Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-03-08
2002-10-15
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S110400, C430S111410, C430S137170, C430S126200, C399S297000
Reexamination Certificate
active
06465144
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a magnetic toner used in image forming methods, such as electrophotography, electrostatic recording, magnetic recording and toner jetting; a process for production of the magnetic toner; and an image forming method, an image forming apparatus and a process cartridge using the magnetic toner.
Hitherto, many proposals have been made regarding a magnetic toner (i.e., a magnetically susceptible toner) and an image forming method using the toner.
U.S. Pat. No. 3,909,258 has proposed a developing method using a magnetic toner, having electroconductivity. According to the proposal, an electroconductive magnetic toner is supplied onto a cylindrical electroconductive sleeve enclosing a magnet at an inside thereof and is caused to contact an electrostatic latent image for development. In this instance, at the developing position, an electroconductive path is formed of the toner particles between a recording member surface and the sleeve surface, charges are guided to the toner particles from the sleeve via the electroconductive path, and the charged toner particles are attached onto an image part of an electrostatic image due to a Coulomb force acting between the image part and the toner particles, thereby to effect a development. The developing method using such an electroconductive magnetic toner is an excellent method capable of obviating the problems accompanying the conventional two-component developing method, but on the other hand, involves a problem that it becomes difficult to effect the transfer of a developed image from the recording member to a final supporting material, such as plain paper, because the toner is electro-conductive.
As a developing method using a high-resistivity magnetic toner allowing electrostatic transfer, a developing method using dielectric polarization of toner particles is known. However, such a method involves essential problems of a slow developing speed or inability of obtaining a sufficiently high image density.
Other known developing methods using a high-resistivity insulating magnetic toner includes a method wherein toner particles are triboelectrically charged through friction between individual toner particles, friction between a sleeve and toner particles, etc. This method is accompanied with a problem that the toner particles are liable to have an insufficient triboelectric charge leading to image defects due to charging failure because of a low opportunity of contact between the toner particles and the friction member and the magnetic toner particles used contain much magnetic powder exposed to the toner particle surfaces.
Japanese Laid-Open Patent Application (JP-A) 55-18656 and others have proposed a jumping developing method, wherein a magnetic toner is applied as a very thin coating layer, then triboelectrically charged and then brought to very proximity to an electrostatic image to develop the electrostatic image. This method is excellent in that the magnetic toner is applied in a very thin layer on the sleeve to increase the opportunity of contact between the sleeve and the toner, thereby allowing a sufficient triboelectric charge. However, such a developing method using an insulating magnetic toner is accompanied with uncertain factors inherent to the use of an insulating magnetic toner. Such uncertain factors are caused by exposure of a portion of magnetic fine powder mixed and dispersed in a substantial amount in the insulating magnetic toner, and as a result, several performances, such as developing performance and durability, required of a magnetic toner, are changed or deteriorated.
It is considered that the above-mentioned problem encountered in the case of using a conventional magnetic toner containing magnetic powder has been principally caused by exposure of the magnetic powder to the magnetic toner surface. More specifically, if magnetic powder having a relatively low resistivity is exposed to the surface of magnetic toner particles principally composed of a resin having a larger resistivity, toner performance lowering are caused, such as a lowering in toner chargeability, lowering in toner flowability, and a lowering in image density or occurrence of a density irregularity called sleeve ghost caused by liberation of the magnetic powder due to friction between individual toner particles and between toner particles and the regulating member during a long term of use. Hitherto, proposals have been made regarding magnetic iron oxide contained in magnetic toners, but have left problems yet to be solved.
For example, JP-A 62-279352 has proposed a magnetic toner containing silicon-containing magnetic iron oxide. In the magnetic iron oxide, silicon (element) is intentionally incorporated at an inner part of magnetic iron oxide particles, but the flowability of a magnetic toner containing the magnetic iron oxide has still left a room for improvement.
Japanese Patent Publication (JP-B) 3-9045 has proposed to control the shape of magnetic iron oxide particles into a spherical one by adding a silicate salt. As a result of the use of a silicate salt for particle shape control, the magnetic iron oxide particles contain much silicon inside thereof and have little silicon at the surfaces, thereby having a smooth surface, so that the resultant toner is caused to have somewhat improved flowability but the adhesion between the magnetic iron oxide particles and the binder resin constituting the magnetic toner is insufficient.
JP-A 61-34070 has proposed a process for producing triiron tetroxide characterized by addition of a hydrosilicate solution during oxidation to triiron tetroxide. The triiron tetroxide obtained through this process retains Si at proximity to its surface, but the Si is present in a layer proximate to the surface, so that the surface thereof is weak against a mechanical impact such as abrasion.
On the other hand, a toner is generally produced through the pulverization process, wherein toner ingredients such a a binder resin, a colorant, etc., are melt-kneaded for uniform dispersion, pulverized and classified to recover toner particles of a desired particle size. According to this process, however, the range of material selection is restricted if toner particle size reduction is intended. For example, it is necessary that the colorant-dispersed resin is sufficiently fragile and can be finely pulverized by an economically feasible apparatus. As a result of providing a fragile colorant-dispersed resin from this requirement, an actual high-speed pulverization of the colorant-dispersed resin is liable to result in particles of a broad particle size range, particularly including a relatively large proportion of fine powder fraction (excessively pulverized particles). Moreover, a toner of such a highly fragile material is liable to be further fine pulverization or powder formation during its use as a developer in a copying machine, etc.
Further, according to toner production by the pulverization process, it is difficult to completely uniformly disperse solid particles, such as magnetic powder or colorant into a resin, and a lower degree of dispersion is liable to result in increased fog and a lower image density. Further, the pulverization process essentially and inevitably results in exposure of magnetic iron oxide particles to the toner particle surfaces, thus leaving problems regarding toner flowability and charging stability in a severe environment.
Thus, the pulverization process essentially poses a limit in production of small-size toner particles required for high resolution and high-quality images, as it is accompanied with inevitable problems regarding uniform chargeability and flowability of the toner.
On the other hand, as the toner particle size is reduced, the particle size of the magnetic material used therefor is necessarily reduced correspondingly. For example, as for magnetite which is a magnetic material having a wide applicability and also functioning as a colorant, a higher coloring power is given at a smaller particle size and a smaller p
Chiba Tatsuhiko
Hashimoto Akira
Komoto Keiji
Kukimoto Tsutomu
Magome Michihisa
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