JP3463957B2 - 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. More specifically, the surface of the particles is coated with magnetite containing iron-zinc oxide to give a black color and to improve the magnetic properties in a well-balanced manner. In particular, the present invention relates to magnetite particles used in the application of material powder for electrostatic copying magnetic toner, black pigment powder for paints, and a method for producing the same.

[0002]

2. Description of the Related Art Recently, magnetic magnetite has been used in various fields, especially for magnetic toner of electrostatic copying machines. The method for producing this magnetic magnetite is generally classified into a dry method and a wet method. Among them, in the wet method, an alkaline aqueous solution is added to an aqueous solution containing ferrous ions to carry out an oxidation reaction under specific conditions. The way to do it is the mainstream.

Among these wet methods, some proposals have been made for a method for producing magnetite particles containing zinc for the purpose of improving various properties of powder. For example, the manufacturing method disclosed in Japanese Examined Patent Publication No. 59-43408 is one of the representative ones. In this manufacturing method, after adding an alkaline aqueous solution to the ferrous salt, total F in the aqueous solution is added.
Oxidize until the ratio of divalent Fe to e falls within a specific range, and then add a water-soluble zinc compound so as to achieve a specific Zn / Fe ratio, and react at a specific free hydroxyl ion concentration and solution temperature. Is to obtain spinel type iron oxide. Regarding the particles obtained by this method, "a perfect (non-brownish) black color is obtained,
It has a coercive force of about 0 Oe ”, but although this particle can obtain the corresponding characteristics, it cannot be said that it is sufficient in terms of saturation magnetization, etc., and the particle diameter is extremely large, so that it was generated. There is a problem in that the quality of the magnetic toner, especially when dispersed in the toner, has an adverse effect such as excessive protrusion or uneven distribution on the surface thereof.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art and to have a BET specific surface area of 7.0 m ^2.
The present invention provides a magnetite particle having a particle size of at least 1 g / g and being relatively small, excellent in oil absorption property, not impairing the degree of blackness, and improved in magnetic property in a well-balanced manner, and a method for producing the same.

[0005]

DISCLOSURE OF THE INVENTION As a result of intensive investigations by the present inventors to achieve the above object, the Zn / Fe molar ratio (%) in the magnetite particles is 0.2 to 1.8%. As described above, by adding the ferrous salt containing zinc at the end of the oxidation reaction and further proceeding the oxidation reaction,
It was concluded that the effect of the powder described in JP-A-43408 on the blackness is minimized and the magnetic properties are improved in a well-balanced manner.

[0006] That is, the present invention is a magnet
The molar ratio (%) of Zn / Fe in the whole iron particles is 0.
With an iron-zinc oxide coating layer of 2% or more and less than 0.5%
And saturation magnetization 79 emu / g (79 A · m ² / kg)
Above, blackness (L) 19.5 or less by color difference meter, JIS
According to K 5101, the oil absorption amount is 30 ml / 100 g or more, and a solution containing magnetite particles and a ferrous salt as a main component is mixed with an alkaline aqueous solution in an amount equal to or more than iron, and then a free hydroxyl group concentration is obtained. 1-3 g /
After completion of the oxidation reaction while maintaining the ratio to 1, the ferrous salt containing zinc was added so that the Zn / Fe molar ratio (%) in the entire magnetite particles would be 0.2 to 1.8%. , PH 6.0-9.0, and the oxidation reaction is carried out again.

The manufacturing method of the present invention will be described in more detail below. First, in the present invention, a solution containing a ferrous salt as a main component is mixed with an aqueous alkaline solution in an amount equal to or more than iron to produce ferrous hydroxide. Examples of the solution containing a ferrous salt as a main component include a ferrous sulfate aqueous solution and the like. Also,
Examples of the alkaline aqueous solution include sodium hydroxide aqueous solution.

After a solution containing a ferrous salt as a main component and an alkaline aqueous solution are mixed to produce ferrous hydroxide, an oxygen-containing gas, preferably air, is blown into the ferrous hydroxide to produce 60.
The oxidation reaction is carried out at -100 ° C, preferably 80-90 ° 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. In this oxidation reaction, take care so that the concentration of free hydroxyl groups is 1 to 3 g / 1.

