JP3419941B2 - Magnetite particles and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetite particles and a method for producing the same, and more specifically, it is fine particles obtained by growing a thin iron-zinc oxide layer on magnetite particles, which is black and has a high saturation magnetization. The present invention relates to magnetite particles having high powder resistance, particularly used for magnetic powders for electrostatic copying magnetic toners and black pigment powders for paints, and a method for producing the same.

[0002]

2. Description of the Related Art Recently, magnetite particles produced by an aqueous solution reaction have been widely used as a material for magnetic toners of dry type electronic copying machines, printers and the like. Although various general development characteristics are required for magnetic toners, in recent years, with the development of electrophotographic technology, especially copying machines and printers using digital technology have rapidly developed, and the required characteristics have become more advanced. . That is, in addition to conventional characters, it is also required to output graphics and photographs, and in particular, some printers have the capability of 400 dots or more per inch, and the latent image on the photoconductor becomes more precise. ing. for that reason,
There is a strong demand for high reproducibility of fine lines in development. Further, in electrostatic transfer, it is necessary that the magnetite particles themselves have high electric resistance in order to stabilize the image density.

The method for producing this magnetic magnetite is generally classified into a dry method and a wet method. In the wet method, an alkaline aqueous solution is added to an aqueous solution containing ferrous ions, and under certain conditions. The main method is to carry out an oxidation reaction.

Among these wet methods, some proposals have been made on a method for producing zinc-containing magnetite particles or the like for the purpose of improving various properties of the powder.

For example, Japanese Patent Laid-Open No. 57-77031 discloses a method in which a zinc salt is added after oxidizing a ferrous salt within a specific range, but the obtained particles have low saturation magnetization. In addition, the publication describes that if ZnO.Fe ₂ O ₃ is present alone, it becomes brownish and the blackness is lowered.

Japanese Unexamined Patent Publication (Kokai) No. 62-91423 and Japanese Unexamined Patent Publication (Kokai) No. 3-1160 disclose spinel type ferrite particles in which zinc is uniformly distributed from the inside of the particles to the surface.

Fe₃O_FourHas a reverse spinel structure
Or, Fe of octahedral site²⁺ And Fe³⁺ Exchange of electrons with
It is known that a change in the electrical conductivity
It In fact, the obtained Fe₃O_Four10 particles²-10³Ω
・ Many cm.

Japanese Unexamined Patent Publication (Kokai) No. 6-310318 discloses granular magnetite particles having a particle surface coated with Zn _x Fe _{2 + y} O _z , which has a heat resistance of Hc 150 Oe or less and good coloring. It is a good one. However, it is not sufficient in terms of not impairing black color while having high saturation magnetization and high resistance, which is a subject of the present invention.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves these problems of the prior art, and provides magnetite particles having high saturation magnetization and powder resistance and not impairing the degree of blackness of powder, and a method for producing the same. The purpose is to do.

[0010]

The above object of the present invention is achieved by providing a thin iron-zinc oxide layer having a high zinc content on the surface of magnetite particles.

That is, the magnetite particles of the present invention are
The surface of the particles is coated with a thin layer of iron-zinc oxide, and the Zn / Fe molar ratio of the entire magnetite particles is 0.002-0.0.
30, the molar ratio of Zn / Fe in the iron-zinc oxide thin layer is 0.5 to 1.5, the saturation magnetization is 80 emu / g or more, the powder resistance is 1 × 10 ⁴ Ω · cm or more, and the blackness by a color difference meter (L)
It is characterized by being 20 or less.

In the magnetite particles of the present invention, Zn / F
The molar ratio of e is 0.002 to 0.030. When the Zn / Fe molar ratio in the magnetite particles is less than 0.002, the BET specific surface area is 7.0 m ² / g or more, and the particles have a relatively small particle size, so that the magnetic properties, particularly the saturation magnetization are deteriorated. On the other hand, when the Zn / Fe molar ratio in the magnetite particles exceeds 0.030, the iron-zinc oxide thin layer that should be thinly coated on the surface of the magnetite particles becomes thick,
Reduction of saturation magnetization due to collapse of zinc distribution in the coating layer and Zn described in the above-mentioned JP-A-57-77031.
Since the O.Fe ₂ O ₃ layer is thickly formed on the particle surface, the blackness of the powder is impaired.

