Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-11-22
2002-09-10
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
Reexamination Certificate
active
06447972
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charge-providing member for use in electrophotography, electrostatic recording method, electrostatic printing method, etc. More particularly, the present invention relates to a one-component developing sleeve or carrier for the development of an electrostatic latent image, an electrostatic latent image developer comprising such a carrier for the development of an electrostatic latent image, and a magnetic sleeve for carrying such an electrostatic latent image developer.
Processes for rendering image data visible via electrostatic image such as electrophotographic process find wide application in various fields. An electrophotographic process normally comprises forming an electrostatic latent image on a photoreceptor or electrostatic recording material by various means, and then allowing a particulate electroscopic material called toner to be attached to the electrostatic latent image to develop and render the electrostatic image visible. Developers for this purpose can be roughly divided into two groups, i.e., two-component developer comprising a supporting particulate material called carrier and a particulate toner which are triboelectrically charged mutually to provide the toner with a proper amount of positive or negative charge and one-component developer comprising a single particulate toner such as magnetic toner which is triboelectrically charged mutually with a development sleeve. In particular, the two-component developer comprises a carrier which itself is capable of stirring, conveying and electrifying. Thus, the functions required for the developer can be separately considered. Accordingly, this type of a developer can be easily designed and thus finds wide application.
Carriers for this purpose can be roughly divided into two groups, i.e., coated carrier having a coat layer provided on the surface thereof and uncoated carrier free of coat layer. The coated carrier is superior to the uncoated carrier taking into account charging properties and life of developer. Thus, various coated carriers have been developed and put in practical use. The coated carrier has various requirements. In particular, the coated carrier is required to invariably provide the toner with a proper chargeability (amount and distribution of charge), exhibit stable charging properties even with environmental change and maintain these proper and stable charging properties over an extended period of time. In order to meet these requirements, it is important that the carrier has proper electrical properties, a sufficient resistance to change in environmental factors such as humidity and temperature and high impact resistance and friction resistance and maintain desired charge-providing properties over an extended period of time. To this end, various coated carriers have been proposed.
The two-component developer can be electrified when the toner and the carrier are triboelectrically charged with each other. However, triboelectrical charging is liable to change of charge level under some environmental conditions. In general, the two-component developer can be easily charged to a high level under low temperature and low humidity conditions but can be easily charged to a low level under high temperature and high humidity conditions. Accordingly, the two-component developer is disadvantageous in that environmental change is accompanied by the reduction of density upon high level electrification or occurrence of fog upon low level electrification.
Referring to the charging properties of resin for coating carrier, the change in electrification accompanying environmental change (hereinafter referred to as “environmental change”) increases as the electrification capacity becomes higher. For example, a carrier comprising a polymethacrylic acid methyl as a coating resin can be charged to a higher level than a carrier comprising a polystyrene but shows a greater environmental change than the other. In other words, a resin material having a high polarity can be charged to a high level but shows a great environmental change. On the contrary, a resin material having a low polarity shows a small environmental change but can be charged to a low level. It is thus difficult for coated carrier to provide a developer which can be charged to a desired level and shows a small environmental change.
The carrier is also required to maintain a desired charge level over an extended period of time (maintenance of chargeability). The deterioration of the carrier is mainly attributed to fixing of toner components to the surface of carrier coating resin or peeling of the coating resin. In order to prevent these troubles, it has been practiced to use a fluororesin or silicone resin so that the surface energy of the coating resin can be lowered to prevent staining or select a resin which is strong enough to resist peeling. However, a resin material having a low surface energy exhibits a poor adhesivity to particulate nucleus material. It has thus been keenly desired to accomplish low stainability and high peeling resistance at the same time.
As solution to some of these problems, JP-A-61-80161 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-61-80162 and JP-A-61-80163 propose that by coating the surface of a carrier core material with a copolymer of nitrogen-containing alkyl (meth)acrylate fluoride and vinyl monomer or a copolymer of alkyl (meth)acrylate fluoride and nitrogen-containing vinyl monomer, a coated carrier can be obtained which can be difficultly stained with a toner and external additives and thus has a relatively long life.
However, a fluororesin has poor charging properties. When a fluororesin is copolymerized with a nitrogen-containing vinyl monomer or methylmethacrylic acid ester monomer having a high polarity to enhance its chargeability, it is newly disadvantageous in that it shows an increased environmental change.
JP-A-59-104664 focuses on methacrylic acid ester monomer and proposes a carrier coated with a polymer of methacrylic acid cycloalkyl ester aimed at moisture resistance.
However, this carrier is disadvantageous in that it can be charged to a lower level than methyl methacrylate. This carrier is also disadvantageous in that the coating resin is brittle and has a poor adhesivity to particulate nucleus material.
In order to eliminate these disadvantages, JP-A-7-114219 proposes a copolymer of methacrylic acid cycloalkyl ester and methyl methacrylate.
However, even when the copolymerizing ratio of the two components is adjusted in various ways, it is difficult to accomplish the desired charge level and environmental stability at the same time. Thus, it has been difficult to accomplish reliability requirements for carrier, i.e., charge level, maintenance of chargeability and environmental stability at the same time.
SUMMARY OF THE INVENTION
Therefore, the present invention is intended to solve the foregoing problems and provide a charge-providing member for the development of an electrostatic latent image, carrier for the development of an electrostatic latent image and electrostatic latent image developer which can fairly charge a toner to a proper and stable level, have a resistance to environmental change high enough to maintain a stable charging level and can maintain these charging properties over an extended period of time, and a sleeve for carrying such a developer.
The inventors made extensive studies of elimination of the foregoing problems of the prior art. The inventors studied a hundred and scores of coating resins. As a result, resins for charge-providing member or carrier are found which exhibit excellent charging properties under humid conditions, less charge enhancement under low humid conditions and excellent charge maintenance. Further, the study of the control over the structure of coat layer and the core material resulted in the provision of a carrier optimum for charge level and charge maintenance. Moreover, the application of a toner having a high sphericity to the foregoi
Nakajima Tomohito
Ota Kozo
Suzuki Chiaki
Takahashi Sakon
Chapman Mark
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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