Carrier for electrophotographic image formation, developer for electrophotographic image formation, electrophotographic image forming method, electrophotographic image forming apparatus, and process cartridge

Abstract

To provide a carrier for electrophotographic image formation that can prevent a reduction in the resistance and a reduction in the electrification of a carrier even in long-term printing, and can prevent the occurrence of carrier adhesion and background fogging.SOLUTION: A carrier for electrophotographic image formation includes, in a coating layer, conductive spherical inorganic fine particles (A) and conductive acicular inorganic fine particles (B). The conductive spherical inorganic fine particles (A) have a diameter of 0.30 μm or more and 0.90 μm or less. The conductive acicular inorganic fine particles (B) have a long side with a length of 1.30 μm or more and 1.90 μm or less and a short side with a length of 0.05 μm or more and 0.30 μm or less. At least one of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) contain tin oxide doped with an antimony compound. The content of the conductive acicular inorganic fine particles (B) included in the coating layer is 20 mass% or more and 40 mass% or less based on the total amount of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a carrier for electrophotographic image formation, a developer for electrophotographic image formation, an electrophotographic image forming method, an electrophotographic image forming apparatus, and a process cartridge. [Background technology]

[0002] In recent years, with the increasing trend in printing speed, there has been a strong demand for carriers that have the ability to impart charge to toner more quickly and have a life that can withstand long-term high-speed printing.

[0003] During long-term printing, fluctuations in carrier charge and resistance can occur if toner spent (degraded toner adheres to the carrier surface) or if the carrier coating layer is worn away due to repeated collisions between carriers or between carrier and toner. If the carrier charge decreases, the carrier will no longer be able to impart an appropriate charge to the toner, which can lead to toner scattering (toner accumulation outside the developing device) and fogging (toner development in non-printed areas of the print medium). Furthermore, if the carrier resistance decreases, carrier adhesion (carrier development in printed areas) is more likely to occur.

[0004] As a technique for suppressing fluctuations in carrier charge and resistance, for example, Patent Document 1 describes that including conductive fine particles in the coating layer makes it possible to prevent changes in resistance and charge over a long period of time. Also, Patent Document 2 describes that including resin fine particles in the coating layer and applying an impact before crosslinking makes the coating resin harder, thereby suppressing decreases in charge and resistance even during long-term use. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, when the carrier surface is worn away during long-term printing, the amount of exposed conductive particles on the carrier surface changes, causing a problem of unstable carrier resistance. Also, in Patent Document 2, if the hardness of the resin is increased, the risk of toner spent increases, which may lead to a decrease in charging.

[0006] An object of the present invention is to provide a carrier for electrophotographic image formation that can suppress a decrease in the resistance and charge of the carrier even under long-term printing, and can prevent the occurrence of carrier adhesion and background fogging. [Means for solving the problem]

[0007] The electrophotographic image forming carrier of the present invention as a means for solving the above problems comprises: A carrier for electrophotographic image formation comprising core particles and a coating layer covering the core particles, wherein the coating layer contains conductive spherical inorganic fine particles (A) and conductive acicular inorganic fine particles (B), The conductive spherical inorganic fine particles (A) have a diameter of 0.30 μm or more and 0.90 μm or less, the conductive acicular inorganic fine particles (B) have a long side of 1.30 μm or more and 1.90 μm or less and a short side of 0.05 μm or more and 0.30 μm or less, At least one of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) contains tin oxide doped with an antimony compound, The content of the conductive acicular inorganic fine particles (B) contained in the coating layer is 20% by mass or more and 40% by mass or less based on the total amount of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B). [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a carrier for electrophotographic image formation that can suppress a decrease in the resistance and charge of the carrier even under long-term printing, and can prevent the occurrence of carrier adhesion and background fogging. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of an electrophotographic image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating an example of a process cartridge according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors have conducted extensive research and have found that a coating layer of an electrophotographic image-forming carrier contains conductive spherical inorganic particles (A) and conductive acicular inorganic particles (B), wherein the conductive spherical inorganic particles (A) have a diameter of 0.30 μm or more and 0.90 μm or less, the conductive acicular inorganic particles (B) have long sides of 1.30 μm or more and 1.90 μm or less and short sides of 0.05 μm or more and 0.30 μm or less, at least one of the conductive spherical inorganic particles (A) and the conductive acicular inorganic particles (B) contains tin oxide doped with an antimony compound, and the content of the conductive acicular inorganic particles (B) in the coating layer is 20% by mass or more and 40% by mass or less with respect to the total amount of the conductive spherical inorganic particles (A) and the conductive acicular inorganic particles (B), thereby making it possible to suppress a decrease in the resistance and charge of the carrier even during long-term printing.

[0011] The shape of the conductive acicular inorganic fine particles (B) makes it easy to form conductive paths that penetrate from the carrier core to the carrier surface, which makes it easy to impart conductivity to the carrier, and even when the coating layer is scraped off, there is no significant change in the amount of exposed conductive acicular fine particles on the carrier surface, which makes it possible to suppress fluctuations in carrier resistance even during long-term printing.

[0012] Furthermore, doping tin oxide with an antimony compound can produce a highly resistivity adjusting agent. This, combined with the shape of the conductive acicular inorganic fine particles (B), creates a synergistic effect, making it easier to impart conductivity to the carrier, allowing carriers with the desired conductivity to be obtained with smaller formulation amounts. This allows the amount of non-magnetic components contained in the coating layer to be reduced, making carrier particles less likely to be transferred, thereby improving carrier adhesion quality.

[0013] On the other hand, if only conductive acicular inorganic particles (B) are used, the formulation amount of conductive inorganic particles will be reduced, which may result in a risk of reduced film durability. Therefore, by using them in combination with conductive spherical inorganic particles (A), the formulation amount can be increased and the conductive spherical inorganic particles (A) can be arranged to fill in areas where conductive acicular inorganic particles (B) are not present, thereby significantly improving durability. Furthermore, the charge control agent contained in the coating layer can be uniformly dispersed, thereby suppressing fluctuations in charge during long-term printing.

[0014] The electrophotographic imaging carrier of the present invention will be described in more detail below.

[0015] (Electrophotographic image forming carrier) The carrier for electrophotographic image formation of the present invention comprises core particles and a coating layer that coats the core particles, and the coating layer contains at least two types of conductive inorganic fine particles.

[0016] <Coating layer> The coating layer covers the surface of the core particles of the carrier for electrophotographic imaging. The coating layer contains at least two or more types of conductive inorganic fine particles and, if necessary, further contains other components such as spherical inorganic fine particles (C), resins, and coupling agents.

[0017] <<Conductive inorganic particles>> The coating layer contains conductive spherical inorganic fine particles (A) and conductive acicular inorganic fine particles (B) as conductive inorganic fine particles.

[0018] The conductive spherical inorganic fine particles (A) are conductive spherical inorganic fine particles. The diameter of the conductive spherical inorganic fine particles (A) is 0.30 μm or more and 0.90 μm or less, and more preferably 0.40 μm or more and 0.70 μm or less. If the diameter is less than 0.30 μm, it becomes difficult to form a conductive path within the carrier coating layer, and as a result, a larger amount is required to achieve the desired conductivity. As a result, the non-magnetic components of the carrier particles increase, resulting in poor carrier adhesion and particle detachment during long-term printing. Furthermore, if the diameter is greater than 0.90 μm, some particles may not be fully contained in the carrier coating layer, leading to the risk of particle detachment.

[0019] The conductive acicular inorganic fine particles (B) are acicular inorganic fine particles having electrical conductivity. The conductive acicular inorganic fine particles (B) are characterized by having a long side of 1.30 μm to 1.90 μm and a short side of 0.05 μm to 0.30 μm. If the long side is greater than 1.90 μm, some particles may not be fully contained in the carrier coating layer, or excessive conductive paths may be formed, resulting in a significant decrease in carrier resistance. If the long side is less than 1.30 μm, it becomes difficult to form conductive paths that penetrate from the core surface to the coating layer surface, making resistance fluctuations more likely to occur during long-term printing.

[0020] The content of the conductive acicular inorganic fine particles (B) is from 20% to 40% by mass based on the total amount of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B). By setting the content to from 20% to 40% by mass, the durability of the carrier can be improved and an appropriate conductive path can be formed in the carrier coating layer, thereby suppressing fluctuations in carrier resistance under long-term printing.

