JP5310994B2 - Magnetic iron oxide particle powder for magnetic toner and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic iron oxide particle powder for magnetic toner which is high in flowability and resolution, and is superior in blackness when used as magnetic toner particles of small particle size, and to provide a method of manufacturing the magnetic iron oxide particle powder. <P>SOLUTION: The magnetic iron oxide particle powder for magnetic toner is composed of magnetite particles containing silicone of 0.10 to 0.30 &mu;m in average particle size by 0.1 to 0.9% by atom for Fe in terms of Si, and shaped basically in hexahedrons having curved-surface ridges, a shape coefficient &Phi; satisfying 1.05&lt;&Phi;&lt;1.40. The magnetic iron oxide particle powder is obtained by through first-stage reaction wherein magnetite particles are produced by heating and passing an oxygen-containing gas through a ferrous salt reaction solution containing ferrous iron colloid produced through reaction of an alkali hydroxide solution of 0.80 to 0.99 in equivalence with a first ferrous salt solution and ferrous salt, and second-stage reaction wherein magnetite particles are produced by adding an alkali hydroxide solution &ge;1.00 in equivalence to the remaining Fe<SP>2+</SP>and then heating and passing an oxygen-containing gas. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention is a fine particle having a particle size of 0.10 to 0.30 μm, excellent fluidity, and has a low residual magnetization when used as a magnetic toner particle having a small particle diameter. Aggregation is less likely to animate, resulting in better dispersibility in the resin, less difference in characteristics between magnetic toner particles, higher resolution, and greater Fe ²⁺ for excellent blackness. The present invention relates to iron particle powder and a method for producing the same.

  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.

  In recent years, with the improvement in performance of electrostatic copying machines, such as miniaturization and speeding up, improvement in characteristics of magnetic toner as a developer, that is, fogging is suppressed, and a magnetic toner having a small particle diameter capable of obtaining high resolution has been developed. There is a strong demand. Since hexagonal and octahedral magnetic particles come into contact with each other on the surface of the magnetic substance, agglomerates that cannot be separated from each other by mechanical shearing force are easily generated and dispersed in the resin. As a result, a difference in characteristics between magnetic toner particles is generated, resulting in a decrease in image density and fogging.

  Since the fluidity of the magnetic toner greatly depends on the surface state of the magnetic particles exposed on the surface of the magnetic toner, it is necessary that the fluidity of the magnetic particle powder itself is excellent, such as octahedron and hexahedron. When the particles are angular, the fluidity as magnetic particles is poor, and when the toner is a magnetic toner, the fluidity is also poor. On the other hand, the fluidity as magnetic particles is good when the particles are round such as spherical, and the fluidity is also good when magnetic particles are used. Therefore, there is a demand for a rounded magnetic particle powder having a good fluidity even when a magnetic toner is used.

The blackness of the magnetic particle powder is “powder and powder metallurgy” Vol. 26, No. 7, pp. 239-240. “The blackness of the sample depends on the Fe (II) content and the average particle size. The 0.2 μm powder is a bluish black powder and is most suitable as a black pigment .... When the Fe (II) content is 10% or more, there is a slight difference in the blackness, but the sample Each sample changes from black to reddish brown when the Fe (II) content is reduced to 10% or less. ” In the case of magnetite particle powder of about 5 μm, it is known that it depends mainly on the Fe ²⁺ content. Therefore, there is a demand for magnetite particle powder having a high Fe ²⁺ content and high blackness.

Magnetite particle powders used as magnetic particle powders for magnetic toners include octahedron magnetite particle powder (Japanese Patent Publication No. 44-668) and spherical magnetite particles (Japanese Patent Publication No. 62-51208). However, these are described in Japanese Patent Application Laid-Open No. 3-201509 as “... the magnetite particle powder having an octahedron has a Fe ²⁺ content in a molar ratio of 0.3 to 0.45 with respect to Fe ^3+. Although the degree of blackness is excellent, the residual magnetization is large and magnetic aggregation is likely to occur, so the dispersibility is poor and the miscibility with the resin is poor .... Spherical magnetite The particle powder has small remanent magnetization and hardly causes magnetic aggregation, so it has excellent dispersibility and good mixing with the resin. However, the Fe ²⁺ content is 0.28 at most in molar ratio to Fe ^3+. Therefore, the conventional spherical or octahedral magnetite particles do not have sufficient characteristics, as described in the above.

