JP5260118B2 - Carrier core material for electrophotographic developer and production method thereof, magnetic carrier for electrophotographic developer, and electrophotographic developer - Google Patents

Description

  The present invention relates to a carrier for a two-component electrophotographic developer used in a two-component electrophotographic developer by mixing with a toner.

  In recent years, devices such as copying machines and printers using an electrophotographic system have been widely used, and their uses have been diversified. In the market, there is a growing demand for higher image quality for the electrophotography and longer life for the developer for electrophotography.

  Conventionally, in a two-component electrophotographic developer, it has been considered that the image quality of electrophotography can be improved by reducing the particle size of toner particles used. However, as the toner particles become smaller in size, the charging ability of the toner particles decreases. In order to cope with the decrease in the charging ability of the toner particles, carrier particles (hereinafter sometimes referred to as “carrier”) used in the two-component electrophotographic developer mixed with the toner are small. Measures were taken to increase particle size and specific surface area. However, the carrier having the reduced particle size has a problem that it is likely to cause abnormal phenomena such as carrier adhesion and carrier scattering.

  As means for suppressing carrier adhesion and carrier scattering, for example, the magnetic susceptibility is 67 emu / g to 88 emu / g in a magnetic field of 1000 Oe as seen in Patent Document 1, and the difference in magnetic susceptibility between the scattered matter and the main body is 10 emu / g or less. By using the carrier core material for an electrophotographic developer (which is a magnetic particle of ferrite, which may be hereinafter referred to as “carrier core material”) constituting the carrier specified in 1), the holding power of the magnetic brush is increased. A way to improve it has been proposed.

  On the other hand, as the speed of the developing machine increases, the stirring load in the developing machine increases, and there is a problem that the resin on the surface of the magnetic carrier is peeled off due to stirring stress. As a result, the carrier core material is exposed, and charge leakage occurs. Since such charge leakage is one of the causes of image quality degradation, measures are taken such as making charge leakage difficult by increasing the insulation of the carrier core material itself. From this point of view, a carrier core material having high insulation as seen in Patent Document 2 has been proposed.

Japanese Patent Laid-Open No. 2002-296846 Japanese Patent Application Laid-Open No. 07-084414

  From the above, it is required to increase the magnetic susceptibility and the insulation of the carrier core material in order to reduce the image quality abnormality in the electrophotographic development method. The magnetic susceptibility in the present invention refers to the magnetic susceptibility in the external magnetic field 1000 Oe unless otherwise specified.

  However, since the magnetic properties of ferrite magnetic materials generally used as carrier core materials change due to slight fluctuations in the synthesis conditions, it has been difficult to produce carriers with sufficient properties with good reproducibility. .

The present invention has been made under the above-mentioned circumstances, and provides a carrier core material for an electrophotographic developer having a high magnetic susceptibility and a high insulating property, and a method for producing the same. Further, the carrier core for an electrophotographic developer is provided. It is to provide a magnetic carrier for an electrophotographic developer using the material and an electrophotographic developer.

The present inventors have general formula as the carrier core material: Mn in x _Fe manganese ferrite represented by _3-x O _4, we will show techniques for controlling the magnetic properties, the results valent iron element contained in the manganese ferrite It has been found that the magnetic characteristics and electrical characteristics can be adjusted by adjusting the number to a predetermined range.
Furthermore, in order to obtain a carrier core material excellent in magnetic susceptibility and insulating properties, the present inventors set the valence of the iron element in the carrier core material to _x of the general formula: Mn _x Fe _3-x O ₄ It was found that it was necessary to adjust to the optimum range according to. And the manufacturing method of the carrier core material which can be controlled so that the valence of an iron element may become the optimal range was discovered, and this invention was completed.

That is, the first invention for solving the problem is:
_Formula: consists _{Mn x Fe 3-x O 4} ( where 0 <x ≦ 1) Mn ferrite you express in,
The valence of the iron element in the Mn ferrite is {(8-2 × x) / (3-x) +0.005} or more and {(8-2 × x) / (3-x) +0.05} or less. The carrier core material for an electrophotographic developer, wherein the carrier core material is in the range of.

The second invention is
The carrier core material for an electrophotographic developer according to the first invention, wherein the magnetic susceptibility under an external magnetic field of 1000 Oe: σ ₁₀₀₀ satisfies σ ₁₀₀₀ ≧ 60 emu / g.

The third invention is
The carrier core material for an electrophotographic developer according to the first or second invention, wherein the average particle size is 10 μm or more and 80 μm or less.

