JP5360701B2 - Carrier core material for electrophotographic developer, carrier, production method thereof, and electrophotographic developer using the carrier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier core material for an electrophotographic developer and a carrier capable of obtaining a desired resistance such as a medium resistance or a high resistance while having high magnetization not only without using heavy metals but also substantially without using Mn, having excellent charging characteristics, and having both of surface properties with appropriate ruggedness and uniform shapes, to provide a method for manufacturing them, and to provide an electrophotographic developer using the carrier, capable of extending service life, having a high charge amount and excellent in charging stability. <P>SOLUTION: The carrier core material for an electrophotographic developer contains Mg by 2 to 8.5 wt.%, Ti by 0.1 to 1.25 wt.% and Fe by 60 to 70 wt.%, and includes a BET specific surface area of 0.075 to 0.11 m<SP>2</SP>/g. The carrier for an electrophotographic developer includes the above carrier core material coated with a resin. The method for manufacturing the carrier core material or the carrier is disclosed. The electrophotographic developer uses the above carrier. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a carrier core material for an electrophotographic developer used in a two-component electrophotographic developer used in a copying machine, a printer, and the like, a carrier, a production method thereof, and an electrophotographic developer using the carrier. .

  The electrophotographic development method is a method in which toner particles in a developer are attached to an electrostatic latent image formed on a photoreceptor and developed, and the developer used in this method is composed of toner particles and carrier particles. The two-component developer and the one-component developer using only toner particles.

  Among these developers, as a developing method using a two-component developer composed of toner particles and carrier particles, the cascade method has been used in the past, but at present, the magnetic brush method using a magnet roll is the mainstream. It is.

  In the two-component developer, the carrier particles are agitated together with the toner particles in the developing box filled with the developer, thereby imparting a desired charge to the toner particles, and thus being charged. A carrier material for transporting toner particles to the surface of the photoreceptor to form a toner image on the photoreceptor. The carrier particles remaining on the developing roll holding the magnet are returned to the developing box from the developing roll, mixed and stirred with new toner particles, and used repeatedly for a certain period.

  Unlike the one-component developer, the two-component developer has the function of mixing and stirring the carrier particles with the toner particles, charging the toner particles, and further transporting the toner particles. Good controllability. Therefore, the two-component developer is suitable for a full-color developing device that requires high image quality and a device that performs high-speed printing that requires image maintenance reliability and durability.

  In the two-component developer used in this manner, image characteristics such as image density, fog, vitiligo, gradation, and resolving power show predetermined values from the initial stage, and these characteristics are in the printing life period. It needs to be kept stable without fluctuating inside. In order to maintain these characteristics stably, it is necessary that the characteristics of the carrier particles contained in the two-component developer are stable.

  Conventionally, iron powder carriers such as iron powder whose surface is covered with an oxide film or iron powder whose surface is coated with a resin have been used as carrier particles for forming a two-component developer. Since such an iron powder carrier has high magnetization and high conductivity, there is an advantage that an image with a good reproducibility of the solid portion can be easily obtained.

  However, such an iron powder carrier has a heavy true specific gravity of about 7.8 and is too high in magnetization, so that the toner constituent components on the surface of the iron powder carrier are mixed by stirring and mixing with toner particles in the developing box. Fusing, so-called toner spent, is likely to occur. The generation of such toner spent reduces the effective carrier surface area and tends to reduce the triboelectric charging ability with the toner particles.

  Moreover, in the resin-coated iron powder carrier, the resin on the surface peels off due to stress during durability, and the core material (iron powder) with high conductivity and low dielectric breakdown voltage is exposed, which may cause charge leakage. . Due to such charge leakage, the electrostatic latent image formed on the photoconductor is destroyed, and a crack or the like is generated in the solid portion, so that it is difficult to obtain a uniform image. For these reasons, iron powder carriers such as oxide-coated iron powder and resin-coated iron powder are no longer used.

  In recent years, instead of iron powder carriers, ferrite with a true specific gravity of about 5.0, which is light and has a low magnetization, or a resin-coated ferrite carrier whose surface is coated with a resin has been widely used. Lifespan has increased dramatically.

  As a method for producing such a ferrite carrier, a predetermined amount of ferrite carrier raw material is mixed, calcined, pulverized, and then fired after granulation. Depending on conditions, calcining may be omitted. is there.

  Recently, environmental regulations have become stricter, and the use of metals such as Ni, Cu, and Zn has been avoided, and the use of metals suitable for environmental regulations has been demanded, and it is used as a carrier core material. The ferrite composition has shifted from Cu—Zn ferrite, Ni—Zn ferrite to Mn ferrite using Mn, Mn—Mg—Sr ferrite and the like.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-337828) discloses a ferrite carrier core material for electrophotography in which the surface is divided into regions of 2 to 50 per 10 μm square by grooves or streaks, and the main component is manganese ferrite. Have been described. This ferrite carrier core material has a uniform composition, constant surface properties, good fluidity, high magnetization, low resistance, and an electron using a ferrite carrier in which this ferrite carrier core material is coated with a resin. Photographic developers are said to have a fast charge rise and a stable charge over time.

  In Patent Document 1, in order to produce the ferrite carrier core material as described above, a composite oxide mainly composed of Fe and Mn having a molar ratio of Fe to Mn (Fe / Mn) of 4 to 16 is crushed. It has been shown that in a production method in which granulation, firing, and further pulverization and classification are performed after mixing, firing is performed in an atmosphere having an oxygen concentration of 5% by volume or less.

  However, Mn is also subject to various laws and regulations, and a new carrier core material that does not use Mn as well as the above various heavy metals is demanded.

As an alternative to a carrier core material using Mn, a carrier core material using Mg has been proposed. For example, Patent Document 2 (JP 2005-162597), wherein _{X a Mg b Fe c Ca d} O e (X is Li, Na, Ti, etc., or a combination thereof) Mg-based ferrite material represented by (carrier Core material), saturation magnetization is 30 to 80 emu / g, and dielectric breakdown voltage is 1.5 to 5.0 kV. With this Mg-based ferrite material, high image quality and compliance with environmental regulations are achieved. It is supposed to be possible.

Patent Document 3 (Japanese Patent Publication No. 2006-524627) discloses an Mg-based ferrite material (carrier core material) represented by the formula Mg _a Fe _b Ca _c O _d and has a saturation magnetization of 30 to 80 emu / g. It is said that the dielectric breakdown voltage is 1.5 to 5.0 kV, and is composed of a clean material that complies with environmental regulations, and a high-quality image that is clear, rich in gradation, and free from fog is obtained.

