Resin-coated carrier for electrophotographic developer

Abstract

A resin-coated carrier for an electrophotographic developer according to the present invention which has magnetic particles and a resin layer for coating the surface of the magnetic particles, wherein: the resin layer contains barium titanate particles; the barium titanate particles include one or more transition elements selected from the group consisting of Fe, Mn and Zr; the content of said transition elements in the barium titanate particles is 600-2,000 ppm by mass, inclusive; and the content of Zr in the magnetic particles is 0.05-2.25 parts by mass, inclusive, with respect to 100 parts by mass of the magnetic particles.

Description

Resin-coated carrier for electrophotographic developer

[0001] The present invention relates to a resin-coated carrier for electrophotographic developers, which is used in two-component electrophotographic developers used in copying machines, printers, and the like.

[0002] In order to improve the durability of two-component developers, resin-coated carriers containing titanate compounds in the resin coating layer and developers containing the same have been reported as measures to prevent contamination (spent) of toner-derived components on carriers and developing machine components.

[0003] Patent Document 1 proposes a carrier comprising carrier particles, the carrier particles comprising a carrier core and a coating layer covering the surface of the carrier core, the coating layer having an inner layer containing first barium titanate particles and an outer layer containing a silicone resin and a second barium titanate, the number-average primary particle diameter of the first barium titanate particles being 20 nm or more and less than 100 nm, and the number-average primary particle diameter of the second barium titanate particles being 100 nm or more and less than 500 nm. Patent Document 2 proposes a carrier comprising carrier particles, the carrier particles comprising a carrier core and a coating layer covering the surface of the carrier core, the coating layer containing a silicone resin and specific particles, the specific particles including first barium titanate particles and carbon black particles directly or indirectly attached to the surface of the first barium titanate particles, the content of barium titanate in the coating layer being 4 parts by mass or more and 47 parts by mass or less per 100 parts by mass of the silicone resin.

[0004] Patent Document 3 proposes a magnetic carrier having magnetic carrier core particles and a resin coating layer formed on the surface of the magnetic carrier core particles, wherein the magnetic carrier contains titanate compound particles having a perovskite structure in the resin coating layer, and the titanate compound particles have a niobium atom content of 500 ppm or more and 5000 ppm or less in terms of oxide.

[0005] Patent Document 4 proposes an electrophotographic developer having composite oxide particles in which a third metal atom selected from the group consisting of metal atoms belonging to Group 5A of the long form periodic table is contained in metal titanate particles containing titanium as a first metal atom and a second metal atom in an amount of 0.009 to 0.350 wt %.

[0006] Patent Document 5 proposes a two-component developer including a carrier comprising carrier particles having a carrier core and a coating layer coating the surface of the carrier core, wherein the coating layer comprises a coating resin and barium titanate particles, the coating resin comprises a silicone resin, the number average primary particle diameter of the barium titanate particles is 100 nm or more and 500 nm or less, the content of the barium titanate particles is 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin, the ratio of the mass of the coating layer to the mass of the carrier core is 0.09% by mass or more and 4.90% by mass or less, and the coverage of the carrier core is 80.0% or more and less than 100.0%, and the coverage is the ratio of the area of ​​the coated region coated with the coating layer to the area of ​​the surface of the carrier core.

[0007] Japanese Patent Publication No. 2023-026089 Japanese Patent Publication No. 2023-014693 Japanese Patent Publication No. 2022-061925 International Patent Publication No. 2010 / 007905 International Publication No. 2023 / 281882

[0008] Patent Documents 1 to 3 describe that resin-coated carriers improve durability and image quality. Patent Document 1 claims that by incorporating barium titanate particles of different particle sizes in the inner and outer layers of the coating layer, carrier development and cleaning defects can be suppressed. Patent Document 2 claims that by incorporating first barium titanate particles as specific particles in the resin coating layer, image defects and fogging, known as development ghosts, in which an image area formed in the first rotation appears darker on the full-area halftone image in the second rotation, can be suppressed, and image density stability can be improved. Patent Document 3 claims that by incorporating titanate compound particles with a perovskite structure containing Nb atoms in the resin coating layer of the carrier, image quality can be improved under low printing speeds and environmental fluctuations. Patent Document 4 claims that by incorporating composite oxide particles composed of first, second, and third metal atoms in an electrophotographic developer, charge stability, such as charge rise time, is excellent in high-temperature, high-humidity environments and low-temperature, low-humidity environments. Patent Document 5 describes that by incorporating barium titanate particles having a number-average temporary particle diameter of 100 nm or more and 500 nm or less into the carrier coat layer, it is possible to achieve excellent fogging resistance and suppress poor cleaning.

[0009] However, there is a constant demand for further improvements in image quality stability and durability. For example, under harsh conditions such as long periods of continuous printing in extremely hot and humid environments, it is necessary to devise ways to ensure high charge stability and continue to provide high-quality image output.

[0010] Therefore, an object of the present invention is to provide a resin-coated carrier for an electrophotographic developer that can enhance charging stability in an extremely high-temperature and high-humidity environment and can sufficiently suppress the occurrence of development memory, which will be described later.

