JP2020024274A - Carrier core material - Google Patents

Abstract

To provide a carrier core material constituted of ferrite particle which have low density, and in which irregularities are formed on the surfaces thereof.SOLUTION: The carrier core material satisfies the following condition: A convexoconcave air gap rate calculated from the following formula (1) is 4.5% or higher and 8.0% or lower, an internal air gap rate calculated from the following formula (2) is 2.0% or higher and 20.0% or lower, a volume average particle diameter is 30 μm or larger and 40 μm or smaller, a ratio of an individual particle size distribution not larger than a particle diameter 26 μm is 14 No.% or lower, and apparent density is 2.02 g/cmor higher and 2.15 g/cmor lower. In formulae of a convexoconcave air gap rate (%)=(envelope area-particle area A)/envelope area x 100 ..... (1), and internal air gap rate (%)=(particle are A-particle area B)/particle area A×100 ...(2), the envelope area: an area of a face surrounded by a line (envelope line) connecting apexes of protrusions of a particle cross section, the particle area A: a particle cross section area including the internal air gap, and the particle area B: a particle cross section area not including the internal air gap.SELECTED DRAWING: Figure 1

Description

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

  For example, in an image forming apparatus such as a facsimile, a printer, and a copying machine using an electrophotographic method, a toner is attached to an electrostatic latent image formed on a surface of a photoreceptor to form a visible image, and the visible image is formed on paper. Then, the image is fixed by heating and pressing. From the viewpoint of high image quality and colorization, a so-called two-component developer containing a carrier and a toner is widely used as a developer.

  In a developing method using a two-component developer, a carrier and a toner are stirred and mixed in a developing device, and the toner is charged to a predetermined amount by friction. Then, the developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically transferred to the photoconductor through the magnetic brush, thereby forming an electrostatic latent image on the photoconductor. Visualize. The carrier after the movement of the toner is separated from the developing roller, and is mixed again with the toner in the developing device. Therefore, as the characteristics of the carrier, a magnetic characteristic for forming a magnetic brush and a charging characteristic for imparting a desired charge to the toner are required. As such a carrier, a so-called coated carrier in which the surface of a carrier core material made of magnetite, various ferrites, or the like is coated with a resin has been widely used.

  2. Description of the Related Art In recent years, in order to respond to market demands for higher image forming speeds in image forming apparatuses, there has been a tendency to increase the rotational speed of a developing roller and increase the amount of developer supplied to a developing area per unit time.

  However, when the stirring / conveying speed of the developer in the developing device increases as the image forming speed increases, the stress applied to the developer increases, and the components constituting the toner fuse to the surface of the carrier. “Toner spent” tends to occur. When toner spent occurs, the charge-imparting ability of the carrier is reduced, and the image density is reduced.

  Therefore, it has been proposed that the density of the carrier is reduced to reduce the stress applied to the developer and suppress the toner spent. For example, Patent Literature 1 proposes lowering the sintering temperature in a carrier core material manufacturing process to suppress the growth of grains and to make the carrier core material porous while leaving voids inside. Patent Document 2 proposes a resin-filled carrier that fills a void formed inside a carrier core with resin. Further, Patent Document 3 proposes a hollow-type carrier using holes for venting gas generated in a manufacturing process of a carrier core material.

  On the other hand, in order to meet the market demand for higher image quality, it is also required to stabilize image density and reduce edge defects. Here, the edge defect refers to a phenomenon in which, for example, when a halftone image is formed adjacent to a solid image in a high-speed image forming apparatus, a boundary portion of the halftone image with the solid image becomes white. The present inventors believe that this edge defect occurs due to the counter charge of the carrier remaining on the developing roller after development, and the toner that has moved onto the photoconductor is pulled back to the carrier. Therefore, in order to reduce edge defects, it is conceivable to make the carrier core material uneven so that a part of the carrier core material is exposed from the resin coating layer to smoothly release the counter charge.

JP 2013-145300 A JP 2006-337579 A JP 2007-34249 A

  However, when the density is reduced by providing a void inside the carrier core material, the particle strength of the carrier core material is reduced, and the particles are easily crushed by stirring or the like in the developing device. In particular, particles having a small particle size are easily crushed. Then, there is a possibility that the crushed particle pieces move to the photosensitive drum and damage the photosensitive drum, thereby deteriorating the image quality.

  Also, in order to reduce the density by providing voids inside the carrier core material, it is necessary to reduce the temperature and time in the firing step, whereas to make the surface of the carrier core material uneven, Conventionally, it is necessary to increase the firing temperature and lengthen the firing time, and it has conventionally been difficult to simultaneously achieve the low density and the unevenness of the carrier core material.

  An object of the present invention is to provide a carrier core material in which defects caused by toner spent and crushed pieces (such as scratches on a photosensitive drum) and edge defects are less likely to occur.

  Another object of the present invention is to provide a carrier for an electrophotographic developer and an electrophotographic developer capable of stably obtaining an image of good quality even when used in a high-speed image forming apparatus.

According to the present invention, there is provided a carrier core material composed of ferrite particles, wherein the concavo-convex porosity calculated from the following formula (1) is 4.5% or more and 8.0% or less, and the following formula (2) Is 2.0% or more and 20.0% or less, the volume average particle diameter is 30 μm or more and 40 μm or less, and the ratio of particle diameter 26 μm or less in the number particle size distribution is 14 number% or less, carrier core material apparent density equal to or less than 2.02 g / cm ³ or more 2.15 g / cm ³ is provided.
Concavo-convex void ratio (%) = (envelope area−particle area A) / envelope area × 100 (1)
Internal porosity (%) = (particle area A−particle area B) / particle area A × 100 (2)
In the formula, the envelope area: the area of the surface surrounded by the line (envelope) connecting the vertices of the convex portions of the particle cross section. Particle area A: particle cross-sectional area including internal voids Particle area B: particle break including internal voids area

  In the carrier core material having the above structure, the maximum peak-to-valley depth Rz of the ferrite particles is preferably 1.8 μm or more and 3.0 μm or less.

