JP2756845B2 - Hexahedral magnetite particle powder and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetite particle powder which has a black color and is excellent in mixing with a resin due to a small magnetic cohesive force, and its use. It concerns the manufacturing method.

The main use of the magnetite particle powder according to the present invention is a material particle powder for a magnetic toner.

[Conventional technology]

Conventionally, as one method of developing an electrostatic latent image, a so-called one-component magnetic toner using, as a developer, composite particles obtained by mixing and dispersing magnetic particles such as magnetite particles in a resin without using a carrier. Is widely known and widely used.

In recent years, along with high performance of copying machines, such as higher speed, higher image quality, and continuity, there has been a strong demand for improved characteristics of a magnetic toner as a developer. It is required to have a black color and to be excellent in mixing with a resin.

This fact is described in Japanese Patent Application Laid-Open No. 55-65406, entitled "Generally, the following characteristics are required for magnetic powders for magnetic toners in such a one-component system. The magnetic toner may contain a colorant, but it is preferable that the powder itself has a black color and no colorant is used. Good thing: the degree of microscopic mixing in the toner is important for the properties of the toner. "

The blackness of magnetite particle powder is as follows: "The blackness of the sample depends on the Fe (II) content and the average particle size. Powder with an average particle size of 0.2 μm is a bluish black powder and is most suitable as a black pigment. ‥‥ Fe (II) content is 10
%, There is a slight difference in the degree of blackness, but all the samples are black. When the Fe (II) content is reduced to 10% or less, each sample changes from black to reddish brown. It is known that, in the case of magnetite particle powder of about 0.1 to 0.5 μm used for magnetic toner, it mainly depends on the Fe ²⁺ content.

In order to improve the mixing property between the magnetite particle powder and the resin, it is necessary that the magnetite particle powder be excellent in dispersibility. It is required that the cohesive force be small.

Incidentally, the magnetic field strength of KO1KOe in Japanese Patent Application Laid-Open No. 63-128356 almost corresponds to the magnetic field strength near the developing sleeve when developing using the magnetic capsule toner of the present invention. The magnetic toner is generally 1KOe.
Since it is used under an external magnetic field of a degree, it is desired that the residual magnetization of the magnetite particle powder contained in the magnetic toner is as small as possible after applying an external magnetic field of 1 KOe.

Conventionally, magnetite particle powder used as magnetic particle powder for magnetic toner was obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an equivalent or more of Fe ⁺² in the aqueous solution of ferrous salt. Octahedral magnetite particle powder obtained by aerating an oxygen-containing gas into a suspension containing ferrous hydroxide colloid having a pH of 10 or more (Japanese Patent Publication No.
Or a ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with 0.80 to 0.99 equivalents of alkali hydroxide relative to Fe ⁺² in the aqueous ferrous salt solution. The first step of generating spherical magnetite particles by passing oxygen-containing gas into the aqueous ferrous salt reaction solution, and after the first step reaction, adding 1.00 equivalent or more of alkali hydroxide to the remaining Fe ^+2. Spherical magnetite particles obtained by heating and oxidizing at pH 10 or higher (JP-B-62-5120)
No. 8).

[Problems to be solved by the invention]

The magnetite particle powder that is black and has excellent mixing with the resin is currently the most required, but the octahedral magnetite particle powder described above has a Fe ^{+ 2} content of 0.3 to 0.4 in molar ratio to Fe ³⁺
It is about 5 and excellent in blackness, but because the residual magnetization is large and magnetic aggregation is likely to occur,
Poor dispersibility and poor mixing with resin. Further, magnetite particles exhibited a spherical supra is mixed with the excellent dispersibility resin since the residual magnetization is less likely to occur magnetic agglomeration is small is good, Fe ²⁺ content of Fe ^{3 Since the} molar ratio is at most about 0.28 with respect to ^+, it becomes slightly brownish black and inferior in blackness.

Accordingly, an object of the present invention is to provide a magnetite particle powder which is black and has excellent mixing properties with a resin due to low magnetic cohesion.

[Means for solving the problem]

The technical problem can be achieved by the present invention as described below.

