Abstract:
A charge roll includes a roll member that contacts an image carrier and rotates, the roll member including a conductive material that charges the surface of the image carrier, and the roll member having particles on the outer circumferential surface of the roll member to have a surface roughness within a predetermined range.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2006-263410 filed Sep. 27, 2006. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a charge roll, a process cartridge using the charge roll, an image forming apparatus using the charge roll, a charging method using the charge roll, and a cleaning method of the charge roll. 
     2. Related Art 
     Charging devices of electrophotographic method image forming apparatuses, such as copying machines, printers, and the like, are known that carry out contact charging of a photoreceptor by making direct contact of a conductive charge roll to the photoreceptor. Such contact charging develops substantially small amounts of ozone and nitrogen oxides, and, since power efficiency is also good, such contact charging has recently become mainstream. 
     SUMMARY 
     According to an aspect of the present invention, the charge roll comprises a roll member that contacts an image carrier and rotates, the roll member having a conductive material that charges the surface of the image carrier, and the roll member having particles on the outer circumferential surface of the roll member to have a surface roughness within a predetermined range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic structural drawing showing an image forming apparatus according to a first exemplary embodiment of the present invention; 
         FIG. 2  is a structural drawing showing the vicinity of a charge roll used for the image forming apparatus shown in  FIG. 1  and of a cleaning roll; 
         FIG. 3  is a structural drawing showing the charge roll; 
         FIG. 4  is a drawing showing schematically the surface layer of the charge roll; 
         FIG. 5  is a drawing showing schematically the surface layer of the charge roll in a second exemplary embodiment of the present invention; and 
         FIG. 6  is a drawing schematically showing the surface layer of the charge roll in a third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Explanation will now be given of exemplary embodiments of an image forming apparatus  1  of the present invention with reference to the drawings. 
     The image forming apparatus  1  according to a first exemplary embodiment of the present invention is shown in  FIG. 1 . 
     This image forming apparatus  1  performs image processing based on the color image information sent from an image data input device, such as a personal computer (not shown), and forms a color image on recording paper P with an electrophotographic method. 
     The image forming apparatus  1  is provided with image forming units  10 Y,  10 M,  10 C, and  10 K that form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, when it is necessary to distinguish between the colors of yellow, magenta, cyan, and black, the letters Y, M, C, and K will be added after reference numerals, and when it is not necessary to distinguish between the colors of yellow, magenta, cyan, and black, the letters Y, M, C, and K will be omitted. 
     The image forming units  10 Y,  10 M,  10 C, and  10 K are arranged in series in the direction of movement of an endless intermediate transfer belt  30  in the sequence of image forming units  10 Y,  10 M,  10 C, and  10 K. This intermediate transfer belt  30  is tensioned in a secondary transfer unit around a back up roll  34 , for supporting the intermediate transfer belt  30  from the back surface thereof, and plural tensioning rolls  32 . Moreover, the intermediate transfer belt  30  is disposed so as to be inserted between each of photoreceptor drums  12 Y,  12 M,  12 C, and  12 K, which serve as the image carriers of the image forming units  10 Y,  10 M,  10 C, and  10 K, and their respective primary transfer rolls  16 Y,  16 M,  16 C, and  16 K that are disposed opposite thereto. 
     Next, the configuration of the image forming units  10 Y,  10 M,  10 C, and  10 K and the operation of image formation will be described by way of the image forming unit  10 Y that forms the yellow toner image. 
     The surface of the photoreceptor drum  12 Y is uniformly charged with a charge roll  13 Y. Next, a laser beam L corresponding to a yellow image is irradiated to the surface of the photoreceptor drum  12 Y from a light exposure apparatus  14 Y. Thereby, an electrostatic latent image corresponding to the yellow image is formed on the surface of the photoreceptor drum  12 Y. 