[0021] There are no particular limitations on the method for measuring the diameter of the conductive spherical inorganic fine particles (A) and the lengths of the long and short sides of the conductive acicular inorganic fine particles (B), and these can be appropriately selected depending on the purpose. For example, before the production of the carrier for electrophotographic image formation, they can be measured using the Nanotrac UPA series (manufactured by Nikkiso Co., Ltd.). After the production of the carrier for electrophotographic image formation, they can be confirmed by cutting the coating layer of the carrier for electrophotographic image formation with an FIB and observing the cross section with an SEM, EDX, or the like. Specifically, the electrophotographic imaging carrier was mixed into an embedding resin (a two-part, 30-minute curing epoxy resin manufactured by Devcon), allowed to harden overnight, and then mechanically polished to prepare a rough cross-sectional sample. The cross-sectional sample was polished using a cross-section polisher (SM-09010 manufactured by JEOL) at an acceleration voltage of 5.0 kV and a beam current of 120 μA. The polished cross-section was then photographed using a scanning electron microscope (Merlin manufactured by Carl Zeiss) at an acceleration voltage of 0.8 kV and a magnification of 30,000x. The photographed image was imported into a TIFF file, and the lengths of 100 particles were measured using Image-Pro Plus manufactured by Media Cybernetics, and the average values ​​were calculated. However, the confirmation method is not limited to this. The thickness of the coating layer can also be measured from the captured image in a similar manner. However, since there is variation in the length of each microparticle and there is also variation in the thickness of the coating layer depending on the location, measurements should be taken for a statistically acceptable number of particles.

[0022] At least one of the conductive spherical inorganic particles (A) and the conductive acicular inorganic particles (B) contains tin oxide doped with an antimony compound. Since the conductive inorganic particles contain a highly conductive antimony compound, the carrier can be imparted with high conductivity by simply adding a small amount of conductive inorganic particles. The low content of conductive inorganic particles can prevent the conductive inorganic particles from being detached or the particles from being exposed due to scraping of the coating layer.

[0023] Furthermore, when the conductive inorganic fine particles are surface-treated with tin oxide doped with an antimony compound, even if the conductive inorganic fine particles crumble into fragments in the coating layer, they will not be detached from the coating layer, thereby preventing a decrease in the electrical resistance of the carrier for electrophotographic image formation.

[0024] The method of surface treatment with tin oxide doped with an antimony compound is not particularly limited and can be appropriately selected depending on the purpose. For example, a surface treatment method can be used in which a hydrochloric acid solution of stannic chloride and antimony trichloride and a sodium hydroxide solution are added in parallel to a suspension of a substrate powder in which alumina has been dispersed, the pH is adjusted, and then the resulting mixture is washed and filtered by decantation, dried, fired, and pulverized.

[0025] The antimony compound is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include diantimony pentoxide, diantimony trioxide, etc. Among these, diantimony pentoxide is preferred because it can provide excellent charging stability and prevent toner scattering and carrier adhesion. Diantimony pentoxide is also preferred because it is less harmful to the human body.

[0026] The content of the conductive inorganic fine particles is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 to 60 parts by mass, more preferably 30 to 50 parts by mass, relative to 100 parts by mass of the coating layer. When the content is 20 to 60 parts by mass, detachment of the conductive inorganic fine particles and exposure of the fine particles due to scraping of the coating layer can be suppressed, thereby preventing carrier adhesion.

[0027] The substrate for the conductive inorganic fine particles is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include metal fine particles such as gold, silver, copper, silica, and aluminum, titanium oxide, tin oxide, zinc oxide, zirconium oxide, indium oxide, antimony oxide, calcium oxide, ITO, silicone oxide, colloidal silica, aluminum oxide, yttrium oxide, cobalt oxide, copper oxide, iron oxide, manganese oxide, niobium oxide, vanadium oxide, selenium oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, boron nitride, silicon nitride, potassium titanate, hydrotalcite, antimony compounds, tin oxide doped with tungsten, and indium oxide doped with tin. Among these, aluminum oxide and titanium oxide are preferred, and aluminum oxide is more preferred because it can provide better charging stability and can better prevent carrier adhesion.

[0028] The conductivity of the conductive inorganic fine particles (hereinafter sometimes referred to as "volume resistivity") is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 0.5 Ω·cm or more and 4.0 Ω·cm or less. When the conductivity is 4.0 Ω·cm or less, high conductivity can be imparted to the electrophotographic image forming carrier even when the amount of conductive inorganic fine particles added is small. When the conductivity is 0.5 Ω·cm or less, high conductivity and durability can be achieved at the same time.

[0029] <<Spherical inorganic fine particles (C)>> The spherical inorganic fine particles (C) may be made of the same material as the substrate of the conductive inorganic fine particles, or may be made of a different material. When the coating layer contains the spherical inorganic fine particles (C), the durability of the coating layer against friction is improved, and deterioration due to wear and abrasion can be suppressed.

[0030] The durability of the coating layer can be improved by including conductive inorganic fine particles. However, the electrical resistance of the carrier for electrophotographic image formation changes depending on the content of the conductive inorganic fine particles. Therefore, by including spherical inorganic fine particles (C), the durability of the coating layer can be ensured while maintaining a constant electrical resistance.

[0031] The spherical inorganic fine particles (C) are not particularly limited and can be appropriately selected depending on the purpose. Examples include metal fine particles such as gold, silver, copper, silica, and aluminum, titanium oxide, tin oxide, zinc oxide, zirconium oxide, indium oxide, antimony oxide, calcium oxide, ITO, silicone oxide, colloidal silica, aluminum oxide, yttrium oxide, cobalt oxide, copper oxide, iron oxide, manganese oxide, niobium oxide, vanadium oxide, selenium oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, boron nitride, silicon nitride, potassium titanate, hydrotalcite, antimony compounds, tungsten-doped tin oxide, and tin-doped indium oxide. Particularly preferred materials include barium sulfate, magnesium oxide, and magnesium hydroxide. These may be used alone or in combination of two or more. Among these, barium sulfate is preferred because it provides excellent charging stability and can prevent toner scattering and carrier adhesion. Barium sulfate is also preferred because it is white and has a high charging ability for negatively charged toner.

[0032] The spherical inorganic fine particles (C) are preferably white in color, since they have little effect on the color of the toner even when they are detached from the coating layer.

[0033] The content of the spherical inorganic fine particles (C) is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 15 parts by mass or more and 70 parts by mass or less, and more preferably 20 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the coating layer.

[0034] The equivalent circle diameter of the spherical inorganic fine particles (C) is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 400 nm to 900 nm, and more preferably 600 nm to 900 nm in terms of obtaining better charging stability. If the equivalent circle diameter is 400 nm or more, the spherical inorganic fine particles (C) can be present in a state of protruding convexly from the surface of the coating layer, ensuring charging properties with the toner. If the equivalent circle diameter is 900 nm or less, the equivalent circle diameter of the spherical inorganic fine particles (C) relative to the thickness of the coating layer is large enough to be sufficiently held by the resin, making it difficult for the spherical inorganic fine particles (C) to detach from the coating layer. The method for measuring the circle-equivalent diameter of the spherical inorganic fine particles (C) is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured by the same method as the method for measuring each length of the conductive inorganic fine particles.

[0035] <<Resin>> The resin is not particularly limited and can be appropriately selected depending on the purpose. Examples include silicone resin, acrylic resin, amino resin, polyvinyl resin, polystyrene resin, halogenated olefin resin, polyester, polycarbonate, polyethylene, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, polyhexafluoropropylene, copolymers of vinylidene fluoride and vinyl fluoride, and fluoro terpolymers such as terpolymers of tetrafluoroethylene, vinylidene fluoride and a non-fluorinated monomer. These may be used alone or in combination of two or more. Among these, silicone resin and acrylic resin are preferred because they can further increase the durability of the coating layer.

[0036] Acrylic resin has high adhesiveness and low brittleness, giving it excellent abrasion resistance, but because it has high surface energy, when combined with toner that is prone to spent, the toner spent can accumulate, resulting in a decrease in charge amount, etc. By using acrylic resin in combination with silicone resin, which has low surface energy, toner component spent is less likely to occur, solving the above problem. On the other hand, silicone resins have poor abrasion resistance due to their low adhesiveness and high brittleness, so by achieving a good balance between the properties of acrylic resins and silicone resins, it is possible to obtain a coating layer that is less susceptible to toner spent and has excellent abrasion resistance.

[0037] The acrylic resin is not particularly limited as long as it is a resin containing an acrylic component, and can be appropriately selected depending on the purpose. The acrylic resin may be used alone, or may be used simultaneously with at least one other component that undergoes a crosslinking reaction. The other components that undergo the crosslinking reaction are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include amino resins and acid catalysts. The amino resin is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include guanamine and melamine resins. The acid catalyst is not particularly limited and can be appropriately selected depending on the purpose. Examples include fully alkylated catalysts, methylol group types, imino group types, and those having reactive groups such as methylol group or imino group types.

