Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-01-05
2001-04-03
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...
Reexamination Certificate
active
06210850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-coated carrier for an electrophotographic developer used in copying or printing machines, particularly for full color image formation and to an electrophotographic developer containing the carrier.
2. Description of the Related Art
A two-component developer used in electrophotography comprises a toner and a carrier. The carrier is mixed and agitated with the toner in a development box to give a desired quantity of charges to the toner and carries the charged toner particles onto an electrostatic latent image formed on a photoreceptor to form a toner image.
The carrier remains on the magnet roll and is returned to the development box, where it is again mixed and agitated with fresh toner particles for repeated use.
Therefore, the carrier is required to exhibit desired characteristics, especially charging properties for toner particles, constantly in any environment over its service life.
Conventional developers, however, undergo a so-called spent-toner phenomenon that toner particles adhere by fusion to the surface of the carrier particles due to the stress of friction and/or collision of carrier particles with each other or with the wall of a development box. The stress also causes a resin coat of carrier particles to separate and fall off the core. On account of these phenomena, the carrier characteristics such as charge quantity and carrier resistance vary, which can result in image deterioration (such as change in image density and fog) or toner scattering.
In order to prevent the deterioration of carrier characteristics, studies have been made on the resin for coating the surface of a carrier. Of various resins proposed to date acrylic resins and silicone resins have now been prevailing.
Acrylic resins exhibit good adhesion to a carrier core, and an acrylic resin-coated carrier has excellent charging ability, particularly for a negatively chargeable toner, and therefore, has been used widely. However, acrylic resin-coated carrier has a disadvantage of poor resistance against the spent-toner phenomenon. A silicone-coated carrier, on the other hand, has poor charging ability, although it is resistant to the spent-toner phenomenon owing to its low surface energy. Recently, an amino-containing silicone-coated carrier has been proposed (Japanese Patent Laid-Open No. 104522/95), in which the charging ability is improved to the level of acrylic resin-coated carriers by incorporating an amino group to the coating silicone resin.
Since a silicon coating layer is highly insulating, a silicone-coated carrier causes the developer to change (increase) the charge quantity during use, which results in variation of image characteristics. Change in image density with an increase of charge quantity during use is very problematical particularly in full color image formation having weight attached to gradation.
Acryl-modified silicone-coated carriers have been proposed as a carrier possessing both the merits of the acrylic resin-coated carrier and the silicone-coated carrier as disclosed in Japanese Patent Laid-Open Nos. 157751/80 and 234501/96. The coated carriers disclosed are excellent in both charging ability and charging stability and superior to the acryl resin-coated one in resistance against the spent-toner phenomenon.
However, the conventional acryl-modified silicone-coated carriers have poor fluidity. In particular, fluidity of those particles having an average particle size as small as 60 &mgr;m or less are so poor that carrier transfer properties on the magnet roll during development are reduced to reduce the ability of developing the photoreceptor with a toner. The poor fluidity also causes non-uniform mixing with toner particles in the development box.
In regards to resistance to a spent phenomenon, the conventional acryl-modified silicone-coated carriers are, while superior to acrylic resin-coated carriers as mentioned above, still inferior to silicone-coated carriers, which is problematic particularly to carrier particles for full color machines which are brought into contact with toner particles more frequently. The aforementioned problems have not been settled as yet.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a carrier for an electrophotographic developer which has high toner charging ability, stable charging properties during development, and excellent resistance against a spent-toner phenomenon, and an electrophotographic developer containing the carrier.
Another object of the invention is to provide a resin-coated carrier for an electrophotographic developer which exhibits satisfactory fluidity, showing satisfactory transfer properties on a magnet roll during development even when it has an average particle size of 60 &mgr;m or even smaller and thereby giving a toner satisfactory developing ability on a photoreceptor, and which also exhibits excellent charging stability against environmental changes, and to provide an electrophotographic developer containing the carrier.
As a result of extensive study, the present inventors have found that the above objects are accomplished by using, as a carrier coating resin, an acryl-modified silicone resin at a specific weight ratio of acrylic resin to silicone resin and a specific molar ratio of methyl group to other organic groups in the silicone resin, to provide a resin-coated carrier having high charging ability and excellent charging stability during development.
Having been completed based on the above finding, the present invention provides a carrier for an electrophotographic developer which comprises a carrier core coated with an acryl-modified silicone resin the silicone resin of which has a methyl group and other organic groups, the molar ratio of the methyl group to all the organic groups inclusive of the methyl group [methyl group/(methyl group+other organic groups)]being 64 mol % or higher and lower than 70 mol %, and the acrylic resin to silicone resin weight ratio ranging from {fraction (2/8)}to {fraction (4/6)}.
The present invention also provides an electrophotographic developer comprising the above-described carrier and a nonmagnetic toner.
The resin-coated carrier for an electrophotographic developer according to the present invention shows high toner charging ability, stable charging properties during development, and excellent resistance to a spent-toner phenomenon. Further, the coated carrier of the present invention has satisfactory fluidity enough to have satisfactory transfer properties on a magnet roll during development even with small particle size of not greater than 60 &mgr;m and to secure satisfactory development on a photoreceptor with a toner, and excellent charging stability against environmental changes. Containing such a carrier, the developer according to the present invention maintains initial image forming characteristics for an extended period of time.
REFERENCES:
patent: 5079124 (1992-01-01), Kawata et al.
patent: 5652079 (1997-07-01), Mochizuki et al.
patent: 0 405 503 (1991-01-01), None
patent: 0 932 083 (1999-07-01), None
patent: 55-157751 (1980-12-01), None
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patent: 7-104522 (1995-04-01), None
patent: 8-234501 (1996-09-01), None
patent: 63-174054 (1998-07-01), None
Ogata Masahiro
Sugiura Takao
Takagi Kazunori
Yamaya Masaaki
Yoshikawa Yuji
Goodrow John
Powdertech Co., Ltd.
Young & Thompson
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