JP2016080991A - Carrier core material, carrier for electrophotographic development using the same, and electrophotographic developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier core material that can increase the amount of toner supplied to a developing area and prevent the surface of a photoreceptor from being damaged with a magnetic brush.SOLUTION: There are provided ferrite particles containing 5 number% to 20 number% of coupled particles in which two to five spherical particles are coupled to each other, where the coupled particles are particles each having a base particle having the largest particle diameter and one to four child particles having smaller particle diameters than that of the base particle coupled to each other, and at least one of the child particles has a particle diameter larger than half the particle diameter of the base particle. It is preferable that the maximum depth from the peak to the valley Rz on the surfaces of normal particles other than the coupled particles be 1.5 μm or more.SELECTED DRAWING: Figure 1

Description

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

  For example, in an image forming apparatus such as a facsimile, printer, or copier using an electrophotographic method, a toner is attached to an electrostatic latent image formed on the surface of a photosensitive member to make a visible image, and the visible image is formed on paper. After being transferred to, etc., it is fixed by heating and pressing. A so-called two-component developer including a carrier and a toner is widely used as a developer from the viewpoint of high image quality and colorization.

  In the developing method using a two-component developer, the carrier and the toner are stirred and mixed in the developing device, and the toner is charged to a predetermined amount by friction. Then, a developer is supplied to the rotating developing roller, a magnetic brush is formed on the developing roller, and the toner is electrically moved to the photosensitive member via the magnetic brush, so that an electrostatic latent image on the photosensitive member can be formed. Visualize. The carrier after the toner movement remains on the developing roller and is mixed with the toner again in the developing device. For this reason, as a characteristic 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 coating 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. Further, the carrier core material used so far for the coating carrier has a spherical shape.

  In recent years, in order to meet the market demand for higher image forming speed in image forming apparatuses, the rotation speed of the developing roller tends to be increased to increase the amount of developer supplied per unit time to the developing area.

  However, the coating carrier using the spherical carrier core material has a problem that the toner density to the developing area is insufficient and the image density is lowered. For example, there has been a problem called “development memory” in which the image density decreases due to the influence of the image one round before the developing roller.

  Therefore, by making the surface of the carrier core material uneven, or by making the shape of the carrier core material irregular, the frictional resistance with the surface of the photoreceptor and the frictional resistance between the carriers are increased, and the amount of toner supplied to the development area is increased. Techniques for increasing the number have been proposed (for example, Patent Documents 1 and 2).

JP 2013-25204 A JP 2007-148452 A

  However, if the surface of the carrier core material is made uneven, the coating resin is thickly formed in the recesses when the carrier is formed, so that the surface unevenness after forming the carrier becomes insufficient and the toner retention is not sufficient. In addition, unequal polygonal and massive carriers have been proposed as irregularly shaped carriers. However, due to extreme irregularities that deviate from the spherical shape, the magnetic brushes become harder and harder, and the magnetic brush becomes photosensitive. The surface of the photoconductor may be damaged by rubbing the surface of the photoconductor.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a carrier core material that can increase the amount of toner supplied to the development area and that does not damage the surface of the photoreceptor by a magnetic brush.

  Another object of the present invention is to provide an electrophotographic developer carrier and an electrophotographic developer capable of stably forming a good image quality even after long-term use.

  According to the present invention, 5% by number to 20% by number of bonded particles in which 2 to 5 spherical particles are bonded are included, and the bonded particles include a mother particle having the largest particle size and particles larger than the mother particles. It is a particle in which 1 to 4 child particles having a small diameter are combined, and the particle size of at least one child particle of the child particle is larger than ½ of the particle size of the mother particle, A carrier core material made of ferrite particles is provided.

  In the binding particles, since the mother particles and the child particles are present in a form in which the bonding portions are shared, the particle sizes of the mother particles and the child particles in this specification are determined by scanning electron microscope (Japan) In an image photographed at a magnification of 250 times using JSM-6510LA (manufactured by Denki Co., Ltd.), each particle was calculated by approximating the sphere to a spherical shape from an area excluding the binding portion of the binding particle.

