Abstract:
A precision release agent management system for an electrostatographic reproduction apparatus fuser device. The precision release agent management system includes a reservoir adapted to contain a release agent. A wick absorbs release agent from the reservoir. A metering member receives release agent from the wick, which is supported for resiliently urging into operative contact with the metering member. A blade member is associated with the metering member to establish a desired thickness of release agent on the metering member, and a donor member is adapted to receive release agent from the metering member, and operatively contact the fuser device to apply the release agent thereto. A plurality of features is associated with the reservoir for precise alignment of he donor member, the metering member, and the metering blade.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to a fusing apparatus for an electrostatographic reproduction device, and more particularly to a precision release agent management system for the fusing apparatus for an electrostatographic reproduction device.  
       BACKGROUND OF THE INVENTION  
       [0002]     In electrostatographic reproduction apparatus, such as electrophotographic copier/duplicators, printers, or the like, a light image of an original document to be printed or copied is typically recorded by either digital or analog devices as an electrostatic latent image upon a photosensitive member. Subsequently, the latent image is rendered visible (i.e., developed) by application of electrostatically charged marking particles, commonly referred to as toner. The developed toner image can be either fixed directly upon the photosensitive member, or transferred from the photosensitive member to another support substrate, or receiver member, such as a sheet of plain paper, with subsequent affixing of the toner image thereto.  
         [0003]     In order to fix or otherwise fuse the toner material onto a receiver member permanently, it is generally necessary to apply heat so as to elevate the toner material to a temperature at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent into the fibers or pores of the receiver member or to otherwise adhere to the surface thereof. Thereafter, as the toner material cools, solidification occurs causing the toner material to be bound firmly to the receiver member.  
         [0004]     One method for thermal fusing of toner images onto a receiver member has been to pass the receiver member with an unfused toner image thereon between a nip formed by a pair of opposed roller members that are in contact with each other, wherein at least one of the roller members is heated. During operation of a fusing system of this type, the receiver member to which the toner image is electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roller thereby to affect heating of the toner image within the nip. Typical of such fusing devices are two roller systems wherein a fuser roller is coated with an adhesive material, such as a silicone rubber; other low surface energy elastomers, such as a Viton® fluoroelastomers available from E. I. DuPont De Nemours of Wilmington, Del.; or other low surface energy material, such as tetrafluoroethylene polymer resins like, for example, Teflon® resins also sold by DuPont.  
         [0005]     In the foregoing fusing systems, however, since the toner image is tackified by heat, it frequently happens that a part of the image carried on the receiver member will be retained by the heated fuser roller and not penetrate into the receiver member surface. This tackified material can stick to the surface of the fusing roller and come in contact with a subsequent receiver member bearing another toner image to be fused. Thus, a tackified image, which has been partially removed from a first receiver member, may thereafter transfer to a subsequent second receiver member in non-image portions of the second receiver member. In addition, a portion of the tackified image of the second receiver member may also adhere to the heated fuser roller. In this way and with the fusing of subsequent sheets bearing toner images, the fuser roller can eventually become thoroughly contaminated and unusable, thereby requiring replacement of the fuser roller itself. In addition, since the fuser roller continues to rotate when there is no substrate bearing a toner image to be fused, toner that may be adhered to the fuser roller can be transferred from the fuser roller to the pressure roller, and also to other rollers and components associated with the fuser system, thereby contaminating the overall fuser system. The foregoing conditions are referred to generally in the printing/copying art as “offset”. Attempts have been made to control heat transfer to the toner and thereby control offset. However, even with adhesive surfaces provided by the silicone elastomers and the other materials mentioned hereinabove, this has not been entirely successful.  
