JP2023145902A - Carrier core material, electrophotographic development career using the same and electrophotographic developer - Google Patents

Abstract

To provide a carrier core having low apparent density and capable of preventing career scattering from being caused.SOLUTION: A carrier core material constituted of ferrite particles includes a composite oxide of a Ca element of 1.7 mass% or more and 6.5 mass% or less and an Si element of 1.4 mass% or more and 5.2 mass% or less. A magnetization σ1k of the ferrite particles when applying a magnetic field of 79.58×103 A/m (1000 oersteds) is 58Am2/kg or more and 75Am2/kg or less; an apparent density is 1.90 g/cm3 or more and 2.20 g/cm3 or less; and a pore volume is less than 0.010 mL/g.SELECTED DRAWING: Figure 1

Description

The present invention relates to a carrier core material, a carrier for electrophotographic development, and a developer for electrophotography using the same.

For example, in image forming devices such as facsimiles, printers, and copiers that use electrophotography, toner is attached to an electrostatic latent image formed on the surface of a photoreceptor to make it visible, and this visible image is transferred to paper. After transferring the image onto a paper, etc., it is fixed by applying heat and pressure. From the viewpoint of high image quality and colorization, so-called two-component developers containing carrier and toner are widely used as developers.

In a developing method using a two-component developer, carrier and toner are stirred and mixed in a developing device, and the toner is charged to a predetermined amount by friction. Then, developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically moved to the photoreceptor via the magnetic brush, forming an electrostatic latent image on the photoreceptor. Visualized. After the toner has been transferred, the carrier is peeled off from the developing roller and mixed with the toner again in the developing device.

In recent years, efforts have been made to save power by reducing the stirring power in developing devices, and to stabilize image quality by suppressing "toner spent" in which toner components fuse to the surface of the carrier. It has been proposed to reduce the weight of the carrier core material by providing a void therein and further filling the internal void with resin (Patent Documents 1 and 2, etc.).

However, although the carrier core material with internal voids has a lower apparent density, it is difficult to control the coating resin that seeps into the internal voids of the carrier core material when coating the surface of the carrier core material with resin. Therefore, variations tend to occur in the amount of resin coated on the surface of the carrier core material. If there is variation in the amount of coating resin, carrier properties will vary and problems such as carrier scattering will likely occur.

In addition, as a method to reduce the apparent density of the carrier core material and improve particle strength, SiO ₂ (silicon dioxide), which has a lower true density than ferrite, which is the main component of the carrier core material, is added as a raw material component of the carrier core material. However, since SiO ₂ easily adsorbs moisture, there are concerns about practical problems such as deterioration of the charging characteristics of the carrier core material in a high temperature and high humidity environment.

JP2016-170224A Japanese Patent Application Publication No. 2009-086093

Therefore, the present invention has been made in view of such conventional problems, and its purpose is to provide a carrier in which toner spent is less likely to occur, the amount of coating resin on the surface of the carrier core material is not varied, and carrier scattering is less likely to occur. The purpose is to provide core material.

Another object of the present invention is to provide a carrier and developer with excellent stability in image quality.

The carrier core material according to the present invention that achieves the above object is a carrier core material composed of ferrite particles, and is a composite oxide of Ca element and Si element (hereinafter referred to as "CaSi composite oxide"). ), contains Ca element 1.7% by mass or more and 6.5% by mass or less, contains Si element 1.4% by mass or more and 5.2% by mass or less, and has a magnetic field of 79.58×10 ³ The magnetization σ _1k of the ferrite particles when A/m (1000 Oe) is applied is in the range of 58 Am ² /kg or more and 75 Am ² /kg or less, and the apparent density is 1.90 g/cm 3 or more and 2.20 g/cm ³ or more. cm ³ or less, and is characterized by a pore volume of less than 0.010 mL/g.

In the carrier core material having the above configuration, it is preferable that the true density of the ferrite particles is in a range of 4.00 g/cm ³ or more and 4.75 g/cm ³ or less.

Further, in the carrier core material having the above configuration, it is preferable that the saturation magnetization σ _S of the ferrite particles is in a range of 67 Am ² /kg or more and 90 Am ² /kg.

Further, in the carrier core material having the above configuration, it is preferable that the residual magnetization σ _r of the ferrite particles is 2.0 Am ² /kg or less, and the coercive force H _c is 20 Oe or less.

Further, in _the carrier core material having the above configuration _, the ferrite particles have a composition represented by the general formula ( _Mn It is preferable that the content is 2.0% by mass or more and 4.0% by mass or less, and the Si element is contained in 2.0% by mass or more and 4.0% by mass or less.

Further, in the carrier core material having the above configuration, it is preferable that the content mass ratio Ca/Si of Ca element to Si element is 0.5 or more and 2.0 or less.

Further, according to the present invention, there is provided a carrier for electrophotographic development, characterized in that the surface of the carrier core material described above is coated with a resin.

Further, according to the present invention, there is provided an electrophotographic developer containing the above-described carrier for electrophotographic development and a toner.

Note that magnetization σ _1k , apparent density, pore volume, true density, saturation magnetization σ _S , residual magnetization σ _r , and coercive force H _c are values measured by the measurement method in Examples described later.

Further, in this specification, "ferrite particles", "carrier core material", "carrier for electrophotographic development", and "toner" each mean an aggregate (powder) of individual particles. In this specification, unless otherwise specified, "~" is used to include the numerical values listed before and after it as lower and upper limits.

According to the carrier core material of the present invention, toner spent is suppressed. Further, the amount of resin coated on the surface of the carrier core material does not vary, and carrier scattering is suppressed.

According to the carrier for electrophotographic development and the developer for electrophotography of the present invention, occurrence of carrier scattering, etc. is suppressed, and images of good image quality can be obtained stably over a long period of time.

These are the XRD measurement results for the carrier core material of Example 7. These are the XRD measurement results for the carrier core material of Example 13. These are the XRD measurement results for the carrier core material of Comparative Example 1. These are the XRD measurement results for the carrier core material of Comparative Example 12. These are the XRD measurement results for the carrier core material of Comparative Example 14. FIG. 1 is a schematic diagram showing an example of a developing device using a carrier according to the present invention.