  Moreover, it is preferable that the maximum peak-valley depth Rz of the surface of normal particles other than the said binding particle is 1.5 micrometers or more. In addition, the measuring method of the maximum mountain valley depth Rz of a carrier core material is demonstrated in the Example mentioned later.

  The carrier core material according to the present invention preferably has a volume average particle diameter (hereinafter sometimes simply referred to as “average particle diameter”) of 25 μm or more and less than 50 μm.

  In addition, according to the present invention, there is provided an electrophotographic developing carrier characterized in that the surface of the carrier core material described above is coated with a resin.

  Furthermore, according to the present invention, there is provided an electrophotographic developer comprising the electrophotographic developer carrier described above and a toner.

  According to the carrier core material of the present invention, the amount of toner supplied to the development area can be increased, and the occurrence of “development memory” can be suppressed. Further, the surface of the photoreceptor is not damaged by the magnetic brush. Thereby, if the developer containing the carrier core material according to the present invention is used, a good image quality can be stably formed even for a long period of use.

2 is a SEM photograph of the carrier core material of Example 1. 4 is a SEM photograph of the carrier core material of Example 2. 4 is a SEM photograph of the carrier core material of Example 3. 4 is a SEM photograph of a carrier core material of Comparative Example 1. 4 is a SEM photograph of a carrier core material of Comparative Example 2. 4 is a SEM photograph of a carrier core material of Example 4. 6 is a SEM photograph of the carrier core material of Example 5. 6 is a SEM photograph of a carrier core material of Example 6. 4 is a SEM photograph of a carrier core material of Comparative Example 3. It is a schematic diagram showing an example of a developing device using a carrier according to the present invention.

  As a result of intensive studies on whether or not the toner supply amount to the development area can be increased without damaging the surface of the photoconductor with a magnetic brush, the present inventors have determined that the bonded particles, in which several ferrite spherical particles are bonded, are bonded to the carrier core. It has been found that a predetermined number ratio may be contained in the material, and the present invention has been achieved. That is, the carrier core material made of the ferrite particles according to the present invention includes 5 to 20% by number of bonded particles in which 2 to 5 spherical particles are bonded, and the bonded particles have the largest particle size. A particle and 1 to 4 child particles having a particle diameter smaller than that of the mother particle, and the particle diameter of at least one child particle of the child particle is 1 of the particle diameter of the mother particle. It is characterized by being larger than / 2. The carrier core material is a powder made of ferrite particles. Here, ferrite particles other than the binding particles according to the present invention are used as normal particles.

  If the carrier core contains a predetermined number of irregularly bonded particles that are largely deviated from the spherical shape, in which the mother particles and the child particles are bonded, the toner is taken in between the normal spherical particles and the bonded particles. Space can occur. The toner taken into the space between the normal spherical particles and the binding particles is conveyed to the developing area by the rotation of the developing roller, and the toner taken into the space appears on the surface of the magnetic brush and develops. Contribute to. In addition, unlike conventional unequal polygonal shapes or massive carriers, the bonded particles used in the present invention are particles in which spherical particles are bonded to each other, and thus have no corners. For this reason, even if the surface of the photoreceptor is rubbed with a magnetic brush, the surface of the photoreceptor is not damaged at the corners of the particles. In addition, since the particle size of at least one child particle is larger than 1/2 of the particle size of the mother particle, the space between the normal spherical particle and the binding particle into which the toner can be taken in and the space between the binding particles are increased. large. As a result, more toner is transported to the development area, and the occurrence of “development memory” is effectively suppressed.

  In the bonded particles used in the present invention, the composition of the mother particles and the child particles may be the same or different.

  Such a binding particle can be obtained, for example, by increasing the holding time at the firing temperature or adjusting the pulverization operation after firing in the carrier core manufacturing process described later. According to this method, the content ratio of the binding particles in the carrier core material can be easily adjusted,

  The content ratio of the binding particles in the carrier core material is 5% to 20% by number. When the content ratio of the binding particles is less than 5% by number, the amount of toner supplied to the developing region may be insufficient. On the other hand, when the content ratio of the binding particles exceeds 20% by number, the fluidity of the carrier core material However, when the image formation speed is increased, sufficient image density cannot be obtained when the carrier is not sufficiently circulated and moved within the magnetic brush. A more preferable content ratio of the binding particles is in the range of 10% by number to 20% by number.

