Patent Publication Number: US-8121513-B2

Title: Electrophotographic printer having a transfer roller

Description:
TECHNICAL FIELD 
     The present invention relates to an electrophotographic printer in which a toner image formed on a photoconductor drum is transferred via a transfer roller onto a recording medium and in which the surface of the rotating transfer roller after the transfer is cleaned by a transfer roller cleaning device. 
     BACKGROUND ART 
     In an electrophotographic printer in which a toner image formed on the rotating photoconductor drum is transferred by the primary transfer onto the surface of the rotating transfer roller and the toner image transferred to the rotating transfer roller is then transferred by the secondary transfer onto a moving recording medium for image formation, the surface of the rotating transfer roller immediately after the toner image has been transferred onto the moving recording medium has a residual amount of toner adhered in the state that it has almost dried because a carrier solution is absorbed on the recording medium. 
     In removing a residual toner on the surface of a rotating transfer roller, it is generally effective to scrape off a major portion of residual toner with a cleaning blade and then to wipe off minute adhered residual toner which have not been removed by the cleaning blade. 
     However, the residual toner if they remain almost dried cannot be well scraped off by the cleaning blade and there is also a problem in durability of the cleaning blade. 
     Accordingly, of transfer roller cleaning devices of this type, there has been known one in which downstream of a transfer area on the transfer roller of an image onto the recording medium in the rotation direction of the rotating transfer roller, there are disposed in order from upstream in the rotation direction of the transfer roller a wiping roll rotating reversely in rubbing contact with the surface of the rotating transfer roller and a blade scraper whereby the wiping roll is supplied with a cleaning solution from a supply nozzle while the wiping roll is rotated so that residual toner remaining on the surface of the transfer roller can be wiped off with the cleaning solution, followed by removal of still adhered residual toner with the blade scraper, thereby cleaning the surface of the transfer roller (see JP 2007-11142 A). 
     In the known transfer roller cleaning device mentioned above in which the wiping roll supplied with the cleaning solution is rotated in rubbing contact with the surface of the transfer roller, the cleaning solution is applied to the residual toner on the surface of the transfer roller where the wiping roll is in rubbing contact with the transfer roller. Consequently, when the transfer roller is rotated at a high speed, it may not be done in time to clean residual toner with the cleaning solution; hence it is hard to meet the requirement for high speed printing with a continuous web of paper. 
     DISCLOSURE OF THE INVENTION 
     With the such problems taken in account, it is an object of the present invention to provide a transfer roller cleaning device in an electrophotographic printer with the ability to meet the requirement for high speed printing on a continuous web of paper as the printing medium and to make minimum the amount of toner that remains on the surface of a rotating transfer roller even in high-speed production of a printed matter. 
     In order to achieve the object mentioned above, there is provided in accordance with the present invention an electrophotographic printer in which a toner image formed on a rotating photoconductor drum is transferred via a rotating transfer roller onto a recording medium and in which a surface of the rotating transfer roller after the transfer is cleaned by a transfer roller cleaning device, characterized in that it comprises a carrier solution supply device disposed in an area upstream of the transfer roller cleaning device in the rotation direction of the rotating transfer roller for supplying the surface of the rotating transfer roller with a carrier solution. 
     The transfer roller cleaning device may include: disposed in the rotation direction of the rotating transfer roller, a blade scraper in contact with the surface of the rotating transfer roller and a wiping roll rotating reversely in rubbing contact with the surface of the rotating transfer roller; a brush roll disposed to rotate reversely in contact with the surface of the rotating wiping roll, a portion of the bush roll being immersed in the carrier solution; and a squeezing roll disposed to rotate normally in pressure contact with the surface of the rotating wiping roll. 
     According to the present invention, the ability to supply the surface of a transfer roller with a carrier solution upstream of an area where cleaning is effected by the transfer roller cleaning device allows residual toner adhered as dried to the transfer roller surface prior to the cleaning effected by the transfer roller cleaning device to become softened with the carrier solution, thereby to allow cleaning to be effected with the transfer roller cleaning device so as to minimize the amount of toner that remains on the surface of a rotating transfer roller even in high-speed printing on a continuous web of paper as the recording medium 
     In the transfer roller cleaning device mentioned above, the wiping roll in rubbing contact with the transfer roller is supplied with the carrier solution and is cleaned of its surface by means of a brush roll whereby if it is formed of a sponge, its cleaning effect becomes so thorough as to extend to its surface pore insides, thereby improving its ability to clean while making it available over a prolonged time period. The result is an efficient production in the maintenance and operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the Drawings: 
         FIG. 1  is an explanatory view illustrating the makeup of an electrophotographic printer in which the present invention is curried out; and 
         FIG. 2  is a cross sectional view illustrating the essential part of a form of implementation of the present invention. 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
       FIG. 1  is an explanatory view illustrating the makeup of an electrophotographic printer in which the present invention is curried out. As shown, a photoconductor drum  1  is opposed to and in contact with a transfer roller  2  which in turn is opposed to and in contact with a backup roll  3 . 
