Abstract:
In a developing device, a developing roller has an outer peripheral surface movable in a moving direction upon rotation of the developing roller to transfer developing agent to a developing region having a width in an axial direction of the developing roller. A thickness regulation blade includes a rubber portion. The rubber portion provides a contact region in contact with the outer peripheral surface to provide a nip region relative to the developing roller. The contact region includes a first region; and a second region. The first region and the second region each extends in the axial direction by a length at least equal to or greater than the width of the developing region. The first region has a first surface roughness. The second region is positioned downstream of the first region in the moving direction and has a second surface roughness finer than the first surface roughness.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2014-071269 filed Mar. 31, 2014. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a developing device that includes a developing roller and a thickness regulation blade regulating the thickness of developer carried by the developing roller. 
     BACKGROUND 
     Hitherto, a developing device in an electro-photographic image forming apparatus includes a casing, a developing roller, and a blade. The casing accommodates developer. The developing roller carries the developer. The blade contacts the developing roller with the developer interposed therebetween and regulates the thickness of the developer layer carried by the developing roller. Further, the blade includes a rubber portion and a support plate. The rubber portion regulates the thickness of the developer layer carried by the developing roller. The support plate supports the rubber portion. 
     In the developing device, the developing roller carries the developer accommodated in the casing. The rubber portion has a contact region that forms a nip with respect to the developing roller, and regulates the thickness of the developer layer carried by the developing roller in the contact region. Further, the developing roller carries the developer of which the thickness is regulated to a developing region between a photosensitive drum and the developing roller, and supplies the developer to an electrostatic latent image formed on the surface of the photosensitive drum, so that a developer image is formed thereon (see Japanese Patent Application Publication No. H06-186838). 
     SUMMARY 
     In the above-described technique, however, when the surface roughness of the contact region of the rubber portion is coarse, the thickness of the developer layer carried by the developing roller varies in a rotation axis direction of the developing roller. Thus, the developer density in an image printed on a sheet may be uneven in the rotation axis direction of the developing roller. 
     Meanwhile, when the surface roughness of the contact region of the rubber portion is fine, the thickness of the developer layer carried by the developing roller becomes substantially uniform in the rotation axis direction of the developing roller. However, when the surface roughness of the contact region of the rubber portion is fine, a friction force applied from the contact region of the rubber portion to the developer increases between the developing roller and the rubber portion. Then, the developer or the external additive released from the developer is locally fixed to the upstream end of the contact region at the nip of the developing roller in a moving direction. 
     Specifically, the developer layer carried on the developing roller is thinned while passing through the nip. That is, most developer passes through the upstream end of the contact region compared to the other portion of the contact region. Consequently, when the surface roughness of the contact region of the rubber portion is fine, the pressure between the rubber portion and the developing roller increases at the upstream end of the contact region, and the friction force applied from the contact region of the rubber portion to the developer increases between the rubber portion and the developing roller. Then, the developer or the external additive released from the developer is locally fixed to the upstream end of the contact region at the nip of the developing roller in the moving direction. 
     In this way, a region of the rubber portion where the developer or the external additive released from the developer is fixed thins the thickness of the developer layer more compared to a region where the developer or the external additive is not fixed. As a result, a vertical stripe may be formed on an image when the image is formed on the sheet. 
     In order to solve this problem, the surface roughness of the blade should be set optimally so that the above-described problems do not occur. However, highly precise processing is needed so as to optimally set the surface roughness of the blade, and hence the rubber portion is not easily produced. 
     In view of the foregoing, it is an object of the disclosure to provide a developing device capable of easily producing a thickness regulation blade while preventing failures in image formation. 
     In order to attain the above and other objects, the disclosure provides a developing device that includes a developing roller; and a thickness regulating blade. The developing roller is rotatable about a rotation axis defining an axial direction. The developing roller has an outer peripheral surface movable in a moving direction upon rotation of the developing roller to transfer developing agent to a developing region having a width in the axial direction. The thickness regulation blade includes a support portion; and a rubber portion. The rubber portion is supported by the support portion and provides a contact region in contact with the outer peripheral surface to provide a nip region relative to the developing roller. The rubber portion includes a first region; and a second region. The first region extends in the axial direction by a length at least equal to or greater than the width of the developing region, and is positioned in alignment with the developing region in the moving direction. The first region has a first surface roughness. The second region extends in the axial direction by a length at least equal to or greater than the width of the developing region, and is positioned in alignment with the developing region in the moving direction. The second region is positioned downstream of the first region in the moving direction and has a second surface roughness finer than the first surface roughness. 
