Ferrite particles, carrier core material for electrophotographic developer, carrier for electrophotographic developer, and electrophotographic developer

Abstract

To provide a carrier core material which offers a superior capability to charge toner and a good charge rising property, and to provide an electrophotographic developer carrier and electrophotographic developer.SOLUTION: In order to solve the above problem, a carrier core material is provided, consisting of ferrite particles mainly composed of a structure represented by a composition formula (MO)x(Fe2O3)y, where M represents Mn alone or a combination of Mn and at least one metal element selected from the group consisting of Fe, Mg, Cu, Zn, Ni, and Li, and x+y=100 mol%, and containing La of 0.01-2.0 mol%, inclusive. The carrier core material is used to produce an electrophotographic developer carrier and an electrophotographic developer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to ferrite particles, carrier core material for electrophotographic developers, carrier for electrophotographic developers, and electrophotographic developers. [Background technology]

[0002] Electrophotographic development is a method of developing photographs by depositing toner from a developer onto an electrostatic latent image formed on a photoreceptor. Developers used in this method are divided into two-component developers consisting of toner and a carrier, and one-component developers using only toner. Historically, methods such as the cascade process were used for developing two-component developers, but currently, the magnetic brush method using a magnetic roll is the mainstream.

[0003] In the magnetic brush method, the toner is charged by agitating and mixing the carrier and toner in a developing box filled with developer. The carrier is then transported to the surface of the photoreceptor by a developing roll that holds a magnet. At this time, the charged toner is transported to the surface of the photoreceptor by the carrier. After a toner image is formed on the photoreceptor by electrostatic action, the carrier remaining on the developing roll is collected back into the developing box, agitated and mixed with new toner, and reused repeatedly for a certain period of time.

[0004] Unlike single-component developers, two-component developers allow for the design of the carrier's magnetic and electrical properties separately from the toner, resulting in better control during developer design. Therefore, two-component developers are suitable for full-color developing equipment where high image quality is required, and for high-speed printing equipment where reliability and durability in image maintenance are essential.

[0005] In the two-component developer used in this way, in order to obtain good image characteristics, a carrier with a high charge imparting ability to the toner is required. For example, in Patent Document 1 and Patent Document 2, it is said that a carrier with a high charge imparting ability to the toner can be obtained by adding Ti or Sr and using ferrite particles with appropriately controlled surface irregularities as the carrier core material.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, even in the carrier using the above conventional ferrite particles (Patent Document 1 and Patent Document 2) as the carrier core material, the charge imparting ability cannot be said to be sufficient. In addition, in order to realize high-speed and high-definition printing, etc., the ability to quickly impart charge to the toner immediately after the start of printing, that is, the charge rise property needs to be further improved.

[0008] Therefore, an object of the present invention is to provide ferrite particles, a carrier core material for electrophotographic developer, a carrier for electrophotographic developer, and an electrophotographic developer having a high charge imparting ability to the toner and good charge rise property.

Means for Solving the Problems

[0009] In order to solve the above problems, the carrier core material according to the present invention has a composition formula (MO) x (Fe2O3) y (where M is Mn and Mg and x>0、 x + y = 100 mol%), and is composed of ferrite particles containing La in 0.05 mol% or more and 2.0 mol% or less, and is characterized in that.

[0010] In the carrier core material according to the present invention, it is preferable that it contains Sr or Ca in an amount of 0.1 mol% to 2.0 mol%.

[0012] In the carrier core material relating to the present invention, the compositional formula is (MnO) a (MgO) b (Fe2O3) c (However, it is preferable that the expression is given by 25≦a≦55, 0≦b≦20, 45≦c≦65, and a+b+c=100(mol%).

[0013] To solve the above problems, the electrophotographic developer carrier according to the present invention is characterized by comprising the carrier core material and a resin coating layer provided on the surface of the carrier core material.

[0014] To solve the above problems, the electrophotographic developer according to the present invention is characterized by comprising the above-mentioned electrophotographic developer carrier and toner.

[0015] The electrophotographic developer according to the present invention is also preferably used as a replenishment developer. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a carrier core material, an electrophotographic developer carrier, and an electrophotographic developer that have a high ability to impart charge to toner and good charge rise time. [Modes for carrying out the invention]

[0017] Embodiments of the carrier core material, the carrier for electrophotographic developer, and the electrophotographic developer according to the present invention will be described below. In this specification, unless otherwise specified, ferrite particles, carrier core material, carrier for electrophotographic developer, and electrophotographic developer refer to aggregates of individual particles, i.e., powders. The ferrite particles constituting the carrier core material described below are not limited to carrier core material for electrophotographic developers, but can also be used in various applications such as magnetic inks, magnetic fluids, magnetic fillers, fillers for bonded magnets, fillers for electromagnetic wave shielding materials, and electronic component materials.

[0018] 1. Carrier core material First, the carrier core material relating to the present invention has the composition formula (MO) x (Fe2O3) y It is composed of ferrite particles represented as (where M is Mn, or at least one metallic element selected from the group consisting of Mn and Fe, Mg, Cu, Zn, Ni, Li, and x+y=100mol), and contains 0.01mol% to 2.0mol% of La.

[0019] The inventors of this case have found that by including lanthanum (La) within the above range in a carrier core material composed of ferrite particles represented by the above compositional formula, the ability to impart charge to the toner is enhanced, and the charge rise time is improved. The exact mechanism is not clear, but it is thought to be as follows.

[0020] The ferrite represented by the above compositional formula has a spinel-type crystal structure. The ionic radius of La is larger compared to the ionic radii of elements corresponding to M such as Mn and Mg (hereinafter referred to as "M elements"). Therefore, La is not incorporated into the spinel-type crystal phase and tends to segregate at grain boundaries. It is considered that La segregated at grain boundaries undergoes a solid-phase reaction with Fe and M elements to form La-Fe compounds and La-M compounds. By including La and these La compounds, high-resistance ferrite particles with less charge leakage are easily obtained compared to the case where they are not included. Also, when La and these La compounds are present at grain boundaries, it is considered that the growth of the spinel-type crystal phase is suppressed and appropriate surface irregularities occur. As a result, it is considered that good triboelectrification with toner can be achieved. Also, when La and La compounds are present at grain boundaries, charge transfer during triboelectrification with toner occurs smoothly, and a carrier core material with good charge rising property can be obtained. Furthermore, in the above compositional formula, by setting the composition to include Mn as M, a carrier core material with high magnetization and high resistance can be obtained compared to the case of using other elements, and the above effects due to La addition can be made more prominent. Hereinafter, the carrier core material will be described in more detail.

[0021] 1-1. Ferrite Composition As described above, the ferrite particles constituting the carrier core material are (MO) x (Fe2O3) y (where M is Mn or at least one metal element selected from the group consisting of Mn and Fe, Mg, Cu, Zn, Ni, Li, and x + y = 100 (mol%)). The ferrite having such a spinel-type crystal structure exhibits soft magnetism and is suitable as a carrier core material for electrophotographic developers because it is also easy to adjust electrical properties such as resistance.

[0022] In particular, it is preferable that M is Mn or M is Mn and Mg. By making Mn an essential component of the composition, the magnetization at low magnetic fields can be increased. Furthermore, the inclusion of Mn prevents re-oxidation of ferrite during furnace removal after the final firing. Additionally, the inclusion of Mg makes it easier to obtain high-resistance ferrite particles.