In the carrier core material of the structure, preferably a pore volume of at most 0.01 cm ³ / g or more 0.040 cm ³ / g.

In the carrier core material of the structure, preferably a true density of less 4.900g / cm ³ or more 5.000 g / cm ^3.

In the carrier core material of the structure, preferably magnetization sigma _1k when a magnetic field is applied ^{79.58 × 10 3 A / m (} 1000 oersted) is less than 50 Am ² / kg or more 70 Am ² / kg.

In the carrier core material of the structure, BET specific surface area is preferably less 0.100M ² / g or more 0.300m ² / g.

In the carrier core material of the structure, the composition of the ferrite _{particles, MnO: 35mol% ~55mol%,} Fe 2 O 3: 45mol% ~65mol%, MgO: below 2 mol%, a part of SrO: 0.1 mol% It is preferably substituted with で 5.0 mol%.

  Further, according to the present invention, there is provided an electrophotographic developing carrier, wherein the surface of the carrier core material described in any of the above is coated with a resin.

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

  The method for measuring the envelope area, the particle area A, the particle area B, the maximum peak and valley depth Rz, the pore volume, and the true density will be described in Examples below.

  Since the carrier core material of the present invention has a lower density than the conventional one, even if the stirring / conveying speed of the developer is increased, the stress applied to the developer is suppressed and the generation of toner spent is suppressed. Further, since the irregularities are formed on the surface of the carrier core material, the convex portions of the carrier core material are exposed on the surface of the resin coating layer, and the leakage of the counter charge after the development is smoothly performed. Furthermore, since the ratio of particles having a particle diameter of 26 μm or less, which is easily crushed by stirring or the like, is small, problems such as scratches on the photosensitive drum due to crushed pieces are effectively suppressed.

  ADVANTAGE OF THE INVENTION According to the carrier for electrophotographic development and the developer for electrophotography of this invention, the image of high quality can be obtained stably even when used for a high-speed image forming apparatus.

It is a particle sectional view of a carrier core material. FIG. 3 is a diagram for explaining a concave / convex porosity. It is a figure explaining internal porosity. 4 is an SEM photograph of the carrier core material of Example 1. 3 is a cross-sectional SEM photograph of the carrier core material of Example 1. FIG. 1 is a schematic diagram illustrating an example of a developing device using a carrier according to the present invention.

  In the present invention, the irregular porosity calculated from the above equation (1) is used as an index of the surface irregularity of the carrier core material, and the internal porosity calculated from the above equation (2) as an index of the particle density of the carrier core material. Was used. The uneven porosity and the internal porosity will be described with reference to FIGS. 1, 2 and 3. FIG.

  1, 2 and 3 are cross-sectional views of the same particle, FIG. 1 is a cross-sectional view of the particle of the carrier core material, and FIG. FIG. 3 is a diagram illustrating a particle area A (particle cross-sectional area including internal voids) as a hatched region, and FIG. 3 is a diagram illustrating a particle area B (particle cross-sectional area not including internal voids) as a hatched region.

The porosity of the concavo-convex is the area obtained by removing the particle area A shown by oblique lines from the envelope area surrounded by the envelope lines shown by thick lines in FIG. 2, that is, the envelope of the area colored in gray in FIG. It shows the ratio to the area. Further, the internal porosity is an area obtained by subtracting the particle area B indicated by oblique lines in FIG. 3 from the particle area A indicated by oblique lines in FIG. 2, that is, the void portion inside the particles colored in gray in FIG. The ratio of the area to the particle area A is shown.
As described above, calculation is performed on each particle, and the average voidage of the 100 particles is used to obtain the uneven porosity and the internal porosity. The particles to be measured had a particle diameter of 20 μm or more in a cross-sectional SEM photograph as shown in FIG.

  One of the great features of the present invention is that the above-described uneven porosity is 4.5% or more and 8.0% or less. By setting the porosity of the unevenness in the above range, the counter charge charged by the frictional charging can be released from the carrier core material partially exposed from the resin coating layer. A more preferred lower limit of the uneven porosity is 5.0% or more, and a more preferred upper limit is 7.0%.

  In the present invention, it is also a great feature that the internal porosity is 2.0% or more and 20.0% or less. By setting the internal porosity within the above range, the density of the carrier core material is reduced, and even when the stirring / conveying speed is increased, an increase in stress applied to the developer is suppressed, and toner spent is suppressed. A more preferred lower limit of the internal porosity is 3.0%, and a more preferred upper limit is 15%.

  In the carrier core material of the present invention, the volume average particle diameter (hereinafter sometimes referred to as “average particle diameter”) is in the range of 30 μm to 40 μm, and the ratio of particle diameter 26 μm or less in the number particle size distribution is 14% by number. It was as follows. As described above, when the internal porosity of the particles increases, the particles having a small particle diameter are particularly easily crushed.In the present invention, the content of the particles having a small particle diameter is reduced, and the content of the particles having a small particle diameter is reduced. Problems such as scratches on the photosensitive drum. The smaller the ratio of the particle size of 26 μm or less in the number particle size distribution, the better. However, the lower limit is usually about 4% due to the limit of sieving.

The apparent density of the carrier core material of the present invention (AD) is 2.02 g / cm ³ or more 2.15 g / cm ³ or less. When the apparent density is in this range, toner spent, edge defects, and the like are suppressed.

