JP2010097171A - Carrier core material for electrophotographic developer, method for manufacturing the same, carrier for electrophotographic developer and electrophotographic developer - Google Patents

Abstract

A high-strength carrier core material, a method for producing the same, and an electrophotographic developer containing the carrier powder.
An electron having a true specific gravity of 4.90 to 5.05 g / cm ³ , a specific surface area of 0.05 to 0.35 m ² / g, and containing SiO ₂ in an amount of 0.01 to 4 wt%. A carrier core material for a photographic developer is provided.
[Selection] Figure 5

Description

  The present invention relates to a carrier core material for an electrophotographic developer that achieves high durability and a long life, a method for producing the same, a carrier for an electrophotographic developer, and an electrophotographic developer.

  The electrophotographic dry development method is a method in which powder toner, which is an electrophotographic developer, is attached to an electrostatic latent image on a photoreceptor, and the attached toner is transferred to a predetermined medium such as paper and developed. is there. This method is roughly classified into a method using a one-component developer containing only toner and a method using a two-component developer containing toner and a magnetic carrier as an electrophotographic developer. In recent years, two-component developers that can easily control the charge of toner, obtain a stable high image quality, and are capable of high-speed development have become the mainstream of electrophotographic developers.

  In a developing method using a two-component developer, a carrier is stirred and mixed with toner in a developing machine, the toner is given a desired charge, a magnetic brush is formed on a magnet roll, and the charged toner is photosensitive. It is transported over the body. The carrier remaining on the magnet roll returns to the developing machine again, is agitated and mixed with new toner, and is repeatedly used for a certain period.

  As the network of offices has progressed and the service system has been enhanced, the system has shifted from a system in which service personnel change the developer to a maintenance-free era, and there is a demand for higher durability and longer life of the developer. It is getting higher.

  In recent years, electrophotographic developing machines have been trending toward full color, high image quality, and high speed. Especially, with high speed, the stirring load increases in the developing machine, and the magnetic carrier is cracked or chipped due to stirring stress. Has occurred. As a result, cracks and chipped particles cause carrier scattering, resulting in image quality degradation.

In order to solve the above-mentioned problem, Patent Document 1 proposes that the slurry be manufactured under the conditions in which the particle size of the slurry is set to a certain range or less and the preliminary firing and the main firing are limited.
In Patent Document 2, a binder removal process is performed without using a sintering aid, and a high strength carrier is obtained and carrier scattering is reduced by improving the interparticle variation in the surface properties of the carrier core material. Has been proposed.

JP 2007-271663 A JP 2007-273505 A

However, according to studies by the present inventors, for example, the change rate (strength) of the average particle diameter before and after crushing of the magnetic carrier described in Patent Documents 1 and 2 is 74% or more and 85% or more, respectively. It was. In this case, it was found that the magnetic carrier needs to be further strengthened because cracks and chipping particles of the magnetic carrier are generated due to agitation stress in the developing machine and carrier adhesion occurs.
Here, further research was conducted, and the ground strength of the particle strength of the magnetic carrier was obtained that the internal structure of the particle was important, not the variation in the surface property of the particle. That is, in Patent Document 2 described above, the magnetic carrier is manufactured at a high temperature up to 1400 ° C., but abnormal grain growth is caused in the high temperature sintering process, causing segregation of internal vacancies. It is believed that there is.

  The present invention has been made under the above-mentioned circumstances, and the problem to be solved is a carrier core material for an electrophotographic developer that is high in strength and hardly generates cracks and chipped particles in a developing machine, and its carrier It is to provide a manufacturing method, a carrier for an electrophotographic developer using the carrier core material for the electrophotographic developer, and an electrophotographic developer.

  In order to solve the above-mentioned problems, the present inventors have made researches, found carrier core particles having predetermined internal pores exhibiting epoch-making strength, and completed the present invention.

That is, the first invention for solving the above-described problem is
The true specific gravity is 4.90 to 5.05 g / cm ³ ;
The specific surface area is 0.05 to 0.35 m ² / g;
A carrier core material for electrophotographic developer which comprises magnetite particles have a SiO ₂ containing 0.01~4wt%.

The second invention is
The carrier core material for an electrophotographic developer according to the first invention, wherein the volume porosity is in the range of 3 to 6%.

The third invention is
The carrier core material for an electrophotographic developer according to the first or second invention, wherein the magnetite particles have an average particle diameter (D50) of 25 to 40 μm.