One of the major features of the carrier core material according to the present invention is that the carrier core material is composed of ferrite particles, the carrier core material contains a CaSi composite oxide, and contains 1.7% by mass or more of Ca element. .5% by mass or less, and 1.4% by mass or more and 5.2% by mass or less of Si element.
As mentioned above, conventionally, in order to lower the apparent density of the carrier core material, SiO ² (true density _: It was proposed that SiO 2 (approximately 2.2 g/cm ³ ) be added as a raw material component of the carrier core material, but since SiO ₂ easily adsorbs moisture, the charging characteristics of the carrier core material may deteriorate in high temperature and high humidity environments. There were some problems such as a drop in performance.
Therefore, the inventors of the present invention have conducted extensive research to find a material that is less susceptible to the effects of the usage environment such as humidity and has a lower true density than ferrite and does not have a significant effect on the charging characteristics of the carrier core material as a substitute for SiO ₂ . . As a result, the present invention was made based on the knowledge that a CaSi composite oxide such as CaSiO ₃ (true density: about 2.9 g/cm ³ ) satisfies the above conditions.

In this specification, the CaSi complex oxide includes complex oxides in the narrow sense composed of Ca (calcium), Si (silicon), and O (oxygen) such as _CaSiO3 , as well as complex oxides in the narrow sense that include Fe. Also included are composite oxides in which metal elements constituting ferrite, such as (iron) and Mn (manganese), are solidly dissolved.

The fact that the CaSi composite oxide is contained in the carrier core material can be confirmed by, for example, powder X-ray diffraction (XRD) measurement and component analysis. Specifically, in the measured X-ray diffraction pattern, a peak of diffraction intensity exists in the range where the incident angle 2θ is 26.60° or more and 27.30° or less, and the component analysis described below shows that the carrier core material is Ca. This can be confirmed from the fact that the element and Si element are contained.

In a narrowly defined composite oxide, a peak of diffraction intensity exists at a position where the incident angle 2θ is 26.84°. Further, in a narrowly defined composite oxide, for example, an oxide in which Fe is dissolved in solid solution, a peak of diffraction intensity exists at a position where the incident angle 2θ is 27.13°. The X-ray diffraction pattern of _the carrier core material of Example 13 shown in FIG. A peak and a diffraction intensity peak derived from an oxide ((Ca,Fe)SiO ₃ ) in which Fe is dissolved in a solid solution in a complex oxide in a narrow sense appear.

Note that the XRD measurement is performed as follows.
(Powder X-ray diffraction (XRD) measurement)
Powder X-ray diffraction measurement of the carrier core material is performed using "Ultima IV" manufactured by Rigaku Corporation. A Cu tube (Kα) is used as the X-ray source, and X-rays are generated under the conditions of an accelerating voltage of 40 kV and a current of 20 mA. Diverging slit opening angle is 1°, scattering slit opening angle is 1°, receiving slit width is 0.3 mm, scanning mode is FT, step width is 0.0100°, counting time is 10 seconds, number of integration is 1, scanning The range is 26.0≦2θ≦27.5.

The CaSi composite oxide is preferably CaSiO ₃ and CaSiO ₃ in which a ferrite constituent metal element such as Fe or Mn is dissolved as a solid solution. It is preferable that the CaSi composite oxide is initially added together with the raw material components of the ferrite, but even if CaSiO ₃ is initially added, some or all of the CaSiO ₃ may form the ferrite due to reactions in the manufacturing process. In some cases, a metal element (such as Fe) is transformed into a composite oxide (for example, (Ca, Fe)SiO ₃ ) in which a metal element (such as Fe) is dissolved. The effects of the present invention can be achieved even with such a composite oxide containing Fe or the like as a solid solution. Note that Ca and Si raw materials may be added and mixed together with the ferrite raw material components so that CaSiO ₃ is synthesized and contained in the ferrite particles in the firing process, but CaSiO ₃ is not a ferrite raw material component. It is preferable that it is initially added together with the above.

The content of Ca element in the carrier core material of the present invention is in the range of 1.7% by mass or more and 6.5% by mass or less. When the content of Ca element is less than 1.7% by mass, the apparent density increases and toner spent tends to occur. On the other hand, if the content of Ca element is more than 6.5% by mass, the magnetization σ _1k becomes low and carrier scattering tends to occur. The content of Ca element is more preferably in the range of 2.0% by mass or more and 4.0% by mass or less.

The content of Si element in the carrier core material of the present invention is in the range of 1.4% by mass or more and 5.2% by mass or less. When the content of Si element is less than 1.4% by mass, the apparent density increases and toner spent tends to occur. On the other hand, if the content of the Si element is more than 5.2% by mass, the magnetization σ _1k becomes low and carrier scattering tends to occur. A more preferable content of Si element is in the range of 2.0% by mass or more and 4.0% by mass or less.

The magnetization σ _1k of the carrier core material of the present invention is in the range of 58 Am ² /kg or more and 75 Am ² /kg or less. When the magnetization σ _1k is lower than 58 Am ² /kg, carrier scattering tends to occur. On the other hand, if the magnetization σ _1k is higher than 75 Am ² /kg, the magnetic brush formed on the outer periphery of the developing roller becomes hard and the density of the magnetic brush becomes low, which may result in an insufficient amount of developer being conveyed to the developing area. There is.

The apparent density of the carrier core material of the present invention is preferably in the range of 1.90 g/cm ³ or more and 2.20 g/cm ³ or less. A more preferable apparent density of the carrier core material is in the range of 1.97 g/cm ³ or more and 2.19 g/cm ³ or less.

The pore volume of the carrier core material of the present invention is less than 0.010 mL/g. If the pore volume is 0.010 mL/g or more, the amount of resin coating the carrier core material will vary and carrier scattering will likely occur. A more preferable pore volume of the carrier core material is in the range of 0.005 mL/g or more and 0.008 mL/g or less.

The true density of the carrier core material of the present invention is preferably in the range of 4.00 g/cm ³ or more and 4.75 g/cm ³ or less. If the true density of the carrier core material is lower than 4.00 g/cm ³ , the proportion of CaSi composite oxide is high, and the magnetization per particle is decreased, which may cause carrier scattering. On the other hand, if the true density is higher than 4.75 g/cm ³ , toner spent may occur. A more preferable true density of the carrier core material is in the range of 4.56 g/cm ³ or more and 4.69 g/cm ³ or less. The true density of the carrier core material can be adjusted mainly by the content of CaSi composite oxide. It can also be adjusted by changing the ferrite composition constituting the carrier core material.

