JP5858591B2 - Carrier core material, electrophotographic carrier and electrophotographic developer using the same - Google Patents

Description

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

  For example, in image forming apparatuses such as facsimiles, printers, and copiers using an electrophotographic system, an electrostatic latent image formed on the surface of an electrostatic latent image carrier (hereinafter sometimes referred to as “photosensitive member”). Is visualized with a developer, and the visible image is transferred onto paper or the like, and then 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 development using the two-component developer, a plurality of magnetic poles are built in, and a developer carrier (hereinafter sometimes referred to as a “development sleeve”) that carries the developer on the surface and a photosensitive member are spaced at a predetermined interval. In a region where the photosensitive member and the developing sleeve face each other (hereinafter referred to as a “developing region”), a magnetic brush that gathers and stands up is placed on the developing sleeve. In addition to the formation, a developing bias voltage is applied between the photosensitive member and the developing sleeve, and toner is attached to the electrostatic latent image on the surface of the photosensitive member.

  As such a carrier, one having characteristics such as high magnetization and high chargeability is desired. For example, Patent Document 1 proposes a method for manufacturing a carrier core material made of ferrite particles having a low Mn content, high magnetization, and high chargeability.

JP 2011-164224 A

  However, the magnetic properties and chargeability of conventional ferrite particles have not been fully satisfactory.

Therefore, the present invention has been made in view of such conventional problems, and an object thereof is to provide a carrier core material having high magnetization and high chargeability.

The carrier core material according to the present invention that achieves the above object has a composition formula Sr _x Mn _y Fe _z O ₁₉ (where 0 <x <3, 0.7 ≦ y ≦ 3.5, 9.0 ≦ z ≦ 11). .3, a compound represented by a x + y + z = 13. ) is characterized by comprising the ferrite particles present on the particle surfaces. Note that the analysis of the particle surface in this specification is based on energy dispersive x-ray spectroscopy (EDS), and a specific analysis method will be described in detail in Examples described later. The analysis depth of the EDS surface is about 1 μm.

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

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

According to the carrier core material of the present invention, high chargeability can be realized while maintaining high magnetization, and excellent image quality can be obtained over a long period of time.

It is a figure which shows the composition change of Sr ferrite by oxygen concentration and sintering temperature. 2 is an SEM photograph of a carrier core material made of ferrite particles of Example 1. 2 is an EDS mapping photograph of Sr of a carrier core material made of ferrite particles of Example 1. It is a XRD analysis result about the carrier core material which consists of a ferrite particle of Example 9. It is a figure which shows the relationship between (sigma) _1k and charge amount ratio in an Example and a comparative example.

The carrier core material according to the present invention has a composition formula Sr _x Mn _y Fe _z O ₁₉ (where 0 <x <3, 0.7 ≦ y ≦ 3.5, 9.0 ≦ z ≦ 11.3, x + y + z = 13)) is characterized by being composed of ferrite particles present on the surface of the particles .

In order to produce a compound represented by the composition formula Sr _x Mn _y Fe _z O ₁₉ , it is important to use Sr ₄ Fe ₆ O ₁₃ as a raw material of Sr component and to perform firing in a manufacturing process under predetermined conditions. It is. Until now, SrCO ₃ has been generally used as the Sr component raw material, but in this case, the compound represented by the composition formula Sr _x Mn _y Fe _z O ₁₉ is not generated. Details will be described later.

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 several tens μm to several hundreds μm, more preferably about several tens μm, and the particle size distribution is sharp. Is preferred.

Although there is no limitation in particular in the manufacturing method of the carrier core material of this invention, the manufacturing method demonstrated below is suitable. In addition, "-" shown in this specification is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit unless there is particular notice.

First, the Fe component raw material and the Mn component raw material are weighed and temporarily fired. The pre-baking temperature is preferably in the range of 750 ° C to 900 ° C. Moreover, an air atmosphere is preferable as the atmosphere at the time of temporary firing. As the Fe component material, Fe ₂ O ₃ or the like is preferably used. As the Mn component raw material, MnCO ₃ , Mn ₃ O ₄ or the like can be suitably used.

