Patent Publication Number: US-6339688-B1

Title: Air filtering apparatus of liquid electrophotographic printer

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application INNER AIR CLEANING APPARATUS FOR LIQUID ELECTROPHOTOGRAPHIC PRINTER filed with the Korean Industrial Property Office on Oct. 2, 1999 and there duly assigned Serial No. 42497/1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an air filtering apparatus in a liquid electrophotographic printer, and more particularly, an air filtering apparatus for effectively sucking air in the liquid electrophotographic printer and removing pollutants contained in the air. 
     2. Description of the Related Art 
     A liquid electrophotographic printer emits various types of pollutants, such as solvent and carbon materials and ozone, during a developing and printing process. The pollutants are generated from printing mechanisms and materials when a printable image is developed and printed on a sheet of paper by using the printing, materials in the developing and printing process. Air inside of the printer is contaminated with the pollutants which cause serious problems against both the printable image and the printing mechanisms. Moreover, the air containing the pollutants has a more harmful effects on human being if it is blown out of the printer. 
     The solvent evaporates during the developing process into the air inside of the printer and sticks to a laser scanner and a photoreceptor web bearing the printable image in the printer while the carbon material is generated during drying the printable image formed on the photoreceptor web and transferring the printable image from the photoreceptor web to the sheet of paper in the developing and printing process. The ozone is generated from a plurality of chargers disposed adjacent to the photoreceptor web during initializing and changing the photoreceptor web with a high voltage. 
     Most of the pollutants are not effectively removed in a conventional printer. Although a filtering apparatus is installed in the printer to eliminate the solvent contained in the air, neither the structure of a duct of the filtering apparatus nor the location of the duct installed inside of the printer is enough to filter the air containing the pollutants. Since the air containing the pollutants is not efficiently sucked into the duct, the pollutants can not be properly removed from the printer. Therefore, a life span of the printer is shortened, and the quality of the printed image becomes deteriorated. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a filtering apparatus able to protect mechanical parts and maintain the quality of a printed image. 
     It is another object to provide a filtering apparatus in a printer able to effectively remove pollutants contained in air inside of the printer. 
     It is yet another object to provide a filtering apparatus able to filter air containing pollutants generated from printing materials used in a printer. 
     It is still another object to provide a filter apparatus able to uniformly suck air near a charger, developing unit, and a photoreceptor web in a printer. 
     It is a further object to provide a filtering apparatus suitable for use with a charger initializing or charging a photoreceptor web during a developing and printing process. 
     It is also an object to provide a filtering apparatus having a duct able to be mounted on a charger initializing or charging a photoreceptor web in a printer. 
     These and other objects may be achieved by providing a liquid electrophotographic printer with a filtering apparatus including a charger having a discharge wire charging a photoreceptor web to a predetermined level of electric potential, a laser scanner forming an electrostatic latent image on the charged photoreceptor web, a development unit developing the electrostatic latent image to a printable image, a transfer unit printing the printable image on a sheet of paper, a suction device having a duct mounted on the charger and sucking air in the printer, and a filtering device filtering pollutants contained in the air sucked by the suction device. 
     The suction device of the air filtering apparatus includes a discharge wire connected to a voltage source, a holder supporting the discharge wire, a grid net attached to one side of the holder and facing the photoreceptor web, a plurality of openings formed on the holder, a cover coupled to the other side of the holder, a hollow portion formed inside of the cover, a slot formed on the cover and connecting the openings to the hollow portion, an exhaust hole connected to one end of the hollow portion, and a suction pump connected to the exhaust hole and sucking air inside of the printer through the openings, the slot, the exhaust hole, and the exhaust hole. 
     The slot varies in width from one end to the other end of the slot. The width of the slot disposed remote from the exhaust hole is greater than the slot disposed adjacent to the exhaust hole. The width of the slot increases from one end of the slot to the other end of the slot. 
     The suction device includes a discharge wire connected to a voltage source, a shield plate accommodating the discharge wire, a plurality of slots formed on the shield plate, a holder attached to the shield plate, a passage formed between the shield plate and the holder, and an exhaust hole formed on one end of the passage. Air around the discharge wire is sucked through the slots, the passage, and the exhaust hole. 
     The suction device is mounted on a main charger initializing the photoreceptor web. A plurality of suction devices mounted on each corresponding charger charging the photoreceptor web are disposed adjacent to each corresponding development unit. Each exhaust hole of the suction devices is connected to a shared pipe. The suction pump is connected to the shared pipe. A plurality of filters suitable to filter pollutants such as solvent and carbon materials and ozone are connected to the suction pump. 
