JP4771045B2 - Magnetic iron oxide particle powder - Google Patents

Description

  The present invention relates to magnetic iron oxide particles composed of magnetite particles having fine particles having a particle size of 0.05 to 0.30 μm, excellent in dispersibility while being octahedral, and having a high remanent magnetization value. Is. When the magnetic iron oxide particle powder according to the present invention is used as a magnetic toner particle having a small particle diameter, it is possible to obtain a magnetic toner with high resolution by suppressing fogging.

  Conventionally, as one of the electrostatic latent image developing methods, a so-called “one-component magnetic toner” in which a composite particle in which magnetic particle powder such as magnetite particle powder is mixed and dispersed in a resin without using a carrier is used as a developer. Is widely known and widely used.

  Recently, as the electrostatic copying machine has been improved in performance, such as downsizing and speeding up, the characteristics of the magnetic toner as a developer has been improved, that is, the magnetic toner having a small particle diameter capable of suppressing fogging and obtaining high resolution has been developed. There is a strong demand.

Conventionally used spherical magnetite particles have a low remanent magnetization value, so the magnetic stress decreases when the magnetic toner has a small particle size, and the toner is less likely to be agitated on the sleeve and charged uniformly. As a result, a toner with insufficient charging is generated, which causes fogging. In addition, the spherical particles have a small residual magnetization value and are less likely to cause magnetic agglomeration, so they have excellent dispersibility and good mixing with the resin. However, the Fe ²⁺ content is low, so the color is slightly brownish black. It is difficult to say that the blackness is sufficient.

  Therefore, in order to solve the above problems, there is a strong demand for magnetic particles having a high remanent magnetization value and excellent dispersibility.

On the other hand, the magnetite particle powder having an octahedron has a high Fe ²⁺ content and excellent blackness, but has a large residual magnetization value and easily causes magnetic aggregation, and is an angular particle. For this reason, the dispersibility is poor and the miscibility with the resin is poor.

  Various attempts have been made to obtain magnetite particles having a high remanent magnetization value and excellent dispersibility (Patent Documents 1 to 4).

JP-A-2-44030 JP-A-3-201509 JP-A-6-144840 Japanese Patent Laid-Open No. 11-153882

In view of the above-described problems, magnetic particles having a fine particle size of 0.05 to 0.30 μm, excellent dispersibility, a high residual magnetization value, and excellent blackness due to a large amount of Fe ²⁺ Although iron oxide particle powders are currently in most demand, such magnetic iron oxide particle powders have not yet been provided.

The magnetite particles described in the above-mentioned Patent Document 1 have a cubic shape with chamfered edges, but have a BET specific surface area of 0.5 to ⁵ m ² / g and a large particle size. It has a bulky shape and is inferior in dispersibility.

  Further, the magnetite particle powder described in the above-mentioned Patent Document 2 is a magnetite particle powder having a hexahedron shape, and its dispersibility is not sufficient because its particle shape is angular.

  Further, the magnetite particles described in Patent Document 3 are substantially hexahedral in shape, and each ridge line of the hexahedron has a planar shape, but has an angular shape and is inferior in dispersibility. It is.

  Moreover, although the above-mentioned patent document 4 has described the magnetite particle | grains whose ridgeline part of an octahedron is a planar polyhedron, it is an angular shape and is inferior to dispersibility.

Therefore, the present invention is a fine particle having a particle size of 0.05 to 0.30 μm, has a high remanent magnetization value, and is excellent in dispersibility, so that it is used as a magnetic toner particle having a small particle size. Another object of the present invention is to provide a magnetic iron oxide particle powder that is suitably used for a magnetic toner that has a stable toner charge amount, little fogging, and is excellent in blackness due to a large amount of Fe ²⁺ .

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

  That is, the present invention is a magnetite particle powder having an average particle diameter (d) of 0.05 to 0.30 μm, the particle shape is based on octahedron, and each ridge line of the octahedron is curved. A magnetic iron oxide particle powder composed of magnetite particles.

