WO2019198304A1 - Ferrite particles, carrier core material for electrophotographic developers, ferrite carrier for electrophotographic developers, and electrophotographic developer - Google Patents

Abstract

The present invention addresses the problem of providing: ferrite particles having magnetic properties and electric properties suitable as a carrier core material for electrophotographic developers; and a carrier core material for electrophotographic developers, a ferrite carrier for electrophotographic developers and an electrophotographic developer, in each of which the ferrite particles are used. For the purpose of solving the problem, ferrite particles are provided, each of which has a spinel-type crystalline structure represented by the compositional formula: Mn_xFe_yO₄ (wherein 0 < x, y = 3-x), the ferrite particles being characterized in that the Mn occupation ratio in site A is 0.200 to 0.655 inclusive. Also provided are a carrier core material for electrophotographic developers, a ferrite carrier for electrophotographic developers, and an electrophotographic developer, each of which contains the ferrite particles.

Description

Ferrite particles, carrier core material for electrophotographic developer, ferrite carrier for electrophotographic developer, and electrophotographic developer

The present invention relates to a ferrite particle, a carrier core material for an electrophotographic developer, a ferrite carrier for an electrophotographic developer, and an electrophotographic developer.

Ferrite is a magnetic oxide mainly composed of ferric oxide, and ferrite powder is its powder. Since ferrite is a metal oxide, it exhibits insulating properties. Further, the ferrite powder can be easily mixed with other materials. Therefore, ferrite powder has been used as a functional material in various applications that require magnetism and insulation.

For example, an electrophotographic developer based on a two-component development system generally includes a toner and a carrier, and the carrier generally uses a ferrite powder as a core material and the periphery thereof is coated with a resin. In the electrophotographic developer, the carrier functions as a charge imparting agent that charges the toner by being mixed and stirred with the toner, and also functions as a carrier that conveys the charged toner to the electrostatic latent image position. The carrier that has functioned as a carrier is recovered, mixed and stirred with toner, and reused.

In recent years, most copiers or printing apparatuses (hereinafter referred to as “electrophotographic developing machines”) adopting a two-component development system have adopted a reversal development system, and a high AC bias voltage is applied during development. Applied to the carrier. When the electrical resistance of the carrier is low, such as magnetite, a charge leakage phenomenon is likely to occur, the electrostatic latent image formed on the photoreceptor is destroyed, and it is difficult to uniformly deposit toner at a predetermined image density. become. As a result, unevenness in the image density of the solid portion occurs, and image defects such as so-called scratches occur on the image.

Therefore, instead of magnetite that has been widely used conventionally, in recent years, Mn represented by a composition formula such as “Mn _x Fe _y O ₄ ” (where 0 <x ≦ 1, y = 3-x) and the like. Ferrite has been used (for example, see Patent Document 1). Since Mn ferrite has a higher electrical resistance than magnetite, the phenomenon of charge leakage is less likely to occur, and the occurrence of scratches or the like is not observed.

JP 2011-248311 A

By the way, in recent years, an electrophotographic developing machine is required to print an image with a high printing rate such as a photograph at high speed with high image quality. When an image with a high printing rate is repeatedly printed, the number of times of toner replenishment is larger than when an image with a low printing rate such as a document is printed. In other words, the toner is replenished in a short cycle. At that time, in order to obtain good image characteristics from the initial stage, even if the charge amount of the carrier temporarily decreases at the timing of toner replenishment, it is necessary to quickly return the charge amount of the carrier to the level before toner replenishment. is there. That is, in order to obtain good image characteristics from the initial stage, a carrier having a quick charge rising in a predetermined frequency band corresponding to the applied bias voltage is required. The printing rate is the ratio of the printing area per page.

Also, when a core material with high electrical resistance is used, if an image with a high printing rate is repeatedly printed, the charge necessary for charging from the inside of the core material to the carrier surface may be insufficient. When such a carrier charge-down phenomenon occurs, image defects such as fogging occur. Therefore, it is required that the electrical resistance of the core material is not too high in order to realize the long life of the electrophotographic developer while satisfying the demand for high image quality and high speed printing. For these reasons, the electrical resistance of the core material is required to be an appropriate height that can suppress the occurrence of the charge leakage phenomenon and can suppress the occurrence of the charge-down phenomenon.

Then, the subject of this invention is the ferrite particle which has a magnetic characteristic suitable for the carrier core material for electrophotographic developers, and the electrical property, The carrier core material for electrophotographic developers using the said ferrite particle, The ferrite for electrophotographic developers It is to provide a carrier and an electrophotographic developer.

As a result of diligent research, the inventors of the present invention paid attention to the crystal structure of ferrite particles and adopted the following crystal structure, while maintaining suitable magnetic properties for the carrier core material for electrophotographic developer, The inventors have found that ferrite particles having a quick charge rise can be obtained, and have solved the above problems.

The ferrite particles according to the present invention are ferrite particles having a spinel crystal structure represented by a composition formula of Mn _x Fe _y O ₄ (where 0 <x, y = 3-x), The occupation ratio is 0.200 or more and 0.655 or less.

The ferrite particles according to the present invention preferably have a y / x value of 1.95 or more and 2.05 or less in the composition formula.

It is preferable that the true density of the ferrite particles according to the present invention is 4.6 g / cm ³ or more and 5.0 g / cm ³ or less.

The volume average particle size of the ferrite particles according to the present invention is preferably 15 μm or more and 100 μm or less.

The carrier core material for an electrophotographic developer according to the present invention includes the above ferrite particles.

The ferrite carrier for an electrophotographic developer according to the present invention includes the ferrite particles and a resin coating layer provided on the surface of the ferrite particles.

The electrophotographic developer according to the present invention includes the above-described ferrite carrier for an electrophotographic developer and a toner.

The electrophotographic developer according to the present invention is preferably used as a replenishment developer.

According to the present invention, ferrite particles having magnetic and electrical properties suitable for a carrier core material for an electrophotographic developer, a carrier core material for an electrophotographic developer using the ferrite particles, a ferrite carrier for an electrophotographic developer, and An electrophotographic developer can be provided.

Hereinafter, ferrite particles according to the present invention, a carrier core material for electrophotographic developer (hereinafter referred to as “core material” or “core material of carrier”), and a ferrite carrier for electrophotographic developer (hereinafter referred to as “carrier”). ) And an embodiment of an electrophotographic developer. In the embodiment described below, a case where the ferrite particles according to the present invention are applied to the core material and the like will be described as an example. However, the use of the ferrite particles according to the present invention is not limited to these, for example, various functional fillers such as magnetic ink, magnetic fluid, magnetic filler, bond magnet filler, and electromagnetic shielding material filler, and electronic components. It can be used as various electronic materials such as materials.

<Embodiment of ferrite particles>
1. First, an embodiment of a ferrite particle according to the present invention will be described. The ferrite particles referred to in the present invention are ferrite particles having a spinel crystal structure represented by the composition formula Mn _x Fe _y O ₄ (where 0 <x, y = 3-x), The occupation ratio is 0.200 or more and 0.655 or less. Here, unless otherwise specified, the term “ferrite particles” means an aggregate (powder) of ferrite particles, and when referring to individual ferrite particles, they are simply referred to as particles. Further, the “occupancy ratio” refers to a ratio of a predetermined atom existing at a predetermined lattice point at a predetermined lattice point. Further, the ferrite particles referred to in the present invention are composed of three kinds of elements of Mn, Fe, and O, and are substantially free of other elements except for inevitable impurities (accompanying impurities) caused by raw materials. .