[0023] Furthermore, the ferrite particles are (MnO) a (MgO) b (Fe2O3) c (However, it is more preferable that it be represented by the following compositional formula: 25≦a≦55, 0≦b≦20, 45≦c≦65, a+b+c=100(mol%).

[0024] By setting the Mn content to 25 mol% or more, the relative increase in Fe content can be suppressed, and the proportion of magnetite component in the ferrite particles can be prevented from increasing. Therefore, the decrease in magnetization on the low-field side can be suppressed, and the occurrence of carrier adhesion can be suppressed. In addition, it becomes easier to adjust to a good resistance value for electrophotographic printing, so the occurrence of fogging, deterioration of gradation, and image defects such as white spots can be suppressed. Furthermore, toner consumption can be kept at an appropriate level. By setting the Mn content to 55 mol% or less, the resistance can become too high, and the occurrence of image defects such as white spots can be suppressed.

[0025] The content of Mg is preferably 20 mol% or less. The content of Mg may be 0 mol%, but by making the composition contain Mg, as described above, it becomes easier to obtain high-resistance ferrite particles. At this time, by setting the content of Mg to 2 mol% or more, the content of Mn becomes appropriate with respect to the content of Fe, and it becomes even easier to adjust the magnetization and resistance of the ferrite particles within a favorable range for electrophotographic printing. Therefore, it is possible to suppress the occurrence of image defects such as fogging, deterioration of gradation, occurrence of streaks, and carrier scattering. Furthermore, when magnesium hydroxide is used as the Mg raw material, if the firing temperature during the production of the ferrite particles is low, hydroxyl groups may remain in the ferrite particles. By setting the content of Mg to 20 mol% or less, the amount of residual hydroxyl groups present due to the raw materials can be reduced. Therefore, it is possible to suppress the fluctuation of electrical properties such as the charge amount and resistance of the ferrite particles due to the residual hydroxyl groups being affected by the ambient humidity, and to make the environmental dependence of the electrical properties of the ferrite particles better.

[0026] The ferrite particles are magnetic oxides mainly composed of ferric oxide. Therefore, basically, a < c, and by setting the content of Fe to 45 mol% or more and 65 mol% or less, it becomes easy to adjust the magnetization and resistance of the ferrite particles within a favorable range for electrophotographic printing.

[0027] 1-2. La content The carrier core material contains La within the above range. If the La content is less than 0.01 mol%, the above-described effects cannot be sufficiently obtained, which is not preferable. However, the La content here refers to the content of the La element when the total amount in terms of Fe2O3 and the oxide MO of the M element contained in the ferrite particles is 100 mol.

[0028] Also, the La content was determined by ICP mass spectrometry for the elemental composition of each ferrite particle, and was taken as the value representing the content of the La element in mol% as described above.

[0029] When the La content exceeds 2.0 mol%, the effects obtained from the presence of La saturate. Furthermore, if the La content increases significantly beyond 2.0 mol%, the La content becomes relatively large compared to Fe and M elements, which may lead to defects in the spinel-type crystal structure, such as lattice defects, or defects in the structure of the La compound at grain boundaries, potentially creating gaps at the grain boundaries. Such structural defects can easily lead to charge leakage, potentially worsening the charge rise. Moreover, if charge leakage exceeds the charge imparting ability, the amount of charge itself decreases, making it difficult to obtain highly charged carriers. In addition, resistance tends to decrease as the La content increases. Fluidity also tends to decrease. Therefore, a high La content is undesirable because it reduces the charge rise.

[0030] To obtain the desired effect from the addition of La, the La content is more preferably 0.05 mol% or more and 1.0 mol% or less. In particular, to obtain an electrophotographic developer with good charge rise, the La content is preferably 0.8 mol% or less, more preferably 0.6 mol% or less, and even more preferably 0.5 mol% or less.

[0031] 1-3. Sr / Ca The carrier core material preferably contains 0.1 mol% to 2.0 mol% of Sr or Ca along with La. By including a small amount of Sr or Ca in ferrite particles having a spinel-type crystal structure, these elements segregate at the grain boundaries and react with Fe in a solid phase to form Sr-Fe compounds or Ca-Fe compounds such as Sr ferrite or Ca ferrite. Furthermore, since the ionic radii of La are similar to those of Sr and Ca, adding Sr or Ca may result in some La being incorporated into the Sr-Fe compounds or Ca-Fe compounds. However, because Fe and M elements are relatively more abundant, La-Fe compounds or La-M compounds are formed. The formation of these compounds suppresses the growth of the spinel-type crystal phase, thereby promoting surface roughness. If the Sr or Ca content exceeds 2.0 mol%, it is undesirable because it leads to decreased fluidity, decreased magnetization, and the chlorine components in the raw material tend to remain as Sr chloride and Ca chloride, resulting in decreased charge imparting ability.

[0032] The Sr or Ca content also refers to the content of Sr or Ca element when the total amount of Fe2O3 and M element oxides (MO equivalent) contained in the ferrite particles is taken as 100 mol.

[0033] 1-4. Magnetic properties For the carrier core material mentioned above, the saturation magnetization measured by VSM when a magnetic field of 1K·1000 / 4π·A / m is applied is approximately 55Am. 2 / kg or more 70Am 2 The range is less than / kg. Saturation magnetization is 55Am 2 / kg or more 70Am 2In the range of less than / kg, the magnetic force of the core material is high, which effectively suppresses carrier scattering caused by low magnetization, and the dense grain allows for uniform toner retention. In the ferrite particles represented by the above composition formula, there is a trade-off relationship between saturation magnetization and electrical resistance, but as explained below, by including La in the above range, it is possible to obtain a carrier core material with high resistance that is less prone to charge leakage than conventional materials while achieving a saturation magnetization suitable for good high-quality electrophotographic printing, and to obtain an electrophotographic developer with good charge rise when performing high-speed printing. A more preferable range is a saturation magnetization of 58Am 2 / kg or more67Am 2 A value of less than / kg is desirable.

[0034] 1-5. Electrical Characteristics By incorporating La within the specified range, the above carrier core material achieves a resistance value of approximately 1.0 × 10⁻¹⁰ when measured at an electrode distance of 6.5 mm and an applied voltage of 1000 V in a normal temperature and humidity environment (23°C, 55% relative humidity). 7 (Ω) or more 1.0×10 9 It exhibits a value of less than or equal to (Ω). That is, its logarithm (logΩ) is between 7.0 and 9.0, making it possible to obtain a carrier core material with high resistance. By using such a high-resistance carrier core material and providing a resin coating layer on its surface to create a carrier for electrophotographic developers, a high charge amount can be obtained, and the charge rise time can be improved. At the same time, even when the resin coating layer peels off during stirring with toner and the core material is exposed, carrier scattering due to charge injection can be suppressed.

[0035] 1-6. Powder properties (1) Apparent density (AD) The apparent density (g / cm³) of the carrier core material 3 ) is preferably 2.10 or more and 2.40 or less.

[0036] The apparent density referred to here is the value measured using the funnel method in accordance with JIS Z 2504:2012. When the apparent density of the carrier core material is within the range expressed by the above formula, it has fewer internal voids and high strength, so it can prevent cracking and chipping even when strong mechanical stress is applied during mixing and stirring with toner, for example, during high-speed printing. Therefore, carrier scattering is suppressed and good image characteristics can be obtained even during high-speed printing.

