JP2023062747A - Carrier core material, electrophotographic development carrier using the same, and electrophotographic developer - Google Patents

Abstract

To provide a carrier core material capable of suppressing toner spent, white spots in images, and carrier scattering even when image forming speed is fast or when used for a prolonged period of time.SOLUTION: A carrier core material provided herein is composed of ferrite particles and features a saturation magnetization σs of 75 Am2/kg to 90 Am2/kg, inclusive, a pore volume of 0.008 cm3/g or more and less than 0.020 cm3/g, a maximum height Rz of 1.4 μm to 2.0 μm, inclusive, and a particle deformity rate of 10 to 50%, inclusive, as measured by a predetermined measurement method.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a carrier core material, an electrophotographic development carrier and an electrophotographic developer using the same.

For example, in image forming apparatuses such as facsimiles, printers, and copiers that use electrophotography, toner is applied to an electrostatic latent image formed on the surface of a photoreceptor to make it visible. etc., and then fixed by applying heat and pressure. A so-called two-component developer containing a carrier and a toner is widely used as a developer from the viewpoint of high image quality and colorization.

In a developing method using a two-component developer, carrier and toner are agitated and mixed in a developing device, and the toner is charged to a predetermined amount by friction. Then, developer is supplied to a rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically transferred to the photoreceptor via the magnetic brush to form an electrostatic latent image on the photoreceptor. visualized. After the toner has moved, the carrier is peeled off from the developing roller and mixed with the toner again in the developing device. For this reason, the carrier is required to have properties such as movement to the developing roller, magnetic properties for forming a magnetic brush, charging properties for imparting a desired charge to the toner, and durability in repeated use.

As such a carrier, magnetic particles such as magnetite and various ferrites coated with a resin are generally used. Magnetic particles as a carrier core material are required to have not only good magnetic properties but also good triboelectrification properties with respect to toner. Various shapes have been proposed as carrier core materials satisfying such characteristics.

For example, for the purpose of suppressing peeling of the coating resin from the carrier core material due to long-term use, at least one of Sr (strontium) and Ca (calcium) is contained in a specific amount, and the average length of grains appearing on the particle surface A carrier core material has been proposed in which the frequency of grains having a thickness RSm of a specific value or more is set to a specific value or less (Patent Document 1). For the purpose of suppressing toner spent, in which toner components adhere to the carrier surface, it has also been proposed to set the surface irregularity spacing Sm of the carrier core material to a specific value or less and the surface roughness Ra to a predetermined value or more. (Patent Document 2).

JP 2016-184130 A JP 2007-286092 A

By the way, in recent years, in order to respond to the market demand for higher image forming speed in image forming apparatuses, there is a tendency to increase the rotation speed of the developing roller to increase the amount of developer supplied to the developing area per unit time. .

However, when the amount of developer supplied to the developing region is increased as the image forming speed increases, the stress applied to the developer increases, causing peeling of the coating resin from the carrier core material and abrasion of the coating resin. easier. Toner spent also tends to occur.

When the coating resin is peeled off from the carrier core material or the coating resin is worn, the carrier core material is exposed to the surface, charge injection occurs from the exposed portion, and the carrier adheres to the photoreceptor, resulting in so-called image white spots. There is Further, when toner spent on the surface of the carrier occurs, the ability of the carrier to impart charge to the toner may decrease. Further, when the stress applied to the developer increases, the carrier core material may crack or chip.

In order to suppress peeling of the coating resin from the carrier core material, it is conceivable to increase the pore volume of the carrier core material so as to exert a strong anchoring effect on the coating resin. If it is too large, the magnetization per particle of the carrier core material may decrease, causing carrier scattering.

Accordingly, an object of the present invention is to provide a carrier core material capable of suppressing toner spent, image white spots, and carrier scattering even when the image forming speed is high or even after long-term use, and an electrophotographic development carrier and an electrophotographic carrier using the same. To provide a developer.

A carrier core material according to the present invention for achieving the above object is a carrier core material composed of ferrite particles, having a saturation magnetization σ _s of 75 Am ² /kg or more and 90 Am ² /kg or less, and a pore volume of 0.008 cm. ³ /g or more and less than 0.020 cm ³ /g, the maximum height Rz is 1.4 μm or more and 2.0 μm or less, and the irregular shape ratio of the particles measured by the following measurement method is in the range of 10% or more and 50% or less. It is characterized by
(Method for measuring anomalous shape rate of particles)
Measuring device: Injection type image analysis particle size distribution meter Measurement sample amount: 0.07 g
The measurement was carried out after dispersion in a screw vial (capacity 9 cm ^{3 )} filled with 9 cm ³ of polyethylene glycol 400.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: relative measurement Measurement volume: 0.95 cm ³
Analysis: Dark Detection Threshold: 169 (fill in holes)
O-Roughness filter: 0.5
Filter condition:
ISO Area Diameter: minimum value 5, maximum value 100, inner range (analysis conditions)
Analysis filter condition I:
ISO Area Diameter: Minimum 25, Maximum 55, Inner Range Analysis Filter Condition II:
ISO Area Diameter: minimum value 25, maximum value 55, inner range ISO Solidity: minimum value 0.98, maximum value 1, outer range Ell. Ratio: minimum value 0.8, maximum value 1, the number of particles counted under the inner range analysis filter condition II is divided by the number of particles counted under the analysis filter condition I to calculate the deformity ratio.

In the carrier core material having the above structure, the average length RSm of grains appearing on the particle surface is preferably 5.0 μm or more and 7.1 μm or less.

In the carrier core material having the above configuration, magnetization σ _1k in a magnetic field of 79.58×10 ³ A/m (1000 Oersted) is preferably 61 Am ² /kg or more and 75 Am ² /kg 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 according to any one of the above is coated with a resin.

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

According to the carrier core material of the present invention, it is possible to suppress toner spent, image white spots, and carrier scattering even when the image forming speed is high or when the carrier is used for a long period of time.