The spinel crystal structure has the same crystal structure as that of the natural mineral spinel belonging to the cubic system, and its unit cell is represented by 8 (MeFe ₂ O ₄ ). The unit cell contains 8 divalent metals, 16 trivalent metals, and 32 oxygen. In “8 (MeFe ₂ O ₄ )”, “Me” means a divalent metal. Thirty-two oxygens form a close cubic lattice. There are two types of lattice points where metal ions are arranged, which are referred to as A site (or 8a position) and B site (or 16d position), respectively. The A site is a position corresponding to the center of a tetrahedron surrounded by four oxygens, and the B site is a position corresponding to the center of an octahedron surrounded by six oxygens. There are 8 A sites and 16 B sites in the unit cell.

In ferrite having a spinel crystal structure, when a divalent metal ion (Me ²⁺ ) is arranged at the A site, it is called a positive spinel, and when a divalent metal ion is arranged at the B site, It is called reverse spinel and is represented by the following chemical formula. In Mn ferrite, the divalent metal ion (Me ²⁺ ) is Mn ²⁺ or Fe ²⁺ , and the trivalent metal ion is Fe ³⁺ . Therefore, the Mn occupancy at the A site corresponds to the proportion of Mn ²⁺ existing (occupied) among the eight A sites in the unit cell.
Positive spinel: Me ²⁺ ↓ [Fe ³⁺ ₂ ↑] O ₄
Reverse spinel: Fe ³⁺ ↓ [Me ²⁺ Fe ³⁺ ↑] O ₄

There is a report that the Mn ferrite represented by the composition formula of MnFe ₂ O ₄ is a positive spinel having a Mn occupation ratio of about 0.8 to 0.9, that is, 80 to 90% at the A site (for example, (1975 ) “Magnetic Handbook” Asakura Shoten, p610-p612).

However, the inventors of the present invention are ferrite particles represented by the above composition formula Mn _x Fe _y O ₄ (where 0 <x, y = 3-x), and the values of x and y are the same. In addition, it was found that by changing the binder removal treatment conditions before the main firing, ferrite particles having a Mn occupation ratio at the A site different from that of the conventional Mn ferrite can be obtained. At that time, while adopting the main firing conditions suitable for ferritizing the raw material, by changing only the binder removal treatment conditions, while maintaining the same magnetic characteristics as the conventional Mn ferrite, Found that ferrite particles exhibiting different electrical characteristics can be obtained. The inventors of the present invention have found that the ferrite particles in which the Mn occupancy in the A site is within the above range have magnetic characteristics and electrical characteristics suitable for the carrier core, and have come to the present invention. . Hereinafter, description will be made in the order of Mn occupation ratio, composition, and powder characteristics.

(1) Mn Occupancy In the present invention, the Mn occupancy at the A site indicates the proportion of Mn present at the A site. When the Mn occupation ratio at the A site is “1”, it means that Mn2 ⁺ is present in all of the eight A sites. From the composition of the ferrite particles according to the present invention, when the Mn occupation ratio at the A site is 0.200 or more and 0.655 or less, the Fe occupation ratio at the A site is 0.800 or less and 0.345 or more. However, the sum of the Mn occupancy and the Fe occupancy at the A site is not necessarily “1”. This is because various lattice defects may be present, such as when Mn ²⁺ or Fe ²⁺ originally supposed to be arranged at a certain lattice point is replaced by an impurity (atom), or when the lattice point is a vacancy. .

The “occupancy ratio” here refers to a value obtained by analyzing a diffraction pattern of a sample obtained by a neutron diffraction method based on Rietveld analysis. An X-ray diffraction method is known as a method for analyzing a crystal structure. However, as described above, the ferrite particles according to the present invention are represented by the composition formula of Mn _x Fe _y O ₄ (where 0 <x, y = 3-x). Since the ionic radii and atomic weights of Mn and Fe are approximately the same, it is difficult to accurately analyze at what site and at what valence the atoms constituting the ferrite exist in the X-ray diffraction method. is there. On the other hand, when a sample is irradiated with a neutron beam, a diffraction pattern having a negative scattering length is obtained from Mn, and a diffraction pattern having a positive scattering length is obtained from Fe. Therefore, according to the neutron diffraction method, it is easy to distinguish between Mn and Fe, and the occupancy of each atom at each site can be accurately analyzed as compared with the X-ray diffraction method.

As a neutron diffractometer, for example, the industrial-use beamline iMATERIA installed in the MLF Materials and Life Sciences Research Facility MLF at the J-PARC (Ibaraki Prefecture) High-Intensity Proton Acceleration Facility, or owned by the Japan Atomic Energy Agency The beam line SANS-J of the research reactor JRR-3 can be used. Further, when analyzing a diffraction pattern, analysis software “Z-Rietveld” distributed from J-PARC can be used.

As described above, the ferrite particles whose Mn occupancy at the A site measured in the above manner is within the above range have magnetic characteristics and electrical characteristics suitable for the core material of the carrier. On the other hand, when the Mn occupation ratio at the A site is larger than 0.655, it is difficult to obtain magnetic characteristics and electrical characteristics suitable for the core material of the carrier. That is, when the Mn occupancy at the A site is larger than 0.655, for example, the magnetization is high, but the electrical resistance and / or dielectric constant is higher or lower than the range suitable for the carrier core, Although the electrical resistance and / or dielectric constant are within the range suitable for the carrier core material, it is difficult to obtain magnetic characteristics and electrical characteristics suitable for the carrier core material, such as low magnetization. On the other hand, in the Mn ferrite represented by the above composition formula, it is difficult to produce ferrite particles having a Mn occupation ratio at the A site smaller than 0.200.

From the viewpoint of obtaining ferrite particles having suitable magnetic properties and electrical properties by the carrier core material, the Mn occupation ratio at the A site is more preferably 0.630 or less. In the spinel crystal structure, when fired by a conventionally known method, Mn exists more stably at the A site. Therefore, from the viewpoint of easy production, the lower limit value of the Mn occupancy ratio at the A site is preferably 0.350 or more, more preferably 0.450 or more, and 0.500 or more. Further preferred.

(2) Composition The ferrite particles are represented by the above composition formula, satisfying the conditions of 0 <x, y = 3-x, and as long as the Mn occupancy at the A site is within the above range, x and y The value is not particularly limited. However, the value of y / x is preferably 1.90 or more and 2.10 or less, more preferably 1.92 or more and 2.08 or less, and particularly preferably 1.95 or more and 2.05 or less. preferable. Ferrite particles having a composition with a y / x value within the above range can easily control the Mn occupancy at the A site within the above range, and can provide magnetic and electrical characteristics suitable for the carrier core material. It is because it is easy to be done.

On the other hand, if the value of y / x is less than or equal to the lower limit value, the Mn content is small, and the electric resistance and dielectric constant tend to be lower than those suitable for the carrier core material. For this reason, it is difficult to sufficiently suppress image defects caused by low electrical resistance of the core material such as the leak phenomenon, which is not preferable. On the other hand, when the value of y / x is equal to or greater than the upper limit value, the Mn content increases, and the saturation magnetization tends to be lower than the range suitable for the carrier core material. As a result, it is difficult to sufficiently suppress image defects caused by the saturation magnetization of the core material, such as carrier scattering, being not preferable.

Here, “x” and “y” are composition ratios in terms of Mn and Fe in terms of moles determined based on the contents (mass%) of Mn and Fe measured by inductively coupled plasma (ICP) emission spectroscopic analysis.