The saturation magnetization σ _s of the carrier core material of the present invention is preferably in the range of 67 Am ² /kg or more and 90 Am ² /kg or less. If the saturation magnetization σ _s is less than 67 Am ² /kg, the magnetization per particle becomes small, which may cause carrier scattering. On the other hand, when the saturation magnetization σ _s exceeds 90 Am ² /kg, the magnetic brush formed on the outer periphery of the developing roller becomes hard, the density of the magnetic brush becomes low, and the amount of developer conveyed to the developing area becomes insufficient. There is a risk. More preferably, the saturation magnetization σ _s is in the range of 70 Am ² /kg or more and 80 Am ² /kg or less.

Further, the residual magnetization σ _r of the carrier core material of the present invention is preferably in a range of 2.0 Am ² /kg or less. If the residual magnetization σ _r exceeds 2.0 Am ² /kg, it may become difficult to separate the carrier from the developing roller. A more preferable residual magnetization σ _r is in the range of 1.5 Am ² /kg or less.

Further, the coercive force H _c of the carrier core material of the present invention is preferably in the range of 20 Oe (20×10 ³ /(4π) A/m) or less. If the coercive force H _c exceeds 20 oersteds, carrier fluidity and charge imparting ability may deteriorate, and toner scattering may easily occur. A more preferable coercive force H _c is in the range of 15 Oersteds or less.

The composition of the ferrite particles constituting the carrier core material according to the present invention is preferably expressed by the compositional formula Mn _X Fe _3-X O ₄ (0<X<3). Preferably, Ca is contained in a range of 2.0% by mass to 4.0% by mass, and Si is contained in a range of 2.0% by mass to 4.0% by mass.

Here, the content mass ratio Ca/Si of Ca element and Si element is preferably in the range of 0.5 or more and 2.0 or less.

The volume average particle diameter (hereinafter sometimes referred to as "average particle diameter") _D50 measured by a laser diffraction particle size distribution analyzer of the carrier core material of the present invention is preferably in the range of 30 μm or more and 50 μm or less, and more preferably Preferably it is in the range of 30 μm or more and 40 μm or less. Further, the cumulative value of particle diameters of 22 μm or less in the volume-based integrated particle size distribution is preferably 1.5% or less. If the cumulative value of particles with a particle diameter of 22 μm or less exceeds 1.5%, carrier scattering may occur.

(Production method)
Although there is no particular limitation on the method for manufacturing the carrier core material of the present invention, the manufacturing method described below is suitable.

First, the raw materials for ferrite, a CaSi composite oxide such as CaSiO ₃ , and, if necessary, conventionally known additives are weighed. Examples of raw materials for ferrite include Fe component raw materials and Mn component raw materials. As the Fe component raw material, Fe ₂ O ₃ and the like are preferably used. MnCO ₃ , Mn ₃ O ₄ and the like are used as raw materials for the Mn component. In addition, since the amount ratio of Fe, Mn, Ca, and Si in the raw materials is almost directly reflected in the composition ratio of each element in the carrier core material, the amounts of each of the Fe component raw material, Mn component raw material, and CaSi composite oxide are , the carrier core material may be adjusted to a desired composition ratio.

Next, the raw materials are introduced into a dispersion medium to prepare a slurry. The CaSi composite oxide may be added to the dispersion medium at this point, or may be mixed into the wet-pulverized slurry described later. Water is suitable as the dispersion medium used in the present invention. The dispersion medium may contain a binder, a dispersant, etc., if necessary, in addition to the above-mentioned calcined raw materials. As the binder, for example, polyvinyl alcohol can be suitably used. The amount of binder to be blended is preferably such that the concentration in the slurry is approximately 0.1% by mass to 2% by mass. Further, as the dispersant, for example, ammonium polycarboxylate, methacrylic acid polymer, etc. can be suitably used. The amount of the dispersant to be blended is preferably such that the concentration in the slurry is approximately 0.1% by mass to 2% by mass. In addition, a reducing agent such as carbon black, a pH adjuster such as ammonia, a lubricant, a sintering accelerator, etc. may be added. The solid content concentration of the slurry is preferably in the range of 50% by mass to 90% by mass. More preferably, it is 60% by mass to 80% by mass. When it is 60% by mass or more, there are few intraparticle pores in the granules, and insufficient sintering during firing can be prevented.

Note that the weighed raw materials may be mixed, pre-calcined and granulated, and then added to a dispersion medium to produce a slurry. The temperature for pre-firing is preferably in the range of 750°C to 1000°C. If it is 750°C or higher, it is preferable because partial ferrite formation occurs during temporary calcination, the amount of gas generated during calcination is small, and solid-solid reactions proceed sufficiently. On the other hand, if the temperature is 1000° C. or lower, sintering during temporary calcination is weak and the raw material can be sufficiently pulverized in the subsequent slurry pulverization step, which is preferable. Generally, CaSiO ₃ can maintain its crystalline state without melting or decomposing in a temperature range of 1540° C. or lower. Furthermore, an atmospheric atmosphere is preferable as the atmosphere during the temporary firing.

Next, the slurry produced as described above is wet-pulverized. For example, wet pulverization is performed for a predetermined period of time using a ball mill or a vibration mill. The average particle size of the raw material after pulverization is preferably 5 μm or less, more preferably 2 μm or less. It is preferable that a vibration mill or a ball mill contain media of a predetermined particle size. Examples of media materials include iron-based chromium steel and oxide-based zirconia, titania, and alumina. The form of the pulverization process may be either continuous or batch. The particle size of the pulverized material is adjusted by the pulverization time, rotation speed, material and particle size of the media used, etc.

By controlling the particle size of the CaSi composite oxide, it is also possible to control the level of residual magnetization σ _r of the carrier core material. After subjecting the slurry containing the dispersion medium and the ferrite component raw material to wet pulverization treatment, a slurry mixed with CaSi composite oxide having an average particle size of 12 μm is obtained, and further operations including spray drying described below are performed. σ _r can be lowered compared to the case where a CaSi composite oxide having an average particle size of less than 12 μm is mixed. Although the mechanism by which σ _r of the carrier core material can be controlled by controlling the particle size of the CaSi composite oxide in this way is currently unknown, the present inventors have discovered that the CaSi composite oxide present inside the carrier core material We speculate that if the average particle size is small, the number of CaSi composite oxide particles in one particle of the carrier core material increases and the number of grain boundaries increases, which inhibits the return of magnetic spin and increases residual magnetization. ing. The upper limit of the average particle size of the CaSi composite oxide is preferably 50% or less of the average particle size of the carrier core material because variation in magnetic force occurs within the particles. More preferably, the average particle size of the CaSi composite oxide is 40% or less of the average particle size of the carrier core material.

