Patent Publication Number: US-9841697-B2

Title: Cleaning member, process cartridge, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-013400 filed Jan. 27, 2016. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a cleaning member, a process cartridge, and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a cleaning member including a core and an elastic layer helically wound around an outer peripheral surface of the core so as to extend from one end to the other end of the core. When the cleaning member is rotated by a member to be cleaned, a non-contact region in which a first end portion and a second end portion of the elastic layer in an axial direction of the core are not in contact with the member to be cleaned is in a range from approximately 0° to approximately 60° in terms of a rotation angle of the cleaning member viewed from one side in the axial direction of the core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic perspective view of a cleaning member according to an exemplary embodiment; 
         FIG. 2  shows a schematic plan view of the cleaning member according to the exemplary embodiment; 
         FIG. 3A  is a schematic sectional view of a first end portion of the cleaning member according to the exemplary embodiment; 
         FIG. 3B  is a schematic sectional view of a second end portion of the cleaning member according to the exemplary embodiment; 
         FIG. 3C  is a schematic sectional view of a second end portion of the cleaning member according to the exemplary embodiment; 
         FIG. 3D  illustrates a non-contact region of the cleaning member according to the exemplary embodiment; 
         FIG. 3E  is a schematic sectional view of a first end portion of the cleaning member according to the exemplary embodiment; 
         FIG. 3F  is a schematic sectional view of a second end portion of the cleaning member according to the exemplary embodiment; 
         FIG. 4  is an enlarged sectional view of an elastic layer of the cleaning member according to the exemplary embodiment; 
         FIG. 5  is an enlarged sectional view of an elastic layer of the cleaning member according to the exemplary embodiment; 
         FIG. 6  is an enlarged sectional view of an elastic layer of the cleaning member according to the exemplary embodiment; 
         FIG. 7A  illustrates a step of an example of a method for manufacturing the cleaning member according to the exemplary embodiment; 
         FIG. 7B  illustrates a step of an example of a method for manufacturing the cleaning member according to the exemplary embodiment; 
         FIG. 7C  illustrates a step of an example of a method for manufacturing the cleaning member according to the exemplary embodiment; 
         FIG. 8  is a schematic diagram illustrating an image forming apparatus according to the exemplary embodiment; 
         FIG. 9  is a schematic diagram illustrating a process cartridge according to the exemplary embodiment; and 
         FIG. 10  is a schematic enlarged view of a section around a charging member (charging device) illustrated in  FIGS. 8 and 9 . 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention will now be described. Components having the same functions and effects are denoted by the same reference numerals throughout the drawings, and the description thereof may be omitted. 
     Cleaning Member 
       FIG. 1  a schematic perspective view of a cleaning member  100  according to the exemplary embodiment.  FIG. 2  shows a schematic plan view of the cleaning member  100  according to the exemplary embodiment.  FIGS. 3A to 3C, 3E , and  3 F are schematic sectional views of end portions of the elastic layer  104  of the cleaning member  100  according to the exemplary embodiment. More specifically,  FIGS. 3A and 3E  are sectional views of the cleaning member  100  taken along line IIIA, IIIE-IIIA, IIIE in  FIG. 2 , that is, sectional views in which a first end portion  111  of the elastic layer  104  is sectioned in the circumferential direction of a core  102 .  FIGS. 3B, 3C, and 3F  are sectional views of the cleaning member  100  taken along line IIIB, IIIC, IIIF-IIIB, IIIC, IIIF in  FIG. 2 , that is, sectional views in which a second end portion  113  of the elastic layer  104  is sectioned in the circumferential direction of the core  102 . 
       FIG. 3D  illustrates a non-contact region in which the cleaning member and the member to be cleaned are not in contact with each other according to the present exemplary embodiment. In  FIG. 3D , a cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  and a cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  are superposed.  FIG. 4  is an enlarged sectional view of the elastic layer  104  of the cleaning member  100  according to the present exemplary embodiment. 
       FIG. 4  is a sectional view of the elastic layer  104  taken along line IV-IV in  FIG. 2 , that is, in the circumferential direction of the core  102 . 
     As illustrated in  FIGS. 1 to 4 , the cleaning member  100  according to the present exemplary embodiment is, for example, a roll-shaped member including the core  102 , the elastic layer  104 , and an adhesive layer  106  that bonds the core  102  and the elastic layer  104  together. 
     The elastic layer  104  is, for example, helically wound around the outer peripheral surface of the core  102 . The elastic layer  104  includes, for example, a strip-shaped elastic member  108  (see  FIGS. 7A to 7C : hereinafter also referred to as “strip  108 ”) that is helically wound around the core  102  from one end to the other end of the core  102 . More specifically, the elastic layer  104  is helically wound around the core  102  from one end to the other end of the core  102  such that the core  102  serves as the helical axis and such that portions of the strip  108  are arranged with gaps therebetween. 
       FIG. 3A  is a sectional view of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  and viewed in the direction from the first end to the second end in the axial direction of the core  102 .  FIG. 3B  is a sectional view of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  and viewed in the direction from the first end to the second end in the axial direction of the core  102 . 
     Referring to  FIG. 3A , the first end portion  111  of the elastic layer  104  covers the lower semicircular segment of the core  102  in  FIG. 3A . Referring to  FIG. 3B , the second end portion  113  of the elastic layer  104  covers the upper semicircular segment of the core  102  in  FIG. 3B . As illustrated in  FIGS. 3A and 3B , the length over which the elastic layer  104  covers the core  102  in the circumferential direction is ½ of the circumference of the core  102  at each of the first end portion  111  and the second end portion  113 . 
     Although not illustrated, when viewed in the direction from the first end to the second end in the axial direction of the core  102 , and when the cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  and the cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  are superposed, an edge  111 A of the first end portion  111  of the elastic layer  104  and an edge  113 A of the second end portion  113  of the elastic layer  104  overlap. 
     More specifically, the boundary between a region in which the first end portion  111  comes into contact with a member to be cleaned and a region in which the first end portion  111  does not come into contact with the member to be cleaned at the edge  111 A of the first end portion  111  overlaps the boundary between a region in which the second end portion  113  comes into contact with the member to be cleaned and a region in which the second end portion  113  does not come into contact with the member to be cleaned at the edge  113 A of the second end portion  113 . 
       FIG. 3C  is a sectional view of the second end portion  113  of another example of the elastic layer  104  included in the cleaning member  100  according to the present exemplary embodiment taken in the circumferential direction of the core  102 . Referring to  FIG. 3C , the second end portion  113  of the elastic layer  104  covers a portion of the upper semicircular segment of the core  102  in  FIG. 3C . As illustrated in  FIG. 3C , the length over which the core  102  is covered in the circumferential direction is less than ½ of the circumference of the core  102  at the second end portion  113  of the elastic layer  104 . In this example, the cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  is the same as  FIG. 3A . Namely, the first end portion  111  of the elastic layer  104  covers the lower semicircular segment of the core  102  in  FIG. 3A , and the length over which the core  102  is covered in the circumferential direction is ½ of the circumference of the core  102 . 
     In this example, when viewed in the direction from the first end to the second end in the axial direction of the core  102 , and when the cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  and the cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  are superposed, as illustrated in  FIG. 3D , the edge  111 A of the first end portion  111  and the edge  113 A of the second end portion  113  do not overlap. In other words, there is a region in which neither of the end portions of the elastic layer  104  covers the core  102  in the circumferential direction. 
