Developer carrier, developing device using the developer carrier, and process cartridge using the developer carrier

Abstract

A developer carrier is provided which is capable of stably imparting charging to a toner over a long term without change of a physical shape of its surface, material composition, and the like even in endurable use and which is capable of forming a satisfactory image while avoiding the occurrence of toner contamination and toner charge-up. That is, the developer carrier is characterized in that: it comprises at least a substrate and a resin coating layer formed on a surface of the substrate; and the resin coating layer comprises at least graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60 or graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1 of 0.64 or more.

What is claimed is:  
     
         1 . A developer carrier that carries a developer for visualizing an electrostatic latent image retained on an electrostatic latent image-bearing member, wherein: 
 the developer carrier comprises at least a substrate and a resin coating layer formed on a surface of the substrate;    the resin coating layer comprises at least graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60 or graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1, which is an average value of circularity obtained by the following expression (1), of 0.64 or more.    Circularity=(4 ×A )/{( ML ) 2 ×π}  (1)    [In the expression, ML represents the maximum length of Pythagorean theorem of a particle projected image, and A represents an area of the particle projected image.]   
     
     
         2 . A developer carrier according to  claim 1 , wherein the resin coating layer contains the graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60.  
     
     
         3 . A developer carrier according to  claim 2 , wherein a coefficient of friction (μs) of the resin coating layer of 0.10 to 0.35.  
     
     
         4 . A developer carrier according to  claim 2 , wherein the graphitized particles (i) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         5 . A developer carrier according to  claim 2 , wherein a number-average particle diameter of the graphitized particles (i) is 0.5 to 25 μm.  
     
     
         6 . A developer carryier according to  claim 1 , wherein the resin coating layer contains graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1, which is an average value of circularity obtained by the expression (1), of 0.64 or more.  
     
     
         7 . A developer carrier according to  claim 6 , wherein the graphitized particles (ii) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         8 . A developer carrier according to  claim 6 , wherein a number-average particle diameter of the graphitized particles (ii) is 0.5 to 25 μm.  
     
     
         9 . A developer carryier according to  claim 6 , wherein the resin coating layer further contains conductive fine particles.  
     
     
         10 . A developer carrier according to  claim 6 , wherein the resin coating layer further contains spherical particles which imparts unevenness to a surface of the resin coating layer and which has a number-average particle diameter of 1 to 30 μm.  
     
     
         11 . A developer carrier according to  claim 6 , wherein the resin coating layer is a conductive coating layer with a volume resistivity of 10 −2  to 10 5  Ω·cm.  
     
     
         12 . A developer carrier according to  claim 6 , wherein an arithmetic mean roughness Ra of the resin coating layer is 0.3 to 3.5 μm.  
     
     
         13 . A developer carrier according to  claim 6 , wherein: 
 the resin coating layer further comprises scaly or acicular graphite with a degree of graphitization P B ( 002 ) of 0.35 or less; and    the degree of graphitization P(002) of the graphitized particles (ii) and the degree of graphitization P B ( 002 ) of the scaly or acicular graphite satisfy the following relationship:      P   B (002)≦= P (002).    
     
     
         14 . A developer carrier according to  claim 13 , wherein the graphitized particles (ii) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         15 . A developer carrier according  claim 13 , wherein a number-average particle diameter of the graphitized particles (ii) is 0.5 to 25 μm.  
     
     
         16 . A developer carrier according to  claim 13 , wherein the resin coating layer further contains conductive fine particles.  
     
     
         17 . A developer carrier according to  claim 13 , wherein the resin coating layer further contains lubricating particles.  
     
     
         18 . A developer carrier according to  claim 13 , wherein the resin coating layer further contains spherical particles which imparts unevenness to the resin coating layer.  
     
     
         19 . A developer carrier according to  claim 13 , wherein the resin coating layer has a volume resistivity of 10 −2  to 10 5  Ω·cm.  
     
     
         20 . A developer carrier according to  claim 13 , wherein an arithmetic mean roughness Ra of the resin coating layer is 0.3 to 3.5 μm.  
     