[0038] The silicone resin is not particularly limited and can be appropriately selected depending on the purpose. Examples include modified silicone resins modified with alkyd, polyester, epoxy, acrylic, urethane, etc., and straight silicone resins consisting only of organosiloxane bonds. The modified silicone resin may be a commercially available product, such as KR206 (alkyd-modified), KR5208 (acrylic-modified), ES1001N (epoxy-modified), or KR305 (urethane-modified), manufactured by Shin-Etsu Chemical Co., Ltd., or SR2115 (epoxy-modified) or SR2110 (alkyd-modified), manufactured by Dow Corning Toray Silicone Co., Ltd. These may be used alone or in combination of two or more. The straight silicone resin may be a commercially available product, such as KR271, KR255, or KR152 manufactured by Shin-Etsu Chemical Co., Ltd., or SR2400, SR2406, or SR2410 manufactured by Dow Corning Toray Silicone Co., Ltd. These may be used alone or in combination of two or more. As the silicone resin, other components that undergo a crosslinking reaction, charge amount adjusting components, etc. may also be used simultaneously.

[0039] When the resin is a silicone resin, an acrylic resin, or a combination of these, the strength of the film can be increased by crosslinking the silanol groups through condensation using a polycondensation catalyst.

[0040] The condensation polymerization catalyst is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, aluminum-based catalysts, etc. Among these, titanium-based catalysts are preferred. As the titanium catalyst, titanium diisopropoxybis(ethylacetoacetate) is preferred from the viewpoints of its great effect in promoting the condensation reaction of silanol groups and its resistance to catalyst deactivation.

[0041] <<Coupling Agent>> The coupling agent can be contained in the coating layer, and this allows the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) to be stably dispersed in the coating layer.

[0042] The coupling agent is not particularly limited and can be appropriately selected depending on the purpose. For example, when the resin contains a silicone resin, a silane coupling agent can be suitably used.

[0043] The silane coupling agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethyltriethoxy ... Examples of suitable silanes include methyldisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, and methacryloxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride. These may be used alone or in combination of two or more.

[0044] The silane coupling agent may be suitably synthesized or a commercially available product may be used. There are no particular limitations on commercially available products and they can be appropriately selected depending on the purpose. Examples include AY43-059, SR6020, SZ6023, SH6026, SZ6032, SZ6050, AY43-310M, SZ6030, SH6040, AY43-026, AY43-031, sh6062, Z-6911, sz6300, sz6075, sz6079, sz6083, sz6070, sz6072, Z-6721, and AY43 AY43-004, Z-6187, AY43-021, AY43-043, AY43-040, AY43-047, Z-6265, AY43-204M, AY43-048, Z-6403, AY43-206M, AY43-206E, Z6341, AY43-210MC, AY43-083, AY43-101, AY43-013, AY43-158E, Z-6920, Z-6940 (manufactured by Toray Silicone Co., Ltd.), and the like.

[0045] The content of the silane coupling agent is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.1% by mass or more and 10.0% by mass or less relative to the silicone resin. When the content is 0.1% by mass or more, the adhesion between the core particles, conductive inorganic fine particles, and spherical inorganic fine particles (C) and the silicone resin is improved, and the peeling of the coating layer during long-term use can be prevented. When the content is 10.0% by mass or less, toner filming during long-term use can be prevented.

[0046] <<Average thickness of coating layer>> The average thickness of the coating layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.50 μm or more, more preferably 0.50 μm or more and 1.00 μm or less. When the average thickness is 0.50 μm or more, there are no missing parts in the coating layer, and the conductive inorganic fine particles, spherical inorganic fine particles (C), etc. can be sufficiently held.

[0047] The average thickness of the coating layer can be measured, for example, by observing the cross section of the carrier using a transmission electron microscope (TEM), measuring the thickness of the resin portion of the coating layer covering the carrier surface, and averaging the measured values. Note that the thickness of the coating layer consisting of the conductive inorganic fine particles and the resin portion on the inorganic fine particles B is not included in the measurement. The thickness h (μm) can be determined by averaging measurements taken at any 50 points on the cross section of the carrier.

[0048] <Core particles> The core particles are not particularly limited as long as they are magnetic core particles and can be appropriately selected depending on the purpose, and examples thereof include resin particles in which magnetic materials such as ferromagnetic metals such as iron and cobalt, iron oxides such as magnetite, hematite and ferrite, various alloys and compounds are dispersed in a resin, etc. Among these, ferrite is preferred from the viewpoint of its low environmental impact. The ferrite is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include Mn ferrite, Mn-Mg ferrite, Mn-Mg-Sr ferrite, etc. Among these, Mn ferrite is preferred because it has a relatively high magnetization, which makes it easy to optimize the magnetic moment per carrier particle and can further prevent carrier adhesion.

[0049] The volume average particle size of the core particles is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 10 μm or more and 100 μm or less, and more preferably 30 μm or more and 50 μm or less.

[0050] The BET specific surface area of ​​the core particles is not particularly limited and can be appropriately selected depending on the purpose. 2 / g or more 0.50m 2 / g or less is preferable, and 0.03m 2 / g or more 0.35m 2 / g or less is more preferable, and 0.05m 2 / g or more 0.25m 2 / g or less is particularly preferred.

[0051] <Volume average particle size of carrier for electrophotographic image formation> The volume average particle diameter of the carrier for electrophotographic image formation is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 μm to 100 μm, and more preferably 20 μm to 60 μm in view of being more suitable for the recent trend toward higher image quality. When the volume average particle diameter is 20 μm or more, carrier adhesion can be prevented. When the volume average particle diameter is 100 μm or less, a finer image can be formed without deteriorating the reproducibility of image details. The method for measuring the volume average particle size is not particularly limited and can be appropriately selected depending on the purpose. For example, the volume average particle size can be measured using a Microtrac particle size distribution meter (model HRA9320-X100), SRA type (manufactured by Nikkiso Co., Ltd.).

[0052] <Method of manufacturing a carrier for electrophotographic image formation> The method for producing the carrier for electrophotographic image formation is not particularly limited and can be appropriately selected depending on the purpose, and for example, it can be produced by a known method.

[0053] Specifically, conductive inorganic particles, resin, coupling agent, organic solvent, and optionally other components are mixed and dispersed for 10 minutes using a homomixer or the like to prepare a coating layer forming liquid (hereinafter sometimes referred to as "coating liquid"). The coating layer forming liquid is then applied to the surface of the core particles. The core particles coated with the coating layer forming liquid are baked and cooled, and after cooling, they are crushed using a sieve with 100 μm openings to obtain a carrier for electrophotographic image formation.

[0054] The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, butyl acetate, synthetic isoparaffin hydrocarbons, etc. These may be used alone or in combination of two or more. Among these, toluene is preferred.

[0055] The content of the organic solvent is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 4,000 parts by mass or more and 9,000 parts by mass or less relative to the total amount of the coating layer forming liquid.

[0056] The method for applying the coating layer forming liquid is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include immersion, spraying, brush coating, etc. Specific examples of the application method include a method using a Spira Coater SP-40 (manufactured by Okada Seiko Co., Ltd.) or the like at a temperature of 60° C. and a rate of 30 g / min.

[0057] The firing method is not particularly limited and can be appropriately selected depending on the purpose. For example, firing can be performed by external heating, internal heating, etc. Examples of equipment used for firing include a fixed electric furnace, a fluidized electric furnace, a rotary electric furnace, a burner furnace, and an equipment equipped with a microwave. A specific firing method includes, for example, firing in an electric furnace at 230°C for 1 hour.

[0058] (Electrophotographic image forming developer) The developer for electrophotographic image formation of the present invention contains the carrier for electrophotographic image formation of the present invention and the toner, and further contains other components as needed. The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a release agent, a charge control agent, and an external additive.

[0059] <Toner> The toner is not particularly limited and can be appropriately selected depending on the purpose, but preferably contains a binder resin and a colorant, and may contain other components as necessary.

[0060] <<Binder resin>> The binder resin is not particularly limited and can be appropriately selected depending on the purpose. Examples of the binder resin include homopolymers of styrene and its substitution products, such as polystyrene, poly-p-styrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, and styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polyester, polyurethane, epoxy resin, polyvinyl butyral, polyacrylic acid, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or aromatic hydrocarbon resin, and aromatic petroleum resin. These may be used alone or in combination of two or more.