       FIGS. 3E and 3F  are sectional views of the first end portion  111  and the second end portion  113 , respectively, of another example of the elastic layer  104  included in the cleaning member  100  according to the present exemplary embodiment taken in the circumferential direction of the core  102 . 
     As illustrated in  FIG. 3E , the first end portion  111  of the elastic layer  104  covers the lower semicircular segment of the core  102  and a portion of the upper semicircular segment of the core  102  in  FIG. 3E . As illustrated in  FIG. 3F , the second end portion  113  of the elastic layer  104  covers the upper semicircular segment of the core  102  and a portion of the lower semicircular segment of the core  102  in  FIG. 3E . Referring to  FIGS. 3E and 3F , the length over which the elastic layer  104  covers the  102  in the circumferential direction is greater than or equal to ½ of the circumference of the core  102  at each of the first end portion  111  and the second end portion  113 . 
     Although not illustrated, when viewed in the direction from the first end to the second end in the axial direction of the core  102 , and when the cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  and the cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  are superposed, the edge  111 A of the first end portion  111  and the edge  113 A of the second end portion  113  do not overlap. Regions in which the end portions of the elastic layer  104  cover the core  102  in the circumferential direction overlap. 
     Referring to  FIG. 10 , when the member to be cleaned is a charging member  14 , for example, a load F is applied to both ends of a conductive core  14 A so that the charging member  14  is pressed against a photoconductor  12  and elastically deformed along the peripheral surface of an elastic foam layer  14 B so as to form a nipping portion. In addition, a load F′ is applied to both ends of the core  102  so that the cleaning member  100  is pressed against the charging member  14  and the elastic layer  104  is elastically deformed along the peripheral surface of the charging member  14  so as to form a nipping portion. Thus, the nipping portions that extend in the axial direction of the charging member  14  and the photoconductor  12  are formed while bending of the charging member  14  is suppressed. The cleaning member  100  is rotated in the direction of arrow Z by the rotation of the charging member  14 . 
     When the elastic layer  104  is simply wound around the core  102 , the elastic layer  104  has a non-contact region in which the first end portion  111  and the second end portion  113  in the axial direction of the core  102  are not in contact with the charging member  14  when the cleaning member  100  is rotated by the charging member  14 . When the non-contact region is large, the first end portion  111  and the second end portion  113  of the elastic layer  104  easily slip relative to the charging member  14 , and the cleaning member  100  cannot be easily rotated by the charging member  14 . Accordingly, adhesion of toner or the like to the member to be cleaned (filming of toner or the like, which is hereinafter referred to simply as “filming”) may occur on the surface of the charging member  14 . As a result, the image density becomes uneven. 
     In this specification, the non-contact region is a region in which neither of the first end portion  111  and the second end portion  113  of the elastic layer  104  is in contact with the member to be cleaned (for example, the charging member  14 ) when the cleaning member  100  is rotated by the member to be cleaned. More specifically, the non-contact region is a region in which neither of the end portions of the elastic layer  104  covers the core  102  in the circumferential direction, as illustrated in  FIG. 3D . 
     In the cleaning member  100  according to the present exemplary embodiment, the non-contact region, in which the first end portion  111  and the second end portion  113  of the elastic layer  104  in the axial direction of the core  102  are not in contact with the member to be cleaned when the cleaning member  100  is rotated by the member to be cleaned, is in the range from 0° to 60° or from approximately 0° to approximately 60° in terms of the rotation angle of the cleaning member  100  viewed from one side in the axial direction of the core  102 . 
     As described above, in the example illustrated in  FIG. 3D , the cleaning member  100  is configured such that the region in which the first end portion  111  of the elastic layer  104  covers the core  102  and the region in which the second end portion  113  of the elastic layer  104  covers the core  102  do not overlap. Accordingly, the edge  111 A of the first end portion  111  and the edge  113 A of the second end portion  113  do no overlap. Therefore, there is a region in which the end portions of the elastic layer  104  do not cover the core  102  in the circumferential direction. 
     In this case, there is a non-contact region in which neither of the first end portion  111  and the second end portion  113  of the elastic layer  104  is in contact with the charging member  14  when the cleaning member  100  is rotated by the charging member  14 . 
     When the rotation angle viewed from one side in the axial direction of the core  102  is greater than 60°, the non-contact region is too large. Therefore, the cleaning member  100  cannot be rotated by inertia, and it becomes difficult for the cleaning member  100  to follow the charging member  14 . Since it becomes difficult to ensure sufficient ability of the cleaning member  100  to follow the charging member  14 , the first end portion  111  and the second end portion  113  of the elastic layer  104  easily slip relative to the charging member  14 , and filming easily occurs. Accordingly, the image density is easily reduced. 
     In the case where the rotation angle viewed from one side in the axial direction of the core  102  is less than or equal to 60°, even if there is a non-contact region when the cleaning member  100  is rotated by the charging member  14 , the cleaning member  100  is rotated by inertia and follows the rotation of the charging member  14 . Thus, the cleaning member  100  has sufficient ability to follow the rotation of the charging member  14 . The occurrence of slipping of the first end portion  111  and the second end portion  113  of the elastic layer  104  relative to charging member  14  is suppressed, and the occurrence of filming is suppressed as a result. Therefore, the occurrence of unevenness in the image density is suppressed. 
     Accordingly, it is inferred that the cleaning member  100  according to the present exemplary embodiment having the above-described structure is capable of suppressing the occurrence of unevenness in the image density. 
     The “rotation angle of the cleaning member viewed from one side in the axial direction of the core” according to this specification will now be described. Assume that a cross section of the first end portion of the elastic layer taken in the circumferential direction of the core so as to pass through a region where the first end portion projects most in the circumferential direction of the core and a cross section of the second end portion of the elastic layer taken in the circumferential direction of the core so as to pass through a region where the second end portion projects most in the circumferential direction of the core are superposed as viewed from one side in the axial direction of the core. In this state, the “rotation angle of the cleaning member viewed from one side in the axial direction of the core” is the angle between the straight line that passes through the boundary between a region in which the first end portion comes into contact with the member to be cleaned and a region in which the first end portion does not come into contact with the member to be cleaned and the center of the core and the straight line that passes through the boundary between a region in which the second end portion comes into contact with the member to be cleaned and a region in which the second end portion does not come into contact with the member to be cleaned and the center of the core. 
     For example, referring to  FIG. 3D , a cross section of the first end portion  111  of the elastic layer  104  taken in the circumferential direction of the core  102  so as to pass through a region where the first end portion  111  projects most in the circumferential direction and a cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  so as to pass through a region where the second end portion  113  projects most in the circumferential direction are superposed as viewed from one side in the axial direction of the core  102 . In this state, when observed in the direction from the first end portion  111  to the second end portion  113 , the above-described rotation angle is the angle θ 2  between the line X that extends from the boundary between a region in which the first end portion  111  comes into contact with the member to be cleaned and a region in which the first end portion  111  does not come into contact with the member to be cleaned toward the center of the core  102  and the line Y that extends from the boundary between a region in which the second end portion  113  comes into contact with the member to be cleaned and a region in which the second end portion  113  does not come into contact with the member to be cleaned toward the center of the core  102 . 