(3) True density The true density of the ferrite particles is preferably 4.5 g / cm ³ to 5.5 g / cm ³ . When the ferrite particles are used as a carrier core material or carrier, if the true density is less than 4.5 g / cm ³ , the magnetization per ferrite particle is lowered, and carrier scattering tends to occur. On the other hand, it is difficult to obtain a true density exceeding 5.5 g / cm ³ from the composition of the ferrite particles. However, when the ferrite particles are used for uses other than the carrier, it is preferable to have a true density corresponding to each use. From this viewpoint, the true density of the ferrite particles is more preferably 4.6 g / cm ³ to 5.0 g / cm ³ .

However, the true density here is a value measured according to JIS R 1620: 1995 by the pycnometer method.

(4) Volume average particle size The volume average particle size of the ferrite particles can be appropriately adjusted according to the application. When the ferrite particles according to the present invention are used as a carrier core or carrier, the volume average particle diameter is preferably 15 μm or more and 100 μm or less. If the volume average particle size of the ferrite particles is less than 15 μm, carrier scattering tends to occur, which is not preferable. On the other hand, if the volume average particle diameter of the ferrite particles exceeds 100 μm, image defects are likely to occur, which is not preferable. From these viewpoints, the volume average particle diameter is more preferably 20 μm or more and 65 μm or less, and further preferably 25 μm or more and 50 μm or less.

However, the volume average particle diameter here is a value measured in accordance with JIS Z 8825: 2013 by a laser diffraction / scattering method.

2. Physical properties 2-1. Magnetic Properties When the ferrite particles are used as a carrier core material or carrier, the saturation magnetization when 1000 oersted (Oe) is applied is preferably 50 emu / g or more, more preferably 60 emu / g or more, and 65 emu. / G or more is more preferable. Further, the saturation magnetization when 3000 oersted (Oe) is applied is preferably 50 emu / g or more, more preferably 60 emu / g or more, and further preferably 80 emu / g or more. Further, the saturation magnetization at the time of applying 5000 oersted (Oe) is preferably 50 emu / g or more, more preferably 65 emu / g or more, and further preferably 75 emu / g or more. When the saturation magnetization is lower than these lower limit values, the magnetic force is low and carrier scattering tends to occur, which is not preferable. On the other hand, if the saturation magnetization becomes too high, the magnetic brush becomes stiff and undesirably caused by scratches and roughness, and the developed image quality deteriorates. From this point of view, the saturation magnetization when 1000 oersted (Oe) is applied is preferably 80 emu / g or less. Similarly, the saturation magnetization when 3000 oersted (Oe) is applied is preferably 90 emu / g or less, and the saturation magnetization when 5000 oersted (Oe) is applied is preferably 90 emu / g or less.

Here, the saturation magnetization is a value measured using a vibrating sample magnetometer.

2-2. Electrical Characteristics (1) Volume resistivity When the ferrite particles are used as a carrier core material or carrier, the volume resistivity at an applied voltage of 50 V is preferably 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm. When the volume resistivity exceeds 1 × 10 ¹⁰ Ω · cm, the electric resistance becomes too high, and there is a possibility that the movement of electric charge accompanying frictional charging is hindered. In the case of a volume resistance of less than 1 × 10 ² Ω · cm, the resistance is too low, and a leak phenomenon is likely to occur in a high-temperature and high-humidity environment, which may cause a decrease in charging. If the volume resistance of the ferrite particles is within the above range, an electrophotographic image can be developed with high image quality.

Furthermore, the volume resistivity of the ferrite particles is preferably 1.8 × 10 ⁹ Ω · cm or less in order to suppress a decrease in the charge amount of the electrophotographic developer even when printing is repeated at a high printing rate. It is more preferably 1 × 10 ⁸ Ω · cm or less, and further preferably 1 × 10 ⁷ Ω · cm or less. The electrical resistance of the ferrite particles is not too high and is reasonably high, so that when the ferrite particles are used as a carrier core material or carrier, charge transfer from the inside of the ferrite particles to the carrier surface is performed quickly, The charge rising of the developer is also improved.

Here, the volume resistivity means a value at an applied voltage of 50 V measured using an electrometer.

(2) Dielectric Constant Here, the dielectric constant (ε) is represented by a complex dielectric constant (ε′−jε ″) (where “j” is an imaginary unit). The real part (ε ') of the complex dielectric constant is a physical quantity indicating the ease of polarization of the substance, that is, the ease of change of the charge distribution due to the external electric field, and the imaginary part (ε'') It is a physical quantity that represents the amount of loss that part of the electrical energy is lost as heat when an alternating electric field is applied. The real part is expressed as relative permittivity, and the imaginary part is also called dielectric loss.

By the way, an electrophotographic developer by a two-component development system includes a toner and a carrier. In the developer box of the electrophotographic developing machine, the toner and the carrier are always stirred and mixed. That is, the toner and the carrier are always in a fluid state. For this reason, it is considered that the movement of charges due to contact charging between the toner and the carrier is performed in an extremely short time of about 10 ⁻⁶ to 10 ⁻⁹ seconds. The carrier is generally composed of a core material and a resin coating layer that covers the surface of the core material. At the time of contact charging, the charge generated by the polarization of the core material moves to the toner through the resin coating layer. Note that, in a portion where the resin coating layer is thin or a portion where the resin coating layer does not exist, the charge generated on the surface of the core material moves directly to the toner. Therefore, in order to evaluate the charging ability of the core material, it is necessary to evaluate the ease of polarization (relative dielectric constant) of the core material in the above extremely short time. However, for example, it is actually difficult to evaluate the relative dielectric constant of the core material by applying a voltage for an extremely short time such as 10 ⁻⁶ to 10 ⁻⁹ seconds. Therefore, in the present invention, the ferrite particles as the core material are not evaluated based on the frequency response of the relative permittivity when an AC voltage of 10 ⁶ to 10 ⁹ Hz is applied, rather than evaluating the time response of the relative permittivity. We decided to evaluate the speed of charge rise.

That is, if ferrite particles having a higher dielectric constant are used as a core material at a high frequency, carriers with a quick charge rise can be obtained. As a result, even when an image with a high printing rate is repeatedly printed, good image characteristics can be obtained from the initial stage even when toner is replenished. On the other hand, if the dielectric constant of the ferrite particles becomes too high, the charging ability of the core material becomes too high, and therefore, when an image with a high printing rate is repeatedly printed, a charge-up phenomenon tends to occur. For this reason, it is difficult to extend the life of the carrier. On the other hand, if the relative permittivity of the ferrite particles is low, the core material is difficult to polarize and a carrier having sufficient charging ability cannot be obtained. Therefore, when the ferrite particles are used as the core material of the carrier, it is preferable that the relative dielectric constant has an appropriate height in a high frequency band of 1 MHz or higher.

The complex dielectric constant of the dielectric generally decreases as the frequency of the applied AC voltage increases. From this point of view, when the ferrite particles are used as the core material or carrier of the carrier, the relative dielectric constant (ε ′) at 1 MHz is preferably 30.0 to 125.0, and the dielectric loss factor (ε ″) is The relative dielectric constant (ε ′) at 1 GHz is preferably 10.0 to 28.0, and the dielectric loss factor (ε ″) is preferably 5. It is preferably 0 to 28.0.

If the complex dielectric constant is within the above range, when the ferrite particles are used as the core material of the carrier, the carrier is polarized in a very short time when a bias AC voltage is applied, and the carrier surface is charged (or positive). Hole) can be easily generated, charge rising of the carrier is good, and occurrence of the charge-up phenomenon can be suppressed.

