Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-02-21
2003-07-22
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...
C430S109300, C430S109400, C430S110300, C430S114000, C430S111410, C430S122520, C430S125320, C430S126200, C430S902000
Reexamination Certificate
active
06596452
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic toner for rendering latent images visible in image-forming processes such as electrophotography, electrostatic recording, magnetic recording and toner jetting, and also relates to an image-forming method making use of the magnetic toner.
2. Related Background Art
A number of methods are conventionally known as electrophotography. In general, copies or prints are obtained by forming an electrostatic latent image on an electrostatic latent image bearing member (hereinafter also “photosensitive member”) by utilizing a photoconductive material and by various means, subsequently developing the electrostatic latent image by the use of a toner to form a toner image as a visible image, transferring the toner image to a transfer medium such as paper as occasion calls, and then fixing the toner image to a recording medium by the action of heat, pressure, or heat-and-pressure.
Apparatus for such image formation include copying machines and printers. In recent years, as printers, LED printers or LBP printers are prevailing in the recent market. As a trend of techniques, there is a tendency toward higher resolution. More specifically, those which hitherto have a resolution of 240 dpi or 300 dpi are being replaced by those having a resolution of 600 dpi, 800 dpi or 1,200 dpi. Accordingly, with such a trend, developing systems are now required to achieve a high minuteness. Copying machines have also made progress to have high functions, and hence they trend toward digital systems. In this trend, chiefly employed is a method in which electrostatic latent images are formed by using a laser. Hence, the copying machines also have come to have a high resolution. Also, with an improvement in image quality, it is much sought to achieve a higher speed and a longer service life.
In developing systems used in such printers and copying machines, toner images formed on the photosensitive member in the step of development are transferred to a recording medium in the step of transfer via, or not via, an intermediate member. Any transfer residual toner and fogging toner at non-image areas, left on the photosensitive member are removed in the step of cleaning, and is stored in a waste toner container. In this cleaning step, blade cleaning, fur brush cleaning, roller cleaning and so forth are conventionally used. When viewed from the standpoint of apparatus, the whole apparatus must be made larger in order to provide such a cleaning means. This has been a bottleneck in attempts to make apparatus compact. In addition, from the viewpoint of ecology, a system that may produce no waste toner is long-awaited in the sense of effective utilization of toner. Thus, it is sought to provide a toner having a high transfer efficiency and less causing fog.
From the viewpoint of making apparatus compact, one-component developing systems are preferable because they require no carrier particles such as ferrite particles or iron powder which are required in two-component developing systems. Also, since in the two-component developing systems the concentration of toner in two-component developers must be kept constant, a device for detecting toner concentration so as to supply the toner in the desired quantity is required, resulting in a large size for the developing assemblies. In the one-component developing system, on the other hand, such a device is not required, and hence the developing assemblies can also be made small and light-weight as being preferable. Magnetic toners used in such image-forming processes are commonly chiefly composed of a binder resin and a magnetic material and besides contain additives such as a charge control agent and a release agent which are used to bring out properties necessary as toners. As a colorant of the magnetic toner, the magnetic material is used as it is as the colorant, or a non-magnetic inorganic compound, organic pigment or dye is used together with the magnetic material. As the release agent, used are waxes sparingly compatible with the binder resin, as exemplified by low-molecular weight polyethylene and low-molecular weight polypropylene.
However, developing systems making use of an insulating magnetic toner have a problem concerning the insulating magnetic toner used. The problem is that, in insulating magnetic toner particles, a finely powdery magnetic material is mixed and dispersed in a considerable quantity, and it affects fluidity and triboelectric chargeability of the magnetic toner because magnetic fine particles constituting the magnetic material stand partly uncovered to the surfaces of toner particles, consequently causing variation or deterioration of various performances required for the magnetic toner, in relation to developing performance and running performance of the magnetic toner. This is presumed to be due to the fact that magnetic fine particles having a relatively lower electrical resistance than the resin constituting the magnetic toner particles are present at the surfaces of the magnetic fine particles. Also, the chargeability of the magnetic toner also has a great influence on development and transfer, and is closely concerned with image quality. Accordingly, it is sought to provide a magnetic toner which can stably provide a high charge quantity.
To cope with this problem, proposals concerning magnetic iron oxides to be contained in magnetic toners are hitherto made, but there is room for further improvement.
For example, Japanese Patent Application Laid-Open No. 62-279352 discloses a magnetic toner containing a magnetic iron oxide incorporated with silicon element. In such a magnetic iron oxide, the silicon element is intentionally brought into existence inside the magnetic iron oxide, but there is room for further improvement in the fluidity of the magnetic toner containing the magnetic iron oxide. Japanese Patent Publication No. 3-9045 discloses adding a silicate to control the shape of magnetic iron oxide to be spherical. In the magnetic iron oxide thereby obtained, the silicon element is rich distributed inside the magnetic iron oxide fine particles because of the use of the silicate for the controlling of particle shape of magnetic fine particles and the silicon element is less present at the surfaces of the magnetic iron oxide fine particles, thus, because of a high smoothness of the magnetic iron oxide fine particles, the fluidity of the magnetic toner can be improved to a certain extent. However, it is preferable to more improve the close adhesion between the binder resin constituting magnetic toner particles and the magnetic iron oxide. Japanese Patent Application Laid-Open No. 61-34070 discloses a process for producing triiron tetraoxide by adding a hydroxosilicate solution to triiron tetraoxide in the course of oxidation reaction. The triiron tetraoxide fine particle obtained by this process has silicon element in the vicinity of its surface, but the silicon element is present in layer in the vicinity of the surface of the triiron tetraoxide fine particles. Hence, there is a problem that the surface is weak to mechanical shock such as friction.
Meanwhile, toners are produced by melt-mixing a binder resin, colorant and so forth and uniformly dispersing them, followed by pulverization by means of a fine griding mill and then classification by means of a classifier to obtain toners having the desired particle diameters (pulverization process). To make toners have fine particle diameters, there is a limit to the range of material selection. For example, colorant-dispersed resin compositions must be brittle enough to be pulverizable by means of economically available production apparatus. Since the colorant-dispersed resin compositions are made brittle because of such a requirement, particles having particle diameters in a broad range tend to be formed when such compositions are actually pulverized at a high speed, so that, in particular, fine particles (particles having been pulverized in excess) having a relatively large proportion are formed in a larg
Chiba Tatsuhiko
Hashimoto Akira
Komoto Keiji
Kukimoto Tsutomu
Magome Michihisa
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