The fourth invention is:
A step of mixing a Fe raw material, a SiO ₂ raw material, and carbon to obtain a slurry having a solid content concentration of 75 wt% or more;
A step of spray-drying the slurry to obtain a granulated product;
Firing the granulated product at a temperature of 960 ° C. or higher and 1130 ° C. or lower to obtain a fired product having a magnetic phase;
A method for producing a carrier core material for an electrophotographic developer, comprising: subjecting the obtained fired product to a pulverization treatment to form a powder, and thereafter giving a predetermined particle size distribution.

The fifth invention is:
An electrophotographic developer carrier characterized in that the surface of the carrier core material for an electrophotographic developer according to any one of the first to third inventions is coated with a resin.

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

The carrier core material for an electrophotographic developer according to the present invention has high mechanical strength. The electrophotographic developer carrier according to the present invention produced using the electrophotographic developer carrier core material has high resistance to agitation stress in the electrophotographic developing machine. Therefore, stable and good image quality characteristics can be obtained by using the electrophotographic developer according to the present invention including the carrier for the electrophotographic developer in a high-performance electrophotographic developing machine or MFP (multi-function printer). In addition to extending the electrophotographic developer replacement life.

It is the relationship between the true specific gravity and the fine powder increase rate in the carrier core material according to the present invention. It is the relationship between the specific surface area and fine powder increase rate in the carrier core material which concerns on this invention. It is the relationship between the calcination temperature and fine powder increase rate in manufacture of the carrier core material which concerns on this invention. It is the relationship between the volume porosity and fine powder increase rate in manufacture of the carrier core material which concerns on this invention. 2 is a cross-sectional photograph of carrier core particles according to Example 1. 3 is a cross-sectional photograph of carrier core particles according to Comparative Example 1.

The carrier core material for an electrophotographic developer according to the present invention has a true specific gravity of 4.90 to 5.05 g / cm ³ , a specific surface area of 0.05 to 0.35 m ² / g, and SiO _2. Is magnetite particles containing 0.01 to 4 wt%.
The inventors have a true specific gravity of 4.90 to 5.05 g / cm ³ and a BET specific surface area of 0.8.
It has been found that the mechanical strength is specifically increased in a carrier core material for an electrophotographic developer (hereinafter sometimes simply referred to as “carrier core material”) having a thickness of from 0.5 to 0.35 m ² / g. This is because the carrier core particles contain predetermined uniform and fine internal vacancies inside, thereby increasing the mechanical strength of the magnetite particles, and as a result, the carrier core material composed of the magnetite particles. We believe that the mechanical strength increases.
Furthermore, since the carrier core material contains 0.01 to 4 wt% of SiO ₂ , it is possible to prevent the occurrence of abnormal grain growth of the crystal during sintering and insufficient sintering during sintering. It is thought that low-intensity particles due to can be reduced.

  Further, since the carrier core material is a magnetite particle having an average particle diameter (D50) of 25 to 40 μm, magnetization of each carrier particle is secured, so that the carrier adhesion phenomenon is suppressed and the electrophotographic development is performed. It was found that desirable image quality characteristics were obtained.

  Hereinafter, the present invention is as follows. 1. carrier core material for electrophotographic developer; 2. Electrophotographic developer carrier; 3. Production method of carrier core material for electrophotographic developer 4. Production method of carrier for electrophotographic developer The electrophotographic developer will be described in this order.

1. Carrier core material for electrophotographic developer <Physical properties>
The carrier core material according to the present invention is a magnetite particle having a true specific gravity of 4.90 to 5.05 g / cm ³ and a specific surface area of 0.05 to 0.35 m ² / g. It is preferable that the magnetite particles have a true specific gravity of 4.90 g / cm ³ or more because strength reduction due to the magnetite particles containing many internal vacancies can be prevented. On the other hand, a true specific gravity of 5.05 g / cm ³ or less is preferable because it can prevent a decrease in internal vacancies and a decrease in strength due to abnormal grain growth in the magnetite particles.