Further, the present invention is a magnetite particle powder having an average particle diameter (d) of 0.05 to 0.30 μm, the particle shape is based on octahedron, and each ridge line of the octahedron is curved. A magnetic iron oxide particle powder comprising magnetite particles, wherein the axial ratio (l / w) defined by the following formula is 1.2 ≦ l / w <1.6.
Axial ratio = l / w
l: major axis diameter of magnetic iron oxide particles in projected view w: minor axis diameter of magnetic iron oxide particles in projected diagram

  In the magnetite particle powder according to the present invention, one or more elements selected from Mn, Zn, Ni, Cu, Al, Ti, and Si may be contained in an amount of 0 to 10.0 atomic% with respect to Fe. A magnetic iron oxide particle powder characterized by

Further, the present invention provides the magnetic iron oxide particle powder, wherein the relationship between the residual magnetization value (σr) and the average particle diameter (d) when the measurement magnetic field is 796 kA / m is within the range of the following formula: is there.
−50d + 17 <σr <−50d + 20

The magnetic iron oxide particles according to the present invention are fine particles having a particle size of 0.05 to 0.30 μm, have a high residual magnetization value and excellent dispersibility, and have a high blackness due to a large amount of Fe ^2+. Since it is excellent, the charge amount of the toner is stabilized when used as a magnetic toner having a small particle diameter, and therefore it can be suitably used as a magnetic particle powder for a magnetic toner for electrophotography.

  The configuration of the present invention will be described in more detail as follows.

  First, the magnetic iron oxide particle powder according to the present invention will be described.

The magnetic iron oxide particles according to the present invention are composed of magnetite particles (( FeO ₂ ) x · Fe ₂ O ₃ , 0 <x ≦ 1) in terms of composition.

  The particle shape of the magnetic iron oxide particles according to the present invention is based on an octahedron as shown in the transmission electron micrograph of FIG.

  The particles constituting the magnetic iron oxide particle powder according to the present invention preferably have an axial ratio represented by the following formula exceeding 1.2 and less than 1.6. When the axial ratio is less than 1.2, it is close to a spherical shape and the coercive force is lowered, which is not preferable. On the other hand, when the axial ratio exceeds 1.6, it is an angular octahedron, and good dispersibility cannot be obtained. More preferably, it is the range of 1.25 to 1.55, and still more preferably 1.30 to 1.50.

Axial ratio = l / w
l: major axis diameter of magnetic iron oxide particles in projected view w: minor axis diameter of magnetic iron oxide particles in projected diagram

  The magnetic iron oxide particle powder according to the present invention has an average particle diameter (d) of 0.05 to 0.30 μm. When the average particle diameter is less than 0.05 μm, the number of particles in a unit volume increases so that the number of contacts between the particles increases, so that the adhesion between the powder layers increases, and in the case of using a magnetic toner, The dispersibility to become worse. When it exceeds 0.30 μm, the number of magnetic iron oxide particles contained in one toner particle decreases, and the distribution of magnetic iron oxide particles is uneven for each toner particle. As a result, the toner is uniformly charged. Sexuality is impaired. Preferably it is the range of 0.10-0.25 micrometer.

  The magnetic iron oxide particle powder according to the present invention is an element other than iron, if necessary, and one or more elements selected from Mn, Zn, Ni, Cu, Al, Ti, and Si with respect to Fe. 10 to 10 atomic%. In addition, since environmental stability falls when it contains abundant silicon, 0-0.8 atomic% is preferable, More preferably, it is 0-0.6 atomic%.

  In the magnetic iron oxide particle powder according to the present invention, the relationship between the residual magnetization value σr (Am2 / kg) at 798 kA / m and the average particle diameter d (μm) is in a range satisfying −50d + 17 <σr <−50d + 20. It is preferable. When the remanent magnetization value exceeds the upper limit value for each particle diameter d, the magnetic cohesive force becomes too strong, and in the case of a magnetic toner, the dispersibility of the magnetic particles in the toner deteriorates and the charging stability of the toner is reduced. descend. On the other hand, when the residual magnetization value is less than the lower limit value for each particle diameter d, the magnetic sensitive stress becomes weak, the scattering to the photosensitive drum is likely to occur, and fogging occurs.