[0011] As a result of intensive research into the above-mentioned problems, the present inventors have found that, in a carrier having magnetic particles and a resin layer coating the surfaces of the magnetic particles, the coating resin layer (hereinafter also referred to simply as coating layer) contains barium titanate particles, the barium titanate particles contain a predetermined amount of a predetermined transition element, and the magnetic particles contain a predetermined amount of Zr, and although the principle behind this has not been clearly clarified, the presence of the predetermined amount of transition element in the barium titanate in the coating layer and the presence of Zr in the magnetic particles (magnetic core material) stabilizes the charge transfer state within the carrier particles, and as a result, it is possible to obtain a resin-coated carrier for electrophotographic developer that can improve charging stability in extremely high-temperature and high-humidity environments and can sufficiently suppress the occurrence of development memory.

[0012] That is, the present invention provides a resin-coated carrier for electrophotographic developers, which comprises magnetic particles and a resin layer covering the surfaces of the magnetic particles, the resin layer containing barium titanate particles, the barium titanate particles containing at least one transition element selected from the group consisting of Fe, Mn, and Zr, the content of the transition element in the barium titanate particles being 600 ppm or more and 2000 ppm or less, and the content of Zr in the magnetic particles being 0.05 parts by mass or more and 2.25 parts by mass or less per 100 parts by mass of the magnetic particles. Note that, in this specification, "ppm" refers to "ppm by mass."

[0013] In the resin-coated carrier for an electrophotographic developer according to the present invention, the content of Zr in the barium titanate particles is preferably 300 ppm or more and 1500 ppm or less.

[0014] In the resin-coated carrier for an electrophotographic developer according to the present invention, the true specific gravity of the barium titanate particles is 6.00 g / m ３ 9.00g / m or more ３ It is preferable that:

[0015] In the resin-coated carrier for an electrophotographic developer according to the present invention, the ratio c / a calculated by XRD (X-ray diffraction) measurement of the barium titanate particles is preferably 1.0080 or more and 1.0090 or less.

[0016] In the resin-coated carrier for an electrophotographic developer according to the present invention, the content of barium titanate in the resin-coated carrier for an electrophotographic developer is preferably 0.05% by mass or more and 1.95% by mass or less.

[0017] According to the present invention, it is possible to provide a resin-coated carrier for an electrophotographic developer that can enhance charging stability in an extremely high-temperature and high-humidity environment and can sufficiently suppress the occurrence of development memory.

[0018] Specific embodiments of the present invention will be described. Note that the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. In the present invention, a combination of two or more preferred embodiments is a more preferred embodiment.

[0019] The resin-coated carrier for an electrophotographic developer according to the present invention has magnetic particles and a resin layer that coats the surfaces of the magnetic particles, and contains barium titanate particles in the resin layer. The barium titanate particles contain at least one transition element selected from the group consisting of Fe, Mn, and Zr, and the content of the transition element in the barium titanate particles is 600 ppm or more and 2000 ppm or less. The content of Zr in the magnetic particles is 0.05 parts by mass or more and 2.25 parts by mass or less, relative to 100 parts by mass of the magnetic particles.

[0020] The resin-coated carrier for electrophotographic developer according to the present invention comprises magnetic particles (carrier core material) and a resin layer covering the surfaces of the magnetic particles. The magnetic particles used as the carrier core material include iron powder, magnetite particles, resin carrier particles, and ferrite particles, which have been conventionally used as carriers for electrophotographic developers. Among these, ferrite containing at least one element selected from Mn, Mg, Li, Ca, Sr, and Ti is particularly preferred. Considering the recent trend toward reducing environmental impact, including waste regulations, it is preferable that the heavy metals Cu, Zn, and Ni are not contained in excess of the range of unavoidable impurities (accompanying impurities).

[0021] Furthermore, the magnetic particles of the resin-coated carrier for electrophotographic developer according to the present invention contain a predetermined amount of Zr and a barium titanate coating containing a predetermined amount of a predetermined transition element, thereby improving charging stability and suppressing the occurrence of development memory in extremely high-temperature, high-humidity environments. The content of Zr in the magnetic particles is 0.05 parts by mass or more and 2.25 parts by mass or less, preferably 0.10 parts by mass or more and 2.00 parts by mass or less, and more preferably 0.20 parts by mass or more and 1.50 parts by mass or less, relative to 100 parts by mass of the magnetic particles. In one preferred embodiment, the content of Zr is preferably 0.05 parts by mass or more and 2.00 parts by mass or less, and more preferably 0.05 parts by mass or more and 1.50 parts by mass or less, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the Zr content is preferably 0.10 parts by mass or more and 2.25 parts by mass or less, more preferably 0.10 parts by mass or more and 2.00 parts by mass or less, and even more preferably 0.10 parts by mass or more and 1.50 parts by mass or less, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the Zr content is preferably 0.20 parts by mass or more and 2.25 parts by mass or less, more preferably 0.20 parts by mass or more and 2.00 parts by mass or less, and even more preferably 0.20 parts by mass or more and 1.50 parts by mass or less, relative to 100 parts by mass of the magnetic particles. Here, development memory refers to a phenomenon in which the influence of a previous image appears in a subsequent image. Specifically, this refers to an image defect in which, in an image having a length of at least one rotation of the developing roller, an image in which a solid image portion and a non-image portion are adjacent to each other is followed by a halftone portion, and the image density of the halftone portion becomes non-uniform due to the influence of the image one rotation of the developing roller, resulting in a decrease in image density. One of the reasons for this development memory occurrence mechanism is the presence of weakly charged toner remaining on the developing roller. On the other hand, although the reason is not clear, it is thought that by incorporating barium titanate particles containing a predetermined amount of a predetermined transition element into the coating layer of a resin-coated carrier for electrophotographic developer using magnetic particles containing a predetermined amount of Zr, it is possible to obtain a constant charge transfer speed while maintaining the desired charge retention ability, thereby making it possible to obtain a developer with a narrow charge distribution, preventing the occurrence of weakly charged toner and suppressing the occurrence of development memory.