In addition, the magnetite particles of the present invention may be iron-subsite.
The Zn / Fe molar ratio in the lead oxide thin layer is 0.5 to 1.5.
Is. When the Zn / Fe molar ratio is less than 0.5,
The powder resistance is 1 × 10^Four It does not exceed Ω · cm, and again
If the Zn / Fe molar ratio exceeds 1.5, Zn (OH)₂
The saturation magnetization tends to decrease due to single precipitation of

In the magnetite particles of the present invention, an iron-silicon oxide thin layer may be coated on the iron-zinc oxide thin layer. This improves the fluidity of the magnetite particles.

Further, in the method for producing magnetite particles of the present invention, the ferrous salt aqueous solution and the alkaline aqueous solution are mixed to carry out the oxidation reaction, and after the oxidation reaction is completed, the Zn / Fe molar ratio in the solution is 0.5 to 1 0.5 and the Zn / Fe molar ratio in the entire magnetite particles obtained is 0.002-0.0.
A ferrous salt aqueous solution containing zinc whose concentration is adjusted to 30 is added to adjust the pH to 6.0 to 9.0, and the oxidation reaction is performed again.

The manufacturing method of the present invention will be described below. First, in the present invention, an aqueous ferrous salt solution and an aqueous alkaline solution are mixed to produce ferrous hydroxide. Examples of the ferrous salt aqueous solution include ferrous sulfate aqueous solution. Examples of the alkaline aqueous solution include sodium hydroxide aqueous solution.

An aqueous ferrous salt solution and an aqueous alkali solution are mixed to form a ferrous hydroxide slurry, and then an oxygen-containing gas, preferably air, is blown into the ferrous hydroxide slurry to 60 to 100 ° C. The oxidation reaction is preferably carried out at 80 to 90 ° C. The amount of the oxidation reaction at this time is adjusted by adjusting the amount of the oxygen-containing gas blown in while observing the analysis value of the unreacted ferrous hydroxide during the reaction.

After the reaction is advanced from the start of the oxidation until the amount of unreacted ferrous hydroxide becomes almost zero, the zinc / Fe molar ratio in the magnetite particles is adjusted to 0.002 to 0.030. After adding the aqueous ferrous salt solution containing ions to the slurry, the oxidation reaction is performed again.

Further, the Zn / Fe molar ratio in the iron-zinc compound thin layer on the surface of the particles is adjusted to 0.5 to 1.5.
A ferrous salt aqueous solution containing the above zinc ions is prepared.
The iron-zinc compound thin layer thus obtained is Zn /
Despite the compound phase having a large molar ratio of Fe, the iron-zinc compound phase on the particle surface has a small thickness, and thus the blackness does not decrease.

In addition, in the present invention, a p-type solution is added when the ferrous salt aqueous solution containing zinc is added to the slurry to further promote the oxidation reaction.
H should be adjusted to 6.0 to 9.0, preferably 8.0 to 9.0. When the pH is less than 6.0, goethite particles may be generated in the reaction slurry, and the pH is 9.0.
If it exceeds, there is no difference in the characteristics of the particles, but it is uneconomical because an additional alkali must be added additionally.

After the completion of this oxidation reaction, an aqueous ferrous salt solution containing silicon may be further added to the slurry, and oxygen gas may be blown into the slurry to carry out the oxidation reaction again. As a result, the iron-silicon oxide layer is formed on the outermost layer of the magnetite particles.

After completion of the oxidation reaction, magnetite particles are obtained by further carrying out the usual washing, filtering, drying and pulverizing steps. In this way, magnetite particles having the above-mentioned characteristics are obtained.

In the present invention, the portion referred to as "surface" means the first zinc-containing first coating which is further coated from the surface of the magnetite particles obtained with the initial ferrous salt and the alkaline aqueous solution. It refers to the magnetite thin film formed after the addition of iron salt until the end of the reaction.

