applicants have observed during fuser printing performance tests that paper edges, particularly of thick paper, can occasionally leave wear marks on the topcoat of the fuser surface. These paper edge marks can show up on wider paper as gloss-variation artifacts when subsequent prints are made on a substrate covering the worn area. Moreover, for printing special images, particularly one with in-track stripes of area of no toners, foreign materials from paper are seen to periodically accumulate on the surface of the topcoat due to the absence of toners. Such foreign materials may be, for example, the fine particulate clay or calcium carbonate fillers often present on the surface of the paper being printed. The accumulation of such foreign particulate material on the surface of the topcoat can result in undesirable artifacts, such as a gloss variation band artifact occurring when printing a different image content subsequently as a full page image. 
     In the past, to avoid such artifacts, the fuser members were simply replaced. To obviate the need and expense associated with completely replacing the fuser members, the applicants developed an in-line method for refurbishing fuser members in-situ which is described and claimed in commonly assigned, copending U.S. application Ser. No. 11/746,083. 
     The applicants have subsequently observed that paper edges, particularly of thick paper, can also leave wear marks on the topcoat of the pressure member surface, and that foreign materials from paper can also periodically accumulate on the surface of the pressure member topcoat. Consequently, undesirable image artifacts may be caused by the pressure members as well as the fuser members in electrophotographic printers. The present invention is a method for refurbishing pressure members within an electrophotographic printer that obviates the need and expense associated with completely replacing the pressure members 
     The practice of the proposed refurbishing scheme and the accessory surface cleaning scheme depends on the severity of the artifact present on the pressure member surface, which in turn is a function of the service history of the pressure member. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of resurfacing a pressure member having an outer surface formed from a high temperature fluorothermoplastic. When it is determined that the outer surface is in need of resurfacing, the pressure member is rotated at a speed of at least 1 rpm while engaging the outer surface of the fuser member with at least one heating roller at a pressure of at least 5 psi at a temperature of at least 10° C. below the fluorothermoplastic melting temperature for a time sufficient to resurface of the outer surface of the pressure member. 
     When the pressure member is in operation in an electrophotographic printer having a fuser member that is externally heated by a heater roller assembly, the method may further include the steps of replacing the fuser member with the pressure member, rotating the pressure member at the aforementioned speed via the fuser member drive, and implementing the aforementioned temperature and pressure on the outer surface of the pressure member via the heater roller assembly of the printer. To expedite the these steps of the method, both the fuser member and the pressure member may be mounted within the electrophotographic printer by a quick-release assembly that allows the operator to quickly and easily remove the fuser and pressure members from their normal, operational positions on the frame of the printer and to install the pressure member in the operational position of the fuser member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side, cross-sectional schematic view of an electrophotographic printer where the method of the invention may be easily implemented, including a fuser member, a heater roller assembly for externally heating the fuser member, a pressure member having substantially the same diameter as the fuser member, and quick-release assemblies for removing and mounting the fuser and pressure members with respect to the printer frame. 
         FIG. 2  is an exploded, perspective view illustrating how a fuser or pressure roller is detachably connected to the fuser roller mounting frame via a quick-release assembly. 
         FIG. 3  is a side, partial cross-sectional view of the quick-release assembly shown in  FIG. 2 , illustrating in phantom how the spring-loaded locking pins are manually extended and retracted to lock and unlock a fuser or pressure roller to the mounting frame. 
         FIG. 4  is a side, cross-sectional schematic view of the electrophotographic printer of  FIG. 1  illustrating how the first steps of the method of the invention are implemented by removing the fuser roller from the printer frame and mounting the pressure roller into the operational position of the fuser member. 
         FIG. 5  is a side, cross-sectional schematic view of the electrophotographic printer of  FIG. 1  illustrating how the last steps of the method of the invention are implemented by using the heater roller assembly to refurbish the outer surface of the pressure roller. 
     
    
    
     For a better understanding of the present invention together with other advantages and capabilities thereof, reference is made to the following description and appended claims in connection with the preceding drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention can be applied to refurbishing pressure members with thermoplastic topcoat materials, such as FEP (polyfluorinated ethylene-propylene), PFA (perfluoroalkoxy-tetrafluoroethylene), or PTFE (polytetrafluoroethylene). The instant invention is not dependent on how the pressure member is manufactured, i.e., not affected by whether the topcoat is sleeve molded, sintered with dispersion, sprayed or transfer-coated, etc. The method of the present invention will increase the usable life of the pressure member owing to its ability to remove surface irregularities and restore a uniform gloss surface finish to the pressure member. 
