Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-03-07
2004-02-24
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111350, C399S270000
Reexamination Certificate
active
06696213
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of developing a latent electrostatic image used for the electrophotography, the electrostatic recording, and the electrostatic printing.
2. Background of the Invention
Methods of electrophotographic development are divided into two groups, namely, so called a one-component developer method using toner as the main component and a two-component developer method using a mixture of toner and carrier such as glass beads, magnetic carrier, or their coated with a resin
As two-component developer method relies on the use of carrier for increasing the charged area for the toner, they are more stable in the charging properties than the most one-component developer method and thus favorable for ensuring the reproduction of high quality images in a long-run operation. Also, the two-component developer method is high in the toner feeding capability to a developing area and can hence be incorporated into high-speed apparatuses.
Such a two-component developer method is commonly employed in the digital electrophotography where a latent electrostatic image is printed on a photosensitive member with laser beam or the like and developed to a visible image.
Also, to cope with the decrease in size of the minimum unit area (a dot or pixel) of latent image while the increase in the density for improving the resolution, the reproducibility of highlight, and the color quality, various modifications of the method have been proposed with respect to processing conditions and developers (toner and carrier).
With regard to the two-component developer methods, in the during development, where assuming the traveling speed (mm/sec) of photosensitive member is Vp (sec) and the width of the image development area (the contacted width of the photosensitive member with the developer) is L (mm), a period of the time during a latent image being held in direct contact with a developer (=a developing period) is represented by An expression L/Vp (sec), if the L is smaller and the Vp is bigger, the developing period becomes shorter. And this shorten developing time declines the degree of development, thus causing undesired decrease of image density, non-uniform density in half toned image, making trace mark of developing brush, causing cutoffs in fine lines in image, forming white voids(blanks) of small size of dots in image and the like, thus deteriorating the quality of reproduced image.
For eliminating above mentioned drawbacks, a technique was introduced which included, for example, means for elevating the electric voltage of the photosensitive member to re the developing electric-potential and means for increasing traveling speed Vr mm/sec) of a developing sleeve so as to coincide with traveling speed Vp (sec/mm) of a photosensitive member moving in the same direction to bring in the more amount of developer to expand the contacting area of the developer with the latent electrostatic image. The rise of developing electric-potential of the photosensitive member is however suffered from an abundant electric charge passing through thereto, thus causing shortening of the life of the photosensitive member, therefore generally adopted means for overcoming the problem are those for increasing the amount of developer to be contacted.
Although an increased amount of developer to be contact by mean of using a difference between rotation speeds of developing sleeve and photosensitive member results in general a higher density of solid image, however the change in optical density and the occurrence of white voids are also very noticeable, especially at edge regions of solid image area and half toned image area. Such phenomenon appears at the area where the latent electric potential is varied sharply and discontinuously.
When the value of the Vr/Vp is greater than 1 with the photosensitive member rotating in the same direction as of the developing sleeve (referred to as forward rotation hereinafter), the carrier is traveling so as to outrun the latent electrostatic image which is also traveling.
Accordingly, at boundary region where the latent electrostatic image varies from background part to image part, developer arrives the background part before it enters into the solid part of image, thereby the toner particles held in carriers remain shifted (repelled) to the developing sleeve at the side opposite to the background part of the latent electrostatic image, by the effect of an electric potential equal to V
B
−V
D
, (where the V
B
is the biased direct-current and the V
D
is the charge potential).
Therefore, when the Vr/Vp is considerably greater than 1, the developer may fail to rapidly feed toner particles to the boundary between the background region and the solid image region, thus generating a white voids(blanks) in the trailing end (rear end of the latent image advancing forward) of the solid region.
During the developer is passing through the background region, its toner particles remain shifted to the sleeve side and less contacted to the photosensitive member. It may say additionally that this phenomenon (shifting of toner particles to tile sleeve side) will contribute to the protection from smears of the background.
As developer arrives from the background region to the trailing end of an image region, the developing area is now going to transfer the toner particles to the latent image for developing it by the effect of a developing potential (V
L
−V
B
, where the V
L
is the post-exposure potential and the V
B
is the biased direct-current potential), however on the time, the toner particles may hardly be supplied to be transferred, because they having been drifted to the sleeve side.
As a result, a more number of white voids will appear at trailing end of the halftone image area than at trailing end of the solid image area This can be explained by the developing electric-potential is a lower level at the half-tone region. It is now noted that the white voids(blanks) in the solid image are referred to as solid trailing end blanks and the white voids in the half-tone image are referred to as half-tone trailing end blanks hereinafter.
When the photosensitive member and the developing sleeve rotate in opposite directions (referred to as reverse rotation hereinafter), the foregoing phenomena may create blanks at the boundary between a background region and a solid region. The reverse rotation, unlike the forward rotation, permits the blanks in the leading end of the solid image.
Also, when Vr/Vp is smaller than 1 with the forward rotation, the carrier moves towards the latent electrostatic image hence generating a state resemble to the reverse rotation state and causing the blanks to appear in the leading end of the solid image.
For eliminating declinations in the image quality derived from the difference of the developing direction, some attempts were proposed which minimize the difference in the speed between the photosensitive member and the developing sleeve, however they were hard to give success. When the difference in the speeds is minimized, the image density may be declined or the smears of the background area may be generated. It is hence unsuccessful to provide a two-component developer method which can satisfy the both requirements of eliminating blanks and smears.
While digital technologies have been significantly developed for improving the image quality in recent years, the drawbacks pertinent to the developing direction(where the traveling speed of the developing sleeve is faster than that of the latent electrostatic image) may include not only the trailing end blanks in the developed image but also cutouts of the horizontal line, thickening of the vertical line, fault in the sharpness of characters (thickened in the vertical and thinned in the horizontal), and carrier deposition. It is hence desired to provide a further improvement of the method.
Problems that the Invention is to Solve
It is An object of the present invention to provide a developing method which can eliminate a
Kotsugai Akihiro
Yamaguchi Kimitoshi
Goodrow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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