Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1998-01-14
2001-02-27
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109500, C430S111400
Reexamination Certificate
active
06194114
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-fixable developer for electrophotograph to be used favorably as electrostatic toner and, more specifically, to a heat-fixable developer for electrophotograph favorable on using as an electrostatic toner which exhibits no offset phenomenon and causes no staining on the carrier, on the photosensing body and on the heating roller and which is superior in the releasing easiness of the heating roller upon the heat-fixing, in the anti-blocking property and in the fixing performance.
DESCRIPTION OF THE RELATED TECHNIQUES
Electrostatic toner is used in electrostatic photography for developing a latent image of electrostatic charge formed on a photosensitive substrate by light exposure-charging into visible image. The electrostatic toner comprises, as the developer, electrostatically chargeable fine powder of resin containing dispersed therein particulate colorant, such as carbon black or other color pigment. Electrostatic toners are generally classified into dry two-component toner used as a mixture of electrostatically chargeable fine powder such as above with a carrier component, such as iron powder or glass powder; wet toner as a disperse system using an organic solvent, such as isoparaffin or the like; and dry unicomponent toner of the electrostatically chargeable fine powder mentioned above dispersed in a gas phase.
The image obtained by being developed on a photosensitive material using an electrostatic toner is fixed, after the toner image is transferred onto a paper, or directly when the image is obtained by a direct development on a paper having a photosensitive layer, by means of heat or by using vapour of a solvent. In particular, fixing by means of a heating roller brings about advantages, such that the thermal efficiency is high due to contacting fixing and, thus, the image can be fixed even using a heat source of relatively low temperature and that it is adapted for a high speed photocopying.
Due to the growing extension of the application range of electrophtography in recent years, in particular, demand for fixing electrostatic toner image with an energy lower than that used in the prior art becomes increased. For example, reduction of electric power consumption by the heating roller is requested as the incorporation of electrophotography in household devices and instruments progresses. Also a high-speed fixing ability is required for toners for use in output terminals of high-speed devices, such as computers.
When, however, an image is to be fixed by contacting a heating element, such as heating roller, a so-called offset phenomenon may occur, namely, a phnomenon in which a part of the electrostatic toner is held affixed on the heating element and is transferred onto a portion of the subsequent image and developed. In particular, when the temperature of the heating roller is lower, the electrostatic toner will not sufficiently be softened, so that fixing performance on a paper or film becomes deteriorated and the offset phenomenon will be apt to occur. Also, when the heating element is brought to higher temperature for increasing the effect and velocity of the fixing for high speed photocopying, an offset phenomenon may often be caused. Therefore, such a measure as an impregnation of the heating roller surface with a silicone oil or a lubrication of the heating roller surface with a silicone oil supplied thereto, has been incorporated for eliminating the offset phenomenon, which may cause, in reverse, a problem of inducing a staining of the heating roller.
For the binder resin as one of the component of the electrostatic toner, there have been employed various thermoplastic resins, wherein especially a lower molecular weight copolymer of styrene/(meth)acrylate has find its wide use, since it provides many practical advantages such that it attains a better electrostatic chargeability, permits easy fixing due to its proper softening point at aroud 100° C., causes scarce staining of the photosensitive surface with permission of easy cleaning thereof, has a low hygroscopic property, reveals a better miscibility with carbon black as colorant and is easy to be pulverized.
However, the conventional electrostatic toner in which a binding resin of the styrene/(meth)acrylate lower molecular weight copolymer is used has problems, for example, in that it is liable to suffer from easy occurrence of offset phenomenon on fixing by a heating roller of lower temperature or in a high-speed photocopy.
For solving such problems, there was proposed to add a polyolefin wax as releasing agent to the electrostatic toner [Japanese Patent Kokai Nos. 49-65231 A (corresponding to U.S. Pat. No. 4917982), 49-65232 A (corresponding to U.S. Pat. No. 4921771), 50-27546 A, 55-153944 A and 58-59455 A]. However, even the electrostatic toner having addition of polyolefin wax mentioned above does not reveal sufficient fixing performance under the low energy fixing condition of recent years and has not succeeded in preventing occurrence of offset phenomenon.
In addition, another problem may occur, for example, in that the toner with addition of polyolefin wax exhibits a decreased anti-blocking property, so that blocking of the toner may sometimes occur within the toner cartridge to thereby disrupt toner supply to the photosensitive surface.
Moreover, there may occur a so-called filming phenomenon, in which substances with lower crystallizability contained in the polyolefin wax will adhere onto the carrier, photosensitive surface, heating roller and so on, resulting in an adverse effect on the formation of electrostatic latent image on the photosensitive surface and on the electrostatic charge of the toner to thereby deteriorate the quality of the resulting image considerably.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a heat-fixable developer for electrophotography to be used for electrostatic toner which is superior in the ability of releasing from the heating roller, especially in a low energy fixing, together with superiorities in the resistance to blocking of toner and in the fixing without suffering from occurrence of offset phenomenon and from staining on the carrier, photosensitive surface, heating roller and so on and, thus, is favorable as electrostatic toner.
The inventors had been in sound researches for attaining the above-mentioned object and found that the object was able to be attained by using, as a wax to be added to the electrostatic toner, a specific ethylene/ aromatic vinyl compound copolymer obtained by using a metallocene catalyst, which has led to the present invention.
The heat-fixable developer for electrophotography according to the present invention, comprises a binder resin (A), a colorant (B) and a releasing agent (C),
wherein the releasing agent (C) comprises at least one ethylene/aromatic vinyl compound copolymers selected from the group consisting of copolymer i) and copolymer ii)
the copolymer i) being an ethylene/aromatic vinyl compound copolymer obtained by co-polymerizing ethylene and an aromatic vinyl compound in the presence of a metallocene catalyst (D) and
the copolymer ii) being an ethylene/aromatic vinyl compound copolymer obtained by a heat-degradation of a copolymer produced by co-polymerizing ethylene and an aromatic vinyl compound in the presence of a metallocene catalyst (D).
DETAILED DESCRIPTION OF THE INVENTION
For the component (A), namely, the binder resin of the heat-fixable developer for electrophotography according to the present invention (in the following, sometimes referred to simply as the developer), any resin which permits to preserve the image visualized by the colorant (B) by fixing on a paper or film for long term and which is superior in the electrostatical chargeability, in the fixing performance and in the missibility with the colorant (B) together with a suitable softening point (at around 100° C.) can be used without any special limitation. For such a resin, there may be used, for example, thermoplastic resins conventionally employed fo
Morizono Kenichi
Sakai Hideki
Toyoda Hideo
Tsutsui Toshiyuki
Birch & Stewart Kolasch & Birch, LLP
Dote Janis L.
Mitsui Chemicals Inc.
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