1. Technical Field
The present invention relates to a developing device that develops an electrostatic latent image formed on an image supporting body, by a liquid developer including toner and carrier liquid, and an image forming apparatus that forms an image by transferring a developer image developed by a developing device to a recording medium and fixing the image.
2. Related Art
A variety of image forming apparatuses have been proposed that develop and visualize an electrostatic latent image by using a liquid developer of high viscosity, in which toner composed of solid components is dispersed in liquid solvent serving as carrier liquid. The developer used in the image forming apparatus is a developer in which solid components (toner particles) are suspended in organic solvent (carrier liquid) of high viscosity which is composed of silicon oil, mineral oil, edible oil, or the like and has electrical insulation properties. As for the toner particle, an extremely minute particle having a particle diameter of approximately 1 μm is used, thereby being able to achieve higher image quality in comparison with conventional dry type image forming apparatuses that use a toner particle having a particle diameter of 7 μm.
JP-A-2002-99151 discloses an image forming apparatus that seeks to improve development efficiency by uniformly coating a liquid developer on a developing roller through the adjustment of the contact pressure of a blade coming into contact with an anilox roller or the adjustment of the rotary speed of the anilox roller.
JP-A-2002-287513 discloses an image forming apparatus in which an intermediate roller is provided between a coating roller and a developing roller and the intermediate roller and the coating roller are rotated at the same speed and in the same direction as each other. According to this image forming apparatus, since the developing roller does not come into direct contact with the coating roller, abrasion and damage due to a recessed portion formed in the surface of the coating roller do not occur, so that the developing roller suffers reduced mechanical stress and its life can be prolonged.
In this manner, in image forming apparatuses that use a liquid developer, a coating roller (anilox roller) having a recessed portion in its surface is used in order efficiently to scoop up liquid developer and, at the same time, precisely measure liquid developer.
However, in a case where the coating roller (anilox roller) with a recessed portion formed in the surface in this way is used, the transfer pattern of liquid developer by the recessed portion appears, thereby leading to unevenness in the film thickness of liquid developer. In particular, in JP-A-2002-287513, as can be seen in the graph of FIG. 8 thereof showing the relationship between the roller velocity ratio of the developing roller and the intermediate roller and the coating amount of liquid developer that is coated on the developing roller, a region where the roller velocity ratio is 1.0 or less becomes a non-uniform region, and therefore cannot be used for image formation.
In an image forming apparatus, the resolution of an image formed can be improved by reducing the coating amount of the developer that is coated on the developing roller (by thinning the film thickness of liquid developer). However, in the image forming apparatus of JP-A-2002-287513, since the lower limit of the coating amount, that is, the film thickness of liquid developer is restricted, higher resolution cannot be realized.