     The electrostatic latent image corresponding to the yellow image on the surface of the photoreceptor drum  12 Y is developed by toner carried on a development roll  18 Y, disposed in a development device  15 Y, to which a development bias is applied, and forms a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt  30  by contact-pressure from the primary transfer roll  16 Y and electrostatic attraction force due to a transfer bias applied to the primary transfer roll  16 Y. 
     In this primary transfer, not all of the yellow toner image is transferred to the intermediate transfer belt  30 ; some remains as transfer residue yellow toner on the photoreceptor drum  12 Y. External additives in the toner also adhere to the surface of the photoreceptor drum  12 Y. A portion after primary transfer of the photoreceptor drum  12 Y passes a position facing a cleaning device  20 Y and the transfer residue toner on the surface of the photoreceptor drum  12 Y and the like is removed. Thereafter, the surface of the photoreceptor drum  12 Y is again charged by the charge roll  13 Y for the next image formation cycle. 
     As shown in  FIG. 1 , in the image forming apparatus  1 , the same image forming process as described above is conducted in the image forming units  10 Y,  10 M,  10 C, and  10 K at a timing in consideration of differences in the relative positions of the image forming units  10 Y,  10 M,  10 C, and  10 K, the toner images of the respective colors of yellow, magenta, cyan, and black are sequentially superposed on the intermediate transfer belt  30 , and a multiple toner image is formed. 
     Then, the multiple toner image is transferred at once from the intermediate transfer belt  30  to the recording paper P, which is conveyed at a predetermined timing to a secondary transfer position A, by electrostatic attraction force of a secondary transfer roll  36  to which a transfer bias is applied. 
     The recording paper P to which the multiple toner image has been transferred is separated from the intermediate transfer belt  30  and thereafter conveyed to a fixing device  31 , where the multiple toner image is fixed to the recording paper P by heat and pressure to form a full-color image. 
     The transfer residue toner on the intermediate transfer belt  30  that has not been transferred to the recording paper P is collected by an intermediate transfer belt cleaner  33 . 
     In such an image forming apparatus  1 , there are process cartridges  62 Y,  62 M,  62 C, and  62 K that are each made up integrally from the respective photoreceptor drum  12  disposed in each of the image forming units  10 Y,  10 M,  10 C, and  10 K, the charge roll  13 , the cleaning device  20 , and the like. These process cartridges  62 Y,  62 M,  62 C, and  62 K are respectively configured so as to be attachable and detachable to/from an image forming device body  60 . 
     As shown in  FIG. 2 , the charge roll  13  is disposed in contact with the photoreceptor drum  12  at an upper portion of the photoreceptor drum  12 . The structure of this charge roll  13  is described later. There is a cleaning roll (for example, a sponge roll)  50 , which cleans the surface of the charge rolls  13 , disposed at the top of the charge roll  13 . The cleaning roll  50  is one in which a sponge layer  54  is formed around the perimeter of a shaft  52 , and the shaft  52  is rotatably supported. The cleaning roll  50  is pressed to the charge roll  13  with a predetermined pressing force by springs (not shown) that are arranged at both ends of the shaft  52 . By so doing, the sponge layer  54  of the cleaning roll  50  is elastically deformed along the circumferential surface of the charge roll  13  to form a nip portion. 
     A motor (not shown) is connected to a support shaft of the photoreceptor drum  12 , and the photoreceptor drum  12  is driven to rotate with a clockwise rotation as viewed in  FIG. 2  (the direction of the arrow  2 ). Moreover, the charge roll  13  is driven by the rotation of the photoreceptor drum  12  and rotates in the direction of the arrow  4 . Moreover, the cleaning roll  50  is driven by the rotation of the charge roll  13  and rotates in the direction of the arrow  6 . Foreign matter, such as toner and external additives on the surface of the charge roll  13 , are cleaned by the driven rotation of the cleaning roll  50 . It should be noted that, as an alternative configuration, it may be configured such that the charge roll  13  or the cleaning roll  50  has a motor connected thereto and is/are rotated independently. 