  In the carrier core material of the present invention, the maximum peak / valley depth Rz on the surface of normal particles other than the binding particles is preferably 1.5 μm or more. If the maximum peak / valley depth Rz of the normal particle surface is 1.5 μm or more, the space formed between the normal particles also increases, and more toner is taken into this space and the amount of toner transported to the development area And image defects such as “development memory” are further suppressed. A preferable upper limit value of the maximum valley depth Rz on the particle surface is 2.5 μm, and more preferably 2.0 μm.

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

The composition of the ferrite particles constituting the carrier core material of the present invention is not particularly limited, and the composition formula M _X Fe _{3 -X} O ₄ (where M is Mg, Mn, Ca, Ti, Sr, Cu, Zn, Ni) And at least one metal element selected from the group consisting of: 0 ≦ X ≦ 1). Among these, the general formula _{(MnO) x (MgO) y} (Fe 2 O 3) is represented by z, x, y, z is 45mol% ~55mol% respectively, 0 to 20 mol%, a 30 mol% 50 mol% , MnO and / or MgO is preferably substituted by 0.15 mol% to 1.0 mol% with SrO.

  Although there is no limitation in particular in the manufacturing method of the carrier core material of this invention, the manufacturing method demonstrated below is suitable.

First, the Fe component raw material and the M component raw material are weighed. M is at least one metal element selected from divalent metal elements such as Mg, Mn, Ca, Ti, Cu, Sr, Zn, and Ni. As the Fe component 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. As the Ca component raw material, at least one compound selected from CaO, Ca (OH) ₂ , CaCO _{3 and the} like is preferably used. As the Sr component raw material, SrCO ₃ , Sr (NO ₃ ) ₂ or the like is preferably used.

  Next, the raw material is charged into a dispersion medium to prepare a slurry. Water is preferred as the dispersion medium used in the present invention. In addition to the calcined raw material, a binder, a dispersant and the like may be blended in the dispersion medium as necessary. For example, polyvinyl alcohol can be suitably used as the binder. As a compounding quantity of a binder, it is preferable that the density | concentration in a slurry shall be about 0.5 mass%-2 mass%. Moreover, as a dispersing agent, polycarboxylate ammonium etc. can be used conveniently, for example. The blending amount of the dispersing agent is preferably about 0.5% by mass to 2% by mass in the slurry. In addition, you may mix | blend a lubricant, a sintering accelerator, etc. The solid content concentration of the slurry is desirably in the range of 50 mass% to 90 mass%. More preferably, it is 60 mass%-80 mass%. If it is 60% by mass or more, there are few intra-particle pores in the granulated product, and insufficient sintering during firing can be prevented.

  In addition, after mixing the weighed raw materials, pre-baking and pulverizing, it may be put into a dispersion medium to produce a slurry. The pre-baking temperature is preferably in the range of 750 ° C to 900 ° C. If it is 750 degreeC or more, since part ferrite-ization by calcination advances, the amount of gas generation at the time of baking is small, and reaction between solids fully advances, it is preferable. On the other hand, if it is 900 degrees C or less, since sintering by calcination is weak and a raw material can fully be grind | pulverized at a later slurry grinding | pulverization process, it is preferable. Moreover, an air atmosphere is preferable as the atmosphere at the time of temporary firing.

  Next, the slurry produced as described above is wet pulverized. For example, wet grinding is performed for a predetermined time using a ball mill or a vibration mill. The average particle diameter of the raw material after pulverization is preferably 5 μm or less, more preferably 1 μm or less. The vibration mill or ball mill preferably contains a medium having a predetermined particle diameter. Examples of the material of the media include iron-based chromium steel and oxide-based zirconia, titania, and alumina. As a form of a grinding | pulverization process, any of a continuous type and a batch type may be sufficient. The particle size of the pulverized product is adjusted depending on the pulverization time and rotation speed, the material and particle size of the media used, and the like.