     In all embodiments, the pressure members are preferably cylindrically symmetrical, i.e., a cross-section of the roller taken at a right angle to the roller axis anywhere along the length of the member or roller has radial symmetry around the roller axis. The length of the roller thereof determines the range of the printing width of the substrate. 
       FIG. 1  schematically illustrates an electrophotographic printer  100  where the method of the invention may be easily implemented, including a fuser member  110 , a heater roller assembly  135  for externally heating the fuser member  110 , air jets  155 ,  156  for simulating a thermal load on the fuser member during the warm-up up the printer  100 , a pressure member  160  having substantially the same diameter as the fuser member  110 , and quick-release assemblies  182  for removing and mounting the fuser and pressure members  110 ,  160  with respect to a printer frame  170  (shown in  FIG. 2 ). During normal operation of the printer  100 , paper sheets  168  having an image formed by a pattern of dry, particulate toner are conveyed via a conveyor  169  into the nip defined between the fuser member  110  and the pressure member  160 . The heat and pressure applied to the paper sheets fuses the toner into a permanent image into the paper. 
     The fuser member  110  includes a plurality of annular layers  112 ,  113 , and  114  that surround a generally concentric central core  116 . Core  116  is usually formed from a metal, such as stainless steel, steel, aluminum, etc. The primary requisite for the material for core  116  is that it be sufficiently stiff to support the force placed upon it during a printing operation, and able to withstand a possibly higher temperature than the surface of the member  110  where there is an optional internal heating source, such as the quartz-halogen light  117  illustrated in cross-section at the center of rotation of the member  110 . For externally heated fuser members, the internal heat source  117  can be optional, though in most practical cases, the internal heat supply is used in combination with the external heat provided by the heater roller assembly  135  to fuse the toners for print quality manipulation. The various annular layers that overlie the core  116  include a resilient layer, also termed a cushion layer  113 , and tie layers, adhesion promotion layers, and primer layers  114  for bonding the cushion layer with the outmost layer  112 . The outermost layer  112  is a toner release layer which includes a thermoplastic fluoropolymer such as PTFE, PFA, and FEP, etc. and blends thereof. The fuser member  110  is detachably mounted to a frame,  170  in the printer  100  by way of a quick release mechanism  182  (indicated in phantom). 
     The pressure member  160  preferably has the same structure and diameter as the previously described fuser member  110 , including a plurality of annular layers  162 ,  163 , and  164  that surround a generally concentric central core  166  formed from a metal, such as stainless steel, steel, aluminum, etc. Like the fuser member  110 , the pressure member  160  includes an internal heat source in the form of a quartz-halogen light  167  illustrated in cross-section at the center of rotation of the member  160 . The various annular layers that overlie the core  166  include a resilient layer, also termed a cushion layer  163 , and tie layers, adhesion promotion layers, and primer layers  164  for bonding the cushion layer  163  with the outmost layer  162 . Like the fuser member  110 , the outermost layer  162  of the pressure member  160  is a toner release layer which includes a thermoplastic fluoropolymer such as PTFE, PFA, and FEP, etc. and blends thereof. The pressure member  160  is likewise detachably mounted to a frame  170  in the printer  100  by way of a quick release mechanism  182  (indicated in phantom). 
     The heater rollers  140 ,  150  of the heater roller assembly  135  are made of rigid materials, such as chrome-plated steel.  FIG. 1  also schematically shows the temperature sensors  142 ,  152 , the over-temp devices  143 ,  153 , the heating elements  141 ,  151  of the heater rollers  140 ,  150  and a program-controllable loading assembly C for engaging the heater rollers  140 ,  150  against the surface of the fuser member  110  at a desired pressure both during normal printing service for externally heating the fuser member  110  to fuse printer toner, and during the pressure member  160  during the implementation of the method of the invention. The loading assembly C may include any one of pneumatic cylinders, a motor-cam combination, a lead screw mechanism or solenoids to control engagement pressure. For this invention, the proximity of the over-temp devices  143 ,  153  to the topcoat  112  is adjustable and the temperature sensors  142 ,  152  are calibrated for temperature range up to around the melting point of the topcoat  162  allowing much higher temperature set points needed for pressure member surface refurbishing than those used in the normal printing. When the pressure member refurbishing program is activated, the proximity of the over-temp sensor is adjusted to be farther away from the topcoat surface  162  to a pre-determined distance in the range of 0.5 mm to 3 mm such that it can serve its function as the fusible safety device for higher than the normal printing temperature set points. The heater roller engagement pressure, and temperature and rotational speed of the pressure member  160  then follow a programmed function which is known to best produce a refurbished pressure member surface. 
