Carrier set and developer set

Abstract

To provide a carrier set that can form an image having a desired image density and can prevent the occurrence of fogging, and a developer set using the carrier set.SOLUTION: A carrier set includes a first carrier including first carrier particles, and a second carrier including second carrier particles. The first carrier particle has a first carrier core, and a first coat layer covering the surface of the first carrier core. The first coat layer contains polyimide resin and fluororesin particles. The second carrier particle has a second carrier core, and a second coat layer covering the surface of the second carrier core. The second coat layer contains silicone resin and barium titanate particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carrier set and a developer set. [Background technology]

[0002] In the electrophotographic method, for example, a two-component developer (hereinafter, sometimes simply referred to as a developer) containing a carrier and a toner is used. The developer is required to be able to form an image having a desired image density. The developer is also required to be able to suppress the occurrence of fogging.

[0003] To meet these requirements, developers using carriers containing carrier particles having a carrier core and a coating layer covering the surface of the carrier core have been studied. Furthermore, in order to stabilize the charge amount of the toner, adding inorganic particles (e.g., ferroelectrics) to the coating layer of the above-mentioned carrier has also been studied. For example, a carrier having a coating layer containing a coating resin and barium titanate particles has been proposed as such a carrier (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-33631 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even with a developer using the carrier described in Patent Document 1, it is not possible to form an image having a desired image density and to sufficiently suppress the occurrence of fogging.

[0006] The object of the present invention has been made in consideration of the above-mentioned problems, and is to provide a carrier set that can form an image having a desired image density and suppress the occurrence of fogging, and a developer set that uses the above-mentioned carrier set. [Means for solving the problem]

[0007] The carrier set of the present invention comprises a first carrier containing first carrier particles and a second carrier containing second carrier particles. The first carrier particles have a first carrier core and a first coating layer covering the surface of the first carrier core. The first coating layer contains polyimide resin and fluororesin particles. The second carrier particles have a second carrier core and a second coating layer covering the surface of the second carrier core. The second coating layer contains silicone resin and barium titanate particles.

[0008] The developer set of the present invention is a developer set using the above-described carrier set, and includes a first developer containing the first carrier and toner, and a second developer containing the second carrier and toner. [Effects of the Invention]

[0009] The carrier set and developer set of the present invention can form an image having a desired image density and can also suppress the occurrence of fogging. [Brief explanation of the drawings]

[0010] [Figure 1] 3A and 3B are diagrams showing an example of a first carrier particle and an example of a second carrier particle. [Figure 2] FIG. 3 is a diagram showing an example of a first coating layer of a first carrier particle. [Figure 3] FIG. 4 is a diagram showing an example of a second coating layer of a second carrier particle. [Figure 4] FIG. 2 is a diagram illustrating an example of a toner particle. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described below. The toner is an aggregate (e.g., powder) of toner particles. The external additive is an aggregate (e.g., powder) of external additive particles. The carrier is an aggregate (e.g., powder) of carrier particles. Unless otherwise specified, evaluation results (values ​​indicating shape, physical properties, etc.) for powders (more specifically, powders of toner particles, powders of external additive particles, powders of carrier particles, etc.) are number averages of values ​​measured for a corresponding number of particles of the powder.

[0012] Unless otherwise specified, the "main component" of a material refers to the component that is contained in the largest amount in the material by mass. The compound name may be followed by "based" to collectively refer to the compound and its derivatives. When the compound name is followed by "based" to refer to the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative. Acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Each component described in this specification may be used alone or in combination of two or more.

[0013] Volume median diameter (D 50 ) is the median diameter measured using a laser diffraction / scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.) unless otherwise specified. The number average primary particle diameter is the number average of the equivalent circle diameters of primary particles (Heywood diameter: the diameter of a circle having the same area as the projected area of ​​a primary particle) measured using a scanning electron microscope unless otherwise specified. The number average primary particle diameter is, for example, the number average of the equivalent circle diameters of 100 primary particles.

[0014] Unless otherwise specified, the softening point (Tm) is a value measured using a high-speed flow tester (Shimadzu Corporation, "CFT-500D"). In the S-shaped curve measured using the high-speed flow tester (horizontal axis: temperature, vertical axis: stroke), the softening point is the temperature at which "(baseline stroke value + maximum stroke value) / 2" is obtained. Unless otherwise specified, the melting point (Mp) is the temperature of the maximum endothermic peak in the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC-6220"). This endothermic peak appears due to melting of the crystallized portion. Unless otherwise specified, the glass transition point (Tg) is a value measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC-6220") in accordance with "JIS (Japanese Industrial Standards) K7121-2012." In an endothermic curve measured with a differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature of the inflection point due to glass transition (specifically, the temperature at the intersection of the extrapolated line of the baseline and the extrapolated line of the falling line) corresponds to the glass transition point.

[0015] Unless otherwise specified, the measured values ​​of acid value and hydroxyl value are values ​​measured in accordance with JIS (Japanese Industrial Standards) K0070-1992. Unless otherwise specified, the measured values ​​of mass average molecular weight (Mw) are values ​​measured using gel permeation chromatography. Unless otherwise specified, the strength of chargeability is the ease of triboelectric charging relative to a standard carrier provided by the Imaging Society of Japan. For example, the test object is triboelectrically charged by stirring it with a standard carrier (anionic: N-01, cationic: P-01) provided by the Imaging Society of Japan. For example, using a Q / m meter (Trek Model 212HS), the charge amount per unit mass of the test object before and after triboelectric charging is measured. The greater the change in charge amount per unit mass before and after triboelectric charging, the stronger the chargeability of the test object. The above explains the meanings of the terms used in this specification and the measurement method.

[0016] <First embodiment: carrier set> The carrier set according to the first embodiment of the present invention comprises a first carrier including first carrier particles and a second carrier including second carrier particles. The first carrier particles have a first carrier core and a first coating layer that coats the surface of the first carrier core. The first coating layer contains polyimide resin and fluororesin particles. The second carrier particles have a second carrier core and a second coating layer that coats the surface of the second carrier core. The second coating layer contains silicone resin and barium titanate particles.

[0017] As will be described later in a second embodiment, the carrier set of the present invention can be used as a developer set by combining it with a toner. The developer set can be used to form an image in, for example, an electrophotographic device (image forming device). In the developer set, the carrier and toner are stirred in the developing device, thereby charging the toner.

[0018] The carrier set of the present invention is suitable for use in a so-called trickle development image forming apparatus. After starting development of an electrostatic latent image with initial developer (initial toner and initial carrier) in a developing device, a trickle development image forming apparatus develops the electrostatic latent image with the developer in the developing device while discharging the developer from the developing device and replenishing replenishment developer (replenishment toner and replenishment carrier) into the developing device. During image formation, carrier is replenished into the developing device along with toner, and only the excess carrier from the developing device is discharged. This prevents deterioration of the carrier in the developing device. Furthermore, suppressing carrier degradation reduces the frequency of carrier replacement in the developing device. When the carrier set of the present invention is used in a trickle development image forming apparatus, it is preferable to use the first carrier as the initial carrier and the second carrier as the replenishment carrier.

