The present invention relates to a developing electrode for use in developing an electrostatic latent image.
The electrostatic latent image is usually formed by utilizing an electronic photographic method or by applying pulses of high voltage level to a stylus electrode provided adjacent to the surface of a dielectric layer.
Various kinds of methods for developing electrostatic latent images are well known in the art, such as for example, the cascade method, the magnetic brush method, the powder cloud method and the liquid developer method.
Recently, the developing electrode has become practical in the developing methods set forth above in order to obtain a clean copy.
The electrostatic latent image is formed on a photo-conductive insulator mounted on a conductive substrate or the image is formed on a surface of a dielectric layer. When the image has a large area, voltage contrast at the central area of the latent image becomes lower as compared to the peripheral area of the image, since the peripheral area has the boundary area between a charged area and an uncharged area but the central area of the image does not have such a boundary area. Therefore, an electric field is formed inward of the photo-conductive insulator or the dielectric layer but the electric lines of force are only slightly at the outside near the central area of the image. When the development operation is carried out under these conditions, a large amount of the developer is deposited onto the peripheral area but the developer is only scarcely deposited onto the central area of the image. This effect is referred to as the edge development effects, which is well known in the art.
The electric lines of force created from the central area of the latent image may be changed by installing a developing electrode made of conductive material such as metal in a manner so as to adjoin the latent image, thereby intensifying the electric field formed between the developing electrode and the latent image. The electric field is greatly intensified as the distance between the developing electrode and the latent image is made shorter.
The developing electrode must be provided close to the path of the photosensitive paper or the surface of the dram in the developing section, but the electrode must be installed in a manner not to disturb the replenishment of the developer including toner at a proper concentration onto the surface of the photosensitive paper or the dram. The developing electrode of the prior art tended to disturb the replenishment of the developer onto the surface of the photosensitive paper or the dram when the developing electrode is disposed close to the path of the photosensitive paper or the surface of the dram, since the developing electrode of the prior art is made of a metal plate of a flat configuration or a curved configuration. Therefore, the developing electrode of the prior art must be disposed in a manner so as to provide an appropriate distance between the developing electrode and the surface of the photosensitive paper or the dram. However, when the distance between the developing electrode and the surface of the photosensitve paper or the dram is increased, the electric field intensifying effect may be weaken. There has been some suggested solutions such as to make the developing electrode of a material in order to eliminate the above-mentioned defects. When a mesh electrode is used for the developing electrode, the replenishment of the developer may be smoothly accomplished, but the mesh electrode can not be positioned close to the path of the photosensitive paper or the surface of the dram at all times, since the mesh is so soft.