  Then, the pulverized slurry is spray-dried and granulated. Specifically, the slurry is introduced into a spray dryer such as a spray dryer, and granulated into a spherical shape by spraying into the atmosphere. The atmospheric temperature during spray drying is preferably in the range of 100 ° C to 300 ° C. Thereby, a spherical granulated product having a particle size of 10 μm to 75 μm is obtained. Next, the obtained granulated product is classified using a vibration sieve to produce a granulated product having a predetermined particle size range.

  Next, the granulated material is put into a furnace heated to a predetermined temperature and fired by a general method for synthesizing ferrite particles, thereby generating ferrite particles. The firing temperature is preferably in the range of 1100 ° C to 1300 ° C. When the firing temperature is 1100 ° C. or lower, the phase transformation is less likely to occur and the sintering is less likely to proceed. On the other hand, if the firing temperature exceeds 1300 ° C., excessive grains may be generated due to excessive sintering. The content ratio of the binding particles can also be adjusted by the holding time at the firing temperature. Usually, when the holding time is increased, the content ratio of the binding particles increases. The holding time is preferably 6 hours or more, and more preferably 8 hours or more. The rate of temperature increase up to the firing temperature is preferably in the range of 250 ° C / h to 500 ° C / h. The oxygen concentration in the firing step is preferably controlled in the range of 0.05% to 5%.

  The fired product thus obtained is pulverized. Specifically, for example, the fired product is pulverized by a hammer mill or the like. The form of the granulation step may be either a continuous type or a batch type. Also by this pulverization treatment, the content ratio of the binding particles can be adjusted. That is, the stronger the impact force applied to the fired product is, the longer the binding of the binding particles is eliminated and the content ratio of the binding particles decreases.

  After the pulverization treatment, classification may be performed, if necessary, in order to align the particle size within a predetermined range. As a classification method, a conventionally known method such as air classification or sieve classification can be used. In addition, after primary classification with an air classifier, the particle size may be aligned within a predetermined range with a vibration sieve or an ultrasonic sieve. Furthermore, you may make it remove a nonmagnetic particle with a magnetic field separator after a classification process. The particle diameter of the ferrite particles is preferably 25 μm or more and less than 50 μm.

  Thereafter, if necessary, the ferrite particles after classification 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 air atmosphere or a mixed atmosphere of oxygen and nitrogen. The heating temperature is preferably in the range of 200 ° C to 800 ° C, and more preferably in the range of 250 ° C 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 desired chargeability and the like, the outer periphery 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). ) Resin, polystyrene, (meth) acrylic resin, polyvinyl alcohol resin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, and other thermoplastic elastomers, and fluorosilicone resins.

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

  As a method of coating the resin on the carrier core material, for example, a spray drying method, a fluidized bed method, a spray drying method using a fluidized bed, an immersion method, or the like can be used. Among these, the fluidized bed method is particularly preferable in that it can be efficiently applied 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 resin solution sprayed and the spraying time.

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

  The electrophotographic developer according to the present invention is obtained by mixing the carrier prepared as described above and a toner. The mixing ratio of the carrier and the toner is not particularly limited, and may be determined as appropriate based on the developing conditions of the developing device to be used. Generally, the toner concentration in the developer is preferably in the range of 1% by mass to 15% by mass. When the toner density is less than 1% by mass, the image density becomes too low, while when the toner density exceeds 15% by mass, toner scattering occurs in the developing device, and the toner adheres to the background portion such as internal dirt or transfer paper. This is because there is a risk of malfunction. A more preferable toner concentration is in the range of 3% by mass to 10% by mass.

  As the toner, toner produced by a conventionally known method such as a polymerization method, a pulverization classification method, a melt granulation method, or a spray granulation method can be used. Specifically, a binder resin containing a thermoplastic resin as a main component and containing a colorant, a release agent, a charge control agent and the like can be suitably used.

  In general, the particle diameter 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 a volume average particle diameter 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. These 1 type (s) or 2 or more types can be used in combination.