[0022] When the magnetic particles are ferrite particles, ferrite particles with a high porosity can also be used, and in this case, the porosity of the ferrite particles can be filled with resin to form a resin-filled ferrite carrier.

[0023] The average particle size of the magnetic particles is preferably 20 to 60 μm. When the average particle size is 20 μm or more, carrier adhesion can be effectively prevented. When the average particle size is 60 μm or less, good image quality can be obtained.

[0024] The resin constituting the resin layer that coats the surface of the magnetic particles can be appropriately selected depending on the toner to be combined, the environment in which the magnetic particles are used, etc. The type of resin is not particularly limited, but examples include fluororesins (e.g., polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene), acrylic resins (e.g., polymethyl methacrylate), fluoroacrylic resins, acrylic-styrene resins, epoxy resins, polyamide resins, polyamideimide resins, polyester resins (e.g., polyethylene terephthalate), unsaturated polyester resins, urea resins, melamine resins, alkyd resins, phenolic resins, silicone resins, and modified silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins. Among these, silicone resins are preferred, and silicone resins made of organopolysiloxane are more preferred. Organopolysiloxanes are compounds in which organic groups are attached to siloxane bonds. Examples of the organic groups contained in organopolysiloxanes include methyl groups, ethoxy groups, propyl groups, butyl groups, and phenyl groups, and the organopolysiloxane may contain one or more of these groups as organic groups.

[0025] The amount of resin coating the magnetic particle surface is preferably 0.5 parts by mass or more and 4.0 parts by mass or less per 100 parts by mass of magnetic particles. When the resin coating amount is 0.5 parts by mass or more per 100 parts by mass of magnetic particles, the magnetic particle surface can be more reliably coated with the resin, resulting in excellent charging characteristics. On the other hand, when the resin coating amount is 4.0 parts by mass or less per 100 parts by mass of magnetic particles, the lubricity of the magnetic particle surface is improved, resulting in high anti-spent properties. In addition, aggregation of carrier particles during production can be suppressed, improving productivity. Furthermore, when used as an electrophotographic developer, the fluidity and charge amount in the actual machine are stable, allowing stable developer properties to be exhibited.

[0026] The resin layer contains particles composed of barium titanate (barium titanate particles). The inclusion of barium titanate particles can enhance charging characteristics. The barium titanate content in the resin-coated carrier for electrophotographic developer is preferably 0.05% by mass to 1.95% by mass, more preferably 0.10% by mass to 1.37% by mass. This can further enhance charging stability in extremely high-temperature and high-humidity environments and sufficiently suppress the occurrence of development memory. In a preferred embodiment, the barium titanate content in the resin-coated carrier for electrophotographic developer is preferably 0.05% by mass to 1.37% by mass. In a preferred embodiment, the barium titanate content in the resin-coated carrier for electrophotographic developer is preferably 0.10% by mass to 1.95% by mass, more preferably 0.10% by mass to 1.37% by mass.

[0027] The content of barium titanate in the resin layer is preferably 5 parts by mass or more and 60 parts by mass or less, more preferably 10 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the resin layer. In a preferred embodiment, the content of barium titanate in the resin layer is preferably 5 parts by mass or more and 50 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the resin layer. In a preferred embodiment, the content of barium titanate in the resin layer is preferably 10 parts by mass or more and 60 parts by mass or less, more preferably 10 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the resin layer.

[0028] The barium titanate particles contain at least one transition element selected from the group consisting of Fe, Mn, and Zr. The content of the transition element in the barium titanate particles is 600 ppm to 2000 ppm, preferably 650 ppm to 1500 ppm, and more preferably 700 ppm to 1000 ppm. In a preferred embodiment, the content of the transition element in the barium titanate particles is 600 ppm to 1500 ppm, and more preferably 600 ppm to 1000 ppm. In a preferred embodiment, the content of the transition element in the barium titanate particles is 650 ppm to 2000 ppm, more preferably 650 ppm to 1500 ppm, and even more preferably 650 ppm to 1000 ppm. In a preferred embodiment, the content of the transition element in the barium titanate particles is preferably 700 ppm or more and 2000 ppm or less, more preferably 700 ppm or more and 1500 ppm or less, and even more preferably 700 ppm or more and 1000 ppm or less. By containing barium titanate particles containing a predetermined amount of a predetermined transition element in the coating layer of a resin-coated carrier for an electrophotographic developer and by having Zr present in the magnetic particles, it is possible to improve charging stability in an extremely high-temperature and high-humidity environment and to sufficiently suppress the occurrence of development memory.

