JP2021117281A - Ferrite carrier core material, electrophotographic development carrier using the same, and electrophotographic developer - Google Patents

Abstract

To provide a ferrite carrier core material which suppresses image memory, exhibits less wear on a resin coating layer even after prolonged use, and suppresses carrier adhesion.SOLUTION: A ferrite carrier core material features particles with a maximum peak-valley depth Rz of 1.95-2.38 μm. inclusive, an average length RSm of 7.20-8.50 μm, inclusive, the product of Rz and RSm being 15.8 or greater, and a deformity rate of 46% or greater as measured by a predetermined method.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ferrite carrier core material, a carrier for electrophotographic development using the same, 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 adhered to an electrostatic latent image formed on the surface of a photoconductor to make a visible image, and this visible image is made into a 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 the development method using a two-component developer, the carrier and the toner are stirred and mixed in the developing apparatus, 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 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 remains on the developing roller and is mixed with the toner again in the developing apparatus. Therefore, as carrier characteristics, magnetic characteristics for forming a magnetic brush, charging characteristics for imparting a desired charge to toner, and durability in repeated use are required.

As such a carrier, one in which the surface of magnetic particles such as magnetite and various ferrites is coated with a resin is generally used. Magnetic particles as a carrier core material are required to have good triboelectric properties with respect to toner as well as good magnetic properties. Various shapes have been proposed as carrier core materials satisfying such characteristics.

For example, for the purpose of suppressing a memory image (a phenomenon in which the influence of the front image appears in the rear image), a specific amount of strontium (Sr) and silicon (Si) is contained, and the maximum mountain valley depth Rz of the particles and its standard deviation σ It has been proposed to use manganese (Mn) ferrite particles in a specific range as a carrier core material (Patent Document 1). Further, 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 and calcium (Ca) is contained in a specific amount, and the average length RSm of grains appearing on the particle surface is increased. It has also been proposed to use a carrier core material in which the frequency of grains having a predetermined value or more is set to a predetermined value or less (Patent Document 2).

JP-A-2017-31031 Japanese Unexamined Patent Publication No. 2016-184130

A part of the carrier core material in a resin-coated carrier in which the surface of the carrier core material is resin-coated by increasing the maximum mountain valley depth Rz of the particles, that is, by advancing the unevenness of the particle surface as in the technique proposed in Patent Document 1. Is exposed on the surface, the electrical resistance of the resin-coated carrier is reduced, and the generation of memory images is suppressed.

However, if the carrier core material particles are deformed while the grain size is small, the grains may be excessively sharpened. If the resin-coated carrier having such excessively sharpened grains is continuously used, the mechanical stress on the resin-coated carrier in the magnetic brush becomes large, the resin-coated layer is worn, and the carrier core material is surfaced more than necessary. May be exposed to.

Charge injection is likely to occur in the developed region of the resin-coated carrier in which the carrier core material is exposed on the surface, and as a result, “carrier adhesion” may occur in which the resin-coated carrier moves to the photoconductor drum.

The present invention has been made in view of such conventional problems, and an object of the present invention is that the image memory can be suppressed, and excessive surface exposure of the carrier core material due to wear of the resin coating layer even after long-term use. It is an object of the present invention to provide a carrier core material which is less likely to cause carrier adhesion.