[0037] In contrast, if the apparent density falls below 2.10, cracks and chips may occur if strong mechanical stress is applied during mixing and stirring with toner, for example, during high-speed printing. If carriers crack or chip, image defects may occur due to carrier scattering, or they may adhere to and damage the photoreceptor drum and fuser roller. On the other hand, if the apparent density exceeds 2.40, the number of internal voids decreases, but the crystal grains become coarser due to oversintering. In this case, if La or La compounds are segregated at the grain boundaries, cracks and chips are more likely to occur starting from the grain boundaries, which is undesirable because it may cause image defects due to carrier scattering or damage to the photoreceptor drum and fuser roller.

[0038] (2) BET specific surface area The BET specific surface area (m²) of the carrier core material. 2 The value per g is preferably between 0.07 and 0.20.

[0039] The BET specific surface area referred to here can be, for example, a value measured using a specific surface area measuring device (model: Macsorb HM model-1208 (manufactured by Mountec Co., Ltd.)). When the BET specific surface area is within the above range, the surface irregularities are within an appropriate range relative to the particle size. Therefore, the surface of the carrier core material can be well coated with resin. In addition, because the difference in surface irregularities relative to the particle size is small, it is possible to suppress the concentration of load on the convex parts when mechanical stress is applied to the surface, thereby preventing cracking and chipping. Therefore, by obtaining a carrier for electrophotographic developer using this carrier core material, it is possible to suppress the peeling of resin from the surface during mixing and stirring with toner, preventing cracking and chipping of the carrier and preventing carrier scattering.

[0040] In contrast, if the BET specific surface area is less than 0.07, the surface irregularities of the ferrite particles relative to their particle size become small or too small. As a result, when the surface of the carrier core material is coated with resin, the resin tends to peel off easily during mixing with toner. When the resin peels off from the surface of the carrier, the core material is exposed in that area. That is, the surface of the ferrite particles, which are magnetic particles, is exposed, making it easier for carrier scattering and image defects due to reduced chargeability to occur. On the other hand, if the BET specific surface area exceeds 0.20, the surface irregularities become large or too large relative to the particle size, which can lead to poor fluidity, difficulty in coating the protrusions with resin, and exposure of the protrusions. Therefore, it may not be possible to obtain a carrier with sufficient charge-impregnating properties for the toner. Furthermore, when the surface irregularities become large, mechanical stress is applied to the protrusions on the carrier surface during mixing with toner, etc., causing the load to concentrate on the protrusions and making the carrier prone to cracking and chipping, which is undesirable. In other words, it may not be possible to maintain the strength of the carrier when using a developer, which is undesirable.

[0041] (3) Volume-average particle size (D 50 ) When the ferrite particles are used as a core material for an electrophotographic developer carrier, their volume average particle size (D 50 The volume-average particle size is preferably between 24 μm and 40 μm. However, the volume-average particle size referred to here is the value measured in accordance with JIS Z 8825:2013 by laser diffraction / scattering method. When the volume-average particle size is within this range, the ability to impart charge to the toner is high, and this charge imparting ability can be maintained over a long period of time. Therefore, the lifespan of the electrophotographic developer can be extended.

[0042] In contrast, the volume-average particle size (D) of the ferrite particle is 50 If the volume average particle size (D) of the ferrite particle is less than 24 μm, carrier scattering is more likely to occur due to the small particle size. 50If the particle size is less than 24 μm, the ferrite particles tend to aggregate due to their small size. When these ferrite particles are used as a core material and their surface is coated with resin to form a carrier, if the ferrite particles are aggregated, it becomes impossible to properly coat the surface of each individual ferrite particle with resin. Subsequently, if the aggregated ferrite particles break apart during the manufacturing or use of the developer, the developer will have a higher content of large carriers in areas that are not coated with resin. Therefore, it is undesirable to manufacture a developer using a carrier with such ferrite particles as a core material, as it may not be possible to obtain sufficient charge imparting properties to the toner.

[0043] On the other hand, the volume-average particle size (D) of the ferrite particle 50 When the volume average particle size (D) exceeds 40 μm, the particle size of each individual particle constituting the powder becomes larger. 50 Compared to small ferrite particles, the surface area of ​​carriers contributing to triboelectric charging with toner is smaller when considering the powder as a whole. As a result, sufficient charge transfer to the toner may not be achieved. To improve this, if irregularities are added to the surface of individual ferrite particles to increase the surface area of ​​each ferrite particle, the surface area of ​​carriers contributing to triboelectric charging with toner can be increased. In this case, the charge transfer to the toner is improved, but mechanical stress is applied to the protrusions on the carrier surface during mixing with toner, etc., making the carriers more prone to cracking and chipping, which is undesirable. In other words, it may not be possible to maintain the strength of the carriers when using a developer, which is undesirable.

[0044] (4) Flow rate (FR) The fluidity of the ferrite particles is preferably between 22 sec / 50g and 42 sec / 50g. When the fluidity of the ferrite particles is within this range, when the ferrite particles are used as a carrier for electrophotographic developer, the carrier has good fluidity, and the frequency and strength of contact with the toner can be ensured.

[0045] The fluidity (FR) referred to here is the value measured in accordance with JIS Z2502:2012.

[0046] 2. Carrier for electrophotographic developer Next, the carrier for electrophotographic developer according to the present invention will be described. The carrier for electrophotographic developer according to the present invention is characterized by comprising the ferrite particles and a resin coating layer provided on the surface of the ferrite particles. That is, the ferrite particles are used as the core material of the carrier for electrophotographic developer. As the ferrite particles have been described above, the resin coating layer will be described here mainly.

[0047] (1) Types of coating resins The type of resin constituting the resin coating layer (coating resin) is not particularly limited. For example, fluororesins, acrylic resins, epoxy resins, polyamide resins, polyamide-imide resins, polyester resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, phenolic resins, fluoroacrylic resins, acrylic-styrene resins, silicone resins, etc., can be used. In addition, modified silicone resins obtained by modifying silicone resins with acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamide-imide resins, alkyd resins, urethane resins, fluororesins, etc., may also be used. For example, from the viewpoint of suppressing resin peeling due to mechanical stress received during stirring and mixing with toner, the coating resin is preferably a thermosetting resin. Suitable thermosetting resins for the coating resin include epoxy resins, phenolic resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, and resins containing them. However, as mentioned above, the type of coating resin is not particularly limited, and an appropriate one can be selected as appropriate depending on the type of toner to be combined and the usage environment.

[0048] Furthermore, the resin coating layer may be constructed using one type of resin, or using two or more types of resins. When using two or more types of resins, the two or more resins may be mixed to form one resin coating layer, or multiple resin coating layers may be formed. For example, it is preferable to provide a first resin coating layer with good adhesion to the ferrite particles on the surface of the ferrite particles, and a second resin coating layer on the surface of the first resin coating layer to impart the desired charge imparting performance to the carrier.

[0049] (2) Amount of resin coating The amount of resin coating the surface of the ferrite particles (resin coating amount) is preferably 0.1% by mass or more and 10% by mass or less relative to the ferrite particles used as the core material. If the amount of resin coating is less than 0.1% by mass, it becomes difficult to sufficiently coat the surface of the ferrite particles with resin, making it difficult to obtain the desired charge imparting ability. Furthermore, if the amount of resin coating exceeds 10% by mass, aggregation of carrier particles occurs during manufacturing, which is undesirable because it reduces productivity such as yield and also causes fluctuations in developer properties such as the fluidity of the developer or the charge imparting ability to toner in the actual machine.