2-3. Electromagnetic attenuation factor The ferrite particles can be used for the various applications described above in addition to the carrier core material. The ferrite particles according to the present invention have a large electromagnetic wave attenuation rate in the frequency range of 0.1 GHz to 1.0 GHz as compared with the ferrite particles whose Mn occupancy at the A site is outside the range of the present invention, in particular, 0.1 GHz. The electromagnetic wave attenuation rate in the range of ~ 0.5 GHz is large. Therefore, the ferrite particles according to the present invention can be suitably used as an electromagnetic shielding material or the like in the frequency band. The electromagnetic wave attenuation rate is a value measured in accordance with IEC62333-3.

3. Method for Producing Ferrite Particles (1) Outline Next, a method for producing the ferrite particles described above will be described. The ferrite particles can employ a general method for producing ferrite particles used for applications such as a carrier core material, except that the binder removal treatment is performed in a non-oxidizing atmosphere.

First, a general method for producing ferrite particles will be described. Fe raw material and Mn raw material are respectively prepared and weighed so as to obtain a predetermined molar ratio. As the Fe raw material, iron oxide such as Fe ₂ O ₃ is used. As the Mn raw _material, it can be used MnCO 3, _Mn 3 _{O 4} and the like.

Each of the weighed raw materials is pulverized and mixed for 1 hour or more, preferably 1 to 20 hours in a ball mill, sand mill, vibration mill or the like in a wet or dry manner. The slurry thus obtained is dried, further pulverized and then calcined at a temperature of 700 to 1200 ° C. After calcination, the dispersion is further pulverized with a wet bead mill, wet ball mill, wet vibration mill or the like until the volume average particle size becomes 0.5 to 5.0 μm, more preferably 1.0 to 3.0 μm. Then, various additives such as a binder are added, the viscosity is adjusted, and then granulated and dried.

Next, a binder removal treatment is performed for 2 to 4 hours at a predetermined temperature lower than that during the main firing. The strength reduction of the ferrite particles can be prevented by performing the binder removal treatment.

Next, the granulated product that has been subjected to the binder removal treatment is held at 1150 ° C. to 1350 ° C. for 1 to 24 hours, and then subjected to main baking. The firing atmosphere at this time is performed in an inert gas (for example, N ₂ gas) atmosphere having an oxygen concentration of less than 0.1 vol%, preferably 0.05 vol% or less. During the main firing, the ferritization reaction proceeds and Mn ferrite is generated. The temperature during the main firing is more preferably 1150 ° C. to 1300 ° C., and further preferably 1180 ° C. to 1250 ° C.

The fired product obtained in this way is crushed and classified, and adjusted to a desired particle size. Thereafter, the magnetization and resistance can be appropriately adjusted by subjecting the fired product after pulverization and classification to surface oxidation treatment in the air or in an atmosphere in which the oxygen concentration is controlled as necessary.

(2) Binder removal Ferrite particles are generally produced by the method described above. Conventionally, the binder removal treatment is generally performed in the atmosphere. The inventors of the present invention have the same composition by performing the binder removal treatment in a non-oxidizing atmosphere, and the Mn occupancy at the A site is the same as that of the conventional Mn ferrite even if the main firing conditions are the same. It has been found that different ferrite particles can be obtained. Here, the non-oxidizing atmosphere refers to an inert gas (for example, N ₂ gas) atmosphere having an oxygen concentration of less than 0.1 vol%, preferably 0.05 vol% or less.

Further, the binder removal treatment is performed at a temperature lower than the temperature during the main firing. The temperature lower than the temperature at the time of the main firing is a temperature lower than 1150 ° C. at which Mn ferrite starts to be generated, preferably about 600 ° C. to 1050 ° C., and preferably about 650 ° C. to 950 ° C. More preferably, the temperature is about 700 to 900 ° C. By performing the binder removal treatment in a non-oxidizing atmosphere at a temperature lower than that of the main firing, it is possible to generate magnetite partially substituted with Mn while suppressing the generation of Mn ferrite. Magnetite has an inverse spinel crystal structure and is represented by Fe ³⁺ ↓ [Fe ²⁺ Fe ³⁺ ↑] O ₄ . The magnetite partially substituted with Mn means a magnetite in which a part of lattice points (mainly B sites) where Fe should originally exist are substituted with Mn.

Thereafter, by carrying out the main firing, the crystal structure changes, and Mn ferrite having a positive spinel crystal structure is generated. As a result, a Mn ferrite having a higher ratio of reverse spinel phase than that of a conventional Mn ferrite can be obtained. By appropriately adjusting the temperature during the binder removal treatment and the temperature during the main firing, the Mn occupancy at the A site can be appropriately adjusted, and the ferrite particles according to the present invention can be obtained.

<Embodiment of carrier core material for electrophotographic developer and ferrite carrier for electrophotographic developer>
The ferrite particles according to the present invention described above can be used as a carrier for an electrophotographic developer by itself. Preferably, the ferrite particles are used as a core material of a carrier, and a resin coating layer is provided on the surface of the ferrite particles. A developer carrier is preferred.

The resin constituting the resin coating layer is not particularly limited, and various resins can be used. For the positively chargeable toner, for example, a fluorine resin, a fluorine-acrylic resin, a silicone resin, a modified silicone resin, or the like can be used. For negatively chargeable toners, for example, acrylic resins, acrylic-styrene resins, mixed resins of acrylic-styrene resins and melamine resins, cured resins thereof, silicone resins, modified silicone resins, polyester resins Resins, epoxy resins, urethane resins, polyethylene resins, and the like can be used.

If necessary, a charge control agent, an adhesion improver, a primer treatment agent or a resistance control agent may be added. Examples of charge control agents and resistance control agents include various silane coupling agents, various titanium coupling agents, borides such as conductive carbon and titanium boride, titanium oxide, iron oxide, aluminum oxide, chromium oxide, and silicon oxide. Examples of the oxide include, but are not particularly limited to.

The coating amount of such a resin is preferably 0.05% by mass to 10.0% by mass, and particularly preferably 0.5% by mass to 7.0% by mass with respect to the core material. If it is less than 0.05% by mass, it is difficult to form a uniform coating layer on the surface of the carrier, and if it exceeds 10.0% by mass, aggregation between carriers occurs.

Further, as a resin coating method, the resin is generally diluted with a solvent and coated on the surface of the core material. Examples of the solvent used here include toluene, xylene, butyl cellosolve (ethylene glycol monobutyl ether acetate), methyl ethyl ketone, methyl isobutyl ketone, methanol, and the like when the resin is soluble in an organic solvent. Alternatively, water may be used if it is an emulsion resin. Further, as a method for coating the core material with the coating resin as described above, known methods such as brush coating method, dry method, spray drying method using fluidized bed, rotary drying method, immersion drying method using universal agitator It can coat | cover by etc. In order to improve the coverage, a fluidized bed method is preferred.

When the resin is coated on the core material and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave baking. Good. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.

Thus, after the resin is coated and baked on the surface of the core, it is cooled, crushed, and the particle size is adjusted to obtain a resin-coated carrier.

The carrier of the present invention obtained as described above is mixed with toner and used as a two-component developer.

<Embodiment of electrophotographic developer>
The electrophotographic developer according to the present invention uses the carrier according to the present invention. The electrophotographic developer according to the present invention is preferably a two-component electrophotographic developer containing the carrier and toner.

In the electrophotographic developer of the present invention, the toner used together with the carrier is not particularly limited. For example, various toners produced by a known method such as a suspension polymerization method, an emulsion polymerization method, or a pulverization method can be used. For example, a binder resin, a colorant, a charge control agent, etc. are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin screw extruder or the like and uniformly dispersed, and after cooling, finely pulverized with a jet mill or the like Then, after classification, for example, a toner classified by an air classifier or the like to have a desired particle size can be used. When the toner is produced, a wax, magnetic powder, a viscosity modifier, and other additives may be included as necessary. Further, an external additive can be added after classification.