     
         21 . A developing device which comprises: a developer container that receives a developer; and a developer carrier that carries the developer in a thin layer form, which is received in the developer container; wherein: the device feeds the developer carried on the developer carrier to a developing area that faces an electrostatic latent image-bearing member, and visualizes an electrostatic latent image retained on the electrostatic latent image-bearing member by developing the electrostatic latent image with the developer which have been fed to the developing area, 
 the developer carrier comprises at least a substrate and a resin coating layer formed on a surface of the substrate, and    the resin coating layer comprises at least graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60 or graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1, which is an average value of circularity obtained by the following expression (1), of 0.64 or more.    Circularity=(4 ×A )/{( ML ) 2 ×π}  (1)    [In the expression, ML represents the maximum length of Pythagorean theorem of a particle projected image, and A represents an area of the particle projected image.]   
     
     
         22 . A developing device according to  claim 21 , wherein the resin coating layer contains the graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60.  
     
     
         23 . A developing device according to  claim 22 , wherein a coefficient of friction (μs) of the resin coating layer of 0.10 to 0.35.  
     
     
         24 . A developing device according to  claim 22 , wherein the graphitized particles (i) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         25 . A developing device according  claim 22 , wherein a number-average particle diameter of the graphitized particles (i) is 0.5 to 25 μm.  
     
     
         26 . A developing device according to  claim 21 , wherein the resin coating layer contains graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1, which is an average value of circularity obtained by the expression (1), of 0.64 or more.  
     
     
         27 . A developing device according to  claim 26 , wherein the graphitized particles (ii) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         28 . A developing device according  claim 26 , wherein a number-average particle diameter of the graphitized particles (ii) is 0.5 to 25 μm.  
     
     
         29 . A developing device according to  claim 26 , wherein the resin coating layer further comprises conductive fine particles.  
     
     
         30 . A developing device according to  claim 26 , wherein the resin coating layer further comprises spherical particles which imparts unevenness to a surface of the resin coating layer and which has a number-average particle diameter of 1 to 30 μm.  
     
     
         31 . A developing device according to  claim 26 , wherein the resin coating layer is a conductive coating layer with a volume resistivity of 10 −2  to 10 5  Ω·cm.  
     
     
         32 . A developing device according to  claim 26 , wherein an arithmetic mean roughness Ra of the resin coating layer is 0.3 to 3.5 μm.  
     
     
         33 . A developing device according to  claim 26 , wherein: 
 the resin coating layer further comprises scaly or acicular graphite with a degree of graphitization P B (002) of 0.35 or less; and    the degree of graphitization P(002) of the graphitized particles (ii) and the degree of graphitization P B (002) of the scaly or acicular graphite satisfy the following relationship:      P   B (002)≦ P (002).    
     
     
         34 . A developing device according to  claim 33 , wherein the graphitized particles (ii) are obtained by graphitizing meso-carbon micro bead particles or bulk mesophase pitch particles.  
     
     
         35 . A developing device according  claim 33 , wherein a number-average particle diameter of the graphitized particles (ii) is 0.5 to 25 μm.  
     
     
         36 . A developing device according to  claim 33 , wherein the resin coating layer further contains conductive fine particles.  
     
     
         37 . A developing device according to  claim 33 , wherein the resin coating layer further contains lubricating particles.  
     
     
         38 . A developing device according to  claim 33 , wherein the resin coating layer further contains spherical particles which imparts unevenness to the resin coating layer.  
     
     
         39 . A developing device according to  claim 33 , wherein the resin coating layer has a volume resistivity of 10 −2  to 10 5  Ω·cm.  
     
     
         40 . A developing device according to  claim 33 , wherein an arithmetic mean roughness Ra of the resin coating layer is 0.3 to 3.5 μm.  
     
     
         41 . A process cartridge which integrally comprises at least (I) an electrostatic latent image-bearing member for retaining an electrostatic latent image and (II) developing means for forming the electrostatic latent image into a developed image with a developer in a developing area, the process cartridge is detachably attached to a main body of an image forming apparatus, wherein: 
 the developing means comprises a developer container that receives the developer; and a developer carrier that carries the developer in a thin layer form on a surface thereof, which is received in the developer container; the developer carrier feeds the developer to the developing area;    the developer carrier comprises at least a substrate and a resin coating layer formed on a surface of the substrate; and    the resin coating layer contains at least graphitized particles (i) with a degree of graphitization p(002) of 0.20 to 0.95 and an indentation hardness HUT [68] of 15 to 60 or graphitized particles (ii) with a degree of graphitization p(002) of 0.20 to 0.95 and an average circularity SF-1, which is an average value of circularity obtained by the following expression (1), of 0.64 or more.    Circularity=(4 ×A )/{( ML ) 2 ×π}  (1)    [In the expression, ML represents the maximum length of Pythagorean theorem of a particle projected image, and A represents an area of the particle projected image.]