Next, the calcined raw material is pulverized, and the Sr component raw material is weighed and put into a dispersion medium to prepare a slurry. The use of Sr ₄ Fe ₆ O ₁₃ as the Sr component raw material is important in producing a compound represented by Sr _x Mn _y Fe _z O ₁₉ in the firing step described later. The reason will be described later. Water is preferred as the dispersion medium used in the present invention. In addition to the Fe component raw material, Mn component raw material, and Sr component 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. The blending amount of the binder is preferably about 0.5 to 2% by mass in the slurry. Moreover, as a dispersing agent, polycarboxylate ammonium etc. can be used conveniently, for example. As the blending amount of the dispersant, the concentration in the slurry is preferably about 0.5 to 2% by mass. 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 to 90% by 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 size of the raw material after pulverization is preferably 10 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 to 300 ° C. Thereby, a spherical granulated product having a particle size of 10 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 vibration sieve or the like. The preferable average particle diameter of the granulated product is in the range of 10 μm to 200 μm.

  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.

Here, when Sr ₄ Fe ₆ O ₁₃ is used as the Sr component raw material, as shown in the following reaction formula (1), after Mn ferrite is generated, Sr ferritization proceeds, so Fe in Sr ferritization The component source is Mn ferrite, and a compound represented by Sr _x Mn _y Fe _z O ₁₉ is produced. Although the detailed mechanism is unknown, when the value of x is zero or exceeds 3, the crystallinity of the Sr ferrite is remarkably lowered, so that the effect of stabilizing the charging property cannot be obtained. Therefore, the value of x is set to a range greater than 0 and less than 3. More preferably, it is the range of 0.5-2.0. Further, since the charge amount can be increased, the value of y is set in the range of 0.7 to 3.5. Since the value of z is x + y + z = 13, it was determined by back calculation.
Sr ₄ Fe ₆ O ₁₃ + Fe ₂ O ₃ + Mn ₃ O ₄ → Sr ₄ Fe ₆ O ₁₃ + MnFe ₂ O _{4
→ Sr x Mn y Fe z O} 19 + MnFe 2 O 4 ······ (1)
(However, 0 <x <3, 0.7 ≦ y ≦ 3.5, 9.0 ≦ z ≦ 11.3, x + y + z = 13.)

On the other hand, when using SrCO ₃ that has been generally used as a raw material for Sr components, Sr ferrite is formed before Mn ferrite is formed as shown in the following reaction formula (2). source of Fe component in the reduction is a _Fe 2 _{O 3,} and generates the _SrFe 12 _{O 19,} the compound represented by Sr _x Mn _y Fe _{z O 19} does not generate.
SrCO ₃ + Fe ₂ O ₃ + Mn ₃ O ₄ → SrFe ₁₂ O ₁₉ + Fe ₂ O ₃ + Mn ₃ O ₄
→ SrFe ₁₂ O ₁₉ + MnFe ₂ O ₄ (2)

In addition, when Sr ₄ Fe ₆ O ₁₃ having a large particle size is used as the Sr component raw material, Sr ferritization does not occur until the reactivity decreases and the temperature becomes high, and the compound represented by Sr _x Mn _y Fe _z O ₁₉ Is desirable because it is more easily generated. The particle size of Sr ₄ Fe ₆ O ₁₃ as the Sr component raw material is preferably in the range of 5 μm to 10 μm.