[0029] The barium titanate particles may contain only one, two, or all of Fe, Mn, and Zr. The above content means the total amount of the transition elements contained.

[0030] Among the above-mentioned transition elements, the barium titanate particles preferably contain Zr. When the barium titanate particles contain Zr, the Zr content in the barium titanate particles is preferably 300 ppm to 1500 ppm, more preferably 350 ppm to 1000 ppm, and even more preferably 400 ppm to 800 ppm. In a preferred embodiment, the Zr content in the barium titanate particles is preferably 300 ppm to 1000 ppm, and even more preferably 300 ppm to 800 ppm. In a preferred embodiment, the Zr content in the barium titanate particles is preferably 350 ppm to 1500 ppm, more preferably 350 ppm to 1000 ppm, and even more preferably 350 ppm to 800 ppm. In a preferred embodiment, the Zr content in the barium titanate particles is preferably 400 ppm to 1500 ppm, more preferably 400 ppm to 1000 ppm, and even more preferably 400 ppm to 800 ppm. This allows for more effective suppression of development memory during continuous printing while suppressing the occurrence of fogging. Furthermore, when the barium titanate particles contain Fe, the Fe content in the barium titanate particles is preferably 150 ppm to 400 ppm, and more preferably 200 ppm to 350 ppm. In a preferred embodiment, the Fe content in the barium titanate particles is preferably 150 ppm to 350 ppm. In a preferred embodiment, the Fe content in the barium titanate particles is preferably 200 ppm to 400 ppm, and more preferably 200 ppm to 350 ppm. The content of Fe may be 0. When the barium titanate particles contain Mn, the content of Mn in the barium titanate particles is preferably 30 ppm or more and 100 ppm or less, and more preferably 40 ppm or more and 90 ppm or less.In a preferred embodiment, the Mn content in the barium titanate particles is preferably 30 ppm or more and 90 ppm or less. In a preferred embodiment, the Mn content in the barium titanate particles is preferably 40 ppm or more and 100 ppm or less, and more preferably 40 ppm or more and 90 ppm or less. The Mn content may be 0.

[0031] The BET specific surface area of ​​the barium titanate particles used in the present invention is 2.00 m ２ / g or more 20.00m ２ / g or less, and ２ / g or more 10.00m ２ In a preferred embodiment, the BET specific surface area of ​​the barium titanate particles is 2.00 m / g or less. ２ / g or more 10.00m ２ In a preferred embodiment, the BET specific surface area of ​​the barium titanate particles is 2.50 m / g or less. ２ / g or more 20.00m ２ / g or less, and ２ / g or more 10.00m ２ When the BET specific surface area is within the above range, high charging stability can be maintained and the occurrence of development memory during continuous printing can be more effectively suppressed.

[0032] The true specific gravity of the barium titanate particles used in the present invention is 6.00 g / m ３ 9.00g / m or more ３ Preferably, the content is 6.50 g / m or less. ３ 8.00g / m or more ３ In one preferred embodiment, the true specific gravity of the barium titanate particles is 6.00 g / m or less. ３ 8.00g / m or more ３ In one preferred embodiment, the true specific gravity of the barium titanate particles is 6.50 g / m or less. ３ 9.00g / m or more ３ Preferably, the content is 6.50 g / m or less.３ 8.00g / m or more ３ It is more preferable that the toner has a temperature and humidity of 100 to 200° C. or less. This makes it possible to further improve the charging stability in an extremely hot and humid environment, and to more effectively suppress the occurrence of development memory.

[0033] Furthermore, c / a, calculated from the lattice constants c and a of barium titanate particles calculated by XRD measurement, is an index representing the shape and symmetry of the crystal structure, and is preferably 1.0080 or more and 1.0090 or less, and more preferably 1.0083 or more and 1.0088 or less. In a preferred embodiment, c / a of the barium titanate particles is preferably 1.0080 or more and 1.0088 or less. In a preferred embodiment, c / a of the barium titanate particles is preferably 1.0083 or more and 1.0090 or less, and more preferably 1.0083 or more and 1.0088 or less. This can further improve charging stability in extremely high-temperature and high-humidity environments, and can more effectively suppress the occurrence of development memory.

