Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-08-31
2003-12-23
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...
C430S124300, C430S125320
Reexamination Certificate
active
06667140
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a toner for use in an image forming method, such as electrophotography, electrostatic recording and toner jetting, and an image forming method using such a toner.
Hitherto, various electrophotographic image forming methods have been proposed, e.g., in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. Generally, in these methods, an electrical latent image is formed on a photosensitive member using a photoconductor material by various means and then developed with a toner to form a toner image. The toner image is transferred onto a transfer material such as paper, as desired, directly or indirectly, and fixed onto the transfer material, e.g., by heating, pressing or heating and pressing or with solvent vapor. Further, in the case of including such a step of transferring toner image, a step of removing the transfer residual toner onto the photosensitive member is generally included, and the above-mentioned steps are repeated for subsequent image forming cycles.
Particularly, in full-color image formation, electrostatic latent images and generally developed with a magenta toner, a cyan toner, a yellow toner and a black toner to form respective color toner images in superposition to reproduce multicolor images.
Further, in recent years, apparatus utilizing electrophotography have been used not only as copying machines for reproducing originals but also for printers for computers, personal copiers for individual users and facsimile apparatus using plain paper, thus being rapidly developed and various requirements being posed thereon. Also for copying machines, development to a higher functionality is being effected by digital image forming technique. Particularly, extensive development has been made regarding size reduction, higher speed and color image formation by the image forming apparatus, and further higher reliability and resolution are being strongly desired. For example, the required resolution which was at a level of 200-300 dpi (dots per inch) has been enhanced to 400-1200 dpi, and further to a level of 2400 dpi.
In contrast with such demands, it has been a general trend that image forming apparatus are designed to be composed of simpler parts and elements. As a result, further higher functionality is required of a toner, it is a present state that a better image forming apparatus cannot be accomplished without realization of further improved toner performances.
For example, in recent years, as a transfer device for electrostatically transferring a toner image on an (electrostatic latent) image-bearing member or an intermediate transfer member onto a transfer material, a so-called contact or abutting transfer device including a roller-shaped transfer member supplied with a voltage from an external supply and abutted against the image-bearing member or intermediate transfer member via the transfer material is being increasingly used from the viewpoints of size reduction of the enter image forming apparatus and prevention of ozone generation.
For such an abutting transfer device, the sphering of a toner particle shape is effective for providing an improved transferability and enhancing the durability against mechanical stress exerted by the device, but on the other hand, this results in smaller specific surface area and volume of toner particles, so that the dispersibility of a colorant inside the toner particles seriously affects the transferability and matching with the transfer device of the toner particle.
Further, in a conventional electrophotographic image forming apparatus, a corona discharger utilizing corona shower generated by applying a high DC voltage of 6-8 kV to a metal wire has been frequently used as a non-contact charging means for uniformly charging a surface of an image-bearing member such as a photosensitive drum as a member to be charged. Such a non-contact charging means is very effective as a means for uniformly charging the image-bearing member surface to a desired potential but leaves problems regarding size reduction of image forming apparatus, use of lower-voltage power supply, prevention of ozone generation, and longer life of photosensitive drum and charging device. For this reason, in recent years, a so-called contact charging means using a charging member contacting the image-bearing member and supplied with a prescribed voltage to charge the image-bearing member has been widely commercialized.
The charging member or charge-supply member used in such contact charging means may assume various forms inclusive of rollers, blades, brushes and magnetic brushes. Among these, an electroconductive roller-form charging member (hereinafter sometimes referred to as a “charging roller”) has been preferably used from the viewpoint of charging stability.
The surface charging of a member to be charged by the contact charging means may be effected by (1) direct charge injection from the charging member to the member to be charged, or (2) minute discharge caused between the charging member and the member to be charged. For the former charging mechanism, the image-bearing member as a member to be charged has to be provided with a surface charge injection layer (chargeable layer), and for the latter mechanism, it is necessary to apply a bias voltage in excess of a discharge threshold voltage to the charging member.
In the case where the latter mechanism is used for providing a photosensitive member surface potential Vd (dark-part potential) required in latent image formation in an electrophotographic image forming method according to a DC-charging scheme of using a DC voltage component alone for application to the charging member, it is necessary to apply a DC voltage corresponding to the sum of Vd and Vth to the charging member such as a charging roller.
On the other hand, an AC-charging scheme of applying a bias voltage obtained by superposing an AC voltage component of at least 2×Vth with a DC voltage corresponding to a desired Vd is also known as disclosed in JP-A 63-149668. This is an excellent charging scheme for obtaining a charged state of the charged member which is less affected by environmental conditions by utilizing a smoothing effect of the AC voltage for charging the charged member to a potential Vd which is a central value of the AC voltage applied to the charged member. This charging scheme has left room for improvement regarding a size reduction of voltage supply and a longer life of photosensitive drum as the charged member.
For the above-mentioned contact charging means, it is necessary to provide an appropriate degree of intimate contact between the charging member and the charged member. Accordingly, the charging roller for example controls its abutting state against the charged member by having a resistance layer imparted with a moderate elasticity on an electro-conductive support, thereby aiming at an improved charge uniformity on the charged member and prevention of charge leakage due to pinholes or damages on the charged member. However, it is difficult to maintain such a good contact state between the charging member and the charged member, thus being liable to result in image defects due to charging failure which has been left as a problem to be solved. For example, if transfer residual toner remaining on the photosensitive drum surface is attached to the charging roller surface, the roller surface resistivity is locally increased to fail in uniform charging of the photosensitive drum surface, thus resulting in image defects, such as image fog, image density irregularity and streak image defects in worse cases.
The above-mentioned problems become pronounced in the case of using a small diameter photosensitive drum for which improvements in cleaning of transfer residual toner and intimate contact between the charging member and the drum as the charged member are difficult, or in the case of using a higher process speed, and have provided technical obstacles against the use of smaller image forming apparatus, and a lower voltage supply, a higher image qual
Fukushima Motoya
Katsuta Yasushi
Ohno Manabu
Tosaka Emi
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