The fourth invention is:
A magnetic carrier for an electrophotographic developer, wherein the carrier core material for an electrophotographic developer according to any one of the first to third inventions is coated with a resin.

The fifth invention is:
An electrophotographic developer comprising the carrier for an electrophotographic developer according to the fourth invention and a toner.

  According to the present invention, it is possible to provide a carrier for an electrophotographic developer and an electrophotographic developer that can reduce abnormal phenomena such as carrier adhesion when used as an electrophotographic developer for a copying machine, a printer, or the like. I can do it.

  Hereinafter, the present invention is as follows. Carrier core material, 2. 2. manufacturing method of carrier core material; Carrier, 4. 4. electrophotographic developer, The measurement method for each physical property value will be described in this order.

1. Carrier core material <composition>
Material constituting the carrier core material according to the present invention have the general _formula is Mn ferrite represented by _{Mn x Fe 3-x O 4} ( where 0 <x ≦ 1).
When the valence (theoretical value) of Fe is obtained from the general formula, the valence of Mn is divalent and the valence of O is -2.
2 × x + Fe valence (theoretical value) × (3-x) + (− 2) × 4 = 0,
Fe valence (theoretical value) = (8-2 × x) / (3-x).
However, when the present inventors actually measured the valence of Fe based on a method for deriving the valence of the iron element described later, the theoretical valence of Fe obtained from the general formula may be different. I found out. The difference between the measured value and the theoretical value of the Fe valence in this Mn _x Fe _{3 -x} O ₄ is caused by the peroxidation or overreduction of the Fe element during the production of the core material, particularly in the firing step. This is probably because the ratio of Fe (II) ions to Fe (III) ions in the center deviates from the original ratio.

The present inventors have further studied, and when the difference between the measured value and the theoretical value of Fe valence in Mn _x Fe _3-x O ₄ is within a predetermined range, the Mn _x Fe _3-x O ₄ It has been found that the carrier core material constituted by the above satisfies both magnetic properties and insulation properties at a high level.
Specifically, the difference between the measured value and the theoretical value of Fe valence is A
(However, A = Fe valence (actual value) −Fe valence (theoretical value) = Fe valence (actual value) − (8-2 × x) / (3-x))
It is found that when 0.005 ≦ A ≦ 0.05, the carrier core material satisfies both the magnetic properties and the insulating properties at a high level.
A method for deriving the valence of the iron element will be described later.

<Magnetic properties>
In the substance constituting the carrier core material according to the present invention, the magnetic susceptibility: σ ₁₀₀₀ under an external magnetic field of 1000 Oe satisfies σ ₁₀₀₀ ≧ 60 emu / g. This is because, when the magnetic susceptibility of the carrier core agent satisfies the above range, the holding force of the magnetic brush is increased in the developing machine, and the carrier adhesion phenomenon is less likely to occur.

<Particle size>
The carrier core material according to the present invention preferably has an average particle size of 10 μm or more and 80 μm or less. If the particle diameter of the carrier core material is 10 μm or more, the magnetization of each carrier particle increases, so that the carrier adhesion phenomenon can be suppressed. If the particle size is 80 μm or less, desired image quality characteristics can be obtained when an electrophotographic image is developed.

2. Next, a carrier core material manufacturing method will be described in the order of a carrier core material, a granulation step, and a firing step.
<Raw material for carrier core>
The composition of the magnetic carrier core material according to the present invention may be metallic iron or a compound thereof and metallic manganese or a compound thereof. However, from the viewpoint that it can exist stably under normal temperature and pressure, oxides such as Fe ₂ O ₃ , Mn ₂ O ₃ , and Mn ₃ O ₄ are generally used.
In addition, in the production of the carrier core material according to the present invention, it is a preferable mode to add a substance that becomes a reducing agent to the raw material in order to adjust the valence of the iron element.

As the reducing agent to be blended in the raw material, carbon powder, polycarboxylic acid organic material, polyacrylic acid organic material, maleic acid, acetic acid, polyvinyl alcohol organic material, or a mixture thereof is preferably used.
It is necessary to adjust the addition amount of the reducing agent so that the valence of the iron element after firing becomes a target value. The optimum amount varies depending on the kind of the substance to be the reducing agent, the ratio of the iron element and the manganese element, the form of the raw iron compound / manganese compound, and the temperature / atmosphere during firing. Therefore, it is necessary to set an appropriate amount according to each manufacturing condition. The method for determining the amount will be described in the “Examples” (summary of Examples 1 to 4 and Comparative Examples 1 to 4) column below. In general, when Fe ₂ O ₃ is used as the iron-based material and Mn ₃ O ₄ is used as the manganese material, it is added in the range of 0.1% by mass to 1.0% by mass with respect to Fe ₂ O ₃ . Is preferred.