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

The ferrite carrier core material according to the present invention (hereinafter, may be simply referred to as “carrier core material”) that achieves the above object has a maximum mountain valley depth Rz of particles of 1.95 μm or more and 2.38 μm or less. The average length RSm is 7.20 μm or more and 8.50 μm or less, the product of Rz and RSm is 15.8 or more, and the deformation rate of the particles measured by the following measuring method is 46% or more. ..
(Measurement method of particle deformity rate)
Measuring device: Injection type image analysis Particle size distribution meter Measurement sample: 0.07 g
The measurement was carried out after dispersion in a screw tube bottle (capacity: 9 ml) containing 9 ml of polyethylene glycol 400.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: Relative measurement Measured quantity: 0.95 ml
Analysis: Dark detection threshold: 169 (fills holes)
O-Roughness filter: 0.5
* O-Roughness = Percentage of parts removed before the surface becomes smooth Filter condition:
ISO Area Diameter: Minimum value 5, Maximum value 100, Inner range * ISO Area Diameter = Diameter of a circle with a pixel image equal to the projected particle area (analysis condition)
Analysis filter condition I:
ISO Area Diameter: Minimum value 25, Maximum value 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 * ISO Solidity = Ratio of particle area to the area of the convex hull surrounding the particle Ell. Ratio: Minimum value 0.8, maximum value 1, inner range * Ell. Ratio = Ratio of the minor axis to the major axis of the inertial ellipse The deformity ratio is calculated by dividing the number of particles counted under the analysis filter condition II by the number of particles counted under the analysis filter condition I.

Further, the carrier core material having the above structure _{has a composition represented by (Mn x} Fe _3-x ) O ₄ (where 0 <x <3), and Sr is 0.01 mol% or more and 0.50 mol. % Or less, and Sn is preferably contained in an amount of 0.01 mol% or more and 0.50 mol% or less.

Further, in the carrier core material having the above structure, it is preferable that x is 0.01 or more and 2 or less.

Further, it is preferable that the carrier core material having the above structure contains 0.10 mol% or more and 0.22 mol% or less of Si.

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 developing agent characterized by containing the above-mentioned electrophotographic developing carrier and toner.

According to the carrier core material according to the present invention, the development memory can be suppressed, and the resin coating layer is less likely to be worn even after long-term use, and the occurrence of carrier adhesion can be suppressed.

Further, by using the developing agent 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 1. It is a schematic diagram which shows an example of the developing apparatus using the carrier which concerns on this invention.

A major feature of the present invention is that the maximum mountain valley depth Rz of the particles, the average length RSm of the particles, the product of the maximum peak valley depth Rz and the average length RSm, and the deformation rate of the particles measured by the measurement method are specified. A major feature is that the range is satisfied at the same time. More specifically, when the maximum mountain valley depth Rz of the particles and the deformation rate of the particles are within a specific range, a part of the carrier core material is exposed on the surface of the resin-coated carrier and the electrical resistance is lowered, so that the memory image Occurrence is suppressed. At the same time, the average length RSm of the particles is in a specific range, that is, the grain size is larger than before, so that excessive sharpening of the grains is suppressed and mechanical stress on the resin coating carrier in the magnetic brush is suppressed. Is reduced and wear of the resin coating layer is suppressed.

Hereinafter, the configuration of the present invention will be described individually. First, in the present invention, the maximum mountain valley depth Rz of the particles is in the range of 1.95 μm or more and 2.38 μm or less. When the maximum mountain valley depth Rz is in this range, the image memory and carrier adhesion are suppressed. A more preferable range of the maximum mountain valley depth Rz is a range of 2.10 μm or more and 2.35 μm or less.

Next, the average length RSm of the particles in the present invention is in the range of 7.20 μm or more and 8.50 μm or less. When the average length RSm is in this range, excessive sharpening of the grain is suppressed, mechanical stress on the resin coating carrier in the magnetic brush is reduced, and wear of the resin coating layer is suppressed. A more preferable range of the average length RSm is a range of 7.44 μm or more and 8.00 μm or less.

The product of the maximum mountain valley depth Rz and the average length RSm is 15.8 or more. If the product is less than 15.8, the developing memory and the resin coating layer are worn. A more preferable lower limit of the product is 16.5.

The deformation rate of the particles measured by the measuring method in the present invention is 46% or more. When the deformation rate of the carrier core material is less than 46%, when the surface of the carrier core material is coated with resin to form a resin-coated carrier, the carrier core material is less exposed on the resin-coated carrier surface and accumulates in the carrier core material. The counter charge is less likely to be released, and development memory is likely to occur. The deformation rate of the carrier core material is more preferably 46% or more, still more preferably 50% or more.