4 is an SEM photograph of the carrier core material of Example 1. FIG. 10 is an SEM photograph of a carrier core material of Comparative Example 8. FIG. 10 is an SEM photograph of the carrier core material of Comparative Example 9. FIG. 1 is a schematic diagram showing an example of a developing device using an electrophotographic developer according to the present invention; FIG.

(Carrier core material)
A major feature of the carrier core material according to the present invention is that the saturation magnetization σ _s , the pore volume, the maximum height Rz, and the irregularity of the particles measured by the above-described measuring method are all within specific ranges. The main feature is fulfillment. More specifically, carrier scattering is mainly suppressed by setting the saturation magnetization σ _s and the pore volume within specific ranges. Moreover, when the pore volume and the maximum height Rz are within specific ranges, an anchoring effect is exhibited, and peeling of the coating resin mainly due to long-term use is suppressed. Further, by setting the maximum height Rz and the deformity ratio within the specific ranges, abrasion of the coating resin mainly due to long-term use is suppressed. Toner spent is mainly suppressed by setting the maximum height Rz and the deformity ratio within specific ranges.

The configuration of the present invention will be individually described below. First, in the present invention, the saturation magnetization σ _s of the carrier core material is in the range of 75 Am ² /kg or more and 90 Am ² /kg or less. When the saturation magnetization σ _s is less than 75 Am ² /kg, carrier scattering is likely to occur, while when the saturation magnetization σ _s exceeds 90 Am ² /kg, the magnetic brush formed on the developing roller becomes coarse, resulting in deterioration of image quality. Sometimes. A preferable range of saturation magnetization σ _s is 80 Am ² /kg or more and 90 Am ² /kg or less.

Next, the pore volume of the carrier core material in the present invention is in the range of 0.008 cm ³ /g or more and less than 0.020 cm ³ /g. If the pore volume is less than 0.008 cm ³ /g, a sufficient anchoring effect cannot be obtained and the coating resin ^may peel off. Magnetization is lowered and carrier scattering is likely to occur.

The maximum height Rz of the carrier core material in the present invention is in the range of 1.4 μm or more and 2.0 μm or less. If the maximum height Rz is less than 1.4 μm, a sufficient anchoring effect cannot be obtained and the coating resin may peel off. Coating resin may be worn and image white spots may occur.

The deformation rate of the carrier core material measured by the measuring method of the present invention is in the range of 10% or more and 50% or less. If the irregularity ratio is less than 10%, the toner spent on the surface of the carrier becomes difficult to be scraped off, and the ability to impart charge to the toner is reduced, which may lead to deterioration in image quality. On the other hand, if the deformity rate exceeds 50%, the coating resin may be worn, resulting in image white spots. A preferable range of deformity ratio is 15% or more and 47% or less.

Next, the average length RSm of the carrier core material in the present invention is preferably in the range of 5.0 μm or more and 7.1 μm or less. When the average length RSm is within this range, excessive sharpening of the grains is suppressed, the mechanical stress on the resin-coated carrier in the magnetic brush is reduced, and abrasion of the resin coating layer is easily suppressed. A more preferable range of the average length RSm is 6.0 μm or more and 7.1 μm or less.

In the present invention, the magnetization σ _1k of the carrier core material is preferably 61 Am ² /kg or more and 75 Am ² /kg or less. When the magnetization _σ1k is within this range, carrier scattering is easily suppressed and the developer is easily transported to the developing area. A more preferable range of magnetization σ _1k is from 64 Am ² /kg to 70 Am ² /kg.

The ferrite particles constituting the carrier core material of the present invention are preferably composed mainly of a material represented by the composition formula (Mn _x Fe _3-x )O ₄ (where 0<x<3). . Here, the main component means a material containing more than 50% by mass. Furthermore, it is preferable that Si (silicon) is contained at 0.06 mol % or more and 0.20 mol % or less with respect to the total number of moles of the particle composition. When the Si content is less than 0.06 mol %, there is a possibility that the deformed shape of the grains will progress while the grain size is small, and the sharpening of the grains will be excessively promoted. On the other hand, when the Si content exceeds 0.20 mol %, the decomposition/melting and diffusion of the particles are accelerated, which may excessively promote the energy-stable spheroidization. The Si content can usually be adjusted by adjusting the amount of the Si raw material added, but it can also be adjusted by adjusting the amount of a mixed raw material that is a mixture of the Si raw material and other raw materials. In Examples described later, a mixed raw material containing Fe and Si and a mixed raw material containing Mn and Si are used, and the content of Si is adjusted by the amount of the mixed raw material added. The addition amount of the Si raw material when using the mixed raw material is calculated from the Si content of the mixed raw material.

Further, the ferrite particles constituting the carrier core material of the present invention contain 0.01 mol % or more and 0.50 mol % or less of Sr (strontium) and 0.01 mol % of Sn (tin) with respect to the total number of moles of the particle composition. It may contain 01 mol % or more and 0.50 mol % or less. When Sr is contained in the above amount, Sr ferrite is partially generated in the firing process, and a magnetoplumbite type crystal structure is formed, thereby facilitating the formation of irregularities on the surface of the carrier core material. On the other hand, Sn has a sintering inhibitory action, and when Sn is contained in the above amount together with Sr, it is possible to suppress excessive deformation of the particles compared to the case where only Sr is contained. Formed on the surface. A more preferable Sr content is in the range of 0.10 mol % or more and 0.50 mol % or less. A more preferable Sn content is in the range of 0.10 mol % or more and 0.50 mol % or less.

Further, the ferrite particles constituting the carrier core material of the present invention may contain 0.01 mol % or more and 0.60 mol % or less of Ca (calcium) with respect to the total mol number of the particle composition. By containing the above amount of Ca, the electrical properties, magnetic properties, and shape properties of the carrier core material are adjusted to desired ranges. A preferable content range of Ca is 0.40 mol % or more and 0.60 mol % or less.

The volume average particle diameter of the carrier core material of the present invention is preferably in the range of 25 μm or more and less than 50 μm, more preferably in the range of 30 μm or more and 40 μm or less.