<Granulation process>
After weighing the metallic iron or its compound and the reducing agent, they are slurried by mixing and stirring them in a medium liquid such as water (slurry step). Prior to the slurrying, if necessary, the raw material mixture may be subjected to a dry pulverization treatment. The mixing ratio of the raw material powder and the medium liquid is preferably such that the slurry has a solid content concentration of 50 to 90% by mass. The medium liquid is prepared by adding a binder, a dispersant and the like to water. It is preferable to further wet-grind the slurry obtained by mixing and stirring.

By introducing the slurry into a spray dryer, granulation can be suitably performed.
The atmospheric temperature during spray drying may be about 100 to 300 ° C. Thereby, the granulated powder whose particle diameter is 10-200 micrometers can be obtained in general (granulation process). It is desirable to adjust the particle size of the resulting granulated powder by removing coarse particles and fine powder using a vibration sieve or the like in consideration of the final particle size of the product.

<Baking process>
The obtained granulated powder is put into a heated furnace and fired to produce the desired manganese ferrite.
Here, in order to adjust the valence of the iron element to a target range, as described in the above-mentioned <Raw material for carrier core>, carbon alone or an organic reducing agent is added to the raw material. However, if the oxygen concentration in the furnace is too high, the reduction reaction does not proceed smoothly, and an oxidation reaction of the carrier core material generated during cooling occurs. For this reason, it becomes difficult to adjust the valence of the iron element to a desired range. For this reason, it is required to perform firing by adjusting the oxygen concentration of the introduced gas so that the oxygen concentration in the firing furnace is preferably 3% or less, more preferably 1% or less.

Regarding the firing temperature, the reducing atmosphere necessary for ferritization can be reached by adjusting the amount of the reducing agent added as described above. However, in order to obtain a reaction rate that can ensure sufficient productivity during industrialization, a temperature of 350 ° C. or higher is necessary, and if the firing temperature is 1500 ° C. or lower, excessive sintering of particles does not occur, It becomes easy to obtain a fired product in the form of powder. From this viewpoint, the firing temperature is preferably in the range of 350 ° C. or higher and 1500 ° C. or lower. More preferably, the temperature is 700 ° C. or higher and 1300 ° C. or lower, and more preferably 1000 ° C. or higher and 1300 ° C. or lower.
It is desirable to adjust the particle size of the obtained fired product at this stage. For example, particles having a desired particle diameter can be obtained by pulverizing the fired product with a hammer mill or the like and classifying with a vibrating sieve or the like.

3. Carrier for electrophotographic developer The carrier core material according to the present invention is coated with a silicone-based resin or the like, and the carrier for electrophotographic developer can be obtained by imparting chargeability and improving durability. The method for coating the silicone resin or the like may be performed by a known method.

4). Electrophotographic developer The electrophotographic developer according to the present invention can be obtained by mixing the carrier according to the present invention and an appropriate toner.

5. Measuring method of each physical property value,
Describes how to measure each physical property value.
<Particle size distribution>
The particle size distribution of the carrier core material was measured using a microtrack (manufactured by Nikkiso Co., Ltd., Model: 9320-X100). From the obtained particle size distribution, an integrated particle size D50 up to a volume ratio of 50% was calculated. In the present invention, the value of D50 is described as the average particle diameter of the core material.

<Magnetic properties>
The magnetic properties of the carrier core material were measured using a VSM (manufactured by Toei Industry Co., Ltd., VSM-P7) to obtain a magnetic susceptibility σ ₁₀₀₀ (emu / g) in an external magnetic field of 1000 Oe.

<Resistivity>
The electrical resistivity at an applied voltage of 250 V was defined as the resistivity in the present invention.
The resistivity was measured as follows.
Two brass plates having a thickness of 2 mm whose surfaces were electropolished as electrodes were arranged so that the distance between the electrodes was 2 mm, and 200 mg of the powder to be measured was placed in the gap between the two electrode plates, and then each electrode A magnet having a cross-sectional area of 240 mm ² is arranged behind the plate and a bridge of the powder to be measured is formed between the electrodes, a DC voltage of 250 V is applied between the electrodes, and the current value flowing through the powder to be measured is 4 It was measured by the terminal method. The resistivity of the powder to be measured was calculated from the current value, the distance between the electrodes of 2 mm, and the cross-sectional area of 240 mm ² .
Various magnets can be used as long as the powder can form a bridge. In the present invention, a permanent magnet (ferrite magnet) having a surface magnetic flux density of 1500 gauss is used.