[0061] The binder resin for pressure fixing is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyolefins such as low-molecular-weight polyethylene and low-molecular-weight polypropylene; olefin copolymers such as ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, and ionomer resin; epoxy resin, polyester, styrene-butadiene copolymer, polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenolic resin, and phenol-modified terpene resin. These may be used alone or in combination of two or more.

[0062] <<Coloring agent>> The colorant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the colorant include yellow pigments such as cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, and tartrazine lake; orange pigments such as molybdenum orange, permanent orange GTR, pyrazolone orange, Balkan orange, indanthrene brilliant orange RK, benzidine orange G, and indanthrene brilliant orange GK; red iron oxide, cadmium red, permanent red 4R, lithol red, pyrazolone red, watching red calcium salt, lake red D, and brilliant calcium carbonate. Examples of suitable pigments include red pigments such as Rhodamine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, and Brilliant Carmine 3B; purple pigments such as Fast Violet B and Methyl Violet Lake; blue pigments such as Cobalt Blue, Alkali Blue, Victoria Blue Lake, Phthalocyanine Blue, Metal-Free Phthalocyanine Blue, Partially Chlorinated Phthalocyanine Blue, Fast Sky Blue, and Indanthrene Blue BC; green pigments such as Chrome Green, Chromium Oxide, Pigment Green B, and Malachite Green Lake; azine pigments such as carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black; black pigments such as metal salt azo pigments, metal oxides, and composite metal oxides; and white pigments such as titanium oxide. These pigments may be used alone or in combination. Transparent toners may not require any pigments.

[0063] <<Release Agent>> The release agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyolefins such as polyethylene and polypropylene, fatty acid metal salts, fatty acid esters, paraffin wax, amide wax, polyhydric alcohol wax, silicone varnish, carnauba wax, ester wax, etc. These may be used alone or in combination of two or more.

[0064] <<Charge control agent>> The charge control agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include nigrosine; azine dyes having an alkyl group having 2 to 16 carbon atoms; CI Basic Yellow 2 (CI41000), CI Basic Yellow 3, CI Basic Red 1 (CI45160), CI Basic Red 9 (CI42500), CI Basic Violet 1 (CI42535), CI Basic Violet 3 (CI42555), CI Basic Violet 10 (CI45170), CI Basic Violet 14 (CI42510), CI Basic Blue 1 (CI42025), CI Basic Blue 3 (CI51005), CI Basic Blue 5 (CI42140), CI Basic Blue 7 (CI42595), CI Basic Blue 9 (CI52015), CI Basic Blue 24 (CI52030), CI Basic Examples of suitable dyes include basic dyes such as Blue 25 (CI 52025), CI Basic Blue 26 (CI 44045), CI Basic Green 1 (CI 42040), and CI Basic Green 4 (CI 42000); lake pigments of these basic dyes; quaternary ammonium salts such as CI Solvent Black 8 (CI 26150), benzoylmethylhexadecylammonium chloride, and decyltrimethylchloride; dialkyltin compounds such as dibutyl and dioctyl; dialkyltin borate compounds; guanidine derivatives; polyamine resins such as vinyl polymers containing amino groups and condensation polymers containing amino groups; metal complex salts of monoazo dyes; salicylic acid; complexes of dialkylsalicylic acid, naphthoic acid, and dicarboxylic acids with Zn, Al, Co, Cr, Fe, and the like; sulfonated copper phthalocyanine pigments; organic boron salts; fluorine-containing quaternary ammonium salts; and calixarene compounds. These may be used alone or in combination.

[0065] <<External additives>> The external additive is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include inorganic particles such as silica, titanium oxide, alumina, silicon carbide, silicon nitride, and boron nitride; and resin particles such as polymethyl methacrylate particles and polystyrene particles having an average particle size of 0.05 μm to 1 μm obtained by soap-free emulsion polymerization. These may be used alone or in combination of two or more.

[0066] (Electrophotographic image forming method and electrophotographic image forming apparatus) The electrophotographic image forming method of the present invention includes an electrostatic latent image forming step, a toner image forming step, a transfer step, and a fixing step, and may include other steps as necessary. The electrophotographic image forming apparatus of the present invention includes an electrostatic latent image forming means, a toner image forming means, a transfer means, a fixing means, and may include other means as required.

[0067] The electrostatic latent image forming step is a step of forming an electrostatic latent image on an electrostatic latent image carrier, and can be carried out by the electrostatic latent image forming means.

[0068] The toner image forming step is a step of developing the electrostatic latent image with the developer for electrophotographic image formation to form a toner image, and can be carried out by the toner image forming unit. The toner image forming means is not particularly limited and can be appropriately selected depending on the purpose, but a means for developing with a developer having a magnetic brush formed thereon to form a toner image is preferred.

[0069] Here, a premix development method may be adopted as the development method, in which a premix developer in which toner and carrier are mixed in advance is replenished. In the premix development method, the excess carrier in the developing device is discharged as excess developer. This gradually refreshes the developer in the developing device. This can extend the replacement cycle associated with developer deterioration and eliminate the effort required for developer replacement.

[0070] The transfer step is a step of transferring a toner image onto a recording medium, and can be carried out by the transfer means.

[0071] The fixing step is a step of fixing the toner image transferred onto the recording medium to form an image, and can be carried out by the fixing unit.

[0072] The other steps are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a static elimination step, a cleaning step, a recycling step, and a control step. The other means are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a static elimination means, a cleaning means, a recycling means, and a control means.

[0073] 1 is a diagram illustrating an example of an electrophotographic image forming apparatus according to an embodiment of the present invention. Although a printer is shown as an example of the electrophotographic image forming apparatus of this embodiment, the electrophotographic image forming apparatus is not particularly limited as long as it is capable of forming an image using toner in a copier, facsimile, multifunction machine, or the like.

[0074] The electrophotographic image forming apparatus 200 includes a paper feed section 210 , a conveying section 220 , an image forming section 230 , a transfer section 240 , and a fixing unit 250 .

[0075] The paper feed section 210 includes a paper feed cassette 211 in which paper sheets P to be fed are stacked, and a paper feed roller 212 that feeds the paper sheets P stacked in the paper feed cassette 211 one by one.

[0076] The conveying section 220 includes a roller 221 that conveys the paper P fed by the paper feed roller 212 toward the transfer section 240, a pair of timing rollers 222 that hold the leading end of the paper P conveyed by the roller 221 and wait, sending the paper to the transfer section 240 at a predetermined timing, and a paper discharge roller 223 that discharges the paper P with the fixed color toner image onto a paper discharge tray 224.

[0077] The image forming section 230 includes, at predetermined intervals from left to right in the figure, an image forming unit Y that forms an image using a developer containing yellow toner, an image forming unit C that uses a developer containing cyan toner, an image forming unit M that uses a developer containing magenta toner, an image forming unit K that uses a developer containing black toner, and an exposure device 233.

[0078] It should be noted that when referring to any of the image forming units (Y, C, M, K), it is referred to as an image forming unit.

[0079] The developer contains toner and carrier. The four image forming units (Y, C, M, K) have substantially the same mechanical configuration, except for the developer used in each.

[0080] The image forming units (Y, C, M, K) are provided so as to be rotatable clockwise in Fig. 1. The image forming units (Y, C, M, K) include photoconductors (231Y, 231C, 231M, 231K), chargers (232Y, 232C, 232M, 232K), developers (180Y, 180C, 180M, 180K), and cleaners (236Y, 236C, 236M, 236K).

[0081] Electrostatic latent images and toner images are formed on the photoconductors (231Y, 231C, 231M, 231K). When referring to any one of the photoconductors (231Y, 231C, 231M, 231K), it will be referred to as the photoconductor 231.

[0082] The chargers (232Y, 232C, 232M, 232K) uniformly charge the surfaces of the photoconductors (231Y, 231C, 231M, 231K). Note that any one of the chargers (232Y, 232C, 232M, 232K) may be referred to as the charger 232.

[0083] The developing units (180Y, 180C, 180M, 180K) develop the electrostatic latent images formed on the surfaces of the photosensitive members (231Y, 231C, 231M, 231K) by the exposure unit 233 into toner images using toner of each color. Note that any one of the developing units (180Y, 180C, 180M, 180K) will be referred to as developing unit 180.

[0084] The cleaners (236Y, 236C, 236M, 236K) are equipped with doctor blades and remove toner remaining on the surfaces of the photoconductors (231Y, 231C, 231M, 231K). Note that any one of the cleaners (236Y, 236C, 236M, 236K) will be referred to as cleaner 236.