The maximum peak-to-valley depth Rz of the ferrite particle surface in the carrier core material of the present invention is preferably in the range of 1.8 μm or more and 3.0 μm or less. When the maximum peak-to-valley depth Rz of the ferrite particle surface is in the above range, the space formed between the ferrite particles becomes large, so that more toner is taken into this space and the amount of toner supplied to the development area increases. It is possible to cope with an increase in image forming speed. A more preferable range of the maximum peak-valley depth Rz is a range of 2.0 μm or more and 2.5 μm or less. As will be described later, the maximum peak-valley depth Rz of the ferrite particle surface can be controlled by the amount of SrFe ₁₂ O ₁₉ added to the raw material and the firing conditions in the production process, as in the case of the uneven porosity. Details will be described later.

Pore volume in the carrier core material of the present invention is 0.01 cm ³ / g or more 0.040 cm ³ / g preferably in the following range. When the pore volume is in the above range, the internal void becomes an appropriate range. When the pore volume is in the range of 0.01 cm ³ / g or more, the weight per carrier particle is reduced, carrier friction is reduced, and toner spent is reduced. On the other hand, if the pore volume exceeds 0.040 cm ³ / g, the internal voids become too large and the magnetization per carrier particle becomes small, so that carrier scattering is likely to occur. A more preferred range of pore volume is in the range of less 0.02 cm ³ / g or more 0.03 cm ³ / g.

True density of the carrier core material of the present invention is 4.900g / cm ³ or more 5.000 g / cm ³ is preferably in a range of about. When the true density of the carrier core material is within the above range, the stirring torque in the developing device can be reduced while maintaining the magnetic characteristics and the electric characteristics. Further, the stress applied to the developer by being stirred in the developing device can be greatly reduced.

Further, the magnetization sigma _1k when a magnetic field is applied ^{79.58 × 10 3 A / m (} 1000 Oe) in the carrier core material of the present invention is preferably not more than 50 Am ² / kg or more 70 Am ² / kg.

There is no particular limitation on the composition of the ferrite particles constituting the carrier core material of the present invention, the composition formula _{M X Fe 3-X O 4} ( where, M is, Mg, Mn, Ca, Ti , Sr, Cu, Zn, Sr , Ni, at least one metal element selected from the group consisting of 0 <X <1). Among these, the composition of the ferrite _{particles, MnO: 35mol% ~55mol%,} Fe 2 O 3: 45mol% ~65mol%, MgO: below 2 mol%, a part of SrO: 0.1mol% ~5.0mol %.

Next, a method for producing the carrier core material of the present invention will be described. Conventionally, the addition of Sr (strontium) and the adjustment of the oxygen concentration in the firing step have been performed to make the particle surface uneven. Further, in order to promote the crystal growth of the particles, the temperature and time of the firing step are set to a high temperature and a long time. However, with such a conventional method, although the surface of the particles can be made uneven to some extent, sintering inside the particles is promoted and internal voids are hardly formed, so that the density of the particles cannot be reduced. The present inventors have intensively studied whether the carrier core material composed of ferrite particles can reduce the density while maintaining the uneven shape, and as a result, using SrFe ₁₂ O ₁₉ as a raw material, peripheral that the crystal growth in the direction is inhibited radial i.e. irregularities of growth inspired particle surface to the particle outward progresses, and the particle size than the preliminary calcination raw material (non-calcined raw material with SrFe ₁₂ O ₁₉ It has been found that the use of (large) makes it possible to reduce the surface unevenness and the density of the particles. When SrFe ₁₂ O ₁₉ is used as a raw material, if the firing conditions are a high temperature and a reducing atmosphere, the decomposition of SrFe ₁₂ O ₁₉ is promoted, and the crystal growth in the circumferential direction is not sufficiently suppressed, and the surface unevenness is increased. It was also found that the activity was not promoted. From these findings, it has been found that the carrier core material according to the present invention having predetermined surface irregularities and internal voids is preferably manufactured by the method described below. In addition, the manufacturing method of the carrier core material according to the present invention is not limited to this.

First, the Fe component raw material and the M component raw material are weighed. Note that M is at least one metal element selected from divalent metal elements such as Mg, Mn, Ca, Ti, Cu, Zn, and Ni. As the Fe component raw material, Fe ₂ O ₃ or the like is preferably used. As the M component raw material, MnCO ₃ , Mn ₃ O _{4 and the} like can be used for Mn, and MgO, Mg (OH) ₂ and MgCO ₃ can be suitably used for Mg. Further, as the Ca component raw material, at least one compound selected from CaO, Ca (OH) ₂ , CaCO _{3 and the} like is suitably used.

  Next, the prepared raw material mixed powder is calcined. The temperature of the preliminary firing is preferably in a range of 750 ° C. or more and less than 900 ° C. A temperature of 750 ° C. or higher is preferable because ferrite formation by calcining partially proceeds and the reaction between solids sufficiently proceeds. On the other hand, when the temperature is lower than 900 ° C., sintering by calcination is weak, and the raw material can be sufficiently pulverized in the subsequent slurry pulverization step, which is preferable. The atmosphere during the preliminary firing is preferably an air atmosphere.

Then, the calcined raw material is disintegrated. The calcined raw material is pulverized by, for example, wet grinding using a ball mill or a vibration mill for a predetermined time. It is desirable that the average particle diameter of the calcined raw material after pulverization is about several μm. Whereas the average particle size of the non-precalcined raw materials conventionally used is usually submicron, the calcined raw material having a significantly larger particle size is used in the production of the carrier core material according to the present invention. The combined use of such a calcined raw material and SrFe ₁₂ O ₁₉ makes it possible to make the surface of the particles uneven and reduce the density. The particle size of the calcined raw material after the pulverization is adjusted by the pulverizing time, the rotation speed, the material and the particle size of the medium used, and the like.