Moreover, since the specific surface area of the magnetite particles constituting the carrier core material according to the present invention is 0.05 m ² / g or more, grain coarsening due to sintering between particles or excessive sintering can be prevented. preferable. On the other hand, if the specific surface area of the magnetite particle is 0.35 m ² / g or less, it is a particle having a small number of pores (open pores) opened on the surface of the magnetite particle, and cracks and chipping particles due to the open pore are generated. Can be prevented, which is preferable.
Furthermore, in the carrier core material according to the present invention, by containing 0.01 wt% or more of SiO ₂ , it is possible to prevent the abnormal particle growth of the magnetite crystal during the sintering. On the other hand, if SiO ₂ is 4 wt% or less, it is considered that low-strength magnetite particles due to insufficient sintering during sintering can be reduced.

<Particle size>
The carrier core material according to the present invention preferably has an average particle size (D50) of 25 μm or more and 40 μm or less.
If the particle diameter of the carrier core material is 25 μm or more, the magnetization of each carrier particle is ensured and the carrier adhesion phenomenon is suppressed, which is preferable. A particle size of 40 μm or less is preferable because desired image quality characteristics can be obtained upon electrophotographic development.

<Magnetic properties>
The carrier core material according to the present invention preferably has a magnetic susceptibility: σ ₁₀₀₀ under an external magnetic field of 1000 Oe of 30 emu / g or more. This is because when the carrier core material has σ ₁₀₀₀ of 30 emu / g or more, the holding force of the magnetic brush formed in the electrophotographic developing machine becomes strong, and the carrier adhesion phenomenon is suppressed.

<Electrical resistance>
The carrier core material according to the present invention preferably has an electric resistance of 10 ⁵ Ω or more at an applied voltage of 50V. If the electrical resistance is 10 ⁵ Ω or more, when the carrier core material is coated with a resin to form a carrier, the voltage dependence of the electrical resistance is reduced, and charge leakage is less likely to occur.

Here, the electrical resistance at an applied voltage of 50 V can be obtained as follows.
Two brass plates having a thickness of 2 mm and having an electropolished surface as electrodes are placed on an insulating plate (for example, an acrylic plate coated with Teflon (registered trademark)) placed horizontally so that the distance between the electrodes is 2 mm. To place. At this time, the normal direction of the two electrode plates is horizontal. After inserting 200 ± 1 mg of the powder to be measured into the gap between the two electrode plates, a magnet having a cross-sectional area of 240 mm ² is arranged behind each electrode plate to form a bridge of the powder to be measured between the electrodes. . In this state, a DC voltage of 10 V, 25 V, 50 V, or 100 V is applied between the electrodes, the value of the current flowing through the powder to be measured is measured by the four-terminal method, and the electric resistance value is calculated. The value was taken as electric resistance. Various magnets can be used as long as the powder can form a bridge, but in the examples described later, a permanent magnet (ferrite magnet) having a surface magnetic flux density of 1000 gauss or more is used.

2. Carrier for electrophotographic developer The carrier core material according to the present invention is coated with a silicone resin, an acrylic resin, or the like to improve the charging property and durability, thereby improving the electrophotographic developer carrier (in the present invention). , Sometimes simply described as carrier). The covering method of the silicone resin or acrylic resin can be performed by a known method.

<Carrier strength>
The present inventors examined the problem that the carrier generates fine powder when subjected to agitation stress in the electrophotographic developing machine. As a result, when the carrier core material constituting the carrier is put into a crushing tester and crushed, the rate of change in the cumulative value of the particle size (hereinafter referred to as fine powder) in the crushed pieces of 22 μm or less of the carrier core material before and after the crushing. By measuring the increase rate, it is possible to evaluate the generation state of the fine powder due to the stirring stress of the carrier in the electrophotographic developing machine and the influence of the fine powder on the electrophotographic image. did. Specifically, when the fine powder increase rate was 4% or less, carrier adhesion hardly occurred even after 100K sheets of electrophotographic development, and good electrophotographic image quality was obtained.
That is, it is shown that the carrier composed of the carrier core material according to the present invention does not generate fine powder that affects the image even when subjected to stirring stress in the electrophotographic developing machine. Therefore, when an electrophotographic developer containing the carrier and a known toner is applied to an electrophotographic developer, fine powder can hardly be generated, and image quality deterioration such as carrier scattering caused by the fine powder does not occur.

3. Method for Producing Carrier Core Material for Electrophotographic Developer A method for producing a carrier core material according to the present invention will be described in the order of a carrier core material, a granulation step, and a firing step.

