JP2022071924A - Carrier core material - Google Patents

Abstract

To provide a carrier core material that can suppress a development memory and the concentration unevenness of an image.SOLUTION: The carrier core material is formed of ferrite particles represented by a composition formula (MnO)x(MgO)y(Fe2O3)z (x denotes a value in the range of 30 mol% to 55 mol%, both inclusive, y denotes a value of 20 mol% or smaller, and z denotes a value in the range of 40 mol% to 60 mol%, both inclusive, and x+y+z=100 mol%). Ca is contained in the range of 0.1 mol% to 1.0 mol%, both inclusive, and Zr is included in the range of 0.1 mol% to 1.0 mol%, both inclusive.SELECTED DRAWING: Figure 1

Description

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

For example, in an image forming apparatus such as a facsimile, a printer, or a copier using an electrophotographic method, toner is attached to an electrostatic latent image formed on the surface of a photoconductor to make a visible image, and this visible image is printed on paper. After transferring to, etc., it is fixed by heating and pressurizing. From the viewpoint of high image quality and colorization, a so-called two-component developer containing a carrier and a toner is widely used as a developer.

In a developing method using a two-component developer, the carrier and toner are stirred and mixed in a developing device, and the toner is charged to a predetermined amount by friction. Then, a developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically transferred to the photoconductor via the magnetic brush to obtain an electrostatic latent image on the photoconductor. Visualize. After the toner is transferred, the carrier is peeled off from the developing roller and mixed with the toner again in the developing apparatus. Therefore, as the characteristics of the carrier, the magnetic characteristics for forming the magnetic brush, the charging characteristics for imparting a desired charge to the toner, and the durability in repeated use are required.

As such a carrier, one in which the surface of magnetic particles (carrier core material) such as magnetite or various ferrites is coated with a resin is generally used. However, when a resin-coated carrier in which the surface of the carrier core material is coated with resin is mixed with toner to form a two-component developer, the image density is reduced due to the influence of the image one round before the developing roller. There was a problem called ".

It is presumed that this developing memory is caused by the high electrical resistance of the resin-coated carrier, and as one of the countermeasures, for example, in Patent Document 1, the shape of the carrier core material is set as a specific shape, and the resin-coated carrier is used. A technique has been proposed in which the carrier core material is exposed from the surface at a predetermined ratio to suppress the development memory. Further, Patent Document 2 proposes a technique of incorporating Sr (strontium) to form minute irregularities on the surface of particles of a carrier core material.

Japanese Unexamined Patent Publication No. 2010-256759 Japanese Unexamined Patent Publication No. 2012-159642

However, when added to Sr in the carrier core material, an oxide having the composition SrFe ₁₂ O ₁₉ precipitates. Since the oxide has a high residual magnetization and a high holding force, the fluidity of the carrier may decrease, and the carrier may be poorly detached from the developing roller. Then, uneven density may appear in the image due to such a decrease in the fluidity of the carrier and poor detachment from the developing roller.

Therefore, an object of the present invention is to provide a carrier core material that can suppress the development memory and also suppress the density unevenness of the image.

Another object of the present invention is to provide a carrier for electrophotographic development and a developer for electrophotographic, which can stably form a good image quality image even after long-term use.

The carrier core material according to the present invention that achieves the above object has a composition formula (MnO) _x (MgO) _y (Fe _{2O 3} ) _z (where x: 30 mol% or more and 55 mol% or less, y: 20 mol% or less, z). : A carrier core material composed of ferrite particles represented by 40 mol% or more and 60 mol% or less, x + y + z = 100 mol%), in which Ca is 0.1 mol% or more and 1.0 mol% or less, and Zr is 0.1 mol. It is characterized in that it is contained in a range of% or more and 1.0 mol% or less.

In this specification, the contents of Ca and Zr are values measured by the method described in Examples described later. Further, in the present specification, "ferrite particles", "carrier core material", "carrier for electrophotographic development", and "developer for electrophotographic development" each mean an aggregate (powder) of individual particles. be.

In the carrier core material having the above structure, the maximum mountain valley depth Rz on the surface of the ferrite particles is preferably 1.7 μm or more and 2.5 μm or less.

Further, in the carrier core material having the above structure, the residual magnetization σ _r of the ferrite particles is preferably 1.0 (A · m ² / kg) or less.

Further, in the carrier core material having the above configuration, the holding force _Hc of the ferrite particles is preferably 10 (A / m × 10 ³ / (4π)) or less.

Further, in the carrier core material having the above structure, the pore volume measured by the mercury intrusion method is preferably 0.003 cm ³ / g or more and 0.02 cm ³ / g or less.

Further, in the carrier core material having the above configuration, the magnetization σ _{1 k} of the ferrite particles when a magnetic field of 79.58 × 10 ³ A / m (1000 oersted) is applied is 45 Am ² / kg or more and 75 Am ² / kg or less. preferable.

Further, in the carrier core material having the above structure, it is preferable that the volume average particle diameter (hereinafter, may be referred to as “average particle diameter”) D ₅₀ of the ferrite particles is 20 μm or more and 75 μm or less.

Further, according to the present invention, there is provided a carrier for electrophotographic development, wherein the surface of the carrier core material according to any one of the above is coated with a resin.

Further, according to the present invention, there is provided an electrophotographic developer characterized by containing the above-mentioned electrophotographic developing carrier and toner.

In addition, "maximum mountain valley depth Rz", "residual magnetization σ _r ", "holding force H _c " _, "pore volume", "magnetization σ _{1 k} ", and "volume average particle diameter D ₅₀ " are described in Examples described later. It is a value measured by the described method.