     According to another aspect, the present invention provides a developing device that includes a developing roller; and a thickness regulation blade. The developing roller is rotatable about a rotation axis defining an axial direction. The developing roller has an outer peripheral surface movable in a moving direction upon rotation of the developing roller to transfer developing agent to a developing region having a width in the axial direction. The thickness regulation blade includes a support portion; and a rubber portion. The rubber portion is supported by the support portion and extends in the axial direction. The rubber portion has an upstream end in the moving direction, a first end portion and a second end portion in the axial direction, an inner side surface extending in the moving direction, an outer side surface extending in the moving direction and positioned outward of the inner side surface in the axial direction, and a bottom surface. A first notch and a second notch are formed in the first end portion and the second end portion, respectively. The first notch and the second notch each has an open end at the upstream end. The inner surface of the first notch and the inner surface of the second notch are aligned with a boundary of the developing region in the moving direction. The rubber portion provides a contact region in contact with the outer peripheral surface to provide a nip region relative to the developing roller. The contact region includes a first region; and a second region. The first region extends in the axial direction from the inner surface of the first notch to the inner surface of the second notch. The first region has a first surface roughness. The second region extends in the axial direction from a portion outward of the outer surface of the first notch to a portion outward of the outer surface of the second notch. The second region is positioned downstream of the first region in the moving direction and has a second surface roughness finer than the first surface roughness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of this disclosure as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic cross-sectional view of a laser printer; 
         FIG. 2  is a schematic cross-sectional view of a developing unit; 
         FIG. 3  is an enlarged view of a contact portion of a developing roller and a rubber portion of a thickness regulation blade; 
         FIG. 4  is an explanatory diagram showing a positional relationship of a photosensitive drum, the developing roller, and the thickness regulation blade in a rotation axis direction of the developing roller; 
         FIG. 5  is an enlarged view of one end of the rubber portion in the rotation axis direction of the developing roller; 
         FIG. 6  is an explanatory diagram showing a device for processing a mold; 
         FIGS. 7A, 7B and 7C  are diagrams showing the mold viewed from a spraying direction of a nozzle shown in  FIG. 6 ,  FIG. 7A  is an explanatory diagram explaining a process of a region corresponding to a first region of the rubber portion in the mold,  FIG. 7B  is an explanatory diagram explaining a process of a region corresponding to a second region of the rubber portion in the mold,  FIG. 7C  is an explanatory diagram explaining a process of a region corresponding to a third region of the rubber portion in the mold; 
         FIG. 8  is an explanatory diagram showing a configuration of a rubber portion in a modification; and 
         FIG. 9  is an explanatory diagram showing a contact state of the developing roller and the rubber portion with developer interposed therebetween. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     The first embodiment will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     1. Overall Configuration of Laser Printer  1   
     First, an overall configuration of a laser printer  1  will be described with reference to  FIG. 1 . The laser printer  1  includes a main body frame  10 , a sheet feeding unit  20 , an image forming unit  30 , and a sheet discharging unit  40 . The sheet feeding unit feeds a sheet. The image forming unit forms an image on the sheet fed by the sheet feeding unit  20 . The sheet discharging unit  40  discharges the sheet having an image formed thereon by the image forming unit  30  to the outside of the main body frame  10 . 
     The image forming unit  30  includes an exposure device  50 , a process unit  60 , and a fixing device  70 . The exposure device  50  is configured to form an electrostatic latent image on the outer peripheral surface of a photosensitive drum  82 , and is disposed at the upper portion of the main body frame  10 . The process unit  60  is attachable to or detachable from the main body frame  10 , and includes a drum unit  80  and a developing unit  90  as an example of a developing device. 
     The drum unit  80  includes a drum frame  81 , the photosensitive drum  82 , a charger  83 , and a transfer roller  84 . The photosensitive drum  82  forms an electrostatic latent image on the outer peripheral surface thereof. The charger  83  uniformly charges the outer peripheral surface of the photosensitive drum  82 . The transfer roller  84  transfers a developer image carried on the outer peripheral surface of the photosensitive drum  82  onto a sheet. The photosensitive drum  82  includes an image forming region A (see  FIG. 4 ) where an electrostatic latent image is formed. 