<Raw material for carrier core>
The raw material of the magnetite particles constituting the carrier core material according to the present invention may be metallic iron or an oxide thereof. Specifically, Fe ₂ O ₃ , Fe ₃ O ₄ , Fe, and the like that exist stably at normal temperature and pressure are preferably used.
On the other hand, amorphous silica, crystalline silica, colloidal silica, or the like is preferably used as the raw material for SiO ₂ to be contained in the magnetite particles.

In the method for manufacturing a carrier core material according to the present invention, the reduction reaction is advanced. Therefore, a reducing agent may be further added to the slurry raw material described above. As the reducing agent, carbon powder, polycarboxylic acid organic substances, polyacrylic acid organic substances, maleic acid, acetic acid, polyvinyl alcohol organic substances, and mixtures thereof are preferably used.
When carbon powder is used as the reducing agent, the amount of carbon added is preferably 0.6 to 1.4 wt%. If the amount of carbon added is 0.6 to 1.4 wt%, the carrier core material is magnetized at an oxygen concentration of 1% or less and a firing temperature of 960 to 1130 ° C., which is preferable.

Water is added to the slurry raw material described above and mixed and stirred, so that the solid content concentration is 75 wt% or more, preferably 77 wt% or more. If the solid content concentration of the slurry raw material is 75 wt% or more, the pores of the pellets during granulation become uniform, and the true specific gravity in the carrier core material after firing is 4.90 to 5.05 g / cm ³ . This is preferable because a high-strength carrier can be obtained.

<Granulation process>
Granulation of the slurry obtained by mixing and stirring is performed using a spray dryer. In addition, it is also preferable to further wet-grind the slurry before the granulation.
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. In consideration of the final particle size of the product, it is desirable to adjust the particle size by removing coarse particles having a particle size of 100 μm or more and fine particles having a particle size of 15 μm or less using a vibration sieve or the like.

<Baking process>
The obtained granulated powder is put into a furnace heated to about 960 to 1130 ° C. and held for 1 to 24 hours and fired to produce a desired fired product. At this time, it is necessary to perform firing by adjusting the oxygen concentration of the introduced gas so that the oxygen concentration in the firing furnace is preferably 1% or less, more preferably 0.3% or less.
If the oxygen concentration in the furnace is 1% or less, the reducing agent in the granulated powder acts effectively, the reduction from hematite to magnetite proceeds, and the decrease in the magnetic force of the fired product can be avoided.

With respect to the firing temperature, a reducing atmosphere necessary for ferritization can be reached by adjusting the reducing agent.
However, from the viewpoint of obtaining a reaction rate capable of ensuring sufficient productivity during industrialization, a temperature of 960 ° C. or higher is preferable. On the other hand, if the said calcination temperature is 1130 degrees C or less, excessive sintering of particle | grains will not occur and a baked material can be obtained with the form of a powder. From this viewpoint, the firing temperature is 96.
It is preferably in the range of 0 to 1130 ° C. By firing at this temperature, the true specific gravity in the particles after firing becomes 4.90 to 5.05 g / cm ³ and has a sufficient strength, so that a good form is obtained.
It is desirable to adjust the particle size of the obtained fired product at this stage. For example, the carrier core material particles having a desired particle diameter can be obtained by roughly pulverizing the fired product with a hammer mill or the like and classifying with a vibrating sieve or the like.

4). Method for producing carrier for electrophotographic developer The carrier core material according to the present invention is coated with a silicone-based resin, an acrylic resin, or the like, and the carrier for electrophotographic developer is improved by imparting chargeability and improving durability. Can be obtained. The covering method of the silicone resin or acrylic resin can be performed by a known method.

The obtained electrophotographic developer carrier was mixed with a known toner to prepare an electrophotographic developer. The electrophotographic developer was placed in a developing machine, image evaluation was performed, and the state of carrier adhesion was visually observed.
When the fine powder increase rate was 4% or less, carrier adhesion did not occur in electrophotography, and good image quality was obtained.
It shows that the carrier according to the present invention does not generate fine powder that affects the image even with stirring stress in the electrophotographic developing machine. Therefore, when an electrophotographic developer containing the carrier and toner is applied to an electrophotographic developer, almost no fine powder can be generated, and image quality degradation such as carrier scattering caused by the fine powder does not occur.

5). Electrophotographic Developer The electrophotographic developer carrier according to the present invention can be mixed with an appropriate known toner to obtain the electrophotographic developer according to the present invention.