  Thus, although the carrier core material using Mg is proposed, since magnetization and resistance are generally in a trade-off relationship, it is difficult to achieve both high magnetization and characteristics such as medium resistance to high resistance. Therefore, by adding Mn, the trade-off relationship between magnetization and resistance is relaxed to realize high magnetization, medium resistance to high resistance, and it is currently used as a carrier core material for electrophotographic developer. However, as described above, it is becoming difficult to use Mn with the strengthening of various heavy metal regulations.

  In addition, in a Mg-based carrier core material in which Mn is not intentionally added, as a method of realizing high magnetization and medium resistance to high resistance even with a conventional firing method, a desired resistance can be obtained by surface oxidation after firing. Efforts to match the level have been made, but it cannot be said that the above trade-off relationship has been sufficiently solved.

Conventionally, it has been known that Mg-based ferrite can increase magnetization by being produced with an excess of Fe. However, the resistance is extremely low due to the excess of Fe. In addition, Fe-excess Mg-based ferrite is characterized by a sharp decrease in magnetization due to high oxygen concentration during surface firing or surface oxidation. This phenomenon is due to oxidation of Fe ²⁺ contained in magnetite. It is believed that.

  On the other hand, the firing temperature of Mg-based ferrite that does not contain a transition metal other than Fe is as high as about 1250 to 1350 ° C., and not only the surface properties required for the carrier core material can be obtained with almost no unevenness, The carrier core particles are likely to aggregate during firing and contain many particles that are not spherical. Therefore, a carrier core material for an electrophotographic developer that does not intentionally contain a heavy metal, has a shape that has high magnetization, medium resistance to high resistance, and a surface property that has moderate unevenness has not been obtained. Is the current situation.

JP 2006-337828 A Japanese Patent Laid-Open No. 2005-162597 JP 2006-524627 A

  Therefore, the object of the present invention is to obtain a desired resistance such as medium resistance or high resistance while being highly magnetized without substantially using not only each heavy metal but also Mn, excellent charging characteristics, and moderate Carrier core material for electrophotographic developer having both surface properties with uniform irregularities, a carrier, a method for producing the same, and a long life using the carrier, and a high charge amount Another object of the present invention is to provide an electrophotographic developer having excellent charging stability.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention contain a certain amount of Mg, Ti , Sr and Fe, and preferably at least Fe and Ti other than the spinel structure constituting Mg ferrite. The present inventors have found that a carrier core material having a crystal structure of an oxide to be contained and having a specific surface area within a certain range and a carrier coated with a resin can achieve the above object, and have reached the present invention.

That is, the present invention contains 2 to 8.5 wt% Mg, 0.1 to 1.25 wt% Ti, 0.37 to 2.5 wt% Sr and 60 to 70 wt% Fe, A carrier core material for an electrophotographic developer, which has a BET specific surface area of 0.075 to 0.11 m ² / g.

  The carrier core material for an electrophotographic developer of the present invention preferably contains a crystal structure of an oxide containing at least Fe and Ti in addition to the spinel structure constituting Mg ferrite.

  The carrier core material for an electrophotographic developer of the present invention preferably has a Mn content of 1% by weight or less.

The carrier core material for an electrophotographic developer of the present invention, magnetization is 45~75Am ² / kg when a magnetic field was applied in the 3K · 1000 / 4π · A / m, a residual magnetization of 2~10Am ² / kg and a coercive The magnetic force is desirably 10 to 80 3K · 1000 / 4π · A / m.

  The carrier core material for an electrophotographic developer according to the present invention preferably has an average particle size of 15 to 120 μm as measured by a laser diffraction particle size distribution analyzer.

  The carrier core material for an electrophotographic developer according to the present invention preferably has a shape factor SF-2 (roundness) of 100 to 120.

The carrier core material for an electrophotographic developer according to the present invention preferably has a volume resistance of 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm at an applied voltage of 50V.

The carrier core material for an electrophotographic developer according to the present invention is desirably surface-oxidized to form an oxidized film, and the volume resistance at an applied voltage of 50 V is 1 × 10 ⁶ to 1 × 10 ^10. It is preferable that the volume resistance at an applied voltage of 1000 V is 6 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm.

  The present invention provides a carrier for an electrophotographic developer in which the surface of the carrier core material is coated with a resin.

  In the carrier for an electronic developer according to the present invention, the resin is preferably an acrylic resin, a silicone resin, or a modified silicone resin.

In the present invention, each compound of Fe, Ti 2 , Mg, and Sr is pulverized, mixed, calcined, granulated, and the resulting granulated product is subjected to primary firing, main firing, further pulverization, classification. in the manufacturing method of the carrier core material for electrophotographic developer to surface oxidation treatment, the main baking is, method of manufacturing the carrier core material for an electrophotographic developer, wherein the oxygen concentration is carried out at 5 vol% or less Is to provide.

  The present invention provides a method for producing a carrier for an electrophotographic developer, wherein the surface of the carrier core obtained by the above production method is coated with a resin.

  The present invention provides an electrophotographic developer comprising the above carrier or the carrier obtained by the above production method and a toner.

  The carrier core material for an electrophotographic developer according to the present invention can obtain a desired resistance such as a medium resistance or a high resistance while being highly magnetized without using not only each heavy metal but also Mn. It has excellent characteristics and also has a surface shape with moderate irregularities and a uniform shape. An electrophotographic developer comprising a carrier and a toner obtained by coating the carrier core material with a resin has a long life, has a high charge amount, and is excellent in charging stability. Moreover, the carrier core material and the carrier can be stably produced on an industrial scale by the production method of the present invention.

  Hereinafter, the best mode for carrying out the present invention will be described.

<Carrier Core Material and Carrier for Electrophotographic Developer According to the Present Invention>
In the carrier core material for an electrophotographic developer according to the present invention, Mg is 2 to 8.5% by weight, preferably 2.2 to 8.3% by weight, more preferably 2.4 to 8.3% by weight, Ti. 0.1 to 1.25 wt%, preferably 0.15 to 1.25 wt%, more preferably 0.18 to 1.25 wt%, Fe 60 to 70 wt%, preferably 60 to 68.%. 5% by weight, more preferably 60 to 67% by weight. Within the above composition range, medium resistance to high resistance can be obtained while being highly magnetized, and charging characteristics are stable and good when used as a carrier for an electrophotographic developer.

  Since Mg is negatively negative in terms of MgO electronegativity, it has a very good compatibility with negative toners, and it is possible to obtain a developer having a good rise in charge composed of a Mg ferrite carrier containing MgO and a full color toner. I can do it.

