Image forming apparatus and method for producing charging roll

Abstract

An image forming apparatus includes a rotatable image carrying member, on a surface of which an electrostatic latent image is formed, and a charging roll that is in contact with the image carrying member to charge the surface of the image carrying member to a prescribed potential. The charging roll has, in non-image forming areas in both end parts in an axial direction of the charging roll, large diameter parts having a larger outer diameter than an outer diameter of a center part of the charging roll, and small diameter parts having a smaller outer diameter than the outer diameter of the center part inside the large diameter parts in the axial direction. Differences in outer diameter of the large diameter part and the small diameter part from the outer diameter of the center part each is approximately 0.25% or less of the outer diameter of the center part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will be described in detail based on the following figures, wherein:

FIG. 1 is a schematic constitutional view showing an image forming apparatus according to an exemplary embodiment of the invention;

FIG. 2 is an illustration schematically showing an arrangement of a charging roll according to an exemplary embodiment of the invention;

FIG. 3 is an enlarged view schematically showing an end part in an axial direction of a charging roll according to an exemplary embodiment of the invention;

FIG. 4 is a diagram showing measurement results of relationship of the occurrence of abnormal discharge with respect to the concave and convex amounts in the end part and the nip load;

FIG. 5A is an illustration showing a measurement result of a discharge trace of a conventional charging roll; and

FIG. 5B is an illustration showing a measurement result of a discharge trace of a charging roll according to an exemplary embodiment of the invention.

Claims

1. An image forming apparatus comprising: a rotatable image carrying member, on a surface of which an electrostatic latent image is formed, anda charging roll that is in contact with the image carrying member to charge the surface of the image carrying member to a prescribed potential,the charging roll having, in non-image forming areas in both end parts in an axial direction of the charging roll, large diameter parts having a larger outer diameter than an outer diameter of a center part of the charging roll, and small diameter parts having a smaller outer diameter than the outer diameter of the center part inside the large diameter parts in the axial direction, anddifferences in outer diameter of the large diameter part and the small diameter part from the outer diameter of the center part each being approximately 0.25% or less of the outer diameter of the center part.

2. The image forming apparatus as claimed in claim 1, wherein the charging roll is in contact with the image carrying member at a load of approximately 500 gf or more.

3. The image forming apparatus as claimed in claim 1, wherein the charging roll comprises an elastic material at least on a surface thereof, and the elastic material has a hardness of from approximately 60° to approximately 80° in Asker C hardness.

4. A method for producing a charging roll that is in contact with an image carrying member to charge a surface of the image carrying member to a prescribed potential, the method comprising: providing, in both end parts in an axial direction of a roll corresponding to non-image forming areas of the image carrying member, large diameter parts having a larger outer diameter than an outer diameter of a center part in the axial direction; andproviding, at an inside of the large diameter parts in the axial direction, small diameter parts having a smaller outer diameter than the outer diameter of the center part in the axial direction,a difference in outer diameter of the large diameter part from the outer diameter of the center part in the axial direction being approximately 0.25% or less of the outer diameter of the center part, anda difference in outer diameter of the small diameter part from the outer diameter of the center part in the axial direction being approximately 0.25% or less of the outer diameter of the center part.

5. The method for producing a charging roll as claimed in claim 4, wherein at least a surface of the roll comprises an elastic material, and the elastic material has a hardness of from approximately 60° to approximately 80° in Asker C hardness.