         [0006]     It has also been proposed to provide toner release agents such as silicone oil, and in particular poly(organosiloxane) oils like poly(dimethylsiloxane), that are applied to the surface of the fuser roller to act as a polymeric release agent and thereby reduce offset. The use of such release agents is reported, for example, in U.S. Pat. Nos. 3,964,431 and 4,056,706, the teachings of which are incorporated herein by reference. These release agents possess a relatively low surface energy and have been found generally suitable for use in a heated fuser roller environment. In practice, a thin layer of poly(organosiloxane) oil (also referenced as silicone oil hereinafter) release agent is applied to the surface of the heated fuser roller to form an interface between the fuser roller surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser toning nip and thereby reduces the amount of toner which offsets to the fuser roller surface.  
         [0007]     Various methods are known for applying release agent materials to a fuser member such as a heated fuser roll. One such system comprises a Release Agent Management (RAM) system including a donor roll that contacts the fuser member to which the oil or release agent material is applied. The donor roll also contacts a metering roll, which conveys the oil from a supply of oil to the donor roll. With such a system, it is customary to use a metering blade to meter the silicone oil or other suitable release agent material to a desired thickness onto a metering roll. In the fusing of monochrome (i.e. black on a conventional imaging substrate) the uniformity of the oil layer on the metering roll is not so critical compared to that required for color toner images, particularly, those associated with transparency substrate materials used for optically projecting the color images.  
       SUMMARY OF THE INVENTION  
       [0008]     In view of the above, this invention is directed to a precision release agent management system for an electrostatographic reproduction apparatus fuser device. The precision release agent management system includes a reservoir adapted to contain a release agent. A wick absorbs release agent from the reservoir. A metering member receives release agent from the wick, which is supported for resiliently urging into operative contact with the metering member. A blade member is associated with the metering member to establish a desired thickness of release agent on the metering member, and a donor member is adapted to receive release agent from the metering member, and operatively contact the fuser device to apply the release agent thereto. A plurality of features is associated with the reservoir for precise alignment of he donor member, the metering member, and the metering blade.  
         [0009]     The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:  
         [0011]      FIG. 1  is a schematic, front, cross-sectional view of a fuser system incorporating the precision release agent management system in accordance with the present invention;  
         [0012]      FIG. 2  is an enlarged view, partly in cross-section, of the precision release agent management system in accordance with the present invention;  
         [0013]      FIG. 3  is a view, in perspective, of a precision locating frame for elements of the precision release agent management system of  FIG. 2 ;  
         [0014]      FIG. 4  is a front view, similar to  FIG. 2 , showing a take-up slot, and associated forces, to provide the metering roller of the precision release agent management systems of  FIG. 2  with a self-locking function; and  
         [0015]      FIG. 5  is a rear view, similar to  FIG. 2 , showing a spring loaded wick holder for the precision release agent management system of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     Referring to the accompanying drawings,  FIG. 1  shows an exemplary fuser system  10  for a typical electrostatographic reproduction apparatus. The fuser device  10  includes a fuser roller  20  and an elastomeric pressure roller  28 , which form a toning nip  30 . A supply of polymeric release agent  33  is shown provided in a polymeric release agent reservoir  34 . The fuser roller  20  can be made of any material known to the art and which employs an outer surface comprised of a material, which uses or can use a polymeric release agent as described hereinafter. Generally, the outer surfaces of the fuser roller  20  and pressure roller  28  comprise an elastomeric material, such as silicone elastomers, fluoroelastomers, and so-called interpenetrating networks of silicone and fluoroelastomers. Such materials are disclosed, for example, in the U.S. Patents previously incorporated herein by reference, as well as U.S. Pat. Nos. 5,141,788; 5,166,031; 5,281,506; 5,366,772; 5,370,931; 5,480,938; 5,846,643; 5,918,098; 6,037,092; 6,099,673; and 6,159,588, the teachings of which are also incorporated herein by reference. Another type of suitable material is a fluorocarbon-based, curable, thermoplastic random copolymer material, which in preferred embodiments utilize so-called THV thermoplastic fluoropolymers, such as those polymer materials disclosed in U.S. Patent Application entitled “FLUOROCARBON THERMOPLASTIC RANDOM COPOLYMER COMPOSITION”, U.S. Ser. No. 09/609,561, filed Jun. 30, 2000, the teachings of which are also incorporated herein by reference in their entirety.  