Next, the granulated calcined raw material and SrFe ₁₂ O ₁₉ are charged into a dispersion medium to prepare a slurry. The addition of SrFe ₁₂ O ₁₉ is for promoting the unevenness of the particle surface as described above. Water is suitable as the dispersion medium used in the present invention. If necessary, a binder, a dispersant, and the like may be added to the dispersion medium. As the binder, for example, polyvinyl alcohol can be suitably used. It is preferable that the amount of the binder is about 0.5% by mass to 2% by mass in the slurry. As the dispersant, for example, ammonium polycarboxylate and the like can be suitably used. It is preferable that the amount of the dispersant is adjusted so that the concentration in the slurry is about 0.5 to 2% by mass. In addition, a lubricant, a sintering accelerator and the like may be blended. The solid concentration of the slurry is desirably in the range of 50% by mass to 90% by mass. More preferably, it is 60% by mass to 80% by mass.

  Next, the slurry prepared as described above is wet-pulverized. For example, wet pulverization is performed for a predetermined time using a ball mill or a vibration mill. It is preferable that a medium having a predetermined particle diameter is included in a vibration mill or a ball mill. Examples of the material of the media include iron-based chromium steel, oxide-based zirconia, titania, and alumina. The form of the pulverizing step may be any of a continuous type and a batch type. The particle size of the pulverized material is adjusted according to the pulverizing time, the rotation speed, the material and the particle size of the medium to be used, and the like.

  Then, the pulverized slurry is granulated by spray drying. Specifically, the slurry is introduced into a spray drier such as a spray drier, and is sprayed into the atmosphere to granulate into a sphere. The ambient temperature during spray drying is preferably in the range of 100C to 300C. Thereby, a spherical granulated product having a particle size of 10 μm to 200 μm is obtained. In addition, it is desirable that the obtained granules have a sharp particle size distribution by removing coarse particles and fine powder using a vibration sieve or the like.

Next, the granulated material is put into a furnace heated to a predetermined temperature to generate ferrite particles. The firing temperature is preferably in the range of 1100 ° C or more and less than 1200 ° C. If the sintering temperature is lower than 1100 ° C., the ferrite-forming reaction hardly occurs, and sintering hardly proceeds, so that the unevenness of the particles may not be promoted. If the firing temperature is 1200 ° C. or higher, excessive crystals may be generated due to decomposition of SrFe ₁₂ O ₁₉ and excessive sintering. The heating rate up to the firing temperature is preferably in the range of 200 ° C./h to 500 ° C./h.

Here, it is recommended that the oxygen concentration in the firing step be increased during temperature rise and sintering, and lower during cooling than during sintering. By raising the temperature in the firing step and setting the inside of the firing furnace at the time of sintering to an oxidizing atmosphere, decomposition of SrFe ₁₂ O ₁₉ is suppressed, crystal growth in the circumferential direction is suppressed, and surface unevenness is promoted. Specifically, the oxygen concentration at the time of temperature rise and sintering is set in the range of 15000 ppm to 210,000 ppm, and the oxygen concentration at the time of cooling is lower than that.

  The fired product thus obtained is pulverized if necessary. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the pulverizing step may be any of a continuous type and a batch type. Classification is performed so that the average particle diameter is within a predetermined range and the ratio of the particle diameter of 26 μm or less in the number particle size distribution is equal to or less than a predetermined value. In order to set the average particle diameter to a predetermined range and to set the ratio of the particle diameter of 26 μm or less to a predetermined value or less, classify and remove the particle diameter of 26 μm or less and classify and remove the particles of the predetermined particle diameter and larger than the average particle diameter. It may be necessary to adjust the average particle size. As the classification method, a conventionally known method such as air classification or sieve classification can be used. After the primary classification by an air classifier, the particle size distribution may be adjusted to a predetermined shape by a vibration sieve or an ultrasonic sieve. Further, after the classification step, the nonmagnetic particles may be removed by a magnetic field separator.

  Thereafter, if necessary, the classified powder (fired product) may be heated in an oxidizing atmosphere to form an oxide film on the particle surface to increase the resistance of the ferrite particles (high resistance treatment). ). The oxidizing atmosphere may be an air atmosphere or a mixed atmosphere of oxygen and nitrogen. Further, the heating temperature is preferably in the range of 200 to 800 ° C, and more preferably in the range of 250 to 600 ° C. The heating time is preferably in the range of 0.5 hours to 5 hours.

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

  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) A) resins, polystyrene, (meth) acrylic resins, polyvinyl alcohol resins, thermoplastic elastomers such as polyvinyl chloride, polyurethane, polyester, polyamide, and polybutadiene, and fluorosilicone resins.

  As a method for coating the carrier core material with a resin, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, and the like can be used. Among them, the fluidized bed method is particularly preferred in that the coating can be performed efficiently with a small amount of resin. The resin coating amount can be adjusted by, for example, the amount of the resin solution to be sprayed or the spraying time in the case of the fluidized bed method.

  Generally, the average particle diameter of the carrier is preferably in the range of 30 μm to 40 μm.

  The electrophotographic developer according to the present invention is obtained by mixing the carrier and the toner prepared as described above. The mixing ratio of the carrier and the toner is not particularly limited, and may be appropriately determined based on the developing conditions of the developing device used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass to 15% by mass. If the toner concentration is less than 1% by mass, the image density becomes too low, while if the toner concentration exceeds 15% by mass, the toner scatters in the developing device, and the toner adheres to the inside of the apparatus and the background portion such as transfer paper. This is because there is a possibility that a malfunction may occur. A more preferred toner concentration is in the range of 3% by mass to 10% by mass.