That is, in the present invention, the Fe ²⁺ content is 0.1 in molar ratio to Fe ³⁺ .
3 to 0.5, the specific surface area is 3.0 to 15.0 m ² / g, 1 kO
The residual magnetization σr after applying an external magnetic field of e is given by the equation σ
r (emu / g) = 0.92 × specific surface area value + b (where b = 1.6 to
A magnetite particle powder comprising hexahedral magnetite particles in the range shown in 3), a ferrous salt aqueous solution, and an alkaline aqueous solution having an equivalent amount or less to Fe ²⁺ in the ferrous salt aqueous solution are obtained. The ferrous hydroxide colloid is partially oxidized by passing an oxygen-containing gas into the aqueous ferrous salt reaction solution containing the ferrous hydroxide colloid having a pH in the range of 6.0 to 7.5, thereby partially oxidizing the magnetite nucleus. Particles are generated, and then an oxygen-containing gas is passed through the aqueous ferrous salt reaction solution containing the magnetite core particles and the ferrous hydroxide colloid in a pH range of 8.0 to 9.5 to grow the magnetite core particles. Fe ²⁺ content consisting of performing the reaction is Fe ³⁺
The molar ratio is 0.3 to 0.5, and the specific surface area is 3.0 to 15.
0 m ² / g, and the residual magnetization σr after applying an external magnetic field of 1 kOe is given by the formula σr (emu / g) = 0.92 × specific surface area value + b
(However, b = 1.6-3) It is a manufacturing method of the magnetite particle powder which consists of the hexahedron magnetite particle which is in the range shown by b.

[Action]

First, the most important point in the present invention is the range of pH 6.0 to 7.5 obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an equivalent or less of Fe ^{2+ in the} aqueous solution of ferrous salt. Of ferrous hydroxide colloid. The ferrous hydroxide colloid is partially oxidized by passing an oxygen-containing gas into the ferrous salt reaction aqueous solution to generate magnetite core particles, and then the magnetite core particles and the ferrous hydroxide colloid When an oxygen-containing gas is passed through a ferrous salt reaction aqueous solution containing pH 8.0 to 9.5 in the pH range, a magnetite particle powder having a black color and a small magnetic cohesion is obtained. is there.

The magnetite particle powder according to the present invention has a hexahedral particle shape as shown in the scanning electron micrograph of FIG. 2 described later, and has a Fe ²⁺ content of 0.3 to 0.5 in a molar ratio to Fe ^3+. Therefore, the color is bluish black, and the magnetic cohesion is small due to the small residual magnetization σr after applying an external magnetic field of 1 KOe.

The magnetite particle powder according to the present invention has a BET specific surface area of 3.0 to 15.0 m ² / g.

The particle shape of the magnetite particle powder obtained by aerating an oxygen-containing gas into the suspension containing the ferrous hydroxide colloid having a pH of 10 or more is represented by a transmission electron microscope photograph of the particles. Although there is a report that the planar shape shown is captured and made into a hexahedral shape or a cubic shape, as shown in the scanning electron micrograph of FIG. 5 after capturing the three-dimensional shape of the particle, it actually exhibits an octahedron. This is different from the particle shape of the magnetite particles according to the present invention.

Also, JP-A-48-99700 and the Powder and Powder Metallurgy Association, Autumn Meeting, Showa 46, p. 112, lines 14-19, include a ferrous hydroxide colloid containing aqueous ferrous hydroxide solution. It is disclosed that magnetite particles exhibiting a hexahedron are generated by performing a magnetite growth reaction in a pH range of 4 to 6 while blowing an oxygen-containing gas, and the obtained magnetite particle powder is shown in Comparative Example 7 described later. As described above, the goethite particle powder is apt to be mixed in the magnetite particle powder, and the Fe ²⁺ content is completely different from the magnetite particle powder according to the present invention, and is inferior in blackness.

Now, a description will be given of a part extracted from many examples performed by the inventor as follows.

FIG. 1 shows the relationship between the specific surface area of the magnetite particle powder and the residual magnetization after applying an external magnetic field of 1 KOe. In FIG. 1, the symbol △ indicates octahedral magnetite particle powder, and the symbol ○ indicates hexahedral magnetite particle powder.

As shown in FIG. 1, the magnetite particles having a hexahedron according to the present invention have a smaller residual magnetization than the magnetite particles having an octahedron.

Generally, the particle size of magnetite particles and the remanent magnetization are closely related, and the smaller the particle size, that is,
As the BET specific surface area increases, the residual magnetization tends to increase. In the present invention, the magnetite particles having the BET specific surface area and the residual magnetization in the range surrounded by the straight lines a, b, c and d in FIG. Has been obtained.

