JP2814019B2 - Needle-like magnetite particle powder for magnetic toner and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a crystallite size of 100 to 200 mm, an axial ratio (major axis diameter / minor axis diameter) of 1.5 to 10.0, and a remanent magnetization value. Is 1
The present invention relates to a magnetic toner material particle powder comprising acicular magnetite particles of 0 to 30 emu / g and a method for producing the same.

[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. "

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. High cohesion is required.

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 value of the magnetite particle powder contained in the magnetic toner be as small as possible after applying an external magnetic field of 1 KOe.

On the other hand, a magnetic toner having excellent fine line reproducibility and gradation is disclosed in Japanese Patent Application Laid-Open No. 1-2221754, "{5 μm or less toner particles are effective in solving the problem of sharpness of image quality}. "
As described, it is desired to reduce the particle size. However, since the surface area of the magnetic toner increases as the particle diameter decreases, the charge amount of the magnetic toner particles abnormally increases from an appropriate value.

Such a phenomenon is due to the mixing of the magnetic particles with the resin,
That is, it also occurs due to the hydrophobic treatment of the magnetic particle powder performed to enhance the dispersibility and adhesion to the binder resin.

This fact indicates that the resistance of the toner itself increases due to the hydrophobic treatment of the magnetic powder described in JP-A-2-97968. The charge amount of the magnetic toner fluctuates from an appropriate value to a further increasing direction. If the charge amount is abnormally increased from an appropriate value, the thickness of the toner coat layer on the sleeve becomes uneven, the image density is reduced, and the image quality is reduced. It is on the street.

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.
-668), a ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with 0.80 to 0.99 equivalents of alkali hydroxide with respect to Fe ^{+ 2} in the aqueous ferrous salt solution. To the ferrous salt reaction aqueous solution, by aerating an oxygen-containing gas, the first stage for producing spherical magnetite particles, and after the first stage reaction, adding 1.00 equivalent or more of alkali hydroxide to the remaining Fe ^{+ 2.} Spherical magnetite particle powder obtained by heating and oxidizing at pH 10 or higher (Japanese Patent Publication No. 62-51208)
Publication), or a dry type obtained by heating and dehydrating acicular hematite particles obtained by heating and dehydrating acicular goethite particles in a temperature range of 200 to 600 ° C. in a reducing gas at a temperature range of 300 to 500 ° C. And magnetic toners using the acicular magnetite particles of the method (Japanese Patent Application Laid-Open No. 54-158931).

[Problems to be solved by the invention]

In recent years, as the performance of copying equipment has increased, such as speed, image quality, and continuity, magnetite particles have been improved with various surfactants and coupling agents in order to enhance the compatibility with resins. Although the surface is hydrophobized, when the particle shape of the magnetite particles is the aforementioned octahedron or the aforementioned spherical shape, it is possible to expose a part of the magnetite particles on the particle surface of the magnetic toner particles. Because of the difficulty, the charge amount tends to be larger than an appropriate value.

Since the aforementioned acicular magnetite particle powder is acicular, a part thereof is exposed on the surface of the magnetic toner particles, so that the resistance of the surface of the magnetic toner particles can be lowered and the charge amount can be stabilized. Sintering caused by heat treatment by heat or heat reduction reduces the miscibility with the resin, and the magnetite particles obtained by heat reduction increase as the residual magnetization value exceeds 30 emu / g, resulting in magnetic aggregation. Also easily occur.

A magnetic toner disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-97968 contains at least a magnetic powder whose surface is subjected to hydrophobic treatment and a non-magnetic metal oxide in the form of a needle which has not been subjected to hydrophobic treatment. The iron oxide hydrous or hematite as a needle-shaped nonmagnetic metal oxide has a yellowish brown or reddish brown color, which impairs blackness.

Therefore, the present invention has a black color and a low remanent magnetization value, so that the magnetic cohesion is small, and sintering by a heat treatment in a reducing atmosphere is not caused as in the dry method. It is an object of the present invention to obtain acicular magnetite particles which have excellent mixing properties and can be exposed from the surface of the magnetic toner particles.

[Means for solving the problem]

The present inventor has made various studies on the above-mentioned technical problems, and as a result, has arrived at the present invention.

That is, the present invention is for a magnetic toner comprising needle-like magnetite particles having a crystallite size of 100 to 200 °, 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. The acicular maghemite particles obtained by heating and dehydrating the acicular magnetite particle powder and the acicular lipid crocite particles in a temperature range of 200 to 500 ° C. are reacted with an aqueous ferrous salt solution and an aqueous alkali hydroxide solution. Disperse in the resulting alkaline suspension containing ferrous hydroxide colloid, and heat and stir the suspension in a non-oxidizing atmosphere in a temperature range of 40 to 100 ° C. to generate acicular magnetite particles. And a method for producing acicular magnetite particle powder for a magnetic toner.

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

The crystallite size of the acicular magnetite particles of the present invention is 100
~ 200. If it exceeds 200 °, the coercive force and the saturation magnetization increase, so that the residual magnetization also becomes too high.

If it is desired to obtain a material having a particle size of less than 100 °, it is not industrial because it is extremely difficult to control the conditions for forming acicular lipid crocite particles, heat dehydration and the generation of magnetite particles.

The axial ratio (major axis diameter / minor axis diameter) of the acicular magnetite particles of the present invention is from 1.5 to 10.0, and preferably from 2.0 to 6.0.
If the axial ratio is less than 1.5, the magnetic toner particles cannot be exposed on the surface of the magnetic toner particles, so that the charge amount cannot be properly maintained. If the axial ratio exceeds 10.0,
It is not preferable because the residual magnetization value increases due to shape anisotropy.

 Incidentally, the average major axis diameter is 0.1 to 1.0 μm.

Residual magnetization value (σr) of the acicular magnetite particles of the present invention
Is 10 to 30 emu / g. If it exceeds 30 emu / g, the magnetic cohesive force is undesirably high as in the case of the acicular magnetite particles obtained by the dry method. Those with less than 10 emu / g
Since it is necessary to reduce the crystallite size, it is not industrial as in the above reason.

The coercive force at an external magnetic field of 1 KOe is 150 to 300 Oe.

In the present invention, acicular lipid crocite particle powder is used as a starting material. For example, the technical means disclosed in JP-B-36-21705, JP-B-37-2006, JP-B-43-2214, and the like, and the Ceramic Industry Association, Vol. 86, No. 9 (1978), No. 381- "‥‥ Iron hydroxide (I
When a small amount of phosphate is added when the precipitate of I) is oxidized in a neutral aqueous solution, γ-FeOOH is obtained in a single phase.
The needle-like lipid closite particle powder can be obtained by the technical means as described in "‥".

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

In the present invention, acicular lipid clocite particles
By heating and dehydrating in a temperature range of 0 to 500 ° C, preferably in a temperature range of 200 to 350 ° C, acicular maghemite particles are obtained. If the temperature is lower than 200 ° C., it is not sufficiently dehydrated, so that it is not possible to maintain a needle shape when magnetite particles are formed. If the temperature exceeds 500 ° C., hematite is mixed, and the crystallite size is undesirably large.

As the aqueous ferrous salt solution in the present invention, ferrous sulfate, ferrous chloride and the like can be used.

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

The suspension containing the ferrous hydroxide colloid obtained by reacting the aqueous ferrous salt solution and the aqueous alkali hydroxide solution in the present invention is alkaline. The reason for the alkalinity is not preferable because the ferrous hydroxide colloid is not sufficiently formed in the acidic state and the ferrous salt remains. Preferably, the pH is above 10.

The addition amount of the aqueous ferrous salt solution is 17.0 to 38.0% by weight in terms of Fe with respect to the acicular maghemite particles, preferably
25.0-36.0% by weight. If less than 17.0% by weight,
Insufficient blackness due to insufficient magnetite conversion,
If it exceeds 38.0% by weight, unreacted ferrous hydroxide colloid is mixed.

In the present invention, the suspension is heated and stirred in a temperature range of 40 to 100 ° C. If the temperature is lower than 40 ° C., the reactivity is not sufficient, and it is difficult to make magnetite. If the temperature exceeds 100 ° C., it is not industrial because an apparatus such as an autoclave is required.

The atmosphere in the case of heating and stirring is a non-oxidizing atmosphere. In the case of an oxidizing atmosphere, the ferrous hydroxide colloid is oxidized and the formation of magnetite of the acicular maghemite particles is inhibited.

[Action]

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

500 needle needle crocite particles as nuclei
By heating and dehydrating at a temperature lower than 0 ° C., acicular maghemite particles having a small crystallite size can be obtained, and then dispersing the acicular maghemite particles in an alkaline suspension containing ferrous hydroxide colloid. The acicular magnetite particles of the present invention can be obtained only by a wet reaction in which acicular magnetite particles are formed 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 dehydration by heating at a high temperature exceeding 500 ℃,
It becomes acicular hematite particles and the crystallite size increases,
When magnetite is used, needle-like properties cannot be maintained.

In addition, when needle-like goethite particles are used as the nucleus, it is not preferable because even heating dehydration results in needle-like hematite particles.

Next, by using the acicular maghemite particles, the growth of crystallite size can be suppressed only by the above-mentioned wet reaction, the remanence value is low, and the particles do not sinter due to the wet reaction, and dispersibility can be reduced. Excellent acicular magnetite particles can be obtained.

As the wet reaction, the acicular magnetite particles can be obtained by converting a nucleus crystal into the acicular maghemite particles using a technical means disclosed in, for example, Japanese Patent Publication No. 51-9719.

In addition, as a technical means by wet reaction, for example, USP
A suspension by mixing a Fe ₂ O ₃ · H ₂ O and FeO · H ₂ O as disclosed in Japanese Patent No. 2631085, is heated to a temperature of about 200 ° F (about 93 ℃) Fe ₃ O There is also a method of setting ₄ , but this method is not preferable because it is difficult to maintain the needle shape of the obtained Fe ₃ O ₄ .

Also, when the acicular maghemite particles are formed into acicular magnetite particles by a dry method in which a reducing gas such as the above-described hydrogen gas is passed and heated and reduced, the crystallite size is 200 μm.
When Å is exceeded, the particle size increases, the remanence value increases, and the particles are sintered by the heat treatment, so that the mixing property with the resin deteriorates.

〔Example〕

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

In the following Examples, Comparative Examples and Reference Examples, the crystallite size was calculated from the half-value width of the diffraction line using a "X-ray diffractometer RAD-IIA" (manufactured by Rigaku Corporation). The average major axis diameter and the axial ratio (major axis diameter / minor axis diameter) are the average values of the results of electron micrograph observation, and include the coercive force (Hc) and the residual magnetization value (Scherrer). σr)
And the magnetization value (σm) are “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.

<Production of needle-like lipid crocite particles> Reference Example 1 2 l of a 0.6 mol / l FeSO ₄ aqueous solution was put in a reaction vessel, and N ₂ gas 5
Stir while aerating l / min, and add 1.2N NaOH to this aqueous solution.
2 l of the aqueous solution was added to obtain a suspension of the Fe (OH) ₂ colloid.
The liquid temperature was 45 ° C.

8 ml of a 0.6 mol / l Na ₂ HPO ₄ aqueous solution was added to the suspension,
While maintaining the liquid temperature at 45 ° C., the oxidation reaction was carried out for 4.5 hours while passing air at 15 l / min to produce a tan precipitate.

The resulting yellow-brown precipitate was separated, washed with water and dried by a conventional method to obtain 105 g of yellow-brown acicular lipid crocite particles.

The average length of major axis of the obtained acicular lipid crocite particles was 0.36 μm, and the axial ratio was 5.6.

Further, as is clear from the electron micrograph (× 30,000) shown in FIG. 1, the sample was needle-like, and the peak shown in the X-ray diffraction diagram in FIG. 2 was lipid crocite.

Reference Example 2 2 l of a 0.6 mol / l FeSO ₄ aqueous solution was placed in a reaction vessel, and N ₂ gas 5
Stir while aerating l / min, and add 1.2N NaOH to this aqueous solution.
2 l of the aqueous solution was added to obtain a suspension of the Fe (OH) ₂ colloid.
The liquid temperature was 45 ° C.

10 ml of an aqueous solution of 0.6 mol / l Na ₂ HPO ₄ was added to the suspension, and while maintaining the liquid temperature at 45 ° C., the oxidation reaction was carried out for 4.5 hours while passing air at 15 l / min to give a yellow-brown color. A precipitate formed.

The resulting yellow-brown precipitate was separated, washed with water and dried by a conventional method to obtain 106 g of yellow-brown acicular lipid crocite particles.

The average length of major axis of the obtained acicular lipid crocite particles was 0.26 μm, and the axial ratio was 5.0.

Further, as a result of observation with an electron microscope, it was acicular, and as a result of X-ray diffraction, it was a lipid closite.

<Production of Acicular Maghemite Particles> Examples 1-2 Comparative Examples 1-2; Example 1 100 g of acicular lepiddocrosite particles obtained in Reference Example 1
Was heated and dehydrated at 400 ° C. for 5 hours to obtain 90 g of red-brown acicular maghemite particles.

The crystallite size of the obtained acicular maghemite particle powder is
The average major axis diameter was 41 mm, and the axial ratio was 4.3.

In addition, as is clear from the electron micrograph (× 30000) shown in FIG. 3, it was needle-like, and the peak shown in the X-ray diffraction diagram in FIG. 4 was maghemite.

Example 2, Comparative Examples 1 and 2 Acicular maghemite particles and acicular hematite particles were obtained in the same manner as in Example 1 except that the treated acicular lipid crocite particles and the heating and dehydrating temperature were variously changed. .

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

<Production of Acicular Magnetite Particles> Examples 3 to 4 Comparative Examples 3 to 6; Example 3 500 ml of 50 g of the acicular maghemite particles obtained in Example 1 was used.
184 ml of 1.7 mol / l FeSO ₄ aqueous solution in a suspension dispersed in water
(35% by weight converted to Fe for acicular maghemite particles
Corresponds to. ) Was added thereto and the mixture was stirred while passing N ₂ gas at 5 l / min, and the liquid temperature was adjusted to 85 ° C. Subsequently, while passing N ₂ gas at 5 l / min, a 9.0N NaOH aqueous solution was added to the suspension to adjust the pH to 12.0, and Fe (OH) ₂ colloid was formed.
The mixture was stirred at a temperature of 3 ° C. for 3 hours to form a black precipitate. The formed black precipitate was separately washed with water and dried by a conventional method to obtain 72 g of black needle-like magnetite particles.

The crystallite size of the obtained acicular magnetite particle powder is
144 °, the average major axis diameter was 0.22 μm, the axial ratio was 4.0, the coercive force was 219 Oe, and the residual magnetization value was 21.8 emu / g.

Further, as is clear from the electron micrograph (× 30,000) shown in FIG. 5, the particles were acicular, and the peak shown in the X-ray diffraction diagram in FIG. 6 was magnetite.

Example 4 and Comparative Examples 3 and 4 Example 4 except that the kind of the particles to be treated, the amount of the aqueous ferrous salt solution added, the pH of the suspension of the aqueous alkali hydroxide solution, and the temperature of the production treatment were variously changed. In the same manner as in Example 3, magnetite particles were produced.

Comparative Examples 5-6 Needle-like goethite particle powder was used as a starting material, and after heating and dehydration, it was reduced by heating in an H ₂ gas atmosphere to obtain needle-like magnetite particle powder.

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

(Effect of the Invention) The acicular magnetite particles according to the present invention have a small crystallite size of 100 to 200 °, a low remanent magnetization of 10 to 30 emu / g, and an axial ratio of 1.5 to 10.0, which is obtained by a wet method. Since it is a needle-like magnetite particle powder, it has low magnetic cohesion and excellent mixing with resin, can be exposed from the particle surface of magnetic toner particles, and has a black color, It is suitable as a material powder for a one-component magnetic toner used in a latent image developing method.

Incidentally, the needle-like magnetite particles of the present invention are hydrophobized on the particle surface with various surfactants, coupling agents and the like, so that the toner is easily exposed as needles, so that an appropriate charge amount can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an acicular lipid closite particle powder obtained in Reference Example 1, FIG. 3 is an acicular maghemite particle powder obtained in Example 1, and FIG. 3 is an electron micrograph (× 30000) showing the particle structure of each of the acicular magnetite particles obtained in Example 3. FIGS. 2, 4 and 6 show Reference Example 1, Example 1, and Example 3. It is each X-ray-diffraction figure.

Front page of the continuation (72) inventor Fujioka Yaichi Inoue Hiroshima, Hiroshima Prefecture, Naka-ku, Funairiminami 4-chome, in the examiner No. 1 No. 2 Toda Kogyo Co., Ltd. Innovation Center Kazuo (58) investigated the field (Int.Cl. ^6, (DB name) G03G 9/083 C01G 9/08

Claims (2)

(57) [Claims] 1. A needle for magnetic toner comprising needle-like magnetite particles having a crystallite size of 100 to 200 °, an axial ratio of 1.5 to 10.0, and a residual magnetization value of 10 to 30 emu / g at an external magnetic field of 1 KOe. Magnetite particle powder. 2. The method of claim 2, wherein the acicular lipid clocite particles are heated to 200 to 500 ° C.
The needle-shaped maghemite particles obtained by heating and dehydrating in a temperature range of are dispersed in an alkaline suspension containing a ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution. 2. The acicular magnetite particle powder for a magnetic toner according to claim 1, wherein the suspension is heated and stirred in a non-oxidizing atmosphere in a temperature range of 40 to 100 ° C. to produce acicular magnetite particles. Manufacturing method.