[0085] The image forming units (Y, C, M, K) are also provided with toner cartridges (234Y, 234C, 234M, 234K) and sub-hoppers (160Y, 160C, 160M, 160K).

[0086] The toner cartridges (234Y, 234C, 234M, 234K) contain toner of each color. Note that any one of the toner cartridges (234Y, 234C, 234M, 234K) will be referred to as the toner cartridge 234.

[0087] The sub-hoppers (160Y, 160C, 160M, 160K) are used to replenish the toner supplied from the toner cartridges (234Y, 234C, 234M, 234K). Note that any one of the sub-hoppers (160Y, 160C, 160M, 160K) will be referred to as sub-hopper 160.

[0088] The sub-hopper 160 transports the toner supplied from the toner cartridge 234 and supplies it to the developing device 180. The developing device 180 uses the toner supplied by the sub-hopper 160 to develop the electrostatic latent image formed on the photosensitive member 231.

[0089] The photoreceptor 231 is not particularly limited in structure, size, etc., and can be appropriately selected from known photoreceptors. The shape of the photoreceptor 231 is not particularly limited, and can be appropriately selected depending on the purpose, and examples thereof include a drum shape and a belt shape. The material of the photoreceptor 231 is not particularly limited, and can be appropriately selected depending on the purpose, and examples thereof include inorganic photoreceptors such as amorphous silicon and selenium, and organic photoreceptors (OPC) such as polysilane and phthalopolymethine.

[0090] Examples of organic photoreceptors include multilayer photoreceptors having a laminated structure in which a layer (charge generation layer) in which a charge generation material such as metal-free phthalocyanine, titanyl phthalocyanine, or gallium phthalocyanine is dispersed in a binder resin and a layer (charge transport layer) in which a charge transport material is dispersed in a binder resin are stacked on a support such as an aluminum drum, and single-layer photoreceptors having a single-layer photosensitive layer in which both a charge generation material and a charge transport material are dispersed in a binder resin on a support. In single-layer photoreceptors, a hole transport agent and an electron transport agent can also be added to the photosensitive layer as charge transport materials. An undercoat layer may also be provided between the support and the multilayer charge generation layer or single-layer photosensitive layer.

[0091] The charger 232 is not particularly limited, but examples thereof include known contact chargers equipped with conductive or semiconductive rolls, brushes, films, rubber blades, etc., and non-contact chargers that utilize corona discharge such as corotrons and scorotrons.

[0092] The charger 232 is preferably disposed in contact with or out of contact with the photoconductor 231, and charges the surface of the photoconductor 231 by applying a DC voltage and an AC voltage in a superimposed manner.

[0093] Furthermore, the charger 232 is a charging roller that is arranged close to the photosensitive member 231 but without contacting it via a gap tape, and it is preferable that the surface of the photosensitive member 231 is charged by applying a DC voltage and an AC voltage superimposed on the charging roller.

[0094] The exposure device 233 emits laser light L based on image information from a light source 233a, and reflects the laser light L on a polygon mirror 233b (233bY, 233bC, 233bM, 233bK) that is driven to rotate by a motor, and irradiates the photosensitive member 231 (231Y, 231C, 231M, 231K).

[0095] The exposure device 233 is not particularly limited as long as it can expose the surface of the photosensitive member 231 charged by the charger 232 in the form of an image to be formed. Examples of the exposure device 233 include various exposure devices such as a copying optical system, a rod lens array system, a laser optical system, and a liquid crystal shutter optical system.

[0096] Alternatively, a backlight system may be employed in which exposure is performed imagewise from the back side of the photosensitive member 231 .

[0097] The developing device 180 is not particularly limited as long as it is capable of developing using a developer. The developing device 180 is preferably a developing device that stores a developer and applies the developer to the electrostatic latent image in a contact or non-contact manner, and more preferably a developing device that includes a developer container.

[0098] Developer 180 may be a single color developer or a multi-color developer.

[0099] There are no particular limitations on the cleaner 236 as long as it is capable of removing toner remaining on the surface of the photoreceptor 231. As the cleaner 236, a cleaner equipped with a cleaning member such as a magnetic brush cleaner, an electrostatic brush cleaner, a magnetic roller cleaner, a blade cleaner, a brush cleaner, or a web cleaner is preferred.

[0100] The photosensitive drum 231 from which the toner has been removed by the cleaner 236 is then neutralized to remove any remaining potential, thereby completing the series of image forming processes carried out on the photosensitive drum 231.

[0101] The transfer unit 240 includes a drive roller 241 and a driven roller 242, an intermediate transfer belt 243 that can rotate counterclockwise in the figure as the drive roller 241 is driven, primary transfer rollers (244Y, 244C, 244M, 244K) that are arranged opposite the photosensitive element 231 across the intermediate transfer belt 243, and secondary opposing rollers 245 and 246 that are arranged opposite each other across the intermediate transfer belt 243 at the position where the toner image is transferred to the paper.

[0102] In this embodiment, an elastic intermediate transfer belt may be used as the intermediate transfer belt 243. For example, an elastic intermediate transfer belt may be formed by laminating a flexible elastic layer on a rigid base layer that provides relatively good flexibility. In addition, a guide member for preventing deviation may be provided on the inner peripheral surface of the intermediate transfer belt 243 to prevent the intermediate transfer belt 243 from meandering.

[0103] The fixing unit 250 has a heater installed inside and is equipped with a fixing belt 251 that heats the paper P, and a pressure roller 252 that forms a nip by rotatably applying pressure to the fixing belt 251. This applies heat and pressure to the color toner image on the paper P, fixing the color toner image. The paper P with the fixed color toner image is discharged to a paper discharge tray 224 by a paper discharge roller 223, completing the series of image formation processes.

[0104] (Process cartridge) The process cartridge according to the present invention is formed so as to integrally support an electrostatic latent image carrier and a means for developing an electrostatic latent image formed on the electrostatic latent image carrier using the above-described developer for electrophotographic image formation of the present invention.

[0105] FIG. 2 is a diagram illustrating an example of a process cartridge according to an embodiment of the present invention. The process cartridge 10 has an electrostatic latent image carrier 11, a charging device 12 that charges the electrostatic latent image carrier 11, a developing device 13 that develops the electrostatic latent image formed on the electrostatic latent image carrier 11 using the electrophotographic image forming developer of the present invention to form a toner image, and a cleaning device 14 that removes toner remaining on the electrostatic latent image carrier 11 after the toner image formed on the electrostatic latent image carrier 11 has been transferred to a recording medium, and is detachable from the main body of an image forming apparatus such as a copier or printer. [Example]

[0106] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0107] (Production Example 1) <Manufacture of Carrier 1> The resin used was 200 parts by mass of an acrylic resin solution (solid content: 20% by mass), 2,000 parts by mass of a silicone resin solution (product name: SR2410, manufactured by Dow Toray Co., Ltd., solid content: 40% by mass), 35 parts by mass of an aminosilane (product name: SH6020, manufactured by Dow Toray Co., Ltd., solid content: 100% by mass) as a coupling agent, and aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive spherical inorganic fine particles (A). 490 parts by mass of titanium dioxide (equivalent circle diameter: 0.5 μm), 210 parts by mass of titanium dioxide (long side diameter: 1.7 μm, short side diameter: 0.10 μm) surface-treated with tin oxide doped with antimony pentoxide as conductive needle-shaped inorganic microparticles (B), 700 parts by mass of barium sulfate (equivalent circle diameter: 0.60 μm) as spherical inorganic microparticles (C), and 6,000 parts by mass of toluene as an organic solvent were mixed and dispersed for 10 minutes using a homomixer to obtain a coating layer forming liquid. Using a Spira Coater SP-40 (manufactured by Okada Seiko Co., Ltd.), the coating layer forming liquid was applied to the surface of Mn ferrite (volume average particle size: 36 μm) as core particles at a rate of 30 g / min in an atmosphere of 60°C and then dried to form a coating layer on the surface of the core particles. The core particles with the coating layer formed thereon were fired in an electric furnace at 230°C for 1 hour and then cooled. After cooling, the core particles were crushed using a sieve with 100 μm openings to obtain Carrier 1 used in the examples. The content of the conductive inorganic fine particles was 30 parts by mass relative to 100 parts by mass of the coating layer.