[0050] (3) Additives The resin coating layer may contain additives intended to control the electrical resistance, charge amount, and charging rate of carriers, such as conductive agents and charge control agents. Examples of conductive agents include conductive carbon, oxides such as titanium oxide and tin oxide, or various organic conductive agents. However, since conductive agents have low electrical resistance, adding too much conductive agent can easily cause charge leakage. Therefore, the content of the conductive agent is preferably 0.25% to 20.0% by mass relative to the solid content of the coating resin, more preferably 0.5% to 15.0% by mass, and even more preferably 1.0% to 10.0% by mass.

[0051] Examples of charge control agents include various charge control agents commonly used for toners, and silane coupling agents. The types of charge control agents and coupling agents are not particularly limited, but charge control agents such as nigrosine-based dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, as well as aminosilane coupling agents and fluorine-based silane coupling agents, can be preferably used. The content of the charge control agent is preferably 0.25% to 20.0% by mass, more preferably 0.5% to 15.0% by mass, and even more preferably 1.0% to 10.0% by mass, relative to the solid content of the coating resin.

[0052] (4) Charge When the amount of charge (30 min value) by the carrier is measured by the method described later, it is possible to achieve a high charge of 50 μc / g or more by using the carrier core material according to the present invention, an even higher charge of 55 μc / g or more can be achieved, and an even higher charge of 60 μc / g or more can be achieved.

[0053] (5) Static electricity buildup When the amount of charge (10 sec value) and the amount of charge (60 sec value) by the carrier are measured by the method described later, and the charge rise is determined by the calculation formula described later, a good charge rise of 1.5 or less can be achieved by using the carrier core material according to the present invention, an even better charge rise of 1.4 or less can be achieved by appropriately adjusting the La content within the range specified in the present invention, an even better charge rise of 1.3 or less can be achieved, and an even better charge rise of 1.2 or less can be achieved.

[0054] 3. Electrophotographic developer Next, embodiments of the electrophotographic developer according to the present invention will be described. The electrophotographic developer includes the above-mentioned electrophotographic developer carrier and toner.

[0055] As the toner constituting the electrophotographic developer, for example, polymerized toner produced by polymerization and pulverized toner produced by pulverization can both be preferably used. These toners may contain various additives and can be any toner as long as they can be used in combination with the carrier as an electrophotographic developer.

[0056] Toner volume average particle size (D 50 The volume average particle size (D) of the toner is preferably 2 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less. 50 If the range is within that range, an electrophotographic developer capable of producing high-quality electrophotographic prints can be obtained.

[0057] The mixing ratio of carrier to toner, i.e., the toner concentration, is preferably 3% by mass or more and 15% by mass or less. An electrophotographic developer containing toner at this concentration makes it easier to obtain the desired image density and can better suppress fogging and toner scattering.

[0058] On the other hand, when using the electrophotographic developer as a replenishment developer, it is preferable that the amount of toner is 2 to 50 parts by mass per 1 part by mass of carrier.

[0059] The above-described electrophotographic developer can be suitably used in various electrophotographic developing devices that employ a magnetic brush development method, in which a carrier is attracted and attached to a magnetic drum or the like by magnetic force to form a brush-like structure for transporting toner, and the toner is attached to an electrostatic latent image formed on a photoreceptor or the like while a bias electric field is applied to form a visible image. The electrophotographic developer can be used not only in electrophotographic developing devices that use a DC bias electric field when applying the bias electric field, but also in electrophotographic developing devices that use an alternating bias electric field, which is a DC bias electric field superimposed with an AC bias electric field.

[0060] 4. Manufacturing method The following describes the ferrite powder, the carrier core material for electrophotographic developer, the carrier for electrophotographic developer, and the method for manufacturing the electrophotographic developer according to the present invention.

[0061] 4-1. Carrier core material The carrier core material according to the present invention can be manufactured as follows.

[0062] First, the above composition formula ((MO) x (Fe2O3) y After weighing an appropriate amount of raw materials to obtain the desired ferrite composition represented by (wherein M is Mn, or at least one metallic element selected from the group consisting of Mn and Fe, Mg, Cu, Zn, Ni, Li, and x+y=100mol%), the materials are ground and mixed in a ball mill or vibratory mill for 0.5 hours or more, preferably 1 hour or more and 20 hours or less.

[0063] Specifically, the raw materials are weighed and ground together so that Fe and the desired M element are at values ​​x and y, respectively. Fe2O3 can be suitably used as the Fe raw material. For the M element raw material, oxides, hydroxides, carbonates, etc. of each M element can be used. For example, if the M element is Mn, MnO2, Mn2O3, Mn3O4, and MnCO3 can be used as Mn raw materials (M element raw materials). If the M element is Mg, Mg(OH)2, MgCO3, etc. can be used as Mg raw materials (M element raw materials). The same applies if the M element is any other element.

[0064] Furthermore, the La raw material is weighed so that the La content is within the desired range, and added to the Fe raw material and the M element raw material. Similarly, when adding Sr or Ca, the Sr raw material or Ca raw material is weighed so that it is within the desired range, and added to the Fe raw material and the M element raw material.

[0065] As the La raw material, La2O3 (lanthanum(III) oxide) or La2(CO3)3 can be used. As the Sr raw material, SrO, Sr(OH)2, SrCO3, etc. can be used. As the Ca raw material, CaO, Ca(OH)2, CaCO3, etc. can be used.

[0066] It is preferable to adjust the viscosity of the slurry obtained by grinding and mixing the raw materials in this manner to 2 poise or more and 4 poise or less by adding a dispersant, binder, etc., as needed. In this case, polyvinyl alcohol or polyvinylpyrrolidone can be used as the binder. If necessary, calcination can be performed at 800°C to 1200°C to advance the ferrite reaction. Calcination is performed by grinding the weighed raw materials in a dry media mill (vibration mill, 1 / 8 inch diameter stainless steel beads) for 2 to 24 hours, forming the resulting pulverized material into pellets using a roller compactor, and then calcining at 800°C to 1200°C under air. The resulting calcined material is further ground in a ball mill or vibration mill, etc., and then the slurry is prepared as described above.

[0067] Granules are obtained by spraying the slurry, which has been adjusted as described above, using a spray dryer and drying it. In this case, the granulation conditions are preferably such that the discharge rate is between 20 Hz and 50 Hz, the atomizer disc rotation speed is between 11,000 rpm and 20,000 rpm, and the drying temperature is between 100°C and 500°C. For example, to obtain ferrite particles with an apparent density within the above range, it is preferable to set the atomizer disc rotation speed to between 11,000 rpm and 16,000 rpm and the drying temperature to between 150°C and 300°C.

[0068] Next, it is preferable to classify the granules before firing them to remove fine particles contained in the granules, in order to obtain ferrite particles with uniform particle size. The classification of the granules can be carried out using known methods such as air flow classification or sieving.

[0069] Next, the classified granules are calcined. It is preferable to perform a primary calcination to remove binders and other substances as needed, followed by a main calcination. When performing the primary calcination, it is preferable to set the calcination temperature between 600°C and 1100°C.