  As the toner, those produced by a conventionally known method 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 and containing a coloring agent, a release agent, a charge control agent, and the like can be suitably used.

  Generally, 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 as an average particle size measured by a Coulter counter.

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

  For mixing the carrier and the toner, a conventionally known mixing device can be used. For example, a Henschel mixer, a V-type mixer, a tumbler mixer, a hybridizer and 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 preferable. FIG. 6 is a schematic diagram illustrating an example of a developing device that performs magnetic brush development. The developing device shown in FIG. 6 has a rotatable developing roller 3 containing a plurality of magnetic poles, a regulating blade 6 for regulating the amount of developer on the developing roller 3 conveyed to the developing section, and is arranged in parallel in the horizontal direction. Formed between the two screws 1 and 2 and the two screws 1 and 2 for stirring and transporting the developer in opposite directions to each other, and developing from one screw to the other screw at both ends of both screws. And a partition plate 4 which allows the developer to move and prevents the developer from moving except at both ends.

  The two screws 1 and 2 have helical 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 discharge the developer. They are transported in opposite directions. Then, at both ends of the screws 1 and 2, the developer moves from one screw to the other screw. As a result, the developer composed of the toner and the carrier is constantly circulated and stirred in the apparatus.

On the other hand, the developing roller 3 has a developing magnetic pole N ₁ , a conveying magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole N ₃ as a magnetic pole generating means inside a metal cylindrical body having a surface having irregularities of several μm. , comprising a fixed magnet disposed five pole blade pole S ₂ in order. When the development 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 carried on the surface of the developing roller 3 is transported to the developing area after its layer is regulated by the regulating blade 6.

  In the developing area, a bias voltage in which an AC voltage is superimposed on a DC voltage is applied to the developing roller 3 from the power supply 8. The DC voltage component of the bias voltage is a potential between the background portion potential and the image portion potential on the surface of the photosensitive drum 5. 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 to 5 kV, and the frequency is preferably in the range of 1 to 10 kHz. Further, the waveform of the bias voltage may be any of a rectangular wave, a sine wave, and a triangular wave. As a result, the toner and the carrier vibrate in the developing area, and the toner adheres to the electrostatic latent image on the photosensitive drum 5 to perform development.

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 Mixed with undeveloped developer. Then the scooping pole N _3, new developer is supplied from the screw 1 to the developing roller 3.

  Although the developing roller 3 has five magnetic poles in the embodiment shown in FIG. 6, the moving amount of the developer in the developing area is further increased, and the pumping property and the like are further improved. For this reason, the number of magnetic poles may be increased to eight, ten, or twelve.

(Example 1)
50.0 mol of Fe ₂ O ₃ (average particle size: 0.8 μm) and 50.0 mol of Mn ₃ O ₄ (average particle size: 2 μm) were weighed in terms of MnO, and pelletized by a roller compactor. The obtained pellets were preliminarily fired at 850 ° C. in a rotary firing furnace under an atmospheric condition. The mixture was pulverized with a dry bead mill for 6 hours to obtain a calcined raw material (average particle size: 2.2 μm). The calcined material 20.0kg and _SrFe 12 _{O 19} (average particle size: 1.2 [mu] m) 3.0 kg were dispersed in purified water 7.6 kg, and the ammonium polycarboxylate dispersant as a dispersing agent were added 139g A mixture was obtained. 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 of about 140 ° C. with a spray dryer to obtain a dried granulated product having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 30 μm or less were removed from the granulated product using a sieve.
The granulated product was put into an electric furnace and heated to 1120 ° C. over 5 hours. Thereafter, firing was carried out by maintaining the temperature at 1120 ° C. for 3 hours. The oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 100,000 ppm at the temperature rising stage and 2000 ppm at the cooling stage.
The obtained fired product was pulverized with a hammer mill and classified using a vibration sieve to obtain a fired product having an average particle diameter of 36.3 μm and a ratio of 26 μm or less in the number particle size distribution of 11.6 number%.
Next, the obtained fired product was kept at 390 ° C. in an air atmosphere for 1.5 hours to perform an oxidation treatment (resistance increasing treatment) to obtain a carrier core material.
The composition, powder characteristics, shape characteristics, magnetic characteristics, and the like of the obtained carrier core material were measured by the methods described below. Tables 1 and 2 show the measurement results.

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

  The obtained carrier and a toner having an average particle diameter of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer. In this case, the carrier and the toner were adjusted so that the weight of the toner / (the weight of the toner and the carrier) = 5/100. Hereinafter, a developer was obtained in the same manner for all the comparative examples. The obtained developer was evaluated in an actual machine described later. Table 2 shows the evaluation results.

(Example 2)
A fired product having an average particle diameter of 37.4 μm and a particle size distribution of 26 μm or less in particle size distribution of 11.7% by number was obtained in the same manner as in Example 1 except that the electric furnace temperature in the firing step was changed to 1140 ° C. .

(Example 3)
Except that the temperature of the electric furnace in the firing step was changed to 1160 ° C., a fired product having an average particle diameter of 37.3 μm and a particle diameter of 26 μm or less in a number particle size distribution of 13.4% by number was obtained in the same manner as in Example 1. .

(Comparative Example 1)
The average particle diameter was 36.3 μm, and the proportion of particles having a particle diameter of 26 μm or less in the particle size distribution was 15.0 in the same manner as in Example 1 except that fine particles having a particle diameter of 25 μm or less were removed from the granulated product using a sieve. % Fired product was obtained.

(Comparative Example 2)
Except that the temperature of the electric furnace in the firing step was changed to 1200 ° C., a fired product having an average particle diameter of 37.1 μm and a particle diameter of 26 μm or less in a number particle size distribution of 13.2% by number was obtained in the same manner as in Example 1. .

