Patent Publication Number: US-6701111-B2

Title: Liquid image developing system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-1886, filed Jan. 12, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid image developing system, and more particularly, to a liquid image developing system having a simplified structure using a high-concentration developer. 
     2. Description of the Related Art 
     In general, liquid image developing systems form an electrostatic latent image corresponding to a desired image by scanning light on a photosensitive body, developing the electrostatic latent image using a developer in which powder-shaped toner is mixed with a liquid solvent, and printing the developed electrostatic latent image on a paper. 
     FIG. 1 is an example of a conventional image developing system, disclosed in U.S. Pat. No. 5,255,058. As shown in FIG. 1, the conventional image developing system includes a photoconductive drum  10  charged at a predetermined voltage by a photoconductor charging apparatus  14 , and an imaging apparatus  16  (i.e., a laser scanning apparatus) to form an electrostatic latent image of a desired image by scanning light onto the charged photoconductive drum  10  and creating a relative voltage difference. The image developing system also includes a developer supplying unit to develop the electrostatic latent image by supplying a developer to the photoconductive drum  10 , and an intermediate transfer member  30  to transfer the developed image onto the photoconductive drum  10  and print the transferred image onto a paper  72 . 
     The developer supplying unit prepares the developer with a toner concentration of less than 3% solid and supplies the developer between the photoconductive drum  10  and a development roller  38 . For this purpose, the developer supplying unit includes concentration cartridges  82  and  84  containing a concentrated developer with a toner concentration of 25% solid, a solvent cartridge  86  containing pure solvent, and toner reservoirs  55 ,  57 ,  59 , and  61  to mix the concentrated developer from the concentration cartridges  82  and  84  with the solvent from the solvent cartridge  86  and preparing a developer with a uniform concentration of about 2-3% solid. The developer supplying unit further includes a multicolor liquid developer spray assembly  20  to pump the developing solvent prepared in the toner reservoirs  55 ,  57 ,  59 , and  61  to pumps  90 ,  92 ,  94 , and  96 , respectively, and to supply the developer to the development roller  38 , and a collecting unit to collect excess developer left after the electrostatic latent image is developed. In addition, the collecting unit includes a collection container  50  to collect the developer supplied between the development roller  38  and the photoconductive drum  10  and to return the developer to the toner reservoirs  55 ,  57 ,  59 , and  61  for each color, and a squeeze roller  26  to impress the photoconductive drum  10  on which the image is developed, and to squeeze the solvent contained in the developed image. The collecting unit further includes a separator  66  to collect the squeezed developer through the collection container  50 , to separate color toner from the collection container  50  and to return the solvent to a solvent reservoir  65 . 
     In the above structure, in order to perform a development operation, a developer having four colors, such as yellow (Y), magenta (M), cyan (C), and black (K), with a toner concentration of about 2-3% solid, is provided in the toner reservoirs  55 ,  57 ,  59 , and  61 . Of course, in the case of a system developing a single color, such as black, only one developer is required. In order to prepare a developer for each color, the developer supplying unit fabricates a developer with a corresponding concentration by supplying the concentrated developer and the pure solvent from the concentration cartridges  82  and  84  and the solvent cartridge  86  to the toner reservoirs  55 ,  57 ,  59 , and  61 , respectively. For this purpose, each of the toner reservoirs  55 ,  57 ,  59 , and  61  measures the concentration of the developer that is mixed according to a concentration sensor (not shown). Likewise, when the developer is prepared, the development operation begins. First, the photoconductor charging apparatus  14  charges the photoconductive drum  10  to a predetermined potential. In this state, the imaging apparatus  16  scans light on the charged photoconductive drum  10  to form an electrostatic latent image of a desired image. Subsequently, the pumps  90 ,  92 ,  94 , and  96  operate such that the developer provided in the toner reservoirs  55 ,  57 ,  59 , and  61  is supplied between the development roller  38  and the photoconductive drum  10  through the multicolor liquid developer spray assembly  20 , thereby forming the electrostatic latent image. The developed image is transferred to the intermediate transfer member  30  and is printed directly onto the paper  72  if the developed image is formed of only one color. However, if a color image is implemented by overlapping a developer having a plurality of colors, the charge, exposure, and development operations are repeated for each of the colors. For example, if there are four colors, such as yellow (Y), magenta (M), cyan (C), and black (K), the developed image for each color is overlapped on the intermediate transfer member  30 . The overlapped color image is printed onto the paper  72  passing through a space between the intermediate transfer member  30  and an impression roller  71 . 