  Moreover, although magnetite particle powder (Patent Document 1: Japanese Patent Application Laid-Open No. 3-201509) having a hexahedron has been proposed, the fluidity is not sufficient because the particle shape is angular.

  Conventionally, in order to improve the characteristics of magnetite particles, investigations have been made on a production method in which Si is added during a magnetite formation reaction. For example, a silicon component is added to a ferrous salt solution and 1.0% of iron is added. After mixing with ~ 1.1 equivalent of alkali, the pH is maintained at 7 to 10 to carry out an oxidation reaction, and in the middle of the reaction, 0.9 to 1.2 equivalent of the initial alkali is added and insufficient iron is added. In addition, there is a method of obtaining magnetite particles by performing an oxidation reaction while maintaining the pH at 6 to 10 (Patent Document 2: JP-A-5-213620).

  Various attempts have been made to improve hexahedral magnetite particles. For example, cubic shaped magnetite particles with chamfered edges (Patent Document 3: Japanese Patent Laid-Open No. 2-44030), magnetite particles having a substantially hexahedral shape, and each ridge line of the hexahedron is planar. Powder (Patent Document 4: JP-A-6-144840), magnetite particles having a hexahedral shape and a coercive force of 40 to 80 Oe (Patent Document 5: JP-A-9-22143), 0.9 in terms of Si It contains magnetite particles (Patent Document 6: Japanese Patent Laid-Open No. 9-59024) containing ˜1.7 atomic% silica and each ridge line is curved on the basis of hexahedron, and has various shapes including phosphorus, aluminum, and silicon. Magnetite particles (Patent Document 7: JP-A-10-101339), magnetite particles with controlled saturation magnetization, residual magnetization and coercive force (Patent Document 8: Special 2000-335922 JP), each vertex and edge lines of the hexahedral magnetite particles (Patent Document 9 is curved: JP 2007-178717 JP) and the like are known.

JP-A-3-201509 JP-A-5-213620 JP-A-2-44030 JP-A-6-144840 JP 9-22143 A Japanese Patent Laid-Open No. 9-59024 Japanese Patent Laid-Open No. 10-101339 JP 2000-335922 A JP 2007-178717 A

In view of the above-mentioned problems, the particle size is a fine particle of 0.10 to 0.30 μm, excellent in fluidity, and when used as a magnetic toner particle having a small particle size, the residual magnetization is low, For magnetic toners that are excellent in dispersibility in resin due to the difficulty of agglomeration of magnetic properties, hardly cause differences in properties between magnetic toner particles, have high resolution, and have excellent blackness due to high Fe ²⁺ Magnetic iron oxide particle powders are currently in most demand, but such magnetic iron oxide particle powders for magnetic toner have not yet been provided.

  That is, the magnetite particles described in the above-mentioned Patent Document 2 (JP-A-5-213620) are obtained by adding 1.0 to 1.1 equivalents of alkali with respect to ferrous iron in the primary reaction. The magnetite particles obtained have a large particle size distribution and a uniform particle size.

The magnetite particles described in the above-mentioned Patent Document 3 (JP-A-2-44030) have a cubic shape with chamfered edges, but have a BET specific surface area of 0.5 to ⁵ m ² / g. In addition, it has a large particle size, an angular shape, and poor fluidity.

  In addition, the magnetite particles described in Patent Document 4 (Japanese Patent Laid-Open No. 6-144840) are substantially hexahedral in shape, and each ridge line of the hexahedron has a planar shape, but is angular. The shape is inferior in fluidity.

  Further, the magnetite particles described in the above-mentioned Patent Document 5 (Japanese Patent Laid-Open No. 9-22143) have a normal hexahedron shape and are inferior in fluidity.

  Moreover, although the magnetite particle | grains described in the above-mentioned patent document 6 (Unexamined-Japanese-Patent No. 9-59024) have described the magnetite particle | grains in which each ridgeline is a curved surface shape on the basis of a hexahedron, as shown in a following comparative example. The remanent magnetization value is high.

  The magnetite particles described in the above-mentioned Patent Document 7 (Japanese Patent Laid-Open No. 9-22143) have a normal hexahedron shape, inferior fluidity, and a high residual magnetization value. is there.

  The magnetite particles described in the above-mentioned Patent Document 8 (Japanese Patent Laid-Open No. 2000-335922) have a normal hexahedron shape and are inferior in fluidity.

