JPH04204949A - Needle-shaped magnetite particle powder for magnetic toner and its production - Google Patents

Abstract

PURPOSE:To decrease magnetic flocculation force to increase mixing property with resin and to expose the surface of toner particles and to make the grain black by specifying the grain size, aspect ratio and residual magnetization of needle-shaped magnetite grains. CONSTITUTION:The magnetite grains are controlled to 100-200Angstrom grain size, 1.5-10.0 aspect ratio and 10-30emu/g residual magnetization for 1KOe external magnetic field. These needle-shaped magnetite grains are prepared by heating and dehydrating needle--shaped lepidochrosite grains at 200-500 deg.C to obtain needle-shaped maghemite grains, dispersing the maghemite grains in an alkali suspension containing iron hydroxide colloid produced by the reaction of iron (II) salt aq. and alkali hydroxide aq., and then heating while stirring the suspension in a nonoxidative atmosphere at 40-100 deg.C.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to a crystallite having a crystallite size of 100 to 200,
A magnetic toner material particle powder consisting of acicular magnetite particles having an axial ratio (major axis diameter/minor axis diameter) of 1.5 to 10.0 and a residual magnetization value of 10 to 30 emu/g, and a method for producing the same It is related to.

[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 magnetophyte particles are mixed and dispersed in a resin without using a carrier. This developing method is widely known and widely used.

Recently, as the performance of copying equipment has increased, such as faster speeds, higher image quality, and continuous use, there has been a strong demand for improved characteristics of magnetic toner, which is the developer. It is required to have a black color and to have excellent miscibility with 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. Must have a durable blackness.Although a coloring agent may be included in the magnetic toner, the powder itself has a black color and it is preferable not to use a coloring agent. Good mixability.

...The degree of microscopic mixing in the toner is important for the properties of the toner. ...as described in J.

In order to improve the mixability of the magnetite particles and the resin, it is necessary that the magnetite particles have excellent dispersibility. It is required that the cohesive force is small.

In addition, ``...1K'' of JP-A-63-128356
The strength of the magnetic field Oe 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 XOe, so the residual magnetization value of the magnetite particles contained in the magnetic toner is also the value after applying an external magnetic field of I KOe. is desired to be as small as possible.

On the other hand, magnetic toner with excellent fine line reproducibility and gradation is effective in solving the problem of sharpness of image quality as described in Japanese Patent Application Laid-Open No. 1-221754. According to the description "...", a reduction in particle size is desired. However, since the surface area of the magnetic toner increases as the particle size decreases, the amount of charge on the magnetic toner particles abnormally increases from the appropriate value.

Such a phenomenon also occurs due to the hydrophobization treatment of the magnetic particles, which is performed to improve the miscibility of the magnetic particles with the resin, that is, the dispersibility and adhesion to the binder resin.

This fact is shown in Japanese Unexamined Patent Publication No. 2-97968 [...
By hydrophobizing the magnetic powder, the resistance of the toner itself increases...the amount of charge of the magnetic toner changes from an appropriate value to an increasing value. If the amount of charge increases abnormally from a proper value, the thickness of the toner coating layer on the sleeve becomes uneven, the image density decreases, and the quality of the image deteriorates.

It is as stated in ``...''.

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 equivalent to or more of Fe"2 in the ferrous salt aqueous solution. Magnetite particle powder exhibiting an octahedron obtained by bubbling oxygen-containing gas into a suspension containing ferrous hydroxide colloid with pI (10 or more)
(Japanese Patent Publication No. 44-668), ■ Hydroxide obtained by reacting an aqueous ferrous salt solution with an alkali hydroxide equivalent of 0.80 to 0.9 g based on the amount of Fe in the aqueous ferrous salt solution. A first stage in which spherical magnetite particles are generated by passing an oxygen-containing gas into a ferrous salt reaction aqueous solution containing ferrous colloid;
Magnetite particle powder exhibiting a spherical shape obtained by adding 0.00 equivalent or more of alkali hydroxide and heating and oxidizing at pH 10 or more (Japanese Patent Publication No. 62-51208);
Or, ■ Dry method needles obtained by heating and reducing acicular hematite particles obtained by heating and dehydrating acicular goethite particles at a temperature range of 200 to 600°C in a reducing gas at a temperature range of 300 to 500°C. Magnetic toners (Japanese Unexamined Patent Application Publication No. 158931/1983, etc.) using magnetite particles may be mentioned.