     Next, explanation will be given of details of the charge roll  13 . 
     The charge roll  13  is disposed in contact with the surface of the photoreceptor drum  12 , and the surface of the photoreceptor drum  12  is charged by applying a direct current voltage, or a direct current voltage on which an alternating voltage is overlapped. The charge roll  13  is provided at the perimeter of a shaft  40  with an electrically resistive resilient layer  42 , as shown in  FIG. 3 . The electrically resistive resilient layer  42  is divided, in sequence from the outside, into an electrically resistive layer  46  and a resilient layer  44  which supports the electrically resistive layer  46 . Moreover, in order to impart durability and resistance to contamination to the charge roll  13 , a surface layer  48  is formed to the outside of the electrically resistive layer  46 . 
     A material that has electrical conductivity is used for the material of the shaft  40 , and generally iron, copper, brass, stainless steel, aluminum, nickel, and the like are used. Moreover, materials other than metals may be used as long as they have conductivity and moderate rigidity, for example, resin moldings with dispersed conductive particles and the like therein, ceramics, and the like, may also be used. Moreover, in addition to the profile of a roller, it is also possible to use a hollow pipe shape. 
     A material with conductive or semiconductive properties is used for the material of the resilient layer  44 , and generally resin material or rubber material is used in which conductive particles or semiconductive particles are dispersed therein. Examples of materials that may be used as resin materials include synthetic resins, such as polyester resin, acrylic resins, melamine resins, epoxy resins, urethane resins, silicone resins, urea resins, polyamide resins, and the like. Examples of materials that may be used as rubber materials include ethylene-propylene rubber, polybutadiene, natural rubber, polyisobutylene, chloroprene rubber, silicone rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, and ethylene oxide rubber, or foamed materials formed by foaming the above. 
     Examples of particles that may be used as conductive particles or semiconductive particles include: carbon black; metals, such as zinc, aluminum, copper, iron, nickel, chromium, and titanium; metal oxides, such ZnO-AL 2 O 3 , SnO 2 —Sb 2 O 3 , In 2 O 3 —SnO 2 , ZnO—TiO 2 , MgO—Al 2 O 3 , FeO—TiO 2 , TiO 2 , SnO 2 , Sb 2 O 3 , In 2 O 3 , ZnO, and MgO; and ionic compounds, such as quaternary ammonium salts. Such materials may be used singly, or combinations of two or more thereof may be used. Furthermore, the following may be used as required, either used singly or in combinations of two or more thereof: inorganic fillers, such as talc, alumina, and silica; and organic fillers, such as fine particles of fluororesins or silicone rubbers. 
     Conductive particles or semiconductive particles dispersed in a binder resin may be used as materials for the electrically resistive layer  46  and the surface layer  48 , with the electrical resistance thereof being controlled. The resistivity is preferably about 10 3  to about 10 14  Ωcm. Moreover, the average film thickness of the electrically resistive layer  46  or the surface layer  48  is preferably about 0.01 to about 1000 μm. As such a binder resin the following may be used: acrylic resins, cellulose resins, polyamide resins, methoxy methylated nylon, ethoxy methylated nylon, polyurethane resins, polycarbonate resins, polyester resins, polyethylene resins, polyvinyl resins, polyarylate resins, polythiophene resins, polyolefin resins, such as PFA, FEP and PET, styrene butadiene resins, melamine resins, epoxy resins, urethane resins, silicone resins, urea resins, and the like. 
     As the conductive particles or semiconductive particles dispersed in the electrically resistive layer  46  and the surface layer  48 , in the same manner as in the resilient layer  44 : the carbon black, metals, metal oxides, and ionic compounds, such as quaternary ammonium salts that exhibit ionic conductivity may be used, either singly or as two or more mixed together. Moreover, as required, addition may be made of: antioxidants, such as hindered phenols, and hindered amines; inorganic fillers, such as clay, kaolin, talc, silica, and alumina; organic fillers, such as fine particles of fluororesins or silicone resins; and lubricants, such as silicone oils. These may be added singly or two or more may be added. Furthermore, surfactants and charge controlling agents, and the like may be added as required. 