  Moreover, although the magnetite particle | grains described in the above-mentioned patent document 9 (Unexamined-Japanese-Patent No. 2007-178717) have described the magnetite particle | grains in which each ridgeline is a curved surface shape on the basis of a hexahedron, as shown in a following comparative example. The remanent magnetization value is high.

Therefore, the present invention is a fine particle having a particle size of 0.10 to 0.30 μm, excellent fluidity, and low residual magnetization when used as a magnetic toner particle having a small particle size. For magnetic toners that have good dispersibility in resin because of difficult agglomeration, high resolution due to less property difference between magnetic toner particles, and excellent blackness due to high Fe ²⁺ It is a technical problem to provide magnetic iron oxide particle powder.

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

That is, the present invention is a magnetite particle having an average particle diameter (d) of 0.10 to 0.30 μm and containing 0.1 atomic% or more and less than 0.9 atomic% of silicon with respect to Fe in terms of Si. The particle shape is based on a hexahedron, each ridge line of the hexahedron is a curved surface, and the shape factor Φ defined by the following formula is 1.05 <Φ ≦ 1.36. A magnetic iron oxide particle powder for magnetic toner (Invention 1).
Shape factor Φ = l / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view

Further, the present invention has an average particle diameter (d) of 0.10 to 0.30 μm, contains 0.1 atomic% or more and less than 0.9 atomic% of silicon with respect to Fe in terms of Si, Al, Ti Mg, Co, Zr, Mn, Zn, Ni, Cu, S, Na, P, Ca, Ce, Sr, Ba, Cr, Sn, Bi, or one or more elements selected from 0 to 20 atoms % ( May be 0 atomic%) , the particle shape of which is based on a hexahedron, each ridge of the hexahedron is a curved surface, and the shape factor Φ defined by the following equation is 1 .05 <Φ ≦ 1.36 . Magnetic iron oxide particle powder for magnetic toner comprising magnetite particles (Invention 2).
Shape factor Φ = l / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view

Further, the present invention is characterized in that the relationship between the remanent magnetization value (σr (Am ² / kg) ) and the average particle diameter (d (μm) ) when the measurement magnetic field is 79.6 kA / m satisfies the following formula: This is a magnetic iron oxide particle powder for magnetic toner (Invention 3).
σr ≦ −40d + 14.8

In addition, the present invention provides a hydroxide aqueous solution obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution of 0.80 to 0.99 equivalent to the ferrous salt in the aqueous ferrous salt solution. A first stage reaction in which an oxygen-containing gas is passed through a ferrous salt reaction aqueous solution containing a ferrous colloid while heating in a temperature range of 70 to 100 ° C. to generate magnetite particles, and the remaining after completion of the first stage reaction A two-stage reaction with a second stage reaction in which an aqueous solution of alkali hydroxide of 1.00 equivalent or more with ^respect to Fe ²⁺ is added and oxygen-containing gas is aerated while heating in a temperature range of 70 to 100 ° C. to generate magnetite particles. In the method for producing a magnetite particle powder comprising: a water-soluble silicate in an aqueous solution of an alkali hydroxide aqueous solution, a ferrous salt solution, or a ferrous salt aqueous solution containing ferrous hydroxide colloid; 0.1 in conversion The oxygen-containing gas is adjusted to a pH of 7.0 or more and less than 8.0 by adding an aqueous alkali hydroxide solution at the start of aeration of the oxygen-containing gas in the first-stage reaction. This is a method for producing magnetic iron oxide particle powder for magnetic toner as described above (Invention 4).

The magnetite particles according to the present invention are fine particles having a particle size of 0.10 to 0.30 μm, have excellent fluidity, and have low remanent magnetization, thereby suppressing magnetic aggregation between magnetic particles. black when used as a magnetic toner having a particle size, the difference in characteristics can hardly occur between the easy dispersion in the resin toner particles, by the fog can be suppressed, since it is high and Fe ²⁺ is large resolution It is optimal as a magnetic powder for magnetic toner for electrophotography because of its excellent strength.

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

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

The magnetic iron oxide particle powder according to the present invention is composed of magnetite particles (( FeO ₂ ) x · Fe ₂ O ₃ , 0 <x ≦ 1) in terms of composition, and if necessary, a metal element other than iron, Al, Ti Mg, Co, Zr, Mn, Zn, Ni, Cu, S, Na, P, Ca, Ce, Sr, Ba, Cr, Sn, Bi, and one or more metal elements selected from Fe 0 to 20 atomic%. The particle shape is based on a hexahedron as shown in the transmission electron micrograph of FIG. 1 described later, and each ridge line of the hexahedron is a curved surface. Preferably, on the basis of a cube, each ridge line of the cube is curved.