The carrier core material according to the present invention has a composition represented by the composition formula (Mn _x Fe _3-x ) O ₄ (where 0 <x <3), and has an Sr of 0.01 mol% or more and 0. It is preferably contained in an amount of .50 mol% or less, and more preferably 0.01 mol% or more and 0.50 mol% or less of Sn. By containing the above amount of Sr, a part of Sr ferrite is generated in the firing step, a magnetoplumbite-type crystal structure is formed, and the uneven shape on the surface of the carrier core material is easily promoted. On the other hand, Sn has a sintering inhibitory effect, and by containing Sn together with Sr in the above amount, it is possible to prevent the particles from being excessively deformed as compared with the case where only Sr is contained, and the desired unevenness is formed in the particles. Formed on the surface. For example, by containing Sr and Sn, even when the firing temperature is 1200 ° C. or higher, which is higher than the conventional one, spheroidization due to decomposition / melting of material components is suppressed and the uneven shape of the surface is maintained and promoted. Will be done. A more preferable Sr content is preferably in the range of 0.1 mol% or more and 0.50 mol% or less. Further, the more preferable Sn content is in the range of 0.1 mol% or more and 0.40 mol% or less.

In the present invention, it is preferable that Si is contained in an amount of 0.10 mol% or more and 0.22 mol% or less. If Si is less than 0.10 mol%, the particles may be deformed in a state where the grain size is small, and the sharpening of the grain may be excessively promoted. On the other hand, if Si exceeds 0.22 mol%, decomposition / melting and diffusion of particles are promoted, and spheroidization, which is energetically stable, may be excessively promoted. Normally, the Si content can be adjusted by the amount of the Si raw material added, but it can also be adjusted by the amount of the mixed raw material in which the Si raw material and other raw materials are mixed. In the examples described later, a mixed raw material containing Fe and Si and a mixed raw material containing Mn and Si are used, and the Si content is adjusted by the amount of the mixed raw material added. When a mixed raw material is used, the amount of the Si raw material added is calculated from the Si content of the mixed raw material.

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, and more preferably in the range of 30 μm or more and 40 μm or less.

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 Fe component raw material, the Mn component raw material, the Sr component raw material, the Sn component raw material, the Si component raw material, and, if necessary, conventionally known additives are weighed. As the Fe component raw material, Fe ₂ O ₃ or the like is preferably used. As the Mn component raw material, MnCO ₃ , Mn ₃ O _{4, and the} like can be used. _{Further, SrCO 3} and Sr (NO ₃ ) ₂ can be used as the Sr component raw _{material, SnO 2} and SnO can be used as the Sn component raw _{material, and SiO 2 and the} like are preferably used as the Si component raw material. Some Fe component raw materials and Mn component raw materials contain a predetermined amount of Si, and when such Fe component raw materials and Mn component raw materials having a Si content are used, the Fe component raw materials and the Mn component raw materials are contained. When the amount of Si added is sufficient, the Si component raw material does not have to be blended. On the contrary, when the amount of Si contained in the Fe component raw material and the Mn component raw material is insufficient, the Si component raw material is supplemented and blended.

Next, the raw material is put into a 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 polycarboxylic acid 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 solid-solid reaction proceeds sufficiently, which is preferable. On the other hand, when the temperature is 1000 ° C. or lower, sintering by calcining is weak and the raw material can be sufficiently crushed in the subsequent slurry crushing 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-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 chrome 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 granulated product 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 on 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 0.05% to 10%. 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 set in the range of 0.05% to 1.5%. The oxygen concentration in temperature raising, sintering, and cooling is preferably controlled in the range of 0.05% to 10%.

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 vibrating sieve or an ultrasonic sieve. Further, after the classification step, the non-magnetic particles may be removed by a magnetic field beneficiation machine. The particle size of the ferrite particles is preferably 25 μm or more and less than 50 μm.

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 desired chargeability and the like, the outer circumference of the carrier core material is coated with a resin to obtain an electrophotographic developing carrier.

