1. Field of the Invention
The present invention relates to a developing apparatus and method capable of developing a latent image formed on an image carrier with a liquid type developer having high viscosity and density, and in particular, to a developer applying and removing apparatus and a method which forms a thin layer of developer having an almost constant thickness on a developing device in a way that avoids forming "ghost" images during development of the latent image.
2. Description of the Related Art
A conventional developing apparatus used in an image forming apparatus, which develops a latent image formed on the image carrier by an electro-photographic method with liquid type developer having high viscosity and density, is disclosed in Japanese Patent Application Laid Open Nos. 07-239614 and. 08-123205, for example. In the conventional image forming apparatus, a photoconductive (P.C.) surface of an image carrier is uniformly charged by a charge-applying device and then exposed by an image writing device based upon image data, thereby forming a latent image thereon. A liquid type-developing device then develops the latent image. The liquid type-developing device includes liquid type developer composed of dimethyl siloxane oil, for example, having high viscosity and an insulating character, and toner particles dispersed therein in high ratio, which function to make the latent image visible.
The liquid type developer is stored in a developer storing device and is applied to a developing belt or developing roller by a developer applying device to form a thin developer layer having even thickness on a surface of the developing belt or developing roller. The latent image is developed when the developer layer passes through a developing station and the toner therein spreads to the latent image area formed on the P.C. material, thereby forming a visible toner image thereon. The toner image is then transferred onto a copysheet by a transfer device and then fixed on the copysheet by a fixing device. A charge-removing device removes charge remaining on the surface of the P.C. material after transfer of the toner image, and a cleaning device also removes toner remaining thereon, thereby completing an image forming cycle.
However, if a developer layer to be formed on the surface of the developing belt or roller is not even, it causes a density variation of the toner image or non sharpness thereof. Therefore, the developer layer should be evenly formed on the surface of the developing roller.
To apply developer and form a thin developer layer on a developer belt, a developer-applying roller is generally used, as configured in an ink applying system for a duplicating machine. The thin developer layer is spread on a latent image pattern formed on the P.C. drum, but the developer does not spread onto a background portion of the latent image pattern, thereby remaining on the surface of the developer belt.
When new developer is applied onto the surface of the developer belt after a developing operation, a thickness of the developer layer varies between a portion of the surface of the developer belt from which the developer was removed to develop the latent image and a portion in which the developer remains, giving rise to an unevenness of the developer layer. As a result, a ghost, which is an image pattern of an image previously formed, is made when a next latent image is developed by the developing belt having the above-described unevenness of the thickness of the developer layer. To avoid such a ghost, a leveling mechanism that levels ink before duplication is employed in the duplicating machine, for example.
However, since a latent image pattern generally varies somewhat, as does an amount of developer remaining after developing, a thickness of developer correspondingly varies even after leveling thereof by a leveling mechanism. To avoid such a problem, and as presently recognized, developer remaining on the surface of the developing belt should be entirely removed before new developer is applied.
Thus, a special developer-removing roller that removes the developer remaining on the surface of the developing belt is required, and as a result, a developing device is made to be complex. The complexity problem is particularly serious in a full-color image-forming apparatus, since a plurality of the special developer-removing rollers is needed to remove different color developer from the developing belt and so this type of conventional developing device is necessarily bulky.