The pulverized slurry is then spray dried and granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer, and is sprayed into the atmosphere to form spherical granules. The atmospheric temperature during spray drying is preferably in the range of 100°C to 300°C. As a result, spherical granules with a particle size of 10 μm to 200 μm are obtained. Next, if necessary, the obtained granules are classified using a vibrating sieve to produce granules having a predetermined particle size range.

Next, the granulated material is placed in a furnace heated to a predetermined temperature and fired using a common method for synthesizing ferrite particles, thereby producing ferrite particles. The firing temperature is preferably in the range of 1050°C to 1350°C. More preferably, the temperature is in the range of 1100°C to 1250°C. When the firing temperature is 1050° C. or lower, phase transformation is less likely to occur and sintering is also less likely to proceed. Furthermore, if the firing temperature exceeds 1350° C., excessive sintering may result in generation of excessive grains. Since the ferrite particles of the present invention contain a CaSi composite oxide, if the temperature increase rate is fast, there is a risk that the particles will not be able to maintain their spherical shape due to the difference in shrinkage rate during firing. In particular, the rate of temperature increase from 500°C to the firing temperature is preferably in the range of 100°C/h to 500°C/h. The holding time at the firing temperature is preferably 2 hours or more. The oxygen concentration during heating, firing, and cooling is preferably controlled within the range of 0.05% to 21%.

The fired product thus obtained is granulated if necessary. Specifically, the fired product is pulverized using, for example, a hammer mill. The form of the granulation process may be either continuous or batch. Further, after the disintegration treatment, classification may be performed, if necessary, in order to align the particle size within a predetermined range. As the classification method, conventionally known methods such as wind classification and sieve classification can be used. Further, after primary classification using an air classifier, the particle size may be adjusted to a predetermined range using a vibrating sieve or an ultrasonic sieve. Furthermore, after the classification step, non-magnetic particles may be removed using a magnetic field separator. The volume average particle diameter of the ferrite particles is preferably 30 μm or more and less than 50 μm.

Thereafter, if necessary, the classified ferrite particles may be heated in an oxidizing atmosphere to form an oxide film on the particle surface to increase the resistance of the ferrite particles (high resistance treatment). The oxidizing atmosphere may be an air atmosphere or a mixed atmosphere of oxygen and nitrogen. Further, the heating temperature is preferably in the range of 200°C or more and 800°C or less, and more preferably in the range of 360°C or more and 550°C or less. The heating time is preferably in the range of 0.5 hours or more and 5 hours or less. Note that, from the viewpoint of homogenizing the surface and interior of the ferrite particles, it is desirable that the heating temperature is low. The spinel-type ferrite particles produced as described above are used as the carrier core material of the present invention.

(Carrier for electrophotographic development)
The carrier for electrophotographic development according to the present invention is obtained by coating the surface of the carrier core material produced as described above with a resin.

Conventionally known resins can be used to coat the surface of the carrier core material, such as polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene), etc. ) resins, polystyrene, (meth)acrylic resins, polyvinyl alcohol resins, thermoplastic elastomers such as polyvinyl chloride, polyurethane, polyester, polyamide, and polybutadiene, and fluorosilicone resins.

In order to coat the surface of the carrier core material with a resin, a resin solution or dispersion may be applied to the carrier core material. Solvents for coating solutions include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ether solvents such as tetrahydrofuran and dioxane; ethanol, propanol, and butanol. One or more of alcoholic solvents such as; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; and amide solvents such as dimethylformamide and dimethylacetamide can be used. . The concentration of the resin component in the coating solution is generally in the range of 0.001% by mass to 30% by mass, particularly 0.001% by mass to 2% by mass.

As a method for coating the carrier core material with the resin, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, a dipping method, etc. can be used. Among these, the fluidized bed method is particularly preferred since it allows efficient coating with a small amount of resin. For example, in the case of a fluidized bed method, the amount of resin coating can be adjusted by adjusting the amount of resin solution sprayed and the spraying time.

The particle diameter of the carrier is generally preferably in the range of 30 μm or more and 50 μm or less, particularly in the range of 30 μm or more and 40 μm or less in volume average particle diameter.

(electrophotographic developer)
The electrophotographic developer according to the present invention is made by mixing the carrier prepared as described above and a toner. The mixing ratio of carrier and toner is not particularly limited, and may be appropriately determined based on the developing conditions of the developing device used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass or more and 15% by mass or less. If the toner concentration is less than 1% by mass, the image density becomes too thin, while if the toner concentration exceeds 15% by mass, toner scatters in the developing device, causing toner to stain inside the device or to the background areas such as transfer paper. This is because problems such as adhesion may occur. A more preferable toner concentration is in the range of 3% by mass or more and 10% by mass or less.

As the toner, those manufactured by conventionally known methods such as polymerization method, crushing classification method, melt granulation method, spray granulation method, etc. can be used. Specifically, a binder resin whose main component is a thermoplastic resin containing a coloring agent, a mold release agent, a charge control agent, etc. can be suitably used.

Generally, the particle size of the toner is preferably in the range of 5 μm or more and 15 μm or less, more preferably 7 μm or more and 12 μm or less, as measured by a Coulter Counter volume average particle size.

A modifier may be added to the toner surface if necessary. Examples of the modifier include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, and polymethyl methacrylate. These can be used alone or in combination of two or more.

A conventionally known mixing device can be used to mix the carrier and toner. For example, a Henschel mixer, a V-type mixer, a tumbler mixer, a hybridizer, etc. can be used.