The binder resin used for producing the toner is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer. Furthermore, resins such as rosin-modified maleic resin, epoxy resin, polyester, polyethylene, polypropylene, polyurethane, and silicone resin can be used alone or as a mixture as required.

Examples of the charge control agent used in the production of the toner include nigrosine dyes, quaternary ammonium salts, organometallic complexes, chelate complexes, and metal-containing monoazo dyes.

A conventionally known dye and / or pigment can be used as the colorant used in producing the toner. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used.

As other external additives, silica, titanium oxide, barium titanate, fluororesin fine particles, acrylic resin fine particles and the like can be used alone or in combination. Moreover, you may add surfactant, a polymeric agent, etc. suitably.

The electrophotographic developer according to the present invention is characterized by using the carrier according to the present invention, and other matters are optional. That is, the above-described electrophotographic developer is only one aspect of the present invention, and can be appropriately changed within a range that does not depart from the spirit of the present invention, such as a toner configuration.

Next, the present invention will be specifically described with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

The ferrite particles of Example 1 were produced as follows. First, Fe ₂ O ₃ powder and Mn ₃ O ₄ powder were prepared as Fe raw material and Mn raw material, respectively. Then, a _Fe 2 _{O 3,} and a _Mn 3 _{O 4} 1 molar ratio: were weighed each raw material so that 0.334. After the raw materials were weighed, water was added thereto, and the slurry was prepared by pulverizing and mixing with a wet ball mill. Next, the slurry was dried, further pulverized, and calcined in the air (oxygen concentration 20.8 vol%) at a temperature of 1000 ° C. After pre-baking, after pulverizing with a bead mill until the volume average particle size becomes 1.5 μm, various additives such as a dispersant and a binder are added, and after adjusting the viscosity, granulated and dried to obtain dry granulated powder. It was. Next, the dried granulated powder was debindered for 2 hours in an electric furnace at a temperature of 850 ° C. in an N ₂ gas atmosphere with an oxygen concentration of 0.1 vol% or less, and then the oxygen concentration at a temperature of 1200 ° C. in an electric furnace. Was fired for 4 hours in an N ₂ gas atmosphere of 0.1 vol% or less. Thereafter, the fired product was crushed with a hammer mill and further classified to produce ferrite particles. Table 1 shows the production conditions.

In Example 2, ferrite particles were produced in the same manner as in Example 1 except that the firing temperature during main firing was 1250 ° C. (see Table 1).

In Example 3, ferrite particles were produced in the same manner as in Example 1 except that the firing temperature during main firing was 1300 ° C. (see Table 1).

In Example 4, ferrite particles were produced in the same manner as in Example 1 except that the binder removal treatment was performed using a rotary kiln instead of an electric furnace (see Table 1).

Comparative example

[Comparative Example 1]
In Comparative Example 1, ferrite particles were produced in the same manner as in Example 1 except that the binder removal treatment and main firing were performed in the atmosphere (see Table 1).

[Comparative Example 2]
In Comparative Example 2, ferrite particles were produced in the same manner as in Example 1 except that the main calcination was performed in the air (see Table 1).

[Comparative Example 3]
In Comparative Example 3, ferrite particles were produced in the same manner as in Example 1 except that the firing temperature during the main firing was 1000 ° C. (see Table 1).

[Comparative Example 4]
In Comparative Example 4, ferrite particles were produced in the same manner as in Example 1 except that the binder removal treatment was performed in the atmosphere (see Table 1).

<Evaluation>
1. Evaluation Method The ferrite particles of Examples 1 to 4 and Comparative Examples 1 to 4 manufactured as described above were subjected to chemical analysis and crystal structures were determined based on the powder X-ray diffraction method and the powder neutron diffraction method. Analyzed. Further, the powder characteristics, magnetic characteristics, and electrical characteristics were evaluated for each ferrite particle. Hereinafter, each evaluation item and measurement method will be described.

1-1. Chemical Analysis (1) Composition The composition of each ferrite particle was determined by ICP emission spectroscopy / mass spectrometry as follows. First, 0.2 g of ferrite particles were weighed, and 60 ml of pure water plus 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid was heated to prepare an aqueous solution in which the ferrite particles were completely dissolved. This aqueous solution was set in an ICP analyzer (ICPS-1000IV, Shimadzu Corporation), and the content (mass%) of each metal component in the ferrite particles was determined. Further, the content of each metal component was converted into a molar ratio, and the values of “x” and “y” in the above composition formula were obtained, and the value of “y / x” was calculated. The results are shown in Table 2.

(2) the amount of ^{Fe 2+ Fe 2+} content in the ferrite particles was determined by oxidation-reduction titration with potassium permanganate solution. The oxidation-reduction titration was performed according to JIS M 8213-1995, and a potassium permanganate solution was used instead of the potassium dichromate solution. The results are shown in Table 2. Fe ^{2+ in} each ferrite particle is caused by magnetite in the ferrite particle. Therefore, by evaluating the amount of Fe ²⁺ in each ferrite particle, it can be confirmed whether or not Mn ferrite is generated.

1-2. Crystal structure analysis 1-2-1. Powder X-Ray Diffraction Analyzes the crystal phase composition ratio (% by mass) of each ferrite particle by the powder X-ray diffraction method, the peak position (° 2θ) of the (311) plane which is the main peak of the spinel phase, and the peak plane area The half width (° 2θ) and the lattice constant (a axis, b axis, c axis) were measured.

As an X-ray diffractometer, “X'PertPRO MPD” manufactured by Panalical Co., Ltd. was used. A Co tube (CoKα ray) was used as the X-ray source. As the optical system, a concentrated optical system and a high-speed detector “X'Celarator” were used. The measurement was performed by continuous scanning at 0.2 ° / sec. The measurement results are processed using data for analysis “X'Pert HighScore”, the crystal structure is identified, and the obtained crystal structure is refined so that the abundance ratio in terms of mass is used as the phase composition ratio of each crystal phase. Calculated. In the powder X-ray diffraction, as described above, since it is difficult to separate the peaks of Mn ferrite and magnetite (Fe ₃ O ₄ ), it is handled as a spinel phase, and other crystal structures (Fe ₂ O ₃ , Mn ₂ O ₃ ) are Each abundance ratio was calculated. Therefore, the phase composition ratio of the “spinel phase” shown in Table 3 is that Mn ferrite (MnFe ₂ O ₃ ) phase having a spinel type crystal structure, magnetite (Fe ₃ O ₄ ), part of Fe is substituted with Mn. It means the total phase composition ratio of the phase in which a part of Fe is substituted with Mn in maghemite (γ-Fe ₂ O ₄ ). In addition, Table 3 shows the peak position (° 2θ), peak surface area, and half-value width (° 2θ) of the (311) plane, which is the main peak of the spinel phase. Table 4 shows the lattice constants (a-axis, b-axis, c-axis) of each ferrite particle for each crystal phase.

In identifying the crystal structure, “O” is an essential element, and “Fe” and “Mn” are elements that may be contained. In addition, the X-ray source can be measured without problems even with a Cu tube, but in the case of a sample containing a large amount of Fe, the background becomes larger than the peak to be measured, so it is better to use a Co tube. preferable. In addition, the optical system may obtain the same result even when the parallel method is used, but measurement with a concentrated optical system is preferable because the X-ray intensity is low and measurement takes time. Further, the speed of the continuous scan is not particularly limited, but the peak intensity of the (311) plane which is the main peak of the spinel structure is 50,000 cps or more in order to obtain a sufficient S / N ratio when analyzing the crystal structure. Then, the ferrite particles were set in the sample cell so that the particles were not oriented in a specific preferred direction.