     Referring to  FIGS. 3E and 3F , when the region in which the first end portion  111  of the elastic layer  104  covers the core  102  and the region in which the second end portion  113  of the elastic layer  104  covers the core  102  overlap, one or both of the first end portion  111  and the second end portion  113  of the elastic layer  104  are in contact with the charging member  14  when the cleaning member  100  is rotated by the charging member  14 . Therefore, the above-described non-contact region is not provided. In this case, since the non-contact region is not provided, the rotation angle (θ 2 ) viewed from one side in the axial direction of the core  102  is 0°. 
     In the cleaning member  100  according to the present exemplary embodiment, the rotation angle viewed from one side in the axial direction of the core  102  (angle θ 2 ) is 60° or approximately 60° or less. To further suppress the occurrence of unevenness in the image density, the rotation angle viewed from one side in the axial direction of the core  102  (angle θ) may be 30° or less or approximately 30° or less, more preferably 15° or less or approximately 15° or less, and still more preferably, 0° or approximately 0°. 
     As described above, in the cleaning member  100  according to the present exemplary embodiment illustrated in  FIGS. 3A and 3B , the edge  111 A of the first end portion  111  and the edge  113 A of the second end portion  113  overlap. In this case, the rotation angle viewed from one side in the axial direction of the core  102  (angle θ 2 ) is 0°. In the case where this angle is 0°, one of the first end portion  111  and the second end portion  113  is in contact with the charging member  14  when the cleaning member  100  is rotated by the charging member  14 . Therefore, the non-contact region is not provided. Accordingly, the cleaning member  100  has sufficient ability to follow the charging member  14 , and the occurrence of filming is easily suppressed. As a result, the occurrence of unevenness in the image density is further suppressed. 
     In addition, as described above, when the cleaning member  100  according to the present exemplary embodiment illustrated in  FIGS. 3E and 3F  is observed in the direction from the first end portion  111  to the second end portion  113  along the axial direction of the core  102 , and when the first end portion  111  and the second end portion  113  of the elastic layer  104  are superposed, the non-contact region is not provided and the regions in which the elastic layer  104  covers the core  102  in the circumferential direction overlap. 
     In this case, when the cleaning member  100  is rotated by the charging member  14 , the circumferential cover length over which the core  102  is covered in the circumferential direction is long at both end portions of the elastic layer  104 . Therefore, the frictional force between the elastic layer  104  and the charging member  14  is easily increased, and the ability of the cleaning member  100  to follows the rotation of the charging member  14  is easily improved. Accordingly, the occurrence of slipping is further suppressed, and therefore the occurrence of filming is further suppressed. As a result, the occurrence of unevenness in the image density may be further suppressed. 
     When the circumferential cover length of the elastic layer  104  is greater than or equal to ½ or approximately ½ of the circumference of the core  102  at least at one of the first end portion  111  and the second end portion  113  in the axial direction, the occurrence of unevenness in the image density may be further suppressed. Furthermore, when the circumferential cover length is greater than or equal to ½ or approximately ½ of the circumference of the core  102  at least at one of the first end portion  111  and the second end portion  113  in the axial direction, not only is the occurrence of unevenness in the image density further suppressed, but the ability of the cleaning member  100  to follow the charging member  14  may be easily balanced between the end portions of the elastic layer  104 . 
     Furthermore, when the regions in which the end portions of the elastic layer  104  cover the core  102  overlap in a cross section of the second end portion  113  of the elastic layer  104  taken in the circumferential direction of the core  102  and viewed in the direction from the first end to the second end along the axial direction, the occurrence of unevenness in the image density may be further suppressed. 
     Here, the “circumferential cover length” is the maximum length over which the elastic layer  104  covers the outer peripheral surface of the core  102  in the circumferential direction at least at one of the first end portion  111  and the second end portion  113  of the elastic layer  104 . 
     Although the first end portion  111  and the second end portion  113  of the elastic layer  104  have been described with reference to  FIGS. 3A to 3F , the end portions are not limited to this. There is no particular limitation regarding the end portions of the elastic layer  104  as long as the non-contact region in which the first end portion  111  and the second end portion  113  of the elastic layer  104  are not in contact with the charging member  14  is 60° or less or approximately 60° or less in terms of the rotation angle viewed from one side in the axial direction of the core  102 . 
     A charging device, a transfer device, a unit for an image forming apparatus, a process cartridge, and an image forming apparatus including the cleaning member  100  having the above-described structure are capable of suppressing a reduction in performance due to insufficient cleaning of a member to be cleaned, such as a charging member or a transfer member. 
     The individual components will now be described. 
     First, the core  102  will be described. 
     The material of the core  102  may be a metal, an alloy, or a resin. 
     Examples of the metal or alloy include metals such as iron (for example, free-machining steel), copper, brass, aluminum, and nickel, and alloys such as stainless steel. 
     Examples of the resin include polyacetal resin; polycarbonate resin; acrylonitrile-butadiene-styrene copolymer; polypropylene resin; polyester resin; polyolefin resin; polyphenylene ether resin; polyphenylene sulfide resin; polysulfone resin; polyether sulfone resin; polyarylene resin; polyether imide resin; polyvinyl acetal resin; polyketone resin; polyether ketone resin; polyether ether ketone resin; polyaryl ketone resin; polyether nitrile resin; liquid crystal resin; polybenzimidazole resin; polyparabanic acid resin; vinyl polymer or copolymer obtained by polymerizing or copolymerizing one or more vinyl monomers selected from a group including aromatic alkenyl compound, methacrylic acid ester, acrylic acid ester, and vinyl cyanide compound; diene-aromatic alkenyl compound copolymer; vinyl cyanide-diene-aromatic alkenyl compound copolymer; aromatic alkenyl compound-diene-vinyl cyanide-N-phenyl maleimide copolymer; vinyl cyanide-(ethylene-diene-propylene (EPDM))-aromatic alkenyl compound copolymer; polyolefin resin; vinyl chloride resin; and chlorinated vinyl chloride resin. These resins may be used individually or in combination. 
     The material, surface processing method, etc., may be selected as necessary. In particular, when the core  102  is made of a metal, the core  102  may be plated. When an electrically non-conductive material, such as a resin, is used, the material may be subjected to a typical process for imparting electrical conductivity, such as plating, or be used as is. 
     The elastic layer  104  will now be described. 
     The elastic layer  104  is a layer made of a material that returns to its original shape after being deformed by application of external force of 100 Pa. The elastic layer  104  may either be an elastic foam layer or a non-foamed elastic layer. The elastic layer  104  may be composed of an elastic foam layer to increase the cleaning performance. The elastic foam layer is a layer made of a material having voids, in other words, a foamed material. 
     Examples of the material of the elastic layer  104  include foaming resins such as polyurethane, polyethylene, polyamide, and polypropylene, rubber materials such as silicone rubber, fluorine rubber, urethane rubber, ethylene propylene diene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), chlorinated polyisoprene, isoprene, styrene-butadiene rubber, hydrogenated polybutadiene, or butyl rubber, or mixtures of two or more of these materials. 
     An assistant agent such as a foaming aid, a foam stabilizer, a catalyst, a curing agent, a plasticizer, or a vulcanization accelerator may be added to these materials. 
     In particular, the elastic layer  104  may be made of polyurethane foam having a high tensile strength to prevent damage to the member to be cleaned due to scratching and to prevent tearing and breaking over a long period of time. 