The range surrounded by the straight lines a, b, c and d is represented by the following equation.

σr (emu / g) = 0.92 × specific surface area value + b (however, specific surface area = 3.0 to 15 m ² / g, b = 1.6 to 3) Next, various conditions for implementing the present invention will be described.

As the ferrous salt aqueous solution used in the present invention,
There are aqueous ferrous sulfate and aqueous ferrous chloride.

Examples of the alkaline aqueous solution used in the present invention include an aqueous solution of an alkali hydroxide such as an aqueous solution of sodium hydroxide, an aqueous solution of an alkali carbonate such as sodium carbonate, potassium carbonate and ammonium carbonate, and aqueous ammonia.

The addition amount of the alkaline aqueous solution in the present invention is equal to or less than the equivalent of Fe ²⁺ in the aqueous ferrous salt solution, and if it exceeds the equivalent, octahedral magnetite particle powder is generated.

The reaction for producing magnetite core particles in the present invention is performed at pH 6.
It is performed in the range of 0 to 7.5.

When the pH is lower than 6.0 or when the pH is higher than 7.5, magnetite particle powder having a hexahedron having asymmetric particle size is generated.

The partial oxidation of the ferrous hydroxide colloid in the present invention is preferably 30% or less based on the total Fe ^{2+ in} consideration of the particle size of the generated hexahedral magnetite particles.

The growth reaction of magnetite particles in the present invention is pH 8.
It is in the range of 0 to 9.5.

When the pH is less than 8.0, spherical magnetite particle powder is generated.

When the pH exceeds 9.5, octahedral magnetite particles are formed.

The oxidizing means in the present invention is performed by passing an oxygen-containing gas (for example, air) through the liquid.

The reaction temperature in the present invention is usually in the range of 45 to 100 ° C., which is the temperature at which magnetite particles are formed.

When the temperature is lower than 45 ° C., acicular goethite particles are mixed in the hexahedral magnetite particle powder.

When the temperature exceeds 100 ° C., hexahedral magnetite particle powder is generated, but it requires a special device such as an autoclave and is not industrial.

The hexahedral magnetite particle powder according to the present invention
When the Fe ²⁺ content is less than 0.3 in molar ratio with ^respect to Fe ³⁺ ,
Blackness decreases.

If the residual magnetization σr is greater than 3 in the equation σr (emu / g) = 0.92 × specific surface area value + b, the magnetic cohesion becomes large, which is not preferable as magnetic particle powder for magnetic toner. In the above formula, the value of b is more preferably in the range of 1.6 to 2.5.

〔Example〕

Next, the present invention will be described with reference to Examples and Comparative Examples.

In the following Examples and Comparative Examples, the shapes of the particles were observed with a scanning electron microscope, and the particle size distribution of the particles was observed with a transmission electron microscope.

The specific surface area of the particles is indicated by a value measured by the BET method, and the remanent magnetization is expressed by "vibrating sample magnetometer VSM-3S-1".
5 "(manufactured by Toei Kogyo Co., Ltd.) and a value measured after applying an external magnetic field of 1 KOe.

The Fe ²⁺ content was indicated by a value determined by the following chemical analysis method. That is, in an inert gas atmosphere, 25 cc of a mixed solution containing phosphoric acid and sulfuric acid at a ratio of 2: 1 to 0.5 g of the magnetic particle powder is added to dissolve the magnetic particle powder. After adding a few drops of diphenylaminosulfonic acid as an indicator to the diluted solution of the aqueous solution, redox titration was performed using an aqueous solution of potassium dichromate. The end point was defined as the time when the above-mentioned diluted solution turned purple, and it was calculated from the amount of the aqueous potassium dichromate solution used up to the end point.

The a ^* value representing reddish color and the b ^* value representing blueish color were measured by using a multi-source spectrophotometer MSC-IS-2D (manufactured by Suga Reagent Co., Ltd.). L depending on space
^* Value, a ^* value, and b ^* value are measured respectively, and the Commission Internationale de l'Eclairage, CI
E) Values are shown according to the 1976 (L ^* , a ^* , b ^* ) uniform perceived color space. As the a ^* value representing the reddishness approaches 0 and the negative value of the b ^* value representing the bluishness increases, the blackness becomes excellent and the bluish black is obtained.