  The magnetic iron oxide particle powder according to the present invention has an average particle diameter of 0.10 to 0.30 μm. When the average particle diameter is less than 0.10 μm, the amount of particles in a unit volume increases too much, and the number of contacts between the particles increases. Dispersibility in the resin becomes poor. 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. More preferably, it is 0.12-0.28 μm.

In the magnetic iron oxide particle powder according to the present invention, the shape factor Φ represented by the following formula is in the range of more than 1.05 and less than 1.4. The range is preferably 1.15 to 1.38, more preferably 1.18 to 1.30. When the shape factor Φ is 1.05 or less, the shape factor is spherical and the coercive force is low, which is not preferable. In addition, when the shape factor Φ is 1.4, it is an angular hexahedron, and good fluidity cannot be obtained.
Shape factor Φ = l / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view

  The magnetic iron oxide particle powder according to the present invention contains 0.1 atomic% or more and less than 0.9 atomic% of silicon in terms of Si with respect to Fe. When the Si content is less than 0.1 atomic%, angular hexahedral particles are obtained and the fluidity is inferior. In the case of 0.9 atomic% or more, the amount of silicon contained increases, so that the BET specific surface area increases, and as a result, the amount of adsorbed water may increase. May affect stability. The silicon content is preferably 0.12 to 0.89 atomic%, more preferably 0.15 to 0.85 atomic%.

The magnetic iron oxide particles according to the present invention have a residual magnetization (σr) at a measurement magnetic field of 79.6 kA / m and a range satisfying a relational expression of σr ≦ −40d + 14.8 with an average particle diameter d (μm). It is preferable. When the residual magnetization exceeds the upper limit value for each particle diameter d, the magnetic aggregation becomes strong. When the magnetic toner is used, the dispersion in the resin is deteriorated and the characteristic difference among the toner particles is generated. Characteristics are degraded.
More preferably, both satisfy −40d + 10.8 ≦ σr and 1 ≦ σr. When the remanent magnetization value is less than the lower limit for each particle diameter d, the magnetic stress becomes weak, the scattering to the photosensitive drum is likely to occur, and fogging occurs.

The magnetic iron oxide particle powder according to the present invention has a saturation magnetization value of 80 to 92 Am ² / kg (80 to 92 emu / g), preferably 85 to 90 Am ² / kg (85 to 90 emu / g). The value of 92 Am ² / kg is a theoretical value of magnetite and does not exceed this value. When the amount is less than 80 Am ² / kg, the amount of Fe ^{2+ in} the particles decreases, and thus a reddish color is obtained.

  The magnetic iron oxide particle powder according to the present invention has a compressibility, which is an index of fluidity, of 55 or less, preferably 50 or less. If it exceeds 55, it is not preferable in terms of fluidity.

  The magnetic iron oxide particle powder according to the present invention has an angle of repose θ, which is another index of fluidity, of 50 ° or less, preferably 49 ° or less. When it exceeds 50 °, the fluidity is not preferable.

The magnetic iron oxide particle powder according to the present invention has an Fe ²⁺ content of 15.0 to 24.0% by weight, preferably 17 to 24% by weight, based on the total weight of the magnetic iron oxide particles. When the amount is less than 15.0% by weight, sufficient blackness cannot be obtained. When it exceeds 24.0% by weight, it is easily oxidized and inferior in environmental stability.

When a coating film is prepared by the method described later using the magnetic iron oxide particle powder according to the present invention, the 60 ° gloss of the coating film having a thickness of 24 μm is 75% or more, preferably 80% or more. When the 60 ° glossiness of the coating film is less than 75%, it is difficult to say that the dispersion in the resin is excellent.