The apparent density of the carrier core material of the present invention is preferably in the range of 2.00 g/cm ³ or more and 2.50 g/cm ³ or less, more preferably 2.10 g/cm ³ or more and 2.40 g/cm ³ or less. .

The fluidity (sec/50 g) of the carrier core material of the present invention is preferably in the range of 25 to 40, more preferably in the range of 28 to 40.

(Manufacturing method of carrier core material)
The method for producing the carrier core material of the present invention is not particularly limited, but the production method described below is suitable.

First, the necessary component materials are weighed so as to obtain the desired composition. Also, if necessary, conventionally known additives are weighed. For example, Fe (iron) component raw material is preferably Fe ₂ O ₃ or the like. MnCO ₃ , Mn ₃ O ₄ and the like are used as the Mn (manganese) component raw material. SrCO ₃ and Sr(NO ₃ ) ₂ are used as Sr component materials, SnO ₂ and SnO are used as Sn component materials, and SiO ₂ and the like are preferably used as Si component materials. Some Fe component raw materials and Mn component raw materials contain a predetermined amount of Si. When the amount of Si added is sufficient, the Si component raw material does not have to be blended. Conversely, when the amount of Si contained in the Fe component raw material and the Mn component raw material is insufficient for the amount of Si to be added, the Si component raw material is supplemented.

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. The dispersion medium may contain, if necessary, a binder, a dispersant, and the like, in addition to the temporary firing raw material. As the binder, for example, polyvinyl alcohol can be preferably used. As for the blending amount of the binder, it is preferable that the concentration in the slurry is about 0.1% by mass to 2% by mass. Moreover, as a dispersing agent, for example, ammonium polycarboxylate can be suitably used. It is preferable that the concentration of the dispersant 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 desirably in the range of 50% by mass to 90% by mass. More preferably 60% by mass to 80% by mass. If it is 60% by mass or more, there are few intra-particle pores in the granules, and insufficient sintering during firing can be prevented.

Alternatively, the weighed raw materials may be mixed, calcined and pulverized, and then added to the dispersion medium to prepare a slurry. The calcination temperature is preferably in the range of 750°C to 1000°C. If 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, if it is 1000° C. or less, sintering by temporary firing is weak, and the raw material can be sufficiently pulverized in the subsequent slurry pulverization process, which is preferable. In addition, an air atmosphere is preferable as the atmosphere during calcination.

Next, the slurry prepared as described above is wet pulverized. For example, it is wet pulverized for a predetermined time using a ball mill or vibration mill. The volume-average particle size _D50 indicating 50% of the particle size in the cumulative particle size distribution of the pulverized raw material is preferably 1.0 μm or less. Also, the value of volume particle size _D90 , which represents 90% of the particle size in the cumulative particle size distribution, is preferably 3.0 μm or less. A vibration mill or a ball mill should preferably contain media having 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 a continuous type or a batch type. The particle size of the pulverized product is adjusted by the pulverization time, rotation speed, material and particle size of the media used, and the like.

The viscosity of the slurry is preferably 1000 cP or less, more preferably 100 cP or less.

Then, the produced slurry is spray-dried and granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer, and sprayed into the atmosphere to form spherical granules. The ambient temperature during spray drying is preferably in the range of 100°C to 300°C. As a result, spherical granules having 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. The apparent density AD of the granules is preferably in the range of 1.40 g/cm ³ to 1.75 g/cm ³ and more preferably in the range of 1.50 g/cm ³ to 1.58 g/cm ³ . By setting the apparent density of the granules within the above range, it becomes easier to adjust the pore volume of the carrier core material within the specified range of the present invention. When the apparent density of the granules is low, the pore volume tends to be large, and when the apparent density of the granules is high, the pore volume tends to be small. The apparent density of the granules can be adjusted by, for example, the type (composition) of the raw material, the particle size of the slurry, the type and amount of the dispersant, and the like.

Next, the granules are put into a furnace heated to a predetermined temperature and fired by a general method for synthesizing ferrite particles, thereby producing ferrite particles. The firing temperature is preferably in the range of 1100°C to 1350°C. When the firing temperature is 1100° C. or less, phase transformation is less likely to occur and sintering is less likely to proceed. Also, if the firing temperature exceeds 1350° C., there is a possibility that excessively large grains may be generated due to excessive sintering. The heating rate up to the firing temperature is preferably in the range of 250° C./h to 500° C./h. The retention time at the firing temperature is preferably 2 hours or more. The unevenness of the ferrite particle surface can also be adjusted by the oxygen concentration in the firing process. Specifically, the oxygen concentration during firing is set to 0.3 vol % to 1.2 vol %. Also, the oxidation state of the ferrite phase may be adjusted by making the oxygen concentration during cooling lower than the oxygen concentration during firing. Specifically, it is preferable to control the oxygen concentration in the range of 0.3 vol % to 1.2 vol % during firing and the oxygen concentration in the range of 0.1 vol % to 0.8 vol % during cooling.

The baked product thus obtained is pulverized if necessary. Specifically, for example, the fired product is pulverized using 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 carried out in order to arrange the particle size within a predetermined range. As a classification method, conventionally known methods such as wind classification and sieve classification can be used. Further, after primary classification with an air classifier, the particle size may be adjusted to a predetermined range with a vibrating sieve or an ultrasonic sieve. Furthermore, after the classification process, non-magnetic particles may be removed by a magnetic field separator. The volume average particle size of the ferrite particles is preferably 25 μm or more and less than 50 μm.

After that, 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. Moreover, 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 350° 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 desired chargeability and the like, the outer circumference of the carrier core material is coated with a resin to obtain a carrier for electrophotographic development.

(Carrier for electrophotographic development)
Conventionally known resins can be used as the resin for coating the surface of the carrier core material. Examples include polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene ) 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 the coating solution 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. cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; amide solvents such as dimethylformamide and dimethylacetamide. . 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, an immersion method, or the like can be used. Among these, the fluidized bed method is particularly preferred because it can be applied efficiently with a small amount of resin. The amount of resin coating can be adjusted, for example, in the case of a fluidized bed method, by adjusting the amount of resin solution to be sprayed and the spraying time.