[0108] The volume average particle size of the core particles, the circle equivalent diameters of the conductive spherical inorganic fine particles (A) and spherical inorganic fine particles (C), and the long side diameter and short side diameter of the conductive acicular inorganic fine particles B were measured by the following methods. [Method for measuring the volume average particle size of core particles] A Microtrac particle size distribution analyzer (manufactured by Nikkiso Co., Ltd.) SRA type was used to measure within the set range of 0.7 μm or more and 125 μm or less. [Method for measuring the circle-equivalent diameter of conductive spherical inorganic fine particles (A) and spherical inorganic fine particles (C)] Conductive inorganic fine particles (A) and spherical inorganic fine particles (C) before forming a carrier were used for measurement with a Nanotrac UPA series (manufactured by Nikkiso Co., Ltd.). [Method for measuring the long and short side diameters of conductive acicular inorganic fine particles (B)] Using a transmission electron microscope (TEM), 50 particles were observed and their long and short side diameters were measured.

[0109] The average thickness of the coating layer of the obtained carrier 1 was measured by the following method and was found to be 0.50 μm. [Method for measuring the average thickness of the coating layer] The cross section of the carrier was observed using a transmission electron microscope (TEM), and the thickness T from the surface of the core particle to the surface of the coating layer was measured at 50 points at 0.2 μm intervals along the carrier surface, and the obtained measurements were averaged to calculate the thickness.

[0110] (Production Example 2) Carrier 2 used in the examples was obtained in the same manner as in Production Example 1, except that the equivalent circle diameter of the aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 0.9 μm.

[0111] (Production Example 3) Carrier 3 used in the examples was obtained in the same manner as in Production Example 1, except that the equivalent circle diameter of aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 0.3 μm.

[0112] (Production Example 4) Carrier 4 used in the examples was obtained in the same manner as in Production Example 1, except that the long side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 1.9 μm.

[0113] (Production Example 5) Carrier 5 used in the examples was obtained in the same manner as in Production Example 1, except that the long side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 1.3 μm.

[0114] (Production Example 6) Carrier 6 used in the examples was obtained in the same manner as in Production Example 1, except that the short side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 0.30 μm.

[0115] (Production Example 7) Carrier 7 used in the examples was obtained in the same manner as in Production Example 1, except that the short side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as the conductive acicular inorganic microparticles (B) was changed to 0.05 μm.

[0116] (Production Example 8) Carrier 8 used in the examples was obtained in the same manner as in Production Example 1, except that the amount of aluminum oxide (equivalent circle diameter: 0.5 μm) surface-treated with tin oxide doped with diantimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 420 parts by mass, and the amount of titanium oxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm) surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 280 parts by mass.

[0117] (Production Example 9) Carrier 9 used in the examples was obtained in the same manner as in Production Example 1, except that the amount of aluminum oxide (circle equivalent diameter: 0.5 μm) surface-treated with tin oxide doped with diantimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 560 parts by mass, and the amount of titanium oxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm) surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 140 parts by mass.

[0118] (Production Example 10) Carrier 10 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, ``aluminum oxide surface-treated with tin oxide doped with antimony pentoxide (equivalent circle diameter: 0.5 μm)'' as the conductive spherical inorganic fine particles (A) was changed to ``aluminum oxide surface-treated with tin oxide doped with antimony trioxide (equivalent circle diameter: 0.5 μm)'', and ``titanium oxide surface-treated with tin oxide doped with antimony pentoxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm)'' as the conductive acicular inorganic fine particles (B) was changed to ``titanium oxide surface-treated with tin oxide doped with antimony trioxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm)''.

[0119] (Production Example 11) Carrier 11 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, "aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide (equivalent circle diameter: 0.5 μm)" as the conductive spherical inorganic microparticles (A) was changed to "titanium oxide surface-treated with tin oxide doped with diantimony pentoxide (equivalent circle diameter: 0.5 μm)".

[0120] (Production Example 12) Carrier 12 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, "aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide (equivalent circle diameter: 0.5 μm)" as the conductive spherical inorganic microparticles (A) was changed to "tin oxide doped with diantimony pentoxide (equivalent circle diameter: 0.5 μm)."

[0121] (Manufacturing Example 13) In Production Example 1, the amount of aluminum oxide (equivalent circle diameter: 0.5 μm) surface-treated with tin oxide doped with antimony pentoxide as the conductive spherical inorganic microparticles (A) was changed to 280 parts by mass, the amount of titanium oxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm) surface-treated with tin oxide doped with antimony pentoxide as the conductive acicular inorganic microparticles (B) was changed to 120 parts by mass, and barium sulfate (equivalent circle diameter: 0.60 μm) was not used as the spherical inorganic microparticles (C) except that carrier 13 used in the example was obtained in the same manner as Production Example 1.

[0122] (Manufacturing Example 14) Carrier 14 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, "barium sulfate (equivalent circle diameter: 0.60 μm)" as the inorganic fine particles (C) was changed to "magnesium oxide (equivalent circle diameter: 0.60 μm)".

[0123] (Manufacturing Example 15) Carrier 15 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, "barium sulfate (equivalent circle diameter: 0.60 μm)" as inorganic fine particles (C) was changed to "hydrotalcite (equivalent circle diameter: 0.60 μm)".

[0124] (Manufacturing Example 16) Carrier 16 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, ``barium sulfate (equivalent circle diameter: 0.60 μm)'' as the inorganic fine particles (C) was changed to ``magnesium hydroxide (equivalent circle diameter: 0.60 μm).''

[0125] (Manufacturing Example 17) Carrier 17 used in the examples was obtained in the same manner as in Production Example 1, except that in Production Example 1, ``barium sulfate (equivalent circle diameter: 0.60 μm)'' as the inorganic fine particles (C) was changed to ``aluminum hydroxide (equivalent circle diameter: 0.60 μm).''

[0126] (Manufacturing Example 18) Carrier 18 used in the comparative example was obtained in the same manner as in Production Example 1, except that the equivalent circle diameter of the aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide as the conductive spherical inorganic microparticles (A) was changed to 1.0 μm.

[0127] (Manufacturing Example 19) Carrier 19 used in the comparative example was obtained in the same manner as in Production Example 1, except that the equivalent circle diameter of the aluminum oxide surface-treated with tin oxide doped with diantimony pentoxide as the conductive spherical inorganic microparticles (A) was changed to 0.2 μm.

[0128] (Manufacturing Example 20) Carrier 20 used in the comparative example was obtained in the same manner as in Production Example 1, except that the long side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 2.0 μm.

[0129] (Manufacturing Example 21) Carrier 21 used in the comparative example was obtained in the same manner as in Production Example 1, except that the long side diameter of the titanium oxide surface-treated with tin oxide doped with diantimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 1.2 μm.

[0130] (Manufacturing Example 22) Carrier 22 used in the comparative example was obtained in the same manner as in Production Example 1, except that the amount of aluminum oxide (circle equivalent diameter: 0.5 μm) surface-treated with tin oxide doped with antimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 350 parts by mass, and the amount of titanium oxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm) surface-treated with tin oxide doped with antimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 350 parts by mass.

[0131] (Manufacturing Example 23) Carrier 23 used in the comparative example was obtained in the same manner as in Production Example 1, except that the amount of aluminum oxide (equivalent circle diameter: 0.5 μm) surface-treated with tin oxide doped with antimony pentoxide as conductive spherical inorganic microparticles (A) was changed to 630 parts by mass, and the amount of titanium oxide (long side diameter: 1.7 μm, short side diameter: 0.1 μm) surface-treated with tin oxide doped with antimony pentoxide as conductive acicular inorganic microparticles (B) was changed to 70 parts by mass.

[0132] (Toner manufacturing) <Synthesis of polyester resin> Into a reaction vessel equipped with a condenser, a stirrer, and a nitrogen inlet tube, 65 parts by mass of an ethylene oxide 2-mol adduct of bisphenol A, 86 parts by mass of a propionoxide 3-mol adduct of bisphenol A, 274 parts by mass of terephthalic acid, and 2 parts by mass of dibutyltin oxide were charged, and the mixture was reacted at normal pressure and 230°C for 15 hours, and then reacted under a reduced pressure of 5 mmHg to 10 mmHg for 6 hours to obtain a polyester resin. The polyester resin obtained had a number average molecular weight (Mn) of 2,300, a weight average molecular weight (Mw) of 8,000, a glass transition temperature (Tg) of 58°C, an acid value of 25 mgKOH / g, and a hydroxyl value of 35 mgKOH / g.