     The developing unit  90  includes a developing frame  91  and a developing roller  92 . The developing frame  91  is detachably attached to the drum unit  80  and accommodates developer. The developing roller  92  carries the developer. The developing roller  92  contacts the image forming region A of the photosensitive drum  82  so as to form a developing region B (see  FIG. 4 ) between the developing roller  92  and the photosensitive drum  82 . Further, the developing roller  92  carries the developer to the developing region B, and supplies the developer to the electrostatic latent image formed on the image forming region A of the photosensitive drum  82 . 
     The fixing device  70  is configured to fix a developer image formed on the sheet. The fixing device  70  includes a heating roller  71  and a pressing roller  72 . The heating roller  71  includes a heater. The pressing roller  72  contacts the heating roller  71 . The developer image formed on the sheet is fixed onto the sheet while passing between the heating roller  71  and the pressing roller  72 . 
     2. Configuration of Developing Unit  90   
     Next, the configuration of the developing unit  90  will be described with reference to  FIG. 2 . 
     As illustrated in  FIG. 2 , the developing unit  90  includes the developing frame  91 , the developing roller  92 , a supply roller  93 , and a thickness regulation blade  100 . 
     The developing frame  91  includes a developing chamber  91   a  and a developer accommodation chamber  91   b . The developing chamber  91   a  supports the developing roller  92  and the supply roller  93 . The developer accommodation chamber  91   b  accommodates the developer. In the present embodiment, the developer is a positively-chargeable nonmagnetic monocomponent toner. Further, a silica particle as an example of an external additive for improving the flowability is added to the toner. Incidentally, the external additive may be titania or alumina. 
     The developing roller  92  is supported by the developing frame  91  through a bearing. The developing roller  92  includes a metal shaft  92   a  and an elastic layer  92   b . The elastic layer  92   b  is provided in the periphery of the metal shaft  92   a , and is formed of urethane rubber. Incidentally, the elastic layer  92   b  may be formed of silicone rubber. The supply roller  93  is supported by the developing frame  91 . The supply roller  93  includes a metal shaft and an elastic layer. The elastic layer is provided in the periphery of the metal shaft, and is formed of a sponge. 
     The thickness regulation blade  100  is disposed so as to regulate the thickness of the developer layer carried by the developing roller  92 . A base end of the thickness regulation blade  100  is supported by the developing frame  91 , and the front end thereof contacts the developing roller  92  with the developer interposed therebetween. Further, the thickness regulation blade  100  includes a rubber portion  101  and a support plate  102 . The support plate  102  supports the rubber portion  101 . The rubber portion  101  is formed of silicone rubber, and is stuck to the support plate  102  with an adhesive. The support plate  102  is composed of an elastic thin metal plate. A base end  102   a  of the support plate  102  is supported by the developing frame  91 , and a front end  102   b  thereof supports the rubber portion  101 . 
     3. Detailed Description of Rubber Portion  101   
     Next, the rubber portion  101  as the characteristic portion of the embodiment will be described with reference to  FIGS. 3 to 5 . 
     As illustrated in  FIG. 3 , the rubber portion  101  is formed in a semi-cylindrical shape so as to protrude toward the developing roller  92 . A surface  101   d  of the rubber portion  101  contacts an outer peripheral surface  92   a  of the developing roller  92  with the developer interposed therebetween, and includes a contact region  110  in contact with the outer peripheral surface  92   a  to provide a nip N relative to the developing roller  92 . The contact region  110  includes a first region  120  and a second region  130 . The first region  120  extends toward the downstream side from an upstream end  111  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X. The second region  130  is disposed at the downstream side in relation to the first region  120  at the nip N of the developing roller  92  in the moving direction X. 
     The first region  120  extends from the upstream end  111  of the contact region  110  toward the center C of the nip N. The second region  130  extends from a downstream end  112  of the contact region  110  toward the center C of the nip N. Consequently, the first region  120  and the second region  130  are connected to each other at the center C of the nip N. 
