Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-09-18
2001-11-20
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...
C430S111350, C430S137130
Reexamination Certificate
active
06319646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carrier for use in a developer for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic printing method, an electrostatic recording method or the like method. In addition, the present invention relates to a method for manufacturing the carrier.
2. Discussion of the Background
Two component developers which are constituted of a carrier and a toner are widely used for developing an electrostatic latent image formed on an image bearing member by an electrophotographic method, an electrostatic printing method, an electrostatic recording method or the like method. In particular, in recent years resin-coated carriers in which a core material is coated with a resin are typically used to enhance the durability of the carrier. Such resin-coated carriers have a good electric insulation property, and therefore, the resin-coated carriers have a good charge imparting property. In addition, the surface of the resin-coated carriers have good smoothness, and therefore the carriers have good durability.
However, the resin-coated carriers have a drawback in that the carriers produce images having a poor solid image in which only the edge portions of the solid image are emphasized and the other portions thereof has poor image density (hereinafter this phenomenon is referred to as an edge-emphasized image). In attempting to remedy this drawback, a half-coated carrier in which a part of the surface of carrier particles is coated with a resin (i.e., projected portions of the core material are exposed without being coated) has been proposed in Japanese Laid-Open Patent Publications Nos. 3-160463 and 4-93954. Since in the half-coated carrier project portions of the core material are exposed without being coated, the half-coated carrier has relatively low electric resistance. Therefore, the charges tend to be easily transferred, resulting in formation of a solid image having high image density (without causing an edge-emphasized image). However, since the half-coated carrier has relatively low electric resistance, a charge whose polarity is opposite to that formed on an image bearing member is injected to the carrier, resulting in occurrence of a carrier adhesion problem in that the carrier itself adheres to the image bearing member.
In addition, in recent years a toner recycle system is used in image forming apparatus in which toner particles, which are collected in the image forming apparatus without being used for developing electrostatic latent images, are reused to protect environment. Namely, the toner recycle system is such that toner particles remaining on an image bearing member without being transferred to a receiving paper are collected by a cleaning device, and the collected toner particles are supplied again to the developing area or the toner supplying device to be reused. In the collected toner particles, external additives of the toner particles tend to be embedded into the toner particles, and therefore the surface of the carrier is hardly abraded by the toner. Therefore the surface of the carrier is hardly refreshed, i.e., the toner tends to accumulate on the surface of the carrier, resulting in occurrence of a spent-toner problem. When the spent-toner problem occurs, the charge quantity of the developer deteriorates, resulting in occurrence of background fouling in the resultant toner images. Therefore, the developer has a short life. In particular, the half-coated carrier has projected portions which are not coated with a resin, and therefore this spent-toner problem easily occurs.
Because of these reasons, a need exists for a developer having good durability and capable of producing images having good image qualities even when used for an image forming apparatus using a toner recycle system for a long time.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a carrier useful for a developer having the following advantages:
(1) having good durability without causing the spent-toner problem;
(2) not causing the carrier adhesion problem; and
(3) capable of producing images having good image qualities such as high image density even when used for an image forming apparatus using a toner recycle system.
Briefly this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a carrier which includes a magnetic core material having a surface coated with a resin, wherein the carrier satisfies the following relationship:
1.0≦C
2
/C
1
≦1.3
wherein C
1
represents a charge quantity of a developer (
1
) including the carrier and a first toner after the developer (
1
) is subjected to a frictional treatment once, wherein concentration of the first toner in the developer (
1
) is 3% by weight; and C
2
represents a charge quantity of a developer (
2
) which includes the carrier separated from the developer (
1
) subjected to the frictional charge treatment and a second toner when the charge quantity is measured after the developer (
2
) is subjected to the frictional charge treatment once, wherein concentration of the second toner in the developer (
2
) is 3% by weight, wherein the first toner and the second toner can be the same or different.
Preferably, the carrier satisfies the following relationships:
1.0≦C
2
/C
1
≦1.3, and 1.0≦C
3
/C
2
≦1.3
wherein C
1
and C
2
are defined above, and C
3
represents a charge quantity of a developer (
3
) which includes the carrier separated from the developer (
2
) and a third toner when the charge quantity is measured after the developer (
3
) is subjected to the frictional charge treatment once, wherein concentration of the third toner in the developer (
3
) is 3% by weight, wherein the third toner is the same as or different from either or both of the first and second toners.
The surface of the carrier particles preferably has one or more micro projections having an irregular circular shape whose average minor diameter is from about 100 nm to about 200 nm when observed by an AFM (Atomic Force Microscope) method.
The resin coated on the surface of the carrier preferably includes a silicone resin.
In addition, the carrier preferably has a dynamic current of from 0.1 &mgr;A to 0.5 &mgr;A.
In another aspect of the present invention, a method for manufacturing the above-mentioned carrier including the steps of coating a core material with a resin solution including a resin at a concentration not less than 10% by weight, and crosslinking the resin while fluidizing the carrier.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention in conjunction with the accompanying drawing.
REFERENCES:
patent: 5652079 (1997-07-01), Mochizuki et al.
patent: 5683844 (1997-11-01), Mammino
patent: 5952143 (1999-09-01), Ootaki et al.
patent: 01300097 (1989-11-01), None
patent: 02207565 (1990-08-01), None
Goodrow John
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh Technology Research Inc.
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