Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-02-10
2001-07-10
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...
C430S122520, C399S267000
Reexamination Certificate
active
06258501
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus and a developing agent used in the apparatus and, more particularly, to an image forming apparatus for performing development by the magnet rotating development method and a two-component developing agent containing magnetic toner and carrier for use in the apparatus.
An image forming apparatus using the magnet rotating development method is disclosed in, e.g., Jpn. Pat. Appln. KOKOKU Publication No. 7-40156. In this apparatus, a developing roller facing an image carrier for carrying an electrostatic latent image is composed of a hollow cylindrical rotary sleeve made of a nonmagnetic material and a magnetic roll formed inside this sleeve, said magnetic roll having a plurality of magnetic poles and being able to rotate independently of the sleeve.
In the magnet rotating development method, a two-component developing agent containing magnetic carrier and magnetic toner formed by adding a magnetic material to the surfaces of toner particles is applied to the developing roll. The magnetic roll and the sleeve are rotated in the same direction or in opposite directions to convey the developing agent to a development region while the developing agent itself is rotated. In this magnet rotating development method, control of the specific toner density is easier than in the common magnet fixed development method, so the specific toner density can be increased. This increases the toner conveyance amount and raises the development efficiency. When the magnetic roll and the sleeve are rotated in the same direction, the rotating direction of the developing agent is opposite to its conveyance direction. When the magnetic roll and the sleeve are rotated in opposite directions, the rotating direction of the developing sleeve is the same as its conveyance direction. This is suitable for high-speed development because the conveyance amount can be further increased.
In two-component development by the magnet fixed development method, the specific toner density on a developing roll is commonly about 6 wt %. However, in two-component development by the magnet rotating development method, the specific toner density stays around about 50 wt %. The result is the advantage that so-called beads carry over which is a phenomenon in which the carrier on a developing roll adheres to an image carrier hardly occurs. In the magnetic fixed development method, to prevent this carrier transfer and control the charge amount, the surface of a magnetic carrier is coated with a silicon-based coating material.
Unfortunately, in magnetic toner used in the magnet rotating development method, a magnetic powder is mixed in and adhered to the toner in an amount of 4.5 wt % with respect to the toner weight. Although high-quality images can be provided initially, the externally added magnetic powder causes some inconveniences.
Representative inconveniences are the following three phenomena.
The first is an increase in wear of the surface of a photoreceptor due to the externally added magnetic powder. When the surface of a photoreceptor wears, its sensitivity lowers, so no stable electrostatic charge can be provided any longer. This reduces the life of the photoreceptor.
The second is an increase in wear of a cleaning blade due to the externally added magnetic powder. When a cleaning blade wears, inferior cleaning takes place, leading to deterioration of images.
The third is an increase in wear of the surface film of a heat roller due to the externally added magnetic powder. When the surface film of a heat roller wears, high-temperature offset occurs. This reduces the life of the heat roller.
These inconveniences significantly reduce the prescribed life of an apparatus when the externally added magnetic powder is used.
In contrast, toner containing no magnetic powder effectively eliminates the above inconveniences. However, at high temperatures and high humidities conventional magnetic carrier such as a Cu—Zn carrier causes inferior electrostatic charge. Accordingly, image density lowers when a developing agent containing such carrier is used. Also, when highly chargeable magnetic carrier is used, the chargeability of the toner becomes too high. Consequently, image density lowers when sheets are continuously fed. Furthermore, highly chargeable magnetic carrier has small electrical resistance and magnetic force margins and hence is difficult to rationalize.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its first object to provide an image forming apparatus capable of preventing deterioration of the image quality and life by minimizing damage to a photoreceptor surface, a cleaning blade, and a heat roller surface film, and also capable of maintaining a good charging characteristic and forming images having high image density even at high temperatures and high humidities or even after being left to stand for twenty-four hours.
It is the second object of the present invention to provide a developing agent capable of preventing deterioration of the image quality and life by minimizing damage to a photoreceptor surface, a cleaning blade, and a heat roller surface film due to a second magnetic powder present on a toner surface, and also capable of maintaining a good charging characteristic and forming high-quality images having high image density, with no flocculation of particles of the developing agent, even at high temperatures and high humidities or even after being left to stand for twenty-four hours.
According to one aspect of the present invention, there is provided a developing agent comprising toner which contains toner particles containing a first magnetic powder and a binder resin and contains a second magnetic powder added in an amount of 4 wt % or less with respect to the weight of the toner particles, and manganese-magnesium-based carrier.
According to the second aspect of the present invention, there is provided an image forming apparatus comprising
at least one image carrier,
a developing unit, a transfer unit, and a cleaning device arranged in order on the image carrier to oppose the image carrier, the developing unit containing a developing agent comprising toner which contains toner particles containing a first magnetic powder and a binder resin and contains a second magnetic powder added in an amount of 4 wt % or less with respect to the weight of the toner particles, and manganese-magnesium-based carrier, and comprising a developing roller which comprises a hollow cylindrical rotary sleeve for carrying the developing agent and a magnet roll having a plurality of magnetic poles and capable of rotating independently of the sleeve, and
a fixing unit having a pair of fixing rollers placed downstream of the transfer unit.
When the present invention is used, the magnetic powder amount used can be reduced while a satisfactory charging characteristic is maintained. Therefore, it is possible to prevent deterioration of the image quality and life by minimizing damage to a photo-receptor surface, a cleaning blade, and a heat roller film surface. It is also possible to maintain a good charging characteristic and obtain high-quality images having high image density, with no flocculation of particles of a developing agent, even at high temperatures and high humidities or even after the developing agent is left to stand for twenty-four hours.
REFERENCES:
patent: 5853937 (1998-12-01), Asawae et al.
patent: 5976747 (1999-11-01), Sato et al.
patent: 6087057 (2000-07-01), Hakata et al.
patent: 9-6106 (1997-01-01), None
patent: 2888490 (1999-02-01), None
Foley & Lardner
Goodrow John
Toshiba Tec Kabushiki Kaisha
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