JP2019023715A - Carrier core material - Google Patents

Abstract

To provide a carrier core material that reduces the occurrence of a ghost phenomenon even when used for a high-speed image forming apparatus and reduces the occurrence of carrier scattering and a reduction in charge providing property to toner due to a long-term use.SOLUTION: A carrier core material is formed of ferrite particles, where the surface of a particle body of the ferrite particle is covered by a coupling agent; the maximum height Rz of the particle body of the ferrite particle is 1.3 μm or more and 3.0 μm or less; and the coupling agent is an aliphatic compound having 10 to 22 carbon atoms, inclusive, and having a functional group (excluding a silanol group and an alkoxysilyl group). The functional group is preferably at least one of a carboxyl group, an amino group, and a phosphate group.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carrier core material and the like, and more particularly to a carrier core material made of ferrite particles.

  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 is peeled off from the developing roller and mixed with the toner again in the developing device. For this reason, as the characteristics of the carrier, magnetic characteristics for forming a magnetic brush, charging characteristics for imparting a desired charge to the toner, and durability in repeated use are required.

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

  For example, Patent Document 1 proposes a ferrite carrier core material for electrophotographic development containing Sr, having a specific shape, and having nonmagnetic fine particles attached to the particle surface or the inner surface of the pores. Patent Document 2 proposes a carrier core material having irregularities and pores on the surface, and a ratio of an intrusion pore volume value and an infiltration pore volume value obtained by a mercury intrusion method within a predetermined range. .

JP2013-137456A JP2011-8199A

  However, when a carrier whose core is coated with a resin is mixed with a toner to form a two-component developer, in the high-speed image forming apparatus, although one development roller has a normal image density, From the second round onward, a phenomenon in which the image density becomes thin (hereinafter referred to as “ghost phenomenon”) may occur.

  Accordingly, an object of the present invention is to provide a carrier core material that is less likely to cause a ghost phenomenon even when used in a high-speed image forming apparatus, and is less likely to cause a decrease in chargeability to toner due to carrier scattering or long-term use. There is to do.

  Another object of the present invention is to provide an electrophotographic developer carrier and an electrophotographic developer that can stably form a good image quality even when used for a long period of time.

  The carrier core material according to the present invention that achieves the above object is a carrier core material composed of ferrite particles, wherein the surface of the ferrite particle particle body is coated with a surface treatment agent, and the ferrite particle particle body An aliphatic compound having a maximum height Rz of 1.3 μm or more and 3.0 μm or less, the surface treatment agent having 10 to 22 carbon atoms and having a functional group (excluding silanol groups and alkoxysilyl groups). It is characterized by being.

  In the carrier core material configured as described above, it is preferable that the functional group is at least one of a carboxyl group, an amino group, and a phosphate group.

In the carrier core material configured as described above, the specific resistance when a voltage of 100 V is applied by the bridge resistance measurement method is preferably 1.5 × 10 ⁹ Ωcm or less.

  In the carrier core material having the above-described configuration, it is preferable that the specific resistance when the voltage of 100 V is applied to the specific resistance when the voltage of 1000 V is applied by the bridge resistance measurement method is 1 to 10 times.

In the present specification, the specific resistance of the carrier core material by the bridge resistance measurement method is measured as follows. Two brass plates having a thickness of 2 mm whose surfaces were electropolished as electrodes were placed so that the distance between the electrodes was 2 mm, and 200 mg of the carrier core material was inserted into the gap between the two electrode plates, and then each electrode plate A magnet having a cross-sectional area of 240 mm ² is placed behind and a bridge of the carrier core material is formed between the electrodes. A DC voltage of 100 V or 1000 V is applied between the electrodes, and the current value flowing through the carrier core material is 4 terminals. Measure by the method. The specific resistance of the carrier core material is calculated from the measured current value, the distance between the electrodes of 2 mm, and the cross-sectional area of 240 mm ² .

  In the carrier core material having the above structure, the carbon content is preferably 0.0025% by mass or more and 0.0120% by mass or less.

  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.

  In the electrophotographic developing carrier having the above-described configuration, the resin is preferably a (meth) acrylic resin or a (meth) acrylic / styrene mixed resin. In the present specification, “(meth) acrylic resin” means a general term for methacrylic resin and acrylic resin.

  According to the present invention, there is also provided an electrophotographic developer comprising the above-described electrophotographic developing carrier and a toner.

  According to the carrier core material of the present invention, even when used in a high-speed image forming apparatus, a ghost phenomenon is unlikely to occur, and the charge imparting property to toner due to carrier scattering and long-term use hardly occurs.

  Further, according to the electrophotographic developer carrier and the electrophotographic developer of the present invention, a good image quality can be stably formed even for a long period of use.

