JP5748258B2 - Carrier core material for electrophotographic developer and method for producing the same - Google Patents

Description

  The present invention relates to a carrier core material for an electrophotographic developer and a method for producing the same, and more particularly to a carrier core material for an electrophotographic developer used for electrophotographic development in a developing machine such as a copying machine or a printer and a method for producing the same.

  Conventionally, in a developing machine such as a copying machine or a printer, a method such as a cascade method or a magnetic brush developing method is used as an electrophotographic developing method. The magnetic brush development method is a method that is generally used in recent years. After a toner image is visualized on an electrostatic latent image formed on a photosensitive drum via a magnetic brush, it is thermally fixed. This is a method for obtaining an image. In recent magnetic brush development methods, the toner is electrostatically oriented on the particles of an electrophotographic developer carrier (hereinafter referred to as “carrier”) rather than a one-component developer that forms a magnetic brush with only toner. Two-component developers that form magnetic brushes are often used.

  In a two-component developer, a carrier is used in which the surface of a core material constituting carrier particles (hereinafter referred to as “carrier core material”) is coated with a toner and a reversely chargeable resin. In this magnetic brush developing method using a two-component developer, carrier particles and toner particles are mixed and stirred in a developing machine to charge the toner particles and adhere them to the carrier particles. Next, the charged toner particles move from and adhere to the electrostatic latent image formed on the photosensitive member or electrostatic recording member from the magnetic brush formed by the carrier particles. An image can be obtained by transferring the toner adhering to the electrostatic latent image onto the paper surface. Therefore, the charge imparting ability of the carrier particles to the toner at the time of stirring is greatly related to image formation.

  Further, if the charge amount of the carrier particles is high, the developing machine itself has many merits. For example, by using carrier particles having a high charge amount, the amount of necessary carrier particles can be reduced, so that the weight of the developing machine can be reduced and the load on the magnetic drum can be reduced. In order to increase the charge amount of the carrier particles, it is common to change the type and thickness of the resin that coats the carrier core material, or to add additives as appropriate. It is also affected by the characteristics of the carrier core material used as a base.

  In the two-component developer, the toner particles are supplied and consumed every time they are developed, and are always replaced with new toner particles, whereas the carrier particles remain in the developing machine and are repeatedly used. Therefore, the carrier particles are required to have characteristics that do not change over a long period of repeated use, that is, durability.

  In order to maintain the charge amount of carrier particles, we propose to reduce stress between carrier particles by reducing the number of deformed particles in the core particles (carrier core material) and making the particles uniform in size by making the grain diameter uniform. (For example, refer to Patent Document 1).

JP 2008-96977 A (paragraph number 0034-0040)

  However, as a result of investigations by the present inventors, it has been found that the carrier particles of Patent Document 1 have the ability to impart charge to the toner of the carrier due to repeated development, and a stable image cannot be obtained over a long period of time. . This is because the resin film covering the carrier particles is worn and peeled by repeated stirring and mixing in the developing machine, and the carrier core material that is the base is exposed, or the carrier particles are removed by the toner spent. This is probably because the effective area decreases.

  Therefore, in view of such a conventional problem, the present invention provides a carrier core material for an electrophotographic developer that does not deteriorate the charge imparting ability of the carrier to the toner even when used for a long time, and a method for producing the same. Objective.

  As a result of diligent research to solve the above-mentioned problems, the present inventors dried and granulated a mixture obtained by mixing and stirring an iron compound powder, a manganese compound powder, and a phosphorus compound powder in a solvent. Thereafter, the obtained granulated material is baked in an inert gas atmosphere at a temperature of 1100 to 1300 ° C., preferably higher than 1100 ° C. and 1200 ° C. or lower, so that the carrier can be charged to the toner even when used for a long period of time. It has been found that a carrier core material for an electrophotographic developer that does not deteriorate the imparting ability can be produced, and the present invention has been completed.

