Abstract:
The present invention includes a removable cover used to isolate a photoconductor drum from at least one other component in a toner cartridge. The photoconductor drum includes a cylinder coated with a photoconductive substance. Another embodiment includes a method of reducing electrostatic charges on the photoconductor drum including the steps of isolating the photoconductor drum from other components in a toner cartridge with a removable cover, removing the removable cover prior to insertion of the toner cartridge into an image device and inserting the toner cartridge into the image device.

Description:
TECHNICAL FIELD 
     The present invention is generally related to toner cartridges in imaging devices and specifically to the reduction or elimination of electrostatic charge buildup on toner cartridges during transit. 
     BACKGROUND 
     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 a desired image on a print medium, which is usually some type of paper. Once the toner particles are applied to the paper, the paper is advanced along a 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, the toner particles are fused to the paper through a process of heat and pressure. 
     FIG. 4 is a diagram of a typical laser printing device  400  employing an electrophotography (EP) process. For monochromatic printing, a single color of toner particles  401  (e.g., black) are held in a toner supply hopper  402 . The toner particles  401  are typically small plastic (e.g., styrene) particles on the order of 5 microns (10 −6 ) meter in size. An agitator, or stirring blade,  403  is provided in the toner supply hopper  402  and is typically made of plastic or mylar and ensures toner particles  401  are uniformly positioned along a developer sleeve  404  while inducing a negative charge onto the toner particles  401  in the range of −30 to −40 micro coulomb per grami (μc/g). The developer sleeve  404  rotates in a counterclockwise direction about an internal stationary magnet  405  which acts as a shaft. The toner particles  401  are attracted to the rotating developer sleeve  404  by the magnetic forces of the stationary magnet  405 . A doctor blade  406  helps in charging toner particles  401  and meters out a precise and uniform amount of toner particles  401  onto developer sleeve  404  as its outer surface rotates external to toner supply hopper  402 . A developer sealing blade  407  removes excess toner particles  401  affixed to developer sleeve  404  as its outer surface rotates back into toner supply hopper  402 . 
     A primary charging roller (PCR)  408  conditions an organic photoconductor (OPC) drum  409  using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum  409 . Production of the uniform charge by PCR  408  also creates the effect of erasing residual charges left from a previous cycle. 
     A major component of the EP process is OPC drum  409 . OPC drum  409  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  408 . Initially, the unexposed surface potential of the OPC drum  409  is 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 cylinder or 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 drum  409 . 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 aluminum substrate. 
     A laser beam  410  exposes OPC drum  409  one line at a time at the precise locations that will receive toner particles  401  (paper locations which correspond to the image being printed). OPC drum  409  is discharged from −600V to approximately −100V at points of exposure to laser beam  410 , creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles  401  are magnetically attracted to rotating developer sleeve  404 . Alternatively, if nonmagnetic toner is used, developer sleeve  404  may comprise a foam roller to mechanically capture toner particles  401 . In this case, an open cell foam roller may be included to apply toner to developer sleeve  404 . The still negatively charged toner particles  401  held by developer sleeve  404  are attracted to the relatively positively charged areas of the surface of OPC drum  409  and “jump” across a small gap to the relatively positively charged latent image on OPC drum  409  creating a developed image. 
     Paper to receive toner particles  401  from OPC drum  409  is transported along paper path  411  between OPC drum  409  and transfer roller  412 , with the developed image transferred from the surface of OPC drum  409  to the paper. The transfer occurs by action of transfer roller  412  which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles  401  to move to the paper. A wiper blade  413  cleans the surface of the OPC drum  409  by scraping off the waste (untransferred) toner into waste hopper  415 , while recovery blade  414  prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles  401 , is passed through a nip region between heated roller  416  and pressure roller  417  where the is toner particles  401  are melted and fused (or “bonded”) to the paper. Heated roller  416  and pressure roller  417  are together referred to as a fuser assembly. 
     During shipping of a toner cartridge, internal parts such as OPC drum  409 , PCR  408 , transfer roller  412 , and developer roller sleeve  404 , may rub relative to each other thereby creating static charges. Large static charges may become trapped in the organic photoconductor (OPC) on OPC drum  409  and cause a defect in printer operations when the toner cartridge is positioned in an imaging device such as a printer or copier. This effect is called “plus charge memory” or “rubbed memory.” Rubbed memory may be negative or positive. A negative charge trapped inside of the organic photoconductor (OPC) will create a repelling action leaving a portion of OPC drum  409  uncharged. Uncharged portions of OPC drum  409  may result in non-printed areas on a printed page. 
     During normal operation PCR  408  is arranged to uniformly charge the surface of OPC drum  409 . However, the charge trapped during transit in the organic material of OPC drum  409  disrupts the constant charge field transferred from PCR  408 . This causes a non-uniform charge across the surface of OPC drum  409  resulting in uneven print density and other defects on a printed page. Thus, to eliminate these printing defects it is necessary that a constant charge be applied to OPC drum  409  prior to modulation of the charge by a laser or projected image. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system which uses a removable cover to isolate an organic photoconductor from at least one other component of a toner cartridge. The present invention also includes a method of reducing electrostatic charge on a photoconductor including the steps of isolating the photoconductor from other components in a toner cartridge with a removable cover, removing the removable cover prior to insertion of the toner cartridge into an electrophotographic printing device and inserting the toner cartridge into the device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a simplified cartridge in cross-section with a removable cover according to the present invention in place; 
     FIG. 2 shows a flow diagram of a method of reducing or eliminating plus charge memory; 
     FIG. 3 is a perspective view of a cover for an OPC drum including a conductive layer according to an embodiment of the invention; 
     FIG. 4 is a side view of a simplified cartridge cross-section of the prior art; and 
     FIG. 5 is a cross-section of a cover material including a conductive layer. 