It is a figure which shows the change of the specific resistance of the carrier core material by an applied voltage. 1 is a schematic diagram illustrating an example of a developing device using an electrophotographic developer according to the present invention. It is a schematic diagram of the apparatus which measures the dynamic resistivity of a carrier.

  As a result of intensive studies to obtain a carrier core material that does not cause the above-described ghost phenomenon even when used in a high-speed image forming apparatus, the present inventors have found that the ghost phenomenon causes toner to move to the photoreceptor. After that (after development), it was found that this was caused by the charge (counter charge) of the carrier remaining on the developing roller.

  In other words, the ghost phenomenon is that the developed carrier needs to be peeled off from the developing roller and mixed with the toner again in the developing device, and a counter charge is generated in the carrier, so that a mirror image is formed between the carrier and the developing roller. It was found that the force was generated, and it was difficult to peel off the carrier from the developing roller, and the developer having a lowered toner concentration was conveyed again to the developing area.

  Therefore, in order to reduce the counter charge of the carrier, the carrier core material is formed in an uneven shape so that a part of the carrier core material is exposed even after resin coating, and the carrier is connected to the developing roller and magnetically connected. The first idea was that when the brush was formed, the counter charge should flow to the developing roller so that the exposed portions of the carrier core were connected.

  However, if the unevenness of the carrier core material is made too large, the carrier fluidity is lowered and the toner may not be mixed smoothly. Therefore, the unevenness of the carrier core material needs to be within a predetermined range so that the fluidity of the carrier does not deteriorate too much. On the other hand, if the unevenness of the carrier core material is small, the entire carrier core material is covered with the coating resin, and the exposed portion is reduced, which may make it difficult to release the countercharge accumulated in the carrier core material.

  Therefore, in the present invention, the surface treatment agent that coats the surface of the ferrite particle body is intensively studied, and the unevenness of the particle body surface of the ferrite particle constituting the carrier core material is suppressed within a predetermined range, and at the same time, the surface of the ferrite particle body is specified. The coating was performed with a surface treatment agent, and the coating resin was guided so as to collect in the recesses on the surface of the particle body. Thereby, the convex part of the particle body surface comes to be exposed without being covered with the coating resin.

  One of the major features of the carrier core material according to the present invention is that the maximum height Rz of the ferrite particles is 1.3 μm or more and 3.0 μm or less. When the maximum height Rz of the ferrite particle main body is within this range, the fluidity of the carrier is not impaired, and in addition to the treatment with the surface treatment agent described later, the carrier core material is coated on the surface of the resin-coated carrier. The counter charge accumulated in the carrier core material is exposed to the outside effectively. Thereby, a ghost phenomenon is suppressed. A more preferable range of the maximum height Rz is a range of 2.2 μm or more and 2.7 μm or less.

  The uneven shape of the ferrite particle body surface can be controlled by adjusting the Sr and chlorine contents, the sintering conditions in the manufacturing process, and the like. Details will be described later.

  Another major feature of the carrier core material according to the present invention is that the surface of the ferrite particles is coated with a specific surface treatment agent. A major feature is that an aliphatic compound having 10 to 22 carbon atoms and having a functional group (excluding silanol group and alkoxysilyl group) is used as the surface treatment agent. Until now, silane coupling agents have been used as surface treatment agents for carrier core materials. In FIG. 1, the vertical axis represents the specific resistance (Ωcm) of the carrier core material, and the horizontal axis represents the applied voltage (V). The carrier core material surface-treated with the silane coupling agent did not have a large difference in specific resistance when the applied voltage was 500 V or higher compared with that before the surface treatment, but compared with that before the surface treatment on the low voltage side where the applied voltage was 100 V. The specific resistance has increased. If the specific resistance of the carrier core material is increased even on the low voltage side, it is difficult to release the counter charge accumulated in the carrier core material, and a ghost phenomenon is likely to occur.

  On the other hand, the carrier core material surface-treated with oleic acid (an aliphatic compound (fatty acid) having 18 carbon atoms and a carboxyl group) did not have a large difference in specific resistance before and after the surface treatment in the range of applied voltage of 100V to 1000V. As a result, in the carrier core material surface-treated with oleic acid, the counter charge accumulated in the carrier core material was effectively released to the outside and the ghost phenomenon was suppressed. The present inventors have further studied the surface treatment agent based on the experimental results, and have obtained an aliphatic compound having 10 to 22 carbon atoms and having a functional group (excluding silanol group and alkoxysilyl group). When it was used, the knowledge that the specific resistance of the carrier core material did not change greatly before and after the surface treatment was obtained. In the present specification, “to” means that the numerical values before and after that are included as a lower limit value and an upper limit value.

