Patent Publication Number: US-2010129120-A1

Title: Developing Device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Japanese Patent Application No. 2008-299559, which was filed on Nov. 25, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing device which comprises a development roller configured to carry liquid toner, and a cleaning blade configured to scrape off the liquid toner carried on the development roller. 
     2. Description of Related Art 
     A developing device comprising a development roller is known, in which liquid toner made by mixing toner particles in a carrier liquid is carried on the development roller. The development roller supplies an electrostatic latent image formed on a photoconductor drum with toner particles in the liquid toner, so that a toner image is formed on the photoconductor drum. In this developing device, if liquid toner is newly coated or applied on liquid toner remaining on the development roller after the development roller supplies the electrostatic latent image on the photoconductor drum with part of the toner particles in the liquid toner (i.e., after development), the thickness of the liquid toner layer on the development roller becomes nonuniform, which leads to deterioration in the obtained image quality. For this reason, it is necessary to scrape off the liquid toner remaining on the development roller after development. 
     For the purposes of improving the development efficiency from the development roller to the photoconductor drum as well as preventing toner particles from adhering to a non-latent image area, an operation for applying an electric field to the liquid toner layer on the development roller before development so that the toner particles coagulate on a surface of the development roller, which is so-called compaction, is generally carried out. However, because of this compaction, the carrier liquid is separated from the toner particles and the toner particles coagulate on the surface of the development roller, so that when the liquid toner after the development is scraped off by means of the cleaning blade, the separated carrier liquid flows across the surface of the cleaning blade and the aggregated toner particles remain at the edge of or on the surface of the cleaning blade. The size of the aggregated toner particles is thus increased, and disadvantageously the collection and reuse of the toner cannot be performed. 
     In order to overcome the above disadvantage, for example, Japanese Laid-open Patent Publication No. 2006-30719 discloses a developing device which comprises an electric field roller disposed apart from a development roller at a predetermined interval, and a cleaning blade provided downstream from the electric field roller with respect to a rotating direction of the development roller and configured to scrape off the liquid toner carried on the development roller by the rotation of the development roller. According to this developing device, an electric voltage is applied to the electric filed roller, and the electric field roller and the development roller rotate in the same direction; that is, the electric field roller and the development roller rotate in such a direction that their opposing surfaces move in the opposite directions to each other (i.e., against rotation). Therefore, aggregation of toner particles will be weakened. 
     However, even if the development roller and the electric field roller make an against rotation, in some cases, it may be insufficient to weaken the aggregation of toner particles on the surface of the development roller. 
     In view of the above, the present invention seeks to provide a developing device, which can disaggregate the toner particles carried on the development roller after compaction and development in a simple configuration and which can collect and reuse the liquid toner in a simple way. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a developing device comprises: a development roller configured to rotate while carrying liquid toner which comprises a carrier liquid and toner particles contained in the carrier liquid; a cleaning blade configured to contact with the development roller to scrape off the liquid toner carried on the development roller by the rotation of the development roller; and a cleaning roller provided adjacent to the development roller and upstream from the cleaning blade with respect to a rotating direction of the development roller. In this developing device, the development roller and the cleaning roller are configured to rotate in such a direction that outer peripheral surfaces thereof move in opposite directions to each other at a contact surface where the cleaning roller contacts with the development roller. 
     With this configuration of the present invention, the development roller and the cleaning roller are configured to contact with each other while allowing rotations of the development roller and the cleaning roller, and at their contact surface the development roller and the cleaning roller rotate in the opposite directions. This enables the cleaning roller to reliably scrape off the toner particles that have been carried on the development roller by means of compaction. Further, even if toner particles remaining on the development roller pass through between the cleaning roller and the development roller at the contact surface, toner particles which travel with the development roller by the rotation of the development roller and toner particles which travel with the cleaning roller by the rotation of the cleaning roller collide with each other, so that the toner particles carried on each roller are well dispersed into the carrier liquid. 
     The toner particles are dispersed in the carrier liquid, and this can prevent the toner particles from accumulating at the end face of the cleaning blade. Therefore, it is possible to collect and reuse the carrier liquid and the toner particles scraped off by the cleaning roller and the cleaning blade in a simple way. Further, since it is not necessary to apply an electric voltage to the cleaning roller, an aggregation of the toner particles carried on the development roller can be disaggregated in a simple configuration without requiring an electric voltage applying means. 
     According to the present invention, the toner particles are well dispersed in the carrier liquid by a simple configuration that the development roller and the cleaning roller are configured to rotate in such a direction that outer peripheral surfaces thereof move in opposite directions to each other at the contact surface where the cleaning roller contacts with the development roller. Therefore, it is possible to disaggregate the toner particles carried on the development roller after compaction and development in a simple configuration, and also to collect and reuse the liquid toner in a simple way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To better understand the claimed invention, and to show how the same may be carried into effect, reference will now be made, by way of example only to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a laser printer; and 