    
    
     DETAILED DESCRIPTION 
     During shipping and handling of toner cartridges, vibrations cause various components of a toner cartridge to rub against each other possibly resulting in a buildup of electrostatic charges. These electrostatic charges may become trapped inside or on a photoconductor roller such as OPC drum  102  (FIG.  1 ). The present invention prevents or eliminates these electrostatic charges by mechanically and electrically insulating the photoconductor roller from surrounding structures of the toner cartridge. The reduction or elimination of these charges prevents or reduces defects on printed materials resulting from the accumulation of these charges. 
     Extensive efforts have been directed to minimize the type and extent of rubbing between components with packaging design changes and boxes designed to reduce vibrations. The present invention isolates one of the components, preferably by enveloping that component in a packaging material preferably a resilient foam, or similar electrically isolating material, such as a thin film during shipping. This material is designed to be easily removed prior to or as part of inserting the toner cartridge into a printer. 
     This insulated packing layer may also be connected to an existing toner dam provided in toner cartridges. Removal of this toner dam is required to start the toner to flow into the developer area. Typically, a pull tab  111  (FIG. 1) is connected to the internal toner dam that must be removed before the toner cartridge is used in the printer. Similarly, a temporary protective removable cover (hereinafter simply a “removable cover”) of the present invention must also be removed before the toner cartridge is inserted into the printer or at least prior to. use of the toner cartridge should removal be possible after insertion and installation. 
     The removable cover preferably slides in-between the OPC drum  102  and any other component which may contact it. The present invention may further include an electrical connection  112  to a ground to drain charges which may build up on the removable cover. This may be accomplished by laminating conductive material, such as an aluminum film, to the removable cover. 
     The removable cover functions to reduce or eliminate high voltage electrostatic charges on the order of 250 or more volts. Voltages of this magnitude may be caught or trapped in the organic materials of the OPC drum  102 . Used in combination with electrical drains included in the packaging and/or the chassis of the printer, the removable cover bleeds off most or all of this static charge to reduce or eliminate charges trapped in or on the OPC drum  102 . 
     Referring to FIG. 1, a removable cover  101  is installed during assembly so as to almost completely encircle OPC drum  102 , positioned between OPC drum  102  and one or more of the following components: primary charge roller (PCR)  103 , cleaning blade  104 , wiper blade  105 , transfer roller  106 , and developer roller  107 . As its primary function, removable cover  101  isolates OPC drum  102  from these other components to reduce or eliminate the generation of static charges. Removable cover  101  may be made of a foam material such as polyurethane and may include a conductive laminate made of, for example, an aluminum film. The cushioning provided by the foam of removable cover  101  helps dampen vibration between the components. The removable cover  101  may also drain away to ground any remaining charge generated by components rubbing together if the conductive laminate is included. Thus, the conductive layer is grounded to packaging material so that any electrostatic charge drains off away from OPC drum  102  to ground. 
     The removable cover  101  may be connected to toner dam  108 , by a tab  111  or other structure. During shipping, both removable cover  101  and toner dam  108  remain in place and are only removed immediately before the toner cartridge is installed into the printer or, after installation if the configuration permits. Removable cover  101  may be removed in a direction indicated by arrow  109  and toner dam  108  may be removed in a direction indicated by arrow  110 . If the two are interconnected, as discussed above, removal of one will serve to remove the other. 
     FIG. 2 is a diagram of a method of reducing or eliminating charge memory, a component of a printing system. In step  201  an insert, such as a foam insert, is placed between an organic photoconductor OPC drum  102  (FIG. 1) and at least one other system component which together with the OPC drum  102  may generate an electrostatic charge during shipment. In a preferred embodiment a removable cover or insert  101  (FIG. 1) electrically isolates OPC drum  102  from all other system components. An insert tab may be included on the insert  101  to assist in its removal. This insert tab may be connected to a pull tab  111  preventing toner leakage during shipment or transit in step  201 . The insert  101  may include a conductive layer  302  (FIG. 3) which is attached to ground in step  203 . The toner cartridge is shipped in this protected shipping configuration in step  204 . Before the toner cartridge is used, the insert  101  is removed in step  205  together with a toner dam  108  in step  206 . If the insert  101  is connected to toner dam  108 , these may be removed simultaneously. A single pull tab  111  may be connected to both toner dam  108  and insert  101  for ease of removal. In step  207  the toner cartridge is placed in the printer and the printer is operated in step  208 . 
     FIG. 3 shows one possible construction of an alternate embodiment of the removable cover  300  including a laminated construction. In this embodiment the inner foam characteristics of a first laminate  301  help absorb vibration and provide a physical barrier between components, and the conduction properties of a second laminate or conductive layer  302  act to drain to ground any built up static charges. Alternatively, removable cover  300  may be composed of a conductive laminate foam formed on both sides. End  303  of removable cover  300  slides into the toner cartridge. 
     FIG. 5 shows a cross section of a cover material including a conductive layer.