<Iron element valence>
The valence of the iron element in the Mn ferrite constituting the carrier core material was measured by the following method.
This analysis method is an application of oxidation-reduction titration, and consists of (1) determination of Fe ²⁺ , (2) determination of total Fe amount, and (3) calculation of Fe valence. A specific method is shown below.

(1) Determination of Fe ²⁺ First, the carrier core material is dissolved in hydrochloric acid (HCl) water which is a reducing acid in bubbling of carbon dioxide gas. Thereafter, the amount of Fe ²⁺ ions in the solution is quantitatively analyzed by potentiometric titration with a potassium permanganate solution.
Also, in this analysis, elements having only one ionic valence such as Al, Si, Mg, Ca, Ba, Sr, Li, Na etc are not detected by this analysis method. In addition, since Mn ²⁺ ions, which are constituent elements of the carrier core material according to the present invention, are not detected by this titration method, only the Fe ²⁺ concentration in the carrier core material is selectively quantified as a result.

(2) Quantification of total Fe amount The carrier core material was weighed in the same amount as (1) Fe ²⁺ quantification, and dissolved in a mixed acid water of hydrochloric acid and nitric acid. After evaporating this solution to dryness, sulfuric acid water is added and redissolved to volatilize excess hydrochloric acid and nitric acid. Solid Al is added to this solution to reduce Fe ³⁺ in the solution to Fe ²⁺ . Subsequently, this solution was measured by the same analytical means as used in (1) determination of Fe ²⁺ .

(3) Fe average valence of calculation (1) Determination of titer of ^{Fe 2+} represents ^{Fe 2+} quantity, ((2) titer - (1) titer) it does represent the ^{Fe 3+} amount, the following The average valence of Fe was calculated by the calculation formula.
Fe valence = {3 × ((2) titration− (1) titration) + 2 × (1) titration} / (2) titration

In addition to the above methods, there are other oxidation-reduction titration methods for quantifying the valence of iron elements, but the reaction used in this analysis is simple and the interpretation of the obtained results is easy. The reagents and analyzers used in the present invention are excellent in accuracy, and the skill of the analyst is not required.
In addition, XPS (ESCA) and Mossbauer spectroscopy, which are solid spectrum analysis methods, have reported examples of quantifying the valence of iron elements in solids, but these analysis methods require expensive analytical instruments, and spectral spectra Therefore, it can be said that the wet chemical analysis method is excellent in terms of analysis accuracy, sensitivity, and reproducibility.

Example 1
6.8 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 3.2 kg of Mn ₃ O ₄ (average particle size: 0.9 μm) are dispersed in 3.0 kg of pure water, and polycarboxylic acid is used as a dispersant. 60 g of ammonium dispersant was added to form a mixture. The mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry of Fe ₂ O ₃ and Mn ₃ O ₄ . The mixing ratio of the raw materials was calculated so that x = 1.00 in the above-described ferrite composition formula Mn _x Fe _3-x O ₄ . Furthermore, carbon black (Mitsubishi Chemical Corporation Mitsubishi Carbon Black MA-7) was added to the slurry as a reducing agent.
This slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain dry granulated powder having a particle size of 10 to 100 μm. At this time, the granulated powder having a particle size exceeding 100 μm was removed by a sieve.
This granulated powder was put into an electric furnace and fired for 3 hours. At this time, a gas in which oxygen and nitrogen were mixed was flowed into the electric furnace so that the oxygen concentration in the electric furnace was constant. The obtained fired product was pulverized and classified using a sieve, and the magnetic carrier core material for an electrophotographic developer according to Example 1 in which the valence of the iron element was adjusted to the range of 2.95 to 3.00 ( a, b) were obtained. In this example, the value of x of Mn _x Fe _3-x O ₄ , the amount of carbon black (CB) added, the analytical value of the carbon component (analyzed value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Example 2)
Fe ₂ O ₃ (average particle size: 0.6 μm) 7.2 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 2.8 kg was dispersed in 3.0 kg of pure water, and polycarboxylic acid was used as a dispersant. 60 g of ammonium dispersant was added to form a mixture. The mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry of Fe ₂ O ₃ and Mn ₃ O ₄ . The mixing ratio of the raw materials was calculated so that x = 0.86 in the above-described ferrite composition formula Mn _x Fe _3-x O ₄ .
Using this slurry as a raw material with carbon black added as a reducing agent, granulation and firing were performed in the same manner as in Example 1, and the valence of the iron element was adjusted to the range of 2.93 to 2.98. Carrier core materials (ad) according to Example 2 were obtained. In this example, the value of x of Mn _x Fe _3-x O ₄ , the amount of carbon black (CB) added, the analytical value of the carbon component (analyzed value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Example 3)
8.4 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 1.6 kg of Mn ₃ O ₄ (average particle size: 0.9 μm) are dispersed in 3.0 kg of pure water, and polycarboxylic acid is used as a dispersant. 60 g of ammonium dispersant was added to form a mixture. The mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry of Fe ₂ O ₃ and Mn ₃ O ₄ . The mixing ratio of the raw materials was calculated so that x = 0.50 in the above-described ferrite composition formula Mn _x Fe _3-x O ₄ .
Using this slurry as a raw material with carbon black added as a reducing agent, granulation and firing were performed in the same manner as in Example 1, and the valence of the iron element was adjusted to the range of 2.80 to 2.85.
Carrier core materials (ad) according to Example 3 were obtained. In this example, the value of x of Mn _x Fe _3-x O ₄ , the amount of carbon black (CB) added, the analytical value of the carbon component (analyzed value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