     Examples of the polyurethane foam include reaction products of a polyol (e.g., polyester polyol, polyether polyol, or acryl polyol) and an isocyanate (e.g., 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, tolidine diisocyanate, or 1,6-hexamethylene diisocyanate), and materials obtained by causing the reaction products to further react with a chain extender, such as 1,4-butanediol or trimethylol propane. 
     Foaming of polyurethane is generally performed by using, for example, water and a foaming agent such as an azo compound (e.g., azodicarbonamide or azobisisobutyronitrile). 
     An assistant agent such as a foaming aid, a foam stabilizer, or a catalyst may be added to the polyurethane foam. 
     In particular, the polyurethane foam may be an ether-based polyurethane foam because ester-based polyurethane foams have a tendency to deteriorate due to humidity and heat. A silicone oil foam stabilizer is typically used for ether-based polyurethanes. However, image defects caused by migration of silicone oil to the member to be cleaned (e.g., charging roller) may occur during storage (in particular, storage at high temperature and high humidity). The migration of the foam stabilizer to the member to be cleaned may be suppressed and image defects caused by the migration of the foam stabilizer may be reduced by using a foam stabilizer other than silicone oil. 
     Examples of the foam stabilizer other than silicone oil include Si-free organic surfactants (e.g., anionic surfactants such as dodecylbenzenesulfonic acid and sodium lauryl sulfate). A method that does not use a silicone foam stabilizer may also be employed. 
     Whether a foam stabilizer other than silicone oil is used to form the ether-based polyurethane foam is determined by examining whether Si is contained through componential analysis. 
     The width W 1  of the elastic layer  104  (hereinafter referred to also as “helical width W 1 ”) may be 1 mm or more, preferably 1.5 mm or more, and more preferably 2 mm or more. The upper limit of the helical width W 1  depends on a helical angle θ, but is not particularly limited as long as the elastic layer  104  may be wound around the core  102  without overlapping itself. 
     The elastic layer  104  is obtained by helically winding the elastic member  108  (strip  108 ) around the core  102  such that the helical angle θ relative to the axial direction of the core  102  is preferably in the range from 2° to 75°, more preferably from 4° to 75°, and more preferably from 8° to 45°. More specifically, the elastic layer  104  is helically wound around the outer peripheral surface of the core  102  at an angle in the range from 2° to 75° relative to the axial direction Q of the cleaning member  100  (axial direction of the core). 
     Referring to  FIG. 2 , the helical angle θ is an angle (acute angle) between the longitudinal direction P of the elastic layer  104  (helical direction) and the axial direction Q of the cleaning member  100  (axial direction of the core). 
     The thickness D of the elastic layer  104  (thickness of the central portion in the width direction) is preferably in the range from 1.0 mm to 15.0 mm, more preferably from 1.5 mm to 15 mm, and still more preferably from 2 mm to 5 mm. 
     The winding number of the elastic layer  104  wound around the core  102  is preferably 1 or more, more preferably 1.3 or more, and still more preferably 2 or more. The upper limit of the winding number of the elastic layer  104  depends on the length of the core  102 , and is therefore not particularly limited. 
     The coverage of the elastic layer  104  (W 1 /(W 1 +W 2 ), where W 1  is the helical width of the elastic layer  104  and W 2  is a helical gap of the elastic layer  104 ) is preferably in the range from 5% to 90%, more preferably from 8% to 80%, and still more preferably from 10% to 70%. 
     As illustrated in  FIG. 2 , the helical gap W 2  is the distance between the adjacent portions of the elastic layer  104  in the axial direction Q of the cleaning member  100  (axial direction of the core). 
     The thickness D of the elastic layer  104  may be measured as follows. 
     The thickness profile of the elastic layer  104  is measured by scanning the cleaning member  100  in the longitudinal direction (axial direction) of the cleaning member  100  with a laser analyzer (Laser Scan Micrometer, model LSM 6200 produced by Mitsutoyo Corporation) at a traverse speed of 1 mm/s while the position of the cleaning member  100  in the circumferential direction is fixed. Subsequently, the position in the circumferential direction is shifted and the same measurement is performed (measurement is performed at three positions apart from each other by 120°). The thickness D of the elastic layer  104  is calculated on the basis of the determined profiles. 
     To further suppress the occurrence of unevenness in the image density, at least at one of the first end portion  111  and the second end portion  113  in the axial direction, the circumferential cover length over which the elastic layer  104  covers the core  102  in the circumferential direction may be greater than a maximum length W 3  of the elastic layer  104  in a direction perpendicular to the direction in which the elastic layer  104  extends from the first end portion  111  to the second end portion  113  in the longitudinal direction (hereinafter referred to also as “elastic layer width W 3 ”, see  FIG. 2 ). 
     The elastic layer  104  is not limited to a layer composed of a single strip  108 . For example, as illustrated in  FIGS. 5 and 6 , the elastic layer  104  may instead be elastic layers  104 A and  104 B formed of two or more strips  108  (strip-shaped elastic members) that are helically wound around the core  102 . When two or more strips  108  are helically wound around the core  102  to form the elastic layers  104 A and  104 B, the cleaning performance of the cleaning member  100  may be easily increased. 
     The elastic layers formed of two or more strips  108  (strip-shaped elastic members) helically wound around the core  102  may either be the elastic layers  104 A (see  FIG. 5 ) helically wound such that longitudinal sides of adhesion surfaces of the strips  108  (surfaces of the strips  108  that face the outer peripheral surface of the core  102 ) are in contact with each other, or elastic layers  104 B (see  FIG. 6 ) helically wound such that the longitudinal sides of the adhesion surfaces are not in contact with each other. Although not illustrated, the elastic layers may be formed of two strips  108  located so as to face each other in the radial direction with the core  102  provided therebetween. 
     In particular, when the elastic layers are the elastic layers  104 A (see  FIG. 5 ) helically wound such that longitudinal sides of adhesion surfaces of the two strips  108  are in contact with each other, the contact pressure applied to the member to be cleaned is higher than that in the case where a single elastic member having the same helical width W 1  is used ( FIG. 4 ). Therefore, the cleaning performance may be increased. 
     The adhesive layer  106  will now be described. 
     There is no particular limitation regarding the adhesive layer  106  as long as the core  102  and the elastic layer  104  may be bonded to each other. For example, the adhesive layer  106  may be composed of a double-sided adhesive tape or other types of adhesives. 
     A method for manufacturing the cleaning member  100  according to the present exemplary embodiment will now be described. 
       FIGS. 7A to 7C  illustrate steps of an example of a method for manufacturing the cleaning member  100  according to the present exemplary embodiment. 
     First, as illustrated in  FIG. 7A , a sheet-shaped elastic member (polyurethane foam sheet or the like) that has been sliced to a target thickness is prepared. Then, as illustrated in  FIG. 7A , a strip  108  having a target width and length is punched out of the sheet-shaped elastic member by using a punching die. The strip  108  has a projecting portion  110  (projection) that projects from an end portion of the strip  108  in the longitudinal direction at one side in the lateral direction. 
     The projecting portion  110  is provided so as to project in a direction that crosses the longitudinal direction at least at one of the end portions of the strip  108  in the longitudinal direction. The projecting portion  110  may be provided at each of the end portions of the strip  108 . The shape of the projecting portion  110  is not particularly limited. The projecting portion  110  may be provided at each end portion the strip  108  in the longitudinal direction so to project in the direction that crosses the longitudinal direction at one or both sides of the end portion. The projecting portions  110  provided at both end portions of the strip  108  in the longitudinal direction may project in the opposite directions or in the same direction. Each projecting portion  110  may be shaped such that the thickness thereof gradually decreases toward the end thereof in the projecting direction. In this case, the end of the projecting portion  110  in the projecting direction may be pointed. The length of the projecting portion  110  may be greater than or equal to ½ of the circumference of the core  102 . 