[0019] The carrier set of the present invention, having the above-described configuration, can form an image with a desired image density and suppress the occurrence of fogging. The reason for this is presumed to be as follows: Typical toners contain inorganic particles as external additives. As inorganic particles, silica particles are often used in combination with other inorganic particles (e.g., titanium oxide particles and aluminum oxide particles) other than silica particles. Silica particles optimize the fluidity of toner particles and impart positive chargeability to toner particles. Other inorganic particles suppress excessive toner charge. Here, other inorganic particles tend to have low adhesive strength with toner base particles. Therefore, when the toner and carrier are stirred during preparation or printing, other inorganic particles may detach from the toner and adhere to the carrier surface. When other inorganic particles migrate from the toner to the carrier in the developer, the toner charge increases, resulting in a decrease in the image density of the formed image. If the above-described phenomenon occurs at the beginning of printing, the toner charge increases over time, resulting in a decrease in the image density of the formed image over time.

[0020] In contrast, the first carrier has a first coating layer containing polyimide resin and fluororesin particles. The fluororesin particles can form a resin layer with a smooth surface. Polyimide resin is suitable as a binder for fluororesin particles. The first coating layer contains fluororesin particles and polyimide resin, resulting in minimal surface irregularities. Because the first carrier has a first coating layer with minimal surface irregularities, it can only hold a very small amount of other inorganic particles. Therefore, in a developer using the first carrier, immediately after preparation (before use in printing), the maximum amount of other inorganic particles adheres to the surface of the first carrier. In other words, immediately after preparation, there is no room for any more inorganic particles to adhere to the surface of the first carrier. Therefore, in a developer using the first carrier, the amount of other inorganic particles adhering to the first carrier does not increase during printing. Thus, in a developer using the first carrier, the amount of other inorganic particles adhering to the surface of the first carrier does not fluctuate at the beginning of printing, resulting in a stable toner charge.

[0021] On the other hand, silica particles gradually detach from the toner base particles and adhere to the carrier over time during long printing (printing durability). In a developer, if a certain percentage or more of the carrier surface is covered with silica particles, the toner charge decreases, causing fogging in the formed image. In contrast, the second coating layer of the second carrier contains ferroelectric barium titanate particles and a silicone resin. Carriers using such ferroelectrics have excellent toner charging performance. Furthermore, silicone resins can form a layer with numerous nano-order irregularities on their surface. Therefore, the surface of the second carrier has room for numerous silica particles to adhere. As a result, developers using the second carrier are less likely to experience a decrease in toner charge even if a small number of silica particles adhere to the surface of the second carrier. As a result, developers using the second carrier can suppress a decrease in toner charge even if silica particles gradually adhere to the surface of the second carrier during printing durability.

[0022] In this manner, in the carrier set of the present invention, the first carrier can prevent the image density from decreasing over time in the early stages of printing. Furthermore, the second carrier can prevent fogging during printing. Therefore, by using the first carrier as the initial carrier and the second carrier as the replenishment carrier, it is possible to form an image with the desired image density and prevent fogging.

[0023] The carrier set of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross section of a first carrier particle 1, which is an example of a first carrier particle, and a cross section of a second carrier particle 11, which is an example of a second carrier particle. The first carrier particle 1 comprises a first carrier core 2 and a first coating layer 3 that coats the surface of the first carrier core 2. The first coating layer 3 coats the entire surface of the first carrier core 2. The second carrier particle 11 comprises a second carrier core 12 and a second coating layer 13 that coats the surface of the second carrier core 12. The second coating layer 13 coats the entire surface of the second carrier core 12.

[0024] Fig. 2 shows an example of the first coating layer 3. The first coating layer 3 contains a polyimide resin 4 and fluororesin particles 5. Fig. 3 shows an example of the second coating layer 13. The second coating layer 13 contains a silicone resin 14 and barium titanate particles 15.

[0025] An example of the carrier set of the present invention has been described above with reference to Figures 1 to 3. However, in the carrier set of the present invention, the first carrier particles and second carrier particles are not limited to the first carrier particles 1 and second carrier particles 11 shown in Figures 1 to 3. For example, the first coating layer may cover at least a portion of the first carrier core. That is, a portion of the first carrier core may be exposed. Similarly, the second coating layer may cover at least a portion of the second carrier core. That is, a portion of the second carrier core may be exposed. Below, the respective configurations of the first carrier particles and second carrier particles will be described in detail.

[0026] [First carrier particle] The first carrier particles have a first carrier core and a first coating layer that covers the surface of the first carrier core.

[0027] (1st Carrier Core) The first carrier core preferably contains a magnetic material. The first carrier core may be a particle of a magnetic material, or may be a particle including a binder resin and particles of a magnetic material dispersed in the binder resin (hereinafter, sometimes referred to as a resin carrier core).

[0028] Examples of magnetic materials contained in the first carrier cores include ferromagnetic metals (more specifically, iron, cobalt, nickel, and alloys containing one or more of these metals) and ferromagnetic metal oxides. Ferromagnetic metal oxides include ferrite and magnetite, a type of spinel ferrite. Ferrites include, for example, Ba ferrite, Mn ferrite, Mn-Zn ferrite, Ni-Zn ferrite, Mn-Mg ferrite, Ca-Mg ferrite, Li ferrite, Cu-Zn ferrite, and Mn-Mg-Sr ferrite. Examples of methods for producing the first carrier cores include a method comprising the steps of pulverizing and firing a magnetic material. In the production of the first carrier cores, the saturation magnetization of the first carrier can be adjusted by changing the amount of magnetic material added (particularly the proportion of ferromagnetic material). Furthermore, in the production of the first carrier cores, the circularity of the first carrier cores can be adjusted by changing the firing temperature. Commercially available first carrier cores may be used.

[0029] Examples of magnetic material particles used as the first carrier core include ferrite particles. Ferrite particles tend to have sufficient magnetism for image formation with a developer. Ferrite particles manufactured by common manufacturing methods tend not to be perfectly spherical and tend to have moderate surface irregularities. When the first carrier core is a ferrite particle (ferrite core), the arithmetic mean roughness of the surface of the ferrite core (more specifically, the arithmetic mean roughness Ra defined by JIS (Japanese Industrial Standards) B0601-2013) is preferably 0.3 μm or more and 2.0 μm or less, from the viewpoint of improving the adhesion between the surface of the ferrite core and the first coating layer.

[0030] The binder resin in the resin carrier core is preferably a polyester resin, a urethane resin, or a phenol resin, and more preferably a phenol resin. The magnetic material particles in the resin carrier core include, for example, particles containing one or more of the magnetic materials exemplified above.

[0031] In the primary carrier particles, the mass ratio of the primary carrier core to the total mass of the primary carrier core and the first coating layer is preferably 70% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 99% by mass or less.

[0032] The volume median diameter of the first carrier core is preferably 20 μm or more and 60 μm or less. By setting the volume median diameter of the first carrier core to 20 μm or more, the carrier set of the present invention can suppress the occurrence of carrier development. By setting the volume median diameter of the first carrier core to 60 μm or less, the developer set using the carrier set of the present invention can be imparted with good developability.

[0033] The saturation magnetization of the first carrier core in an applied magnetic field of 3000 Oe is preferably 65 emu / g or more and 90 emu / g or less. By setting the saturation magnetization of the first carrier core to 65 emu / g or more, the developer set using the carrier set of the present invention can suppress the occurrence of carrier overdevelopment. By setting the saturation magnetization of the first carrier core to 90 emu / g or less, the developer set using the carrier set of the present invention can be imparted with good developability.