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

  The developing method using the developer of the present invention is not particularly limited, but a magnetic brush developing method is preferable. FIG. 10 is a schematic diagram showing an example of a developing device that performs magnetic brush development. The developing device shown in FIG. 10 is arranged in parallel to the horizontal direction, and a rotatable developing roller 3 incorporating a plurality of magnetic poles, a regulating blade 6 for regulating the amount of developer on the developing roller 3 conveyed to the developing unit. Formed between the two screws 1 and 2 that stir and convey the developer in opposite directions and the two screws 1 and 2, and develops from one screw to the other at both ends of both screws. And a partition plate 4 that allows the developer to move and prevents the developer from moving except at both ends.

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

On the other hand, the developing roller 3 has, as a magnetic pole generating means, a developing magnetic pole N ₁ , a transporting magnetic pole S ₁ , a peeling magnetic pole N ₂ , and a pumping magnetic pole N ₃ inside a metal cylindrical body having a surface with a few μm unevenness. , 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 regulated by the regulating blade 6 and then conveyed to the developing area.

  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 portion potential on the surface of the photosensitive drum 5 and the image portion potential. Further, the background portion potential and the image portion potential are set to a potential 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. The waveform of the bias voltage may be any of a rectangular wave, a sine wave, a triangular wave, and the like. As a result, the toner and the carrier vibrate in the development area, and the toner adheres to the electrostatic latent image on the photosensitive drum 5 and development is performed.

Thereafter, the developer on the developing roller 3 is conveyed to the inside of the apparatus by the conveying magnetic pole S ₁ , peeled off from the developing roller 3 by the peeling electrode N ₂ , and circulated and conveyed again inside the apparatus by the screws 1 and 2 for development. Mix and stir with undeveloped developer. Then, the developer is newly supplied from the screw 1 to the developing roller 3 by the pumping pole N ₃ .

  In the embodiment shown in FIG. 10, the number of magnetic poles built in the developing roller 3 is five. However, in order to further increase the moving amount of the developer in the developing region, and to 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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these examples at all.

Example 1
Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 3.814 kg, SrCO ₃ (average particle size: 0.6 μm) 0.112 kg is pure Dispersed in 5.58 kg of water, 30 g of ammonium polycarboxylate dispersant was added as a dispersant to obtain 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 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 75 μm. Coarse particles having a particle size exceeding 50 μm were removed from the granulated product using a sieve.
This granulated product was put into an electric furnace and heated to 1170 ° C. over 4.5 hours. Then, it baked by hold | maintaining at 1170 degreeC for 10 hours. Thereafter, it was cooled to room temperature over 8 hours. During this time, a gas in which oxygen and nitrogen were mixed was supplied into the furnace so that the oxygen concentration in the electric furnace was 15000 ppm.
The fired product obtained was pulverized once with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and then further twice with a pulverizer (manufactured by DOWA Techno Engineering). By pulverization, a carrier core material having an average particle diameter of 34.0 μm was obtained. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 1 shows an SEM photograph of the carrier core material of Example 1.

Example 2
A carrier core material having an average particle diameter of 35.0 μm was obtained in the same manner as in Example 1 except that the holding time at a firing temperature of 1170 ° C. in Example 1 was 8 hours and the pulverization with the pulverizer was performed once. . The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 2 shows an SEM photograph of the carrier core material of Example 2.

Example 3
A carrier core material having an average particle diameter of 34.9 μm was obtained in the same manner as in Example 1 except that the holding time at a firing temperature of 1170 ° C. in Example 1 was 8 hours, and the granulation treatment with a pulverizer was not performed. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 3 shows an SEM photograph of the carrier core material of Example 3.

Comparative Example 1
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg and Mn ₃ O ₄ (average particle size: 0.9 μm) 3.120 g were used, and the holding time at a firing temperature of 1170 ° C. was 3 hours. And a carrier core material having an average particle diameter of 34.8 μm in the same manner as in Example 1 except that after granulating once with a hammer mill (screen opening: 1.5 mm), the granulating process with a pulverizer was not performed. Got. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 4 shows an SEM photograph of the carrier core material of Comparative Example 1.

Comparative Example 2
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 3.814 g, SrCO ₃ (average particle size: 0.6 μm) 0. Example except that 073 kg was used, the holding time at a firing temperature of 1170 ° C. was 3 hours, the granulation was performed once with a hammer mill (screen opening: 1.5 mm), and then the granulation treatment with a pulverizer was not performed. In the same manner as in Example 1, a carrier core material having an average particle diameter of 32.7 μm was obtained. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 5 shows an SEM photograph of the carrier core material of Comparative Example 2.

