JP5422904B2 - Hydrophobic magnetic iron oxide particle powder for magnetic toner and method for producing the same - Google Patents

Description

  The present invention provides a hydrophobic magnetic iron oxide particle powder for a magnetic toner that has good dispersibility in a nonpolar solvent and has a small amount of water vapor adsorption.

  Conventionally, as one of the electrostatic latent image developing methods, a so-called one-component using a composite particle in which black magnetic iron oxide particle powder such as magnetite particle powder is mixed and dispersed in a resin without using a carrier as a developer. Development methods using magnetic toners are widely known and widely used.

  Recently, with the increase in speed and image quality of laser beam printers and digital copiers, there has been a strong demand for improvement in the characteristics of magnetic toner as a developer. It is desirable that it is contained and dispersed as much as possible.

  Magnetic toner is manufactured by a pulverization method, but is shifting to a polymerization method toner in order to provide functions such as finer and uniform particle diameter and further low-temperature fixability.

  Since the polymerized toner is made by dispersing magnetic iron oxide particles in a polymerizable monomer, it is important to make the magnetic iron oxide particles, which are hydrophilic surfaces, hydrophobic and disperse in the polymerizable monomer. It becomes.

  As a means for hydrophobizing magnetic iron oxide particles by a dry method, a method of treating with a mixer-type mixer or a wheel-type mixer is disclosed (see Patent Document 1). However, by simply mixing the magnetic iron oxide particles and the treatment agent in a dry manner, uniform hydrophobicity is difficult and dispersibility in a nonpolar solvent is poor.

  As a means for hydrophobizing magnetic iron oxide particles in a wet process, a method of treating in an aqueous medium is disclosed (see Patent Document 2). However, magnetic iron oxide particles contain highly hygroscopic phosphorus, have a large water vapor adsorption amount, and have poor dispersibility in nonpolar solvents.

  As a means for hydrophobizing magnetic iron oxide particles in the gas phase, a method is disclosed in which a treatment agent is reacted by vaporization contact (see Patent Document 3). However, since it heat-processes at high temperature, it is easy to aggregate and its dispersibility in a nonpolar solvent is bad.

  As another means, a method of processing by kneading is disclosed (see Patent Document 4). However, the processing time is short and non-uniform.

Japanese Patent Laid-Open No. 03-221965 JP 2005-263619 A JP 2000-327948 A JP 2006-232578 A

  Therefore, the present invention provides a hydrophobized magnetic iron oxide particle powder that solves the various problems described above.

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

That is, in the present invention, the magnetic iron oxide particle surface is coated with a silane coupling agent of 5.0 × 10 ^{−3 to} 1.5 × 10 ⁻² (5.0E-3 to 1.5E-2) mmol / m ^2. The hydrophobic magnetic iron oxide particle powder having an average particle diameter of 0.05 to 0.5 μm, wherein the gloss of the coating film in which the hydrophobic magnetic iron oxide particle powder is dispersed in styrene / n-butyl acrylate is Hydrophobic magnetic iron oxide particle powder for magnetic toner having 60% or more and P content of 0.05 wt% or less (Invention 1).

  Moreover, this invention is the said hydrophobic magnetic iron oxide particle powder whose sticking rate of a silane coupling agent is 80% or more (this invention 2).

In addition, the present invention is the hydrophobic magnetic iron oxide particle powder having a water vapor adsorption amount (V90) of 0.4 mg / m ² or less in an atmosphere having a temperature of 25 ° C. and a relative humidity of 90% (Invention 3).

  In the present invention, the core magnetic iron oxide particles are hydrophobized in an aqueous medium and then dried, and the obtained dried product is heat-treated while rotating at 120 ° C. or less and a peripheral speed of 10 m / sec or more. This is a method for producing hydrophobic magnetic iron oxide particle powder (Invention 4).

