JPH03201509A - Magnetite particle powder displaying hexahedron and manufacture thereof - Google Patents

Abstract

PURPOSE:To display black while reducing magnetic fluocculation force, and to improve mixing properties with a resin by composing the title magnetite particle powder of magnetite particles, in which Fe<2+> content is specified to Fe<3+>, residual magnetization of which after an external magnetic field of 1kOe is applied is kept within a specific range and which displays a hexahedron. CONSTITUTION:A gas containing oxygen is ventilated through a ferrous salt reaction aqueous solution containing ferrous hydroxide colloid at pH6.0-7.5 acquired by reacting a ferrous salt aqueous solution and an alkaline aqueous solution of equivalent or less to Fe<2+> in the solution, and ferrous hydroxide colloid is oxidized partially, thus forming magnetite nucleus particles. The gas containing oxygen is ventilated through the ferrous salt reaction aqueous solution containing the magnetite nucleus particles and the ferrous hydroxide colloid within a range of pH8.0-9.5, and the growth reaction of the magnetite nucleus particles is conducted. Accordingly, magnetite particle powder, residual magnetization sigmar of which after an external magnetic field having a mol ratio of 0.3-0.5 to Fe<3+> or Fe<2+> content and 1kOe is applied is kept within a range shown in the formula and which displays a hexahedron consists of magnetite particles, is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides magnetite particles that are black in color and have excellent miscibility with resins due to their small magnetic cohesive force, and magnetite particles thereof. It concerns the manufacturing method.

The main use of the magnetite particles according to the present invention is as material particles for magnetic toner.

[Conventional technology]

Conventionally, as one of the methods for developing electrostatic latent images, so-called component-based magnetic toner is used as a developer using composite particles in which magnetic particles such as magnetite particles are mixed and dispersed in a resin without using a carrier. This developing method is widely known and widely used.

In recent years, with the increasing performance of copying equipment such as higher speeds, higher N'l, and continuous use, there has been a strong demand for improved characteristics of magnetic toner, which is the developer. It is required that the magnetic particles have a black color and have excellent miscibility with the resin.

This fact is explained in Japanese Patent Application Laid-Open No. 55-65406, "Generally, the following properties are required for magnetic powder for magnetic toner in such a -component method... iv) For practical use. The magnetic toner must have a blackness that can withstand the color.Although a coloring agent can be contained in the magnetic toner, it is preferable that the powder itself has a black color and no coloring agent is used. vi)
Good miscibility with resin.

...The degree of microscopic mixing in the toner is important for the properties of the toner. It is as stated in ``...''.

The blackness of magnetite particle powder is determined by the following: "The blackness of the sample depends on the Fe (Ill content and average particle size,
The powder having an average particle size of 0.2 μm is a bluish black powder and is most suitable as a black pigment. ...Fe(I)
When the content is 10% or more, there is a slight difference in the degree of blackness, but all the samples are black.

Fe ([When the content of 1 decreases to 10% or less, each sample changes from black to reddish brown."), the magnetite particle powder of about 0.1 to 0.5 μm used for magnetic toner. It is known that this is mainly influenced by the Fe'' content.

In order to improve the mixability of magnetite particles and resin, it is necessary that the magnetite particles have excellent dispersibility, and for this purpose, the residual magnetization is as small as possible to improve the magnetic It is required that the cohesive force be small.

Incidentally, r = = l in Japanese Patent Application Laid-Open No. 128356/1983
The strength of the magnetic field of KOe approximately corresponds to the strength of the magnetic field near the developing sleeve when performing development using the magnetic capsule toner of the present invention. '', magnetic toner is generally used under an external magnetic field of about I KOe, so the residual magnetization of the magnetite particles contained in the magnetic toner also has a value after applying an external magnetic field of I KOe. It is desired that it be as small as possible.