(Developing device)
Although there are no particular limitations on the developing method using the developer of the present invention, a magnetic brush developing method is suitable. FIG. 6 is a schematic diagram showing an example of a developing device that performs magnetic brush development. The developing device shown in FIG. 6 includes a rotatable developing roller 3 that includes a plurality of magnetic poles, and a regulating blade 6 that regulates the amount of developer on the developing roller 3 that is conveyed to the developing section, which are arranged in parallel in the horizontal direction. It is formed between two screws 1 and 2 that agitate and convey the developer in opposite directions, and the developer is transferred from one screw to the other at both ends of both screws. The developer is provided with a partition plate 4 that allows the developer to move and prevents the developer from moving at areas other than both ends.

The two screws 1 and 2 have spiral blades 13 and 23 formed on the shaft portions 11 and 21 at the same inclination angle, and are rotated in the same direction by a drive mechanism (not shown) to remove the developer. Transport in opposite directions. Then, the developer moves from one screw to the other screw at both ends of the screws 1 and 2. As a result, the developer consisting of toner and carrier is constantly circulated and stirred within the device.

On the other hand, the developing roller 3 has a developing magnetic pole N 1 , a conveying magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole _{N 3} as magnetic pole generating means inside a metal cylindrical body with irregularities of several μm on the surface. , a fixed magnet in which five magnetic poles of blade magnetic pole _S2 are arranged in sequence. When the cylindrical body of the developing roller 3 rotates in the direction of the arrow, the developer is pumped up from the screw 1 to the developing roller 3 by the magnetic force of the pumping magnetic pole _N3 . The developer carried on the surface of the developing roller 3 is layer-regulated by the regulating blade 6 and then conveyed to the developing area.

In the developing region, a bias voltage obtained by superimposing an alternating current voltage on a direct current voltage is applied to the developing roller 3 from a transfer voltage power source 8 . The DC voltage component of the bias voltage has a potential between the background potential and the image potential on the surface of the photosensitive drum 5. Further, the background potential and the image potential are potentials between the maximum value and the minimum value of the bias voltage. The peak-to-peak voltage of the bias voltage is preferably in the range of 0.5 kV to 5 kV, and the frequency is preferably in the range of 1 kHz to 10 kHz. Further, the waveform of the bias voltage may be any one such as a rectangular wave, a sine wave, or a triangular wave. As a result, the toner and carrier vibrate in the development area, and the toner adheres to the electrostatic latent image on the photoreceptor drum 5 to perform development.

Thereafter, the developer on the developing roller 3 is transported into the apparatus by the transport magnetic pole _S1 , peeled off from the developing roller 3 by the peeling electrode _N2 , and circulated again within the apparatus by the screws 1 and 2 to be used for development. It is not mixed with developer and stirred. Then, developer is newly supplied from the screw 1 to the developing roller 3 by the pumping pole _N3 .

In the embodiment shown in FIG. 6, the number of magnetic poles built into the developing roller 3 is five, but in order to further increase the amount of movement of the developer in the developing area and to further improve pumping performance, etc. Of course, the number of magnetic poles may be increased to 8, 10, or 12.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way.

(Example 1)
As raw materials, 22.13 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 8.60 kg of Mn ₃ O ₄ (average particle size: 3.4 μm), and 3.42 kg of CaSiO ₃ (average particle size: 12 μm) were used. It was dispersed in 11.40 kg of pure water, and 279.3 g of an ammonium polycarboxylate dispersant was added as a dispersant to prepare a mixture. This mixture was pulverized using a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air at about 140° C. using a spray dryer to obtain dry granules having a particle size of 10 μm to 75 μm. Fine particles with a particle size of 25 μm or less were removed from this granulated product using a sieve.
The granules were placed in an electric furnace and held at 1145° C. for 3 hours to perform firing. The oxygen concentration in the electric furnace was adjusted to be 3000 ppm.
The obtained fired product was granulated using a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 35.9 μm.

The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

Next, the surface of the carrier core material thus obtained was coated with a resin to produce a carrier. Specifically, 450 parts by mass of silicone resin and 9 parts by mass of (2-aminoethyl)aminopropyltrimethoxysilane were dissolved in 450 parts by mass of toluene as a solvent to prepare a coating solution. This coating solution was applied to 50,000 parts by mass of a carrier core material using a fluidized bed coating device, and heated in an electric furnace at a temperature of 300° C. to obtain a carrier. Carriers were obtained in the same manner for the following Examples and Comparative Examples.

The obtained carrier and toner having an average particle diameter of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer. In this case, the carrier and toner were adjusted so that the mass of toner/(mass of toner and carrier)=5/100. Developers were obtained in the same manner for all Examples and Comparative Examples. The obtained developer was evaluated on an actual machine as described below. The evaluation results are shown in Tables 1 and 2. The following examples and comparative examples were also evaluated on actual equipment in the same manner. The evaluation results are shown in Table 2.

(Example 2)
A carrier core material having an average particle diameter of 36.0 μm was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1170° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 3)
A carrier core material having an average particle diameter of 35.6 μm was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1200° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 4)
The carrier core material of Example 3 was held in the air at a temperature of 420° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 5)
A carrier core material having an average particle diameter of 35.7 μm was obtained in the same manner as in Example 1, except that 3.42 kg of CaSiO ₃ (average particle diameter: 5 μm) having different average particle diameters was used as the raw material.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 6)
A carrier core material having an average particle diameter of 35.8 μm was obtained in the same manner as in Example 5 except that the electric furnace temperature in the firing step was changed to 1170° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 7)
The carrier core material of Example 6 was held in the air at a temperature of 420° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Further, FIG. 1 shows an XRD measurement diagram of the carrier core material of Example 7.

(Example 8)
A carrier core material having an average particle size of 34.9 μm was obtained in the same manner as in Example 5 except that the electric furnace temperature in the firing step was changed to 1200° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 9)
The carrier core material of Example 8 was held in the air at a temperature of 400° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 10)
As raw materials, 22.13 kg of Fe ₂ O ₃ (average particle size: 0.6 μm) and 8.64 kg of Mn ₃ O ₄ (average particle size: 3.4 μm) were dispersed in 11.40 kg of pure water, and as a dispersant. A mixture was prepared by adding 279.3 g of an ammonium polycarboxylate dispersant. This mixture was pulverized using a wet ball mill (media diameter: 2 mm), and 3.42 kg of CaSiO ₃ (average particle size: 12 μm) was added to obtain a mixed slurry. A carrier core material was obtained.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 11)
The carrier core material of Example 10 was subjected to oxidation treatment (high resistance treatment) by holding it in the air at a temperature of 420° C. for 1.5 hours.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 12)
A carrier core material having an average particle diameter of 35.9 μm was obtained in the same manner as in Example 10 except that the electric furnace temperature in the firing step was changed to 1170° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 13)
The carrier core material of Example 12 was subjected to oxidation treatment (high resistance treatment) by holding it in the air at a temperature of 400° C. for 1.5 hours.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Further, FIG. 2 shows an XRD measurement diagram of the carrier core material of Example 13.

