Image forming apparatus and image forming method

Abstract

To provide an image forming apparatus or an image forming method excellent in fogging prevention properties.SOLUTION: In an image forming apparatus of a trickle development system of storing two-component developer including toner and carrier A in a developing machine, replenishing toner in correspondence with the toner to be consumed by development, and replenishing carrier for replenishment B, the carrier A has a magnetic core material A and a resin coating layer A covering the magnetic core material A, and the resin coating layer A does not include metal oxide particles, and the carrier for replenishment B has a magnetic core material B and a resin coating layer B covering the magnetic core material B, and the resin coating layer B includes metal oxide particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and an image forming method. [Background technology]

[0002] Patent Document 1 discloses a replenishment developer for use in a developing method in which a latent image on a latent image holder is developed using a developing machine containing a two-component developer consisting of toner and carrier, while the development is carried out while replenishment developer is being replenished, the replenishment developer containing carrier and toner in a weight ratio of 1 part carrier to 1 to 30 parts toner, and the carrier has the same electrical resistance as the carrier already contained in the developing machine, but imparts a higher amount of charge to the toner.

[0003] Patent Document 2 discloses a carrier having core particles and a coating layer that coats the core particles, wherein the coating layer contains a resin, inorganic fine particles, and an aluminum catalyst, and the aluminum catalyst contains one or more aluminum chelate compounds selected from the group consisting of diisopropoxyaluminum ethylacetoacetate, isopropoxybisethylacetoacetate aluminum, aluminum trisethylacetoacetate, and aluminum dibutoxide ethylacetoacetate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-223960 [Patent Document 2] Japanese Patent Publication No. 2023-5605 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an image forming apparatus or an image forming method that is superior in fogging suppression compared to when metal oxide particles are contained in the resin coating layers of both carrier A and replenishment carrier B. [Means for solving the problem]

[0006] Means for solving the above problems include the following aspects. <1> An image forming apparatus employing a trickle development system, in which a two-component developer containing toner and carrier A is stored in a developing machine, toner is replenished in accordance with the toner consumed during development, and replenishment carrier B is replenished, wherein the carrier A has a magnetic core material A and a resin coating layer A that coats the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B that coats the magnetic core material B, and the resin coating layer B contains metal oxide particles. <2> The metal oxide particles include at least one selected from the group consisting of silica particles, alumina particles, and titania particles. <1> 2. The image forming apparatus according to claim 1 . <3> The metal oxide particles include silica particles. <2> 2. The image forming apparatus according to claim 1 . <4> The volume average particle diameter D of the metal oxide particles is more than 3 nm and 85 nm or less. <1> ~ <3> 10. The image forming apparatus according to claim 9, wherein: <5> The content of the metal oxide particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer B. <1> ~ <4> 10. The image forming apparatus according to claim 9, wherein: <6> The ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less. <3> 2. The image forming apparatus according to claim 1 . <7> The ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishing carrier B is 0.5 or more and 8 or less. <1> ~ <6> 10. The image forming apparatus according to claim 9, wherein: <8> An image forming method using a trickle development system in which a two-component developer containing toner and carrier A is contained in a developing machine, and toner is replenished in accordance with the toner consumed during development, and replenishment carrier B is replenished, wherein the carrier A has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B coating the magnetic core material B, and the resin coating layer B contains metal oxide particles. <9> The metal oxide particles include at least one selected from the group consisting of silica particles, alumina particles, and titania particles. <8> The image forming method according to claim 1. <10> The metal oxide particles include silica particles. <9> The image forming method according to claim 1. <11> The volume average particle diameter D of the metal oxide particles is more than 3 nm and 85 nm or less. <8> ~ <10> 10. The image forming method according to claim 9, wherein the image forming method is a method for forming an image. <12> The content of the metal oxide particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer B. <8> ~ <11> 10. The image forming method according to claim 9, wherein the image forming method is a method for forming an image. <13> The ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less. <10> The image forming method according to claim 1. <14> The ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishing carrier B is 0.5 or more and 8 or less. <8> ~ <13> 10. The image forming method according to claim 9, wherein the image forming method is a method for forming an image. [Effects of the Invention]

[0007] <1> or <2> According to the invention, an image forming apparatus is provided which is superior in fogging suppression compared to when the resin coating layers of both carrier A and replenishment carrier B contain metal oxide particles. <3> According to the invention, an image forming apparatus is provided that is superior in fogging suppression properties compared to when the inorganic particles are titania particles or alumina particles. <4> According to the invention, an image forming apparatus is provided that is more excellent in fogging suppression than when the volume average particle diameter D of the metal oxide particles is 3 nm or less or exceeds 85 nm. <5> According to the present invention, an image forming apparatus is provided that has better fogging suppression properties than when the content of the metal oxide particles is less than 10% by mass or more than 60% by mass relative to the total mass of the resin coating layer B. <6> According to the present invention, an image forming apparatus is provided that has better fogging suppression properties than when the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is less than 1.2 or more than 5. <7> According to the present invention, an image forming apparatus is provided that has better fogging suppression properties than when the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is less than 0.5 or more than 8.

[0008] <8> or <9> According to the invention, an image forming method is provided which is superior in fogging suppression compared to the case where metal oxide particles are contained in the resin coating layers of both carrier A and replenishment carrier B. <10> According to the invention, an image forming method is provided which is superior in fogging suppression properties compared to when the inorganic particles are titania particles or alumina particles. <11> According to the invention, an image forming method is provided which is superior in fogging suppression properties compared to when the volume average particle diameter D of the metal oxide particles is 3 nm or less or exceeds 85 nm. <12> According to the present invention, an image forming method is provided which has better fogging suppression properties than when the content of the metal oxide particles is less than 10% by mass or more than 60% by mass relative to the total mass of the resin coating layer B. <13> According to the present invention, an image forming method is provided which is superior in fogging suppression compared to when the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is less than 1.2 or more than 5. <14> According to the present invention, an image forming method is provided which has better fogging suppression properties than when the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is less than 0.5 or more than 8. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this specification, "electrostatic image developing carrier" is also referred to as "carrier," "electrostatic image developing toner" is also referred to as "toner," and "electrostatic image developer" is also referred to as "developer."

[0011] (Image forming device) The image forming apparatus according to this embodiment is an image forming apparatus of a trickle development type, in which a two-component developer containing toner and carrier A is stored in a developing machine, toner is replenished in accordance with the toner consumed during development, and replenishment carrier B is replenished, in which the carrier A has a magnetic core material A and a resin coating layer A that coats the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B that coats the magnetic core material B, and the resin coating layer B contains metal oxide particles.

[0012] Conventional image forming devices use a trickle system, which adds carrier along with the toner consumed during development and gradually replaces the carrier in the developing device to suppress changes in charge amount and stabilize image density. In conventional trickle-type image forming devices, when replenishment carrier is added, degraded carrier and non-degraded replenishment carrier are discharged at a 1:1 ratio, and it is assumed that the degraded carrier is gradually replaced by the replenishment carrier at a constant rate. In conventional image forming devices, it takes a long time for the contaminated carrier to be discharged, especially when printing low image density and a small number of pages with extremely low toner consumption, which can worsen the initial decrease in developer charge and cause fogging. In the image forming apparatus according to this embodiment, carrier A contained in the developing machine has a magnetic core material A and a resin coating layer A that coats the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and refill carrier B has a magnetic core material B and a resin coating layer B that coats the magnetic core material B, and the resin coating layer B contains metal oxide particles. Therefore, when refill carrier B, which is a highly reliable carrier with high fluidity and carrier A that is a degraded carrier with low fluidity, is added to carrier A, which is a degraded carrier with low fluidity, a difference in fluidity between the carriers occurs, and carrier A with poor fluidity is selectively discharged, thereby suppressing a decrease in developer charge and toner fogging.

[0013] The configuration of the image forming apparatus according to this embodiment will be described in detail below.

[0014] <Carrier A and supply carrier B> The image forming apparatus according to this embodiment is an image forming apparatus using a trickle development method, in which a two-component developer containing toner and carrier A is stored in a developing machine, and toner is replenished in accordance with the toner consumed during development, and carrier B is replenished. Furthermore, the carrier A has a magnetic core material A and a resin coating layer A that coats the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the refill carrier B has a magnetic core material B and a resin coating layer B that coats the magnetic core material B, and the resin coating layer B contains metal oxide particles. In this embodiment, when the term "carrier" is used, it refers to both carrier A and refill carrier B unless otherwise specified; when the term "magnetic core material" is used, it refers to both magnetic core material A and magnetic core material B unless otherwise specified; and when the term "resin coating layer" is used, it refers to both resin coating layer A and resin coating layer B unless otherwise specified.

