Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-11-05
2003-01-14
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...
C430S111310, C430S111320, C430S111350
Reexamination Certificate
active
06506531
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a magnetic carrier having excellent durability and exhibiting a correspondingly stable charging performance.
In electrophotographic processes, a photosensitive member comprising a photoconductive substance, such as selenium, OPC (organic photoconductor) or a-Si (amorphous-silicon) is used to form an electrostatic latent image thereon by various means. Such a latent image may be developed by a magnetic brush developing scheme by electrostatically attaching a toner charged to a polarity opposite to that of the latent image in a normal development mode or a toner charge to a polarity identical to that of the latent image in a reversal development scheme to visualize the latent image.
In the development, carrier particles called a magnetic carrier are used to impart an appropriate amount of positive or negative charge to a toner by triboelectrification and also convey the toner to a developing region in proximity to the surface of the photosensitive member having the latent image thereon under application of a magnetic force exerted from a magnet enclosed within a developing sleeve via the developing sleeve.
Hitherto, as such carrier particles, iron articles, ferrite particles and so-called binder-type particles that are composite particles formed by dispersing magnetic fine particles in a binder resin, have been proposed or commercialized. These carriers have widely ranging electrical resistivities from a low value as exhibited by iron particles to a high value as exhibited by the binder-type particles. Further, optimum resistivities are present depending on developing systems using them. For this reason, it has been frequently practiced to use such carrier particles as magnetic core particles and coating the core particles with various resins to adjust the resistivity.
In recent years, electrophotography has been widely adopted in copying machines and printers which are required to comply with various types of images including thin lines, small characters, photographic images and color originals. There are also demands for higher image quality, higher image speed and continuous image forming performances, and these demands are becoming more and more intense.
As carrier particles for complying with such demands, light-weight composite particles having a specific gravity of 2-4 have been widely used so as not to break the toner even under high-speed and continuous image formation.
There is an incessant demand for carrier particles having further improved performances, and particularly a magnetic carrier having a higher performance in charging a small-particle size toner for providing a higher quality of full-color images.
More specifically, it is important to impart a uniform charge to a toner, and to provide that the charging performance does not change during long hours of continuous use or against an environmental change. For exhibiting such performances, the magnetic carrier is required to exhibit an excellent durability.
Hitherto, as magnetic carriers having improved durability, there have been proposed various types of magnetic carriers inclusive of (1) a magnetic carrier obtained by surface coating magnetic carrier particles with a silicone resin coating layer comprising a silane coupling agent, etc. (Japanese Laid-Open Patent Application (JP-A) 60-140951, JP-A 62-121463 and JP-A 7-104522), (2) a magnetic carrier obtained by surface-coating magnetic carrier particles with a coupling agent and then with a silicone resin (JP-A 60-19156 and JP-A 62-121463), and (3) a magnetic carrier obtained by surface-coating magnetic carrier particles with an amino-silane coupling agent and then with a layer of coating resin having a functional group reactive with the amino-silane coupling agent (JP-A 4-198946).
In this way, magnetic carriers having excellent durability have been proposed, but such magnetic carriers having a satisfactory level of durability have not been obtained.
For example, the above-mentioned magnetic carrier or type (1) is liable to cause peeling of the coating layer after long hours of use, thus resulting in a change in charging performance leading to image problems as shown in Comparative Examples appearing hereinafter.
Regarding the above-mentioned magnetic carriers of types (2) and (3), the coupling agent is liable to be mixed within the coating resin layer during the resin coating thereon. As a result, insufficient adhesion between the magnetic carrier particles and the coating resin layer results, whereby the coating layer is liable to be peeled during long hours of use, thus resulting in image problems.
SUMMARY OF THE INVENTION
A generic object of the present invention is to provide a magnetic carrier having solved the above-mentioned problems of the conventional magnetic carriers.
A more specific object of the present invention is to provide a magnetic carrier for electrophotography exhibiting excellent durability, whereby when it is used in mixture with a toner in a developer even for a long period, the magnetic carrier does no cause the peeling of the coating layer but retains a stable charging performance, thus continually providing clear images.
According to the present invention, there is provided a magnetic carrier, comprising: composite particles each comprising at least inorganic compound particles and a binder resin, wherein
said inorganic compound particles have been surface-treated with a lipophilizing agent having a functional group (A) selected from the group consisting of epoxy group, amino group, mercapto group, organic acid group, ester group, ketone group, halogenated alkyl group and aldehyde group, and
said composite particles are surface-coated with a coupling agent having a functional group (B) different from the functional group (A) of the lipophilizing agent and selected from the group consisting of epoxy group, amino group and mercapto group.
According to another aspect of the present invention, there is provided a magnetic carrier, comprising: composite particles each comprising at least inorganic compound particles and a binder resin, wherein
said inorganic carrier particles have been surface-treated with a lipophilizing agent having a functional group (A) selected from the group consisting or epoxy group, amino group, mercapto group, organic acid group, ester group, ketone group, halogenated alkyl group and aldehyde group, and
said composite particles are surface-coated with a coating resin having a functional group (C) different from the functional group (A) of the lipophilizing agent and selected from the group consisting of epoxy group, amino group, organic acid group, ester group, ketone group and halogenated alkyl group.
The above mentioned and other objects and features of the invention will be better understood upon consideration of the following detailed description concluding with specific Examples and Comparative Examples.
DETAILED DESCRIPTION OF THE INVENTION
As a result of our investigation on the type of coated magnetic carriers obtainable by using composite particles comprising at least inorganic carrier particles and a binder resin as magnetic carrier core particles and forming a coating layer on the composite particles for suppressing the peeling of the coating layer, it has been found possible to effectively suppress the peeling of the coating layer by surface-treating the inorganic carrier particles with a lipophilizing agent having a specific functional group (A) and also surface-coating the composite particles with a coupling agent having a specific functional group (B) different from the functional group (A) or with a resin having a specific functional group (C) different from the functional group (A) to provide the coating layer.
Hereinbelow, the magnetic carrier obtained by coating the composite particles with the coupling agent is sometimes called “a first-type carrier”, and the magnetic carrier obtained by coating the composite particles with the resin is sometimes called “a second-type carrier”.
A most important feature of the first-type
Fukugauchi Masaaki
Hakata Toshiyuki
Kakihara Hiroomi
Mikuriya Yushi
Okada Kenji
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