Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-02-12
2003-05-13
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...
C430S106200, C428S405000, C428S407000
Reexamination Certificate
active
06562532
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a black magnetic toner and black magnetic composite particles for the black magnetic toner, and more particularly, to black magnetic composite particles for high-resistant black magnetic toner, which are not only more excellent in fluidity and blackness but also show an excellent dispersibility in a binder resin due to a less amount of carbon black desorbed or fallen-off from the surface of each particle; a process for producing the black magnetic composite particles; and a high-resistant black magnetic toner using the black magnetic composite particles which is more excellent in fluidity and blackness.
As one of conventional electrostatic latent image-developing methods, there has been widely known and generally adopted a so-called one component system development method of using as a developer, a magnetic toner comprising composite particles prepared by mixing and dispersing magnetic particles such as magnetite particles in a resin, without using a carrier.
The conventional development methods of using one-component magnetic toner have been classified into CPC development methods of using a low-resistance magnetic toner, and PPC development methods of using a high-resistant magnetic toner.
In the CPC methods, the low-resistance magnetic toner used therefor has an electric conductivity, and is charged by the electrostatic induction due to electric charge of the latent images. However, since the charge induced on the magnetic toner is lost while the magnetic toner is transported from a developing zone to a transfer zone, the low-resistance magnetic toner is unsuitable for the PPC development method of using an electrostatic transfer method. In order to solve this problem, there have been developed the insulated or high-resistant magnetic toners having a volume resistivity as high as not less than 1×10
13
&OHgr;·cm.
As to the insulated or high-resistant magnetic toner, it is known that the developing characteristics thereof are affected by magnetic particles exposed to the surface of the magnetic toner, or the like.
Recently, with the high image quality such as high image density or high tone gradation, or with the high copying speed of duplicating machines, it has been strongly demanded to further enhance characteristics of the insulted or high-resistant magnetic toners as a developer, especially a fluidity thereof.
With respect to such demands, in Japanese Patent Application Laid-Open (KOKAI) No. 53-94932(1978), there has been described “these high-resistant magnetic toners are deteriorated in fluidity due to the high electric resistance, so that there arises such a problem that non-uniformity of developed images tend to be caused. Namely, although the high-resistant magnetic toners for PPC development method can maintain necessary charges required for image transfer, the magnetic toners are frictionally charged even when they are present in other steps than the transfer step, where the magnetic toners are not required to be charged, e.g., in a toner bottle or on the surface of a magnetic roll, or also slightly charged by mechano-electrets during the production process of these magnetic toners. Therefore, the magnetic toners tend to be electrostatically agglomerated, resulting in deterioration of fluidity thereof”, and “It is an another object of the present invention to provide a high-resistant magnetic toner for PPC development method which is improved in fluidity, can be prevented from causing non-uniformity of developed images, and has an excellent image definition and tone gradation, thereby obtaining high-quality copies by indirect copying methods”.
In recent years, with the reduction in particle size of the insulated or high-resistant magnetic toners, it has been increasingly required to enhance the fluidity thereof.
With respect to such a fact, in “Comprehensive Data Collection for Development and Utilization of Toner Materials” published by Japan Scientific Information Co., Ltd., page 121, there has been described “With extensive development of printers such as ICP, a high image quality has been required. In particular, it has been demanded to develop high-precision or high-definition printers. In Table 1, there is shown a relationship between definitions obtained by using the respective toners. As is apparent from Table 1, the smaller the particle size of wet toners, the higher the image definition is obtained. Therefore, when a dry toner is used, in order to enhance the image definition, it is also required to reduce the particle size of the toner . . . As reports of using toners having a small particle size, it has been proposed that by using toners having a particle size of 8.5 to 11 &mgr;m, fogs on a background can be improved and toner consumption can be reduced, and further by using polyester-based toners having a particle size of 6 to 10 &mgr;m, an image quality, a charging stability and lifetime of the developer can be improved. However, when such toners having a small particle size are used, it has been required to solve many problems. There are problems such as improvement in productivity, sharpness of particle size distribution, improvement in fluidity, etc.”.
Further, black magnetic toners widely used at the present time, have been required to show a high degree of blackness and a high image density for line images and solid area images on copies.
With respect to this fact, on page 272 of the above-mentioned “Comprehensive Data Collection for Development and Utilization of Toner Materials”, there has been described “Powder development is characterized by a high image density. However, the high image density as well as the fog density as described hereinafter, greatly influences image characteristics obtained”.
There is a close relationship between properties of the magnetic toner and those of the magnetic particles mixed and dispersed in the magnetic toner.
That is, the fluidity of the magnetic toner is largely varied depending upon surface condition of the magnetic particles exposed to the surface of the magnetic toner. Therefore, the magnetic particles themselves have been strongly required to show an excellent fluidity.
The degree of blackness and density of the magnetic toner are also largely varied depending upon the degree of blackness and density of the magnetic particles as a black pigment contained in the magnetic toner.
As the black pigment, magnetite particles have been widely used from the standpoints of magnetic properties such as saturation magnetization or coercive force, low price, color tone or the like. In addition to the magnetite particles, carbon black fine particles may be added. However, in the case where the carbon black fine particles are used in a large amount, the volume resistivity thereof is lowered to less than 1.0×10
13
&OHgr;·cm, so that it is not possible to use the obtained toner as an insulated or high-resistant magnetic toner. Further, the dispersibility of the magnetite particles in the binder resin is deteriorated.
Hitherto, in order to enhance the fluidity of the black magnetic toner, there have been many attempts of improving the fluidity of the magnetite particles mixed and dispersed in the magnetic toner. For example, there have been proposed (1) a method of forming spherical-shaped magnetite particles (Japanese Patent Application Laid-Open (KOKAI) No. 59-64852(1984)), (2) a method of exposing a silicon compound to the surface of magnetite particles (Japanese Patent Publication (KOKOKU) No. 8-25747(1996)), or the like.
Black magnetic composite particles for black magnetic toner, which have not only a more excellent fluidity and blackness, but also an excellent dispersibility in a binder resin, are presently strongly demanded. However, black magnetic composite particles capable of satisfying all of these requirements have not been obtained yet.
Namely, the above-mentioned spherical magnetite particles show a higher fluidity than those of cubic magnetite particles, octahedral magnetite particles or the like. However, the fluidity of the sph
Hayashi Kazuyuki
Ishitani Seiji
Morii Hiroko
Tanaka Yasuyuki
Nixon & Vanderhye P.C.
Rodee Christopher
Toda Kogyo Corporation
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