Example 4
9.7 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 0.3 kg of Mn ₃ O ₄ (average particle size: 0.9 μm) are dispersed in 3.0 kg of pure water, and polycarboxylic acid is used as a dispersant. 60 g of ammonium dispersant was added to form a mixture. The mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry of Fe ₂ O ₃ and Mn ₃ O ₄ . The mixing ratio of the raw materials is calculated so that x = 0.1 in the above-described ferrite composition formula Mn _x Fe _3-x O ₄ .
Using this slurry as a raw material with carbon black added as a reducing agent, granulation and firing were performed in the same manner as in Example 1, and the valence of the iron element was adjusted to the range of 2.69 to 2.74. Carrier core materials (ad) according to Example 4 were obtained. In this example, the value of x of Mn _x Fe _3-x O ₄ , the amount of carbon black (CB) added, the analytical value of the carbon component (analyzed value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Comparative Example 1)
In Example 1, except that the amount of carbon black added as a reducing agent and the oxygen concentration of the introduced gas were changed, the carrier core material (a) was processed in the same manner as in Example 1 and the valence of the iron element was adjusted. Obtained. In this comparative example, the charged value of x of Mn _x Fe _3-x O ₄ , the added amount of carbon black (CB), the analytical value of the carbon component (the analytical value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Comparative Example 2)
In Example 2, except that the amount of carbon black added as a reducing agent and the oxygen concentration of the introduced gas were changed, the same processing as in Example 2 was carried out to adjust the valence of the iron element (ad) ) In this comparative example, the charged value of x of Mn _x Fe _3-x O ₄ , the added amount of carbon black (CB), the analytical value of the carbon component (the analytical value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Comparative Example 3)
In Example 3, the carrier core material (ad) was processed in the same manner as in Example 3 except that the amount of carbon black added as the reducing agent and the oxygen concentration of the introduced gas were changed, and the valence of the iron element was adjusted. ) In this comparative example, the charged value of x of Mn _x Fe _3-x O ₄ , the added amount of carbon black (CB), the analytical value of the carbon component (the analytical value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Comparative Example 4)
In Example 4, except that the amount of carbon black added as the reducing agent and the oxygen concentration of the introduced gas were changed, the same processing as in Example 4 was performed to adjust the valence of the iron element (ad) ) In this comparative example, the charged value of x of Mn _x Fe _3-x O ₄ , the added amount of carbon black (CB), the analytical value of the carbon component (the analytical value at the stage of the granulated product before firing) Table 1 shows the firing temperature during firing and the oxygen concentration of the introduced gas.

(Summary of Examples 1-4 and Comparative Examples 1-4)
Table 1 shows the difference A between the measured value and the theoretical value of the Fe valence in the carrier core materials in Examples 1 to 4 and Comparative Examples 1 to ₄ , the analytical value of x of Mn _x Fe _{3 -x} O ₄ , and the magnetic Properties, electrical properties, particle size are shown.