Therefore, in the present invention, it is described that the water-soluble zinc compound is added during the reaction in which a large amount of unreacted ferrous hydroxide remains.
The method is completely different from the manufacturing method disclosed in Japanese Patent No. 031, and is characterized in that the reaction for generating magnetite particles as a base is once terminated, the particle size is almost determined, and then the surface layer portion is formed. The reason for performing this operation is to suppress the decrease in the blackness of the magnetite particles to a minimum and to improve the magnetic characteristics and the powder resistance in a well-balanced manner.

If the OH group for forming the Zn coating layer is less than 0.3, the Zn _x Fe _{2 + y} O _z fine particles are precipitated alone, and the Zn coating forming layer becomes insufficient. ．
The method is completely different from the manufacturing method of the above-mentioned JP-A-6-310318, which describes that the alkali is 3 to 1.0 mol / l, and in the present invention, it is low alkaline (pH 6 to 9). To form a Zn coating layer.
In JP-A-6-310318, the Zn / Fe molar ratio is Zn / Fe = 0.286 to 0.5 (Zn _x Fe _{2 + y}
O _z : 0.4 ≦ x ≦ 1, 4 ≦ z ≦ 4.3, x + y = 1)
And the Zn / Fe molar ratio of the product obtained in the present invention is Z
n / Fe = lower than 0.5 to 1.5. As a result, in the present invention, a material having a high saturation magnetization, a high resistance and not impairing the black color was obtained.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 As shown in Table 1, 50 liters of ferrous sulfate aqueous solution containing 2.0 mol / l of Fe ²⁺ and 36 liters of 5.0 mol / l sodium hydroxide aqueous solution were mixed and stirred. ,
While maintaining the temperature at 85 ° C., 65 liter / min of air was blown to once terminate the reaction (dough process).

Next, Fe ²⁺ and Zn ²⁺ are each 0.4
Separately prepare 2 liters of an aqueous solution in which ferrous sulfate and zinc sulfate were mixed so as to be 4 mol / l and 0.33 mol / l, add them to the above reaction slurry, and again add 40 liters / m 2.
In air was blown in to terminate the reaction (surface treatment step).

The produced particles thus obtained are subjected to usual washing, filtration,
It was processed by a drying and grinding process. Regarding the magnetite particles thus obtained, Zn / F in the magnetite particles
The e molar ratio and the Zn / Fe molar ratio in the iron-zinc oxide thin layer were measured, and the results are shown in Table 1.

The BET specific surface area, FeO content, magnetic characteristics, powder resistance, blackness (L
Value), particle shape, zinc elution rate, fluidity (spatula angle)
Was evaluated. The results are shown in Table 2.

(Measurement Method) (1) Specific Surface Area Using Shimadzu-Micromeritics Model 2200 BET Meter.

(2) Magnetic characteristics Using a vibration data type magnetometer VSM-P7 type manufactured by Toei Kogyo,
Measure saturation magnetization at 10KOe and 1KOe.

(3) 10 g of the powder resistance sample was put in a holder and a pressure of 600 kg / cm ² was applied to form a tablet mold of 25 mmφ, an electrode was attached, and measurement was performed under a pressure of 150 kg / cm ² . The powder resistance value of the magnetite particles was obtained by calculating from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.

(4) Blackness (L value) After 0.5 g of magnetite particles and 0.7 g of linseed oil were kneaded with a Hoover-type Mahler, a clear lacquer of 4.5 was added thereto.
g and kneaded further well. This was applied onto mirror-coated paper using a 4 mil applicator, dried, and then color-measured with a color difference meter.

(5) Particle shape It was observed with a scanning electron microscope.

(6) Zn elution rate The relationship between the zinc elution rate and the iron elution rate of the obtained particles was measured as follows. That is, 25 g of a sample was put into 5 liters of 1N hydrochloric acid, dissolved by stirring at 50 ° C., the filtrate was filtered by a 0.1 μm membrane, and the elution rate at each time was obtained by high frequency inductively coupled plasma (ICP). The results are shown in Table 3 and FIG.

From these results, it was confirmed that zinc was eluted at an early stage and zinc was present only on the surface of magnetite particles.

(7) Flowability (spatula angle) Using a powder tester manufactured by Hosokawa Micron Co., Ltd., the sample powder was piled up on a spatula (dish), the inclination angle of the side surface of the deposited powder was measured, and the operation procedure was followed. The spatula angle was measured.