The electrophotographic developer was placed in a developing machine, image evaluation was performed, and the state of carrier adhesion was visually observed.
According to the electrophotographic developer according to the present invention, carrier adhesion is not observed in the initial images at 50K sheets and 100K sheets, or 1 to 10 carrier adhesions are observed. It was sufficiently suppressed.

The method for producing an electrophotographic developer carrier core material according to the present invention will be specifically described below with reference to examples.
In showing examples of the present invention, first, a method of measuring each physical property value will be described.

<Analysis of SiO ₂ content>
The SiO ₂ content of the carrier core material was quantitatively analyzed according to the silicon dioxide weight method described in JIS M8214-1995. SiO ₂ content of the carrier core material described in this invention is the amount of SiO ₂ which is obtained by quantitatively analyzing in the silicon dioxide by weight method.

<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 up to a volume ratio of 50% (may be referred to as D50 in the present invention) 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.

<True specific gravity, volume porosity>
For the volume porosity of the carrier core material, the carrier core material was crushed, and the difference in true specific gravity of the carrier core material before and after the pulverization was evaluated as a hole. Specifically, the volume porosity was determined from the following formula. The true specific gravity of the carrier core material of the pulverized powder was measured with a gas displacement pycnometer (Ultra Pycnometer 1000 manufactured by Quantachrome).
The volume porosity was calculated by the following (Formula 1). The volume porosity was P, the true specific gravity of the carrier core material before pulverization was ρ1, and the true specific gravity of the carrier core material after pulverization was ρ2.
P (%) = (ρ2−ρ1) / ρ2 × 100 (Equation 1)
In addition, about the volume porosity measuring method of the said carrier core material, Unexamined-Japanese-Patent No. 2008-232817 has a detailed description.

<Specific surface area>
The specific surface area (BET) of the carrier core material was measured based on JISZ8830-2001.

<Measurement of carrier strength>
30 g of the carrier according to the present invention was put into a sample mill (Kyoritsu Riko Co., Ltd. SK-M10 type), and a crushing test was performed at a rotational speed of 14000 rpm for 60 seconds.
Then, using the rate of change of the cumulative value of the crushed pieces (volume) of 22 μm or less before and after the crushing as the fine powder increase rate, a laser diffraction particle size distribution measuring device (Microtrack, Model 9320-X100 manufactured by Nikkiso Co., Ltd.) ).

<Evaluation of carrier scattering>
The electrophotographic developer carrier according to the present invention and a known toner are mixed with a V-type mixer or the like to produce an electrophotographic developer sample.
Next, an image evaluation test was performed using the electrophotographic developer sample. In the initial stage, when carrier scattering was not observed in the images of 50K sheets and 100K sheets, it was evaluated as ◎, when 1 to 10 carrier scattering were observed, ◯, and when 10 or more carrier scattering were observed, it was evaluated as ×.

Example 1
10 kg of Fe ₂ O ₃ (average particle size: 0.6 μm) is dispersed in 2.5 kg of pure water, 100 g of an ammonium polycarboxylate dispersant as a dispersant, 100 g of carbon black as a reducing agent, and SiO ₂ raw material 530 g of colloidal silica (solid content concentration 50%) was added to obtain a mixture. As a result of measuring the solid content concentration at this time, it was 79 wt%. The mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry.

  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 at 1000 ° C. for 3 hours. At this time, it flowed into the electric furnace whose atmosphere was adjusted so that the oxygen concentration in the electric furnace was 0.05%. The obtained fired product was classified using a sieve after pulverization to obtain an average particle size of 35 μm, and a carrier core material according to Example 1 was obtained.

Table 1 shows the material properties, magnetic properties, and electrical properties of the obtained carrier core material.
The fine increase rate of the carrier core material according to Example 1 was as small as 1.06%, and it was found that the strength of the carrier was high.

(Example 2)
A carrier core material according to Example 2 was obtained in the same manner as in Example 1 except that 10 kg of Fe ₂ O ₃ was dispersed in 3.34 kg of pure water so that the solid concentration was 75 wt%.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 2.
The fine powder increase rate of the carrier core material according to Example 2 was as small as 1.29%, and it was found that the carrier strength was high.

(Example 3)
A carrier core material according to Example 3 was obtained by performing the same treatment as in Example 1 except that the firing temperature was 1050 ° C.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 3.
The fine increase rate of the carrier core material according to Example 3 was as small as 2.13%, and it was found that the carrier strength was high.