Magnetite particles conventionally used as magnetic particles for magnetic toners are obtained by reacting an aqueous ferrous salt solution with an alkaline aqueous solution in an amount equal to or more than the amount of Pe'' in the aqueous ferrous salt solution. Magnetite particle powder exhibiting an octahedron obtained by aerating an oxygen-containing gas into a suspension containing ferrous hydroxide having a pH of 10 or higher (
Japanese Patent Publication No. 44-668> or ■ ferrous salt aqueous solution and p e + 1 in the ferrous salt aqueous solution from 0.80 to 0.
．． A first step of generating spherical magnetite particles by passing an oxygen-containing gas through a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid obtained by reacting 9 g equivalent of alkali hydroxide; - After the completion of the reaction, residual Fe''
Magnetite particle powder exhibiting a spherical shape obtained by adding 1.00 equivalent or more of alkali hydroxide to 2 and heating and oxidizing at 91110 or more (Japanese Patent Publication No. 62-5120
Publication No. 8).

[Problem a that the invention attempts to solve]

Magnetite particles, which are black in color and have excellent miscibility with resin, are currently in demand in large quantities, but the magnetite particles with octahedral shapes mentioned above have a high Fe" content. is 0.0 in molar ratio to Fe50.
3 to 0.45, which is excellent in terms of blackness, but because the residual magnetization is large and magnetic aggregation is likely to occur, the dispersibility is poor<m and the miscibility with fats is poor. Also,
The spherical magnetite particles mentioned above have small residual magnetization and are less likely to cause magnetic agglomeration, so they have excellent dispersibility and good mixability with resin.
Since the molar ratio to "e" is at most about 0.28, the black color is slightly brownish, and the degree of blackness is poor.

Therefore, the technical object of the present invention is to obtain magnetite particles that are black in color and have excellent miscibility with resins due to their small magnetic cohesive force.

[Means to solve problems]

The technical vsa can be distantly related to the present invention as follows.

That is, in the present invention, the Fet* content is 0.3 to 0.5 in molar ratio to Fe'', and the residual magnetization σr after applying an external magnetic field of Oe to 1 is expressed by the formula σr(emu/ g)
= 0.92X specific surface area value + b (however, specific surface area = 3.0
~15°0rrf/g, b = 1.6 to 3) Magnetite particle powder consisting of hexahedral magnetite particles and a ferrous salt aqueous solution and Fet'' in the ferrous salt aqueous solution. A ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid with a pH range of 6.0 to 7.5 obtained by reacting an alkaline aqueous solution of an equivalent amount or less to the above water is The ferrous oxide colloid is partially oxidized to produce magnetite core particles, and then added to a ferrous salt reaction aqueous solution containing the magnetite core particles and ferrous hydroxide colloid at p) 18.0 to 9.5. The growth reaction of the magnetite core particles is carried out by aerating an oxygen-containing gas in the range of
The content is 0.3 to 0.5 in molar ratio to Fe''', and the residual magnetization σr after applying an external magnetic field of IKOe is expressed by the formula σr (emu/g) = 0.92X specific surface area. Value + b (however, specific surface area = 3.0 to 15.0 po/g,
This is a method for producing magnetite particle powder consisting of magnetite particles exhibiting a hexahedral shape in the range shown by b = 1.6 to 3).

[For production]

First, the most important point in the present invention is that the pl! 5
partially oxidize the ferrous hydroxide colloid to form magnetite core particles by bubbling an oxygen-containing gas into the ferrous salt reaction aqueous solution containing the ferrous hydroxide colloid in the range of P) 18.0 to the ferrous salt reaction aqueous solution containing the magnetite core particles and ferrous hydroxide colloid.
This is the fact that when oxygen-containing gas is aerated in the range of ~9.5, magnetite particles that are black in color and have a small magnetic cohesive force are obtained.

The magnetite particles according to the present invention have a hexahedral particle shape as shown in the scanning electron micrograph of FIG.
．． 5, it has a bluish black color, and the residual magnetization σ after applying an external magnetic field of I KOe.
Since r is small, magnetic aggregation is small.

The particle shape of the magnetite particles obtained by aerating oxygen-containing gas into the suspension containing ferrous hydroxide colloid with a pH of 10 or more described in (2) above is shown in a transmission electron micrograph of the shadows of the particles. There are reports that the planar shape shown in Figure 5 is hexahedral or cubic, but as shown in the scanning electron micrograph in Figure 5 below, which shows the three-dimensional shape of the particle, it is actually octahedral. This is different from the particle shape of the magnetite particles according to the present invention.