[0034] (First coating layer) The first coating layer contains a polyimide resin and fluororesin particles. The first coating layer preferably further contains carbon black particles. The total content of the polyimide resin, fluororesin particles, and carbon black particles in the first coating layer is preferably 90% by mass or more, and more preferably 100% by mass.

[0035] The mass of the first coating layer relative to 100 parts by mass of the first carrier core is preferably 0.5 parts by mass or more and 10.0 parts by mass or less. By setting the mass of the first coating layer to 0.5 parts by mass or more, exposure of the first carrier core can be suppressed. By setting the mass of the first coating layer to 10.0 parts by mass or less, the first carrier can easily charge the toner.

[0036] (Polyimide resin) Polyimide resin is a thermosetting resin. After being heat-cured, the polyimide resin has good adhesion to inorganic materials such as ferrite. Furthermore, after being heat-cured, the polyimide resin has excellent heat resistance. Therefore, by using a polyimide resin as a binder for the first coating layer, the fluororesin particles can be firmly adhered to the first carrier core.

[0037] Furthermore, polyimide resins tend to have lower heat shrinkage than other resins (e.g., polyamide-imide resins). Generally, in the carrier manufacturing process, heat treatment may be performed after the surface of the carrier core is coated with a resin. When the carrier core is coated with a resin with high heat shrinkage, the resin may shrink due to the heat treatment, exposing the carrier core. Exposure of the carrier core may cause the resin to peel off, resulting in a decrease in carrier performance. In contrast, polyimide resins have low heat shrinkage, so they can be prevented from shrinking and exposing the carrier core when subjected to the heat treatment. As a result, the durability of the first carrier can be improved by using a polyimide resin as the binder for the first coating layer.

[0038] Furthermore, fluororesin particles have extremely low surface adhesion. In contrast, polyimide resins exhibit good adhesion to materials with low surface adhesion, such as fluororesin particles. Therefore, by using polyimide resin as the binder for the first coating layer, it is possible to prevent the fluororesin particles from falling off.

[0039] The polyimide resin is preferably an aromatic polyimide resin having an aromatic ring in the main chain, such as an imidized product of a polymer (polyamic acid) of a tetracarboxylic dianhydride and a diamine compound.

[0040] The content of polyimide resin in the first coating layer is preferably 10.0% by mass or more and 80.0% by mass or less, and more preferably 20.0% by mass or more and 40.0% by mass or less. By setting the content of polyimide resin to 10.0% by mass or more, it is possible to effectively prevent fluororesin particles from being detached from the first coating layer. By setting the content of polyimide resin to 80.0% by mass or less, it becomes easier for the first carrier to charge the toner.

[0041] (Fluororesin particles) The fluororesin particles contain a fluororesin. The content of the fluororesin in the fluororesin particles is, for example, 90% by mass or more, and preferably 100% by mass.

[0042] Examples of fluororesins include polytetrafluoroethylene (PTFE), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene, polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer.

[0043] As the fluororesin particles, PTFE particles, PFA particles, or FEP particles are preferred, and PFA particles or FEP particles are more preferred. Among fluororesins, PFA and FEP are excellent in chemical resistance, heat resistance, and electrical properties, as well as in abrasion resistance and processability. Therefore, by using PFA particles or FEP particles as the fluororesin particles, it is possible to impart preferable carrier properties to the first carrier and to easily produce the first carrier.

[0044] The number average primary particle diameter of the fluororesin particles is preferably 50 nm or more and 500 nm or less, and more preferably 200 nm or more and 300 nm or less. By setting the number average primary particle diameter of the fluororesin particles to 50 nm or more and 500 nm or less, detachment of the fluororesin particles from the first coating layer can be effectively suppressed.

[0045] The content of the fluororesin particles in the first coating layer is preferably 20.0% by mass or more and 90.0% by mass or less, and more preferably 60.0% by mass or more and 80.0% by mass or less. By setting the content of the fluororesin particles to 20.0% by mass or more, the first carrier can easily charge the toner. By setting the content of the fluororesin particles to 90.0% by mass or less, the amount of polyimide resin in the first coating layer is ensured. As a result, detachment of the fluororesin particles from the first coating layer can be effectively suppressed.

[0046] (carbon black particles) The carbon black particles promote charge transfer in the first coating layer. The first carrier can promote the imparting of charge to the toner particles by containing carbon black particles in the first coating layer. As a result, the developer set using the carrier set of the present invention can more effectively suppress the occurrence of fogging. Furthermore, the carbon black particles in the first coating layer can suppress fluctuations in the charge amount of the toner even when the toner concentration in the developer fluctuates.

[0047] The number-average primary particle diameter of the carbon black particles is preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 60 nm or less. By setting the number-average primary particle diameter of the carbon black particles to 10 nm or more, the developer using the carrier set of the present invention can more effectively suppress the occurrence of fogging. By setting the number-average primary particle diameter of the carbon black particles to 200 nm or less, the carbon black particles can be suppressed from detaching from the first coating layer.

[0048] In the first coating layer, the content of carbon black particles relative to 100 parts by mass of resin (total mass of polyimide resin and fluororesin particles) is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, and more preferably 0.5 parts by mass or more and 4.0 parts by mass or less. By setting the carbon black particle content to 0.1 parts by mass or more, the developer set using the carrier set of the present invention can more effectively suppress the occurrence of fogging. By setting the carbon black particle content to 10.0 parts by mass or less, detachment of carbon black particles from the first coating layer can be suppressed.

[0049] (Other ingredients) The first coating layer may further contain small amounts of other components in addition to the polyimide resin, fluororesin particles, and carbon black particles. Examples of other components include conductive materials other than carbon black particles and additives. Examples of conductive materials other than carbon black particles include metal oxide particles (e.g., titanium oxide particles and tin oxide particles) and organic conductive materials. Examples of additives include charge control agents, adhesion promoters, and crosslinking agents.

[0050] [Manufacturing method of the first carrier] An example of a method for manufacturing the first carrier will be described below. The method for manufacturing the first carrier includes a coating step of coating the surface of the first carrier core with a coating liquid, and a heating step of heating the coated first carrier core.

[0051] (Coating process) In this process, the surface of the first carrier core is coated with a coating liquid. The coating liquid contains a polyimide resin (e.g., uncured polyimide resin), fluororesin particles, a solvent, and other components (e.g., carbon black particles) that are added as needed. This process yields a first carrier core coated with the coating liquid.

[0052] Methods for coating the surfaces of the first carrier cores with a coating liquid include, for example, immersing the first carrier cores in the coating liquid and spraying the coating liquid onto the first carrier cores in a fluidized bed. When immersing the first carrier cores in the coating liquid, a small amount of the coating liquid is applied to the convex portions on the surface of the first carrier core, while a large amount of the coating liquid is applied to the concave portions on the surface of the first carrier core, which tends to result in uneven application of the coating liquid. In contrast, spraying the coating liquid onto the first carrier cores in a fluidized bed tends to result in uniform application of the coating liquid to both the convex portions and the concave portions on the surface of the first carrier core. Based on the above, spraying the coating liquid onto the first carrier cores in a fluidized bed is preferred as a method for applying the coating liquid onto the surfaces of the first carrier cores.