Example 4
A carrier core material according to Example 4 was obtained by performing the same treatment as in Example 1 except that the firing temperature was 1100 ° C.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 4.
The fine powder increase rate of the carrier core material according to Example 4 was as small as 1.61%, and it was found that the strength of the carrier was high.

(Example 5)
A carrier core material according to Example 5 was obtained except that the firing temperature was 1075 ° C. and 795 g of colloidal silica was added as the SiO ₂ raw material.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 5.
The fine increase rate of the carrier core material according to Example 5 was as small as 1.55%, and it was found that the carrier strength was high.

(Example 6)
A carrier core material according to Example 6 was obtained in the same manner as in Example 1 except that the baking temperature was 1050 ° C. and 130 g of colloidal silica was added as the SiO ₂ raw material.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 6.
The fine powder increase rate of the carrier core material according to Example 6 was as small as 2.80%, and it was found that the carrier strength was high.

(Example 7)
A carrier core material according to Example 7 was obtained in the same manner as in Example 1 except that the firing temperature was 1050 ° C. and 265 g of colloidal silica was added as the SiO ₂ raw material.
Table 1 shows the material characteristics, magnetic characteristics, and electrical characteristics of the carrier core material according to Example 7.
The fine powder increase rate of the carrier core material according to Example 7 was as small as 0.95%, and it was found that the carrier strength was high.

(Comparative Example 1)
A carrier core material according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the addition amount of SiO ₂ was changed to 0 wt%.
Table 1 shows the material properties, magnetic properties, and electrical properties of the carrier core material according to Comparative Example 1.
The increase rate of fine powder of the carrier core material according to Comparative Example 1 was as large as 10.55%, and it was found that the carrier strength was low.

(Comparative Example 2)
A carrier core material according to Comparative Example 2 was obtained in the same manner as in Example 1 except that 10 kg of Fe ₂ O ₃ was dispersed in 10 kg of pure water and the solid concentration was 50 wt%.
Table 1 shows the material properties, magnetic properties, and electrical properties of the carrier core material according to Comparative Example 2.
The fine increase rate of the carrier core material according to Comparative Example 2 was as large as 9.58%, and it was found that the carrier strength was low.

(Comparative Example 3)
A carrier core material according to Comparative Example 3 was obtained in the same manner as in Example 1 except that the firing temperature was 930 ° C.
Table 1 shows the material properties, magnetic properties, and electrical properties of the carrier core material according to Comparative Example 3.
The fine increase rate of the carrier core material according to Comparative Example 3 was as large as 12.86%, and it was found that the carrier strength was low.

(Comparative Example 4)
A carrier core material according to Comparative Example 4 was obtained in the same manner as in Example 1 except that the firing temperature was 1150 ° C.
Table 1 shows the material properties, magnetic properties, and electrical properties of the carrier core material according to Comparative Example 4.
The fine increase rate of the carrier core material according to Comparative Example 4 was as large as 13.01%, and it was found that the carrier strength was low. The electrical resistance value was broken down (BD).

(Comparative Example 5)
A carrier core material according to Comparative Example 5 was obtained in the same manner as in Example 1 except that the firing temperature was 950 ° C.
Table 1 shows the material properties, magnetic properties, and electrical properties of the carrier core material according to Comparative Example 5.
The fine increase rate of the carrier core material according to Comparative Example 5 was as large as 8.06%, and it was found that the carrier strength was low. The electrical resistance value was broken down (BD).

(Summary of Examples 1-7 and Comparative Examples 1-5)
From the data in Table 1, FIG. 1 is a graph in which the fine particle increase rate is taken on the vertical axis and the true specific gravity is taken on the horizontal axis, and FIG. 2 is a graph in which the fine powder increase rate is taken on the vertical axis and the specific surface area is taken on the horizontal axis. Created. Further, from the data in Table 1, FIG. 3 is a graph in which the vertical axis represents the fine powder increase rate, the horizontal axis represents the firing temperature, and the vertical axis represents the fine powder increase rate, and the horizontal axis represents the volume porosity. FIG. 4 was created. Moreover, the SEM photograph (3,000 times) of the particle | grain cross section which concerns on Example 1 is SEM of the particle | grain cross section which concerns on FIG.
A photograph (3,000 times) is shown in FIG.