[Problem to be solved by the invention]

As the performance of modern copying equipment increases, such as higher speeds, higher image quality, and greater continuity, magnetite particles are coated with various surfactants, coupling agents, etc. to improve their miscibility with resins. If the surface of the magnetite particles has been subjected to hydrophobization treatment, but the shape of the magnetite particles is octahedral as described in (2) above or spherical as in (2) above, a part of the magnetite particles are exposed on the particle surface of the magnetic toner particles. Since this is difficult, the amount of charge tends to be larger than the appropriate value.

Since the acicular magnetite particle powder mentioned above is acicular, a part of it is exposed on the particle surface of the magnetic toner particles.
Although it is possible to lower the surface resistance of magnetic toner particles and stabilize the amount of charge, the sintering of the particles caused by thermal dehydration and thermal reduction heat treatment deteriorates the miscibility with the resin, and the magnetite obtained by thermal reduction deteriorates. The higher the residual magnetization value of the particles exceeds 30 emu/g, the higher the magnetic aggregation becomes likely to occur.

Furthermore, the magnetic toner disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-97968, which contains at least a magnetic powder whose surface has been subjected to a hydrophobization treatment and an acicular non-magnetic metal oxide which has not been subjected to a hydrophobization treatment. Since acicular nonmagnetic metal oxides such as hydrated iron oxide and hematite are yellowish brown to reddish brown, they inhibit blackness.

Therefore, the present invention has a black color and has a low residual magnetization value, so the magnetic cohesive force is small, and unlike the dry method, sintering due to heat treatment in a reducing atmosphere does not occur, so it is compatible with resin. The technical object is to obtain acicular magnetite particles that have excellent mixability and can be exposed from the surface of magnetic toner particles.

[Means to solve problems]

The present inventor has arrived at the present invention as a result of various studies regarding the above-mentioned technical problems.

That is, in the present invention, the crystallite size is 100 to 200, the axial ratio is 1.5 to 10.0, and the external magnetic field is 1 KO.
Acicular magnetite particles for magnetic toner and acicular lepidocrocite particles comprising acicular magnetite particles having a residual magnetization value of 10 to 30 emu/g at
An alkaline compound containing ferrous hydroxide colloid obtained by reacting acicular maghemite particles obtained by heating and dehydrating in a temperature range of 0 to 500"C with a ferrous salt aqueous solution and an alkali hydroxide aqueous solution. Acicular magnetite particle powder for magnetic toner is produced by dispersing it in a suspension and heating and stirring the suspension in a non-oxidizing atmosphere at a temperature range of 40 to 100°C to generate acicular magnetite particles. It is a manufacturing method.

Next, various conditions for implementing the present invention will be described.

The crystallite size of the acicular magnetite particles of the present invention is 100
~200 people. If the number of participants exceeds 200, the coercive force and saturation magnetization value will become high, and the residual magnetization value will also become too high, which is not preferable.

If one attempts to obtain less than 100 particles, it will be extremely difficult to control the conditions for producing acicular lepidocrocite particles, heating dehydration, and producing magnetite particles, which is not industrially possible.

The acicular magnetite particles of the present invention have an axial ratio (major axis diameter/minor axis diameter) of 1.5 to 10.0, preferably 2.0 to 6.
It is 0. If the axial ratio is less than 1.5, the toner particles cannot be exposed on the surface of the magnetic toner particles, making it impossible to maintain an appropriate amount of charge. If the axial ratio exceeds 10.0, the residual magnetization value will increase due to shape anisotropy, which is not preferable.

Note that the average major axis diameter is 0.1 to 1.0 μm.

Residual magnetization value (σr) of acicular magnetite particles of the present invention
is 10-30 eIlu/g. 30 emu/g
If it exceeds this, the magnetic cohesive force becomes strong like the acicular magnetite particles obtained by the dry method, which is not preferable.

If it is less than 10 emu/g, the crystallite size must be reduced, so it is not industrially suitable for the same reason as above.