[0053] (Heating process) In this process, the coated first carrier core is heated to remove the solvent contained in the coating liquid. If the coating liquid contains uncured polyimide resin, the uncured polyimide resin is thermally cured. As a result, a first coating layer is formed from the coating liquid. Heating conditions can be, for example, a heating temperature of 150°C to 300°C and a heating time of 30 minutes to 90 minutes.

[0054] [Second carrier particle] The second carrier particles have a second carrier core and a second coating layer covering the surface of the second carrier core. The second carrier core can be, for example, the same as the first carrier core. Therefore, a description of the second carrier core will be omitted.

[0055] (Second coating layer) The second coating layer contains a silicone resin and barium titanate particles. The second coating layer preferably further contains carbon black particles. The total content of the silicone resin, barium titanate particles, and carbon black particles in the second coating layer is preferably 90% by mass or more, and more preferably 100% by mass.

[0056] The mass of the second coating layer relative to 100 parts by mass of the second carrier core is preferably 0.5 parts by mass or more and 10.0 parts by mass or less. By setting the mass of the second coating layer to 0.5 parts by mass or more, exposure of the second carrier core can be suppressed. By setting the mass of the second coating layer to 10.0 parts by mass or less, the second carrier can easily charge the toner.

[0057] (silicone resin) Silicone resin is a resin having a polysiloxane structure (e.g., alkylpolysiloxane structure). Examples of silicone resins include silicone resins having methyl groups and epoxy resin-modified silicone resins. Examples of silicone resins having methyl groups include silicone resins having methyl groups but not phenyl groups, and silicone resins having methyl groups and phenyl groups (hereinafter sometimes referred to as "methylphenylsilicone resin"). As the silicone resin, methylphenylsilicone resin or epoxy resin-modified silicone resin is preferred.

[0058] The content of the silicone resin in the second coating layer is preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less. By setting the content of the silicone resin to 60% by mass or more, it is possible to prevent the barium titanate particles from being detached from the second coating layer. By setting the content of the silicone resin to 95% by mass or less, it is possible to ensure a sufficient amount of barium titanate particles in the second coating layer.

[0059] The second coating layer preferably contains only a silicone resin as the resin, but may further contain other resins. The content of the silicone resin in the entire resin contained in the second coating layer is preferably 90 mass % or more, and more preferably 100 mass %.

[0060] The content of the silicone resin in the second coating layer is preferably 0.3 parts by mass or more and 8.0 parts by mass or less per 100 parts by mass of the carrier core. By setting the content of the silicone resin to 0.3 parts by mass or more, it is possible to suppress the detachment of barium titanate particles from the second coating layer. By setting the content of the silicone resin to 8.0 parts by mass or less, it is possible to suppress the occurrence of fogging in the developer set using the carrier set of the present invention.

[0061] (barium titanate particles) The barium titanate particles contain barium titanate. The content of barium titanate in the barium titanate particles is, for example, 90% by mass or more, and preferably 100% by mass.

[0062] The number-average primary particle diameter of the barium titanate particles is preferably 40 nm to 400 nm, more preferably 60 nm to 200 nm, and more preferably 80 nm to 120 nm. By setting the number-average primary particle diameter of the barium titanate particles to 40 nm or more, the developer set using the carrier set of the present invention can suppress the occurrence of fogging. By setting the number-average primary particle diameter of the barium titanate particles to 500 nm or less, the barium titanate particles can be suppressed from detaching from the second coating layer.

[0063] In the second coating layer, the content of barium titanate per 100 parts by mass of silicone resin is preferably 2.0 parts by mass or more and 100.0 parts by mass or less, more preferably 4.0 parts by mass or more and 60.0 parts by mass or less, and even more preferably 15.0 parts by mass or more and 40.0 parts by mass or less. By setting the content of barium titanate particles to 2.0 parts by mass or more, the developer set using the carrier set of the present invention can more effectively suppress the occurrence of fogging. By setting the content of barium titanate particles to 100.0 parts by mass or less, detachment of barium titanate particles from the second coating layer can be suppressed.

[0064] (Method of manufacturing barium titanate particles) The method for producing barium titanate particles is not particularly limited, but examples thereof include hydrothermal synthesis. Barium titanate particles produced by hydrothermal synthesis have voids inside them, resulting in a low true specific gravity. Furthermore, the particle size distribution of barium titanate particles produced by hydrothermal synthesis is sharp. For these reasons, barium titanate particles produced by hydrothermal synthesis are likely to be uniformly dispersed in the second coating layer, making it easy to obtain a second carrier with uniform charge-imparting ability. For these reasons, it is preferable that the barium titanate particles are a hydrothermal synthesis product.

[0065] (carbon black particles) The carbon black particles contained in the second coating layer may be the same as the carbon black particles contained in the first coating layer.

[0066] In the second coating layer, the content of carbon black particles relative to 100 parts by mass of silicone resin is preferably 1.0 part by mass or more and 20.0 parts by mass or less, and more preferably 5.0 parts by mass or more and 10.0 parts by mass or less. By setting the content of carbon black particles to 1.0 part by mass or more, the developer set using the carrier set of the present invention can more effectively suppress the occurrence of fogging. By setting the content of carbon black particles to 20.0 parts by mass or less, detachment of carbon black particles from the second coating layer can be suppressed.

[0067] (Other ingredients) The second coating layer may further contain components other than the silicone resin, barium titanate particles, and carbon black particles, such as the components exemplified for the first coating layer.

[0068] [Second carrier manufacturing method] The second carrier can be manufactured in the same manner as the first carrier, except for changing the composition of the coating liquid used in the coating step, so only the coating liquid will be described below.

[0069] (coating liquid) The coating liquid contains a silicone resin (for example, an uncured silicone resin), barium titanate particles, a solvent, and other components (for example, carbon black particles) that are added as needed.

[0070] <Second embodiment: developer set> A developer set according to a second embodiment of the present invention uses the carrier set described in the first embodiment. The developer set of the present invention includes a first developer containing a first carrier and a toner, and a second developer containing a second carrier and a toner.

[0071] The developer set of the present invention is preferably a developer set used in an image forming apparatus using a trickle development system. In this case, the first developer is preferably used as an initial developer contained in the developing device. The second developer is preferably used as a replenishment developer that is replenished into the developing device after the initial developer has started to be used. The first developer used as the initial developer has a first carrier as its main component and contains a small amount of toner. The second developer used as the replenishment developer has a toner as its main component and contains a small amount of carrier.

[0072] The first developer is obtained by mixing the first carrier and toner while stirring them using, for example, a mixer (more specifically, for example, a bowl mill and a rocking mixer (registered trademark)). The toner concentration in the first developer is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less.

[0073] The second developer is obtained by, for example, mixing the second carrier and toner while stirring them using the mixer described above. The toner concentration in the second developer is preferably 60% by mass or more and 97% by mass or less, and more preferably 80% by mass or more and 92% by mass or less. Since the first carrier and the second carrier have already been described in the first embodiment, only the toner will be described below.

[0074] [toner] The toner includes toner particles. The toner particles include toner base particles and external additives that adhere to the surfaces of the toner base particles. The external additives include inorganic particles and resin particles. The toner includes toner particles. Details of the toner will be described below with reference to the drawings as appropriate.