Example 4
Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, MgO (average particle size: 0.8 μm) 0.183 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 2.773 kg, SrCO ₃ 0.013 kg (average particle size: 0.6 μm) was dispersed in 5.58 kg of pure water, and 30 g of an ammonium polycarboxylate dispersant was added as a dispersant to obtain 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 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 75 μm. Coarse particles having a particle size exceeding 50 μm were removed from the granulated product using a sieve.
This granulated product was put into an electric furnace and heated to 1300 ° C. over 4.5 hours. Then, it baked by hold | maintaining at 1300 degreeC for 6 hours. Thereafter, it was cooled to room temperature over 8 hours. During this time, a gas in which oxygen and nitrogen were mixed was supplied into the furnace so that the oxygen concentration in the electric furnace was 15000 ppm.
The obtained fired product was pulverized once with a hammer mill (screen opening: 0.3 mm) and then pulverized once with a pulverizer to obtain a carrier core material having an average particle diameter of 33.5 μm. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 6 shows an SEM photograph of the carrier core material of Example 4.

Example 5
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, MgO (average particle size: 0.8 μm) 0.403 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 3.051 kg , SrCO ₃ (average particle size: 0.6 μm) 0.097 kg, holding time at a firing temperature of 1300 ° C. was set to 8 hours, and pulverization was not performed by a pulverizer, as in Example 4. A carrier core material having an average particle size of 36.5 μm was obtained. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 7 shows an SEM photograph of the carrier core material of Example 5.

Example 6
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, MgO (average particle size: 0.8 μm) 0.605 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 2.669 kg , SrCO ₃ (average particle size: 0.6 μm) 0.067 kg and a carrier core having an average particle size of 36.3 μm in the same manner as in Example 4 except that the holding time at a firing temperature of 1300 ° C. was 8 hours. The material was obtained. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 8 shows an SEM photograph of the carrier core material of Example 6.

Comparative Example 3
Fe ₂ O ₃ (average particle size: 0.6 μm) 7.985 kg, MgO (average particle size: 0.8 μm) 0.605 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 2.669 kg pure water Dispersed in 5.58 kg, 30 g of ammonium polycarboxylate dispersant was added as a dispersant to obtain 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 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 μm to 75 μm. Coarse particles having a particle size exceeding 50 μm were removed from the granulated product using a sieve.
This granulated product was put into an electric furnace and heated to 1200 ° C. over 4.5 hours. Then, it baked by hold | maintaining at 1200 degreeC for 3 hours. Thereafter, it was cooled to room temperature over 8 hours. During this time, a gas in which oxygen and nitrogen were mixed was supplied into the furnace so that the oxygen concentration in the electric furnace was 15000 ppm.
The fired product obtained was pulverized once with a hammer mill (screen opening: 1.5 mm) to obtain a carrier core material having an average particle size of 33.6 μm. The composition, physical properties, maximum ridge / valley depth Rz, combined particle diameter ratio, combined particle ratio, developer characteristics, and the like of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Table 2. FIG. 9 shows an SEM photograph of the carrier core material of Comparative Example 3.

(Composition analysis)
(Analysis of Fe)
The carrier core material containing iron element was weighed and dissolved in a mixed acid water of hydrochloric acid and nitric acid. After evaporating this solution to dryness, sulfuric acid water is added and redissolved to volatilize excess hydrochloric acid and nitric acid. Solid Al is added to this solution to reduce all Fe ³⁺ in the solution to Fe ²⁺ . Subsequently, the amount of Fe ²⁺ ions in the solution was quantitatively analyzed by potentiometric titration with a potassium permanganate solution to obtain a titer of Fe (Fe ²⁺ ).
(Analysis of Mn)
The Mn content of the carrier core material was quantitatively analyzed according to the 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 amount of Mn 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 amount of Mg obtained by this quantitative analysis by ICP.
(Sr analysis)
The Sr content of the carrier core material was determined by ICP quantitative analysis as in the case of Mg analysis.

