JPH06130720A - Magnetic granular powder for magnetic toner and its production - Google Patents

Abstract

PURPOSE:To produce the magnetic granular powder for the magnetic toner having a large residual magnetization and excellent in fluidity. CONSTITUTION:One hundred pts.wt. of an octahedral spinel-structure iron oxide granular powder having a BET specific surface shown by 6/(rho.d3)XPHIs (rho is the sp.gr. of the spinel-structure iron oxide grain, d3=0.1-0.5mum where d3 is the area mean diameter, and 1.60<PHIs<=1.80 where PHIs is the area shape factor) is admixed with 0.5-3.5 pts.wt., expressed in terms of SiO2, of a fine silica grain to obtain an octahedral spinel-structure iron oxide grain coated with the fine silica grain. In this case, an increment in the BET specific surface is controlled to 1-5m<2>/g and the ratio of the amts. of both grains to 1.0-4.5. The magnetic granular powder for the magnetic toner consists of this octahedral spinel- structure iron oxide granular powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic particle powder for a magnetic toner having a large residual magnetization and excellent fluidity, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as one of electrostatic latent image developing methods, a so-called one in which composite particles obtained by mixing and dispersing magnetic particle powder such as magnetite particle powder in resin without using a carrier is used as a developer. The developing method using a component type magnetic toner is widely known and widely used.

Recently, as the speed of copying machines has increased, there has been a strong demand for improvement of fine line reproducibility and high image quality such as gradation. For that reason, the magnetic toner has a large residual magnetization. Cage,
Moreover, excellent fluidity is strongly required.

Regarding the fluidity of the magnetic toner, Japanese Patent Laid-Open Publication No. Sho 5
Japanese Patent Laid-Open No. 3-94932 discloses that such a high-resistance magnetic toner has high resistance and thus has poor fluidity and tends to cause uneven development. That is, the high-resistance magnetic toner for PPC is transferred. While it is possible to maintain the necessary charging, the toner bottle or the magnetic roll surface, etc. may be charged slightly by friction charging or mechano-electret in the manufacturing process even in processes other than the transfer process where charging is not required. By virtue of the presence of such particles, charge aggregation is likely to occur, which leads to a decrease in fluidity. "" Another object of the present invention is to provide a high resistance magnetic toner for PPC having improved fluidity. Therefore, it is intended to obtain a high-quality indirect type copy which has no development unevenness and is therefore excellent in resolution and gradation. "

In order to obtain the magnetic toner having the above-mentioned characteristics, it is required that the magnetic particle powder has a large residual magnetization and excellent fluidity.

As a magnetic particle powder having a large remanent magnetization, an octahedral spinel type iron oxide particle powder has been conventionally known. The remanent magnetization value of the magnetic particle powder is closely related to the particle size of the magnetic particles, and the remanent magnetization tends to increase as the particle size decreases. Diameter (μm) ×
If expressed by the residual magnetization value (emu / g), 2 (μm · emu /
The value exceeds g).

Regarding the fluidity of magnetic toners, it has hitherto been mainly attempted to improve the fluidity by subjecting the magnetic toner itself to some treatment, for example, a silicon compound which is a fluidity modifier. A method in which fine particles are kneaded with a resin so as to be contained inside or on the surface of the magnetic toner (Japanese Patent Laid-Open No. 53-53113)
-94932, JP-A-59-223451, JP-A-60-26953, JP-A-2-733.
No. 62, Japanese Patent Publication No. 21860/1992) and a method of treating the particle surface of the magnetic toner with fine particles such as a silicon compound as the fluidity modifier (Japanese Patent Laid-Open No. 63-8750).

On the other hand, a method in which silica gel SiO ₂ .nH ₂ O is adhered and bonded to the surface of the magnetic particles so that a silicon compound is present on the surface of the magnetic particle powder for magnetic toner (JP-A-2-73362). There is a method of forming a film of a neutralized product of a silicate compound on the surface of magnetic particles (JP-A-57-201244).

[0009]

The magnetic particle powder for magnetic toner having a large remanent magnetization and excellent fluidity is currently most demanded, but the above-mentioned known methods and In such a case, since the existence form of the silicon compound and the like on the particle surface, the uniformity of the distribution state, the fixing strength, etc. are insufficient, the fluidity of the magnetic particle powder cannot be said to be sufficiently excellent.