That is, the method for producing a carrier core material for an electrophotographic developer according to the present invention comprises drying and granulating a mixture obtained by mixing and stirring an iron compound powder, a manganese compound powder and a phosphorus compound powder in a solvent. Then, the obtained granulated product is fired at a temperature of 1100 to 1300 ° C., preferably higher than 1100 ° C. and 1200 ° C. or lower in an inert gas atmosphere. In this method for producing a carrier core material for an electrophotographic developer, the oxygen concentration in the inert gas atmosphere is preferably 1% by mass or less. Further, as an iron compound, a metal Fe, Fe ₃ O ₄ and Fe ₂ O at least one can be used which are selected from the ₃ group consisting of, preferably iron compound is iron oxide. Manganese compounds, metal _Mn, preferably at _{MnO 2, Mn 2 O 3,} Mn 3 O 4 and MnCO 1 or more _{to 3} selected from the group consisting of, phosphorus compounds, phosphorus _alone, P 2 _{O 5} And at least one selected from the group consisting of Ca ₃ (PO ₄ ) ₂ and the amount of the phosphorus compound is preferably 0.1 to 5% by mass in the mixture. The solvent is preferably water.

In addition, the carrier core material for an electrophotographic developer according to the present invention contains soft ferrite represented by Mn _x Fe _3-x O ₄ (where 0 <x ≦ 1), and has a grain interface that divides the particle surface. It is characterized in that manganese element and phosphorus element are segregated. In the carrier core material for an electrophotographic developer, the amount of phosphorus element is preferably 0.1 to 5% by mass with respect to the carrier core material. Moreover, it is preferable that the groove depth in the grain interface which divides | segments the surface of the particle | grains of a carrier core material is 0.2 micrometer or more. Further, the magnetization of the carrier core material in an external magnetic field of 1000 Oe is preferably 65 emu / g or more, and the particle diameter is preferably 10 to 100 μm.

  A carrier for an electrophotographic developer according to the present invention comprises any one of the above-described carrier core materials for electrophotographic development and a resin coated with the carrier core material. Furthermore, an electrophotographic developer according to the present invention is characterized by comprising the above-described electrophotographic developer carrier and a toner mixed with the carrier.

  According to the present invention, it is possible to produce a carrier core material for an electrophotographic developer that does not deteriorate the charge imparting ability of the carrier to the toner even after long-term use.

3 is a scanning electron micrograph (SEM image) of the carrier core material obtained in Example 2. FIG. 3 is an SEM image of a carrier core material obtained in Comparative Example 1. 6 is an SEM image of a carrier core material obtained in Comparative Example 2. 6 is a SEM image of a carrier core material obtained in Comparative Example 3. 4 is a mapping image of manganese element on the surface of the carrier core material obtained in Example 2. FIG. 3 is a mapping image of phosphorus element on the surface of the carrier core material obtained in Example 2. FIG. 4 is a mapping image of manganese element on the surface of the carrier core material obtained in Comparative Example 1. FIG. 3 is a mapping image of phosphorus elements on the surface of a carrier core material obtained in Comparative Example 1. FIG. 6 is a mapping image of manganese element on the surface of the carrier core material obtained in Comparative Example 2. 6 is a mapping image of phosphorus elements on the surface of a carrier core material obtained in Comparative Example 2. 6 is a mapping image of manganese element on the surface of the carrier core material obtained in Comparative Example 3. 7 is a mapping image of phosphorus elements on the surface of a carrier core material obtained in Comparative Example 3. FIG.

  Embodiments of the method for producing a carrier core material for an electrophotographic developer according to the present invention include a step of preparing an iron compound powder, a manganese compound powder and a phosphorus compound powder as raw materials (raw material adjusting step), and using these raw materials as a solvent. A step of mixing and stirring to prepare a slurry (mixing / slurry step), a step of drying and granulating the resulting slurry (granulation step), and an inert gas from the resulting granulated product And a step of baking at a temperature of 1100 to 1300 ° C., preferably higher than 1100 ° C. and 1200 ° C. or lower in an atmosphere (baking step). Hereinafter, these steps will be described in detail.

(Raw material adjustment process)
First, an iron compound, a manganese compound, and a phosphorus compound are prepared as raw materials for the carrier core material. As the iron compound, it is preferable to use metal Fe, Fe ₃ O ₄ , Fe ₂ O ₃ or the like. As the manganese compound, it is preferable to use metal Mn, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , MnCO ₃ or the like. As the phosphorus compound, it is preferable to use phosphorus alone, P ₂ O ₅ , Ca ₃ (PO ₄ ) ₂ or the like. These raw materials are preferably used in the form of powder, and the primary particle size of each raw material is preferably 3.0 μm or less. This is because if the particle size of the raw material is fine, the respective raw materials can be sufficiently mixed together and a carrier core material having a uniform composition can be produced.