[0034] Barium titanate can be obtained by any of the following methods: solid phase method, hydrothermal synthesis method, alkoxide method, and oxalate method. The following describes a production method using the oxalate method as an example. (1) First, 0.5 to 2.0 mol / L of TiCl ４ and 0.5 to 2.0 mol / L BaCl ２ (2) The aqueous solution of (1) is adjusted so that the molar ratio of Ba to Ti (Ba / Ti) is 1. (3) Compounds such as acetates, carbonates, nitrates, lactates, or alkoxides of each element (e.g., Fe(NO)) are added to the solution of (1) so that the Fe, Mn, and Zr contents of the finally obtained barium titanate are the desired amounts of the present application. ３ ) ３ , MnCO ３ , Zr(CO ３ ) ２) is added and mixed thoroughly. (3) An aqueous solution of oxalic acid is prepared at 1.0 to 5.0 mol / L and heated to 50°C. (4) The (2) solution and the (3) solution are mixed and adjusted so that the molar ratio of oxalic acid to Ti (oxalic acid / Ti) is 1.5 to 2.0, and the mixture is aged for 1 hour while mixing thoroughly. (5) The oxalate obtained in (4) is repeatedly washed until the pH of the washing solution becomes neutral, producing barium titanyl oxalate crystals containing the desired elements. (6) The crystals of (5) are wet-pulverized using deionized water in a bead mill and then dried. (7) The pulverized material of (6) is further heated in air at 500 to 600°C for 4 hours and thermally decomposed to produce barium titanate containing the desired elements. (8) The barium titanate of (7) is further heated under reduced pressure (0.1 Pa) at 800 to 1000°C for 8 hours to adjust the crystallinity to the desired level.

[0035] The resin-coated carrier for electrophotographic developer according to the present invention may contain a conductive agent, a charge control agent, etc. in the resin layer that coats the surfaces of the magnetic particles. Examples of the conductive agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents. Examples of the charge control agent include various charge control agents commonly used for toners and silane coupling agents.

[0036] The content of the conductive agent is preferably 0.01 to 1.00 parts by mass, more preferably 0.05 to 0.80 parts by mass, more preferably 0.05 to 0.50 parts by mass, even more preferably 0.10 to 0.50 parts by mass, particularly preferably 0.10 to 0.30 parts by mass, and most preferably 0.10 to 0.20 parts by mass. In one preferred embodiment, the content of the conductive agent is preferably 0.01 to 0.80 parts by mass, more preferably 0.01 to 0.50 parts by mass, even more preferably 0.01 to 0.30 parts by mass, and particularly preferably 0.01 to 0.20 parts by mass, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the content of the conductive agent is preferably 0.05 to 1.00 parts by mass, more preferably 0.05 to 0.80 parts by mass, even more preferably 0.05 to 0.50 parts by mass, particularly preferably 0.05 to 0.30 parts by mass, and most preferably 0.05 to 0.20 parts by mass, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the content of the conductive agent is preferably 0.10 to 1.00 parts by mass, more preferably 0.10 to 0.80 parts by mass, even more preferably 0.10 to 0.50 parts by mass, particularly preferably 0.10 to 0.30 parts by mass, and most preferably 0.10 to 0.20 parts by mass, relative to 100 parts by mass of the magnetic particles.

[0037] The content of the charge control agent is preferably 0.01 to 1.00 parts by mass, more preferably 0.05 to 0.80 parts by mass, more preferably 0.05 to 0.60 parts by mass, even more preferably 0.05 to 0.50 parts by mass, particularly preferably 0.10 to 0.50 parts by mass, and most preferably 0.10 to 0.30 parts by mass. In one preferred embodiment, the content of the charge control agent is preferably 0.01 to 0.80 parts by mass, more preferably 0.01 to 0.60 parts by mass, even more preferably 0.01 to 0.50 parts by mass, and particularly preferably 0.01 to 0.30 parts by mass, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the content of the charge control agent is preferably 0.05 to 1.00 parts by mass, more preferably 0.05 to 0.80 parts by mass, even more preferably 0.05 to 0.60 parts by mass, particularly preferably 0.05 to 0.50 parts by mass, and most preferably 0.05 to 0.30 parts by mass, relative to 100 parts by mass of the magnetic particles. In a preferred embodiment, the content of the charge control agent is preferably 0.10 to 1.00 parts by mass, more preferably 0.10 to 0.80 parts by mass, even more preferably 0.10 to 0.60 parts by mass, particularly preferably 0.10 to 0.50 parts by mass, and most preferably 0.10 to 0.30 parts by mass, relative to 100 parts by mass of the magnetic particles.

[0038] <Method for Manufacturing Resin-Coated Carrier for Electrophotographic Developer> Next, a method for manufacturing a resin-coated carrier for electrophotographic developer will be described. First, an appropriate amount of magnetic particle raw material (e.g., ferrite raw material) is weighed to obtain a predetermined composition, and then pulverized and mixed using a ball mill or vibration mill for 0.5 hours or more, preferably 1 to 20 hours. The pulverized material thus obtained is pelletized using a pressure molding machine or the like, and then pre-fired at a temperature of 700 to 1200°C. It is also possible to pulverize the material without using a pressure molding machine, add water to form a slurry, and then granulate using a spray dryer. Furthermore, if it is desired to reduce the apparent density, the pre-fire step may be omitted.

[0039] After the calcination, the mixture is further pulverized in a ball mill or a vibration mill, and then water and, if necessary, a dispersant, a binder, etc. are added to adjust the viscosity, followed by granulation, controlling the oxygen concentration, and maintaining the mixture at a temperature of 1000 to 1500° C. for 1 to 24 hours for main calcination. When pulverizing the mixture after calcination, water may be added and the mixture may be pulverized in a wet ball mill or a wet vibration mill, etc.

[0040] The fired product thus obtained is pulverized and classified by conventional methods such as air classification, mesh filtration, and sedimentation to adjust the particle size to a desired particle size.