In addition, JP-A-48-99700 and Powder Metallurgy Association 1972 Autumn Conference Lecture Summary Collection, page 112, No. 14
Lines ~19 show p[+4~6 while blowing oxygen-containing gas into the ferrous salt reaction aqueous solution containing ferrous hydroxide colloid.
It is disclosed that hexahedral magnetite particles are produced by carrying out a magnetite growth reaction in the range of In addition, the content of Fe'' is completely different from that of the magnetite particles according to the present invention, and the degree of blackness is inferior.

Some of the many examples carried out by the present inventor will now be extracted and explained as follows.

FIG. 1 shows the relationship between the specific surface area of magnetite particles and the residual magnetization after applying an external magnetic field of 1 Oe. In FIG. 1, Δ marks indicate magnetite particle powder exhibiting an octahedral shape, and O marks indicate magnetite particle powder exhibiting a hexahedral shape.

As shown in FIG. 1, the hexahedral magnetite particles according to the present invention have smaller residual magnetization than the octahedral magnetite particles.

Generally, there is a close relationship between the particle size and residual magnetization of magnetite particles, and the smaller the particle size, the more B
The larger the ET specific surface area, the larger the residual magnetization tends to be, and in the present invention, magnetite particles having a BET specific surface area and residual magnetization in the range surrounded by straight lines a, b, c, and d in FIG. is obtained.

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

σr (emu/g) −0,92X specific surface area value +b(
However, specific surface area = 3.0 to 15.0 po/g, b = 1
．． 6-3) Next, various conditions for implementing the present invention will be described.

Examples of the ferrous salt aqueous solution used in the present invention include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution.

The alkaline aqueous solution used in the present invention includes:
Alkaline hydroxide aqueous solution such as sodium hydroxide aqueous solution,
Examples include aqueous alkaline carbonate solutions such as sodium carbonate, potassium carbonate, and ammonium carbonate, and aqueous ammonia.

The amount of the alkaline aqueous solution added in the present invention is equal to or less than the equivalent amount to p e 1 * in the ferrous salt aqueous solution, and if the amount exceeds the equivalent amount, magnetite particles having an octahedral shape are produced.

The production reaction of magnetite core particles in the present invention is carried out at pH 6.
, 0 to 7.5.

When the pH is less than 6.0, and when the pH exceeds 7.5, magnetite particles having a hexahedral shape with asymmetric particle size are produced.

The partial oxidation of ferrous hydroxide colloid in the present invention is
When considering the particle size of the generated hexahedral magnetite particles, it is preferable that the amount is 30% or less based on the total Fe''.

The growth reaction of magnetite particles in the present invention is carried out at pH 8.
, in the range of 0 to 9.5.

When the pH is less than 8.0, spherical magnetite particles are produced.

If the pH exceeds 9.5, octahedral magnetite particles are produced.

The oxidation means in the present invention is carried out by passing an oxygen-containing gas (for example, air) into 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 produced.

When the temperature is lower than 45° C., goethite particles having an acicular shape are mixed in the magnetite particles having a hexahedral shape.

Even when the temperature exceeds 100° C., hexahedral magnetite particles are produced, but this requires special equipment such as an autoclave, which is not industrially practical.

F of magnetite particle powder exhibiting hexahedron according to the present invention
When the molar ratio of the e'''' content to Fe'' is less than 0.3, the degree of blackness decreases.

The residual magnetization σr is expressed by the formula σr (emu/g) = 0.92X
In the specific surface area value +b, if b exceeds 3, the magnetic cohesive force becomes large, which is not preferable as a magnetic particle powder for magnetic toner. In the above formula, the value of b is 1.6
The range of ˜2.5 is more preferable.

〔Example〕

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

In the Examples and Comparative Examples below, the shape of the particles was observed using a scanning electron microscope, and the particle size distribution of the particles was observed using a transmission electron microscope.

The specific surface area of the particles is shown as a value measured by the BET method, and the residual magnetization is measured using a "vibrating sample magnetometer VSM-3S".
-15J (manufactured by Toei Kogyo ■) after applying an external magnetic field of 1 Koe.

The Fe'' content was shown as a value determined by the chemical analysis method described below. 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 is added to 0.5 g of magnetic particle powder to dissolve the magnetic particle powder. After adding several drops of diphenylaminosulfonic acid as an indicator to the diluted solution of this dissolved aqueous solution, redox titration was performed using an aqueous potassium dichromate solution. The end point was defined as the time when the diluted solution turned purple, and the end point was calculated from the amount of potassium dichromate aqueous solution used to reach the end point.