[0070] Furthermore, the main firing is preferably carried out in an inert or weakly oxidizing atmosphere, at a temperature of 1100°C to 1300°C for 4 to 24 hours. If the firing temperature is below 1100°C, sintering will not proceed well, and internal voids are likely to occur, potentially reducing strength. If the firing temperature exceeds 1300°C, excessive sintering will occur, potentially degrading the shape and reducing fluidity. The heating rate to reach the main firing temperature is preferably in the range of 100°C / h to 500°C / h.

[0071] Subsequently, the calcined material is crushed and classified to obtain ferrite particles. The particle size is adjusted to the desired size using existing classification methods such as wind classification, mesh filtration, or sedimentation. For dry recovery, recovery can also be performed using a cyclone or similar device. When adjusting the particle size, two or more of the aforementioned classification methods may be selected and implemented, or one classification method may be used with modified conditions to remove coarse and fine particles.

[0072] Subsequently, if necessary, the surface resistance of the ferrite particles can be adjusted by performing a surface oxidation treatment by heating the surface of the ferrite particles at a low temperature. The surface oxidation treatment can be performed by heat-treating the ferrite particles in an oxygen-containing atmosphere such as air using a rotary electric furnace or a batch electric furnace at a temperature of 400°C to 730°C, preferably 450°C to 650°C. If the heating temperature during the surface oxidation treatment is lower than 400°C, the surface of the ferrite particles may not be sufficiently oxidized, and the desired surface resistance characteristics may not be obtained. On the other hand, if the heating temperature is higher than 730°C, in the case of manganese-containing ferrite, the oxidation of manganese progresses too much, and the magnetization of the ferrite particles decreases, which is undesirable. To form a uniform oxide film on the surface of the ferrite particles, it is preferable to use a rotary electric furnace. However, this surface oxidation treatment is an optional step.

[0073] 4-2. Carriers for electrophotographic developers The electrophotographic developer carrier according to the present invention has a resin coating layer on the surface of a carrier core material composed of the above-mentioned ferrite particles. The resin constituting the resin coating layer is as described above. When forming the resin coating layer on the surface of the ferrite particles, known methods such as the brush application method, the spray drying method using a fluidized bed, the rotary drying method, and the immersion drying method using a universal stirrer can be employed. To improve the ratio of the resin coating area to the surface of the ferrite particles (resin coating rate), it is preferable to employ the spray drying method using a fluidized bed. Regardless of which method is employed, the resin coating treatment can be performed on the carrier core material once or multiple times. The resin coating liquid used when forming the resin coating layer may contain the above-mentioned additives. Furthermore, since the amount of resin coating on the surface of the carrier core material is as described above, a detailed explanation is omitted here.

[0074] After applying a resin coating liquid to the surface of the carrier core material, baking may be performed using an external heating method or an internal heating method as needed. For external heating, a fixed or fluidized electric furnace, a rotary electric furnace, or a burner furnace can be used. For internal heating, a microwave furnace can be used. When using a UV-curing resin as the coating resin, a UV heater should be used. Baking must be performed at a temperature above the melting point or glass transition point of the coating resin. When using a thermosetting resin or a condensation-crosslinking resin as the coating resin, baking must be performed at a temperature at which the curing of these resins is sufficiently advanced.

[0075] 4-3. Electrophotographic Developer Next, a method for producing an electrophotographic developer according to the present invention will be described. The electrophotographic developer according to the present invention comprises the above-mentioned electrophotographic developer carrier and toner. As described above, either polymerized toner or pulverized toner can be preferably used as the toner.

[0076] Polymerized toner can be manufactured by known methods such as suspension polymerization, emulsion polymerization, emulsion agglutination, ester extension polymerization, and phase transition emulsification. For example, a colored dispersion obtained by dispersing a colorant in water using a surfactant is mixed and stirred with a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium. The polymerizable monomer is emulsified and dispersed in the aqueous medium, and polymerization is carried out while stirring and mixing. Then, a salting-out agent is added to salt out the polymer particles. Polymerized toner can be obtained by filtering, washing, and drying the particles obtained by salting out. After that, if necessary, an external additive may be added to the dried toner particles.

[0077] Furthermore, in manufacturing these polymerized toner particles, a toner composition containing polymerizable monomers, surfactants, polymerization initiators, colorants, etc., is used. Fixing improvers and charge control agents may be added to this toner composition.

[0078] For example, pulverized toner can be obtained by thoroughly mixing binder resin, colorant, charge control agent, etc., in a mixer such as a Henschel mixer, then melt-kneading and uniformly dispersing the mixture in a twin-screw extruder, etc., cooling, finely pulverizing it with a jet mill, etc., and then classifying it, for example, with an air classifier, etc., to obtain toner with the desired particle size. If necessary, wax, magnetic powder, viscosity modifier, and other additives may be included. Furthermore, external additives can be added after classification.

[0079] Next, the present invention will be specifically described with reference to examples and comparative examples. However, the present invention is not limited to the following examples. [Examples]

[0080] (1) Carrier core material In Example 1, Fe, Mn, and Mg raw materials were weighed in molar ratios of Fe2O3:50.0, MnO equivalent:40.0, and MgO equivalent:10.0, respectively. In addition, La raw material was weighed in a molar ratio of La:0.30 to 100 of these ferrite raw materials. Here, ferric oxide was used as the Fe2O3 raw material, trimanganese tetroxide as the MnO raw material, magnesium oxide as the MgO raw material, and lanthanum(III) oxide as the La raw material.

[0081] Water was added to the weighed raw material and it was finely ground using a bead mill or the like to obtain a slurry. The particle size (primary particle diameter after grinding) of the obtained slurry was measured using a laser diffraction particle size distribution analyzer (LA-950, Horiba, Ltd.), and D 50 It is approximately 2.2 μm, D 90 It was 3.3 μm.

[0082] Furthermore, an appropriate amount of dispersant was added to the slurry prepared as described above, and 0.4% by mass of PVA (polyvinyl alcohol) was added as a binder relative to the solid content (amount of calcined material in the slurry). Then, granulation and drying were performed using a spray dryer. The particle size of the resulting granules was adjusted.

[0083] Subsequently, the granulated material was subjected to final firing in a tunnel-type electric furnace by holding it at a firing temperature (holding temperature) of 1230°C for 3 hours in an atmosphere with an oxygen concentration of 0.3 volume%. During this time, the heating rate was 150°C / hour and the cooling rate was 110°C / hour. The resulting fired material was crushed using a hammer crusher, and then classified using a gyroshifter (vibrating screen) and a turboclassifier (airflow classifier) ​​to adjust the particle size. Low-magnetic-force materials were separated by magnetic separation to obtain ferrite particles.

[0084] The obtained ferrite particles were subjected to surface oxidation treatment in a rotary electric furnace equipped with a hot section and a cooling section following the hot section, and then cooled to obtain ferrite particles that had undergone surface oxidation treatment. In the surface oxidation treatment, an oxide film was formed on the surface of the ferrite particles at 450°C in an atmospheric environment in the hot section. The main manufacturing conditions for the ferrite particles of Example 1 are shown in Table 1.

[0085] (2) Carrier for electrophotographic developer The ferrite particles described above were used as a core material, and the ferrite particles were coated with a silicone resin as described below to obtain the carrier of Example 1.