(Comparative Example 3)
Except having changed the electric furnace temperature to 1220 degreeC in the baking process, it carried out similarly to the comparative example 1, and obtained the average particle diameter 34.9 micrometers, and the ratio of the particle diameter of 26 micrometers or less in a number particle size distribution is 23.6 number%. .

(Comparative Example 4)
As raw materials, 20.0 kg of Fe ₂ O ₃ (average particle size: 0.6 μm), 9.9 kg of Mn ₃ O ₄ (average particle size: 2 μm), and 0.33 kg of SrCO ₃ (average particle size: 0.6 μm) were used. The mixture was dispersed in 10.0 kg of pure water, and 180 g of an ammonium polycarboxylate-based dispersant was added as a dispersant to form a mixture. 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 of about 140 ° C. with a spray dryer to obtain a dried granulated product 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 granulated product using a sieve.
The granulated product was put into an electric furnace and heated to 1200 ° C. over 5 hours. After that, baking was performed by holding at 1200 ° C. for 3 hours. The oxygen concentration in the furnace was adjusted so that the oxygen concentration in the electric furnace was 15000 ppm at the temperature rising stage and 5000 ppm at the cooling stage.
The obtained fired product was pulverized by a hammer mill and classified using a vibrating sieve to obtain a fired product having an average particle diameter of 34.6 μm and a ratio of particle diameter of 26 μm or less in the number particle size distribution of 23.5% by number. .
Next, the obtained fired product was kept at 390 ° C. in an air atmosphere for 1.5 hours to perform an oxidation treatment (resistance increasing treatment) to obtain a carrier core material.
The composition, powder characteristics, shape characteristics, magnetic characteristics, and the like of the obtained carrier core material were measured by the methods described below. Tables 1 and 2 show the measurement results.

(Comparative Example 5)
Except for changing the electric furnace temperature to 1160 ° C. in the firing step, a fired product having an average particle diameter of 34.5 μm and a ratio of particle diameter of 26 μm or less in the number particle size distribution of 22.3% by number was obtained in the same manner as in Comparative Example 4. .

(Comparative Example 6)
5.0.0 mol of Fe ₂ O ₃ (average particle diameter: 0.8 μm), 41.5 mol of Mn ₃ O ₄ (average particle diameter: 2 μm) in terms of MnO, and 8.10 mol of MgO (average particle diameter: 0.8 μm). 0mol and CaCO ₃ (average particle size: 0.6 .mu.m) were weighed so as to 0.5mol in terms of CaO, and pelletized with a roller compactor. The obtained pellets were preliminarily fired in a rotary firing furnace at 800 ° C. under atmospheric conditions. The mixture was pulverized with a dry bead mill for 6 hours to obtain a calcined raw material (average particle size: 1.4 μm). 20.0 kg of this calcined raw material was dispersed in 6.7 kg of pure water, and 120 g of an ammonium polycarboxylate-based dispersant was added as a dispersant to form a mixture. 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 of about 140 ° C. with a spray dryer to obtain a dried granulated product having a particle size of 10 μm to 75 μm. Fine particles having a particle size of 30 μm or less were removed from the granulated product using a sieve.
This granulated product was put into an electric furnace and heated to 1115 ° C. over 4 hours. Thereafter, firing was performed by maintaining the temperature at 1115 ° C. for 3 hours. Then, it was cooled to 500 ° C. at a cooling rate of 2 ° C./min. A gas mixture of oxygen and nitrogen was supplied into the furnace so that the oxygen concentration in the electric furnace was 12000 ppm.
The obtained fired product was pulverized with a hammer mill and classified using a vibrating sieve to obtain a fired product having an average particle diameter of 32.8 μm and a ratio of particle diameter of 26 μm or less in the number particle size distribution of 24.6 number%. .
The composition, powder characteristics, shape characteristics, magnetic characteristics, and the like of the obtained carrier core material were measured by the methods described below. Tables 1 and 2 show the measurement results.

(Composition analysis)
(Analysis of Fe)
A carrier core material containing an iron element was weighed and dissolved in a mixed acid aqueous solution of hydrochloric acid and nitric acid. After evaporating the solution to dryness, sulfuric acid aqueous solution is added and redissolved to volatilize excess hydrochloric acid and nitric acid. Solid Al is added to this solution to reduce all Fe ³⁺ in the solution to Fe ²⁺ . Subsequently, the amount of Fe ²⁺ ions in this solution was quantitatively analyzed by potentiometric titration with a potassium permanganate solution to determine the titer of Fe (Fe ²⁺ ).
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed according to a ferromanganese analysis method (potentiometric titration method) described in JIS G1311-1987. The Mn content of the carrier core material described in the present invention is the Mn content obtained by quantitative analysis by this ferromanganese analysis method (potentiometric titration method).
(Analysis of Mg)
The Mg content of the carrier core material was analyzed by the following method. The carrier core material according to the present invention was dissolved in an acid solution, and quantitative analysis was performed by ICP. The Mg content of the carrier core material described in the present invention is the Mg content obtained by the quantitative analysis by this ICP.
(Analysis of Ca)
The Ca content of the carrier core material was determined by quantitative analysis by ICP as in the analysis of Mg.
(Sr analysis)
The Sr content of the carrier core material was determined by ICP quantitative analysis in the same manner as Mg analysis.

(Apparent density AD)
The apparent density of the carrier core was measured according to JIS Z2504.

(Flow rate FR)
The flow rate of the carrier core material was measured according to JIS Z2502.