(Example 14)
A carrier core material having an average particle diameter of 34.3 μm was obtained in the same manner as in Example 10, except that 3.42 kg of CaSiO ₃ (average particle diameter: 5 μm) having different average particle diameters was used as the raw material.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 15)
A carrier core material having an average particle diameter of 35.6 μm was obtained in the same manner as in Example 14 except that the electric furnace temperature in the firing step was changed to 1170° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 16)
A carrier core material having an average particle diameter of 35.1 μm was obtained in the same manner as in Example 14 except that the electric furnace temperature in the firing step was changed to 1200° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Example 17)
The carrier core material of Example 16 was subjected to oxidation treatment (high resistance treatment) by holding it in the air at a temperature of 400° C. for 1.5 hours.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 1)
As raw materials, 24.59 kg of Fe ₂ O ₃ (average particle size: 0.6 μm) and 9.60 kg of Mn ₃ O ₄ (average particle size: 3.4 μm) were dispersed in 11.40 kg of pure water, and as a dispersant. A mixture was prepared by adding 279.3 g of an ammonium polycarboxylate dispersant. This mixture was pulverized using a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air at about 140° C. using a spray dryer to obtain dry granules having a particle size of 10 μm to 75 μm. Fine particles with a particle size of 25 μm or less were removed from this granulated product using a sieve.
The granules were placed in an electric furnace and held at 1110° C. for 3 hours to perform firing. The oxygen concentration in the electric furnace was adjusted to be 3000 ppm.
The obtained fired product was granulated using a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 35.9 μm.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Further, FIG. 3 shows an XRD measurement diagram of the carrier core material of Comparative Example 1.

(Comparative example 2)
A carrier core material having an average particle diameter of 35.9 μm was obtained in the same manner as in Comparative Example 1 except that the electric furnace temperature in the firing step was changed to 1200° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 3)
A carrier core material having an average particle diameter of 35.7 μm was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1110° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 4)
A carrier core material having an average particle diameter of 35.3 μm was obtained in the same manner as in Example 5 except that the electric furnace temperature in the firing step was changed to 1110° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 5)
A carrier core material having an average particle diameter of 35.8 μm was obtained in the same manner as in Example 10 except that the electric furnace temperature in the firing step was changed to 1110° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 6)
A carrier core material having an average particle diameter of 35.3 μm was obtained in the same manner as in Example 14 except that the electric furnace temperature in the firing step was changed to 1110° C.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 7)
The carrier core material of Example 1 was held in the air at a temperature of 400° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 8)
The carrier core material of Example 1 was held in the air at a temperature of 420° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 9)
The carrier core material of Example 14 was subjected to oxidation treatment (high resistance treatment) by holding it in the air at a temperature of 400° C. for 1.5 hours.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 10)
The carrier core material of Example 5 was held in the air at a temperature of 440° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative Example 11)
As raw materials, 34.20 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 13.35 kg of Mn ₃ O ₄ (average particle size: 3.4 μm), and 2.45 kg of CaSiO ₃ (average particle size: 5 μm) were used. It was dispersed in 16.70 kg of pure water, and 408.0 g of ammonium polycarboxylate dispersant was added as a dispersant to prepare a mixture. This mixture was pulverized using a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air at about 140° C. using a spray dryer to obtain dry granules having a particle size of 10 μm to 75 μm. Fine particles with a particle size of 25 μm or less were removed from this granulated product using a sieve.
The granules were placed in an electric furnace and held at 1145° C. for 3 hours to perform firing. The oxygen concentration in the electric furnace was adjusted to be 3000 ppm.
The obtained fired product was granulated using a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 35.0 μm.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 12)
The carrier core material of Comparative Example 11 was held in the air at a temperature of 400° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Further, FIG. 4 shows an XRD measurement diagram of the carrier core material of Comparative Example 12.

(Comparative example 13)
As raw materials, 28.09 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 10.96 kg of Mn ₃ O ₄ (average particle size: 3.4 μm), and 10.95 kg of CaSiO ₃ (average particle size: 5 μm) were used. It was dispersed in 16.70 kg of pure water, and 408.0 g of ammonium polycarboxylate dispersant was added as a dispersant to prepare a mixture. This mixture was pulverized using a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air at about 140° C. using a spray dryer to obtain dry granules having a particle size of 10 μm to 75 μm. Fine particles with a particle size of 25 μm or less were removed from this granulated product using a sieve.
The granules were placed in an electric furnace and held at 1170° C. for 3 hours to perform firing. The oxygen concentration in the electric furnace was adjusted to be 3000 ppm.
The obtained fired product was granulated using a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 35.8 μm.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(Comparative example 14)
The carrier core material of Comparative Example 13 was held in the air at a temperature of 400° C. for 1.5 hours to undergo oxidation treatment (high resistance treatment).
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Further, FIG. 5 shows an XRD measurement diagram of the carrier core material of Comparative Example 14.

