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US005843610A [ii] Patent Number:  Date of Patent:
 MAGNETIC PARTICLES FOR MAGENTIC TONER AND PROCESS FOR PRODUCING THE SAME
 Inventors: Naoki Uchida; Kazuo Fujioka; Koso Aoki; Hiromitsu Misawa; Minoru Kozawa, all of Hiroshima-ken, Japan
 Assignee: Toda Kogyo Corporation, Japan
 Appl. No.: 955,104
 Filed: Oct. 21, 1997
Related U.S. Application Data
 Division of Ser. No. 664,088, Jun. 14, 1996.  Foreign Application Priority Data
Jun. 15, 1995 [JP] Japan 7-174202
 Int. CI.6 G03G 9/083
 U.S. CI 430/106.6
 Field of Search 430/106.6, 108
 References Cited
U.S. PATENT DOCUMENTS
4,952,617 8/1990 Ayala et al 106/456
4,992,191 2/1991 Mori et al 252/62.59
5,055,136 10/1991 Wiese et al 106/456
5,422,215 6/1995 Takagi et al 430/106.6
5,424,810 6/1995 Tomiyiama et al 355/251
5,470,660 11/1995 Misawa et al 252/62.59
5,599,627 2/1997 Aoki et al 252/62.59
U.S. Patent Dec. 1, 1998 Sheet 1 of 2 5,843,610
U.S. Patent Dec. 1, 1998 Sheet 2 of 2 5,843,610
MAGNETIC PARTICLES FOR MAGENTIC
TONER AND PROCESS FOR PRODUCING
This is a rule 60 division of application Ser. No. 08/664, 5 088, filed Jun. 14, 1996, now pending.
BACKGROUND OF THE INVENTION
The present invention relates to magnetic particles for a magnetic toner and a process for producing the same. More 1° particularly, the present invention relates to magnetic iron oxide containing Fe2+ particles (magnetic Fe2+-containing iron oxide particles) for a magnetic toner, which have an excellent fluidity and a high coercive force, which can suppress background development and, hence, produce a :5 high resolution when the magnetic Fe2+-containing iron oxide particles are used for a magnetic toner, and which have a high black chromaticity due to a high Fe2+ content. The present invention also relates to a process for producing such magnetic iron oxide particles. 20
A development process using, as a developer, composite particles which are produced by mixing and dispersing magnetic particles such as magnetite particles with a resin without using a carrier, in other words, what is called a one component magnetic toner is well known and generally used 25 as one of the electrostatic latent image development processes.
With the recent improvement of the performances of copying machines such as a miniaturization of an electro- ^ static copying machine and an increase in the copying speed, the improvement of the properties of a magnetic toner as a developer has been keenly demanded. That is, a magnetic toner composed of small-diameter particles which can suppress background development and hence, produce a high 3J resolution is in strong demand. Spherical magnetic particles which have conventionally been used have a low coercive force, so that when the magnetic particles are used for a magnetic toner composed of small-diameter particles, they are suffering from the following problem. Since the magnetic attraction is lowered, the toner is difficult to stir on a sleeve and difficult to be uniformly charged. As a result, the toner which is insufficiently charged causes background development.
To solve this problem, magnetic particles having a high 45 coercive force and an excellent fluidity are now eagerly demanded.
Since the fluidity of a magnetic toner is largely dependent upon the surface state of the magnetic particles which are exposed to the surface of the toner, it is necessary that the 50 magnetic particles themselves have an excellent fluidity. Angular magnetic particles such as octahedral and hexahedral magnetic particles have a poor fluidity, and when the angular magnetic particles are produced into a magnetic toner, the toner also has a poor fluidity. On the other hand, 55 roundish magnetic particles have a good fluidity, and when the roundish magnetic particles are produced into a magnetic toner, the toner also has a good fluidity.
Therefore, roundish magnetic particles such as spherical magnetic particles, which can produce a magnetic toner 60 having a good fluidity, are now required as a material.
It is known that the black chromaticity of magnetic particles is chiefly influenced by the Fe2+ content when the magnetic particles are magnetite particles having a size of about 0.1 to 0.5 fim which are used for a magnetic toner, as 65 described in pp. 239 to 240 of Powder and Powder Metallurgy, Vol 26, No. 7, as "The black chromaticity of a
sample is influenced by the Fe(II) content and the average particle size, and powder having an average particle size of 0.2 fim is bluish black powder, and it is the most suitable as a black pigment.... Every sample containing not less than 10% of Fe(II) has a black color although there is a slight difference in black chromaticity. If the Fe(II) content is lowered to less than 10%, the color of each sample changes from black to reddish brown."
Fe2+-containing iron oxide particles having a high Fe2+ content and a high black chromaticity are, therefore, required.
Examples of the magnetic particles used as magnetic particles for a magnetic toner are octahedral magnetite particles (Japanese Patent Publication (KOKOKU) No. 44-668(1969)) and spherical magnetite particles (Japanese Patent Publication (KOKOKU) No. 62-51208(1987)). The conventional spherical and octahedral magnetite particles, however, do not have sufficient properties, as described in Japanese Patent Application Laid-Open (KOKAI) No. 3-201509(1991), as "The Fe2+ content of octahedral magnetite particles is about 0.3 to 0.45 in a molar ratio with respect to Fe3+, and although they are excellent in the black chromaticity, they have such a large residual magnetization that they are apt to cause magnetic cohesion, so that they have a poor dispersibility and they do not mix well with a resin .... Spherical magnetite particles have such a small residual magnetization that they are reluctant to magnetic cohesion, so that they have an excellent dispersibility and they mix well with a resin. However, since the Fe2+ content is about 0.28 at most in molar ratio with respect to Fe3+, the particles have a slightly brownish black color, in other words, they are inferior in black chromaticity . . . ."
Although hexahedral magnetite particles are proposed (Japanese Patent Application Laid-Open (KOKAI) No. 3-201509(1991)), since the hexahedral magnetite particles are angular, the fluidity cannot be said to be sufficient.
A manufacturing process including the step of adding silicon component during the reaction for producing magnetite in order to improve the properties of magnetite particles have conventionally been investigated. The processes proposed are, for example, a process (Japanese Patent Application Laid-Open (KOKAI) No. 5-213620(1993)) for producing magnetite particles comprising the steps of adding a silicon component to a solution of a ferrous salt, mixing 1.0 to 1.1 equivalents of an alkali with respect to iron to the resultant solution, carrying out an oxidation reaction while maintaining the pH at 7 to 10, adding iron in the middle of the reaction so that the iron is 0.9 to 1.2 equivalents based on the initial alkali, and carrying out an oxidation reaction while maintaining the pH at 6 to 10; and a process (Japanese Patent Publication (KOKOKU) No. 3-9045 (1991)) for producing spherical magnetite particles by blowing an oxygen-containing gas into an aqueous reaction solution of a ferrous salt containing a ferrous hydroxide colloid which is obtained by reacting 0.80 to 0.99 equivalent of an alkali hydroxide with respect to Fe2+ by a two-staged reaction comprising the steps of adding 0.1 to 5.0 atm % of a water-solluble silicate (calculated as Si) based on Fe so as to produce magnetite nuclear particles and adding not less than 1.00 equivalent of an alkali hydroxide with respect to the remaining Fe2+.
The magnetite particles obtained by the above-described processes are, for example, magnetite particles (Japanese Patent Application Laid-Open (KOKAI) No. 5-213620 (1993)) which contain a silicon component inside the particles, which have 0.1 to 2.0 wt % of a silicon component