     The strip  108  may be easily wound around the core  102  at the end portions thereof when both end portions of the strip  108  in the longitudinal direction are provided with the projecting portions  110  and the projecting portions  110  provided at the end portions of the strip  108  project in the opposite directions along the direction that crosses the longitudinal direction of the strip  108 . To further suppress the occurrence of unevenness in the image density, the length of the projecting portions  110  may be greater than or equal to ½ of the circumference of the core  102 . 
     A double-sided adhesive tape that serves as the adhesive layer  106  (hereinafter referred to also as “double-sided adhesive tape  106 ”) is bonded to one surface of the sheet-shaped elastic member. Thus, the strip  108  (strip-shaped elastic member with the double-sided adhesive tape  106 ) having a target width and length is obtained. 
     Next, as shown in  FIG. 7B , the strip  108  is arranged such that the surface on which the double-sided adhesive tape  106  is attached faces upward. In this state, one end of the releasing paper of the double-sided adhesive tape  106  is detached, and an end portion of the core  102  is placed on the portion of the double-sided adhesive tape from which the releasing paper is detached. 
     Then, as illustrated in  FIG. 7C , while detaching the releasing paper of the double-sided adhesive tape, the core  102  is rotated at a target speed so that the strip  108  is wound around the outer peripheral surface of the core  102 . Thus, the cleaning member  100  including the elastic layer  104  that is helically wound around the outer peripheral surface of the core  102  is obtained. 
     In the present exemplary embodiment, to suppress the restoring force of the strip  108  and prevent separation of the end portions of the strip  108  in the longitudinal direction from the core  102 , the strip  108  may be wound around the core  102  such that the elastic deformation of the strip  108  (variation in thickness in the central region in the width direction) is small. More specifically, the angle at which the strip  108  is wound around the core  102  and the tension applied when the strip  108  is wound around the core  102  may be controlled depending on the thickness of the strip  108 . 
     Here, when the strip  108  that forms the elastic layer  104  is arranged around the core  102 , the strip  108  may be placed on the core  102  such that the longitudinal direction of the strip  108  is at a target angle (helical angle) with respect to the axial direction of the core  102 . The outer diameter of the core  102  may be, for example, in the range from 2 mm to 12 mm. 
     In the case where a tension is applied to the strip  108  when the strip  108  is wound around the core  102 , the tension may be such that no gap is provided between the core  102  and the double-sided adhesive tape  106  on the strip  108 . When the tension is too high, it becomes difficult to suppress the restoring force of the strip  108 . In addition, the tensile permanent elongation increases, and the elastic force applied by the elastic layer  104  during cleaning tends to decrease. More specifically, the tension may be such that the length of the strip  108  is increased by 0% to 5% of the original length. 
     The strip  108  tends to expand when the strip  108  is wound around the core  102 . The amount of expansion differs depending on the position in the thickness D direction of the strip  108 . The outermost portion tends to expand by a large amount, and accordingly the elastic force thereof may decrease. Therefore, the amount of expansion of the outermost portion of the strip  108  caused when the strip  108  is wound around the core  102  is preferably about 5% of the original length of the outermost portion of the strip  108 . 
     The amount of expansion is determined by the radius of curvature of the strip  108  wound around the core  102  and the thickness of the strip  108 . The radius of curvature of the strip  108  wound around the core  102  is determined by the outer diameter of the core  102  and the winding angle of the strip  108  (helical angle θ). 
     The radius of curvature of the strip  108  wound around the core  102  may be in the range from, for example, ((core outer diameter/2)+1 mm) to ((core outer diameter/2)+15 mm), and is preferably in the range from ((core outer diameter/2)+1.5 mm) to ((core outer diameter/2)+5.0 mm). 
     The strip  108  may be subjected to a compressing process at the ends of the projecting portions  110  of the strip  108  in the projecting directions. In such a case, the thickness and elastic modulus are smaller than those in the case where the compressing process is not performed. Therefore, when the elastic layer  104  is formed of the strip  108  that has been subjected to the compressing process at the ends of the projecting portions  110  in the projecting direction, the restoring force applied to the end portions of the elastic layer  104  is reduced and separation of the elastic layer  104  from the core  102  is easily suppressed. 
     When the elastic layer  104  is formed of the strip  108  that has been subjected to the compressing process at the ends of the projecting portions  110  in the projecting direction, at least one of the end regions including the edges  111 A and  113 A of the first and second end portions  111  and  113  of the elastic layer  104  does not come into contact with the charging member  14 . Therefore, the end regions may be the non-contact regions. In this case, the end of a portion that is not subjected to the compressing process in the at least one of the end regions including the edges  111 A and  113 A of the first and second end portions  111  and  113  of the elastic layer  104  is determined as the start point. Then, the rotation angle viewed from one side in the axial direction of the core  102  is observed by the above-described method. 
     Image Forming Apparatus Etc. 
     An image forming apparatus according to the present exemplary embodiment will now be described with reference to the drawings. 
       FIG. 8  is a schematic diagram illustrating an image forming apparatus  10  according to the present exemplary embodiment. 
     Referring to  FIG. 8 , the image forming apparatus  10  according to the present exemplary embodiment is, for example, a tandem color image forming apparatus. Process cartridges (see  FIG. 9 ) for the respective colors, which are yellow ( 18 Y), magenta ( 18 M), cyan ( 18 C), and black ( 18 K), are disposed in the image forming apparatus  10  of the present exemplary embodiment. Each process cartridge includes a photoconductor (image carrier)  12 , a charging member  14 , and a developing device. The process cartridges are detachably attached to the image forming apparatus  10 . 
     The photoconductor  12  includes, for example, a conductive cylindrical body having a diameter of 25 mm and a photoconductor layer made of an organic photosensitive or the like that covers the surface of the conductive cylindrical body. The photoconductor  12  is rotated at a process speed of, for example, 150 mm/sec by a motor (not shown). 
     The surface of the photoconductor  12  is charged by the charging member  14  disposed on the surface of the photoconductor  12 , and is subjected to image exposure by a laser beam LB emitted from an exposure device  16  at a location downstream of the charging member  14  in the rotation direction of the photoconductor  12 . Thus, an electrostatic latent image that corresponds to image information is formed on the surface of the photoconductor  12 . 
     The electrostatic latent images formed on the photoconductors  12  are developed by developing devices  19 Y,  19 M,  19 C, and  19 K for yellow (Y), magenta (M), cyan (C), and black (K), respectively, so that toner images of the four colors are formed. 
     When, for example, a color image is to be formed, the surface of each of the photoconductors  12  for the respective colors is subjected to the charging, exposure, and developing processes corresponding to yellow (Y), magenta (M), cyan (C), or black (K). Accordingly, yellow (Y), magenta (M), cyan (C), and black (K) toner images are formed on the surfaces of the photoconductors  12  for the respective colors. 
     The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photoconductors  12  are transferred onto a recording sheet  24 , which is transported to the outer peripheral surfaces of the photoconductors  12  by a sheet transport belt  20 , at positions where the photoconductors  12  oppose transfer members  22  with the sheet transport belt  20  interposed therebetween. The sheet transport belt  20  is supported by supporting rolls  40  and  42  at the inner peripheral surface thereof while a tension is applied thereto. The recording sheet  24  that has received the toner images from the photoconductors  12  is transported to a fixing device  64 . The toner images are fixed to the recording sheet  24  by being heated and pressed by the fixing device  64 . Then, when printing is to be performed on only one side, the recording sheet  24  with the toner images fixed thereto is ejected onto an ejection unit  68  in the upper section of the image forming apparatus  10  by an ejection roller  66 . 