1-2-2. Powder Neutron Diffraction The Mn occupancy at the A site of the spinel phase of each ferrite particle was determined by analyzing the diffraction pattern obtained by powder neutron diffraction by the Z-Rietbeld method. As a neutron diffractometer, an industrial use beam line iMATERIA BL-20 installed at the MLF, Materials and Life Science Research Facility, J-PARC (Ibaraki), a high-intensity proton acceleration facility was used.
Each sample was filled in a cylindrical standard sample cell made of vanadium having a diameter of 6 mm and a height of 50 mm. The proton accelerator was operated at 125 kW, and double-frame measurement was performed by a TOF (Time Of Flight) method so that the neutron count was 70 Mcount or more at room temperature and in the atmosphere (300 K) to obtain a neutron diffraction pattern. At that time, three detectors, a back detector bank, a 90 degree detector bank, and a low angle detector bank, were used as detectors.

The obtained diffraction pattern was analyzed using analysis software “Z-Rietveld” (Windows (registered trademark) version, ver 1.0.2). As an analysis target, a diffraction peak in a region of q> 6 ＜ ⁻¹ and d <1Å was designated. At this time, the space group Fd-3m, 227_1 representing the spinel crystal structure is designated, “Fe” and “Mn” occupy the A site or the B site, respectively, and the temperature factor is isotropic. The atomic coordinates of “O”, the lattice constant, and the occupancy at each site of each atom (Fe, Mn, O) were fitted. As a constraint condition at that time, the sum of the occupation ratios of “Fe” and “Mn” at the A site and the B site was set to “1”. Table 3 shows the Mn occupancy and Fe occupancy at the A site analyzed in this manner.

1-3. Powder Characteristics (1) True Density True density was measured at 25 ° C. using methanol as a dispersion medium according to JIS R 1620-1995 by a pycnometer method.

(2) BET specific surface area The BET specific surface area of each ferrite particle was measured using a specific surface area measuring device (Macsorb HM model-1208, manufactured by Mountec Co., Ltd.). First, about 10 g of each ferrite particle was placed on a medicine wrapping paper, and deaerated with a vacuum dryer until the degree of vacuum became −0.1 MPa or less. Then, it heated at 200 degreeC for 2 hours, and removed the water | moisture content adhering to the surface of a ferrite particle. Subsequently, about 0.5 to 4 g of ferrite particles from which moisture was removed were placed in a standard sample cell dedicated to the apparatus, and accurately weighed with a precision balance. Subsequently, the weighed ferrite particles were set in the measurement port of the apparatus and measured. The measurement was performed by a one-point method. The measurement atmosphere was a temperature of 10 to 30 ° C. and a relative humidity of 20 to 80% (no condensation).

(3) Volume average particle size The volume average particle size of each ferrite particle was measured using a Microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd. The sample was prepared as follows. Water was used as a dispersion medium. 10 g of sample and 80 ml of water were placed in a 100 ml beaker, and 2 to 3 drops of a dispersant (sodium hexametaphosphate) were added. Next, using an ultrasonic homogenizer (UH-150 type, manufactured by SMT Co. LTD.), The output level was set to 4 and dispersion was performed for 20 seconds. Thereafter, bubbles formed on the beaker surface were removed. The sample thus prepared was measured with the above-mentioned Microtrac particle size analyzer.
Table 2 shows the measurement results for the true density, BET specific surface area, and volume average particle diameter of each ferrite particle.

1-4. Magnetic Properties Saturation magnetization, residual magnetization, and coercive force of each ferrite particle when 1000 oersted (hereinafter 1 kOe) is applied, 3000 oersted (hereinafter 3 kOe) is applied, and 5000 oersted (hereinafter 5 kOe) are applied as follows. It was measured.

(I) VSM measurement (1 kOe, 5 kOe)
Using a vibrating sample magnetometer (VSM-C7-10A, manufactured by Toei Kogyo Co., Ltd.), saturation magnetization, residual magnetization, and coercive force were measured when 1 kOe and 5 kOe were applied.
The specific procedure is as follows. First, the obtained ferrite particles were filled in a cell having an inner diameter of 5 mm and a height of 2 mm, and set in the apparatus. In the above apparatus, saturation magnetization, residual magnetization, and coercivity when the applied magnetic field was 1 kOe were obtained. Specifically, the following procedure was followed. First, a magnetic field was applied and sweeped to 1K · 1000 / 4π · A / m (= 1 kOe). Next, the applied magnetic field was decreased to create a hysteresis curve on the recording paper. In this hysteresis curve, the magnetization when the applied magnetic field is 1K · 1000 / 4π · A / m is the saturation magnetization, and the magnetization when the applied magnetic field is 0K · 1000 / 4π · A / m is the residual magnetization. did. In this hysteresis curve, the coercive force is the strength of the external magnetic field when the residual magnetization becomes zero when the applied magnetic field is decreased. Further, the saturation magnetization, the residual magnetization, and the coercive force in the applied magnetic field of 5 kOe were obtained in the same manner as described above except that the magnetic field was swept up to 5 K · 1000 / 4π · A / m (= 5 kOe).

(Ii) BHH measurement (3kOe)
Using a DC magnetism automatic measurement / analysis device (BHH-15, manufactured by Riken Denshi Co., Ltd.), saturation magnetization, residual magnetization, and coercive force were measured when 3 kOe was applied. The specific procedure is as follows. First, a magnetic field measuring H coil and a magnetization measuring 4πI coil were installed between the electromagnets. Here, the sample was placed in a 4πI coil. The outputs of the H coil and the 4πI coil whose magnetic field H was changed by changing the current of the electromagnet were integrated, and a hysteresis curve was created on the recording paper with the H output as the X axis and the 4πI coil as the Y axis. Here, the measurement conditions were as follows: sample filling amount: about 1 g, sample filling cell: inner diameter 7 mmφ ± 0.02 mm, height 10 mm ± 0.1 mm, 4πI coil: 30 turns. In this hysteresis curve, the magnetization when the applied magnetic field is 3K · 1000 / 4π · A / m (= 3 kOe) is the saturation magnetization, and the magnetization when the applied magnetic field is 0K · 1000 / 4π · A / m. Was defined as remanent magnetization. In this hysteresis curve, the coercive force is the strength of the external magnetic field when the residual magnetization becomes zero when the applied magnetic field is decreased.
Table 5 shows the magnetic properties of each ferrite particle.

1-5. Electrical characteristics (1) Volume resistivity The volume resistivity of each ferrite particle was measured as follows. First, after filling a sample into a cylinder made of fluororesin having a cross-sectional area of 4 cm ² so as to be 4 mm in height, electrodes were attached to both ends, and a weight of 1 kg was placed thereon to measure resistance. The resistance is measured by using an electrometer (insulation resistance meter model 6517A manufactured by KEITHLEY), increasing the applied voltage stepwise by 50 V every 5 seconds up to an applied voltage of 1000 V (electric field of 2500 V / cm). The current value after 2 seconds was read, and the resistance value at each voltage was calculated. Then, volume resistivity was calculated | required from the cross-sectional area and height.