In addition, the coercive force in the external magnetic field IKOe is 150 to 30
It is 00e.

In the present invention, acicular lepidic crocite particles are used as a starting material. For example, Tokuko Sho 36-2170
Publication No. 5, Special Publication No. 37-2006, Special Publication No. 43-
Technical means disclosed in Publication No. 2214, etc. and Ceramic Industry Association Journal Vol. 86, No. 9 (1978), pp. 381-387, When a small amount of phosphate is added during oxidation in an aqueous solution of
-FeOOH is obtained in a single phase, and acicular lepidic crocite particle powder can be obtained by the technical means as described.

The average major axis diameter of the acicular lepidocrocite particles used in the present invention is 0.1 to 1.0 μm, and the axial ratio (major axis diameter/minor axis diameter) is 1.5 to 10.0.

In the present invention, 20 acicular lepidocrocite particles are used.
Temperature range from 0 to 500'C, preferably from 200 to 350'C
Acicular maghemite particles are obtained by heating and dehydration in a temperature range of ℃. If the temperature is lower than 200° C., sufficient dehydration will not occur, making it impossible to maintain the acicular shape during generation of magnetite particles. When the temperature exceeds 500℃, hematite is mixed,
This is not preferable because the crystallite size also increases.

The ferrous salt aqueous solution in the present invention includes ferrous sulfate,
Ferrous chloride or the like can be used.

As the aqueous alkali hydroxide solution in the present invention, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. can be used.

The suspension containing the ferrous hydroxide colloid obtained by reacting the ferrous salt aqueous solution and the alkali hydroxide aqueous solution in the present invention is alkaline. The reason for alkalinity is that acidity is not preferable because ferrous hydroxide colloid is not sufficiently produced and ferrous salt remains. It is desirable that the pH is above 10.

The amount of the ferrous salt aqueous solution added is 17.0 to 38.0% by weight, preferably 25.0 to 36.0% by weight, in terms of Fe, based on the acicular maghemite particles. If it is less than 17.0% by weight, sufficient magnetization cannot be achieved and the degree of blackness is insufficient, and if it exceeds 38.0% by weight, unreacted ferrous hydroxide colloids will be mixed in.

In the present invention, the suspension is heated and stirred in a temperature range of 40 to 100°C. If the temperature is less than 40°C, the reactivity is insufficient and it is difficult to form magnetite. If it exceeds 10'c, equipment such as an autoclave is required, which is not industrially practical.

Further, the atmosphere in the case of heating and stirring is a non-oxidizing atmosphere, and in the case of an oxidizing atmosphere, oxidation of the ferrous hydroxide colloid occurs and magnetization of the acicular maghemite particles is inhibited.

[For production]

First, the most important point in the present invention is that the crystallite size of the acicular magnetite particles is extremely small, so the residual magnetization value is as low as 10 to 30 emu/g, and the axial ratio is 1.5.
~10.0.

500 using acicular lepidic crocite particles as nucleus crystals
Acicular maghemite particles with a small crystallite size can be obtained by heating and dehydrating at a temperature below °C, followed by dispersing the acicular maghemite particles in an alkaline suspension containing ferrous hydroxide colloid. The acicular magnetite particles of the present invention can only be obtained by a wet reaction in which acicular magnetite particles are produced by heating and stirring in a non-oxidizing atmosphere at a temperature in the range of 40 to 100°C.

On the other hand, when heated and dehydrated at a high temperature exceeding 500℃,
It becomes acicular hematite particles and the crystallite size increases,
When magnetite is used, it becomes impossible to maintain acicularity.

In addition, when acicular goethite particles are used as nucleus crystals,
Even if it is heated and dehydrated, it becomes acicular hematite particles, which is not preferable.

Next, using the above-mentioned acicular maghemite particles, the growth of crystallite size can be suppressed only by the above-mentioned wet reaction, and the residual magnetization value is low. Acicular magnetite particles with excellent properties are obtained.

As this wet reaction, for example, Japanese Patent Publication No. 51-9719
The acicular maghemite particles are obtained by converting the nucleus crystals into the acicular maghemite particles using the technical means disclosed in the publication.