Since TiO ₂ is slightly negative in electronegativity, it is not compatible with minus toners originally, but it is minus as a compound (oxide) of Fe and Ti within a range less than 1.25% by weight. By including the toner carrier, the influence on the charging property can be minimized.

If the Fe content is less than 60% by weight, it means that the nonmagnetic component and / or low magnetization component increases due to the relative increase in the addition amount of Mg and / or Ti, and the desired magnetic properties cannot be obtained. However, if it exceeds 70% by weight, the effect of adding Mg and / or Ti cannot be obtained, and the carrier core material is substantially equivalent to magnetite. The Mg content is best around Mg: Fe ²⁺ = 1: 2 to 1: 3. If the Mg content is less than 2% by weight, the amount of magnesium ferrite phase produced in the carrier core material is small, and the amount of magnetite phase produced is relatively increased, so that the coercive force increases and the desired magnetic properties cannot be obtained. If it exceeds 8.5% by weight, magnesium oxide may be generated in addition to magnesium ferrite in the carrier core material, and desired magnetic properties may not be obtained. If the Ti content is less than 0.15% by weight, there is a possibility that desired magnetic properties may not be obtained due to a small amount of Fe and Ti composite oxides. If the Ti content exceeds 1.25% by weight, Fe and Ti Since the nonmagnetic phase due to the composite oxide of Ti becomes dominant, there is a possibility that the magnetization becomes too low to obtain desired magnetic characteristics.

The carrier core material for an electrophotographic developer according to the present invention has a BET specific surface area of 0.075 to 0.11 m ² / g. When the BET specific surface area is less than 0.075 m ² / g, since the core surface has few irregularities, the anchor effect of the resin after resin coating cannot be obtained, and the life as an electrophotographic carrier may be shortened. If the surface area exceeds 0.11 m ² / g, the resin surface irregularities on the surface of the core material are so large that the resin can easily penetrate, so that there is a possibility that desired characteristics as an electrophotographic carrier cannot be obtained. This BET specific surface area is measured by the following.

(BET specific surface area)
Using an automatic specific surface area measuring apparatus GEMINI 2360 (manufactured by Shimadzu Corp.), it can be determined from the N ₂ adsorption amount of carrier particles measured by adsorbing N ₂ as an adsorption gas. Here, the measurement tube used for measuring the N ₂ adsorption amount was baked for 2 hours at 50 ° C. in a reduced pressure state before the measurement. Further, 5 g of carrier particles were filled in this measuring tube, and after pretreatment at a temperature of 30 ° C. for 2 hours under reduced pressure, N ₂ gas was adsorbed at 25 ° C., and the amount of adsorption was measured. These adsorption amounts are values calculated from the BET equation by drawing an adsorption isotherm.

  The carrier core material for an electrophotographic developer according to the present invention contains an oxide crystal structure containing at least Fe and Ti in addition to the spinel structure constituting Mg ferrite. By adding Ti to Fe-excess Mg-based ferrite, a composite oxide containing Fe and Ti with relatively low magnetization can be generated in the range of magnetization, in addition to the spinel crystal structure compound constituting ordinary ferrite. It is possible to control only the resistance without changing the magnetization by oxidizing the composite oxide containing Fe and Ti preferentially over the spinel phase during the surface oxidation treatment. That is, the resistance is adjusted by changing the valence of Fe contained in the composite oxide containing Fe and Ti. The crystal structure is measured by the following.

(Measurement of crystal structure: X-ray diffraction measurement)
“X′PertPRO MPD” manufactured by Panalical Co., Ltd. was used as a measuring apparatus. Using a Co tube (CoKα ray) as an X-ray source and a concentrated optical system and a high-speed detector “X'Celarator” as an optical system, the measurement was performed by a step scan of 0.02 °. The measurement results were processed using data for analysis “X'Pert HighScore” in the same manner as in the crystal structure analysis of ordinary powders, and the crystal structure was identified. When identifying the crystal structure, Fe and O are essential elements, and Mg, Ti, and Sr are elements that may be contained. In addition, the X-ray source can be measured without problems even with a Cu tube, but in the case of a sample containing a large amount of Fe, the background becomes larger than the peak to be measured, so it is better to use a Co tube. preferable. In addition, the optical system may obtain the same result even when the parallel method is used, but measurement with a concentrated optical system is preferable because the X-ray intensity is low and measurement takes time. Furthermore, the count time at each point of the step scan is such that the peak intensity of the (311) plane of the spinel structure is about 200,000 cps, and the carrier core material is set in the sample cell so that the particles are not oriented in a specific preferred direction. And measured.

MgFe ₂ O ₄ is a typical spinel structure constituting Mg ferrite. However, as can be seen from the composition ratio of the elements, since Fe is excessive, a part of Mg is replaced with Fe and formally Mg _x Fe. _The crystal structure represented by _{y-xO 4} , (Mg _x Fe _1-x ) (Mg _{x ′} Fe _{1-x ′} ) ₂ O _4, etc., and all of which are partially substituted with Sr In addition, it also includes those in which lattice defects are periodically included in the spinel structure by firing in a non-oxidizing atmosphere.

FeTiO ₃ and Fe ₂ TiO ₅ are typical crystal structures of oxides containing Fe and Ti, but Fe is overwhelmingly abundant as compared to Ti, and other than Fe _x TiO _y (FeTiO 3). _{3) x (Fe 2 O 3} ) y, Fe (Fe x Ti y) O 4, (Fe x Ti 1-x) (Fe x 'Ti 1-x') crystal structure and is represented by _{O 4} or the like that All oxides represented by Sr _a Fe _b Ti _c O _d partially substituted with Sr are also included, and the crystal structure contains lattice defects periodically by firing in a non-oxidizing atmosphere. It is also included.

The carrier core material for an electrophotographic developer according to the present invention, that Yusuke 0.37 to 2.5 wt% including the Sr. When Sr is not added, Fe ₂ O ₃ is generated and magnetization is often reduced when firing is performed at a high oxygen concentration, but Sr ferrite is generated instead of Fe ₂ O ₃ by adding Sr, Even if the oxygen concentration is touched, the magnetization is easily stabilized. Furthermore, the effect of further increasing the resistance and the charge amount of the core material can be expected due to the effect of Sr moving to the grain surface during primary firing and main firing. When the content of Sr exceeds 2.5% by weight, the fluidity of the developer on the magnetic brush may be abruptly deteriorated because it begins to hard ferrite.

The crystal structure of the oxide containing Sr and Fe includes Sr ferrite expressed as SrO.6Fe ₂ O ₃ or SrFe ₁₂ O ₁₉ as described above, and the carrier core material for electrophotographic development according to the present invention. It may be contained in.