After the reaction is advanced from the start of oxidation until the unreacted ferrous hydroxide becomes almost zero, the Zn / Fe molar ratio (%) in the magnetite particles is 0.2 to 1.8%, preferably Is added to a ferrous salt containing zinc ions so as to be 0.3 to 1.2%, and then the oxidation reaction is performed again.

When the Zn / Fe molar ratio in the magnetite particles is less than 0.2%, the BET specific surface area is 7.0 m ² /
When the value is g or more, the particles have a relatively small particle size, so that the magnetic properties, particularly the saturation magnetization, deteriorate. On the other hand, Zn in magnetite particles
When the / Fe molar ratio (%) exceeds 1.8%, the saturation magnetization decreases due to the collapse of the Zn distribution in the particles, and
ZnO described in Japanese Patent Publication No. 59-43408 mentioned above.
Since the Fe ₂ O ₃ layer is formed thick on the surface of the particles, the blackness of the powder is significantly impaired.

The molar ratio (%) of Zn / Fe in the iron-zinc oxide on the surface of the particles produced later is preferably 7-5.
It is desirable to adjust to 0%, more preferably 10 to 40%. When the molar ratio (%) of Zn / Fe in the iron-zinc oxide is less than 7%, uneven distribution of zinc in the iron-zinc oxide on the particle surface is not preferable, and 50%.
If it exceeds, the zinc is excessively exposed on the surface of the ZnOFe ₂ O ₃ particles, resulting in a decrease in blackness.

In the present invention, a ferrous salt containing zinc is added, and the pH when the oxidation reaction is further advanced is 6.0 to 9.
It is preferable to adjust it to 0, preferably 8.0 to 9.0. p
When H is less than 6.0, goethite particles may be generated in the reaction slurry, and when pH exceeds 9.0, there is no difference in the characteristics of the particles, but an additional alkali should be added. It is uneconomical.

After the completion of the oxidation reaction, the washing which is normally carried out,
Magnetite particles are obtained through the steps of filtration, drying and pulverization.

The magnetite particles thus obtained have good characteristics such as a saturation magnetization of 79 emu / g or more, a blackness (L) by a color difference meter of 19.5 or less, and an oil absorption amount of 30 ml / 100 g or more according to JIS K 5101. Have.

In the present invention, the portion referred to as "surface" is the first zinc-containing first coating containing zinc on the surface of the magnetite particles obtained with the original 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, according to the present invention, it is described that the water-soluble zinc compound is added during the reaction in which an unreacted ferrous hydroxide remains in a considerable amount.
The manufacturing method is completely different from the manufacturing method disclosed in Japanese Patent No. 408, and it is characterized in that the reaction for generating the magnetite particles as the base is once terminated, the size of the particles is almost determined, and then the surface layer portion is formed. The reason for performing this operation is to suppress the decrease in blackness of the magnetite particles to a minimum and to improve the magnetic characteristics in a well-balanced manner.

[0017]

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

[0018]Example 1 Fe²⁺ Ferrous sulfate aqueous solution 65 containing 1.54 mol / l
Liter and 2.38 mol / l aqueous sodium hydroxide
88 liters of the solution were mixed and stirred.

After adjusting the residual sodium hydroxide in the mixed aqueous solution to 2.1 g / l, while maintaining the temperature at 80 ° C., 65 liter / min of air was blown in to terminate the reaction once.

Next, Fe²⁺ Contains 1.27 mol / l
Zn in the ferrous sulfate aqueous solution²⁺ 0.5 mol / l
2.25 liters of mixed aqueous solution to which zinc sulfate was added
Prepared separately, added to the above reaction slurry, and again
The reaction was terminated by blowing in air at a bottle / min.
The resulting particles are washed, filtered, dried, and crushed in the usual manner.
Processed by.

The magnetite particles thus obtained were evaluated for specific surface area, magnetic properties, oil absorption and colorimetry by the methods described below. The results are shown in Table 2. (Measurement Method) (1) Specific Surface Area Using Shimadzu Micromeritics Model 2200 BET Meter. (2) Magnetic characteristics Using Toei Kogyo's vibration data type magnetometer VSM-P7 type,
Measure saturation magnetization at 10 KOe. (3) 0.5 g of colorimetric magnetite particles and 0.7 g of linseed oil were kneaded with a Hoover-type Mahler, and then clear lacquer 4.5
g and kneaded further well. This was applied onto mirror-coated paper using a 4 mi1 applicator, dried, and then measured with a color difference meter. (4) Oil absorption amount According to JIS method (JIS K 5101 pigment test method) (5) Zn elution rate The relationship between the elution rate of zinc and the elution rate of iron 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 this result, it was confirmed that zinc was eluted at an early stage and zinc was present only on the surface of magnetite particles.