     In the electrophotographic printer, the photoconductor drum  1  is rotated by a drive means such as a motor (not shown) at a constant speed in a direction of the arrow. The surface of the photoconductor drum  1  is charged uniformly with electricity in the dark by a charging unit  4  and then has an electrostatic latent image formed thereon of an original light figure when irradiated by an exposure unit  5  for image formation. Thereafter, the electrostatic latent image when passing through its processing region is visualized by a developing unit  6 , forming a toner image on the surface of the photoconductor drum  1 . 
     The toner image on the surface of the photoconductor drum  1  is primarily transferred on the surface of the transfer roller  2  in its transfer region by a bias pressure applied through the transfer roller  2  and a nip voltage between the drums. This primarily transferred toner image is secondarily transferred in its second transfer region on a recording medium  7  passing through between the transfer roller  2  and the backup roll  3 . 
     The recording medium  7  on which the toner image is secondarily transferred has the toner image fixed thereon by a fixing unit (dryer) not shown and then is discharged out of the printer. On the other hand, after the primary transfer, a residual potential that remains on the photoconductor drum  1  is removed by a static eliminator  8 . And, the carrier solution and a residual toner that remain on the photoconductor drum  1  after the primary transfer is completed are removed by a photoconductor drum cleaning device  9  in an area downstream of the static eliminator  8 . 
     In the Figure, reference numeral  10  indicates a transfer roller cleaning device disposed opposite to a surface of the transfer roller  2  upstream of a transfer area in which it is opposite to and in contact with the photoconductor drum  1 . And, reference numeral  11  indicates a carrier solution supply device disposed opposite to a surface of the transfer roller  2  upstream of the transfer roller cleaning device  10 . And, the transfer roller cleaning device  10  and the carrier solution supply device  11  are constructed as shown in  FIG. 2 . 
     The transfer roller cleaning device  10  shown in  FIG. 2  comprises a blade scraper  12 , a wiping roll  13 , a squeezing roll, a brush roll  15  and a case  16  to house them. 
     The blade scraper  12  comprises a pair of blades  12   a  and  12   b  whose ends are in frictional sliding (rubbing) contact with the transfer roller  2  and a bracket  17  to which the two blades  12   a  and  12   b  are fastened in the state that they are spaced apart in a direction in which the transfer roller  2  is rotated. And, the bracket  17  is securely connected to a side of the case  16  via a fastening element (mounting screw)  18  such that loosening the fastening element  18  allows the bracket  17  to be rotated for adjusting the strength of pressure contact of the blades  12   a  and  12   b  against the peripheral surface of the transfer roller  2 . Each of the ends of the blades  12   a  and  12   b  is positioned above a center of rotation of the bracket  17  at the fastening element  18 . Thus, with the bracket  17  rotated clockwise in  FIG. 2 , the rubbing force by the two blades  12   a  and  12   b  increases. Then, with the two blades  12   a  and  12   b  spaced apart vertically, the rubbing force by the upstream blade  12   a  positioned upper is made greater than that by the downstream blade  12   b  positioned lower. 
     Disposed under the blade scraper  12  is a guide  19  for accepting a solution scraped off by the blade scraper  12 , the solution guide  19  communicating with a drip tray  20  disposed at the lower part of the case  16 . 
     The wiping roll  13  lies downstream of the blade scraper  12  and is rotated reversely in direction with respect to the peripheral surface of the rotating transfer roller  2  while in contact therewith. The wiping roll  13  is formed over its peripheral portion of a sponge and rotated reversely in direction with respect to the peripheral surface of the transfer roller  2  to rub and wipe the surface of the transfer roller  2 . 
     Disposed under the wiping roll  13 , the squeezing roll  14  is in pressure contact with the wiping roll  13  upstream of a point of contact of the wiping roll  13  with the transfer roller  2 . The squeezing roll  14  is rotated normally in direction with respect to the peripheral surface of the rotating wiping roll  13 . Under the squeezing roll  14  there is disposed the drip tray  20  mentioned above. 
     The brush roll  15  is disposed to contact with the peripheral surface of the wiping roll  13  downstream of an area of rubbing contact of the wiping roll  13  with the transfer roller  2  and upstream of the squeezing roll  14  contacting with the wiping roll  13 . And, the brush roll  15  is rotated reversely in direction with respect to the peripheral surface of the wiping roll  13 . Under the brush roll  15  there is disposed a trough  21  for accepting the cleaning carrier solution and a lower part of the brush roll  15  is immersed in the carrier solution in the trough  21 . 