     The recording sheet  24  is supplied from a sheet container  28  by a feed roller  30  and transported to the sheet transport belt  20  by transport rolls  32  and  34 . 
     In the case where double-side printing is to be performed, the recording sheet  24  with the toner images fixed to a first surface (front surface) thereof by the fixing device  64  is not ejected onto the ejecting unit  68  by the ejection roller  66 . Instead, the ejection roller  66  is rotated in the reverse direction while the rear end of the recording sheet  24  is held by the ejection roller  66 , and the transport path of the recording sheet  24  is switched to a sheet transport path  70  for double-side printing. A transport roller  72  installed on the sheet transport path  70  for double-side printing transports the recording sheet  24  in the reversed state to the sheet transport belt  20  again, and toner images are transferred onto a second surface (rear surface) of the recording sheet  24  from the photoconductors  12 . The toner images on the second surface (rear surface) of the recording sheet  24  are fixed by the fixing device  64 , and the recording sheet (transfer-receiving member) is ejected onto the ejecting unit  68 . 
     After the transferring of the toner images, cleaning blades  80  remove residual toner, paper dust, etc., from the surfaces of the photoconductors  12  to prepare for the next image formation every time the photoconductors  12  are rotated one turn. Each cleaning blade  80  is disposed on the surface of the corresponding photoconductor  12  at a position downstream of the position where the photoconductor  12  opposes the corresponding transfer member  22  in the rotation direction of the photoconductor  12 . 
     As shown in  FIG. 8 , each transfer member  22  is, for example, a roller including a conductive core (not shown) and a conductive elastic layer (not shown) surrounding the conductive core. The conductive core is rotatably supported. A cleaning member  100 A for cleaning the transfer member  22  is in contact with the transfer member  22  at a side opposite to the photoconductor  12 . The transfer member  22  and the cleaning member  100 A form a transfer device (unit). The cleaning member  100  according to the present exemplary embodiment (see  FIG. 1 ) is used as the cleaning member  100 A. 
     A case in which the cleaning member  100 A is continuously in contact with the transfer member  22  and rotated by the transfer member  22  will be described herein. However, the cleaning member  100 A may either be continuously in contact with the transfer member  22  and rotated by the transfer member  22 , or be brought into contact with the transfer member  22  and rotated by the transfer member  22  only when the transfer member  22  is to be cleaned. 
     As shown in  FIG. 10 , the charging member  14  is, for example, a roller including a conductive core  14 A and an elastic foam layer  14 B surrounding the conductive core  14 A. The conductive core  14 A is rotatably supported. A cleaning member  100  for cleaning the charging member  14  is in contact with the charging member  14  at a side opposite to the photoconductor  12 . The cleaning member  100  is part of a charging device (unit). The cleaning member according to the present exemplary embodiment is used as the cleaning member  100 . 
     A case in which the cleaning member  100  is continuously in contact with the charging member  14  and rotated by the charging member  14  will be described herein. However, the cleaning member  100  may either be continuously in contact with the charging member  14  and rotated by the charging member  14 , or be brought into contact with the charging member  14  and rotated by the charging member  14  only when the charging member  14  is to be cleaned. 
     A load F is applied to both ends of the conductive core  14 A so that the charging member  14  is pressed against the photoconductor  12  and elastically deformed along the peripheral surface of an elastic foam layer  14 B so as to form a nipping portion. In addition, a load F′ is applied to both ends of the core  102  so that the cleaning member  100  is pressed against the charging member  14  and the elastic layer  104  is elastically deformed along the peripheral surface of the charging member  14  so as to form a nipping portion. Thus, the nipping portions that extend in the axial direction of the charging member  14  and the photoconductor  12  are formed while bending of the charging member  14  is suppressed. 
     The photoconductor  12  is rotated in the direction of arrow X by a motor (not shown), and the charging member  14  is rotated in the direction of arrow Y by the rotation of the photoconductor  12 . The cleaning member  100  is rotated in the direction of arrow Z by the rotation of the charging member  14 . 
     Structure of Charging Member 
     The charging member will now be described. However, the structure of the charging member is not limited by the following description. 
     The structure of the charging member is not particularly limited. For example, the charging member may include a core and an elastic foam layer or a resin layer instead of the elastic foam layer. The elastic foam layer may have a single-layer structure or a multilayer structure including plural layers having various functions. The elastic foam layer may be surface-treated. 
     The material of the core may be free-machining steel or stainless steel. The material and the surface treatment method may be selected as appropriate depending on the property such as slidability. The core may be plated. When an electrically non-conductive material is used, the material may be subjected to a typical process for imparting electrical conductivity, such as plating, or be used as is. 
     The elastic foam layer is a conductive elastic foam layer. The conductive elastic foam layer may contain, for example, an elastic material such as rubber, a conductive agent such as carbon black and an ion conductive agent for adjusting the resistance of the conductive elastic foam layer, and, as necessary, any additives commonly added to rubber, such as a softener, a plasticizer, a curing agent, a vulcanizing agent, a vulcanization accelerator, an antioxidant, and a filler such as silica or calcium carbonate. The elastic foam layer is formed by coating the peripheral surface of the conductive core with a mixture to which the materials commonly added to rubber are added. Examples of the conductive agent for adjusting the resistance include carbon black blended with a matrix material and a material in which an electrically conductive material that uses electrons and/or ions as charge carriers, such as an ion conductive material, is dispersed. The elastic material may be foamed. 
     The elastic material constituting the conductive elastic foam layer is formed by, for example, dispersing a conductive agent in a rubber material. Examples of the rubber material include silicone rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, acrylonitrile-butadiene copolymer rubber, and blend rubber of these materials. These rubber materials may be foamed or unfoamed. 
     Examples of the conductive agent include electronic conductive agents and ion conductive agents. Examples of the electronic conductive agents include fine particles composed of carbon black such as Ketjen black and acetylene black; pyrolytic carbon and graphite; various conductive metals such as aluminum, copper, nickel, and stainless steel and alloys thereof; conductive metal oxides such as tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solution, and tin oxide-indium oxide solid solution; and insulating materials having surfaces subjected to a conductivity imparting treatment. Examples of the ion conductive agent include perchlorates and chlorates of oniums such as tetraethylammonium and lauryltrimethylammonium; and perchlorates and chlorates of alkali metals and alkaline earth metals such as lithium and magnesium. 
     These conductive agents may be used alone or in combination of two or more. The amounts of these conductive agents added are not particularly limited. The amount of the electronic conductive agent may be 1 to 60 parts by weight relative to 100 parts by weight of rubber material. The amount of the ion conductive agent may be 0.1 to 5.0 parts by weight relative to 100 parts by weight of rubber material. 
     A surface layer may be formed in the surface of the charging member. The material of the surface layer may be resin, rubber, etc., and is not particularly limited. For example, polyvinylidene fluoride, ethylene tetrafluoride copolymers, polyester, polyimide, and copolymer nylon may be used. 
     Examples of the copolymer nylon include those that contain at least one of nylon 6,10, nylon 11, and nylon 12 as a polymerization unit. Examples of other polymerization unit contained in the copolymer include nylon 6 and nylon 6,6. The ratio of a polymerization unit constituted by nylon 6,10, nylon 11, and/or nylon 12 in the copolymer may be 10% by weight or more in total. 
     The polymer materials may be used alone or in combination of two or more. The number-average molecular weight of the polymer material is preferably 1,000 to 100,000 and more preferably 10,000 to 50,000. 