As the resin for coating the surface of the carrier core material, conventionally known resins can be used, 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 can be mentioned.

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 solvent such as; cellosolve-based solvent such as ethyl cellosolve and butyl cellosolve; ester-based solvent such as ethyl acetate and butyl acetate; one or more kinds of amide-based solvent such as dimethylformamide and dimethylacetamide can be used. .. 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 25 μm or more and less than 50 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 photography according to the present invention is formed 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 scatters in the developing device and the toner adheres to the background such as stains on the machine and 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 produced 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 or a combination of two or more of these 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 preferable. FIG. 2 shows a schematic diagram showing an example of a developing apparatus that performs magnetic brush development. The developing apparatus shown in FIG. 2 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 spread the developer. Transport in opposite directions. Then, the developer moves from one screw to the other at both ends of the screws 1 and 2. As a result, the developer composed of toner and carrier is constantly circulated and agitated 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 tubular body having irregularities of several μm on the surface. , comprising a fixed magnet disposed five pole blade pole S ₂ in order. When the cylindrical body of the developing roller 3 is rotated in the arrow direction, by the magnetic force of the magnetic pole N _3, the developer is pumped from the screw 1 to the developing roller 3. 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 inter-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 bias voltage waveform 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.

Developer then on the developing roller 3 is conveyed into the apparatus by the conveyor pole S _1, and peeled from the developing roller 3 by the peeling electrode N _2, in the apparatus is recirculated conveyed by the screw 1 and 2, subjected to developing Mix and stir with undeveloped agent. Then the scooping pole N _3, new developer is supplied from the screw 1 to the developing roller 3.

In the embodiment shown in FIG. 2, 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.

Hereinafter, the present invention will be described in more detail 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% of SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 7.35 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% of SiO 2} ) 0.82 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. did. This mixture was pulverized by 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 a dry granulated product having a particle size of 10 μm to 75 μm.
This granulated product was placed in an electric furnace and heated to 1300 ° C. at an oxygen concentration of 1.0% over 4.5 hours. After that, calcination was carried out by holding at 1300 ° C. at an oxygen concentration of 0.4% to 1.0% for 3 hours. Then, it was cooled at an oxygen concentration of 0.4% over 6 hours.
The obtained fired product is pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm), classified using a vibrating sieve, and a carrier having a volume average particle size of 36.8 μm. Obtained a core material.
Apparent density (AD), fluidity (FR), volume average particle size (average particle size), pore volume, BET specific surface area, true density, shape characteristics (Rz, RSm, deformation rate) of the obtained carrier core material Was measured by the method shown below. The measurement results are shown in Tables 1 and 2. The carrier core materials according to the following Examples and Comparative Examples were also measured by the same method, and the measurement results are shown in Tables 1 and 2. Further, FIG. 1 shows an SEM photograph (magnification of 1000 times) of the obtained carrier core material.

Example 2
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 6.12 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% SiO 2} ) 2.04 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. A carrier core material having a volume average particle diameter of 37.3 μm was obtained in the same manner as in Example 1.

Example 3
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 4.08 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% SiO 2} ) 4.08 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. A carrier core material having a volume average particle diameter of 35.4 μm was obtained in the same manner as in Example 1.

Example 4
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% of SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 4.08 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% of SiO 2} ) 4.08 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. The mixture was pulverized with a wet ball mill (media diameter 3 mm) to obtain a mixed slurry.
This mixed slurry was sprayed into hot air at about 210 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 75 μm. A carrier core material having a volume average particle size of 35.9 μm was used in the same manner as in Example 1 except that fine particles having a particle size of 25 μm or less and coarse particles having a particle size of 54 μm or more were removed from the granulated product using a sieve. Obtained.

Example 5
The granulated product is placed in an electric furnace and heated to 1270 ° C. at an oxygen concentration of 1.0% over 4.5 hours, and then maintained at 1270 ° C. at an oxygen concentration of 0.4% to 1.0% for 3 hours. After that, a carrier core material having a volume average particle diameter of 35.7 μm was obtained in the same manner as in Example 1 except that the mixture was cooled at an oxygen concentration of 0.4% for 6 hours.