Furthermore, the am value representing reddishness and the b0 value representing bluishness can be determined using a multi-light source spectrophotometer. 1SC-l5-2
0 (manufactured by Suga Test Instruments) using Hunter's Lab
Measure the L0 value, a0 value, and b1 value by space,
Commission Intern
ationale de l'Eclairage,
CIE) 1976 (L”a”b”) Values expressed according to the uniform perceptual color space.The closer the a8 value, which represents reddishness, approaches O,
The larger the negative value, the better the degree of blackness, and the black color becomes bluish.

The sample piece for measurement was made by kneading 0.5 g of magnetite particle powder and 1 part of castor oil into a paste using a two-bar type muller, adding 4.5 g of clear lacquer to this paste, kneading it, and making it into a paint.
It was obtained by applying it using a 1 applicator.

Example I Ferrous sulfate aqueous solution containing 1.5 mol#!
ffi and 2.64-N NaOH aqueous solution 201 were mixed to produce a ferrous salt aqueous solution containing Fe(OH)t at pH 6.9 and temperature 90°C.

The above ferrous salt aqueous solution containing Fe(0■)8 was added at a temperature of 90°C.
A ferrous salt aqueous solution containing magnetite particles and Fe(OH)z was produced by blowing air at 80ffi/min for 25 minutes at .

Next, the above magnetite particles and Fe(OH)!
1.83 J of a 3.78-N NaOH aqueous solution to a ferrous salt aqueous solution containing! was added, and 501 air per minute was aerated for 280 minutes at a temperature of 90° C. to generate magnetite particles.

The generated particles were washed with water, separated in an oven, dried, and pulverized by a conventional method.

As is clear from the scanning electron micrograph (X20000) shown in FIG. 2, the obtained magnetite particles are hexahedral particles, and as shown in the transmission electron micrograph (X20000) shown in FIG. was uniform.

This magnetite particle powder exhibiting a hexahedral shape is RIOT
The specific surface area is 7.0 rrf/g and the residual magnetization is 7.
゜1 ewpH/g, and as a result of chemical analysis, P
The molar ratio of e"" content to Fe" was 0.38, giving it a bluish black color.
The value was +0.04 and the bs value was -1.74.

Examples 2 to 3, Comparative Examples 1 to 4 Type, concentration, and usage amount of Fe'' aqueous solution in magnetite core particle production reaction, type, concentration, and usage amount of alkaline aqueous solution, pH1 temperature, and in magnetite core particle growth reaction Magnetite particles were produced in the same manner as in Example 1, except that the type, concentration and amount of alkaline aqueous solution used, and pH1 temperature were varied.

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

As shown in the transmission electron micrograph shown in FIG. 4, the magnetite particles obtained in Example 2 were uniform in particle size. Furthermore, the magnetite particles obtained in Example 3 were also uniform in particle size.

As a result of transmission electron microscopy observation, the magnetite particles obtained in Comparative Examples 1 and 2 were particles with asymmetric particle sizes.

Comparative Example 5 Ferrous sulfate aqueous solution 2 containing Fe” 1.5 sol/j!
01 and a 3.40-N NaOH aqueous solution 201 were mixed to produce an aqueous solution containing Fe(OR)t at a p of 2.5 and a temperature of 90°C.

Above Fe(OH)! 100 j per minute at a temperature of 90°C in an aqueous solution containing of air was passed through the tube for 220 minutes to produce magnetite particle powder.

The obtained magnetite particle powder is an octahedral particle as shown in the scanning electron micrograph (x 20,000) shown in Fig. 5, and as shown in the transmission electron micrograph (x 20,000) in Fig. 6. , the particle size was asymmetric.

This octahedral magnetite particle powder is BlET
The specific surface area is 4.5%/g and the residual magnetization is 7°9.
It was as high as emu/g. In addition, as a result of chemical analysis, the Fe content was 0.40 in molar ratio to Fe, the am value was -0.02, the b0 value was -2.02, and the color was a bluish black color. It was exhibiting.