         [0017]     Particulate imaging material  40 , such as toner, disposed on a receiver  42  is fused into the receiver  42  at the fusing nip  30  by the application of heat and pressure. As shown, a heating lamp  44  is connected to a control circuit  46 . The heating lamp  44 , as known to those skilled in the art, may be provided inside the core of the fuser roller  20  as shown in  FIG. 1 . The fuser roller  20  can also be externally heated by a heated roller (not shown), which is opposed to and can ride along in frictional contact with the fuser roller  20 . This external heat source may replace or merely assist the internal lamp  44 . It should be understood, however, that depending on the particulate imaging material  40  used, in some cases only pressure may need to be applied to fuse particulate imaging material  40  into the receiver  42 .  
         [0018]     A wicking device  32  in a form including of a wick  36 , absorbs polymeric release agent  33  contained within reservoir  34 . The wick  36  conveys the polymeric release agent  33  from reservoir  34  by wicking action to a metering roller  48 , which contacts or is otherwise placed in close proximity to wick  36 . Due to the rotational action (as shown by the arrow within metering roller  48  in  FIG. 1 ) of metering roller  48 , such contact with wick  36  draws a thin film of the polymeric release agent  33  onto the exterior surface of metering roller  48 . A metering blade  49  is positioned above the polymeric release agent level in reservoir  34  and adjacent to metering roller  48  such that the amount of polymeric release agent applied and thickness of the film can be controlled to desired levels. The metering roller  48  can be positively driven, but is more conveniently driven by frictional contact with a release agent donor roller  50  as described hereinafter.  
         [0019]     Disposed in an opposed, contacting relationship and intermediate position between the fuser roller  20  and the metering roller  48  is a release agent donor roller  50 . The release agent donor roller  50 , due to rotational action (as shown by the arrow within donor roller  50  in  FIG. 1 ) and contact with metering roller  48 , receives the polymeric release agent  33  from metering roller  48  and delivers the polymeric release agent as a thin film to the outer surface of the fuser roller  20 . Fuser roller  20  due to rotational action (as shown by the arrow within fuser roller  20  in  FIG. 1 ) thereafter delivers the polymeric release agent to fusing nip  30 , such that the presence of the polymeric release agent on the surface of the fuser roller  20  thereby acts to prevent or at least substantially reduce offset of particulate imaging material  40  on the fuser roller surface  20 . A continuous supply of polymeric release agent  33  is provided, which is applied by the fuser roller  20  in an effective amount of from about  1  to about  20  milligrams per letter size receiver  42 , on which particulate imaging material  40  is fixed. This polymeric release agent  33  is discussed further hereinafter.  
         [0020]     Referring now to  FIG. 2 , the release agent donor roller  50  comprises a base member, which is generally in the form of a solid or hollow cylindrical shaft of any convenient diameter, typically from about 8 millimeters to 22 millimeters in diameter. Disposed on the base member is a polymeric outer layer, which layer can have a thickness that varies, but is preferably from about 3 about to about 6 millimeters thick. The outer layer can be thicker than the foregoing range or harder in durometer if desired to adjust for quality and thickness characteristics of the polymeric release agent  33  at the fusing nip  30 . Typically the donor roller  50  is from about 12 to 18 inches in length. The donor roller  50  can be positively driven, but is conveniently driven by frictional contact with fuser roller  20 .  