     Moreover, the following methods may be used to form these layers: a blade coating method, a wire bar coating method, a spray coating method, an immersion coating method, a bead coating method, an air knife coating method, a curtain coating method, and the like. 
     As shown in  FIG. 4 , in an aspect of the present invention, the surface layer  48  of the charge roll  13  having a predetermined surface roughness is formed by kneading the particles  49  into a binder resin  48 A. That is, minute irregularities are formed in the outermost face of the surface layer  48  by the particles  49 . The particles  49  may be either spherical or of undefined shape. Here, in order to make the configuration simple to understand, the binder resin  48 A and the particles  49  of the surface layer  48  are shown schematically in  FIG. 4 . 
     The ten-point average surface roughness Rz of the surface layer  48  is preferably about 3 to about 12 μm, more preferable about 7 to about 12 μm, and particularly preferably about 10 to about 12 μm. By setting the ten-point average surface roughness Rz within such ranges, foreign matter, such as a toner and external additives, do not readily adhere to the surface layer  48 , and the resistance of the surface layer  48  to contamination becomes high. On the other hand, when the ten-point average surface roughness Rz is less than about 3 μm there is concern that foreign matter, such as a toner and external additives, may adhere thereto. Moreover, when the ten-point average surface roughness Rz is greater than about 12 μm, toner, paper dust, and the like, readily collect in the irregular parts. Furthermore, when the ten-point average surface roughness Rz is greater than about 12 μm, local abnormal discharge occurs and uniform charging is hindered by the large height differences of the irregularities, and image defects like fine white deletions tend to occur. 
     Here, the ten-point average surface roughness Rz in question is the surface roughness specified according to JIS B0601 (1994). Although the ten-point average surface roughness Rz could be measured using a surface roughness tester or the like, in the present exemplary embodiment, a contact type surface roughness tester (Trade name: SURFCOM 570A, made by Tokyo Seimitsu Co., Ltd.) is used, in an environment of 23° C. and 55% RH. When measuring the surface layer  48 , the measurement distance is about 2.5 mm, and using a diamond tipped stylus (5 μm R and 90° cone shape), the location is changed and measurements are carried out three times. The average of these measurements is calculated for the ten-point average surface roughness Rz of the surface layer  48 . 
     A material with high electrical resistance is preferable for the material of the particles  49 , and, for example, polymer particles, such as polyimide and methacrylic resins, and inorganic particles, such as silica, or ceramic particles may be used. 
     Also, it is preferable that the volume average particle size of the particles  49  is about 1% to about 50% of the average film thickness of the surface layer  48  (the length dimension of the particles  49  is about 1% to about 50% relative to the layer thickness dimension of the binder resin  48 A). It is difficult to obtain the desired ten-point average surface roughness Rz if the volume average particle size of the particles  49  is less than about 1% of the average film thickness of the surface layer  48 . Moreover, if the volume average particle size of the particles  49  exceeds about 50% of the average film thickness of the surface layer  48  then, depending on the blending quantity of the particles  49 , it is difficult to obtain the desired ten-point average surface roughness Rz. In the present exemplary embodiment, the average film thickness of the surface layer  48  is for example, about 3 to about 15 μm, and the volume average particle size of the particles  49  is set, for example, at about 1.0 to about 7.5 μm. Here, the blending quantity of the particles  49  is set as about 5 to about 35 volume % relative to the binder resin  48 A. 
     Here, the volume average particle size of the particles  49  is the value measured using a Coulter counter (Trade name: COULTER COUNTER TA-II, made by Coulter Co., Ltd.). In this case, measurements are made with the optimal aperture for the particle size level of the particles. 
     Also, the average film thickness of the surface layer  48  is the value obtained by cutting off cross sections of the surface layer  48 , carrying out multiple measurements of the cross sections using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and taking the average value therefrom. 