(2) Dielectric constant Frequency response of a complex dielectric constant (ε = ε′−jε ″) of a sample molded by the following method using a material impedance analyzer E4991B and a dielectric constant test fixture 16453A manufactured by KeyLight Technology Was measured. At this time, the frequency was swept from 1 MHz to 3 GHz on a logarithmic scale, and the amplitude of the measurement voltage was 100 mV. Further, no DC bias voltage was applied.

The sample was molded by the following method. First, 90 wt% of the ferrite particles produced in each of Examples and Comparative Examples were mixed with 10 wt% of a fluororesin, and then about 1 g was sampled. Each obtained mixture was put into a mold having a diameter of 13 mm, pressure-molded at 50 kN, and then heat-cured at 180 ° C. for 2 hours as a sample.

1-6. Electromagnetic attenuation rate A sample was prepared using each ferrite particle, and the electromagnetic wave attenuation rate was measured in accordance with IEC62333-3. Specifically, the measurement was performed as follows. First, 7 g of ferrite particles were added to 30 g of 10 wt% PVA aqueous solution to prepare a paste. The content of ferrite particles in the paste is 70 wt% with respect to the solid content (PVA and ferrite particles) in the paste. The paste was molded with a baker type applicator and dried to form a 0.5 mm thick sheet. This was cut into a 30 mm square to prepare a sample. The sample is attached to a measuring jig (Line Decoupling Measuring Equipment model: KLD-1) manufactured by Kanto Electronics Application Development Co., Ltd., and a network analyzer (E5071C) manufactured by KeyLight Technology is used as a measurement range between 0.1 GHz and 1.0 GHz. The electromagnetic wave attenuation rate of each sample was measured.

2. Evaluation Results (1) Ferrite Particle Composition and Mn Occupancy Rate The ferrite particles of Examples 1 to 4 were subjected to binder removal treatment in an N ₂ gas atmosphere with an oxygen concentration of 0.1 vol% or less at a temperature of 850 ° C. It is obtained by performing the main firing in an N ₂ gas atmosphere having an oxygen concentration of 0.1 vol% or less in a temperature range of 1200 ° C. to 1300 ° C. On the other hand, the ferrite particles of Comparative Examples 1 to 4 are different from the examples in the binder removal treatment conditions and / or the main firing conditions, but the other production conditions are the same as those in Example 1.

Referring to the chemical analysis results shown in Table 2, the ferrite particles of Examples 1 to 4 and Comparative Examples 1 to 4 have substantially the same values of “x” and “y” in the above composition formulas, Chemical analysis confirms that the ferrite particles have the same composition.

On the other hand, from the results of the crystal structure analysis by powder XRD diffraction shown in Table 3, it was confirmed that the phase composition ratio of the crystal phase of each ferrite particle differs depending on the binder removal treatment conditions and / or the main firing conditions.

Specifically, it is as follows. From Table 3, it is confirmed that the ferrite particles of Examples 1 to 4 account for 99.9% of the spinel phase.
The ferrite particles of Examples 1 to 4 have an Fe ²⁺ amount of 0.22% by mass to 0.11% by mass (see Table 2), and the spinel phase is mainly composed of the Mn ferrite phase. The content is considered low. The ferrite particles of Examples 1 to 4 were subjected to binder removal treatment at a lower temperature (850 ° C.) than the main firing in a non-oxidizing atmosphere (N ₂ gas atmosphere), and Mn ferrite in an N ₂ gas atmosphere It was obtained by carrying out the main firing at a temperature suitable for the production of. Therefore, it was confirmed that ferrite particles having a spinel phase with a phase composition ratio of 99.9% are generated by performing main firing at a temperature suitable for generation of Mn ferrite in an N ₂ gas atmosphere.

On the other hand, in the ferrite particles of Comparative Example 1 and Comparative Example 2, the proportion of the spinel phase is as small as 1.2% and 0.6%. On the other hand, the ferrite particles of Comparative Example 1 and Comparative Example 2 have a large proportion of the hematite phase (Fe ₂ O ₃ ) and the Mn ₂ O ₃ phase. I think this is due to the following reasons. First, in Comparative Example 1, since the binder removal process and the main baking process are performed in the atmosphere, magnetite and Mn ferrite are not generated, and as a result, the proportion of the spinel phase is considered to be small. In Comparative Example 2, although the binder removal treatment is performed in an N ₂ gas atmosphere, the magnetite once produced during the binder removal treatment is oxidized during the firing to Fe ₂ O ₃ by performing the firing in the atmosphere. I think. Therefore, it is confirmed from Comparative Example 1 and Comparative Example 2 that it is difficult to obtain a spinel phase when the atmosphere during the main baking is air, regardless of the atmosphere during the binder removal treatment.

In Comparative Example 3, both the binder removal treatment and the main calcination are performed in an N ₂ gas atmosphere. However, in Comparative Example 3, the main baking temperature is as low as 1000 ° C. It is considered that Mn ferrite (MnFe ₂ O ₄ ) is generated in a temperature range of about 1150 ° C. to 1350 ° C. Therefore, in Comparative Example 3, although magnetite is generated at a certain rate during the binder removal treatment, the firing temperature is lower than the temperature at which Mn ferrite is considered to be generated, so that the composition ratio of the spinel phase in the ferrite particles is from Example 1 to Compared with Example 4, it is thought that it was as low as 77.0%.

Similar to the ferrite particles of Examples 1 to 4, the ferrite particles of Comparative Example 4 have a high phase composition ratio of the spinel phase of 99.9%. The ferrite particles of Comparative Example 4 were obtained in the same manner as in Example 1 except that the atmosphere during the binder removal treatment was different. As described above, it is difficult to separate the peaks of Mn ferrite and magnetite (Fe ₃ O ₄ ) by powder XRD diffraction. Therefore, when confirming the amount of Fe ²⁺ of the ferrite particles of Comparative Example 4, Fe ²⁺ content of the ferrite particles of Comparative Example 4 is greater when compared with ferrite particles in Examples 1 to 4. The ferrite particles of Comparative Example 4 are obtained by performing a binder removal treatment in the atmosphere. Therefore, the ferrite particles of Comparative Example 4 have a spinel phase composition ratio of 99.9%, while the ferrite particles of Comparative Example 4 have a magnetite phase and / or maghemite phase content of Examples 1 to 4. It is thought that it is large compared with the ferrite particles.

Next, looking at the Mn occupancy at the A site of the spinel phase of each ferrite particle (see Table 3), the ferrite particles of Examples 1 to 4 are 0.6056 to 0.6504, and the scope of the present invention Is within. On the other hand, the Mn occupancy at the A site in Comparative Examples 1 to 4 in which the main calcination was performed in the atmosphere or the main calcination temperature was less than 1150 ° C. was 0.655 or more. It is confirmed that the crystal structure is different from Example 4.

The ferrite particles of Comparative Example 1 and Comparative Example 2 have a low phase composition ratio of the spinel phase as described above, and the Mn occupancy at the A site is also different from the ferrite particles of Examples 1 to 4.
As described above, the ferrite particles of Comparative Example 3 have a low main firing temperature, Mn ferrite is not generated, and maghemite in which part of Fe is substituted with Mn is generated. It is thought that it was about 97.
The ferrite particles of Comparative Example 4 were fired at the same firing temperature as in Example 1, but the atmosphere during the binder removal treatment was different from that in Example 1, and the binder removal treatment was performed in the air. Yes. Therefore, it is considered that the Mn ferrite phase was generated while partly becoming a magnetite phase and / or a maghemite phase during the main firing. As a result, the spinel phase composition ratio of the ferrite particles of Comparative Example 4 was almost the same as that of Examples 1 to 4, but the Mn occupancy at the A site was higher than that of Examples 1 to 4. it is conceivable that.