  The hydrophobic magnetic iron oxide particle powder for magnetic toner according to the present invention has a silane coupling agent sticking rate by heat-treating the surface of the magnetic iron oxide particle, which is hydrophobized in an aqueous medium, while rotating at high speed. It is a hydrophobic magnetic iron oxide particle powder having good dispersibility in styrene / n-butyl acrylate because it has a high P content of 0.05 wt% or less and therefore has a low water vapor adsorption amount. Suitable for use.

  Hereinafter, the present invention will be described in detail.

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

The coating amount of the silane coupling agent of the hydrophobic magnetic iron oxide particles according to the present invention is 5.0 × 10 ^{−3 to} 1.5 × 10 ⁻² mmol / m ² (5.0E-3 to 1.5E). -2 mmol / m ² ). In the case of less than 5.0 × 10 ⁻³ mmol / m ² (5.0E−3 mmol / m ² ), the hydrophobization treatment is insufficient, the water vapor adsorption amount is increased, and the dispersibility is deteriorated. When it exceeds ^{1.5 × 10 -2 mmol / m 2} (1.5E-2mmol / m 2) , the dispersibility is deteriorated by aggregation. It is preferably 7.0 × 10 ^{−3 to} 1.2 × 10 ⁻² mmol / m ² (7.0E-3 to 1.2E-2 mmol / m ² ).

  It is preferable that the hydrophobic magnetic iron oxide particle powder according to the present invention has a silane coupling agent fixing rate of 80% or more evaluated by a measurement method described later. When the fixing rate is less than 80%, the amount of eluted hydrophobizing agent is increased, resulting in poor dispersibility. More preferably, it is 82% or more, and the upper limit is about 99%.

  The hydrophobic magnetic iron oxide particle powder according to the present invention preferably has an adhesion amount as a carbon amount of a silane coupling agent evaluated by a measurement method to be described later, preferably 0.5 to 2.0 wt%, more preferably 0.5. -1.5 wt%.

  The hydrophobic magnetic iron oxide particles according to the present invention preferably have a fixed amount of 0.4 to 2.0 wt% as a carbon amount of a silane coupling agent evaluated by a measurement method to be described later, more preferably 0. It is 45-1.20 wt%.

The average particle diameter of the hydrophobic magnetic iron oxide particles according to the present invention is 0.05 to 0.5 μm.
When the average particle diameter is less than 0.05 μm, the cohesive force between the magnetic iron oxide particles is large and dispersion becomes difficult. When it exceeds 0.5 μm, the coloring power is inferior and the hiding power is low. Preferably it is 0.1-0.3 micrometer, More preferably, it is 0.15-0.25 micrometer.

  The hydrophobic magnetic iron oxide particle powder according to the present invention has a glossiness of 60% or more when dispersed in styrene / n-butyl acrylate to form a coating film. When the glossiness of the coating film is less than 60%, it means that the dispersibility is bad and the dispersion state in the toner is bad. Preferably it is 64% or more, More preferably, it is 64 to 80%.

The BET specific surface area of the hydrophobic magnetic iron oxide particle powder according to the present invention is preferably 3.0 to 13.0 m ² / g. When the BET specific surface area is less than 3.0 m ² / g, the dispersibility in styrene / n-butyl acrylate is poor due to aggregation. When the BET specific surface area exceeds 13.0 m ² / g, the hydrophobization treatment is insufficient and the water vapor adsorption amount (V90) increases. More preferably, it is 4.0-12.0 m < ² > / g.

The water vapor adsorption amount (V90) of the hydrophobic magnetic iron oxide particles according to the present invention is preferably 0.40 mg / m ² or less. When the water vapor adsorption amount (V90) exceeds 0.40 mg / m ² , dispersibility in styrene / n-butyl acrylate is deteriorated. More preferably, it is 0.30 mg / m ² or less, and the lower limit is about 0.10 mg / m ² .

  The content of P in the hydrophobic magnetic iron oxide particles according to the present invention is preferably 0.05 wt% or less. When it exceeds 0.05 wt%, the water vapor adsorption amount increases and the dispersibility deteriorates. Preferably it is 0.04 wt% or less, More preferably, it is 0.03 wt%.