(Content of bound particles and particle size)
The shape of the carrier core material was photographed at a magnification of 250 times using a scanning electron microscope (manufactured by JEOL Ltd .: JSM-6510LA). Arbitrary 400 particles were selected from the photographed image, the number of binding particles was counted, and the ratio of the number of binding particles contained in the 400 particles was defined as the binding particle content rate.
The bonded particles are particles in which a mother particle having the largest particle size and 1 to 4 child particles having a smaller particle size than the mother particle are bonded, and at least one child particle of the child particles The particle size was larger than ½ of the particle size of the mother particles. And since the base particles and the child particles are present in a form in which the binding particles share the binding portion in the binding particles, the particle size of the base particles and the child particles is determined by scanning electron microscope (manufactured by JEOL Ltd .: JSM-6510LA) was used to calculate each of the particles by spherical approximation from the region excluding the binding portion of the binding particles in an image taken at a magnification of 250 times.

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

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

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

(Magnetic properties)
Using a vibration sample type magnetometer (VSM) dedicated to room temperature (“VSM-P7” manufactured by Toei Kogyo Co., Ltd.), the external magnetic field ranges from 0 to 79.58 × 10 ⁴ A / m (10000 Oersted) for one cycle. And magnetization σ _1k (Am ² / kg) in a magnetic field of 79.58 × 10 ³ A / m (1000 Oersted) was measured.

(Maximum valley depth Rz)
Using an ultra-deep color 3D shape measurement microscope (“VK-X100” manufactured by Keyence Corporation), the surface was observed with a 100 × objective lens. Specifically, first, ferrite particles were fixed to an adhesive tape having a flat surface, a measurement field of view was determined with a 100 × 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. Also, data in the Z direction was acquired by connecting the height positions of the lenses when the intensity of the reflected light from the surface was maximized. These X, Y, and Z direction position data were connected to obtain a three-dimensional shape of the ferrite particle surface. Note that an auto photographing function was used to capture the three-dimensional shape of the ferrite particle surface.
The measurement of each parameter was performed using particle roughness inspection software (manufactured by Mitani Corporation). First, as pretreatment, three-dimensional shape particle recognition and shape selection on the surface of the obtained ferrite particles were performed. Particle recognition was performed by the following method. Of the three-dimensional shape obtained by photographing, the maximum value in the Z direction is set to 100% and the minimum value is set to 0%. The region corresponding to 100 to 35% was extracted, and the contour of the independent region was recognized as the particle contour. Next, coarse, fine, and association particles were excluded by shape selection. By performing this shape selection, it is possible to reduce an error at the time of correcting the polarities thereafter. Specifically, particles corresponding to an area equivalent diameter of 28 μm or less, 38 μm or more, and an acicular ratio of 1.15 or more were excluded. Here, the acicular ratio is a parameter calculated from the ratio of the maximum length / diagonal width of the particle, and the diagonal width is the shortest distance between the two straight lines when the particle is sandwiched between two straight lines parallel to the maximum length. Represents.
Next, the part used for analysis was extracted from the three-dimensional shape of the surface. First, a 15.0 μm square is drawn around the center of gravity obtained from the particle contour recognized by the above method. 21 parallel lines were drawn in the drawn square, and 21 roughness curves corresponding to the line segment were taken out.

  Since the ferrite particles are substantially spherical, the extracted roughness curve has a certain curvature as the background. For this reason, as a background correction, an optimal quadratic curve was fitted and correction subtracted from the roughness curve was performed. In this case, a low-pass filter was applied with an intensity of 1.5 μm, and the cut-off value λ was 80 μm.

  The maximum mountain valley depth Rz was obtained as the sum of the highest mountain height and the deepest valley depth in the roughness curve. The measurement of the maximum height Rz described above is performed in accordance with JIS B0601 (2001 version). In calculating the maximum height Rz, an average value of 30 particles was used as an average value of each parameter.