(2) Magnetic properties Next, when looking at the magnetic properties of each ferrite particle (see Table 5), all of the ferrite particles of Examples 1 to 4 have high saturation magnetization, and have magnetic properties suitable for the carrier core material. Can be confirmed. As described above, the ferrite particles of Comparative Examples 1 to 3 have a low magnetic property because the phase composition ratio of the spinel phase is low. On the other hand, the ferrite particles of Comparative Example 4 have a high phase composition ratio of the spinel phase, and have the same magnetic characteristics as the ferrite particles of Examples 1 to 4.

(3) Electrical Characteristics In addition, looking at the electrical characteristics of each ferrite particle (see Table 6), the volume resistivity of the ferrite particles of Examples 1 to 4 is 1.65 × 10 ⁶ Ω · cm to 1.55. × 10 ⁹ Ω · cm, which has an electric resistance suitable for the core material of the carrier. In particular, the volume resistivity of the ferrite particles of Examples 2 to 4 is not too high and is suitable for the carrier core material. On the other hand, the volume resistivity of the ferrite particles of Comparative Examples 1 to 4 is slightly higher than the ferrite particles of Examples 2 to 4, but the ferrite particles of Comparative Examples 1 to 4 are also used as the core material of the carrier. Appropriate volume resistivity is shown.

On the other hand, looking at the complex dielectric constant of each ferrite particle, the relative dielectric constant (ε ′) and dielectric loss (ε ″) of the ferrite particles of Examples 1 to 4 are 1 MHz (10 ⁶ Hz) to 1 GHz ( It shows a high value at any frequency of 10 ⁹ Hz). Therefore, if a bias voltage is applied to the ferrite particles of Examples 1 to 4, it can be rapidly polarized in an extremely short time. Therefore, if the ferrite particles are used as the core material of the carrier, it is possible to obtain a carrier that has excellent charging ability and quick charge rising. In contrast, the ferrite particles of Comparative Examples 1 to 3 are both too low in relative dielectric constant (ε ′) and dielectric loss (ε ″) compared to the ferrite particles of Examples 1 to 4. . Therefore, the core material is difficult to polarize when a bias voltage is applied, and a carrier having sufficient charging ability cannot be obtained. On the other hand, when compared with the ferrite particles of Examples 1 to 4, both of the relative permittivity (ε ′) and the dielectric loss (ε ″) of the ferrite particles of Comparative Example 4 are too high. For this reason, the charging ability of the carrier becomes too high, and therefore, a charge-up phenomenon is likely to occur when printing of an image with a high printing rate is repeated. Therefore, it is difficult to extend the life of the carrier.

(4) Electromagnetic wave attenuation rate When the electromagnetic wave attenuation rate was measured for the samples prepared using the ferrite particles of the examples and the comparative examples, the electromagnetic waves at frequencies of 0.1 GHz to 1.0 GHz of Examples 1 to 4 were measured. The attenuation rate was 0.95 dB to 3.27 dB, and the electromagnetic wave attenuation rate at 0.1 GHz to 0.5 GHz was 1.53 dB to 3.27 dB. On the other hand, the electromagnetic wave attenuation rate at frequencies of 0.1 GHz to 1.0 GHz in Comparative Examples 1 and 2 is 0.00 dB to 0.24 dB, and the electromagnetic wave attenuation rate at 0.1 GHz to 0.5 GHz is 0.00 dB to 0. .24 dB. Further, in Example 3, the electromagnetic wave attenuation rate at a frequency of 0.1 GHz to 1.0 GHz is 0.58 dB to 1.75 dB, and the electromagnetic wave attenuation rate at 0.1 GHz to 0.5 GHz is 0.75 dB to 1.75 dB. In Comparative Example 4, the electromagnetic wave attenuation rate at a frequency of 0.1 GHz to 1.0 GHz was 0.90 dB to 2.93 dB, and the electromagnetic wave attenuation rate at 0.1 GHz to 0.5 GHz was 1.62 dB to 2.93 dB. . The electromagnetic wave attenuation rate at a frequency of 0.25 GHz is shown below. In the sample using the ferrite particles of this example, compared with the samples using the ferrite particles of Comparative Examples 1 to 3, the electromagnetic wave attenuation rate is particularly high in the frequency band of 0.1 GHz to 0.5 GHz. It was confirmed that the electromagnetic shielding characteristics are high in the band. Note that the Mn occupation ratio at the A site of the ferrite particles of Comparative Example 4 is 0.6560, and the samples using the ferrite particles of Comparative Example 4 are almost the same as the samples using the ferrite particles of Examples 1 to 4. The electromagnetic wave attenuation rate was shown. As described above, the ferrite particles of Comparative Example 4 do not have electrical characteristics suitable for the core material of the carrier, but are more suitable for use as an electromagnetic shielding material than the ferrite particles of Comparative Examples 1 to 3.

Electromagnetic wave attenuation rate (dB) of each example and each comparative example at 0.25 GHz
Example 1: 1.8 (dB) Comparative Example 1: 0.1 (dB)
Example 2: 2.0 (dB) Comparative Example 2: 0.0 (dB)
Example 3: 2.4 (dB) Comparative Example 3: 1.2 (dB)
Example 4: 2.5 (dB) Comparative Example 4: 2.2 (dB)

According to the ferrite particles according to the present invention, ferrite particles having magnetic and electrical characteristics suitable for a carrier core material for an electrophotographic developer, a carrier core material for an electrophotographic developer using the ferrite particles, and an electrophotographic developer Ferrite carrier and electrophotographic developer can be provided.
The ferrite particles according to the present invention are different from the conventional Mn ferrite in that the Mn occupancy at the A site is within the scope of the present invention, while having magnetic properties and electrical resistance equivalent to the conventional Mn ferrite, In a high frequency band of 1 MHz or higher, the relative dielectric constant can be set to a value suitable for a carrier core material for an electrophotographic developer. As a result, it is possible to quickly polarize when a predetermined bias voltage is applied, and it is possible to obtain a carrier having a quick charge rise. Therefore, by applying the ferrite particles according to the present invention to the carrier core material of the electrophotographic developer, it is possible to obtain good image characteristics from the initial stage even when repeatedly printing images with a high printing rate, It becomes possible to achieve a long life of the carrier.
Further, the ferrite particles have high electromagnetic shielding properties and can be suitably used for electromagnetic shielding materials.

Claims (8)

1. Ferrite particles having a spinel type crystal structure represented by a composition formula Mn _x Fe _y O ₄ (where 0 <x, y = 3-x),
   A ferrite particle having a Mn occupancy at A site of 0.200 or more and 0.655 or less.
2. The ferrite particle according to claim 1, wherein in the composition formula, a value of y / x is 1.95 or more and 2.05 or less.
3. The ferrite particle according to claim 1 or 2, wherein the true density of the ferrite particle is 4.6 g / cm ³ or more and 5.0 g / cm ³ or less.
4. The ferrite particles according to any one of claims 1 to 3, wherein the ferrite particles have a volume average particle size of 15 µm or more and 100 µm or less.
5. A carrier core material for an electrophotographic developer comprising the ferrite particles according to any one of claims 1 to 4.
6. A ferrite carrier for an electrophotographic developer, comprising: the ferrite particles according to any one of claims 1 to 4; and a resin coating layer provided on a surface of the ferrite particles.
7. An electrophotographic developer comprising the ferrite carrier for an electrophotographic developer according to claim 6 and a toner.
8. The electrophotographic developer according to claim 7, which is used as a replenishment developer.