Patent Publication Number: US-7907884-B2

Title: Cleaning member and image forming apparatus

Description:
RELATED APPLICATION 
     This application is base on patent application No. 2006-112102 filed in Japan, the entire content of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a cleaning member preferably used for cleaning off toner particles remaining on a bearing surface of an image bearing member such as photosensitive drum in an electrophotographic image forming apparatus. Also the present invention relates to an image forming apparatus including that cleaning member. 
     BACKGROUND OF THE INVENTION 
     A conventional electrophotographic image forming apparatus has an image bearing member such as photosensitive drum. The image bearing member supports a toner powder image made through a visualization of an electrostatic latent image by the use of toner particles. The toner powder image is then transferred to a medium such as paper. In this transfer operation, not all the toner particles are transferred onto the medium and a small number of particles stay untransferred on the image bearing member. The untransferred toner particles are then removed from the image bearing member by a cleaning member. 
     JP 2001-51565 A discloses a cleaning member in the form of blade. As illustrated in  FIG. 7 , a blade cleaning needs a formation of wedge-like static mass of powder  500  in a triangle zone defined by the surface of the image bearing surface  502  and the blade  504  on the upstream side of the contact region  506  with respect to the moving direction  508  of the image bearing surface  502 . The static mass of powder  506 , which includes small fragments of toner particles T and additives mixed with or added into the toner, prevents toner particles from moving into the contact region where they can be adhered onto the image bearing surface  502 . A part of the mass, i.e., a small amount of toner fragments and additives, flows out of the mass through between the image bearing surface  504  and the opposed blade  502 . The loss is compensated by new fragments and additives to be transported by the image bearing surface  504 , which results in that the amount of the mass is maintained substantially constant. The amount of toner fragments and additives flowing out of the mass can be controlled by the appropriate selection of the material of the blade  504  and/or adjusting the contact force of the blade  504  against the image bearing surface  502 . As discussed above, the mass favorably and effectively prevents the toner particles from passing through the contact region and then scattering into the air which would cause a contamination of the apparatus. 
     The size of the mass, i.e., the amount of toner fragments and additives forming the mass, can be changed according to the conditions of image formations, for example, the amount of toner particles used for the development of the electrostatic latent image. This results in the change of size of the mass. In particular, the use of toner with less additives and/or the use of smaller toner particles tends to change the size of the mass, which fails to ensure a stable cleaning of the toner particles from the image bearing surface and then causes an unwanted aggregation of the toner particles within the triangle zone which would flow out through the contact region. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a cleaning member capable of cleaning off toner particles from the image bearing surface in a stable manner, irrespective of the types of toner and the conditions of image formation. Another object of the present invention is to provide an image forming apparatus including such cleaning member. 
     The cleaning member is elastically forced on a bearing surface, for cleaning off particles from the bearing surface by a movement of the bearing surface relative to the cleaning member. In particular, the cleaning member has first and second portions capable of forming first and second ramps having first and second acute internal angles on upstream and downstream sides of a contact region with respect to a moving direction of the bearing surface, respectively, the contact region being defined between the cleaning member and the bearing surface when the cleaning member is forced on the bearing surface. 
     According to the present invention, the ramp on the upstream side scrapes off particles on the bearing member in a stable and effective manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a diagram schematically showing components of the image forming apparatus according to the present invention; 