[0015] <<Resin coating layer>> The carrier A has a resin coating layer A, and the resin coating layer A does not contain metal oxide particles, and the replenishing carrier B has a resin coating layer B, and the resin coating layer B contains metal oxide particles. Resins that can be used to form the resin coating layer include styrene-acrylic acid copolymers; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins.

[0016] From the viewpoint of image density stability, the resin coating layer preferably contains an acrylic resin having an aliphatic cyclic structure and an amino group, and more preferably contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. The aliphatic cyclic structure is preferably a cycloalkyl group, more preferably a cyclohexyl group. Specific examples of the acrylic resin having a cyclohexyl group include a homopolymer of an acrylic monomer having a cyclohexyl group, and a copolymer of an acrylic monomer having a cyclohexyl group and another monomer. Examples of acrylic monomers having a cyclohexyl group include cyclohexyl acrylate and cyclohexyl methacrylate. Furthermore, preferred examples of structural units having an aliphatic cyclic structure include structural units derived from cyclohexyl (meth)acrylate. From the viewpoint of image density stability, the acrylic resin having a structural unit with an aliphatic cyclic structure preferably contains 80% by mass or more of the structural unit with an aliphatic cyclic structure. As the acrylic monomer having an amino group, dialkylaminoalkyl(meth)acrylate is preferred, and dimethylaminoethyl(meth)acrylate is more preferred. From the viewpoint of image density stability, the acrylic resin having a structural unit having an amino group preferably contains 0.05% by mass or more and 5% by mass or less of the structural unit having an amino group, and more preferably 0.1% by mass or more and 2% by mass or less.

[0017] The resin coating layer B contains metal oxide particles. Examples of metal oxide particles include titania, silica, alumina, zinc oxide, tin oxide, antimony-doped tin oxide, tin-doped indium oxide, and aluminum-doped zinc oxide. The metal oxide particles may be contained either alone or in combination of two or more types. Among these, from the viewpoint of fogging suppression, the metal oxide particles are preferably at least one type of particles selected from the group consisting of silica, titania and alumina, and more preferably silica particles.

[0018] From the viewpoint of fogging suppression, the volume average particle diameter D of the metal oxide particles is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 85 nm or less, even more preferably 5 nm or more and 70 nm or less, and particularly preferably 6 nm or more and 30 nm or less. Within the above range, the metal oxide particles are appropriately embedded in the resin coating layer and detachment is suppressed, so that the replenishment carrier B has an excellent contamination suppression effect and excellent fluidity, resulting in even better fogging suppression. The volume average particle size of the metal oxide particles can be controlled, for example, by adjusting various conditions when producing the metal oxide particles.

[0019] The volume average particle size D of the metal oxide particles is measured as follows. The particle size distribution of the particles to be measured is measured using a Coulter Counter LS13 (manufactured by Beckman Coulter, Inc.) Based on the particle size distribution measured, a cumulative volume distribution is drawn for each divided particle size range (channel) from the smallest diameter side to measure the particle size distribution. Then, in the volume cumulative distribution drawn from the small diameter side, the particle diameter at 50% of the cumulative distribution is defined as the volume average particle diameter D. The volume average particle diameter D of the metal oxide particles can also be determined by analyzing the cross section of the magnetic particles. Specifically, the volume average particle diameter D of the metal oxide particles is determined by averaging the circle equivalent diameters of 100 metal oxide particles contained in the resin coating layer of the magnetic particles. Preferably, observation and analysis are performed using an FE-SEM capable of high-resolution imaging. Examples include the Regulus series "SU8010," "Regulus8100," "Regulus8220," "Regulus8230," "Regulus8240," and "ULTRA55" manufactured by Hitachi High-Tech Corporation, and the "JSM-IT800" manufactured by JEOL Ltd. The number average particle diameter of the inorganic particles contained in the resin coating layer may be the volume average particle diameter D of the inorganic particles measured with a laser diffraction / scattering particle size distribution measuring device.

[0020] The metal oxide particles contained in the resin coating layer may be metal oxide particles themselves, or may be metal oxide particles (sometimes referred to as mother particles) whose surfaces have been hydrophobized. From the viewpoint of fogging suppression, however, surface-treated metal oxide particles are preferred, and metal oxide particles whose surfaces have been hydrophobized are more preferred.

[0021] The surface treatment of metal oxide particles is carried out, for example, by preparing a treatment liquid by mixing a silicon-containing organic compound, which is a hydrophobic treatment agent, with a solvent, and mixing the metal oxide particles with the treatment liquid under stirring, and then continuing to stir. After the surface treatment, a drying treatment is carried out to remove the solvent from the treatment liquid.

[0022] Examples of the silicon-containing organic compound used for the surface treatment of the metal oxide particles include alkoxysilane compounds, silazane compounds, and silicone oils.

[0023] Examples of alkoxysilane compounds used for the hydrophobic treatment of the surfaces of metal oxide particles include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, n-octyltrimethoxysilane, decyltriethoxy ... Examples of suitable silanes include triethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane.

[0024] Examples of silazane compounds used for the hydrophobic treatment of the surfaces of metal oxide particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0025] Examples of silicone oils used for the surface treatment of metal oxide particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0026] As the solvent used in preparing the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, an alcohol (e.g., methanol, ethanol, propanol, butanol) is preferred, and when the silicon-containing organic compound is a silicone oil, a hydrocarbon (e.g., benzene, toluene, normal hexane, normal heptane) is preferred.

[0027] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass.

[0028] The amount of the silicon-containing organic compound used for the surface treatment is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the metal oxide particles.

[0029] From the viewpoint of fogging suppression, the content of metal oxide particles in the resin coating layer B is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 60% by mass or less, even more preferably 15% by mass or more and 50% by mass or less, and particularly preferably 20% by mass or more and 40% by mass or less, relative to the total mass of the resin coating layer B. Within the above range, a contamination suppression effect is exhibited, a mechanism for selectively discharging degraded carrier in the developing machine is achieved, and fogging suppression is more excellent.

[0030] In addition, the resin coating layer preferably contains resin particles from the viewpoint of fogging suppression. As the resin particles, melamine resin particles are preferred from the viewpoint of fogging suppression. Furthermore, the resin coating layer preferably contains carbon black from the viewpoint of fogging suppression. Among these, it is preferable that the resin coating layer A contains carbon black and melamine resin particles from the viewpoint of fogging suppression. From the viewpoint of fogging suppression, the resin coating layer B preferably contains silica particles and melamine resin particles, and more preferably contains silica particles, carbon black and melamine resin particles. From the viewpoint of fogging suppression, the content of the resin particles in the resin coating layer B is preferably less than the content of the metal oxide particles. From the viewpoint of fogging suppression, the content of resin particles in the resin coating layer is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 40% by mass or less, even more preferably 5% by mass or more and 35% by mass or less, and particularly preferably 10% by mass or more and 32% by mass or less, relative to the total mass of the resin coating layer. From the viewpoint of fogging suppression, the content of carbon black in the resin coating layer is preferably less than the content of at least one kind of particles selected from the group consisting of silica, titania and alumina in the resin coating layer. From the viewpoint of fogging suppression, the content of carbon black in the resin coating layer is preferably less than the content of resin particles in the resin coating layer. From the viewpoint of fogging suppression, the content of carbon black in the resin coating layer is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, even more preferably 2% by mass or more and 35% by mass or less, and particularly preferably 5% by mass or more and 32% by mass or less, relative to the total mass of the resin coating layer.

[0031] Methods for forming a resin coating layer on the surface of magnetic particles include, for example, a wet method and a dry method. The wet method is a method that uses a solvent to dissolve or disperse the resin that constitutes the resin coating layer. On the other hand, the dry method is a method that does not use the solvent.

[0032] Examples of wet manufacturing methods include an immersion method in which magnetic particles are immersed in a resin liquid for forming a resin coating layer to coat them; a spray method in which a resin liquid for forming a resin coating layer is sprayed onto the surface of magnetic particles; a fluidized bed method in which magnetic particles are fluidized in a fluidized bed and a resin liquid for forming a resin coating layer is sprayed onto them; and a kneader coater method in which magnetic particles and a resin liquid for forming a resin coating layer are mixed in a kneader coater and the solvent is removed. The resin liquid for forming the resin coating layer used in the wet manufacturing method is prepared by dissolving or dispersing the resin and other components in a solvent. The solvent is not particularly limited as long as it can dissolve or disperse the resin, and examples of the solvent that can be used include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane.

