Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-12-12
2004-08-31
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108100, C430S111400
Reexamination Certificate
active
06783910
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a toner for developing electrostatic images used in image forming methods, such as electrophotography, electrostatic recording or electrostatic printing, particularly a toner suitable for hot roller fixation.
Hitherto, a large number of electrophotographic processes have been known, inclusive of those disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. In these processes, in general, an electrostatic latent image is formed on a photosensitive member comprising a photoconductive material by various means, then the latent image is developed with a toner, and the resultant(toner image is, after being transferred onto a transfer material such as paper etc., as desired, fixed by heating, pressing, or heating and pressing, or with solvent vapor to obtain a copy or print carrying a fixed toner image.
As for the step of fixing the toner image onto a sheet material such as paper which is the final step in the above process, various methods and apparatus have been developed, of which the most popular one is a heating and pressing fixation system using hot rollers.
In the heating and pressing system, a sheet carrying a toner image to be fixed (hereinafter called “fixation sheet”) is passed through hot rollers, while a surface of a hot roller having a releasability with the toner is caused to contact the toner image surface of the fixation sheet under pressure, to fix the toner image. In this method, as the hot roller surface and the toner image on the fixation sheet contact each other under a pressure, a very good heat efficiency is attained for melt-fixing the toner image onto the fixation sheet to afford quick fixation.
It is however a current state that different toners are used for different models of copying machines and printers. This is primarily because the different models adopt different fixing speeds and fixing temperatures. More specifically, in the fixing step, a hot roller surface and a toner image contact each other in a melted state and under a pressure, so that a part of the toner is transferred and attached to the fixing roller surface and then re-transferred to a subsequent fixation sheet to soil the fixation sheet. This is called an offset phenomenon and is remarkably affected by the fixing speed and temperature. Generally, the fixing roller surface temperature is set to be low in case of a slow fixing speed and set to be high in case of a fast fixing speed. This is because a constant heat quantity is supplied to the toner image for fixation thereof regardless of a difference in fixing speed.
However, the toner on a fixation sheet is deposited in several layers, so that there is liable to occur a large temperature difference between a toner layer contacting the heating roller and a lowermost toner layer particularly in a hot-fixation system using a high heating roller temperature. As a result, a topmost toner layer is liable to cause an offset phenomenon in case of a high heating roller temperature, while a low-temperature offset is liable to occur because of insufficient melting of the lowermost toner layer in case of a low heating roller temperature.
In order to solve the above problem, it has been generally practiced to increase the fixing pressure in the case of a fast fixing speed in order to promote the anchoring of the toner onto the fixation sheet. According to this method, the heating roller temperature can be somewhat lowered and it is possible to obviate a high-temperature offset phenomenon of an uppermost toner layer. However, as a very high shearing force is applied to the toner layer, there are liable to be caused several difficulties, such as a winding offset that the fixation sheet winds about the fixing roller, the appearance of a trace in the fixed image of a separating member for separating the fixation sheet from the fixing roller, and inferior copied images, such as resolution failure of line images and toner scattering, due to a high pressure.
Accordingly, in a high-speed fixing system, a toner having a lower melt viscosity is generally used than in the case of low speed fixation, so as to lower the heating roller temperature and fixing pressure, thereby effecting the fixation while obviating the high-temperature offset and winding offset. However, in the case of using such a toner having a low melt viscosity in low speed fixation, an offset phenomenon is liable to be caused because of the low viscosity.
Accordingly, there has been desired a toner which shows a wide fixable temperature range and an excellent anti-offset characteristic and is applicable from a low speed apparatus to a high speed apparatus.
On the other hand, in recent years, there have been also desired high-quality copy or print images in accordance with the use of digitalized copying machines and fine toner particles.
More specifically, it has been desired to obtain a photographic image accompanied with characters, so that the character images are clear while the photographic image is excellent in density gradation faithful to the original. Generally, in a copy of a photographic image accompanied with characters, if the line density is increased so as to provide clear character images, not only the density gradation characteristic of the photograph image is impaired, but also the halftone part thereof are roughened.
Further, resolution failure (collapsion) of line images and scattering are liable to be caused at the time of fixation as described above, so that the image qualities of the resultant copy images are rather liable to be deteriorated.
Further, in case where the line image density is increased, because of an increased toner coverage, a thick toner image is pushed against a photosensitive member to be attached to the photosensitive member in the toner transfer step, so that a so-called transfer failure (or a hollow image), i.e., a partial lack toner image (line images in this case), in the transferred image, is liable to be caused, thereby providing poor quality of copy images. On the other hand, in case where the gradation characteristic of a photographic image is intended to be improved, the density of characters or line images are liable to be lowered, thus providing unclear images.
In recent years, there has been obtained some improvement in density gradation characteristic by a system including image density readout and digital conversion. However, a further improvement has been desired.
Regarding density gradation characteristic, it is impossible to obtain a linear relationship between a developing potential (difference between a photosensitive member potential and a developer-carrying member potential) and a resultant (copy) image density. More specifically, as shown in
FIG. 1
, a characteristic curve (e.g., a solid curve representing a case of providing a maximum intensity of 1.4) becomes downwardly convex at a low developing potential and upwardly convex at a high developing potential. Accordingly, in a halftone region, a slight change in developing potential leads to a remarkable change in image density. This provides a complexity in obtaining a satisfactory density gradation characteristic.
Generally, copied images appear clearer because of an edge effect so that clear line images can be retained in case where a maximum density of ca. 1.30 is attained at a solid image part which is less affected by the edge effect.
In case of a photographic image, however, the maximum density of a photograph appears less at a glance because of its surface gloss but actually amounts to a very high level of 1.90-2.00. Accordingly, in a copy of a photographic image, even if the surface gloss is suppressed, a solid part image density of ca. 1.4-1.5 is required since a density increase due to the edge effect cannot be excepted because of a large image area.
Accordingly, in providing a copy of a photographic image accompanied with characters, it becomes very important to obtain a developing potential-image density relationship which is close to the first order (linear) one and also a maximum imag
Doujo Tadashi
Kohtaki Takaaki
Mikuriya Yushi
Unno Makoto
Canon Kabushiki Kaisha
Dote Janis L.
Fitzpatrick ,Cella, Harper & Scinto
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