     A conductive material may be added to the surface layer to control the resistance. The conductive material may have a particle size of 3 μm or less. 
     Examples of the conductive agent for adjusting the resistance include carbon black and conductive metal oxide particles blended with a matrix material, and a material in which an electrically conductive material that uses electrons and/or ions as charge carriers, such as an ion conductive material, is dispersed. 
     Examples of carbon black used as a conductive agent include Special Black 350, Special Black 100, Special Black 250, Special Black 5, Special Black 4, Special Black 4A, Special Black 550, Special Black 6, Color Black FW200, Color Black FW2, and Color Black FW2V produced by Orion Engineered Carbons, and MONARCH 1000, MONARCH 1300, MONARCH 1400, MOGUL-L, and REGAL 400R produced by Cabot Corporation. 
     Carbon black may have a pH of 4.0 or less. 
     The conductive metal oxide particles used as conductive particles for adjusting the resistance are not particularly limited, and any conductive agents may be used as long as electrons are used as charge carriers. For example, conductive particles of tin oxide, antimony-doped tin oxide, zinc oxide, anatase-type titanium oxide, or indium tin oxide (ITO) may be used. These materials may be used alone or in combination of two or more, and may have any particle size. Preferably, tin oxide, antimony-doped tin oxide, or anatase-type titanium oxide is used. More preferably, tin oxide or antimony-doped tin oxide is used. 
     The surface layer may be made of a fluorine-based or silicone-based resin. In particular, the surface layer may be made of a fluorine-modified acrylate polymer. Particles may be added to the surface layer. Insulating particles such as alumina or silica particles may be added to form recesses in the surface of the charging member so that the frictional load imposed during contact with the photoconductor is decreased and the wear resistance between the charging member and the photoconductor is improved. 
     The outer diameter of the charging member may be in the range from 8 mm to 16 mm. The outer diameter is measured by using a commercially available caliper or a laser outer-diameter measuring device. 
     The microhardness of the charging member may be in the range from 45° to 60°. The hardness may be reduced by increasing the amount of plasticizer added or using a low-hardness material such as silicone rubber. 
     The microhardness of the charging member may be measured by using MD-1 hardness meter produced by Kobunshi Keiki Co., Ltd. 
     The image forming apparatus of the present exemplary embodiment includes process cartridges each including a photoconductor (image carrier), a charging device (unit constituted by a charging member and a cleaning member), a developing device, and a cleaning blade (cleaning device). However, the image forming apparatus is not limited to this, and each process cartridge may instead include a charging device (unit constituted by a charging member and a cleaning member) and one or more selected from a photoconductor (image carrier), an exposing device, a transfer device, a developing device, and a cleaning blade (cleaning device) as necessary. Alternatively, each process cartridge may include a transfer device (unit constituted by a transfer member and a cleaning member) and one or more selected from a photoconductor (image carrier), an exposing device, a charging device, a developing device, and a cleaning blade (cleaning device) as necessary. It should be noted that these devices and members need not be formed into a cartridge and may be directly installed in the image forming apparatus. 
     In the image forming apparatus of the present exemplary embodiment, the charging device is a unit constituted by the charging member and the cleaning member, and the transfer device is a unit constituted by the transfer member and the cleaning member. In other words, the charging member and the transfer member are the members to be cleaned. However, the member to be cleaned is not limited to this, and may instead be a photoconductor (image carrier), a transfer device (transfer transport belt or sheet transport belt), an intermediate-transferring-type second transfer device (second transfer member or second transfer roller), or an intermediate transfer member (intermediate transfer belt). The unit constituted by the member to be cleaned and the cleaning member in contact with the member to be cleaned may be directly installed in the image forming apparatus or may be formed into a cartridge as with the above-described process cartridge and installed in the image forming apparatus. 
     The structure of the image forming apparatus of the present exemplary embodiment is not limited to the above-described structure. Image forming apparatuses of an intermediate transfer type and other known types may be employed. 
     EXAMPLES 
     The present invention will now be described by using Examples. However, the present invention is not limited by Examples described below. 
     Example 1 
     Preparation of Cleaning Roller  1   
     A strip having rectangular projecting portions at both ends thereof is cut out of a sheet made of urethane foam (EP-70 produced by Inoac Corporation) having a thickness of 2.5 mm as an elastic member. Next, a double-sided adhesive tape (4801-015 produced by Sumitomo 3M Limited) having a thickness of 0.15 mm is attached to the entire surface of the prepared strip such that the centers thereof in the width direction coincide. Thus, a strip with a double-sided adhesive tape is obtained. The strip with the double-sided adhesive tape is placed on a horizontal table so that the releasing paper attached to the double-sided adhesive tape faces downward, and is bonded to a metal core (overall length 236 mm, core diameter 4 mm, and core circumference 12.56 mm) made of nickel-plated free-machining steel while a tension is applied to the strip so that the overall length of the strip is increased by 0% to 5%. Thus, a cleaning roller  1  (cleaning member) including an elastic layer helically wound around the metal core at a helical angle of 12° from one end to the other end of the metal core is obtained. The elastic layer is formed such that the circumferential cover length at the first end portion, the circumferential cover length at the second end portion, and the rotation angle viewed from one side in the axial direction of the core (angle of non-contact region) are as shown in Table 2, and such that the metal core is exposed over a length of 6 mm at both ends. 
     Examples 2-5 and 7-11 and Comparative Examples 1 and 2 
     Preparation of Cleaning Rollers  2 - 5  and  7 - 11  and Comparative Cleaning Rollers  1  and  2   
     Cleaning rollers  2 - 5  and  7 - 11  and comparative cleaning rollers  1  and  2  are prepared in a manner similar to cleaning roller  1  except that the circumferential cover length at the first or second end portion, the angle of non-contact region, the helical angle θ, the winding number, and the core diameter are set to values shown in Table 2. 
     Example 6 
     Preparation of Cleaning Roller  6   
     Cleaning roller  6  is prepared in a manner similar to cleaning roller  3  except that the elastic member is made of melamine foam (Basotect W produced by BASF). 
     Evaluation 
     The prepared cleaning rollers are evaluated in terms of the following performance, which will be described below, and image quality. For the evaluation, the following charging roller is used. 
     Preparation of Charging Roller 
     Preparation of Elastic Roller 
     A mixture having the composition shown in Table 1 is kneaded with an open roll, and a conductive elastic layer is formed on a surface of a conductive core, which is made of SUS303 and has a diameter of 6 mm and an overall length of 240 mm, with an adhesive layer interposed therebetween by using a press. The conductive elastic layer has an outer diameter of 10 mm and a length of 224 mm. Then, the roller is polished until the outer diameter thereof is reduced to 9.0 mm. Thus, an elastic roller having a conductive elastic layer is formed. 
                         TABLE 1                   Blending Ratio           (Parts by       Material Type   Weight)                                            Rubber   Epichlorohydrin Rubber (Hydrin T3106/   100           Zeon Corporation)       Conductive   Carbon Black (#55/Asahi Carbon   20       Agent   Co., Ltd.)           Benzyltriethylammonium Chloride   1           (Kanto Chemical Co., Inc.)       Vulcanizing   Sulfur (Sulfax PS/Tsurumi Chemical   0.5       Agent   Industries Co., Ltd.)       Vulcanization   Tetramethylthiuram Disulfide (Nocceler   1.5       Accelerator   TT/Ouchi Shinko Chemical Industrial           Co., Ltd.)           Dibenzothiazyl Disulfide (Nocceler   1.5           DM/Ouchi Shinko Chemical Industrial           Co., Ltd.)       Auxiliary   Zinc Oxide (Zinc Oxide Type I/Seido   5       Vulcanization   Chemical Industry Co., Ltd.)       Accelerator       Filler   Calcium Carbonate (Silver W/Shiraishi   20           Kogyo Kaisha, Ltd.)       Slip Agent   Stearic Acid (Kanto Chemical Co., Inc.)   1                    
Formation of Surface Layer
 