The particle size of the carrier is generally in the range of 25 μm or more and less than 50 μm in terms of volume average particle diameter, preferably in the range of 30 μm or more and 40 μm or less.

(Electrophotographic developer)
The electrophotographic developer according to the present invention is obtained by mixing the carrier prepared as described above and the toner. The mixing ratio of the carrier and the toner is not particularly limited, and may be appropriately determined depending on the developing conditions of the developing device to be used. In general, 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 low. On the other hand, if the toner concentration exceeds 15% by mass, the toner scatters in the developing device and the toner adheres to the inside of the machine and the background of the transfer paper. This is because there is a possibility that a malfunction 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 produced by a conventionally known method such as a polymerization method, a pulverization classification method, a melt granulation method, a spray granulation method, or the like can be used. Specifically, a binder resin containing a thermoplastic resin as a main component and containing a colorant, a release agent, a charge control agent, etc. can be preferably used.

The particle size of the toner is preferably in the range of 5 μm to 15 μm, more preferably in the range of 7 μm to 12 μm, in terms of volume average particle size measured by a Coulter counter.

If necessary, a modifier may be added to the surface of the toner. Modifiers include, for example, silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethyl methacrylate, and the like. These can be used singly or in combination of two or more.

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 or the like can be used.

The development method using the developer of the present invention is not particularly limited, but a magnetic brush development method is preferred. FIG. 4 is a schematic diagram showing an example of a developing device that performs magnetic brush development. In the developing device shown in FIG. 4, a rotatable developing roller 3 containing 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 section are arranged in parallel in the horizontal direction. is formed between two screws 1 and 2 for agitating and conveying the developer in opposite directions to each other and between the two screws 1 and 2. At both ends of both screws, development is carried out from one screw to the other screw. A partition plate 4 is provided which allows movement of the developer and prevents movement of the developer except at both ends.

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

On the other hand, the developing roller 3 has a magnetic pole generating means in which 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 are provided inside a metal cylindrical body having an uneven surface of several μm. , blade poles _S2 having five poles arranged in sequence. When the cylindrical body of the developing roller 3 rotates in the direction of the arrow, the developer is drawn up from the screw 1 to the developing roller 3 by the magnetic force of the drawing 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 area, a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied from the transfer voltage power source 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 photosensitive drum 5 . Also, the background portion potential and the image portion 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. Also, the waveform of the bias voltage may be rectangular, sine, or triangular. 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 for development.

After that, the developer on the developing roller 3 is conveyed into the apparatus by the conveying magnetic pole _S1 , separated from the developing roller 3 by the separating electrode _N2 , and circulated and conveyed again in the apparatus by the screws 1 and 2 for development. Not mixed with developer and agitated. Then, the developer is newly supplied from the screw 1 to the developing roller 3 by the scooping pole _N3 .

In the embodiment shown in FIG. 4, the number of magnetic poles incorporated in the developing roller 3 is five. Of course, the number of magnetic poles may be increased to 8, 10, or 12 poles.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 43.55 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 8.17 kg, Mn ₃ O ₄ (average particle size: 2.1 μm, containing 0.55% by mass of SiO ₂ ) 8.33 kg, SrCO ₃ (average particle size: 0.6 μm) 332.9 g, SnO ₂ (average particle size: 5.6 μm) 273.4 g is dispersed in 20.48 kg of pure water, 180.1 g of carbon black as a reducing agent, 366.3 g of ammonium polycarboxylate dispersant as a dispersant, and 42% aqueous ammonia as a pH adjuster. .8 g was added to form the mixture. At this time, the Si content in the mixture was adjusted to 0.17 mol % with respect to the total of Fe, Mn, Sr, Sn and Si. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1110° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1110° C. for 3 hours at an oxygen concentration of 1.0 vol % to 0.4 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill ("Hammer Crusher NH-34S" manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to produce a volume average particle size of 34.9 μm. Particles were obtained. The obtained sintered particles were subjected to an oxidation treatment by being held at a temperature of 400° C. in the atmosphere for 1 hour, and a carrier core material according to Example 1 was obtained.
Apparent density, fluidity, volume average particle diameter (average particle diameter), magnetic properties, static electrical resistance, pore volume, true density, maximum height Rz, average length RSm, and deformity of the obtained carrier core material The rate was measured by the method shown below, and image white spots, carrier scattering, and toner spent were evaluated according to the criteria shown below. The physical properties of the carrier core materials according to the following examples and comparative examples were measured by the same method and evaluated according to the same criteria. Further, FIG. 1 shows a SEM photograph of the carrier core material of Example 1. As shown in FIG. The white line in the lower right of FIG. 1 has a length of 10 μm (the same applies to FIGS. 2 and 3).

(Example 2)
As raw materials, 37.76 kg of Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) and 14.26 kg of Mn ₃ O ₄ (average particle size: 3.4 μm) were mixed with 17 pure water. 379.8 g of ammonium polycarboxylate dispersant as a dispersant and 36.4 g of 25% by mass aqueous ammonia as a pH adjuster were added to prepare a mixture. At this time, the content of Si in the mixture was adjusted to 0.08 mol % with respect to the total of Fe, Mn and Si. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry 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 the granules using a sieve.
The granules were placed in an electric furnace and heated to 1170° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1170° C. for 3 hours at an oxygen concentration of 1.0 vol % to 0.4 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to be fired to a volume average particle size of 35.5 μm. Particles were obtained. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 350° C. in the atmosphere for 1 hour, and a carrier core material according to Example 2 was obtained.

(Example 3)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 37.76 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 14.26 kg, CaCO ₃ ( 370.1 g of average particle size: 1.1 μm) is dispersed in 17.49 kg of pure water, 379.8 g of ammonium polycarboxylate-based dispersant as a dispersant, and 36.4 g of 25% by mass ammonia water as a pH adjuster. were added to form a mixture. At this time, the content of Si in the mixture was adjusted to 0.08 mol % with respect to the total of Fe, Mn, Ca and Si. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry 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 the granules using a sieve.
The granules were placed in an electric furnace and heated to 1270° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1270° C. for 3 hours at an oxygen concentration of 0.4 vol % to 1.0 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve, and fired to a volume average particle size of 36.0 μm. Particles were obtained. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 440° C. in the atmosphere for 1 hour, and a carrier core material according to Example 3 was obtained.