  The aliphatic compound having 10 to 22 carbon atoms and having a functional group (excluding silanol group and alkoxysilyl group) used in the present invention may be either saturated or unsaturated. Examples of such aliphatic compounds include fatty acids such as decanoic acid, lauric acid, myristic acid and oleic acid, stearylamine, dodecylphosphoric acid and the like.

  When treating the particle body of ferrite particles with a surface treatment agent, as described later, the particle body and the surface treatment agent solution are mixed and stirred, and then the heat treatment is performed to evaporate the solvent to surface-treat the particle body surface. It is desirable to coat with an agent. As described above, the surface of the particle body is uneven, and therefore, when the particle body and the surface treatment agent solution are mixed and agitated, the surface treatment agent solution collects more in the recesses than the protrusions on the particle body surface. Cheap.

  In addition, in the present invention, since the binding force of the surface treatment agent to the coating resin is weaker than that of a conventionally used surface treatment agent such as a silane coupling agent, the coating resin attached to the ferrite particles is peeled off or moved. It tends to occur, and a portion with a small amount of coating resin adhering to the surface of the ferrite particle or a portion where the ferrite particle is exposed is likely to occur.

  Thus, in the carrier core material of the present invention, since the surface treatment agent is present in a large amount in the recesses of the ferrite particle body, when the carrier core material is resin-coated, the coating resin is present in the recesses in which the surface treatment agent is abundant. Gravitate. In addition, since the binding force of the surface treatment agent with the coating resin is weaker than conventional surface treatment agents such as silane coupling agents, when the ferrite particles and the coating resin are stirred and mixed, by collision and friction between the ferrite particles, The coating resin adhering to the convex part of the ferrite particle is also peeled off from the ferrite particle surface and moves to the concave part. As a result, a portion with a small amount of coating resin adhering or an exposed portion of the carrier core material is generated on the convex portion of the carrier core material subjected to the resin coating process.

  In addition, the detection of the surface treatment agent on the particle main body surface of the ferrite particles can use a conventionally known detection method, for example, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), infrared spectroscopy (IR) ) Etc. can be used. It is also possible to detect the surface treatment agent on the surface of the ferrite particles from the SEM photograph and EDS element mapping.

  Moreover, it is preferable that the usage-amount of a surface treating agent is 0.0025 mass% or more and 0.0120 mass% or less with respect to a carrier core material by the carbon content used as the parameter | index. In addition, the measuring method of carbon content is mentioned later.

The specific resistance of the carrier core material according to the present invention when the voltage of 100 V is applied by the bridge resistance measurement method is preferably 1.5 × 10 ⁹ Ωcm or less. Moreover, it is preferable that the specific resistance at the time of voltage 100V application is 1 time or more and 10 times or less with respect to the specific resistance at the time of voltage 1000V application by bridge resistance measuring method. When the specific resistance of the carrier core is within such a range, the counter charge accumulated in the carrier core is effectively released to the outside, and the ghost phenomenon is effectively suppressed.

The composition of the particle body of the ferrite particles in the present invention is not particularly limited. For example, the general formula M _X Fe _{3 -X} O ₄ (where M is a metal such as Mg, Mn, Cu, Zn, Ni, 0 <X < The particle | grains of the composition represented by 1) are mentioned. Sr, Ti, and Ca may also be included. Among these, Mn ferrite particles containing Sr and MnMg ferrite particles containing Sr are preferably used. By containing Sr, a part of Sr ferrite is generated in the firing step, a magnetoplumbite type crystal structure is formed, and the uneven shape on the surface of the ferrite particles is easily promoted.

  The particle diameter of the carrier core material of the present invention is not particularly limited, but the volume average particle diameter is preferably in the range of 20 μm to 60 μm, and the particle size distribution is preferably sharp.

  Next, the manufacturing method of the ferrite particle which comprises the carrier core material of this invention is demonstrated. Although there is no limitation in particular in the manufacturing method of a ferrite particle, the manufacturing method demonstrated below is suitable.

First, the Fe component raw material and the M component raw material are weighed to produce a raw material mixed powder. M is at least one metal element selected from divalent metal elements such as Mg, Mn, Ca, Cu, Zn, and Ni. If necessary, an Sr component raw material or a Ti component raw material is added. As the Fe component material, Fe ₂ O ₃ or the like is preferably used. As the M component material, MnCO ₃ , Mn ₃ O ₄ or the like can be used if it is a Mn component material, and MgO, Mg (OH) ₂ , or MgCO ₃ can be suitably used if it is an Mg component material. As the Ca component raw material, at least one compound selected from CaO, Ca (OH) ₂ , CaCO _{3 and the} like is preferably used. Also, when adding Sr _{component, SrCO 3, Sr (NO 3} ) 2 and the like are preferably used. TiO ₂ is preferably used as the Ti component raw material.