The saturation magnetization value of the magnetic iron oxide particle powder according to the present invention is preferably 80 to 92 Am ² / kg, more preferably 82 to 90 Am ² / kg. The value of 92 Am ² / kg is a theoretical value of magnetite and does not exceed this value. If it is less than 80 Am ² / kg, the amount of Fe ^{2+ in} the particles is reduced and it is reddish, which is not preferable.

The remanent magnetization value of the magnetic iron oxide particle powder according to the present invention is preferably 6.0 to 11.0 Am ² / kg, and more preferably 6.5 to 10.5 Am ² / kg. When the remanent magnetization value is less than 6.0 Am ² / kg, the magnetic stress becomes weak, the scattering to the photosensitive drum is likely to occur, and fogging occurs. When the remanent magnetization value exceeds 11.0 Am ² / kg, the magnetic cohesive force becomes too strong, and in the case of a magnetic toner, the dispersibility of the magnetic particles in the toner deteriorates and the charging stability of the toner decreases. There are things to do.

  The coercive force Hc of the magnetic iron oxide particles according to the present invention is preferably 6.37 to 10.4 kA / m (80 to 130 Oe), more preferably 6.76 to 9.95 kA / m (85 to 125 Oe). is there. When the coercive force is less than 6.37 kA / m, the magnetic stress becomes weak, the scattering to the photosensitive drum is likely to occur, and fogging occurs. When the coercive force exceeds 10.4 kA / m, the magnetic cohesive force becomes too strong, and when the magnetic toner is used, the dispersibility of the magnetic particles in the toner is deteriorated and the charging stability of the toner is lowered. Sometimes.

The Fe ²⁺ content of the magnetic iron oxide particles according to the present invention is preferably 15 to 24% by weight, more preferably 17 to 22% by weight, based on the total weight of the magnetic iron oxide particles. When the amount is less than 15% by weight, sufficient blackness cannot be obtained. If it exceeds 24% by weight, it tends to be oxidized and has poor environmental stability.

The BET specific surface area value of the magnetic iron oxide particle powder according to the present invention is preferably 5.0 to 12.0 m ² / g. If it exceeds 12.0 m ² / g, the number of particles in the unit volume increases so that the number of contacts between the particles increases, so that the adhesive force between the powder layers increases, and in the case of using a magnetic toner, it goes into the resin. The dispersibility of becomes worse. When it is less than 5.0 m ² / g, the number of magnetic iron oxide particles contained in one toner particle decreases, and the distribution of magnetic iron oxide particles is uneven for each toner particle. The uniformity of charging is impaired. More preferably, it is 6.0-10.0 m < ² > / g.

  The magnetic iron oxide particles according to the present invention preferably have a soluble Na content of 200 ppm or less, more preferably 100 ppm or less. When it exceeds 200 ppm, the hygroscopicity is increased and the charging stability of the toner is lowered.

  Next, a method for producing magnetic iron oxide particles according to the present invention will be described.

  The magnetic iron oxide particle powder according to the present invention is obtained by reacting an aqueous ferrous salt solution with 1.01 to 1.5 equivalents of an aqueous alkali hydroxide solution with respect to the ferrous salt in the aqueous ferrous salt solution. An oxygen-containing gas is passed through the ferrous salt reaction aqueous solution containing ferrous hydroxide colloid thus heated to a temperature range of 70 to 100 ° C. to conduct an oxidation reaction until the iron oxidation reaction rate is 40 to 80%. The pH of the ferrous salt reaction solution containing the first stage reaction for generating nucleated magnetite particles and the nucleated magnetite particles after completion of the first stage reaction and the ferrous hydroxide colloid is 4.0 to 7.0. Then, the second stage reaction in which an oxygen-containing gas is aerated while heating in a temperature range of 70 to 100 ° C. to generate magnetite particles, and the pH of the reaction solution after completion of the second stage reaction is 9.0. After making the above adjustments, a third-stage reaction that performs an oxidation reaction It can be obtained by.