         FIGS. 2A to 2C  show the operation of a cleaning mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT 
     A detailed description will be given of an exemplary embodiment of the present invention with reference to the drawings. 
     Overall Configuration of Laser Printer  
     As seen in  FIG. 1 , a laser printer  1  mainly includes a process unit  5  configured to transfer a toner image onto a sheet P. Although not shown in the drawings, the laser printer  1  also includes other known equipment, such as a sheet feed unit configured to feed a sheet P to the process unit  5 , an exposure device configured to expose a photoconductor drum  51  with light, and a fixing device configured to thermally fix a toner image that has been transferred onto a sheet P. 
     The process unit  5  mainly includes a photoconductor drum  51 , a charger  52 , a liquid toner reservoir  53 , a supply roller  54 , an intermediate roller  55 , a development roller  56 , a compaction charger  57 , a cleaning mechanism  58 , and a transfer roller  59 . Details of the cleaning mechanism  58  will be described later, and other components will be described below. 
     The photoconductor drum  51  is a drum-shaped organic photoconductor, and an outer peripheral surface of the photoconductor drum  51  functions as an image carrying surface on which an electrostatic latent image is formed. The photoconductor drum  51  rotates in the counterclockwise direction of  FIG. 1  when it is powered by a motor (not shown). 
     The charger  52  is disposed opposite to and apart from the photoconductor drum  51  at a predetermined interval. The charger  52  is configured to uniformly charge the surface (image carrying surface) of the photoconductor drum  51 . 
     The liquid toner reservoir  53  is a reservoir for storing liquid toner LT. The liquid toner LT contains toner particles mixed in a nonvolatile carrier liquid. The liquid toner LT stored in the liquid toner reservoir  53  is supplied onto the development roller  56  via the supply roller  54 , etc., and is collected from the development roller  56  by means of the cleaning mechanism  58 . The collected liquid toner LT returns to the liquid toner reservoir  53  after readjustment of the concentration thereof. 
     The supply roller  54  rotates in the clockwise direction of  FIG. 1  when it is powered by the motor (not shown). The supply roller  54  is configured such that the liquid toner LT stored in the liquid toner reservoir  53  is carried on the surface of the supply roller  54  and supplied onto the intermediate roller  55  by the rotation of the supply roller  54 . 
     The intermediate roller  55  is a roller having recesses on an outer peripheral surface thereof so that a predetermined amount of the liquid toner LT is carried in the recesses. The intermediate roller  55  rotates in the counterclockwise direction of  FIG. 1  when it is powered by the motor (not shown). Since the liquid toner LT is supplied onto the development roller  56  via the intermediate roller  55 , the development roller  56  is always supplied with a constant amount of liquid toner LT. 
     The development roller  56  is a roller having an outer peripheral surface configured to carry the liquid toner LT. The development roller  56  rotates in the clockwise direction of  FIG. 1  when it is powered by the motor (not shown). The development roller  56  contacts with the photoconductor drum  51  so that toner particles contained in the liquid toner LT that is carried on the development roller  56  are supplied onto an electrostatic latent image formed on the photoconductor drum  51 , to thereby form a toner image on the photoconductor drum  51 . The development roller  56  is made of a material (e.g., urethane rubber) softer than that of a cleaning roller  58 B to be described later. 
     The compaction charger  57  is configured to apply an electric field to the liquid toner LT carried on the development roller  56  so that the toner particles in the carrier liquid are pressed against (aggregated at) the surface of the development roller  56 . 
     The transfer roller  59  is a roller arranged opposite to the photoconductor drum  51  so as to nip therebetween a sheet P conveyed from the sheet feed unit. A toner image formed on the photoconductor drum  51  is transferred onto the sheet P when the sheet P passes through between the transfer roller  59  and the photoconductor drum  51 . 
     In the process unit  5  configured as described above, the surface of the photoconductor drum  51  is uniformly charged by the charger  52 , and is exposed to a laser beam LB emitted from the exposure device. Therefore, the electric potential of the exposed areas lowers, so that an electrostatic latent image associated with an image data is formed on the surface of the photoconductor drum  51 . In the meantime, the liquid toner LT stored in the liquid toner reservoir  53  is supplied onto the development roller  56  via the supply roller  54  and the intermediate roller  55 . 
     Thereafter, toner particles contained in the liquid toner LT carried on the development roller  56  are supplied onto the electrostatic latent image formed on the photoconductor drum  51 , so that a toner image corresponding to the electrostatic latent image is formed on the photoconductor drum  51 . The toner image formed on the photoconductor drum  51  is then transferred onto the sheet P when the sheet P conveyed from the sheet feed unit is nipped and passes through between the photoconductor drum  51  and the transfer roller  59 . 
     Configuration of Cleaning Mechanism  
     Next, the configuration of the cleaning mechanism  58  will be described in detail. 
     As seen in  FIG. 1 , the cleaning mechanism  58  includes a cleaning blade  58 A and a cleaning roller  58 B. 
     The cleaning blade  58 A contacts with the development roller  56  to scrape off the liquid toner LT carried on the development roller  56  by the rotation of the development roller  56 . To be more specific, the cleaning blade  58 A is positioned adjacent to the development roller  56  and downstream from a contact surface between the development roller  56  and the photoconductor drum  51  with respect to the rotating direction of the development roller  56 , so that the liquid toner LT remaining on the development roller  56  can be scraped off after a part of, the toner particles is supplied from the development roller  56  onto the photoconductor drum  51  (i.e., after development). 