Example 6
The granulated product is placed in an electric furnace and heated to 1250 ° C. at an oxygen concentration of 1.0% over 4.5 hours, and then maintained at 1250 ° C. at an oxygen concentration of 0.4% to 1.0% for 3 hours. After that, a carrier core material having a volume average particle diameter of 34.9 μm was obtained in the same manner as in Example 1 except that the mixture was cooled at an oxygen concentration of 0.4% for 6 hours.

Example 7
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 2.04 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% SiO 2} ) 6.12 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. A carrier core material having a volume average particle diameter of 35.3 μm was obtained in the same manner as in Example 1.

Comparative Example 1
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 14.52 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 5.44 kg, SrCO ₃ (average) 111 g of particle size: 0.6 μm) _{and 91 g of SnO 2} (average particle size: 5.6 μm) were dispersed in 6.9 kg of pure water, 60.5 g of carbon black as a reducing agent, and ammonium polycarboxylate as a dispersant. A carrier core material having a volume average particle size of 35.9 μm was obtained in the same manner as in Example 1 except that 121 g of a dispersant and 14.2 g of aqueous ammonia as a pH adjuster were added to prepare a mixture.

Comparative Example 2
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 7.76 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% SiO 2} ) 0.41 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. A carrier core material having a volume average particle diameter of 36.7 μm was obtained in the same manner as in Example 1.

Comparative Example 3
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 21.78 kg, Mn ₃ O ₄ (average particle size: 3.4 μm) 0.82 kg, Mn ₃ O ₄ (Average particle size: 2.1 μm, _{containing 0.55% SiO 2} ) 7.35 kg, SrCO ₃ (average particle size: 0.6 μm) 167 g, SnO ₂ (average particle size: 5.6 μm) 136.4 g Disperse in 10.35 kg of pure water, add 90.76 g of carbon black as a reducing agent, 181.5 g of ammonium polycarboxylic acid dispersant as a dispersant, and 21.2 g of aqueous ammonia as a pH adjuster to form a mixture. A carrier core material having a volume average particle diameter of 35.2 μm was obtained in the same manner as in Example 1.

Comparative Example 4
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm, _{containing 0.08% SiO 2} ) 14.52 kg, Mn ₃ O ₄ (average particle size: 2.1 μm, containing 0.55% _{SiO 2)} ) 5.55 kg, SrCO ₃ (average particle size: 0.6 μm _{) 111.4 g, SnO 2} (average particle size: 5.6 μm) 91 g was dispersed in 6.9 kg of pure water, and 60 carbon black was used as a reducing agent. Carriers having a volume average particle size of 37.0 μm in the same manner as in Example 1 except that 5.5 g, 121 g of ammonium polycarboxylate dispersant as a dispersant, and 14.2 g of aqueous ammonia as a pH adjuster were added to prepare a mixture. Obtained a core material.

Comparative Example 5
A dry granulated product having a particle size of 10 μm to 75 μm was prepared in the same manner as in Example 1 except that SrCO ₃ (average particle size: 0.6 μm) and SnO _{2 (average particle size: 5.6 μm) were not added as raw materials.} Obtained.
The granulated product was placed in an electric furnace and heated to 1200 ° C. at an oxygen concentration of 1.3% over 4.5 hours, and then calcined by holding it at 1200 ° C. at an oxygen concentration of 1.3% for 3 hours. Then, a carrier core material having a volume average particle diameter of 35.8 μm was obtained in the same manner as in Example 1 except that the mixture was cooled at an oxygen concentration of 1.3% for 6 hours.

Comparative Example 6
A dry granulated product having a particle size of 10 μm to 75 μm was obtained in the same manner as in Comparative Example 1 except that _{SnO 2} (average particle size: 5.6 μm) was not added as a raw material.
The granulated product was placed in an electric furnace and heated to 1300 ° C. at an oxygen concentration of 1.0% over 4.5 hours, and then calcined by holding it at 1200 ° C. at an oxygen concentration of 1.0% for 3 hours. Then, a carrier core material having a volume average particle size of 36.8 μm was obtained in the same manner as in Comparative Example 1 except that the mixture was cooled at an oxygen concentration of 0.5% for 6 hours.

