1. Field of the Invention
The present invention relates to a developer apparatus which develops an electrostatic latent image formed on an image carrying body by means of a two-component developer, and an image forming apparatus, such as a copying machine, printer, and the like, which comprising such the developer apparatus.
2. Description of the Related Art
In an image forming apparatus, such as a copying machine, printer, or the like, which forms an image on paper by means of an electrophotographic method, an electrostatic latent image formed on an image carrying body, such as a photosensitive drum, is developed by a developer apparatus and converted into a real toner image. This toner image is transferred onto paper by a transfer apparatus. The paper onto which the toner image has been transferred is conveyed to a fixing apparatus, and heated and pressurized by the fixing apparatus, thereby fixing the toner image, whereupon the paper is output from the machine. By this means, one sequence of an image forming operation is completed.
By the way, there are developer apparatuses which develop an electrostatic latent image on an image carrying body by using a two-component developer comprising a toner and a carrier. Such a developer apparatus comprises a toner carrying body, such as a developer roller, which is disposed so as to oppose an image carrying body, and a two-component developer carrying body, such as a magnetic roller, which is disposed in the vicinity of the toner carrying body. In a developer apparatus of this kind, a thin layer of toner is formed on the toner carrying body by supplying the toner of the two-component developer carried on the two-component developer carrying body to the toner carrying body. And, the electrostatic latent image on the image carrying body is developed by this toner layer (touchdown development) and thus converted into a real toner image.
In a developer apparatus such as that described above, it is necessary to carry out the formation of the thin layer of toner on the toner carrying body and the recovery of undeveloped toner on the toner carrying body, in a simultaneous fashion. Consequently, there have been problems such as a ghost phenomenon in which the historical trace of previous toner consumption is left in the thin layer of toner on the toner carrying body due to defects in recovering the undeveloped toner, or the like, or the problem of charging up of the toner on the toner carrying body.
In order to resolve the problem described above, Japanese Patent Application Laid-open No. 2005-274924, for instance, proposes disposing a magnetic pole on the opposite side of the toner carrying body from the two-component developer carrying body, and promoting the recovery of undeveloped toner from the toner carrying body by creating a strong magnetic brush between the toner carrying body and the two-component developer carrying body.
By the way, in recent years, printers and copying machines capable of outputting at speeds of 50 pages per minute in the case of color machines, have been developed, and high-speed printers and copying machines exceeding an output speed of 100 pages per minute in the case of monochrome machines have been developed.
If the touchdown developing method proposed in Japanese Patent Application Laid-open No. 2005-274924 is adopted in a high-speed machine of this kind, in order to form a sufficient thin layer of toner on the toner carrying body, it is necessary to respond by raising the concentration of toner in the two-component developer, or raising the bias voltage for forming the thin layer or toner, or the like. If measures of this kind are adopted, then scattering of toner is liable to occur between the toner carrying body and the two-component developer carrying body. Furthermore, there are also problems in that leaks are liable to occur between the toner carrying body and the two-component developer carrying body, giving rise to image abnormalities in which the image is not printed accurately onto the paper, as well as causing soiling of the interior of the apparatus.