     The cleaning roller  58 B is a metal roller. The cleaning roller  58 B is positioned to contact with the development roller  56  while allowing rotation of the development roller  56 . The cleaning roller  58 B is positioned upstream from the cleaning blade  58 A with respect to the rotating direction of the development roller  56 . To be more specific, the cleaning roller  58 B is pressed against the development roller  56  made of a material softer than that of the cleaning roller  58 B in such a manner as to cause the outer peripheral surface of the development roller  56  to deform inward (see  FIG. 2A ). In this condition, the cleaning roller  58 B rotates in the same direction as the development roller  56  does (i.e., clockwise direction of  FIG. 2A ) when it is powered by the motor (not shown). In other words, the development roller  56  and the cleaning roller  58 B rotate in such a direction that their opposing surfaces F 1 , F 2  (see  FIG. 2A ) move in the opposite directions to each other at the contact surface where the cleaning roller  58 B contact with the development roller  56 . 
     Operation of Cleaning Mechanism  
     Next, the operation of the cleaning mechanism  58  will be described in detail with reference to  FIGS. 2A to 2C . For the purpose of explanation, the amount of an inward deformation of the development roller  56  caused by the cleaning roller  58 B and the size of toner particles are shown in an exaggerated manner. 
     As seen in  FIGS. 2A and 2B , the liquid toner LT remaining on the development roller  56  after development first collides with the cleaning roller  58 B. At this time, since the opposing surfaces F 1 , F 2  of the cleaning roller  58 B and the development roller  56  move in the opposite directions at their contact surface while strongly and frictionally contacting with each other, the toner particles T adhering to the surface of the development roller  56  after compaction are scraped off by the cleaning roller  58 B in a reliable manner. 
     Further, if the toner particles T carried on the development roller  56  pass through between the cleaning roller  58 B and the development roller  56 , as seen in  FIG. 2C , toner particles T 1  which travel with the development roller  56  by the rotation of the development roller  56  and toner particles T 2  which travel with the cleaning roller  58 B by the rotation of the cleaning roller  58 B collide with each other. Therefore, the toner particles T carried on each roller  56 ,  58 B are well dispersed in the carrier liquid C. 
     Accordingly, the toner particles T are dispersed in the carrier liquid C, and this can prevent the toner particles T from accumulating at an end face Al of the cleaning blade  58 A. 
     According to the present embodiment as described above, the following advantageous effects can be expected. 
     The toner particles T are well dispersed in the carrier liquid C by a simple configuration that the development roller  56  and the cleaning roller  58 B to which an electric voltage is not applied are configured to rotate in such a direction that their opposing surfaces F 1 , F 2  move in the opposite directions to each other at the contact surface where the cleaning roller  58 B contacts with the development roller  56 . Therefore, it is possible to disaggregate the toner particles T carried on the development roller  56  after compaction and development in a simple configuration, and also to collect and reuse the liquid toner LT in a simple way. 
     The development roller  56  is made of a material softer than that of the cleaning roller  58 B, and the cleaning roller  58 B is positioned to cause the outer peripheral surface of the development roller  56  to deform inward. This makes it possible to reduce the amount of toner particles T passing through between the development roller  56  and the cleaning roller  58 B. As a result, an accumulation of the toner particles T at the end face A 1  of the cleaning blade  58 A can be prevented in a more reliable manner. 
     Since the cleaning roller  58 B is made of metal, the surface of the cleaning roller  58 B can be made smooth. Therefore, when the development roller  56  and the cleaning roller  58 B rotate in such a manner that their opposing surfaces F 1 , F 2  move in the opposite directions at their contact surface while strongly contacting with each other, the development roller  56  is less susceptible to damage on the surface thereof. 
     Although the present invention has been described in detail with reference to the above embodiment and the accompanying drawings, the present invention is not limited to this specific embodiment and various changes and modifications may be made without departing from the scope of the appended claims. 
     In the above-described embodiment, the cleaning roller  58 B is positioned to cause the outer peripheral surface of the development roller  56  to deform inward. However, the present invention is not limited to this specific embodiment. For example, the cleaning roller may be positioned to slightly contact with the development roller. 
     In the above-described embodiment, the whole process unit  5  is defined as the developing device. However, the present invention is not limited to this specific embodiment. For example, in the case where the process unit  5  is divided into one or more drum cartridges each having a photoconductor drum  51 , etc., and one or more developer cartridges each having a development roller  56 , the developing device according to the present invention may be adopted for the developer cartridge. Further, in the case where the developer cartridge is divided into a development unit mainly comprising the development roller  56  and a toner cartridge having the liquid toner reservoir  53 , the developing device according to the present invention may be adopted for the development unit. 
     In the above-described embodiment, the present invention has been applied to the laser printer  1 . However, the present invention is applicable to other image forming apparatuses, such as a copying machine and a multifunction device. Further, the kinds of the carrier liquid and the toner particles of the liquid toner, etc. may be set arbitrarily where appropriate. 
     Example  
     A working example of the above-described embodiment will be described below. To be more specific, the following experimental result shows advantageous effects achieved by the cleaning mechanism. 
     Various conditions for this experiment are as follows: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 (1) Liquid toner 
                   