[0086] First, a silicone resin solution (10% by mass of resin solids) was prepared by mixing silicone resin and toluene. The ferrite particles of Example 1 were mixed with this resin solution using a universal stirrer to coat the surface of the ferrite particles with the resin solution. At that time, an amount of resin solution was used such that the resin solids content was 0.5% by mass relative to the ferrite particles. Subsequently, the ferrite particles coated with the resin solution were heated in a heat exchange type stirring and heating device at 220°C for 2 hours while stirring, to volatilize the volatile components contained in the resin solution and dry the ferrite particles. This yielded the electrophotographic developer carrier of Example 1, which has a resin coating layer on the surface of the ferrite particles.

[0087] (3) Electrophotographic developer The above-mentioned electrophotographic developer carrier and toner were mixed using a turbulent mixer for 30 minutes to obtain a developer (toner concentration 7.0% by weight). Here, commercially available negative polarity toner (cyan toner, average particle size approximately 6.0 μm) used in full-color printers was used. [Examples]

[0088] In this example, the carrier core material for Example 2 was manufactured in the same manner as in Example 1, except that the La raw material was weighed so that the molar ratio was 100 parts ferrite raw material to 0.01 parts La. The main manufacturing conditions for Example 2 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. [Examples]

[0089] In this example, the carrier core material for Example 3 was manufactured in the same manner as in Example 1, except that the La raw material was weighed so that the molar ratio was ferrite raw material:100 to La:0.05. The main manufacturing conditions for Example 3 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. [Examples]

[0090] In this example, the carrier core material of Example 4 was manufactured in the same manner as in Example 1, except that the La raw material was weighed so that the molar ratio was 1.00 for ferrite raw material:100. The main manufacturing conditions of Example 4 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this electrophotographic developer carrier. [Examples]

[0091] In this example, the carrier core material of Example 5 was manufactured in the same manner as in Example 1, except that the La raw material was weighed so that the molar ratio of La to ferrite raw material was 100. The main manufacturing conditions of Example 5 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. [Examples]

[0092] In this example, the carrier core material of Example 6 was manufactured in the same manner as in Example 1, except that, in addition to La, SrO raw material was weighed and added so that the molar ratio was ferrite raw material:100 to Sr:0.1. However, SrCO3 was used as the SrO raw material. Similarly, SrCO3 was also used as the Sr raw material in Examples 7, 8, Comparative Example 3, Comparative Example 6, and Comparative Example 7, which will be described later. The main manufacturing conditions for Example 6 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. [Examples]

[0093] In this example, the carrier core material of Example 7 was manufactured in the same manner as in Example 1, except that, in addition to La, Sr raw material was weighed and added so that the molar ratio was 0.5 for 100 parts ferrite raw material. The main manufacturing conditions of Example 7 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this electrophotographic developer carrier. [Examples]

[0094] In this example, the carrier core material of Example 8 was manufactured in the same manner as in Example 1, except that, in addition to La, Sr raw material was weighed and added so that the molar ratio was 2.0 for 100 parts ferrite raw material. The main manufacturing conditions of Example 8 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this electrophotographic developer carrier. [Examples]

[0095] In this example, the carrier core material of Example 9 was manufactured in the same manner as in Example 1, except that Ca raw material was weighed and added in addition to La so that the molar ratio was Ca:0.5 to 100 of the ferrite raw material. However, CaCO3 was used as the Ca raw material. Similarly, CaCO3 was also used as the Ca raw material in Comparative Examples 4 and 5, which will be described later. The main manufacturing conditions of Example 9 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. [Examples]

[0096] In this example, the Fe and Mn raw materials were weighed in molar ratios of Fe2O3:65.0 and MnO equivalent:35.0, respectively, and the carrier core material of Example 10 was manufactured in the same manner as in Example 1, except that the Mg raw material was not used. The main manufacturing conditions of Example 10 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and the electrophotographic developer was manufactured using this carrier. [Examples]

[0097] In this example, the carrier core material for Example 11 was manufactured in the same manner as in Example 1, except that the Fe, Mn, and Mg raw materials were weighed in molar ratios of Fe2O3:60.0, MnO equivalent:39.5, and MgO equivalent:0.5, respectively. The main manufacturing conditions for Example 11 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier. Comparative Example

[0098] [Comparative Example 1] In this comparative example, ferrite particles for Comparative Example 1 were manufactured in the same manner as in Example 1, except that La was not added. The main manufacturing conditions for Comparative Example 1 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the ferrite particles were used as a core material, and an electrophotographic developer was manufactured using this carrier.

[0099] [Comparative Example 2] In this comparative example, the carrier core material for Comparative Example 2 was manufactured in the same manner as in Example 1, except that the La raw material was weighed so that the molar ratio of La to ferrite raw material was 100. The main manufacturing conditions for Comparative Example 2 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0100] [Comparative Example 3] In this comparative example, the carrier core material for Comparative Example 3 was manufactured in the same manner as in Example 1, except that La was not added, and Sr raw material was weighed and added in a molar ratio of 0.5 Sr to 100 ferrite raw material. The main manufacturing conditions for Comparative Example 3 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0101] [Comparative Example 4] In this comparative example, the carrier core material for Comparative Example 4 was manufactured in the same manner as in Example 1, except that La was not added, and Ca raw material was weighed and added in a molar ratio of Ca:0.5 to ferrite raw material:100. The main manufacturing conditions for Comparative Example 4 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0102] [Comparative Example 5] In this comparative example, the Fe and Mg raw materials were weighed in molar ratios of Fe2O3:80.0 and MgO equivalent:20.0, respectively. The carrier core material for Comparative Example 5 was manufactured in the same manner as in Example 1, except that Mn raw material was not used and La was not added, while Ca raw material was weighed and added in molar ratios of Ca:1.0 to ferrite raw material:100. The main manufacturing conditions for Comparative Example 5 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0103] [Comparative Example 6] In this comparative example, the Fe and Mn raw materials were weighed in molar ratios of Fe2O3:65.0 and MnO equivalent:35.0, respectively. Mg raw material was not used, and La was not added. On the other hand, Sr raw material was weighed and added in molar ratios of ferrite raw material:100 to Sr:0.5 mol%, except that the carrier core material for Comparative Example 6 was manufactured in the same manner as in Example 1. The main manufacturing conditions for Comparative Example 6 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0104] [Comparative Example 7] In this comparative example, the carrier core material for Comparative Example 7 was manufactured in the same manner as in Example 1, except that Fe, Mn, and Mg raw materials were weighed in molar ratios of Fe2O3:60.0, MnO equivalent:39.5, and MgO equivalent:0.5, respectively, and no La was added, while Sr raw material was weighed and added in molar ratios of ferrite raw material:100 to Sr:0.5. The main manufacturing conditions for Comparative Example 7 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0105] [Comparative Example 8] In this comparative example, the carrier core material for Comparative Example 8 was manufactured in the same manner as in Example 1, except that Fe and Mg raw materials were weighed in molar ratios of Fe2O3:60.0 and MgO equivalent:20.0, respectively, and La raw material was weighed and added in a molar ratio of La:1.0 to ferrite raw material:100, instead of using Mn raw material. The main manufacturing conditions for Comparative Example 8 are shown in Table 1. Furthermore, a carrier for electrophotographic developer was manufactured in the same manner as in Example 1, except that the carrier core material was used, and an electrophotographic developer was manufactured using this carrier.