According to the carrier core material according to the present invention, the development memory can be suppressed and the density unevenness of the image can be suppressed.

Further, by using the developer containing the carrier core material according to the present invention, it is possible to stably form a good image quality image even after long-term use.

It is an SEM photograph of the carrier core material of Example 11. It is an SEM photograph of the carrier core material of the comparative example 3. FIG. It is a schematic diagram which shows an example of the developing apparatus using the developer for electrophotographics which concerns on this invention.

As a result of diligent studies to obtain a developing memory and a carrier core material capable of suppressing density unevenness, the present inventors have obtained a predetermined amount of Ca (calcium) in the carrier core material composed of ferrite particles having a predetermined composition. The present invention has been found that by containing Zr (zyrylene), the surface of the carrier core material can be made uneven and the developing memory can be suppressed without causing a decrease in the fluidity of the carrier or a defect in detachment from the developing roller. It came to.

That is, one of the major features of the carrier core material according to the present invention is that Ca is contained in the range of 0.1 mol% or more and 1.0 mol% or less, and Zr is contained in the range of 0.1 mol% or more and 1.0 mol% or less. Is.

When Ca is contained alone in the carrier core material, a crystal phase of the Ca—Fe—O compound is generated, and the surface unevenness of the carrier core material can be achieved to some extent, but the generation of the developing memory is not sufficiently suppressed. On the other hand, when Zr is contained in the carrier core material together with Ca, the crystal phase of the Ca—Zr—O compound is preferentially generated during firing and stays at the grain boundaries of the ferrite particles in the in-plane direction of the ferrite particles. Growth is suppressed and surface unevenness of ferrite particles is promoted. In addition, the Ca-Zr-O compound is less likely to cause an increase in the residual magnetization and holding power of the carrier core material as compared with the conventionally used oxides of Sr and Fe.

The content ratios of Ca and Zr are both in the range of 0.1 mol% or more and 1.0 mol% or less. If the content ratio of Ca and Zr is less than 0.1 mol%, the desired effect of the present invention cannot be obtained. On the other hand, if the content ratio of Ca and Zr exceeds 1.0 mol%, the holding power _Hc of the carrier core material may increase and uneven concentration may occur.

The ferrite particles constituting the carrier core material of the present invention have a composition formula (MnO) _x (MgO) _y (Fe _{2O 3} ) _z (however, x: 30 mol% or more and 55 mol% or less, y: 20 mol% or less, z: It has a composition of 40 mol% or more and 60 mol% or less, x + y + z = 100 mol%). When the x is more than 55 mol% and the y is more than 20 mol%, the magnetization of the carrier core material is too low, and there is a possibility that problems such as carrier adhesion may occur in actual use. If x is less than 30 mol%, the magnetization of the carrier core material becomes high, so that image unevenness may occur.

The maximum mountain valley depth Rz of the surface of the ferrite particles constituting the carrier core material of the present invention is preferably in the range of 1.7 μm or more and 2.5 μm or less. When the maximum mountain valley depth Rz on the surface of the ferrite particles is less than 1.7 μm, the carrier core material is sufficiently exposed on the surface of the resin-coated carrier when the surface of the carrier core material is coated with the resin to form a resin-coated carrier. Therefore, the counter charge accumulated in the resin-coated carrier may not be smoothly discharged to the outside, and a developing memory may be generated. On the other hand, if the maximum mountain valley depth Rz on the surface of the ferrite particles exceeds 2.5 μm, the fluidity of the resin-coated carrier may decrease and uneven concentration may occur. A more preferable range of the maximum mountain valley depth Rz is a range of 1.7 μm or more and 2.2 μm or less. The maximum mountain valley depth Rz on the surface of the ferrite particles can be controlled by the amount of Ca and Zr added to the raw material, the firing conditions in the manufacturing process, and the like.

The residual magnetization σ _r of the ferrite particles constituting the carrier core material of the present invention is preferably 1.0 (A · m ² / kg) or less. If the residual magnetization σ _r of the ferrite particles exceeds 1.0 (A · m ² / kg), carrier detachment failure from the developing roller may occur and density unevenness may appear in the image. A more preferable upper limit value of the residual magnetization σ _r of the ferrite particles is 0.8 (A · m ² / kg). The preferable lower limit of the residual magnetization σ _r is 0.5 (A · m ² / kg).

The holding force H _c of the ferrite particles constituting the carrier core material of the present invention is preferably 10 (A / m × 10 ³ / (4π)) or less. If the holding force H _c of the ferrite particles exceeds 10 (A / m × 10 ³ / (4π)), the carrier may be poorly detached from the developing roller and uneven density may appear in the image. A more preferable upper limit value of the holding force _Hc of the ferrite particles is 9.5 (A / m × 10 ³ / (4π)). The preferable lower limit of the holding force H _c is 5.0 (A / m × 10 ³ / (4π)).

The pore volume of the ferrite particles constituting the carrier core material of the present invention is preferably in the range of 0.003 cm ³ / g or more and 0.02 cm ³ / g or less. If the pore volume of the ferrite particles is less than 0.003 cm ³ / g, the magnetization per carrier core material particle becomes too large, and carrier detachment failure from the developing roller may occur, resulting in uneven density in the image. be. On the other hand, when the pore volume of the ferrite particles exceeds 0.02 cm ³ / g, the internal voids become too large and the magnetization per carrier core material particle becomes too small, so that carrier scattering is likely to occur. A more preferable range of the pore volume of the ferrite particles is 0.004 cm ³ / g or more and 0.015 cm ³ / g or less.