This fact will be described below. The method of attaching or coating the fluidity modifier on the particle surface of the magnetic particles is performed by using the silicon compound which is the fluidity modifier because the size of the magnetic particles is larger than the size of the silicon compound which is the fluidity modifier. In comparison with the above-mentioned method of kneading fine particles such as the above with a resin, the silicon compound or the like adhering to the surface of the magnetic particles will be distributed in a large amount on the surface without being buried inside the magnetic toner. As compared with the method described above, the fluidity modifier is less likely to be released, and the fluidity of the magnetic toner is expected to be improved.

However, in the above-mentioned method, silica gel SiO ₂ .nH ₂ O is adhered and bonded to the particle surface of the magnetic particles to suppress the fluctuation of the charge amount due to the humidity fluctuation by utilizing the water absorption and water discharge characteristics of the silica gel. The purpose is to improve the environmental stability by keeping the charge amount constant, and as shown in the comparative example below, the improvement of the fluidity of the magnetic toner is not sufficient.

In the above-mentioned method, since the neutralized product of the silicate compound existing on the surface of the magnetic particles is not in the form of fine particles but in the form of a coating film, the magnetic toner is compared with the case where fine particles are present between the magnetic toners. The fluidity of the magnetic toner cannot be improved because the mutual adhesive force increases.

In the case of the above-mentioned method, when the magnetic toner is charged on the sleeve, the fluidity modifier is applied from the particle surface of the magnetic toner by the contact between the magnetic toners or the impact caused by the contact between the magnetic toner and the sleeve. Fine particles such as certain silicon compounds are desorbed.

Therefore, the present invention has a technical object to improve the fluidity of octahedral spinel iron oxide particles.

[0015]

The above technical problems can be achieved by the present invention as follows. That is, according to the present invention, the general formula 6 / (ρ · d ₃ ) × Φs [ρ: specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) = 0.1 to 0.5 μ
m, 1.60 <Φs (area shape factor) ≦ 1.80] and 100 parts by weight of octahedral spinel iron oxide particle powder having a BET specific surface area of 0.5 to 0.5 of silica fine particles in terms of SiO _2. 3.5 parts by weight of the BET specific surface area obtained by admixing 3.5 parts by weight of the octahedral spinel-type iron oxide particles with the silica fine particles adhering to the surface thereof is ¹ to 5 m ² / Magnetic particle powder for magnetic toner comprising octahedral spinel iron oxide particle powder having a ratio of 1.0 to 4.5 with respect to the amount of silica fine particles, and a general formula. 6 / (ρ ・
d ₃ ) × Φs [ρ: specific gravity of spinel type iron oxide particles, d
₃ (area average diameter) = 0.1-0.5 μm, 1.60 <Φ
s (area shape factor) ≤ 1.80] octahedral spinel iron oxide particle powder 10 having a BET specific surface area of 10
0.5 parts by weight of silica fine particles in an amount of 0 to 3 parts by weight in terms of SiO ₂ .
BET in which the silica fine particles are adhered to the particle surface of the octahedral spinel-type iron oxide particles by adding 5 parts by weight and mixing by compression, shearing and spatula using a wheel type kneader The increase amount of the specific surface area is within the range of 1 to 5 m ² / g with respect to the BET specific surface area value, and the ratio to the amount of the silica fine particles is 1.0 to
A method for producing magnetic particle powder for a magnetic toner, which comprises obtaining an octahedral spinel type iron oxide particle powder having a range of 4.5.

Next, various conditions for carrying out the present invention will be described. The magnetic particle powder according to the present invention has the general formula 6
/ (Ρ · d ₃ ) × Φs [ρ: specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) = 0.1 to 0.5 μm, 1.
60 <Φs (area shape factor) ≦ 1.80] B
0 silica particles in terms of SiO ₂ octahedrally spinel iron oxide particles 100 parts by weight with ET specific surface area.
5 to 3.5 parts by weight are added and mixed, and the increase width of the BET specific surface area formed by adhering the silica fine particles to the particle surface of the octahedral spinel type iron oxide particles is 1 to 5 m with respect to the BET specific surface area value. It is an octahedral spinel-type iron oxide particle powder having a ratio of ² / g and a ratio of 1.0 to 4.5 with respect to the amount of the silica fine particles.

The octahedral spinel type iron oxide particles which are the particles to be treated in the present invention are particles having a shape in which the bottom surfaces of two quadrangular pyramid particles are united with each other and those having a similar shape by observation with a scanning electron microscope. If so, it may be slightly deformed, or the surface may be smooth or uneven, in other words, the area shape factor may be in the range of 1.60 <Φs ≦ 1.80.