     As illustrated in  FIG. 4 , the first region  120  of the contact region  110  is disposed in the entire width of the developing region B, extending in the rotation axis direction by a length at least equal to the width of the developing region B. Specifically, the first region  120  is disposed at least from a first imaginary line L 1  to a second imaginary line L 2 . The first imaginary line L 1  passes through one end of the developing region B in the rotation axis direction of the developing roller  92  and is perpendicular to the rotation axis direction of the developing roller  92 . The second imaginary line L 2  passes through the other end of the developing region B in the rotation axis direction of the developing roller  92  and is perpendicular to the rotation axis direction of the developing roller  92 . Incidentally, the width of the developing region B matches the width of the image forming region A of the photosensitive drum  82 . 
     The second region  130  of the contact region  110  is disposed in the entire width of the developing region B, extending in the rotation axis direction by a length at least equal to the width of the developing region B. Specifically, the second region  130  is disposed from one end  101   a  of the rubber portion  101  to the other end  101   b  thereof in the rotation axis direction of the developing roller  92 . Consequently, the dimension of the second region  130  in the rotation axis direction of the developing roller  92  is longer than the dimension of the first region  120  in the rotation axis direction of the developing roller  92 . Incidentally, one end  101   a  of the rubber portion  101  is an end which is disposed at the left side when the drawing paper of  FIG. 4  is viewed from the upside, and the other end  101   b  of the rubber portion  101  is an end which is disposed at the right side when the drawing paper of  FIG. 4  is viewed from the upside. 
     Further, the surface roughness of the first region  120  is coarser than the surface roughness of the second region  130 . In the present embodiment, the surface roughness is set as an arithmetic average roughness value Ra. It is preferable that the arithmetic average roughness value Ra of the first region  120  is within the range of 0.5 μm to 0.8 μm. It is further preferable that the arithmetic average roughness value Ra of the first region  120  is within the range of 0.6 μm to 0.7 μm. In the present embodiment, the arithmetic average roughness value Ra of the first region  120  is 0.6 μm. 
     It is preferable that the arithmetic average roughness value Ra of the second region  130  is within the range of 0.1 μm to 0.4 μm. It is further preferable that the arithmetic average roughness value Ra of the second region  130  is within the range of 0.2 μm to 0.3 μm. In the present embodiment, the arithmetic average roughness value Ra of the second region  130  is 0.2 μm. Further, the arithmetic average roughness value Ra of the first position  120  does not have an orientation. In addition, the arithmetic average roughness value Ra of the second region  130  does not have an orientation. 
     Here, the arithmetic average roughness value Ra can be measured by, for example, the following method. The surface roughness values of the first region  120  and the second region  130  are measured by SURFCOM 5000DX manufactured by TOKYO SEIMITSU CO., LTD. on the basis of JIS B0633. The measurement is performed while extraneous matter such as developer and the like is not stuck to the surfaces of the first region  120  and the second region  130 . Further, the measurement direction of the surface roughness corresponds to two directions, that is, the rotation axis direction of the developing roller  92  and the moving direction X at the nip N of the developing roller  92 , and the measurement position of the surface roughness corresponds to three positions, that is, one end, the center, and the other end of each of the first region  120  and the second region  130  in the rotation axis direction of the developing roller  92 . The surface roughness values of the first region  120  and the second region  130  are calculated in a manner such that the surface roughness values measured at six positions in this way are averaged. 
     Further, the contact region  110  includes a pair of third regions  140  and a pair of notches  150 . The pair of third regions  140  extend toward the upstream side in the moving direction X at the nip N of the developing roller  92  from both ends of the second region  130  in the rotation axis direction of the developing roller  92 . The pair of notches  150  are disposed between the first region  120  and the pair of third regions  140  in the rotation axis direction of the developing roller  92 . The pair of third regions  140  and the pair of notches  150  have the same structure respectively. In the description below, the third region  140  which is disposed at the left side when the drawing paper of  FIG. 4  is viewed from the upside and the notch  150  which is disposed at the left side when the drawing paper of  FIG. 4  is viewed from the upside will be described. 
     The third region  140  is disposed outside the developing region B. In other words, the third region  140  is disposed between one end  101   a  of the rubber portion  101  and the first region  120  in the rotation axis direction of the developing roller  92 . 
     The notch  150  is disposed outside the developing region B. In other words, the notch  150  is disposed between the first region  120  and the third region  140 . Further, the notch  150  is formed in such a way as to be recessed toward the downstream side at the nip N of the developing roller  92  in the moving direction X from an upstream end  101   c  of the rubber portion  101  at the nip N of the developing roller  92  in the moving direction X. 