In addition, as a technical means using wet reaction, for example, USP
Feze3-H disclosed in Publication No. 2631085
2O and Fe0-)1.0 are mixed to form a suspension, and about 2
Although there is a method of heating Fe50□ to a temperature of 00°F (approximately 93°C), this method is not preferred because it is difficult to maintain the acicularity of the resulting Fe30a.

Also, when the acicular maghemite particles are made into acicular magnetite particles by a dry method in which the above-mentioned reducing gas such as hydrogen gas is passed through and heated to reduce the acicular magnetite particles, the crystallite size is 200.
They become larger than humans, their residual magnetization value becomes high, and their miscibility with resin deteriorates because the particles sinter together due to heat treatment.

〔Example〕

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

In addition, the crystallite size in the following Examples, Comparative Examples, and Reference Examples is determined by the Schiller (Scherrer ), the average major axis diameter and axial ratio (major axis diameter/minor axis diameter) are the average values of the results of electron micrograph observation, coercive force (Hc), residual magnetization value (σr ) and magnetization value (σm) are “vibrating sample magnetometer VS
IK using M-3S-15J (manufactured by Toei Kogyo ■)
The values are shown as values measured after applying an external magnetic field of Oe.

<Generation of acicular lepidocrocite particles> Reference example 1 0.6 mol/i! 2IV of FeSO4 aqueous solution was placed in a reaction vessel, stirred while bubbling N2 gas at 5j2/min, and 1.2N NaOH aqueous solution 21 was added to this aqueous solution to obtain a suspension of Fe(0)i)z colloid. Ta. The liquid temperature was 45°C.

8 d of 0.6 mol/l Na, HPO, aqueous solution was added to the suspension, and while maintaining the liquid temperature at 45°C, 151
The oxidation reaction was carried out for 4.5 hours while blowing air at a rate of /min to form a yellow-brown precipitate.

The generated yellow-brown precipitate was divided into ovens, washed with water, and dried to obtain 105 g of yellow-brown acicular lepidocrocite particles using a conventional method.
I got it.

The average major axis diameter of the obtained acicular lepidocrocite particles was 0.36 μm, and the axial ratio was 5.6.

Further, as is clear from the electron micrograph (x30000) shown in Section 1, it was needle-shaped, and the peak shown in the X-ray diffraction diagram of Section 2 was lepidocrocite.

Reference Example 2 A 0.6 mol/j2 FeSO4 aqueous solution 21 was placed in a reaction vessel, stirred while bubbling N2 gas at 5 I/min, and a 1.2N NaOH aqueous solution 21 was added to this aqueous solution. Add
A suspension of Fe(Off)z colloid was obtained. The liquid temperature is 45
It was set as ゛C.

0.6 mol/l of Na, HPO, aqueous solution was added to the suspension, and the solution temperature was maintained at 45°C.
The oxidation reaction was carried out for 4.5 hours while blowing air at a rate of /min to form a yellow-brown precipitate.

The generated yellow-brown precipitate was divided into furnaces, washed with water, and dried to obtain 106 g of yellow-brown needle-shaped lepidocrocite particles using a conventional method.
I got it.

The obtained acicular lepidocrocite particles had an average major axis diameter of 0.26 μm and an axial ratio of 50.

Furthermore, as a result of electron microscopic observation, it was needle-shaped, and as a result of X-ray diffraction, it was found to be lepidocrocite.

<Generation of acicular maghemite particles> Examples 1 to 2 Comparative Examples 1 to 2; Example 1 100 acicular lepidocrocite particles obtained in Reference Example 1
g was dehydrated by heating at 400''C for 5 hours to obtain 90 g of reddish brown acicular maghemite particle powder.

The crystallite size of the obtained acicular maghemite particles is 4.
One patient had an average major axis diameter of 0.28 μm and an axial ratio of 4.3.

Moreover, as is clear from the electron micrograph (x30000) shown in FIG. 3, it was needle-shaped, and the peak shown in the X-ray diffraction diagram of FIG. 4 was magnetite.

Example 2, Comparative Examples 1 to 2 Acicular maghemite particles and acicular hematite particles were obtained in the same manner as in Example 1, except that the acicular lepidocrocite particles to be treated and the heating dehydration temperature were variously changed. .

