Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-03-25
2003-12-30
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111320, C430S111350
Reexamination Certificate
active
06670088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carrier for use in a two-component developer for developing latent electrostatic images, and a two-component developer using the above-mentioned carrier.
2. Discussion of Background
A two-component developer for use in the electro-photographic process is mainly composed of a toner component and a carrier component.
Carrier particles constituting the carrier are mixed and stirred together with the toner particles in a development unit so as to triboelectrically charge the toner particles and impart a desired polarity and charge quantity thereto. After that, the carrier particles lead the toner particles which are, as mentioned above, provided with a predetermined charge quantity, to a latent electrostatic image formed on the surface of a photoconductor, where the toner particles are separated from the carrier particles and deposited on the latent electrostatic image, thereby forming a toner image on the photoconductor.
The carrier particles are then returned to the development unit and mixed and stirred with other remaining toner particles. Thus, the carrier particles are repeatedly used. Therefore, the carrier particles are required to constantly impart a desired charge quantity to the toner particles while in use, regardless of the change in environmental conditions.
However, in conventional developers, during the process of making a number of copies, there take place two major problems resulting from the collision between one carrier particle and another carrier particle and the friction between the carrier particles and the mechanical portions of the development unit.
One of the above-mentioned problems is a so-called spent phenomenon that a toner film is formed on the surface of the carrier particles. The other problem is that a resin-coated surface layer of each carrier particle tends to peel off or to be removed from the core particle.
Those problems occur because of a long-term stirring operation in the development unit. Consequently, the charging performance of the carrier is lowered, and the chargeability of the obtained developer is decreased, with the result that the quality of the obtained toner image is lowered, for example, the image density is insufficient or there occurs fogging in the image.
To inhibit the problems such as the spent phenomenon and the peeling of the resin-coated surface layer from the core particles for use in the carrier particles, there are proposed a variety of resins for the preparation of the above-mentioned surface layer of the carrier particles. However, no resin is satisfactory in terms of all the requirements for the carrier particles.
For instance, carrier particles coated with a styrene or acrylic polymer resin has a drawback in durability although the mechanical strength is sufficient. Namely, such carrier particles show relatively high critical surface tension, so that the surfaces of the carrier particles are apt to be contaminated during the repeated operations for a long period of time.
With respect to the conventional carrier particles coated with a silicone monomer resin, although the resistance to surface contamination of the carrier particles is excellent, the mechanical strength is poor. As a result, the silicone-monomer-resin coated surface layer of the carrier particles is readily worn out and peeled off through so long stirring operation.
For the purpose of reducing the wear and the peeling of the surface layer of the carrier particles, it is proposed in Japanese Laid-Open Patent Application 55-157751 to coat the core particles with a resin-modified silicone resin, in particular, an alkyd-resin-modified silicone resin or an epoxy-resin-modified silicone resin for the preparation of the resin-coated carrier particles. According to this method, the mechanical strength of the carrier particles is improved. However, the polarity of such a resin for use in the surface layer of the carrier particles is not strong enough for the resin-coated carrier particles to impart stable charge quantity to the toner particles.
Furthermore, in line with the trend toward resource saving, there is an increasing demand for efficient development using a minimum amount of developer. Therefore, the carrier for use in the two-component developer is required to have sufficient durability and a long life.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide a carrier for use in a two-component developer, having excellent durability and a long life, and stable triboelectric charging characteristics so as to produce high quality toner images for an extended period of time.
A second object of the present invention is to provide a two-component developer employing the above-mentioned carrier.
The first object of the present invention can be achieved by a carrier for use in a two-component developer for developing a latent electrostatic image, comprising carrier particles, each of the carrier particles comprising a core particle and a coating layer provided on the surface of the core particle, with the coating layer comprising an amino-group-containing modified silicone resin.
The second object of the present invention can be achieved by a two-component developer for developing a latent electrostatic image, comprising a toner and the above-mentioned carrier.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that the stability of triboelectric charging between the toner particles and the carrier particles can be improved when each of the carrier particles comprises a core particle and a coating layer provided thereon comprising at least an amino-group-containing modified silicone resin. The reason for this is that the amino group to be contained in the coating layer of the carrier particle shows a remarkably strong positive polarity.
Further, when the coating layer for use in the carrier particle comprises an amino-group-containing organic compound or an amino-group-containing silicone compound and a resin-modilfied silicone resin in combination, the same effects as stated above can be obtained.
According to the present invention, the amino-group-containing modified silicone resin for use in the coating layer may be prepared by modifying a silicone resin using an amino-group-containing organic compound, preferably using an amino-group-containing resin. The preparation method for such a modified silicone resin is as follows:
[Method (1)]
There is proposed a method of carrying out the condensation reaction between an amino-group-containing resin, such as an amino-group-containing acrylic resin, alkyd resin, melamine resin, epoxy resin, phenolic resin, esterified epoxy resin, urethane resin, polyester resin or ethyl cellulose resin, and a silicone resin having a functional group capable of undergoing the condensation reaction with the above-mentioned amino-group-containing resin.
In the above-mentioned method (1), the resin employed to modify the silicone resin comprises an amino group. The silicone resin subjected to modification has a functional group capable of undergoing the condensation reaction with the above-mentioned amino-group-containing resin. The silicone resin may further comprise an amino group.
Examples of such a functional group for use in the silicone resin are hydroxyl group; an alkoxyl group having 1 to 4 carbon atoms, such as methoxy group or ethoxy group; an alkenyloxy group having 2 to 4 carbon atoms, such as vinyloxy group; phenoxy group; carboxyl group; and epoxy group such as ethyleneoxide group or glycidyl group.
The above-mentioned functional group may be bonded to a silicon atom directly, or through an alkylene group or an arylene group.
The molecular weight of the silicone resin to be subjected to modification is not particularly limited. It is preferable that the average molecular weight of the silicone resin be in the range of 90 to 500,000, more preferably in the range of 300 to 500,000 before the silicone resin is subjected to modification.
A silicone resin represented by the fol
Higuchi Hiroto
Matsuda Hiroaki
Sugiyama Akemi
Suzuki Masanori
Dote Janis L.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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