Abstract:
Developing roller comprising a conductive mandrel with at least an elastic conductive base layer and a charge providing layer. The base layer is located closer to the mandrel than the charge providing layer. The base layer is roughened before the charge providing layer is applied to the base layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application EP 08075296.7 filed on Apr. 15, 2008, the contents of which are incorporated herein by reference in their entirety. This application is also related to U.S. application Ser. No. 12/424,413 filed on Apr. 15, 2009. 
     FIELD 
     The present disclosure relates to a developing roller comprising a conductive mandrel with at least an elastic conductive base layer and a charge providing layer, whereby the base layer is located closer to the mandrel than the charge providing layer. 
     The present disclosure also relates to a developing apparatus comprising such a developing roller as well as a method for providing such a developing roller. 
     BACKGROUND 
     Developing rollers, known, for example, from U.S. Pat. No. 6,714,754 B2, are used in an image forming apparatus for developing an electrostatic latent image on a surface of an image bearing member by use of a non magnetic toner to form a toner image. To obtain good images, the requirements of the developing roller are relatively high, especially with respect to the conductivity, hardness, uniformess of the surface etcetera. Furthermore, it is important that the charge providing layer has a good connection to the base layer to prevent local separation or peeling off of the charge providing layer due to the friction between the charge providing layer and the parts of the non magnetic toner. 
     By the developing roller according to the above mentioned patent, an elastic intermediate layer is provided between the charge providing layer and the base layer. 
     However, this has the disadvantage that an additional layer needs to be formed on the developing roller. Such an elastic intermediate layer often comprises a solvent to have a good adherence. Such solvent is not good for the environment. Furthermore, the electrical conductivity of such an elastic layer is relatively poor. 
     SUMMARY 
     According to a first aspect, a developing roller comprising a conductive mandrel with at least an elastic conductive base layer and a charge providing layer is provided, wherein the base layer is located closer to the mandrel than the charge providing layer, and wherein the base layer is roughened before the charge providing layer is applied to the base layer. 
     According to a second aspect, a method for providing a developing roller comprising a conductive mandrel with at least an elastic conductive base layer and a charge providing layer is provided, comprising: locating the base layer closer to the mandrel than the charge providing layer, roughening the base layer and, after that, applying the charge providing layer to the base layer. 
     Further aspects of the present disclosure can be found in the specification, drawings and claims of the present application. 
     In the present disclosure, a developing roller is provided whereby a good connection between the charge providing layer and the base layer is obtained. 
     This is achieved by roughening the base layer before the charge providing layer is supplied through the base layer. 
     By roughening the surface of the base layer, a good connection is obtained between the base layer and the charge providing layer without the necessity of an elastic intermediate layer. 
     Preferably, the surface of the base layer is being roughened by blasting. Although the surface of the base layer can also be roughened by grinding, blasting is being preferred because it can create finer and more uniform surface structure than grinding. Furthermore, by blasting, a more uniform roughness over the whole surface is obtained than by grinding. A uniform surface is advantageous for obtaining a uniform charge providing layer and has a good toner transfer property and print quality. 
     An embodiment of the developing roller according to the present disclosure is characterized in that, before the charge providing layer is applied to the base layer, the base layer has a surface roughness Ra of 0.1&lt;Ra&lt;3. 
     With such a surface roughness a good connection between the base layer and the charge providing layer is obtained and also a good printing quality can be realized. 
     A further embodiment of the developing roller according to the present disclosure is characterized in that the ratio between the surface roughness of the base layer in axial direction and radial direction of the developing roller is 0.5&lt;Ra (axial direction)/Ra (radial direction)&lt;2. 
     With such a ratio a good uniformity over the total surface of the developing roller is obtained resulting in a good printing quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will now be explained with reference to the drawings in which 
         FIG. 1  is a cross section of a first embodiment of a developing roller according to the present disclosure, 
         FIG. 2  is a cross section of a second embodiment of a developing roller according to the present disclosure, 
         FIG. 3  shows on a large scale a blasted surface, 
         FIG. 4  shows on a large scale a grinded surface, 
         FIG. 5  shows in a schematic view a roller with only a base layer and an enlargement of the surface relief of the base layer of the roller. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a developing roller  1  according to the present disclosure, which comprises a conductive mandrel  2  with a diameter in the range of, e.g., 6 mm to 20 mm. On mandrel  2 , a base layer  3  of, for example, 4 mm is provided. Base layer  3  is made, for example, of silicone rubber containing conductive adhesives to control the electric resistivity. The silicone material can be Shinetsu KE1379AB. With this silicone material, the hardness of the base layer is desirably less than 65 Asker C. The outer surface  4  of the base layer  3  is roughened or abraded by blasting. The blasting media material can be silica glass, ceramic, metal or plastic. 
     In this embodiment, plastic media IEPCO MS400BT has been used. The size of the blasting media will be desirably less than 500 μm. When blasted, the blasting media is jetted out of the nozzle by air pressure in the blasting chamber. By this blasting method, the surface  4  is roughened, whereby the surface roughness Ra is controlled to be between 0.1 and 3.0 μm. 
     Roughness may be measured using contact or non-contact methods. Contact methods involve dragging a measurement stylus across the surface; these instruments include profilometers. Non-contact methods include interferometry, confocal microscopy, electrical capacitance, laser microscope and electron microscopy. The surface roughness is determined amongst others by the air pressure of blasting, the distance between blasting nozzle head and the surface, the hardness of the rubber surface and the nozzle transfers speed. 
     Due to the roughened surface, the surface energy is lowered down so that the charge providing layer  5  can easily can be adhered thereon. By blasting a finer and more uniform surface structure can be obtained (see  FIG. 3 ) than by grinding (see  FIG. 4 ). The ratio of the surface roughness in Ra axial direction and Ra radial direction on the base layer needs to be 0.5&lt;Ra(axial direction)/Ra(radial direction)&lt;2 to obtain a relatively uniform roughened surface in order to obtain uniform print pictures. 
     The charge providing layer  5  comprises elastic polymers, wherein polyurethane and conductive adhesives are mixed. Table 1 shows one example of a mixture for a charge providing layer  5 . 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 constituent 
                 Additive amount [%] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Baytron P 
                 31.5 
               