The area shape factor 1.60 <Φs ≦
1.80 is obtained from the value of the specific surface area of many particles recognized to fall within the range defined by the octahedron shape, and in the case of true spherical particles, Φs = 1.0.
Based on this, the area shape factor of octahedral grains is 1.6
It is expressed as 0 <Φs ≦ 1.80.

Compositionally, magnetite particles ( F
eO _x · Fe ₂ O ₃ , 0 <x ≦ 1), maghematite particles, divalent metals other than Fe (Mn, Ni, Zn, Cu, M)
So-called ferrite particles containing one or more of g, Co and the like), and any of them can achieve the effects intended by the present invention.

The particle size of the octahedral spinel type iron oxide particle powder in the present invention is 0.1 to 0.5 μm.
If it is less than 0.1 μm, the cohesive force between the magnetic particles is large and the dispersibility becomes difficult, and it becomes difficult to adhere the silica fine particles to the surface of the magnetic particles, and the effect of the present invention cannot be obtained. .

When the particle size exceeds 0.5 μm, the silica fine particles can be attached to the surface of the magnetic particles, but the concentration distribution of the magnetic particles occurs inside or on the surface of the magnetic toner or between the magnetic toner particles. This causes deterioration of image characteristics and the like, and is not preferable as a magnetic toner.

As the octahedral spinel type iron oxide particle powder in the present invention, a known powder may be used, and the remanent magnetization has an area average particle diameter (μm) × remanent magnetization value (emu / g).
If it is shown by, the value is more than 2 (μm · emu / g).

The silica fine particles in the present invention are represented by the general formula (SiO ₂ ) n, and commercially available colloidal silica or hydrophobic silica fine powder may be used.

The silica fine particles preferably have a BET specific surface area of 100 to 450 m ² / g. 100 m ² / g
If it is less than the range, it is difficult to improve the fluidity of the magnetic particles themselves, and as a result, it is difficult to improve the fluidity of the magnetic toner. If it exceeds 450 m ² / g, the amount of water adsorbed to the magnetic substance increases in a high temperature and high humidity environment, and the fluidity of the magnetic particles themselves deteriorates.
The fluidity of the magnetic toner is also reduced. Considering the fluidity of the magnetic particle powder, 150 to 400 m ² / g is more preferable.

In the present invention, the mixing ratio of the octahedral spinel type iron oxide particle powder and the silica fine particle is 0.5 in terms of SiO ₂ conversion based on 100 parts by weight of the octahedral spinel type iron oxide particle powder. ~ 3.5 parts by weight.
If the amount is less than 0.5 part by weight, it is difficult to improve the fluidity of the magnetic particles themselves, and as a result, the fluidity of the magnetic toner cannot be improved. If the amount exceeds 3.5 parts by weight, the amount of moisture adsorbed on the magnetic material increases in a high temperature and high humidity environment, and the fluidity of the magnetic particles themselves decreases, and as a result, the fluidity of the magnetic toner also decreases. . Further, the increase in the number of silica fine particles not involved in magnetism lowers not only the magnetization value of the magnetic particles but also the magnetization value of the magnetic toner.

The increase width of the BET specific surface area of the magnetic particle powder according to the present invention is in the range of 1 to 5 m ² / g. When the increase width of the BET specific surface area is less than 1 m ² / g, the fluidity of the magnetic particle powder itself cannot be improved, and as a result,
The fluidity of the magnetic toner cannot be improved, either. 5m ²
When it exceeds / g, the amount of moisture adsorbed on the magnetic material increases in a high temperature and high humidity environment, and the fluidity of the magnetic particles themselves decreases, and as a result, the fluidity of the magnetic toner also decreases. Considering the fluidity of the magnetic particle powder and the magnetic toner, the increase width of the BET specific surface area is preferably in the range of ² to 4 m ² / g.

In the octahedral spinel type iron oxide particle powder according to the present invention, the increase width of the BET specific surface area is within the range of 1.0 to 4.5 with respect to the amount of silica fine particles. When it is less than 1.0, the number of silica fine particles attached to the magnetic particles is reduced, and it becomes difficult for the silica fine particles to uniformly and densely adhere to the surface of the magnetic particles, so that the effect of the present invention can be obtained. Absent. When it exceeds 4.5, the amount of water adsorbed on the magnetic material increases in a high temperature and high humidity environment, and the fluidity of the magnetic particles themselves decreases, and as a result, the fluidity of the magnetic toner also decreases.

