Patent ID: 6823159
Filing Date: 2004-11-23
Classification: G03G

Abstract:
An image forming apparatus comprising:an electrophotographic photosensitive member; charging means for applying voltage to a charge member to charge said electrophotographic photosensitive member; electrostatic latent image forming means for forming an electrostatic latent image on the charged electrophotographic photosensitive member; and developing means for developing the electrostatic latent image, wherein said developing means is provided with at least a developer holding member having a developer holding member surface and configured to hold a one-component developer containing a toner on its developer holding member surface and a developer regulating member configured to regulate a layer thickness of a developer layer of the one-component developer on said developer holding member, wherein said electrophotographic photosensitive member and said developer holding member are set opposite to each other to form a developing section, wherein said developer regulating member regulates the one-component developer to form a thin layer of the one-component developer on the developer holding member surface, wherein in said developing section, the toner in the one-component developer is transferred to the electrostatic latent image held on the surface of said electrophotographic photosensitive member to form a toner image, wherein the peripheral speed of said electrophotographic photosensitive member is 150 mm/second or more, wherein the toner has a weight-average particle-diameter of from 5 to 12 &mgr;m, and of the toner having a circle-equivalent diameter of 3 &mgr;m or more, particles with a circularity a of 0.900 or more, found according to formula (1) are present at a rate of 90% or more in a number-based cumulative value, wherein circularity a=L0/Lâ€ƒâ€ƒ(1), wherein L0 denotes the circumference of a circle having the same projected area as a particle image, and L denotes the circumference of the particle image, andwherein the toner satisfies the following conditions I) or ii): I) the relationship between a cut rate Z and a weight-average particle diameter X of the toner satisfies expression (2) cut rate Z&lE;5.3Ã—Xâ€ƒâ€ƒ(2), wherein the cut rate Z is represented by expression (3)Z=(1âˆ’B/A)Ã—100â€ƒâ€ƒ(3), where A represents a concentration, defined as the number of particles/&mgr;l, of all particles measured with a flow-type particle image analyzer FPIA-1000 manufactured by TOA MEDICAL ELECTRONICS CO.,LTD., and B represents a concentration, defined as the number of particles/&mgr;l, of the measured particles the circle-equivalent diameters of which are 3 &mgr;m or more, wherein the relationship between a number-based cumulative value Y of particles having a circularity of 0.950 or more and a weight-average particle diameter X of the toner satisfies expression (4):Y&gE;exp 5.51Ã—Xâˆ’0.645â€ƒâ€ƒ(4), where X is in the range from 5.0 to 12.0 &mgr;m; andii) the relationship between a cut rate Z and a weight-average particle diameter satisfies expression (5) cut rate Z>5.3Ã—Xâ€ƒâ€ƒ(5) and the relationship between a number-based cumulative value Y of particles having a circularity of 0.950 or more and a weight-average particle diameter X satisfies expression (6)Y&gE;exp 5.37Ã—Xâˆ’0.545â€ƒâ€ƒ(6), where X is in the range from 5.0 to 12.0 &mgr;m, wherein the peripheral speed ratio of said developer holding member to said electrophotographic photosensitive member is 1.2 or less at said developing section.