     The suction devices disposed adjacent to the transfer unit includes a main duct having two branch ducts disposed adjacent to both sides of the transfer unit and slots formed on the branch ducts. An exhaust hole is formed on one end of the main duct and coupled to a suction pump. A plurality of filters are connected to the suction pump in order to remove pollutants contained in the air inside of the printer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages, thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a schematic diagram of major elements of conventional liquid electrophotographic printer; 
     FIG. 2 is a perspective view showing a main charger shown in FIG. 1; 
     FIGS. 3A and 3B are an exploded perspective view and a cross-sectional view showing an air filtering apparatus according to the principle of the present invention, respectively; 
     FIGS. 4A and 4 b  are an exploded perspective view and a cross-sectional view showing an air filtering apparatus according to a second embodiment of the present invention, respectively; and 
     FIG. 5 is a partially exploded perspective view showing an air filtering apparatus according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a conventional liquid electrophotographic printer such as a typical color laser printer. A photoreceptor web  10  circulates around a plurality of rollers  11  while being supported by rollers  11 . An electrostatic latent image is formed by a laser scanner  13  on photoreceptor web  10 . The electrostatic latent image is developed by a development unit  12 , and a printable image of a predetermined color is formed on photoreceptor web  10 . The developed printable image is printed on a sheet of paper S by a transfer unit  14 . 
     Development unit  12  uses a developer, which is a mixture of toner powder and a liquid solvent, in developing the electrostatic latent image. The solvent evaporates during a developing process at the development unit  12  and a transferring process at the transfer unit  14 , and the evaporated solvent remains in air inside of the printer. When the amount of the evaporated solvent increases, the evaporated solvent sticks to photoreceptor web  10  or laser scanner  13  and cause a serious problem in forming and developing the electrostatic latent image on photoreceptor web  10  and printing the printable image on the paper S. 
     A charger charges a surface of photoreceptor web  10  to predetermined electric potential so that the electrostatic latent image can be formed on photoreceptor web  10 . The charger includes a main charger  20   a  performing initialization by charging photoreceptor web  10  after an printable image has been printed on a sheet of paper S and a topping charger  20   b  charging photoreceptor web  10 . An electrostatic latent image is formed on photoreceptor web  10  whenever photoreceptor web  10  passes each development unit  12 . The operating principles of these two chargers are same. For example, the main charger  20   a  has discharge wires  21  discharging photoreceptor web  10  when a voltage is supplied from a power source  15  to discharge wires  21  through an electrode  15 ′, as shown in FIG.  2 . Photoreceptor web  10  is charged to a predetermined voltage by a corona discharge of the discharge wires  21 . Photoreceptor web  10  must be charged to about 600 volts while discharge wires  21  themselves discharge a very high voltage reaching an instantaneous voltage of several thousand volts. Some oxygens (O 2 ) near the charger are changed to ozone (O 3 ) due to the high voltage. Ozone has strong bleaching and oxidizing capabilities so that life span of elements, such as a photoreceptor web, a developing unit, and a transferring unit, in the printer may be shortened when the amount of ozone increases with repeated use of the printer. 
     Returning now to FIGS. 3A and 3B, an air filtering apparatus of a liquid electrophotographic printer is mounted on a main charger  100  charging and initializing a photoreceptor web  10 . Although the air filter apparatus mounted on main charger  100  is used for mainly removing the ozone generated from main charger  100 , both ozone generated at a topping charger and solvent and carbon materials generated from a developing unit and a transferring unit are removed by the filtering apparatus mounted on main charger  100 . 
     A holder  120  contains and supports a discharge wire  101 . A first electric power V 1    171  coupled to discharge wire  101  applies a voltage of 6-7 kV to discharge wire  101 . An upper portion of holder  120  is open to photoreceptor web  10  and covered by a grid net  130 . A plurality of openings  121  such as slits are formed on bottom portion of holder  120 . Grid net  130  is installed to control an electric potential charged to 600-700 V by a second electric power V 2    172  which is independent of the first electric power V 1    171 . This arrangement is for achieving a state of balance between photoreceptor web  10  and grid net  130  after photoreceptor web  10  is charged to 600-700 V which is the electric potential charged to grid net  130 . The electric potential of photoreceptor web  10  can be adjusted by adjusting the electric potential of gridnet  130 . An upper surface of holder  120  made of metal contacts one side of grid net  130  so that the second electric power  172  and the grid net  130  can be electrically connected. 
     A cover  110  is coupled to a bottom of holder  120  where the openings  121  are formed. A hollow portion  110   a  is formed inside of the cover  110  and, a slot  111  is formed on cover  110  and couples hollow portion  110   a  to openings  121 . An exhaust hole  112  are formed on one end of hollow portion  110   a . Thus, air around photoreceptor web  10  is exhausted to exhaust hole  112  through an exhaust path including grid net  130 , openings of holder  120 , and slot  111  and hollow portion  110   a  of cover  110 . A suction pump  140  is connected to the exhaust hole  112  of cover  110 . When the suction pump  140  operates, air near main charger  100  and photoreceptor web  10  passes through grid net  130  and is sucked through openings  121  of holder  120  and slot  111  of cover  110 . Then, the sucked air is blown along hollow portion  110   a  and is exhausted through exhaust hole  112 . 