(The number ratio of less than or equal to the average particle diameter _{D 50} and particle size 26 .mu.m)
The average particle diameter _{D 50} and the following number ratio particle size 26μm of a carrier core material was measured using a laser diffraction particle size distribution analyzer (manufactured by Nikkiso Co., Ltd. "Microtrac Model 9320-X100").

(Pore volume)
The measurement of the pore volume was performed as follows. As the evaluation device, POREMASTER-60GT manufactured by Quantachrome was used. Specifically, the measurement conditions are as follows: Cell Stem Volume: 0.5 ml, Headpressure: 20 PSIA, 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, 1.200 g of a sample was weighed and filled into a 0.5 ml (cc) cell for measurement. The value obtained by subtracting the volume A (ml / g) at 100 PSI from the volume B (ml / g) at 10000.00 PSI was defined as the pore volume.

(BET specific surface area)
Using a BET one-point specific surface area measuring device ("Macsorb HM model-1208", manufactured by Mountech), 8.500 g of a sample was filled in a cell having a volume of 5 mL, and the sample was degassed at 200 ° C for 30 minutes and measured.

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

(Roughness porosity, internal porosity)
The carrier core material is dispersed in the resin, and the resin is filled into the carrier core material by performing a vacuum defoaming process, then applied to an auxiliary plate, and heat-treated at a temperature of 200 ° C. for 20 minutes to cure the resin. Was. Thereafter, the carrier core material was cut using a cross session polisher (SM-09010, manufactured by JEOL Ltd.). Then, the cross section of the carrier core material was photographed with a scanning electron microscope (JSM-6510LA type, manufactured by JEOL Ltd.). Image analysis software from the captured image (Image-Pro Plus, Media Cybernetics, Inc.) was used to envelope area (area when connecting the convex portion of the figure, [mu] m ^2), including grain area A <voids, [mu] m ² ) And the particle area B <excluding voids, μm ² >. In the cross-sectional observation image, since there is also an image in which the end of the carrier core material is cut in the visual field, particles of 20 μm or more were selected for the measurement. Each area was calculated for each particle, and the average value of 100 particles was defined as the envelope area (μm ² ), particle area A (μm ² ), and particle area B (μm ² ) of the carrier core material. Then, each porosity was calculated from the following formula.
Porosity (%) = (envelope area−particle area B) / envelope area × 100
Concavo-convex porosity (%) = (envelope area−particle area A) / envelope area × 100
Internal porosity (%) = (particle area A−particle area B) / particle area A × 100

(Method of measuring maximum valley depth Rz)
Using a super-depth color 3D shape measuring microscope (“VK-X100” manufactured by Keyence Corporation), the surface was observed with a 100 × objective lens to determine the surface. Specifically, first, the carrier core material was fixed on an adhesive tape having a flat surface, and the measurement visual field was determined with a 100 × objective lens. Then, the focus was adjusted to the adhesive tape surface using an autofocus function. The flat adhesive tape surface on which the carrier core material was fixed was irradiated with a laser beam from the vertical direction (Z direction), and the surface was scanned in the X and Y directions. Further, 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 maximum. The three-dimensional shape of the surface of the carrier core material was obtained by joining these position data in the X, Y and Z directions. Note that an automatic photographing function was used to capture the three-dimensional shape of the carrier core material surface.
The measurement of each parameter was performed using the particle roughness inspection software (Mitani Shoji). First, as a pretreatment, the three-dimensional shape of the obtained carrier core material was subjected to particle recognition and shape selection. Particle recognition was performed by the following method. Of the three-dimensional shapes obtained by imaging, the maximum value in the Z direction is 100% and the minimum value is 0%, and the range from the maximum value to the minimum value is equally divided into 100. The region corresponding to 100 to 35% was extracted, and the outline of the independent region was recognized as a particle outline. Next, particles such as coarse, fine and aggregated particles were excluded by shape selection. By performing this shape selection, it is possible to reduce the error at the time of the porosity correction performed later. Specifically, particles corresponding to an area equivalent diameter of 28 μm or less, 38 μm or more, and a needle ratio of 1.15 or more were excluded. Here, the acicular ratio is a parameter calculated from the ratio of the maximum length of the particle / diagonal width, and the diagonal width is the shortest distance between two straight lines when the particle is sandwiched by two straight lines parallel to the maximum length. Represents
Next, a part used for analysis was extracted from the three-dimensional shape of the surface. First, a square having a side length of 15.0 μm is drawn around the center of gravity obtained from the particle outline recognized by the above method. Twenty-one parallel lines were drawn in the drawn square, and 21 roughness curves corresponding to the line segments were extracted.

  Since the carrier core material has a substantially spherical shape, the extracted roughness curve has a constant curvature as a background. Therefore, as a background correction, an optimal quadratic curve was fitted, and correction was performed to subtract from the roughness curve. In this case, a low-pass filter was applied at an intensity of 1.5 μm, and the cutoff value λ was 80 μm.

  The maximum peak-valley depth Rz was obtained as the sum of the highest peak height and the deepest trough depth in the roughness curve. The measurement of the maximum height Rz described above is performed based on JIS B0601 (2001 version). In calculating the maximum height Rz, the average value of 50 particles was used as the average value of each parameter.

(Magnetic properties)
An external magnetic field of 0 to 79.58 × 10 ⁴ A / m (10000 Oersted) was continuously applied for one cycle using a vibration sample magnetometer (VSM) (“VSM-P7” manufactured by Toei Kogyo Co., Ltd.) dedicated to room temperature. Σ _1k and saturation magnetization _s when a magnetic field of 79.58 × 10 ³ A / m (1,000 Oe) was applied.