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

  Examples of the alkali hydroxide aqueous solution in the present invention include an aqueous solution of an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, an aqueous solution of an alkaline earth metal hydroxide such as magnesium hydroxide and calcium hydroxide, An aqueous alkali carbonate such as sodium carbonate, potassium carbonate or ammonium carbonate, aqueous ammonia, or the like can be used.

The amount of the aqueous alkali hydroxide solution used before the pH adjustment in the first stage reaction is 1.01-1.50 equivalents with respect to Fe ²⁺ in the ferrous salt aqueous solution. Preferably it is the range of 1.05-1.30 equivalent. When the amount is less than 1.01 equivalent, spherical magnetite is generated and magnetite particles having a desired shape cannot be obtained. If it exceeds 1.50 equivalents, the particle size distribution becomes large and a uniform particle size cannot be obtained.

  The oxidation rate of iron in the first stage reaction is 40 to 80%. When the oxidation reaction rate is less than 40%, the shape of the obtained magnetic iron oxide particles approaches a spherical shape, and magnetic iron oxide particles having the desired shape and magnetic properties cannot be obtained. When the oxidation reaction rate exceeds 80%, the shape of the obtained magnetic iron oxide particles approaches an octahedron and has an edge (angular shape). A preferable range of the oxidation reaction rate is 45 to 75%, and more preferably 50 to 70%.

  The reaction temperature in the first stage reaction is 70 to 100 ° C. When the temperature is lower than 70 ° C., acicular goethite particles are mixed. Magnetite particles are produced even when the temperature exceeds 100 ° C., but it is not industrially easy because an apparatus such as an autoclave is required.

  The oxidizing means is performed by venting an oxygen-containing gas (for example, air) into the liquid.

  In the first stage reaction, an aqueous alkali hydroxide solution or the like is added and adjusted so that the pH of the suspension is in the range of 9.0 to 12.0 when oxygen-containing gas aeration starts. More preferably, the pH is in the range of 9.5 to 11.5. When the suspension pH is less than 9.0, spherical particles and hexahedral particles are generated, and the coercive force is low. When the suspension pH exceeds 12.0, the particle size distribution of the generated magnetite particles becomes wide, which is not preferable.

  In the second stage reaction, an aqueous sulfuric acid solution or the like is added so that the pH of the suspension at the start of the second stage reaction is 4.0 to 7.0. When the pH of the suspension is less than 4.0, acicular goethite particles are mixed. When the pH of the suspension is 7.0 or more, hexahedral and octahedral magnetite precipitates on the surface of the nucleated magnetite particles obtained by the first stage reaction, and the desired shape cannot be obtained. Preferably it is the range of 5.0-6.9.

  In the third stage reaction, after the completion of the second stage reaction, sodium hydroxide or the like is added to the reaction solution to adjust the pH value of the reaction solution to 9.0 or more. When the pH value during the third stage reaction is less than 9.0, unreacted iron remains in the reaction solution, which is not preferable because the stability of the magnetite particle powder is lowered. Preferably it is 10.0-12.0.

  The reaction temperature of the second stage reaction and the third reaction may be the same as that of the first stage reaction. Further, the oxidizing means may be the same.

  In addition, sufficient stirring is required for the required time between the addition of the raw materials and the first stage reaction, between the first stage reaction and the second stage reaction, and between the second stage reaction and the third stage reaction. May be performed.

  If necessary, in each stage reaction, by adding a salt of one or more elements selected from Mn, Zn, Ni, Cu, Al, Ti, and Si as elements other than iron, Can be contained. As the salt, sulfate, nitrate, chloride and the like can be used. The total amount of the salt added is preferably 0 to 10 atomic%, more preferably 0 to 8 atomic%, and still more preferably 0 to 5 atomic% with respect to Fe.

  Next, a magnetic toner using the magnetic iron oxide particle powder according to the present invention will be described.