[0133] <Prepolymer synthesis> Into a reaction vessel equipped with a condenser, a stirrer, and a nitrogen inlet tube, 682 parts by mass of bisphenol A ethylene oxide 2-mol adduct, 81 parts by mass of bisphenol A propylene oxide 2-mol adduct, 283 parts by mass of terephthalic acid, 22 parts by mass of trimellitic anhydride, and 2 parts by mass of dibutyltin oxide were charged, and the mixture was reacted at 230°C under normal pressure for 8 hours, and then reacted under a reduced pressure of 10 mmHg to 15 mHg for 5 hours to obtain an intermediate polyester resin. The resulting intermediate polyester resin had a number average molecular weight (Mn) of 2,100, a weight average molecular weight (Mw) of 9,600, a glass transition temperature (Tg) of 55°C, an acid value of 0.5 mgKOH / g, and a hydroxyl value of 49 mgKOH / g. Next, 411 parts by mass of the intermediate polyester resin, 89 parts by mass of isophorone diisocyanate, and 500 parts by mass of ethyl acetate were added to a reaction vessel equipped with a cooling tube, a stirrer, and a nitrogen inlet tube, and the mixture was reacted at 100°C for 5 hours to obtain a prepolymer. The free isocyanate content of the obtained prepolymer was 1.60% by mass, and the solid content concentration of the prepolymer (after standing at 150° C. for 45 minutes) was 50% by mass.

[0134] <Synthesis of Ketimine Compounds> 30 parts by mass of isophoronediamine and 70 parts by mass of methyl ethyl ketone were placed in a reaction vessel equipped with a stirrer and a thermometer, and the mixture was reacted at 50° C. for 5 hours to obtain a ketimine compound. The amine value of the obtained ketimine compound was 423 mol / L.

[0135] <Masterbatch production> A mixture was obtained by mixing 1,000 parts by mass of water, 540 parts by mass of carbon black Printex 35 (manufactured by Degussa, DBP oil absorption: 42 mL / 100 g, pH: 9.5), and 1,200 parts by mass of the polyester resin using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.). Next, the mixture was kneaded using a two-roll mill at 150°C for 30 minutes, rolled and cooled, and pulverized using a pulverizer (manufactured by Hosokawa Micron Corporation) to obtain a masterbatch.

[0136] <Preparation of aqueous medium> 306 parts by mass of water, 265 parts by mass of a 10% by mass suspension of tricalcium phosphate, and 1.0 part by mass of sodium dodecylbenzenesulfonate were mixed, stirred, and dissolved uniformly to obtain an aqueous medium.

[0137] <Preparation of Toner Material Liquid> 70 parts by weight of the polyester resin, 10 parts by weight of the prepolymer, and 100 parts by weight of ethyl acetate were placed in a beaker and stirred to dissolve. Then, 5 parts by weight of paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd., melting point: 75°C) as a release agent, 2 parts by weight of MEK-ST (manufactured by Nissan Chemical Industries, Ltd.), and 10 parts by weight of the masterbatch were added, and the mixture was passed three times using a bead mill, Ultraviscomill (manufactured by Imex Co., Ltd.), under conditions of a liquid feed rate of 1 kg / h, a disk peripheral speed of 6 m / s, and a filling amount of zirconia beads with a particle size of 0.5 mm, 80% by volume. Then, 2.7 parts by weight of the ketimine compound was added and dissolved to obtain a toner material liquid.

[0138] <Emulsification and dispersion process> 150 parts by weight of the aqueous medium was placed in a container and stirred at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), after which 100 parts by weight of the toner material liquid was added and mixed for 10 minutes to obtain an emulsified slurry.

[0139] <Solvent removal process> 100 parts by mass of the resulting emulsified slurry was placed in a Kolben equipped with a stirrer and a thermometer, and the emulsified slurry was stirred at a peripheral stirring speed of 20 m / min at 30° C. for 12 hours to remove the solvent.

[0140] <Cleaning process> 100 parts by mass of the solvent-removed emulsified slurry was filtered under reduced pressure to obtain a filter cake. 100 parts by mass of ion-exchanged water was added to the filter cake, and the mixture was mixed at 12,000 rpm for 10 minutes using a TK homomixer, followed by filtration. This procedure was repeated two more times. Thereafter, 20 parts by mass of a 10% by mass aqueous solution of sodium hydroxide was added to the obtained filter cake, and the mixture was mixed for 30 minutes at a rotation speed of 12,000 rpm using a TK homomixer, followed by filtration under reduced pressure. Thereafter, 300 parts by mass of ion-exchanged water was added to the obtained filter cake, and the mixture was mixed for 10 minutes at a rotation speed of 12,000 rpm using a TK homomixer, followed by filtration. This operation was repeated two more times. Further, 20 parts by mass of 10% by mass hydrochloric acid was added to the obtained filter cake, and the mixture was mixed for 10 minutes at a rotation speed of 12,000 rpm using a TK homomixer, followed by filtration to obtain a washed filter cake.

[0141] <Surfactant amount adjustment process> 300 parts by mass of ion-exchanged water was added to the filtered cake after washing, and the mixture was mixed for 10 minutes at 12,000 rpm using a TK homomixer. The electrical conductivity of the resulting toner dispersion was measured, and the surfactant concentration of the toner dispersion was calculated using a surfactant concentration calibration curve prepared in advance. From this value, ion-exchanged water was added so that the surfactant concentration reached the target surfactant concentration of 0.05% by mass, thereby obtaining a toner dispersion.

[0142] <Surface treatment process> The obtained toner dispersion was heated in a water bath at a heating temperature T1 of 55°C for 10 hours while being mixed at a rotation speed of 5,000 rpm using a TK homomixer. Thereafter, the toner dispersion was cooled to 25°C and filtered. 300 parts by mass of ion-exchanged water was added to the obtained filter cake, and the mixture was mixed at a rotation speed of 12,000 rpm using a TK homomixer for 10 minutes, followed by filtration to obtain a final filter cake.

[0143] <Drying process> The resulting final filter cake was dried in a circulating air dryer at 45° C. for 48 hours and sieved through a 75 μm mesh to obtain toner base particles.

[0144] <External additive processing step> 100 parts by mass of the obtained toner base particles were mixed with 3.0 parts by mass of hydrophobic silica having a volume average particle size of 100 nm, 1.0 part by mass of titanium oxide having a volume average particle size of 20 nm, and 1.5 parts by mass of hydrophobic silica having a volume average particle size of 15 nm in a Henschel mixer to obtain a toner.

[0145] (Examples 1 to 17 and Comparative Examples 1 to 6) 930 parts by mass of each of Carriers 1 to 23 and 70 parts by mass of the toner were mixed (mass ratio 93:7), and then stirred for 5 minutes at 81 rpm using a Turbula mixer to obtain developers for evaluation.

[0146] Table 1 shows the diameter of the conductive spherical inorganic particles (A), the long side diameter and short side diameter of the conductive acicular inorganic particles (B), and the content of the conductive acicular inorganic particles (B) relative to the total amount of the conductive spherical inorganic particles (A) and the conductive acicular inorganic particles (B) for each carrier used in the examples and comparative examples.

[0147] [Table 1]

[0148] The developers of the examples and comparative examples were evaluated for "background fogging," "image density," "carrier adhesion (edge)," "carrier adhesion (solid)," and "charging stability over time" based on the following evaluation criteria.

[0149] <Skin Coverage> The developer was set in a digital full-color multifunction printer (Pro C9100, manufactured by Ricoh Co., Ltd.) and 1 million copies of a character chart (each character approximately 2mm x 2mm) with an image area ratio of 5% were printed. After that, the toner on the photoreceptor after development was transferred onto tape, and the difference in image density with that of the untransferred tape was measured using a 938 Spectrodensitometer (manufactured by X-Rite). The "background fogging" was evaluated based on the following evaluation criteria. A rating of "△" or better on the following criteria indicates that the product is usable. [Evaluation criteria] ◎: Image density difference is 0 or more and less than 0.005 ○: The difference in image density is 0.005 or more and less than 0.01 △: The difference in image density is 0.01 or more and less than 0.02 ×: The difference in image density is 0.02 or more

[0150] <Image density> The developer was set in a digital full-color multifunction printer (Pro C9100, manufactured by Ricoh Co., Ltd.) and printed 100,000 copies of a character chart (character size approximately 2mm x 2mm) with an image area ratio of 5% in an environmental evaluation room (a low-temperature, low-humidity environment of 10°C and 15%). Three solid white images and three solid black images were then printed (brand: RICOH MyPaper, A3 paper), and the image density was evaluated visually. The visual image density was compared with an image sample and the "image density" was evaluated based on the following evaluation criteria. A rating of "△" or better in the evaluation criteria below indicates that the product is usable. [Evaluation criteria] ⊚: Image density is equivalent to that of the image sample. ○: It is not clear from the standpoint of the image itself, but the image density is low compared to the sample. △: When viewed alone, it is clear that the image density is low. ×: The image density is clearly low.