     Further, as illustrated in  FIG. 5 , the second region  130  of the contact region  110  includes an extension region  131  which extends in the rotation axis direction of the developing roller  92  with respect to one end  121  of the first region  120  in the rotation axis direction of the developing roller  92 . Incidentally, one end  121  of the first region  120  is an end which is disposed at the leftmost side when the drawing paper of  FIG. 5  is viewed from the upside among the ends of the first region  120  in the rotation axis direction of the developing roller  92 . 
     The third region  140  extends toward the upstream side at the nip N of the developing roller  92  in the moving direction X from an upstream end  132  of the extension region  131  at the nip N of the developing roller  92  in the moving direction X. Further, the surface roughness of the third region  140  is coarser than the surface roughness of the first region  120 . It is preferable that the arithmetic average roughness value Ra of the third region  140  is within the range of 0.8 μm to 1.4 μm. It is further preferable that the arithmetic average roughness value Ra of the third portion  140  is within the range of 1.0 μm to 1.2 μm. In the present embodiment, the arithmetic average roughness value Ra of the third region  140  is 1.0 μm. Consequently, the arithmetic average roughness values Ra of the first region  120 , the second region  130 , and the third region  140  increase in order of the second region  130 , the first region  120 , and the third region  140 . 
     The notch  150  is formed in a portion which is surrounded by one end  121  of the first region  120  in the rotation axis direction of the developing roller  92 , the upstream end  132  of the extension region  131  at the nip N of the developing roller  92  in the moving direction X, and one end  141  of the third region  140  in the rotation axis direction of the developing roller  92 . Incidentally, one end  141  of the third region  140  corresponds to an end which is disposed near the first region  120 . 
     In other words, the notch  150  has an open end at the upstream end of the rubber portion  101  in the moving direction X. The notch  150  also has an inner side surface, an outer side surface, and a bottom surface. The inner side surface of the notch  150  extends in the moving direction X and is aligned with one end  121  of the first region  120  in the rotation axis direction of the developing roller  92 . The outer side surface of the notch  150  extends in the moving direction X and is aligned with an inner end of the third region  140  in the rotation axis direction of the developing roller  92 . The bottom surface of the notch  150  extends in the rotation axis direction of the developing roller  92  and is aligned with the upstream end  132  of the extension region  131 , the upstream end of the second region  130 , and the downstream end of the first region  120 . That is, in the present embodiment, the downstream end of the first region  120 , the upstream end of the second region  130 , the upstream end  132  of the extension region  131 , and the bottom surface of the notch  150  are aligned with the center C of the nip N in the moving direction X. 
     4. Method of Processing Surface  101   d  of Rubber Portion  101  at Desired Surface Roughness 
     Next, an example of a method of processing the surface  101   d  of the rubber portion  101  at a desired surface roughness will be described with reference to FIGS.  6  and  7 . 
     The rubber portion  101  is molded by pouring melted urethane rubber into a mold  160 . Further, a blasting process is performed on a portion corresponding to the contact region  110  of the rubber portion  101  in the mold  160  by an existing blasting device  170  in order to apply a desired surface roughness thereto. Hereinafter, a blasting process in the mold  160  will be described in detail. 
     First, there is a need to measure the dimension of the contact region  110  of the rubber portion  101  when a blasting process is performed on the mold  160 . The dimension measurement method is performed in the following procedure. 
     First, the rubber portion  101  contacts the developing roller  92  which carries a thinned developer layer. At this time, the contact pressure of the rubber portion  101  with respect to the developing roller  92  is set to 5 N/m. Here, the contact pressure corresponds to the contact pressure when the developer layer is thinned by the rubber portion  101 . Subsequently, the developing roller  92  is separated from the rubber portion  101 . Then, the developer which is carried by the developing roller  92  is stuck to the rubber portion  101 . At this time, the area of the developer stuck to the rubber portion  101  matches the contact region  110  of the rubber portion  101 . That is, the dimension of the contact region  110  of the rubber portion  101  can be measured by measuring the dimension of the area of the developer stuck to the rubber portion  101 . 