[0106] <evaluation> The ferrite particles obtained in each example and comparative example as described above were evaluated for their magnetic, electrical, and mechanical properties. Furthermore, for the electrical properties, the amount of charge and charge rise time were evaluated using the electrophotographic developer obtained in each example and comparative example as described above. The evaluation methods / measurement methods and evaluation results are described below.

[0107] 1. Evaluation Method / Measurement Method 1-1.ICP mass spectrometry In ICP mass spectrometry, first, 0.2 g of ferrite particles produced in each example and comparative example was weighed, and 60 ml of pure water was mixed with 20 ml of 1 N hydrochloric acid and 20 ml of 1 N nitric acid. This mixture was heated to prepare an aqueous solution in which the ferrite particles were completely dissolved. An ICP analyzer (Shimadzu ICPS-1000IV) was used to measure the content of Fe, Mn, Mg, Sr, and La (wt%), and the composition of the ferrite particles constituting each carrier core material was determined.

[0108] 1-2. Magnetic properties Saturation magnetization, remanent magnetization, and coercivity were measured using a vibrating sample type magnetic measuring device (model: VSM-C7-10A (manufactured by Toei Kogyo Co., Ltd.)). The specific measurement procedure is as follows: First, ferrite particles produced in each example and comparative example were used as samples, and the samples were filled into cells with an inner diameter of 5 mm and a height of 2 mm and set in the above device. Then, a magnetic field was applied and swept down to 1 K·1000 / 4π·A / m (=1 kOe). Next, the applied magnetic field was decreased and a hysteresis curve was created on recording paper. From the data of this curve, the magnetization at an applied magnetic field of 1 K·1000 / 4π·A / m was read, and the saturation magnetization (σs), remanent magnetization (σr), and coercivity (Hc) were determined.

[0109] 1-3. Electrical Characteristics (1) Resistor The ferrite particles produced in each example and comparative example were used as samples, and their resistance (Ω) was determined under normal temperature and humidity conditions (23°C, 55% relative humidity) using the following procedure. First, non-magnetic parallel plate electrodes (10 mm × 40 mm) were placed opposite each other with a spacing of 6.5 mm, and 200 mg of the sample was packed between them. The sample was held between the parallel plate electrodes by a magnet attached to the parallel plate electrodes (surface magnetic flux density: 1500 Gauss, magnet area in contact with electrodes: 10 mm × 30 mm). A voltage of 1000 V was then applied between the opposing parallel plate electrodes, and the resistance was measured using an electrometer (KEITHLEY, insulation resistance meter model 16517A). At that time, the sample was exposed for 12 hours or more in a constant temperature and humidity chamber where the ambient temperature and humidity were adjusted to the above-mentioned normal temperature and humidity conditions.

[0110] (2) Charge

[0111] 50 g of the electrophotographic developer prepared in each example and comparative example was used as a sample, and each developer was exposed to the respective environmental conditions described below for 12 hours or more. After that, the developer was placed in a 50 cc glass bottle and stirred at a rotation speed of 100 rpm. The developer was then withdrawn 10 seconds and 60 seconds after the start of stirring, respectively, and used as a sample for measuring the amount of charge.

[0112] As a charge measurement device, a magnetic roll was constructed by arranging eight magnets (magnetic flux density 0.1T) with alternating north and south poles inside a cylindrical aluminum tube (hereinafter referred to as a sleeve) with a diameter of 31 mm and a length of 76 mm. A cylindrical electrode with a 5.0 mm gap from the sleeve was placed on the outer circumference of the sleeve.

[0113] After uniformly adhering 0.5g of the above sample onto the sleeve, and while keeping the outer aluminum tube fixed, a DC voltage of 2000V was applied between the outer electrode and the sleeve for 60 seconds while rotating the inner magnetic roll at 100 rpm, thereby transferring the toner in the developer to the outer electrode. At this time, an electrometer (KEITHLEY insulation resistance meter model 6517A) was connected to the cylindrical electrode to measure the amount of charge of the transferred toner. After 60 seconds, the applied voltage was turned off, the rotation of the magnetic roll was stopped, the outer electrode was removed, and the weight of the toner transferred to the electrode was measured. The amount of charge was calculated from the measured charge and the weight of the transferred toner.

[0114] (3) Static buildup The amount of charge measured for a sample stirred for 10 seconds was designated as the "10-sec value," and the amount of charge measured for a sample stirred for 60 seconds was designated as the "60-sec value." The rise time of the charge was then calculated based on the following formula. The amount of charge measured for a sample stirred for 30 minutes ("30-min value") was also measured.

[0115] Charge rise time = 60sec value / 10sec value

[0116] 1-4. Powder properties (1) Apparent density (AD) This apparent density was measured in accordance with JIS Z2504:2012 (Test method for apparent density of metal powders).

[0117] (2) BET specific surface area The ferrite particles produced in each example and comparative example were used as samples, and the BET specific surface area was determined using a specific surface area analyzer (Macsorb HM model-1208, Mountec Co., Ltd.) according to the following procedure. First, approximately 20 g of the sample was placed in a glass petri dish and then degassed to -0.1 MPa in a vacuum dryer. After degassing and confirming that the vacuum level in the glass petri dish had reached -0.1 MPa or lower, it was heated at 200°C for 2 hours. Approximately 5 to 7 g of the pre-treated sample was placed in a standard sample cell dedicated to the above-mentioned specific surface area analyzer. The mass of the sample placed in the standard sample cell was accurately weighed using a precision balance. The standard sample cell containing the sample was then set in the measurement port, and the BET specific surface area was measured using the single-point method at a temperature of 10°C to 30°C and a relative humidity of 20% to 80%. At the end of the measurement, the mass of the sample was entered, and the calculated value was taken as the measured value of the BET specific surface area.

[0118] (3) Volume-average particle size (D 50 ) Volume-average particle size (D 50 The volume-average particle size was measured using a Microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd. as follows: Ferrite particles produced in each example and comparative example were used as samples. 10 g of each sample and 80 ml of water were placed in a 100 ml beaker, 2 to 3 drops of dispersant (sodium hexametaphosphate) were added, and the mixture was dispersed for 20 seconds using an ultrasonic homogenizer (UH-150 model manufactured by SMT.Co.LTD.) at output level 4. The bubbles formed on the surface of the beaker were removed to prepare the sample. The volume-average particle size of the sample was then measured using the Microtrac particle size analyzer.

[0119] (4) Flow rate (FR) The fluidity was measured in accordance with JIS Z 2502:2012 (Test method for fluidity of metal powders). In this test, 50 g of ferrite particles produced in each example and comparative example was poured into a funnel with an orifice diameter of 2.63 mm, and the time (seconds) it took for the particles to flow down was measured and defined as the fluidity.

[0120] 2. Evaluation Results Tables 2 to 4 show the measurement results for each of the above evaluation items.

[0121] (1) Composition Table 2 shows the content percentages of each component as determined by ICP mass spectrometry. In Table 2, the content percentages of La, Sr, and Ca represent the content (mol%) of La, Sr, or Ca elements when the total amount of Fe2O3, MnO (an oxide of element M), and MgO contained in each ferrite particle is taken as 100 mol. As shown in Table 2, the La content in the carrier core materials of Examples 1 to 11 is within the range specified by the present invention.