(Comparative Example 15)
As raw materials, 14.43 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 4.62 kg of Mn ₃ O ₄ (average particle size: 2 μm), and 1.04 kg of MgO were mixed. This mixture was pelletized using a roller compactor. The obtained pellets were pre-calcined in a rotary kiln at a temperature of 850° C. under atmospheric conditions. The mixture was ground in a dry bead mill for 6 hours to obtain a calcined raw material. The obtained calcined powder was dispersed in 7.12 kg of water, 149.5 g of CaCO ₃ and 219.7 g of an aqueous solution containing 21% methacrylic acid polymer were added, and the mixture was pulverized using a wet ball mill (media diameter 2 mm). A mixed slurry was obtained.
This mixed slurry was sprayed into hot air at about 130° C. using a spray dryer to obtain dry granulated powder. At this time, granulated powder other than the target particle size distribution was removed using a sieve.
This granulated powder was put into an electric firing furnace, and main firing was performed at a temperature of 1110° C. for a holding time of 3 hours. Thereafter, it was cooled for 6 hours at an oxygen concentration of 7500 ppm. The obtained fired product was cracked and classified using a sieve to obtain a carrier core material having an average particle size of 36.2 μm and a proportion of 0.9% having a particle size of 22 μm or less.
The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

(composition analysis)
(Analysis of Fe)
A carrier core material containing iron element was weighed and dissolved in a mixed acid water of hydrochloric acid and nitric acid. After this solution is evaporated to dryness, sulfuric acid water is added to dissolve it again and excess hydrochloric acid and nitric acid are volatilized. Solid Al is added to this solution to reduce all Fe ³⁺ in the solution to Fe ²⁺ . Subsequently, the amount of Fe ²⁺ ions in this solution was quantitatively analyzed by potentiometric titration with a potassium permanganate solution, and the titration amount of Fe (Fe ²⁺ ) was determined.
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed in accordance with the ferromanganese analysis method (potentiometric titration method) described in JIS G1311-1987. The Mn content of the carrier core material described in this specification is the Mn amount obtained by quantitative analysis using this ferromanganese analysis method (potentiometric titration method).
(Analysis of Ca)
The Ca content of the carrier core material was analyzed using the following method. The carrier core material according to the present invention was dissolved in an acid solution and quantitatively analyzed by ICP. The Ca content of the carrier core material described in the present invention is the Ca amount obtained by this quantitative analysis by ICP.
(Analysis of Si)
The Si content of the carrier core material was quantitatively analyzed in accordance with the silicon dioxide gravimetric method described in JIS M8214-1995.

(apparent density AD)
The apparent density of the carrier core material was measured in accordance with JIS Z 2504.

(Flow rate FR)
The fluidity of the carrier core material was measured in accordance with JIS Z 2502.

(Average particle diameter _D50 and ratio of particle diameters of 22 μm or less)
The average particle diameter D ₅₀ of the carrier core material and the volume proportion of particles with a particle diameter of 22 μm or less were measured using a laser diffraction particle size distribution analyzer (“Microtrack Model 9320-X100” manufactured by Nikkiso Co., Ltd.).

(pore volume)
The evaluation device used was POREMASTER-60GT manufactured by Quantachrome. The specific measurement conditions are:
Cell Stem Volume: 0.5cm ³
Headpressure: 20PSIA
Surface tension of mercury: 485.00erg/ ^cm2
Contact angle of mercury: 130.00 degrees
High pressure measurement mode: Fixed Rate
Motor Speed: 1
High pressure measurement range: 20.00~10000.00PSI
Then, 1.500 g of the sample was weighed and filled into a 0.5 cm ³ cell for measurement. Further, the value obtained by subtracting the volume A (cm ³ /g) at 60 PSI from the volume B (cm ³ /g) at 10,000 PSI was defined as the pore volume.

(BET specific surface area)
Examples 1 to 17, Comparative Examples 1 to 12, and Comparative Example 15 were evaluated using a BET single point specific surface area measurement device (manufactured by Mountec Co., Ltd., model: Macsorb HM model-1208). Specifically, 10.000 g of the sample was weighed (8.000 g was used for the carrier core materials of Comparative Examples 13 and 14 because 10.000 g could not be filled into the cell) and filled into a cell with a diameter of 15 mm. The measurement was then carried out at 200°C and degassed for 30 minutes.

(true density)
The true density of the carrier core material was measured using "ULTRA PYCNOMETER 1000" manufactured by Quantachrome.

(Magnetic properties)
Using a vibrating sample magnetometer (VSM) dedicated to room temperature (VSM-P7 manufactured by Toei Kogyo Co., Ltd.), an external magnetic field was applied continuously for one cycle in the range of 0 to 79.58 x 10 ⁴ A/m (10,000 Oe). Magnetization σ _1k , saturation magnetization σ _s , residual magnetization σ _r , and coercive force H _c were measured when a magnetic field of 79.58×10 ³ A/m (1000 Oe) was applied.

(static electrical resistance)
Two 2 mm thick brass plates with electrolytically polished surfaces were arranged as electrodes so that the distance between the electrodes was 2 mm, and 200 mg of carrier core material was inserted into the gap between the two electrode plates. A magnet with a cross-sectional area of 240 mm ² is placed behind the electrode to form a bridge of the powder to be measured between the electrodes, and a DC voltage of 100 V, 500 V, and 1000 V is applied between the electrodes to determine the value of the current flowing through the carrier core material. It was measured by the 4-terminal method. The electrical resistance of the carrier core material was calculated from the current value, the distance between the electrodes of 2 mm, and the cross-sectional area of ²⁴⁰ mm.

(Evaluation of Toner Spent)
A developing device having the structure shown in FIG. 6 was manufactured (peripheral speed v ₁ of the developing roller: 259 mm/sec, circumferential speed v ₂ of the photoreceptor drum: 131 mm/sec, distance between the photoreceptor drum and the developing roller: 0.3 mm). After putting in the two-component developer and driving the developing device for a time equivalent to the time required to print 100k sheets of A4 landscape paper (equivalent time to print 100k sheets), the carrier was extracted from the developer, and it was exposed to a scanning electron microscope ( JSM-6510LA model (manufactured by JEOL Ltd.)), and the number ratio of carriers to which toner was fused to the surface was measured.
"◎": The ratio of the number of carriers to which the toner was fused was less than 0.5%.
"Good": The ratio of the number of carriers to which the toner was fused was 0.5% or more and less than 1.0%.
"Δ": The ratio of the number of carriers to which the toner was fused was 1.0% or more and less than 5.0%.
"x": The ratio of the number of carriers to which the toner was fused was 5.0% or more.