[0041] Thereafter, if necessary, the surface can be heated at a low temperature to perform an oxide film treatment, thereby adjusting the electrical resistance. The oxide film treatment is carried out using a general rotary electric furnace, a batch electric furnace, or the like, and heat treatment is carried out at, for example, 300 to 700°C. The thickness of the oxide film formed by this treatment is preferably 0.1 nm to 5 μm. If the thickness is less than 0.1 nm, the effect of the oxide film layer is small, and if it exceeds 5 μm, problems such as reduced magnetization or excessively high resistance, resulting in reduced developability, are likely to occur. Furthermore, if necessary, reduction may be carried out before the oxide film treatment.

[0042] Next, the surfaces of the magnetic particles are coated with a resin. Carrier characteristics, particularly electrical characteristics such as charging characteristics, are often affected by the materials and properties present on the magnetic particle surface. Therefore, by coating the surface with an appropriate resin, the desired carrier characteristics can be precisely adjusted.

[0043] Known coating methods include brush coating, dry coating, spray drying using a fluidized bed, rotary drying, and immersion drying using a universal mixer. Of these, the spray drying method using a fluidized bed is preferred, as it allows for a uniform resin coating on the surface.

[0044] After the surfaces of the magnetic particles are coated with a resin, they may be appropriately heat-treated using an external heating method such as a fixed-type electric furnace, a fluidized-type electric furnace, a rotary-type electric furnace, a heated kneader, or a burner furnace, or an internal heating method such as microwaves. This heat treatment is generally called baking or curing. In the case of a thermosetting resin, this heat treatment can harden the resin, and in the case of a thermoplastic resin, this heat treatment can make the surface of the coating resin smoother, both of which allow the coating resin to adhere to the surface of the magnetic particles.

[0045] Although the resin-coated carrier for an electrophotographic developer according to the present invention has been described above, the present invention is not limited to this.

[0046] Example 1: MnO: 49.9 mol%, MgO: 0.1 mol%, Fe ２ O ３ : MnO, MgO, and Fe in an amount of 50.0 mol% ２ O ３ Furthermore, 0.37 parts by mass of ZrO was weighed out relative to 100 parts by mass of these metal oxides. ２ The mixture was weighed and added, water was added, and the mixture was pulverized in a wet ball mill for 10 hours, mixed, dried, and held at 950°C for 4 hours. The mixture was then pulverized in a wet ball mill for 24 hours. The resulting slurry was granulated and dried, and held at 1270°C for 6 hours in an atmosphere with an oxygen concentration of 2%, followed by crushing and particle size adjustment to obtain ferrite particles (carrier core material). This carrier core material had an average particle size of 35 μm and was pulverized in an applied magnetic field of 3000 (10 ３ / 4π・A / m) the saturation magnetization is 76A ２ / kg.

[0047] Next, 100 parts by mass of the carrier core material were mixed with 2.00 parts by mass of silicone resin (silicone resin powder, KR480 manufactured by Shin-Etsu Chemical Co., Ltd.), 0.12 parts by mass of conductive agent (carbon black, #3400B manufactured by Mitsubishi Chemical Corporation), 0.20 parts by mass of charge control agent (aminosilane coupling agent, KBM603 manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.20 parts by mass of barium titanate particles shown in Table 1, and then loaded into a fluidized bed coating device to perform coating.

[0048] The mixture was then placed in a heated kneader, heated from room temperature to 250°C at a rate of 5°C / min, stirred and kneaded for 2 hours, then the heater was turned off, cooled with stirring for 30 minutes, and discharged from the apparatus.

[0049] Thereafter, the particles were deflocculated using a vibrating sieve with 200M mesh, and non-magnetic materials were removed using a magnetic separator. Thereafter, coarse particles were removed again using a vibrating sieve to obtain a resin-coated carrier for an electrophotographic developer in which the surface of a carrier core material was coated with a resin.

[0050] Examples 2 and 3 Resin-coated carriers for electrophotographic developers were obtained in the same manner as in Example 1, except that the amount of barium titanate particles added was changed as shown in Table 1.

[0051] Examples 4 to 8 Resin-coated carriers for electrophotographic developers were obtained in the same manner as in Example 1, except that the barium titanate particles shown in Table 1 were used and the amounts added were changed as shown in Table 1.

[0052] <Examples 9 and 10> In preparing the carrier core material, ZrO was added so that the Zr content in the carrier core material was the value in Table 1. ２ A resin-coated carrier for an electrophotographic developer was obtained in the same manner as in Example 1, except that the amount of added was changed.

[0053] Comparative Examples 1 to 5 Resin-coated carriers for electrophotographic developers were obtained in the same manner as in Example 1, except that barium titanate particles shown in Table 1 were used and the amounts added were changed as shown in Table 1. As the barium titanate particles, BT-03 manufactured by Sakai Chemical Industry Co., Ltd. was used in Comparative Example 1, and AKBT-S manufactured by Nippon Chemical Industry Co., Ltd. was used in Comparative Example 4.

