JP2009086340A - Carrier core material for electrophotographic developer and manufacturing method therefor, carrier for electrophotographic developer, and electrophotographic developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier core material for a two components type electrophotographic developer excellent also in mechanical strength, while having sufficient surface irregularity enough to obtain high adhesiveness when coating resin. <P>SOLUTION: This carrier core material uses, as a core material, a magnetic particle having 8.0 or more to 30.0 or less of value of BET specific surface area/true-sphere equivalent specific surface area, 0.050 μm or less of surface coarseness Ra value measured by reflection electron image analysis in a scanning electron microscope, and 2.40 g/cc or more of apparent density, by precipitating fine structure on a particle surface. The carrier core material is obtained by heat-treating rollingly the magnetic particle in a temperature range within 600°C-1000°C under a high reducing atmosphere. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  The role of the carrier for the electrophotographic developer in the two-component electrophotographic development method is to provide charge to the toner by mixing and stirring with the toner in the developing device, and to use the toner as a carrier. It is to be transported up. The carrier after the toner conveyance remains on the magnet roll and is mixed with the toner again in the developing device. For this reason, the carrier is required to have charging characteristics that impart a desired charge to the toner and durability that can withstand repeated use.

  In general, a carrier for a two-component electrophotographic developer (which may be simply referred to as “carrier” in the present invention) is a magnetic material such as magnetite in order to ensure the above-described charging characteristics and durability. It is used in the form of a particle core material (in the present invention, sometimes described as “carrier core material”) coated with a resin. However, when the electrophotographic developer is used for a long period of time, the carriers are repeatedly contacted in the developing device, so that the resin coated on the carrier is worn or peeled off. As a result of this wear and peeling, there is a problem that the charge imparting ability of the carrier is lowered, so that the image quality of the developed electrophotography is deteriorated and it is difficult to obtain stable development characteristics over a long period of time.

  For this problem, particles having moderate irregularities on the surface are used as the carrier core material, and the coated resin is soaked into the concave portion of the carrier core material, thereby improving the adhesion between the carrier core material and the resin, It has been proposed to improve durability. For example, Patent Document 1 describes a carrier core material in which the ratio of the specific surface area of the core material to the true sphere equivalent specific surface area of the core material is 1.6 to 4.0.

JP 2002-207323 A

  However, according to the results of the study by the present inventors, the durability of the carrier coated with the resin according to the prior art including Patent Document 1 is insufficient, and the charging characteristics deteriorate due to long-term use. Confirmed to do. Therefore, the present inventors considered to further increase the surface area of the carrier core material in order to improve the durability. Here, since the magnetic particles used as the carrier core material are generally manufactured by a firing method, it is conceivable to lower the firing temperature in order to increase the surface area of the carrier core material. However, if the firing temperature is lowered in order to increase the surface area of the carrier core material, the progress of the sintering becomes insufficient, and a large number of pores remain inside and on the surface of the carrier core material particles. And in such a porous carrier core material in which a large number of pores remain inside and on the surface, it has been found that cracks generated by impact propagate through the pores. That is, cracking and chipping occur during carrier stirring in the developing device, and there is a problem in mechanical strength.

  The present invention has been made under the above-described circumstances, and uses a carrier core material having high adhesion to a resin despite the absence of pores that cause a decrease in particle strength, and the carrier core material. It is to provide a carrier and an electrophotographic developer.

  In order to solve the above-mentioned problems, the present inventors have conducted research, and a method of forming an extremely fine structure on the surface of the carrier core material while sufficiently increasing the apparent density by sufficiently proceeding with the sintering. As a result, the present invention was completed.

That is, the first invention for solving the above-described problem is:
A carrier core material for an electrophotographic developer,
When the specific surface area of the carrier core material measured by the BET method is the BET specific surface area, and the specific surface area when the carrier core material is assumed to be a true sphere is the true sphere equivalent specific surface area, [BET specific surface area] / [ True spherical equivalent surface area] is 8.0 or more and 30.0 or less,
The value of the surface roughness Ra measured by reflection electron image analysis with a scanning electron microscope is 0.050 μm or less,
It is a carrier core material for an electrophotographic developer characterized by having an apparent density of 2.40 g / cc or more.