(Toner spent)
After stirring the developer for 36 hours, the carrier was extracted from the developer, observed with a scanning electron microscope (JSM-6510LA type, manufactured by JEOL Ltd.), and the number ratio of the carrier with the toner fused to the surface was measured. .
“◎”: The ratio of the number of carriers fused with the toner was less than 0.5%.
“○”: The ratio of the number of carriers fused with the toner was 0.5 or more and less than 1.0%.
“Δ”: The ratio of the number of carriers fused with the toner was 1.0 or more and less than 5.0%.
“×”: The ratio of the number of carriers fused with the toner was 5.0% or more.

(Evaluation of edge defects)
A developing device having the structure shown in FIG. 6 (a peripheral speed Vs of the developing roller: 406 mm / sec, a peripheral speed Vp of the photosensitive drum: 205 mm / sec, a distance between the photosensitive drum and the developing roller: 0.3 mm) was used. The component developer was charged, and three images each for evaluation (solid black-halftone) were printed at the initial stage and after 10k printing, and the degree of white spots at the boundary between the solid black portion and the halftone portion was visually observed according to the following criteria. evaluated.
“◎”: No white spots were observed at the boundary, and the image was good.
“○”: White spots are observed, but within the allowable range (usable).
"△": White spots were confirmed and cannot be used.
“×”: Clear white spots were confirmed.

(Vertical line)
The surface of the photoreceptor drum after 10k printing was observed using a laser microscope, and evaluated according to the following criteria.
"◎": No vertical stripes.
“○”: A level with some vertical stripes but no problem.
“×”: A vertical stripe is a problematic level.

  In the carrier core materials of Examples 1 to 3, the number ratio of the carrier in which the toner spent was less than 1.0% was good, and the edge defect and the vertical streak after 10k printing were at a level at which there was no problem in practical use. Was something.

  On the other hand, in the carrier core material of Comparative Example 1, the number of particles having a particle size of 26 μm or less was as large as 15.0% by number in the number particle size distribution, and many vertical streaks were generated on the photosensitive drum after printing 10k.

Further, the carrier core material of Comparative Example 2 in which the internal porosity was as low as 1.8% and the AD was as high as 2.19 g / cm ³ , and the internal porosity was as low as 0.2% and the AD was 2.20 g / cm ³ and higher, the number particle size carrier core material of Comparative example 3 the following proportions particle size 26μm was often 23.6% by number in the distribution, the ratio of the number of carriers toner spent occurs is often 1.0 or more Was.

  The carrier core material of Comparative Example 4 in which the irregular porosity was as low as 2.9% and the internal porosity was as low as 0.7%, and the ratio of the particle size of 26 μm or less in the number particle size distribution was as large as 23.5%, was the toner. The proportion of the number of spent carriers was as high as 5.0% or more, and edge defects were observed at the initial stage and after 10k printing.

  In the carrier core material of Comparative Example 5, in which the porosity of the concavo-convex was as low as 2.8% and the ratio of the particle size of 26 μm or less in the number particle size distribution was as large as 22.3% by number, the number ratio of the carrier in which toner spent occurred was reduced. As many as 1.0% or more, edge defects were observed at the initial stage and after 10k printing. In addition, many vertical stripes were formed on the photoconductor drum after printing 10k.

  The carrier core material of Comparative Example 6, which had a low asperity porosity of 4.0% and a large proportion of particle size of 26 μm or less in the number particle size distribution of 24.6 number%, had practical problems after the initial and 10k printing. Some edge defects were found. In addition, many vertical stripes were formed on the photosensitive drum after printing 10k.

3 developing roller 5 photosensitive drum

Claims (9)

A carrier core material composed of ferrite particles,
The concavo-convex porosity calculated from the following formula (1) is 4.5% or more and 8.0% or less,
The internal porosity calculated from the following equation (2) is 2.0% or more and 20.0% or less;
The volume average particle diameter is 30 μm or more and 40 μm or less, and the ratio of the particle diameter of 26 μm or less in the number particle size distribution is 14 number% or less,
A carrier core material having an apparent density of 2.02 g / cm ³ or more and 2.15 g / cm ³ or less.
Concavo-convex void ratio (%) = (envelope area−particle area A) / envelope area × 100 (1)
Internal porosity (%) = (particle area A−particle area B) / particle area A × 100 (2)
In the formula, the envelope area: the area of the surface surrounded by the line (envelope) connecting the vertices of the convex portions of the particle cross section. Particle area A: particle cross-sectional area including internal voids Particle area B: particle break including internal voids area   2. The carrier core material according to claim 1, wherein the maximum peak-to-valley depth Rz of the ferrite particles is 1.8 μm or more and 3.0 μm or less. A pore volume of 0.01 cm ³ / g or more 0.040 cm ³ / g or less is claim 1 or 2 the carrier core material according. The carrier core material according to any one of claims 1 to 3, wherein a true density is 4.900 g / cm ³ or more and 5.000 g / cm ³ or less. 5. The carrier core material according to claim 1, wherein a magnetization σ _1k when a magnetic field of 79.58 × 10 ³ A / m (1000 Oersted) is applied is 50 Am ² / kg or more and 70 Am ² / kg or less. The carrier core material according to any of claims 1 to 5 BET specific surface area is less than 0.100M ² / g or more 0.300m ² / g. The composition of the ferrite _{particles, MnO: 35mol% ~55mol%,} Fe 2 O 3: 45mol% ~65mol%, MgO: below 2 mol%, a part of SrO: and replaced with 0.1mol% ~5.0mol% The carrier core material according to any one of claims 1 to 6, which is a carrier core material.   A carrier for electrophotographic development, wherein the surface of the carrier core material according to any one of claims 1 to 7 is coated with a resin.   An electrophotographic developer comprising the electrophotographic developing carrier according to claim 8 and a toner.