Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-08
2002-04-30
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111410, C399S308000
Reexamination Certificate
active
06379857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming color images according to a process of electrophotography or electrostatic recording. More precisely, the invention relates to such a method for forming a color image with a two-component developer including a color toner and a carrier, for printers, duplicators, facsimiles and others for printing out color images, especially full-color images.
2. Description of the Related Art
Heretofore, the main stream of electrophotography to produce visible images by developing latent images having been formed on a latent image holding member includes a method of unary development where a latent image formed on a holding member is brought into contact with a thin toner layer formed on a developer holding member so that it is developed with the toner, and a method of binary development where a developer that contains a toner and a magnetic carrier is held on a developer holding member having a magnet therein to provide a magnetic brush, and a latent image formed on a holding member is brought into contact with the magnetic brush so that it is developed with the toner.
Single component development will be better than two-component development in that the size and the weight of the apparatus for it could be readily reduced, but it involves some problems in that the amount of the toner to be applied to and held on the developer holding member is often difficult to stabilize and the electrostatic charge of the toner is difficult to control as compared with that of the two-component developer for two-component development. On the other hand, in two-component development, the amount of the two-component developer to be applied to and held on the developer holding member can be well stabilized as the holding member is assisted by the magnetic force of the magnet which it has therein. In this, in addition, the toner and the carrier to be used are stirred so that the toner is electrostatically charged through friction. Accordingly, in such two-component development, the frictional electrostatic charge of the toner could be well controlled to a relatively high degree by appropriately selecting the characteristics of the toner, the stirring condition and the toner concentration in the developer, and therefore the electrostatically charged toner that will often fluctuate depending on the ambient environment and the processing time could be readily stabilized to ensure high reliability to give high-quality images.
For forming color images, the degree of development must be accurately controlled to realize the intended color formation, for which, therefore, two-component developers are much used as it is easy to well control the degree of electrification of the toner therein.
In two-component development, the developer resistance has a significant influence on the quality of the images formed. In a process of such two-component development, in general, the peripheral velocity of the developer holding member is kept higher than that of the latent image holding member in order that a sufficient amount of the developer could be supplied to the development zone. In this, however, if the developer resistance is high, image defects will be often inevitable owing to the velocity difference between the developer holding member and the latent image holding member. In such a case where the peripheral speed of the developer holding member differs from that of the latent image holding member, the developer holding member will be influenced by the electric field of the other latent image region that differs from the region of the latent image to be actually developed therewith, before it reaches the region of the latent image holding member which is kept in contact with a magnetic brush with which the latent image in the region is actually developed (the region is hereinafter referred to as a development nip region). If so, the electrostatic charge of the developer will partly vary, and the image developed in such a condition could not faithfully reproduce the latent image. As a result, in a region where the latent image structure varies to a great extent, significant image defects will be inevitable in the developed image area. For example, the density of the trail edge of the solid image adjacent to a non-image area will be thinned; or in a region where a half-tone image and a solid image exist at random, the lead edge of the solid image and the trail edge of the half-tone image will be lost (the image defects are hereinafter referred to as “edge deletions”).
The development fluctuation in color images results in color drift therein, and therefore the requirement for preventing image defects such as edge deletions in solid images and half-tone images is greater than that for preventing them in monochromatic images.
For preventing such image defects, for example, one technique is proposed in Japanese Patent Publication No. 31422/1995, which includes reducing the carrier resistance for preventing edge deletions in solid images. Reducing the carrier resistance as proposed could be effective for preventing edge deletions in solid images, but is often still problematic in that a wax-containing small-particle toner to improve the fixing properties and a small-particle carrier that constitute a developer will both adhere to a latent image-holding member in the step of developing the latent image with the developer. If so, the developed image on the support could not form a suitable nip in and around the carrier-containing region therein when it is transferred onto a recording medium or onto an intermediate transfer medium, since the particle size of the toner greatly differs from that of the carrier. As a result, the carrier-containing region in the developed image Will result in transfer failure, thereby causing edge deletions in solid images. Transfer failure in image formation causes deletions in monochromatic images, or causes color drifts (hereinafter referred to as “deletions”) in multi-developed and multi-transferred color images, and these image defects are often serious in image formation.
SUMMARY OF THE INVENTION
The present invention is to solve the problems as above in the related art and to attain the aims to be mentioned below. Specifically, the invention is to provide a method for image formation capable of stably outputting high-quality images with no image density unevenness for a long period of time, in which the images formed are free from image defects of so-called deletions or edge deletions therein and which ensures good and uniform developability everywhere in the latent image region to be developed while preventing the latent image holding member used from being degraded.
To attain the aims as above, the invention provides the following:
<1> A method for forming a color image including a step of forming a latent image on a latent image holding member, a step of developing the latent image on the latent image holding member with a two-component developer on a developer holding member disposed to face the latent image holding member, and a step of transferring the thus-developed toner image onto a transfer medium, wherein the developer holding member is a cylindrical sleeve having a diameter of at most 20 mm, the two-component developer contains a carrier and a toner, and the developer resistance is at least 10
13
&OHgr; in an electric field of 2 V/&mgr;m.
<2> A method for forming a color image including a step of forming a latent image on a latent image holding member, a step of developing the latent image on the latent image holding member with a two-component developer on a developer holding member disposed to face the latent image holding member, and a step of transferring the thus-developed toner image onto a transfer medium, wherein the latent image holding member is a cylindrical sleeve having a diameter of at most 40 mm, and the resistance of the two-component developer is at least 10
13
&OHgr; in an electric field of 2 V/&mgr;m.
In the image-forming method of the inventio
Iizuka Akihiro
Ishida Haruhide
Kataoka Rieko
Taguchi Tetsuya
Yoshihara Koutarou
Chapman Mark
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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