Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-05-26
2001-05-15
Rodee, Christopher D. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110100, C430S126200
Reexamination Certificate
active
06232027
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a toner having a negative triboelectric chargeability used in a recording method utilizing electrophotography, electrostatic recording, electrostatic printing or toner jet recording, and an image forming method using the toner.
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., via or without via an intermediate transfer member, 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.
In the developing step, it is necessary for such a toner to be provided with a positive or negative charge depending on the polarity of an electrostatic image to be developed and the developing mode (normal development mode or reversal development mode).
A toner can be charged by utilizing a triboelectric chargeability of a resin as a toner component, but the toner chargeability in this case is unstable so that the resultant image density is lowered at the start of image formation and the resultant images are liable to be foggy. For this reason, it has been frequently practiced to add a charge control agent to the toner to provide the toner with a desired triboelectric chargeability.
The charge control agents known in the art nowadays include: negatively chargeable charge control agents inclusive of metal complex salts of monoazo dyes; metal complexes or metal complex salts of hydroxycarboxylic acids, dicarboxylic acids and aromatic diols; and polymeric compounds or resins containing an acidic component. On the other hand, known positively chargeable charge control agents include: nigrosine dyes, azine dyes, triphenylmethane dyes and pigments, quaternary ammonium salts, and polymers having a quaternary ammonium salt as a side chain.
However, most of such known charge control agents are colored ones, thus being not usable in color toners in many cases. Further, those of colorless, white or pale-colored applicable to color toners have still left functionally unsatisfactory points, such as difficulty in formation of uniform highlight images and a large fluctuation in image density during continuous image formation.
Other points to be further improved may include: a difficulty in obtaining a good balance between image density and fog prevention, a difficulty in obtaining a sufficient image density in a high humidity environment, a poor dispersibility in a resin, and adverse effects on storage stability, fixability and anti-offset property of the resultant toner.
As known charge control agents, metal complexes or metal complex salts of aromatic carboxylic acids have been proposed in Japanese Laid-Open Patent Application (JP-A) 53-127726, JP-A 57-111541, JP-A 57-124357, JP-A 57-104940, JP-A 61-69073, JP-A 61-73963, JP-A 61-267058, JP-A 62-105156, JP-A 62-145255, JP-A 62-163061, JP-A 63-208865, JP-A 3-276166, JP-A 4-84141, and JP-A 8-160668. Charge control agents proposed in these references are generally excellent in performance of imparting triboelectric chargeability, but few of them are satisfactory in providing a stable developing performance regardless of environmental condition change, continued use and condition of use even when used in a simple developing device structure. Few of them provide a stable developing performance in a long term of continuous image formation when used in a high-speed image forming machine. Further, some of them are affected by other toner materials (binder resin, colorant, etc.), thus posing a constraint on the selection of such other toner materials.
As for the step of fixing the toner image onto a sheet (transfer) material such as paper which is the final step in the above-mentioned electrophotographic process, various methods and apparatus have been developed, of which the most popular one is a heating and pressing fixation system using hot rollers, or a fixed heat generating heater for fixation via a heat-resistant film.
In the heating and pressing system using hot rollers, 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.
In the fixing step, however, a hot roller surface and a toner image contact each other in a softened or 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 relatively low in case of a slow fixing speed and set to be relatively 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.
The toner image 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 a so-called high-temperature offset phenomenon in case of a high heating roller temperature, while a so-called 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 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 occurrence of a trace in the fixed image of a separating member for separating the fixation sheet from the fixing roller, and inferior fixed images, such as resolution failure of line images and toner scattering, due to a high pressure.
In recent years, there has been frequently used recycled paper (paper prepared by reusing used paper) as paper for copying machines or printers in order to meet social demands for reductions in weight and amount of paper wastes as a result of office automation. Such recycled paper is generally produced by adding a filler principally comprising talc or calcium carbonate in a proportion of 10-20% as ash content, which is larger than that (ca. 5%) of the case of non-recycled paper. When such recycled paper is used in a copying machine or printer for a long period, a filler used for the recycled paper is liable to be detached or liberated therefrom to attach to and accumulate at a fixing member (e.g., fixing roller or pressure roller), thus lowering a releasability. As a result, the toner is liable to attach to the fixed image surface or the back surface of the transfer material (paper) to result in image defects in some cases, so that a further improvement is required.
Hitherto, as toner binder resins, polyester
Doujo Tadashi
Endo Minekazu
Matsunaga Satoshi
Mizoh Yuichi
Nakahara Toshiaki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Rodee Christopher D.
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