[0075] Fig. 4 shows an example of a toner particle 21 contained in the toner. The toner particle 21 shown in Fig. 4 includes a toner base particle 22 and an external additive 23 attached to the surface of the toner base particle 22. The external additive 23 includes resin particles 23a and inorganic particles 23b.

[0076] The toner particles have been described above with reference to the drawings. However, the toner particles may have a structure different from that of the toner particles 21 shown in FIG. 4. Specifically, the toner particles may contain particles other than resin particles and inorganic particles as external additives (hereinafter, these may be referred to as "other external additive particles"). The toner mother particles may be capsule toner particles that include a toner core and a shell layer that covers the toner core.

[0077] (resin particles) The resin particles function as spacers that prevent the inorganic particles from being detached from the toner base particles and from being embedded in the toner base particles. As the resin particles, styrene-(meth)acrylic resin particles are preferred.

[0078] The styrene-(meth)acrylic resin particles contain a styrene-(meth)acrylic resin. The styrene-(meth)acrylic resin is a copolymer of styrene and an acrylic monomer. Examples of the acrylic monomer include (meth)acrylic acid, (meth)acrylonitrile, and (meth)acrylic acid alkyl ester.

[0079] Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0080] The styrene-(meth)acrylic resin is preferably a copolymer of styrene and butyl (meth)acrylate.

[0081] The number-average primary particle diameter of the resin particles is preferably 20 nm or more and 300 nm or less, and more preferably 20 nm or more and 100 nm or less. By setting the number-average primary particle diameter of the resin particles to 20 nm or more, it is possible to prevent the resin particles from being embedded in the toner base particles. Furthermore, by setting the number-average primary particle diameter of the resin particles to 300 nm or less, it is possible to prevent the resin particles from being detached from the toner base particles.

[0082] From the viewpoint of fully exerting the function of the resin particles while suppressing detachment from the toner base particles, the content of the resin particles in the toner particles is preferably 0.1 parts by mass or more and 3.0 parts by mass or less, and more preferably 0.3 parts by mass or more and 1.0 parts by mass or less, per 100 parts by mass of the toner base particles.

[0083] (Inorganic particles) Examples of inorganic particles include silica particles and particles of metal oxides (more specifically, aluminum oxide particles, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate). The toner preferably contains, as inorganic particles, silica particles and inorganic particles other than silica particles (particularly, aluminum oxide or titanium oxide). The number-average primary particle diameter of the inorganic particles is preferably 1 nm or more and 100 nm or less, more preferably 5 nm or more and 40 nm or less.

[0084] When the toner particles contain inorganic particles, the content thereof is preferably 0.01 parts by mass to 10.0 parts by mass, more preferably 0.1 parts by mass to 5.0 parts by mass, relative to 100 parts by mass of the toner base particles.

[0085] (Toner base particles) The toner base particles contain, for example, a binder resin and at least one selected from the group consisting of a colorant, a charge control agent, and a release agent. The binder resin, the colorant, the charge control agent, and the release agent will be described below.

[0086] (binder resin) To obtain a toner with excellent low-temperature fixability, the toner base particles preferably contain a thermoplastic resin as a binder resin, and more preferably contain the thermoplastic resin in a proportion of 85% by mass or more of the total binder resin. Examples of thermoplastic resins include polyester resins, styrene-based resins, acrylic ester-based resins (more specifically, acrylic ester polymers, methacrylic ester polymers, etc.), olefin-based resins (more specifically, polyethylene resins, polypropylene resins, etc.), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, etc.), polyamide resins, and urethane resins. Copolymers of these resins, i.e., copolymers in which any repeating unit is introduced into the above resins (more specifically, styrene-acrylic resins, styrene-butadiene-based resins, etc.), can also be used as binder resins.

[0087] The binder resin is preferably a polyester resin. The polyester resin is a polymer of one or more polyhydric alcohol monomers and one or more polycarboxylic acid monomers. Instead of the polycarboxylic acid monomers, polycarboxylic acid derivatives (more specifically, polycarboxylic acid anhydrides, polycarboxylic acid halides, etc.) may be used.

[0088] The polyester resin is preferably an amorphous polyester resin. It is often impossible to measure a clear melting point for an amorphous polyester resin. Therefore, a polyester resin whose endothermic curve measured using a differential scanning calorimeter does not clearly show an endothermic peak can be considered an amorphous polyester resin.

[0089] (coloring agent) As the colorant, known pigments or dyes can be used in accordance with the color of the toner, and examples of the colorant include black colorants, yellow colorants, magenta colorants, and cyan colorants.

[0090] An example of a black colorant is carbon black. The black colorant may also be a colorant toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

[0091] In the toner, the content of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0092] (charge control agent) Charge control agents are used, for example, to obtain toners with excellent charge stability and charge buildup characteristics. The charge buildup characteristics of a toner are an indicator of whether the toner can be charged to a predetermined charge level in a short period of time. Examples of charge control agents include positive charge control agents and negative charge control agents. By incorporating a positive charge control agent into the toner base particles, the cationic character (positive chargeability) of the toner can be strengthened. By incorporating a negative charge control agent into the toner base particles, the anionic character (negative chargeability) of the toner can be strengthened. Examples of positive charge control agents include pyridine, nigrosine, and quaternary ammonium salts. In the toner, the content of the charge control agent is preferably 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the binder resin.

[0093] (mold release agent) The release agent is used, for example, for the purpose of obtaining a toner with excellent hot offset resistance. Examples of the release agent include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant-derived waxes, animal-derived waxes, mineral-derived waxes, ester waxes mainly composed of fatty acid esters, and waxes in which fatty acid esters are partially or completely deoxidized. A preferred release agent is a plant-derived wax (e.g., carnauba wax). In the toner, the content of the release agent is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the binder resin.

[0094] The toner particles may contain known additives as needed. The volume median diameter of the toner particles is preferably 4 μm or more and 12 μm or less. The volume median diameter of the toner base particles is preferably 4 μm or more and 12 μm or less, and more preferably 5 μm or more and 9 μm or less.

[0095] [Toner manufacturing method] An example of a toner manufacturing method will be described. The toner manufacturing method includes a toner base particle preparation step for preparing toner base particles and an external addition step for attaching external additives to the surfaces of the toner base particles. The external additives include resin particles and inorganic particles.

[0096] (Toner base particle preparation process) In the toner base particle preparation step, the toner base particles are prepared by, for example, a pulverization method or an aggregation method. In the toner base particle preparation step, the toner base particles are preferably prepared by a pulverization method. That is, in the toner, the toner base particles are preferably pulverized toner base particles.

[0097] (External addition process) In this step, the external additive is attached to the surface of the toner base particles. As a method for attaching the external additive to the surface of the toner base particles, for example, a method of mixing the toner base particles and the external additive particles while stirring them using a mixer can be mentioned. [Example]

[0098] The present invention will be described in more detail below using examples, but the present invention is not limited to the scope of the examples.

[0099] The number-average primary particle diameters of the barium titanate particles, carbon black particles, and carrier cores were measured using a scanning electron microscope (field-emission scanning electron microscope, "JSM-7600F" manufactured by JEOL Ltd.) In measuring the number-average primary particle diameter, the circle-equivalent diameters (Heywood diameter: diameter of a circle having the same area as the projected area of ​​a primary particle) of 100 primary particles were measured, and the number-average value was calculated.

[0100] <Preparation of carrier> Carriers (C-1) to (C-11) shown in Table 1 were prepared by the following method. First, the components used in the preparation of the carriers will be described.