  The magnetic toner in the present invention has a volume average diameter of 3 to 12 μm, preferably 5 to 10 μm.

  The magnetic toner in the present invention comprises the magnetic iron oxide particle powder and the binder resin, and may contain a release agent, a colorant, a charge control agent, other additives and the like as necessary. The ratio of the binder resin to the magnetic iron oxide particle powder is 10 to 900 parts by weight, preferably 20 to 400 parts by weight, based on 100 parts by weight of the magnetic iron oxide particle powder.

  As the binder resin, a vinyl polymer obtained by polymerizing or copolymerizing vinyl monomers such as styrene, alkyl acrylate ester and alkyl methacrylate ester can be used. Examples of styrene as a monomer constituting the binder resin include styrene and substituted products thereof, and examples of the alkyl acrylate include acrylic acid, methyl acrylate, ethyl acrylate, and butyl acrylate. The copolymer preferably contains 50 to 95% by weight of a styrene component. Moreover, a polyester resin, an epoxy resin, a polyurethane resin, etc. can be used for a binder resin as needed.

  The magnetic toner in the present invention can be produced by mixing, kneading, kneading and pulverizing methods, suspension polymerization method or emulsion polymerization method.

<Action>
The magnetic iron oxide particles according to the present invention have an octahedron shape and each ridge line of the octahedron is a curved surface, resulting in a shape anisotropy due to the octahedron and residual magnetization. The value is close to that of octahedral magnetite particles, each ridgeline is a curved surface with no angularity, and the apex portion and the central portion are also curved, resulting in excellent dispersibility, and Fe ²⁺ Since the content is sufficiently large, the blackness is excellent.

  Usually, when controlling the particle shape of magnetite particles, a silicon compound is added during the reaction, but the magnetic iron oxide particles according to the present invention have three stages of magnetite formation reaction, and the oxidation rate and Since it can be obtained by controlling the pH value of the reaction solution, it is not necessary to add a large amount of silicon compound, and the magnetic iron oxide particle powder composed of the obtained magnetite particle powder is excellent in environmental stability.

  Representative examples of the present invention are as follows.

  The average particle diameter of the black magnetic iron oxide particles was indicated by the average value (Martin diameter) of the numerical values measured from the electron micrograph.

  Moreover, the specific surface area was shown by the value measured by BET method.

  The magnetic characteristics were measured using an “oscillating sample type magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) up to an external magnetic field of 798 kA / m (10 kA / m).

  The particle shape was observed with a scanning electron microscope (Hitachi S-800) and a transmission electron microscope (JEOL JEM-100S).

  The axial ratio of the magnetic iron oxide particles is measured by extracting 250 or more magnetic iron oxide particles randomly from a transmission electron microscope (JEOL JEM-100S) observation (magnification 10,000 times) as a projection diagram. The longest diameter was measured as the major axis diameter l, and the shortest diameter of the particles was measured as the minor axis diameter w.

Axial ratio = l / w
l: major axis diameter of magnetic iron oxide particles in projected view w: minor axis diameter of magnetic iron oxide particles in projected diagram

  The amount of elements other than Fe in the magnetic iron oxide particles is a value measured using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to “General X-ray fluorescence analysis rules” of JIS K0119. Indicated.

The Fe ²⁺ content of the magnetic iron oxide particles was indicated by the value obtained by the following chemical analysis method. That is, in an inert gas atmosphere, 25 cc of a mixed solution containing phosphoric acid and sulfuric acid in a ratio of 2: 1 is added to 0.5 g of magnetic particle powder to dissolve the magnetic particles. After adding several drops of diphenylamine sulfonic acid as an indicator to the diluted solution of the aqueous solution, redox titration using an aqueous potassium dichromate solution was performed. The end point was when the diluted solution was purple, and the amount was calculated from the amount of the aqueous potassium dichromate solution used to reach the end point.