These raw materials are used by weighing so that the carrier core material after firing satisfies desired characteristics. For example, when producing ferrite magnetic particles having a composition represented by MnFe ₂ O ₄ as a carrier core material, a manganese compound and an iron compound are added so that the ratio of manganese element to iron element in the raw material is 1: 2. What is necessary is just to measure and use. Further, the phosphorus compound may be used by weighing it so that it becomes 0.1 to 5.0% by mass in the raw material.

(Mixing / slurry process)
Next, the raw materials weighed as described above are dispersed in a solvent and stirred to prepare a slurry in which the raw materials are mixed. As the solvent, water is preferably used from the viewpoint of handling, and it is preferable to add a dispersant or the like to the solvent as necessary. Further, in order to uniformly mix the raw materials, a mechanical dispersion treatment may be performed on the raw material slurry.

(Granulation process)
Next, the obtained slurry is sprayed into a dry air and granulated to obtain a roughly spherical granulated powder of 10 to 100 μm. For this granulation, a general spray drying apparatus capable of spraying the slurry by supplying drying air may be used.

(Baking process)
Next, the obtained granulated powder (precursor particles) is fired to obtain a magnetic powder having a magnetic phase. This firing is performed by putting the granulated powder into a heated furnace and heating it for a predetermined time. The firing temperature may be set to a temperature range in which the target magnetic phase is generated, but is preferably set to a temperature of 1100 to 1300 ° C, more preferably set to a temperature higher than 1100 ° C and 1200 ° C or lower. preferable. By baking in this temperature range, a carrier core material in which a manganese-phosphorus compound is segregated at the grain interface that divides the particle surface can be obtained. In order to prevent decomposition of the magnetic phase, the atmosphere in the furnace at the time of firing is preferably adjusted so that the oxygen concentration becomes 1% by mass or less by flowing an inert gas such as nitrogen gas or argon gas. In addition, since the fired product is cured by sintering, it is preferable to obtain a magnetic powder having a desired particle size distribution by pulverizing with a pulverizer or the like and then classifying with a sieve.

(Manufacture of carrier and electrophotographic developer)
The carrier is manufactured by coating the surface of the carrier core manufactured by the above-described embodiment of the method for manufacturing the carrier core with a resin such as silicone resin. Thus, by covering the carrier core material with the resin, the ability to impart charge to the toner and the durability can be improved. A charge amount adjusting agent or conductive powder may be added to the resin covering the surface of the carrier core material. Also, a two-component electrophotographic developer is produced by mixing the carrier thus produced with a toner having a desired particle diameter.

(Carrier core)
The carrier core material manufactured according to the embodiment of the carrier core material manufacturing method described above contains soft ferrite represented by Mn _x Fe _3-x O ₄ (where 0 <x ≦ 1), and has a particle surface. Manganese element and phosphorus element are segregated at the grain interface that divides.

  A carrier core material containing such soft ferrite exhibits high magnetization. Further, as a result of the study by the present inventors, when manganese element and phosphorus element are segregated at the grain interface dividing the particle surface of the carrier core material, a substance having a high ability to impart charge to the toner is present at the grain interface. It was found that the carrier core material was localized. That is, the manganese-phosphorus compound produced by segregation of manganese element and phosphorus element has extremely high chargeability. By dispersing this compound on the surface of the carrier core material particles, the carrier core material itself can be applied to the toner. It was found that the charge imparting ability can be improved.

  Moreover, it is preferable that the groove depth in the grain interface which divides | segments the surface of the particle | grains of a carrier core material is 0.2 micrometer or more. As described above, when the groove depth is 0.2 μm or more, an excellent chargeable manganese-phosphorus compound can be present at a sufficient depth in the recesses on the surface of the carrier core particles.

  In addition, the concave portions on the surface of the carrier core material particles are less likely to collide with each other during stirring and mixing in the developing machine, the resin film is less likely to wear and peel, and the surface of the carrier core material is exposed. This is considered to be a region where toner spent is difficult to occur. Therefore, if a compound having a high ability to impart toner to toner is segregated in the recess, the ability to impart toner to the toner in the recess remains high even if the resin film is worn or toner spent on the protrusion of the particle. Therefore, it is considered that the charge imparting ability of the carrier particles to the toner as a whole is maintained.