In addition, in order to make the uneven shape formed on the surface of the ferrite particle into the shape defined in the present invention, it is preferable to add a chlorine component in addition to Sr. As a result, the uneven shape defined by the present invention is easily formed. Although the mechanism by which Sr and chlorine are easily formed to form the uneven shape defined in the present invention has not yet been fully elucidated, a compound of chlorine and Sr, for example, SrClOH is used in the granulation process described later. It is presumed that the granulated product produced and containing this compound will affect the crystal growth of the ferrite particles and form a desired uneven shape in the firing step described later. Examples of the chlorine component raw material include HCl and FeCl ₃ . The addition amount of chlorine is preferably 0.05 mol% or more and 1.0 mol% or less with respect to the Fe element constituting the ferrite.

Generally, the grade for industrial products of Fe ₂ O ₃ used as an Fe raw material contains tens to hundreds of ppm of chlorine as impurities. Fe ₂ O ₃ used in the present invention contains a chlorine content of 300 ppm or less. When a granulated product is produced without adding a chlorine component, the chlorine content contained in the granulated product is 0.02 mol% or less.

  Next, the prepared raw material mixed powder is temporarily fired. 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, there is little gas generation amount at the time of baking, and reaction between solids fully progresses, and 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.

  Then, the calcined raw material is pulverized and charged into a dispersion medium to prepare a slurry. Note that the raw material mixed powder may be charged into the dispersion medium without pre-baking to produce 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%.

  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 10 μm or less, more preferably 5 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 diameter of 10 μm to 200 μm is obtained. In addition, it is desirable that the obtained granulated product has a sharp particle size distribution by removing coarse particles and fine powder using a vibrating sieve or the like.

  Next, the granulated material is put into a furnace heated to a predetermined temperature, and sintered 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 lower than 1100 ° C., the ferritization reaction is difficult to occur and the sintering is difficult to proceed, so that Sr ferrite does not precipitate and the unevenness of the particles may not be promoted. On the other hand, if the firing temperature exceeds 1300 ° C., excessive grain may be generated due to excessive sintering. The rate of temperature increase 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 is increased during temperature rising and sintering, and is lower during cooling than during sintering. By raising the temperature in the firing step and increasing the oxygen concentration during sintering, precipitation of Sr ferrite is promoted to make the particles uneven. Specifically, the oxygen concentration is in the range of 5000 ppm to 15000 ppm. Further, by reducing the oxygen concentration at the time of cooling as compared with that at the time of sintering, the ferrite phase may be oxidized or the reprecipitation of Sr ferrite once decomposed in the sintering stage may be suppressed. Specifically, the oxygen concentration is set to a range of less than 8000 ppm. Thereby, the unevenness of the particles can be achieved, and at the same time, the decrease in magnetic force due to the oxidation of the ferrite phase and the suppression of the increase in residual magnetization caused by the precipitation of Sr ferrite can be achieved.

  The ferrite particles thus obtained are pulverized as necessary. 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. And if necessary, classification may be performed in order to make the particle size in 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 volume average particle diameter of the ferrite particles is preferably in the range of 20 μm to 60 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 to 800 ° C, 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.

  Next, the particle main body surface of the produced ferrite particles is treated with a surface treatment agent. As the surface treatment agent, an aliphatic compound having 10 to 22 carbon atoms and having a functional group (excluding silanol group and alkoxysilyl group) is used. The functional group is preferably at least one of a carboxyl group, an amino group, and a phosphate group. Specific examples of the aliphatic compound suitably used as the surface treatment agent in the present invention include fatty acids such as stearic acid, oleic acid, palmitic acid, myristic acid, lauric acid, decanoic acid, sodium oleate, and oleic acid. Sodium salts of fatty acids such as potassium, soaps that are potassium salts, metal soaps that are metal salts other than fatty acid and sodium and potassium, such as magnesium stearate, barium stearate, zinc stearate, calcium stearate, stearylamine, oleylamine, palmityl Amines such as amine, myristylamine and decylamine, stearyl phosphate, dodecyl phosphate and the like are used. Among these, it is particularly preferable to use at least one of fatty acid, stearylamine, and dodecylphosphoric acid from the viewpoint of impurities and the like.