     The wiping roll  13 , the squeezing roll  14  and the brush roll  15  are interlocked together by a gear mechanism and driven by a single motor (not shown) as their common drive source whose speed of rotation can freely be controlled and that the wiping roll  13  can controllably be rotated to follow rotation of the transfer roller  2  or can freely be set at an optimum speed of rotation for rotation of the transfer roller  2 . Note that each of the rolls  13 ,  14  and  15  may also be driven individually by a single motor. And, driving the wiping roll  13  in rubbing contact with the transfer roller  2  with a single motor allows the number of rotation of the wiping roll  13  to be selected as desired at an optimum number of rotation which is high in cleaning effect and permits an optimum cleaning effect to be achieved over an entire range of all usable image recording speeds following changes in image recording speed. 
     The carrier solution supply device  11  shown in  FIG. 2  comprises a carrier solution supply roll  22 , a carrier solution source roll  23  and a case  24  to house them. 
     The carrier solution supply roll  22  may be a roller whose surface is plated with chromium and driven by a single motor so that it is rotated normally in direction with respect to the peripheral surface of the rotating transfer roller  2  and in contact therewith and that the ratio of its surface velocity to that of the transfer roller  2  can be adjusted as desired. Also, a bracket (not shown) which is disposed to support the case  24  on the machine body of electrophotographic printer is driven by a cylinder unit (not shown) mounted on the main frame so that it can be moved rotationally or slidably towards and away from the transfer roller  2  and that such rotational or sliding movement of the case  24  may adjust the contact pressure between the carrier solution supply roll  22  and the transfer roller  2 . It may be noted that an upper limit of the contact pressure is then set by a stopper (not shown). 
     The carrier solution source roll  23  may be a rubber wound roll which is interlocked and driven via gears with the carrier solution supply roll  22  so as to rotate normally in direction with respect to the peripheral surface of the rotating carrier solution supply roll  22 . And, the carrier solution source roll  23  is supported by an eccentric bearing such that turning the eccentric bearing may move its shaft position towards and away from the carrier solution supply roll  22  to adjust the contact pressure of the carrier solution source roll  23  against the carrier solution supply roll  22 . 
     The carrier solution source roll  23  has a lower part thereof immersed in the carrier solution in a carrier solution reserving trough  25  so that as it is rotated while contacting with them, the carrier solution can be supplied onto the carrier solution supply roll  22 . And, its rate of supply is adjusted by increasing and decreasing the contact pressure mentioned above. 
     In the form of implementation described above, the carrier solution used in the transfer roller cleaning device  10  and the carrier solution supply device  11  may be a solvent for the liquid toner used in development in the development unit  6 . 
     In the makeup mentioned above, the surface of the transfer roller  2  after the secondary transfer to the recording medium  7  during a printing operation of the electrophotographic printer has a thin film of the carrier solution applied from the carrier solution supply roll  22  in the carrier solution supply unit  11  and is then cleaned by the transfer roller cleaning device  10 . 
     At that time, the surface of the transfer roller  2  which has secondarily transferred in the transfer area to the recording medium  7  has the carrier solution contained in the toner absorbed into the recording medium  7  becomes dried while the residual toner that remain are also dried. However, the residual toner supplied with the carrier solution from the carrier solution supply roll  22  are softened. 
     The major portion of the residual toner thus softened are, together with the carrier solution applied for softening, first scraped off by the scraping blades  12   a  and  12   b  of the blade scraper  12 . The residual toner and carrier solution scraped off are led through the guide  19  into the drip tray  20 . 
     Subsequently, the surface of the transfer roller  2  is brought into rubbing contact with the reversely rotating wiping roll  13  by which fine residual toner and carrier solution which have not be taken off by the blade scraper  12  are wiped off by the wiping roll  13 . And, the wiping roll  13  contaminated by wiping off is cleaned with the rotating brush roll  15  in pressure contact with the wiping roll  13  and a flushing carrier solution supplied through the brush roll  15 . And, the flushing carrier solution supplied onto the wiping roll  13  from the brush roll  15  is squeezed off by the squeezing roll  14  before the wiping roll  13  is brought into rubbing contact with the photoconductor drum  1 . The carrier solution squeezed off is discharged through the tray  20  into the outside. 
     While in the form of implementation described above, the blade scraper  12  is shown comprising two scraping blades  12   a  and  12   b , they may be replaced by one or three or more blades. 
     As the wiping roller  13  in the transfer roller cleaning device  10  is made of sponge, its large capacity of absorbing the residual toner and the carrier solution is advantageously exploited to cleanly clean the surface of the transfer roller  2 . The surface of the sponge roll easily damaged are beneficially cleaned by the brush roller  15  for its use over a prolonged service life.