The firing temperature is preferably in the range of 1100 ° C to 1300 ° C. When the firing temperature is less than 1100 ° C., phase transformation is less likely to occur and sintering is difficult to proceed. When the firing temperature exceeds 1300 ° C., excessive grains may be generated due to over-sintering. The rate of temperature increase up to the firing temperature is preferably in the range of 250 ° C / h to 500 ° C / h. Moreover, what is necessary is just to adjust a baking atmosphere suitably in the range whose oxygen concentration is 0.001%-21%. However, as shown in FIG. 1, it should be noted that Sr ₃ Fe ₂ O ₆ is generated when the oxygen concentration is lowered even when the firing temperature is 1200 ° C., for example. As shown in the following reaction formula (3), the produced Sr ₃ Fe ₂ O ₆ has a composition in which the number of Sr atoms is larger than the number of Fe atoms, and decomposes into Sr _x Mn _y Fe _z O ₁₉ when the temperature is lowered. When the cooling rate is in the range of 200 ° C./h to 500 ° C./h, the diffusion of Sr atoms cannot be made in time, and a high portion in which the value of x exceeds 3 remains in Sr _x Mn _y Fe _z O ₁₉ . Therefore, it is important that the firing temperature and the oxygen concentration are within a range in which Sr ₃ Fe ₂ O ₆ is not generated.
SrFe ₁₂ O ₁₉ + MnFe ₂ O ₄ → Sr ₃ Fe ₂ O ₆ + MnFe ₂ O _{4
→ Sr x Mn y Fe z O} 19 + MnFe 2 O 4 ······ (3)
(However, x> 3, 0.7 ≦ y ≦ 3.8, 7.5 ≦ z ≦ 9.3, x + y + z = 13)

  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 particle diameter of the ferrite particles is preferably in the range of several tens of μm to several hundreds of 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.

The carrier core material of the present invention comprising the ferrite particles produced as described above is coated with a resin and used as a carrier for electrophotographic development .

As the resin for coating the surface of the carrier core material , conventionally known resins can be used, for example, polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene). ) Resin, polystyrene, (meth) acrylic resin, polyvinyl alcohol resin, polyvinyl chloride, polyurethane, polyester, polyamide, polybutadiene, and other thermoplastic elastomers, and fluorosilicone resins.

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

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

  The particle diameter of the carrier is generally preferably in the range of 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 (s) or 2 or more types can be used in combination.

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

(Preparation of raw material Sr ₄ Fe ₆ O ₁₃ )
Sr ₄ Fe ₆ O ₁₃ as an Sr component raw material was produced by the following method. As starting materials, Fe ₂ O ₃ (average particle size: 0.6 μm) 6.7 kg and SrCO ₃ (average particle size: 0.1 μm) 8.3 kg were dispersed in 5.0 kg of water as a dispersant. 150 g of an ammonium polycarboxylate dispersant was added to form a mixture. The solid content concentration of this mixture was 75% by weight. This mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 to 200 μm. From this granulated product, coarse particles were separated using a sieve mesh having a mesh size of 48 μm, and fine particles were separated using a sieve mesh having a mesh size of 25 μm. This granulated powder was put into an electric furnace and fired at 1100 ° C. for 3 hours. The firing atmosphere was an air atmosphere. The obtained fired product was pulverized with a hammer mill to obtain an Sr component raw material.

Example 1
A carrier core material made of Mn ferrite particles was produced by the following method. As a starting material, 15.9 kg of Fe ₂ O ₃ (average particle size: 0.6 μm) and 5.9 kg of Mn ₃ O ₄ (average particle size: 0.8 μm) are mixed, and the mixed powder is mixed with a rotary kiln. And pre-baked at 850 ° C. The obtained calcined powder was pulverized to an average particle size of 1.5 μm using a ball mill. Disperse pulverized calcined powder and 231 g of the prepared Sr ₄ Fe ₆ O ₁₃ (average particle size: 7.1 μm) in 4.8 kg of water, and 132 g of ammonium polycarboxylate dispersant as a dispersant. Added to make a mixture. The solid content concentration of this mixture was 82% by weight. This mixture was pulverized by a wet ball mill (media diameter 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 130 ° C. with a spray dryer to obtain a dry granulated product having a particle size of 10 to 200 μm. From this granulated product, coarse particles were separated using a sieve mesh having a mesh size of 48 μm, and fine particles were separated using a sieve mesh having a mesh size of 25 μm. This granulated powder was put into an electric furnace and fired at 1300 ° C. for 3 hours. The firing atmosphere was an oxygen concentration of 15000 ppm. The obtained fired product was pulverized with a hammer mill and then classified using a vibration sieve. Next, oxidation treatment (high resistance treatment) was further performed at a temperature of 380 ° C. for 1 hour in an air atmosphere to obtain a carrier core material made of ferrite particles.