  The carrier core material for an electrophotographic developer according to the present invention preferably has a Mn content of 1% by weight or less. Although Mn is not intentionally contained, the inclusion of a very small amount of Mn as an impurity derived from the raw material is not a problem. The contents of these Fe, Mg, Ti, Sr and Mn are measured by the following.

(Contents of Fe, Mg, Ti, Sr and Mn)
0.2 g of carrier core material is weighed, 60 ml of pure water plus 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid is heated to prepare an aqueous solution in which the carrier core material is completely dissolved, and an ICP analyzer (Shimadzu Corporation) The contents of Fe, Mg, Ti, Sr, and Mn were measured using ICPS-1000IV).

The carrier core material for an electrophotographic developer according to the present invention preferably has a magnetization of 45 to 75 Am ² / kg when a magnetic field of 3K · 1000 / 4π · A / m is applied. If the magnetization at 3K · 1000 / 4π · A / m is less than 45 Am 2 / g, the scattered matter magnetization may deteriorate and cause image defects due to carrier adhesion. If the magnetization exceeds 75 Am 2 / g, the magnetic brush There is a possibility that the top of the developer becomes too hard and the image quality is deteriorated. The residual magnetization is desirably ^{2 to} 10 Am ² / kg. The remanent magnetization at 3K · 1000 / 4π · A / m is not less than ² Am ² / kg in the composition according to the present invention. If it exceeds 10 Am ² / kg, the fluidity of the developer in the developing device deteriorates, and it becomes impossible to sufficiently stir the developer and give the toner triboelectric charge. The coercivity is not less than 10 3 K · 1000 / 4π · A / m in the composition according to the present invention. If it exceeds 80 3K · 1000 / 4π · A / m, the fluidity of the developer in the developing device deteriorates, and the developer cannot be sufficiently stirred to give the toner triboelectric charge. Magnetization, remanent magnetization and coercivity are measured by:

(Magnetic properties)
It measured using the integral type BH tracer BHU-60 type (made by Riken Denshi Co., Ltd.). A magnetic field measuring H coil and a magnetization measuring 4πI coil are placed between the electromagnets. In this case, the sample is placed in a 4πI coil. The outputs of the H coil and the 4πI coil whose magnetic field H is changed by changing the current of the electromagnet are respectively integrated, and the H output is drawn on the X axis, the output of the 4πI coil is drawn on the Y axis, and a hysteresis loop is drawn on the recording paper. As measurement conditions, sample filling amount: about 1 g, sample filling cell: inner diameter 7 mmφ ± 0.02 mm, height 10 mm ± 0.1 mm, 4πI coil: measured with 30 turns.

  The carrier core material for an electrophotographic developer according to the present invention preferably has an average particle size measured by a laser diffraction particle size distribution measuring device of 15 to 120 μm, more preferably 15 to 80 μm, and most preferably 15 to 60 μm. . If the volume average particle size is less than 15 μm, carrier adhesion tends to occur, which is not preferable. If the volume average particle diameter exceeds 120 μm, the image quality tends to deteriorate, which is not preferable. This volume average particle size is measured by:

(Volume average particle size)
As a device, a Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100) was used. Water was used as the dispersion medium.

  The carrier core material for an electrophotographic developer according to the present invention preferably has a shape factor SF-2 (roundness) of 100 to 120. The shape factor SF-2 is a value obtained by dividing the value obtained by squaring the carrier projection perimeter length by the value obtained by dividing the value by the carrier projection area by 4π, and multiplying it by 100. The shape of the carrier is close to a sphere. The value becomes closer to 100. If the shape factor SF-2 of the carrier core material exceeds 120, it means that the unevenness of the resin on the surface of the core material is large, and the resin tends to penetrate, so that there is a possibility that desired characteristics cannot be obtained as an electrophotographic carrier. is there. This shape factor SF-2 (roundness) is measured by the following.

(Shape factor SF-2 (roundness))

The volume resistance of the carrier core material for an electrophotographic developer according to the present invention at an applied voltage of 50 V is desirably 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm. If the volume resistance is less than 1 × 10 ⁶ Ω · cm, the resistance is too low, which may cause a decrease in charge. When the volume resistance exceeds 1 × 10 ¹⁰ Ω · cm, the resistance becomes too high, and there is a possibility that the movement of electric charge accompanying triboelectric charging is hindered. A method for measuring this volume resistance will be described later.

  The surface of the carrier core material for an electrophotographic developer according to the present invention is desirably oxidized. The thickness of the oxidized film formed by this surface oxidation treatment is preferably 0.1 nm to 5 μm. If the thickness is less than 0.1 nm, the effect of the oxide film layer is small, and if it exceeds 5 μm, the magnetization is lowered or the resistance becomes too high, so that problems such as a reduction in developing ability tend to occur. Moreover, you may reduce | restore before an oxidation process as needed.

Volume resistivity in this oxidation process is applied voltage 50V of the carrier core ^{material, 6 × 10 6 ~1 × 10} 10 Ω · cm, and the volume resistivity of the applied voltage ^{1000V, 10 10 Ω · 6 ×} 10 6 ~1 × It is desirable to be cm. When the volume resistance at an applied voltage of 50 V is less than 1 × 10 ⁶ Ω · cm, the resistance is too low, which may cause a decrease in charging. If the volume resistance at an applied voltage of 50 V exceeds 1 × 10 ¹⁰ Ω · cm, the resistance becomes too high, and there is a possibility that the movement of electric charge accompanying frictional charging is hindered. If the volume resistance at an applied voltage of 1000 V is less than 6 × 10 ⁶ Ω · cm, the resistance is too low, which may cause a decrease in charging. When the volume resistance at an applied voltage of 1000 V exceeds 1 × 10 ¹⁰ Ω · cm, the resistance becomes too high, and there is a possibility that the movement of electric charges accompanying frictional charging is hindered. This volume resistance is measured by:

(Volume resistance)
A sample was filled in a fluororesin cylinder having a cross-sectional area of 4 cm ² so that the height was 4 mm, electrodes were attached to both ends, and a weight of 1 kg was further placed thereon to measure resistance. The resistance was measured by applying a measurement voltage of 50 V with a Keithley 6517A type insulation resistance measuring instrument, measuring the resistance after 5 seconds, and calculating the volume resistance.

  In the carrier for an electrophotographic developer according to the present invention, the surface of the carrier core material is coated with a resin.