The oxidation reaction rate of the ferrous salt in the first stage reaction was calculated by the following formula by measuring the Fe 2+ content in the reaction solution.
(A−B) ÷ A × 100 = Oxidation reaction rate (%)
However, A is the content of Fe 2+ in the reaction solution immediately after mixing the aqueous ferrous salt solution and the aqueous alkaline solution, and B is the Fe 2+ in the ferrous salt reaction solution containing a mixture of ferrous hydroxide and magnetite particles. Content.

  The content of the soluble sodium salt in the magnetic iron oxide particle powder was indicated by a value measured with an “inductively coupled plasma atomic emission spectrophotometer SPS-4000 type” (manufactured by Seiko Denshi Kogyo Co., Ltd.).

  The volume average diameter of the toner was measured using a Coulter Counter TA-II (Couter Electronics Co.).

The toner charge amount was precisely weighed with 0.5 g of toner and 4.75 g of iron powder carrier (TEFV-200 / 300, manufactured by Powder Tech Co., Ltd.) in a glass sample bottle having an internal volume of 15 cc, and a paint conditioner was used. Frictional charging was performed, and the triboelectric charge amount was measured using a “blow-off charge amount measuring device” (manufactured by Toshiba Chemical Corporation). The charging stability of the toner was evaluated in four grades from A to X.
A: The rise of charge is good and stable.
○: Rise of charge is good, but it is a little difficult to stabilize.
Δ: Charging rises poorly and is difficult to stabilize.
×: Charging rise is poor and the charge amount fluctuates greatly

The dispersed state of the magnetic particles in the toner was sliced with a microtome and observed with a transmission electron microscope (JEOL JEM-100S). The dispersion state of the magnetic particle powder in the toner was evaluated in four stages from A to X.
◎: The dispersion state of the magnetic powder is very good. ○: The dispersion state of the magnetic powder is good. △: Part of the magnetic powder is aggregated. ×: The aggregation of the magnetic powder is conspicuous.

Example 1
Add 26.7 liters of ferrous sulfate aqueous solution containing Fe ²⁺ 1.5 mol / l to 25.9 liters of 3.4N aqueous sodium hydroxide solution prepared in the reactor in advance (to 1.10 equivalents to Fe ²⁺ ). Applicable)), a ferrous salt suspension containing ferrous hydroxide colloid at pH 10.5 and temperature 90 ° C. was produced. The ferrous salt suspension containing the ferrous hydroxide colloid was oxidized at a temperature of 90 ° C. with 100 l of air per minute for 80 minutes until the oxidation reaction rate of the ferrous salt reached 60%. Reaction was performed (first stage reaction).

  Next, an aqueous sulfuric acid solution was added to the ferrous salt suspension containing the magnetite nuclei particles so that the suspension had a pH of 6.5, and 100 l of air was aerated at a temperature of 90 ° C. Magnetite particles were generated (second stage reaction).

Next, an aqueous alkali hydroxide solution was added to the ferrous salt suspension containing the magnetite particles so that the pH of the suspension was 10.5, and 100 l of air was aerated at a temperature of 90 ° C. Magnetite particles were generated (third stage reaction).
The produced particles were washed with water, filtered, dried and pulverized by a conventional method. As is apparent from the electron micrograph (× 50000) shown in FIG. 1, the obtained magnetite particles have octahedral shapes, ridges are curved, and the particle sizes are uniform. The average particle size was 0.20 μm and the axial ratio was 1.40.

Further, as a result of the oxidation-reduction titration, the magnetite particle powder had an Fe ²⁺ amount of 18.5% by weight and had sufficient blackness. The amount of soluble Na was 50 ppm. The magnetic properties were a coercive force of 8.04 kA / m, a saturation magnetization value of 85.5 Am ² / kg, and a residual magnetization value of 8.5 Am ² / kg.

Examples 2-8, Comparative Examples 1-5;
Various types of ferrous salt aqueous solution, types of alkali hydroxide aqueous solution in the first stage reaction, alkali equivalent ratio of the first stage reaction, oxidation reaction rate during the first stage reaction, reaction temperature and pH in each reaction stage Magnetite particle powder was obtained in the same manner as in Example 1 except that the amount was changed.