(Evaluation of carrier scattering)
A developing device having the structure shown in FIG. 6 was manufactured (peripheral speed v ₁ of the developing roller: 259 mm/sec, circumferential speed v ₂ of the photoreceptor drum: 131 mm/sec, distance between the photoreceptor drum and the developing roller: 0.3 mm). The number of black spots found in the image area after charging the two-component developer and driving the developing device for a time equivalent to the time required to print 100k sheets of A4 horizontal paper (time equivalent to printing 100k sheets) is α. The number of sunspots found in the background area was set as β, and carrier scattering was evaluated according to the following criteria.
“○”: 0≦α+β≦6 pieces “×”: 7 pieces≦α+β

According to the XRD measurement results in FIG. 1, in the carrier core material of Example 7 to which CaSiO ₃ with an average particle size of 5 μm was initially added, the peak of the diffraction intensity was the same as the peak position of the diffraction intensity of CaSiO ₃ (Ca, Fe). One exists between the peak position of the diffraction intensity of SiO ₃ . This is because during the manufacturing process such as firing of the carrier core material, Fe is dissolved in a part (surface layer) of CaSiO ₃ to form (Ca,Fe)SiO ₃ and the peak position of the diffraction intensity shifts to the higher angle side. considered to be a thing.
Furthermore, according to the XRD measurement results in FIG. 2, the carrier core material of Example 13 to which CaSiO ₃ (average particle size 12 μm) having a larger average particle size than that used in Example 7 was initially added had a peak in diffraction intensity. There are two positions between the peak position of the diffraction intensity of CaSiO ₃ and the peak position of the diffraction intensity of (Ca,Fe)SiO ₃ . This is similar to the carrier core material of Example 7, although Fe is dissolved in a solid solution in a part (surface layer) of CaSiO ₃ , since the average particle size of CaSiO ₃ is large, CaSiO ₃ remains inside the particles, resulting in It is considered that the two diffraction intensity peaks are derived from CaSiO ₃ and (Ca,Fe)SiO ₃ .

As described above, the XRD measurement results show that the carrier core materials of Examples 7 and 13 contain CaSi composite oxides such as CaSiO ₃ and (Ca,Fe)SiO ₃ . Moreover, the XRD measurement results of the carrier core materials of Examples other than Examples 7 and 13 were also similar.

On the other hand, according to the XRD measurement results shown in FIG. 3, in the carrier core material of Comparative Example 1 in which no Ca component raw material or Si component raw material was added as raw material components, the incident angle 2θ was 26.60° or more and 27.30°. No peak of diffraction intensity appeared in the following range. In other words, it can be seen that the carrier core material does not contain CaSi composite oxide because the diffraction intensity does not have a peak in the range of the incident angle 2θ of 26.60° or more and 27.30° or less.

According to the XRD measurement results shown in FIG. 4, in the carrier core material of Comparative Example 12 in which the amount of CaSiO ₃ added as a raw material component is small, the diffraction intensity falls within the range of incident angle 2θ from 26.60° to 27.30°. Although a peak appears, the peak intensity value is low, and it can be seen that the peak position shifts toward the peak position of (Ca,Fe)SiO ₃ . Furthermore, according to the XRD measurement results shown in FIG. 5, the carrier core material of Comparative Example 14, which has a large amount of CaSiO ₃ added as a raw material component, diffracts at an incident angle 2θ in the range of 26.60° to 27.30°. It can be seen that an intensity peak appears and the peak intensity value becomes high.

As is clear from Tables 1 and 2, in the evaluation of toner spent, the carrier core materials of Examples 1 to 17 having the structure of the present invention had a ratio of less than 5.0% of carriers to which toner was fused. There was no problem in actual use, and in the evaluation of carrier scattering, the number of black spots found in the image area and background area was 6 or less, which caused no problem in actual use.

On the other hand, in the carrier core materials of Comparative Examples 1 and 2 that did not contain CaSi composite oxide, the apparent density was as high as 2.39 g/cm ³ and a large amount of toner spent was generated.

In the carrier core materials of Comparative Examples 3 to 6, in which the firing temperature was as low as 1100° C., the pore volume was large and the amount of resin coated on the surface of the carrier core material varied, causing carrier scattering.

The carrier core materials of Comparative Examples 7 to 10, which were subjected to high resistance treatment, had high apparent densities and caused toner spent. In addition, the carrier core material of Comparative Example 10 had a low magnetization σ _1k and carrier scattering occurred.

The carrier core materials of Comparative Examples 11 and 12, which had a small content of CaSi composite oxide, had a high apparent density and generated a large amount of toner spent. On the other hand, in the carrier core materials of Comparative Examples 13 and 14, which had a high content of CaSi composite oxide, the magnetization σ _1k was low and carrier scattering occurred.

In the carrier core material of Comparative Example 15 in which the composition of the carrier core material was MnMg ferrite and did not contain CaSi composite oxide, the pore volume was large, the magnetization σ _1k was low, and carrier scattering occurred.

According to the carrier core material of the present invention, toner spent is suppressed and carrier scattering is also suppressed.

3 Developing roller 5 Photosensitive drum

Claims (8)

A carrier core material composed of ferrite particles,
Contains a composite oxide of Ca element and Si element,
Contains Ca element from 1.7% by mass to 6.5% by mass,
Contains Si element from 1.4% by mass to 5.2% by mass,
The magnetization σ _1k of the ferrite particles when a magnetic field of 79.58×10 ³ A/m (1000 Oe) is applied is in the range of 58 Am ² /kg or more and 75 Am ² /kg or less,
The apparent density is in the range of 1.90 g/cm ³ or more and 2.20 g/cm ³ or less,
A carrier core material having a pore volume of less than 0.010 mL/g. The carrier core material according to claim 1, wherein the true density of the ferrite particles is in the range of 4.00 g/cm ³ or more and 4.75 g/cm ³ or less. The carrier core material according to claim 1 or 2, wherein the ferrite particles have a saturation magnetization σ _S of 67 Am ² /kg or more and 90 Am ² /kg or less. The residual magnetization σ _r of the ferrite particles is 2.0 Am ² /kg or less,
The carrier core material according to any one of claims 1 to 3, which has a coercive force H _c of 20 Oe or less. The ferrite particles have a composition represented by the general formula (Mn _x Fe _3-X )O ₄ (where 0<X<3) as a main component,
Contains Ca element from 2.0% by mass to 4.0% by mass,
The carrier core material according to any one of claims 1 to 4, containing 2.0% by mass or more and 4.0% by mass or less of Si element. The carrier core material according to any one of claims 1 to 5, wherein the content mass ratio Ca/Si of Ca element and Si element is 0.5 or more and 2.0 or less. A carrier for electrophotographic development, characterized in that the surface of the carrier core material according to any one of claims 1 to 6 is coated with a resin. An electrophotographic developer comprising the carrier for electrophotographic development according to claim 7 and a toner.