[0151] <Carrier adhesion (edge)> The developer was loaded into a digital full-color multifunction printer (Pro C9100, manufactured by Ricoh Co., Ltd.) and printed one million copies of a character chart (each character approximately 2mm x 2mm) with an image area ratio of 5%. The digital full-color multifunction printer was then placed in an environmental evaluation room (a low-temperature, low-humidity environment of 10°C and 15%) for one day. Subsequently, under development conditions of a charging potential (Vd) of -630V and a development bias of -500V DC, an A3-sized image was printed, with solid areas and blank paper alternately arranged vertically and horizontally, with each square being 170µm x 170µm. The number of squares with white areas due to carrier adhesion at the borders of each square was counted. The "carrier adhesion (edge)" was evaluated based on the number of squares measured, using the following evaluation criteria. A rating of "Fair" or better in the following evaluation criteria indicates practical use. [Evaluation criteria] ◎:0 pieces ○: 1 or more and 3 or less △: 4 or more and 10 or less ×: 11 or more

[0152] <Carrier adhesion (solid)> The developer was loaded into a digital full-color multifunction printer (Pro C9100, manufactured by Ricoh Co., Ltd.) and 1 million copies of a character chart (each character approximately 2mm x 2mm) with an image area ratio of 5% were printed. Then, in an environmental evaluation room (a low-temperature, low-humidity environment of 10°C and 15%), the following conditions were met: charging potential (Vd): -600V, potential after exposure of the image area (solid): -100V, and development bias: DC -500V. The power was then turned off during image formation, interrupting the process, and the number of carrier particles adhering to a 10mm x 100mm area of ​​the photoreceptor after transfer was measured. The "carrier adhesion (solid)" was evaluated based on the number of carrier particles measured, using the following evaluation criteria. A rating of "Fair" or better on the following criteria indicates practical use. [Evaluation criteria] ◎:0 pieces ○: 1 or more and 3 or less △: 4 or more and 10 or less ×: 11 or more

[0153] <Charge stability over time> The developer was loaded into a digital full-color multifunction printer (Pro C9100, manufactured by Ricoh Co., Ltd.), and one million images with an image area ratio of 40% were printed. The absolute values ​​of the charge amount before printing (Q1) and the charge amount after printing (Q2) calculated based on the following formula (1) were determined as the rate of change in charge amount. The charge amount (Q1) was measured using a blow-off device TB-200 (manufactured by Toshiba Chemical Co.) on a developer obtained by triboelectrically charging a mixture of carriers 1 to 23 and toner in a mass ratio of 93:7. The charge amount (Q2) was measured using the blow-off device on the carrier from which the toner had been removed. A rating of "Fair" or better in the following evaluation criteria indicates practical use. Formula (1): Rate of change (%) = [(Q1-Q2) / Q1] x 100 [Evaluation criteria] ◎: 0% or more and less than 5% ○: 5% or more and less than 10% △: 10% or more but less than 20% ×: 20% or more

[0154] Table 2 shows the evaluation results of the examples and comparative examples.

[0155] [Table 2]

[0156] The results of Examples 1 to 17 and Comparative Examples 1 to 6 show that, by setting the diameter of the conductive spherical inorganic fine particles (A), the long side diameter, short side diameter and content of the conductive acicular inorganic fine particles (B) within the specified numerical ranges, a carrier for electrophotographic image formation can be obtained that can suppress a decrease in carrier resistance and charge even under long-term printing, and can prevent carrier adhesion and background fogging.

[0157] The embodiments of the present invention are as follows, for example. <1> A carrier for electrophotographic image formation comprising core particles and a coating layer covering the core particles, wherein the coating layer contains conductive spherical inorganic fine particles (A) and conductive acicular inorganic fine particles (B), The conductive spherical inorganic fine particles (A) have a diameter of 0.30 μm or more and 0.90 μm or less, the conductive acicular inorganic fine particles (B) have a long side of 1.30 μm or more and 1.90 μm or less and a short side of 0.05 μm or more and 0.30 μm or less, At least one of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) contains tin oxide doped with an antimony compound, The carrier for electrophotographic image formation is characterized in that the content of the conductive acicular inorganic fine particles (B) contained in the coating layer is 20% by mass or more and 40% by mass or less based on the total amount of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B). <2> The antimony compound is diantimony pentoxide. <1> 1. The electrophotographic imaging carrier according to claim 1. <3> At least one of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) has aluminum oxide as a base particle. <1> from <2> 10. The carrier for electrophotographic imaging according to claim 9, wherein the carrier is a fluororesin. <4> The coating layer contains spherical inorganic fine particles (C) in addition to the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B). <1> from <3> 10. The carrier for electrophotographic imaging according to claim 9, wherein the carrier is a fluororesin. <5> The spherical inorganic fine particles (C) contain barium sulfate. <4> 1. The electrophotographic imaging carrier according to claim 1. <6> <1> from <5> 10. A developer for electrophotographic imaging, comprising the carrier for electrophotographic imaging according to claim 9. <7> <6> 1. A method for forming an electrophotographic image, comprising forming an image using the developer for forming an electrophotographic image described in 1. <8> <6> 10. An electrophotographic image forming apparatus comprising the developer for electrophotographic image forming according to claim 19. <9> <6> 10. A process cartridge comprising the developer for electrophotographic image formation described above.

[0158] The aforementioned <1> from <5> The electrophotographic image forming carrier according to <6> The electrophotographic image forming developer according to the <7> The electrophotographic image forming method according to the <8> and the electrophotographic image forming apparatus described in <9> The process cartridge described in the above can solve the above-mentioned problems in the prior art and achieve the above-mentioned object of the present invention. [Explanation of symbols]

[0159] 10 Process cartridge 11 Electrostatic latent image carrier 12 Charging device 13 Developing device 14 Cleaning device 160 Sub Hopper 180 Developer 200 Electrophotographic image forming apparatus 210 Paper feed section 211 Paper cassette 212 Paper feed roller 220 Conveyor 221 Laura 222 Timing roller 223 Paper ejection roller 224 Paper output tray 230 Image creation section 231 Photoreceptor 232 Charger 233 Exposure device 234 Toner Cartridge 236 Cleaner 240 Transcription Unit 241 Drive roller 242 driven roller 243 Intermediate transfer belt 244 Primary transfer roller 245 Secondary opposing roller 246 Secondary transfer roller 250 Fixing unit 251 Fixing belt 252 pressure roller [Prior art documents] [Patent documents]

[0160] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-090644 [Patent Document 2] Patent No. 4748237

Claims

1. A carrier for electrophotographic image formation comprising core particles and a coating layer covering the core particles, wherein the coating layer contains conductive spherical inorganic fine particles (A) and conductive acicular inorganic fine particles (B), The conductive spherical inorganic fine particles (A) have a diameter of 0.30 μm or more and 0.90 μm or less, the conductive acicular inorganic fine particles (B) have a long side of 1.30 μm or more and 1.90 μm or less and a short side of 0.05 μm or more and 0.30 μm or less, At least one of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B) contains tin oxide doped with an antimony compound, a content of the conductive acicular inorganic fine particles (B) contained in the coating layer being 20% ​​by mass or more and 40% by mass or less based on the total amount of the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B).

2. 2. The electrophotographic imaging carrier of claim 1, wherein said antimony compound is diantimony pentoxide.

3. 2. The carrier for electrophotographic imaging according to claim 1, wherein at least one of said conductive spherical inorganic fine particles (A) and said conductive acicular inorganic fine particles (B) has aluminum oxide as a base particle.

4. 2. The carrier for electrophotographic image formation according to claim 1, wherein the coating layer contains spherical inorganic fine particles (C) in addition to the conductive spherical inorganic fine particles (A) and the conductive acicular inorganic fine particles (B).

5. 5. The carrier for electrophotographic imaging according to claim 4, wherein the spherical inorganic fine particles (C) contain barium sulfate.

6. A developer for electrophotographic imaging, comprising the carrier for electrophotographic imaging according to claim 1 .

7. 7. An electrophotographic image forming method, comprising forming an image using the developer for electrophotographic image forming according to claim 6.

8. 7. An electrophotographic image forming apparatus comprising the developer for electrophotographic image forming according to claim 6.

9. A process cartridge comprising the developer for electrophotographic image formation according to claim 6.

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