         FIG. 2  is a partial enlarged perspective view of a cleaning member according to the present invention; 
         FIG. 3  is a partial enlarged side elevational view showing a contact portion of the cleaning device which is not forced to the image bearing member; 
         FIG. 4  is a partial enlarged side elevational view showing the contact portion of the cleaning device which is forced to the image bearing member; 
         FIG. 5  is a partial enlarged side elevational view of showing the upstream ramp is flipped over into the contact region between the cleaning member and the image bearing member; 
         FIGS. 6A and 6B  are diagrams showing a method for forming the elastic layer on the substrate; and 
         FIG. 7  is a partial enlarged side elevational view of the conventional cleaning member which forms a mass of powder on the upstream side of the cleaning member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following descriptions of the preferred embodiments are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses. 
       FIG. 1  schematically shows structural components mounted within an image forming apparatus, generally indicated by reference numeral  10 , such as a copy machine, a printing machine, a faxing machine and a complex machine including copying, printing and faxing functions. 
     The structural components of the image forming apparatus  10  will be discussed briefly together with the operations thereof. The image forming apparatus  10  includes an image bearing member or photosensitive drum  12  in the form of cylinder having an outer peripheral image bearing surface. The drum  12 , which is drivingly coupled to a drive unit  110 , is rotated in the clockwise direction. During the rotation of the drum  12 , the image bearing surface of the drum  12  is electrically charged evenly by a charging device  14 . The charged image bearing surface of the drum  12  is exposed to image light projected from an image projection device  16  to form an electrostatic latent image thereon. The electrostatic latent image is then developed by a developing device  18  by the use of toner made of toner particles into a toner powder image. The toner image is transferred onto a receiving medium or an intermediate transfer belt  20  at a first transfer region. The transfer belt  20  is entrained around a plurality of rollers including rollers  22  and  24  so that it faces the drum  12  at the first transfer region. Either one of the two rollers  22  and  24  is drivingly coupled to a drive unit  120  so that the transfer belt  20  is circulated in the counterclockwise direction. The transfer of the toner from the drum  12  onto the belt  20  is attained by the aid of a transferring device  26  mounted inside the belt  20  and closely opposed to the drum  12  at the first transfer region. The toner image on the belt  20  is transported by the movement of the belt  20  into a second transfer region where a second transfer device  28  is provided to face the outer peripheral surface of the belt  20 , so that the toner image is transferred onto a receiving medium such as a sheet S passing between the belt  20  and the transfer device  28 . Although not shown, the sheet S is then transported into a fixing device where the toner image is fused and fixed onto the sheet S. Finally, the sheet S bearing the fixed image is transported to a discharge tray or a finishing device where it is sorted. 
     Although most of the toner particles on the drum  12  are transferred onto the belt  20 , part of toner particles remain on the drum  12  without being transferred onto the belt  20 . Likewise, although most of the toner particles on the belt  20  are transferred onto the sheet S, part of the toner particles remain on the belt  20  without being transferred onto the sheet S. In order to remove the untransferred toner particles from the drum  12  and the belt  20 , the image forming apparatus includes first and second cleaning device  32  and  34  for cleaning off toner particles from the drum  12  and belt  20 , respectively. The cleaning device  32  has a cleaning member  36  in the form of blade for scraping off toner particles from the image bearing surface of the drum  12  and a container  38  for receiving the scraped off toner particles. Likewise, the cleaning device  34  has a cleaning member  40  in the form of blade for scraping off toner particles from the image bearing surface of the belt  20  and a container  42  for receiving the scraped off toner particles. The structures of the cleaning members  36  and  40  will be discussed in great details in the later discussions. 