  As the surface treatment method, a dry treatment method and a wet treatment method can be used, but the wet treatment method is desirable from the viewpoint of reliably exposing a part of the ferrite particles after resin coating. In the wet treatment method, first, a surface treatment agent is added to water or an aqueous alcohol solution to prepare a surface treatment agent aqueous solution. Ferrite particles are charged into a stirrer and stirred, and a surface treating agent aqueous solution is dropped or sprayed onto the stirred ferrite particles. Next, the temperature is raised while continuing stirring to volatilize the alcohol. Thereafter, the ferrite particles are taken out from the stirrer and dried by a dryer. After drying, some of the ferrite particles agglomerate, so a pulverization treatment is performed if necessary.

  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, (meth) acrylic / styrene mixed resin, polyvinyl alcohol resin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, and other thermoplastic elastomers, fluorine Examples thereof include silicone resins. In addition, a (meth) acrylic resin and a (meth) acrylic / styrene mixed resin are particularly preferable in terms of adhesion to the surface of the carrier core material in the present invention.

  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, a dipping method, a dry coating method, or the like can be used. In addition, when coat | covering the carrier core material concerning this invention, the dry-type coating method is especially preferable.

  The particle diameter of the carrier is generally preferably in the range of 10 μm to 200 μm, particularly 20 μm to 60 μm 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 and more preferably in the range of 7 μm to 12 μm in terms of the 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 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. 2 is a schematic diagram showing an example of a developing device that performs magnetic brush development. The developing device shown in FIG. 2 is arranged in parallel to a 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 , separated from the developing roller 3 by the separation magnetic pole N ₂ , and circulated and conveyed again inside the apparatus by the screws 1 and 2 for development. Mix and stir with undeveloped developer. In the developer using the carrier core material of the present invention, peeling from the developing roller 3 by the peeling pole N ₂ it can be smoothly performed. Then, the developer is newly supplied from the screw 1 to the developing roller 3 by the pumping magnetic pole N ₃ . This prevents the ghost phenomenon.

  In the embodiment shown in FIG. 2, the number of magnetic poles built in the developing roller 3 is five. However, in order to further increase the amount of movement of the developer in the developing region and to further improve the pumping performance and the like. Of course, the number of magnetic poles may be increased to 8 poles, 10 poles or 12 poles.

Example 1
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 20.3 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 9.7 kg, SrCO ₃ (average particle size: 0.6 μm) 0. 312 kg was dispersed in 10.0 kg of pure water, 120 g of carbon black as a reducing agent, 180 g of an ammonium polycarboxylate dispersant as a dispersing agent, and 151 g of hydrochloric acid (35 wt% aqueous solution) were added 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. Fine particles having a particle size of 25 μm or less 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. Thereafter, firing was performed by holding at 1200 ° C. for 8 hours. Thereafter, it was cooled to room temperature over 10 hours. At this time, the oxygen concentration in the electric furnace was 0.5%.
The obtained fired product was pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve. The classified fired product was further subjected to a high resistance treatment at a temperature of 460 ° C. for 1 hour in an air atmosphere to obtain a ferrite particle body.

  To the obtained ferrite particle body 2.2 kg, 0.040 g of oleic acid (18 carbon atoms) as a surface treatment agent and 1000 g of ethanol as a solvent were added to a universal stirrer (Model: 5DM-L-03 manufactured by Dalton). -R) for 1 hour at a temperature of 30 ° C. Thereafter, the temperature was raised to 100 ° C. to evaporate ethanol as a solvent, followed by stirring for 1 hour. The obtained dried product was pulverized with a vibrating sieve having an opening of 75 μm to obtain a carrier core material whose surface having an average particle diameter of 34.2 μm was treated with oleic acid.