The measurement specimen was made into a paste by binding 0.5 g of magnetite particle powder and 1.0 cc of castor oil with a Hoover-type muller, adding 4.5 g of clear lacquer to the paste, kneading the mixture, and forming a paint. And obtained by application.

Example 1 Ferrous sulfate aqueous solution containing 1.5 mol / Fe ²⁺ 20 and 2.64−
An aqueous solution of ferrous salt containing Fe (OH) ₂ was produced at pH 6.9 and at a temperature of 90 ° C. by mixing with an N NaOH aqueous solution 20.

Air at 80 ° C./minute was passed through the aqueous ferrous salt solution containing Fe (OH) ₂ at 90 ° C. for 25 minutes to produce an aqueous ferrous salt solution containing magnetite particles and Fe (OH) ₂ .

Then, to the ferrous salt aqueous solution containing the magnetite particles and Fe (OH) ₂ , 3.78-N NaOH aqueous solution 1.83 was added,
Magnetite particles were produced by passing air at a rate of 8.5 and a temperature of 90 ° C. at a rate of 50 min / min for 280 min.

The produced particles were washed with water, separated, dried and pulverized by a conventional method.

The obtained magnetite particle powder is a hexahedral particle, as is clear from the scanning electron micrograph (× 20000) shown in FIG. 2, and the transmission electron micrograph (×
20000), the particle size was uniform.

This hexahedral magnetite particle powder has a BET specific surface area of 7.0 m ² / g, a residual magnetization of 7.1 emu / g, and as a result of chemical analysis, the Fe ²⁺ content is reduced to Fe ³⁺ . On the other hand, the molar ratio was 0.38, indicating a bluish black color. The a ^* value of the black particle powder was +0.04 and the b ^* value was -1.74.

Examples 2-3, Comparative Examples 1-4 Kind, concentration, and amount of aqueous solution of Fe ²⁺ , kind, concentration, and amount of alkaline aqueous solution, pH, temperature, and growth reaction of magnetite nucleus particles in generation reaction of magnetite nucleus particles The magnetite particles were produced in the same manner as in Example 1, except that the kind, concentration and amount of use, pH and temperature of the alkaline aqueous solution in Example 1 were variously changed.

The main production conditions at this time are shown in Table 1, and various properties of the produced magnetite particles are shown in Table 2.

The magnetite particle powder obtained in Example 2 was a particle having a uniform particle size as shown in a transmission electron micrograph shown in FIG. The magnetite particle powder obtained in Example 3 was also a particle having a uniform particle size.

The magnetite particle powder obtained in Comparative Example 1 and Comparative Example 2 was a particle having an uneven particle size as a result of observation with a transmission electron microscope.

Comparative Example 5 An aqueous ferrous sulfate solution containing 1.5 mol / Fe ²⁺ 20 and 3.40−
An N aqueous solution of NaOH 20 was mixed to produce an aqueous solution containing Fe (OH) ₂ at pH 12.5 and a temperature of 90 ° C.

The above aqueous solution containing Fe (OH) ₂ at a temperature of 90 ° C per minute
Air of 100 was aerated for 220 minutes to produce magnetite particle powder.

The obtained magnetite particle powder is an octahedral particle, as apparent from the scanning electron micrograph (× 20000) shown in FIG. 5, and the transmission electron micrograph (×
20000), the particle size was uneven.

This octahedral magnetite particle powder had a BET specific surface area of 4.5 m ² / g and a high residual magnetization of 7.9 emu / g. Also, as a result of the chemical analysis, the Fe ²⁺ content was
^The molar ratio to ³⁺ is 0.40, the a ^* value is -0.02, b ^*
The value was -2.02, and the color was bluish black.

Comparative Example 6 Ferrous sulfate aqueous solution containing Fe ²⁺ 1.5 mol / 20 and 2.76−
N 2 NaOH aqueous solution 20 (corresponding to 0.92 equivalents to Fe ²⁺ ), and mixed with Fe (OH) at a pH of 7.1 and a temperature of 90 ° C.
An aqueous ferrous salt solution containing ₂ was produced.

Air at a temperature of 90 ° C. was passed through the above aqueous ferrous salt solution containing Fe (OH) ₂ at 240 ° C. for 240 minutes to produce an aqueous ferrous salt solution containing magnetite particles.