(Example 4)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 37.76 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 14.26 kg, CaCO ₃ ( 370.1 g of average particle size: 1.1 μm) is dispersed in 17.49 kg of pure water, 379.8 g of ammonium polycarboxylate-based dispersant as a dispersant, and 36.4 g of 25% by mass ammonia water as a pH adjuster. were added to form a mixture. At this time, the content of Si in the mixture was adjusted to 0.08 mol % with respect to the total of Fe, Mn, Ca and Si. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry 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 the granules using a sieve.
The granules were placed in an electric furnace and heated to 1240° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1240° C. for 3 hours at an oxygen concentration of 1.0 vol % to 0.4 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to obtain a volume average particle size of 36.0 μm. A carrier core material according to Example 4 was obtained.

(Comparative example 1)
Granules were obtained by the same procedure as in Example 1, except that coarse particles having a particle size of 54 μm or more were not removed by sieving.
The resulting granules are heated to 1300° C. over 4.5 hours at an oxygen concentration of 1.0 vol%, and then held at 1300° C. at an oxygen concentration of 1.0 vol% to 0.4 vol% for 3 hours. The fired particles according to Comparative Example 1 having a volume average particle diameter of 35.4 μm were obtained in the same manner as in Example 1, except that the particles were fired at an oxygen concentration of 0.4 vol % and cooled over 6 hours. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 445° C. in the atmosphere for 1 hour, and a carrier core material according to Comparative Example 1 was obtained.

(Comparative example 2)
Granules were obtained by the same procedure as in Example 1, except that coarse particles having a particle size of 54 μm or more were not removed by sieving.
The resulting granules are heated to 1250° C. over 4.5 hours at an oxygen concentration of 1.0 vol%, and then held at 1250° C. at an oxygen concentration of 1.0 vol% to 0.4 vol% for 3 hours. The fired particles according to Comparative Example 2 having a volume average particle diameter of 34.9 μm were obtained in the same manner as in Example 1, except that the particles were fired at an oxygen concentration of 0.4 vol % and cooled over 6 hours. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 440° C. in the atmosphere for 1 hour, and a carrier core material according to Comparative Example 2 was obtained.

(Comparative Example 3)
Granules were obtained by the same procedure as in Example 1, except that coarse particles having a particle size of 54 μm or more were not removed by sieving.
The obtained granules are heated to 1200° C. over 4.5 hours at an oxygen concentration of 1.0 vol%, and then held at 1200° C. at an oxygen concentration of 1.0 vol% to 0.4 vol% for 3 hours. and cooled for 6 hours at an oxygen concentration of 0.4 vol % to obtain calcined particles according to Comparative Example 3 having a volume average particle size of 35.7 μm in the same manner as in Example 1. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 450° C. in the atmosphere for 1 hour, and a carrier core material according to Comparative Example 3 was obtained.

(Comparative Example 4)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 28.94 kg, Mn ₃ O ₄ (average particle size: 2.1 μm, containing 0.55 mass of SiO _{2 )} % content) was dispersed in 13.62 kg of pure water, and 111.6 g of carbon black as a reducing agent and 250.8 g of ammonium polycarboxylate dispersant as a dispersant were added to prepare a mixture. At this time, the Si content of the mixture was adjusted to 0.28 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1200° C. over 4.5 hours at an oxygen concentration of 0.5 vol %. After that, sintering was performed by holding at 1200° C. for 2.5 hours with an oxygen concentration of 0.5 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.5 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to produce a volume average particle size of 34.4 μm. Particles were obtained. The obtained calcined particles were subjected to an oxidation treatment by being held in the air at a temperature of 425° C. for 1 hour, and a carrier core material according to Comparative Example 4 was obtained.

(Comparative Example 5)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 23.23 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 8.71 kg, CaCO ₃ ( 107.7 g of average particle size: 1.1 μm) is dispersed in 10.82 kg of pure water, 95.8 g of carbon black as a reducing agent, 194.8 g of ammonium polycarboxylate dispersant as a dispersant, and a pH adjuster. As a mixture, 22.6 g of 25% by mass aqueous ammonia was added to form a mixture. At this time, the Si content of the mixture was adjusted to 0.08 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry 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 the granules using a sieve.
The granules were placed in an electric furnace and heated to 1300° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1300° C. for 3 hours at an oxygen concentration of 1.0 vol % to 0.4 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve, and fired to a volume average particle size of 36.0 μm. Particles were obtained. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 460° C. in the atmosphere for 1 hour, and a carrier core material according to Comparative Example 5 was obtained.

(Comparative Example 6)
As raw materials, 14.34 kg of Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO 2 ), Mn ₃ O ₄ (average particle size: 2.1 μm, containing 0.55% by mass of SiO ₂ ) containing) 4.62 kg and MgO 1.04 kg were mixed. This mixture was pelletized with a roller compactor. The obtained pellets were calcined in a rotary kiln at 850° C. under atmospheric conditions. The mixture was pulverized for 6 hours with a dry bead mill to obtain a calcined powder.
The obtained calcined powder and 149.5 g of CaCO ₃ (average particle size: 1.1 μm) were dispersed in 7.12 kg of pure water, and 219.7 g of an aqueous solution containing 21% methacrylic acid polymer was added as a dispersant. to form a mixture. At this time, the Si content of the mixture was adjusted to 0.23 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1150° C. over 4.5 hours at an oxygen concentration of 1.6 vol %. After that, firing was carried out by holding at 1300° C. for 3 hours at an oxygen concentration of 1.6 vol % to 0.64 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.64 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to compare the volume average particle size of 35.4 μm. A carrier core material according to Example 6 was obtained.