     Furthermore, for the material of the particles  49 , semiconductive properties may be imparted to the particles by mixing and embedding conductive fine powder into the particles. The conductive fine powders include: metals such as gold, silver, and copper; carbon black; and also metal oxides, such as powders of titanium oxide, magnesium oxide, zinc oxide, aluminum oxide, calcium carbonate, aluminum borate, potassium titanate, and calcium titanate; and fine powders formed by covering the surface of the powder of titanium oxide, zinc oxide, barium sulfate, aluminum borate, or potassium titanate, with the powder of tin oxide, carbon black, or a metal. These may be used independently or combinations of two or more may be used together. The conductive fine powder may be of the same materials as for the above conductive particles included in the binder resin  48 A of the surface layer  48  (for example, carbon black and the like). 
     Moreover, the material of the particles  49  may be formed from the same resins as for the binder resin  48 A. By using the same resin as used in the binder resin  48 A, good compatibility is achieved and the adhesion becomes high between the particles  49  and binder resin  48 A. 
     Preferably used materials for the binder resin  48 A are polyvinylidene fluoride, copolymers of tetrafluoroethylene, polyester, polyimide, and copolymer nylons. Examples that may be given of such copolymer nylons are those that include therein one or more of the polymerization units Nylon 610, Nylon 11, and Nylon 12, and other polymerization units which may be included these copolymers are Nylon 6, Nylon 66, and the like. Alcohol soluble copolymerization nylon is used in the present exemplary embodiment. 
     On the other hand, as another configuration, as shown in  FIG. 5 , depending on the volume average particle size and blending quantity of particles  49 A, the volume average particle size of the particles  49 A may also be made greater than the average film thickness of the surface layer  48 . In such cases, the desired ten-point average surface roughness Rz is controlled by making a state in which a portion of the circumferential surface of the particles  49 A bulges out of the surface of the surface layer  48 . In  FIG. 5 , so that the configuration is simple to understand, the binder resin  48 A and the particles  49 A are shown schematically. 
     Or, as still another configuration, as shown in  FIG. 6 , a thinly coated protective layer  70  may be formed at the outside (the outermost face) of the surface layer  48  of the charge roll  13 . The thickness of this protective layer  70  is preferably about 10 μm or less. Even if the protective layer  70  is formed, the ten-point average roughness of the outermost surface may be set to the predetermined range by the particles  49 . It should be noted that, so that the configuration thereof may be simply understood, the binder resin  48 A, the particles  49 , and the protective layer  70  are shown schematically in  FIG. 6 . 
     Next, explanation will be given of the cleaning roll  50 . 
     A free cutting steel, stainless steel, or the like is used as the material of the shaft  52  of the cleaning roll  50 . The material and any surface treatment method of the shaft  52  may be selected according to the application, such as the required sliding properties, and materials that do not have conductivity may be made conductive by carrying out processing using standard treatments, such as plating treatment, and, of course, the material may be used as it is. Moreover, in order that the cleaning roll  50  may contact the charge roll  13  through the sponge layer  54  with an appropriate nip pressing force, the shaft  52  material is of a strength that does not bend during nipping, or the shaft diameter is selected to have sufficient rigidity relative to the shaft length. 
     The sponge layer  54  of the cleaning roll  50  includes a foam which has a porous three-dimensional configuration, with cavities and irregular portions (referred to below as cells) existing inside or at the surface thereof, and the sponge layer  54  has an elasticity. Foaming resin or rubber materials may be used for the sponge layer  54 , and selection may be made from polyurethane, polyethylene, polyamide, olefins, melamine or polypropylene, NBR, EPDM, natural rubbers and styrene butadiene rubbers, chloroprene, silicone, and nitrile. Thereby, the cleaning roll  50  having many cells may be manufactured cheaply. The cleaning roll  50  efficiently cleans foreign matter, such as external additives while being driven by the rubbing friction of the charge roll  13 , and at the same time it is necessary to ensure that defects are not imparted to the surface of the charge roll  13  due to the cleaning roll  50  rubbing the surface of the charge roll  13 . Moreover, it is necessary to ensure that there is no shredding or breakup occurs in the sponge layer  54  over a long period of time. For this reason, polyurethane is especially preferably used as the material of the sponge layer  54 , due to its tearing strength and tensile strength. 