                   
               
               
                 Carrier: 
                 paraffin oil 
               
               
                 Toner particles: 
                 epoxy resin 
               
               
                 Concentration of toner: 
                 30% (weight 
               
               
                   
                 concentration) 
               
               
                 Viscosity: 
                 200 mPa · s 
               
               
                 (2) Development roller: 
               
               
                 Urethane rubber 
                 φ22 mm 
                 Circumferential speed: 
               
               
                   
                   
                 160 mm/s 
               
               
                 (3) Cleaning roller: 
               
               
                 SUS 
                 φ8 mm 
                 Circumferential speed: 
               
               
                   
                   
                 160 mm/s 
               
            
           
           
               
            
               
                 (Cleaning roller and Development roller rotate in the opposite directions 
               
               
                 at their contact surface.) 
               
            
           
           
               
               
               
            
               
                 (4) Amount of inward 
                 200 μm 
                   
               
               
                 deformation: 
               
               
                 (5) Thickness of toner layer on 
                 approx. 5 μm 
               
               
                 the development roller: 
               
               
                 (6) Applied voltage of corotron 
                 approx. 3 kV 
               
               
                 wire (compaction charger) 
               
               
                 (7) Thickness of cleaning blade 
                 3 mm 
               
               
                 (height from the surface of the 
               
               
                 development roller) 
               
               
                   
               
            
           
         
       
     
     An experiment was carried out under the above experimental conditions to visually check whether or not toner particles accumulate at the end face of the cleaning blade. The experiment showed that the liquid toner scraped off by the cleaning blade was smoothly collected without accumulating at the end face of the cleaning blade.