Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-11-27
2004-11-16
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109400, C430S109200, C430S120400
Reexamination Certificate
active
06818370
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a toner for developing an electrostatic latent image, to a toner container containing such a toner and to an apparatus for forming images such as a copying machine, a printing machine or a facsimile machine of a single color-, multicolor- or full color-type.
The present day offices are flooded with office electric appliances such as personal computers, printers, copiers, scanners, and facsimile machines. Documents including text documents, graphs etc. are created using personal computers. Moreover, occasion where such documents are printed in color is increasing. Many of the images output by the printers are solid, line, or halftone images. Marketing needs for the image quality are changing accordingly and needs such as high reliability are increasing.
A developer used in an image forming method such as electrophotography, electrostatic recording or electrostatic printing is deposited onto a latent image bearing member, typically a photoconductor. The developer is transferred from the photoconductor to a transfer medium such as a transfer paper and fixed on a surface thereof. Known developers include a two-component developer composed of a carrier and a toner and a one-component developer containing no carrier.
In case of the two-component developer, the carrier is used for charging and transporting the developer in a stable manner. The two-component developer, however, has a problem because the toner particles gradually adhere on the surface of the carrier. Moreover, the concentration of the toner in the developer gradually decreases as only the toner is consumed. Moreover, since the ratio of the toner and the carrier in the developer has to be kept constant, there arises a problem that size of the apparatus becomes large.
The one-component developer is free from the above problems and, therefore, the size of the apparatus can be compact. Hence, the one-component developer is popular and widely used in present day developing systems. The one-component developer can be classified into two types; i.e. a magnetic toner and a non-magnetic toner.
The magnetic toner includes a magnetic material such as magnetite and is held on a developer carrier such as a developing sleeve having a magnet provided therein. The magnetic toner forms a layer on the sleeve with the thickness thereof being adjusted by a suitably thickness control member such as a blade or a roller. The magnetic toner is practically increasingly used recently for small-size printers.
The non-magnetic toner of the one-component developer, on the other hand, is supported on a developing sleeve by electrostatic force. Thus, the non-magnetic toner is supplied to the substrate by being pressed with a supply roller to form a layer thereon. The thickness of the toner layer is adjusted by a suitable thickness control member such as a blade or a roller. Since the non-magnetic toner does not contain a magnetic material which has unavoidably a color, there is obtainable an advantage over the magnetic developer that the non-magnetic toner can be suitably used for color image formation. Moreover, the image forming apparatus that uses the non-magnetic developer does not require any magnet and can be made light-weight and compact and, therefore, is widely used as full color printers.
However, the one-component developer has a lot of problems to be solved. In particular, charging and transportation failures tend to occur when image formation is continuously repeated for a considerably long period of time at a high speed. Namely, as described above, the one-component developer, after it is transported onto the developing sleeve, forms a thin layer by means of the thickness controlling member and is contacted with the latent image on the photoconductor. At that time, contact between the toner and the developing sleeve and between the toner and the thickness controlling member is only for a very short period of time. Therefore, a time for which the toner is charged by friction is very short. As a result, in contrast to the two-component development system using the carrier, more of the toner tends to have a low or opposite charge in the one-component development system. In the non-magnetic one-component system particularly, the toner is transported typically by means of at least one toner transport member. It is known that the thickness of the toner layer on the toner transport member surface must be as thin as possible. When the toner layer is thick, only a portion near the surface of the toner layer is charged and it becomes difficult to evenly charge the whole toner layer. Thus, it is necessary that the toner should be quickly charged to provide the desired level of charging amount.
It is also important that the material constituting the toner supplying member, thickness controlling member and developing sleeve should be suitably selected to provide the one-component, non-magnetic toner with sufficient electric charges. Further, the non-magnetic toner should be forcibly pressed by toner supplying member and thickness controlling member against the developing sleeve so as to sufficiently charge the toner. Under such conditions, however, the toner is heated by friction to cause “toner filming” as a result of melt-adhesion of the toner, in particular the binder resin thereof, on the developing sleeve. The filming results in shortening of the service life of the developing sleeve as well as unstable chargeability of the toner. In addition, the mechanical impact applied to the toner causes grinding thereof, which results in reduction of the density of the images as well as formation of white spots in the images due to failure of proper toner transportation on the sleeve. Thus, the image forming machine is unable to withstand usage over a long period of service, and there is a problem that an image formation unit called a “process cartridge” has to be replaced at an early stage such as every few-thousand copies.
Thermal characteristics of toner, especially a binder resin thereof, also play an important role in image formation. A press heating fixation method has been generally adopted for fixing a toner image on an image receiving sheet such as paper. In such a method, the image-bearing sheet is brought into pressure contact with a heat roll for fixing the image thereon. Since the heating efficiency is high, the fixation of image can be carried out at a high speed. To further improve the fixation speed, it is necessary that the toner should be fixed at a lower temperature, i.e. the softening point of the binder resin of the toner should be low.
At this time, when the temperature of the heat roll is excessively high, the toner is excessively melted and adhered to the heat roll and further transferred to a succeeding transfer sheet (hot offset). For the purpose of preventing the hot offset, an attempt has been made to use a heat roll having a surface made of a releasing property and to apply a releasing agent such as silicone oil to the surface of the heat roll. This method is effective to prevent hot offset when the toner used has low temperature fixability. However, such a toner has a problem because the storage stability thereof is low.
For the production of a full color image, at least three color toner images (cyan, magenta and yellow toner images and, if necessary, a black toner image) are successively formed on a transfer sheet and the superimposed images are fixed simultaneously. Thus, the thickness of the fixed image is unavoidably large. In order to produce clear color images, therefore, a toner for use in full color image forming is required to provide an image with suitable gloss. Further, in order to prevent formation of cracks or delamination of the image, the toner is required to provide an image having suitable fixing strengths.
Properties of the binder resin constituting a toner are main factors of fixation characteristics of the toner. Styrene-acrylate copolymer resins, polyester resins and polyol resins are generally used as a binder resin. It is known that styren
Fushimi Hiroyuki
Katoh Kohki
Nanya Toshiki
Uchinokura Osamu
Yagi Shinichiro
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Rodee Christopher
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