The magnetization σ _1k of the ferrite particles constituting the carrier core material of the present invention is preferably 45 Am ² / kg or more and 75 Am ² / kg or less. If the magnetization σ _1k of the ferrite particles is less than 45 Am ² / kg, the magnetic force becomes too small and carrier scattering may occur. On the other hand, if the magnetization σ _1k of the ferrite particles exceeds 75 Am ² / kg, the magnetic force becomes too large and the carrier may not be detached from the developing roller, resulting in uneven density in the image.

The average particle diameter D ₅₀ of the ferrite particles constituting the carrier core material of the present invention is preferably in the range of 20 μm or more and 75 μm or less, and more preferably in the range of 30 μm or more and 40 μm or less. Further, it is preferable that the particle size distribution of the ferrite particles is sharp.

The method for producing the ferrite particles constituting the carrier core material of the present invention is not particularly limited, but the production method described below is suitable.

First, the Fe component raw material, the Mn component raw material, the Mg component raw material, the Ca component raw material, the Zr component raw material, and, if necessary, the additive are weighed. Fe ₂ O ₃ or the like is preferably used as the raw material for the Fe component. MnCO ₃ , Mn ₃ O ₄ , etc. can be used as the Mn component raw material, MgO, Mg (OH) ₂ , MgCO ₃ , MgFe ₂ O ₄ can be used as the Mg component raw material, and CaO, CaO, can be used as the Ca component raw material. Ca (OH) ₂ , CaCO ₃ , etc. can be used, and ZrO ₂ , ZrCl ₄ , etc. can be used as the Zr component raw material.

Next, the raw material is put into the dispersion medium to prepare a slurry. Water is suitable as the dispersion medium used in the present invention. In addition to the temporary firing raw material, a binder, a dispersant, or the like may be added to the dispersion medium, if necessary. As the binder, for example, polyvinyl alcohol can be preferably used. The amount of the binder to be blended is preferably such that the concentration in the slurry is about 0.1% by mass to 2% by mass. Further, as the dispersant, for example, ammonium polycarboxylate or the like can be preferably used. The amount of the dispersant to be blended is preferably such that the concentration in the slurry is about 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 and the like may be blended. 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, the pores in the particles are small in the granulated product, and it is possible to prevent insufficient sintering during firing.

The weighed raw materials may be mixed, calcined and pulverized, and then charged into a dispersion medium to prepare a slurry. The temperature of the tentative firing is preferably in the range of 750 ° C to 1000 ° C. When the temperature is 750 ° C. or higher, partial ferrite formation by calcination proceeds, the amount of gas generated during calcination is small, and the reaction between solids proceeds sufficiently, which is preferable. On the other hand, when the temperature is 1000 ° C. or lower, sintering by calcination is weak and the raw material can be sufficiently pulverized in the subsequent slurry pulverization step, which is preferable. Further, the atmosphere at the time of temporary firing is preferably an atmospheric atmosphere.

Next, the slurry produced as described above is wet-ground and pulverized. For example, wet pulverization is performed for a predetermined 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 1 μm or less. It is preferable that the vibration mill or the ball mill contains a medium having a predetermined particle size. Examples of the material of the media include iron-based chromium steel, oxide-based zirconia, titania, and alumina. The form of the crushing step may be either a continuous type or a batch type. The particle size of the crushed material is adjusted by the crushing time, rotation speed, material and particle size of the media used, and the like.

Then, the crushed slurry is spray-dried to be granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer and sprayed into the atmosphere to granulate into a spherical shape. The atmospheric temperature during spray drying is preferably in the range of 100 ° C to 300 ° C. As a result, a spherical granule having a particle size of 10 μm to 200 μm can be obtained. Then, if necessary, the obtained granulated product is classified using a vibrating sieve to prepare a granulated product having a predetermined particle size range.

Next, the granulated product is put into a furnace heated to a predetermined temperature and fired by a general method for synthesizing ferrite particles to generate ferrite particles. The firing temperature is preferably in the range of 1100 ° C to 1350 ° C. When the firing temperature is 1100 ° C. or lower, phase transformation is less likely to occur and sintering is less likely to proceed. Further, if the firing temperature exceeds 1350 ° C., excessive grain may be generated due to excessive sintering. The rate of temperature rise up to the firing temperature is preferably in the range of 250 ° C./h to 500 ° C./h. The holding time at the firing temperature is preferably 2 hours or more. The unevenness of the surface of the ferrite particles can also be adjusted by the oxygen concentration in the firing process. Specifically, the oxygen concentration is set to 500 ppm to 100,000 ppm. Further, the oxidation state of the ferrite phase may be adjusted by lowering the oxygen concentration at the time of cooling to the oxygen concentration at the time of firing. Specifically, the oxygen concentration is in the range of 500 ppm to 15,000 ppm. The oxygen concentration in raising, sintering, and cooling is preferably controlled in the range of 500 ppm to 100,000 ppm.

The fired product thus obtained is pulverized as necessary. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the pulverization step may be either a continuous type or a batch type. Further, after the pulverization treatment, if necessary, classification may be performed in order to make the particle size within a predetermined range. As the classification method, conventionally known methods such as wind power classification and sieve classification can be used. Further, after the primary classification with a wind power classifier, the particle size may be adjusted to a predetermined range with a vibration sieve or an ultrasonic sieve. Further, after the classification step, the non-magnetic particles may be removed by a magnetic field beneficiation machine. The average particle size of the ferrite particles is preferably in the range of 20 μm or more and 75 μm or less.