[0033] An example of a dry manufacturing method is a method in which a mixture of magnetic particles and a resin for forming a resin coating layer is heated in a dry state to form a resin coating layer. Specifically, for example, the magnetic particles and the resin for forming the resin coating layer are mixed in a gas phase and heated to melt, thereby forming a resin coating layer.

[0034] The thickness of the resin coating layer is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 5 μm or less.

[0035] The exposed ratio of the magnetic particles on the surface of the carrier is preferably 2% to 20%, more preferably 2% to 10%, and even more preferably 3% to 8%.

[0036] The exposed ratio of the magnetic particles on the surface of the carrier is determined by X-ray photoelectron spectroscopy (XPS) using the following method. Prepare a target carrier and magnetic particles obtained by removing the resin coating layer from the target carrier. Examples of methods for removing the resin coating layer from the resin-coated magnetic particles include, for example, a method of dissolving the resin component with an organic solvent to remove the resin coating layer, and a method of removing the resin coating layer by heating at about 800 °C to cause the resin component to disappear. Use the carrier and the magnetic particles with the resin coating layer removed as measurement samples respectively, quantify Fe (atomic%) by XPS, and calculate (Fe of resin-coated magnetic particles) ÷ (Fe of magnetic particles) × 100, which is taken as the exposure ratio (%) of the magnetic particles.

[0037] The exposure ratio of the magnetic particles on the surface of the carrier can be controlled by the amount of resin used for forming the resin coating layer. The larger the amount of resin relative to the amount of magnetic particles, the smaller the exposure ratio.

[0038] <<Value of SiB / SiA>> When the metal oxide particles are silica particles, the value of the ratio SiB / SiA of the surface silica amount SiA of the carrier A and the surface silica amount SiB of the replenishing carrier B is preferably 1 or more and 8 or less, more preferably 1.2 or more and 5 or less, and particularly preferably 2 or more and 4 or less from the viewpoint of fog suppression. When within the above range, a difference in fluidity occurs between the carrier A and the replenishing carrier B in the developing machine, and the deteriorated carrier A in the developing machine is selectively discharged. As a method for adjusting the surface silica amount of the carrier A and the replenishing carrier B, it can be controlled by the amount of silica particles contained in the coating resin layer. The larger the amount of silica particles relative to the resin, the larger the surface silica amount of the carrier.

[0039] The method for measuring the surface silica amount of the carrier in the present disclosure is as follows. Use the carrier as a sample, analyze it by X-ray Photoelectron Spectroscopy (XPS) under the following conditions, and measure the peak intensity of all elements. Then, determine the ratio (atomic%) of Si from the peak intensities of all elements obtained. ·XPS apparatus: VersaProbeII manufactured by ULVAC-PHI, Inc. · Etching gun: Argon gun · Accelerating voltage: 5 kV · Emission current: 20 mA · Sputtering area: 2 mm × 2 mm · Sputtering rate: 3 nm / min (in terms of SiO2 conversion) Also, when measuring the surface silica amount of the carrier in the developer, separation by blow-off is performed. Specifically, about 20 g of the developer is sampled, and toner is removed from the developer by blow-off to isolate only the carrier. For the obtained carrier, the ratio of Si (atomic%) is determined from X-ray photoelectron spectroscopy under the above conditions.

[0040] <<Value of BETB / BETA>> The value of the ratio BETB / BETA of the BET specific surface area BETA of the carrier A and the BET specific surface area BETB of the replenishing carrier B is preferably 0.2 or more and 10 or less, more preferably 0.5 or more and 8 or less, and particularly preferably 1 or more and 5 or less from the viewpoint of fog suppression. When it is within the above range, a difference in fluidity occurs between the carrier A and the replenishing carrier B in the developing machine, and the deteriorated carrier A in the developing machine is selectively discharged. As a method for adjusting the BET specific surface area of the carrier A and the replenishing carrier B, for example, a method of adjusting by the amount of carbon black and melamine resin particles with respect to the resin can be mentioned.

[0041] The method for measuring the BET specific surface area of the carrier in the present disclosure is as follows. The measurement of the BET specific surface area of the carrier is performed by nitrogen substitution and the three-point method using a SA3100 specific surface area measurement device (manufactured by Beckman Coulter). Specifically, 5 g of magnetic particles are placed in a cell, degassing treatment is performed at 60°C for 120 minutes, and it is performed using a mixed gas of nitrogen and helium (30:70).

[0042] <<Magnetic particles>> The magnetic particles are not particularly limited, and known magnetic particles used as a core material of a carrier can be used. Specific examples of the magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles in which porous magnetic powder is impregnated with resin; and magnetic powder-dispersed resin particles in which magnetic powder is dispersed in resin.

[0043] In this embodiment, ferrite particles are suitable as the magnetic particles. In this embodiment, the ferrite particles preferably contain at least one selected from calcium oxide and strontium oxide. Calcium oxide and strontium oxide are easily incorporated into the surface of ferrite particles, and the presence of calcium or strontium on the surface of ferrite particles is thought to suppress charge leakage from the ferrite particles, thereby resulting in a relatively high charge on the carrier surface. This carrier prevents the toner from becoming low-charged in the developer, thereby further suppressing fogging and improving thin line reproducibility (e.g., suppressing thickening, crushing, or blurring of thin lines). This effect is particularly noticeable when forming a low-density image of the same color after repeatedly forming a high-density, monochromatic image at a higher speed.

[0044] In this embodiment, the ferrite particles contain at least one selected from calcium oxide and strontium oxide, and the total content of calcium and strontium is preferably 0.1% by mass or more and 2.0% by mass or less relative to the total mass of the ferrite particles. When the total content of calcium and strontium is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the total content of calcium and strontium is 2.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistivity and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (e.g., thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the total content of calcium element and strontium element is preferably 0.1 mass % or more and 2.0 mass % or less, more preferably 0.2 mass % or more and 1.5 mass % or less, and even more preferably 0.5 mass % or more and 1.2 mass % or less, based on the entire ferrite particles.

[0045] In this embodiment, the ferrite particles contain calcium oxide, and the calcium content is preferably 0.2 mass% or more and 2.0 mass% or less relative to the total mass of the ferrite particles. When the calcium content is 0.2 mass% or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the calcium content is 2.0 mass% or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance value and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the calcium element content is preferably 0.2 to 2.0 mass %, more preferably 0.5 to 1.5 mass %, and even more preferably 0.5 to 1.0 mass %, based on the total mass of the ferrite particles.

[0046] In this embodiment, the ferrite particles contain strontium oxide, and the strontium content is preferably 0.1% by mass or more and 1.0% by mass or less relative to the total mass of the ferrite particles. When the strontium content is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the strontium content is 1.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the content of strontium element is preferably 0.1 mass % to 1.0 mass %, more preferably 0.4 mass % to 1.0 mass %, and even more preferably 0.5 mass % to 0.8 mass %, based on the total mass of the ferrite particles.

[0047] The contents of calcium and strontium contained in the ferrite particles are measured by X-ray fluorescence analysis. The X-ray fluorescence analysis of the ferrite particles is performed by the following method. Qualitative and quantitative analysis is performed using an X-ray fluorescence analyzer (Shimadzu Corporation, XRF1500) under the following conditions: X-ray output: 40 V / 70 mA, measurement area: 10 mm diameter, measurement time: 15 minutes. The elements to be analyzed are selected based on the elements detected in the qualitative analysis. The main elements selected are iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), strontium (Sr), oxygen (O), and carbon (C). The mass percentage (%) of each element is calculated by referring to separately prepared calibration curve data.

[0048] The volume average particle size of the magnetic particles is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 180 μm or less, and even more preferably 25 μm or more and 60 μm or less.

[0049] The magnetic force of the magnetic particles is, for example, 50 emu / g or more, preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3000 oersteds. The saturation magnetization is measured using a vibrating sample magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is placed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the instrument. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is created on recording paper. The saturation magnetization, remanent magnetization, and coercive force are determined from the curve data.

[0050] The volume resistivity of the magnetic particles is, for example, 10 5 Ω cm or more 10 9 Ω·cm or less, 10 7 Ω cm or more 10 9 Ω·cm or less is preferable. The volume resistivity (Ω·cm) of magnetic particles is measured as follows: 2The object to be measured is placed flat on the surface of the circular jig on which the electrode plate is arranged, with a thickness of 1 mm to 3 mm, to form a layer. 2 The layer is sandwiched between two electrode plates. To eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plates placed on the layer, and then the layer thickness (cm) is measured. The electrodes above and below the layer are connected to an electrometer and a high-voltage power supply generator. A high voltage is applied to both electrodes so that the electric field becomes 103.8 V / cm, and the current value (A) that flows at this time is read. The measurement environment is a temperature of 20°C and a humidity of 50% RH. The formula for calculating the volume electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R represents the volume electrical resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) at an applied voltage of 0 V, and L represents the layer thickness (cm). The coefficient 20 is the area of ​​the electrode plate (cm 2 )

[0051] <<Carrier characteristics>> The volume average particle size of the carrier is preferably 15 μm or more and 510 μm or less, more preferably 20 μm or more and 180 μm or less, and even more preferably 25 μm or more and 60 μm or less.