  The magnetization of the carrier core material in an external magnetic field of 1000 Oe is preferably 65 emu / g or more. If the value of this magnetization is 65 emu / g or more, the so-called carrier scattering phenomenon in which carrier particles are scattered on the photosensitive member side due to centrifugal force on the magnetic drum in the developing machine can be suppressed.

  Moreover, it is preferable that the particle diameter of a carrier core material is 10-100 micrometers. When the particle size is 10 μm or less, it is difficult to suppress the carrier scattering phenomenon, and when the particle size is 100 μm or more, it is difficult to obtain desired image characteristics.

  Also, the ability to impart charge to the toner and durability can be improved by coating the surface of the carrier core material with a resin or the like to produce a carrier for an electrophotographic developer. By mixing this carrier with an appropriate toner, a two-component electrophotographic developer can be produced.

  As described above, by increasing the charge imparting ability of the carrier core material before resin coating to the toner, even if the coating film is worn or peeled off, the charge imparting ability of the carrier core material to the toner is unlikely to deteriorate. In addition, it is possible to remarkably suppress the deterioration of the charge imparting ability to the toner by localizing the region having a high ability to impart charge to the toner in the concave portion of the surface of the particle of the carrier core material. As a result, it is possible to produce a carrier that has excellent durability and does not deteriorate the ability of the carrier core material to impart charge to the toner even when used repeatedly for a long period of time. Since this carrier does not reduce the amount of toner particles transported to the photoreceptor, it can prevent the image quality from deteriorating.

  Examples of the carrier core material for an electrophotographic developer and the production method thereof according to the present invention will be described in detail below.

[Example 1]
While 6.8 kg of Fe ₂ O ₃ (average particle size 0.6 μm) as a starting material, 3.2 kg of Mn ₃ O ₄ (average particle size 0.9 μm) and 15 g of red phosphorus powder are dispersed in 3.0 kg of pure water. Then, 60 g of ammonium polycarboxylate dispersant was added and mixed. This mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry of Fe ₂ O ₃ , Mn ₃ O ₄ and red phosphorus. The mixing ratio of the starting materials was calculated so that the composition formula of ferrite was MnFe ₂ O ₄ .

  After adding 30 g of carbon black (Mitsubishi Chemical Black MA7 manufactured by Mitsubishi Chemical Co., Ltd.) as a reducing agent to the slurry thus obtained, the slurry was sprayed into hot air at about 130 ° C. with a spray dryer. A dry granulated powder of 100 μm was obtained.

  The granulated powder having a particle size exceeding 100 μm was removed from the granulated powder with a sieve, and then put into an electric furnace and baked at 1200 ° C. for 3 hours. In this firing, a mixed gas of oxygen and nitrogen was allowed to flow into the electric furnace to make the oxygen concentration 100 ppm. The fired product thus obtained was pulverized and then classified by a sieve to obtain a carrier core material having an average particle size of 35 μm.

[Example 2]
Same as Example 1 except that 7.2 kg of Fe ₂ O ₃ (average particle size 0.6 μm), 2.8 kg of Mn ₃ O ₄ (average particle size 0.9 μm) and 15 g of red phosphorus powder were used as starting materials. By this method, a carrier core material having an average particle diameter of 35 μm was obtained. The mixing ratio of the starting materials was calculated so that the composition formula of ferrite was Mn _0.85 Fe _2.15 O ₄ .

[Example 3]
Same as Example 1 except that 7.2 kg Fe ₂ O ₃ (average particle size 0.6 μm), 2.8 kg Mn ₃ O ₄ (average particle size 0.9 μm) and 30 g red phosphorus powder were used as starting materials. By this method, a carrier core material having an average particle diameter of 35 μm was obtained.

[Example 4]
Same as Example 1 except that 8.4 kg Fe ₂ O ₃ (average particle size 0.6 μm), 1.6 kg Mn ₃ O ₄ (average particle size 0.9 μm) and 15 g red phosphorus powder were used as starting materials. By this method, a carrier core material having an average particle diameter of 35 μm was obtained. The mixing ratio of the starting materials was calculated so that the composition formula of ferrite was Mn _0.5 Fe _2.5 O ₄ .

