Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-07-07
2002-06-04
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...
C430S017000, C430S018000
Reexamination Certificate
active
06399265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent film for forming a toner image, and a process for forming a toner image. More specifically, the present invention relates to a process for forming a toner image in accordance with an electrophotographic process.
2. Related Background Art
In the general process for forming a full-color image, a full-color image has heretofore been formed in the following manner. A magenta toner image is formed by uniformly charging a photosensitive member of a photosensitive drum, conducting image exposure with a laser beam modulated by magenta image signals of an original document to form an electrostatic latent image on the photosensitive drum, developing the electrostatic latent image by a magenta developing device to form a magenta toner image on the photosensitive drum, and transferring the magenta toner image developed on the photosensitive drum by means of a charger for transfer to a recording medium that has been fed.
After completion of the above-described development and transfer, the photosensitive drum is then subjected to static charge elimination by a charger for static charge elimination, cleaned and again charged by a primary charger to conduct the formation of a cyan toner image on the photosensitive drum and the transfer of the cyan toner image to the recording medium, to which the magenta toner image has been transferred, in the same manner as described above. Further, this process is successively conducted as to a yellow color and a black color to transfer the toner images of the four colors to the recording medium. Furthermore, the toner images of the four colors are fixed to the recording medium by the action of heat and pressure by a fixing means such as a fixing roller, thereby forming a full-color image.
In recent years, such image forming apparatus have not been limited to use only as copying machines for office management for copying so-called original documents, and have begun to be used in the fields of printers as output devices for computers and personal copying for individual use. Besides the field typified by such a laser beam printer, the development of facsimiles for plain paper making use of the basic technology is also rapidly growing.
Therefore, in such an image forming apparatus as described above, smaller size, lighter weight, higher speed and higher image quality, and higher reliability have been pursued, and so the apparatus has come to be constructed by simpler elements at various points. As a result, toners have also been required to have higher performance. Therefore, an excellent image forming apparatus has not come to be realized unless improvement in the performance of the toners has been achieved.
In keeping with the various needs of copying in recent years, the demand for color copying has rapidly increased. In order to more faithfully copy an original color image, still higher image quality and higher resolution have been desired. From these points of view, toners used in a color-image forming process are required to be good in melting ability and color-mixing ability upon application of heat, and there is hence a demand for development of toners high in sharply melting ability, which have a low softening point and a low melting temperature. The use of such toners high in sharply melting ability enables widening the color tone reproducibility range of copies and is able to obtain color copies faithful to the original color image.
However, such toners high in sharply melting ability generally have high affinity for a fixing roller and tend to offset to the fixing roller. In particular, in the case of a fixing means in a color-image forming apparatus, there is a tendency to easily cause offset due to increase in the thickness of toner layers by the formation of a plurality of toner layers composed of magenta toner, cyan toner, yellow toner and black toner on a recording medium.
In order to improve the releasability of toners from a fixing roller, it has heretofore been conducted to, for example, form the surface of the fixing roller with a material having excellent release property (for example, silicone rubber or fluororesin) for the toners and further coat the surface with a thin film of a liquid having high release property, such as silicone oil or fluorine-containing oil to prevent offset and the fatigue of the roller surface. This method is extremely effective in that the offset of toners is prevented, but involves problems that a device for feeding an anti-offset liquid is required to complicate the fixing device and that the oil applied causes delamination or peeling between layers making up the fixing roller to consequently facilitate shortened life of the fixing roller.
In keeping with the various needs of copying in recent years, various kinds of paper, coated paper and plastic films have been used as recording mediums. In particular, attention is paid to the necessity of light-transmitting sheets (OHP sheets) for utilizing an over-head projector (OHP) for presentation. The OHP sheet has low oil-absorbing capability, unlike paper, so that the oil used in the above-described fixing device adheres to the surface of the OHP sheet. As a result, the OHP sheet, on which an image has been formed, has been unable to avoid having a sticky feel due to the adhesion of the oil and incurs deterioration of the image quality. In addition, there is a possibility that a releasing oil such as silicone oil may be evaporated by heat to contaminate the interior of the fixing device, or that problems such as treatment of recovered oil may arise.
Accordingly, it is greatly expected to establish a fixing system which can solve the above-described problems and does not require oil application upon the fixing of an image, and to develop novel toners for that purpose.
In order to achieve the above subject, Japanese Patent Application Laid-Open No. 61-273554 discloses a toner comprising a release agent such as a wax. In case of the toner containing a wax, the thermal conductivity of the toner is enhanced by virtue of the wax which melts at a lower temperature. As a result, the fixing at a low temperature is feasible. More preferably, the wax melted upon fixing is also able to act as a release agent, and so offset at a high temperature can be prevented without applying a release agent such as an oil to the fixing roller.
When a color toner image or full-color toner image is formed on a light-transmitting sheet using an electrophotographic system according to a dry developing process and the image is projected by means of an OHP apparatus, there is presented a phenomenon that the projected image exhibits a grayish tone as a whole though the full-color image on the light-transmitting sheet shows sufficient coloring property, and so the range of color tone reproduction becomes very narrow. This phenomenon presents itself for the following reason. Namely, since the unfixed toner image formed on the light-transmitting sheet with a smooth surface is not fully made fluid even by heating upon image fixing and retains graininess, incident light is scattered upon projection to cast a shadow on the screen. In a middle tone area or highlight area of image, at which the image density is low, in particular, the absorption by the dye or pigment in the toner of each color is lowered due to the decreased number of toner particles. Therefore, the color tone to be reproduced becomes grayish.
On the other hand, when a toner image formed on a recording medium such as plain paper is visually observed, an reflected image of light struck on the toner image is visually observed. Therefore, the image quality is scarcely influenced even when some graininess is left on the toner surface. When the toner image is observed or projected on a screen as transmitted light like OHP, however, the light transmission property is deteriorated due to the scattering of light if the shape of the toner particles is clearly retained, so that the tone becomes grayish. Accordingly, a recording medium used in OH
Canon Kabushiki Kaisha
Chapman Mark
Fitzpatrick ,Cella, Harper & Scinto
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