Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-03-15
2002-11-26
Chapman, Mark (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C399S330000, C399S331000, C399S333000
Reexamination Certificate
active
06485878
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming method.
BACKGROUND OF THE INVENTION
In color toner images in which a desired color is formed by laminating toner layers having three primary colors (color layering), with the view of improving color reproduction properties, it is required that color matching be conducted by smoothing the surface (interface) of the toner layer surface of each color. In order to smooth the interlayer of said toner layers, it is advantageous to use a toner having a low melt viscosity during fixing. On the other hand, widely employed, as a system to fix color toner images, is a heating roller fixing system utilizing a fixing unit provided with a heating roller as well as with a pressure roller.
However, when color toner images, comprised of toners having a low melt viscosity, are fixed utilizing said heating roller fixing system, and subsequently the fixed image is peeled off from said heating roller, so-called offset phenomena tend to occur. In order to minimize said offset phenomena, a relatively large amount of silicone oil is applied to the surface of said heating roller so that adhesion between said heating roller and said toner is reduced.
However, in such a system, problems occur in which silicone oil which is applied to the surface of the heating roller is soaked into the transfer paper sheets (an image forming support) to result in degradation of writability of said transfer sheet, and in addition, said silicone oil adheres to the leading edge of the transfer sheet which is brought into contact with said heating roller. Further, when PET sheets, for overhead projection use, are employed as the image forming support, problems also occur in which said silicone oil remains on the surface of said PET sheet to result in stickiness.
When color images are fixed employing the heating roller system described above, no means has been known which sufficiently exhibits both color reproduction properties (smoothness of each color toner layer) and offsetting resistance (releasability in a fixing unit in which no silicone oil is supplied or only a very small amount of silicone oil is supplied).
Multicolor image forming methods include a method in which an electrostatic latent image corresponding to a color is formed on a latent image bearing body, and a multicolor image is formed by repeating the development and transfer process for each color. Said method, however, requires that said electrostatic latent image bearing support is subjected to repetition of development and transfer processes under the frequency of developing each color. Therefore, the rate of image formation is low compared to that of a single color image formation. Thus, when full-color images are formed, said rate is not more than ¼ of the single color rate.
Accordingly, when said method is utilized, it is difficult to increase the rate of full-color image formation.
On the other hand, methods, in which even full-color images are formed at high speed, include a method, generally called a tandem method, in which an electrostatic latent image bearing body corresponding to each color is provided, and an image formed on each body is transferred so as to form a full-color image.
In said method, since a latent image forming process, a development process, and a transfer process are formed for each color, the rate of image formation is the same as that of a single color formation. Thus, said method exhibits an advantage which makes it possible to achieve full-color image formation at high speed.
However, in said method, since each color image is formed utilizing an individual electrostatic latent image bearing body, it is required to stabilize the developed amount of each color to control the color balance. Further, since an image is formed by transferring a toner image formed on each electrostatic latent image bearing body onto an image support and subsequently by fixing the transferred image, problems occur in which when adhesion of any of color images onto said image support is different, image stability during fixing deteriorates.
The electrostatic latent image bearing body as previously described is commonly an electrophotographic photoreceptor, which is hereinafter referred occasionally to simply as a photoreceptor.
On the other hand, preferably employed as a fixing method is a so-called heating roll method due to the simplicity, and the like, of such a unit. In this fixing method, since the fixing roller is brought into contact with a toner, releasing agents are preferably incorporated into said toner to assure sufficient releasability.
However, in a toner which is prepared employing a conventional pulverization method, materials dispersed into toner particles exist non-uniformly on a broken surface. Particularly, materials such as releasing agents, which melt quickly in the narrow temperature range, tend to be concentrated on the surface so that surface properties among toner particles tend to be non-uniform. Due to that, it becomes difficult to stabilize the developed amount as well as to assure uniform adhesion among the toner particles of each color. As a result, problems occur in which fluctuation tends to result and color reproduction properties, required for quality color images, are degraded.
On the other hand, a so-called polymerization toner has been known which is prepared utilizing a polymerization method. Of said polymerization toners, a toner prepared by utilizing a suspension polymerization method is comprised of spherical toner particles with uniform surface properties. Thus, it is supposed that uniformity among toner particles is enhanced. However, the particle shape tends to become spherical and adhesion onto an electrostatic latent image bearing body as well as onto an image support is enhanced. As a result, problems tend to occur in which transferability is degraded and image repellency during fixing occurs.
As a result, by employing the image forming method comprised of said tandem method, at present, it is difficult to obtain consistent image quality over an extended period of time.
Known as a color image forming method has been a method utilizing a so-called intermediate transfer system in which a latent image formed on a latent image bearing body is developed employing a toner; instead of transferring the resulting toner image directly onto an image forming support, it is temporarily transferred onto an intermediate transfer body, and subsequently retransferred onto said image forming support.
In said intermediate transfer method, by transferring a toner image formed on a latent image bearing body onto an intermediate transfer body several times (for example, 4 times), each color toner layer is laminated on said intermediate transfer body (color layering). In this case, when the last color toner image is transferred onto the intermediate transfer body, the charge amount of the toner, constituting the color toner image which has been first transferred onto said intermediate transfer body, decreases occasionally. In order to minimize the decrease in the charge amount of the toner image in the lower layer, it is required to employ a toner with stable chargeability.
On the other hand, widely employed as a means to fix toner images formed on an image forming support, is a heating roller system, employing a fixing unit provided with a heating roller as well as with a pressure roller.
In said system, a toner is brought into contact with the surface of said heating roller. As a result, so-called offset phenomena tend to occur. Herein, in order to minimize said offset phenomena, a method is employed in which a relatively large amount of silicone oil is applied to the surface of said heating roller so as to provide releasability.
However, when a relatively large amount of silicone oil is employed, problems occur in which silicone oil adheres onto an image forming support and the mechanism of the fixing unit itself becomes more complex. Accordingly, it is desirous that releasability be provided in the toner itself so that the coating amount of
Horiuch Kazuhisa
Matsushima Asao
Nagase Tatsuya
Shirose Meizo
Soeda Kaori
Bierman, Muserlian and Lucas
Chapman Mark
Konica Corporation
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