Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-10-16
2004-01-06
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...
C430S111100, C430S120400, C430S124300, C430S126200
Reexamination Certificate
active
06673502
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a carrier for the development of electrostatic latent image for use in electrophotography, electrostatic recording, electrostatic printing, etc. The invention also relates to a developer for the development of electrostatic latent image comprising the carrier and to an image forming method using the developer.
BACKGROUND OF THE INVENTION
A method which comprises making image data visible via electrostatic image such as electrophotography has wide application at present. Electrophotography has heretofore normally employed a process which comprises forming an electrostatic latent image on a photoreceptor or electrostatic recording material by various means, and then allowing electroscopic particulate material called toner to be attached to the electrostatic latent image to develop and make the electrostatic latent image visible. The toners to be used for this purpose can be roughly divided into two groups. That is, one of them is a two-component developer arranged such that a supporting particle such as carrier and a particulate toner are mixing by each other to cause electrification so that the toner is provided with a proper amount of positive or negative charge. The other of them is one-component developer comprising a toner alone such as magnetic toner. In particular, the two-component developer can provide the carrier itself with functions such as agitation, conveyance and electrification, making it possible to separate functions required for developer. Thus, the two-component developer has found wide application because of easy design.
However, the two-component developer for use in frictional electrification is readily subject to change of electrification level when affected by environmental change. In general, high electrification can easily occur under low temperature and low humidity conditions while low electrification can easily occur under high temperature and high humidity conditions. Thus, the two-component developer is disadvantageous in that environmental change leads to the reduction of density in the case of high electrification or to the occurrence of fog in the case of low electrification.
Processes for the preparation of a toner can be roughly divided into two groups, i.e., a process involving conventional dry melt-knead grinding method and a wet process involving granulation of a toner in a liquid. The wet process has been given more attention from the standpoint of reduction of diameter of toner, sharpness of particle size distribution, freedom of shape control, reduction of energy cost of production, etc. However, since granulation is effected in a liquid, a hydrophilic group can be easily left on the surface of the toner, causing moistening under high humidity conditions and hence deteriorating chargeability. Therefore, the conventional developer comprising a toner obtained by such a wet process is disadvantageous in that it exhibits deteriorated chargeability under high humidity conditions.
The change of electrification (environmental dependence) of the carrier becomes larger as the chargeability of the coating resin increases. For example, a carrier comprising a polymethyl methacrylate as a coating resin has a higher electrification level but exhibits a higher environmental dependence than that comprising a polystyrene as a coating resin. In other words, a resin material containing a group having a high polarity has a high electrification level but exhibits a high environmental dependence while a resin material having a low polarity has a low environmental dependence but has a lower electrification level. Thus, it is difficult to allow both the toner and carrier to keep desired electrification level and provide chargeability which has little environmental dependence.
A carrier is required to have a good electrification-maintaining property. In other words, the carrier is required to maintain desired electrification level over an extended period of time. The deterioration of carrier has been heretofore considered attributed to the following two causes.
Firstly, the deterioration of carrier is attributed to the fixing of toner components to the surface of the carrier coating resin. When a toner and external additives having a polarity opposite to that of the carrier are attached to the carrier, the chargeability of the carrier is deteriorated. Further, since the toner is insulating, the carrier to which the toner has been attached shows a raised resistivity.
Secondly, when the coated carrier is subject to stress with time, the coating resin is peeled off to reduce the amount of the coating resin. As a result, the carrier exhibits deteriorated chargeability. Further, when the core material is exposed, the carrier exhibits deteriorated chargeability and lowered resistivity.
In order to solve these problems, it has been proposed to use a fluororesin or silicone resin as coating resin so that the surface energy of the coating resin can be reduced to prevent pollution of the surface of carrier or raise the strength of the coating resin so that the peeling off or loss of the coat layer can be prevented. However, since such a low surface energy material has a deteriorated adhesion to core material, it is very difficult to provide the coating resin with both pollution resistance and peeling resistance.
JP-A-2-114271 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) proposed a carrier coated with a copolymer of (meth)acrylic acid ester monomer with a monomer having a carboxyl group for the purpose of enhancing the adhesion of coating resin to improve the electrification maintaining property. The carboxyl group to be used in this proposal is effective to enhance the negative chargeability of carrier and hence the adhesion to core material such as metal and durability. However, the carboxyl group, which is a hydrophilic group, comes up to the surface of the coating resin to exhibit hygroscopicity, deteriorating chargeability and hence making it easy for the carrier to be contaminated to disadvantage.
JP-A-61-80161, JP-A-61-80162, and JP-A-61-80163 proposed that when the surface of a carrier core material is coated with a copolymer of nitrogen-containing fluorinated alkyl (meth)acrylate and vinyl monomer or a copolymer of fluorinated alkyl (meth)acrylate and nitrogen-containing vinyl monomer, a coated carrier having a relatively prolonged life which can difficultly be contaminated by toner or external additives can be provided. However, this approach is disadvantageous in that since a fluororesin has an insufficient chargeability, the resulting carrier has a raised environmental dependence when copolymerized with a nitrogen-containing vinyl monomer or methyl methacrylate ester monomer having a highly chargeable polar group.
Paying attention to methacrylic acid ester monomer for the purpose of solving the problem of environmental dependence, JP-A-59-104664 proposed a carrier coated with a methacrylic acid cycloalkyl ester polymer having an excellent moisture resistance. However, this carrier has a low electrification level, high brittleness and a deteriorated adhesion to core material as compared with that coated with methyl methacrylate.
In order to solve the foregoing problem, JP-A-7-114219 proposed a carrier coated with a copolymer of methacrylic acid cycloalkyl ester and methyl methacrylate. However, cycloalkyl ester is brittle and thus can be easily peeled off. Further, when the composition ratio of methyl methacrylate is increased, the resulting environmental stability is deteriorated, making it impossible to accomplish desired durability and environmental dependence at the same time.
Further, JP-A-60-66264 proposed a carrier coated with a copolymer containing tertiary butyl acrylate component and methyl acrylate component. The incorporation of two or more such (meth)acrylic acid esters makes it easier to control chargeability than coated carrier comprising a homopolymer alone. However, since this coating exhibits deteriorated adhesion to core material and becom
Eguchi Atsuhiko
Nakajima Tomohito
Nakazawa Hiroshi
Takagi Masahiro
Takahashi Sakon
Dote Janis L.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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