(Comparative Example 7)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 14.52 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 5.44 kg, SrCO ₃ ( 111.4 g of average particle size: 0.6 μm) and 91.0 g of SnO ₂ (average particle size: 5.6 μm) were dispersed in 6.90 kg of pure water, and 60.5 g of carbon black was used as a reducing agent. 121.0 g of ammonium polycarboxylate-based dispersant and 14.0 g of 25% by mass ammonia water as a pH adjuster were added to prepare a mixture. At this time, the Si content of the mixture was adjusted to 0.08 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1230° C. over 4.5 hours at an oxygen concentration of 1.0 vol %. After that, firing was carried out by holding at 1230° C. for 3 hours at an oxygen concentration of 1.0 vol % to 0.4 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.4 vol %.
The resulting fired product is pulverized with a hammer mill ("Hammer Crusher NH-34S" manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to produce a volume average particle size of 35.3 μm. Particles were obtained. The obtained calcined particles were subjected to an oxidation treatment by being held at a temperature of 450° C. in the atmosphere for 1 hour, and a carrier core material according to Comparative Example 7 was obtained.

(Comparative Example 8)
As raw materials, 20.86 kg of Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ), Mn ₃ O ₄ (average particle size: 2.1 μm, containing 0.55 mass of SiO ₂ % content), 0.74 kg of MgO, and 131.0 g of CaCO ₃ were mixed. This mixture was pelletized with a roller compactor. The obtained pellets were calcined in a rotary kiln at 850° C. under atmospheric conditions. The mixture was pulverized for 6 hours with a dry bead mill to obtain a calcined powder.
The obtained calcined powder was dispersed in 10.55 kg of pure water, and 122.0 g of carbon black as a reducing agent and 180.0 g of ammonium polycarboxylate dispersant as a dispersant were added to prepare a mixture. At this time, the Si content of the mixture was adjusted to 0.27 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry granules having a particle size of 10 μm to 75 μm. Fine particles with a particle size of 33 μm or less and coarse particles with a particle size of 43 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1110° C. over 3 hours at an oxygen concentration of 0.5 vol %. After that, firing was carried out by holding at 1300° C. for 3 hours at an oxygen concentration of 0.5 vol % to 0.65 vol %. After that, it was cooled over 6 hours at an oxygen concentration of 0.65 vol %.
The resulting fired product is pulverized with a hammer mill ("Hammer Crusher NH-34S" manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibration sieve to be fired to a volume average particle size of 33.0 μm. Particles were obtained. The obtained sintered particles were subjected to an oxidation treatment by being held in the atmosphere at a temperature of 385° C. for 1 hour, and a carrier core material according to Comparative Example 8 was obtained. FIG. 2 shows an SEM photograph of the carrier core material of Comparative Example 8. As shown in FIG.

(Comparative Example 9)
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 20.13 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 3.47 kg, Mn ₃ O ₄ 6.45 kg (average particle size: 2.1 μm, containing 0.55% by mass of SiO ₂ ) and 220.1 g of SrCO ₃ (average particle size: 0.6 μm) were dispersed in 7.43 kg of pure water and dispersed. 180.0 g of ammonium polycarboxylate-based dispersant as an agent, 180.0 g of 25 mass % aqueous ammonia as a pH adjuster, and 6.25 g of colloidal silica having a solid content of 48 wt % were added to prepare a mixture. At this time, the Si content of the mixture was adjusted to 0.28 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by a spray dryer to obtain dry granules having a particle size of 10 μm to 90 μm. Fine particles with a particle size of 37 μm or less and coarse particles with a particle size of 50 μm or more were removed from the granules using a sieve.
The granules were placed in an electric furnace and heated to 1110° C. over 3 hours at an oxygen concentration of 2.50 vol %. After that, firing was carried out by holding at 1110° C. with an oxygen concentration of 2.50 vol % to 1.25 vol % for 3 hours. After that, it was cooled over 6 hours at an oxygen concentration of 1.25 vol %.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to produce a volume average particle size of 37.3 μm. Particles were obtained. The obtained sintered particles were subjected to an oxidation treatment by being held in the air at a temperature of 405° C. for 1 hour, and a carrier core material according to Comparative Example 9 was obtained. FIG. 3 shows an SEM photograph of the carrier core material of Comparative Example 9. As shown in FIG.

(Comparative Example 10)
As raw materials, 7.98 kg of Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) and 2.02 kg of MgO were mixed. This mixture was pelletized with a roller compactor. The obtained pellets were calcined in a rotary kiln at 850° C. under atmospheric conditions. The mixture was pulverized for 6 hours with a dry bead mill to obtain a calcined powder.
The obtained calcined powder and Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 18.62 kg, Mn ₃ O ₄ (average particle size: 2.1 μm, containing SiO ₂ 9.08 kg of CaCO 3 (containing 0.55% by mass) and 203.6 g of CaCO ₃ (average particle size: 1.1 μm) were dispersed in 12.70 kg of pure water, and 188.0 g of ammonium polycarboxylate-based dispersant was used as a dispersant. was added to form a mixture. At this time, the Si content of the mixture was adjusted to 0.21 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
This granulated product was placed in an electric furnace and heated to 1210° C. over 4.5 hours while waiting. After that, firing was carried out by holding at 1210° C. for 4 hours while waiting. After that, it was cooled in air for 8 hours.
The resulting fired product was pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to compare the volume average particle size of 36.0 μm. A carrier core material according to Example 10 was obtained.

(Comparative Example 11)
As raw materials, 9.58 kg of Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) and 2.42 kg of MgO were mixed. This mixture was pelletized with a roller compactor. The obtained pellets were calcined in a rotary kiln at 850° C. under atmospheric conditions. The mixture was pulverized for 6 hours with a dry bead mill to obtain a calcined powder.
The obtained calcined powder and Fe ₂ O ₃ (average particle size: 0.6 μm, containing 0.08% by mass of SiO ₂ ) 22.33 kg, Mn ₃ O ₄ (average particle size: 2.1 μm, containing SiO ₂ 0.55% by mass) was dispersed in 15.15 kg of pure water, and 226.7 g of ammonium polycarboxylate-based dispersant was added as a dispersant to prepare a mixture. At this time, the Si content of the mixture was adjusted to 0.21 mol %. This mixture was pulverized by a wet ball mill (media diameter: 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air of about 210° C. by 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 and coarse particles with a particle size of 54 μm or more were removed from the granules using a sieve.
This granulated product was placed in an electric furnace and heated to 1210° C. over 4.5 hours while waiting. After that, firing was carried out by holding at 1210° C. for 4 hours while waiting. After that, it was cooled in air for 8 hours.
The resulting fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to compare the volume average particle size of 35.6 μm. A carrier core material according to Example 11 was obtained.

