Abstract:
The present invention includes a method of sealing a toner supply to a developer sleeve including the steps of introducing a static-electric charge on toner particles to create charged toner particles and inducing an attractive charge onto each end of the developer sleeve. The static-electric charge and the attractive charge result in toner particles being attracted to the ends of the developer sleeve which create a barrier of charged toner particles to prevent leakage of the charged toner particles.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to imaging devices and specifically to the reduction or elimination of toner leakage past toner seals in imaging devices through the use of capacitive or static charge.  
         BACKGROUND  
         [0002]    Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form the desired image on the print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure.  
           [0003]    [0003]FIG. 7 is a diagram of typical laser printing device  700  employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles  701  is held in toner supply hopper  702 . Toner particles  701  are typically small plastic (e.g., styrene) particles on the order of 5 microns (10 −6  meter) in size. Agitator (or stirring blade)  703  is typically made of plastic such as mylar and ensures toner particles  701  are uniformly positioned along developer sleeve  705  while inducing a negative charge onto the toner particles in the range of −30 to −80 micro coulomb per gram (μc/g). Developer sleeve  705  rotates in a counterclockwise direction about an internal stationary magnet  704  acting as a shaft. Toner particles  701  are attracted to the rotating developer sleeve  705  by the magnetic forces of stationary magnet  704 . Doctor blade  706  charges the toner and metes out a precise and uniform amount of toner particles  701  onto developer sleeve  705  as its outer surface rotates external to toner supply hopper  702 . Developer sealing blade  707  removes excess toner particles  701  affixed to developer sleeve  705  as its outer surface rotates back into toner supply hopper  702  and prevents toner particles  701  from falling out of toner supply hopper  702  onto paper, along the length of developer sleeve  705 .  
           [0004]    Primary charging roller (PCR)  708  conditions organic photoconductor (OPC) drum  709  using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum  709 . Production of the uniform charge by PCR  708  also has the effect of erasing residual charges left from any previous printing or transfer cycle.  
           [0005]    A critical component of the EP process is OPC drum  709 . OPC drum  709  is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PCR  708 . Initially, the unexposed surface potential of the OPC is charged to approximately −600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a charge transport layer (CTL), charge generation layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the underlying aluminum substrate.  
           [0006]    Scanning laser beam  710  exposes OPC drum  709  one line at a time at the precise locations that are to receive toner (paper locations which correspond to dark areas of the image being printed). OPC drum  709  is discharged from −600V to approximately −100V at points of exposure to laser beam  710 , creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles  701  are magnetically attracted to rotating developer sleeve  705 . Alternatively, if a nonmagnetic toner is used, developer sleeve  705  may comprise a developer roller to mechanically capture and transport toner particles  701 . In this case, an open cell foam roller may be included to apply toner to developer sleeve  705 . The still negatively charged toner particles held by developer sleeve  705  are attracted to the relatively positively charged areas of the surface of OPC drum  709  and “jump” across a small gap to the relatively positively charged latent image on OPC drum  709  creating a “developed” image on the drum.  
           [0007]    Paper to receive toner from OPC drum  709  is transported along paper path  711  between OPC drum  709  and transfer roller  712 , with the developed image transferred from the surface of OPC drum  709  to the paper. The transfer occurs by action of transfer roller  712  which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles and causing them to move onto the paper. Wiper blade  713  cleans the surface of the OPC drum  709  by scraping off the waste (untransferred) toner into waste hopper  715 , while recovery blade  714  prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller  716  and pressure roller  717  where the toner is melted and fused (or “bonded”) to the paper. Heated roller  716  and pressure roller  717  are together referred to as the fuser assembly.  
           [0008]    Referring to FIG. 8, color printing follows a slightly different procedure in that a foam roller  801  (1 of 4) is used to deposit particular color toner particles (e.g., CMYK: cyan, magenta, yellow and black) onto developer roller  802  for the corresponding color. Foam roller  801  is made of an open cell foam with bias, while developer roller  802  has a coated exterior charged with a bias of between −350 to −450 VDC.  
           [0009]    One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner from the hopper. Leakage sometimes occurs at the ends of developer sleeve  705  (FIG. 7). Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer sleeve  705 . Some printers employ a foam or felt mechanical seal at the ends of developer sleeve  705  as a physical barrier to prevent toner particles from slipping past the interface between developer sleeve  705  and toner supply hopper  702 . Alternatively, when the toner exhibits magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer sleeve  705  to attract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Unfortunately such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.  
           [0010]    Accordingly, a need exists for a structure and method for reducing toner leakage in a toner cartridge.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention includes a method of sealing a toner supply to a developer sleeve, the method including the steps of introducing a static-electric charge on toner particles to create charged toner particles and inducing an attractive charge onto each end of the developer sleeve. The static-electric charge and the attractive charge result in toner particles being attracted to the ends of the developer sleeve which create a barrier of charged toner particles to prevent leakage of the charged toner particles.  
           [0012]    Another embodiment of the present invention is directed at a sealing apparatus for sealing an interface between a toner supply and a developer sleeve. In this embodiment the invention includes electrostatically charged toner particles and a charged seal on each end of the developer sleeve. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a side view of a toner hopper and includes a developer roller and seal according to an embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a sectional side view of a developer roller and seal arrangement according to an embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a longitudinal sectional view of a developer roller and seal arrangement according to an embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a view of developer roller and seal as viewed from inside a toner supply hopper;  
         [0017]    [0017]FIG. 5 is an exploded perspective view of a developer roller in mating relationship with an end seal at or close to one end of the developer roller;  
         [0018]    [0018]FIG. 6 is a flow chart of a method according to one embodiment of the present invention;  
         [0019]    [0019]FIG. 7 is side view of a simplified cartridge cross-section according to the prior art; and  
         [0020]    [0020]FIG. 8 is a side view of a simplified cartridge cross-section for color toner particles according to the prior art.  