[0052] The magnetic force of the carrier is, for example, 40 emu / g or more, preferably 50 emu / g or more, in terms of saturation magnetization in a magnetic field of 1000 oersted. The saturation magnetization is measured in the same manner as for measuring the saturation magnetization of magnetic particles, except that the magnetic field is swept up to 1000 oersted.

[0053] The volume resistivity of the carrier (at 25°C) is, for example, 1 x 10 7 Ω cm or more 1×10 15 Ω·cm or less, 1×10 8 Ω cm or more 1×10 14 Ω·cm or less is preferable, and 1×10 8 Ω cm or more 1×10 13 It is more preferable that the volume resistivity of the carrier is Ω·cm or less. The volume resistivity of the carrier is measured in the same manner as that of the magnetic particles.

[0054] <Two-component developer> In the image forming apparatus according to this embodiment, the two-component developer contained in the developing machine contains toner and carrier A. Furthermore, the replenishment of the replenishment carrier B may be carried out using the replenishment carrier B alone, or may be carried out using a two-component developer containing toner and the replenishment carrier B, but is preferably carried out using a two-component developer containing toner and the replenishment carrier B.

[0055] The two-component developer contained in the developing machine is prepared by mixing the toner and carrier A at an appropriate mixing ratio. The mixing ratio (mass ratio) of the toner to the carrier A is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0056] The trickle amount of replenishment carrier B when replenishment is performed (= the content of carrier in the two-component developer to be replenished) is not particularly limited, but from the viewpoint of fogging suppression, it is preferably 1% by mass or more and 25% by mass or more, more preferably 2% by mass or more and less than 15% by mass or more, and particularly preferably 5% by mass or more and 10% by mass or less.

[0057] <<Toner for developing electrostatic images>> The toner is not particularly limited, and known toners can be used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be used, and an infrared absorbing toner using an infrared absorbing agent instead of a colorant can also be used. The toner may contain a release agent, various internal additives, external additives, etc.

[0058] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0059] The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.

[0060] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0061] The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 to 1,000,000, more preferably 7,000 to 500,000. The number average molecular weight (Mn) of the polyester resin is preferably 2,000 to 100,000. The molecular weight distribution (Mw / Mn) of the polyester resin is preferably 1.5 to 100, more preferably 2 to 60. The weight-average molecular weight and number-average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh Corporation GPC HLC-8120GPC measuring instrument and a Tosoh Corporation TSKgel SuperHM-M (15 cm) column in tetrahydrofuran (THF) as a solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0062] The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0063] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0064] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0065] The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0066] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0067] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0068] The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

[0069] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0070] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that coats the core. The toner particles of the core-shell structure may be composed of, for example, a core composed of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer composed of a binder resin.

[0071] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less. The volume average particle size (D50v) of toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter) and an ISOTON-II (manufactured by Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% by weight aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles ranging from 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled.

[0072] -External additives- Examples of external additives include inorganic particles, such as SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). n , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, etc.

[0073] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is preferably, for example, 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0074] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0075] The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0076] -Toner manufacturing method- The toner is obtained by producing toner particles and then externally adding an external additive to the toner particles. The toner particles may be produced by either a dry production method (e.g., a kneading and pulverization method) or a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular restrictions on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0077] <Mechanisms of the image forming apparatus> The image forming apparatus according to this embodiment preferably comprises an image carrier, a charging means for charging the surface of the image carrier, an electrostatic image forming means for forming an electrostatic image on the surface of the charged image carrier, a developing means for containing an electrostatic image developer and using the electrostatic image developer to develop the electrostatic image formed on the surface of the image carrier as a toner image, a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing means for fixing the toner image transferred to the surface of the recording medium. Furthermore, the image forming apparatus according to this embodiment preferably includes a developer cartridge that contains replenishment developer containing replenishment carrier B.

[0078] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0079] Furthermore, the image forming apparatus according to the present embodiment is preferably an image forming apparatus comprising: a developer cartridge containing replenishment developer containing replenishment carrier B; an image carrier; a charging device that charges the surface of the image carrier; an electrostatic image forming device that forms an electrostatic image on the surface of the charged image carrier; a developing device that contains developer containing the replenishment developer replenished from the developer cartridge and develops the electrostatic image formed on the surface of the image carrier as a toner image using the developer; a transfer device that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; and a fixing device that fixes the toner image transferred to the surface of the recording medium.

[0080] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0081] An example of an image forming apparatus according to this embodiment will be described with reference to the drawings. The image forming apparatus shown in FIG. 1 is configured to employ a trickle development system in which a developer cartridge contains a developer including a replenishment carrier B, the developer is supplied to a developer container in the developing device by a developer supplying means, and at least a portion of the developer contained in the developer container is discharged by a developer discharging means. The image forming apparatus shown in FIG. 1 is configured to employ a reclaim system in which residual toner remaining on the surface of the image carrier is collected by a cleaning device and returned to the developing device for reuse.

[0082] The image forming apparatus 100 comprises an image carrier 110 that rotates in the clockwise direction indicated by the arrow a in FIG. 1 , a charging device 120 that is provided above the image carrier 110 and faces the image carrier 110, and that negatively charges the surface of the image carrier 110, an electrostatic image forming device 130 that writes an image to be formed with a developer (toner) on the surface of the image carrier 110 that has been charged by the charging device 120, thereby forming an electrostatic image, a developing device 140 that is provided downstream of the electrostatic image forming device 130, and that attaches toner to the electrostatic image formed by the electrostatic image forming device 130, thereby forming a toner image on the surface of the image carrier 110, and an image developing device 140. The image forming apparatus includes an endless belt-like intermediate transfer belt 150 that travels in the direction indicated by arrow b while contacting the holder 110 and transfers the toner image formed on the surface of the image holder 110, a static eliminator 160 that eliminates static electricity from the surface of the image holder 110 after the toner image has been transferred to the intermediate transfer belt 150, making it easier to remove residual toner remaining on the surface, a cleaning device 170 that acts as residual toner recovery means and removes and recovers residual toner on the surface of the image holder 110, and residual toner transport means 174 that transports the residual toner removed and recovered by the cleaning device 170 and supplies it to the developing device 140.

[0083] The charging device 120, the electrostatic image forming device 130, the developing device 140, the intermediate transfer belt 150, the charge removing device 160, and the cleaning device 170 are arranged in a clockwise direction on a circumference surrounding the image carrier 110.

[0084] The intermediate transfer belt 150 is held in a tensioned state by support rolls 150A and 150B, a backing roll 150C, and a driving roll 150D from the inside, and is driven in the direction of arrow b with the rotation of the driving roll 150D. A primary transfer roll 151 is provided on the inside of the intermediate transfer belt 150 facing the image carrier 110, which positively charges the intermediate transfer belt 150 and causes the toner on the image carrier 110 to be attracted to the outer surface of the intermediate transfer belt 150. A secondary transfer roll 152 is provided on the outside below the intermediate transfer belt 150, facing the backing roll 150C, which positively charges the recording paper P and presses it against the intermediate transfer belt 150 to transfer the toner image formed on the intermediate transfer belt 150 onto the recording paper P.

[0085] Further provided below the intermediate transfer belt 150 are a recording medium supply device 153 that supplies recording paper P to the secondary transfer roll 152, and a fixing device 180 that fixes the toner image while transporting the recording paper P on which the toner image has been formed by the secondary transfer roll 152.

[0086] The recording medium supply device 153 includes a pair of transport rolls 153A and a guide slope 153B that guides the recording paper P transported by the transport rolls 153A toward the secondary transfer roll 152. On the other hand, the fixing device 180 includes fixing rolls 181, which are a pair of heat rolls that fix the toner image by heating and pressing the recording paper P onto which the toner image has been transferred by the secondary transfer roll 152, and a transport conveyor 182 that transports the recording paper P toward the fixing rolls 181.

[0087] The recording paper P is transported in the direction indicated by the arrow c by the recording medium supply device 153, the secondary transfer roll 152, and the fixing device 180.