[0101] Polyimide resin solution: a solution containing uncured polyimide resin ("COMPOCERAN (registered trademark) H801D" manufactured by Arakawa Chemical Industries, Ltd., resin concentration 15% by mass) Polyamide-imide resin solution: a solution containing polyamide-imide resin ("COMPOCERAN (registered trademark) AI301" manufactured by Arakawa Chemical Industries, Ltd., resin concentration: 18% by mass) PFA particles: Custom-made by DuPont, number-average primary particle diameter 250 nm FEP particles: Custom-made by DuPont, number-average primary particle diameter 250 nm PTFE particles: Custom-made by DuPont, number-average primary particle diameter 250 nm Carrier core: Manganese ferrite particles (manufactured by DOWAIP Creation Co., Ltd., volume median diameter 20.3 μm, saturation magnetization 67 emu / g) Silicone resin solution (KR-255): Methylphenyl silicone resin-containing solution ("KR-255" manufactured by Shin-Etsu Chemical Co., Ltd., resin concentration: 50% by mass) Silicone resin solution (KR-301): Methylphenyl silicone resin-containing solution ("KR-301" manufactured by Shin-Etsu Chemical Co., Ltd., resin concentration: 40% by mass) Silicone resin solution (ES-1001N): Epoxy resin-modified silicone resin-containing solution ("ES-1001N" manufactured by Shin-Etsu Chemical Co., Ltd., resin concentration: 45% by mass) Barium titanate particles: Particles containing barium titanate produced by hydrothermal synthesis ("BT-01" manufactured by Sakai Chemical Industry Co., Ltd., number average primary particle diameter: 102 nm) Carbon black particles (EC): Carbon black (Ketjenblack (registered trademark) EC300J, manufactured by Lion Specialty Chemicals Co., Ltd., number average primary particle diameter 39.5 μm) Carbon black particles (MA): Carbon black ("MA100" manufactured by Mitsubishi Chemical Corporation, number-average primary particle diameter 24 nm)

[0102] [Career (C-1)] The coating solution was prepared by dispersing PFA particles and carbon black particles (EC) in a polyimide resin solution. The amounts of each component were adjusted so that the ratio of PFA particles, uncured polyimide resin, and carbon black particles (EC) was 70:30:2.

[0103] Using a fluidized bed coating device ("Spiraflow (registered trademark) SFC-5" manufactured by Freund Corporation), the entire amount of the above-mentioned coating liquid (containing 3 parts by mass of solids) was sprayed onto 100 parts by mass of carrier cores to coat them. In this way, carrier cores coated with the coating liquid were obtained. Next, the carrier cores coated with the coating liquid were heated at 200°C for 60 minutes. This resulted in a carrier (C-1) comprising a carrier core and a coating layer covering the carrier core. The coating layer contained a polyimide resin, PFA particles, and carbon black particles.

[0104] [Career (C-2)] A carrier (C-2) was prepared in the same manner as in the preparation of the carrier (C-1), except that an equal amount of FEP particles was used in place of the PFA particles in the preparation of the coating liquid.

[0105] [Career (C-3)] A coating liquid was prepared by dispersing the following materials using a homomixer. Silicone resin solution (KR-255): 361.2 parts by weight (resin amount 180.6 parts by weight) Barium titanate particles: 18.1 parts by weight (10.0 parts by weight per 100 parts by weight of silicone resin) Carbon black particles (EC): 14.4 parts by weight (8.0 parts by weight per 100 parts by weight of silicone resin) Toluene: 1444.8 parts by mass

[0106] (Coating process and heating process) Using a fluidized bed coating device (Powrex Corporation, "FD-MP-01 D type"), 5000 parts by mass of carrier cores were fluidized, and the entire amount of the coating solution (containing 213.1 parts by mass of solids) was sprayed onto the carrier cores. In this way, carrier cores coated with the coating solution were obtained. The coating conditions were an inlet air temperature of 75°C and an inlet air volume of 0.3 m. 3 The rotor speed was set to 400 rpm. The carrier cores coated with the coating solution were then baked in an electric furnace at 200°C for 1 hour. This resulted in a carrier (C-3) having carrier cores and a coating layer covering the carrier cores. The coating layer contained silicone resin, barium titanate particles, and carbon black particles.

[0107] [Career (C-4)] Carrier (C-4) was prepared in the same manner as carrier (C-3), except that the amount of barium titanate used in preparing the coating liquid was changed to 54.2 parts by mass (30.0 parts by mass per 100 parts by mass of silicone resin).

[0108] [Career (C-5)] A carrier (C-5) was prepared in the same manner as in the preparation of the carrier (C-1), except that an equal amount of PTFE particles was used in place of the PFA particles in the preparation of the coating liquid.

[0109] [Career (C-6)] Carrier (C-6) was prepared in the same manner as carrier (C-1), except for the following changes: In the preparation of carrier (C-6), an equal amount of FEP particles was used in place of PFA particles in the preparation of the coating solution; and in the preparation of carrier (C-6), an equal amount (in terms of resin volume) of polyamideimide resin solution was used in place of the polyimide resin solution.

[0110] [Career (C-7)] A carrier (C-7) was prepared in the same manner as in the preparation of the carrier (C-1), except that an equal amount of carbon black particles (MA) was used in place of the carbon black particles (EC) in the preparation of the coating liquid.

[0111] [Career (C-8)] A carrier (C-8) was prepared in the same manner as in the preparation of the carrier (C-3), except that no barium titanate particles were used in the preparation of the coating liquid.

[0112] [Career (C-9)] Carrier (C-9) was prepared in the same manner as carrier (C-3), except that an equal amount of silicone resin solution (KR-301) was used in place of silicone resin solution (KR-255) in the preparation of the coating liquid.

[0113] [Carrier (C-10)] Carrier (C-10) was prepared in the same manner as carrier (C-3), except that an equal amount of silicone resin solution (ES-1001N) was used in place of silicone resin solution (KR-255) in the preparation of the coating liquid.

[0114] [Carrier (C-11)] A carrier (C-11) was prepared in the same manner as in the preparation of the carrier (C-3), except that an equal amount of carbon black particles (MA) was used instead of the carbon black particles (EC) in the preparation of the coating liquid.

[0115] [Carrier (C-12)] A carrier (C-12) was prepared in the same manner as in the preparation of the carrier (C-1), except that the PFA particles were not used in the preparation of the coating liquid.

[0116] In Tables 3 and 4 below, "BaTiO3 particles," "parts by mass," "PI," "PAI," "Si(KR-255)," "Si(KR-301)," and "Si(ES-1001N)" represent "barium titanate particles," "parts by mass per 100 parts by mass of resin contained in the resin solution," "polyimide resin solution," "polyamide-imide resin solution," "silicone resin solution (KR-255)," "silicone resin solution (KR-301)," and "silicone resin solution (ES-1001N)," respectively.

[0117] [Table 1]

[0118] [Toner Preparation] Toners (T-1) to (T-3) shown in Table 2 were prepared by the following method: First, raw materials used in preparing each toner were prepared.