Table 1 shows the main manufacturing conditions and characteristics at this time.

<Production of acicular magnetite particles> Examples 3 to 4 Comparative Examples 3 to 6; Example 3 50 g of acicular maghemite particle powder obtained in Example 1 was
1.7 mol/l Fe in suspension in 0 d water
SO4 aqueous solution 92 relatives (F for acicular maghemite particles
This corresponds to 35% by weight in terms of e. ) and N.

Gas 54! /min while stirring, and bring the liquid temperature to 85.
It was set as ゛c. Subsequently, 9. A NaOH aqueous solution of ON was added to adjust the pH to 12.0 to produce Fe(O)I)z colloid, and the suspension was stirred at a temperature of 85°C for 3 hours to produce a black precipitate. The black precipitate is separated into a furnace, washed with water, and dried to obtain black acicular magnetophyte particles powder 7 using a conventional method.
2g was obtained.

Crystallites of the obtained acicular magnetite particle powder.

The number of children was 144, the average major axis diameter was 0.22 μm, and the axial ratio was 4.
°0, coercive force is 2190e, and residual magnetization value is 21.
It was 8 e stiffness u/g.

Moreover, as is clear from the electron micrograph (x30000') shown in FIG. 5, it is needle-shaped, and the peak shown in the X-ray diffraction diagram of FIG. 6 is magnetite.

Example 4, Comparative Examples 3 to 4 Except for varying the type of particle powder to be treated, the amount of ferrous salt aqueous solution added, the pH of the suspension of alkali hydroxide aqueous solution, and the temperature of raw acid treatment. Magnetite particles were produced in the same manner as in Example 3.

Comparative Examples 5 to 6 Acicular goethite particles were used as a starting material, heated and dehydrated, and then heated and reduced in an H2 gas atmosphere to obtain acicular magnetite particles.

Table 2 shows the main manufacturing conditions and characteristics at this time.

Table 1 [Effects of the invention] The acicular magnetite particles according to the present invention have a crystallite size as small as 100 to 200 people and a residual magnetization value of 10 to 3Q.
Since it is an acicular magnetite particle powder obtained by a wet method with a low emu/g and an axial ratio of 1.5 to 10.0, it has a small magnetic cohesive force and has excellent miscibility with resin. Since it can be exposed from the particle surface of the magnetic toner particles and has a black color, it is suitable as a one-component magnetic toner material powder used in a method for developing electrostatic latent images.

In addition, the acicular magnetite particles of the present invention may be mixed with various surfactants,
By treating the surface of the particles with a coupling agent or the like to make them hydrophobic, the particles can also be used as toner particles because they are acicular and easily exposed, so that an appropriate amount of charge can be maintained.

[Brief explanation of the drawing]

Fig. 1 shows the acicular lepidic crocite particles obtained in Reference Example 1, Fig. 3 shows the acicular maghemite particles obtained in Example 1, and Fig. 5 shows the acicular lepidic crocite particles obtained in Example 3. It is an electron micrograph (x 30000) showing the particle structure of each magnetite particle powder, and concave 2, concave 4 and FIG.
X-ray diffraction diagrams of Reference Example 1, Example 1, and Example 3 of 6 Patent Izushio Toda Kogyo Co., Ltd. Tomoe ("130000) Figure 2 2θ Figure 3 times + 2θ

Claims (1)

[Claims] 1. Acicular magnetite having a crystallite size of 100 to 200 Å, an axial ratio of 1.5 to 10.0, and a residual magnetization value of 10 to 30 emu/g in an external magnetic field of 1 KOe. Acicular magnetite particle powder for magnetic toner consisting of particles. 2. Water obtained by reacting acicular maghemite particles obtained by heating and dehydrating acicular lepidocrocite particles at a temperature range of 200 to 500°C with an aqueous ferrous salt solution and an aqueous alkali hydroxide solution. Acicular magnetite particles are produced by dispersing ferrous oxide colloid in an alkaline suspension and heating and stirring the suspension in a non-oxidizing atmosphere at a temperature range of 40 to 100°C. The method for producing acicular magnetite particle powder for magnetic toner according to claim 1.