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

In the present invention, ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with 0.80 to 0.99 equivalent of an aqueous alkali hydroxide solution with respect to the ferrous salt in the aqueous ferrous salt solution. A first stage reaction in which an oxygen-containing gas is passed through a ferrous salt reaction aqueous solution containing iron colloid while heating in a temperature range of 70 to 100 ° C. to generate magnetite particles, and Fe remaining after the completion of the first stage reaction ^A two-stage reaction with a second stage reaction in which an aqueous alkali hydroxide solution of 1.00 equivalent or more is added to ²⁺ , heated to a temperature range of 70 to 100 ° C. and aerated with an oxygen-containing gas to generate magnetite nuclei particles In the method for producing magnetite particle powder comprising, an aqueous solution of alkali hydroxide, ferrous salt solution or ferrous salt solution containing ferrous hydroxide colloid, water-soluble silicate is converted to Si for Fe 0.1 Oxygen content is added by adding an alkali hydroxide aqueous solution at the start of aeration of oxygen-containing gas in the first stage reaction and adjusting the pH to 7.0 or more and less than 8.0. A gas is passed through to obtain magnetic iron oxide particles for magnetic toner composed of magnetite particles whose particle shape is basically a hexahedron and each ridge line of the hexahedron is a curved surface.

  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 alkali hydroxide aqueous solution used before the pH adjustment in the first stage reaction is 0.80 to 0.99 equivalents with respect to Fe ²⁺ in the ferrous salt aqueous solution. Preferably it is the range of 0.85-0.99 equivalent. When the amount is less than 0.80 equivalent, goethite is mixed in the product, and the target magnetite particles cannot be obtained as a single phase. If it exceeds 0.99 equivalents, the particle size distribution becomes large and a uniform particle size cannot be obtained.

  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.

  As the water-soluble silicate used in the present invention, sodium silicate, potassium silicate and the like can be used. The addition amount of the water-soluble silicate is 0.1 atomic percent or more and less than 0.9 atomic percent, preferably 0.12 to 0.89 atomic percent in terms of Si with respect to Fe. If it is less than 0.1 atomic%, it becomes an angular hexahedral particle and is inferior in fluidity. On the other hand, in the case of 0.9 atomic% or more, the amount of silicon contained increases, so the BET specific surface area increases. As a result, the amount of adsorbed water increases, and when toner is used, the environmental stability of the toner is increased. May be affected.

  The water-soluble silicate in the present invention is involved in the shape of the magnetite particles to be produced. Therefore, the addition timing of the water-soluble silicate is in the ferrous salt reaction aqueous solution containing ferrous hydroxide colloid. It is necessary to ventilate an oxygen-containing gas to produce magnetite particles, and either an alkali hydroxide aqueous solution, a ferrous salt solution, or a ferrous reaction aqueous solution containing a ferrous hydroxide colloid Can be added.

In the first-stage reaction, an aqueous alkali hydroxide solution is added at the start of aeration of the oxygen-containing gas to adjust the pH of the suspension to a range of 7.0 or more and less than 8.0. More preferably, the pH is in the range of 7.1 to 7.9. When the suspension pH is less than 7.0, spherical particles are formed, the Fe ²⁺ content is low, and sufficient blackness cannot be obtained. When the suspension pH exceeds 8.0, angular hexahedral particles or octahedral particles are formed, resulting in poor fluidity.

The amount of the alkali hydroxide aqueous solution used in the second stage reaction is 1.00 equivalent or more with respect to the remaining Fe ²⁺ at the start of the second stage reaction. If it is less than 1.00 equivalent, the remaining Fe ²⁺ does not precipitate in its entirety. Practically, the amount is preferably 1.00 equivalent or more and considering industrial properties. As a result, in the second stage reaction, the pH of the suspension is in the range of 9-12.

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

  In addition, sufficient stirring may be performed for a required time between the raw material addition and the first stage reaction, and between the first stage reaction and the second stage reaction, if necessary.

If necessary, it is a metal element other than iron, from Al, Ti, Mg, Co, Zr, Mn, Zn, Ni, Cu, S, Na, P, Ca, Ce, Sr, Ba, Cr, Sn, Bi. The metal element can be contained by adding a metal salt of one or more metal elements selected. As the metal salt, sulfate, nitrate, chloride and the like can be used. The total amount of the metal salt is preferably 0 to 20 atom%, more preferably 0 to 18 atom%, based on Fe as a total amount.

  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 15 μm, preferably 5 to 12 μm.

  The magnetic toner in the present invention comprises the magnetic iron oxide particle powder for magnetic toner and a 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 for magnetic toner is 10 to 900 parts by weight, preferably 10 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 prepared by a known method such as mixing, kneading, and pulverization. Specifically, the magnetic iron oxide particle powder for magnetic toner and the binder resin, and if necessary, The magnetic iron oxide particles are prepared by first thoroughly mixing the colorant, release agent, charge control agent, other additives, etc. with a mixer, and then melting and kneading the resin with a heating kneader to make them compatible. Etc. are dispersed and cooled and solidified, and the resulting resin kneaded product is pulverized and classified to obtain a magnetic toner.