[Comparative Example 1]
Example, except that 7.2 kg Fe ₂ O ₃ (average particle size 0.6 μm) and 2.8 kg Mn ₃ O ₄ (average particle size 0.9 μm) were used as starting materials and no red phosphorus powder was added. 2 was used to obtain a carrier core material having an average particle diameter of 35 μm.

[Comparative Example 2]
A carrier core material having an average particle size of 35 μm was obtained in the same manner as in Example 2 except that the temperature during firing was 1100 ° C.

[Comparative Example 3]
A carrier core material having an average particle size of 35 μm was obtained in the same manner as in Example 1 except that 10.0 kg of Fe ₂ O ₃ (average particle size 0.6 μm) and 15 g of red phosphorus powder were used as starting materials. The mixing ratio of the starting materials was calculated so that the composition formula Fe ₃ O ₄ of magnetite was obtained.

  Thus, about the carrier core material obtained in Examples 1-4 and Comparative Examples 1-3, composition analysis, the measurement of a particle size, evaluation of a magnetic characteristic, calculation of an average groove depth, and the charge amount are as follows. Was calculated.

(Composition analysis)
From the solutions obtained by completely dissolving the carrier core materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 in hydrochloric acid, quantitative analysis of phosphorus was performed by ICP analysis (ICPS-7510 manufactured by Shimadzu Corporation). It was. As a result, the analytical value of phosphorus in the carrier core material is 0.33 mass% (Example 1), 0.14 mass% (Example 2), 0.26 mass% (Example 3), and 0.25 mass. % (Example 4), 0.02% by mass (Comparative Example 1), 0.26% by mass (Comparative Example 2), and 0.28% by mass (Comparative Example 3).

(Particle size)
About the particle size distribution of the carrier core material obtained in Examples 1-4 and Comparative Examples 1-3, it measured using the micro track | truck (Model-9320-X100 by Nikkiso Co., Ltd.). As a result, the particle diameter of the carrier core material (the value of the accumulated particle diameter D ₅₀ up to a volume ratio of 50%) is 35.5 μm (Example 1), 34.7 μm (Example 2), 34.5 μm (Example) 3) 34.5 μm (Example 4), 36.2 μm (Comparative Example 1), 35.3 μm (Comparative Example 2), and 34.2 μm (Comparative Example 3).

(Magnetic properties)
As the magnetic properties of the carrier core materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3, magnetization was measured using VSM (VSM-P7 manufactured by Toei Kogyo Co., Ltd.), and an external magnetic field of 1000 Oe.
Magnetization σ ₁₀₀₀ (emu / g) was obtained. As a result, the magnetization σ ₁₀₀₀ is 69.7 emu / g (Example 1), 69.6 emu / g (Example 2), 69.6 emu / g (Example 3), and 72.6 emu / g (Example 4). 70.9 emu / g (Comparative Example 1), 70.9 emu / g (Comparative Example 2), and 67.1 emu / g (Comparative Example 3).

(Groove depth)
About the depth of the groove | channel in the grain interface which divides | segments the surface of the particle | grains of the carrier core material obtained in Examples 1-4 and Comparative Examples 1-3, height measurement is carried out with respect to the range of 10 micrometers square near the center of particle | grains. The height at the deepest place from the average line was defined as the groove depth, and the groove depth for 50 particles was averaged to obtain the average groove depth. The value of the groove depth was calculated by scanning the particle surface using a laser microscope (OLS30-LSU manufactured by Olympus Corporation). As a result, the average groove depth of the carrier core material is 0.34 μm (Example 1), 0.38 μm (Example 2), 0.42 μm (Example 3), 0.28 μm (Example 4), 0 These were 0.13 μm (Comparative Example 1), 0.15 μm (Comparative Example 2), and 0.28 μm (Comparative Example 3).

(Core charge amount)
38 g of each of the carrier core materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 and 2.0 g of a commercially available toner (a general toner having a particle size of 6 μm for monochrome use) are placed in a glass bottle and placed in a shaker. The sample was charged and stirred for 20 minutes to obtain a charge measurement sample. The charge amount (μC / g) was calculated by measuring the charge applied to the toner by the carrier core material with respect to 500 mg of this charge amount measurement sample. The charge was measured using a charge measuring device (STC-1-C1 type manufactured by Nippon Piotech Co., Ltd.), a suction pressure of 7.0 kPa, and a 750 mesh SUS network as a suction mesh. As a result, the core material charge amount was 18.3 μC / g (Example 1), 21.1 μC / g (Example 2), 19.5 μC / g (Example 3), 17.2 μC / g (Example). 4) 14.5 μC / g (j Comparative Example 1), 11.4 μC / g (Comparative Example 2), and 9.2 μC / g (Comparative Example 3).