The second invention is
The carrier core material for an electrophotographic developer according to the first invention, wherein a value of σ1000, which is a magnetic susceptibility in an external magnetic field of 1000 Oe, is 20 emu / g or more and 75 emu / g or less.

The third invention is
The carrier core material for an electrophotographic developer according to the first or second invention, wherein the main component is magnetite or manganese ferrite.

The fourth invention is:
The carrier core material for an electrophotographic developer according to any one of the first to third inventions, wherein the average particle size is 15 μm or more and 80 μm or less.

The fifth invention is:
The carrier core for an electrophotographic developer according to any one of the first to fourth inventions, wherein the rate of decrease in the charge amount after stirring for 24 hours is 10% or less of the initial charge amount. It is a material.

The sixth invention is:
A surface treatment method for a magnetic powder, characterized in that the magnetic powder is heat-treated in an atmosphere having an oxygen partial pressure of 10 ⁻¹⁰ MPa or less while rolling in a temperature range of 600 ° C. to 1000 ° C.

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

The eighth invention
An electrophotographic developer comprising the carrier for an electrophotographic developer according to the seventh invention and a toner.

  The carrier for an electrophotographic developer using the carrier core material according to the present invention has high adhesion between the carrier core material and the resin, and the carrier core material has high particle strength, so that repeated electrophotographic development over a long period of time. Demonstrate durability.

  The carrier core material according to the present invention has the specific surface area of the carrier core material measured by the BET method as the BET specific surface area, and the specific surface area when the carrier core material is assumed to be a true sphere is the true sphere equivalent specific surface area. In this case, the value of [BET specific surface area] / [true spherical equivalent surface area] is 8.0 or more and 30.0 or less. That is, the carrier core material according to the present invention has an extremely wide specific surface area corresponding to 8 to 30 times the true sphere equivalent surface area. That is, the carrier core material according to the present invention has a large number of uneven structures on the surface.

  Although the carrier core material according to the present invention has a very wide specific surface area corresponding to 8 to 30 times its true sphere equivalent surface area, the surface was measured by reflection electron image analysis with a scanning electron microscope. The value of roughness Ra is 0.050 μm or less. That is, there is no large unevenness on the surface of the carrier core material according to the present invention. A method for measuring the surface roughness Ra by reflection electron image analysis of a scanning electron microscope will be described later.

From the evaluation result obtained from the measurement result of the BET method that there are many uneven structures on the surface and the evaluation result obtained from the measurement result of the scanning electron microscope that there is no large unevenness on the surface, the present invention It is considered that the surface of the carrier core material according to the present invention has an extremely fine uneven structure when viewed microscopically and has a flat shape when viewed macroscopically as the entire carrier core material.
And since the carrier core material according to the present invention improves the adhesion with the resin by the extremely fine uneven structure, the carrier and the electrophotographic developer according to the present invention can exhibit high durability. it is conceivable that. On the other hand, since the carrier core material according to the present invention has a flat structure as a whole, there is a portion that is likely to cause cracking and chipping of particles when carriers collide with each other in the developing device. It does not exist, and it is thought that high image characteristics can be maintained.
Furthermore, the apparent density of the carrier core material according to the present invention is 2.40 g / cc or more. That is, the carrier core material has almost no pores inside and on the surface of the particles. Therefore, from this point of view, it is considered that the mechanical strength is strong, and when the carriers collide with each other in the developing device, cracking and chipping of the particles hardly occur and high image characteristics can be maintained.

The magnetic particles serving as the carrier core material according to the present invention have a value of σ1000, which is a magnetic susceptibility in an external magnetic field of 1000 Oe, of 20 emu / g or more and 75 emu / g or less. When the magnetic susceptibility is 20 emu / g or more, the magnetic attractive force for forming the magnetic brush can be secured, so that the carrier scattering phenomenon does not occur.
On the other hand, when the magnetic susceptibility is 75 mu / g or less, it can be avoided that the magnetic brush formed on the magnet roll poses a risk of damaging the photoreceptor.

