Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2001-05-22
2003-07-22
Nguyen, Cam (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S618000, C423S632000, C502S325000, C502S326000, C502S338000, C502S352000
Reexamination Certificate
active
06596255
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to tin-containing granular magnetic oxide particles and a process for producing the same, and more particularly, to tin-containing granular magnetic oxide particles having a high blackness, a small magnetization value and an excellent dispersibility, and a process for producing such particles. The tin-containing granular magnetic oxide particles of the present invention are useful as a color pigment for paints, printing inks, rubbers and plastics, a magnetic toner material, a magnetic carrier material or the like.
Granular magnetic oxide particles showing a good blackness have been extensively used as black color pigment for paints, printing inks, rubbers and plastics. Further, the granular magnetic oxide particles are ferromagnetic particles and, therefore, have also been used as magnetic particles for magnetic toner and magnetic carrier employed in electrostatic copying systems, e.g., in the form of composite particles prepared by mixing and dispersing the granular magnetic oxide particles in resin.
Various properties of a coating film containing a color pigment are varied depending upon dispersibility of the pigment in the coating film. For example, when the pigment has a good dispersibility in vehicle or resin, it is possible to not only obtain a coating film having a clear color tone, but also improve properties of the pigment particles such as tinting property and hiding property. Further, the obtained coating film is enhanced in gloss, clearness, mechanical properties and air-impermeability, resulting in high durability of the coating film. Therefore, the pigment particles are required to exhibit an excellent dispersibility in vehicle or resin.
Also, with the recent tendency toward miniaturization and higher-speed performance of electrostatic copying machines, it has been demanded to provide a magnetic toner and a magnetic carrier capable of exhibiting excellent properties such as a high density development and a high definition. These properties have a close relationship with various properties and dispersibility of magnetic particles contained in resin.
For example, when the amount of the magnetic particles contained in the magnetic toner is increased in order to achieve the high density development, the magnetic particles tend to be magnetically agglomerated together, so that the magnetic toner is attached onto a developed latent image in the form of massive particles, thereby failing to accurately develop fine latent images and reproduce images having a high definition. In addition, when the magnetic particles have a poor dispersibility in resin, the magnetic particles are inhibited from being uniformly dispersed in the resin, so that the resultant magnetic toner particles become magnetically non-uniform, or the content of the magnetic particles in the magnetic toner is lowered. As a result, it is not possible to achieve the high density development and obtain images having a high definition.
Further, in order to obtain images having a high density and a high definition, it has been required not only to minimize a magnetization value of the magnetic particles so as not to generate a magnetic alloy agglomerated together even when the amount of the magnetic particles contained in resin is increased, but also to maximize the Fe
2+
content of the magnetic particles so as to enhance dispersibility of the magnetic particles in resin and attain a sufficient blackness.
The granular magnetic oxide particles having a small magnetization value are produced by mixing an alkaline aqueous solution such as an aqueous sodium hydroxide solution in an aqueous ferrous salt solution such as an aqueous ferrous sulfate solution to neutralize the aqueous ferrous salt solution; adding an aqueous solution containing a zinc compound such as zinc hydroxide to the mixed solution; and then passing an oxidative gas through the resultant mixture at a temperature of 60 to 100° C. (Japanese Patent Application Laid-Open (KOKAI) No. 4-184354 (1992)). However, the granular magnetic oxide particles obtained by the above method have a small Fe
2+
content and, therefore, fail to show a sufficient blackness.
In addition, the granular magnetic oxide particles having a small magnetization value are produced by mixing 24.0 to 99.2% by weight of hematite or a mixture of hematite and magnetite, 0.8 to 76.0% by weight of a Sn compound (calculated as Sn) and 0.1 to 4.0% by weight of a liquid or solid substance containing —C—C— or —C═C— in a molecule thereof; and sintering the resultant mixture at a temperature of 1,200 to 1,450° C. in an inert gas atmosphere (Japanese Patent Application Laid-Open (KOKAI) No. 7-115009(1995)). However, since the granular magnetic oxide particles obtained by the above method are sintered at as high a temperature as 1,200 to 1,450° C., it has been found that as a dispersion characteristic a depth of a groove of at which three or more continuous lines each having a length of not less than 10 mm are developed in a pigment dispersion test using a grind-meter when measured by Hoover's muller method according to JIS K5101 (1991) 9.1, is as large as 100 &mgr;m. This indicates that the granular magnetic oxide particles obtained by the conventional method is deteriorated in dispersibility.
Further, the magnetic oxide particles having a good dispersibility are produced by adding to an aqueous ferrous salt solution, a silicon salt and a salt of at least one metal element selected from the group consisting of Mn, Zn, Ni, Cu, Co, Cr, Cd, Al, Sn and Mg in an amount of 0.2 to 4.0% by weight based on the weight of iron element contained in the ferrous salt; adding an alkaline aqueous solution such as an aqueous sodium hydroxide solution to the obtained mixed aqueous solution; passing air through the obtained aqueous solution containing ferrous hydroxide while maintaining the pH value thereof to not less than 7 to oxide ferrous hydroxide, thereby obtaining a magnetic iron oxide seed crystal; adding an aqueous ferrous salt solution such as an aqueous ferrous sulfate solution to the aqueous solution; and then passing air through the resultant solution while maintaining the pH value thereof to 6 to 10 to growth the magnetic iron oxide seed crystal (Japanese Patent Application Laid-Open (KOKAI) No. 11-249335(1999)). However, in this KOKAI, it is suggested that the content of the salt of at least one metal element selected from the group consisting of Mn, Zn, Ni, Cu, Co, Cr, Cd, Al, Sn and Mg is increased, the obtained magnetic oxide particles tend to be deteriorated in dispersibility.
As a result of the present inventors' earnest studies to solve the above problem, it has been found that by mixing an aqueous ferrous salt solution, an aqueous solution containing a tin compound in an amount of 10 to 30 mol % (calculated as Sn) based on ferrous iron and an aqueous alkali solution, thereby obtaining a suspension containing Fe- and Sn-containing precipitates; and then subjecting the resultant suspension containing Fe- and Sn-containing precipitates to hydrothermal treatment, the obtained tin-containing granular magnetic oxide particles can exhibit a high blackness, a small magnetization value and an excellent dispersibility. The present invention has been attained based on the above finding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide granular magnetic oxide particles exhibiting a sufficient blackness, a small magnetization value and an excellent dispersibility, and a process for producing such granular magnetic oxide particles.
To accomplish the aim, in a first aspect of the present invention, there are provided tin-containing granular magnetic oxide particles comprising spinel-type crystal represented by the formula:
Fe
3-x
Sn
x
O
4
wherein x is 0.14 to 0.48, and
having a Fe
2+
content of 17 to 22% by weight, a lattice constant of 8.41 to 8.49 Å, a magnetization value of 20 to 50 Am
2
/kg when measured under an applied magnetic field of 79.6 kA/m, and a depth of a groove of not m
Kageyama Hiroyuki
Misawa Hiromitsu
Nakamura Tatsuya
Tabuchi Mitsuharu
Takeuchi Tomonari
National Institute of Advanced Industrial Science and Technology
Nguyen Cam
Nixon & Vanderhye P.C.
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