     Both the fuser member  110  and pressure member  160  can be a fuser or pressure plate, fuser or pressure roller, fuser or pressure belt or any other member on which a release coating is desirable. The support for the fuser or pressure member can be a metal element with or without additional layers adhered to the metal element. The metal element can take the shape of a cylindrical core, plate or belt. The metal element can be made of, for example, aluminum, stainless steel or nickel. The surface of the metal element can be rough, but it is not necessary for the surface of the metal element to be rough to achieve good adhesion between the metal element and the layer attached to the metal element. The additional support layers adhered to the metal element consist of layers of materials useful for fuser and pressure members, such as silicone rubbers, and an adhesion promoter layer to the metal element. 
     The fluoropolymer resin outer layer includes a fluoropolymer material, such as a semicrystalline fluoropolymer or a semicrystalline fluoropolymer composite. Such materials include polytetrafluoroethylene (PTFE), polyperfluoroalkoxy-tetrafluoroethylene (PFA), polyfluorinated ethylene-propylene (FEP), poly(ethylenetetrafluoroethylene), polyvinylfluoride, polyvinylidene fluoride, poly(ethylene-chloro-trifluoroethylene), polychlorotrifluoroethylene and mixtures of fluoropolymer resins. Some of these fluoropolymer resins are commercially available from DuPont as Teflon™ or Silverstone™ materials. 
     With reference now to  FIGS. 2 and 3 , both the fuser and the pressure member  110 ,  160  are detachably connected to their respective support frames by way of quick-release mechanisms  182  disposed on either side of the members.  FIG. 2  specifically illustrates how the pressure member  160  may be detachably mounted in particular to the fuser mounting frame  170 , since such mounting is a key step in the implementation of the method of the invention. 
     The fuser mounting frame  170  includes a pair of opposing side plates  172  (of which only one is shown) connected together by horizontal support members  174   a, b , and  c . The pressure roller  160  has a pair of opposing, disc-shaped side plates  178 , each of which includes a stub shaft or gudgeon  180  extending from its center. The gudgeons  180  on either side of the pressure member  160  are rotatably mounted in the quick-release assemblies  182 . As will be explained in more detail hereinafter, the quick-release assemblies  182  may be slid into and secured within a square shaped recess  209  present in each of the side plates  172  of the mounting frame  170 . 
     Each quick-release assembly  182  includes a support frame  183  having plate-like inner and outer portions  184   a,    184   b  which are spaced apart to define slots  185   a,    185   b  on either side of the support frame  183 . These slots  185   a,    185   b  are dimensioned to slidably receive the side edges of the square shaped recess  209  of the fuser mounting frame  170 . The support frame  183  also carries a roller bearing  186  into which the gudgeon  180  is journalled, and a drive gear  187  that is non-rotatably coupled to the gudgeon by a keyway formed by the engagement of a flat side  188  of the gudgeon against a flat side  189  in the central opening of the drive gear  187 . A locking plate  190  slides into an annular groove  192  at the distal end of the gudgeon  180  to secure the quick-release assembly  182  to the gudgeon  180  in much the same fashion that a common cotter pin functions. A set screw  194  secures the locking plate  190  in place. The stem  196  of the quartz-halogen light extends from the distal end of the gudgeon  180  as shown, and is mounted on a support flange  197 . 
     With specific reference to  FIG. 3 , the locking and unlocking components of each of the quick-release assemblies  182  include a handle  198  connected to a pair of spring-loaded locking pins  200   a ,  200   b . Each of these locking pins  200   a ,  200   b  is disposed in a bore  201  in the outer portion  184   b  of the support frame  183  having an enlarged diameter portion  203 . Each of these locking pins  200   a,    200   b  includes an annular flange  205  that captures a compression spring  207  between itself and an opposing end of the enlarged diameter portion  203 . In operation, the handle  198  is pulled out to the position indicated in phantom, which in turn withdraws the end of the pins  200   a ,  200   b  inside the bore  201 . The pressure member  160  is then moved upwardly such that the edges of the side plate  172  on either side of recess  209  are slid into the slots  185   a ,  185   b  on either side of the quick-release frame  183 . When the ends of the locking pins  200   a ,  200   b  are in alignment with pin receiving holes  210   a ,  210   b , the handle  198  is then released, which allows the biasing force of the spring  207  to insert the ends of the locking pins  200   a ,  200   b  into the holes  210   a ,  210   b  in the side plate  172 . 