  The composition of the magnetic particles is not particularly limited as long as the magnetic susceptibility is satisfied, but magnetite or manganese ferrite is particularly preferable. These materials are preferable because they have an appropriate magnetic susceptibility and a small residual magnetization.

  The particle diameter of the carrier core material according to the present invention is preferably 15 μm or more and 80 μm or less. This is because if the particle size is 15 μm or more, the magnetization per particle can suppress carrier scattering, and if the particle size is 80 μm or less, deterioration of image characteristics can be avoided.

In the carrier core material according to the present invention, the reduction rate of the charge amount after stirring for 24 hours is 10% or less of the initial charge amount. In general, the carrier is agitated for a long time in the developing machine, whereby the resin coat described later is peeled off and the charge amount is lowered. Such deterioration of the charge amount causes a change in the developed image quality, so that it is difficult to obtain a stable image quality over a long period of time. In this regard, since the carrier core material according to the present invention has a large number of extremely fine irregularities on the surface as described above, it is possible to improve the adhesion between the core material and the resin. In order to improve the adhesion between the core material and the resin, it is considered that the reduction rate of the charge amount after stirring for 24 hours can be suppressed to 10% or less of the initial charge amount.

  In addition, the carrier core material according to the present invention is preferably used as a carrier for electrophotographic development by coating a silicone resin or the like for imparting chargeability and improving durability. The coating method may be performed by a known method.

  Hereinafter, the manufacturing method of the carrier core material according to the present invention will be described. A method for producing a carrier core material according to the present invention is as follows. 1. Granulation step of precursor particles. 2. a firing step for obtaining a magnetic phase; 3. Surface treatment process for generating fine irregularities on the surface. 4. Preparation of carrier core material according to the present invention; The carrier according to the present invention, the preparation of an electrophotographic developer, and each step will be described separately.

1. Granulation Step of Precursor Particles A known granulation method may be used to obtain particles serving as a precursor of the carrier core material according to the present invention, but a spray drying method is particularly preferably used. When granulation is performed by spray drying, precursor particles having a desired particle size distribution can be obtained by mixing and dispersing raw material powder in water to form a slurry, and then spraying the slurry in dry air.

  Specifically, it is preferable to adjust the solid content concentration of the slurry between 50% and 90%. In order to maintain the particle shape of the granulated product, it is effective to add an appropriate binder to water as the medium liquid. As the binder, for example, polyvinyl alcohol can be preferably used, and the concentration in the medium liquid may be about 0.5 to 2.0% by mass. Further, a dispersant is generally added to the slurry. As the dispersant, for example, an ammonium polycarboxylate-based one can be preferably used, and the concentration in the medium liquid may be about 0.5 to 2.0% by mass. Furthermore, phosphorus, boric acid or the like can be added as a sintering accelerator to the lubricant or the slurry.

As the raw material powder, for example, in the production of magnetite, metal Fe, Fe ₃ O ₄ , Fe ₂ O _{3 and the} like are preferably used. In the case of manganese ferrite, the metals Fe, Fe ₃ O ₄ and Fe ₂ O _{3 as} Fe sources and the metals Mn, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ and MnCO _{3 as} Mn sources are predetermined. It is better to weigh and mix so that

2. Firing step for obtaining a magnetic phase Next, the precursor particles obtained by granulation are fired to obtain a magnetic phase. Firing is performed by putting the granulated powder into a heated furnace and heating it for a predetermined time. The firing temperature may be set to a temperature range in which the target magnetic phase is generated. For example, when producing magnetite or soft ferrite, firing is generally performed in a temperature range of 1000 to 1300 ° C. As the firing furnace, a general heating furnace such as an electric furnace may be used.