(Image memory)
The surface of the obtained carrier core material was coated with a resin to prepare a carrier. Specifically, 450 parts by weight of a silicone resin and 9 parts by weight of (2-aminoethyl) aminopropyltrimethoxysilane were dissolved in 450 parts by weight of toluene as a solvent to prepare a coating solution. This coating solution was applied to 50000 parts by weight of a carrier core material using a fluid bed type coating apparatus and heated in an electric furnace at a temperature of 300 ° C. to obtain a carrier. Hereinafter, carriers were obtained in the same manner for all of the 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 toner / (weight of toner and carrier) = 5/100. Hereinafter, developers were obtained in the same manner for all of the Examples and Comparative Examples. The developer thus obtained was developed into a developing device having the structure shown in FIG. 10 (developing sleeve peripheral speed Vs: 406 mm / sec, photosensitive drum peripheral speed Vp: 205 mm / sec, photosensitive drum-developing sleeve distance: 0. 3 mm), an image in which a solid image portion and a non-image portion are adjacent to each other in the longitudinal direction of the photosensitive drum, and a halftone of a wide area thereafter is obtained after the initial and 200,000 sheets are formed, and the developing roller 2 Measure the image density between the area where the solid image on the first development roller of the circumference is developed and the area where it is not, using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.), and determine the difference. Evaluation was made according to the following criteria. The results are shown in Table 2.
“◎”: Less than 0.003 “O”: 0.003 or more and less than 0.006 “Δ”: 0.006 or more and less than 0.020 “X”: 0.020 or more

  As is apparent from Table 2, in the developers using the carrier core materials of Examples 1 to 6 that satisfy the content ratio of the binding particles defined in the present invention, the occurrence of “development memory” was suppressed.

  On the other hand, in the developer using the carrier core material of Comparative Examples 1 to 3 having a binding particle content of 4.2% by number or less, “development memory” was observed.

  According to the carrier core material of the present invention, the amount of toner supplied to the development area can be increased, and the surface of the photoconductor is not damaged by the magnetic brush and is useful.

3 Developing roller 5 Photosensitive drum C Carrier

According to the present invention, 5 to 20% by number of bonded particles having 2 to 5 spherical particles bonded together are included, the normal particles other than the bonded particles are spherical, and the bonded particles have the largest particle size. It is a particle in which a large mother particle and 1 to 4 child particles having a particle diameter smaller than that of the mother particle are combined, and the particle size of at least one child particle of the child particle is the particle size of the mother particle. A carrier core material composed of ferrite particles characterized by being larger than 1/2 of the above is provided.

As a result of intensive studies on whether or not the toner supply amount to the development area can be increased without damaging the surface of the photoconductor with a magnetic brush, the present inventors have determined that the bonded particles, in which several ferrite spherical particles are bonded, are bonded to the carrier core. It has been found that a predetermined number ratio may be contained in the material, and the present invention has been achieved. That is, the carrier core material made of the ferrite particles according to the present invention includes 5 to 20% by number of bonded particles in which 2 to 5 spherical particles are bonded, and the bonded particles have the largest particle size. A particle and 1 to 4 child particles having a particle diameter smaller than that of the mother particle, and the particle diameter of at least one child particle of the child particle is 1 of the particle diameter of the mother particle. It is characterized by being larger than / 2. The carrier core material is a powder made of ferrite particles, and here, ferrite particles other than the binding particles according to the present invention are used as normal particles.

Such a binding particle can be obtained, for example, by increasing the holding time at the firing temperature or adjusting the pulverization operation after firing in the carrier core manufacturing process described later. According to this method, Ru can adjust the content of binding particles in the carrier core easily.

Claims (5)

5 to 20% by number of bonded particles in which 2 to 5 spherical particles are combined are included,
The bonded particles are particles in which a mother particle having the largest particle size and 1 to 4 child particles having a smaller particle size than the mother particle are bonded,
A carrier core material comprising ferrite particles, wherein a particle diameter of at least one child particle of the child particles is larger than ½ of a particle diameter of the mother particle.   The carrier core material according to claim 1, wherein the maximum peak-valley depth Rz on the surface of normal particles other than the binding particles is 1.5 µm or more.   The carrier core material according to claim 1, wherein the volume average particle diameter is 25 μm or more and less than 50 μm.   A carrier for electrophotographic development, wherein the surface of the carrier core material according to claim 1 is coated with a resin.   An electrophotographic developer comprising the carrier for electrophotographic development according to claim 4 and a toner.