Comparative Example 6 Ferrous sulfate aqueous solution containing 1.5 mol/f of Fe” 20
1 and 2.76-N NaOH aqueous solution 20 e (Fe
(corresponds to 0.92 equivalent to
7. An aqueous ferrous salt solution containing re (OH) z was produced at a temperature of 90°C.

The above ferrous salt aqueous solution containing Fe(OH)z was heated to a temperature of 90°C.
A ferrous salt aqueous solution containing magnetite particles was produced by blowing air at 100 l/min for 240 minutes.

Next, a 3.78-N NaOH aqueous solution (1.8!) was added to the ferrous salt aqueous solution containing the magnetite particles. Add l (l for residual Fe''°, 1 h for 46 equivalents), ρ old 2
, 5. Magnetite particles were generated by blowing 201 air per minute for 60 minutes at a temperature of 90°C.

The generated particles were washed with water, separated in an oven, dried, and pulverized by a conventional method.

As a result of scanning electron microscope observation, the obtained magnetite particles were found to be spherical particles with a BET specific surface area of 6.9 rd/g and a residual magnetization of 4.9 rd/g. γemu/g
Met. In addition, as a result of chemical analysis, the Fe”° content was
The molar ratio to Fe″′ was 0.26, the a′1 value was +0.66, the b1 value was −0.33, and the color was slightly brownish black.

Comparative Example 7 Ferrous sulfate aqueous solution containing 1.5 mol#! of Fe"2.
41 into the reaction vessel, air was blown into the ferrous sulfate aqueous solution at a rate of 342/sin without stirring, and then 1.6 I!
, was immediately heated to 50°C after 20 minutes, and maintained at this temperature for 15 hours to form precipitated particles. The pH at this time was 4.3.

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

As a result of electron microscopy observation, the obtained powder particles were found to contain a mixture of acicular particles and hexahedral particles, and as a result of X-ray diffraction,
Peaks of magnetite and goethite were observed.

Incidentally, the p e Z + content of the magnetite particles obtained by magnetically sorting the above particles was 0.23 in molar ratio to Fe34.

Table 2 [Effects of the invention] The hexahedral magnetite particles according to the present invention are as follows:
The molar ratio of Fe content to Fe is 0.3 to 0.5, which gives it a bluish black color, and its low magnetic cohesive force makes it difficult to interact with resin. Since it has excellent mixability, it is suitable as a material particle powder for magnetic toner.

Furthermore, the magnetic toner obtained using the hexahedral magnetite particles according to the present invention exhibits sufficient black color and has excellent image density. It is excellent with no unevenness.

In addition, the hexahedral magnetite particle powder according to the present invention has a bluish black color and has excellent dispersibility, so it can also be used as a well-known pigment powder for paints and pigment powder for resin coloring. Of course you can.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the specific surface area and l of magnetite particles. In FIG. 1, Δ marks indicate magnetite particle powder exhibiting an octahedral shape, and O marks indicate magnetite particle powder exhibiting a hexahedral shape. 2 and 5 are scanning electron micrographs (x 2000G) showing the particle structure of the magnetite particles obtained in Example 1 and Comparative Example 5, respectively, and FIGS. 3, 4, and 6 are respectively 1 is a transmission electron Im mirror photograph (x 20,000) showing the particle structure of magnetite particles obtained in Example 1, Example 2, and Comparative Example 5.

Claims (2)

[Claims] (1) The Fe^2^+ content is 0.3 to 0.5 in molar ratio to Fe^3^+, and the residual magnetization σr after applying an external magnetic field of 1 KOe is expressed by the formula σr(emu /g)=
0.92 x specific surface area value + b (however, specific surface area = 3.0 ~
15.0m^2/g, b=1.6-3) Magnetite particle powder consisting of magnetite particles exhibiting a hexahedral shape. (2) Ferrous salt aqueous solution and Fe^2 in the ferrous salt aqueous solution
Aerating an oxygen-containing gas into a ferrous salt reaction aqueous solution containing ferrous hydroxide colloid with a pH range of 6.0 to 7.5 obtained by reacting an alkaline aqueous solution in an amount equal to or less than ^+. The ferrous hydroxide colloid is partially oxidized to produce magnetite core particles, and then the ferrous salt reaction aqueous solution containing the magnetite core particles and the ferrous hydroxide colloid is adjusted to a pH of 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 carried out by aerating an oxygen-containing gas in the range of claim 5.