3. Surface treatment step for generating fine irregularities on the surface In order to obtain the surface shape of the carrier particles according to the present invention, the obtained fired product is subjected to a strong reducing atmosphere, preferably an oxygen partial pressure of 10 ⁻¹⁰ , following the above-described firing step. Heat treatment is performed by rolling in a temperature range of 600 ° C. to 1000 ° C. in a furnace adjusted to atm or lower.
Therefore, as the heating furnace, a rotary furnace capable of rolling the obtained fired product is used. As a result, a surface treatment for generating fine irregularities on the surface of carrier particles described later can be performed. Specifically, a rotary kiln capable of rotating at about 0.5 rpm to 10 rpm and controlling the atmosphere during firing is preferable.
The strong reducing atmosphere is prepared by flowing a reducing gas such as carbon monoxide or hydrogen, or a mixed gas of the reducing gas and an inert gas such as nitrogen or argon into the furnace. Alternatively, a reducing agent such as carbon may be introduced into the furnace during the surface treatment process.
As a result of the study by the present inventors, if the furnace temperature at the time of the surface treatment process is 600 ° C. or more, a surface shape having a fine structure, which is a feature of the present invention, is obtained, and the furnace temperature is 1000 ° C. or less. If there is, sintering between particles and adhesion to the furnace wall do not occur.
Further, by performing the heat treatment while rolling the heating furnace, it is possible to uniformly form a fine surface structure of particles, and to reduce processing variations.

4). Preparation of carrier core material according to the present invention The carrier core material according to the present invention having a desired particle size distribution can be obtained by classifying the particles after the surface treatment step with a sieve.

5. Preparation of carrier and electrophotographic developer according to the present invention Coating the carrier core material according to the present invention with a resin imparts chargeability and improves durability. A silicone resin or the like is used as the coating resin. The coating method may be performed by a known method. As a result, the carrier according to the present invention can be obtained.
Furthermore, the electrophotographic developer according to the present invention can be obtained by mixing the carrier according to the present invention and an appropriate toner.

"Measuring method"
Hereafter, the measuring method of each characteristic value performed in a present Example and the comparative example is shown.
<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). In the present invention, the value of D50, which is the cumulative particle diameter up to a volume ratio of 50%, is described as the average particle diameter of the powder.

<Magnetic properties>
The magnetic properties of the carrier core material were measured by measuring the magnetic susceptibility using VSM (manufactured by Toei Industry Co., Ltd., VSM-P7) and measuring the magnetic susceptibility σ1000 (emu / g) in an external magnetic field of 1000 Oe.

<Apparent density>
The apparent density of the carrier core material was measured according to JIS-Z2504: 2000.

<Specific surface area>
The specific surface area of the carrier core material was measured on a sample deaerated at 200 ° C. for 15 minutes using a Macsorb (model-1201) manufactured by Mountec. Nitrogen was used as the adsorption gas.

<Surface roughness>
The surface irregularities of the particles are measured using a field emission scanning electron microscope (FE-SEM: S-4700 manufactured by Hitachi) and a three-dimensional shape measuring apparatus attached thereto (RD-500w manufactured by Hitachi, Ltd.). The value of arithmetic surface roughness Ra was calculated by analyzing the backscattered electron image observed by the electron detector.
The value of the surface roughness Ra is an average value of the surface roughness of 50 carrier core particles.
The characteristic value reflecting the surface state was a surface factor constituted by a roughness parameter. However, it was set to W60.
The measurement conditions were an acceleration voltage of 3 kV, a current of 20 μA, and a W.V. D. 12 mm, objective aperture 2, Cond Lens 1: 5, and measurement magnification of 5000 times.

<Charge amount measurement>
For the measurement of the charge amount, a carrier and toner were put in a glass bottle, and this was stirred for 30 minutes by a shaker. After the stirring, the toner is removed by sucking on a 400-mesh sieve screen at a suction pressure of 8.0 kPa for 1 minute, and the charge amount (Q) of the remaining carrier is measured. The charge amount per weight Charge amount ( μC / g) = Q (μC) / M (g)
Was calculated. Where M is the weight of the carrier.