  Next, the magnetic iron oxide particle powder as the core of the present invention will be described.

The magnetic iron oxide particles serving as the nucleus in the present invention have an average particle diameter of 0.05 to 0.5 μm. When the average particle size is less than 0.05 μm, the cohesive force between the magnetic iron oxide particles is large, making it difficult to disperse, which is disadvantageous for the hydrophobic treatment. When it exceeds 0.5 μm, the coloring power is inferior and the hiding power is low. Preferably it is 0.1-0.3 micrometer, More preferably, it is 0.15-0.25 micrometer. The BET specific surface area is 5 to 15 m ² / g.

The magnetic iron oxide particles serving as the nucleus in the present invention are composed of magnetite particles ((FeO) _x .Fe ₂ O ₃ , 0 <x ≦ 1). If necessary, elements other than iron, Si, Al, P, Mn, Ni , Zn, Cu, Mg, Co, or Ti may contain one or more metal elements.

  In addition, when it contains P, it shall be 0.05 wt% or less. When the content of P in the magnetic iron oxide particles serving as the nucleus in the present invention exceeds 0.05 wt%, the water vapor adsorption amount is increased and the dispersibility is deteriorated even if the hydrophobic treatment is performed. Preferably it is 0.04 wt% or less.

  In the magnetic iron oxide particles serving as the core in the present invention, the particle surface may be coated in advance with an intermediate coating comprising at least one selected from Si, Al, and Ti compounds, if necessary.

  By covering the magnetic iron oxide particles serving as the nucleus in the present invention with the intermediate coating, the desorption of the hydrophobizing agent can be further suppressed.

  In the present invention, the primary particle shape of the magnetic iron oxide particle powder serving as the nucleus is an isotropic shape such as an octahedral shape, a hexahedral shape, a granular shape, and a spherical shape. In consideration of dispersibility, a spherical shape is preferable.

  The coercive force of the magnetic iron oxide particle powder as a nucleus in the present invention is preferably 2.4 to 15.9 kA / m (30 to 200 Oe). More preferably, it is 3.2 to 13.5 kA / m (40 to 170 Oe).

The saturation magnetization value of the magnetic iron oxide particles used as the core in the present invention is preferably 81.0-90.0 Am ^{2 /} kg (81.0-90.0 emu / g). More preferably, it is 84.0-90.0 Am < ² > / kg (84.0-90.0 emu / g).

  In the present invention, the magnetic iron oxide particles are prepared by neutralizing and mixing a ferrous salt aqueous solution and an alkali hydroxide aqueous solution, and a ferrous salt reaction aqueous solution containing a ferrous hydroxide colloid obtained by oxygen-containing gas, preferably Oxidation is performed while blowing air into the slurry, and the slurry after the oxidation reaction is filtered and washed to obtain magnetic iron oxide particles. The obtained magnetic iron oxide particle slurry may be dried according to a conventional method and subjected to a hydrophobization treatment. However, considering that the hydrophobization treatment is performed in an aqueous medium, the magnetic iron oxide particles can be directly used without passing through a drying step. It is preferable to hydrophobize using the contained slurry.

  What is necessary is just to adjust the quantity of the alkaline solution at the time of producing | generating a ferrous hydroxide colloid according to the shape of the magnetic iron oxide particle calculated | required. Specifically, spherical particles can be obtained by adjusting the pH of the ferrous hydroxide colloid to be less than 8.0, and hexahedral particles can be obtained by adjusting the pH to 8.0 to 9.5. If it is adjusted to exceed 9.5, octahedral particles can be obtained.

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

  The alkali hydroxide aqueous solution in the present invention uses aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, and the like. Can do.

  The oxidation reaction temperature in this invention is 85-100 degreeC. When the temperature is lower than 85 ° C., acicular hydrous iron oxide particles are easily produced as a by-product, and when the temperature is higher than 100 ° C., magnetic iron oxide particles are produced but are not industrial.