In the present invention, upon kneading and mixing with a resin, a hydrophobizing treatment with a coupling agent such as a titanium coupling agent or a silane coupling agent, a surfactant, etc., which is usually performed to improve dispersibility, is carried out. May be given.

The magnetic particle powder according to the present invention has the general formula 6
/ (Ρ · d ₃ ) × Φs [ρ: specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) = 0.1 to 0.5 μm, 1.
BET shown by 60 <area shape factor Φs ≤ 1.80]
0.5 to 3.5 parts by weight of silica fine particles are added to 100 parts by weight of octahedral spinel type iron oxide particles having a specific surface area and mixed by compression, shearing and spatula using a wheel type kneader. It can be obtained by

The mixing in the present invention is carried out by using a wheel type kneader so that octahedral spinel type iron oxide particles having an increase in BET specific surface area of 1 to 5 m ² / g can be obtained. Good. In consideration of the object of the present invention, the linear load of the wheel type kneader is preferably 30 kg / cm or more, more preferably 40 kg / cm or more.

As the wheel type kneader, specifically,
Simpson mix muller, multi-mill, Stutz mill, backflow kneader, Erich mill, etc. can be applied, but wet pan mill, melanger, whirlmix and quick kneader do not have a shearing action only with a compression and spatula, BET specific surface area increased by 1-5 m ²
It is not possible to obtain octahedral spinel-type iron oxide particles in the range of / g.

Conventionally, in coating the surface of magnetic particles with an organic compound having a hydrophobic group, a method of kneading using a wheel-type kneader or a raider (JP-A-3-
No. 22196), this method aims at improving the kneading property into a resin by reducing the liquid absorption amount, and the present invention for improving the fluidity of magnetic particles is The configuration is different.

[0033]

First, the most important point in the present invention is the general formula 6 / (ρ · d ₃ ) × Φs [ρ: specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) = 0.1 0.5 μm,
B shown by 1.60 <area shape factor Φs ≦ 1.80]
0 silica particles in terms of SiO ₂ octahedrally spinel iron oxide particles 100 parts by weight with ET specific surface area.
5 to 3.5 parts by weight are added and mixed, and the increase amount of the BET specific surface area in which the silica fine particles are attached to the particle surface of the octahedral spinel type iron oxide particles is 1 to 5 m with respect to the BET specific surface area value. ^The octahedral spinel iron oxide particle powder having a ratio of ² / g and a ratio of 1.0 to 4.5 with respect to the amount of the silica fine particles has excellent fluidity. It is a fact.

The octahedral spinel type iron oxide particle powder according to the present invention has excellent fluidity, and particularly, the fluidity index of 60 or more, preferably 65 or more is obtained.

The fluidity of the magnetic toner obtained by using the octahedral spinel type iron oxide particle powder according to the present invention is also excellent. In particular, the fluidity index is 80 or more, preferably 85 or more. can get.

The reason why the octahedral spinel-type iron oxide particle powder according to the present invention has excellent fluidity is that the present inventor, as will be shown in Examples and Comparative Examples below, shows that the octahedral spinel-type iron oxide particle powder has a high degree of fluidity. BE of surface-shaped spinel type iron oxide particles
When the increase width of the T specific surface area is in a specific range as compared with the BET specific surface area before attachment and is in a specific range with respect to the amount of silica fine particles, the particle surface of the octahedral spinel type iron oxide particles is It is considered that this is because the silica fine particles that have adhered are distributed in a large amount and uniformly, and are firmly fixed. When a magnetic toner is produced using the octahedral spinel-type iron oxide particle powder with improved fluidity as described above, poor kneading or magnetic particles during the kneading step with the resin during magnetic toner production. Mutual re-aggregation is less likely to occur, and a large amount of magnetic particles are projected on the surface of the magnetic toner particles. As a result, silica fine particles present on the surface of the octahedral spinel-type iron oxide particles are formed on the surface of the magnetic toner. It is considered that the fluidity of the magnetic toner itself can be improved due to the fact that it is distributed in a large amount and evenly and is hard to be detached.

Further, as shown in the comparative example below, since the Henschel mixer belonging to the blade type kneader usually used for mixing silica fine particles and spinel type iron oxide particles has only a stirring action, The effect of the present invention cannot be obtained.

The following is a description with reference to the drawings. FIG. 3 shows the BET specific surface area value of octahedral spinel-type iron oxide particles obtained by mixing and adhering silica compound particles by varying the kind and amount of the silica compound particles and the linear load of the kneading equipment. Increase width, that is, B after adhesion
It shows the relationship between the difference between the ET specific surface area value and the BET specific surface area value before adhesion (hereinafter referred to as ΔBET).