<Durability evaluation>
As for the durability of the carrier, stirring with a shaker is carried out for 24 hours, and externally, the same operation as the charge amount measurement is performed, the charge amount of the carrier after stirring is measured, and compared with the initial charge amount. It was evaluated by.

Example 1
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 wet ball mill (media diameter 2 mm) ) To obtain a mixed slurry of Fe ₂ O ₃ and Mn ₃ O ₄ . Note that 60 g of ammonium polycarboxylate dispersant was added to the pure water as a dispersant. This mixed slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 to 100 μm.
The dried granulated product was put into an electric furnace and fired at 1150 ° C. for 3 hours to obtain a fired product. The obtained fired product was pulverized and classified using a sieve to obtain a ferrite powder having an average particle size of 36 μm.
Furthermore, 1.0 wt. % Was added to a rotary kiln and heat-treated at 800 ° C. for 1 hour while rolling in a nitrogen gas flow atmosphere to obtain a carrier core material according to Example 1.
Next, in order to evaluate the adhesiveness of the carrier core material to the resin, the carrier core material according to Example 1 was coated with a resin to produce the carrier according to Example 1.
The carrier core material and the resin solution are introduced into a stirrer at a mass ratio of carrier core material: resin solution = 95: 5, and the carrier core material is immersed in the resin solution for 3 hours in a range of 150 to 250 ° C. Stir with heating. As the resin solution, a silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR251) was dissolved in toluene. Thereby, the coating was performed at a ratio of 0.5 part by mass of resin to 100 parts by mass of the carrier core material. The resin-coated carrier core material was heated at 250 ° C. for 5 hours with a hot-air circulating heating device to cure the resin coating layer, whereby the magnetic carrier according to Example 1 was obtained.

The carrier core material according to Example 1 has an average particle diameter of 27.2 μm, an apparent density of 2.44 g / cc, a BET specific surface area of 1.03 m ² / g, and a true spherical equivalent specific surface area of 0.044 m ² / g. [BET specific surface area] / [true sphere equivalent specific surface area] was 23.4, Ra was 0.042 μm, and σ1000 was 61.0 emu / g.
Furthermore, the initial charge amount of the carrier according to Example 1 was 28.3 μC / g, the charge amount after 24 hours was 26.9 μC / g, and the rate of decrease in charge amount after 24 hours was 4.9%. .

Example 2
The same operations as in Example 1 were performed on the sintered ferrite powder except that heat treatment was performed at 900 ° C., and the carrier core material and carrier according to Example 2 were obtained.
The carrier core material according to Example 2 has an average particle diameter of 28.4 μm, an apparent density of 2.42 g / cc, a BET specific surface area of 0.68 m ² / g, and a true spherical equivalent specific surface area of 0.042 m ² / g. [BET specific surface area] / [true sphere equivalent specific surface area] was 16.2, Ra was 0.027 μm, and σ1000 was 52.7 emu / g.
Furthermore, the initial charge amount of the carrier according to Example 2 was 27.6 μC / g, the charge amount after 24 hours was 25.9 μC / g, and thus the rate of decrease in charge amount after 24 hours was 6.2%. It was.

<< Comparative Example 1 >>
The sintered core powder was subjected to the same operation as in Example 1 except that no heat treatment was performed, and the carrier core material and carrier according to Comparative Example 1 were obtained.
The carrier core material according to Comparative Example 1 has an average particle diameter of 27.4 μm, an apparent density of 2.32 g / cc, a BET specific surface area of 0.06 m ² / g, and a true sphere equivalent specific surface area of 0.044 m ² / g. [BET specific surface area] / [true sphere equivalent specific surface area] was 1.36, Ra was 0.017 μm, and σ1000 was 71.3 emu / g.
Further, the initial charge amount of the carrier according to Comparative Example 1 was 27.9 μC / g, the charge amount after 24 hours was 22.4 μC / g, and thus the rate of decrease in charge amount after 24 hours was 19.7%. It was.