     The drive unit  110  for the drum  12  has a rotational drive source  112  such as a motor drivingly coupled with the drum  12  and a control means or drive control  114  for controlling the drive source  112 . The drive control  114  controls the drive source  112  so that the drum  12  rotates in the forward direction, i.e., clockwise direction in the image forming operation described above and rotates in the backward direction, i.e., counterclockwise direction in a recovering operation of the cleaning member  36  which will be described later. Likewise, the drive unit  120  for the belt  20  has a rotational drive source  122  such as a motor drivingly coupled with the roller  22  or  24  and a control means or drive control  124  for controlling the drive source  122 . The drive control  124  controls the drive source  122  so that the belt  20  rotates in the forward direction, i.e., counterclockwise direction in the image forming operation described above and rotates in the backward direction, i.e., clockwise direction in a recovering operation of the cleaning member  40  which will be described later. 
     Discussions will be made in detail to the cleaning members  36  and  40  of the cleaning devices  32  and  34 . The cleaning members  36  and  40  are used for cleaning off toner particles from different members, i.e., drum  12  and belt  20 , made of different materials and in different configurations. Therefore, they may be positioned in difference angles with respect to the image bearing surfaces of the drum  12  and the belt  20  and/or may be set to contact with the drum  12  and belt  20  with different contact forces. The cleaning members  36  and  40 , however, have substantially the same basic structure and attain substantially the same function in scraping off toner particles. 
       FIG. 2  is an enlarged perspective view of the cleaning members  36  and  40  and  FIG. 3  is an enlarged side elevational view of the corner of cleaning members  36  and  40 . 
     Each of the cleaning members  36  and  40  has a substrate  150  in the form of elongated rectangular plate extending in the direction parallel to the central axis  152  of the drum  12 . The plate, which is preferably made of elastic material, has a pair of opposed major surfaces  154  and  156 , a pair of opposed longitudinal side surfaces  158  and  160 , and a pair of end surfaces  162  and  164 . Preferably, the plate has a thickness of about 0.5 to 10 mm. 
     The longitudinal side surface  158  of the substrate  150 , which would be placed adjacent image bearing member  12 ,  20 , supports an elastic layer  170 . The elastic layer  170 , which is made of elastic material, is mounted on substantially the entire portion of the surface  158 . Preferably, the elastic layer  170  has a thickness of about 50 to 500 μm. As indicated in  FIG. 3 , the elastic layer  170  has a major surface  172  away from the side surface  158  of the substrate  150  and a longitudinal side surface  174 . 
     As best shown in  FIG. 3 , a contact portion  176 , which will be brought into contact with the image bearing surface, is defined by a contact sub-portion (second sub-portion)  178  of the substrate  150  including a longitudinal corner edge  180  defined between the major surface  156  and the longitudinal side surface  158  and a contact sub-portion  182  of the elastic layer  170  including a longitudinal corner edge  184  between the major surface  172  and the side surface  174 . Preferably, as best shown in  FIG. 3 , the corner edge  184  of the elastic layer  170  is positioned slightly away from the corner edge  180  of the substrate  150 . 
       FIG. 4  shows a part of the cleaning member  36 ,  40  in which the cleaning member is inclined to the image bearing surface  186  of the image bearing member  12 ,  20  and the contact portion  176 , in particular, the surface portions extending between the corner edges  180  and  184 , is forced onto the image bearing surface with the major surface  172  of the elastic layer  170  positioned on the upstream side of the moving direction  188  of the image bearing member  36 , 40  and with the major surface  156  of the substrate  150  positioned on the downstream side of the moving direction  188 , causing the resiliently deformed contact portion  176  to form a contact region  190 . The cleaning member  36 ,  40  is fixedly supported by, for example, the container  38 , 42 , so that the deformed corner edge  180  of the substrate  150  defines a ramp (second ramp)  192  with an acute internal angle (contact angle) β on the downstream side of the contact region  190  with respect to the moving direction  188  of the image bearing member  186  and also the deformed corner edge  184  of the elastic layer  170  defines a ramp (first ramp)  194  with an acute internal angle α on the upstream side of the contact region  190 . 