  As the mixer, a mixer such as a Henschel mixer or a ball mill can be used. As the heating kneader, a roll mill, a kneader, a twin screw type, an extruder, or the like can be used. The pulverization can be performed by a pulverizer such as a cutter mill or a jet mill, and the classification can also be performed by a known method.

  As another method for obtaining the magnetic toner in the present invention, there is a suspension polymerization method or an emulsion polymerization method. In the suspension polymerization method, a polymerizable monomer, magnetic iron oxide particle powder for magnetic toner, a colorant, In accordance with the polymerization initiator, cross-linking agent, charge control agent, and other additives dissolved or dispersed in the water phase containing the suspension stabilizer while stirring, granulate, It can be polymerized to form toner particles.

  In the emulsion polymerization method, toner particles having an appropriate particle size are obtained by adding an emulsifier to the process of dispersing the monomer, magnetic iron oxide particle powder for magnetic toner, colorant, polymerization initiator and the like in the process of polymerization. Can be formed.

<Action>
First, the most important point in the present invention is that the magnetic iron oxide particle powder according to the present invention is excellent in fluidity and has a low residual magnetization value, so that magnetic aggregation between the magnetic particles can be suppressed. When used as a magnetic toner, it is easy to disperse in the resin and hardly causes a characteristic difference between the toner particles, so that the fog is suppressed and the resolution is high, and since there is a large amount of Fe ^{2+, the blackness} is excellent. This is the fact that magnetic iron oxide particles for magnetic toner can be obtained.

The magnetite particles according to the present invention have a hexahedron shape, and each ridge line of the hexahedron is a curved surface, so that the fluidity is excellent, and magnetic aggregation is suppressed by a low residual magnetization value. Moreover, the content of Fe ²⁺ is sufficiently large and the blackness is excellent.

The magnetite particles according to the present invention are obtained by reacting a ferrous salt aqueous solution with 0.80 to 0.99 equivalent of an alkali hydroxide aqueous solution with respect to the ferrous salt in the ferrous salt aqueous solution. A first-stage reaction in which an oxygen-containing gas is passed through a ferrous salt reaction aqueous solution containing ferrous oxide colloid while heating in a temperature range of 70 to 100 ° C. to generate magnetite particles, and after the completion of the first-stage reaction. Addition of 1.00 equivalent or more of an aqueous alkali hydroxide solution to the remaining Fe ²⁺ , heating to a temperature range of 70 to 100 ° C., and aeration of oxygen-containing gas to generate magnetite nucleation particles In the method for producing a magnetite particle powder comprising a step reaction, a water-soluble silicate is added to Fe in any one of an alkali hydroxide aqueous solution, a ferrous salt aqueous solution or a ferrous salt aqueous solution containing a ferrous hydroxide colloid. Si conversion And 0.1 to less than 0.9 at.%, And the pH is adjusted to 7.0 to less than 8.0 by adding an alkali hydroxide aqueous solution at the start of oxygen-containing gas passage in the first stage reaction. Thus, the magnetite particle powder having the above characteristics can be obtained.

  Representative examples of the present invention are as follows.

  In the following embodiments, examples and comparative examples, the average particle diameter is an average value of values measured from electron micrographs, and the specific surface area is a value measured by the BET method. The magnetic properties were measured using an “oscillating sample type magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) up to an external magnetic field of 79.6 kA / m.

  The particle shape was observed with a transmission electron microscope (Hitachi S-800).

  The shape factor of the magnetic iron oxide particles is measured by randomly extracting 250 or more magnetic iron oxide particles from a transmission electron microscope (JEOL JEM-100S) photograph as a projection view, and calculating the average major axis diameter l and the average short axis. The shaft diameter w was determined and calculated by the following formula.

Shape factor = 1 / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view

  The amount of Si in the magnetic iron oxide particles is indicated by 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.

The Fe ²⁺ content was indicated by a 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 fluidity of the magnetic iron oxide particle powder can be estimated by the degree of compression and the angle of repose θ.

The degree of compression was indicated by a value calculated by measuring the bulk density (ρa) and the tap density (ρt) and substituting these values into the following equation.
Compressibility = [(ρt−ρa) / ρt] × 100 In addition, the smaller the degree of compression, the better the fluidity.