Examples 2 to 6 As shown in Table 1, various amounts of sodium hydroxide aqueous solution in the doughing process, temperature, ferrous sulfate concentration in the surface treatment process, zinc sulfate concentration, and liquid amount were variously changed to carry out. Reaction and treatment were carried out in the same manner as in Example 1 to obtain magnetite particles.

With respect to the magnetite particles thus obtained, the Zn / Fe molar ratio in the magnetite particles and the Zn / Fe molar ratio in the iron-zinc oxide thin layer were measured, and the results are shown in Table 1.
Shown in.

The characteristics and properties of the magnetite particles thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 1 Magnetite particles were obtained by only the dough process of Example 6 and omitting the subsequent surface treatment process.

The characteristics and properties of the magnetite particles thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Examples 2 to 3 As shown in Table 1, the reaction was carried out in the same manner as in Example 1 by varying the amount of aqueous sodium hydroxide solution in the dough process, the ferrous sulfate concentration and the zinc sulfate concentration in the surface treatment process. And treated to obtain magnetite particles.

With respect to the magnetite particles thus obtained, the Zn / Fe molar ratio in the magnetite particles and the Zn / Fe molar ratio in the iron-zinc oxide thin layer were measured, and the results are shown in Table 1.
Shown in.

The characteristics and properties of the magnetite particles thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 4 As shown in Table 1, magnetite particles were obtained based on the example of JP-A-6-310318.

The characteristics and properties of the magnetite particles thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0049]Example 7 Fe²⁺In a ferrous sulfate aqueous solution containing 1.01 mol / l
Si⁴⁺ Sodium silicate to be 0.44 mol / l
Separately prepare 2.3 liters of aqueous solution to which Mu (No. 3) is added
Then, add 15 liters to the slurry produced in Example 2 again.
Blow air at Torr / min to terminate the oxidation reaction.
It was

The produced particles thus obtained are subjected to usual washing, filtration,
It was processed by a drying and grinding process. Further, the characteristics and properties of the magnetite particles thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

According to the present invention, the iron-zinc oxide thin layer is provided on the surface of the magnetite particles, and the Zn / Fe ratio is set to a large phase, so that the characteristics of the magnetite particles before coating can be utilized as they are and the powder resistance can be improved. It became possible to raise.
Therefore, the characteristic values of the magnetite particles before coating the iron-zinc oxide thin layer such as the particle shape, magnetic characteristics, apparent density, oil absorption, blackness, and fluidity are retained as they are, and the powder resistance is 1 × 10 ⁴ It can be Ω · cm or more. Therefore, it is particularly suitable for electrostatic copying magnetic toner.

Further, on the iron-zinc oxide thin layer, iron-
By providing a thin layer of silicon oxide, it is possible to prevent the particles from aggregating with each other and improve the fluidity of the powder. Therefore, it is most suitable for the electrostatic copying magnetic toner.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the elution rate of zinc and the elution rate of iron in magnetite particles of Example 1.

Claims (3)

(57) [Claims] 1. A thin iron-zinc oxide layer is coated on the surface of a particle, and the Zn / Fe molar ratio of the entire magnetite particle is 0.1.
002-0.030, Zn / F in iron-zinc oxide thin layer
The molar ratio of e is 0.5 to 1.5, and the saturation magnetization is 80 emu / g.
As described above, magnetite particles having a powder resistance of 1 × 10 ⁴ Ω · cm or more and a blackness (L) of 20 or less by a color difference meter. 2. The magnetite particles according to claim 1, wherein an iron-silicon oxide layer is coated on the iron-zinc oxide thin layer. 3. A ferrous salt aqueous solution and an alkaline aqueous solution are mixed to carry out an oxidation reaction, and after completion of the oxidation reaction, Zn /
The Fe molar ratio is 0.5 to 1.5, and the Zn / Fe molar ratio in the entire magnetite particles obtained is 0.002.
A ferrous salt aqueous solution containing zinc whose concentration was adjusted to be ~ 0.030 was added to adjust the pH to 6.0 to 9.0,
A method for producing magnetite particles, which comprises carrying out an oxidation reaction again.