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

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

(Volume average particle size (average particle size) and ratio of particle size of 22 μm or less)
The volume average particle size and the ratio of particle sizes of 22 μm or less of the carrier core material were measured using a laser diffraction particle size distribution analyzer (“Microtrac Model 9320-X100” manufactured by Nikkiso Co., Ltd.).

(Magnetic properties)
Using a room temperature vibrating sample magnetometer (VSM) (“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 × 10 ⁴ A / m (10000 Oersted). σ s , remanent magnetization σ _r , coercive force H _c and magnetization σ _1k (Am ² /kg) in a magnetic _field of 79.58×10 ³ A/m (1000 Oersted) were measured, respectively. .

(static electrical resistance)
As electrodes, two brass plates with a plate thickness of 2 mm whose surface was electropolished are arranged so that the distance between the electrodes is 2 mm, and 200 mg of a carrier core material is charged into the gap between the two electrode plates. A magnet with a cross-sectional area of 240 mm ² is placed behind and a bridge of the powder to be measured is formed between the electrodes. was measured by a four-probe method to obtain a resistance value.

(pore volume)
As an evaluation device, POREMASTER-60GT manufactured by Quantachrome was used. Specifically, the measurement conditions are as follows.
Cell Stem Volume: 0.5 cm ³ ,
Head pressure: 20PSIA,
Mercury surface tension: 485.00 erg/cm ² ,
Mercury contact angle: 130.00 degrees,
High pressure measurement mode: Fixed Rate,
Motor Speed: 1,
High pressure measurement range: 20.00-10000.00PSI
1.500 g of the sample was weighed and filled in a 0.5 cm ³ cell for measurement. The pore volume was obtained by subtracting the volume A (cm ³ /g) at 60 PSI from the volume B (cm ³ /g) at 10000 PSI.

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

(Measurement of maximum height Rz and average length RSm)
Using an ultra-deep color 3D shape measuring microscope ("VK-X100" manufactured by Keyence Corporation), the surface was observed with a 100x objective lens. Specifically, first, a carrier core material was fixed to an adhesive tape with a flat surface, and after determining a measurement field of view with a 100-fold objective lens, the autofocus function was used to adjust the focus to the adhesive tape surface. The flat adhesive tape surface on which the carrier core material was fixed was irradiated with a laser beam in the vertical direction (Z direction), and the surface was scanned in the X and Y directions. Data in the Z direction were obtained by connecting the height positions of the lens when the intensity of the reflected light from the surface was maximized. The three-dimensional shape of the surface of the carrier core material was obtained by connecting the position data in the X, Y and Z directions. An automatic photographing function was used to take in the three-dimensional shape of the carrier core material surface.
Each parameter was measured using particle roughness inspection software (manufactured by Mitani Corporation). First, as a pretreatment, three-dimensional particle recognition and shape selection were performed on the surface of the obtained carrier core material. Particle recognition was performed by the following method. Of the three-dimensional shape obtained by imaging, the maximum value in the Z direction is 100%, the minimum value is 0%, and the range from the maximum value to the minimum value is divided into 100 equal parts. An area corresponding to 100 to 35% of this was extracted, and the outline of the independent area was recognized as the grain outline. Next, particles such as coarse particles, fine particles, and aggregates were excluded by shape selection. By performing this shape selection, it is possible to reduce the error in the subsequent curvature correction. Specifically, particles with an equivalent area diameter of 28 μm or less, 38 μm or more, and an acicular ratio of 1.15 or more were excluded. Here, the acicular ratio is a parameter calculated from the ratio of the maximum length/diagonal width of the particle, and the diagonal width is the shortest distance between two straight lines when the particle is sandwiched between two straight lines parallel to the maximum length. represents
Next, the part used for analysis was taken out from the three-dimensional shape of the surface. First, a square with a side length of 15.0 μm is drawn centering on the center of gravity obtained from the particle contour recognized by the above method. 21 parallel lines were drawn in the drawn square, and 21 roughness curves corresponding to the line segments were taken out.

Since the carrier core material has a substantially spherical shape, the extracted roughness curve has a constant curvature as the background. For this reason, the background was corrected by fitting an optimal quadratic curve and subtracting it from the roughness curve. In this case, a low-pass filter was applied with an intensity of 1.5 μm and a cut-off value λ of 80 μm.

The maximum height Rz was obtained as the sum of the height of the highest peak and the depth of the deepest valley in the roughness curve. In calculating the maximum height Rz, the average value of 50 particles was used as the average value of each parameter.

The average length RSm is obtained by averaging the lengths of each element of the roughness curve, which defines a combination of troughs and peaks as one element. In calculating the average length RSm, the average value of 50 particles was used as the average value of each parameter.

The maximum height Rz and the average length RSm described above are measured according to JIS B0601 (2001 version).

(malformation rate)
An injection type image analysis particle size distribution meter (Jusco International Co., Ltd., model: IF-3200) was used as an evaluation device. Specifically, 0.07 g of the sample was weighed, dispersed in a screw tube bottle (capacity 9 cm ³ ) containing 9 cm ³ of polyethylene glycol 400, and then measured.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: relative measurement Measurement volume: 0.95 cm ³
Analysis: Dark Detection Threshold: 169 (fill in holes)
O-Roughness filter: 0.5
In addition, O-Roughness = the ratio of the portion removed until the surface becomes smooth Filter conditions:
ISO Area Diameter: minimum value 5, maximum value 100, inner range Note that ISO Area Diameter = diameter of a circle having a pixel image equal to the particle projected area (analysis conditions)
Analysis filter condition I:
ISO Circularity: minimum 25, maximum 55, inner range analysis filter condition II:
ISO Circularity: minimum value 25, maximum value 55, inner range ISO Solidity: minimum value 0.98, maximum value 1, outer range Note that ISO Solidity = the ratio of the particle area to the area of the convex hull surrounding the particle Ell. Ratio: minimum value 0.8, maximum value 1, inner range Note that Ell. Ratio = ratio of minor axis to major axis of inertial ellipse The number of particles counted under analysis filter condition II was divided by the number of particles counted under analysis filter condition I to calculate the deformity ratio, which is the ratio of deformed particles.