  Table 1 shows the evaluation results of the characteristics of these carrier core materials.

(Surface properties)
In order to evaluate the distribution state (deposition state) of the constituent elements of the elements on the surface of the carrier core material obtained in Examples 1 to 4 and Comparative Examples 1 to 3, SEM-EDS (JSM-manufactured by JEOL Ltd.) 6510LA and JED-2300), element mapping on the surface of the carrier core material was performed from a scanning electron micrograph (SEM image) of the surface of the carrier core material.

  1 to 4 are SEM images of carrier core materials obtained in Example 2 and Comparative Examples 1 to 3, respectively. From these SEM images, the particle surface of any carrier core material is from several μm. It is divided into regions having a size of about a few tens of micrometers, and it can be seen that the grain interface has a groove shape lower than the surface.

  5A and 5B show the results of elemental mapping of manganese and phosphorus in the same field of view as the SEM image of FIG. 1 for the carrier core material obtained in Example 2. FIG. From FIG. 5A and FIG. 5B, it can be seen that in the carrier core material obtained in Example 2, manganese and phosphorus are segregated in the region of the groove dividing the particle surface. Since the manganese element and the phosphorus element are segregated at the same location, it is considered that in the carrier core material obtained in Example 2, the manganese-phosphorus compound is precipitated in the groove on the surface of the particle. Such a segregation state of the manganese-phosphorus compound on the surface of the particles was observed in any of the carrier core materials obtained in Examples 1 to 4.

  6A and 6B show the results of elemental mapping of manganese and phosphorus in the same field of view as the SEM image of FIG. 2 for the carrier core material obtained in Comparative Example 1. FIG. From FIG. 6A and FIG. 6B, in the carrier core material obtained in Comparative Example 1 which is the same method as Example 2 except that the phosphorus compound was not added to the starting material, no phosphorus element was detected and the background level was about Only a signal was obtained. Further, the manganese element was not segregated and was uniformly distributed on the surface of the particles. From this result, it was found that the segregation of manganese element does not occur after firing unless phosphorus element is present in the starting raw material particles as a precursor.

  7A and 7B show the results of elemental mapping of manganese and phosphorus on the carrier core material obtained in Comparative Example 2 in the same field of view as the SEM image of FIG. From FIG. 7A and FIG. 7B, the carrier core material obtained in Comparative Example 2, which is the same method as Example 2 except that the firing temperature was lowered, showed no segregation of manganese element and phosphorus element, and the surface of the particles Uniformly dispersed. From this result, it was found that even if phosphorus element is present in the precursor raw material particles that are precursors, if the firing temperature is too low, migration of atoms hardly occurs and segregation of the manganese-phosphorus compound does not occur. .

  8A and 8B show the results of elemental mapping of manganese and phosphorus in the same field of view as the SEM image of FIG. 4 for the carrier core material obtained in Comparative Example 3. From FIG. 8A and FIG. 8B, in the carrier core material obtained in Comparative Example 3 which is the same method as Example 2 except that the manganese compound was not added to the starting material, the manganese element was not detected, and the background level This signal was only obtained. Further, no segregation of phosphorus element was observed. From this result, it was found that segregation of phosphorus element does not occur unless the manganese element is present in the starting raw material particles as a precursor.

  From these results, it was confirmed that in the carrier core materials obtained in Examples 1 to 4, the manganese-phosphorus compound was segregated at the grain interface dividing the surface of the particles.

  In addition, although the average groove depth of the surface of the carrier core material obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was about 0.2 to 0.4 μm, it was estimated from the surface properties of the particles by SEM images. Then, it is considered that this average groove depth corresponds to the groove depth at the grain interface that divides the surface of the carrier core particle. Further, considering the results of element mapping, it can be determined that the manganese-phosphorus compound is segregated in the recesses having a depth of 0.2 μm or more in the carrier core materials obtained in Examples 1 to 4. . On the other hand, in the carrier core material obtained in Comparative Examples 1 to 3, it can be confirmed that no segregation of a specific compound occurs in the concave portion.