     A liquid in which the mixture described below is dispersed with a bead mill is diluted with methanol, applied to a surface of the conductive elastic layer by dip-coating, and thermally dried at 140° C. for 15 minutes to form a surface layer having a thickness of 10 μm. Thus, a charging roller was obtained. 
                                                Polymeric Material   100 parts by weight           (Copolymer Nylon, Amilan CM8000           produced by Toray Industries, Inc.)           Conductive Agent    60 parts by weight           (Antimony-Doped Tin Oxide, SN-100P           produced by Ishihara Sangyo Kaisha, Ltd.)           Solvent (Methanol)   500 parts by weight           Solvent (Butanol)   240 parts by weight                        
Evaluation
 
Evaluation of Following Performance
 
     Each cleaning roller is mounted in a device in which the cleaning roller is pressed against the prepared charging roller so as to cause a deformation of 0.5 mm and is rotated by the charging roller. The charging roller is rotated at 950 rpm, which corresponds to a linear velocity of about 450 mm/s, and the number of revolutions of the cleaning roller that is contact with the charging roller is measured by a non-contact tachometer. The following performance is evaluated by using the criteria described below. The result of the evaluation is shown in Table 2. 
     Evaluation Criteria for Following Performance 
     G1: Value in the range from 95% to 100% of the theoretical number of revolutions per minute of the cleaning roller. 
     G2: Value in the range of 90% or more and less than 95% of the theoretical number of revolutions per minute of the cleaning roller. 
     G3: Value in the range of 80% or more and less than 90% of the theoretical number of revolutions per minute of the cleaning roller. 
     G4: Value in the range of less than 80% of the theoretical number of revolutions per minute of the cleaning roller. 
     Evaluation of Image Quality 
     DocuPrint CD400-dP450 JM produced by Fuji Xerox Co., Ltd. is converted so that the charging roller is rotated at 1000 rpm, which corresponds to a linear velocity of about 470 mm/s. The charging roller and each of the cleaning rollers prepared as described above are mounted in a process cartridge for DocuPrint CD400-dP450 JM. Fifty thousand images are continuously formed at 28° C. and 85% RH, and then fifty thousand images are continuously formed at 10° C. and 15% RH. After the continuous image forming operation, a halftone image having an image density of 50% is formed on an A4-size paper sheet (C2 paper produced by Fuji Xerox Co., Ltd.) at 10° C. and 15% RH, and whether density unevenness has occurred is visually evaluated. The evaluation result is shown in Table 2. 
     Evaluation Criteria for Image Quality 
     G1: Density unevenness does not occur 
     G2: Very slight density unevenness occurs 
     G3: Slight density unevenness occurs (between G2 and G4) 
     G4: Density unevenness occurs 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Com- 
                 Com- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 parative 
                 parative 
               
               
                   
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
                 Exam- 
               
               
                   
                 ple 1 
                 ple 2 
                 ple 3 
                 ple 4 
                 ple 5 
                 ple 6 
                 ple 7 
                 ple 8 
                 ple 9 
                 ple 10 
                 ple 11 
                 ple 1 
                 ple 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Core Diameter (mm) 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 4 
                 6 
                 4 
                 4 
                 4 
               
               
                 Core Circumference 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 12.56 
                 18.85 
                 12.65 
                 12.56 
                 12.56 
               
               
                 (mm) *1 
               
               
                 ½ Core Circumference 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 9.43 
                 6.28 
                 6.28 
                 6.28 
               
               
                 (mm) 
               
               
                 Circumferential Cover 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 9.42 
                 6.28 
                 6.28 
                 6.28 
                 8.28 
                 9.43 
                 6.02 
                 6.28 
                 4.71 
               
               
                 Length at First End 
               
               
                 Portion (mm) 
               
               
                 Circumferential Cover 
                 6.28 
                 6.28 
                 6.28 
                 6.28 
                 9.42 
                 6.28 
                 6.28 
                 6.28 
                 4.28 
                 9.43 
                 6.02 
                 6.28 
                 4.71 
               
               
                 Length at Second End 
               
               
                 Portion (mm) 
               
               
                 Angle of Non-Contact 
                 60 
                 30 
                 15 
                 0 
                 0 
                 15 
                 15 
                 15 
                 0 
                 0 
                 15 
                 75 
                 75 
               
               
                 Region (°) 
               
               
                 Helical Angle (°) 
                 12 
                 12.3 
                 12.5 
                 12.7 
                 12.7 
                 12.5 
                 3.3 
                 6.3 
                 12.7 
                 18.7 
                 12.7 
                 11.8 
                 11.8 
               
               
                 Winding Number 
                 3.83 
                 3.92 
                 3.96 
                 4.00 
                 4.00 
                 3.96 
                 1.02 
                 1.96 
                 4.00 
                 4.00 
                 4.00 
                 3.79 
                 3.79 
               
               
                 Material of Elastic 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Mela- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
                 Ure- 
               
               
                 Member 
                 thane 
                 thane 
                 thane 
                 thane 
                 thane 
                 mine 
                 thane 
                 thane 
                 thane 
                 thane 
                 thane 
                 thane 
                 thane 
               
               
                   
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
                 Foam 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Evaluation 
                 Following 
                 G3 
                 G2 
                 G2 
                 G1 
                 G1 
                 G2 
                 G3 
                 G2 
                 G1 
                 G1 
                 G2 
                 G4 
                 G4 
               
               
                 Result 
                 Performance 
               
               
                   
                 Density 
                 G3 
                 G2 
                 G1 
                 G1 
                 G1 
                 G3 
                 G3 
                 G2 
                 G1 
                 G1 
                 G1 
                 G4 
                 G4 
               
               
                   
                 Unevenness 
               
               
                   
               
               
                 *1: circumferential cover length (mm) is calculated by using 3.14 as the circular constant 
               
            
           
         
       
     
     The above result shows that the image qualities of Examples are better than those of Comparative Examples. 
     The foregoing description of the exemplary embodiment of the present invention 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 embodiment was 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.