     
    
     DETAILED DESCRIPTION  
       [0021]    The present invention addresses, inter alia, a need to reduce or eliminate leakage of color and other toner particles from printers, copiers, and similar devices. In particular, the invention is applicable to non-magnetic toners, although may be used alone or in combination with magnetic seals and magnetic toner.  
         [0022]    Color toner particles typically do not include iron oxide present in many monochromatic toners and are therefore not magnetic. Therefore magnetic seals cannot normally be used to reduce or eliminate leakage in color print engines. While foam and felt seals have been used, toner being highly fluid, still leaks past these seals. The present invention preferably introduces an electrostatic charge into the toner particles and preferably uses a capacitative charged seal at each end of the developer sleeve to reduce or eliminate the leakage of toner particles. The positively charged capacitative seal attracts electrostatically negatively charged toner particles to build and maintain a physical barrier of toner particles. The strength of the capacitative charge (e.g., voltage applied) may be varied to increase or decrease the size of the toner barrier to prevent toner leakage. Proper balancing of electrostatic charge introduced into the toner particles and the capacitative charge present on the capacitative charged seals ensures a barrier sufficient to prevent toner leakage, while limiting the width of the barrier along the sleeve to allow printing on the entire printable surface.  
         [0023]    [0023]FIG. 1 is an end view of one embodiment of the present invention sectioned near an end of the cartridge including a toner hopper  101 , an agitator  102 , a capacitative end seal  105  and the developer sleeve  103  of a developer roller  108 . Non-magnetic toner particles  107  are held in toner hopper  101 . As agitator  102  rotates within toner hopper  101  an electrostatic charge of about −30 to −40 μc/g is created and transferred to non-magnetic toner particles  107 . Capacitative end seal  105 , preferably biased to about +50V, is included on each end of developer sleeve  103  surrounding central shaft  104  (see FIG. 5). Positively charged capacitative end seal  105  attracts the negatively charged non-magnetic toner particles  107 , and creates a physical barrier to prevent leakage by, at least in part, holding the toner particles to form a dam. Power supply  106  provides DC power for capacitative end seal  105 . Note that, although the present embodiment assumes a nonmagnetic toner, it is equally applicable to magnetic toners and, in such case, is preferably used instead of or in addition to conventional magnetic toner traps or seals. Further, note that the bias voltage is selected to provide a good seal, but still allow the printing across the entire sheet of paper. The size of the dam depends on the bias voltage, the greater the bias voltage, the larger the dam, and vice versa. Thus, the voltage may be varied by the printer&#39;s processor based on the paper size being used, e.g., A4, 8½ inch, 11 inch, etc., and/or the roller size.  
         [0024]    [0024]FIG. 2 is a sectional view of a developer roller  204  including developer sleeve  103  and central shaft  104 , and shows an outer surface of developer sleeve  103  in contact with end seal  105 . As shown, end seal  105  may include an outer insulator  202  surrounding an inner conductor  201 . Outer insulator  202  is preferably made of or includes a deformable material such as foam, felt, nylon brushes, or other suitable sealing material, that conforms to developer sleeve  103  and provides a physical barrier to toner migration past the seal. If the sealing material is not itself a good electrical insulator, then a separate insulating film (not shown) may be used between the sealing material and conductor  201 . Conductor  201  may be made of a variety of conductive materials such as copper, aluminum or a metal impregnated plastic such that a positive charge can be stored and maintained.  
         [0025]    Conductor  201  is positively charged by connecting it to an appropriate voltage source  106  (not shown) via wire  203  as shown in the longitudinal sectional view of FIG. 3. The positive electrostatic field created in the vicinity of conductor  201  attracts the negatively charged toner particles, causing them to create a trap region or dam  301  along an inner surface of end seal  105  and onto an adjacent portion of developer roller  204 . Since the toner particles are electrically isolated from inner conductor  201  by outer insulator  202 , an electrostatic differential is maintained and reinforced as further negatively charged toner particles collect.  
         [0026]    [0026]FIG. 4 is a view of developer roller  204  viewed from a position inside toner supply hopper  101  and showing a buildup of toner particles forming dam  301  at an interface between end seal  105  and developer roller  204 .  
         [0027]    [0027]FIG. 5 is an exploded perspective view of developer roller  204  as it mates with end seal  105  at or close to one end of the roller. Although not shown, a similar end seal is positioned at the far end of developer roller  204  to contain toner and inhibit it from leaking out through that end of the toner cartridge assembly.  
         [0028]    [0028]FIG. 6 is a flow chart depicting the steps required to create and use the toner barrier of the present invention. In step  601  a negative electrostatic charge is introduced into the non-magnetic toner particles by, for example, an agitating device as shown in FIG. 1 as  102 . In step  602  a capacitative charged seal is included on each end of the developer seal. The electrical characteristics of the electrostatically charged non-magnetic toner particles and the capacitative charged seal are adjusted so that toner particles are attracted to the capacitative charged seals in step  603 . This attraction creates a physical barrier, made up, at least in part by the toner particles, in step  604 , which reduces or eliminates leakage of toner from the device.