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

  The hydrophobic magnetic iron oxide particles according to the present invention are prepared by subjecting magnetic iron oxide particles serving as nuclei to hydrophobic treatment in an aqueous medium and then drying, and rotating the dried product at a temperature of 120 ° C. or less and a peripheral speed of 10 m / sec or more. It can be obtained by heat treatment.

  Specifically, the hydrophobizing treatment is performed by adding a silane coupling agent as a hydrophobizing agent while sufficiently dispersing the magnetic iron oxide particles in an aqueous medium.

  The aqueous medium in the hydrophobization treatment may be water alone, or a small amount of alcohol may be added to suppress aggregation of the hydrophobized magnetic iron oxide particles.

The pH of the aqueous medium when performing the hydrophobization treatment is preferably 3 to 7 because the treatment is performed while hydrolyzing the silane coupling agent. Moreover, you may add, after preparing a hydrolyzed solution preliminarily.
As for the temperature of the aqueous medium at the time of performing a hydrophobization process, 30-80 degreeC is preferable.

  As a silane coupling agent in this invention, the compound represented by General formula (1) is preferable.

<Chemical formula 1>
R ¹ _a Si (OR ² ) _4-a
R ¹ : an alkyl group having 15 or less carbon atoms R ² : —CH ₃ , —C ₂ H ₅
a: an integer from 1 to 3

Examples of the silane coupling agent include methyltrioxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, n-hexyltrimethoxysilane, n-octyltriethoxysilane, n-decyltri. And methoxysilane. If necessary, γ-glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, phenyltrimethoxysilane, or the like in which R ¹ is other than an alkyl group may be added.

  The addition amount of the silane coupling agent is 1.0 to 3.5% by weight with respect to the magnetic iron oxide particles serving as a nucleus.

  The processing apparatus used for the hydrophobization treatment is preferably a high shear force disperser such as a disper or a homomixer in order to sufficiently disperse the magnetic iron oxide particles and to prevent hydrophobization and aggregation during the hydrophobization treatment.

  After the hydrophobizing treatment, it is dried according to a conventional method.

  In the present invention, the dried product is heat-treated while being rotated at 120 ° C. or less and at a peripheral speed of 10 m / sec or more. When the temperature at the time of heat treatment exceeds 120 ° C., the condensation reaction proceeds so much that the magnetic iron oxide particles are easily united with each other and the dispersibility is deteriorated. Preferably it is 80-110 degreeC. When the peripheral speed at the time of heat treatment is less than 10 m / sec, the unraveling force is weak, so that the magnetic iron oxide particles are easily united and the dispersibility is deteriorated. Further, the fixing rate is also lowered. A more preferable peripheral speed is 11 to 30 m / sec.

  The heat treatment apparatus is preferably a high-speed rotary mixer such as a Henschel mixer or a high-speed mixer.

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

  The magnetic toner according to the present invention can be obtained by a suspension polymerization method. In the suspension polymerization method, a polymerizable monomer and magnetic iron oxide particle powder are dissolved or mixed with a colorant, a polymerization initiator, a crosslinking agent, a charge control agent, and other additives as necessary. The dispersed monomer composition is added to an aqueous phase containing a suspension stabilizer while stirring, granulated, and polymerized to obtain a desired particle size.

  Of course, it can also be performed by a known method of mixing, kneading, and pulverizing a predetermined amount of binder resin and a predetermined amount of magnetic iron oxide particle powder. Specifically, after the magnetic iron oxide particle powder and the binder resin are mixed sufficiently with a mixer, a mixture further containing a release agent, a colorant, a charge control agent, and other additives as necessary. The magnetic iron oxide particles and the like are dispersed in the binder resin by a heat kneader, and then cooled and solidified to obtain a resin kneaded product. The resin kneaded product is pulverized and classified to obtain a desired particle size. Can be obtained.