  Moreover, it turns out that the carrier core materials obtained in Examples 1 to 4 have higher charging characteristics than the carrier core materials obtained in Comparative Examples 1 to 3. This is presumably because the segregated portion of the manganese-phosphorus compound has high charging characteristics in the carrier core materials obtained in Examples 1 to 4.

(Carrier charge)
The carrier core material obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was subjected to resin coating treatment as follows. That is, a silicone resin (SR-2411 manufactured by Toray Dow Corning Silicone Co., Ltd.) was dissolved in toluene to prepare a resin solution for resin coating with a concentration of 30%. This resin solution, Examples 1 to 4 and Comparative Example The carrier core material obtained in 1 to 3 is charged in a stirrer at a mass ratio of 1: 9, and heated and stirred at 150 to 250 ° C. for 3 hours while immersing the carrier core material in the resin solution. The carrier core material was coated with the resin at a ratio of 3.0 parts by mass of the resin with respect to 100 parts by mass of the carrier core material. The carrier core material coated with this resin was heated at 250 ° C. for 5 hours with a hot air circulation heating device to cure the resin coating layer to obtain a carrier.

  Each of the thus-coated resin-coated carriers (38 g) and commercially available toner (2.0 g) were placed in a glass bottle, loaded into a shaker and stirred for 20 minutes to obtain a charge amount measurement sample. The charge amount (μC / g) was calculated by measuring the charge given to the toner by the carrier in the same manner as the measurement of the core material charge amount described above. This charge amount was used as the initial charge amount of the carrier. Further, after the sample for charge amount measurement was further stirred for 24 hours continuously by a shaker, the charge amount was calculated by the same method, and the difference between the charge amount after stirring for 24 hours and the initial charge amount (initial charge) Amount−charge amount after stirring for 24 hours) was defined as the change amount of charge amount (μC / g) and used as an index of carrier durability. These results are shown in Table 2.

  As shown in Table 2, in the carriers obtained from the carrier core materials of Examples 1 to 4 and Comparative Examples 1 to 3, the initial charge amount is about 20 to 30 μC / g. In the carrier obtained from the carrier core material, the charge amount when stirred for 24 hours is greatly reduced, and is 80% or less of the initial charge amount. On the other hand, in the carriers obtained from the carrier core materials of Examples 1 to 4, the charge amount deterioration is small even when stirred for 24 hours, and the charge amount is maintained at about 95% of the initial charge amount. This is because when the carrier obtained from the carrier core material of Examples 1 to 4 is used as a developer, the toner is charged even if the carrier and the toner are mixed and stirred for a long time in the developing machine due to repeated long-term development. This means that stable image characteristics can be obtained without changing the characteristics.

  The carrier for an electrophotographic developer according to the present invention can be used in a developing machine such as a copying machine or a printer as a carrier capable of maintaining a charge amount and obtaining a stable image quality even when used for a long time. Can do.

Claims (6)

A mixture obtained by mixing and stirring an iron compound powder, a manganese compound powder, and a phosphorus compound powder in a solvent is dried and granulated, and then the obtained granulated product is subjected to 1200 to 1300 in an inert gas atmosphere. by firing ℃ _{temperature, Mn x Fe 3-x O} 4 ( where, 0 <x ≦ 1) consists soft ferrite, denoted by, the groove depth in the grain boundary that divides the surface of the particles 0. A carrier core material for an electrophotographic developer, characterized in that it is 2 μm or more, and manganese element and phosphorus element segregate at the grain interface. The electrophotographic developer amount carrier core material according to claim 1, wherein the amount of the phosphorus element is 0.1 to 5% by mass with respect to the carrier core material. The carrier core material for an electrophotographic developer according to claim 1, wherein the magnetization in an external magnetic field of 1000 Oe is 65 emu / g or more. The carrier core material for an electrophotographic developer according to any one of claims 1 to 3, wherein the particle diameter is 10 to 100 µm. An electrophotographic developer carrier comprising the carrier core material for electrophotographic development according to any one of claims 1 to 4 and a resin coated with the carrier core material. An electrophotographic developer comprising the carrier for electrophotographic development according to claim 5 and a toner mixed with the carrier.

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