Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-06-23
2001-02-06
Goodrow, John (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
06183927
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a toner for use in a recording method according to electrophotography, electrostatic recording, magnetic recording, toner jetting, etc., and an image forming method using the toner.
Hitherto, there have been known many methods for electrophotography, wherein generally an electrostatic (latent) image is formed on a photosensitive member according to various means by utilizing a photoconductive substance, the electrostatic image is developed with a toner to form a visible image (toner image), and the toner image is, after being transferred to a transfer-receiving material, such as paper, fixed onto the transfer-receiving material under application of heat and/or pressure, to form a fixed image, thereby providing a copy or a print.
In conventional full-color copying machines, there has been generally used a method wherein four photosensitive members are used, and electrostatic latent images formed on the respective photosensitive members are developed with a cyan toner, a magenta toner, a yellow toner and a black toner, respectively, and the resultant respective color toner images are sequentially transferred onto a transfer(-receiving) material carried on a belt-form conveyer to form a full-color image; or a method wherein a single photosensitive member is used in combination with a transfer material-holding member disposed opposite the photosensitive member and carrying a transfer material wound about the holding member, and 4 cycles of development and transfer are repetitively performed to form a full-color image.
Further, image forming methods using an intermediate transfer member have also been proposed, inclusive of a full-color image forming method using a drum-shaped intermediate transfer member (U.S. Pat. No. 5,187,526), and a method wherein a toner image formed of a toner having an average particle size of at most 10 &mgr;m is transferred onto an intermediate transfer member and the toner image on the intermediate transfer member is further transferred onto a transfer material (Japanese Laid-Open Patent Application (JP-A) 59-15739).
In such an image forming method using an intermediate transfer member wherein a toner image formed on a photosensitive member is once transferred onto the intermediate transfer member and then again transferred onto a transfer material, it is necessary to realize a high toner transfer efficiency exceeding the conventional level. Further, compared with the case of using a single black toner as in a monochromatic copying machine, the amount of toners on the intermediate transfer member are increased so that it becomes difficult to increase the transfer efficiency and uniformly transfer the four-color toner images, thus being liable to cause a local transfer failure so-called hollow image (dropout) as illustrated in FIG.
1
B.
In an ordinary transfer step, the transfer material and the intermediate transfer member are charged to a polarity opposite to that of the toner, so that the transfer is effected as an electrostatic action. If a transfer bias voltage is increased in such a transfer step, the toner charge is liable to be lowered or the toner is charged to an opposite polarity (these phenomena are hereinafter inclusively referred to as “toner charge leakage”) due to a discharge phenomenon caused between the toner and the photosensitive member or between the photosensitive member and the intermediate transfer member, thus being liable to cause so-called back-transfer that a toner once transferred onto a transfer material is transferred back to the photosensitive member. In a process including a plurality of transfer steps as in the above-mentioned full-color image forming method, an earlier transferred image is more liable to cause back-transfer resulting in a lower image density. If such back-transfer is caused, the resultant image is accompanied with an irregularity, thus failing to provide a high-quality image.
Proposals for improving the transfer efficiency by using a toner subjected to mechanical impact have been proposed in JP-A 2-66559, JP-A 2-87159, JP-A 2-146557, JP-A 2-167566 and JP-A 5-61251. These proposals can provide an improved transfer efficiency which however is not sufficient particularly when used in an image forming apparatus using an intermediate transfer member, thus failing to provide a substantial improvement in preventing back-transfer.
As developing methods for visualizing electrostatic latent images, there have been known the cascade developing method, the magnetic brush developing method, the non-magnetic mono-component developing method and the pressure developing method. Further, there is also frequently used the magnetic monocomponent method wherein a layer of magnetic toner is formed on a rotating sleeve enclosing a magnet therein and is caused to jump onto a photosensitive member under the action of an electric field between the photosensitive member and the sleeve.
Such a mono-component developing scheme can provide a small and light developing apparatus as it does not require carrier particles, such as glass beads or iron powder, as required in the two-component developing scheme. Further, in the two-component developing scheme, the toner concentration in the mixture with carrier particles has to be maintained at constant, so that some means is required for detecting the toner concentration and replenishing the toner at a rate as required. These also result in a larger and heavier developing apparatus. Mono-component developing scheme does not require such means and is also preferred in this respect for providing a smaller and lighter developing apparatus.
In recent years, there has been proposed a so-called contact mono-component developing method wherein a semiconductive developing roller or a developing roller having a surface dielectric layer is pressed against a photosensitive member surface to effect development.
In the monocomponent development method, if a distance is present between the photosensitive member and the toner-carrying member, lines of electric force are liable to be concentrated at edges of an electrostatic latent image, thus causing an edge effect that the toner is localized at the edges of the image because the toner is transferred for development along the lines of electric force, thus being liable to lower the image quality.
The edge effect may be alleviated by reducing the gap between the photosensitive member and the toner-carrying member to the minimum, but it is difficult to set the gap between the photosensitive member and the toner-carrying member to be smaller than the toner layer thickness on the toner-carrying member as a matter of mechanical design.
Accordingly, the contact mono-component development method wherein the toner-carrying member is pressed against the photosensitive member to effect the development, is preferred in order to prevent the edge effect. However, if a surface moving velocity of the toner-carrying member identical to that of the photosensitive member is used, it is difficult to obtain a satisfactory image by developing a latent image on the photosensitive member. Accordingly, in the contact mono-component developing method, the toner-carrying member surface speed is caused to differ from that of the photosensitive member, whereby a portion of the toner on the toner-carrying member is used for developing the latent image on the photosensitive member and another portion of the toner is peeled, thereby providing a developed image which is very faithful to the latent image and free from the edge effect.
As described above, an arrangement of rubbing the photosensitive member surface with the toner and the toner-carrying member is essential in the contact mono-component developing method, the deterioration of the toner is liable to occur during a long term of use, thus resulting in lowerings in toner flowability and uniform chargeability leading to an increased fog and a lower transfer efficiency. Further, along with the lowering in transfer efficiency, the reproducibility of fine dot
Chiba Tatsuhiko
Inaba Kohji
Kawakami Hiroaki
Magome Michihisa
Moriki Yuji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Goodrow John
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