     In cleaning operation, the residual toner particles  100  on the image bearing surface  186  of the image bearing member  12 ,  20  are transported in the direction of arrow  190  to reach the deformed contact portion  176  where the toner particles  100  are scraped or cleaned off by the ramp  194  of the elastic layer  170  and away from the image bearing surface  186 . The scraped toner particles  100  are then received by the container  32 ,  42 . 
     As described above, the ramp  194  acts as the particle mass formed at the triangle area between the image bearing surface and the cleaning member as indicated in  FIG. 7 , which ensures that the toner particles are effectively scraped off from the image bearing member. 
     To maintain the acute angles α and β of the ramps  192  and  194  on the upstream and downstream sides of the contact region, respectively, with respect to the moving direction of the image bearing member even at the rotation of the image bearing member  56 , the materials of the substrate  150  and the elastic layer  170  should be appropriately selected from among elastic materials such as isoprene rubber, butadiene rubber, butyl-rubber, ethylene-propylene rubber, chloroprene rubber, epichlorohydrin rubber, acrylic rubber, urethane rubber, silicon rubber, fluorocarbon rubber, styrene-butadiene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, nitrile rubber and polysulfide rubber. 
     Preferably, the material of the elastic layer  170  has smaller hardness and static friction coefficient than the substrate  150 . Otherwise, ramp  194  of the elastic layer  170  might be drawn into the contact region by the frictional contact with the moving image bearing surface  186  and disappear so that the elastic layer  170  defines instead an obtuse internal angle α′ as illustrated in  FIG. 5 . The end portion of the elastic layer  170  with the obtuse internal angle α′ is evidently unable to scrape off toner particles  100 , in turn allowing the toner particles  100  to flow into the contact region  190  between the contact portion  176  and the image bearing surface  186 . 
     The inventor of the present invention conducted experiments to confirm the fact that the elastic layer  170  of the cleaning member  36 , 40  favorably scrapes off toner particles from the image bearing surface  186 . The experiments were conducted using the cleaning member with the elastic layer and the cleaning member without the elastic layer. In the experiments, the cleaning abilities were evaluated for respective line pressures between the cleaning members and the photosensitive member by measuring the amounts of toner scraped off from the image bearing surface by the cleaning members. 
     Each substrate of the cleaning members was made of urethane rubber and was sized to have a longitudinal length of 250 mm, a width of 15 mm, and a thickness of 2 mm. The elastic layer was made of silicon rubber having a thickness of about 50 μm. The hardness, i.e., durometer hardness, of the substrates and the elastic layer was measured in accordance with a measurement method JIS K6253, in an environment at 25 degrees Celsius and at 60% relative humidity. The measurements showed that the substrate had a hardness of A70. Also confirmed was that the elastic layer had a smaller hardness than the substrate. The static friction coefficients of the substrates and the elastic layer against hard chromium treated brass with a weight of 40 g was measured in accordance with a measurement method JIS K7125 in an environment at 25 degrees Celsius and at 60% relative humidity. The measurements showed that the static friction coefficient of the substrates was 0.9, while that of the elastic layer was less than 0.4. 
     The photosensitive drum was used for the image bearing member, with the image bearing surface made of low-friction material polytetrafluoroethylene (PTFE). The line pressures between the cleaning members and the image bearing surface were set to 10 N/m and 20 N/m. 
     To ensure the reliability of the results, the same amounts of toner of the same type with minimum additives was used for respective cleaning members. The cleaning ability of each cleaning member was evaluated in terms of the amount of toner the cleaning member scraped off. The result is shown in the following Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Cleaning Ability 
               