[0122] (2) Magnetic properties As shown in Table 3, the carrier core materials of Examples 1 to 11 have a saturation magnetization of 59.3 (Am). 2 / kg)~67.3(Am 2 ( / kg), residual magnetization is 0.4 (Am 2 / kg~1.8Am 2 The holding force ( / kg) was within the range of 9.5 (1000 / 4π·A / m) to 15.5 (1000 / 4π·A / m). The carrier core materials of Examples 1 to 5 and Comparative Example 2 differ in their La content, but are otherwise common. Comparative Example 1 is the same carrier core material as Example 1, except that it does not contain La. From these comparisons, it was confirmed that the higher the La content in the carrier core material, the more likely it is to obtain a carrier core material with a lower saturation magnetization value, a higher remanent magnetization value, and a higher coercivity value. Furthermore, it was confirmed that by including La within the range specified in the present invention (0.01 mol% to 2.0 mol%), a magnetization within a range suitable for a carrier core material of an electrophotographic developer can be obtained.

[0123] (3) Electrical characteristics As shown in Table 3, the carrier core materials of Examples 1 to 11 showed resistance values ​​in the range of 7.8 (logΩ) to 8.5 (logΩ), charge rise time of 1.17 to 1.45, and charge amount (30 min value) in the range of 60.1 (μC / g) to 66.8 (μC / g). On the other hand, the carrier core materials of Comparative Examples 1 to 7 showed resistance values ​​in the range of 6.5 (logΩ) to 8.5 (logΩ), charge rise time of 1.60 to 1.73, and charge amount (30 min value) in the range of 49.3 (μC / g) to 61.2 (μC / g). Furthermore, the carrier core material of Comparative Example 8 showed an unmeasurable resistance value, a charge rise time of 1.78, and a charge amount (30 min value) in the range of 44.4 (μC / g).

[0124] Comparing each example with each comparative example, it was confirmed that the carrier core material according to the present invention containing La within the above range exhibits significantly superior values ​​in charge rise and charge amount compared to the carrier core material of the comparative example that does not contain La within the above range. The carrier core material of Comparative Example 8 has a La content of 1.00 mol%, which is within the range specified in the present invention, but the ferrite particles do not contain Mn and do not have the ferrite composition specified in the present invention. The carrier core material of Comparative Example 8 has low magnetization and resistance values, and in particular the resistance is very low, making it difficult to use as a carrier core material for electrophotographic developers from the viewpoint of carrier scattering, and it was confirmed that the effect of La addition cannot be obtained.

[0125] Regarding resistance values, it was confirmed from Examples 1 to 5, and Comparative Examples 1 and 2, that the higher the La content in the carrier core material, the lower the resistance value tends to be.

[0126] Regarding the amount of charge, it was confirmed from Examples 1 to 5 and Comparative Examples 1 and 2 that a higher La content in the carrier core material, within the range of 0 mol% to 2.00 mol%, resulted in a carrier core material with a higher amount of charge. On the other hand, it was confirmed that the effect of La addition on the amount of charge saturates at around 2.00 mol%.

[0127] Regarding the charge rise, a peak was observed in the range of approximately 0.3 mol% to 1.0 mol%. When the La content was 0.3 mol%, the value was 1.27, and when it was 1.0 mol%, it was 1.17, both values ​​closer to "1" compared to other examples, confirming extremely good charge rise. On the other hand, when the La content was less than 0.3 mol%, the charge rise value tended to decrease with increasing La content, and when it exceeded 1.0 mol%, the charge rise value tended to increase with increasing La content.

[0128] (4) Powder properties As shown in Table 4, the carrier core materials of Examples 1 to 11 have an apparent density (AD) of 2.22 g / cm³. 3 )~2.28(g / cm 3 ), BET specific surface area is 0.086 (m² 2 / g)~0.145(m 2 The fluidity (per g) was within the range of 29.5 (sec / 50g) to 33.2 (sec / 50g). On the other hand, the carrier core materials of Comparative Examples 1 to 8 had an apparent density (AD) of 2.21 g / cm³. 3 )~2.42(g / cm 3 ), BET specific surface area is 0.066 (m² 2 / g)~0.120(m 2 The fluidity (per g) was within the range of 28.1 (sec / 50g) to 35.3 (sec / 50g).

[0129] Examples 1, 6-9 are compared with Comparative Examples 1, 3, and 4. When Sr or Ca is added to the carrier core material represented by the above compositional formula, the BET specific surface area increases with surface roughness compared to the case without Sr and Ca. However, the carrier core materials of Examples 7 and 9 contain La along with Sr or Ca, and the BET specific surface area is 0.122 (g / cm²). 3 ), 0.107 (g / cm³) 3 ) On the other hand, the carrier core material of Comparative Example 3 and Comparative Example 4 does not contain La, and has a concentration of 0.101 (g / cm³). 3 ), 0.089 (g / cm³) 3) This means that the carrier core materials of Comparative Examples 3 and 4, which contain Sr or Ca but do not contain La, have a smaller BET specific surface area compared to the carrier core materials of Examples 7 and 9. Nevertheless, the fluidity of the carrier core materials of Examples 6 and 9 is 29.5 sec / 50g and 31.6 sec / 50g, respectively, while the fluidity of the carrier core materials of Comparative Examples 3 and 4 is 35.2 sec / 50g and 33.2 sec / 50g, respectively, indicating a decrease in fluidity. This is thought to be because the particle shape of the carrier core materials of Comparative Examples 3 and 4 is worse compared to the carrier core materials of Examples 6 and 9. If the particle shape is not good, rapid stirring and mixing with toner cannot be performed, resulting in a decrease in the amount of charge and charge rise. Therefore, in order to make the BET specific surface area of ​​the carrier core material of Comparative Examples 3 and 4 similar to that of the case without Sr or Ca, one method is to lower the firing temperature. However, lowering the firing temperature makes it easy for internal voids to form, resulting in a lower specific gravity, making it difficult to increase fluidity, and there is a risk of carrier scattering, so this is undesirable. [Table 1]

[0130] [Table 2]

[0131] [Table 3]

[0132] [Table 4] [Industrial applicability]

[0133] According to the carrier core material of the present invention, it is possible to provide ferrite particles with high charge imparting ability to toner and good charge rise time, a carrier core material for electrophotographic developers, a carrier for electrophotographic developers, and an electrophotographic developer.

Claims

1. Composition formula (MO) ｘ (Fe ２ O ３ ) ｙ A carrier core material characterized by being composed of ferrite particles represented as (where M is Mn and Mg, x > 0, x + y = 100 mol%), and containing 0.05 mol% to 2.0 mol% of La.

2. The carrier core material according to claim 1, comprising Sr or Ca in an amount of 0.1 mol% or more and 2.0 mol% or less.

3. The above compositional formula is (MnO) ａ (MgO) ｂ (Fe ２ O ３ ) ｃ The carrier core material according to claim 1 or claim 2, which is represented by (where 25 ≤ a ≤ 55, 0 ≤ b ≤ 20, 45 ≤ c ≤ 65, a + b + c = 100 (mol%)).

4. A carrier for an electrophotographic developer, comprising a carrier core material according to any one of claims 1 to 3, and a resin coating layer provided on the surface of the carrier core material.

5. An electrophotographic developer characterized by comprising the carrier and toner for the electrophotographic developer described in claim 4.

6. The electrophotographic developer according to claim 5, used as a replenishment developer.

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