[0119] (Synthesis of amorphous polyester resin) A reaction vessel equipped with a thermometer (thermocouple), a dehydration tube, a nitrogen gas inlet tube, and a stirrer (stirring blade) was placed in an oil bath. 1,575 parts by mass of BPA-PO (bisphenol A propylene oxide adduct), 163 parts by mass of BPA-EO (bisphenol A ethylene oxide adduct), 377 g of fumaric acid, and 4 parts by mass of catalyst (dibutyltin oxide) were added to the reaction vessel. A nitrogen atmosphere was then created inside the reaction vessel, and the temperature inside the reaction vessel was raised to 220°C using an oil bath while stirring the contents. Under the nitrogen atmosphere and at 220°C, the contents of the reaction vessel were polymerized for 8 hours while distilling off by-product water. The pressure inside the reaction vessel was then reduced, and the contents of the reaction solution were polymerized for an additional hour under reduced pressure (pressure: 8 kPa) at 220°C. The temperature inside the reaction vessel was then lowered to 210°C, and 336 parts by mass of trimellitic anhydride was added to the reaction vessel. The contents of the reaction vessel were then reacted under conditions of a reduced pressure atmosphere (pressure: 8 kPa) and a temperature of 210°C. The reaction time was adjusted so that the physical properties of the reaction product, an amorphous polyester resin, would be as follows. The reaction product was then removed from the reaction vessel and cooled to obtain an amorphous polyester resin having the following physical properties. Note that the obtained polyester resin was determined to be amorphous because no clear endothermic peak was observed in the endothermic curve measured using a differential scanning calorimeter, and a clear melting point could not be measured.

[0120] (Physical properties of amorphous polyester resin) Softening point (Tm): 100℃ Glass transition temperature (Tg): 50℃ Mass average molecular weight (Mw): 30,000 Acid value: 15mgKOH / g Hydroxyl value: 30 mg KOH / g

[0121] (Preparation of Toner Base Particles) Using an FM mixer ("FM-10B" manufactured by Nippon Coke and Engineering Co., Ltd.), 100 parts by mass of binder resin, 4 parts by mass of colorant, 1 part by mass of charge control agent, and 5 parts by mass of release agent were mixed to obtain a mixture. The binder resin used was the amorphous polyester resin described above. The colorant used was copper phthalocyanine blue pigment (CI Pigment Blue 15:3). The charge control agent used was a quaternary ammonium salt ("BONTRON (registered trademark) P-51" manufactured by Orient Chemical Industries Co., Ltd.). The release agent used was carnauba wax ("Special Carnauba Wax No. 1" manufactured by Kato Yoko Co., Ltd.).

[0122] The resulting mixture was melt-kneaded using a twin-screw extruder ("PCM-30" manufactured by Ikegai Corporation) to obtain a melt-kneaded product. The melt-kneaded product was pulverized using a mechanical pulverizer ("Turbo Mill" manufactured by Freund-Turbo Corporation) to obtain a pulverized product. The pulverized product was classified using a classifier ("Elbow Jet" manufactured by Nittetsu Mining Co., Ltd.). This resulted in powdered toner base particles with a volume median diameter of 6.8 μm.

[0123] (Preparation of Resin Particles) A glass reaction vessel equipped with a thermometer (thermocouple), a stirrer, a reflux condenser, and a nitrogen gas inlet tube was placed in an 80°C water bath. 300 parts by mass of ion-exchanged water and 1 part by mass of di-tert-butyl peroxide were added to the reaction vessel to obtain a solution. While maintaining the resulting solution at 80°C and stirring, 0.2 parts by mass of ammonium persulfate and 60 parts by mass of a monomer mixture were added dropwise to the solution over 1 hour under a nitrogen gas atmosphere. The monomer mixture was a mixture of 20 mol% styrene and 80 mol% butyl methacrylate. The contents of the reaction vessel were then polymerized while stirring. The polymerization reaction conditions were a reaction temperature of 100°C, a reaction time of 3 hours, and a stirring speed of 1400 rpm. The emulsion solution obtained by the reaction was dried to obtain resin particles (R1). The number-average primary particle diameter of the resin particles (R1) was 30 nm.

[0124] (Preparation of Toner (T-1)) 100.0 parts by mass of the above-mentioned toner base particles, 0.5 parts by mass of the above-mentioned resin particles (R1), 1.0 part by mass of silica particles, and 0.5 parts by mass of titanium dioxide particles were mixed for 5 minutes at 4,000 rpm using an FM mixer ("FM-20B" manufactured by Nippon Coke & Engineering Co., Ltd.). The silica particles were "AEROSIL (registered trademark) RA-200" manufactured by Nippon Aerosil Co., Ltd. (BET specific surface area: approximately 150 m). 2 / g, number average primary particle size: approx. 12 nm, density: approx. 2.2 g / cm 3 The titanium dioxide particles used were "NT-TiO2-11" (BET specific surface area: 15 to 35 m) manufactured by EM Japan Co., Ltd. 2 / g, number average primary particle size: approx. 100 nm, density: 4.23 g / cm 3 The resulting mixture was sieved using a 200 mesh (openings 75 μm) sieve to obtain toner (T-1).

[0125] (Preparation of Toner (T-2)) Instead of titanium dioxide particles, aluminum oxide particles (AEROXIDE (registered trademark) Alu C805 manufactured by Nippon Aerosil Co., Ltd., BET specific surface area: 75 to 105 m) were used. 2 Toner (T-2) was prepared in the same manner as in the preparation of toner (T-1), except that 0.75 parts by mass ( / g) of the toner was used.

[0126] (Preparation of Toner (T-3)) Toner (T-3) was prepared in the same manner as in the preparation of toner (T-1), except that resin particles (R1) were not used.

[0127] [Table 2]

[0128] <Preparation of Developer> The carrier and toner shown in Table 3 below were combined to prepare initial developers and replenishment developers. First, 8 parts by mass of toner and 100 parts by mass of carrier were mixed for 30 minutes using a powder mixer (Aichi Electric Co., Ltd.'s "Rocking Mixer (registered trademark)", mixing method: container rotation and shaking method). This resulted in initial developers (A-1) to (A-12) (toner concentration: approximately 7% by mass). Furthermore, using the above powder mixer, 100 parts by mass of toner and 10 parts by mass of carrier were mixed for 30 minutes. This resulted in replenishment developers (B-1) to (B-13) (toner concentration: approximately 91% by mass).

[0129] [Table 3]

[0130] <Evaluation> Initial developers (A-1) to (A-12) and replenishment developers (B-1) to (B-13) were combined as shown in Table 4 below to prepare developer sets of Examples 1 to 14 and Comparative Examples 1 to 10. Then, the image density and fogging when images were formed using the developer sets of each Example and Comparative Example were evaluated. The evaluation results are shown in Table 5 below. However, with the developer set of Comparative Example 10, the toner scattered inside the evaluation machine, making it impossible to form a proper image. Therefore, in Table 5 below, each measurement value is marked with "-".

[0131] [Table 4]

[0132] [Evaluation machine] The evaluation machine used was a color multifunction printer (TASKalfa 7054ci manufactured by Kyocera Document Solutions Inc., photoreceptor drum: amorphous silicon drum). This evaluation machine was equipped with a photoreceptor, a developing device that develops an electrostatic latent image formed on the photoreceptor with developer (more specifically, toner contained in the developer), a developer discharge unit that discharges the developer in the developing device, and a replenishment developer supply unit that replenishes replenishment developer into the developing device.