<Action>
In the present invention, the most important point is that the hydrophobic magnetic iron oxide particle powder according to the present invention has a silane coupling agent of 5.0 × 10 ^{−3 to} 1.5 × 10 ⁻² mmol on the surface of the magnetic iron oxide particle. / M ² (5.0E-3 to 1.5E-2 mmol / m ² ) coated hydrophobic magnetic iron oxide particle powder having an average particle diameter of 0.05 to 0.5 μm, and comprising styrene / n-butyl acrylate Among them, the gloss of the coating film in which the hydrophobic magnetic iron oxide particles are dispersed is 60% or more, and the P content is 0.05 wt% or less, so that the dispersibility in the resin is good. That is the fact.

  The present inventor considers these facts as follows.

  The hydrophobic magnetic iron oxide particle powder coated with the silane coupling agent of the present invention is obtained by subjecting the surface of the magnetic iron oxide particles to a hydrophobized treatment in an aqueous medium at 120 ° C. or less and a peripheral speed of 10 m / sec or more. By heat-treating while rotating, the adhesion rate of the silane coupling agent, which is a hydrophobizing agent, is high, and since the P content is 0.05 wt% or less, the water vapor adsorption amount is low, so styrene / n-butyl acrylate It is considered that the dispersibility in the inside is improved.

  Next, the present invention will be described with reference to examples and comparative examples.

<Average particle size>
The average particle diameter of the magnetic iron oxide particle powder is a value obtained by magnifying a photograph taken with a transmission electron microscope (magnification 10,000 times) four times by the Martin diameter for 300 particles.

<BET specific surface area>
The BET specific surface area of the magnetic iron oxide particle powder was determined by the BET method using Mono Sorb MS-II (manufactured by Yuasa Ionics Co., Ltd.).

<P content>
The content of P in the magnetic iron oxide particle powder was measured using a fluorescent X-ray analyzer 3063M (manufactured by Rigaku Corporation).

<Adhesion amount / Adhesion amount / Adhesion rate>
The amount of adhering hydrophobic magnetic iron oxide particles, the amount of sticking, and the sticking rate were evaluated by measuring the amount of carbon using a carbon analyzer EMIA-80 (manufactured by Horiba, Ltd.).
First, the amount of carbon in the hydrophobic magnetic iron oxide particles was measured and used as the amount of adhesion. Next, 10 g of hydrophobic magnetic iron oxide particles and 100 g of toluene were placed in a 100 ml beaker and irradiated with ultrasonic waves for 30 minutes using an ultrasonic cleaner BRANSONIC 5510 (manufactured by Yamato Scientific Co., Ltd.). Thereafter, the carbon content of the filtered and dried powder was measured and used as the fixed amount. The fixing rate was obtained by the following formula.
Adhesion rate (%) = Adhesion amount / Adhesion amount × 100

<Coating amount>
The coating amount of the silane coupling agent was determined by the following formula.
Covering amount (mmol / m ² ) = (carbon amount / 100 / M × 1000 (mmol / g)) / specific surface area of core particles (m ² / g)
M: total molecular weight of carbon contained in R ¹ group of the silane coupling agent

<Magnetic properties>
The magnetic properties of the magnetic iron oxide particles were shown by values measured with an external magnetic field of 796 kA / m using a vibrating sample magnetometer VSM-3S-15 (manufactured by Toei Industry Co., Ltd.).

<Water vapor adsorption amount (V90)>
Using a water vapor adsorption device BELSORP aqua3 (manufactured by Nippon Bell Co., Ltd.), the water vapor adsorption amount (V90) mg / m ² per unit area of the hydrophobic magnetic iron oxide particle powder at 25 ° C. and relative humidity 90% is shown. .

<Glossiness of styrene / n-butyl acrylate dispersed coating film>
Put a magnetic iron oxide particle powder 20 g, styrene 16 g, n-butyl acrylate 4 g in a 100 ml beaker, place a disperse rotating speed of 1000 rpm for 15 minutes on a PET film, apply with a 1 mil film applicator, The gloss (60 °) of the dried coating film surface was measured with a digital variable gloss meter UGV-5D (manufactured by Suga Test Instruments Co., Ltd.).