<< Comparative Example 2 >>
A carrier core material and a carrier according to Comparative Example 2 were obtained by performing the same operation as in Comparative Example 1 except that the firing temperature was 950 ° C.
The carrier core material according to Comparative Example 2 has an average particle diameter of 27.4 μm, an apparent density of 2.18 g / cc, a BET specific surface area of 0.58 m ² / g, and a true sphere equivalent specific surface area of 0.044 m ² / g. [BET specific surface area] / [true sphere equivalent specific surface area] was 13.2, Ra was 0.025 μm, and σ1000 was 55.0 emu / g.
Furthermore, the initial charge amount of the carrier according to Comparative Example 2 was 27.8 μC / g, the charge amount after 24 hours was 14.5 μC / g, and thus the rate of decrease in charge amount after 24 hours was 47.8%. It was.

Example 3
10.0 kg of Fe ₂ O ₃ (average particle size: 0.6 μm) was dispersed in 3.0 kg of pure water and pulverized by a wet ball mill (media diameter: 2 mm) to obtain a slurry of Fe ₂ O ₃ . Note that 60 g of ammonium polycarboxylate dispersant was added to the pure water as a dispersant. This slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 to 100 μm.
This dried granulated product was put into an electric furnace and fired at 1180 ° C. for 3 hours to obtain a fired product. The fired product obtained was pulverized and classified using a sieve to obtain a magnetite powder having an average particle size of 35 μm.
Furthermore, 1.0 wt. The carrier core material and carrier according to Example 3 were obtained by adding to the rotary kiln and performing heat treatment at 800 ° C. for 1 hour while rolling in a nitrogen gas flow atmosphere.
The average particle size of the carrier core material according to the third embodiment 30.2Myuemu, apparent density 2.45 g / cc, BET specific surface area of 0.98 m ² / g, sphericity equivalent specific surface area of 0.038 m ² / g, therefore [BET specific surface area] / [true sphere equivalent specific surface area] was 25.8, Ra was 0.044 μm, and σ1000 was 55.2 emu / g.
Furthermore, the initial charge amount of the carrier according to Example 3 was 29.0 μC / g, the charge amount after 24 hours was 27.4 μC / g, and thus the rate of decrease in charge amount after 24 hours was 5.5%. It was.

<Summary>
Example 1 in FIG. 1, Example 2 in FIG. 2, Example 3 in FIG. 3, Comparative Example 1 in FIG. 4, and FIG. 5 shows an SEM photograph (1000 × magnification) of the carrier core material according to Comparative Example 2. FIG. 6 shows an FE-SEM photograph (5000 times magnification) of the carrier core material according to Example 1. FIG.
A general carrier core material according to the prior art has a particle shape in which several grains are aggregated as shown in FIG. 4, and the grain portion is relatively smooth. On the other hand, the carrier core material according to the present invention has a fine precipitate on the particle surface and a very large surface irregularity as seen in FIGS. 1 to 3 and 6, and has a specific surface area as described later. Is getting bigger.
On the other hand, the carrier core material according to Comparative Example 2 shown in FIG. 5 is a carrier core material having a specific surface area equivalent to that of the carrier core material according to the present invention by the “reduction in firing temperature” which is a manufacturing method according to the prior art. It is manufactured. However, it can be seen that the carrier core material according to Comparative Example 2 is not sufficiently sintered and is in the form of porous particles.
In addition, this inventor measured Ra value of Example 1 from FIG. The same applies to the following examples and comparative examples.

Table 1 is a list of characteristic values of the carrier core materials according to Examples 1 to 3 and Comparative Examples 1 and 2.
Here, the carrier core materials according to Examples 1 and 2 and Comparative Example 1 are the same up to the firing step for obtaining manganese ferrite as a magnetic phase, but in terms of the condition and the presence or absence of surface modification by the subsequent heat treatment Is different. Compared with the carrier core material according to Comparative Example 1 in which the surface modification treatment by heat treatment was not performed, the carrier core materials according to Examples 1 and 2 that were subjected to the treatment had a specific surface area 10 to 15 times. Thus, the difference in particle shape seen in the SEM image is reflected.
Moreover, Example 3 is a result of the carrier core material whose magnetic phase is magnetite. From the results, by performing the heat treatment according to the present invention, even if the magnetic phase is magnetite, a fine precipitate is generated on the particle surface in the same manner as in Examples 1 and 2, and the surface unevenness is very large, It shows that the specific surface area can be increased.