Then, 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 either an atmospheric atmosphere or a mixed atmosphere of oxygen and nitrogen. The heating temperature is preferably in the range of 200 ° C. or higher and 800 ° C. or lower, and more preferably in the range of 360 ° C. or higher and 550 ° C. or lower. The heating time is preferably in the range of 0.5 hours or more and 5 hours or less. From the viewpoint of homogenizing the surface and the inside of the ferrite particles, it is desirable that the heating temperature is low.

The ferrite particles produced as described above are used as the carrier core material of the present invention. Then, in order to obtain the desired chargeability and the like, the outer periphery of the carrier core material is coated with a resin to form a carrier for electrophotographic development.

Conventionally known resins can be used as the resin for coating the surface of the carrier core material, for example, polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene). ) Resins, polystyrenes, (meth) acrylic resins, polyvinyl alcohol-based resins, polyvinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based thermoplastic estramers, fluorosilicone-based resins, and the like.

To coat the surface of the carrier core material with resin, a resin solution or dispersion may be applied to the carrier core material. As the solvent for the coating solution, 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 Alcohol-based solvents such as; cellosolve-based solvents such as ethyl cellosolve and butyl cellosolve; ester-based solvents such as ethyl acetate and butyl acetate; amide-based solvents such as dimethylformamide and dimethylacetamide can be used alone or in combination of two or more. .. The concentration of the resin component in the coating solution is generally preferably in the range of 0.001% by mass or more and 30% by mass or less, particularly 0.001% by mass or more and 2% by mass or less.

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, or the like can be used. Among these, the fluidized bed method is particularly preferable because it can be applied efficiently with a small amount of resin. For example, in the case of the fluidized bed method, the resin coating amount can be adjusted by the amount of the resin solution to be sprayed and the spraying time.

The particle size of the carrier is generally preferably in the range of 20 μm or more and less than 75 μm in volume average particle size, particularly preferably in the range of 30 μm or more and 40 μm or less.

The developer for electrophotographic processing according to the present invention is made by mixing the carrier and toner produced as described above. The mixing ratio of the carrier and the toner is not particularly limited, and may be appropriately determined from the development conditions of the developing apparatus to be 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 is scattered in the developing device and the toner adheres to the background of stains on the machine or transfer paper. This is because there is a possibility that a problem 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 a polymerization method, a pulverization classification method, a melt granulation method, and a spray granulation method can be used. Specifically, a binder resin containing a thermoplastic resin as a main component containing a colorant, a mold release agent, a charge control agent, or the like can be preferably used.

Generally, the particle size of the toner is preferably in the range of 5 μm or more and 15 μm or less, and more preferably in the range of 7 μm or more and 12 μm or less in terms of the volume average particle size of the Coulter counter.

If necessary, a modifier may be added to the surface of the toner. Examples of the modifier include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethylmethacrylate and the like. One of these or a combination of two or more thereof can be used.

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

The developing method using the developer of the present invention is not particularly limited, but the magnetic brush developing method is suitable. FIG. 3 shows an outline diagram showing an example of a developing device that performs magnetic brush development. The developing apparatus shown in FIG. 3 is arranged in parallel in the horizontal direction with a rotatable developing roller 3 having a plurality of magnetic poles and a regulating blade 6 for regulating the amount of developer on the developing roller 3 conveyed to the developing unit. It is formed between two screws 1 and 2 and two screws 1 and 2 that agitate and convey the developer in opposite directions, and develops from one screw to the other at both ends of both screws. It is provided with a partition plate 4 that allows the agent to move and prevents the developer from moving to 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 charge a 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 composed of toner and carrier is constantly circulated and stirred in the apparatus.

On the other hand, the developing roller 3 has a developing magnetic pole N ₁ , a transport magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole N ₃ as means for generating magnetic poles inside a metal cylindrical body having irregularities of several μm on the surface. It has a fixed magnet in which the _five magnetic poles of the blade magnetic pole S2 are arranged in order. When the tubular body of the developing roller 3 rotates in the direction of the arrow, the developer is pumped from the screw 1 to the developing roller ₃ by the magnetic force of the pumping magnetic pole N3. The developer supported on the surface of the developing roller 3 is layer-regulated by the regulating blade 6 and then conveyed to the developing region.

In the developing region, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied from the transfer voltage power supply 8 to the developing roller 3. The DC voltage component of the bias voltage is a potential between the background potential and the image potential on the surface of the photoconductor drum 5. Further, the background potential and the image potential are potentials between the maximum and minimum values 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. The waveform of the bias voltage may be a rectangular wave, a sine wave, a triangular wave, or the like. As a result, the toner and the carrier vibrate in the developing region, and the toner adheres to the electrostatic latent image on the photoconductor drum 5 to develop.

After that, the developer on the developing roller 3 is conveyed to the inside of the apparatus by the transport magnetic pole S1, is detached from the developing roller ₃ by the peeling electrode N ₂ , is circulated and conveyed again in the apparatus by the screws 1 and 2, and is used for development. Mix and stir with undeveloped developer. Then, the developing agent is newly supplied from the screw 1 to the developing roller ₃ by the pumping electrode N3.

In the embodiment shown in FIG. 3, the number of magnetic poles built in the developing roller 3 is five, but in order to further increase the amount of movement of the developing agent in the developing region and further improve the pumping property and the like. Of course, the number of magnetic poles may be increased to 8 poles, 10 poles, or 12 poles.