  The resin-coated carrier for an electrophotographic developer according to the present invention desirably has a resin coating amount of 0.1 to 10% by weight with respect to the carrier core material. If the coating amount is less than 0.01% by weight, it is difficult to form a uniform coating layer on the surface of the carrier. If the coating amount exceeds 10% by weight, the carriers are aggregated with a decrease in productivity such as a decrease in yield. This causes fluctuations in developer characteristics such as fluidity or charge amount in the actual machine.

  The film forming resin used here can be appropriately selected depending on the toner to be combined, the environment in which it is used, and the like. The type is not particularly limited, for example, fluorine resin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyester resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, phenol resin, fluorine acrylic resin, Examples thereof include acrylic-styrene resins, silicone resins, or modified silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins. In the present invention, acrylic resin, silicone resin or modified silicone resin is most preferably used.

  A conductive agent can be added to the film-forming resin for the purpose of controlling the electrical resistance, charge amount, and charging speed of the carrier. Since the conductive agent itself has a low electric resistance, an excessive amount of the conductive agent tends to cause an abrupt charge leak. Accordingly, the addition amount is 0.25 to 20.0% by weight, preferably 0.5 to 15.0% by weight, particularly preferably 1.0 to 10.0% by weight, based on the solid content of the film-forming resin. %. Examples of the conductive agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents.

  In addition, the film forming resin can contain a charge control agent. Examples of the charge control agent include various charge control agents generally used for toners and various silane coupling agents. This is because, when the core material exposed area is controlled to be relatively small by film formation, the charge imparting ability may decrease, but it can be controlled by adding various charge control agents and silane coupling agents. It is. The types of charge control agents and coupling agents that can be used are not particularly limited, but charge control agents such as nigrosine dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, aminosilane coupling agents, and fluorine-based silane couplings. An agent or the like is preferable.

(Charge amount measurement)
3 g of negatively chargeable commercially available toner and 47 g of a carrier were weighed and placed in a 50 ml glass bottle and exposed for 1 hour in a normal temperature and normal humidity environment (N / N environment: room temperature 25 ° C., humidity 55%). After exposure, mix and stir the mixture so that the glass bottle reaches 100 revolutions with a ball mill in a normal temperature and normal humidity environment, sample after 1 min, 3 min, 10 min, 30 min after the start of stirring, and charge amount made by Epping Measured with a suction charge measuring device.

<Carrier Core Material for Electrophotographic Developer According to the Present Invention and Carrier Manufacturing Method>
Next, the carrier core material for an electrophotographic developer and the method for producing the carrier according to the present invention will be described.

The carrier core material for electrophotographic developer according to the present invention is produced by pulverizing, mixing and calcining each compound of Fe, Ti 2 , Mg and Sr , and granulating the resulting granulated product. Primary firing, main firing, crushing, classification, and surface oxidation treatment are performed.

The method of preparing each granulated product by pulverizing, mixing, and granulating each compound of Fe, Ti , Mg, and Sr is not particularly limited, and a conventionally known method can be adopted, and a dry method is used. Alternatively, a wet method may be used. Fe ₂ O ₃ , TiO ₂ , Mg (OH) ₂ and / or MgCO ₃ are mixed as raw materials, carbon black and / or a binder are further added, and calcined in a non-oxidizing atmosphere or weakly reducing atmosphere, at least 2 It is preferable to generate a ferrite precursor state in which a spinel phase containing valent Fe and a composite oxide phase containing Fe and Ti are present. In the conventional manufacturing method, since a spinel phase is generated from Fe ₂ O ₃ at the time of main firing, considerable energy is required to change the crystal structure, but Fe ₂ O ₃ , TiO ₂ , Mg (OH) ₂ and / or When MgCO ₃ is mixed and carbon black and / or binder is added and calcining is performed, low-temperature firing is possible because ferritization is completed with only a minimum change in the crystal structure in the main firing. . In addition, it is preferable to use polyvinyl alcohol or polyvinylpyrrolidone as a binder.

  In the production method of the present invention, the obtained granulated product is subjected to primary firing and main firing. The primary firing is performed at 500 to 1100 ° C. in a non-oxidizing atmosphere.

  Next, the main baking is performed at 1280 ° C. or lower. The main firing has a more solid crystal structure, and an effect of preventing a decrease in magnetization due to surface oxidation can be expected. By performing the primary firing, it can be fired at a lower temperature in comparison with the case where the primary firing is not performed in the main firing, so that not only the core particles with irregularities are easily formed but also high sphericity can be secured. It becomes.

  In the production method of the present invention, as described above, not only the crystal structure derived from the raw material but also the spinel phase containing at least divalent Fe and Fe and Ti in advance at the time of granulation of the core material particles before the main firing. In the main firing, ferritization can be promoted without passing through hematite by performing primary firing at 500 to 1100 ° C. in a non-oxidizing atmosphere. Compared to the conventional case, low temperature firing at 1280 ° C. or lower is possible.

  In the production method of the present invention, the main baking is performed in an atmosphere having an oxygen concentration of 5% by volume or less. When the oxygen concentration exceeds 5% by volume, the magnetization of the fired product becomes too low, which causes carrier scattering, which is not preferable. In order to obtain a highly magnetized carrier core material, the oxygen concentration is preferably 3% by volume or less, more preferably 1% by volume or less.

  Thereafter, it is collected, dried and classified to obtain a carrier core material. As a classification method, the particle size is adjusted to a desired particle size using an existing air classification, mesh filtration method, sedimentation method, or the like. When dry collection is performed, it can also be collected with a cyclone or the like.

  Thereafter, if necessary, the surface can be heated at a low temperature to perform an oxide film treatment to adjust electric resistance. For the oxide film treatment, a general rotary electric furnace, batch electric furnace or the like is used, and for example, heat treatment is performed at 300 to 800 ° C. In order to uniformly form the oxide film on the core particles, it is preferable to use a rotary electric furnace.

  In the carrier for an electrophotographic developer of the present invention, the surface of the carrier core material is coated with the above resin to form a resin film. As a coating method, it can be coated by a known method such as a brush coating method, a spray drying method using a fluidized bed, a rotary drying method, an immersion drying method using a universal stirrer, or the like. In order to improve the coverage, a fluidized bed method is preferred.

When the resin is coated on the carrier core and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or by microwave It can be burned.
When a UV curable resin is used, a UV heater is used. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.

<Electrophotographic developer according to the present invention>
Next, the electrophotographic developer according to the present invention will be described.
The electrophotographic developer according to the present invention comprises the above-described carrier for an electrophotographic developer and a toner.

