Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-05-13
2001-04-10
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...
C430S111400, C430S126200
Reexamination Certificate
active
06214509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for various recording methods, such as those based on electrophotography, electrostatic recording, magnetic recording and toner jet recording, more particularly to a toner useful for copiers, printers and facsimiles in which a toner image is formed on an electrostatic latent image carrier and the toner image is transferred onto a medium to form the final image.
2. Related Background Art
A number of electrophotographic methods have been proposed. They generally use a photoconductive material to form an electrical latent image on an image carrier (photosensitive member) by various methods, which is developed by a toner into a visible image, transferred, as required, onto transfer medium such as paper or other media, and fixed into the toner image on the above medium by heat, pressure or the like, for copying the image.
Methods to visualize an electrical latent image include cascade, magnetic-brush and pressurization development. Another method uses a magnetic toner, which is scattered by an electric field in a space between a photosensitive member and sleeve using a rotating sleeve with a magnetic pole at the center.
The one-component developing method, dispensing with carrier particles, e.g., glass beads and iron powders, which are necessary for the two-component method, reduces size and weight of the developing device itself. Moreover, the two-component developing method needs concentration of the toner in the carrier to be kept at a constant level, and hence a device which senses the toner concentration and supplies a required quantity of the toner. This further increases size and weight of the developing device. The one-component method does not need such device, and therefore, is more desirable also in this respect.
Recently, the printing devices have been mainly represented by LED and LBP printers, for which techniques are increasingly demanded to improve resolution from the traditional level of 240 or 300 dpi to 400, 600 and further to 800 dpi. The development method is also demanded to be more precise, accordingly. The copier is also becoming more functional, and advancing in the direction of digitalization. This direction is mainly associated with laser-aided formation of electrostatic images, and also demands development methods of higher resolution and precision, as is the case with printers. The toner particles, therefore, are becoming smaller. The smaller toner particles having a specific size distribution have been developed, as disclosed by Japanese Patent Application Laid-Open Nos. 1-112253, 1-191156, 2-214156, 2-284158, 3-181952, and 4-162048.
Recently, in particular, electrophotographic color-image forming devices are going into diversified applications, as they are used more widely, and are required to produce images of higher quality. It is demanded that common photographs, catalogs and maps are copied very finely and precisely to the finest portion, without forming any crushed or broken portion.
In the advanced electrophotographic image-forming devices using digital image signals, a latent image is formed by dots of a specific potential, assembled on a surface of latent image carrier or photosensitive member, where solid-color, halftone and line sections are expressed by changing dot density. This method, however, is liable to suffer problems related to color tone, because the toner particles may not be sufficiently confined in a dot, with some particles sticking out of the dot, making it difficult to secure the toner image corresponding to a dot density at a dark or bright portion of the digital latent image. When dot size is reduced to improve resolution and hence image quality, reproducibility of a latent image formed by fine dots tends to decrease, producing an image insufficient in resolution and particularly poor color tone at high-light sections, and lacking sharpness.
Moreover, the primary charging, transfer process, in which a photosensitive contact member produced by a primary charging and transfer process using conventional corona discharge is used, is becoming the major approach for environmental considerations.
The charging means using corona discharge, e.g., those named corotron and scorotron, generates a large quantity of ozone when negative corona is formed during the discharge. Therefore, the electrophotographic device must be equipped with an ozone-capturing filter, increasing device size and running cost. These problems involved in the corona charge methods cause the problems related to image quality, e.g., distorted image caused by reduced surface resistance of the photosensitive member as a result of contamination with, e.g., nitrogen oxides, and reduced memory of the photosensitive member resulting from ions remaining in the charging device while the electrophotographic device is out of service.
A new charging method was developed to solve the above problems, where a charging member such as roll or blade is brought into contact with the photosensitive member (this approach is hereinafter referred to as direct charging) to form a discharge explained by the Paschen's rule in a narrow space in the vicinity of the contact point. It is to minimize generation of ozone, and the related techniques are already disclosed by, e.g., Japanese Patent Application Laid-Open Nos. 57-178257, 56-104351, 58-40566, 58-139156, 58-150975, and 63-149669. Of these, the method which uses a charging roll as the charging member is more preferable for charging stability.
Direct charging generates a smaller quantity of ozone than corona discharging, conceivably because of different charging mechanisms on the photosensitive member surface, coming from different discharging regions. It is considered that the photosensitive member surface is charged in corona discharging with the ions, coming from dissociated molecules in air, in the discharging region, whereas it is charged in direct charging with a number of electrons reaching the surface by the multiplication effect of the electrons in the discharging region.
It is found, however, direct charging encounters with problems to be solved, different from those involved in corona charging.
Concretely, it is necessary to apply a voltage of at least certain threshold level to the charging member for direct charging to start, because it depends on discharge from a charging member to a member to be charged, such as photosensitive member. For example, when a charging roll is brought into contact with an OPC photosensitive member with a 25 &mgr;m thick photosensitive layer, the photosensitive member starts to increase in surface potential when a voltage of at least around 640 V is applied to the charging member, the surface potential increasing linearly with voltage at an inclination of unity thereafter. This threshold voltage is hereinafter referred to as charge-starting voltage Vth. Therefore, in order to secure a potential Vd on the photosensitive member surface, the charging roll needs a higher DC voltage of Vd+Vth. It was difficult to keep a desired potential on the photosensitive member, because of resistance of the contacting charging member changing by external disturbances, e.g., changed environmental conditions.
In order to further uniformize charging, an AC charging method is proposed, as disclosed by Japanese Patent Application Laid-Open No. 63-149669, where an AC component having a voltage of at least twice as high as Vth between the peaks is added to the DC voltage corresponding to the desired Vd level, and the totaled voltage is applied to the contacting charging member. This is aimed at leveling the potential by the AC voltage, to significantly prevent potential on the member to be charged from external disturbances, such as environmental changes, because it tends to converge to Vd as the central voltage between the AC voltage peaks.
However, the above contacting charging device also basically depends on the mechanism of discharge from the charging member to the photosensitive member, and needs, as described
Handa Satoshi
Ito Masanori
Karaki Yuki
Kasuya Takashige
Kukimoto Tsutomu
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Goodrow John
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