(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 size (D ₅₀ ))
The volume average particle size 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)
As the evaluation device, POREMASTER-60GT manufactured by Quantachrome was used. Specifically, as the measurement conditions,
Cell Stem Volume: 0.5 ml,
Headpressure: 20PSIA,
Surface tension of mercury: 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 to 10000.00 PSI
Then, 1.500 g of the sample was weighed and filled in a 0.5 ml (cc) cell for measurement. Further, the value obtained by subtracting the volume A (ml / g) at 60 PSI from the volume B (ml / g) at 10000 PSI was defined as the pore volume.

(BET specific surface area)
Evaluation was performed using a BET one-point specific surface area measuring device (manufactured by Mountech Co., Ltd., model: Macsorb HM model-1208). Specifically, 5.000 g of the sample was weighed and filled in a standard cell having a diameter of 12 mm, and the sample was degassed at 200 ° C. for 30 minutes for measurement.

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

(Maximum mountain valley depth Rz, average length RSm)
The surface was observed with a 100x objective lens using an ultra-depth 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. The position data in the X, Y and Z directions were joined to obtain a three-dimensional shape of the ferrite particle surface. An autophotographing function was used to capture the three-dimensional shape of the ferrite particle surface.
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% of this was extracted, and the contour of the independent region was recognized as the particle contour. Next, the shape selection excluded particles such as coarse, fine, and associated particles. By performing this shape selection, it is possible to reduce the error at the time of the polar ratio correction performed later. 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 extracted 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 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).

(Atypical rate)
An injection-type image analysis particle size distribution meter (Jasco International Co., Ltd., model: IF-3200) was used. Specifically, 0.07 g of the sample was weighed and measured after being dispersed in a screw tube bottle (capacity: 9 cc) containing 9 cc of polyethylene glycol 400.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: Relative measurement Measured quantity: 0.95 ml
Analysis: Dark detection threshold: 169 (fills holes)
O-Roughness filter: 0.5
* O-Roughness = Percentage of parts removed before the surface becomes smooth Filter condition:
ISO Area Diameter: Minimum value 5, Maximum value 100, Inner range * ISO Area Diameter = Diameter of a circle with a pixel image equal to the projected particle area (analysis condition)
Analysis filter condition I:
ISO Area Diameter: Minimum value 25, Maximum value 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 * ISO Solidity = Ratio of particle area to the area of the convex hull surrounding the particle Ell. Ratio: Minimum value 0.8, maximum value 1, inner range * Ell. Radio = 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.

(Development memory)
The surface of the obtained carrier core material 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 coat solution. This coating solution was applied to 50,000 parts by mass of the carrier core material using a fluidized bed coating device, and heated in an electric furnace at a temperature of 300 ° C. to obtain carriers. Hereinafter, carriers were obtained in the same manner for all Examples and Comparative Examples.
The obtained carrier and toner having an average particle size 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 weight of the toner / (weight 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 used in a developing apparatus having the structure shown in FIG. 2 (developing sleeve peripheral speed Vs: 406 mm / sec, photoconductor drum peripheral speed Vp: 205 mm / sec, distance between photoconductor drum and developing sleeve: 0. 3 mm), the solid image part and the non-image part are adjacent to each other in the longitudinal direction of the photoconductor drum, and then an image in which a wide area of halftone continues is acquired after the initial and 200,000 image formations, and the developing roller 2 Develop roller on the first lap The image density between the developed area and the undeveloped area on the first lap is measured using a reflection densitometer (model number TC-6D manufactured by Tokyo Denshoku Co., Ltd.), and the difference is calculated. It was evaluated according to the following criteria. The results are shown in Table 2.
"○": less than 0.003 "△": 0.003 or more and less than 0.020 "×": 0.020 or more