<Dispersibility in magnetic toner>
The dispersibility of the hydrophobic magnetic iron oxide particles in the magnetic toner was determined by slicing the magnetic toner with an ultramicrotome MT2C (manufactured by RESEACH MANFACTURERING) and observing the cross section with a transmission electron microscope (magnification 10,000 times). The aggregation state of the magnetic iron oxide particle powder was observed and evaluated in four stages. It shows that dispersibility is so good that there are few aggregates.
Aggregate: 0 to 1 Dispersion degree ◎
2-5 pieces ○
5-10 pieces △
11 or more ×

<Manufacture of magnetic iron oxide particles>
(Nuclear particle A)
Ferrous sulfate solution (Fe ²⁺ concentration; 1.723 mol / l, specific gravity; 1.248 g / cc) 31.942 kg, NaOH (18.5 N) 4.806 l (equivalent ratio = 0.95) and water 17. Air was blown into 396 l at 90 ° C. to produce core particles of magnetic iron oxide particles. At this time, Fe ³⁺ / Fe ²⁺ was adjusted to 0.70 (mol%). The pH value of the reaction solution during the production of the core particles was 6.7.

  Next, the NaOH was added so that the pH value of the reaction solution was 10.0, and a reaction for forming a surface layer composed of the fine magnetic iron oxide particles of the remaining ferrous sulfate was performed.

After completion of the formation reaction of the surface layer composed of fine magnetic iron oxide particles on the surface of the core particles, the core particles were washed with water to obtain a magnetic iron oxide particle slurry. A small amount of the magnetic iron oxide particles extracted and dried had an average particle size of 0.19 μm and a BET specific surface area of 9.0 m ² / g. The solid content in the remaining magnetic iron oxide particle slurry was 2.5 kg.

(Nuclear particle B)
Core particle B was prepared in the same manner as core particle A, except that Fe ³⁺ / Fe ²⁺ was 0.90 (mol%) and sodium hexametaphosphate was added as P / Fe ²⁺ in 0.05 (mol%) water. Obtained.

(Nuclear particle C)
Core particle C was obtained in the same manner as core particle A, except that Fe ³⁺ / Fe ²⁺ was changed to 0.50 (mol%).

(Nuclear particle D)
Ferrous sulfate solution (Fe ²⁺ concentration; 1.723 mol / l, specific gravity; 1.248 g / cc) 31.942 kg, NaOH (18.5 N) 4.806 l (equivalent ratio = 0.95) and water 17. Air was blown into 396 l at 90 ° C. and aged for 30 minutes. Thereafter, NaOH was added to adjust the pH value of the reaction solution to 8.9 to produce core particles of magnetic iron oxide particles. Thereafter, the core particle D was obtained in the same manner as the core particle A.

(Nuclear particle E)
Core particle E was obtained in the same manner as core particle A, except that sodium hexametaphosphate was added to water at the time of charging 0.25 (mol%) with P / Fe ²⁺ .

  Table 1 shows various characteristics of the obtained magnetic iron oxide particles serving as nuclei.

Example 1
<Production of hydrophobic magnetic iron oxide particle powder>
The solid content concentration of the obtained core particle slurry was 10 wt%, and the rotation speed of the homomixer was 5000 rpm. The mixture was adjusted to pH 6 and 40 ° C. and sufficiently dispersed, and n-hexyltrimethoxysilane was added to carry out a hydrophobization treatment while performing hydrolysis. The produced hydrophobic magnetic iron oxide particles were filtered, washed with water, and dried at 80 ° C. Thereafter, the dried product was put into a Henschel mixer, heated to 100 ° C., and heat-treated while stirring at a peripheral speed of 15 m / sec for 1 hour to obtain hydrophobic magnetic iron oxide particles.