  On the other hand, although the carrier core material according to Comparative Example 2 has the same specific surface area as the carrier core material according to the present invention without performing the heat treatment according to the present invention, the apparent density is low. This indicates that a large number of pores exist in the particles of the carrier core material according to Comparative Example 2.

Table 1 shows the results of the initial charge amount measurement and the charge amount measurement after stirring for 24 hours for the carriers according to the carrier core materials of Examples 1 to 3 and Comparative Examples 1 and 2, together with the carrier core characteristics. It was described in.
As is clear from the results in Table 1, the carrier particles according to Examples 1 to 3 showed little decrease in the charge amount after stirring for 24 hours, and as a result of shape observation, almost no cracking or chipping of the particles was observed.
From these results, the carrier particles according to Examples 1 to 3 have extremely fine adhesion on the surface because the carrier core material has a fine structure on the surface, and in addition, the apparent density is high and there are almost no pores. This is thought to support the superior mechanical altitude.

  In contrast to the results of the above examples, the carrier according to Comparative Example 1 has a greatly reduced charge amount after stirring for 24 hours compared to the initial value. Further, from the observation of the surface of the carrier after stirring, exposure of the core material portion, which is considered to be caused by wear and peeling of the coating resin, was observed. From this, it is considered that the carrier according to Comparative Example 1 has low adhesion between the resin and the carrier core material because the surface area of the carrier core material is small and the surface unevenness is small.

  Further, in the carrier according to Comparative Example 2 in which the surface unevenness was increased by lowering the firing temperature, the charge amount after 24 hours of stirring was significantly reduced, indicating that the durability was deteriorated. Such a deterioration in the durability of the carrier is considered to be a cause of significant damage to the image characteristics, which is not preferable.

2 is an SEM photograph of a carrier core material according to Example 1. 4 is a SEM photograph of a carrier core material according to Example 2. 4 is a SEM photograph of a carrier core material according to Example 3. 4 is a SEM photograph of a carrier core material according to Comparative Example 1. 4 is a SEM photograph of a carrier core material according to Comparative Example 2. 2 is an FE-SEM photograph of a carrier core material according to Example 1.

Claims (8)

A carrier core material for an electrophotographic developer,
When the specific surface area of the carrier core material measured by the BET method is the BET specific surface area, and the specific surface area when the carrier core material is assumed to be a true sphere is the true sphere equivalent specific surface area, [BET specific surface area] / [ True spherical equivalent surface area] is 8.0 or more and 30.0 or less,
The value of the surface roughness Ra measured by reflection electron image analysis with a scanning electron microscope is 0.050 μm or less,
A carrier core material for an electrophotographic developer, which has an apparent density of 2.40 g / cc or more.   2. The carrier core material for an electrophotographic developer according to claim 1, wherein a value of σ1000 which is a magnetic susceptibility in an external magnetic field of 1000 Oe is 20 emu / g or more and 75 emu / g or less.   The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the main component is magnetite or manganese ferrite.   The carrier core material for an electrophotographic developer according to any one of claims 1 to 3, wherein the average particle size is 15 µm or more and 80 µm or less.   The carrier core material for an electrophotographic developer according to any one of claims 1 to 4, wherein the rate of decrease in the charge amount after stirring for 24 hours is 10% or less of the initial charge amount. A surface treatment method of a magnetic powder, characterized in that the magnetic powder is heat-treated in an atmosphere having an oxygen partial pressure of 10 ⁻¹⁰ MPa or less while rolling in a temperature range of 600 ° C. to 1000 ° C.   A carrier for an electrophotographic developer, wherein the core material according to any one of claims 1 to 5 is coated with a resin.   An electrophotographic developer comprising the carrier for an electrophotographic developer according to claim 7 and a toner.