     A platinum catalyst filter  150  and a carbon filter  160  as a filtering device are installed along the exhaust path and connected to suction pump  140 . The filtering device filters out pollutants from the sucked air. The platinum catalyst filter  150  decomposes the ozone contained in the air utilizing the principle that the decomposition of ozone is expedited as it acts on platinum, lead oxide, manganese oxide or copper oxide. The carbon filter  160  is a filter having superior absorbing capability like active carbon and is installed to collect a solvent contained in the air. As a result, while passing through the filters, the ozone and the solvent are filtered, and filtered air is exhausted to an outside of the printer. Therefore, after the air inside of the printer is sucked to be filtered, and ozone and solvent are removed from the sucked air, the air inside the printer is exhausted to the outside of the printer or returned to the inside of the printer. 
     The width h 1  of slot  111  at the side of the exhaust hole  112  is about 0.5 mm, and slot  111  becomes wider to about 2.0 mm at the position of width h 2  of slot  11  . This is to compensate for the difference in the amount of sucked air by suction pump  140  through slot  111  because suction power at the position near exhaust hole  112  is greater than at the opposite side remote from exhaust hole  112 . The air is uniformly sucked through the entire length of slot  111  . Thus, when suction pump  140  operates, a nearly same amount of air along the entire length of the slot  111  is sucked from slot  111  and exhausted through exhaust hole  112 . 
     FIGS. 4A and 4B show an air filtering apparatus mounted on a topping charger  200  mainly used for removing ozone generated from topping charger  200  while the ozone generated from main charger  100  and the solvent and carbon materials generated from development unit  12  and transfer unit  14  are also removed by the air filter mounted on topping, charger  200 . A holder  210  supports a discharge wire  201  of topping charger  200 , and a shield plate  220  is coupled to holder  210  and disposed between holder  210  and discharger wire  200 . A slot  221  is formed lengthwise on shield plate  220 . When holder  210  is coupled to shield plate  220 , a path  210   a  is formed between holder  210  and shield plate  220  and connected to slot  221 . 
     An exhaust hole  211  is formed at one end of holder  210  and connected to a shared pipe  270  connected to a suction pump  240 . Shared pipe  270  is connected between suction pump  240  and each exhaust hole  211  so that an exhaust path coupled to one suction pump  240  is shared with the adjacent suction device mounted on each topping charger  200  as shown in FIG. 4B. A platinum catalyst filter  250  and a carbon filter  260  are coupled to suction pump  240 . Reference numeral  271  denotes a first electric power for applying a first voltage to discharge wire  201 . Reference numeral  272  denotes a second electric power for applying a second voltage to shield case  220  performing a function of controlling the electric potential discharged from discharge wire  201  to photoreceptor web  10  like the grid net  130  of FIG.  3 A. Reference numeral  280  denotes an insulator. 
     When suction pump  240  operates, air near topping charger  200  is sucked through slot  221  of shield plate  220 , path  210   a  and exhaust hole  211 , and then exhausted through shared pipe  270 . After platinum catalyst filter  250  and carbon filter  260  filter the ozone and the solvent and carbon materials, the filtered air is exhausted. The shape of slot  221  is formed to be narrower at a position near exhaust hole  211  and wider at an opposite side remote from exhaust hole  211 . 
     FIG. 5 shows an air filtering apparatus mounted adjacent to transfer unit  14  transferring the printable image from photoreceptor web  10  to a sheet of paper S. Although the solvent and carbon materials generated from transfer unit  14  is mainly removed by the air filtering apparatus mounted adjacent to transfer unit  14 , the other pollutants generated from the main charger and the topping charger can be removed. A main duct  300  is disposed adjacent to and above transfer unit  14 . A slot  301  like an inlet is formed on a bottom of main duct  300  and is facing transfer unit  14 . Two branch ducts of main duct  300  are disposed on both sides of transfer unit as shown in FIG.  5 . Each one end of the two branches meets at an exhaust hole  302 . A connection pipe  310  is connected to exhaust hole  302  of main duct  300  so that air surrounding transfer unit  14  can be sucked through two branch ducts of main duct  300 , exhaust hole  302 , and connection pipe  310  into a suction pump  320 . Pollutants contained in the air sucked by suction pump  320  is removed by a platinum catalyst filter  330  and a carbon filter  340 . 
     When suction pump  320  operates, the air near the transfer unit  14  is sucked through slot  301  of duct  300 . The air passes through platinum catalyst filter  330  and carbon filter  340  via connection pipe  310  of exhaust hole  302 . While the air passes through platinum catalyst filter  330  and carbon filter  340 , the ozone and the solvent are filtered, and the filtered air is exhausted to the outside of the printer or returned to the inside of the printer. Slot  301  is formed to be narrower at the position near exhaust hole  302  while Slot  301  is formed to be wider at the opposite side remote from exhaust hole  302 . 
     As described above, in the air filtering apparatus of a liquid electrophotographic printer according to the present invention, the air filtering apparatus mounted on either a main charger initializing the photoreceptor web or a top charger charging the photoreceptor web or adjacent to a transfer unit transferring a printable image from the photoreceptor web to a sheet of paper filters air inside of the printer and removes from the air pollutants such as ozone generated from main and top chargers and the solvent and carbon materials generated from a developing unit. Since the filtered air is exhausted, environmental and pollution problems can be reduced, and harmful effects on printing mechanisms by repeated use of the printer can be removed. Therefore, life spans of mechanisms in the printer may be extended, and the quality of the printable image can be maintained.