The bulk density (ρa) was measured by the pigment test method of JIS K5101, and the tap density (ρt) was gently measured using a funnel in a 20 cc graduated cylinder with 10 g of magnetic iron oxide particle powder after the bulk density measurement. After filling and then dropping naturally from a height of 25 mm 600 times, the amount (cc) of the filled magnetic iron oxide particles is read from the scale of the graduated cylinder, and this value is substituted into the following equation. It was shown by the calculated value.
Tap density (g / cc) = 10 (g) / capacity (cc)

The angle of repose θ was measured as follows. First, the sample powder is passed through a 710 μm sieve in advance. A repose angle measuring table with a radius of 3 cm is set, and the sample powder once passed through a 710 μm sieve set 10 cm above is dropped. When the sample powder comes to form a cone on the table, the height x is measured, the sample powder is further dropped, and the cone height x is measured again. If there was no difference in the height x measured twice, x was substituted into the following equation to obtain the value of the angle of repose θ.
tan θ = x / 3
In addition, the smaller the angle of repose θ, the better the fluidity.

  The 60 ° glossiness of a coating film having a thickness of 24 μm can be determined by the following method. 8 g of the polyester resin is dissolved in 20 g of toluene. 8 g of magnetic iron oxide particle powder and 50 g of 1.5 mmΦ glass beads are added to a solution of polyester dissolved in toluene, and dispersed by a paint conditioner for 4 hours to obtain a dispersion. This dispersion is applied onto cast-coated paper using a bar coater using a wet bar having a thickness of 24 μm. After drying, the 60 ° gloss of the coating film was measured using “Gloss meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.).

Example 1
21.3 l of ferrous sulfate aqueous solution containing Fe ²⁺ 1.5 mol / l was added to 17.9 l of 3.4N sodium hydroxide aqueous solution prepared in the reactor in advance (to 0.95 equivalent to Fe ²⁺ Applicable)), a ferrous salt suspension containing ferrous hydroxide colloid at a pH of 6.8 and a temperature of 90 ° C. was produced. At this time, as a silicon component, 58.1 g of No. 3 water glass (SiO ₂ 28.8 wt%) (corresponding to 0.87 atomic% in terms of Si with respect to Fe) diluted to 1 l with water is sodium hydroxide. Added to aqueous solution. After adding 3.4N sodium hydroxide aqueous solution to the ferrous hydroxide suspension containing the ferrous hydroxide colloid, the pH of the suspension was adjusted to 7.6, and then 100 l / min at 90 ° C. Was aerated for 80 minutes to obtain a ferrous salt suspension containing magnetite nuclei particles.

Next, 60 ml of a 9N sodium hydroxide aqueous solution is added to the ferrous salt suspension containing the magnetite nuclei particles (corresponding to 1.5 equivalents of the remaining Fe ²⁺ ), and each time at a pH of 10 and a temperature of 90 ° C. Magnetite particles were generated by aeration of 100 l of air for 30 minutes. The produced particles were washed with water, filtered, dried and pulverized by a conventional method.

  As is apparent from the electron micrograph (× 100000) shown in FIG. 1, the obtained magnetite particles have a cubic shape, a ridge line is a curved surface, an average particle diameter is 0.22 μm, and a shape factor. Φ was 1.22.

Moreover, this magnetite particle powder contains 0.84 atomic% of Si with respect to Fe as a result of fluorescent X-ray analysis, and as a result of oxidation-reduction titration, the amount of Fe ²⁺ is 20.2% by weight, It had sufficient blackness. As for the magnetic properties, the residual magnetization value (σr) was 3.9 Am ² / kg.

Examples 2-7, Comparative Examples 1-4;
Various types of ferrous salt aqueous solution, water glass addition, alkali hydroxide aqueous solution addition in the first stage reaction, reaction temperature, alkali hydroxide type in the second stage reaction, addition amount and reaction temperature A magnetite particle powder was obtained in the same manner as in Example 1 except that. The production conditions at this time are shown in Table 1, and the properties of the obtained magnetite particle powder are shown in Table 2.

  As apparent from the electron micrograph (× 100,000) shown in FIG. 2, the magnetite particle powder obtained in Comparative Example 1 has a hexahedral shape with angular ridges. Compared to liquidity.