[0088] An intermediate transfer body cleaning device 154 having a cleaning blade that removes toner remaining on the intermediate transfer belt 150 after the toner image is transferred to the recording paper P by the secondary transfer roll 152 is provided so as to be positioned opposite the drive roll 150D with the intermediate transfer belt 150 sandwiched therebetween.

[0089] The developing device 140 will be described in detail below. The developing device 140 is disposed facing the image carrier 110 in the development area, and has a developer container 141 that contains, for example, a two-component developer containing toner charged to a negative (-) polarity and carrier charged to a positive (+) polarity. The developer container 141 has a developer container main body 141A and a developer container cover 141B that closes the upper end of the developer container main body 141A.

[0090] The developer storage container main body 141A has inside it a developing roll chamber 142A that houses the developing roll 142, and has adjacent to the developing roll chamber 142A a first stirring chamber 143A and a second stirring chamber 144A adjacent to the first stirring chamber 143A. Also, a layer thickness regulating member 145 is provided inside the developing roll chamber 142A to regulate the layer thickness of the developer on the surface of the developing roll 142 when the developer storage container cover 141B is attached to the developer storage container main body 141A.

[0091] The first stirring chamber 143A and the second stirring chamber 144A are separated by a partition wall 141C, and although not shown, the first stirring chamber 143A and the second stirring chamber 144A are connected at both ends of the partition wall 141C in the longitudinal direction (longitudinal direction of the developing device), and the first stirring chamber 143A and the second stirring chamber 144A form a circulating stirring chamber (143A+144A).

[0092] The developing roll 142 is disposed in the developing roll chamber 142A so as to face the image carrier 110. The developing roll 142 is a magnetic roll (fixed magnet) (not shown) having a magnetic property, and a sleeve is provided on the outside of the developing roll 142. The developer in the first stirring chamber 143A is attracted to the surface of the developing roll 142 by the magnetic force of the magnetic roll, and is transported to the development area. The developing roll 142 has a roll shaft rotatably supported by the developer storage container main body 141A. The developing roll 142 and the image carrier 110 rotate in opposite directions, and the developer attracted to the surface of the developing roll 142 at the opposing portion is transported to the development area in the same direction as the moving direction of the image carrier 110.

[0093] In addition, a bias power supply (not shown) is connected to the sleeve of the developing roll 142, and a predetermined developing bias is applied (in this embodiment, a bias in which an alternating current component (AC) is superimposed on a direct current component (DC) is applied so that an alternating electric field is applied to the developing area).

[0094] The first stirring chamber 143A and the second stirring chamber 144A are provided with a first stirring member 143 (stirring / transporting member) and a second stirring member 144 (stirring / transporting member) that stir and transport the developer. The first stirring member 143 has a first rotation shaft extending in the axial direction of the developing roll 142 and a second rotation shaft The first agitating member 143 and the second agitating member 144 are configured to rotate freely on the developer accommodating container main body 141A. The first agitating member 143 and the second agitating member 144 are arranged so that the rotation of the first agitating member 143 and the second agitating member 144 transports the developers in the first agitating chamber 143A and the second agitating chamber 144A in opposite directions.

[0095] One end of developer supply means 146 for supplying replenishment developer to the second stirring chamber 144A is connected to one longitudinal end of the second stirring chamber 144A, and a developer cartridge 147 containing replenishment developer is connected to the other end of the developer supply means 146. Also, one end of developer discharge means 148 for discharging the contained developer is connected to one longitudinal end of the second stirring chamber 144A, and the other end of the developer discharge means 148 is connected to a developer recovery container (not shown) for recovering the discharged developer.

[0096] In this way, the developing device 140 employs a so-called trickle development method in which replenishment developer is supplied to the developing device 140 (second stirring chamber 144A) from the developer cartridge 147 via developer supply means 146, and old developer is discharged from developer discharge means 148. Specifically, the trickle development method is a development method in which replenishment developer (trickle developer) is gradually supplied into the developing device in order to suppress a decrease in the charging performance of the developer and extend the interval between developer replacements, while development is performed while discharging excess deteriorated developer (containing a large amount of deteriorated carrier).

[0097] Next, the cleaning device 170 will be described in detail. The cleaning device 170 is configured to include a housing 171 and a cleaning blade 172 that is arranged to protrude from the housing 171. The cleaning blade 172 is a plate-like member that extends in the axial direction of the rotation shaft of the image carrier 110, and is provided so that its tip portion (edge ​​portion) comes into contact with a portion of the image carrier 110 downstream in the rotation direction (direction of arrow a) from the transfer position by the primary transfer roll 151 and downstream in the rotation direction from the position where static electricity is removed by the static eliminator 160.

[0098] As the image carrier 110 rotates in the direction of arrow a, the cleaning blade 172 intercepts and removes foreign matter such as residual toner that has adhered to the image carrier 110 without being transferred to the intermediate transfer belt 150 by the primary transfer roll 151 from the image carrier 110.

[0099] Furthermore, a transport member 173 is disposed at the bottom inside the housing 171, and one end of residual toner transport means 174 is connected to the downstream side of the transport member 173 in the transport direction in the housing 171 for transporting the residual toner (developer) removed and collected by the cleaning blade 172 and supplying it to the developing device 140. The other end of the residual toner transport means 174 is connected to the developer supply means 146 so as to merge therewith.

[0100] In this way, the cleaning device 170 transports the residual toner to the developing device 140 (second stirring chamber 144A) through the residual toner transport means 174 as the transport member 173 provided at the bottom of the housing 171 rotates, and the residual toner recovered from the surface of the image carrier 110 is stirred and transported together with the developer (toner) contained in the developing device 140 and reused.

[0101] (Image forming method) The image forming method according to this embodiment is a trickle development type image forming method in which a two-component developer containing toner and carrier A is contained in a developing machine, toner is replenished in accordance with the toner consumed during development, and replenishment carrier B is replenished, wherein the carrier A has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B coating the magnetic core material B, and the resin coating layer B contains metal oxide particles. In addition, the image forming method according to this embodiment preferably uses the image forming apparatus according to this embodiment.

[0102] Conventional image formation methods use a trickle method, which adds carrier along with the toner consumed during development and gradually replaces the carrier in the developing machine to suppress changes in charge amount and stabilize image density. In a conventional trickle-type image forming method, when replenishment carrier is added, degraded carrier and non-degraded replenishment carrier are discharged at a 1:1 ratio, and are gradually replaced by the replenishment carrier at a constant rate. In conventional image forming methods, particularly when printing low-image-quality images with extremely low density and a small number of pages with extremely low toner consumption, it takes a long time for the contaminated carrier to be discharged, which can worsen the initial decrease in developer charge and cause fogging. In the image forming method according to this embodiment, carrier A contained in a developing machine has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and refill carrier B has a magnetic core material B and a resin coating layer B coating the magnetic core material B, and the resin coating layer B contains metal oxide particles. Therefore, when refill carrier B, which is a highly reliable carrier with high fluidity and carrier A that is a degraded carrier with low fluidity, is added to carrier A, which is a degraded carrier with low fluidity, a difference in fluidity between the carriers occurs, and carrier A with poor fluidity is selectively discharged, thereby suppressing a decrease in the charge of the developer and suppressing toner fogging.

[0103] Preferred aspects of the toner, carrier A, refill carrier B, magnetic core material A, resin coating layer A, magnetic core material B, resin coating layer B, and metal oxide particles in the image forming method according to this embodiment are the same as the preferred aspects of the toner, carrier A, refill carrier B, magnetic core material A, resin coating layer A, magnetic core material B, resin coating layer B, and metal oxide particles in the image forming apparatus according to this embodiment described above.

[0104] The image forming method according to the present embodiment preferably includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using a developer containing replenishment carrier B supplied from a developer cartridge, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium. In addition, the image forming method according to this embodiment may be an intermediate transfer method in which a toner image formed on the surface of an image carrier is primarily transferred to the surface of an intermediate transfer member, and the toner image transferred to the surface of the intermediate transfer member is secondarily transferred to the surface of a recording medium. Furthermore, the image forming method according to the present embodiment may include a cleaning step of cleaning the surface of the image carrier after the toner image is transferred and before the charging. The image forming method according to the present embodiment may also include a charge eliminating step of irradiating the surface of the image carrier with charge eliminating light to eliminate charges before charging after transferring the toner image. [Example]

[0105] The present embodiment will be described in detail below with reference to examples, but the present embodiment is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are by mass.