(Example 1)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 12.3 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 4.6 kg, MgFe ₂ O ₄ (average particle size: 3.2 μm) Only 3.1 kg, CaCO ₃ (average particle size: 0.6 μm) 0.100 kg, ZrO ₂ (average particle size: 1.8 μm) 0.122 kg are dispersed in 6.6 kg of pure water, and carbon black is used as a reducing agent. 37 g, 144 g of an ammonium polycarboxylate-based dispersant as a dispersant, and 10 g of aqueous ammonia (25 wt% aqueous solution) were added to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1200 ° C. over 4.5 hours. After that, firing was performed by holding at 1200 ° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted so that it would be 100,000 ppm in the heating stage and 15,000 ppm in the cooling stage.
The obtained fired product was pulverized with a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 35.1 μm.

The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

Next, the surface of the carrier core material thus obtained was coated with a resin to prepare a carrier. Specifically, 450 parts by mass of a 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 coated 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 carriers. 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 the toner were adjusted so that the mass of the toner / (mass of the toner and the carrier) = 5/100. Hereinafter, developing agents were obtained in the same manner for all Examples and Comparative Examples. The obtained developer was evaluated on an actual machine as described later. The evaluation results are shown in Table 1.

(Example 2)
A carrier core material having an average particle diameter of 35.2 μm was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1240 ° C.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 3)
A carrier core material having an average particle diameter of 35.5 μm was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1280 ° C.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 4)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 11.6 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 5.1 kg, Mg Fe ₂ O ₄ (average particle size: 3.2 μm) A carrier core material having an average particle diameter of 35.2 μm was obtained in the same manner as in Example 2 except that 3.3 kg was used.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 5)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 9.9 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 4.8 kg, MgFe ₂ O ₄ (average particle size: 3.2 μm) A carrier core material having an average particle diameter of 34.7 μm was obtained in the same manner as in Example 2 except that 5.3 kg and carbon black were not added.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 6)
A carrier core material having an average particle diameter of 36.4 μm was obtained in the same manner as in Example 4 except that the oxygen concentration in the electric furnace in the firing step was changed to 21%.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 7)
A carrier core material having an average particle diameter of 34.8 μm was obtained in the same manner as in Example 5 except that the oxygen concentration in the electric furnace in the firing step was changed to 21%.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 8)
The average particle size was 35.2 μm in the same manner as in Example 2 except that CaCO ₃ (average particle size: 0.6 μm) 0.149 kg and ZrO ₂ (average particle size: 1.8 μm) 0.184 kg were used as raw materials. Carrier core material was obtained.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 9)
The average particle size was 34.9 μm in the same manner as in Example 2 except that CaCO ₃ (average particle size: 0.6 μm) 0.050 kg and ZrO ₂ (average particle size: 1.8 μm) 0.061 kg were used as raw materials. Carrier core material was obtained.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 10)
A carrier core material having an average particle diameter of 34.7 μm was obtained in the same manner as in Example 6 except that the electric furnace temperature in the firing step was changed to 1270 ° C.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 11)
The average particle size was 34.5 μm in the same manner as in Example 10 except that CaCO ₃ (average particle size: 0.6 μm) 0.050 kg and ZrO ₂ (average particle size: 1.8 μm) 0.061 kg were used as raw materials. Carrier core material was obtained.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Example 12)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 14.5 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 5.4 kg, CaCO ₃ (average particle size: 0.6 μm) 0. Only 0.122 kg of 100 kg and ZrO ₂ (average particle size: 1.8 μm) was dispersed in 6.6 kg of pure water, 37 g of carbon black as a reducing agent, 144 g of an ammonium polycarboxylate dispersant as a dispersant, and ammonia. 10 g of water (25 wt% aqueous solution) was added to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1240 ° C. over 4.5 hours. After that, firing was performed by holding at 1240 ° C. for 3 hours. A carrier core material having an average particle diameter of 35.2 μm is the same as in Example 1 except that the oxygen concentration in the furnace is adjusted so that the oxygen concentration in the electric furnace is 50,000 ppm in the heating stage and 5000 ppm in the cooling stage. Got
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Comparative Example 1)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 11.6 kg, Mn ₃ O ₄ (average particle size: 2.0 μm) 5.1 kg, Mg Fe ₂ O ₄ (average particle size: 3.2 μm) 3.3 kg, SrCO ₃ (average particle size: 0.6 μm) 0.220 kg was dispersed in 6.6 kg of pure water, 69 g of carbon black as a reducing agent, and 100 g of an ammonium polycarboxylate dispersant as a dispersant. , 38 g of hydrochloric acid (35 wt% aqueous solution) was added to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1200 ° C. over 4.5 hours. After that, firing was performed by holding at 1200 ° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted so that it would be 10,000 ppm in the heating stage and 15,000 ppm in the cooling stage.
The obtained fired product was pulverized with a hammer mill and then classified using a vibrating sieve to obtain a carrier core material having an average particle diameter of 34.9 μm.

(Comparative Example 2)
Weigh Fe ₂ O ₃ (average particle size: 0.8 μm) to 50.0 mol and Mn ₃ O ₄ (average particle size: 2.0 μm) to 50.0 mol in terms of MnO, and pelletize with a roller compactor. bottom. The obtained pellets were tentatively calcined in a rotary calcining furnace at 850 ° C. under atmospheric air conditions. The mixture was pulverized with a dry bead mill for 6 hours to obtain a raw material for calcining (average particle size: 2.2 μm). Only 20.0 kg of this calcination raw material and 0.240 kg of SrCO ₃ (average particle size: 0.6 μm) are dispersed in 6.7 kg of pure water, 60 g of carbon black is used as a reducing agent, and ammonium polycarboxylate is used as a dispersant. 120 g of a dispersant was added to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 30 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1200 ° C. over 4.5 hours. After that, firing was performed by holding at 1200 ° C. for 3 hours. The oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 15,000 ppm.
The obtained calcined product was pulverized with a hammer mill and then classified using a vibrating sieve to obtain a calcined product having an average particle diameter of 34.8 μm.
Next, the obtained fired product was held at 380 ° C. for 1 hour in an air atmosphere to perform an oxidation treatment (high resistance treatment) to obtain a carrier core material.

