Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-05-24
2004-12-07
Chapman, Mark A. (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
06828075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carrier used in development of electrically charged latent image in electrophotography, electrostatic recording and electrostatic printing, a developer using the carrier, an image forming apparatus and method using the same.
2. Description of the Related Art
In image forming processes such as electrophotographic process and electrostatic recording in general a developer being obtained by mixing toner and carrier and agitating them is used for developing an electrostatic latent image formed on a latent image-bearing member. The developer is required to be a mixture being properly tribo-charged. There are known two developing methods for developing the electrostatic latent image; a two-component developing method using two-component developer comprising a mixture of a carrier and a toner, and a so-called one-component developing method using one-component developer which does not contain carrier component.
Two-component developing method has an advantage that it can produce comparably stable and excellent images, while it has a shortcoming that it apt to alter the ratio of toner amount and carrier amount being contained therein during processing. On the other hand the later of one-component developing method does not show the above mentioned shortcoming of former method, however has an inconvenience that it is hard to be stabilized in its tribo-electric charge property.
In the course of repeatedly conducted developments of latent images using the two-component developer, toner consisting of toner particles in the developer is gradually consumed and toner concentration in the developer is thus varied, therefore small quantities of toner are periodically added to the developer to compensate for toner consumed during repeated developments if necessary for the purpose of obtaining stable images. With regard to the method for controlling the toner supply, copy machines are in general equipped with sensor such as transparency-detecting sensor, fluidity-detecting sensor, bulk density-detecting sensor or other type of sensors, however sensors for measuring optical densities in images are prevailingly being used at the moment. Controlling method using this densitometric type of sensor is a method in which each optical density of image patterns having been developed on latent image-bearing members are measured using reflected light from irradiation onto the surfaces of the image-bearing members, thereby toner supplies are controlled.
In such two-component developer there are many known techniques in which a hard and high strength coating layer is provided onto each granular carrier particle by using proximate resin materials, with the purposes to prevent toner-filming on the carrier particle, to form the homogenous surface on the carrier particle, to prevent oxidizing of the carrier surface, to prevent decreasing humid tolerability of the carrier, to prolong the life of developer, to prevent carrier deposition onto the photosensitive member surface, to protect from scratching or abrasion of photosensitive member surface, and to control polarity or volume of electric charge in developer. For examples a carrier coated by particular resinous material (as shown in Japanese Unexamined Patent publication of Tokkai Shou No. 58-108548), carriers coated by the resinous layers containing various additives incorporated therein (as shown in Japanese Unexamined Patent publication of Tokkai Shou No. 54-155048, Japanese Unexamined Patent publication of Tokkai Shou No. 57-40267, Japanese Unexamined Patent publication of Tokkai Shou No. 58-108549, Japanese Unexamined Patent publication of Tokkai Shou No. 59-166968, Japanese Unexamined Patent publication of Tokkai Hei No. 1-19584, Japanese Examined Patent publication of Tokkou Hei No. 3-628, Japanese Unexamined Patent publication of Tokkai Hei No. 6-202381), a carrier having an additive provided thereon by adhering (as shown in Japanese Unexamined Patent publication of Tokkai Hei No. 5-273789), and a carrier coated by resinous layer which includes therein an additive of electrically conductive particles, each particle having larger diameter than thickness of the layer (as shown in Japanese Unexamined Patent publication of Tokkai Hei No. 9-160304) are instanced.
Further, Japanese Unexamined Patent publication of Tokkai Hei No. 8-6307 discloses a technique in which benzo-guanamine-n-buthyl alkohol-folmaldehyde copolymer as a main ingredient is used as a carrier coating material, and Japanese Patent No. 2683624 discloses a technique in which a cross-linked material consisting of melamine resin and acrylic resin is used as a coating material.
However the durability and suppression of carrier deposition are still insufficient. Accordingly regarding to the durability, there are problems which include occurrence of toner spent onto carrier surface thereby tribo-electric charge volume becomes unstable, and decrease of coating layer thickness caused by scraping of coated material and thereby decreasing electric resistance. And if good quality images can be demonstrated at initial period of use, but it is encountered that image qualities are gradually declined in relation to the increase of copy numbers, which is a problem must be improved.
The change of carrier amount scooped up by developing roller is caused with scraping the coated layer of carrier coating. Particularly in case of conventional carrier having a coating layer consisting of resin having low surface energy, the coating layer has a high fragility and hence is apt to easily scrape off. As a result, diameter and surface characteristics of the carrier are changed, thus fluidity and bulk density are changed, as a result there is shown a problem that carrier amount scooped up by developing roller is changed with the progress of copying run.
SUMMARY OF THE INVENTION
The present invention has been made in contemplation of above mentioned problems, thus it is an object of the present invention to provide a two-component developer which is free from toner-spent onto the carrier surface, and is eliminated or decreased in the scrape of coated resinous layer on the carrier, thus is capable of providing fine and excellent quality of images with high precision for long period of running time.
Another object of the present invention is to provide a developer showing a few change of carrier amount scooped up onto developing roller for long period of running time.
Above and other objects are attained by the present invention including;
(1) A carrier for electrophotographic developer comprising carrier particles, each carrier particle having at least one surface-coating layer by resin material, wherein the surface-coating layer containing an acrylic resin and a silicone resin, the acrylic resin is in an amount ranging 10 to 90 wt. % based on the total amount of resin coating ingredients;
(2) A carrier for electrophotographic developer according to above paragraph (1), wherein the acrylic resin is a acrylic resin of thermo-harding type;
(3) A carrier for electrophotographic developer according to above paragraph (1), wherein the silicone resin is a silicone resin having condensation reactive functional groups;
(4) A carrier for electrophotographic developer according to above paragraph (1), wherein the surface-coating layer containing particles which have a particle-diameter (D) in the range of 1<[D/h]<5, in the relation of the (D) to the layer thickness (h) of the surface-coating layer;
(5) A carrier for electrophotographic developer according to above paragraph (1), wherein the surface-coating layer containing particles which have a particle-diameter (D) in the range of 1<[D/h]<5, in the relation of the (D) to the layer thickness (h) of the surface-coating layer, the particles having been applied in an amount ranging 50 to 95 wt. % based on the total amount of coating composition ingredients;
(6) A carrier for electrophotographic developer according to above paragraph (1), wherein the carrier conta
Asahina Yasuo
Masuda Minoru
Mochizuki Satoshi
Sugiura Hideki
Suzuki Kousuke
Chapman Mark A.
Ricoh & Company, Ltd.
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