[0106] <Volume average particle size of carrier> The toner was removed from the electrostatic image developer using an arbitrary mesh with an air blower, and the carrier was taken out. The particle size distribution of the carrier was measured using a laser diffraction / scattering particle size distribution analyzer (LS Particle Size Analyzer: LS13 320, manufactured by Beckman Coulter). The obtained particle size distribution was divided into particle size ranges (channels), and the volume cumulative distribution was subtracted from the small particle size side, and the particle size at 50% of the cumulative distribution was defined as the volume average particle size D50.

[0107] <Toner Production> [Preparation of Resin Particle Dispersion (1)] Ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 37 parts Neopentyl glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 65 parts 1,9-nonanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 32 parts Terephthalic acid (Fujifilm Wako Pure Chemical Industries, Ltd.): 96 parts The above materials were charged into a flask, and the temperature was raised to 200°C over 1 hour. After confirming uniform stirring within the reaction system, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240°C over 6 hours while distilling off the resulting water. Stirring was continued at 240°C for 4 hours, yielding a polyester resin (acid value 9.4 mgKOH / g, weight-average molecular weight 13,000, glass transition temperature 62°C). This polyester resin was transferred in its molten state to an emulsifier / disperser (Cavitron CD1010, Eurotech) at a rate of 100 g / min. Separately, a 0.37% concentration dilute ammonia water, prepared by diluting reagent ammonia water with ion-exchanged water, was placed in a tank and heated to 120°C in a heat exchanger. The emulsifier / disperser was operated at a rotor speed of 60 Hz and a pressure of 5 kg / cm. 2 The operation was carried out under the conditions of (a) to (c) to obtain a resin particle dispersion (1) having a volume average particle size of 160 nm and a solid content of 30%.

[0108] [Preparation of Resin Particle Dispersion (2)] Decanedioic acid (Tokyo Chemical Industry Co., Ltd.): 81 parts Hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 47 parts The above materials were charged into a flask, and the temperature was raised to 160°C over 1 hour. After confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200°C over 6 hours while distilling off the produced water, and stirring was continued at 200°C for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40°C under reduced pressure to obtain polyester resin (C1) (melting point 64°C, weight average molecular weight 15,000).

[0109] Polyester resin (C1): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 180 nm, the particles were collected to obtain a resin particle dispersion (2) with a solid content of 20%.

[0110] [Preparation of Colorant Particle Dispersion (1)] Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.): 10 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 80 parts The above materials were mixed and dispersed for 1 hour using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (1) with a volume average particle size of 180 nm and a solid content of 20%.

[0111] [Preparation of Release Agent Particle Dispersion (1)] Paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd.): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 200 nm, the particles were collected to obtain a release agent particle dispersion (1) with a solid content of 20%.

[0112] [Preparation of Toner (1)] ·Resin particle dispersion (1): 150 parts ·Resin particle dispersion (2): 50 parts Colorant particle dispersion (1): 25 parts Release agent particle dispersion (1): 35 parts Polyaluminum chloride: 0.4 parts Ion-exchanged water: 100 parts The above materials were placed in a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (Ultra-Turrax T50, IKA). The flask was then heated to 48°C in an oil bath while stirring. The reaction system was maintained at 48°C for 60 minutes, after which 70 parts of resin particle dispersion (1) was slowly added. The pH was then adjusted to 8.0 using a 0.5 mol / L aqueous sodium hydroxide solution. The flask was then sealed, the stirring shaft was magnetically sealed, and the mixture was heated to 90°C with continued stirring and maintained for 30 minutes. The mixture was then cooled at a rate of 5°C / min, solid-liquid separated, and thoroughly washed with ion-exchanged water. The solid-liquid separated product was redispersed in ion-exchanged water at 30°C and washed with stirring at 300 rpm (revolutions per minute) for 15 minutes. This washing operation was repeated six more times, and when the pH of the filtrate reached 7.54 and the electrical conductivity reached 6.5 μS / cm, solid-liquid separation was performed, followed by vacuum drying for 24 hours to obtain toner particles with a volume average particle size of 5.7 μm.

[0113] 100 parts of the above toner particles and 2.5 parts of silica particles (surface hydrophobized with hexamethyldisilazane, average primary particle size 40 nm) were mixed in a Henschel mixer to obtain toner (1).

[0114] <Preparation of ferrite particles (1)> 1318 parts of Fe2O3, 587 parts of Mn(OH)2, and 96 parts of Mg(OH)2 were mixed and pre-baked at 900°C for 4 hours. The pre-baked product, 6.6 parts of polyvinyl alcohol, 0.5 parts of polycarboxylic acid as a dispersant, and zirconia beads with a media diameter of 1 mm were added to water, and the mixture was ground and mixed in a sand mill to obtain a dispersion. The volume average particle size of the particles in the dispersion was 1.5 μm. The dispersion liquid was used as a raw material and granulated and dried using a spray dryer to obtain granules with a volume average particle size of 37 μm. Next, in an oxygen-nitrogen mixed atmosphere with an oxygen partial pressure of 1%, sintering was performed using an electric furnace at a temperature of 1450 ° C for 4 hours, and then heating was performed in the air at a temperature of 900 ° C for 3 hours to obtain sintered particles. The sintered particles were crushed and classified to obtain ferrite particles (1) with a volume average particle size of 35 μm.

[0115] <Preparation of Metal Oxide Particles to be Added to Carrier Coating Resin Layer> Commercially available silica particles (volume average particle size: 7 nm, specific gravity: 2.2, fumed silica particles surface-treated with hexamethyldisilazane, manufactured by Tokuyama Corporation, product name: HM30S) were prepared and used as metal oxide particles (1).

[0116] [Metal oxide particles (2)] An alkaline catalyst solution was obtained by adding 890 parts of methanol and 210 parts of 9.8% aqueous ammonia to a 1.5 L glass reactor equipped with a stirrer, a dropping nozzle, and a thermometer and mixing them. The alkaline catalyst solution was adjusted to 45°C, and then 550 parts of tetramethoxysilane and 140 parts of 7.6% aqueous ammonia were simultaneously added dropwise over 450 minutes while stirring to obtain silica particle dispersion (A). The silica particles in silica particle dispersion (A) had a volume average particle size of 5 nm and a volume particle size distribution index (the square root of the ratio of the particle size D16v at the 16% cumulative size from the smallest diameter to the particle size D84v at the 84% cumulative size in the volume-based particle size distribution, (D84v / D16v)1 / 2) of 1.2. 300 parts of silica particle dispersion (A) were placed in an autoclave equipped with a stirrer, and the stirrer was rotated at a rotation speed of 100 rpm. While the stirrer continued to rotate, liquefied carbon dioxide was injected into the autoclave from a carbon dioxide cylinder via a pump, and the temperature inside the autoclave was increased with a heater while the pressure inside the autoclave was increased with a pump, until the inside of the autoclave was in a supercritical state of 150°C and 15 MPa. The pressure valve was operated to maintain the inside of the autoclave at 15 MPa while circulating supercritical carbon dioxide, and methanol and water were removed from the silica particle dispersion (A). When the amount of carbon dioxide fed into the autoclave reached 900 parts, the supply of carbon dioxide was stopped, and a powder of silica particles was obtained. The autoclave was maintained at 150°C and 15 MPa using a heater and pump to maintain the supercritical state of carbon dioxide. While continuing to rotate the autoclave's agitator, 50 parts of hexamethyldisilazane per 100 parts of silica particles was injected into the autoclave using an entrainer pump. The autoclave was heated to 180°C and allowed to react for 20 minutes. Supercritical carbon dioxide was then again circulated into the autoclave to remove excess hexamethyldisilazane. The agitation was then stopped, the pressure valve was opened, and the pressure in the autoclave was released to atmospheric pressure, and the temperature was lowered to room temperature (25°C). Thus, silica particles surface-treated with hexamethyldisilazane were obtained. The silica particles had a volume average particle size of 5 nm. The obtained silica particles were designated metal oxide particles (2).

[0117] [Metal oxide particles (3)] The same procedure as for preparing metal oxide particles (2) was used, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 70 nm, thereby obtaining silica particles surface-treated with hexamethyldisilazane. The silica particles had a volume average particle size of 70 nm. The obtained silica particles were designated metal oxide particles (3).

[0118] [Metal oxide particles (4)] The same procedure as for preparing metal oxide particles (2) was used, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 3 nm, and silica particles surface-treated with hexamethyldisilazane were obtained. The silica particles had a volume average particle size of 3 nm. The obtained silica particles were designated metal oxide particles (4).

[0119] [Metal oxide particles (5)] The same procedure as for preparing metal oxide particles (2) was repeated, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 85 nm, thereby obtaining silica particles surface-treated with hexamethyldisilazane. The silica particles had a volume average particle size of 85 nm. The obtained silica particles were designated metal oxide particles (5).