               
                   
                 Ammonia 5% 
                 1.6 
               
               
                   
                 ABU610 
                 65.5 
               
               
                   
                 Rohagit SD15 
                 0.7 
               
               
                   
                 BYK-333 
                 0.1 
               
               
                   
                 BYK-348 
                 0.6 
               
               
                   
                   
               
               
                   
                 Baytron P: H. C. Starck GmbH, ZB-PT Stab PSI, Postfach 2540, 38615 Goslar Germany 
               
               
                   
                 ABU610: Alberdingk, Deusseldorfer Str. 53, 47829 Krefeld, Germany 
               
               
                   
                 Rohagit SD15: PolynerLatex GmbH, D-45764, Marl, Germany 
               
               
                   
                 BYK-333, BYK-348, Chemie GmbH, Abelstr. 14, D-46483 Wesel, Germany 
               
             
          
         
       
     
     The volume sensitivity of the charge providing layer can be from 1×10 2  ohm cm to 1×10 7  ohm cm. In this embodiment, the sensitivity was 5×10 6  ohm cm. 
     Because the charge providing layer  5  is directly applied to the base layer  3 , the ohmic contact is much better than in a case when there is an intermediate layer between the base layer  3  and the charge providing layer  5 . 
       FIG. 2  shows a second embodiment of a developing roller  11  according to the present disclosure which differs from the developing roller  1  in that on the charge providing layer  5  a top layer  6  is applied. The top layer  6  comprises elastic polymers, wherein resin (Struktol VP5307) and latex (Rohagit SD15) are mixed. 
     Table 2 shows one example of the mixture of this top layer  6 . 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 constituent 
                 Additive amount [%] 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Struktol VP5307 
                 96.0 
               
               
                   
                 Ammonia 5% 
                 0.5 
               
               
                   
                 Rohagit SD15 
                 3.0 
               
               
                   
                 BYK-348 
                 0.5 
               
               
                   
                   
               
               
                   
                 Struktol VP5307: Schill-Seilacher Chemosch Spezialitaten, Moorfieer Str. 28, 22113 Hamburg, Germany 
               
             
          
         
       
     
     Table 3 shows the correlation between the surface roughness ratio and the print quality. Samples I-IV were blasted and sample V was ground sample with wet grinding. With wet grinding, a surface  7  as shown in  FIG. 4  will be obtained. As can be seen in table 3, the bonding quality between the base layer  3  and the charge providing layer was good on samples I-IV because of the blasting method, while the bonding and uniformity was not good on sample V. As a result, the print quality on the sample V was also not acceptable. 
     