(Abrasion of resin coating layer)
The prepared two-component developer is charged into a developing device (developing roller peripheral speed Vs: 406 mm / sec, photoconductor drum peripheral speed Vp: 205 mm / sec, photoconductor drum-developing roller distance: 0.3 mm). After printing 1000 blank images, the carrier and the toner were separated by a blow-off cage.
_{The resistance value R 1} (Ω · cm) before printing of this carrier _{and the resistance value R 2} (Ω · cm) after printing 1000 sheets are measured, and the reduction rate ΔR calculated from the following formula is calculated as follows. It was judged.
ΔR = (logR ₁ −logR ₂ ) / logR ₁ × 100 (%)
"○": 20 ≧ ΔR ≧ 0
"△": 40 ≧ ΔR> 20
"X": ΔR> 40

In the resin-coated carriers of Examples 1 to 7 using the carrier core material satisfying the configuration of the present invention, the developing memory was suppressed and the resin-coated layer was hardly worn.

On the other hand, in the resin-coated carriers of Comparative Examples 1 and 2 using carrier core materials having a low Si content and a small Rz × RSm of “15.3” and “15.2”, the grain size was small. As a result of the deformation of the particles and the excessive promotion of sharpening of the grains, the resin coating layer was worn.

Further, a comparative example using a carrier core material having a small Rz × RSm of “15.2” and “15.7” and a small deformation rate of “44.6%” and “43.5%” (rounded). In the resin-coated carriers of No. 3 and Comparative Example 4, although the resin-coated layer was not worn, a developing memory was generated.

A developing memory was generated in the resin-coated carrier of Comparative Example 5 using a carrier core material in which Sr and Sn were not added, Rz and RSm were small, and the deformation rate was small (rounded).

A developing memory was generated in the resin-coated carrier of Comparative Example 6 using a carrier core material in which Sn was not added, the amount of Si added was small, Rz × RSm was small, and the deformation rate was small (rounded).

According to the carrier core material according to the present invention, the development memory can be suppressed, and the resin coating layer is less worn even after long-term use, and the occurrence of carrier adhesion can be suppressed.

3 Develop roller 5 Photoreceptor drum

Claims (6)

Ferrite carrier core material
Maximum mountain valley depth Rz of particles is 1.95 μm or more and 2.38 μm or less,
Average particle length RSm is 7.20 μm or more and 8.50 μm or less,
The product of Rz and RSm is 15.8 or more, and
A ferrite carrier core material characterized in that the deformation rate of particles measured by the following measuring method is 46% or more.
(Measurement method of particle deformity rate)
Measuring device: Injection type image analysis Particle size distribution meter Measurement sample: 0.07 g
The measurement was carried out after dispersion in a screw tube bottle (capacity: 9 ml) containing 9 ml of polyethylene glycol 400.
(Measurement condition)
Spacer thickness: 150 μm
Sampling: 20%
Analysis type: Relative measurement Measured quantity: 0.95 ml
Analysis: Dark detection threshold: 169 (fills 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 value 25, Maximum value 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, inner range The number of particles counted under the analysis filter condition II is divided by the number of particles counted under the analysis filter condition I to calculate the deformation rate. It has a composition represented by (Mn _x Fe _3-x ) O ₄ (where 0 <x <3).
Sr is contained in an amount of 0.01 mol% or more and 0.50 mol% or less.
The ferrite carrier core material according to claim 1, wherein Sn is contained in an amount of 0.01 mol% or more and 0.50 mol% or less. The ferrite carrier core material according to claim 2, wherein x is 0.01 or more and 2 or less. The ferrite carrier core material according to any one of claims 1 to 3, wherein Si is contained in an amount of 0.10 mol% or more and 0.22 mol% or less. A carrier for electrophotographic development, wherein the surface of the ferrite carrier core material according to any one of claims 1 to 4 is coated with a resin. An electrophotographic developer according to claim 5, wherein the electrophotographic developing carrier and toner are included.

Images