Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-06-07
2002-09-24
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S120400
Reexamination Certificate
active
06455218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developer for electrostatic image development which is employed in electrophotographic methods, electrostatic recording methods, and electrostatic printing methods, and relates to an image forming method using the developer.
2. Description of the Related Art
Various electrophotographic methods have been disclosed in, for example, U.S. Pat. No. 2,297,691, Japanese Examined Patent Application, Second Publication No. Sho 42-23910, and Japanese Examined Patent Application, Second Publication No. Sho 43-24748. Commonly, an electrostatic latent image is formed on an electrostatic latent image bearing medium such as a photoconductive photosensitive medium or the like by means of charge or light exposure, and then this electrostatic latent image is developed employing a toner composition containing a colorant in a binder resin. The resulting toner image is transferred to a support medium such as transfer paper or the like and is fixed, and a visible image is thus formed.
In addition, many development methods incorporated as part of the electrophotographic method are known, and these are roughly classified into a two-component development method which employs, as a developer, a mixture of toner and a carrier comprising microparticles (20-500 &mgr;m) such as iron powder, ferrite powder, nickel powder, glass powder and the like, and a single-component development method employing a developer made of a toner only.
Typical examples of the two-component development method include a cascade method described in U.S. Pat. No. 2,618,552 and a magnetic brush development method described in U.S. Pat. No. 2,874,063. In these methods, a carrier is partialyl responsible for functions such as stirring, transfer and charging of the developer, and therefore, the functions of the carrier and those of the toner are clearly separate. Accordingly, the two-component development method has been widely employed at present because it can control charging of the toner and form the developer layer relatively easily and also facilitates more rapid processing.
Although the carrier comprising iron powder, ferrite powder, or the like may afford a high image density by virtue of the low resistance thereof, it presents a number of problems including poor reproducibility of fine lines, poor charging property of the carrier due to the toner spent on the surface of the carrier, imperfection of the image caused by adhesion of the carrier on the photosensitive medium, and the like. On the other hand, the carrier comprising the core particles such as iron powders, ferrite powders, or the like which are coated with a resin composition may improve the reproducibility of fine lines since the carriers coated only with a resin which generally has a high resistance also have a high resistance, and the electric field strength is low at the time of development, affording the edge effects. However, by employing the carriers comprising the coated core particles, a uniform image cannot be obtained and an extreme degradation of the image density may be observed.
In order to prevent the high resistance of the carrier, a carrier having an appropriate resistance by means of dispersing a conductive agent such as a carbon black in a resin is commonly employed. A carrier having a conductive layer as a lower coating layer and a high resistance layer as an upper coating layer, as described in Japanese Unexamined Patent Application, First Publication No. Hei 4-324457; a carrier having a resin layer, as a lower coating layer, which has a thickness of 0.5 to 1.0 &mgr;m and includes a resistance control agent, and another resin layer, as an upper coating layer, which has a thickness of 0.1 to 0.5 &mgr;m and does not include any resistance control agents, as described in Japanese Unexamined Patent Application, First Publication No. Hei 4-358168; and a carrier wherein an insulating coating layer, as the first coating layer, which has a volume resistivity ranging from 10
8
to 10
11
&OHgr;cm and a film thickness of 0.3 to 0.7 &mgr;m is formed on the surface of a core material particle, another insulating coating layer, as the second coating layer, which has a volume resistivity ranging from 1 to 10
4
&OHgr;cm and a film thickness of 0.05 to 0.4 &mgr;m is formed on the first coating layer, and an additional insulating coating layer, as the third coating layer, which has a volume resistivity ranging from 10
8
to 10
10
&OHgr;cm and a film thickness of 0.5 to 1.0 &mgr;m is formed on the second coating layer, as described in Japanese Unexamined Patent Application, First Publication No. Hei 7-219281, have been proposed. In addition, in Japanese Unexamined Patent Application, First Publication No. Hei 8-179570, a carrier wherein a carrier core material is coated with a resin layer containing a carbon black, and subsequently, another resin layer is formed as a surface layer has been proposed.
However, the carriers proposed in these publications have a high resistance since the surface thereof is formed by an insulating layer which does not include any carbon black. Therefore, as described above, the electric field strength is low at the time of development, giving the edge effects. For this reason, the carriers described above cannot sufficiently overcome the problems in that a uniform image cannot be obtained and in that an extreme degradation of the image density may be observed.
In addition, in order to clarify the problems described above, heretofore, a means for optimizing the resistance value of the carrier by including an appropriate amount of a carbon black in a resin for coating the carrier core material, and coating the carrier core material with a resin layer having a constant concentration of the carbon black from the vicinity of the carrier core material to the surface of the resin layer, has been proposed. According to this method, an appropriate resistance value of the carrier can be obtained at the initial stage of printing. However, in a continuous printing for a long period of time, peeling of the resin layer which corresponds to a coating agent for the carrier core material, caused by the stirring in the interior of the development device, may occur, or on the other hand, adhesion of the toner components on the surface of the carrier (hereinafter, referred to as spent toner) may occur, resulting in a large change in the surface characteristics of the carrier. As a result, the resistance value of the carrier at the initial stage of printing may be different from that after printing for a long period of time, and for this reason, printed matter of a uniform quality cannot be obtained.
In particular, recently, due to an improvement of the printing speed, exceeding 20 m/min, the stress caused by the stirring in the interior of the development device is increased, and even in printing for a long period of time, a constant quality in the printed matter is desired. However, the developer which can exhibit a high quality satisfying these properties could not be obtained heretofore.
BRIEF SUMMARY OF THE INVENTION
The present invention aims to overcome the problems described above in a developer for electrostatic image development.
That is, an object of the present invention is to provide a developer for electrostatic image development, which exhibits a stable development and transfer behavior without any variation in triboelectric charging performance, electric resistance, or the like, even when used as a two-component developer.
In addition, another object of the present invention is to provide a developer for electrostatic image development, which affords a printed image with high image quality and high grade without any fogging, by virtue of rapidly reaching the predetermined charge amount when used as a two-component developer.
In addition, another object of the present invention is to provide a developer for electrostatic image development, which exhibits good triboelectric charging performance and good electric resistance, even during high speed prin
Amaya Shinji
Isonaka Takeshi
Kogawara Toshiro
Ohba Katsunori
Armstrong Westerman & Hattori, LLP
Dainippon Ink and Chemicals Inc.
Goodrow John
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