     However, the structure of the system in the operations from preparing the developer to supply and collect the developer is considerably complicated. For this reason, a concentrated high-concentration developer cannot be directly used in the development operation, and instead a low-concentration developer (less than 3% solid) is used in the development operation. If the developer with a low concentration is used, mobility is improved, and thus a difference in density of toner throughout the image is reduced. However, as described above, the concentrated developer and solvent in each of the cartridges  82 ,  84 , and  86 , are sent to the toner reservoirs  55 ,  57 ,  59 , and  61 , and mixed with a developer with the low concentration, and thus an electrostatic latent image is developed having the developer with a low concentration. Then, the solvent contained in the developed image is squeezed and collected so that the developer has a high concentration suitable for printing. To make things worse, the size and cost of embedded devices further amplify the problems of this complicated structure. 
     Thus, in order to solve these problems, a new image developing system is required. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a liquid image developing system having an improved structure in which a high-concentration developer is smoothly used in a development operation without requiring squeezing. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing and other objects of the present invention are achieved by providing a liquid image developing system, including a development container to store a developer having a charge; a photosensitive body; a development roller partially soaked in the developer in the development container and to rotate to form a development nip with the photosensitive body; a depositing portion to attach the developer to a surface of the development roller; a metering portion to regulate the developer attached to the development roller at a uniform thickness at a first end of the development nip; and a cleaning portion to clean the surface of the development roller at a second end of the development nip; wherein the cleaning portion includes an electrical cleaning member which contacts the development roller and removes the developer attached to the surface of the development roller by an electrical attractive force, and a mechanical cleaning member which contacts the development roller and mechanically cleans the developer attached to the surface of the development roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 illustrates a conventional image developing system; 
     FIG. 2 illustrates a liquid image developing system according to an embodiment of the present invention; and 
     FIG. 3 is an illustration of the metering portion shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     FIG. 2 illustrates a liquid image developing system  100  according to an embodiment of the present invention. As shown in FIG. 2, the liquid image developing system  100  includes a cartridge  150  in which a developer is stored, and a development container  140  to which the developer is supplied from the cartridge  150 . High concentration developer having a concentration of about 3-40% solid is used as the developer supplied to the development container  140  from the cartridge  150 . The cartridge  150  includes a case  151 , a tube  152  built in the case  151  in which the developer is contained, and a piston  153  with one side  153   a  attached to the tube  152 , to perform a reciprocating movement in the case  151  and selectively compress and expand the tube  152 . Thus, if the piston  153  compresses the tube  152 , the developer in the tube  152  is supplied to the development container  140  through a supply line  154   a . In the opposite case, if the piston  153  expands the tube  152 , the developer contained in the development container  140  is absorbed into the tube  152  through a collection line  154   b.    
     Within the development container  140  there is a development roller  110  which is partially soaked in the developer and rotates with a photosensitive body  170  to form a development nip N, a metering roller  160  to regulate the developer stained on the circumference of the development roller  110  to a predetermined thickness at a front end of the development nip N, a depositing portion to apply an electric potential to attach the developer to the surface of the development roller  110 , and a cleaning portion to clean the surface of the development roller  110  at a rear end of the development nip N. 
     The depositing portion includes a depositing roller  120  contacting the development roller  110 , and a depositing power supply part  121  to apply a voltage to the depositing roller  120 . The depositing roller  120  is formed of a stainless material and attaches the developer to the development roller  110  by an electric force due to a voltage applied from the depositing power supply part  121 , while being soaked in the developer. The depositing roller  120  may contact the development roller  110 , or may be spaced at a distance of about 50-200 μm (for example, 50-100 μm) away from the development roller  110 . The depositing roller  120  may be a fixed roller or a rotating roller or may have a plate shape having a curvature similar to the circumference of the development roller  110 . 