  FIG. 3 shows the relationship between the average particle diameter d (μm) and the residual magnetization value (σr) of the magnetic iron oxide particle powder for magnetic toner according to the present invention. In general, the particle diameter and the residual magnetization value are closely related, and the residual magnetization value increases as the particle diameter decreases. The magnetic iron oxide particle powder for magnetic toner according to the present invention has a remanent magnetization value lower than that of a conventional angular cube-shaped magnetite particle powder. In the figure, the ● marks relate to the magnetite particle powders obtained in the embodiment of the present invention and Examples 1-7.

The magnetite particles according to the present invention are fine particles having a particle size of 0.10 to 0.30 μm, have excellent fluidity, and have low remanent magnetization, thereby suppressing magnetic aggregation between magnetic particles. black when used as a magnetic toner having a particle size, the difference in characteristics can hardly occur between the easy dispersion in the resin toner particles, by the fog can be suppressed, since it is high and Fe ²⁺ is large resolution It is optimal as a magnetic powder for magnetic toner for electrophotography because of its excellent strength.

2 is an electron micrograph of magnetic iron oxide particles obtained in Example 1. FIG. 2 is an electron micrograph of magnetic iron oxide particles obtained in Comparative Example 1. It is a graph which shows the relationship between the average particle diameter d (micrometer) of the magnetic iron oxide particle in this invention, and residual magnetization value (sigma) r (Am < ² > / kg).

Claims (5)

A magnetite particle having an average particle diameter (d) of 0.10 to 0.30 μm and containing 0.1 atomic% or more and less than 0.9 atomic% of silicon with respect to Fe in terms of Si, the particle shape of which is A magnet for magnetic toner comprising magnetite particles, characterized in that the hexahedron is a base, each ridge line of the hexahedron is curved, and the shape factor Φ defined by the following formula is 1.05 <Φ ≦ 1.36 Iron oxide particle powder.
Shape factor Φ = l / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view The average particle diameter (d) is 0.10 to 0.30 μm, contains 0.1 atomic% or more and less than 0.9 atomic% of silicon with respect to Fe in terms of Si, Al, Ti, Mg, Co, Zr , Mn, Zn, Ni, Cu, S, Na, P, Ca, Ce, Sr, Ba, Cr, Sn, Bi One or more elements selected from 0 to 20 atomic% (at 0 atomic%) may be.) the magnetite particles containing, and its particle shape basically hexahedron, each ridge of the hexahedron is curved, the shape factor defined by the following equation [Phi is 1.05 <Φ ≦ 1 A magnetic iron oxide particle powder for magnetic toner, comprising magnetite particles, characterized by being .36 .
Shape factor Φ = l / w
l: Average major axis diameter of magnetic iron oxide particles in the projected view w: Average minor axis diameter of magnetic iron oxide particles in the projected view 3. The magnetic iron oxide particle powder for magnetic toner according to claim 1, wherein the particle shape is basically a cube, and each ridge line of the cube is a curved surface. The relationship between the residual magnetization value (σr (Am ² / kg) ) and the average particle diameter (d (μm) ) when the measurement magnetic field is 79.6 kA / m satisfies the following formula: The magnetic iron oxide particle powder for magnetic toner according to any one of the above.
σr ≦ −40d + 14.8 A first ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution of 0.80 to 0.99 equivalent to the ferrous salt in the aqueous ferrous salt solution. A first-stage reaction in which an oxygen-containing gas is passed through the iron salt reaction aqueous solution while being heated to a temperature range of 70 to 100 ° C. to generate magnetite particles, and the remaining Fe ²⁺ after the completion of the first-stage reaction is 1.00. Production of magnetite particle powder consisting of a two-stage reaction with a second-stage reaction in which an oxygen hydroxide aqueous solution of an equivalent amount or more is added and an oxygen-containing gas is aerated while being heated to a temperature range of 70 to 100 ° C. In this method, an aqueous solution of an alkali hydroxide aqueous solution, a ferrous salt aqueous solution or a ferrous salt aqueous solution containing a ferrous hydroxide colloid is added to a water-soluble silicate in an amount of 0.1 atom in terms of Si with respect to Fe. % Or more. Add less than 9 atomic%, and adjust the pH to 7.0 or more and less than 8.0 by adding an alkali hydroxide aqueous solution at the start of the oxygen-containing gas passage in the first stage reaction, and vent the oxygen-containing gas. The method for producing magnetic iron oxide particle powder for magnetic toner according to claim 1.