Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-01-22
2004-08-24
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C252S062560, C252S062580, C252S062590, C252S062600, C252S062620, C252S062630, C106S456000, C428S403000
Reexamination Certificate
active
06780555
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to black magnetic iron oxide particles and a magnetic toner, and more particularly, to black magnetic iron oxide particles having not only excellent blackness and electrification property, but also excellent environmental stability capable of maintaining a stable charge amount thereon even under low-temperature and low-humidity conditions or high-temperature and high-humidity conditions, and a magnetic toner using the black magnetic iron oxide particles.
The black magnetic iron oxide particles of the present invention have a black color and, therefore, are useful as black color pigments for paints, printing inks, rubber or resin compositions, or the like, and further as black magnetic particles for magnetic toner.
Magnetite particles are known as typical black pigments, and have been generally used for a long time as colorants for paints, printing inks, cosmetics, rubber or resin compositions, or the like.
In particular, the magnetite particles have been more frequently used as black magnetic iron oxide particles for magnetic toners of one component system in which composite particles obtained by mixing and dispersing black magnetic iron oxide particles in resin are used as a developer.
With recent tendency toward high-speed copying and high-image quality for laser beam printers or digital copying machines, it has been strongly required to improve properties of a magnetic toner used as a developer. For this purpose, the magnetic toner has been required to exhibit not only a sufficient blackness and an improved electrification property, but also an excellent environmental stability capable of maintaining a stable charge amount thereon without any adverse influence due to change in temperature or humidity.
Also, in order to satisfy the above requirements of the magnetic toner, it has been strongly required to improve properties of black magnetic iron oxide particles used in the magnetic toner.
Namely, in order to obtain magnetic toners exhibiting excellent blackness, electrification property and environmental stability, the black magnetic iron oxide particles used therein have been required not only to have a sufficient blackness and an adequate FeO content as well as more excellent dispersibility and electrical properties, but also to exhibit an excellent environmental stability.
It is known that the blackness of the black magnetic iron oxide particles varies depending upon the amount of Fe
2+
(FeO) contained therein. Therefore, in order to obtain the particles having an excellent blackness, the FeO content thereof has been required to be large.
In the consideration of good electrical properties, it is preferred that the black magnetic iron oxide particles have a small FeO content. Namely, the electrical resistance value of the black magnetic iron oxide particles varies depending upon the FeO content. The larger the FeO content, the lower the electrical resistance value, so that it is difficult to use the black magnetic iron oxide particles as a starting material of the magnetic toner. Therefore, the black magnetic iron oxide particles are required not only to exhibit well-balanced blackness and electrical resistance, but also to have an adequate blackness and a high electrical resistance.
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, as described above, FeO contained in the black magnetic iron oxide particles acts for reducing an electrical resistance of the magnetic toner. Therefore, the electrification property of the magnetic toner is considerably influenced by the content of FeO and the distribution of FeO in each black magnetic iron oxide 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 magnetic toner under various environmental conditions rather than the FeO content”.
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 enhance the dispersibility thereof, it has been attempted to coat surfaces of the black magnetic iron oxide particles with a silicon compound, an aluminum compound or the like. In addition, the black magnetic iron oxide particles are fine particles and, therefore, tend to be magnetically agglomerated, 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.
Further, the magnetic toner is required to exhibit stable properties even upon any change in environmental conditions, for example, under low-temperature and low-humidity conditions or under high-temperature and high-humidity conditions. For this reason, the black magnetic iron oxide particles used in the magnetic toner have been strongly required to have an excellent environmental stability and constantly exhibit a stable charge amount.
Hitherto, it has been attempted to improve various properties of the black magnetic iron oxide particles by incorporating different kinds of elements other than iron thereinto, and coating the surface thereof with a plurality of layers (Japanese Patent Application Laid-Open (KOKAI) Nos. 7-240306(1995), 7-267646(1995), 8-48524(1996), 8-50369(1996), 8-101529(1996), 11-157843(1999), 11-189420(1999), 11-314919(1999), 2000-239021, 2000-272923, 2000-335920, 2000-335921, 2000-344527, 2000-344528 and 2000-10821, or the like).
At present, it has been strongly demanded to provide black magnetic iron oxide particles satisfying various properties described above. However, black magnetic iron oxide particles capable of fulfilling these requirements cannot be obtained conventionally.
That is, Japanese Patent Application Laid-Open (KOKAI) No. 7-240306(1995) describes magnetic particles containing silicon inside thereof, having a co-precipitate of silica and alumina present on the surface thereof, and further having fine non-magnetic oxide particles or fine non-magnetic oxide hydroxide particles adhered onto the co-precipitate, which comprise an element selected from the group consisting of Fe, Ti, Zr, Si and Al. Thus, the magnetic particles have an outermost layer composed of the fine non-magnetic particles and, therefore, fail to form a ferrite structure, thereby failing to show an excellent environmental stability.
In Japanese Patent Application Laid-Open (KOKAI) No. 7-267646(1995), it is described that magnetite particles have an outer-shell portion containing at least one metal element selected from the group consisting of Zn, Mn, Cu, Ni, Co, Mg, Cd, Al, Cr, V, No, Ti and Sn. However, since the magnetite particles have a two phase structure, the electrical resistance value thereof is low, and the build-up of electrification and the electrification stability thereof are unsatisfactory.
Japanese Patent Application Laid-Open (KOKAI) No. 8-48524(1996) describes magnetite particles successively coated with an iron-zinc oxide thin film and an iron-silicon oxide thin film on the surface thereof. The magnetite particles show a low electrical resistance value since the outermost layer thereof is not composed of spinel iron oxide containing different kinds of metal elements. Further, the build-up of electrification as well as the electrification stability thereof are unsatisfactory.
Japanese Patent Application Laid-Open (KOKAI) No. 8-50369(1996) describes magnetic particles containing silicon locally present on the surface portion thereof and further containing Zn, Mg or Mn. However, the magnetic Particles not only show a low electrical resistance value, but also are unsatisfactory in build-up of electrification as well as electrification stability. Further, the
Aoki Koso
Kouzawa Minoru
Misawa Hiromitsu
Miura Suehiko
Uchida Naoki
Nixon & Vanderhye P.C.
Rodee Christopher
Toda Kogyo Corporation
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