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

  The magnetite particles obtained in Comparative Examples 1 and 5 were both angular octahedral.

<Usage example>
Next, a usage example is given.

Example 1
After mixing the magnetite particle powder obtained in Example 1, the styrene acrylic resin and other additives at the following mixing ratio, the mixture is heated and melted by a kneader to disperse the magnetite particles in the resin, and after cooling and solidifying, The obtained resin kneaded product was pulverized and classified to obtain a magnetic toner. The obtained magnetic toner had a volume average diameter of 10 μm.

Toner mixing ratio:
140 parts by weight of styrene-acrylic resin,
2 parts by weight of negative charge control agent,
Release agent (polypropylene) 6 parts by weight,
Magnetite particle powder 100 parts by weight,
External additive (hydrophobic silica fine powder) 2 parts by weight.

  Table 3 shows various properties of the obtained magnetic toner.

Use Examples 2-8, Use Comparative Examples 1-5;
A magnetic toner was produced in the same manner as in the above use example except that the type of magnetic iron oxide particle powder was variously changed.

  Table 3 shows various characteristics of the obtained magnetic toner.

  As apparent from the electron micrograph (× 50000) shown in FIG. 2, the magnetite particle powder obtained in Comparative Example 1 has an octahedral shape with square ridgelines. The magnetite particle powder of Example 1 It is inferior in dispersibility compared to.

FIG. 3 shows the relationship between the average particle diameter d (μm) of the magnetic iron oxide particles according to the present invention and the residual magnetization value σr (Am ² / kg). In general, the particle diameter and the residual magnetization value σr are closely related, and the residual magnetization value σr increases as the particle diameter decreases. The magnetic iron oxide particle powder according to the present invention has a residual magnetization value σr equivalent to that of a conventional angular octahedral magnetite particle powder. In the figure, the ● marks are for the magnetite particle powders obtained in Examples 1-8.
In FIG. 3, a dotted line A indicates -50 × d + 17, and a dotted line B indicates -50 × d + 20.

The magnetic iron oxide particles according to the present invention are fine particles having a particle size of 0.05 to 0.30 μm, have excellent dispersibility, and have a high residual magnetization value. Therefore, when used as a magnetic toner having a small particle size. Since the toner has a stable charge amount and a large amount of Fe ²⁺ , it is excellent in blackness and can be suitably used as a magnetic powder for magnetic toner for electrophotography.

Electron micrograph of the magnetite particle powder obtained in Example 1 (50000 times magnification) Electron micrograph of the magnetite particle powder obtained in Comparative Example 1 (50000 times magnification) It is a graph which shows the relationship between the average particle diameter (d) of magnetite particle powder, and a residual magnetization value ((sigma) r). ●: Example, △: Comparative example

Claims (4)

Magnetite particle powder having an average particle diameter (d) of 0.05 to 0.30 μm, the particle shape being based on octahedron, and each ridge line of octahedron being curved, Magnetic iron oxide particle powder consisting of Magnetite particle powder having an average particle diameter (d) of 0.05 to 0.30 μm, the particle shape is based on octahedron, and each ridge line of the octahedron is curved, and is defined by the following equation: A magnetic iron oxide particle powder comprising magnetite particles, wherein the axial ratio (l / w) is 1.2 ≦ l / w <1.6.
Axial ratio = l / w
l: major axis diameter of magnetic iron oxide particles in projected view w: minor axis diameter of magnetic iron oxide particles in projected diagram The magnetite particle powder according to claim 1 or 2, wherein one or two or more elements selected from Mn, Zn, Ni, Cu, Al, Ti, and Si are contained in an amount of 0 to 10.0 atomic% with respect to Fe. Magnetic iron oxide particle powder characterized by 4. The magnetic oxidation according to claim 1, wherein the relationship between the residual magnetization value (σr) and the average particle diameter (d) at a measurement magnetic field of 796 kA / m is within the range of the following formula. Iron particle powder.
−50d + 17 <σr <−50d + 20