  The toner particles constituting the electrophotographic developer of the present invention include pulverized toner particles produced by a pulverization method and polymerized toner particles produced by a polymerization method. In the present invention, toner particles obtained by any method can be used.

  The pulverized toner particles are, for example, a binder resin, a charge control agent, and a colorant are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin screw extruder or the like, cooled, pulverized, classified, After adding the external additive, it can be obtained by mixing with a mixer or the like.

  The binder resin constituting the pulverized toner particles is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, Furthermore, rosin modified maleic acid resin, epoxy resin, polyester resin, polyurethane resin and the like can be mentioned. These may be used alone or in combination.

  Any charge control agent can be used. For example, nigrosine dyes and quaternary ammonium salts can be used for positively charged toners, and metal-containing monoazo dyes can be used for negatively charged toners.

  As the colorant (colorant), conventionally known dyes and pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used. In addition, external additives such as silica powder and titania for improving the fluidity and aggregation resistance of the toner can be added according to the toner particles.

  The polymerized toner particles are toner particles produced by a known method such as a suspension polymerization method, an emulsion polymerization method, an emulsion aggregation method, an ester elongation polymerization method, or a phase inversion emulsification method. Such polymerized toner particles are prepared by, for example, mixing and stirring a colored dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium. Then, the polymerizable monomer is emulsified and dispersed in an aqueous medium, polymerized while stirring and mixing, and then a salting-out agent is added to salt out the polymer particles. Polymerized toner particles can be obtained by filtering, washing and drying the particles obtained by salting out. Thereafter, if necessary, an external additive may be added to the dried toner particles to provide a function.

  Further, in the production of the polymerized toner particles, in addition to the polymerizable monomer, the surfactant, the polymerization initiator, and the colorant, a fixability improving agent and a charge control agent can be blended and obtained. Various characteristics of the polymerized toner particles can be controlled and improved. A chain transfer agent can be used to improve the dispersibility of the polymerizable monomer in the aqueous medium and adjust the molecular weight of the resulting polymer.

  The polymerizable monomer used for the production of the polymerized toner particles is not particularly limited. For example, styrene and its derivatives, ethylene unsaturated monoolefins such as ethylene and propylene, vinyl halides such as vinyl chloride, Α-methylene aliphatic monocarboxylic acids such as vinyl esters such as vinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, dimethylamino acrylate and diethylaminoester methacrylate Examples include esters.

  Conventionally known dyes and pigments can be used as the colorant (coloring material) used in the preparation of the polymerized toner particles. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, and the like can be used. Moreover, the surface of these colorants may be modified using a silane coupling agent, a titanium coupling agent, or the like.

  As the surfactant used in the production of the polymerized toner particles, an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant can be used.

  Here, examples of the anionic surfactant include fatty acid salts such as sodium oleate and castor oil, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, and alkyl naphthalene sulfonic acids. Salt, alkyl phosphate ester salt, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl sulfate ester salt and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester, and oxyethylene-oxypropylene block polymer. . Furthermore, examples of the cationic surfactant include alkylamine salts such as laurylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride. Examples of amphoteric surfactants include aminocarboxylates and alkylamino acids.

  The surfactant as described above can be used usually in an amount in the range of 0.01 to 10% by weight with respect to the polymerizable monomer. Such a surfactant affects the dispersion stability of the monomer and also affects the environmental dependency of the obtained polymerized toner particles. Use in an amount within the above range is preferable from the viewpoint of ensuring the dispersion stability of the monomer and reducing the environmental dependency of the polymerized toner particles.

  For the production of polymerized toner particles, a polymerization initiator is usually used. The polymerization initiator includes a water-soluble polymerization initiator and an oil-soluble polymerization initiator, and any of them can be used in the present invention. Examples of the water-soluble polymerization initiator that can be used in the present invention include persulfates such as potassium persulfate and ammonium persulfate, water-soluble peroxide compounds, and oil-soluble polymerization initiators. Examples thereof include azo compounds such as azobisisobutyronitrile and oil-soluble peroxide compounds.

  When a chain transfer agent is used in the present invention, examples of the chain transfer agent include mercaptans such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, carbon tetrabromide, and the like.

  Further, when the polymerized toner particles used in the present invention contain a fixability improver, a natural wax such as carnauba wax, an olefin wax such as polypropylene or polyethylene can be used as the fixability improver. .

  Further, when the polymerized toner particles used in the present invention contain a charge control agent, the charge control agent to be used is not particularly limited, and nigrosine dyes, quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes, etc. Can be used.

  Examples of the external additive used for improving the fluidity of polymerized toner particles include silica, titanium oxide, barium titanate, fluororesin fine particles, and acrylic resin fine particles. Can be used in combination.

  Furthermore, examples of the salting-out agent used for separating the polymer particles from the aqueous medium include metal salts such as magnesium sulfate, aluminum sulfate, barium chloride, magnesium chloride, calcium chloride, and sodium chloride.

  The volume average particle size of the toner particles produced as described above is in the range of 2 to 15 μm, preferably 3 to 10 μm, and the polymerized toner particles have higher particle uniformity than the pulverized toner particles. . If the toner particles are smaller than 2 μm, the charging ability is lowered, and it is easy to cause fogging and toner scattering, and if it exceeds 15 μm, the image quality is deteriorated.

  An electrophotographic developer can be obtained by mixing the carrier and toner manufactured as described above. The mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 3 to 15% by weight. If it is less than 3% by weight, it is difficult to obtain a desired image density. If it exceeds 15% by weight, toner scattering and fogging are likely to occur.

  The electrophotographic developer according to the present invention prepared as described above uses an electrostatic latent image formed on a latent image holding member having an organic photoconductor layer, while applying a bias electric field to the toner and the carrier. The present invention can be used in digital copiers, printers, fax machines, printers, and the like that use a developing method in which reversal development is performed using a two-component developer magnetic brush. Further, the present invention can also be applied to a full color machine using an alternating electric field, which is a method of superimposing an AC bias on a DC bias when a developing bias is applied from the magnetic brush to the electrostatic latent image side.

  Hereinafter, the present invention will be specifically described based on examples and the like.

Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , and SrCO ₃ were weighed so that the amount of Fe was 8.12 mol, Mg was 1 mol, Ti was 0.135 mol, and Sr was 0.15 mol. Water was added so that the content would be 50% by weight and mixed with a bead mill, and the mixed slurry was granulated with a spray dryer. At this time, PVA was added as a binder component so that the solid content would be 2% by weight, and a polycarboxylic acid-based dispersant was added so that the viscosity of the slurry would be 1 to 2 poises, and the resulting granulated product was 1000%. Temporary firing was performed in a non-oxidizing atmosphere at 0 ° C. in a rotary firing furnace, and ferrite was advanced while removing organic substances, and at the same time a part of iron oxide was reduced. At this time, the magnetization of the calcined product was 46 Am ² / kg.