       FIG. 4  schematically illustrates the first steps of a preferred implementation of the method of the invention. In this preferred implementation, the heater roller assembly  135  is first moved out of pressurized engagement with the fuser roller  110 . Next, the fuser member  110  is removed from the fuser frame  170  by pulling outwardly on the handles  198  of the quick-release assemblies  182  on either side of the fuser member  110 . Such pulling withdraws the locking pins  200   a ,  200   b  from the pin receiving holes  210   a ,  210   b  in the side plates  172  of the fuser frame  170 , allowing the quick-release assemblies  182  to be slid out of the recesses  209 . Next, the pressure member  160  is released from its support frame (not shown) and is installed in the fuser fame  170  via the spring-loaded locking pins  200   a ,  200   b  of its quick-release assemblies  182  (as indicated by the curved arrow) in the same manner as described with respect to the fuser member  110 . 
     Once the pressure member  160  is mounted in the position indicated in  FIG. 5 , a set of specialized programmed schemes are executed to simultaneously heat and pressurize the thermoplastic topcoat  162  of the pressure member  160  to a temperature at least 10° C. below the melting temperature of the outer surface topcoat material, for example, from 280 to 320° C. for PFA and PTFE materials, and at a pressure of at least 5 psi, i.e. to refurbish the topcoat material, by taking advantage of the heater rollers  140 ,  150  which are normally used for externally heating the fuser member  110  to fuse toner during the printing operation. This set of specialized programmed schemes will automatically control the flow of the following steps at a printing press by the main machine control. 
     (1) Raise the temperature of the heater roller higher than that for normal printing operation such that the pressure roller surface temperature is brought to at least 10° C. below the melt temperature of the topcoat materials; 
     (2) Set the fuser roller and the heating roller over-temperature sensors to a pre-determined distance suitable for refurbishing temperature range, other than the normal printing mode set-points; 
     (3) Rotate the fuser member at a rotational speed at least 1 rpm, engage the heater roller with a contact pressure of at least 5 psi and up to a needed level at least 10° C. below the melt temperature of the topcoat materials; 
     (4) Turn on the cooling air via air jets  155 ,  156  to cool the pressure member at a position away from the nip of the heater rollers  140 ,  150  to prevent overheating of the sublayers  163 ,  164  and to have fast recovery to the normal printing mode set-points; 
     (5) Engage the heater rollers  140 ,  150  on the pressure member surface with program-controlled functions of pressure and temperature for a period of time sufficient to refurbish the pressure member, typically a range of 1 to 3 minutes. 
     The present invention preferably is initiated after the pressure member has serviced a same print job for a period of time such that artifact may show up in a subsequent different print job, depending on the printing service requirement. Artifacts that require pressure member refurbishing include paper edge wear marks, foreign materials or paper dust from paper in the area of no toner stripes and/or scratch lines due to the fabric cleaning pad applied directly to the pressure roller surface or any other mishap. The initiation of the pressure member refurbishing program can also be a part of the scheduled maintenance. 
     Before activating the above refurbishing scheme, it is necessary to assure clean surfaces of the pressure member  160  and heater rollers  140 ,  150 , i.e. the pressure member surface  162  should be free of contamination, such as, residual toner or deposit of foreign materials, such as from paper. A method to clean the surfaces of the pressure member  160  as well as the heater rollers  140 ,  150  to precede the method of the present invention is done by non-invasive methods such as by applying soft rags with solvents. 
     EXAMPLE  
     An example is given on a pressure member made of 25-micron-thick PFA (of a melting temperature 305° C.) topcoat, under which is 35-micron-thick Viton, under which is 200-mil-thick silicone rubber. The pressure member serviced for 50,000 A4-equivalent prints of Tabloid sized paper of 300-micron thick on a Nexpress 2100 printing press with external heated fuser assembly and showed de-glossing along the in-track paper edge on the topcoat. The subsequent print on a wider coated paper showed a gloss drop in G60 value by 20 points along the de-glossed edge of the pressure member. The pressure member refurbishing program was activated. After exchanging positions with the fuser member, the pressure member was refurbished at temperature around 300 to 305° C. of the external heater rollers with a programmed pressure that started from 5 psi and increased to 30 psi for about 2 minutes in line to the extent that the paper edge de-glossing was not visible on the pressure member and the subsequent print on a wider coated paper showed non-measurable difference in G60 value on the print that contacted the Tabloid-sized paper edge area of the pressure member. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.