Further, a transmission electron micrograph (× 2,000,000) showing the particle structure of the magnetite particles is shown in FIG. It can be seen from FIG. 2 that iron-zinc oxide is formed on the surface of the magnetite particles.

Examples 2 to 3 and Comparative Examples 1 to 3 As shown in Table 1, the ferrous sulfate concentration and the zinc sulfate concentration of the mixed ferrous sulfate and zinc sulfate mixed solution added after the completion of the oxidation reaction were changed variously. The other conditions were the same as in Example 1. In Comparative Example 1, the ferrous sulfate and zinc sulfate aqueous solutions were not added at the end of the oxidation reaction. Similar to Example 1, the specific surface area, magnetic properties, oil absorption, and colorimetry were evaluated. The results are shown in Table 2.

As is clear from the results shown in Table 2, Example 1
3 to 3 have higher saturation magnetization (σs) than Comparative Examples 1 to 3.

Example 4 and Comparative Example 4 The same method as in Example 1 except that the concentration of the alkaline aqueous solution (sodium hydroxide aqueous solution) before the reaction was changed in order to adjust the particle size as shown in Table 1. Thus, magnetite particles were obtained (Example 4).

Magnetite particles were obtained in the same manner as in Comparative Example 1 except that the concentration of the alkali aqueous solution (sodium hydroxide aqueous solution) before the reaction was changed to adjust the particle size as shown in Table 1. Comparative example 4).

For Example 4 and Comparative Example 4, the specific surface area, magnetic properties, oil absorption, and colorimetry were evaluated as in Example 1. The results are shown in Table 2.

As shown in Table 2, even when Example 4 and Comparative Example 4 are compared, Example 4 has a higher saturation magnetization than Comparative Example 4.

Comparative Example 5 Magnetite particles were produced according to the method of Example 1 described in JP-B-59-43408.

Similar to Example 1, this Comparative Example 5 was evaluated for specific surface area, magnetic properties, oil absorption, and color measurement.
The results are shown in Table 2.

The magnetite particles of Comparative Example 5 have a low L value as a result of colorimetry and are excellent in terms of blackness, but their saturation magnetization is significantly lower than the size of the particles.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

As described above, the magnetite particles of the present invention do not impair the degree of blackness and improve the magnetic characteristics in a well-balanced manner. Further, by adjusting the coating of iron-zinc oxide on the surface of the particles to be thin, it is possible to suppress the decrease in the surface area of the particles, thereby ensuring a sufficient oil absorption amount.
For this reason, it is particularly suitable for use as material powder for electrostatic copying magnetic toner and black pigment powder for paints.

[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.

FIG. 2 is a transmission electron micrograph (× 2,000,000) showing the particle structure of the magnetite particles of Example 1.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Watanabe Inventor Hiroyuki Watanabe 6-1-1, Hibi, Tamano-shi, Okayama Mitsui Mining & Smelting Co., Ltd. (56) Reference JP-A-6-310318 (JP, A) ) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01G 49/08

Claims (2)

(57) [Claims] 1. The entire surface of the magnetite particles on the surface of the particles.
Zn / Fe molar ratio (%) of 0.2% to 0.5%
Having a full iron-zinc oxide coating and a saturation magnetization of 79
Magnetite particles having an emu / g (79 A · m ² / kg) or more, a blackness (L) by a color difference meter of 19.5 or less, and an oil absorption amount of 30 ml / 100 g or more according to JIS K 5101. 2. An oxidation reaction in which a solution containing a ferrous salt as a main component is mixed with an aqueous alkaline solution at an amount equivalent to or more than iron, and then the free hydroxyl group concentration is maintained at 1 to 3 g / 1 to carry out the oxidation reaction. After completion, Zn / Fe in the entire magnetite particles
The ferrous salt containing zinc is added so that the molar ratio (%) of the above is 0.2 to 1.8%, and the pH is adjusted to 6.0 to 9.0.
A method for producing magnetite particles, which comprises carrying out an oxidation reaction again.