(viscosity)
The slurry viscosity was measured using a BROOKFIELD digital viscometer DV-I Prime LV.

(Evaluation of image white spots)
Manufactured in the developing device having the _structure shown in FIG _. A solid black image was printed after the developing device was driven for a time corresponding to printing 100,000 sheets, and the degree of white voids in the solid black portion was visually evaluated according to the following criteria.
"A": No white spots were observed, and the image was good.
"○": Less than 5 white spots "△": 5 to 10 white spots "X": Clearly more than 10 white spots are present.

(Evaluation of carrier scattering)
Manufactured in the developing device having the _structure shown in FIG _. 10 sheets of blank paper were developed, and the number of carriers adhering to the surface of the photoreceptor was counted by observation with a magnifying glass in 5 fields of view, and the average number of adhered carriers per 100 cm ² was obtained. and This evaluation was performed after the developing device was driven for a time corresponding to the time required to print 100,000 A4 vertical sheets (a time corresponding to printing 100,000 sheets).
"◎": Less than 10 "○": 10 or more and less than 30 "△": 30 or more and less than 50 "X": 50 or more

(toner spent)
After the developer was stirred for 36 hours, the carrier was extracted from the developer and observed with a scanning electron microscope (JSM-6510LA type, manufactured by JEOL Ltd.), and the number ratio of carriers with toner fused to the surface was measured. .
"A": 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 toner-fused carriers was 0.5 or more and less than 1.0%.
"Fair": The ratio of the number of carriers fused to the toner 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.

As shown in Table 2, the developers using the carrier core materials of Examples 1 to 3, which satisfy the constitution defined in the present invention, are evaluated for image voids, carrier scattering, and toner spent. Nothing was a problem.

On the other hand, in the developers using the carrier core materials of Comparative Examples 1 and 2, which had a smaller pore volume, a larger maximum height Rz, and a larger deformity rate than the specified range of the present invention, image white spots occurred. . In addition, the developer using the carrier core material of Comparative Examples 3 and 5, which had a smaller pore volume and a higher deformity rate than the specified range of the present invention, and the carrier core material of Comparative Example 4, which had a smaller pore volume, were used. Image white spots also occurred in the developer.

Carrier scattering occurred in the developer using the carrier core material of Comparative Example 6, which had a saturation magnetization σ _s smaller than the specified range of the present invention. Also, the developer using the carrier core material of Comparative Example 7, which has a larger pore volume than the specified range of the present invention, also caused carrier scattering.

In the developer using the carrier core material of Comparative Example 8, which has a saturation magnetization σ _s smaller than the specified range of the present invention and a small deformity ratio, carrier scattering and toner spent occurred, and the carrier core material of Comparative Example 9 was used. In the developer, carrier scattering was not a problem in practical use, but toner spent, which was a problem in practical use, occurred.

A developer using the carrier core material of Comparative Example 9, which has a saturation magnetization σ _s and a pore volume smaller than the specified ranges of the present invention and a large anomaly rate, and a saturation magnetization σ _s and pores larger than the specified ranges of the present invention. In all the developers using the carrier core material of Comparative Example 9 having a small volume, image voids and carrier scattering occurred.

According to the carrier core material of the present invention, it is possible to suppress toner spent, image white spots, and carrier scattering even when the image forming speed is high or when the carrier is used for a long period of time.

3 developing roller 5 photoreceptor drum

Claims (5)

A carrier core material composed of ferrite particles,
Saturation magnetization σ _s is 75 Am ² /kg or more and 90 Am ² /kg or less,
Pore volume is 0.008 cm ³ /g or more and less than 0.020 cm ³ /g,
The maximum height Rz is 1.4 μm or more and 2.0 μm or less,
A carrier core material characterized by having an anomaly rate of particles in the range of 10% or more and 50% or less as measured by the following measuring method.
(Method for measuring anomalous shape rate of particles)
Measuring device: Injection type image analysis particle size distribution meter Measurement sample amount: 0.07 g
The measurement was carried out after dispersion in a screw vial (capacity 9 cm ^{3 )} filled with 9 cm ³ of polyethylene glycol 400.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: relative measurement Measurement volume: 0.95 cm ³
Analysis: Dark Detection Threshold: 169 (fill in holes)
O-Roughness filter: 0.5
Filter condition:
ISO Area Diameter: minimum value 5, maximum value 100, inner range (analysis conditions)
Analysis filter condition I:
ISO Area Diameter: Minimum 25, Maximum 55, Inner Range Analysis Filter Condition II:
ISO Area Diameter: minimum value 25, maximum value 55, inner range ISO Solidity: minimum value 0.98, maximum value 1, outer range Ell. Ratio: minimum value 0.8, maximum value 1, the number of particles counted under the inner range analysis filter condition II is divided by the number of particles counted under the analysis filter condition I to calculate the deformity ratio. 2. The carrier core material according to claim 1, wherein the average length RSm of grains appearing on the particle surface is 5.0 μm or more and 7.1 μm or less. 3. The carrier core material according to claim 1, wherein the magnetization σ _1k in a magnetic field of 79.58×10 ³ A/m (1000 Oersted) is 61 Am ² /kg or more and 75 Am ² /kg or less. 4. A carrier for electrophotographic development, wherein the surface of the carrier core material according to any one of claims 1 to 3 is coated with a resin. An electrophotographic developer comprising the electrophotographic developing carrier according to claim 4 and a toner.

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