(Comparative Example 3)
Fe ₂ O ₃ (average particle size: 0.8 μm) is 50.0 mol, Mn ₃ O ₄ (average particle size: 2.0 μm) is 35.0 mol in terms of MnO, and MgO (average particle size: 0.8 μm). Weighed to 15.0 mol in terms of MgO and pelletized with a roller compactor. The obtained pellets were tentatively calcined in a rotary calcining furnace at 870 ° C. under atmospheric air conditions. The mixture was pulverized with a dry bead mill for 6 hours to obtain a raw material for calcining (average particle size: 2.2 μm). Only 20.0 kg of this calcination raw material and 0.150 kg of CaCO ₃ (average particle size: 0.6 μm) are dispersed in 6.7 kg of pure water, and 73 g of an ammonium polycarboxylate-based dispersant is added as a dispersant to form a mixture. And said. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1250 ° C. over 4.5 hours. After that, firing was performed by holding at 1250 ° C. for 3 hours. The oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 5000 ppm.
The obtained calcined product was pulverized with a hammer mill and then classified using a vibrating sieve to obtain a calcined product having an average particle diameter of 35.8 μm.
Next, the obtained fired product was held at 360 ° C. for 1 hour in an air atmosphere to perform an oxidation treatment (high resistance treatment) to obtain a carrier core material.

(Comparative Example 4)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 14.4 kg, Mn ₃ O ₄ (average particle size: 2.0 μm) 5.6 kg, CaCO ₃ (average particle size: 0.6 μm) 0. Only 131 kg was dispersed in 6.7 kg of pure water, and 55 g of carbon black was added as a reducing agent and 125 g of an ammonium polycarboxylate-based dispersant was added as a dispersant to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
The granulated product was placed in an electric furnace and heated to 1155 ° C. over 4.5 hours. After that, firing was performed by holding at 1155 ° C. for 3 hours. The oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 5000 ppm.
The obtained calcined product was pulverized with a hammer mill and then classified using a vibrating sieve to obtain a calcined product having an average particle diameter of 34.3 μm.
Next, the obtained fired product was held at 425 ° C. for 1 hour in an air atmosphere to perform an oxidation treatment (high resistance treatment) to obtain a carrier core material.

(Comparative Example 5)
The average particle size was 35.6 μm in the same manner as in Example 2 except that CaCO ₃ (average particle size: 0.6 μm) 0.224 kg and ZrO ₂ (average particle size: 1.8 μm) 0.275 kg were used as raw materials. Carrier core material was obtained.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Comparative Example 6)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 14.4 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 5.6 kg, ZrO ₂ (average particle size: 1.8 μm) 0. Only 150 kg was dispersed in 6.8 kg of pure water, and 56 g of carbon black was added as a reducing agent and 125 g of an ammonium polycarboxylate-based dispersant was added as a dispersant to prepare a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1300 ° C. over 4.5 hours. After that, firing was performed by holding at 1300 ° C. for 3 hours. A carrier core material having an average particle diameter of 36.3 μm was obtained in the same manner as in Example 1 except that the oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 5000 ppm.
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Comparative Example 7)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 13.6 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 6.4 kg, SrCO ₃ (average particle size: 0.6 μm) 0. Only 112 kg and 0.093 kg of ZrO ₂ (average particle size: 1.8 μm) were dispersed in 6.6 kg of pure water, and 61 g of carbon black was added as a reducing agent and 121 g of an ammonium polycarboxylate dispersant was added as a dispersant. To make a mixture. This mixture was pulverized with 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. with a spray dryer to obtain dried granules having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 25 μm or less were removed from this granulated product using a sieve.
This granulated product was placed in an electric furnace and heated to 1250 ° C. over 4.5 hours. After that, firing was performed by holding at 1250 ° C. for 3 hours. A carrier core material having an average particle diameter of 35.0 μm is the same as in Example 1 except that the oxygen concentration in the furnace is adjusted so that the oxygen concentration in the electric furnace is 12000 ppm in the heating stage and 7,000 ppm in the cooling stage. Got
The composition, powder characteristics, shape characteristics, magnetic characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 1.

(Composition analysis)
(Analysis of Fe)
The carrier core material containing the iron element was weighed and dissolved in a mixed acid water of hydrochloric acid and nitric acid. After evaporating and drying this solution, sulfuric acid water is added and redissolved to volatilize excess hydrochloric acid and nitric acid. 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 to determine the titration amount of Fe (Fe ²⁺ ).
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed according to the ferromanganese analysis method (potential difference titration method) described in JIS G1311-1987. The Mn content of the carrier core material described in the present specification is the amount of Mn obtained by quantitative analysis by this ferromanganese analysis method (potential difference drip method).
(Analysis of Mg)
The Mg content of the carrier core material was analyzed by the following method. The carrier core material was dissolved in an acid solution and quantitative analysis was performed by ICP. The Mg content of the carrier core material described in the present specification is the Mg content obtained by the quantitative analysis by this ICP.
(Analysis of Ca)
The Ca content of the carrier core material was quantitatively analyzed by ICP in the same manner as the analysis of Mg.
(Analysis of Zr)
The Zr content of the carrier core material was quantitatively analyzed by ICP as in the analysis of Mg.
(Analysis of Sr)
The Sr content of the carrier core material was quantitatively analyzed by ICP as in the analysis of Mg.