The magnetic properties of the obtained carrier core material were measured by the methods described below. Moreover, the composition analysis of the particle | grain surface and the ICP composition analysis were performed about the Sr component by EDS analysis. Table 1 summarizes the measurement results. 2 and 3 show an SEM photograph of the obtained carrier core material and an EDS mapping photograph of Sr.

Next, the surface of the carrier core material of Example 1 obtained in this way was coated with a resin to produce the carrier of Example 1. Specifically, a silicone resin (SR2411 manufactured by Toray Dow Corning) was dissolved in toluene to prepare a coating resin solution. Then, the ferrite particles and the coating resin solution are loaded into the stirrer at a ratio of carrier core material : resin solution = 9: 1 by weight, and the temperature is 150 ° C. to 250 ° C. while the carrier core material is immersed in the resin solution. And stirred for 3 hours. Subsequently, it heated further with the hot-air circulation type heating apparatus at the temperature of 250 degreeC for 5 hours, the coating resin layer was hardened, and the carrier was obtained.

  The obtained carrier and a toner having an average particle size of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer according to Example 1. In this case, the carrier and the toner were adjusted so that the weight of toner / (weight of toner and carrier) = 5/100. Hereinafter, developers were obtained in the same manner for all of the Examples and Comparative Examples. The obtained developer was measured for the charge amount ratio described later. The measurement results are shown in Table 1.

(Magnetic properties)
One cycle in the range of external magnetic field: −10000 to 10000 (A / m × 10 ³ / (4π)) using a vibration sample magnetometer (VSM) (VSM-P7, manufactured by Toei Industry Co., Ltd.) By applying continuously, saturation magnetization σs (A · m ² / kg) and magnetization σ _1k (A · m ² / kg) were measured.

(Composition analysis of particle surface)
The composition of the carrier core material surface was analyzed under the following conditions using an energy dispersive X-ray analysis “JSM-2200” (detector “EX-54185JMV”, software “Analysis Station”) manufactured by JEOL Ltd.
SEM observation / magnification: 4000 times (one particle fits in one field of view)
・ Acceleration voltage: 30.0kV
・ Working distance: WD10
・ Spot size: 70
EDS mapping, number of sweeps: 50 times, PHA mode: T2
-Number of pixels: 1024 x 768
・ Dwell time: 0.1msec
・ Probe tracking: 60 sec
The count value of 1.810 keV measured as the extraction region Sr is divided by the number of pixels to calculate an average value per pixel. Next, the Sr existence region detected when the count number 100 times or more of the average value is 1 square μm or more is visually searched in the mapping visual field. Then, the coordinates of the maximum count number in the Sr existence area are obtained from the line profile in the x-axis direction. Similarly, the coordinates of the maximum count number in the Sr existence area are obtained from the line profile in the y-axis direction. Again, the coordinates of the maximum count number in the Sr existence area are obtained from the line profile in the x-axis direction. The above operation is repeated three times in the x-axis direction and three times in the y-axis direction to determine peak coordinates. A rectangular 1 μm × 1 μm area centering on the determined peak coordinates is set as an extraction area.
Standard data built in the analysis software was used. Quantitative analysis was performed by discriminating the contained elements by qualitative analysis.
Quantitative mode: Simplified quantitative quantitative correction: ZAF method Calculation method: Single unit quantification Sr L (1.806 keV) and Si K (1.739 keV) are close to each other and calculation may be wrong. It was. The calculation was performed excluding nonmetallic elements such as C, N, and O. The calculation was performed excluding metal elements having an atom number% smaller than the error%.
Conversion method It calculated so that it might apply to the following compositional formula from the ratio of atomic% calculated | required by the quantitative analysis.
Compositional formula Sr _x Mn _y Fe _z O ₁₉
(However, x + y + z = 13)
Number of measurements One point is measured from one particle. 30 particles were measured and the average value was taken as the measurement result.