The obtained calcined product was pulverized by a bead mill so that the slurry particle size D ₅₀ was 2 μm. At this time, PVA is added as a binder component so that the solid content is 0.15% by weight, and a polycarboxylic acid-based dispersant is added so that the viscosity of the slurry is 2 to 3 poise, and the obtained pulverized slurry Was re-granulated with a spray dryer and subjected to primary firing in a rotary-type firing furnace at 1000 ° C. in a non-oxidizing atmosphere to promote ferritization while removing organic substances and at the same time reduce some of the iron oxide. . The magnetization after the primary firing was 61 emu / g.

After the primary firing, coarse particles were removed using an 80-mesh sieve and then fired for 16 hours under the conditions of 1180 ° C. and oxygen concentration 0 volume% to obtain a fired product. The obtained fired product was crushed, classified, and subjected to magnetic separation, thereby obtaining carrier core particles having a volume average particle size of 37.1 μm. The magnetization of the carrier core particles was 65 Am ² / kg. When the crystal structure of the obtained carrier core particles was confirmed by an X-ray diffractometer, in addition to the spinel crystal structure containing Mg, the crystal structure of oxides containing Fe and Ti and Sr ferrite was confirmed.

Further, the obtained carrier core particles were subjected to a surface oxidation treatment in a rotary electric furnace under the conditions of a surface oxidation treatment temperature of 680 ° C. and an atmospheric atmosphere to obtain surface oxidized carrier core particles. The magnetization of the carrier core particles subjected to this surface oxidation treatment was 61 Am ² / kg.

  Carrier core particles having a volume average particle diameter of 35.8 μm were obtained in the same manner as in Example 1 except that Fe was 12.92 mol, Mg was 4 mol, Ti was 0.135 mol, and Sr was 0.05 mol. Obtained.

  Carrier core particles having a volume average particle diameter of 37.3 μm were obtained in the same manner as in Example 1 except that Fe was 13.95 mol, Mg was 4 mol, Ti was 0.05 mol, and Sr was 0.15 mol. Obtained.

  Carrier core particles having a volume average particle diameter of 36.7 μm were obtained in the same manner as in Example 1 except that 12.75 mol of Fe, 4 mol of Mg, 0.05 mol of Ti, and 0.05 mol of Sr were used. Obtained.

  Carrier core material having a volume average particle diameter of 36.4 μm as in Example 1 except that Fe is 7.42 mol, Mg is 0.65 mol, Ti is 0.135 mol, and Sr is 0.15 mol. Particles were obtained.

  Carrier core material having a volume average particle diameter of 37.0 μm in the same manner as in Example 1 except that Fe is 6.22 mol, Mg is 0.65 mol, Ti is 0.135 mol, and Sr is 0.05 mol. Particles were obtained.

  Carrier core material having a volume average particle diameter of 36.9 μm as in Example 1 except that Fe is 7.25 mol, Mg is 0.65 mol, Ti is 0.05 mol, and Sr is 0.15 mol. Particles were obtained.

  Carrier core material having a volume average particle diameter of 35.9 μm as in Example 1 except that 6.05 mol of Fe, 0.65 mol of Mg, 0.05 mol of Ti, and 0.05 mol of Sr were used. Particles were obtained.

  Carrier core material particles having a volume average particle size of 36.6 μm were obtained in the same manner as in Example 1 except that the temperature of the main firing was 1250 ° C.

  Carrier core material particles having a volume average particle diameter of 37.6 μm were obtained in the same manner as in Example 1 except that the temperature for the main firing was 1150 ° C.

  After obtaining carrier core particles having an average particle size of 49.3 μm in the same manner as in Example 1, a coating resin obtained by adding Ketjen Black EC600JD manufactured by Lion Corporation to acrylic modified silicone resin KR-9706 manufactured by Shin-Etsu Silicone Co., Ltd. As a fluid bed coater. At this time, the acryl-modified silicone resin solution was prepared by weighing the resin so that the solid content of the resin with respect to the carrier core was 2% by weight and adding toluene so that the solid content of the resin was 10% by weight. Furthermore, Ketjen Black is weighed so as to have a solid content of 10% by weight of the acrylic-modified silicone resin, then added to the resin solution, dispersed for 3 minutes with IKA homogenizer ULTRATURRAX T-50, and used for coating. did. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying for 3 hours with a fluidized dryer set at 210 ° C.

  After obtaining carrier core material particles having an average particle diameter of 48.5 μm by the same method as in Example 1, acrylic resin LR-269 manufactured by Mitsubishi Rayon Co., Ltd. was applied as a coating resin with a mixing stirrer. At this time, a resin solution was used in which the resin was weighed so that the solid content of the resin with respect to the carrier core was 0.5 wt%, and toluene was added so that the solid content of the resin would be 10 wt%. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with a hot air dryer set at 145 ° C. for 2 hours.

Comparative example

(Comparative Example 1)
Carrier core particles having a volume average particle size of 37.0 μm were obtained in the same manner as in Example 1 except that Fe was 16.75 mol, Mg was 5 mol, Ti was 0.15 mol, and Sr was 0.2 mol. Obtained.

(Comparative Example 2)
Carrier core material particles having a volume average particle diameter of 35.1 μm were obtained in the same manner as in Example 1 except that 14.35 mol of Fe, 5 mol of Mg, 0.15 mol of Ti, and 0 mol of Sr were used. .

(Comparative Example 3)
Carrier core material particles having a volume average particle diameter of 35.3 μm were obtained in the same manner as in Example 1 except that 16.45 mol of Fe, 5 mol of Mg, 0 mol of Ti, and 0.2 mol of Sr were used. .

(Comparative Example 4)
Carrier core material particles having a volume average particle size of 35.9 μm were obtained in the same manner as in Example 1 except that Fe was 14.05 mol, Mg was 5 mol, Ti was 0 mol, and Sr was 0 mol.

(Comparative Example 5)
Carrier core material having a volume average particle diameter of 37.4 μm as in Example 1 except that 7.15 mol of Fe, 0.2 mol of Mg, 0.15 mol of Ti, and 0.2 mol of Sr were used. Particles were obtained.

(Comparative Example 6)
Carrier core particles having a volume average particle diameter of 37.7 μm were obtained in the same manner as in Example 1 except that 4.75 mol of Fe, 0.2 mol of Mg, 0.15 mol of Ti, and 0 mol of Sr were used. Obtained.