Examples 2-8, Comparative Examples 1-7
Hydrophobic magnetic iron oxide particles were obtained in the same manner as in Example 1 except that the types of core particles, the types and amounts of silane coupling agents, and the heat treatment conditions were variously changed.

  Tables 2 and 3 show properties of the obtained hydrophobic magnetic iron oxide particles.

  In addition, the comparative example 3 grind | pulverizes by the pin mill, without heat-processing after drying. In Comparative Example 5, n-hexyltrimethoxysilane was gradually added to a rotary furnace heated to 120 ° C., and the vaporized hydrophobizing agent and magnetic iron oxide particles were contacted and reacted, then placed in a large crucible. After heat treatment at 60 ° C. for 60 minutes, the product is pulverized with a pin mill.

Example 1
<Manufacture of magnetic toner>
5 parts by weight of colloidal silica S-150 (manufactured by Hakuto Chemical Co., Ltd.) as a suspension stabilizer was added to 500 parts by weight of ion-exchanged water and heated to 70 ° C. to obtain an aqueous medium.
Styrene: 80 parts by weight n-butyl acrylate: 20 parts by weight Divinylbenzene: 0.3 part by weight Hydrophobic magnetic iron oxide particle powder 82 parts by weight

The mixture was dispersed using a paint conditioner. Into this, 1.5 parts by weight of a polymerization initiator 2,2′-azobis (2,4 dimethylvaleronitrile) was dissolved.
The polymerizable monomer was put into the aqueous medium, and stirred at 8000 rpm for 10 minutes with a homomixer in an N ₂ atmosphere at 70 ° C. to form droplets. Thereafter, the mixture was reacted at 70 ° C. for 8 hours while stirring with a paddle. After completion of the reaction, the suspension stabilizer was removed by adjusting the pH to 12 with NaOH, followed by filtration, washing with water, and drying to obtain magnetic toner 1. The weight average particle diameter was 7.5 μm.

Examples of use 2-12
A magnetic toner was obtained in the same manner as in Use Example 1 except that the kind of the hydrophobic magnetic iron oxide particle powder was variously changed.

  Table 4 shows various properties of the obtained magnetic toner.

The hydrophobic magnetic iron oxide particle powder according to the present invention has a silane coupling agent of 5.0 × 10 ^{−3 to} 1.5 × 10 ⁻² (5.0E- ^{3 to} 1) on the surface of the magnetic iron oxide particle. .5E-2) Hydrophobic magnetic iron oxide particle powder having an average particle diameter of 0.05 to 0.5 μm coated with mmol / m ^{2, wherein} the hydrophobic magnetic iron oxide particle powder is styrene / n-butyl acrylate. Glossiness of dispersed film is 60% or more, and P content is 0.05 wt% or less. Therefore, dispersibility in resin is good, so it is suitable as iron oxide powder for magnetic toner. It is.

Claims (4)

Hydrophobic magnetic iron oxide particles having an average particle diameter of 0.05 to 0.5 μm, wherein the surface of the magnetic iron oxide particles is coated with a silane coupling agent of 5.0 × 10 ^{−3 to} 1.5 × 10 ⁻² mmol / m ² Magnetic properties of the coating film in which the hydrophobic magnetic iron oxide particle powder is dispersed in styrene / n-butyl acrylate having a glossiness of 60% or more and a P content of 0.05 wt% or less. Hydrophobic magnetic iron oxide particle powder for toner. The hydrophobic magnetic iron oxide particle powder according to claim 1, wherein the adhesion rate of the silane coupling agent is 80% or more. The hydrophobic magnetic iron oxide particle powder according to claim 1, wherein a water vapor adsorption amount (V90) in an atmosphere having a temperature of 25 ° C and a relative humidity of 90% is 0.4 mg / m ² or less. The core magnetic iron oxide particles are hydrophobized in an aqueous medium and then dried, and the obtained dried product is heat-treated while rotating at a temperature range of 80 to 120 ° C. and a peripheral speed of 10 m / sec or more. The method for producing hydrophobic magnetic iron oxide particles according to claim 1.