(Charge amount ratio)
Collect 300 mg of electrophotographic developer after stirring for 15 minutes, use Utec EA02 and automatic suction device, suction pressure High, separation mesh 795 mesh, toner collection device filter capsule (EATEC EA010C ) And the amount of charge after 90 seconds of suction was measured. Two measurements were performed on the same sample, and the average value of these was taken as the charge amount of the carrier. The charge amount of the carrier was calculated from the following formula. The measurement environment was a temperature of 25 ° C. and a relative humidity of 50%. Then, the charge amount ratio with the standard carrier was calculated.
Charge amount (μC / g) = Measured charge (nC) ÷ Toner weight (where toner weight = weight after filter capsule suction (g) −weight before filter capsule suction (g))
Ferrite particles were produced in the same manner as in Example 1 except that 15.9 kg of Fe ₂ O ₃ , 6.1 kg of Mn ₃ O ₄ and 0 g of the Sr component raw material were added as standard carriers. The surface of the ferrite particles was coated with a resin to obtain a carrier. Then, the charge amount was measured by the same method as in Example 1.

(Example 2)
A carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that 16.0 kg of Fe ₂ O ₃ , 5.4 kg of Mn ₃ O ₄ and 631 g of Sr ₄ Fe ₆ O ₁₃ were used. The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Example 3)
A carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that 16.1 kg of Fe ₂ O ₃ , 4.9 kg of Mn ₃ O ₄ and 965 g of Sr ₄ Fe ₆ O ₁₃ were used. The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Examples 4 to 12)
Examples 4-6, 7-9, 10-12 have the same composition as Examples 1-3, and obtained carrier cores made of ferrite particles in the same manner as in Example 1 under the production conditions shown in Table 1. The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.
Further, the carrier core material obtained in Example 9 was subjected to XRD analysis. FIG. 4 shows the XRD analysis results. From FIG. 4, it was confirmed that Sr _x Mn _y Fe _z O ₁₉ was deposited on the carrier core material .

(Comparative Examples 1-5)
16.4 kg of Fe ₂ O ₃ , 5.0 kg of Mn ₃ O ₄ and 557 g of SrCO ₃ were obtained, and a carrier core material made of ferrite particles was obtained in the same manner as in Example 1 under the production conditions shown in Table 1. . The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Comparative Example 6)
A carrier core material made of ferrite particles having the same composition as in Example 3 and the same manufacturing conditions as shown in Table 1 was obtained in the same manner as in Example 1. The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(Comparative Example 7)
A carrier core material made of ferrite particles was prepared in the same manner as in Example 1 under the production conditions shown in Table 1 with 15.8 kg of Fe ₂ O ₃ , 5.3 kg of Mn ₃ O ₄ and 790 g of SrFe ₁₂ O _19. Obtained. The magnetic properties of the obtained carrier core material , the composition analysis of the particle surface by EDS analysis, and the ICP composition analysis were conducted in the same manner as in Example 1 for the Sr component. Table 1 summarizes the measurement results. Further, the surface of the obtained carrier core material was coated with a resin to obtain a carrier, and the charge amount of the carrier was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

As is clear from Table 1 and FIG. 5, the carrier core materials of Examples 1 to 12 had high magnetization and high chargeability. On the other hand, in the carrier core materials of Comparative Examples 1 to 7 in which the number of atoms of Sr, Mn, Fe of the compound existing on the particle surface is out of the specified range of the present invention, the desired magnetic properties were obtained. The charge ratio was 2.5 or less, and the chargeability was lower than that of the carrier core material of the example.

According to the carrier core material of the present invention, high chargeability can be realized while maintaining high magnetization, and when used as a carrier, excellent image quality can be obtained over a long period of time.

Claims (4)

It is represented by a composition formula Sr _x Mn _y Fe _z O ₁₉ (where 0 <x <3, 0.7 ≦ y ≦ 3.5, 9.0 ≦ z ≦ 11.3, x + y + z = 13). A carrier core material comprising a ferrite particle in which the compound is present on the particle surface. The carrier core material according to claim 1, wherein the ferrite particles are Mn ferrite particles . Electrophotographic development carrier, characterized in that the claim 1 or 2 the surface of the carrier core material according coated with a resin. An electrophotographic developer comprising the electrophotographic developer carrier according to claim 3 and a toner.