       
         
               
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
                 Sample No 
               
             
          
           
               
                   
                 I 
                 II 
                 III 
                 IV 
                 V 
               
               
                   
               
               
                 Abrasion 
                 Blasting 
                 Blasting 
                 Blasting 
                 Blasting 
                 Wet grinding 
               
               
                 method 
                   
                   
                   
                   
                   
               
             
          
           
               
                 Roughness (Ra) on base layer [μm]: BR base layer roughness 
               
             
          
           
               
                 Axial direction 
                 0.21 
                 0.51 
                 1.5 
                 2.46 
                 1.1 
               
               
                 (BRax) [μm] 
                   
                   
                   
                   
                   
               
               
                 Radial 
                 0.25 
                 0.64 
                 1.62 
                 2.61 
                 2.5 
               
               
                 direction 
                   
                   
                   
                   
                   
               
               
                 (BRra) [μm] 
                   
                   
                   
                   
                   
               
               
                 Ratio 
                 1.190 
                 1.255 
                 1.080 
                 1.061 
                 2.273 
               
               
                 BRra/BRax 
                   
                   
                   
                   
                   
               
               
                 Charge 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
               
               
                 providing layer 
                   
                   
                   
                   
                   
               
             
          
           
               
                 Roughness (Ra) on top layer [μm]: SR = surface layer roughness 
               
             
          
           
               
                 Axial direction 
                 0.21 
                 0.87 
                 0.87 
                 1.83 
                 1.89 
               
               
                 (SRax) [μm] 
                   
                   
                   
                   
                   
               
               
                 Radial 
                 0.32 
                 0.89 
                 0.89 
                 2.56 
                 0.91 
               
               
                 direction 
                   
                   
                   
                   
                   
               
               
                 (SRa) [μm] 
                   
                   
                   
                   
                   
               
               
                 Ratio Sra/SRax 
                 1.524 
                 1.023 
                 1.023 
                 1.399 
                 0.481 
               
               
                 Bonding 
                 Good 
                 Good 
                 Good 
                 Good 
                 Bad 
               
               
                 quality 
                   
                   
                   
                   
                   
               
               
                 Print Quality 
                 Good 
                 Good 
                 Good 
                 Good 
                 Bad 
               
               
                   
                   
                   
                   
                   
                 uniformity 
               
               
                   
               
             
          
         
       
     
       FIG. 5  shows part of a conductive roller  1  according to the present disclosure which comprises a conductive mandrel  2 , which can be rotated in or opposite to the direction indicated with P 1  and a base layer  3  provided on the mandrel  2 . Further, the axial direction of the surface  9  of the base layer  3  has been indicated with ax and the radial direction following the surface  9  of the base layer  3  has been indicated with rad. 
     For obtaining a preferred surface roughness uniformity of the surface  9  of the base layer  3 , the ratio between the surface roughness of the base layer in axial direction (ax) and radial direction (rad) of the developing roller is 0.5&lt;Ra (axial direction)/Ra (radial direction)&lt;2. With such ratio, a uniform surface  9  has been obtained for providing a good connection between the base layer  3  and the charge providing layer  4 . A uniform surface  9  is needed for obtaining good toner transfer properties and print quality with said uniform charge providing layer  4 . 
     Accordingly, what has been shown are a developing roller, a developing apparatus comprising the developing roller, and a method for providing the developing roller. While such roller, apparatus and method have been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the disclosure. It is therefore to be understood that within the scope of the claims, the disclosure may be practiced otherwise than as specifically described herein.