     Next, a blasting process is performed on a portion corresponding to the contact region  110  of the rubber portion  101  in the mold  160 . As illustrated in  FIG. 6 , the blasting device  170  includes a compressor  171 , a pressurized tank  172 , and a nozzle  173 . The pressurized tank  172  has a gas therein. The nozzle  173  sprays a gas which is compressed by the compressor  171  and is stored inside the pressurized tank  171  toward the mold  160 . The nozzle  173  is configured to spray the gas toward the mold  160  while moving in the right and left direction when the drawing paper of  FIG. 6  is viewed from the upside. In other words, the nozzle  173  processes the mold  160  while moving in the right and left direction when the drawing paper of  FIG. 6  is viewed from the upside. 
     Incidentally, the gas includes spherical glass beads. Further, the gas may include amorphous alumina particles. In addition, the blasting device  170  may appropriately change the degree of the desired surface roughness by changing the particle diameter of the glass bead included in the gas. The surface roughness to be given increases as the particle diameter of the glass bead increases. 
     In the present embodiment, three kinds of glass beads having different particle diameters are prepared as a first glass bead, a second glass bead, and a third glass bead. The first glass bead is a glass bead for processing the first region  120  of the contact region  110 . The second glass bead is a glass bead for processing the second region  130  of the contact region  110 . The third glass bead is a glass bead for processing the third regions  140  of the contact region  110 . The particle diameter of the first glass bead is larger than the particle diameter of the second glass bead, and is smaller than the particle diameter of the third glass bead. That is, the particle diameter of the glass bead increases in order of the second glass bead, the first glass bead, and the third glass bead. 
     The blasting process includes three processes, that is, a first process, a second process, and a third process. The first process processes a portion corresponding to the first region  120  of the contact region  110  in the mold  160  using the first glass bead. The second process processes a portion corresponding to the second region  130  of the contact region  110  in the mold  160  using the second glass bead. The third process processes portions corresponding to the third regions  140  of the contact region  110  in the mold  160  using the third glass bead. 
     Specifically, as illustrated in  FIG. 7A , the first process is performed first while masking tape T is attached to portions other than a portion  161  corresponding to the first region  120  of the rubber portion  101  in the mold  160 . Then, a desired surface roughness is given only to the portion  161  corresponding to the first region  120  of the rubber portion  101  in the mold  160 . Subsequently, as illustrated in  FIG. 7B , the second process is performed while masking tape T is attached to portions other than a portion  162  corresponding to the second region  130  of the rubber portion  101  in the mold  160 . Then, a desired surface roughness is given only to the portion  162  corresponding to the second region  130  of the rubber portion  101  in the mold  160 . Subsequently, as illustrated in  FIG. 7C , the third process is performed while masking tape T is attached to a portion other than portions  163  corresponding to the third regions  140  of the rubber portion  101  in the mold  160 . Then, a desired surface roughness is given only to the portions  163  corresponding to the third regions  140  of the rubber portion  101  in the mold  160 . 
     Melted urethane rubber is poured into the mold  160  subjected to the above-described processes. Subsequently, the mold  160  is cooled, and the rubber portion  101  is taken out from the cooled mold  160 . Thus, the rubber portion  101  of the present embodiment is molded. 
     5. Advantageous Effects of First Embodiment 
     (1) The surface roughness of the first region  120  of the contact region  110  is coarser than the surface roughness of the second region  130  of the contact region  110 . 
     As illustrated in  FIG. 9 , the developer layer which is carried by the developing roller  92  is thinned while passing through the nip N. At this time, most developer passes through the upstream end  111  of the contact region  110  compared to the other portion of the contact region  110 . Consequently, when the surface roughness of the contact region  110  of the rubber portion  101  is fine (the arithmetic average roughness value Ra is within the range of 0.1 to 0.4), the pressure between the rubber portion  101  and the developing roller  92  increases at upstream end  111  of the contact region  110 , and the friction force applied from the contact region  110  of the rubber portion  101  to the developer increases between the rubber portion  101  and the developing roller  92 . Thus, the developer or the external additive released from the developer may be locally fixed to the upstream end  111  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X. 
     According to the present embodiment, the friction force which is applied to the developer between the developing roller  92  and the upstream end  111  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X decreases. Consequently, the developer or the external additive released from the developer becomes less locally fixable to the upstream end  111  of the contact region  110 . 
     Subsequently, the developer layer which is uneven in thickness passes through the second region  130  of the contact region  110 . At this time, the friction force which is applied to the developer between the developing roller  92  and the second region  130  of the contact region  10  increases compared to a case in which the developer layer passes through the first region  120 . Then, the unevenness in the thickness of the developer layer decreases compared to a case in which the developer layer passes through the first region  120 . 