That is, FIG. 3 shows that the silica compound fine particles were obtained on the surface of the particles obtained in the same manner as in Example 1 except that the type and amount of the silica compound fine particles and the linear load of the Simpson Mix Mahler were variously changed. FIG. 3 shows the relationship between the amount of silica compound fine particles used and ΔBET for the attached octahedral magnetite particle powder. In FIG.
The octahedral magnetite particles corresponding to the circles had excellent fluidity, and the octahedral magnetite particles powder corresponding to the crosses had poor fluidity. The octahedral magnetite particle powder having excellent fluidity has silica fine particles attached thereto, and the amount of the silica fine particles is within a specific range.
It was confirmed that ET was 1 to 5 m ² / g and the ratio to the amount of silica fine particles was in the range of 1.0 to 4.5. In the figure, a dotted line a is a line where the amount of ΔBET / fine silica particles is 4.5, and a dotted line b is a line where it is 1.0.

FIG. 4 shows that, except that the amount of silica fine particles used and the linear load of the Simpson mix muller were variously changed.
FIG. 2 shows the relationship between ΔBET and fluidity of octahedral magnetite particle powder having silica particles adhered to the surface of the particles obtained in the same manner as in Example 1 described later.
As shown in FIG. 4, the octahedral magnetite particle powder in which silica fine particles are adhered to the particle surface having ΔBET in the range of 1 to 5 m ² / g has excellent fluidity and has a fluidity index of 55 or more. Has been obtained.

[0041]

EXAMPLES Next, the present invention will be explained with reference to examples, comparative examples and use examples. The shapes of particles in the following Examples, Comparative Examples and Use Examples are those observed with a transmission electron microscope and a scanning electron microscope.

As the particle size of the octahedral spinel type iron oxide particles, the area average diameter calculated from the Martin diameter in the projected diameter (the length of the line segment that bisects the projected area in the fixed direction) was used. . The magnetic properties of octahedral spinel iron oxide particles are
It is a value measured under an external magnetic field of 10 kOe using a "vibrating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.). The specific surface area is “Mono Sorb MS-1
1 ”(manufactured by Yuasa Ionics Co., Ltd.).

The specific surface area of the fine silica particles was measured by drying colloidal silica at 120 ° C. to remove water, and measuring the specific surface area of the dried product. ΔBET represents (specific surface area of magnetic particles treated with colloidal silica) − (specific surface area of magnetic particles before treatment with colloidal silica). The fluidity evaluation of the magnetic particle powder and the magnetic toner is a value measured by "Powder tester PT-E type" (manufactured by Hosokawa Micron Co., Ltd.).

Example 1 Area average diameter of 0.40 produced from an aqueous solution by a wet method
μm octahedral magnetite particles powder (BET
Specific surface area 5.0 m ² / g, magnetization value 85.0 emu / g,
Remanent magnetization value 10.5 emu / g) 10 kg, and specific surface area 172 m ² / g colloidal silica (Snowtex ST-40-trade name-manufactured by Nissan Kagaku) 500 g (SiO
₂ for 2 to 100 parts by weight of magnetite powder
(Part by weight) and "Sandmill MPUV-2" (trade name: manufactured by Matsumoto Foundry Iron Works Co., Ltd.), which is a Simpson mix muller, and 60 at a line load of 40 kg / cm.
The silica particles were adhered to the surface of the octahedral magnetite particles after mixing for a minute. The octahedron-shaped magnetite particle powder in which the obtained silica particles were attached to the particle surface had a BET specific surface area of 8.2 m ² / g and ΔBET of 3.2 m ² / g. Further, the fluidity index was excellent at 75, and the magnetic properties were such that the magnetization value was 83.1 emu / g and the residual magnetization value was 10.1 emu / g.
Met.

Examples 2 to 10 and Comparative Examples 1 to 6 In the same manner as in Example 1 except that the type of magnetic particle powder to be treated, the type and amount of silica fine particles, the type of kneading equipment and the line load were variously changed. A spinel-type iron oxide particle powder having silica particles adhered to the particle surface was obtained.

