Charging roller, process cartridge and image forming apparatus

Abstract

An object of the present invention is to provide a charging roller (i) which includes a rubber member whose surface is subjected to a hardening treatment using a solvent containing at least an isocyanate compound and (ii) which can prevent leakage of an ionic conductive agent even if the charging roller is placed under conditions of high temperature and high humidity for a long time. The charging roller is made by forming a rubber layer on a metal core. The rubber layer is an epichlorohydrin based rubber base material to which an ionic conductive agent is added, the rubber layer being subjected to a surface treatment by applying a solution containing the isocyanate compound and heating it. This surface treatment is carried out under such conditions that a coefficient of dynamic friction at a contact portion between the rubber layer and a photoreceptor becomes 0.4 or less.

1 . A charging roller made by forming a rubber layer, contacting an image carrier, on a conductive supporting body,
 the rubber layer being obtained by carrying out, using a solvent containing at least an isocyanate compound, a hardening treatment with respect to a surface of a conductive agent-added rubber layer so that a coefficient of dynamic friction at a contact portion between the conductive agent-added rubber layer and the image carrier is 0.4 or less, the conductive agent-added rubber layer being formed by adding at least an ionic conductive agent to a rubber base material to which a conductive agent is not added   
   
   
       2 . The charging roller as set forth in  claim 1 , wherein the rubber layer is obtained by carrying out a hardening treatment with respect to the surface of the conductive agent-added rubber layer so that the coefficient of dynamic friction at the contact portion between the conductive agent-rubber layer and the image carrier is from 0.27 to 0.4. 
   
   
       3 . The charging roller as set forth in  claim 1 , wherein a surface pressure of the contact portion between the rubber layer of the charging roller and the image carrier is 3.5 g/mm 2  or less. 
   
   
       4 . A process cartridge, comprising a charging roller and an image carrier,
 the charging roller made by forming a rubber layer, contacting the image carrier, on a conductive supporting body, and   the rubber layer being a conductive agent-added rubber layer formed by adding at least an ionic conductive agent to a rubber base material to which a conductive agent is not added, a surface of the conductive agent-added rubber layer being subjected to a hardening treatment using a solvent containing at least an isocyanate compound so that a coefficient of dynamic friction at a contact portion between the conductive agent-added rubber layer and the image carrier is 0.4 or less.   
   
   
       5 . An image forming apparatus, comprising a charging roller and an image carrier,
 the charging roller made by forming a rubber layer, contacting the image carrier, on a conductive supporting body, and   the rubber layer being a conductive agent-added rubber layer formed by adding at least an ionic conductive agent to a rubber base material to which a conductive agent is not added, a surface of the conductive agent-added rubber layer being subjected to a hardening treatment using a solvent containing at least an isocyanate compound so that a coefficient of dynamic friction at a contact portion between the conductive agent-added rubber layer and the image carrier is 0.4 or less.   
   
   
       6 . The image forming apparatus as set forth in  claim 5 , further comprising lubricant applicator for contacting the image carrier to apply a lubricant to the image carrier.