         [0021]     The release agent donor roller  50  is typically in the configuration of an economical, highly reliable, long life cylindrical roller which is preferably conformable with a fuser roller  20  and provides substantially uniform delivery of an effective amount of polymeric release agent  33  as previously described. The polymeric release agents employed with the fusing system can be any of those known to the art, such as those referenced in the U.S. Patents previously incorporated herein by reference. Preferably, the polymeric release agent  33  is a poly(Sloane) oil, most preferably a poly(dialkylsiloxane), and most preferably a poly(dimethylsiloxane) oil. Such poly(organosiloxane) oils can generally have a viscosity of from about 10 to about 200,000 centistokes (cts), and preferably, have a viscosity of from about 40 to about 15,000 cts as measured with a Brookfield viscometer at 25.degree. C. The poly(organosiloxane) oil in preferred embodiments also has functional groups in either a terminal position on the siloxane polymer chain, or pendant to such siloxane chain, or both, such as those polymeric release agents disclosed in U.S. Pat. Nos. 4,029,827; 4,101,686; 4,185,140; and 5,157,445 previously incorporated by reference, which groups can interact with the outer surface of the fuser roller  20  such that a thin film of the polymeric release agent is formed on the surface of such fuser roller. In preferred embodiments, the poly(organosiloxane) oil has functional groups, including carboxy, hydroxy, epoxy, isocyanate, thioether, hydride, amino, or mercapto groups, and more preferably hydride, amino or mercapto groups, to provide an interfacial barrier layer between the fusing surface and toner  40  on receiver  42 . Blends of such poly(organosiloxane) oils may also be used.  
         [0022]     The precision release management system according to this invention is generally designated in  FIG. 2  by the numeral  100 . Such system  100  includes the donor roller  50 , the metering roller  48 , the wick  36 , the metering blade  49 , and the reservoir  34  as described generally above with reference to  FIG. 1 . In order to provide the precision release agent management of the system  100 , these enumerated elements have to be maintained in a particular relationship over a substantial operating range to yield optimum operating characteristics.  
         [0023]     In order to create a streak free release agent film, the metering roller  48  needs to be contacted by the wick  36  in the manner as shown in  FIG. 2 . In addition, the wick  36  also needs to be urged against the metering roller  48  with a predetermined force to guarantee a streak free release agent film on the fuser roller  20 . According to one aspect of this invention, the wick force is generated by a wick-supporting bracket  36   a  that is free to rotate around a pivot pin  56  mounted in the system  100  (in the manner discussed below with reference to  FIG. 3 ). At least one, but preferably a pair of loading (compression) springs  58  is located at both cross-track ends of the bracket  36   a  (only one end shown in  FIG. 2 ). The loading springs  58  are supported on posts  58   a  and generate a wick loading force by urging respective U-shaped portions of the bracket  36   a , in a direction toward the metering roller  48  to urge the wick into engagement with the metering roller at a known predetermined force, substantially uniform along the length of the metering roller. This has the advantage that the wick load on the metering roller  48  is relatively constant over a range of wick thicknesses, caused for example by tolerances in the wick material and the compression of the wick over its life.  
         [0024]     Compared to a system with a fixed (i.e., non-pivoting) wick bracket, the precision release agent management system  100  of this invention, with the spring loaded wick bracket  36   a , induces a much lower drag torque on the metering roller  48 , and thus ultimately on the fuser roller  20 . Maintaining the system drag torque as low as possible is critical for the life of the fuser roller that gets contacted by the precision release agent management system  100 . It also enables the metering roller  48  and the donor roller  50  to rotate at substantially the same speed as the fuser roller  20 . By enabling a low system drag less than 5% speed difference can be achieved. That is, there is substantially no slippage between the rollers, which in turn guarantees consistent properties for the precision release agent management system  100 , and thus application of a consistent and uniform release agent film on the fuser roller  20 .  
         [0025]     A further aspect of this invention is that the precision release agent management system  100  provides accurate alignment (parallelism) of the three components of the system; i.e., the metering roller  48 , the donor roller  50 , and the metering blade  49  (and the metering blade holder  80  described hereinbelow with reference to  FIG. 4 ). Such alignment is necessary for the uniformity and stability of the release agent transfer rate in the system  100  and applied release agent film. Accordingly, guide plates  62 ,  64  are accurately located in, and fixed to, the housing of the reservoir  34  (see  FIG. 3 ). The guide plates  62 ,  64  have various precise locating features that take up and position the three mentioned components in precise alignment to each other. The precise locating features include a first cooperating pair of slots  66   a ,  66   b , a second cooperating pair of slots  68   a ,  68   b , and a plurality of precisely spaced through bores  70   a - 70   b , all positioned at predetermined locations relative to one another in the guide plates  62 ,  64 . The first pair of slots  66   a ,  66   b  is adapted to receive the ends of the donor roller shaft  50   a . The second pair of slots  68   a ,  68   b  is adapted to receive the ends of the metering roller shaft  48   a . The through bores  70   a - 70   e  are adapted to receive pins (not shown) for the metering blade holder  80 . As such, when the shafts  50   a  and  48   a  are respectively received in the slots 68   a ,  68   b  and  66   a ,  66   b , and the pins of the metering blade holder  80  are received in the bores  70   a - 70   e , the elements of the precision release agent management system  100  are precisely located relative to one another and are maintained in such precise arrangement. Any adjustment beyond that provided by these features is therefore not necessary.  