[0120] [Metal oxide particles (6)] The same procedure as for preparing metal oxide particles (2) was used, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 2 nm, thereby obtaining silica particles surface-treated with hexamethyldisilazane. The silica particles had a volume average particle size of 2 nm. The obtained silica particles were designated metal oxide particles (6).

[0121] [Metal oxide particles (7)] The same procedure as for preparing metal oxide particles (2) was used, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 86 nm, thereby obtaining silica particles surface-treated with hexamethyldisilazane. The silica particles had a volume average particle size of 86 nm. The obtained silica particles were designated metal oxide particles (7).

[0122] [Metal oxide particles (8)] The same procedure as for preparing metal oxide particles (2) was repeated, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 30 nm, thereby obtaining silica particles surface-treated with hexamethyldisilazane. The silica particles had a volume average particle size of 30 nm. The obtained silica particles were designated metal oxide particles (8).

[0123] [Metal oxide particles (9)] The same procedure as for preparing metal oxide particles (2) was used, except that the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was adjusted to change the volume average particle size of the silica particles in the silica particle dispersion to 5 nm, and silica particles surface-treated with methyltrimethoxysilane were obtained. The silica particles had a volume average particle size of 5 nm. The obtained silica particles were designated metal oxide particles (9).

[0124] Example 1 <Preparation of Replenishment Carrier B> -Preparation of coating agent for forming resin coating layer- Resin (1): 15.4 parts of cyclohexyl methacrylate polymer (weight average molecular weight: 350,000) Resin (2): 2-(dimethylamino)ethyl methacrylate polymer (weight average molecular weight: 300,000) 0.39 parts Nitrogen-containing resin particles: 3.0 parts melamine resin particles (Eposter S (Nippon Shokubai Co., Ltd.)) Carbon black particles (1): 2.24 parts carbon black (manufactured by Cabot Corporation, product name: VXC72) Metal oxide particles (1): 7.0 parts of silica (volume average particle size: 7 nm, specific gravity: 2.2, fumed silica particles surface-treated with hexamethyldisilazane, manufactured by Tokuyama Corporation, product name: HM30S) Solvent: 300 parts toluene The above materials and glass beads (1 mm in diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 190 rpm for 30 minutes to obtain a coating agent (B1).

[0125] -Creating Carrier B1- 1,000 parts of the ferrite particles (1) and 125 parts of the coating agent (B1) were placed in a kneader and mixed at room temperature (25°C) for 20 minutes, then heated to 70°C and dried under reduced pressure. The dried product was cooled to room temperature (25° C.), and 125 parts of coating agent (B1) was added and mixed at room temperature (25° C.) for 20 minutes, followed by heating to 70° C. and drying under reduced pressure. Next, the dried product was taken out of the kneader and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining carrier B1 (supplement carrier B).

[0126] <Preparation of Carrier A> -Preparation of coating agent for forming resin coating layer- Resin (1): 15.4 parts of cyclohexyl methacrylate polymer (weight average molecular weight: 350,000) Resin (2): 2-(dimethylamino)ethyl methacrylate polymer (weight average molecular weight: 300,000) 0.39 parts Nitrogen-containing resin particles: 3.0 parts melamine resin particles (Eposter S (Nippon Shokubai Co., Ltd.)) Carbon black particles (1): 2.24 parts carbon black (manufactured by Cabot Corporation, product name: VXC72) Solvent: 300 parts toluene The above materials and glass beads (1 mm in diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 190 rpm for 30 minutes to obtain a coating agent (A1).

[0127] -Creating Carrier A1- 1,000 parts of the ferrite particles (1) and 125 parts of the coating agent (A1) were placed in a kneader and mixed at room temperature (25°C) for 20 minutes, then heated to 70°C and dried under reduced pressure. The dried product was cooled to room temperature (25° C.), and 125 parts of coating agent (A1) was added and mixed at room temperature (25° C.) for 20 minutes, followed by heating to 70° C. and drying under reduced pressure. Next, the dried product was taken out of the kneader and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining a carrier A1 (carrier A).

[0128] <Preparation of Electrostatic Image Developer A1> 100 parts of the obtained carrier A1 and 9 parts of the toner (1) were charged into a V blender and stirred for 20 minutes, and then sieved through a sieve with 212 μm openings to obtain electrostatic image developer A1.

[0129] <Preparation of Electrostatic Image Developer B1> 8 parts of the obtained carrier B1 and 92 parts of the toner (1) were charged into a V blender and stirred for 20 minutes, and then sieved through a sieve with 212 μm openings to obtain electrostatic image developer B1.

[0130] <Production of Image Forming Apparatus> The electrostatic image developer A1 was placed in the developing device of Docu Centre Color 450 (manufactured by Fujifilm Business Innovation Co., Ltd.), and the electrostatic image developer B1 was placed in the developer cartridge, to prepare the image recording device of Example 1.

[0131] (Comparative Example 1) -Preparation of coating agent for forming resin coating layer- Cyclohexyl methacrylate polymer (weight average molecular weight: 350,000): 15.4 parts 2-(Dimethylamino)ethyl methacrylate polymer (weight average molecular weight: 300,000): 0.39 parts Melamine resin particles (Eposter S (Nippon Shokubai Co., Ltd.)): 3.0 parts Carbon black (Cabot Corporation, product name: VXC72): 2.24 parts Metal oxide particles (1): 9.0 parts of silica (volume average particle size: 7 nm, specific gravity: 2.2, fumed silica particles surface-treated with hexamethyldisilazane, manufactured by Tokuyama Corporation, product name: HM30S) Toluene: 300 parts The above materials and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 190 rpm for 30 minutes to obtain a coating agent (CA1).

[0132] -Creating Carrier AC1- 1,000 parts of ferrite particles (1) and coating agent (CA1) were placed in a vacuum degassing kneader and stirred at 70°C and 80 kPa for 2 hours, then the temperature was raised to 80°C and the toluene was distilled off at a vacuum of 5 kPa to form a resin-coated carrier. Subsequently, fine and coarse powders were removed using an elbow jet to obtain carrier CA1.

[0133] An image-forming apparatus was produced in the same manner as in Example 1, except that carrier CA1 was used instead of carrier A1.

[0134] (Comparative Example 2) An image-forming apparatus was produced in the same manner as in Example 1, except that the carriers A1 and B1 were used in reverse.

[0135] Examples 2 to 9 An image-forming apparatus was produced in the same manner as in Example 1, except that the metal oxide particles (1) were changed to the particles and particle diameters shown in Table 1 and below. Example 2: Alumina particles (manufactured by EVONIK, product name: AEROXIDE Alu C805) Example 3: Titania particles (manufactured by AEROSIL, product name: TiO2T805) Example 4: Metal oxide particles (2) Example 5: Metal oxide particles (3) Example 6: Metal oxide particles (4) Example 7: Metal oxide particles (5) Example 8: Metal oxide particles (6) Example 9: Metal oxide particles (7)

[0136] (Examples 10 to 13) An image-forming apparatus was produced in the same manner as in Example 1, except that the amount of metal oxide particles (1) added was changed to the content shown in Table 1.

[0137] (Examples 14 to 17) An image forming apparatus was prepared in the same manner as in Example 1, except that the amount of silica particles contained in the coating resin layer was adjusted so that the surface silica amount of the replenishment carrier B was changed to the SiB / SiA value shown in Table 1.

[0138] Examples 18 to 21 Amount of CB and melamine resin particles relative to resin An image-forming apparatus was produced in the same manner as in Example 1, except that the value of BETB / BETA was changed to the value shown in Table 1.

[0139] Example 22 The same image forming apparatus as in Example 1 was used, except that in the preparation of electrostatic image developer B1, 2 parts of the obtained carrier B1 and 98 parts of toner (1) were used to prepare the electrostatic image developer.

[0140] Example 23 The same image forming apparatus as in Example 1 was used, except that carriers A2 / B2 were prepared by a preparation method that did not include the addition of carbon black and melamine resin particles.