(Apparent density AD)
The apparent density of the carrier core material was measured according to JIS Z 2504.

(Fluidity FR)
The fluidity of the carrier core material was measured according to JIS Z 2502.

(Volume average particle diameter D ₅₀ )
The volume average particle diameter D ₅₀ of the carrier core material was measured using a laser diffraction type particle size distribution measuring device (“Microtrack Model 9320-X100” manufactured by Nikkiso Co., Ltd.).

(Pore volume)
The measurement of the pore volume was performed as follows. As the evaluation device, POREMASTER-60GT manufactured by Quantachrome was used. Specifically, the measurement conditions are Cell Stem Volume: 0.5 cm ³ , Headpressure: 20PSIA, surface tension of mercury: 485.00 erg / cm ² , contact angle of mercury: 130.00 degrees, high pressure measurement mode: Fixed Rate. , Motor Speed: 1, high pressure measurement range: 20.00 to 10000.00 PSI, 1.200 g of sample was weighed and filled in a cell of 0.5 cm ³ for measurement. Further, the value obtained by subtracting the volume A (cm ³ / g) at 100 PSI from the volume B (cm ³ / g) at 10000.00 PSI was defined as the pore volume.

(Maximum mountain valley depth Rz, average length RSm)
The surface was observed with a 100x objective lens using an ultra-deep color 3D shape measuring microscope (“VK-X100” manufactured by KEYENCE CORPORATION). Specifically, first, ferrite particles were fixed on an adhesive tape having a flat surface, a measurement field of view was determined with a 100x objective lens, and then the focus was adjusted to the adhesive tape surface using an autofocus function. The flat adhesive tape surface on which the ferrite particles were fixed was irradiated with a laser beam from the vertical direction (Z direction) and scanned in the X direction and Y direction of the surface. In addition, data in the Z direction was acquired by connecting the height positions of the lenses when the intensity of the reflected light from the surface was maximized. These position data in the X, Y and Z directions were joined to obtain a three-dimensional shape of the surface of the ferrite particles. The auto photographing function was used to capture the three-dimensional shape of the surface of the ferrite particles.
Each parameter was measured using particle roughness inspection software (manufactured by Mitani Corporation). First, as a pretreatment, particle recognition and shape selection of the three-dimensional shape of the obtained ferrite particle surface were performed. Particle recognition was performed by the following method.
Of the three-dimensional shapes obtained by photographing, the maximum value in the Z direction is set to 100%, the minimum value is set to 0%, and the range from the maximum value to the minimum value is divided into 100 equal parts. The region corresponding to 100 to 35% was extracted, and the contour of the independent region was recognized as the particle contour. Next, the shape selection excluded particles such as coarse, micro, and association. By performing this shape selection, it is possible to reduce the error during the subsequent pole factor correction. Specifically, particles having an area equivalent diameter of 28 μm or less, 38 μm or more, and a needle-like ratio of 1.15 or more were excluded. Here, the needle-like ratio is a parameter calculated from the ratio of the maximum length / diagonal width of the particles, and the diagonal width is the shortest distance between the two straight lines when the particles are sandwiched between two straight lines parallel to the maximum length. Represents.
Next, the part used for the analysis was taken out from the three-dimensional shape of the surface. First, a 15.0 μm square is drawn centered on the center of gravity obtained from the particle contour recognized by the above method. Twenty-one parallel lines were drawn in the drawn square, and 21 roughness curves on the line segments were taken out.
Since the ferrite particles have a substantially spherical shape, the extracted roughness curve has a constant curvature as a background. Therefore, as a background correction, an optimum quadratic curve was fitted and a correction was performed by subtracting it from the roughness curve. In this case, a low-pass filter was applied with an intensity of 1.5 μm, and the cutoff value λ was set to 80 μm.
The average particle size of the carrier core material used in the analysis was limited to 32 μm to 34 μm. By limiting the average particle size of the carrier core material to be measured to a narrow range in this way, it is possible to reduce the error due to the residue generated during the curvature correction.

The maximum valley depth Rz was calculated as the sum of the height of the highest mountain and the depth of the deepest valley in the roughness curve. For the calculation of the maximum height Rz, the average value of 30 particles was used as the average value of each parameter.

The average length RSm defines the combination of valleys and peaks as one element in the roughness curve, and averages the lengths of each element. For the calculation of the average length RSm, the average value of 30 particles was used as the average value of each parameter.

The measurement of the maximum height Rz and the average length RSm described above is performed in accordance with JIS B0601 (2001 version).

(Magnetic characteristics)
Using a vibrating sample magnetometer (VSM) for room temperature (“VSM-P7” manufactured by Toei Kogyo Co., Ltd.), the external magnetic field is continuously applied for one cycle in the range of 0 to 79.58 × 10 ⁴ A / m (10000 Elstead). When a magnetic field of 79.58 × 10 ³ A / m (1,000 Elstead) was applied, the magnetization σ _{1 k} , saturation magnetization σ _s , residual magnetization σ _r , and coercive force H _c were measured.