     The polyurethane is not particularly limited. It suffices for there to be an accompaniment of a reaction of a polyol such as polyester polyol, polyether polyester, or acrylic polyol, and an isocyanate such as 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4-diphenylmethane diisocyanate, tolidine diisocyanate, or 1,6-hexamethylene diisocyanate, and it is preferable that a chain extender such as 1,4-butanediol or trimethylolpropane is to be mixed in. Further, it is common to cause foaming using water and a foaming agent such as an azo compound like azodicarbonamide or azobisisobutyronitrile. Moreover, auxiliaries such as a foaming aid, a foam adjusting agent, and a catalyst may also be added as needed. 
     Next, explanation will now be given of the experiments for evaluating the staining properties and the cleaning characteristics of the charge roll  13 . 
     For the charge roll  13 , surface coating is carried out in the state in which the particles  49  of resin are mixed with the surface layer  48 , as shown in  FIG. 4 , and samples are prepared by grouping into four grades of respective ten-point average roughnesses Rz, of about 1 to about 2 μm, about 3 to about 4 μm, about 7 to about 8 μm, and about 10 to about 12 to μm. Evaluation of staining properties and cleaning characteristics is performed using these samples. 
     As methods for evaluating staining properties and cleaning characteristics, in the image forming unit  10  of the image forming apparatus  1  shown in  FIG. 1 , a print test is carried out in the state in which the cleaning roll  50  is not attached, and the charge roll  13  is thereby soiled in advance. Next, only the photoreceptor drum  12 , the charge roll  13 , and the cleaning roll  50  are installed, and the photoreceptor drum  12  is rotated a predetermined number rotations, and any changes to the charge roll  13  surface are measured. Here, in this measuring method, grading is carried out of the changes to the degree of whiteness due to external additives adhering to the surface of the charge roll  13 . G1 is good and G5 is poor, and the grade for the staining properties and cleaning characteristics is worse the higher the figure after G A new charge roll  13  is grade G0. Moreover, the allocation of grades for staining properties and for cleaning characteristics differs. For the grading of cleaning characteristics the level at which there is a satisfactory picture is G3 or below, and the when it exceeds G3 then this indicates an NG level. Also, for the grading of staining properties, the worst cases are set to G5 in the 12 evaluation levels (see Table 1), and the grades are divided up to G1 so as to be roughly equal. 
     Alcohol soluble copolymerization nylons are used as the binder resin  48 A of the surface layer  48 , carbon black as a conductive fine powder is embedded in the particles  49 , and the samples are prepared by changing the particle size of the particles  49  and blending quantities to prepare sample materials. There are three levels for the average film thickness of the surface layer  48 , about 3 to about 4 μm, about 8 to about 9 μm, and about 14 to about 15 μm. When the average film thickness of the surface layer  48  is about 3 to about 4 μm, particles whose volume average particle sizes are about 1.5 μm are used, and when the average film thickness of the surface layer  48  is about 8 to about 9 μm, particles whose volume average particle sizes are about 4 μm are used, and when the average film thickness about 14 to about 15 μm, particles whose volume average particle sizes are about 8 μm are used. The blending quantity of the particles is determined according to the roughness, and is about 15% to about 70% (as a weight % relative to the surface layer resin solid content). 
     The evaluation results for the staining properties and cleaning characteristics are shown in Table 1 and Table 2. 
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 EVALUATION OF STAINING PROPERTIES 
               