(Comparative Example 7)
Carrier core particles having a volume average particle size of 36.7 μm were obtained in the same manner as in Example 1 except that Fe was 6.85 mol, Mg was 0.2 mol, Ti was 0 mol, and Sr was 0.2 mol. Obtained.

(Comparative Example 8)
Carrier core particles having a volume average particle diameter of 37.0 μm were obtained in the same manner as in Example 1 except that 4.45 mol of Fe, 0.2 mol of Mg, 0 mol of Ti, and 0 mol of Sr were used. .

(Comparative Example 9)
Carrier core material particles having a volume average particle size of 36.5 μm were obtained in the same manner as in Example 1 except that the temperature for the main firing was 1300 ° C.

(Comparative Example 10)
Carrier core material particles having a volume average particle size of 36.8 μm were obtained in the same manner as in Example 1 except that the temperature for the main firing was 1100 ° C.

  About Examples 1-10 and Comparative Examples 1-10, the manufacturing conditions, volume average particle diameter, BET specific surface area, shape factor, electrical resistance, magnetic properties, chemical analysis and crystal structure of the carrier core material were evaluated, and the results are shown. 1 to Table 4. In Examples 11 and 12, the charging characteristics under normal temperature and humidity were evaluated as electrophotographic carriers, and the results are shown in Table 5.

  As is clear from the results in Tables 1 to 4, the carrier core material for electrophotographic developers obtained in Examples 1 to 10 can withstand use. On the other hand, Comparative Examples 1 to 4 have a low Fe content, and Comparative Examples 2 and 4 have a high Mg content, and thus cannot be used as a carrier core material for an electrophotographic developer. In particular, Comparative Example 3 and Comparative Example 4 that do not contain Ti not only have a low magnetization after the main firing, but also cannot obtain the effect of addition of Ti, so the decrease in the magnetization after the surface oxidation treatment becomes significant. Comparative Example 5 and Comparative Example 7 have not only the surface property that the BET specific surface area becomes too large and the resin coating is sufficient because the content of Mg is small and the content of Sr is large. The remanent magnetization and coercive force of the film became too large to be used as a carrier core material for an electrophotographic developer. In Comparative Example 6 and Comparative Example 8, the Mg content was small and Sr was not contained, so the resistance after the main firing was low. Further, since the resistance at an applied voltage of 1000 V after the surface oxidation treatment was low, it could not be used as a carrier core material for an electrophotographic developer. In Comparative Example 9, although the magnetization was high but the main baking temperature was too high, the BET specific surface area was small, the shape of the carrier core particles was poor, and it could not be used as a carrier core for an electrophotographic developer. In Comparative Example 10, since the main baking temperature is too low, the BET specific surface area becomes large, the unevenness of the carrier core material particles is large, and there is a possibility that the resin coating cannot be sufficiently performed, so that it can be used as a carrier core material for an electrophotographic developer. There wasn't.

  In Examples 11 and 12, the carrier core material was coated with a resin. As shown in Table 5, it was confirmed that sufficient charging characteristics as a carrier can be obtained by coating with a resin.

  The carrier core material for an electrophotographic developer according to the present invention can obtain a desired resistance such as medium resistance or high resistance while being highly magnetized without using not only each heavy metal but also Mn, and high. It has a charge amount and excellent charging stability, and also has a surface shape with appropriate irregularities and a uniform shape. An electrophotographic developer comprising a carrier and a toner obtained by coating the carrier core material with a resin has a long life, has a high charge amount, and is excellent in charging stability. Moreover, the carrier core material and the carrier can be stably produced on an industrial scale by the production method of the present invention.

  Therefore, the present invention can be widely used in the field of full-color machines that particularly require high image quality and high-speed machines that require image maintenance reliability and durability.

Claims (15)

2 to 8.5% by weight of Mg, 0.1 to 1.25% by weight of Ti, 0.37 to 2.5% by weight of Sr and 60 to 70% by weight of Fe, and a BET specific surface area of 0. A carrier core material for an electrophotographic developer, wherein the carrier core material is 075 to 0.11 m ² / g.   The carrier core material for an electrophotographic developer according to claim 1, further comprising a crystal structure of an oxide containing at least Fe and Ti in addition to the spinel structure constituting the Mg ferrite. Claim 1 or electrophotographic developer carrier core material according to 2 Mn content is less than 1 wt%. When a magnetic field of 3K · 1000 / 4π · A / m is applied, the magnetization is 45 to 75 Am ² / kg, the residual magnetization is ² to 10 Am ² / kg, and the coercive force is 10 to 80 3K · 1000 / 4π · A / m. The carrier core material for an electrophotographic developer according to any one of claims 1 to 3 . The carrier core material for an electrophotographic developer according to any one of claims 1 to 4 , wherein an average particle diameter measured by a laser diffraction particle size distribution analyzer is 15 to 120 µm. The carrier core material for an electrophotographic developer according to any one of claims 1 to 5 , wherein the shape factor SF-2 (roundness) is 100 to 120. The carrier core material for an electrophotographic developer according to any one of claims 1 to 6 vol resistance of ^{1 × 10 6 ~1 × 10 10} Ω · cm at an applied voltage of 50 V. The carrier core material for an electrophotographic developer according to any one of claims 1 to 7 , wherein the surface is oxidized to form an oxidized film. Electrophotography according to claim 8 volume resistivity is ^{1 × 10 6 ~1 × 10 10} Ω · cm, and the volume resistivity at an applied voltage of 1000V ^{6 × 10 6 ~1 × 10 10} Ω · cm at an applied voltage of 50V Carrier core material for developer. The electrophotographic developer carrier surface of the carrier core material is coated with a resin according to any one of claims 1-9. The carrier for an electrophotographic developer according to claim 10, wherein the resin is an acrylic resin, a silicone resin, or a modified silicone resin. Electrons for pulverizing, mixing and calcining each compound of Fe, Ti 2 , Mg and Sr , granulating, and subjecting the resulting granulated product to primary firing, main firing, and further crushing, classification, and surface oxidation treatment 10. The carrier core for an electrophotographic developer according to any one of claims 1 to 9, wherein in the method for producing a carrier core material for a photographic developer, the main baking is performed at an oxygen concentration of 5% by volume or less. A method of manufacturing the material. A method for producing a carrier for an electrophotographic developer, wherein the surface of the carrier core material obtained by the production method according to claim 12 is coated with a resin. An electrophotographic developer comprising the carrier according to claim 10 and a toner. An electrophotographic developer comprising a carrier and a toner obtained by the production method according to claim 13 .