[0054] <Comparative Example 6> In the preparation of the carrier core material, ZrO was added so that the Zr content in the carrier core material was the value in Table 1. ２ A resin-coated carrier for an electrophotographic developer was obtained in the same manner as in Example 1, except that the amount of added was changed.

[0055] <Analysis of Barium Titanate Content> The barium titanate content in the resin-coated carriers for electrophotographic developers of Examples 1 to 10 and Comparative Examples 1 to 6 was confirmed by the following method. - Measuring device: Rigaku Corporation, fluorescent X-ray device ZSX Primus IV - Measurement conditions: tube current = 60 mA, tube voltage = 50 kV, EZscan mode - Criteria: Calibration curves for Ti and Ba were created using separately prepared samples containing known amounts of barium titanate, and the carrier coating layers of Examples 1 to 10 and Comparative Examples 1 to 6 were measured, and the contents were calculated from the calibration curves based on the intensity values ​​obtained, to determine whether the desired amount of barium titanate was contained.

[0056] <BET specific surface area of ​​barium titanate particles> The BET specific surface area was measured using a fully automatic BET specific surface area measuring device (Macsorb HM-1230 manufactured by Mountech) according to the following conditions and procedure. - Pretreatment conditions - Charge amount 1 g (±0.05 g) - Cell used: Large capacity cell - Preheater: 200°C, 1 hour - Measurement conditions - Desorption conditions: 200°C, 5 minutes - Cooling time: 4 minutes - Gas adsorption method using nitrogen gas - Measurement procedure (1) Pretreatment was performed. (2) Calibration was performed each time a measurement was made, and the BET specific surface area was calculated using the one-point method.

[0057] <Measurement of Transition Element Content in Barium Titanate Particles> The transition element content was measured using an ICP analyzer (Hitachi High-Tech Science SPS3520UV) under the following conditions and procedure. Pretreatment Conditions: Charge amount: 0.04 g (±0.001 g). The target barium titanate and 4 mL of concentrated nitric acid were placed in a Teflon (registered trademark) high-pressure vessel and heated at 140°C for 9 hours in an air bath. Measurement Conditions: Output: 1.2 kW, carrier gas: 0.32 L / min, plasma gas: 16 L / min, auxiliary gas: 0.5 L / min. A twister chamber was used. Calibration Curve: A calibration curve was created for the measurement target (transition elements) using three or more calibration curve samples. Measurement Procedure: (1) Pretreatment was performed. (2) A calibration curve was created for each measurement, and the mass percentage (ppm) of each element was calculated.

[0058] <True Specific Gravity (True Density) of Barium Titanate Particles> The true specific gravity was measured using a Macpycno (Model MP-300) manufactured by Mountech under the following conditions and procedures. Measurement conditions: Replacement gas: He (purity: 99.9995%); Pot capacity: 20 cc; Gas pressure: 0.15 MPa. Measurement procedures: (1) A sample (BaTiO ３ ) (approximately 30 g). (2) Automatic measurement by the device.

[0059] <Calculation of c / a by XRD Measurement of Barium Titanate Particles> c / a was calculated using a PANalytical X'Pert Pro MRD under the following conditions and procedures. Measurement conditions: Tube: Co tube; Acceleration voltage: 45 kV; Current: 40 mA; Scan range: 15°≦2θ≦90°; Step width: 0.02°; Step speed: 0.05° / min; Divergence slit: 1.0°; Scattering slit: 1.0°; Receiving slit: 0.15 mm; Analysis method: Rietveld analysis; Number of accumulations: 5. Measurement procedure: (1) Fill the sample holder with the target barium titanate. (2) Automatic measurement was performed using the instrument. (3) Rietveld analysis was performed on the measurement results using the instrument's built-in software. (4) Calculate c / a using the obtained lattice constants a and c.

[0060] <Measurement of Zr Content in Carrier Core Material (Magnetic Particles)> The Zr content in the carrier core material of the resin-coated carriers for electrophotographic developers of Examples 1 to 10 and Comparative Examples 1 to 6 was confirmed by the following method. - Measurement sample: 10 ml of a 1.92% NaOH solution was added to 0.20 g of the carrier core material sample of Examples 1 to 10 and Comparative Examples 1 to 6, and the mixture was heated at 230°C for 1 hour. The cooled sample was diluted to 100 ml and used as the analysis sample. - Measurement device: ICP device SPS3520UV manufactured by Hitachi High-Tech Science Corporation - Measurement conditions: A calibration curve was created using a standard solution for a Zr calibration curve. The Zr content was measured using an ICP analyzer.

[0061] <Production of Developer> Using the resin-coated carrier for electrophotographic developer of each Example and each Comparative Example and toner (toner for TASKalfa 2554ci manufactured by Kyocera Document Solutions Inc.), a developer with a toner concentration of 6% by mass was prepared, and image evaluation was performed on the charge amount, occurrence of development memory, and fogging. The results are shown in Table 1. The evaluation method is also shown below.

[0062] <Developing Conditions> A modified TASKalfa 2554ci manufactured by Kyocera Document Solutions Inc. was used as an image formation evaluation machine. Developer and replenishment toner were set, and a paper feed durability test was performed. The development environment was carried out under the following two environmental conditions: room temperature environment: temperature 25°C / humidity 50% (NN), and extremely high temperature and humidity environment: temperature 35°C / humidity 80% (HH). A test chart with a printing area of ​​20% was used.