  Next, 66 g (3.0 wt%) of acrylic / styrene mixed resin was applied to 2.2 kg of the obtained carrier core material using a high speed mixer (“FS-GS-10JD type” manufactured by Fukae Pautech Co., Ltd.). Got. The stirring speed of the high speed mixer was 400 rpm, and the stirring time was 90 minutes.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 2
A carrier core material and a carrier having an average particle diameter of 34.6 μm were obtained in the same manner as in Example 1 except that 0.031 g of myristic acid (14 carbon atoms) was used as the surface treating agent.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 3
A carrier core material and a carrier having an average particle diameter of 34.5 μm were obtained in the same manner as in Example 1 except that 0.026 g of lauric acid (12 carbon atoms) was used as the surface treating agent.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 4
A carrier core material and carrier having an average particle diameter of 34.1 μm were obtained in the same manner as in Example 1 except that 0.022 g of decanoic acid (10 carbon atoms) was used as the surface treating agent.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 5
A carrier core material and a carrier having an average particle diameter of 35.0 μm were obtained in the same manner as in Example 1 except that 72 g of hydrochloric acid (35 wt% aqueous solution) was added as a raw material.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 6
Carrier core material having an average particle diameter of 35.2 μm as in Example 1 except that 0.151 kg of SrCO ₃ (average particle diameter: 0.6 μm) was used as a raw material and hydrochloric acid (35 wt% aqueous solution) was not added. And got a career.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 7
The surface of the average particle diameter of 33.4 μm was olein in the same manner as in Example 5 except that 0.1 g of oleic acid (18 carbon atoms) as a surface treating agent was used for 2.2 kg of the obtained ferrite particle main body. An acid-treated carrier core material and carrier were obtained.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 8
A surface having an average particle diameter of 33.9 μm is stearin in the same manner as in Example 1 except that 0.050 g of stearic acid (18 carbon atoms) is used as a surface treating agent for 2.2 kg of the obtained ferrite particle main body. An acid-treated carrier core material and carrier were obtained.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 9
The surface with an average particle diameter of 33.9 μm is stearyl in the same manner as in Example 1 except that 0.028 g of stearylamine (18 carbon atoms) is used as a surface treating agent for 2.2 kg of the obtained ferrite particle main body. A carrier core material and carrier treated with amine were obtained.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Example 10
A surface having an average particle diameter of 35.0 μm was obtained in the same manner as in Example 1 except that 0.030 g of dodecyl phosphoric acid (12 carbon atoms) was used as a surface treating agent for 2.2 kg of the obtained ferrite particle main body. A carrier core material and a carrier treated with dodecyl phosphate were obtained.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 1
As raw materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 21.5 kg, Mn ₃ O ₄ (average particle size: 0.9 μm) 7.5 kg, MgO (average particle size: 0.8 μm) 1.0 kg , 0.25 kg of SrCO ₃ (average particle size: 0.6 μm) is dispersed in 10.0 kg of pure water, 120 g of carbon black as a reducing agent, 180 g of an ammonium polycarboxylate dispersant as a dispersing agent, hydrochloric acid (35 wt. % Aqueous solution) was added 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 130 ° C. with a spray dryer to obtain a dry 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.
This granulated product was put into an electric furnace and heated to 1200 ° C. over 4.5 hours. Thereafter, firing was performed by holding at 1200 ° C. for 8 hours. Thereafter, it was cooled to room temperature over 10 hours. At this time, the oxygen concentration in the electric furnace was 1.0%.
The obtained fired product was pulverized with a hammer mill (“Hammer Crusher NH-34S” manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve to obtain an average particle size of 34. A carrier core material of 4 μm was obtained.

  Next, 66 g (3.0 wt%) of acrylic / styrene mixed resin was applied to 2.2 kg of the obtained carrier core material using a high speed mixer (“FS-GS-10JD type” manufactured by Fukae Pautech Co., Ltd.). Got. The stirring speed of the high speed mixer was 400 rpm, and the stirring time was 90 minutes.

  The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 2
A carrier having an average particle size of 34.4 μm was obtained in the same manner as in Comparative Example 1 except that the carrier core material was coated with a resin to prepare a carrier, except that the amount of the acrylic / styrene mixed resin was reduced from 66 g to 44 g. It was.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 3
To 2.2 kg of the obtained ferrite particle body, 2.2 g of 3-methacryloxypropyltrimethoxysilane as a silane coupling agent as a surface treatment agent, 550 g of methanol as a solvent and 22 g of water as a universal stirrer (Dalton) (Model: 5DM-L-03-r) and mixed at a temperature of 30 ° C. for 1 hour. Then, after heating up to 120 degreeC and volatilizing methanol which is a solvent, it stirred for 1 hour. Except for performing heat treatment for 2 hours with a blower dryer set at 140 ° C. (MODEL: PHH-102, manufactured by Espec Corp.), and subjecting the resulting dried product to pulverization with a vibrating sieve having an opening of 75 μm. In the same manner as in Example 5, a carrier core material and a carrier having a surface with an average particle diameter of 34.7 μm treated with a surface treatment agent were obtained.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 4
A carrier core material and a carrier whose surface having an average particle diameter of 35.1 μm was treated with a surface treatment agent in the same manner as in Comparative Example 3 except that 1.1 g of 3-methacryloxypropyltrimethoxysilane as a surface treatment agent was used. Obtained.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 5
A surface having an average particle diameter of 34.8 μm was treated with the surface treatment agent in the same manner as in Comparative Example 3 except that 2.2 g of 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane as the surface treatment agent was used. A carrier core material and a carrier were obtained.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

Comparative Example 6
A carrier core material and a carrier having an average particle diameter of 34.1 μm were obtained in the same manner as in Example 1 except that 0.018 g of octanoic acid (8 carbon atoms) was used as the surface treating agent.
The powder properties, magnetic properties, specific resistance measured by the bridge resistance measurement method, dynamic resistivity of the carrier, and the like of the obtained carrier core material were measured by the methods described later. The measurement results are shown in Table 1.