Main manufacturing conditions and various characteristics at this time are shown in Tables 1 to 4. Electron micrographs of FIGS. 1 and 2 (× 20
000) indicates the particle structure of the octahedral magnetite particle powder to be treated used in Examples 1 and 6, respectively.
In Table 1, the BET specific surface area of Snowtex ST-S is 232 m ² / g, and the BET specific surface area of Snowtex ST-XS is 350 m ² / g.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

Use Example 1 The octahedral magnetite particle powder obtained by adhering silica particles to the surface of the particle obtained in Example 1 was mixed with a mixer in the following mixing ratio, and hot rolled with a twin roll.
Melt kneading for 0 minutes. After the kneaded material was cooled, it was roughly pulverized and finely pulverized (fine mill). Further, this was classified to have a volume average diameter of 12 to 13 μm (TA- manufactured by Colter Counter Co., Ltd.
(Measured in II)). The hydrophobic silica fine particle powder was added to 100 parts by weight of the obtained magnetic toner.
A magnetic toner was obtained by externally adding 5 parts by weight. The fluidity index of the magnetic toner was 90. Styrene-acrylic copolymer 100 parts by weight Negative charge control agent 0.5 parts by weight Release agent 6 parts by weight Magnetic particle powder 60 parts by weight

The above magnetic toner was laser shot LBP-
The image quality was evaluated with B406E. As a result, a good image with high reproducibility of fine lines and less fogging and scattering was obtained. Further, since the toner has high fluidity, the toner application state on the sleeve is uniform, the solid black image is uniform, and the fine line reproducibility and the image quality are stable for a long period of time.

Use Examples 2 to 10 and Use Comparative Examples 1 to 6 Use Example 1 except that the treated magnetic particle powder was variously changed.
A magnetic toner was manufactured in the same manner as in. Table 5 shows various characteristics of the magnetic toner.

[0054]

[Table 5]

[0055]

INDUSTRIAL APPLICABILITY The magnetic particle powder according to the present invention has a large remanent magnetization and excellent fluidity as shown in the above-mentioned examples, and is suitable as a magnetic particle powder for magnetic toner. Is. Further, the magnetic toner produced by using the magnetic particle powder according to the present invention also has a large residual magnetization and is excellent in fluidity.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 2000) showing a particle structure of an octahedral magnetite particle powder to be treated used in Example 1.
0).

2 is an electron micrograph (× 2000) showing the particle structure of the octahedral magnetite particles to be treated used in Example 6. FIG.
0).

FIG. 3 shows the amount of silica fine particles used and ΔBE of octahedral magnetite particles formed by adhering silica fine particles to the surface of the particles.
It shows the relationship with T.

FIG. 4 is a graph showing the relationship between ΔBET and fluidity of octahedral magnetite particles in which silica particles are attached to the particle surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiichi Kurita, Eiichi Kurita 4-1-2, Funairi Minami, Naka-ku, Hiroshima City, Hiroshima Prefecture Toda Kogyo Co., Ltd. Creation Center (72) Youji Okano Funairi, Naka-ku, Hiroshima City, Hiroshima Prefecture Minami 4-chome 1-2 Toda Industry Co., Ltd. Creative Center

Claims (2)

[Claims] 1. A general formula 6 / (ρ · d ₃ ) × Φs [ρ:
Specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) =
0.1-0.5 μm, 1.60 <Φs (area shape factor)
≦ 1.80] The octahedron is prepared by adding 0.5 to 3.5 parts by weight of silica fine particles in terms of SiO ₂ to 100 parts by weight of octahedral spinel-type iron oxide particles having a BET specific surface area and mixing them. Of the BET specific surface area obtained by adhering the silica fine particles on the particle surface of the particulate spinel type iron oxide particles is within the range of 1 to 5 m ² / g with respect to the BET specific surface area value, and the silica is A magnetic particle powder for a magnetic toner, which comprises an octahedral spinel iron oxide particle powder having a ratio of 1.0 to 4.5 with respect to the amount of fine particles. 2. The general formula 6 / (ρ · d ₃ ) × Φs [ρ:
Specific gravity of spinel type iron oxide particles, d ₃ (area average diameter) =
0.1-0.5 μm, 1.60 <Φs (area shape factor)
≦ 1.80] 0.5 to 3.5 parts by weight of silica fine particles in terms of SiO _{2 is} added to 100 parts by weight of octahedral spinel iron oxide particles having a BET specific surface area of
By using a wheel type kneader to mix by compression, shear and spatula, the increase amount of BET specific surface area obtained by adhering the silica fine particles to the particle surface of the octahedral spinel type iron oxide particles is Octahedral spinel-type iron oxide particle powder having a BET specific surface area value of 1 to 5 m ² / g and a ratio to the silica fine particle amount of 1.0 to 4.5. A method for producing a magnetic particle powder for a magnetic toner, comprising: