JP2743028B2 - Iron oxide superparamagnetic fine particle powder and method for producing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to iron oxide superparamagnetic fine particle powder having a large magnetization value and excellent oxidation stability and exhibiting black color, and a method for producing the same. It is.

The main use of the iron oxide superparamagnetic fine particle powder according to the present invention is as 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.

Recently, the performance of magnetic toner as a developer has been strongly demanded along with high performance of copying machines, such as higher speed and higher image quality. ,
It is required to have a large magnetization value, excellent kneading properties, and a black color.

This fact is described in Japanese Patent Application Laid-Open No. 55-65406, entitled "Generally, the following various properties are required for a magnetic powder for a magnetic toner in such a one-component system. ‥‥ i) About 10 ³ Oe The magnetic flux density in the magnetic field is as high as possible.
In an external magnetic field of 00 Oe, it is necessary to have a maximum magnetization value σm of about 40 emu / g or more. Iv) Blackness that can withstand practical use. Although a colorant can be contained in the magnetic toner, it is preferable that the powder itself has a black color and no colorant is used. ‥‥ vii) Good mixing with resin.微 The degree of microscopic mixing in the toner is important for the characteristics of the toner. ‥‥ ”.

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

The blackness of magnetic particles such as magnetite particles is determined by the “Powder and Powder Metallurgy”
Vol. 26 No. 7 (1979), pp. 239-240, "The blackness of a sample depends on the Fe (II) content and the average particle size.
‥. ‥‥ When the Fe (II) content is 10% or more, a slight difference is observed in the degree of blackness, but all the samples are black. Fe
(II) When the content decreases to 10% or less, each sample changes from black to reddish brown. It is known that, as described in ‥‥ '', mainly depends on the average particle size of the particles and the Fe ²⁺ content, and the Fe ²⁺ content is 0.16 or more with ^respect to Fe ^{3+ in a} molar ratio of 0.16 or more. It is required that there be.

Conventionally, the pH obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an equivalent or more equivalent of Fe ²⁺ in the aqueous solution of ferrous salt as a magnetic particle powder used for a magnetic toner.
Octahedral magnetite particle powder (JP-B-44-668) obtained by aerating an oxygen-containing gas into a suspension containing 10 or more ferrous hydroxide colloids, or an aqueous ferrous salt solution And 0.80 to Fe ^{2+ in the} ferrous salt aqueous solution.
A first stage for producing spherical magnetite particles by passing oxygen-containing gas through a ferrous salt reaction aqueous solution containing ferrous hydroxide colloid obtained by reacting 0.99 equivalents of alkali hydroxide; and After completion of the one-step reaction, spherical magnetite particles obtained by adding 1.00 equivalent or more of alkali hydroxide to the remaining Fe ²⁺ and heating and oxidizing at pH 10 or more (Japanese Patent Publication No. 62-51208), etc. There is.

[Problems to be solved by the invention]

Magnetic particle powders having a large magnetization value and a small magnetic cohesive force due to the smallest possible residual magnetization and exhibiting black color are currently the most demanded. However, the octahedral magnetite particle powder described above has a large magnetization value of about 80 emu / g,
Although the blackness is excellent, the kneadability is a problem because the residual magnetization is as large as 9 emu / g or more and magnetic aggregation easily occurs. The magnetite particle powder having a spherical shape as described above has a large magnetization value of about 80 emu / g or more, but is slightly brownish black and inferior in blackness. The remanent magnetization is 4 to 6 emu
/ g, which is relatively small as compared with the octahedral magnetite particles, but not yet sufficient.

Heretofore, iron oxide superparamagnetic fine particle powder has been known as a magnetic particle powder having a residual magnetization of about 0.

However, since the iron oxide superparamagnetic fine particles are very fine particles, they are easily oxidized by oxygen in the air and are extremely unstable chemically and magnetically. That is, when taken out into the air, an oxidation reaction occurs due to oxygen in the air, and the magnetization value decreases. Further, the oxidation reaction proceeds during storage in the air, and the saturation magnetization decreases over time and over time. . Further, Fe ²⁺ is oxidized to Fe ³⁺ and turns reddish brown.

Therefore, an object of the present invention is to obtain iron oxide superparamagnetic fine particles having a large magnetization value and excellent oxidation stability.

[Means for solving the problem]

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

That is, the present invention comprises iron oxide superparamagnetic fine particles having an unsaturated fatty acid adsorbed on the particle surface, and has a magnetization value of 50 em.
The iron oxide superparamagnetic fine particle powder comprising at least u / g, a rate of change in magnetization value of 10% or less, and a molar ratio of Fe ²⁺ to Fe ³⁺ of 0.16 to 0.5. An unsaturated fatty acid or a salt thereof is added to an aqueous suspension containing iron oxide superparamagnetic fine particles, and the mixture is stirred at pH 9 or higher at a temperature in the range of 50 to 100 ° C. to obtain a dispersion, and an acid is added to the dispersion. The unsaturated fatty acid is adsorbed on the particle surfaces of the iron oxide superparamagnetic fine particles by adjusting the pH to 7 or less, then washed with water, dehydrated, and then wetted with a water-miscible organic solvent, and then vacuumed. It consists of iron oxide superparamagnetic fine particles in which unsaturated fatty acids are adsorbed on the surface of the particles that are dried, and has a magnetization value of 50 em.
Method for producing iron oxide superparamagnetic fine particle powder having a magnetization ratio of at least u / g of not more than 10% and a Fe ²⁺ content of 0.16 to 0.5 with respect to Fe ^{3+ by} mole ratio It is.

[Action]

First, the most important point in the present invention is that an unsaturated fatty acid or a salt thereof is added to an aqueous suspension containing iron oxide superparamagnetic fine particles, and the mixture is dispersed by stirring at a temperature of pH 9 or higher and a temperature of 50 to 100 ° C. A liquid, and an acid is added to the dispersion to adjust the pH to 7 or less so that unsaturated fatty acids are adsorbed on the surface of the iron oxide superparamagnetic fine particles, then washed with water, dehydrated, and subsequently miscible with water. When wetted in an organic solvent having a viscosity and dried in vacuum, it is possible to obtain iron oxide superparamagnetic fine particles that are extremely stable against oxidation, and as a result, the magnetization value is 50 em.
It is possible to obtain iron oxide superparamagnetic fine particles having a magnetization ratio of not less than u / g and not more than 10%, and having a Fe ²⁺ content of 0.16 to 0.5 with respect to Fe ^{3+ in} molar ratio. It is a fact that you can do it.

Regarding the reason that the superparamagnetic fine particles according to the present invention have a large magnetization value and excellent oxidation stability, the present inventor has shown that an unsaturated fatty acid is added to the particle surface of iron oxide superparamagnetic fine particles as shown in a comparative example described later. After adsorbing, heating and drying in air or vacuum, and after wetting in an organic solvent miscible with water without adsorbing unsaturated fatty acids on the particle surfaces of the iron oxide superparamagnetic fine particles. In any case of vacuum drying, since it is easily oxidized during drying or storage, and the intended oxide superparamagnetic fine particles cannot be obtained,
The synergistic effect of adsorbing unsaturated fatty acids on the particle surface and wetting in an organic solvent miscible with water followed by vacuum drying enables rapid removal of water on the particle surface, resulting in drying or storage It is believed that the oxidation of is suppressed.

The iron oxide superparamagnetic fine particles according to the present invention have almost no remanent magnetization and therefore hardly cause magnetic aggregation, and the surface of each particle is coated with an unsaturated fatty acid. And more excellent kneadability.

Conventionally, there is a method described in JP-B-53-4078 as a method of coating the particle surface of iron oxide superparamagnetic fine particles with oleate ion, which is a kind of unsaturated fatty acid. A superparamagnetic fine powder that is extremely stable against oxidation with the aim of stably extracting it into the air, in which a lipophilic group is adsorbed on the particle surface in a monomolecular layer for the purpose of improving dispersibility in polar solvents. The present invention is quite different from the present invention in the object, configuration and effect.

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

The production of iron oxide superparamagnetic particles in the present invention can be performed by a conventional method, for example, alkali is added to a mixed aqueous solution containing a ferrous salt and a ferric salt in a molar ratio of 1: 2. After the pH is adjusted to 9 or more, a ripening reaction is performed at an appropriate temperature.
It can be produced by a method in which an alkali is added as a precipitant to an oxidizing solution containing 1.1 to 1.5 atoms and then oxidized at a temperature of 50 ° C to 70 ° C (JP-A-57-175734).

The solution in which the iron oxide superparamagnetic fine particles are suspended in the present invention is a solution containing an unsaturated fatty acid or a basic salt thereof at a temperature of 50 to 100 ° C. and having a pH of 9 or more.

When the temperature is lower than 50 ° C., it is difficult to uniformly monodisperse the iron oxide superparamagnetic fine particle powder. When the temperature exceeds 100 ° C., the iron oxide superparamagnetic fine particle powder can be uniformly monodispersed, but it is not industrial or economical because a special device such as an autoclave is required.

When the pH is less than 9, it becomes difficult to uniformly disperse the iron oxide superparamagnetic fine particles and adsorb the unsaturated fatty acid on the surface of each particle.

Examples of the unsaturated fatty acid include monoene unsaturated fatty acids such as oleic acid and erucic acid; and polyene unsaturated fatty acids such as linoleic acid and linoleic acid.

The amount of the unsaturated fatty acid or salt thereof is 200% by weight or less based on the iron oxide superparamagnetic fine particles.

If it exceeds 200% by weight, the amount of unsaturated fatty acids not adsorbed on the surface of the iron oxide superparamagnetic fine particles increases, and the efficiency of removing these fatty acids deteriorates.

The lower limit of the amount of the unsaturated fatty acid or salt thereof added may be such that the unsaturated fatty acid adsorbed on the surface of the iron oxide superparamagnetic particles has a coverage θ of 0.5 or more. Coverage
If it is less than 0.5, superparamagnetic fine particles having excellent oxidation stability cannot be obtained.

The above-mentioned covering ratio θ is a ratio of the particle surface covered with the unsaturated fatty acid, and is a value obtained by the following equation.

w: Weight of unsaturated fatty acid adsorbed per gram of iron oxide superparamagnetic particles (g) M: Molecular weight of unsaturated fatty acid A: Adsorption occupation area of unsaturated fatty acid (Å ² ) S: Iron oxide superparameter as particles to be treated BET specific surface area of magnetic fine particles by N ₂ adsorption (m ² / g) In the present invention, the covering ratio θ of the unsaturated fatty acid molecular layer adsorbed on the particle surfaces of the iron oxide superparamagnetic particles is 0.5 to 0.5%.
1.2.

When the covering ratio θ is less than 0.5, the effect of preventing oxidation becomes insufficient, and it is not possible to obtain iron oxide supermagnetic fine particles having excellent oxidation stability, which is the object of the present invention.

When the covering ratio θ exceeds 1.2, the amount of unsaturated fatty acids not adsorbed on the particle surface increases, so that the particles become hydrophilic powder and are easily oxidized.

In the present invention, the pH is adjusted to 7 or less by adding an acid to the suspension.

As the acid, H ₂ SO ₄ , HCl, CH ₃ COOH and the like can be used.

When the pH exceeds 7, it becomes difficult to form a monomolecular layer of the bimolecular unsaturated fatty acid adsorbed on the particle surface in a dispersion liquid having a pH of 9 or more, and the resulting particle powder becomes a hydrophilic powder. Becomes unstable to oxidation. In addition, the iron oxide superparamagnetic fine particle powder is in a dispersed state in water, and it is difficult to remove it as a precipitate.

When the pH is less than 4, the iron oxide superparamagnetic fine particle powder may be dissolved, so the lower limit is preferably 4.

The washing in the present invention may be performed by a conventional method, for example, by a method such as decantation.

As the organic solvent miscible with water in the present invention,
Methanol, ethanol, acetone, ether and the like can be used, and these low-boiling organic solvents are preferred.

Vacuum drying in the present invention may be performed by a method using a commonly-used vacuum dryer or the like.

〔Example〕

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

The average particle size of the particles in the following Examples and Comparative Examples was determined from the half-value width of the X-ray diffraction line (311) using the Sierra equation.

The magnetic properties were measured using an "oscillating sample magnetometer VSM-3S-15" (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of up to 10 kOe.

The rate of change of the magnetization value was represented by the rate of decrease (%) of the magnetization value after one month at room temperature.

The amount of Fe ²⁺ was measured by a chelate titration method.

The L ^* value (brightness) and the a ^* value were obtained by measuring a colorimetric sample piece with a multi-source spectrophotometer MSC-IS-2D (manufactured by Suga Sampling Machine Co., Ltd.).
L ^* value, a ^* value, b ^* by Hunter's Lab space using
Each value is measured, and the International Commission on Illumination (Commission Int.
ernationale de l'Eclairage, CIE) 1976 (L ^* ,
a ^* , b ^* ) The values are displayed according to the uniform perceived color space. As the a ^* value representing reddishness approaches 0, and as the L ^* value decreases, the degree of blackness increases. The gloss of the coating surface is
Using a digital gloss meter UGV-5D (manufactured by Suga Test Instruments Co., Ltd.), the values were measured at incident angles of 45 ° and 60 °. The higher the gloss, the smoother the surface and the better the kneadability with the resin.

The measurement sample piece was prepared by kneading 0.5 g of iron oxide superparamagnetic particles and 1.0 cc of castor oil with a Hoover-type muller into a paste, adding 4.5 g of clear lacquer to the paste, kneading the mixture, and forming a paint. Obtained by application using a 6 mil applicator.

<Production of Iron Oxide Superparamagnetic Fine Particle Powder> A 1.4 mol / FeSO ₄ aqueous solution 7.75 and a 2.8 mol / FeCl ₃ solution were added to a 3.3 mol / NaOH aqueous solution 34.5 heated to a temperature of 80 ° C.
A mixed solution 15.5 with an aqueous solution 7.75 was added dropwise over 5 minutes while stirring. Then, the mixture was stirred for 30 minutes while maintaining the temperature at 80 ° C., to produce a black precipitate. This is designated as Sample A.

<Adsorption of Unsaturated Fatty Acid to Particle Surface> Examples 1 to 9 Comparative Examples 1 and 2; Example 1 500 ml of sample A slurry (25.1 g as a black particle solid content)
Corresponds to. ) Was added with 67.8 g of a 10 wt% aqueous sodium oleate solution (27 wt% oleic acid based on the solid content of black particles).
%. ) And stirred at pH 11.8 at a temperature of 80 ° C for 30 minutes to obtain a dispersion. The pH by adding 3N-H ₂ SO ₄ in the dispersion
5.5. After cooling to room temperature, it was sufficiently washed with decantation and dehydrated. Next, after moistening in 10 ml of methanol, vacuum drying was performed at room temperature.

As a result of X-ray diffraction, the obtained black powder was spinel-type iron oxide and had an average particle size of 98 ° as shown in the electron micrograph (× 200,000) shown in FIG.

The magnetic properties were such that the magnetization value was 54.2 emu / g, the residual magnetization was 0, the coercive force was 0 Oe, and the Fe ²⁺ content was 0.2 in molar ratio to Fe ³⁺ .

With respect to the coating properties, the L ^* value was 16.55, the a ^* value was 0.09, and the glossiness was 72.1 when the reflection angle was 45 ° and 80.2 when the reflection angle was 60 °.

Examples 2-9, Comparative Examples 1-2 Amount of black precipitate, type and amount of unsaturated fatty acid or salt thereof, pH and temperature during stirring, type of acid in acid addition step and pH after addition, organic Black particle powder was obtained in the same manner as in Example 1 except that the type and amount of the solvent were variously changed.

The main production conditions at this time are shown in Table 1, and various characteristics of the black particle powder and the coating film containing the particles are shown in Table 2.

[Effect of the Invention] The iron oxide superparamagnetic fine particle powder according to the present invention has large saturation magnetization and excellent oxidation stability, and is a particle having excellent blackness, and has no residual magnetization of 0. Due to the fact that it has low magnetic cohesion and excellent kneadability with resin, it is suitable as a material particle powder for magnetic toner.

Incidentally, the iron oxide superparamagnetic particles powder according to the present invention is black, and furthermore, because of its excellent dispersibility due to the fact that unsaturated fatty acids are adsorbed on the particle surface with small magnetic cohesion, Naturally, it can also be used as a well-known pigment powder for paint or pigment powder for resin coloring.

Further, as a black pigment, carbon black which has been conventionally used is a problem in terms of safety and health such as carcinogenicity.However, the iron oxide superparamagnetic fine particle powder according to the present invention is used as a substitute for carbon black. Can be expected.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 200,000) showing the structure of the iron oxide superparamagnetic fine particle powder obtained in Example 1.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-78930 (JP, A) JP-A-57-16101 (JP, A) JP-B-53-4078 (JP, B2)

Claims (2)

(57) [Claims] An iron oxide superparamagnetic fine particle having an unsaturated fatty acid adsorbed on the surface of the particle, having a magnetization value of 50 emu / g or more, a change rate of the magnetization value of 10% or less, and Fe
Iron oxide superparamagnetic fine particles having a ²⁺ content of 0.16 to 0.5 in molar ratio to Fe ³⁺ . 2. An unsaturated fatty acid or a salt thereof is added to an aqueous suspension containing iron oxide superparamagnetic fine particles, and the pH is 9 or more and the temperature is 50 to 1
Agitated in a temperature range of 00 ° C. to form a dispersion, and an acid was added to the dispersion to adjust the pH to 7 or less, whereby unsaturated fatty acids were adsorbed on the particle surfaces of the iron oxide superparamagnetic fine particles, 2. The method for producing iron oxide superparamagnetic fine particle powder according to claim 1, wherein the powder is washed with water, dehydrated, then wetted with an organic solvent miscible with water, and then dried under vacuum.