     Further, when the developer layer passes through the second region  130  after the passage through the first region  120 , the amount of the developer carried by the developing roller  92  decreases. Consequently, the developer or the external additive released from the developer becomes less locally fixable to the second region  130 . 
     Further, there is no need to optimally set the surface roughness of the contact region  110  by the highly precise processing. 
     As a result, failures in image formation can be prevented while the blade is easily produced. 
     (2) The second region  130  extends toward the upstream side from the downstream end  112  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X. 
     This configuration increases the friction force which is applied to the developer between the developing roller  92  and the downstream end  112  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X. Consequently, the unevenness in the thickness of the developer layer decreases after the developer layer passes through the nip N. 
     As a result, failures in image formation can be further prevented. 
     (3) The surface roughness of each of the third regions  140  is coarser than the surface roughness of the first region  120 . 
     According to this configuration, the amount of the developer passing through each of the third regions  140  becomes smaller than the amount of the developer passing through the first region  120 . Consequently, the amount of the developer which is carried by each of the end portions of the developing roller  92  in the rotation axis direction of the developing roller  92  becomes smaller than the amount of the developer which is carried by the developing region B of the developing roller  92 . 
     That is, the leakage of the developer can be suppressed from the end portions of the developing roller  92  in the rotation axis direction along the rotation axis direction of the developing roller  92 . 
     (4) The second region  130  is disposed from one end  101   a  of the rubber portion  101  to the other end  101   b  thereof in the rotation axis direction of the developing roller  92 . 
     According to this configuration, when the developing roller  92  contacts the contact region  110  of the rubber portion  101 , a gap is not easily formed at the nip N of the developing roller  92  in the moving direction X between the developing roller  92  and the downstream end  112  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X. 
     That is, the leakage of the developer can be suppressed from the end portions of the developing roller  92  in the rotation axis direction at the nip N of the developing roller  92  in the moving direction X. 
     &lt;Modifications&gt; 
     While the description has been made in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the above described embodiment. 
     In the above described embodiment, the dimension of the first region  120  at the nip N of the developing roller  92  in the moving direction X is equal to the dimension of the second region  130  at the nip N of the developing roller  92  in the moving direction X. However, the embodiment is not limited thereto. For example, as illustrated in  FIG. 8 , the dimension of the first region  120  may be larger than the dimension of the second region  130 . 
     This configuration decreases the friction force which is applied to the developer between the developing roller  92  and the contact region  110  at the nip N of the developing roller  92  in the moving direction X compared to a case in which the dimension of the first region  120  is smaller than the dimension of the second region  130 . That is, the developer or the external additive released from the developer becomes further less fixable to the rubber portion  101 . 
     Further, in the above described embodiment, the second region  130  is disposed from one end  101   a  of the rubber portion  101  to the other end  101   b  thereof in the rotation axis direction of the developing roller  92 . However, the embodiment is not limited thereto. For example, the dimension of the second region  130  in the rotation axis direction of the developing roller  92  may be equal to the dimension of the first region  120  in the rotation axis direction of the developing roller  92 . That is, the second region  130  may be disposed in such a way as to match the width of the developing region B. 
     Further, in the above described embodiment, the second region  130  extends toward the upstream side from the downstream end  112  of the contact region  110  at the nip N of the developing roller  92  in the moving direction X, and is connected to the first region  120 . However, the embodiment is not limited to thereto. For example, a fourth portion having a surface roughness different from those of the first region  120  and the second region  130  may be formed between the first region  120  and the second region  130 . 
     Further, in the above described embodiment, the surface roughness of the contact region  110  may continuously decrease as it goes from the upstream end  111  of the contact region  110  toward the downstream end  112  thereof. 
     Further, in the above described embodiment, the contact region  110  includes the first region  120 , the second region  130 , the pair of third regions  140 , and the pair of notches  150 . However, the embodiment is not limited thereto. For example, the contact region  110  of the rubber portion  101  may include only the first region  120  and the second region  130 . 
     Further, in the above described embodiment, the mold  160  for molding the rubber portion  101  is formed by the blasting process. However, the embodiment is not limited thereto. For example, the mold  160  for molding the rubber portion  101  may be formed by an electro-discharge machining process or an etching process.