             
          
           
               
                   
                 AVERAGE FILM 
               
               
                   
                 THICKNESS OF 
               
               
                   
                 SURFACE LAYER (μm) 
               
             
          
           
               
                   
                 3~4 
                 8~9 
                 14~15 
               
               
                   
                   
               
             
          
           
               
                 TEN-POINT AVERAGE 
                 1~2 
                 G5 
                 G5 
                 G5 
               
               
                 SURFACE ROUGHNESS 
                 3~4 
                 G3 
                 G4 
                 G4 
               
               
                 (Rz) 
                 7~8 
                 G2 
                 G3 
                 G3 
               
               
                 μm 
                 10~12 
                 G1 
                 G2 
                 G3 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 EVALUATION OF CLEANING CHARACTERISTICS 
               
             
          
           
               
                   
                 AVERAGE FILM 
               
               
                   
                 THICKNESS OF 
               
               
                   
                 SURFACE LAYER (μm) 
               
             
          
           
               
                   
                 3~4 
                 8~9 
                 14~15 
               
               
                   
                   
               
             
          
           
               
                 TEN-POINT AVERAGE 
                 1~2 
                 G4 
                 G5 
                 G5 
               
               
                 SURFACE ROUGHNESS 
                 3~4 
                 G2 
                 G3 
                 G3 
               
               
                 (Rz) 
                 7~8 
                 G2 
                 G2 
                 G3 
               
               
                 μm 
                 10~12 
                 G1 
                 G1 
                 G2 
               
               
                   
               
             
          
         
       
     
     It may be seen from the results shown in Tables 1 and 2 that staining properties and cleaning characteristics may improve as the ten-point average surface roughness Rz increases. 
     Furthermore, a standard print test is carried out using the image forming apparatus  1  shown in  FIG. 1  using the same charge roll  13 , and experiments are conducted to examine the correlation between the numeric value of cleaning characteristics and actual defects (image defects). From these experiments it may be shown that for cleaning characteristics of G3 or below in Table 2, good printing may be maintained for 100,000 sheets. From the results of these experiments, it may be seen that the ten-point average surface roughness Rz is preferable 3 μm or more. Furthermore, for a ten-point average surface roughness Rz of 3 μm or more, there is no variation generated in the cleaning characteristics by the location along the shaft direction of the charge roll  13 , foreign matter may be removed almost uniformly, and also the amount of foreign matter adhering itself may be reduced. 
     Furthermore, with regard to the upper limit of the ten-point average surface roughness Rz, the cleaning characteristics in the region close to 10 μm or more may maintain good values. However, with respect to the initial charging uniformity, if the ten-point average surface roughness Rz exceeds 12 μm, then uneven charge may occur, with white spots and the like, and initial image quality may not be achievable. From the above, it may be effective to mix the particles  49  with the surface layer  48 , as described above, so that the ten-point average surface roughness Rz becomes 3 μm to 12 μm. 
     Next, sandblasting is used as the method for making coarse the roughness of the surface layer of the charge roll  13 , and a sample (Comparative Example) is prepared so that the same ten-point average surface roughness Rz as in the Example is achieved. Evaluation of staining properties and cleaning characteristics is performed using this sample (Comparative Example). 
     It may be possible to achieve the desired ten-point average surface roughness Rz even if sandblasting is used as the method, however, as shown in Table 3, the resistance value that may be important for a charge roll rises to the extent of one figure under all conditions. This may show inferior electrostatic properties, especially in low temperature low humidity environments. Moreover, as shown in Table 3 besides the rise of resistance, the increase in the variation (sigma) in resistance may also be important, and generally when this exceeds 0.1, it may be difficult to achieve uniform charging. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Ini 
                 SANDBLASTING 
                 EXAMPLE 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 DIFFERENCE IN 
                 — 
                 0.95 
                 0.1 
               
               
                 RESISTANCE TO 
               
               
                 THAT OF Ini 
               
               
                 VARIATION IN 
                 0.02 
                 0.27 
                 0.03 
               
               
                 RESISTANCE 
               
               
                   
               
             
          
         
       
     
     Also it may be shown that control of the ten-point average surface roughness Rz by the particles  49  of the aspect of the present invention may have a large effect, even in comparison with the results by the sandblasting. 
     If the volume average particle size of the particles  49  is too small then roughness may not be readily obtained, even if the blending quantity is increased. Moreover, if the volume average particle size of the particles  49  is too large, then the particles  49  tend to readily fall out. About 1% to about 50% of the average film thickness of the surface layer  48  may be suitable for the volume average particle size of the particles  49 . Moreover, by mixing and embedding carbon black as the conductive fine powder into the particles  49 , the variation in the surface resistance of the charge roll  13  may be suppressed, and abnormal discharge does not readily occur. 
     It should be noted that, although the image forming apparatus  1  of the above exemplary embodiment is a configuration with the image forming units of yellow, magenta, cyan, and black disposed in series along the conveying direction of the intermediate transfer belt, the present invention is not limited to this structure. The present invention may also be applied, for example, to a configuration in which toner images of each color are formed one by one on a photoreceptor drum using a rotary development apparatus. 
     The foregoing description of the exemplary embodiment has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiment are chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.