(Electrical resistance)
Two brass plates with a thickness of 2 mm whose surfaces are electrolytically polished as electrodes are arranged so that the distance between the electrodes is 2 mm, and after charging 200 mg of a carrier core material into the gap between the two electrode plates, each electrode plate is used. A magnet with a cross-sectional area of 240 mm ² is placed behind the electrode, and a 500 V DC voltage is applied between the electrodes with a bridge of the powder to be measured formed between the electrodes, and the current value flowing through the carrier core material is measured by the 4-terminal method. It was measured. The electric 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 ² .

(Actual machine evaluation)
(Development memory)
The obtained developer was subjected to a developing apparatus having the structure shown in FIG. 3 (peripheral speed Vs of the developing roller: 406 mm / sec, peripheral speed Vp of the photoconductor drum: 205 mm / sec, distance between the photoconductor drum and the developing roller: 0. 3 mm), the solid image part and the non-image part are adjacent to each other in the circumferential direction of the photoconductor drum, and then an initial image in which a wide area of halftone continues is acquired, and one round of the developing roller on the second round of the developing roller is obtained. The image density between the area where the solid image of the eyes was developed and the area where it was not developed was measured using a reflection densitometer (model number TC-6D manufactured by Tokyo Denshoku Co., Ltd.), and the difference was obtained and evaluated according to the following criteria. The results are shown in Table 1.
"◎": Less than 0.003 "○": 0.003 or more and less than 0.006 "△": 0.006 or more and less than 0.020 "×": 0.020 or more

(Concentration unevenness)
For the three evaluation images by the evaluation machine, the densities at five places per image were measured using a reflection densitometer (model number TC-6D manufactured by Tokyo Denshi Co., Ltd.) and evaluated according to the following criteria.
"◎": The maximum difference in density is less than 0.1, and uneven density cannot be visually recognized.
"○": The maximum difference in density is 0.1 or more and less than 0.2, and uneven density cannot be visually recognized.
“Δ”: The maximum difference in density is 0.2 or more and less than 0.3, and uneven density can be visually recognized.
"X": The maximum difference in density is 0.3 or more, and uneven density is visible and cannot be used.

As is clear from Table 1, in the carrier core materials of Examples 1 to 11 composed of MnMg ferrite containing Ca and Zr, the developing memory and density unevenness were suppressed to a level that would not cause a problem in actual use. Further, even in the carrier core material of Example 12 composed of Mn ferrite containing Ca and Zr, the development memory and density unevenness were suppressed to a level that would not cause a problem in actual use.

On the other hand, in the carrier core material of Comparative Example 1 composed of MnMg ferrite containing Sr, the development memory was suppressed to a level where there was no problem in actual use, but the density unevenness was visible and there was a problem in actual use. Met. Further, even in the carrier core material of Comparative Example 2 composed of Mn ferrite containing Sr, the development memory was suppressed to a level where there was no problem in actual use, but the density unevenness was visible and was at a level where there was a problem in actual use. ..

Further, in the carrier core material of Comparative Example 3 composed of MnMg ferrite containing Ca and not Zr, the density unevenness was suppressed to a level where there is no problem in actual use, but the development memory is at a level where there is a problem in actual use. rice field. Further, even in the carrier core material of Comparative Example 4 composed of Mn ferrite containing Ca and not Zr, the density unevenness was suppressed to a level where there is no problem in actual use, but the development memory is at a level where there is a problem in actual use. there were.

In the carrier core material of Comparative Example 5 composed of MnMg ferrite in which Ca and Zr were excessively contained, the developing memory was suppressed to a level where there was no problem, but the density unevenness was significantly unusable.

In the carrier core material of Comparative Example 6 composed of Mn ferrite containing Zr and not Ca, the density unevenness was suppressed to a level at which there was no problem in actual use, but the development memory was significantly unusable.

In the carrier core material of Comparative Example 7 composed of Mn ferrite containing Zr and Sr, the developing memory was suppressed to a level where there was no problem, but the density unevenness was significantly unusable.

The carrier core material according to the present invention is useful because it can suppress the development memory and also suppress the density unevenness of the image.

3 Develop roller 5 Photoreceptor drum

Claims (9)

Composition formula (MnO) _x (MgO) _y (Fe _{2O 3} ) _z (However, x: 30 mol% or more and 55 mol% or less, y: 20 mol% or less, z: 40 mol% or more and 60 mol% or less, x + y + z = 100 mol%) A carrier core material composed of the represented ferrite particles.
Ca is in the range of 0.1 mol% or more and 1.0 mol% or less,
Zr is in the range of 0.1 mol% or more and 1.0 mol% or less,
A carrier core material characterized by being contained. The carrier core material according to claim 1, wherein the maximum mountain valley depth Rz on the surface of the ferrite particles is 1.7 μm or more and 2.5 μm or less. The carrier core material according to claim 1 or 2, wherein the residual magnetization σ _r of the ferrite particles is 1.0 (A · m ² / kg) or less. The carrier core material according to any one of claims 1 to 3, wherein the holding force H _c of the ferrite particles is 10 (A / m × 10 ³ / (4π)) or less. The carrier core material according to any one of claims 1 to 4, wherein the pore volume measured by the mercury intrusion method is 0.003 cm ³ / g or more and 0.02 cm ³ / g or less. ₁₇ ^{. _ _} Carrier core material. The carrier core material according to any one of claims 1 to 6, wherein the volume average particle diameter D ₅₀ of the ferrite particles is 20 μm or more and 75 μm or less. A carrier for electrophotographic development, wherein the surface of the carrier core material according to any one of claims 1 to 7 is coated with a resin. A developer for electrophotographic processing, which comprises the carrier for developing an electrophotographic photograph according to claim 8 and a toner.

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