         [0026]     The alignment is especially important between the metering blade and the metering roller so that the load between the metering blade edge and the metering roller is consistent, which is vital for a uniform release agent film thickness.  
         [0027]     In order to keep the properties of the precision release agent management system  100  consistent, it is important that during operation the metering roller  48  stays locked in place. On the other hand, the metering roller  48  needs to be easily removable for serviceability of the precision elements of the release agent management system  100 . The arrangement of the features, described with reference to  FIG. 3 , provides for the force F 1  (load of the metering blade 49  on the metering roller  48 ), force F 2  (load of the wick  36  on the metering roller  48 ), the weight F 3  of the metering roller  48 , and the geometry of the metering roller take up slot  68   a ,  68   b  assures that the metering roller  48  is always locked in its place during operation without requiring any additional lock down mechanisms. This arrangement also assures that the removal of the metering roller  48  for system serviceability is easy and quick. For a low drag precision release agent management system  100  given a 12 inch metering roller  20  to achieve a 1 to 2 lb drag the wick load F 2  needs to be 6 to 9 lbs. Likewise to achieve a low metering blade drag in the order of 3.5 to 5.0 oz the blade  49  load F 1  needs to be 4.5 to 6.5 lb.  
         [0028]     In still another aspect of this invention, the metering blade  49  is contained in the metering blade holder  80  in the described manner. The metering blade holder  80  includes a blade holder arm  82 , a blade retainer element  84 , and a loading cup  86 . These blade holder elements are rigidly connected to form a loading arm assembly. The pivot point  88  of this assembly is the pivot point of the blade retainer element  84 . By rotating the loading arm assembly clockwise around its pivot point  88 , the metering blade  49  is loaded against the metering roller  48 . The actual loading force is provided by a compression spring  90  that rests on a base plate  92  coupled to the housing of the reservoir  34 . The compression spring  90  is constrained for movement about a spring retaining stud  94  that keeps the spring  90  in place and engagement with a washer  96  that slides on the spring retaining stud  94 . The action of the spring  90  and the washer  96  transmits a loading force to loading cup  86  and thus the loading arm assembly. That is, in the assembled position, as shown in  FIG. 5 , the loading cup  86  of the loading arm assembly exerts a force on the washer  96  to compress the compression spring  90 , which creates a reaction force that urges the loading arm assembly in a direction that loads the metering blade  49  against the metering roller  48 .  
         [0029]     The load of the metering blade  49  on the metering roller  48  is thus the product of the compression spring  90  and the rubber material of the metering blade  49 . The force that is critical for the appropriate desired rate of the release agent on the metering roller  48  is the force on the edge of the metering blade  49  that contacts the metering roller surface. The balance of the compression spring  90  and the rubber material of the metering blade  49  determines this edge force (blade load), where the spring constant of the compression spring  90  is much lower than the spring constant of the rubber material of the metering blade  49 . The advantage of this blade loading system is that the blade load can be held sufficiently constant despite any tolerances in the parts involved, because slight changes in the deflection of the compression spring  90  causes only little changes in the force it puts out. On the other hand, if the metering blade were loaded up by displacement of the loading arm assembly, slight changes of this displacement, caused by tolerances, would cause significant changes in the metering blade load and would thus change the rate of the release agent significantly as well.