     The cleaning portion includes a plurality of cleaning rollers  131  and  132  to rotate in contact with the development roller  110  in an opposite direction to the development roller  110 . The cleaning roller  131 , which first faces the development roller  110  after the development roller  110  passes through the development nip N, is an electrical cleaning roller. The cleaning roller  131  contacts the development roller  110  while being grounded, and applies an electrical attractive force to the developer. That is, in the present embodiment, toner particles contained in the developer are negatively charged, and thus a negative voltage is applied to the development roller  110  by a development power supply part  111 . Thus, if the grounded electrical cleaning roller  131  contacts the development roller  110 , an electrical attractive force is applied to the developer, and thus the developer moves to the electrical cleaning roller  131 . When the toner particles contained in the developer are positively charged, a positive voltage is applied to the development roller  110 , and the electrical cleaning roller  131  is grounded, and the electrical cleaning roller  131  creates a relatively low electrical potential, and thus an electrical attractive force is also applied to the developer. Also, the electrical cleaning roller  131  removes an electrical latent image formed on the development roller  110 . That is, the developer attaches to the photosensitive body  170  from the development roller  110  through the development nip N in an image portion formed on the photosensitive body  170  by an LSU (laser scanning unit)  190 , whereas the developer does not move to the photosensitive body  170  in a non-image portion. Thus, after the developer passes through the development nip N, an electrical latent image is formed on the surface of the development roller  110  by a difference in the amount of charge between a portion in which the developer remains and a portion in which there is no developer due to the movement to the photosensitive body  170 . This may disturb accurate development in the next development operation, that is, this means that the electrical latent image is planarized to a ground electrical potential by the grounded electrical cleaning roller  131 . The development roller  110  and the electrical cleaning roller  131  may be formed of polyurethane rubber or NBR as a conductive elastomer, having a resistance of about 10 5  to about 10 8  ohm, a hardness of shore A 25-65 degrees, and a surface roughness of Ra 1-4 μm. The cleaning roller  132  is mechanical and contacts the development roller  110  to mechanically clean the developer stained on the surface of the development roller  110 . The cleaning roller  132  is mounted at a rear end of the electrical cleaning roller  131 . The mechanical cleaning roller  132 , having a porous surface, rotates to contact the development roller  110  and cleans toner particles of the developer that is not developed. 
     Finally, the cleaning portion improves the cleaning efficiency by simultaneously performing electrical cleaning and mechanical cleaning. For example, when only mechanical cleaning is performed, cleaning of the development roller  110  may not be completely performed. In such a case, the amount of remaining toner is gradually accumulated, and thus the development roller  110  may deteriorate. Also, due to the remaining electrical latent image, a subsequent development operation may be disturbed. Accordingly, electrical cleaning is performed before mechanical cleaning, thereby improving the cleaning efficiency. 
     In FIG. 2, reference numeral  200  denotes a transfer belt to transfer the image developed on the photosensitive drum and print the transferred image onto the paper, and reference numeral  180  denotes a charging roller to charge the photosensitive body  170 . 
     Only one developing system is provided in the image forming device  100  using a single color, but the above-mentioned developing system can be used in a color image forming device to overlap and print a plurality of colors. 
     In the structure of FIG. 2, in order to perform a development operation, the corresponding cartridge  150  supplies the developer for each color to the development container  140  to charge the developer to a predetermined level. As described above, the charged developer is a high-concentration developer with a concentration of about 3-40% solid (for example, 3-12% solid). After the developer reaches this concentration, the development operation begins. First, bias voltages of about −300 to about −550 V and about −500 to about −1550 V are applied to the development roller  110  and to the depositing roller  120 , respectively. The bias voltage applied to the development roller  110  lies between a voltage of about −900 V applied to the photosensitive body  170  by the charging roller  180  and a voltage of about −100 V applied to a portion in which an electrostatic latent image is formed by the laser scanning unit  190 . If the bias voltage is applied to the development roller  110  in this way, toner particles of the developer are negatively charged, and thus attach to the surface of the development roller  110  by a voltage difference between the development roller  110  and the depositing roller  120 . In this case, toner particles may electrically strongly or weakly attach to the development roller  110 . In this experiment, developer with a concentration of 3-12% solid is used, and the concentration of the developer attached to the development roller  110  by an electric force before passing the metering roller  160  is 6-14% solid, with a mass/area (M/A) of 400-1100 μg/cm 2 . When using a developer with a concentration of 3% solid, which is a relatively low concentration, the concentration of the development roller  110  is 6% solid, which is twice as much as the initial concentration. When a developer with a concentration of 12% solid is used, the concentration of the development roller  110  slightly increased to 12-14% solid. However, before passing the metering blade  160 , a concentration difference of the developer is large, and thus it is difficult to develop an image with a uniform concentration if the electrostatic latent image formed on the photosensitive body  170  is developed without change. 