(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.

(Maximum height 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.
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 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.
Moreover, about the average particle diameter of the carrier core material used for an analysis, it limited to 32-34 micrometers. In this way, by limiting the average particle diameter of the carrier core material to be measured to a narrow range, it is possible to reduce an error due to a residue generated during curvature correction.

  The maximum height Rz was obtained as the sum of the highest mountain height and the deepest valley depth in the roughness curve. In calculating the maximum height Rz, an average value of 30 particles was used as an average value of each parameter.

  The maximum height Rz described above is performed in accordance with JIS B0601 (2001 edition).

(Volume average particle diameter (average particle diameter))
The volume average particle diameter 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.).

(Carbon content)
The amount of carbon was measured by an infrared absorption method. Specifically, 1 g of carrier core material is burned in an oxygen stream, carbon contained in the carrier core material is carbon dioxide, and an infrared absorption detector (manufactured by LECO Japan Co., Ltd., carbon sulfur analyzer “CS-200”). The amount of carbon was calculated by measuring the amount of infrared absorption of carbon dioxide by “type”).

(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.

(Specific resistance by bridge resistance measurement method)
Two brass plates having a thickness of 2 mm whose surfaces were electropolished as electrodes were placed so that the distance between the electrodes was 2 mm, and 200 mg of the carrier core material was inserted into the gap between the two electrode plates, and then each electrode plate A magnet having a cross-sectional area of 240 mm ² is placed behind and a bridge of the carrier core material is formed between the electrodes. A DC voltage of 100 V or 1000 V is applied between the electrodes, and the current value flowing through the carrier core material is 4 terminals. Measured by the method. The specific resistance of the carrier core material was calculated from the measured current value, the distance between the electrodes of 2 mm, and the cross-sectional area of 240 mm ² .

(Evaluation of dynamic resistivity)
As shown in FIG. 3, the dynamic resistivity was measured using a device comprising a carrier stirring section, a developing roller and an aluminum electrode. The apparatus shown in FIG. 3 is filled with the carrier 120g, and the developing roller is opposed to the aluminum electrode with a gap d = 0.055 cm, and the developing roller is rotated at 40 rpm and the aluminum electrode is rotated at 25 rpm. And rotated in the same direction. In this state, the current I when a DC voltage V of 300 V was applied between the developing roller and the aluminum electrode was measured to determine the dynamic resistivity of the carrier in the magnetic brush state.
In this measurement, an aluminum cylinder subjected to bead blasting with a diameter of 30 mm and a length of 100 mm was used as the developing roller, and an aluminum cylinder with a diameter of 30 mm and a length of 100 mm was used as the aluminum electrode, and the distance between the developing roller and the regulating plate was 0. The measurement was carried out with adjustment to 5 mm. At this time, the contact area S between the magnetic brush formed by the carrier and the aluminum electrode was 3.25 cm ² , and the dynamic resistivity was calculated by the following formula. As a DC voltage source, HJPQ-1 * 30 manufactured by Matsusada Precision Co., Ltd. was used, and current I was measured using an 8240 type digital electrometer manufactured by DIC Corporation.
Dynamic resistivity (Ω · cm) = (V / I) × (S / d)
(Where V: DC voltage value, I: current value, S: contact area, d: gap between developing roller and aluminum electrode)

(Development of developer)
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 mass of the toner / (the mass of the toner and the carrier) = 5/100. Hereinafter, developers were obtained in the same manner for all of the Examples and Comparative Examples.

(Actual machine evaluation)
The developing device having the structure shown in FIG. 2 (developing roller peripheral speed Vs: 406 mm / sec, photosensitive drum peripheral speed Vp: 205 mm / sec, photosensitive drum-developing roller distance: 0.3 mm) was produced. A two-component developer was added, and after initial printing, after 1000 sheets were printed, 3 images for evaluation were printed, and ghost phenomenon, carrier scattering, and toner scattering were evaluated according to the following procedures and standards. Table 2 shows the evaluation results.

Ghost Phenomenon The density of five locations per three images for evaluation by the evaluator was measured using a spectral densitometer (X-Rite 504 manufactured by X-Rite) and evaluated according to the following criteria.
“◎”: The maximum density difference is less than 0.03.
“◯”: The maximum density difference is 0.03 or more and less than 0.06.
“Δ”: The maximum density difference is 0.06 or more and less than 0.10.
“×”: The maximum density difference is 0.10 or more.