[0133] An initial developer (specifically, any one of the initial developers (A-1) to (A-12)) was placed in the cyan developing device of the evaluation machine. In addition, a replenishment developer (specifically, any one of the replenishment developers (B-1) to (B-13)) was placed in the replenishment cyan developer supply unit of the evaluation machine.

[0134] [Recording Media] A4 size plain paper ("ColorCopy (registered trademark)" manufactured by Mondi) was used as the recording medium.

[0135] [Image formation] Using the above-mentioned evaluation machine, an image (a character pattern image with a print rate of 4%) was printed on 500,000 sheets of recording medium in an environment with a temperature of 20°C and a humidity of 65% RH. The evaluation machine was set to print seven sheets of recording medium in succession and then stop printing (intermittent printing). When the evaluation machine received a print command, it developed the electrostatic latent image on the photoreceptor with the initial developer in the cyan developing device, and printed on the recording medium. The evaluation machine then discharged the developer in the cyan developing device and replenished the replenishment developer into the cyan developing device, while developing the electrostatic latent image on the photoreceptor with the developer in the cyan developing device, thereby continuing to print on the recording medium.

[0136] In the image formation described above, it is believed that by replenishing and discharging the developer, approximately 50% by mass of the carrier is replaced every time 100,000 sheets of recording media are printed (half-life: 100,000 prints). Because the initial carrier contained in the initial developer is used from the beginning of the printing cycle, by the time the 100,000th sheet of recording media is printed, approximately half of it has been discharged from the cyan developing device. Furthermore, the functionality of the initial carrier remaining in the cyan developing device gradually deteriorates as toner components adhere to its surface. In contrast, the replenishment carrier contained in the replenishment developer is continually replenished to the cyan developing device in a fresh state. As a result, it is believed that by the time the 100,000th sheet of recording media is printed, the initial carrier has little impact on the print results, and the influence of the replenishment carrier has become dominant.

[0137] In the above-mentioned printing, after the first (initial) printing, the 1000th printing, the 100,000th printing, and the 500,000th printing, an evaluation image (an image including a solid image portion and a blank portion) was printed on the recording medium using an evaluation machine. The image density (ID) and the fog density (FD) were measured for each of the recording media on which the evaluation image was printed.

[0138] [Image Density] The image density was measured using a reflection densitometer (SpectroEye (registered trademark) manufactured by X-Rite) to measure the reflection density (image density (ID)) of the solid image portion of the recording medium on which the evaluation image was printed. The image density was judged according to the following criteria.

[0139] (Image density standard) A (good): The image density is 1.30 or higher on all of the 1st, 1000th, 100,000th, and 500,000th sheets. B (bad): The image density is less than 1.30 on at least one of the 1st, 1000th, 100,000th, and 500,000th sheets.

[0140] [Cover] In measuring the fog density, the reflection density of the blank area of ​​the recording medium on which the evaluation image was printed was measured using the reflection densitometer described above. The reflection density of an unprinted recording medium was also measured using the reflection densitometer described above. The fog density was then calculated based on the formula "Fog density = Reflection density of blank area - Reflection density of unprinted recording medium." The fog density was judged according to the following criteria.

[0141] (Fog standard) A (good): The fog density is 0.005 or less on the 1st, 1000th, 100,000th, and 500,000th sheets. B (poor): The fog density exceeds 0.005 on at least one of the 1st, 1000th, 100,000th, and 500,000th sheets.

[0142] In Table 5 below, "initial," "1k," "100k," and "500k" represent "1st sheet," "1000th sheet," "100,000th sheet," and "500,000th sheet," respectively.

[0143] [Table 5]

[0144] As shown in Tables 1 to 5, the carrier sets used in the developer sets of Examples 1 to 14 included a first carrier containing first carrier particles and a second carrier containing second carrier particles. The first carrier particles had a first carrier core and a first coating layer covering the surface of the first carrier core. The first coating layer contained polyimide resin and fluororesin particles. The second carrier particles had a second carrier core and a second coating layer covering the surface of the second carrier core. The second coating layer contained silicone resin and barium titanate particles. The developer sets of Examples 1 to 14 had good image density and fog.

[0145] On the other hand, the carrier sets used in Comparative Examples 1, 3, 4, and 6 did not contain silicone resin and barium titanate particles in the coating layer of the replenishment carrier, but instead contained polyimide resin and fluororesin particles. As a result, in Comparative Examples 1, 3, 4, and 6, the occurrence of fogging could not be suppressed.

[0146] The carrier sets used in Comparative Examples 2, 5, and 7 did not contain polyimide resin and fluororesin particles in the coating layer of the initial carrier, but instead contained silicone resin and barium titanate particles. As a result, image density was poor in Comparative Examples 2, 5, and 7. Furthermore, in Comparative Example 2, the occurrence of fogging could not be suppressed.

[0147] The carrier set used in Comparative Example 8 did not contain a polyimide resin in the coating layer of the initial carrier, but contained a polyamide-imide resin instead. As a result, in Comparative Example 8, the occurrence of fogging could not be suppressed.

[0148] The carrier set used in Comparative Example 9 did not contain barium titanate particles in the coating layer of the refill carrier, and as a result, in Comparative Example 9, the occurrence of fogging could not be suppressed.

[0149] The carrier set used in Comparative Example 10 did not contain fluororesin particles in the coating layer of the initial carrier. As a result, in Comparative Example 10, the toner could not be sufficiently charged by the carrier, and proper image formation could not be performed. [Industrial Applicability]

[0150] The carrier set and developer set of the present invention can be used to form images in, for example, a copier, a printer, or a multifunction machine. [Explanation of symbols]

[0151] 1. First carrier particle 2. First Carrier Core 3 First coating layer 4 Polyimide resin 5 Fluorine resin particles 11 Secondary carrier particles 12 Second Carrier Core 13 Second coating layer 14 Silicone resin 15 Barium titanate particles 21 Toner particles 22 Toner base particles 23 External additives 23a Resin particles 23b Inorganic particles

Claims

1. A carrier set including a first carrier including first carrier particles and a second carrier including second carrier particles, the first carrier particles have a first carrier core and a first coating layer that coats the surface of the first carrier core; the first coating layer contains polyimide resin and fluororesin particles, the second carrier particles have a second carrier core and a second coating layer that coats the surface of the second carrier core; The second coating layer contains a silicone resin and barium titanate particles.

2. The carrier set according to claim 1 , wherein the first coating layer and the second coating layer each further contain carbon black particles.

3. 3. The carrier set according to claim 1, wherein the content of the fluororesin particles in the first coating layer is 20% by mass or more and 90% by mass or less.

4. 3. The carrier set according to claim 1, wherein the content of the barium titanate particles in the second coating layer is 3 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the silicone resin.

5. 3. The carrier set according to claim 1, wherein the fluororesin particles include PFA particles, PTFE particles, or FEP particles.

6. A developer set using the carrier set according to claim 1 or 2, a first developer containing the first carrier and toner; a second developer containing the second carrier and the toner;

7. the first developer is an initial developer contained in a developing device, 7. The developer set according to claim 6, wherein the second developer is a replenishment developer that is replenished into the developing device after the initial developer has been used.

8. the toner comprises toner particles; The toner particles include toner base particles and an external additive attached to the surface of the toner base particles, The developer set according to claim 6 , wherein the external additive contains resin particles and inorganic particles.

Images