1. Field of the Invention
This invention relates to an electrophotographic developing method, and more specifically, to a magnetic brush developing method for forming a toner image of high quality by using a two-component developer comprising a magnetic carrier and a chargeable toner. The invention also pertains to a method for forming an image of high quality easily and conveniently without the need for a high level of mechanical precision in a development section.
2. Description of the Prior Art
In electrophotography using a two-component magnetic developer, a chargeable toner and a magnetic carrier are mixed and the two-component mixture is fed onto a development sleeve equipped with a magnet therein to form a magnetic brush composed of this mixture. By bringing the magnetic brush into frictional contact with an electrophotographic plate bearing a latent electrostatic image, a chargeable toner image is formed on the electrophotographic plate. The chargeable toner, upon frictional contact with the magnetic carrier, is charged to a polarity opposite to that of the latent electrostatic image on the electrophotographic plate. The toner particles on the magnetic brush are attracted and adhered to the latent electrostatic image by the Coulomb force whereby the latent electrostatic image is developed. On the other hand, since the magnetic carrier is attracted by the magnet within the sleeve and its charge is of the same polarity as the charge of the latent electrostatic image, the magnetic carrier remains on the sleeve.
For the frictional contact of the magnetic brush with the photosensitive plate, two methods are available, one involving moving the two in the same direction and the other involving moving them in opposite directions. These methods have their own advantages and disadvantages. The former method of moving the two in the same direction permits soft contact between the magnetic brush and the surface of the photosensitive plate. Hence, the reproducibility of a halftone is excellent and the quality of the resulting image is generally good. But with this method, it is difficult to obtain a high image density. According to the latter method, the magnetic brush contacts the surface of the photosensitive plate while it is in the compressed state, and therefore, a high image density is easy to obtain. On the other hand, it has the defect that the resulting image has a defect called brush marks which are many rows of slender and short white lines extending in the rubbing direction of the brush, or other defects such as tailing frequently occur in the resulting image.