Next, 1.78-N NaOH aqueous solution 1.85 was added to the ferrous salt aqueous solution containing the magnetite particles (with respect to the residual Fe ²⁺ ).
This corresponds to 1.46 equivalents. ), At a temperature of 90 ° C. at a pH of 12.5, and air at 20 min / min was passed for 60 min to produce magnetite particles.

The produced particles were washed with water, separated, dried and pulverized by a conventional method.

The obtained magnetite particle powder was spherical particles as a result of observation with a scanning microscope, and had a BET specific surface area of 6.9 m ^2.
/ g, and the residual magnetization was 4.7 emu / g. As a result of chemical analysis, the Fe ²⁺ content was 0.26 in molar ratio to Fe ³⁺ , the a ^* value was +0.66, the b ^* value was −0.33, and the color was slightly brownish black. Met.

Comparative Example 7 A ferrous sulfate aqueous solution 2.4 containing 1.5 mol / Fe ²⁺ was placed in a reaction vessel, and then the ferrous sulfate aqueous solution was stirred for 3 hours.
/ min at a rate of 2.521-N
After adding aOH aqueous solution 1.6, immediately warm and after 20 minutes
The temperature was raised to 50 ° C. and maintained at that temperature for 15 hours to produce precipitated particles. At this time, the pH was 4.3.

The precipitated particles were washed with water, separated, dried and pulverized by a conventional method.

As a result of observation with an electron microscope, the obtained particle powder contained needle-like particles and hexahedral particles, and as a result of X-ray diffraction, peaks of magnetite and goethite were observed.

The Fe2 ⁺ content of the magnetite particle powder obtained by magnetically sorting the above particle powder was 0.23 with ^respect to Fe3 ^{+ in a} molar ratio.

(Effect of the invention) The magnetite particle powder having a hexahedron according to the present invention has a bluish black color due to the Fe2 ⁺ content being 0.3 to 0.5 in molar ratio with respect to Fe3 ⁺ , and Because of its low magnetic cohesion, it has excellent miscibility with resin, and is therefore suitable as a material particle powder for magnetic toner.

Furthermore, the magnetic toner obtained by using the magnetite particle powder having a hexahedral shape according to the present invention has an excellent image density by exhibiting a sufficient black color, and has a low image cohesion force due to a small magnetic cohesion. Excellent without unevenness.

The hexahedral magnetite particle powder according to the present invention has a bluish black color and is excellent in dispersibility, so that it is also used as a well-known pigment powder for paint or pigment powder for resin coloring. Of course you can.

[Brief description of the drawings]

FIG. 1 shows the relationship between the specific surface area of the magnetite particle powder and the residual magnetization after applying an external magnetic field of 1 KOe. In FIG. 1, the symbol △ indicates octahedral magnetite particle powder, and the symbol ○ indicates hexahedral magnetite particle powder. FIGS. 2 and 5 are scanning electron micrographs (× 20000) showing the particle structures of the magnetite particle powders obtained in Example 1 and Comparative Example 5, respectively, and are shown in FIGS. 3, 4 and 6.
1 is a transmission electron micrograph (× 20000) showing the particle structure of the magnetite particles obtained in Example 1, Example 2 and Comparative Example 5, respectively.

Claims (2)

(57) [Claims] (1) The content of Fe ²⁺ is from 0.3 to 0.5 in molar ratio to Fe ^3+.
Has a specific surface area of 3.0 to 15.0 m ² / g, and a residual magnetization σr after applying an external magnetic field of 1 kOe is represented by an equation σr (em
u / g) = 0.92 × specific surface area value + b (where b = 1.6 to 3), a magnetite particle powder comprising hexahedral magnetite particles in the range shown by: 2. A ferrous salt aqueous solution and Fe in the ferrous salt aqueous solution.
^The oxygen-containing gas is passed through a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid having a pH in the range of 6.0 to 7.5 obtained by reacting an alkaline aqueous solution of 2 equivalent or less with respect to ²⁺ The ferrous hydroxide colloid is partially oxidized to produce magnetite core particles, and then added to the aqueous ferrous salt reaction solution containing the magnetite core particles and the ferrous hydroxide colloid at pH 8.0 to 9.5. The method for producing magnetite particle powder comprising hexahedral magnetite particles according to claim 1, wherein the growth reaction of the magnetite core particles is performed by passing an oxygen-containing gas.