Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-04-13
2002-05-07
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000, C428S195100, C428S199000, C428S208000, C428S690000, C428S690000, C428S900000, C430S106100, C430S108200, C430S111400
Reexamination Certificate
active
06383637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to black magnetic iron oxide particles and a process for producing the black magnetic iron oxide particles, and more particularly, to black magnetic iron oxide particles not only having a sufficient blackness and excellent electrical properties, flowability and electrification property (charging property), but also exhibiting a good compatibility with binder resins such as aromatic vinyl-based resins, acrylic-based resins and copolymer resins thereof, and a good dispersibility in these resins for a magnetic toner, a process for producing the particles, and a magnetic toner using the black magnetic iron oxide particles.
Hitherto, as one of electrostatic latent image development methods, there is well known a development method using a so-called one component magnetic toner as a developer, which contains no carrier and comprises composite particles obtained by mixing and dispersing black magnetic iron oxide particles such as magnetite particles in resins.
With recent tendency toward high speed and high image quality in laser beam printers or digital copying machines, it has been strongly demanded to improve properties of a magnetic toner used therein as a developer. For this reason, the magnetic toner has been required to show not only an improved electrification property and a high flowability, but also stable charging amount and flowability even upon change in environmental conditions such as temperature or humidity.
Due to the fact that the electrification property of the magnetic toner has a close relationship to electrical properties of black magnetic iron oxide particles used therein, it has been strongly demanded to provide black magnetic iron oxide particles having excellent electrical characteristics.
Thus, it has been required that the properties of the black magnetic iron oxide particles are further improved in order to enhance the electrification property of the magnetic toner.
More specifically, in order to obtain a magnetic toner having an excellent electrification property, it is necessary that the black magnetic iron oxide particles used therein have a sufficient blackness, a higher dispersibility and more excellent electrical properties.
In “POWDER AND POWDER METALLURGY”, vol. 26, No. 7, pp. 239-240, it is described that “the degree of blackness of the specimen varies depending upon the content of Fe(II) and the average particle diameter, and particles having an average particle diameter of 0.2 &mgr;m are bluish black and, therefore, are most suitable as black pigments . . . when the content of Fe(II) is not less than 10%, all specimens exhibit a black color though the degrees of blackness thereof are slightly different from each other, and when the content of Fe(II) is reduced to less than 10%, the color of the specimen is changed from black to reddish brown”. As described in the above literature, it is known that the properties of black magnetic iron oxide particles for magnetic toner having a particle diameter of about 0.1 to about 0.5 &mgr;m, varies depending upon mainly the content of Fe
2+
(FeO). Thus, the black magnetic iron oxide particles have been required to have a large FeO content and a high blackness.
The dispersibility of the black magnetic iron oxide particles largely depends upon the surface conditions thereof. Therefore, in order to improve the surface conditions of the black magnetic iron oxide particles and to enhance the dispersibility thereof, it has been attempted to coat surfaces of the black magnetic iron oxide particles with a silicon compound or an aluminum compound. In addition, the black magnetic iron oxide particles tend to be magnetically agglomerated due to fineness thereof, resulting in the deterioration of the blending property with resins. Consequently, it has been required to prevent the black magnetic iron oxide particles from being magnetically agglomerated.
Also, the electrification property of the magnetic toner largely depends upon the surface conditions of the black magnetic iron oxide particles exposed to the surface of the magnetic toner. In particular, FeO contained in the black magnetic iron oxide particles acts for reducing an electrical resistance of the magnetic toner, so that the electrification property of the magnetic toner is considerably influenced by the content of FeO and the distribution of FeO in each particle. In this regard, Japanese Patent Application Laid-Open (KOKAI) No. 4-338971 describes that “the distribution condition of Fe(II) in the surface layer of magnetic iron oxide more highly contributes to stable frictional electrification property of the obtained toner under various environmental conditions rather than the FeO content therein”.
As described above, in order to enhance the dispersibility and electrical properties of the black magnetic iron oxide particles, it is necessary to optimize the FeO content and the abundance of FeO in the surface layer of each black magnetic iron oxide particle.
The magnetic toner has been produced by mixing the magnetic particles with aromatic vinyl resins such as styrene resins or vinyl toluene resins, acryl-based resins such as acrylic resins or methacrylic resins, and copolymer resins thereof. Therefore, the magnetic particles have been required to have an excellent dispersibility in these resins.
In the production of the magnetic toner, when the magnetic particles are kneaded with resins, it is difficult to sufficiently disperse the magnetic particles in resins since the magnetic particles have a hydrophilic surface, so that the magnetic particles are present in the form of agglomerated particles in resins after the kneading. When the non-uniform mixture is pulverized into such a size as required for a magnetic toner, there arise problems such as generation of a magnetic powder from agglomerated particles upon the pulverization or different contents of the magnetic particles in individual toner particles, thereby failing to obtain particles having excellent properties as a magnetic toner.
Consequently, in order to improve the surface conditions of the magnetic particles and to enhance the dispersibility thereof, it has been attempted to coat the surfaces of the magnetic particles with various coupling agents such as silane-based coupling agents and titanium-based coupling agents, or various metal compounds such as aluminum compounds and silicon compounds. Also, the magnetic particles are fine particles and, therefore, tend to be magnetically agglomerated together, resulting in deteriorated blending property with resins. Therefore, it has been required to inhibit the magnetic particles from being magnetically agglomerated together.
The flowability of the magnetic toner largely depends upon the surface conditions of the magnetic iron oxide particles exposed to the surface of the magnetic toner. Therefore, it has been required that the magnetic iron oxide particles themselves show an excellent flowability.
The magnetic toner tends to suffer from inherent drawbacks such as deteriorated flowability due to high resistance thereof. For this reason, it has been attempted to modify the surface of the magnetic toner or the surfaces of the magnetic particles contained in the magnetic toner, or enhance the flowability of the magnetic toner by adding external additives into the magnetic toner.
The magnetic toner is required to exhibit stable properties even upon any change in environmental conditions, for example, under high temperature and high humidity conditions or under low temperature and low humidity conditions. Thus, it has been strongly demanded to provide a magnetic toner capable of constantly showing stable flowability and charging amount.
Conventionally, it has been attempted to improve the dispersibility and electrical properties of the black magnetic iron oxide particles by limiting the FeO content thereof to a specific range (Japanese Patent Application Laid-Open (KOKAI) Nos. 58-189646(1983), 3-201509(1991), 4-338971(1992), 4-141664(1992) and 11-30877(1999)).
At present, it has been strongly de
Aoki Koso
Kozawa Minoru
Misawa Hiromitsu
Miura Suehiko
Shimo Nobuya
Kiliman Leszek
Nixon & Vanderhye
Toda Kogyo Corporation
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