Carrier scattering Initially, after printing 1000 sheets, the carrier on the photoconductor (drum) after printing 10,000 sheets was peeled off with a cellophane tape, and the number per unit area was measured and evaluated according to the following criteria.
“◎”: 0 carriers.
“◯”: 1 to 5 carriers “Δ”: 6 to 10 carriers “×”: 11 or more

Toner scattering For toner scattering, a good level is indicated by “◯”, and a problem-free level is indicated by “X”.

  As is clear from Tables 1 and 2, the carrier core materials of Examples 1 to 4 and 8 were obtained by treating the particle body surface of the ferrite particles with oleic acid, myristic acid, lauric acid, decanoic acid, and stearic acid, respectively. Compared with the carrier core material of Comparative Example 1 which was not subjected to surface treatment, the dynamic resistivity after the carrierization of these carrier core materials was low, and “ghost phenomenon”, “carrier scattering” No “toner scattering” occurred and the evaluation result was good.

  Further, the carrier core material of Example 5 having a maximum height Rz of 2.2 μm and the carrier core material of Example 6 having a maximum height Rz of 1.5 μm also have a low dynamic resistivity after being converted to a carrier, None of “ghost phenomenon”, “carrier scattering” and “toner scattering” occurred, and the evaluation result was good.

  Also in the carrier core material of Example 7 having a large coating amount of oleic acid as a surface treating agent, the dynamic resistivity after the carrierization is low, and any of “ghost phenomenon”, “carrier scattering” and “toner scattering” It did not occur and was a good evaluation result.

  In addition, in the carrier core material of Example 9 using stearylamine having an amino group as a surface treating agent and Example 10 using dodecyl phosphate having a phosphate group, the dynamic resistivity after carrierization is low. None of “ghost phenomenon”, “carrier scattering” and “toner scattering” occurred, and the evaluation result was good.

  In contrast, in the carrier core material of Comparative Example 1 that was not subjected to the surface treatment, a “ghost phenomenon” occurred from the beginning. In addition, in the carrier core material of Comparative Example 2 in which the amount of the coating resin used was 2 wt%, which was less than that of Comparative Example 1, it was confirmed that the influence of the increase in the exposure of the carrier core material was caused and the decrease in the dynamic resistivity of the carrier was estimated. , "Ghost phenomenon" did not occur, but when the number of printed sheets increased due to the decrease in the amount of coating resin, the carrier resin was depleted and the carrier resistance decreased, and "carrier scattering" deteriorated after printing 10,000 sheets At the same time, the carrier was deteriorated and the charge imparting ability was lowered to cause “toner scattering”.

  In the carrier core material of Comparative Examples 3 and 4 using a silane coupling agent having a methacryl group as a surface treatment agent and Comparative Example 5 using a silane coupling agent having an epoxy group as a surface treatment agent, “carrier scattering” and “Toner scattering” showed a good result, but the specific resistance at an applied voltage of 100 V was high and the “ghost phenomenon” was deteriorated.

  Further, the carrier core material of Comparative Example 6 using octanoic acid (8 carbon atoms) as the surface treatment agent showed a high numerical value of the dynamic resistivity after being converted to a carrier, and the “ghost phenomenon” was deteriorated.

3 Developing roller 5 Photosensitive drum

Claims (8)

A carrier core made of ferrite particles,
The surface of the particle body of the ferrite particles is coated with a surface treatment agent,
The maximum height Rz of the ferrite particle body is 1.3 μm or more and 3.0 μm or less,
A carrier core material, wherein the surface treatment agent is an aliphatic compound having 10 to 22 carbon atoms and having a functional group (excluding a silanol group and an alkoxysilyl group).   The carrier core material according to claim 1, wherein the functional group is at least one of a carboxyl group, an amino group, and a phosphate group. The carrier core material according to claim 1 or 2, wherein a specific resistance when a voltage of 100 V is applied by a bridge resistance measurement method is 1.5 x 10 ⁹ Ωcm or less.   The carrier core material according to any one of claims 1 to 3, wherein a specific resistance when a voltage of 100 V is applied is 1 to 10 times that of a specific resistance when a voltage of 1000 V is applied by a bridge resistance measurement method.   Carbon content is 0.0025 mass% or more and 0.0120 mass% or less, The carrier core material in any one of Claims 1-4.   6. A carrier for electrophotographic development, wherein the surface of the carrier core material according to claim 1 is coated with a resin.   The carrier for electrophotographic development according to claim 6, wherein the resin is a (meth) acrylic resin or a (meth) acrylic / styrene mixed resin.   An electrophotographic developer comprising the carrier for electrophotographic development according to claim 6 or 7 and a toner.