Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-08-30
2003-04-08
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110400, C430S111100, C430S111410
Reexamination Certificate
active
06544704
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrostatic image developer used for developing an electrostatic latent image formed on the surface of a latent image carrier body in an electrophotographic method, an electrostatic recording method, and an electrostatic printing method, or the like. More particularly, this invention relates to the electrostatic image developer having a toner and a carrier.
BACKGROUND OF THE INVENTION
In association with social movement of energy saving in recent years, such movement has become active also in the electrophotographic field. A fixing part in particular of electrophotographic equipment consumes a large amount of energy. Therefore, studies in this part have been carried out so as to attain mechanically low power consumption. Regarding toner as a supply, development of toner adequate for an energy-saving fixing device has been urged as well. As measures directed toward achievement of energy saving in the fixing device due to toner, the followings are most popular.
For example, some of binder resins for toner is targeted to stabilize fixability at a low temperature by using a resin having low molecular weight. Although energy saving can be achieved because of low-temperature fixability of toner, the toner itself or toner components may be melted in many cases on the surface of a carrier (hereafter referred to as toner spent) particularly when the binder resin of the toner has a large amount of components having low molecular weight. The carrier surface is soiled with this toner spent, and the charged sites of the carrier decrease, which causes the amount of triboelectric charge as a two-component developer to vary. Resultantly, inconvenience such as occurrence of variation in image density or fog may occur.
In Japanese Patent Application Laid-Open No. 10-198068, detailed description on toner molecular weight for suppression of toner spent has been disclosed. However, low-energy consumption for the fixing device could not sufficiently be achieved with the range of the toner molecular weight in this publication.
Further, as image forming devices such as electrophotographic copiers have been widely used, the purpose of their use also becomes widely, demands of the market for high-definition and high-quality images are increasing. In this technological field, such attempt that toner particle diameter is made smaller to achieve higher quality of image has been made. However, smaller particle diameter makes the surface area per unit weight increase, and the amount of electrification on toner tends to increase. Therefore, lower image density and deterioration of durability are what may be concerned about. In addition, because of the large amount of electrification on toner, adhesion of toner particles is strong and fluidity is lowered. Accordingly, there comes up some problems in stability of toner supply and impartation of triboelectric charge to toner to be supplied. In general, the tendency of increase in the amount of electrification becomes more significant particularly when polyester-based binder of high chargeability is used.
Some types of developers have been proposed for obtaining improved image quality. In Japanese Patent Application Laid-Open No. 51-3244, a nonmagnetic toner for improving image quality obtained by restricting a particle size distribution has been proposed. The toner contains mainly toner particles having particle diameter of 8 to 12 &mgr;m, which are comparatively coarse. Therefore, according to the analysis of the inventors, uniform “deposition” of the toner onto a latent image is difficult with this particle size. Further, the toner has properties such that the particles of 5 &mgr;m or less are contained at 30 number % or less, and the particles of 20 &mgr;m or more are contained at 5 number % or less. Therefore, the particle size distribution is broad, which also tends to decrease the degree of uniformity. In order to form a sharp image using the toner having such coarse toner particles and broad particle size distribution, it is required to increase the apparent image density by embedding space of inter-toner particles through heavy superimposition of the particles on each other. Resultantly, this invention also has a problem such that the amount of toner consumption required for attaining the predetermined image density increases.
Japanese Patent Application Laid-Open No. 54-72054 has made the proposal of a nonmagnetic toner having particle size distribution sharper than the former one. The size of particles having an intermediate weight is as coarse as a range of 8.5 to 11.0 &mgr;m. Therefore, this toner is still in need of some improvements as high-resolution toner. Further, Japanese Patent Application Laid-Open No.58-129437 has made the proposal of a nonmagnetic toner having 6 to 10 &mgr;m average particle diameter and 5 to 8 &mgr;m diameter in most frequency particles. However, the toner contains a small amount of particles of 5 &mgr;m or less at 15 number % or less, which means this invention has little effect on a sharp image.
In accordance with studies by the inventors, it is found that the toner particles of 5 &mgr;m or less sharply reproduce the edge of a latent image and have a main function for solid “deposition” of the toner onto the entire latent image. Particularly, in the electrostatic latent image on a photoreceptor, the edge part as its outline has electric field strength stronger than its internal part because the lines of electric force are concentrated on the edge part. Therefore, sharpness of image quality is determined depending on the quality of the toner particles collecting on this part. According to the inventors, it is found that the amount of the particles of 5 &mgr;m or less is effective in solution of the problem on sharpness of image quality. In Japanese Patent Application Laid-Open No. 2-222966, atoner, that contains toner particles having particle diameter of 5 &mgr;m or less at 15 to 40 number %, has been proposed. It is thought that this invention has achieved significantly improved image quality. However, further improved image quality is desired.
In Japanese Patent Application Laid-Open No. 2-877, a toner, that contains toner particles having particle diameter of 5 &mgr;m or less at 17 to 60number %, has been proposed. The image quality and image density are surely stabilized with this toner. However, it is also found that it is difficult to constantly obtain a predetermined level of image quality. That is because the particle size distribution of the toner varies when an original like a photographic document, that requires a large amount of toner consumption, is repeatedly printed. Further, all the above-mentioned inventions relate only to a nonmagnetic toner developer, with which high image quality has been obtained in terms of reproducibility of fine lines or the like, but measures against background dirt or the like have not been improved yet.
On the other hand, inventions, which suggest average particle diameter and particle size distribution of carrier, have been disclosed in Japanese Patent Application Laid-Open No. 51-3238, Japanese Patent Application Laid-Open No. 58-144839, and Japanese Patent Application Laid-Open No. 61-204646. Japanese Patent Application Laid-Open No. 51-3238 mentions the coarse particle distribution.
However, this invention does not particularly disclose the magnetic property having a close relation with developing performance of the developer or conveyability in the developing device. Further, the carrier in the example contains particles of 250 mesh or more at about 80 weight % or more based on the total weight of the carrier, and its average particle diameter is 60 &mgr;m or more.
Japanese Patent Application Laid-Open No. 58-144839 has disclosed merely the average particle diameter, and neither mentions the amount of fine powder that exerts an effect on carrier adhesion to a photoreceptor and also the amount of coarse powder that exerts an effect on sharpness of an image, nor describes the distribution of the powder in detail.
Hasegawa Kumi
Higuchi Hiroto
Iwamoto Yasuaki
Matsuda Hiroaki
Nakai Hiroshi
Goodrow John
Ricoh & Company, Ltd.
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