     Afterwards, the developer stained on the development roller  110  is regulated by the metering roller  160  to a predetermined and uniform thickness. In this case, the same voltage as that of the depositing roller  120  is applied to the metering roller  160  such that the developer stained on the surface of the development roller  110  does not attach to the metering roller  160  by an electrical force. Meanwhile, in the present embodiment, the thickness of the developer on the surface of the development roller  110  is regulated using a member such as a roller. However, as shown in FIG. 3, a metal plate  160 ′ having a thickness of 0.05-2 microns is formed in an L-shape so that the thickness of the developer on the surface of the development roller  110  is regulated. Of course, due to variations of the metering roller  160 , the concentration and the M/A of the developer stained on the surface of the development roller  110  before the development operation gradually varies. However, when the developer with a concentration of 3-40% solid is used, and these conditions are slightly changed, the concentration and the M/A on the development roller  110  before the development operation is about 18-35% solid and about 150-500 μg/cm 2 , respectively, thereby a relative uniform concentration is achieved. In particular, when the developer with a concentration of about 3-12% solid is used, the concentration and the M/A of the developer stained on the development roller  110  after passing through the depositing roller  120  is about 7-14% solid and about 413-1126 μg/cm 2 , respectively. Furthermore, the concentration and the M/A of the developer stained on the development roller  110  before the development operation after passing through the metering blade  160  is about 19.6-31% solid and about 220-270 μg/cm 2 , respectively. Thus, this is a substantially uniform distribution. In this case, the distance between the depositing roller  120  and the development roller  110  is about 70-100 μm, and the voltage difference between the development roller  110  and the depositing roller  120  is 500 V. When using the system according to the present embodiment, the concentration of the developer before the development operation can be maintained uniform and the developer can be used in the development operation even though a developer within a wide range of a concentration, i.e., 3-12% solid, is used. 
     Subsequently, the electrical latent image that is formed on the photosensitive body  170  through the development nip N is developed using the development roller  110 . In such a case, the concentration of the developer of the image developed on the photosensitive body  170  is high (greater than 25% solid), without the flow of excess solvent. Thus, a transfer operation can be performed without an additional squeezing operation. 
     The toner particles left on the development roller  110  after the development operation are completely removed by the electrical cleaning roller  131  and the mechanical cleaning roller  132 . That is, the electrical cleaning roller  131  removes the developer which does not attach to the photosensitive body  170  and is left on the development roller  110  by an electrical attractive force. Since a relative potential difference created by the grounded electrical cleaning roller  131  is used as the electrical attractive force, additional power consumption does not occur. Afterwards, the mechanical cleaning roller  132  simultaneously cleans the surfaces of the development roller  110  and the electrical cleaning roller  131 , thereby completing cleaning. 
     Meanwhile, the developed image is transferred onto the transfer belt  200 , and if the developed image is formed of only one color, the developed image is printed directly onto the paper. However, in the case of implementing a color image, each image developed by each developing system for four colors, such as yellow (Y), cyan (C), magenta (M), and black (K), is overlapped on the transfer belt  200 , and then is printed onto the paper. 
     In the image developing system, the high-concentration developer can be directly used in the development operation without a dilution operation, and thus the structure to supply the developer can be considerably simplified, and the squeezing operation of squeezing excess solvent can be omitted. In addition, the developer stained on the development roller  110  in the development operation can be maintained at a uniform concentration using the metering roller, and using the cleaning portion to simultaneously perform electrical cleaning and mechanical cleaning after the development operation, thereby achieving a very efficient system which is capable of completely cleaning the remaining developer. 
     As described above, the liquid image developing system according to the present invention has the following advantages. 
     First, since the high-concentration developer in the cartridge is supplied directly to the development container without an additional dilution operation, the structure to supply the developer can be simplified, and thus the overall size of the printer can be reduced. 
     Second, using the metering roller or metal plate, the distribution of the concentration of the developer in the development container and the concentration of the developer on the development roller can be uniform, and thus a controller to dilute the developer and adjust the concentration of the developer is not required. 
     Third, as the concentration of the developer is increased, the spread of the image is reduced, thereby achieving a high quality image capable of preventing the contamination of the non-image portion. 
     Fourth, by performing the development operation using the high-concentration developer, a squeezing operation can be omitted. 
     Fifth, due to high concentration contact development, dwell time can be reduced, thereby increasing printing speed. 
     Sixth, electrical cleaning and mechanical cleaning are simultaneously performed, thereby completely removing the developer stained on the development roller after the development operation and reducing wear on the development roller and improving the reliability of the development operation. 
     Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.