[0141] Examples 24 and 25 An image-forming apparatus was produced in the same manner as in Example 1, except that the metal oxide particles (1) were changed to the particles and particle diameters shown in Table 1 and below. Example 24: Metal oxide particles (8) Example 25: Metal oxide particles (9)

[0142] <Evaluation of fogging suppression> The fogging suppression was evaluated as follows. Using a Docu Centre Color 450 (manufactured by Fujifilm Business Innovation Co., Ltd.) prepared in each Example and Comparative Example, 2,000 sheets of image samples with an image density of 20% were printed on P paper in a high temperature and high humidity environment (28°C, 85% RH). Then, under the same environment, 100 sheets of image samples with an image density of 1% were printed, and the 100th image sample with an image density of 1% was then evaluated according to the following criteria. The 100th sheet output was inspected for fogging with the naked eye and with a 5x magnification loupe and classified as follows: A: No overlapping is permitted on any of the 10 sheets. B: A slight fogging can be seen on one sheet with a magnifying glass, but it is not enough to cause any problems. C: Slight fogging is observed on several sheets with a magnifying glass, but it is minor and does not affect practical use. C-: Fog is visible to the naked eye on one sheet, but is slight and does not affect practical use. D: Fog is visible to the naked eye on several sheets, but is slight and does not affect practical use. E: Fog was visible to the naked eye on all 10 sheets, making them unsuitable for practical use.

[0143] The evaluation results are summarized in Table 1.

[0144] [Table 1]

[0145] As shown in Table 1, the image forming apparatuses and image forming methods of Examples 1 to 25 were superior in fogging suppression compared to the image forming apparatuses and image forming methods of Comparative Examples 1 and 2.

[0146] (((1))) An image forming apparatus of a trickle development type that contains a two-component developer containing toner and carrier A in a developing machine, replenishes toner in accordance with the toner consumed by development, and replenishes replenishment carrier B, wherein the carrier A has a magnetic core material A and a resin coating layer A that coats the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B that coats the magnetic core material B, and the resin coating layer B contains metal oxide particles. (((2))) The image forming apparatus according to (((1))), wherein the metal oxide particles include at least one kind selected from the group consisting of silica particles, alumina particles, and titania particles. (((3))) The image forming apparatus according to (((2))), wherein the metal oxide particles include silica particles. (((4))) The image forming apparatus according to any one of (((1))) to (((3))), wherein the volume average particle diameter D of the metal oxide particles is more than 3 nm and not more than 85 nm. (((5))) An image forming apparatus described in any one of (((1))) to (((4))), wherein the content of the metal oxide particles is 10% by mass or more and 60% by mass or less relative to the total mass of the resin coating layer B. (((6))) The image forming apparatus according to (((3))), wherein the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less. (((7))) An image forming apparatus described in any one of (((1))) to (((6))), wherein the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is 0.5 or more and 8 or less.

[0147] (((8))) An image forming method using a trickle development system in which a two-component developer containing toner and carrier A is contained in a developing machine, and toner is replenished in accordance with the toner consumed during development, and replenishment carrier B is replenished, wherein the carrier A has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles, and the replenishment carrier B has a magnetic core material B and a resin coating layer B coating the magnetic core material B, and the resin coating layer B contains metal oxide particles. (((9))) The image forming method according to (((8))), wherein the metal oxide particles include at least one kind selected from the group consisting of silica particles, alumina particles, and titania particles. (((10))) The image forming method according to (((9))), wherein the metal oxide particles include silica particles. (((11))) The image forming method according to any one of (((8))) to (((10))), wherein the volume average particle diameter D of the metal oxide particles is more than 3 nm and 85 nm or less. (((12))) The image forming method described in any one of (((8))) to (((11))), wherein the content of the metal oxide particles is 10% by mass or more and 60% by mass or less relative to the total mass of the resin coating layer B. (((13))) The image forming method according to (((10))), wherein the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less. (((14))) The image forming method described in any one of (((8))) to (((13))), wherein the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is 0.5 or more and 8 or less.

[0148] According to the inventions (((1))) or (((2))), an image forming apparatus is provided that has superior fogging suppression properties compared to when the resin coating layers of both carrier A and replenishment carrier B contain metal oxide particles. According to the invention related to (((3))), an image forming apparatus is provided which is more excellent in fogging suppression than when the inorganic particles are titania particles or alumina particles. According to the invention related to (((4))), an image forming apparatus is provided which is more excellent in fogging suppression properties than when the volume average particle diameter D of the metal oxide particles is 3 nm or less or exceeds 85 nm. According to the invention related to (((5))), an image forming apparatus is provided which has better fogging suppression properties than when the content of the metal oxide particles is less than 10% by mass or more than 60% by mass relative to the total mass of the resin coating layer B. According to the invention related to (((6))), an image forming apparatus is provided which has better fogging suppression properties than when the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is less than 1.2 or more than 5. According to the invention (((7))), an image forming apparatus is provided which has better fogging suppression properties than when the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is less than 0.5 or more than 8.

[0149] According to the inventions (((8))) or (((9))), an image forming method is provided which is superior in fogging suppression compared to when metal oxide particles are contained in the resin coating layers of both carrier A and replenishment carrier B. According to the invention related to (((10))), an image forming method is provided which is superior in fogging suppression properties compared to when the inorganic particles are titania particles or alumina particles. According to the invention related to (((11))), an image forming method is provided which is more excellent in fogging suppression properties than when the volume average particle diameter D of the metal oxide particles is 3 nm or less or exceeds 85 nm. According to the invention related to (((12))), an image forming method is provided which has better fogging suppression properties than when the content of the metal oxide particles is less than 10% by mass or more than 60% by mass relative to the total mass of the resin coating layer B. According to the invention related to (((13))), an image forming method is provided which is superior in fogging suppression properties compared to when the ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is less than 1.2 or more than 5. According to the invention related to (((14))), an image forming method is provided which has better fogging suppression properties than when the ratio BETB / BETA of the BET specific surface area BETA of the carrier A to the BET specific surface area BETB of the replenishment carrier B is less than 0.5 or more than 8. [Explanation of symbols]

[0150] 100 Image forming device 110 Image holder 120 Charging device 130 Electrostatic image forming device 140 Developing device 141 Developer container 146 Developer supply means 147 Developer Cartridge 148 Developer discharge means 150 Intermediate transfer belt (part of transfer device) 151 Primary transfer roll (part of transfer device) 152 Secondary transfer roll (part of transfer device) 170 Cleaning device 174 Residual toner transport means 180 Fixing device P Recording paper (an example of a recording medium)

Claims

1. In an image forming apparatus of a trickle development type, a two-component developer containing toner and carrier A is stored in a developing unit, and toner is replenished in accordance with the amount of toner consumed in development, and carrier B is replenished, the carrier A has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles; The replenishing carrier B has a magnetic core B and a resin coating layer B that coats the magnetic core B, and the resin coating layer B contains metal oxide particles. Image forming device.

2. 2. The image forming apparatus according to claim 1, wherein the metal oxide particles include at least one kind selected from the group consisting of silica particles, alumina particles, and titania particles.

3. 3. The image forming apparatus according to claim 2, wherein the metal oxide particles include silica particles.

4. 3. The image forming apparatus according to claim 1, wherein the volume average particle diameter D of the metal oxide particles is 3 nm or more and 85 nm or less.

5. 3. The image forming apparatus according to claim 1, wherein the content of the metal oxide particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer B.

6. 4. The image forming apparatus according to claim 3, wherein a ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less.

7. 3. The image forming apparatus according to claim 1, wherein a ratio BETB / BETA of a BET specific surface area BETA of said carrier A to a BET specific surface area BETB of said replenishing carrier B is 0.5 or more and 8 or less.

8. In a trickle development image forming method, a two-component developer containing toner and carrier A is stored in a developing machine, and toner is replenished in accordance with the amount of toner consumed during development, and carrier B is replenished, the carrier A has a magnetic core material A and a resin coating layer A coating the magnetic core material A, and the resin coating layer A does not contain metal oxide particles; The replenishing carrier B has a magnetic core B and a resin coating layer B that coats the magnetic core B, and the resin coating layer B contains metal oxide particles. Image forming method.

9. 9. The image forming method according to claim 8, wherein the metal oxide particles include at least one kind selected from the group consisting of silica particles, alumina particles, and titania particles.

10. The image forming method according to claim 9 , wherein the metal oxide particles comprise silica particles.

11. 10. The image forming method according to claim 8, wherein the volume average particle diameter D of the metal oxide particles is more than 3 nm and not more than 85 nm.

12. 10. The image forming method according to claim 8, wherein the content of the metal oxide particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer B.

13. 11. The image forming method according to claim 10, wherein a ratio SiB / SiA of the surface silica amount SiA of the carrier A to the surface silica amount SiB of the replenishment carrier B is 1.2 or more and 5 or less.

14. 10. The image forming method according to claim 8, wherein a ratio BETB / BETA of a BET specific surface area BETA of the carrier A to a BET specific surface area BETB of the replenishing carrier B is 0.5 or more and 8 or less.

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