  From the results in Table 1, it was confirmed that in each Example and Comparative Example, the value of x calculated from the analysis results was almost equal to the value of x in the raw material charging. It has also been found that the value of A can be controlled in the range of −0.10 to +0.10 by controlling the amount of carbon black added, the firing temperature, and the oxygen concentration of the introduced gas.

Here, in the carrier core material regarding Examples 1-4 and Comparative Examples 1-4, the above A,
The relationship with the magnetic susceptibility σ1000 is shown in FIG. FIG. 1 is a graph in which the horizontal axis is A and the vertical axis is magnetic susceptibility σ1000. In the graph, the carrier core material according to the example where x = 1.00, ■, the carrier core material according to the comparative example is □, the carrier core material according to the example where x = 0.86 is ▲, The carrier core material according to the comparative example is Δ, x = 0.50 is the carrier core material according to the example ◆, the carrier core material according to the comparative example is ◇, and the carrier core according to the example is x = 0.10 The material is plotted with ●, and the carrier core material according to the comparative example is plotted with ○.

  From FIG. 1, it was found that the magnetic susceptibility of the carrier core material varies depending on the value of A. Further, for any carrier core material having x, when 0 ≦ A ≦ 0.05, more preferably 0 ≦ A ≦ 0.03, σ1000 is 62 to 73 emu / g, It can be seen that preferred magnetic properties are exhibited.

  Next, FIG. 2 shows the relationship between A and resistivity in the carrier core materials related to Examples 1 to 4 and Comparative Examples 1 to 4. FIG. 2 is a graph in which the horizontal axis is A and the vertical axis is resistivity. The plot in the graph is the same as in FIG.

  From FIG. 2, it was found that the resistivity of the carrier core material also varies depending on the value of A. Further, for any carrier core material having x, when 0.005 ≦ A ≦ 0.10, more preferably 0.01 ≦ A ≦ 0.10, the resistivity is kept at a high level and preferable electric power is satisfied. It can be seen that it exhibits characteristics.

  As described above, the results shown in FIGS. 1 and 2 show that the carrier core material in the range of 0.005 ≦ A ≦ 0.05 is excellent in both magnetic characteristics and electrical characteristics. Therefore, by using the carrier core material having such a configuration, it is possible to provide an electrophotographic developer carrier and an electrophotographic developer that can reduce abnormal phenomena such as carrier adhesion.

  In Examples 1 to 4 and Comparative Examples 1 to 4, the value of A is controlled in the range of −0.10 to +0.10 by controlling the amount of carbon black added, the firing temperature, and the oxygen concentration of the introduced gas. I explained what I can do. However, the amount of carbon black added, the firing temperature, and the oxygen concentration of the introduced gas to obtain a desired A value are not constant values depending on the scale and type of the manufacturing apparatus. Therefore, it is required to determine the amount of carbon black added, the firing temperature, and the oxygen concentration of the introduced gas in order to obtain a desired A value according to the scale and type of the production apparatus used. In such a case, the iron element in the Mn ferrite described in “5. Method for measuring physical properties, <iron element valence>” in this specification [Best Mode for Carrying Out the Invention] Optimal conditions can be determined using a valence measurement method.

It is a graph which shows the relationship between the valence of the iron element of the magnetic carrier core material for electrophotographic developers, and magnetic susceptibility. It is a graph which shows the relationship between the valence of the iron element of a magnetic carrier core material for electrophotographic developers, and resistivity.

Claims (5)

_Formula: consists _{Mn x Fe 3-x O 4} ( where 0 <x ≦ 1) Mn ferrite you express in,
The valence of the iron element in the Mn ferrite is {(8-2 × x) / (3-x) +0.005} or more and {(8-2 × x) / (3-x) +0.05} or less. A carrier core material for an electrophotographic developer, characterized by being in the range of 2. The carrier core material for an electrophotographic developer according to claim 1, wherein a magnetic susceptibility under an external magnetic field of 1000 Oe: σ ₁₀₀₀ satisfies σ ₁₀₀₀ ≧ 60 emu / g.   3. The carrier core material for an electrophotographic developer according to claim 1, wherein an average particle diameter is 10 μm or more and 80 μm or less.   A magnetic carrier for an electrophotographic developer, wherein the carrier core material for an electrophotographic developer according to any one of claims 1 to 3 is coated with a resin.   An electrophotographic developer comprising the carrier for an electrophotographic developer according to claim 4 and a toner.

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