            
           
           
               
               
               
            
               
                   
                 Line Pressure 
                   
               
            
           
           
               
               
               
            
               
                   
                 20 N/m 
                 10 N/m 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cleaning Member with 
                 Favorable 
                 Favorable 
               
               
                   
                 Elastic Layer 
               
               
                   
                 Cleaning Member 
                 Unfavorable but 
                 Unfavorable and 
               
               
                   
                 without Elastic Layer 
                 Tolerable 
                 Intolerable 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from the Table, the cleaning ability of the cleaning member with the elastic layer was favorable irrespective of the line pressure. In contrast, the cleaning ability of the cleaning member without the elastic layer was increased with the increase of the line pressure but less than that of the cleaning member with the elastic layer at respective line pressures. Evidently, the result indicates that the elastic layer fairly contributes to the improvement of the cleaning ability, i.e., toner scraping ability. 
     As shown in  FIG. 3 , the elastic layer  170  is so positioned that the corner edge  184  of the elastic layer  170  stays back from the corner edge  180  of the substrate  150 . This arrangement may be attained by the conventional ways such as cutting off the longitudinal end of the elastic member or molding the elastic layer on the substrate, however, the inventor of the present invention discovered a favorable method for forming the elastic layer  170 , which will be discussed below. 
     Discussions will be made to a relatively simple method for forming the elastic layer on the substrate while leaving the sub-portion  178  of the substrate  150  uncovered by the sub-portion  182  of the elastic layer  170 . According to this method, as shown in  FIG. 6A , an elastic material  170 ′ in the form of liquid is applied on a flat and smooth plate  198 . Preferably, the plate  198  has a wettability to the elastic material so that the contact angle of the liquid elastic material to the plate is an acute angle equal to or substantially equal to the acute internal angle α. The longitudinal corner edge  180  of the substrate  150  is forced onto the plate  198  so that it forms the ramp  192  with the acute internal angle β. The substrate  150  is slidingly and wipingly moved on the plate  198  while maintaining the deformation of the substrate  150 , so that the exposed longitudinal surface  158  of substrate  150  comes into contact with the elastic material  170 ′. This results in that, as shown in  FIG. 6B , the elastic material  170 ′ is applied onto the exposed longitudinal surface  158  of the substrate  150 . In this state, the applied elastic material  170 ′ has the acute contact angle α on one side away from the substrate  150 . To this end, the liquid elastic material  170 ′ is preferably selected from materials having a contact angle α against the plate  198 . The liquid elastic material  170 ′ then flows up on the exposed surface  158  to form the thin elastic layer due to the surface tension of the liquid. The substrate  150  with the elastic material is maintained for a certain time while maintaining the state shown in  FIG. 6B  to solidify the elastic material, forming the elastic layer  170  as shown in  FIG. 4 . 
     Although the deformed substrate  150  is moved on the plate  198  at the application of the elastic material  170 ′ onto the longitudinal surface  158 , the plate  198  may be moved instead while maintaining the substrate  150  unmoved. 
     The elastic layer  170  may be formed in different ways. For example, according to the alternative method, the liquid elastic material  170 ′ is applied on the surface  158  of the substrate  150 . This can be done by contacting the surface  158  to the liquid elastic material  170 ′. Then, the longitudinal corner edge  180  is forcedly brought into contact with the plate  198  so as to form the ramp  192 . This causes the liquid material on the contact portion of the surface  158  to be removed therefrom, as shown in  FIG. 6B . The remaining elastic material  170 ′ is then solidified to form the stable elastic layer  170 . 
     Although the plate  198  is used in the previous embodiments, it may be replaced by a roller having a smooth peripheral surface. 
     Once the cleaning member is released from the plate  198 , unlike the elastic layer  170  shown in  FIG. 3 , the formed sub-portion  182  of the elastic layer  170  may have a thickness slightly greater or smaller than the major portion of the elastic layer. Also, the released corner edge  184  may have a certain angle greater or less than 90 degrees. It should be noted that the cleaning member with those configurations is also within the scope of the present invention. In other words, it should be understood that the cleaning member falls within the scope of the present invention provided that, when forced onto the image bearing member, it is capable of forming ramps with acute internal angles on the upstream and downstream sides with respect to the movement of the image bearing member. 
     The cleaning member so manufactured ensures that the ramp with the acute internal angle on the upstream side attains a stable and effective scraping of the toner particles from the image bearing surface, irrespective of the types of the toner and/or the amount of toner to be employed for the image formation. 
     The ramp  194  on the upstream side can be flipped over by the temporally increased frictional force against the image bearing member or the toner particles and then drawn into between the substrate and the image bearing member as shown in  FIG. 5 . The flipped portion can be returned into the normal state to recover the ramp  194  simply by moving the contacting image bearing surface in the backward direction. In the recovering operation, the image bearing member is preferably moved back and forth alternately by changing the rotation of the drum  12 /the belt  20  on the basis of instruction from the drive control  114 , 124 . Also, in this operation, the image bearing member is preferably moved back  10  mm or more, for example. 
     The foregoing description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 
     For example, although the substrate and the elastic layer of the cleaning member are made of different materials in the previous embodiment, they may be made of the same material.