1 and 2, when the true specific gravity of the carrier core material according to the example is 4.90 to 5.05 g / cm ³ and the BET is 0.05 to 0.35 m ² / g, the fine powder increase rate It was found that the strength of the carrier core material was high. Moreover, from FIG. 4, the volume porosity is 3
In the range of ˜6%, the increase rate of fine powder was remarkably reduced, and it was also found that the carrier core material has high strength. Further, from the particle cross-sectional photograph according to Example 1 shown in FIG. 5, the inside contains predetermined uniform and fine internal vacancies, the vacancies inside the particles are small, and the crystal size is small. As a result, it can be seen that the carrier core material has a small increase rate of fine powder and remarkably increased mechanical strength.
On the other hand, from the particle cross-sectional photograph according to Comparative Example 1 shown in FIG. As a result, it can be seen that the fine particle increase rate of the particles according to Comparative Example 1 is large, and the carrier core material has significantly reduced mechanical strength.
From the above, it is important to obtain a carrier core material having high strength that the true specific gravity and specific surface area of the carrier core material are controlled from the present invention to have predetermined uniform and fine internal pores inside the particles. It turned out to be.

On the other hand, according to FIG. 3, in the manufacturing process of the carrier core material, a granulated product obtained by spray-drying a slurry having a solid content concentration of 75 wt% or more in which Fe raw material, SiO ₂ raw material, and carbon are mixed is 960 ° C. or higher, 1130 It has been found that a carrier core material with a significantly reduced fine powder increase rate can be obtained by firing at a temperature of ℃ or lower.

  Next, resin coating was performed on the obtained carrier core materials according to Examples 1 to 7 and Comparative Examples 1 to 5, respectively, to obtain magnetic carriers according to Examples 1 to 7 and Comparative Examples 1 to 5. The magnetic carrier was loaded into an image evaluation test and an image evaluation test was performed.

  Specifically, a silicone resin (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in toluene to prepare a coating resin solution. Then, the carrier core materials according to Examples 1 to 7 and Comparative Examples 1 to 5 and the resin solution are loaded into the stirrer at a ratio of carrier core material: resin solution = 9: 1 by weight ratio. Then, the carrier core material was heated and stirred at 150 ° C. to 250 ° C. for 3 hours while being immersed in the resin solution.

  By the stirring, the silicone resin was coated at a ratio of 1.0 wt% with respect to the weight of each carrier core material. The resin-coated carrier core material was placed in a hot air circulation heating device, heated at 250 ° C. for 5 hours, and the coating resin layer was cured, whereby magnetic properties according to Examples 1 to 7 and Comparative Examples 1 to 5 were obtained. Got a career.

As a result of performing an image evaluation test using the obtained magnetic carriers according to Examples 1 to 7 and Comparative Examples 1 to 5, the following was found.
First, the initial image characteristics were very good or good in Examples 1 to 7 and Comparative Examples 2 and 5. Next, in 1 50K sheets, Examples 1 to 5 and 7 maintained a very good level, but in all of Examples 1 to 5 including Comparative Examples 2 and 5, the levels were reduced to unusable levels. . On the 100K sheet, a part of the level was also lowered in Examples 1 to 7, but it was a sufficiently usable level. On the other hand, in Comparative Examples 1-5, it turned out that it became an unusable level in all the examples, and it turned out that the replacement time has already been exceeded from the time of 50K sheets.

Claims (6)

The true specific gravity is 4.90 to 5.05 g / cm ³ ;
The specific surface area is 0.05 to 0.35 m ² / g;
A carrier core material for an electrophotographic developer, comprising magnetite particles containing 0.01 to 4 wt% of SiO ₂ .   The carrier core material for an electrophotographic developer according to claim 1, wherein the volume porosity is in the range of 3 to 6%.   The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the magnetite particles have an average particle diameter (D50) of 25 to 40 µm. A step of mixing a Fe raw material, a SiO ₂ raw material, and carbon to obtain a slurry having a solid content concentration of 75 wt% or more;
A step of spray-drying the slurry to obtain a granulated product;
Firing the granulated product at a temperature of 960 ° C. or higher and 1130 ° C. or lower to obtain a fired product having a magnetic phase;
A method for producing a carrier core material for an electrophotographic developer, comprising: subjecting the obtained fired product to a pulverization treatment to obtain a powder, and then providing a predetermined particle size distribution.   The carrier for an electrophotographic developer according to any one of claims 1 to 3, wherein the surface of the carrier core material for an electrophotographic developer is coated with a resin.   An electrophotographic developer comprising the carrier for an electrophotographic developer according to claim 5 and a toner.