[0063] <Charge amount> - Measuring device: Epping Q / M meter - Measurement sample: Developer extracted from the developing box before printing (0th sheet (0k)) and after printing (30,000th sheet (30k)) - Evaluation criteria: If the absolute value of the difference in charge amount before printing and after 30k in each of the NN environment and HH environment is 5.0 μC / g or less, it is judged as "Good", if it is more than 5.0 μC / g but less than 7.0 μC / g, it is judged as "Good", if it is more than 5.0 μC / g but less than 7.0 μC / g, it is judged as "Poor", and if it is 7.0 μC / g or more, it is judged as "Poor". Also, if the absolute value of the difference in charge amount under the same conditions in the NN environment and the HH environment is 5.0 μC / g or less, it is judged as "Good", if it is more than 5.0 μC / g but less than 10.0 μC / g, it is judged as "Good", and if it is 10.0 μC / g or more, it is judged as "Poor". Evaluation: In the judgment of the charge amount difference in the NN environment, the HH environment, and the charge amount difference in the NN-HH environment, the number of "◯"s that was 3 to 4 and no "×"s was evaluated as "high charge stability," the number of "◯"s that was 0 to 2 and no "×"s was evaluated as "slightly high charge stability," and the number of "×"s that was at least 1 was evaluated as "low charge stability."

[0064] <Development memory> - Measurement device: X-Rite 938 manufactured by Nippon Lithographic Machinery Co., Ltd. - Image used: An image in which a solid image area and a non-image area are adjacent in the longitudinal direction of the photosensitive drum, followed by a wide area of ​​intermediate tones - Measurement sample: Paper output for every 1,000 prints (1k) - Measurement method: In the solid image on the second rotation of the developing roller, the density difference is confirmed between areas where the solid image on the first rotation has been developed and areas where it has not. - Evaluation criteria: A density difference of less than 0.007 is considered to be "no memory occurring", and 0.007 or more is considered to be "memory occurring". - Evaluation: Overall, the evaluation was "X" if it occurred before 10,000 sheets (10k), "△" if it occurred between 10,000 sheets (10k) and 40,000 sheets (40k), "○" if it occurred between 40,000 sheets (40k) and 70,000 sheets (70k), and "◎" if it did not occur until 70,000 sheets (70k).

[0065] <Fogging> - Measurement device: X-Rite 938 manufactured by Nippon Lithographic Machinery Co., Ltd. - Measurement sample: Paper printed every 1k prints - Measurement method: Check the average value of the density measured at four points (four corners of the paper) on an unprinted area. - Measurement criteria: A density difference of less than 0.005 was judged as "no fogging", and 0.005 or more was judged as "fogging occurred". - Evaluation: Overall, the evaluation was "x" if fogging occurred before 10,000 sheets (10k), "△" if fogging occurred between 10,000 sheets (10k) and 40,000 sheets (40k), "○" if fogging occurred between 40,000 sheets (40k) and 70,000 sheets (70k), and "◎" if fogging did not occur by 70,000 sheets (70k).

[0066]

[0067] From the above results, it can be seen that the developers using the resin-coated carriers for electrophotographic developers obtained in Examples 1 to 10 have high charging stability even in extremely high-temperature and high-humidity environments, even when printing is performed continuously, and the occurrence of development memory is suppressed. It can also be seen that the occurrence of fogging is suppressed in Examples 1 to 10.

[0068] According to the present invention, it is possible to provide a resin-coated carrier for an electrophotographic developer that can enhance charging stability in an extremely high-temperature and high-humidity environment and can sufficiently suppress the occurrence of development memory.

[0069] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-085870) filed on May 27, 2024, the contents of which are incorporated herein by reference.

Claims

1. A resin-coated carrier for electrophotographic developers, comprising magnetic particles and a resin layer covering the surfaces of the magnetic particles, wherein the resin layer contains barium titanate particles, the barium titanate particles containing at least one transition element selected from the group consisting of Fe, Mn, and Zr, the content of the transition element in the barium titanate particles being 600 ppm by mass or more and 2000 ppm by mass or less, and the content of Zr in the magnetic particles being 0.05 parts by mass or more and 2.25 parts by mass or less per 100 parts by mass of the magnetic particles.

2. The resin-coated carrier for an electrophotographic developer according to claim 1, wherein the content of Zr in the barium titanate particles is 300 ppm by mass or more and 1500 ppm by mass or less.

3. The true specific gravity of the barium titanate particles is 6.00 g / m ３ 9.00g / m or more ３ 2. The resin-coated carrier for an electrophotographic developer according to claim 1, wherein the resin-coated carrier is:

4. The resin-coated carrier for electrophotographic developer according to claim 1, wherein the ratio c / a calculated by XRD measurement of the barium titanate particles is 1.0080 or more and 1.0090 or less.

5. The resin-coated carrier for electrophotographic developer according to claim 1, wherein the content of barium titanate in the resin-coated carrier for electrophotographic developer is 0.05% by mass or more and 1.95% by mass or less.

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